Highly thermally conductive dual-network carbon-based aerogel cryogenic phase change cool storage material and preparation method thereof

Abstract

The application discloses a high-thermal-conductivity double-network carbon-based aerogel low-temperature phase change cold storage material and a preparation method thereof, and belongs to the technical field of energy storage and composite materials. The composite material comprises a double-thermal-conductivity network aerogel framework composed of polyamide acid (PAA), graphene oxide (GO) and dopamine modified carbon nanotubes (CNT@PDA), and an alkane or alcohol phase change cold storage medium impregnated in the pore channels of the framework. The aerogel framework is prepared through a directional freezing-freeze drying-thermal imidization-high temperature carbonization process to form an anisotropic thermal conduction channel structure. Compared with existing phase change cold storage materials, the composite material prepared by the application has high thermal conductivity, high structural stability and excellent low temperature adaptability, is suitable for cold energy storage processes in the range of-160 DEG C to-20 DEG C, and can significantly improve the cold storage / release efficiency in application scenarios such as LNG cold energy recovery, low temperature energy storage and cold chain transportation.

Description

Technical Field

[0001] This invention belongs to the field of energy storage and composite materials technology, specifically relating to a high thermal conductivity dual-network carbon-based aerogel low-temperature phase change cold storage material and its preparation method for LNG cold energy recovery, low-temperature energy storage or cold chain transportation. Background Technology

[0002] With the continuous development of cryogenic energy utilization and green energy storage technologies, the efficient recovery and utilization of cold energy from liquefied natural gas (LNG) has become a research hotspot in the energy field. LNG releases a large amount of cold energy during its gasification process; each ton of LNG can release approximately 860 MJ of cold energy (about 230 kWh). Storing and utilizing this cold energy can significantly improve energy efficiency and reduce carbon emissions. However, due to the intermittent and fluctuating nature of the LNG gasification process, directly utilizing its cold energy is difficult to achieve a stable output. Therefore, cold energy storage technology is needed to regulate and balance the cold energy.

[0003] Cryogenic storage technology is an important form of thermal energy storage that stores and releases low-temperature energy through phase change materials or sensible heat materials. It plays a crucial role in refrigeration, air conditioning, cold chain transportation, and peak shaving and valley filling in energy systems. Based on the storage medium, cryogenic storage technology is mainly divided into two categories: sensible heat storage and latent heat storage. Sensible heat storage relies on the temperature change of a substance to store energy; typical media include low-temperature water, rock, and ethanol. Latent heat storage utilizes the latent heat effect of heat absorption and release during phase change processes; commonly used materials include ice, brine eutectic crystals, and eutectic organic mixtures. Latent heat storage has the advantages of high energy density and stable temperature during storage and release, making it a key research direction in the field of cryogenic energy storage.

[0004] Currently, latent heat storage materials used in cryogenic environments (below -50 °C) mainly focus on inorganic salt aqueous solutions, alcohol eutectic systems, and organic eutectic mixtures. However, these materials generally suffer from low thermal conductivity, difficulty in precisely controlling phase change temperature, and insufficient cycle stability. During LNG cold energy storage, these problems lead to reduced storage / release rates, decreased storage efficiency, and uneven system heat exchange, thus limiting their practical application in cryogenic energy storage equipment. Inorganic phase change materials based on inorganic salts or their eutectic systems, such as the inorganic eutectic system disclosed in CN117987091A, which uses magnesium chloride as the main material and sodium chloride or ammonium chloride as the eutectic temperature regulator, can cover a phase change temperature range of -60 °C to -20 °C, making them suitable for some ultra-low temperature environments. However, inorganic salt systems generally suffer from low phase change enthalpy, poor cycle stability, and are prone to phase separation and supercooling. Furthermore, at low temperatures, the solvent is prone to crystallization, causing a decrease in storage capacity. In addition, inorganic salt solutions are corrosive to equipment, which is not conducive to its engineering application under long-term cyclic conditions.

[0005] Besides inorganic salt eutectic systems, researchers are also exploring the development of low-temperature organic eutectic phase change materials to achieve high latent heat and adjustable phase change temperatures under cryogenic conditions. For example, CN111826126A discloses a low-temperature phase change cold storage material composed of a mixture of ketones, aldehydes, and alkanes. By adjusting the molar ratio of the components, a phase change temperature range of -77 ℃ to -88 ℃ can be achieved. This material exhibits good tunability and high latent heat of phase change, making it suitable for cryogenic energy storage and low-temperature refrigeration applications.

