Hydrated salt composite phase change material with low leakage and high thermal conductivity and preparation method thereof

Abstract

The invention relates to a low-leakage high-thermal-conductivity hydrated salt composite phase-change material and a preparation method thereof.The preparation method comprises the steps that a proper amount of stearic acid is added into an inorganic hydrated salt phase-change material to adjust the phase-change temperature, and a thickening agent and porous thermal-conductive filler are added to inhibit supercooling and phase separation and improve the thermal conductivity; the problems that an existing inorganic hydrated salt phase change material is prone to leakage and low in heat conduction performance in the phase change process are solved, and the hydrated salt composite phase change material which is stable in shape, high in heat conduction performance and low in leakage is obtained through a simple and convenient technology.

Description

Technical Field

[0001] The present invention belongs to the technical field of composite phase change materials, and relates to a phase change material based on inorganic hydrated salts, in particular to a composite phase change material for energy storage with a low leakage rate and high thermal conductivity and a preparation method thereof. Background Art

[0002] Lithium-ion batteries have high energy density and environmental friendliness, and have been widely used in fields such as electric vehicles and portable electronic devices. However, under high-power working conditions, lithium-ion batteries are prone to generating a large amount of heat, resulting in temperature rise, which affects the performance and lifespan of the batteries. This is currently a major problem affecting the application of lithium-ion batteries.

[0003] Phase Change Materials (PCMs) are widely used in the thermal management system of lithium-ion batteries due to their high latent heat storage capacity. They can effectively absorb the heat generated during the charging and discharging process of the batteries and release it slowly to keep the battery temperature within a safe range. This not only improves the safety of the batteries but also extends their service life.

[0004] Paraffin is a common organic phase change material with low cost and high phase change enthalpy, but it has a low thermal conductivity. Usually, it is compounded with high thermal conductivity materials to form a composite phase change material. Expanded graphite has the advantages of high thermal conductivity, low density, and easy processing, and is often used as a thermal conductivity enhancer for paraffin. Research shows that using paraffin / expanded graphite composite phase change materials can effectively reduce the battery surface temperature and improve the battery discharge capacity. However, paraffin will liquefy during the phase change process, which may cause leakage and affect the reliability of the battery.

[0005] At the same time, due to the flammable characteristics of organic phase change materials in high-temperature environments, when the battery undergoes thermal runaway, the combustion of organic phase change materials will not only significantly increase the fire risk but also accelerate the spread of thermal runaway within the battery pack by releasing a large amount of heat energy.

[0006] Compared with organic phase change materials, inorganic phase change materials represented by inorganic hydrated salts such as CaCl2∙6H2O, Na2HPO4∙12H2O, and Ba(OH)2∙8H2O have outstanding advantages such as non-flammability, large heat storage capacity, low price, and easy availability, enabling them to play an important role in the thermal management system.

[0007] However, hydrated salt phase change materials also have some obvious defects. First, due to their certain solubility and fluidity, when the temperature or environmental conditions change, the hydrated salt may change from solid state to liquid state or lose water, resulting in material leakage or performance degradation. Such leakage not only destroys the stability of the thermal management system, but may also cause corrosion, pollution and even damage to the equipment. Second, there are relatively serious problems such as phase separation and supercooling during the phase change process of inorganic hydrated salts. In addition, most hydrated salt phase change materials have low thermal conductivity, which also affects their heat storage and heat release rates.

[0008] For example, disodium hydrogen phosphate dodecahydrate (DHPD) is a representative hydrated salt phase change material. Its phase change temperature is between 35 and 36 °C and it has a relatively large latent heat of phase change, which can be used for low-temperature heat storage. However, DHPD has a relatively serious supercooling phenomenon, and a large degree of supercooling seriously affects the heat storage and heat release performance of the phase change material.

[0009] Therefore, how to prepare inorganic hydrated salt phase change materials with stable shape, high thermal conductivity and low leakage to ensure their long-term stable thermal management performance has become an important research direction.

