A magnesium-based thermochemical energy storage material and its preparation method

Abstract

The present invention discloses a magnesium-based thermochemical energy storage material and a preparation method thereof. The magnesium-based thermochemical energy storage material comprises a magnesium oxide matrix and a dopant loaded on the magnesium oxide matrix. The microstructure of the magnesium-based thermochemical energy storage material is a nanoscale petal-like lamella, and the dopant is a nitrate. The preparation method of the magnesium-based thermochemical energy storage material comprises the following steps: S1: Stir and mix a magnesium precursor solution and a carbonate solution, filter after reaction; S2: Stir and mix a nitrate solution with the filtration product of step S1, and dry the mixture; S3: Place the dried mixture in step S2 into a high-temperature furnace for calcination. The present invention directly prepares a nitrate-modified magnesium oxide-based thermochemical energy storage material from a magnesium precursor by a one-step calcination method, reduces the preparation steps, lowers the cost, improves the MgO carbonation rate, and enhances the cycle stability.

Description

Technical Field

[0001] The present invention belongs to magnesium-based thermochemical energy storage materials, and particularly relates to a magnesium-based thermochemical energy storage material and a preparation method thereof. Background Art

[0002] Among many energy storage technologies, an important one is to convert temporarily excessive energy into heat energy for storage. Thermal energy storage is achieved by using heat storage materials to store heat energy and release energy when needed, which has great development potential. According to different principles, thermal energy storage can usually be divided into sensible heat energy storage, latent heat energy storage (phase change heat storage), and thermochemical energy storage. Among them, as a frontier heat storage technology, thermochemical energy storage is superior to sensible heat and latent heat energy storage in terms of heat storage temperature and energy storage density. In addition, since thermal energy is stored in the form of chemical energy, theoretically zero loss and long-term storage of thermal energy can be achieved.

[0003] As the basis of thermochemical energy storage technology, thermochemical energy storage materials are the most important component. Among them, the thermochemical heat storage material of the MgO / MgCO3 system with low cost, wide temperature window, high heat storage density, and environmental friendliness is considered to be one of the most promising materials (Formula 1). However, as a solid-phase heat storage material, the MgO / MgCO3 system is also limited by factors such as slow reaction rate, weak cycle stability, and complex preparation, which is not conducive to realizing large-scale industrial production and application.

[0004] Formula 1

[0005] Currently, the synthesis method of existing MgO-based thermochemical energy storage materials is mainly prepared by a two-step method. In the first step, MgO is prepared by reacting a magnesium precursor with a precipitating agent, drying, and calcining. In the second step, a dopant is added to the prepared MgO by a water-soluble method or an alcohol-soluble method, and then dried and calcined again to obtain the final MgO-based thermochemical energy storage material. The preparation process of this method is cumbersome, not only consuming a lot of electric energy in multiple drying and calcining steps, but also prone to sample loss during the transfer process. Summary of the Invention

[0006] In view of the above technical problems, the present invention provides a magnesium-based thermochemical energy storage material and a preparation method thereof. The present invention directly prepares a nitrate-modified magnesium oxide-based thermochemical energy storage material from a magnesium precursor by a one-step calcination method, reducing the preparation steps, lowering the cost, and increasing the carbonation rate of MgO and enhancing the cycle stability.

[0007] To achieve the above object, the technical solution of the present invention is as follows:

[0008] A magnesium-based thermochemical energy storage material, the magnesium-based thermochemical energy storage material includes a magnesium oxide matrix and a dopant loaded on the magnesium oxide matrix. The microstructure of the magnesium-based thermochemical energy storage material is a nanoscale petal-like lamella. The dopant is a nitrate. The nitrate can be in a molten state in the magnesium-based thermochemical energy storage material. The liquid nitrate can reduce the Mg-O bond energy and accelerate the reaction rate between magnesium oxide and carbon dioxide;

[0009] The preparation method of the magnesium-based thermochemical energy storage material includes the following steps:

[0010] S1: Stir and mix the magnesium precursor solution and the carbonate solution, react and then filter;

[0011] S2: Stir and mix the nitrate solution with the filtration product of step S1, and dry the mixture;

[0012] S3: Place the dried mixture in step S2 into a high-temperature furnace for calcination.

