Chloride-based high-temperature composite phase change heat storage material and preparation method thereof

Abstract

The invention discloses a chloride-based high-temperature composite phase change heat storage material and a preparation method thereof, and belongs to a phase change heat storage material, the chloride-based high-temperature composite phase change heat storage material comprises the following components by weight: 45-47 parts of sodium chloride, 38-40 parts of potassium chloride, 15-17 parts of magnesium chloride, 5-10 parts of expanded graphite, and 1-3 parts of alumina. A chloride eutectic matrix in the phase-change material provides the advantages of high latent heat and low cost, expanded graphite is shaped to reduce the leakage risk and improve the safety of a system during application, aluminum oxide can inhibit a corrosion mechanism from forming a protective layer, the corrosion depth is large, the moisture absorption rate is low, the durability problem of chloride salt at high temperature is solved, and stable thermal conductivity is ensured; and the device is suitable for a high-pressure heat storage device, so that the heat release power is improved, the heat loss rate is reduced, the flexibility of power grid energy storage can be supported, and the economic benefit is remarkable.

Description

Technical Field

[0001] This invention relates to a phase change heat storage material, and more specifically, to a chloride-based high-temperature composite phase change heat storage material and its preparation method. Background Technology

[0002] High-temperature phase change thermal energy storage materials (PCMs) play a crucial role in the stable transmission and grid connection of renewable energy, providing the necessary thermal energy storage flexibility to buffer the intermittent output of solar or wind power. However, existing high-temperature PCMs often face several technical challenges, including insufficient insulation, severe corrosion, moisture absorption, and poor cycle stability. These problems directly lead to safety hazards and performance degradation in high-voltage grid applications. For example, traditional nitrate-based PCMs (such as NaNO3-KNO3 mixtures), although having a moderate melting point (approximately 220-300℃), are prone to thermal decomposition and oxidation above 400℃, resulting in a latent heat decay rate as high as 10-20%. Carbonate-based materials (such as K2CO3-Li2CO3) have a high melting point (approximately 500-700℃) and high latent heat (>200 kJ / kg), but are prone to moisture absorption (moisture absorption rate can reach over 20%) and corrosion of metal substrates, forming corrosion products such as Fe3O4 and NiO. At 500℃, the corrosion depth can exceed 50 μm / month after contact with stainless steel. Current technologies have revealed relevant attempts, but they have limitations. For example, shaped PCMs using carbonate matrices achieve shape stability through hierarchical porous calcium magnesium carbonates, but the high-temperature compatibility and corrosion problems of chloride systems remain unresolved, especially the insufficient long-term stability at >500℃. Another example is the preparation method of inorganic salt composite PCMs, which emphasizes melt composite to improve thermal conductivity, but lacks optimization for high-voltage insulation (dielectric strength <5 kV / mm) and cycle decay (>10% after 500 cycles), failing to meet the stringent requirements of grid energy storage. Therefore, while melting point adjustment and nano-reinforcement of chloride PCMs have been explored in existing technologies, the lack of effective integration of shaped structure and corrosion inhibition results in heat loss rates >10% in practical CSP or grid applications, limiting economic efficiency and reliability. Therefore, it is necessary to develop a new phase change material to support the reliable application of grid energy storage systems. Summary of the Invention

[0003] One of the objectives of this invention is to address the aforementioned shortcomings by providing a chloride-based high-temperature composite phase change thermal energy storage material and its preparation method, in order to solve the technical problems of insufficient insulation, severe corrosion, moisture absorption, poor cycle stability, high-temperature compatibility and corrosion of chloride systems in similar materials in the prior art.

[0004] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: The present invention provides a chloride-based high-temperature composite phase change heat storage material, characterized in that it comprises, by weight, 45-47 parts of sodium chloride, 38-40 parts of potassium chloride, 15-17 parts of magnesium chloride, 5-10 parts of expanded graphite, and 1-3 parts of alumina.

[0005] As a preferred embodiment, a further technical solution is that the weight ratio of sodium chloride, potassium chloride, and magnesium chloride is 46:39:15.

[0006] Another aspect of the present invention provides a method for preparing the above-mentioned material, the method comprising the following steps: Step A: Weigh out the corresponding amounts of sodium chloride, potassium chloride and magnesium chloride, mix them, and then heat them in a vacuum furnace to 500-600℃ to melt them. After stirring evenly, a eutectic melt is obtained.

[0007] Step B: Weigh the corresponding amount of expanded graphite and preheat it to 200-300°C, then immerse it in the eutectic melt and perform dispersion treatment to promote penetration.

[0008] Step C: Weigh the corresponding amount of alumina and add it to the eutectic melt. Stir evenly and then degas under vacuum and cool to form the product, thus obtaining the chloride-based high-temperature composite phase change heat storage material to be packaged.