[0010] To solve these defects, currently two main methods are adopted. One is to immerse the inorganic hydrated salt material into the porous material by the melt impregnation method or the vacuum adsorption method, and use the surface tension and hydrogen bonding between molecules to make the porous material adsorb a large amount of hydrated salt phase change material, thereby preventing leakage and suppressing phase separation. The other is to fix the phase change material through core-shell encapsulation, which can not only prevent the leakage of the phase change material, but also greatly alleviate the problems of supercooling and phase separation. However, neither of these two methods can well solve the problem of the thermal conductivity of the phase change material.

[0011] Regarding the current research status, while continuing to explore and develop porous carriers and encapsulation methods with stable structure and good sealing performance, further improving the thermal conductivity of the phase change material to prepare inorganic hydrated salt phase change materials with low cost, excellent performance and simple process has become the focus of research. Summary of the Invention

[0012] The object of the present invention is to solve the problems that the current inorganic hydrated salt phase change materials are prone to leakage and have low thermal conductivity during the phase change process, and to provide a low-leakage and high-thermal-conductivity hydrated salt composite phase change material and its preparation method.

[0013] To achieve the above-mentioned invention object, the hydrated salt composite phase change material of the present invention uses an inorganic hydrated salt phase change material as the phase change material substrate, and adds stearic acid for adjusting the phase change temperature, a thickening agent for suppressing supercooling and phase separation, and a porous heat-conducting filler for improving the heat-conducting performance. After curing to form a shape-stable phase change material, a composite phase change material is formed by encapsulating a layer of liquid fluororubber on the surface of the phase change material. The dosages of stearic acid, the thickening agent, and the porous heat-conducting filler are respectively 2-4 wt%, 1-2 wt%, and 2-4 wt% of the mass of the inorganic hydrated salt phase change material.

[0014] Furthermore, the inorganic hydrated salt phase change material is a conventional inorganic hydrated salt with phase change characteristics that can be used as a phase change material, and the present invention has no special limitation on it. However, further, the inorganic hydrated salt phase change material described in the present invention can preferably be any one of disodium hydrogen phosphate dodecahydrate, barium hydroxide octahydrate, sodium acetate trihydrate, and sodium silicate nonahydrate, or any proportion mixture of several of them.

[0015] Furthermore, the thickening agent can be any one of sodium carboxymethylcellulose, sodium carboxymethyl starch, or sodium alginate.

[0016] Further, the porous heat-conducting filler can preferably be any one of carbon nanotubes or expanded graphite.

[0017] More preferably, the carbon nanotubes can be multi-walled carbon nanotubes or single-walled carbon nanotubes.

[0018] More specifically, the liquid fluororubber described in the present invention is a rubber with a number average molecular weight Mn of about 50,000 and in a viscous liquid state at room temperature, and has excellent high-temperature resistance characteristics, and is mainly used for sealants, anti-corrosion coatings, etc.

[0019] Furthermore, the present invention also provides a preparation method of the hydrated salt composite phase change material, which specifically includes: 1) Adding stearic acid and a thickening agent to the molten inorganic hydrated salt phase change material to obtain a mixture; 2) Adding a porous heat-conducting filler to the mixture, mixing evenly and then cooling and curing to form a composite phase change material; 3) Impregnating a layer of liquid fluororubber on the surface of the composite phase change material and performing natural drying treatment to obtain a hydrated salt composite phase change material encapsulated with fluororubber.

[0020] Furthermore, the cooling and curing time is preferably 5-10 h.

[0021] Further, the natural drying treatment time is preferably 48-72 h.

[0022] Compared with traditional inorganic hydrated salt phase change materials, the hydrated salt composite phase change material of the present invention can maintain high shape stability during the phase change process, its thermal conductivity is increased by at least 150%, and the leakage rate is below 4%.

[0023] The present invention prepares a composite phase change material based on inorganic hydrated salt by a curing and encapsulation method, which not only prevents phenomena such as supercooling and phase separation during the phase change process, but also can significantly improve the thermal conductivity of the phase change material and effectively reduce leakage, and obtains a shape-stable, high-thermal-conductivity and low-leakage hydrated salt composite phase change material through a simple process. Brief Description of the Drawings

[0024] Figure 1 It is a preparation flow chart of the hydrated salt composite phase change material encapsulated with fluororubber in Example 1.