[0013] The magnesium precursor can be magnesium chloride hexahydrate or magnesium nitrate, and the carbonate can be potassium carbonate or sodium carbonate. Due to the reaction chemical formula in the MgO / MgCO3 system, the molar ratio of the magnesium precursor to the carbonate is the same or the carbonate is slightly in excess (for example, within 1.1 times or 1.2 times is acceptable) to ensure that the magnesium precursor reacts fully.

[0014] The nitrate can be LiNO3, NaNO3, KNO3, LiNO3-NaNO3, NaNO3-KNO3, LiNO3-KNO3, LiNO3-NaNO3-KNO3.

[0015] Preferably, the nitrate is a ternary alkali metal nitrate of LiNO3-NaNO3-KNO3. This alkali metal nitrate is selected because its melting point is relatively low, and it can melt earlier during the heating process, promoting the reaction rate of magnesium oxide.

[0016] The mixing ratio of LiNO3-NaNO3-KNO3 can be selected according to the LiNO3-NaNO3-KNO3 phase diagram, as long as it is in a molten state within the working temperature range of the magnesium oxide matrix. Preferably, the molar ratio of LiNO3-NaNO3-KNO3 is 0.3:0.18:0.52. The nitrate at this ratio is a eutectic LiNO3-NaNO3-KNO3 ternary molten salt with a lower melting point, which can melt earlier and accelerate the reaction rate of magnesium oxide.

[0017] Preferably, the molar ratio of the dopant in the magnesium-based thermochemical energy storage material is 5-20. Experiments show that when the doping ratio is greater than 20, the reaction rate does not increase but decreases instead. This may be because the excessive ratio causes the nitrate to block the pores on the surface of magnesium oxide, inhibiting the reaction.

[0018] Preferably, the molar ratio of the dopant to the magnesium-based thermochemical energy storage material is 10-20, and more preferably 20, which can promote higher reaction efficiency.

[0019] Preferably, the calcination temperature in step S3 is 400-450 °C, which can make the obtained energy storage material present a nano-scale petal microporous sheet structure. This can effectively promote the flow of carbon dioxide inside magnesium oxide during the heat release and storage processes of the magnesium-based thermochemical energy storage material, improving the reaction rate. If the temperature is too low, magnesium oxide cannot be produced by the reaction; if the temperature is too high, the microscopic morphology of the nano-scale petal microporous sheet cannot be obtained.

[0020] Furthermore, in step S3, the mixture is heated in a high-temperature furnace at a heating rate of 5 °C / min to 450 °C and calcined for 4 hours.

[0021] Based on the same inventive concept, the present invention provides a preparation method of a magnesium-based thermochemical energy storage material, comprising the following steps:

[0022] S1: Stir and mix a magnesium precursor solution and a carbonate solution, react, and then filter;

[0023] S2: Stir and mix a nitrate solution with the filtration product of step S1, and dry the mixture;

[0024] S3: Place the dried mixture in step S2 into a high-temperature furnace for calcination to obtain the magnesium-based thermochemical energy storage material;

[0025] The magnesium-based thermochemical energy storage material includes a magnesium oxide matrix and a dopant supported on the magnesium oxide matrix. The microstructure of the magnesium-based thermochemical energy storage material is a nano-scale petal sheet layer, and the dopant is a nitrate.

[0026] Preferably, step S1 specifically includes preparing solutions of a magnesium precursor and a carbonate with a molar ratio of 1:1, pouring the carbonate solution into the magnesium precursor solution, stirring, reacting, and then filtering.

[0027] The magnesium precursor is MgCl2·6H2O, and the carbonate is Na2CO3. In addition, the magnesium precursor can also be magnesium nitrate, etc., and the carbonate can also be potassium carbonate, etc.