[0006] However, organic eutectic systems still face several limitations in cryogenic environments. On the one hand, ketones, aldehydes, and alkanes are prone to phase separation or component segregation at low temperatures, leading to poor cycle stability. On the other hand, these materials generally have low thermal conductivity (<0.2 W·m). -1 ·℃ -1 Furthermore, organic systems still pose risks of volatility, flammability, and environmental safety under low-temperature conditions, making them difficult to use stably in open or high-frequency circulation systems for extended periods.

[0007] To improve the thermal response rate of latent heat storage materials, researchers have attempted to introduce high thermal conductivity frameworks to construct composite cold storage materials, such as using graphite, metal foam, or carbon-based aerogel as supporting phases to enhance the system's thermal conductivity. However, metal framework materials are prone to thermal expansion mismatch and structural cracking in cryogenic environments, and their complex structures are difficult and costly to process. While carbon-based composite systems can achieve enhanced thermal conductivity, they usually require the introduction of a high proportion of fillers or binders, which can easily compromise the cold storage capacity and stability of the phase change medium.

[0008] In summary, existing inorganic salt eutectic systems, while offering adjustable temperature ranges, suffer from poor thermal conductivity and are prone to corrosion; organic eutectic systems, despite high latent heat, lack structural stability and exhibit slow thermal response; and sensible heat solid systems have limited energy density and low specific heat. Therefore, developing a novel composite phase change cold storage material that combines high thermal conductivity, structural stability, cryogenic applicability, and cycle durability has become a crucial challenge urgently needing to be addressed in cryogenic energy storage technology, particularly in the field of LNG cold energy recovery. Summary of the Invention

[0009] The purpose of this invention is to overcome the deficiencies in the prior art and provide a high thermal conductivity dual-network carbon-based aerogel low-temperature phase change cold storage material and its preparation method. This material is based on a polyimide-derived high thermal conductivity aerogel framework and possesses excellent thermal conductivity, shape stability, and customizable structural characteristics. It can be widely used in LNG cold energy recovery, cryogenic energy storage, cold chain transportation, and other cryogenic thermal management fields.

[0010] The specific technical solution adopted in this invention is as follows: In a first aspect, the present invention provides a high thermal conductivity dual-network carbon-based aerogel low-temperature phase change cold storage material, comprising a carbon-based aerogel skeleton having oriented vertical channels and a dual thermal conductivity network pore structure, and a low-temperature phase change cold storage medium impregnated in the pore structure. The carbon-based aerogel framework comprises polyamic acid, graphene oxide, and dopamine-modified carbon nanotubes, which are prepared sequentially through directional freezing, freeze drying, thermal imidization, and high-temperature carbonization processes. The low-temperature phase change cold storage medium is at least one of alkanes, alcohols, or a mixture of both.

[0011] Preferably, in the carbon-based aerogel framework, the mass ratio of graphene oxide to polyamic acid is 3:(7-2), and the dopamine-modified carbon nanotubes account for 10% to 30% of the mass of graphene oxide.

[0012] Preferably, the total solid content of the carbon-based aerogel framework is 2 wt% to 6 wt%.

[0013] Preferably, the phase change temperature range of the low-temperature phase change cold storage medium is -160℃ to -20℃.

[0014] Preferably, the high thermal conductivity dual-network carbon-based aerogel low-temperature phase change cold storage material has a thermal conductivity of not less than 1 W·m at -100℃. -1 ·℃ -1 .

[0015] Secondly, this invention provides a method for preparing a high thermal conductivity dual-network carbon-based aerogel low-temperature phase change cold storage material, as detailed below: S1: Polyamic acid and triethanolamine are uniformly dissolved in water at a mass ratio of 1:(0.3~0.6), followed by the sequential addition of graphene oxide dispersion and dopamine-modified carbon nanotube dispersion. After stirring evenly, a PAA / GO / CNT@PDA mixed slurry is obtained. S2: The PAA / GO / CNT@PDA mixed slurry is injected into a mold, and ice crystals are oriented to grow by a unidirectional temperature gradient freezing method. After freeze-drying to remove moisture, an aerogel precursor with an oriented structure is obtained. S3: The aerogel precursor is subjected to thermal imidization treatment, followed by high-temperature carbonization at 2800-3000 °C under an inert atmosphere to reduce graphene oxide in situ and form a dual thermally conductive carbon-based framework. S4: Under vacuum conditions, the dual thermally conductive network carbon-based skeleton is immersed in a liquid low-temperature phase change cold storage medium, and after cooling and solidification, a high thermal conductivity dual-network carbon-based aerogel low-temperature phase change cold storage material is obtained.