[0025] Figure 2 It is an XRD comparison spectrum of products at different stages of the hydrated salt composite phase change material in Example 1.

[0026] Figure 3 It is a DSC diagram of products at different stages of the hydrated salt composite phase change material in Example 1.

[0027] Figure 4 It is a leakage rate diagram of different phase change materials in Example 1 and Comparative Examples 1-4.

[0028] Figure 5 It is a comparison diagram of the thermal conductivity and supercooling degree of the phase change materials in Example 1 and Comparative Examples 1-2.

[0029] Figure 6 It is a comparison diagram of the combustion states of the hydrated salt composite phase change material in Example 1 and organic phase change materials.

[0030] Figure 7 It is a test diagram of the battery thermal management performance of the hydrated salt composite phase change material in Example 1. Embodiments

[0031] The following further describes in detail the specific embodiments of the present invention in conjunction with the drawings and embodiments. The following embodiments are only used to more clearly illustrate the technical solutions of the present invention, so that those skilled in the art can fully understand and utilize the present invention well.

[0032] However, the present invention can be implemented in many other ways different from the following embodiments, and those skilled in the art can also make similar improvements without departing from the connotation of the present invention. Therefore, the protection scope of the present invention is not limited by the following disclosed specific embodiments.

[0033] Unless otherwise defined, all technical and scientific terms used in the present invention have the same meaning as commonly understood by those skilled in the art. The terms used in the specification of the present invention are also only for describing specific embodiments and are not intended to limit the present invention.

[0034] The term "and / or" used in the present invention includes any and all combinations of one or more of the related listed items.

[0035] The terms "a plurality of", "multiple", "multiple times", "multiple groups", etc. used in the present invention, unless otherwise specified, refer to a quantity greater than or equal to 2; "above" includes the number itself, for example, "two or more" includes two, three or more.

[0036] The term "preferred" used in the present invention is only for describing embodiments or examples with better effects and does not constitute a limitation on the protection scope of the present invention.

[0037] The production processes, experimental methods or detection methods involved in the embodiments of the present invention, unless otherwise specified, are all conventional methods in the prior art, and their names and / or abbreviations are all conventional names in the art and are very clear and definite in the relevant application fields. Those skilled in the art can understand the conventional process steps according to the names and apply the corresponding equipment, according to the conventional conditions or the conditions recommended by the manufacturer, or refer to the experimental methods known in the art for implementation.

[0038] There are no special restrictions on the sources of various instruments, equipment, raw materials or reagents used in the embodiments of the present invention. They are all conventional products that can be obtained through regular commercial channels, and can also be prepared according to the conventional methods well-known to those skilled in the art.

[0039] The low-leakage and high-thermal-conductivity hydrated salt composite phase change material of the present invention is specifically prepared according to the Figure 1 preparation flow chart shown.

[0040] First, place the inorganic hydrated salt phase change material in a beaker, continuously heat and stir it in a water bath until the phase change material is fully melted, then add 2-4 wt% of stearic acid based on its mass and continue heating and stirring, and then add 1-2 wt% of thickener based on its mass and heat and stir to complete the reaction to obtain a mixture.

[0041] Then, continue to add 2-4 wt% of porous thermal conductive filler based on the mass of the inorganic hydrated salt phase change material to the mixture, heat and stir to ensure full combination, and then pour it into a pre-prepared mold, and cool and solidify it at room temperature to form a composite phase change material.

[0042] Finally, encapsulate the composite phase change material with liquid fluororubber and place it in a natural ventilation place for drying treatment to obtain a fluororubber-encapsulated hydrated salt composite phase change material.

[0043] In a specific embodiment, the inorganic hydrated salt phase change material may be any one of disodium hydrogen phosphate dodecahydrate, barium hydroxide octahydrate, sodium acetate trihydrate, and sodium silicate nonahydrate, or a mixture of several in any proportion, and preferably disodium hydrogen phosphate dodecahydrate is used.

[0044] In a specific embodiment, the thickener may be sodium carboxymethyl cellulose, sodium carboxymethyl starch, or sodium alginate.