[0028] Preferably, the calcination temperature in step S3 is 400 - 450 °C, which promotes the obtained energy storage material to present a nano - scale petal - shaped microporous sheet structure. This can enable the magnesium - based thermochemical energy storage material to effectively promote the flow of carbon dioxide inside magnesium oxide during the heat release and storage processes, improving the reaction rate. If the temperature is too low, magnesium oxide cannot be produced by the reaction; if the temperature is too high, the microscopic morphology of the nano - scale petal - shaped microporous sheet cannot be achieved.

[0029] Further, in step S3, the mixture is heated to 450 °C at a heating rate of 5 °C / min with a high - temperature furnace and calcined for 4 hours.

[0030] Preferably, step S2 specifically includes preparing a nitrate solution by mixing LiNO3 - NaNO3 - KNO3 alkali metal nitrates with a molar ratio of 0.3:0.18:0.52, stirring and mixing the nitrate solution with the filtration product of step S1, and drying the mixture at 105 - 120 °C for 12 - 24 h.

[0031] Preferably, in step S2, 5 - 20 mol% of nitrates based on the magnesium - based thermochemical energy storage material are weighed and configured into a nitrate solution.

[0032] Due to the adoption of the above - mentioned technical solutions, the present invention has the following advantages and positive effects compared with the prior art:

[0033] The magnesium - based thermochemical energy storage material provided by the present invention directly obtains the energy storage material doped with nitrates through one - step calcination of a magnesium precursor. And the doped nitrates can weaken the lattice energy inside magnesium oxide, accelerate the reaction rate, increase the energy density and cycle stability. Further, the magnesium - based thermochemical energy storage material doped with nitrates is directly prepared from the magnesium precursor by the one - step calcination method, greatly simplifying the preparation process, reducing the energy consumption during the preparation process, and effectively promoting industrial production.

[0034] In another embodiment of the present invention, the calcination temperature is strictly controlled, making the final material present a nano - scale petal - shaped microporous sheet structure. This can enable the magnesium - based thermochemical energy storage material to effectively promote the flow of carbon dioxide inside magnesium oxide during the heat release and storage processes, improving the reaction rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is the microscopic scanning electron microscope picture of the magnesium - based thermochemical energy storage material prepared in Example 1 of the present invention;

[0036] Figure 2 It is the energy storage density curve graph of the magnesium - based thermochemical energy storage material prepared in Example 1 of the present invention;

[0037] Figure 3Cyclic stability diagram of the magnesium-based thermochemical energy storage material prepared in Example 1 of the present invention;

[0038] Figure 4 Energy storage density curve of the magnesium-based thermochemical energy storage material prepared in Example 2 of the present invention;

[0039] Figure 5 Cyclic stability diagram of the magnesium-based thermochemical energy storage material prepared in Example 2 of the present invention;

[0040] Figure 6 Energy storage density curve of the magnesium-based thermochemical energy storage material prepared in Example 3 of the present invention;

[0041] Figure 7 Energy storage density curve of the material MgO-1 prepared in Comparative Example 1 of the present invention;

[0042] Figure 8 Cyclic stability diagram of the material MgO-1 prepared in Comparative Example 1 of the present invention;

[0043] Figure 9 Energy storage density curve of the material MgO-2 prepared in Comparative Example 2 of the present invention;

[0044] Figure 10 Cyclic stability diagram of the material MgO-2 prepared in Comparative Example 2 of the present invention;

[0045] Figure 11 Microscopic scanning electron microscope image of MgO-3 prepared in Comparative Example 3 of the present invention;

[0046] Figure 12 Energy storage density curve of the material MgO-3 prepared in Comparative Example 3 of the present invention;

[0047] Figure 13 Cyclic stability diagram of the material MgO-3 prepared in Comparative Example 3 of the present invention;

[0048] Figure 14 Microscopic scanning electron microscope image of MgO-4 prepared in Comparative Example 4 of the present invention;

[0049] Figure 15 Energy storage density curve of the material MgO-4 prepared in Comparative Example 4 of the present invention.