[0009] As a preferred embodiment, a further technical solution is that the above method also includes step D, mechanically crushing the cooled chloride-based high-temperature composite phase change heat storage material into granules, and sealing it with a metal film to form a tubular module shape.

[0010] A further technical solution is that the particle size of the mechanically crushed particles is 20-50 nm; and the particle filling rate in the metal film is greater than 90%.

[0011] A further technical solution is that the tubular module is mounted on the outside of the insulating heater.

[0012] Compared with the prior art, one of the beneficial effects of the present invention is that the chloride eutectic matrix in the phase change material provides the advantages of high latent heat and low cost, the expanded graphite shaping reduces the risk of leakage and improves the safety of the system during application, the alumina can inhibit the corrosion mechanism to form a protective layer, the corrosion depth is large and the moisture absorption rate is low, which solves the durability problem of chloride salts at high temperature, ensures stable thermal conductivity, improves heat transfer efficiency, is suitable for high-pressure thermal storage devices, improves heat release power and reduces heat loss rate, supports the flexibility of grid energy storage, and has significant economic benefits. Attached Figure Description

[0013] Figure 1 This is a schematic diagram illustrating the microstructure of materials in one embodiment of the present invention.

[0014] Figure 2 This is a DSC curve diagram used to illustrate the materials in one embodiment of the present invention.

[0015] Figure 3 This is a schematic diagram illustrating the tubular module packaging of materials in one embodiment of the present invention. Detailed Implementation

[0016] The chloride-based high-temperature composite phase change thermal energy storage material provided by this invention addresses the low-carbon transformation needs of the power industry, focusing on high-temperature thermal energy storage applications at 400-500℃. It offers high latent heat density and excellent thermal stability to support stable grid connection and efficient thermal energy management of renewable energy. The technical solution emphasizes optimized insulation performance, corrosion resistance, and moisture resistance of the material to ensure safe and reliable operation in grid energy storage systems.

[0017] Specifically, this invention addresses the shortcomings of traditional high-temperature phase change materials in terms of insulation, corrosion resistance, and moisture resistance by developing a composite material based on a NaCl-KCl-MgCl2 ternary eutectic system. This system achieves a low melting point of less than 400°C by optimizing the salt ratio, while introducing expanded graphite and Al2O3 nanoparticles to improve overall performance.

[0018] like Figure 1 and Figure 2 As shown, in one embodiment of the present invention, a chloride-based high-temperature composite phase change heat storage material is provided, comprising, by weight, 45-47 parts NaCl, 38-40 parts KCl, 15-17 parts MgCl2, 5-10 parts expanded graphite, and 1-3 parts Al2O3 nanoparticles. The material forms a ternary eutectic salt phase transition matrix of NaCl-KCl-MgCl2, in which the ratio of NaCl, KCl and MgCl2 is close to 46:39:15, forming the lowest melting point eutectic point (about 385℃), ensuring efficient phase transition in the range of 400-500℃; expanded graphite, as a porous support framework (porosity ≥80%), provides a stabilizing structure, prevents liquid phase leakage and maintains volume stability (change rate ≤5%); Al2O3 nanoparticles (particle size <50 nm), as thermal conductivity enhancers and corrosion inhibitors, form a dense oxide protective layer through surface modification, reducing the interfacial corrosion rate between the material and the metal container to ≤1μm / day, while improving thermal diffusivity and increasing thermal conductivity by more than 1.5 times. The thermophysical properties of this material include a melting point of 380-420℃ (DSC measurement, heating rate 10℃ / min), latent heat of 180-22 kJ / kg (based on eutectic heat capacity integral), thermal conductivity of 1.5-2.5 W / (m·K) (laser scintillation method), dielectric strength ≥10kV / mm, and volume resistivity ≥10 kV / mm. 12Ω⋅m; after contact with 0Cr21Al6 alloy at 500℃ for 60 days, the corrosion depth is ≤ 50μm (SEM analysis) and the moisture absorption rate is ≤5% (weight gain method, relative humidity 80%, 24 hours).

[0019] exist Figure 1 In the simulation, the eutectic salt is uniformly distributed in the expanded graphite skeleton, and the Al2O3 particle size is <50 nm, highlighting the microscopic uniformity and nano-reinforced structure of the composite material. Figure 2 The DSC curve of the material in this embodiment is shown (data: melting point 385℃, latent heat 200 kJ / kg, phase transition peak width ≤10℃).

[0020] In this embodiment, the above-mentioned chloride-based high-temperature composite phase change thermal storage material is prepared through the following steps: Step 1: Weigh out NaCl, KCl and MgCl2 and mix them. Heat the mixture in a vacuum furnace to 500-600℃ to melt it. Stir for 1-2 hours to form a eutectic melt. Ensure that the melt viscosity is ≤10 Pa·s for subsequent impregnation.