[0016] Preferably, in step S1, the mass ratio of polyamic acid to triethanolamine is 1:0.48. After stirring for 2 hours, graphene oxide dispersion is added, followed by sonication for 15 minutes and stirring for 2 hours, and then dopamine-modified carbon nanotube dispersion is added.

[0017] Preferably, in step S2, the freeze-drying temperature is -50 °C, the pressure is <10 Pa, and the time is 72 hours.

[0018] Preferably, in step S3, the temperature of the thermal imidization treatment is 300 °C, the temperature of the high-temperature carbonization is 2800 °C, and the inert atmosphere is high-purity nitrogen, argon, or helium.

[0019] Thirdly, the present invention provides an application of the high thermal conductivity dual-network carbon-based aerogel low-temperature phase change cold storage material based on any one of the first aspects or the high thermal conductivity dual-network carbon-based aerogel low-temperature phase change cold storage material obtained by the preparation method as described in any one of the second aspects in LNG cold energy storage, cryogenic energy recovery, cold chain transportation or cryogenic energy management system.

[0020] Compared with the prior art, the present invention has the following advantages: 1) Unique dual thermal conduction network: Unlike a single carbon skeleton, this invention utilizes the long-range ordered arrangement of GO sheets and the interlayer overlap of CNTs to construct a highly efficient phonon transport channel, which significantly reduces the interfacial thermal resistance.

[0021] 2) Excellent low-temperature adaptability: The skeleton prepared by using an aqueous synthesis route and high-temperature carbonization process still maintains good structural toughness in low-temperature environment, which solves the problem of cold shrinkage and cracking of metal skeleton.

[0022] 3) Highly efficient directional heat transfer: Directional freezing endows the material with an anisotropic microstructure, enabling the composite material to achieve a thermal conductivity of about 1.7 W / (m·℃) in the main heat flow direction, which greatly improves the rate of LNG cold energy recovery. Attached Figure Description

[0023] Figure 1 This is a schematic diagram (cross-sectional view) of the high thermal conductivity dual-network carbon-based aerogel framework prepared in Example 1. Detailed Implementation

[0024] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below. Technical features in various embodiments of the present invention can be combined accordingly without mutual conflict.

[0025] With the rapid development of liquefied natural gas (LNG) energy, the large amount of cryogenic cold energy released during its gasification process has not been efficiently utilized. Existing cold storage materials suffer from problems such as poor thermal conductivity, slow phase change rate, deformation instability, and high manufacturing costs, making it difficult to meet the requirements of cryogenic energy storage for efficient heat exchange and structural stability.

[0026] In view of this, the present invention provides a high thermal conductivity dual-network carbon-based aerogel low-temperature phase change cold storage material with controllable structure, excellent thermal conductivity, and strong low-temperature applicability, as well as a preparation method thereof. The present invention significantly improves the cold storage and release efficiency and structural stability of the low-temperature phase change medium by introducing graphene oxide and carbon nanotubes to construct a "dual thermal conductivity network" and combining it with directional freezing technology.

[0027] This invention provides a high thermal conductivity dual-network carbon-based aerogel low-temperature phase change cold storage material. This solid-liquid phase change cold storage material is suitable for the cryogenic to ultra-cryogenic range. The material mainly comprises a carbon-based aerogel framework with oriented vertical channels and a dual thermally conductive network pore structure, and a low-temperature phase change cold storage medium impregnated within this pore structure. The carbon-based aerogel framework mainly comprises polyamic acid (PAA), graphene oxide (GO), and dopamine-modified carbon nanotubes (CNT@PDA), prepared sequentially through processes such as directional freezing, freeze-drying, thermal imidization, and high-temperature carbonization. The low-temperature phase change cold storage medium is one or more of alkanes (such as n-butane, n-pentane, n-hexane, etc.), alcohols (such as n-heptanol, n-octanol, etc.), or mixtures thereof.

[0028] In this framework structure, carbonized polyimide and reduced graphene oxide sheets form the first-level directional thermal conductivity network, while carbon nanotubes, acting as connecting bridges, are distributed between the sheets to form the second-level thermal conductivity network, thereby endowing the framework with excellent axial thermal conductivity and mechanical strength.

