High-stable nitro-type molten salt energy storage material and preparation method thereof

Abstract

The application relates to a high-stability nitro-type fused salt energy storage material and a preparation method thereof, and belongs to the technical field of fused salt energy storage. The fused salt energy storage material is obtained after a nitro-type fused salt is encapsulated by an aerogel matrix, and the aerogel matrix is formed by freeze-drying treatment of a hydrogel to form a porous aerogel and then reduction carbonization; wherein, according to weight parts, the preparation raw materials of the hydrogel include 70-85 parts of a sodium alginate aqueous solution, 5-10 parts of a sodium chloride aqueous solution, 3-8 parts of graphene oxide and 1-3 parts of gluconolactone. The introduction of graphene oxide enhances the mechanical properties and heat conduction properties of the aerogel matrix, avoids structure collapse of the matrix under fused salt penetration and high-temperature working conditions, and simultaneously, the synergistic effect of graphene oxide, sodium alginate and gluconolactone improves the crosslinking density of the hydrogel, and lays a foundation for subsequent formation of a uniform porous structure.

Description

Technical Field

[0001] This invention belongs to the field of molten salt energy storage technology, specifically relating to a highly stable nitro-based molten salt energy storage material and its preparation method. Background Technology

[0002] Molten salt energy storage technology has shown broad application prospects in fields such as solar thermal power plants, industrial waste heat recovery, and building energy conservation due to its advantages such as high energy storage density, wide operating temperature range, and relatively low cost. In order to solve the problems of easy flow and leakage of molten salt phase change materials in the molten state, uncontrolled volume expansion during phase change, and poor cycle stability, researchers usually use porous matrix loaded with molten salt to prepare composite phase change energy storage materials. Among them, porous matrix prepared by freeze casting technology is one of the commonly used matrix types.

[0003] However, in existing technologies, porous matrices prepared using traditional freeze-casting techniques exhibit poor interfacial bonding stability when combined with molten salt phase change materials. During repeated melt-solidification phase change cycles and in actual use, the molten salt phase change material is prone to seeping out or even leaking from the pores of the porous matrix, severely reducing the energy storage performance and service life of the composite material. Summary of the Invention

[0004] The purpose of this invention is to provide a highly stable nitro-based molten salt energy storage material and its preparation method in order to solve the above-mentioned problems.

[0005] The present invention achieves the above objectives through the following technical solutions:

[0006] This invention provides a highly stable nitro-type molten salt energy storage material, which is obtained by encapsulating nitro-type molten salt in an aerogel matrix. The aerogel matrix is ​​formed by freeze-drying hydrogel to form a porous aerogel, followed by reduction and carbonization.

[0007] The raw materials for preparing the hydrogel, by weight, include: 70-85 parts sodium alginate aqueous solution, 5-10 parts sodium chloride aqueous solution, 3-8 parts graphene oxide and 1-3 parts gluconolactone.

[0008] As a further optimization of the present invention, the nitro-type molten salt is a potassium nitrate-sodium nitrate binary system, wherein the mass ratio of potassium nitrate to sodium nitrate is 35-45:55-65.

[0009] As a further optimization of the present invention, the graphene oxide sheet has a thickness of 5-8 nm and an oxygen-containing functional group content of 10-15%.

[0010] This invention also provides a method for preparing a highly stable nitro-based molten salt energy storage material, comprising the following steps:

[0011] S1, Preparation of hydrogel: Add 1-5% w / v sodium chloride aqueous solution to 1%-3% w / v sodium alginate aqueous solution, stir at 550-650 r / min for 20-35 min to obtain suspension;

[0012] Add graphene oxide to the suspension and stir at 350-450 r / min for 20-35 min. Add glucono-delta-lactone and stir at 500-600 r / min for 10-15 min. Let stand at 25℃ for 3-6 h to obtain a hydrogel.