[0050] Note: Figure 2 、 4 For the energy storage density curves of 6, 7, 9, 12, 15, the meaning of the English vertical coordinate is heat storage density, and the meaning of the English horizontal coordinate is time;

[0051] Figure 3 、 5For the cyclic stability diagrams of 8, 10, and 13, the meaning of the vertical axis in English is the heat storage density, and the meaning of the horizontal axis in English is the number of cycles. Detailed implementation manners

[0052] The following further elaborates in detail on a magnesium-based thermochemical energy storage material and its preparation method proposed by the present invention in combination with the accompanying drawings and specific embodiments. According to the following description, the advantages and features of the present invention will be clearer.

[0053] In the following embodiments of the present invention, the magnesium-based thermochemical energy storage material is named AMN X -MgO. AMN is the abbreviation of LiNO3 - NaNO3 - KNO3, and X is the molar ratio of the molten salt in the MgO-based thermochemical energy storage material, where X ranges from 0 to 20.

[0054] Example 1

[0055] AMN 10 -MgO preparation method includes:

[0056] S1: Weigh equivalent masses of MgCl2·6H2O and Na2CO3 in a molar ratio of 1:1 and place them in beakers respectively. Add 100 mL of deionized water to prepare solutions with concentrations of 0.6 mol / L and 0.8 mol / L; place the beaker containing the Na2CO3 solution on a magnetic stirrer and pour it into the pre-prepared MgCl2·6H2O solution, stir at room temperature for 1 hour, and filter after the reaction;

[0057] S2: Weigh 10 mol% of alkali metal nitrates (LiNO3 - NaNO3 - KNO3 = 0.3:0.18:0.52) and place them in a beaker. Add 40 mL of deionized water to prepare an inorganic salt aqueous solution; add the inorganic salt aqueous solution to the filtered product of step S1, and then place it in a magnetic stirrer to stir evenly; place the evenly stirred mixture in an oven at 120°C and dry for 12 hours;

[0058] S3: Place the dried mixture in a muffle furnace at 450°C and calcine for 4 hours to obtain the MgO-based thermochemical energy storage material doped with nitrates (heating rate 5°C / min); place the cooled sample in an agate mortar, grind it into powder, and seal it in a sealed bag, named AMN 10 -MgO for subsequent use.

[0059] The energy storage density of the MgO-based thermochemical energy storage material was tested using a thermogravimetric analyzer. Weigh 10 mg of the material and place it in an alumina crucible, then put it into the thermogravimetric analyzer. Pass pure N2 into the thermogravimetric analyzer with a gas flow rate of 50 mL / min. Heat it from room temperature to 350 °C at a heating rate of 10 °C / min and keep it at a constant temperature for 10 min to remove moisture and impurity gases. Switch the gas to a mixture of CO2 and N2 (a mixed atmosphere of 40 vol% CO2 and 60 vol% N2 with a flow rate of 50 mL / min), and keep it at a constant temperature of 350 °C for 120 minutes (30 minutes for the cyclic stability test). Then switch the gas to pure N2 (flow rate of 50 mL / min) and heat it to 450 °C and keep it at a constant temperature for 10 minutes. Repeating this cycle can test the energy storage density and cyclic stability of the MgO-based thermochemical energy storage material.

[0060] According to the mass change data during the test process, calculate the energy storage density of the MgO-based thermochemical energy storage material:

[0061] ,

[0062] For the AMN 10 -MgO prepared in Example 1, perform microstructure and thermochemical energy storage density tests. As Figure 1 shown, Figure 1 after calcination in step S3, the MgO-based thermochemical energy storage material presents a nano-level petal-like lamellar structure. Each lamella has a large number of pores, and this special structure is conducive to the flow of CO2 in the material and accelerates the reaction rate. The test results of the energy storage density are as Figure 2 and Figure 3 shown. The energy storage density can reach 1710.07 kJ / kg in 120 minutes. Under the condition of a 30-minute carbonation reaction, after rapid cycling 10 times, the energy storage density decays by 17.41%, and the final energy storage density is 479.36 kJ / kg.