[0045] In a specific embodiment, the porous heat-conducting filler may be carbon nanotubes or expanded graphite, and the carbon nanotubes among them may be multi-walled carbon nanotubes or single-walled carbon nanotubes.

[0046] In a specific embodiment, the liquid fluororubber is purchased from Dongguan Hongke Plastic Raw Material Co., Ltd.

[0047] In a specific embodiment, the water bath temperature and the mixing and stirring time are measured by the standard that the materials always remain in a molten state and can be fully mixed evenly.

[0048] In a specific embodiment, the cooling and solidifying and shaping time is generally controlled within 5 - 10 h.

[0049] In a specific embodiment, the natural drying treatment time is generally 48 - 72 h.

[0050] Unless otherwise specified, for the raw material component dosages, temperature, time and other measurement parameters involved in the embodiments of the present invention, there may be slight deviations within the weighing or measurement accuracy range, and acceptable deviations caused by instrument test accuracy or operation accuracy are allowed. Examples

[0051] Example 1

[0052] Weigh 30 g of disodium hydrogen phosphate dodecahydrate (DHPD) and put it into a beaker. Continuously heat and stir it in a 60 °C water bath for 30 min. After ensuring that DHPD is fully melted, add 1.2 g of stearic acid (SA), and continue to heat and stir in a 60 °C water bath for 1 h. After SA and DHPD fully react, add 0.3 g of sodium carboxymethyl cellulose (CNC-Na), and continue to heat and stir for 1.5 h to complete the reaction to obtain a DHPD-SA / CNC-Na mixture.

[0053] Add 0.6 g of carbon nanotubes (CNT) to the mixture, continue to mix and stir in a 60 °C water bath for 20 min. After ensuring that CNT is fully combined with the mixture, pour it evenly into a pre-prepared mold and cool and shape it at room temperature for 5 h to form a composite phase change material.

[0054] The composite phase change material was immersed in liquid fluororubber. After a layer of liquid fluororubber was evenly encapsulated on the material surface, it was placed in a ventilated place and naturally dried at room temperature for 72 h to prepare a fluororubber-encapsulated hydrated salt composite phase change material, denoted as CNT@DHPD-SA / CNC-Na.

[0055] The prepared CNT@DHPD-SA / CNC-Na phase change material has the characteristics of high thermal conductivity and low leakage rate.

[0056] The material phase was characterized by X-ray diffraction (XRD), and the results are as Figure 2 shown. In the figure, the strong characteristic diffraction peaks of DHPD appear at positions such as 16°, 18.5°, 20°, 20.6°, 30.2°, 30.9°, 31.7°, 40.8°, 50.6°, etc. These characteristic peaks also show the same performance in DHPD-SA / CNC-Na with the addition of SA and CNC-Na, indicating that the addition of SA and CNC-Na did not change the crystal morphology of DHPD.

[0057] At the same time, in CNT@DHPD-SA / CNC-Na, although the same characteristic peaks can still be observed, the addition of CNT may affect the overall crystal structure, resulting in the appearance of new diffraction peaks and the change of the intensity of some peaks. This change may be due to the interaction between CNT and other substances (such as physical adsorption, chemical bonding, etc.), thus affecting the characteristics of the XRD pattern.

[0058] Generally speaking, although the positions and relative intensities of the diffraction peaks of the products at different stages have changed, no new diffraction peaks completely different from the starting material DHPD have appeared, indicating that there may only be physical mixing or weak interaction between substances, but no new substance with a unique crystal structure has been formed, which does not affect the main structure and properties of the original substances.

[0059] Figure 3 The comparison of the phase change performance of the products DHPD, DHPD-SA / CNC-Na and CNT@DHPD-SA / CNC-Na at different stages is shown. The melting point of DHPD is 52.83 °C, which is suitable for the thermal management of lithium-ion batteries. However, after adding other components, the melting points of DHPD-SA / CNC-Na and CNT@DHPD-SA / CNC-Na are increased to 55.42 °C and 55.23 °C respectively. Furthermore, the specific latent heat of CNT@DHPD-SA / CNC-Na is measured to be 84 J / g, which is also lower compared with DHPD.