[0029] In a preferred embodiment of the present invention, the mass ratio of graphene oxide to polyamic acid in the carbon-based aerogel framework is 3:(7-2), the amount of dopamine-modified carbon nanotubes added is 10% to 30% of the mass of graphene oxide, and the total solid content of the carbon-based aerogel framework is 2 wt% to 6 wt%.

[0030] As a preferred embodiment of the present invention, the phase change temperature range of the low-temperature phase change cold storage medium is -160℃ to -20℃.

[0031] As a preferred embodiment of the present invention, the thermal conductivity of the high thermal conductivity dual-network carbon-based aerogel low-temperature phase change cold storage material is not less than 1 W·m at -100℃. -1 ·℃ -1 .

[0032] In practical applications, by adjusting the mixing ratio of the low-temperature phase change cold storage medium components, an adjustable phase change temperature within the range of 0 ℃ to -160 ℃ can be obtained to meet the cold storage requirements of different temperature zones. This is because the alkane and / or alcohol phase change media selected in this invention as cold energy storage carriers have the characteristics of weak intermolecular interactions, high latent heat, and small supercooling. Taking n-pentane, n-hexane, and n-decane as examples, their melting points are -130 ℃, -95 ℃, and -30 ℃, respectively. By adjusting the mixing ratio, a eutectic system within a specific temperature range can be obtained, achieving adjustable cold storage at different cold energy levels (shallow, medium, and deep).

[0033] Based on the above-mentioned high thermal conductivity dual-network carbon-based aerogel low-temperature phase change cold storage material, the present invention also provides a preparation method, which specifically includes the following steps: S1, Construction of the aqueous dispersion system: Polyamic acid (PAA) and triethanolamine were uniformly dissolved in water at a mass ratio of 1:(0.3~0.6). Then, graphene oxide dispersion (dispersed in water) and dopamine-modified carbon nanotube dispersion (dispersed in water) were added in sequence and stirred evenly to obtain PAA / GO / CNT@PDA mixed slurry.

[0034] In a preferred embodiment of the present invention, in this step, polyamic acid and triethanolamine are dissolved in deionized water at a mass ratio of 1:0.48 and stirred for 2 hours to obtain a polyamic acid solution (PAAS). Graphene oxide dispersion is added to the obtained PAAS, and the mixture is sonicated for 15 minutes and then stirred for 2 hours to obtain a PAAS / GO mixed suspension. Finally, CNT@PDA dispersion is added to the obtained PAAS / GO mixed suspension, and stirring is continued for 4 hours to obtain a PAA / GO / CNT@PDA mixed slurry.

[0035] As a preferred embodiment of the present invention, the preparation method of dopamine-modified carbon nanotubes in this step is briefly described as follows: 250 mg of nanotubes were added to 100 mL of Tris-HCl hydrochloric acid buffer solution (pH=8.5) and sonicated for 30 minutes. 300 mg of dopamine hydrochloride was added to the dispersion, and the mixture was continuously magnetically stirred at room temperature for 24 hours to allow dopamine to polymerize in situ on the surface of the carbon nanotubes, forming a coating layer. The resulting solution was centrifuged at 10,000 rpm, the supernatant was discarded, and the precipitate was washed three times with deionized water. The washed precipitate was then freeze-dried under vacuum to obtain dopamine-modified carbon nanotube (CNT@PDA) powder.

[0036] S2, Oriented Structure Forming: The PAA / GO / CNT@PDA mixed slurry prepared in S1 was injected into a mold. A unidirectional temperature gradient freezing method was used with liquid nitrogen or a low-temperature cold source. By controlling the cooling rate, ice crystals were oriented to form a vertical heat-conducting channel structure. After freeze-drying to remove moisture, an aerogel precursor with an oriented structure was obtained.

[0037] In a preferred embodiment of the present invention, the freeze-drying temperature is -50 °C, the pressure is <10 Pa, and the time is 72 hours.

[0038] S3, High-Temperature Carbonization and Network Construction: The aerogel precursor obtained from S2 was subjected to thermal imidization treatment, followed by high-temperature carbonization at 2800–3000 °C under an inert atmosphere to reduce graphene oxide in situ and form a dual thermally conductive carbon-based framework.

[0039] In a preferred embodiment of the present invention, the temperature of the thermal imidization treatment is 300 °C, the temperature of the high-temperature carbonization is 2800 °C, and the inert atmosphere can be high-purity nitrogen, argon or helium.