[0021] Step 2: Preheat the expanded graphite to 200-300℃ (remove moisture, mass loss ≤1%), immerse it in the melt, and ultrasonically disperse it for 30-60 minutes (power 500-1000 W, frequency 20-40 kHz) to promote melt penetration.

[0022] Step 3: Add Al2O3 nanoparticles and stir for 30 minutes (400 rpm) to achieve uniform distribution. After vacuum degassing for 15-30 minutes to remove bubbles, mold at a cooling rate of 1-5℃ / min and control the formation of crystal nuclei to minimize supercooling (≤5℃).

[0023] Step 4: Crushing and Encapsulating with a Double-Layer Metal Membrane. This method achieves uniform distribution of nanoparticles through vacuum and ultrasonic assistance. The heating process follows the temperature model T(t) = T0 + βt (β = 5 − 10 °C / min) to avoid thermal stress and decomposition, optimizing energy consumption. Specifically, the molded material is crushed into particles or modules, vacuum-sealed with a double-layer metal membrane, and a helium leak test is performed after encapsulation to ensure airtightness. This method can achieve a yield of kg-level. The entire preparation process is carried out under a nitrogen protective atmosphere to prevent oxidation contamination.

[0024] Furthermore, regarding the application of the aforementioned materials, they are installed in high-pressure, high-temperature thermal storage and heating devices, where heat storage and release are achieved through tubular encapsulation modules. This method is suitable for power grid energy storage systems, supporting high-temperature operation at 400-500℃ and ≥1000 thermal cycles; for example... Figure 3As shown, the tubular encapsulation module includes a 310 stainless steel shell, internally filled with the aforementioned material, with a heat release power ≥2kW and a duration ≥180 minutes; combined with an insulating heater, it achieves electrical insulation and moisture-proof encapsulation, with a system heat loss rate ≤5%. The heat conduction process follows the Fourier equation. Where α≥0.5×10−6m² / s, ensuring efficient thermal management.

[0025] In this embodiment, the chloride eutectic matrix provides high latent heat (180-220 kJ / kg) and low cost (<0.5 kJ / kg), while expanded graphite shaping reduces leakage risk and improves system safety. The Al2O3 corrosion-inhibiting mechanism forms a protective layer with a corrosion depth ≤50 μm and a moisture absorption rate ≤5%, solving the durability problem of chloride salts at high temperatures. Compared with similar existing technologies, the cycle stability is improved by 20% (≥1000 cycles with ≤5% decay). The preparation method is efficient and uniform, ensuring a thermal conductivity of 1.5-2.5 W / (m·K) and improving heat transfer efficiency by more than 30%. It is suitable for high-pressure thermal storage devices, achieving a heat release power ≥2 kW and a heat loss rate ≤5%, supporting the flexibility of grid energy storage and demonstrating significant economic benefits.

[0026] In a preferred embodiment of the present invention, the mixture comprises, by weight, 46 parts NaCl, 39 parts KCl, 16 parts MgCl2, 8 parts expanded graphite, and 2 parts Al2O3 nanoparticles (purity ≥99%, particle size 20-50 nm). Preparation method: Weigh the above-mentioned salt raw materials (total mass 500g), mix them, and place them in a vacuum furnace (vacuum degree 0.005 Pa). Melt the mixture at a heating rate of 8℃ / min to 550℃. Stir with a magnetic stirrer at 400 rpm for 1.5 hours to form a transparent and homogeneous eutectic melt, ensuring no crystallization residue (verified by optical microscopy). Then, preheat the expanded graphite (expansion ratio 200-300 times, porosity 85%) to 250℃ to remove adsorbed water (mass loss ≤1%), immerse it in the melt, and place it in an ultrasonic device at 800W power and 30kHz frequency for 45 minutes to promote the melt's full penetration into the graphite pores (penetration rate ≥95%, confirmed by X-ray CT scanning). Al2O3 nanoparticles were then slowly added, and stirring continued for 30 minutes to prevent agglomeration. After vacuum degassing for 15 minutes to remove air bubbles, the mixture was cooled to room temperature at a rate of 3℃ / min to form a blocky composite material (density 1.2-1.4 g / cm³). Finally, the formed material was processed into particles with a diameter of 2-4 mm using a mechanical crusher. It was then vacuum heat-sealed using a double-layer metal film (inner aluminum film thickness 0.1 mm, outer stainless steel film thickness 0.05 mm). After sealing, the material had a moisture absorption rate of ≤3% after 24 hours in an environment with a relative humidity of 80%. The resulting material had a melting point of 385℃ (DSC test, heating rate 10℃ / min), a latent heat value of 200 kJ / kg, and a thermal conductivity of 2.0 W / (m·K) (measured by laser scintillation). The microstructure of the material is as follows: Figure 1 As shown, the eutectic salt is uniformly distributed in the graphite framework, and the Al2O3 particles do not agglomerate.