[0060] The above changes are mainly attributed to the addition of thickeners and porous thermal conductive fillers, which reduce the energy storage density of the material. However, although the specific latent heat has decreased, the latent heat density of the phase change material still meets the requirements of battery thermal management and is suitable for the application of phase change materials in this field.

[0061] Example 2

[0062] Weigh 30 g of DHPD, 1.2 g of SA and 0.6 g of CNC-Na and put them into a beaker, mix them evenly, and continuously heat them in an oven at 60 °C for 1.5 h to ensure that they are fully melted and homogenized, obtaining a DHPD-SA / CNC-Na mixture.

[0063] Add 0.9 g of CNT to the mixture, mix and stir in a water bath at 60 °C for 15 min. After ensuring that the CNT is fully combined with the mixture, pour it evenly into a pre-prepared mold and cool and solidify it at room temperature for 10 h to form a composite phase change material.

[0064] Use a brush to evenly apply a layer of liquid fluororubber on the surface of the composite phase change material, and dry it in a ventilated place for 48 h to prepare a fluororubber-encapsulated hydrated salt composite phase change material CNT@DHPD-SA / CNC-Na.

[0065] Example 3

[0066] Weigh 60 g of sodium acetate trihydrate (SAT) and put it into a beaker. Continuously heat and stir it in a water bath at 70 °C for 30 min. After ensuring that the SAT is fully melted, add 2.4 g of SA and continue to heat and stir in a water bath at 70 °C for 1 h. After the SA and SAT have fully reacted, add 0.6 g of sodium alginate (SA) and continue to heat and stir for 1.5 h to complete the reaction and obtain a SAT-SA / SA mixture.

[0067] Add 2.4 g of CNT to the mixture, continue to mix and stir in a water bath at 70 °C for 15 min. After ensuring that the CNT is fully combined with the mixture, pour it evenly into a pre-prepared mold and cool and solidify it at room temperature for 8 h to form a composite phase change material.

[0068] Immerse the composite phase change material in liquid fluororubber, evenly encapsulate a layer of liquid fluororubber on the surface of the material, and dry it in a ventilated place for 72 h to prepare a fluororubber-encapsulated hydrated salt composite phase change material CNT@SAT-SA / SA.

[0069] Comparative Example 1

[0070] Weigh 30 g of DHPD in a beaker, continuously heat and stir it in a water bath at 60 °C for 30 min. After ensuring that the DHPD is fully melted, pour it evenly into a pre-prepared mold and cool and solidify it at room temperature for 5 h to form a phase change material, denoted as DHPD.

[0071] Comparative Example 2

[0072] Weigh 30 g of DHPD and put it into a beaker. Continuously heat and stir in a 60 °C water bath for 30 min. After ensuring that DHPD is fully melted, add 1.2 g of SA. Continue to heat and stir in a 60 °C water bath for 1 h to make SA and DHPD fully react. Then add 0.3 g of CNC-Na and continue to heat and stir for 1.5 h to complete the reaction to obtain a DHPD-SA / CNC-Na mixture.

[0073] Pour the mixture evenly into a pre-prepared mold and cool and solidify at room temperature for 5 h to form a composite phase change material, denoted as DHPD-SA / CNC-Na.

[0074] Comparative Example 3

[0075] Weigh 30 g of DHPD and put it into a beaker. Continuously heat and stir in a 60 °C water bath for 30 min. After ensuring that DHPD is fully melted, add 1.2 g of SA. Continue to heat and stir in a 60 °C water bath for 1 h to make SA and DHPD fully react. Then add 0.3 g of CNC-Na and continue to heat and stir for 1.5 h to complete the reaction to obtain a DHPD-SA / CNC-Na mixture.

[0076] Pour the mixture evenly into a pre-prepared mold and cool and solidify at room temperature for 5 h to form a composite phase change material.

[0077] Immerse the composite phase change material in liquid fluororubber. After uniformly encapsulating a layer of liquid fluororubber on the material surface, dry it in a ventilated place for 48 h to prepare a fluororubber-encapsulated phase change material, denoted as F@DHPD-SA / CNC-Na.