[0040] S4, Vacuum Composite: Under vacuum conditions, the obtained dual thermally conductive carbon-based skeleton is immersed in a liquid low-temperature phase change cold storage medium. The medium is adsorbed by capillary force, and after cooling and solidification, a high thermal conductivity dual-network carbon-based aerogel low-temperature phase change cold storage material is obtained.

[0041] The high thermal conductivity dual-network carbon-based aerogel low-temperature phase change cold storage material prepared by this invention can be applied to LNG cold energy storage, cryogenic energy recovery, cold chain transportation or low-temperature energy management system.

[0042] Compared to traditional brine-water-based phase change systems, the composite phase change material of this invention utilizes the three-dimensional encapsulation effect of an aerogel framework to effectively solve the leakage problem of organic materials during the phase change process, and exhibits no structural collapse during multiple heat absorption and release cycles. Furthermore, thanks to its high energy density and significantly improved thermal conductivity, this material can meet the stringent requirements for efficient heat exchange and stable energy storage in scenarios such as liquefied natural gas cold energy recovery, liquid air energy storage precooling, and cryogenic transportation.

[0043] The methods and effects of the present invention will be specifically illustrated below through examples.

[0044] Example 1 This embodiment provides a high thermal conductivity dual-network carbon-based aerogel low-temperature phase change cold storage material, which is a cryogenic composite phase change cold storage material suitable for LNG vaporization cold energy recovery. It comprises a polyimide-derived high thermal conductivity aerogel framework and a low-temperature alkane phase change medium impregnated therein. The specific preparation method of this material is as follows: A PAA aqueous solution with a solid content of 5wt%-10wt% was prepared by dissolving polyamic acid and triethanolamine in deionized water. Subsequently, an aqueous dispersion of graphene oxide was added to the solution, and the mixture was ultrasonically dispersed for 30 minutes. Then, dopamine-modified carbon nanotubes were added, and the mixture was stirred at 1000 rpm for 4 hours to obtain a PAA / GO / CNT@PDA mixed slurry. The mass ratio of GO to PAA was 3:7, and the amount of CNT@PDA added was 20% of the mass of GO. The mixed slurry was poured into a mold and unidirectionally frozen on a cold stage at -80 ℃. It was then freeze-dried for 72 hours under a vacuum of less than 10 Pa and a temperature of -50 ℃. After drying, the dried aerogel was placed in a tube furnace and heated to 300 ℃ at a heating rate of 5 ℃ / min under a nitrogen atmosphere and held at that temperature for 2 hours for thermal imidization. Subsequently, the sample was transferred to a graphitization furnace and heated to 2800 ℃ at a heating rate of 5 ℃ / min under an argon atmosphere and carbonized / graphitized at high temperature for 2 hours. The sample was then cooled to room temperature with the furnace to obtain a double-network carbon-based aerogel framework with a vertical pore structure.

[0045] The prepared aerogel framework was placed in a vacuum environment and immersed in n-pentane phase change medium. Vacuum adsorption was used to promote the full penetration of mixed alkanes into the pores of the framework. After cooling and solidification, a composite phase change cold storage material was obtained. The phase change temperature of this material is approximately -130 °C, and the latent heat is 115 kJ·kg⁻¹. -1 .

[0046] Tests showed that the carbon-based aerogel framework prepared in this embodiment exhibited obvious anisotropic characteristics.

[0047] like Figure 1The image shows a cross-sectional view of the aerogel framework obtained after carbonization. It can be clearly observed from the image that the aerogel as a whole exhibits a highly ordered parallel layered / textured structure arranged along the freezing direction on a macroscopic scale. This macroscopic ordered texture directly corresponds to the microscopic directional pore structure, which is caused by the vertical growth of ice crystals induced by the unidirectional directional freezing process during preparation.

[0048] In terms of microscopic heat conduction mechanism, these continuous long-range ordered channels parallel to the freezing direction effectively construct a "high-speed channel" for phonon transmission (first-level heat conduction network); at the same time, CNT@PDA acts as a "bridge" connecting the graphene oxide sheets and the carbonized polymer matrix, constructing a secondary heat conduction network.

[0049] Experimental measurements show that this dual-network synergistic effect enables the composite material to achieve a thermal conductivity of 1.5–10.0 W·m in the main heat flow direction. -1 ·℃ -1 A relatively pure organic phase change medium (typically about 0.2 W·m⁻¹) -1 ·℃ -1 It has increased by 5 to 10 times.