[0027] In one application example based on the above preferred embodiment, for a 1m³ heat storage device, the above material is filled into a tubular module (such as...). Figure 3 As shown, the stainless steel 310 outer shell has a wall thickness of 5 mm and an internal filling rate of 92%. Integrated with an insulated heater, it underwent a 60-day continuous operation test at 500℃ (simulating power grid peak-valley regulation), with a corrosion depth ≤40 μm (SEM measurement, Al2O3 protective layer thickness approximately 5 μm). The moisture absorption rate is 3% (weight gain method), and after 1000 thermal cycles (400-500℃ range, rate 5℃ / min), the moisture content decreases by 4% (latent heat retention 96%, coefficient of thermal expansion 8×10⁻⁶). -6 / K, verified by TMA thermomechanical analyzer), heat release power 2 kW, lasting 180 minutes, system heat loss rate 4.5%.

[0028] In another application example of the above preferred embodiment, the proportions were adjusted to 45 parts NaCl, 40 parts KCl, 15 parts MgCl2, 10 parts expanded graphite, and 3 parts Al2O3, using the same preparation method (total mass 1 kg). The resulting material had a thermal conductivity of 2.3 W / (m·K), and the DSC curve was as follows. Figure 2 As shown, the phase change peak width is 8℃, making it suitable for large-scale power grid energy storage systems. Cyclic tests show that its stability is 20% better than that of traditional carbonate materials.

[0029] In another application example of the above preferred embodiment, the proportions are 47 parts NaCl, 38 parts KCl, 17 parts MgCl2, 5 parts expanded graphite, and 1 part Al2O3. After preparation, it is sealed with moisture-proof packaging. The heat release power is 2.5 kW, which lasts for 200 minutes. It is tested under high pressure (10kV) without electrical breakdown and the corrosion depth is ≤50μm [4]. It is suitable for industrial-scale heat storage devices.

[0030] In addition to the above, it should be noted that the terms "one embodiment," "another embodiment," and "embodiment" used in this specification refer to specific features, structures, or characteristics described in connection with that embodiment, which are included in at least one embodiment described in the general description of this application. The appearance of the same expression in multiple places in the specification does not necessarily refer to the same embodiment. Furthermore, when a specific feature, structure, or characteristic is described in connection with any embodiment, the intention is to suggest that implementing such a feature, structure, or characteristic in conjunction with other embodiments also falls within the scope of this invention.

[0031] Although the invention has been described herein with reference to several illustrative embodiments, it should be understood that many other modifications and implementations can be devised by those skilled in the art, which will fall within the scope and spirit of the principles disclosed herein. More specifically, various variations and modifications can be made to the components and / or layout of the subject matter arrangement within the scope of the disclosure, drawings, and claims. Besides variations and modifications to the components and / or layout, other uses will be apparent to those skilled in the art.

Claims

1. A chloride-based high-temperature composite phase change heat storage material, characterized in that: It includes, by weight, 45-47 parts sodium chloride, 38-40 parts potassium chloride, 15-17 parts magnesium chloride, 5-10 parts expanded graphite, and 1-3 parts alumina.

2. The chloride-based high-temperature composite phase change heat storage material according to claim 1, characterized in that: The weight ratio of sodium chloride, potassium chloride, and magnesium chloride is 46:39:

15.

3. A method for preparing the material according to claim 1 or 2, the method comprising the following steps: Weigh out the corresponding amounts of sodium chloride, potassium chloride and magnesium chloride, mix them, and then heat them in a vacuum furnace to 500-600℃ to melt them. After stirring evenly, a eutectic melt is obtained. Weigh out the corresponding amount of expanded graphite and preheat it to 200-300°C, then impregnate it in the eutectic melt and perform dispersion treatment to promote penetration; Weigh out the corresponding amount of alumina and add it to the eutectic melt. Stir evenly and then degas under vacuum and cool to form the product, thus obtaining the chloride-based high-temperature composite phase change heat storage material to be packaged.

4. The preparation method according to claim 3, characterized in that... The method further includes the following steps: The cooled chloride-based high-temperature composite phase change thermal storage material is mechanically crushed into granules and then sealed with a metal film to form a tubular module.

5. The preparation method according to claim 4, characterized in that: The particle size of the mechanically crushed particles is 20-50 nm; and the particle filling rate in the space of the metal film is greater than 90%.

6. The preparation method according to claim 4 or 5, characterized in that: The tubular module is shaped and mounted on the outside of the insulating heater.

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