[0078] Comparative Example 4

[0079] Weigh 30 g of DHPD and put it into a beaker. Continuously heat and stir in a 60 °C water bath for 30 min. After ensuring that DHPD is fully melted, add 1.2 g of SA. Continue to heat and stir in a 60 °C water bath for 1 h to make SA and DHPD fully react. Then add 0.3 g of CNC-Na and continue to heat and stir for 1.5 h to complete the reaction to obtain a DHPD-SA / CNC-Na mixture.

[0080] Add 0.6 g of CNT to the mixture and continue to mix and stir in a 60 °C water bath for 20 min. After ensuring that CNT is fully combined with the mixture, pour it evenly into a pre-prepared mold and cool and solidify at room temperature for 5 h to form a composite phase change material, denoted as CNT*DHPD-SA / CNC-Na.

[0081] Application Example 1

[0082] Take the 5 kinds of phase change materials prepared in Example 1 and Comparative Examples 1-4. After weighing them respectively, place them on filter paper, take them out after heating in an oven at 60 °C for 1.5 h, observe whether there is liquid leakage on the filter paper, weigh them again, and calculate the leakage rate of the phase change materials.

[0083] Figure 4 In (a), (b), (c), (d), (e) and (a'), (b'), (c'), (d'), (e') are the state comparison diagrams of DHPD, DHPD-SA / CNC-Na, F@DHPD-SA / CNC-Na, CNT*DHPD-SA / CNC-Na and CNT@DHPD-SA / CNC-Na before and after the leakage performance test respectively.

[0084] The initial masses of the 5 kinds of phase change materials before heating are 10.2873 g, 7.7684 g, 14.75 g, 11.34 g and 11.206 g respectively, and the corresponding masses after heating are 7.2874 g, 7.0913 g, 13.79 g, 8.84 g and 10.8273 g respectively. By calculating the mass loss, the leakage rates of the respective phase change materials are 29.16%, 8.72%, 6.51%, 22.05% and 3.38% in turn.

[0085] The test results show that different treatment methods have a significant impact on the anti-leakage performance of the phase change materials.

[0086] DHPD showed the highest leakage rate of 29.16% in the experiment, indicating that its thermal stability is poor in a high-temperature environment and it is prone to leakage.

[0087] In contrast, DHPD-SA / CNC-Na showed a lower leakage rate, only 8.72%. This may be because after adding SA and CNC-Na to DHPD, not only the phase change temperature of DHPD was adjusted, but also its stability under high-temperature conditions was effectively improved, thereby enhancing the anti-leakage ability of the material. This result shows that adopting a suitable treatment method can significantly improve the thermal stability of the phase change material and thus improve its anti-leakage performance.

[0088] Furthermore, the leakage rate of F@DHPD-SA / CNC-Na encapsulated with liquid fluororubber for DHPD-SA / CNC-Na was further reduced to 6.51%, proving that liquid fluororubber coating also has certain anti-leakage performance.

[0089] It should be noted that for CNT*DHPD-SA / CNC-Na where CNT was continuously added to the phase change material without encapsulation, a significant increase in the leakage rate to 22.05% occurred. This phenomenon may be related to the addition of CNT changing the crystal structure of the material, resulting in an increased volume expansion rate during the phase change process, indicating that the addition of CNT actually promotes the leakage of the phase change material.

[0090] Meanwhile, a notable and interesting phenomenon is that for CNT@DHPD-SA / CNC-Na with continued liquid fluororubber encapsulation of CNT*DHPD-SA / CNC-Na, the leakage rate significantly decreased to 3.38%, showing the most excellent anti-leakage performance. This result confirms that CNT has a synergistic anti-leakage effect with liquid fluororubber. The curing encapsulation process adopted in the present invention can effectively improve the anti-leakage ability of inorganic hydrated salt phase change materials, providing a reliable method for improving the thermal stability of phase change materials.