[0063] Example 2

[0064] The preparation method of AMN 20 -MgO includes:

[0065] S1: Weigh equivalent masses of MgCl2·6H2O and Na2CO3 at a molar ratio of 1:1 and place them in beakers respectively. Add 100 mL of deionized water to configure solutions with concentrations of 0.6 mol / L and 0.8 mol / L. Place the beaker containing the Na2CO3 solution on a magnetic stirrer and pour it into the pre-prepared MgCl2·6H2O solution, stir at room temperature for 1 hour, and filter after the reaction;

[0066] S2: Weigh 20 mol% of alkali metal nitrates (LiNO3-NaNO3-KNO3 = 0.3:0.18:0.52) and put them into a beaker. Add 40 mL of deionized water to prepare an inorganic salt aqueous solution. Add the inorganic salt aqueous solution to the above-mentioned filtered product, and then put it into a magnetic stirrer to stir evenly. Put the evenly stirred mixture into an oven at 120 °C and dry for 12 hours.

[0067] S3: Put the dried mixture into a muffle furnace at 450 °C and calcine for 4 hours to obtain the molten salt-doped MgO-based thermochemical energy storage material (heating rate 5 °C / min). Put the cooled sample into an agate mortar, grind it into powder, place it in a sealed bag and seal it, named AMN 20 -MgO, for subsequent use.

[0068] Use a thermogravimetric analyzer to test the energy storage density of AMN 20 -MgO material. Weigh 10 mg of the material and put it into an alumina crucible, and place it in a thermogravimetric analyzer. Pass pure N2 into the thermogravimetric analyzer, with a gas flow rate of 50 mL / min. Heat it from room temperature to 350 °C at a heating rate of 10 °C / min and keep it at a constant temperature for 10 min to remove moisture and impurity gases. Switch the gas to a mixture of CO2 and N2 (a mixed atmosphere of 40 vol% CO2 and 60 vol% N2, with a flow rate of 50 mL / min), and keep it at a constant temperature of 350 °C for 120 minutes (keep it at a constant temperature for 30 minutes for the cyclic stability test). Switch the gas to pure N2 (flow rate 50 mL / min), and heat it to 450 °C and keep it at a constant temperature for 10 minutes. By performing such reciprocating cycles, the energy storage density and cyclic stability of AMN 20 -MgO can be tested.

[0069] Perform thermochemical energy storage density tests on the AMN 20 -MgO prepared in Example 2. The test results of the energy storage density are as Figure 4 and Figure 5 shown. The energy storage density can reach 1625.67 kJ / kg in 120 minutes. Under the condition of a 30-minute carbonation reaction, the energy storage density decays by 18.18% after 10 rapid cycles, and the final energy storage density is 450.28 kJ / kg.

[0070] Example 3

[0071] S1: Weigh equivalent masses of MgCl2·6H2O and Na2CO3 at a molar ratio of 1:1 and put them into beakers respectively. Add 100 mL of deionized water to prepare solutions with concentrations of 0.6 mol / L and 0.8 mol / L. Place the beaker containing the Na2CO3 solution on a magnetic stirrer and pour it into the pre-prepared MgCl2·6H2O solution. Stir at room temperature for 1 hour, and filter after the reaction.

[0072] S2: Weigh 5 mol% of alkali metal nitrates (LiNO3-NaNO3-KNO3 = 0.3:0.18:0.52) and put them into a beaker. Add 40 mL of deionized water to prepare an inorganic salt aqueous solution. Add the inorganic salt aqueous solution to the above-mentioned filtered product, and then put it into a magnetic stirrer to stir evenly. Put the evenly stirred mixture into an oven at 120 °C and dry it for 12 hours.

[0073] S3: Put the dried mixture into a muffle furnace at 450 °C and calcine it for 4 hours to obtain the molten salt-doped MgO-based thermochemical energy storage material (heating rate 5 °C / min). Put the cooled sample into an agate mortar, grind it into powder, place it in a sealed bag and seal it, named AMN5-MgO, for subsequent use.