[0013] S2, Preparation of porous aerogel: Take out the hydrogel, rinse it with deionized water 2-3 times, absorb the surface moisture, place it in a freezing device for freezing treatment, take it out and transfer it to a freeze dryer to dry and obtain porous aerogel;

[0014] S3, Preparation of aerogel matrix: The porous aerogel is transferred to a tube furnace, and argon gas is introduced at a flow rate of 50 mL / min to replace the air in the furnace for 30 min. The temperature is increased from room temperature to 200℃ at a rate of 5℃ / min and held for 1 h. The temperature is then increased from 200℃ to 600-900℃ at a rate of 5℃ / min and held for 1-2 h. The heating is turned off, and argon gas is introduced at a rate of 20 mL / min to maintain argon gas flow. The furnace is then cooled to room temperature to obtain the aerogel matrix.

[0015] S4, Encapsulation of molten salt: The temperature of nitro molten salt is 200-250℃, the vacuum degree is 0.05-0.1MPa, the air in the pores of the aerogel matrix is ​​extracted, so that the nitro molten salt permeates and fills the aerogel matrix, completing the encapsulation. The permeation and heat preservation are carried out for 2-4 hours to obtain the molten salt energy storage material.

[0016] As a further optimization of the present invention, the freezing device used in preparing porous aerogels employs programmed cooling freezing or directional freezing.

[0017] As a further optimization of the present invention, the specific steps of programmed cooling freezing are as follows: the freezing space is uniformly reduced from room temperature to -40°C at a cooling rate of 1-5°C / min, and then kept warm for 4-6 hours after reaching the target temperature.

[0018] As a further optimization of the present invention, the specific steps of directional freezing are as follows: a single-sided freezing device is used, the bottom of the hydrogel is in contact with the cold stage, the temperature of the cold stage is set to -40℃, and the temperature is maintained for 4-6 hours.

[0019] As a further optimization of the present invention, the porous aerogel obtained by programmed cooling and freezing grows ice crystals from the outside to the inside during the freezing process, forming a penetrating ice crystal network with a pore size of 5-20 μm.

[0020] As a further optimization of the present invention, the porous aerogel obtained by directional freezing grows ice crystals along the direction of the cold source during the freezing process, forming a parallel oriented pore structure with a pore size of 3-15 μm.

[0021] As a further optimization of the present invention, the cold trap temperature of the freeze dryer is -50°C, the vacuum degree is 10 Pa, and the drying time is 24-48 h.

[0022] The beneficial effects of the present invention are as follows: The aerogel matrix in the present invention is formed by freeze-drying hydrogel to form porous aerogel and then reducing and carbonizing it, which achieves tight encapsulation of nitro molten salt (potassium nitrate-sodium nitrate binary system) and effectively inhibits the leakage and volatilization of molten salt during high-temperature energy storage cycle.

[0023] The introduction of graphene oxide enhances the mechanical and thermal properties of the aerogel matrix, preventing structural collapse under molten salt infiltration and high-temperature conditions. At the same time, the synergistic effect of graphene oxide with sodium alginate and gluconolactone increases the crosslinking density of the hydrogel, laying the foundation for the subsequent formation of a uniform porous structure. Detailed Implementation

[0024] The present application will now be described in further detail. It should be noted that the following specific embodiments are only used to further illustrate the present application and should not be construed as limiting the scope of protection of the present application. Those skilled in the art can make some non-essential improvements and adjustments to the present application based on the above application content.

[0025] Unless otherwise specified, all methods used in this invention are conventional methods known to those skilled in the art, and all reagents and materials used are commercially available products unless otherwise specified.

[0026] In the present invention, the nitro molten salts in Examples 1-3 and Comparative Examples 1-3 are potassium nitrate-sodium nitrate binary systems, and the mass ratio of potassium nitrate to sodium nitrate is 40:60.