[0091] Application Example 2

[0092] Based on the more excellent anti-leakage performance of CNT@DHPD-SA / CNC-Na compared to F@DHPD-SA / CNC-Na and CNT*DHPD-SA / CNC-Na, the present invention selects DHPD, DHPD-SA / CNC-Na, and CNT@DHPD-SA / CNC-Na as the objects for subsequent in-depth research. By comparing and analyzing the thermal properties of different material systems, the influence laws of each component on the thermal conductivity and supercooling degree of the phase change material are systematically investigated, and further explore its performance characteristics and application potential.

[0093] Figure 5 These are the specific test results of the thermal conductivity (a) and supercooling degree (b) of the phase change materials prepared in Example 1, Comparative Example 1, and Comparative Example 2 respectively.

[0094] In the figure, the thermal conductivity of the DHPD matrix material prepared in Comparative Example 1 is 0.3088 W / m·K, showing basic heat conduction ability, but there are relatively serious supercooling phenomena and phase separation problems. The supercooling degree reaches 14.65 °C. At the same time, during supercooling, some components in the liquid precipitate in advance due to the decrease in solubility, forming a precipitated phase. The uneven temperature gradient and cooling rate during the cooling process lead to different solidification degrees in different regions, thus forming a layered structure.

[0095] In Comparative Example 2, by introducing SA and CNC-Na, although its supercooling degree was significantly reduced from 14.65 °C to 9.54 °C, effectively improving the phase separation and supercooling phenomena of DHPD, the thermal conductivity also decreased to 0.1757 W / m·K at the same time. This may be due to the interaction between components causing the internal structure of the material to reorganize, thus affecting the heat conduction path.

[0096] It is worth noting that the introduction of CNT in CNT@DHPD-SA / CNC-Na significantly improves the comprehensive thermal performance of the phase change material. The thermal conductivity is increased to 0.8591 W / m·K, and at the same time, the supercooling degree is further reduced to 3°C. The improvement of this performance is mainly attributed to two factors. One is the inherent high thermal conductivity of CNT, and the other is the effective adsorption of DHPD by its unique pore structure, which can better exert the characteristics of the phase change material.

[0097] The above test results show that the introduction of CNT not only optimizes the thermophysical properties of the phase change material, but also provides a new idea for the development of high-efficiency thermal management materials, and has broad application prospects in application fields that require high-efficiency heat dissipation or precise temperature control.

[0098] Application Example 3

[0099] Organic phase change materials are prone to combustion at higher temperatures. When the battery falls into severe failure and combustion, the organic phase change material will exacerbate the fire hazard and the spread of thermal runaway. Compared with organic phase change materials, inorganic phase change materials have better flame retardancy and will not become combustibles during a fire.

[0100] In this application example, the flame retardancy of CNT@DHPD-SA / CNC-Na was evaluated with the organic phase change material paraffin as a control. Figure 6 In (a) is the combustion state of CNT@DHPD-SA / CNC-Na, and (b) is the combustion comparison state of paraffin.

[0101] It can be seen that in the initial stage of combustion (3 s), no obvious change was observed in CNT@DHPD-SA / CNC-Na, while melting occurred in paraffin; as the combustion time extended to 30 s, CNT@DHPD-SA / CNC-Na remained stable without combustion or melting, but paraffin had completely melted, so the ignition experiment of paraffin was terminated; and it is worth noting that during the continuous observation for 60 s, the physical form of CNT@DHPD-SA / CNC-Na hardly changed.

[0102] Finally, after removing the ignition source, no combustion or smoking phenomenon occurred in CNT@DHPD-SA / CNC-Na, while paraffin completely burned with obvious smoke.

[0103] The above experimental results fully confirm that the phase change material CNT@DHPD-SA / CNC-Na has excellent flame retardancy.

[0104] Application Example 4

[0105] To study the effect of the phase change material CNT@DHPD-SA / CNC-Na on the thermal management performance of lithium-ion batteries, this application example designed a comparative experimental scheme, as shown in Figure 7 Figure (a) below. In the experimental group, the phase change material CNT@DHPD-SA / CNC-Na was uniformly coated on the surface of the lithium-ion battery to form a thermal management module; in the control group, no phase change material was used, and only forced air cooling was used for the heat dissipation of the lithium-ion battery.