[0074] Use a thermogravimetric analyzer to test the energy storage density of AMN5-MgO. Weigh 10 mg of the material and put it into an alumina crucible, and place it in the thermogravimetric analyzer. Pass pure N2 into the thermogravimetric analyzer, with a gas flow rate of 50 mL / min. Heat it from room temperature to 350 °C at a heating rate of 10 °C / min and keep it at a constant temperature for 10 min to remove moisture and impurity gases. Switch the gas to a mixture of CO2 and N2 (40 vol% CO2 and 60 vol% N2 mixed atmosphere, flow rate 50 mL / min), and keep it at a constant temperature of 350 °C for 120 minutes (keep it at a constant temperature for 30 minutes in the cyclic stability test). Switch the gas to pure N2 (flow rate 50 mL / min), and heat it to 450 °C and keep it at a constant temperature for 10 minutes. Repeat this cycle to test the energy storage density and cyclic stability of the MgO-based adsorbent.

[0075] Perform a thermochemical energy storage density test on the AMN5-MgO prepared in Example 3. The test results of the energy storage density are as Figure 6 shown. The energy storage density can reach 1541.89 kJ / kg in 120 minutes.

[0076] Comparative Example 1

[0077] S1: Weigh equivalent masses of MgCl2·6H2O and Na2CO3 at a molar ratio of 1:1 and put them into beakers respectively. Add 100 mL of deionized water to prepare solutions with concentrations of 0.6 mol / L and 0.8 mol / L. Place the beaker containing the Na2CO3 solution on a magnetic stirrer and pour it into the pre-prepared MgCl2·6H2O solution. Stir at room temperature for 1 hour, and filter after the reaction.

[0078] S2: Place the filtered product in a muffle furnace at 450 °C to calcine and prepare MgO.

[0079] S3: Weigh 10 mol% of alkali metal nitrates (LiNO3-NaNO3-KNO3 = 0.3:0.18:0.52) and put them into a beaker. Add 40 mL of deionized water to prepare an inorganic salt aqueous solution. Add the inorganic salt aqueous solution to the MgO prepared above, and then put it into a magnetic stirrer to stir evenly. Put the evenly stirred mixture into an oven at 120 °C and dry it for 12 hours.

[0080] S4: Put the dried mixture into a muffle furnace at 450 °C and calcine it for 4 hours to obtain a sample (heating rate: 5 °C / min). Put the cooled sample into an agate mortar, grind it into powder, place it in a sealed bag and label it as MgO-1 for subsequent use.

[0081] Use a thermogravimetric analyzer to test the energy storage density of the MgO-1 material. Weigh 10 mg of the material and put it into an alumina crucible, and then place it in the thermogravimetric analyzer. Pass pure N2 into the thermogravimetric analyzer with a gas flow rate of 50 mL / min. Heat it from room temperature to 350 °C at a heating rate of 10 °C / min and keep it at a constant temperature for 10 min to remove moisture and impurity gases. Switch the gas to a mixture of CO2 and N2 (a mixed atmosphere of 40 vol% CO2 and 60 vol% N2 with a flow rate of 50 mL / min), and keep it at a constant temperature of 350 °C for 120 minutes (30 minutes for the cyclic stability test). Switch the gas to pure N2 (flow rate: 50 mL / min), heat it to 450 °C and keep it at a constant temperature for 10 minutes. Repeating this process can test the energy storage density and cyclic stability of MgO-1.

[0082] Perform a thermochemical energy storage density test on the MgO-1 prepared in Comparative Example 1. The test results of the energy storage density are as Figure 7 and Figure 8 shown. The energy storage density can reach 863.91 kJ / kg in 120 minutes. Under the condition of a 30-minute carbonation reaction, after 10 rapid cycles, the energy storage density decays by 34.92%, and the final energy storage density is 276.81 kJ / kg.