[0027] Example 1

[0028] Preparation of hydrogel: Add 5 parts of 1% w / v sodium chloride aqueous solution to 70 parts of 1% w / v sodium alginate aqueous solution, stir at 550 r / min for 20 min to obtain suspension;

[0029] Add 3 parts of graphene oxide (graphene oxide sheet thickness 5nm, oxygen-containing functional group content 10%) to the suspension, stir at 350r / min for 20min, add 1 part of gluconolactone, stir at 500r / min for 10min, and let stand at 25℃ for 3h to obtain hydrogel.

[0030] Preparation of porous aerogel: The hydrogel was taken out, rinsed twice with deionized water, the surface moisture was absorbed, and it was placed in a freezing device. The temperature was uniformly reduced from room temperature to -40℃ at a cooling rate of 3℃ / min. After reaching the target temperature, it was kept at that temperature for 4 hours (during the freezing process, ice crystals grow from the outside to the inside of the porous aerogel, forming a penetrating ice crystal network with a pore size of 10μm). After taking it out, it was transferred to a freeze dryer (the cold trap temperature of the freeze dryer was -50℃, the vacuum degree was 10pa, and the drying time was 24 hours) to obtain the porous aerogel.

[0031] Preparation of aerogel matrix: The porous aerogel was transferred to a tube furnace, and argon gas was introduced at a flow rate of 50 mL / min to replace the air in the furnace for 30 min. The temperature was increased from room temperature to 200℃ at a rate of 5℃ / min and held for 1 h. The temperature was then increased from 200℃ to 600℃ at a rate of 5℃ / min and held for 1 h. The heating was turned off, and argon gas was introduced at a rate of 20 mL / min to maintain argon gas flow. The furnace was then cooled to room temperature to obtain the aerogel matrix.

[0032] Encapsulation of molten salt: The temperature of nitro molten salt is 200℃ and the vacuum degree is 0.05MPa. The air in the pores of the aerogel matrix is ​​extracted, so that the nitro molten salt permeates and fills the aerogel matrix, thus completing the encapsulation. The permeation is kept at a constant temperature for 2 hours to obtain the molten salt energy storage material.

[0033] Example 2

[0034] Preparation of hydrogel: 10 parts of 5% w / v sodium chloride aqueous solution were added to 85 parts of 3% w / v sodium alginate aqueous solution and stirred at 650 r / min for 35 min to obtain a suspension;

[0035] Eight parts of graphene oxide (graphene oxide sheet thickness 8 nm, oxygen-containing functional group content 15%) were added to the suspension and stirred at 450 r / min for 35 min. Three parts of gluconolactone were added and stirred at 600 r / min for 15 min. The mixture was then allowed to stand at 25 ℃ for 6 h to obtain a hydrogel.

[0036] Preparation of porous aerogel: The hydrogel was taken out, rinsed three times with deionized water, the surface moisture was absorbed, and it was placed in a freezing device. The temperature was uniformly reduced from room temperature to -40℃ at a cooling rate of 5℃ / min. After reaching the target temperature, it was kept at that temperature for 4 hours (during the freezing process, ice crystals grow from the outside to the inside of the porous aerogel, forming a through-hole ice crystal network with a pore size of 15μm). After taking it out, it was transferred to a freeze dryer (the cold trap temperature of the freeze dryer was -50℃, the vacuum degree was 10pa, and the drying time was 48 hours) to obtain the porous aerogel.

[0037] Preparation of aerogel matrix: The porous aerogel was transferred to a tube furnace, and argon gas was introduced at a flow rate of 50 mL / min to replace the air in the furnace for 30 min. The temperature was increased from room temperature to 200℃ at a rate of 5℃ / min and held for 1 h. The temperature was then increased from 200℃ to 900℃ at a rate of 5℃ / min and held for 2 h. The heating was turned off, and argon gas was introduced at a rate of 20 mL / min to maintain argon gas flow. The furnace was then cooled to room temperature to obtain the aerogel matrix.