[0050] Example 2 This embodiment provides a high thermal conductivity dual-network carbon-based aerogel low-temperature phase change energy storage material, suitable for mid-temperature cold energy recovery (such as the pre-cooling stage of liquid air energy storage systems). It comprises a polyimide-derived high thermal conductivity aerogel framework and a low-temperature alkane-based phase change medium impregnated therein. The preparation method is similar to that of Example 1, but the phase change medium is replaced by a mixture of n-hexane and n-heptanol (volume ratio 7:3). The mixed medium undergoes a reversible phase change near -45 °C, with a latent heat of approximately 145 kJ·kg⁻¹. -1 .

[0051] The phase change medium was kept in a liquid state at 40 °C and injected into a carbon-based aerogel framework (pore size of about 100 μm and porosity of 93%) using a vacuum impregnation method. After standing for 2 hours, it was cooled and solidified to obtain a composite cold storage material in the mid-cooling zone.

[0052] Experimental measurements revealed that the material sample prepared in this embodiment exhibited a significant endothermic and exothermic peak at -47℃, indicating stable phase change behavior. After 10 cycles, the endothermic and exothermic curves overlapped well, demonstrating the material's excellent thermal cycling stability. In a simulation experiment of a liquid air energy storage system, this material achieved a reduction in thermal response time of approximately 38%.

[0053] Example 3 This embodiment provides a high thermal conductivity dual-network carbon-based aerogel low-temperature phase change cold storage material, which is suitable for cold chain transportation and low-temperature storage. This material uses the same PI aerogel framework as in Example 1. Ethylene glycol is selected as the phase change medium, and the composite material is prepared using the same vacuum adsorption-cooling curing process.

[0054] Test results show that the phase transition temperature of this composite material is -13 ℃, and the latent heat is approximately 160 kJ·kg⁻¹. -1 After 20 thermal cycles, its phase transition temperature change is less than 0.5 ℃, and its latent heat retention rate exceeds 98%.

[0055] In contrast, Example 2, employing a PAA / GO / CNT dual-network framework composite, significantly improved the thermal conductivity to 1.72 W / (m·℃) at -60 °C. This represents an approximately 8-fold improvement in thermal conductivity compared to pure phase change materials.

[0056] This result demonstrates that although the volume fraction of the aerogel framework is low (<5%), the vertical channels (first-level network) constructed by directional freezing and the microscopic bridges (second-level network) built by CNTs produce a significant synergistic effect, successfully solving the bottleneck problem of poor thermal conductivity while retaining the high latent heat advantage of organic materials.

[0057] To further verify the performance enhancement effect of the dual-network carbon-based aerogel framework prepared in this invention on phase change cold storage materials, comparative examples 1 (using pure organic phase change media directly without a framework) and 2 (using a conventional aerogel framework prepared by disordered freezing, without directional structure) were set up for comparative testing. The performance test results of each group of samples are summarized in Table 1.

[0058] Table 1 Summary of performance tests of embodiments and comparative examples of the present invention Results Analysis: As shown in Table 1, the following can be concluded: 1) Regarding energy storage density (latent heat): Due to the ultra-high porosity (solid content of only 2 wt%-6 wt%) of the carbon-based aerogel framework prepared in this invention, the phase change medium filling rate in the composite material is extremely high. Therefore, the latent heat of phase change of the composite material (e.g., 148.5 kJ / kg in Example 2) is only slightly lower than that of the pure phase change medium (155.0 kJ / kg in Comparative Example 1), thus maximizing the preservation of the high energy storage density advantage of the medium.

[0059] 2) Regarding thermal conductivity: Although enhanced phonon scattering in cryogenic environments leads to a decrease in thermal conductivity with decreasing temperature (from 1.88 W / (m·℃) in Example 3 to 1.58 W / (m·℃) in Example 1), thanks to the synergistic effect of the "dual thermally conductive network" and "directional channels," the thermal conductivity of the material of this invention is still significantly better than that of pure organic phase change media (0.21 W / (m·℃)) and disordered skeleton composite materials (0.45 W / (m·℃)) in all temperature ranges. Taking Example 2 as an example, at -60℃, its thermal conductivity is about 8 times higher than that of the pure sample and nearly 4 times higher than that of the disordered skeleton.