[0106] The experiment was carried out in an open room-temperature environment, and charge-discharge cycles were carried out at a 2C rate to study the effect of CNT@DHPD-SA / CNC-Na on the surface temperature change of the lithium-ion battery relative to the control group with air cooling.

[0107] The surface temperature changes of the batteries in the two groups of experiments were monitored in real time, and the thermal management effect of CNT@DHPD-SA / CNC-Na was compared and analyzed. The specific results are shown in Figure 7 Figure (b) below.

[0108] The experimental results show that CNT@DHPD-SA / CNC-Na can effectively reduce the surface temperature of the battery, showing a better cooling effect than the air cooling system.

[0109] Specifically, after multiple charge-discharge cycles at a 2C rate, the surface temperature of the lithium-ion battery in the air cooling system reached a maximum of 46.47°C; while the surface temperature of the lithium-ion battery using the CNT@DHPD-SA / CNC-Na material was only 36.92°C at most, and the maximum temperature decreased by 20.55% compared with air cooling.

[0110] This result shows that the phase change material CNT@DHPD-SA / CNC-Na can significantly slow down the heat accumulation generated during the charge and discharge process of the battery, playing a better role in thermal management.

[0111] CNT@DHPD-SA / CNC-Na shows excellent cooling effect at room temperature, far better than simple air cooling. The good thermal conductivity of this material may help to optimize the application of phase change materials in the battery thermal management system (BTMS). Therefore, CNT@DHPD-SA / CNC-Na can effectively improve the safety of lithium-ion batteries and help improve the overall performance and lifespan of batteries in future battery designs.

[0112] The technical features of the above embodiments of the present invention can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope described in the specification of the present invention.

[0113] The above embodiments illustrate several relatively specific and detailed implementation manners of the present invention, but should not be construed as limiting the protection scope of the present invention. It should be noted that those of ordinary skill in the art can make several substitutions, deformations or improvements without departing from the principle and purpose of the present invention, and all of them should be included in the protection scope of the present invention.

Claims

1. A low-leakage and high-thermal-conductivity hydrated salt composite phase change material, which uses an inorganic hydrated salt phase change material as a phase change material base, adds stearic acid for adjusting the phase change temperature, a thickener for inhibiting supercooling and phase separation, and a porous thermally conductive filler for improving thermal conductivity, solidifies to form a shape-stable phase change material, and then encapsulates a layer of liquid fluororubber on the surface of the phase change material to form a composite phase change material, wherein the amounts of stearic acid, thickener and porous thermally conductive filler are 2-4wt%, 1-2wt% and 2-4wt% of the mass of the inorganic hydrated salt phase change material, respectively.

2. The hydrated salt composite phase change material according to claim 1, characterized in that The inorganic hydrated salt phase change material is any one of disodium hydrogen phosphate dodecahydrate, barium hydroxide octahydrate, sodium acetate trihydrate, sodium silicate nonahydrate, or a mixture of any proportions of the above.

3. The hydrated salt composite phase change material according to claim 1, characterized in that The thickener is any one of sodium carboxymethyl cellulose, sodium carboxymethyl starch or sodium alginate.

4. The hydrated salt composite phase change material according to claim 1, characterized in that The porous thermal conductive filler is any one of carbon nanotubes or expanded graphite.

5. The hydrated salt composite phase change material according to claim 4, characterized in that The carbon nanotubes are multi-walled carbon nanotubes or single-walled carbon nanotubes.

6. The method for preparing the low leakage and high thermal conductivity hydrated salt composite phase change material according to claim 1, comprising: 1) adding stearic acid and a thickener to a molten inorganic hydrated salt phase change material to obtain a mixture; 2) Add porous thermal conductive filler to the mixture, mix well, cool and solidify to form a composite phase change material; 3) A layer of liquid fluororubber is impregnated on the surface of the composite phase change material, and the composite phase change material is naturally dried to obtain a fluororubber-encapsulated hydrated salt composite phase change material.

7. The preparation method according to claim 6, characterized in that The cooling and solidification time is 5 to 10 hours.

8. The preparation method according to claim 6, characterized in that The natural drying treatment time is 48 to 72 hours.

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