[0038] Encapsulation of molten salt: The temperature of the nitro molten salt is 250℃ and the vacuum degree is 0.1MPa. The air in the pores of the aerogel matrix is ​​extracted, so that the nitro molten salt permeates and fills the aerogel matrix, completing the encapsulation. The permeation and heat preservation are carried out for 4 hours to obtain the molten salt energy storage material.

[0039] Example 3

[0040] Preparation of hydrogel: 10 parts of 5% w / v sodium chloride aqueous solution were added to 85 parts of 3% w / v sodium alginate aqueous solution and stirred at 650 r / min for 35 min to obtain a suspension;

[0041] Eight parts of graphene oxide (graphene oxide sheet thickness 8 nm, oxygen-containing functional group content 15%) were added to the suspension and stirred at 450 r / min for 35 min. Three parts of gluconolactone were added and stirred at 600 r / min for 15 min. The mixture was then allowed to stand at 25 ℃ for 6 h to obtain a hydrogel.

[0042] Preparation of porous aerogel: The hydrogel was taken out, rinsed three times with deionized water, the surface moisture was absorbed, and it was placed in a freezing device. Directional freezing was used, and a single-sided freezing device was used. The bottom of the hydrogel was in contact with the cold stage. The temperature of the cold stage was set to -40℃ and kept at that temperature for 6 hours (during the freezing process, ice crystals in the porous aerogel grow along the direction of the cold source, forming a parallel oriented pore structure with a pore size of 15μm). After taking it out, it was transferred to a freeze dryer (the cold trap temperature of the freeze dryer was -50℃, the vacuum degree was 10pa, and the drying time was 48 hours) to obtain the porous aerogel.

[0043] Preparation of aerogel matrix: The porous aerogel was transferred to a tube furnace, and argon gas was introduced at a flow rate of 50 mL / min to replace the air in the furnace for 30 min. The temperature was increased from room temperature to 200℃ at a rate of 5℃ / min and held for 1 h. The temperature was then increased from 200℃ to 900℃ at a rate of 5℃ / min and held for 2 h. The heating was turned off, and argon gas was introduced at a rate of 20 mL / min to maintain argon gas flow. The furnace was then cooled to room temperature to obtain the aerogel matrix.

[0044] Encapsulation of molten salt: The temperature of the nitro molten salt is 250℃ and the vacuum degree is 0.1MPa. The air in the pores of the aerogel matrix is ​​extracted, so that the nitro molten salt permeates and fills the aerogel matrix, completing the encapsulation. The permeation and heat preservation are carried out for 4 hours to obtain the molten salt energy storage material.

[0045] Example 4

[0046] Preparation of hydrogel: Add 5 parts of 1% w / v sodium chloride aqueous solution to 70 parts of 1% w / v sodium alginate aqueous solution, stir at 550 r / min for 20 min to obtain suspension;

[0047] Add 3 parts of graphene oxide (graphene oxide sheet thickness 5nm, oxygen-containing functional group content 10%) to the suspension, stir at 350r / min for 20min, add 1 part of gluconolactone, stir at 500r / min for 10min, and let stand at 25℃ for 3h to obtain hydrogel.

[0048] Preparation of porous aerogel: The hydrogel was taken out, rinsed twice with deionized water, the surface moisture was absorbed, and it was placed in a freezing device. Directional freezing was used, and a single-sided freezing device was used. The bottom of the hydrogel was in contact with the cold stage. The temperature of the cold stage was set to -40℃ and kept at that temperature for 6 hours (during the freezing process, ice crystals in the porous aerogel grow along the direction of the cold source to form a parallel oriented pore structure with a pore size of 15μm). After taking it out, it was transferred to a freeze dryer (the cold trap temperature of the freeze dryer was -50℃, the vacuum degree was 10pa, and the drying time was 24 hours) to obtain the porous aerogel.