[0060] Compared with existing phase change cold storage materials, the composite material prepared by this invention has high thermal conductivity, high structural stability and excellent low temperature adaptability. It is suitable for cold energy storage processes in the range of -160℃ to -20℃, and can significantly improve the storage / release efficiency in application scenarios such as LNG cold energy recovery, low temperature energy storage and cold chain transportation.

[0061] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the invention. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the invention. Therefore, all technical solutions obtained through equivalent substitution or transformation fall within the protection scope of the present invention.

Claims

1. A high thermal conductivity dual-network carbon-based aerogel low-temperature phase change cold storage material, characterized in that, It includes a carbon-based aerogel framework with oriented vertical channels and a dual thermally conductive network pore structure, and a low-temperature phase change cold storage medium impregnated in the pore structure; The carbon-based aerogel framework comprises polyamic acid, graphene oxide, and dopamine-modified carbon nanotubes, which are prepared sequentially through directional freezing, freeze drying, thermal imidization, and high-temperature carbonization processes. The low-temperature phase change cold storage medium is at least one of alkanes, alcohols, or a mixture of both.

2. The high thermal conductivity dual-network carbon-based aerogel low-temperature phase change cold storage material according to claim 1, characterized in that, In the carbon-based aerogel framework, the mass ratio of graphene oxide to polyamic acid is 3:(7-2), and the dopamine-modified carbon nanotubes account for 10% to 30% of the mass of graphene oxide.

3. The high thermal conductivity dual-network carbon-based aerogel low-temperature phase change cold storage material according to claim 1, characterized in that, The total solids content of the carbon-based aerogel framework is 2 wt% to 6 wt%.

4. The high thermal conductivity dual-network carbon-based aerogel low-temperature phase change cold storage material according to claim 1, characterized in that, The phase change temperature range of the low-temperature phase change cold storage medium is -160℃ to -20℃.

5. The high thermal conductivity dual-network carbon-based aerogel low-temperature phase change cold storage material according to claim 1, characterized in that, The high thermal conductivity dual-network carbon-based aerogel low-temperature phase change cold storage material has a thermal conductivity of not less than 1 W·m at -100℃. -1 ·℃ -1 .

6. A method for preparing a high thermal conductivity dual-network carbon-based aerogel low-temperature phase change cold storage material, characterized in that, Specifically as follows: S1: Polyamic acid and triethanolamine are uniformly dissolved in water at a mass ratio of 1:(0.3~0.6), followed by the sequential addition of graphene oxide dispersion and dopamine-modified carbon nanotube dispersion. After stirring evenly, a PAA / GO / CNT@PDA mixed slurry is obtained. S2: The PAA / GO / CNT@PDA mixed slurry is injected into a mold, and ice crystals are oriented to grow by a unidirectional temperature gradient freezing method. After freeze-drying to remove moisture, an aerogel precursor with an oriented structure is obtained. S3: The aerogel precursor is subjected to thermal imidization treatment, followed by high-temperature carbonization at 2800-3000 °C under an inert atmosphere to reduce graphene oxide in situ and form a dual thermally conductive carbon-based framework. S4: Under vacuum conditions, the dual thermally conductive network carbon-based skeleton is immersed in a liquid low-temperature phase change cold storage medium, and after cooling and solidification, a high thermal conductivity dual-network carbon-based aerogel low-temperature phase change cold storage material is obtained.

7. The preparation method according to claim 6, characterized in that, In S1, the mass ratio of polyamic acid to triethanolamine is 1:0.

48. After stirring for 2 hours, graphene oxide dispersion is added, followed by sonication for 15 minutes and stirring for 2 hours. Then, dopamine-modified carbon nanotube dispersion is added.

8. The preparation method according to claim 6, characterized in that, In step S2, the freeze-drying temperature is -50 ℃, the pressure is <10 Pa, and the time is 72 hours.

9. The preparation method according to claim 6, characterized in that, In S3, the temperature of the thermal imidization treatment is 300°C, the temperature of the high-temperature carbonization is 2800°C, and the inert atmosphere is high-purity nitrogen, argon, or helium.

10. The application of a high thermal conductivity dual-network carbon-based aerogel low-temperature phase change cold storage material based on any one of claims 1 to 5 or a high thermal conductivity dual-network carbon-based aerogel low-temperature phase change cold storage material obtained by any one of claims 6 to 9 in LNG cold energy storage, cryogenic energy recovery, cold chain transportation or cryogenic energy management system.

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