[0049] Preparation of aerogel matrix: The porous aerogel was transferred to a tube furnace, and argon gas was introduced at a flow rate of 50 mL / min to replace the air in the furnace for 30 min. The temperature was increased from room temperature to 200℃ at a rate of 5℃ / min and held for 1 h. The temperature was then increased from 200℃ to 600℃ at a rate of 5℃ / min and held for 1 h. The heating was turned off, and argon gas was introduced at a rate of 20 mL / min to maintain argon gas flow. The furnace was then cooled to room temperature to obtain the aerogel matrix.

[0050] Encapsulation of molten salt: The temperature of nitro molten salt is 200℃ and the vacuum degree is 0.05MPa. The air in the pores of the aerogel matrix is ​​extracted, so that the nitro molten salt permeates and fills the aerogel matrix, thus completing the encapsulation. The permeation is kept at a constant temperature for 2 hours to obtain the molten salt energy storage material.

[0051] Comparative Example 1

[0052] Preparation of hydrogel: Add 5 parts of 1% w / v sodium chloride aqueous solution to 70 parts of 1% w / v sodium alginate aqueous solution, stir at 550 r / min for 20 min to obtain suspension;

[0053] Four parts of graphene oxide (graphene oxide sheet thickness 5nm, oxygen-containing functional group content 10%) were added to the suspension, stirred at 500r / min for 10min, and allowed to stand at 25℃ for 3h to obtain hydrogel.

[0054] Preparation of porous aerogel: The hydrogel was taken out, rinsed twice with deionized water, the surface moisture was absorbed, and it was placed in a freezing device. Directional freezing was used, and a single-sided freezing device was used. The bottom of the hydrogel was in contact with the cold stage. The temperature of the cold stage was set to -40℃ and kept at that temperature for 6 hours (during the freezing process, ice crystals in the porous aerogel grow along the direction of the cold source to form a parallel oriented pore structure with a pore size of 15μm). After taking it out, it was transferred to a freeze dryer (the cold trap temperature of the freeze dryer was -50℃, the vacuum degree was 10pa, and the drying time was 24 hours) to obtain the porous aerogel.

[0055] Preparation of aerogel matrix: The porous aerogel was transferred to a tube furnace, and argon gas was introduced at a flow rate of 50 mL / min to replace the air in the furnace for 30 min. The temperature was increased from room temperature to 200℃ at a rate of 5℃ / min and held for 1 h. The temperature was then increased from 200℃ to 600℃ at a rate of 5℃ / min and held for 1 h. The heating was turned off, and argon gas was introduced at a rate of 20 mL / min to maintain argon gas flow. The furnace was then cooled to room temperature to obtain the aerogel matrix.

[0056] Encapsulation of molten salt: The temperature of nitro molten salt is 200℃ and the vacuum degree is 0.05MPa. The air in the pores of the aerogel matrix is ​​extracted, so that the nitro molten salt permeates and fills the aerogel matrix, thus completing the encapsulation. The permeation is kept at a constant temperature for 2 hours to obtain the molten salt energy storage material.

[0057] Comparative Example 2

[0058] Preparation of hydrogel: 10 parts of 5% w / v sodium chloride aqueous solution were added to 85 parts of 3% w / v sodium alginate aqueous solution and stirred at 650 r / min for 35 min to obtain a suspension;

[0059] 11 parts of graphene oxide (graphene oxide sheet thickness 8nm, oxygen-containing functional group content 15%) were added to the suspension, stirred at 600r / min for 15min, and allowed to stand at 25℃ for 6h to obtain hydrogel.

[0060] Preparation of porous aerogel: The hydrogel was taken out, rinsed three times with deionized water, the surface moisture was absorbed, and it was placed in a freezing device. The temperature was uniformly reduced from room temperature to -40℃ at a rate of 1℃ / min. After reaching the target temperature, it was kept at that temperature for 4 hours (during the freezing process, ice crystals grow from the outside to the inside of the porous aerogel, forming a through-hole ice crystal network with a pore size of 10μm). After taking it out, it was transferred to a freeze dryer (the cold trap temperature of the freeze dryer was -50℃, the vacuum degree was 10pa, and the drying time was 48 hours) to obtain the porous aerogel.

[0061] Preparation of aerogel matrix: The porous aerogel was transferred to a tube furnace, and argon gas was introduced at a flow rate of 50 mL / min to replace the air in the furnace for 30 min. The temperature was increased from room temperature to 200℃ at a rate of 5℃ / min and held for 1 h. The temperature was then increased from 200℃ to 900℃ at a rate of 5℃ / min and held for 2 h. The heating was turned off, and argon gas was introduced at a rate of 20 mL / min to maintain argon gas flow. The furnace was then cooled to room temperature to obtain the aerogel matrix.

[0062] Encapsulation of molten salt: The temperature of the nitro molten salt is 250℃ and the vacuum degree is 0.1MPa. The air in the pores of the aerogel matrix is ​​extracted, so that the nitro molten salt permeates and fills the aerogel matrix, completing the encapsulation. The permeation and heat preservation are carried out for 4 hours to obtain the molten salt energy storage material.

[0063] Performance testing

[0064] (i) The performance of the molten salt energy storage materials prepared by the methods of Examples 1-4 and Comparative Examples 1-2 was tested in accordance with GB / T45313-2025 "Technical Requirements for Molten Salt Thermal Storage Systems of Solar Thermal Power Plants". The test results are shown in Table 1.

[0065] Table 1

[0066]

[0067] As can be seen from Table 1, the effective thermal storage capacity of Examples 1-4 is 95%-96%, all of which meet the standard qualification line. Among them, Example 2 (96%) is slightly better than the other examples. The thermal storage efficiency is 91%-93%, which meets the standard requirement of ≥90%. Example 2 (93%) has the highest thermal storage efficiency.

[0068] In contrast, the effective thermal storage capacity of Comparative Examples 1-2 is only 78%-82%, far below the qualified threshold of 95%, and the thermal storage efficiency is 75%-76%, significantly lower than the qualified line of 90%, which fails to meet the requirements of system energy utilization efficiency.

[0069] (II) The thermal cycling stability, high-temperature thermal stability and chemical stability of the molten salt energy storage materials prepared by the methods of Examples 1-4 and Comparative Examples 1-2 were tested according to GB / T35170-2017 "Test Methods for Performance of Phase Change Energy Storage Materials". The core parameters of thermal cycling stability were: number of cycles (2000 times) and heating / cooling rate (10℃ / min); the core parameters of high-temperature thermal stability were: aging temperature (20℃ above the phase change point) and aging time (100h). The test results are shown in Table 2.

[0070] Table 2

[0071]

[0072] As can be seen from Table 2, the thermal cycling stability of Examples 1-4 is as follows: the latent heat decay rate is 7%-9%, which is lower than the qualified threshold of 10%, meeting the long-term service requirements of 2000 cycles. Among them, Example 2 has the lowest decay rate and the best thermal cycling stability. The mass loss of high temperature thermal stability is 2%-3%, which is within the qualified range. This indicates that after aging for 100 hours at a temperature 20°C above the phase change point, the thermal decomposition and volatilization loss of the molten salt is low. During the thermal cycling and high temperature aging process, the main components did not undergo significant decomposition and chemical reaction, and the chemical properties are stable.

[0073] In contrast, the thermal cycling stability of Comparative Examples 1-2 showed a latent heat decay rate of 15%, far exceeding the 10% threshold. This means that after 2000 cycles, the heat storage capacity of the molten salt decreased significantly and could not meet the requirements for long-term cyclic use. The high-temperature thermal stability showed a mass loss of 8%-9%, which is 2.7-4.5 times that of the Example Group. This indicates that the molten salt decomposed and volatilized severely during the high-temperature aging process, and under the action of thermal stress, there were significant changes in composition and insufficient chemical stability.

[0074] The embodiments described above are merely examples of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. A highly stable nitro-based molten salt energy storage material, characterized in that, The molten salt energy storage material is obtained by encapsulating a nitro-type molten salt in an aerogel matrix. The aerogel matrix is ​​formed by freeze-drying hydrogel to form a porous aerogel, followed by reduction and carbonization. The raw materials for preparing the hydrogel, by weight, include: 70-85 parts sodium alginate aqueous solution, 5-10 parts sodium chloride aqueous solution, 3-8 parts graphene oxide and 1-3 parts gluconolactone. The nitro-type molten salt is a potassium nitrate-sodium nitrate binary system, wherein the mass ratio of potassium nitrate to sodium nitrate is 35-45:55-65; the graphene oxide sheets have a thickness of 5-8 nm and an oxygen-containing functional group content of 10-15%. The preparation method of the highly stable nitro-type molten salt energy storage material includes the following steps: S1, Preparation of hydrogel: Add 1-5% w / v sodium chloride aqueous solution to 1%-3% w / v sodium alginate aqueous solution, stir at 550-650 r / min for 20-35 min to obtain suspension; Add graphene oxide to the suspension and stir at 350-450 r / min for 20-35 min. Add glucono-delta-lactone and stir at 500-600 r / min for 10-15 min. Let stand at 25℃ for 3-6 h to obtain a hydrogel. S2, Preparation of porous aerogel: Take out the hydrogel, rinse it with deionized water 2-3 times, absorb the surface moisture, place it in a freezing device for freezing treatment, take it out and transfer it to a freeze dryer to dry and obtain porous aerogel; S3, Preparation of aerogel matrix: The porous aerogel is transferred to a tube furnace, and argon gas is introduced at a flow rate of 50 mL / min to replace the air in the furnace for 30 min. The temperature is increased from room temperature to 200℃ at a rate of 5℃ / min and held for 1 h. The temperature is then increased from 200℃ to 600-900℃ at a rate of 5℃ / min and held for 1-2 h. The heating is turned off, and argon gas is introduced at a rate of 20 mL / min to maintain argon gas flow. The furnace is then cooled to room temperature to obtain the aerogel matrix. S4, Encapsulation of molten salt: The temperature of nitro molten salt is 200-250℃, the vacuum degree is 0.05-0.1MPa, the air in the pores of the aerogel matrix is ​​extracted, so that the nitro molten salt permeates and fills the aerogel matrix, completing the encapsulation. The permeation and heat preservation are carried out for 2-4 hours to obtain the molten salt energy storage material.

2. The highly stable nitro-based molten salt energy storage material according to claim 1, characterized in that, The freezing device used in the preparation of porous aerogels employs programmed cooling or directional freezing.

3. The highly stable nitro-based molten salt energy storage material according to claim 2, characterized in that, The specific steps of the programmed cooling and freezing are as follows: the freezing space is uniformly cooled from room temperature to -40℃ at a cooling rate of 1-5℃ / min, and then kept warm for 4-6 hours after reaching the target temperature.

4. The highly stable nitro-type molten salt energy storage material according to claim 3, characterized in that, The specific steps of the directional freezing are as follows: a single-sided freezing device is used, the bottom of the hydrogel is in contact with the cold stage, the temperature of the cold stage is set to -40℃, and the temperature is maintained for 4-6 hours.

5. The highly stable nitro-based molten salt energy storage material according to claim 4, characterized in that, During the freezing process, the porous aerogel obtained by the programmed cooling process grows ice crystals from the outside to the inside, forming a penetrating ice crystal network with a pore size of 5-20 μm.

6. The highly stable nitro-based molten salt energy storage material according to claim 5, characterized in that, During the freezing process, the porous aerogel obtained by the directional freezing process grows ice crystals along the direction of the cold source, forming a parallel oriented pore structure with a pore size of 3-15 μm.

7. The highly stable nitro-based molten salt energy storage material according to claim 6, characterized in that, The freeze dryer has a cold trap temperature of -50℃, a vacuum degree of 10 Pa, and a drying time of 24-48 hours.

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