[0083] Comparative Example 2:

[0084] S1: Weigh equivalent masses of MgCl2·6H2O and Na2CO3 at a molar ratio of 1:1 and put them into separate beakers. Add 100 mL of deionized water to prepare solutions with concentrations of 0.6 mol / L and 0.8 mol / L respectively. Place the beaker containing the Na2CO3 solution on a magnetic stirrer and pour it into the pre-prepared MgCl2·6H2O solution. Stir at room temperature for 1 hour, and then filter after the reaction.

[0085] S2: Place the filtered product in a muffle furnace at 450 °C to calcine and prepare MgO.

[0086] S3: Weigh 20 mol% of alkali metal nitrates (LiNO3-NaNO3-KNO3 = 0.3:0.18:0.52) and put them into a beaker. Add 40 mL of deionized water to prepare an inorganic salt aqueous solution. Add the inorganic salt aqueous solution to the MgO prepared above, and then put it into a magnetic stirrer to stir evenly. Place the evenly stirred mixture in an oven at 120 °C and dry it for 12 hours.

[0087] S4: Put the dried mixture into a muffle furnace at 450 °C and calcine it for 4 hours to obtain a sample (heating rate 5 °C / min). Put the cooled sample into an agate mortar, grind it into powder, place it in a sealed bag and seal it, named MgO-2, for subsequent use.

[0088] Use a thermogravimetric analyzer to test the energy storage density of the MgO-2 material. Weigh 10 mg of the material and put it into an alumina crucible, and place it in the thermogravimetric analyzer. Pass pure N2 into the thermogravimetric analyzer, with a gas flow rate of 50 mL / min. At a heating rate of 10 °C / min, heat it from room temperature to 350 °C and keep it at a constant temperature for 10 min to remove moisture and impurity gases. Switch the gas to a mixture of CO2 and N2 (40 vol% CO2 and 60 vol% N2 mixed atmosphere, flow rate 50 mL / min), and keep it at a constant temperature of 350 °C for 120 minutes. Switch the gas to pure N2 (flow rate 50 mL / min), and heat it to 450 °C and keep it at a constant temperature for 10 minutes.

[0089] Perform a thermochemical energy storage density test on the MgO-2 prepared in Comparative Example 2. The test results of the energy storage density are as Figure 9 and Figure 10 shown. The energy storage density can reach 1045.96 kJ / kg in 120 minutes. Under the condition of a 30-minute carbonation reaction, after 10 rapid cycles, the energy storage density decays by 33.92%, and the final energy storage density is 382.91 kJ / kg.

[0090] Comparative Example 3

[0091] Weigh equivalent masses of MgCl₂·6H₂O and Na₂CO₃ in a molar ratio of 1:1 and place them in separate beakers. Add 100 mL of deionized water to each beaker to prepare solutions with concentrations of 0.6 mol / L and 0.8 mol / L respectively. Place the beaker containing the Na₂CO₃ solution on a magnetic stirrer and pour in the pre-prepared MgCl₂·6H₂O solution. Stir at room temperature for 1 hour, then filter the reaction mixture. Weigh 10 mol% of alkali metal nitrates (LiNO₃ - NaNO₃ - KNO₃ = 0.3:0.18:0.52) and place them in a beaker. Add 40 mL of deionized water to prepare an inorganic salt aqueous solution. Add the inorganic salt aqueous solution to the above-mentioned filtered product and then stir well in a magnetic stirrer. Place the well-stirred mixture in an oven at 120 °C and dry for 12 hours. Place the dried mixture in a muffle furnace at 500 °C and calcine for 4 hours to obtain a molten salt-doped MgO-based thermochemical energy storage material (heating rate 5 °C / min). Cool the sample and grind it into powder in an agate mortar, then seal it in a plastic bag and name it MgO-3 for subsequent use.

[0092] Use a thermogravimetric analyzer to test the energy storage density of the MgO-based thermochemical energy storage material. Weigh 10 mg of the material and place it in an alumina crucible, then place it in the thermogravimetric analyzer. Pass pure N₂ into the thermogravimetric analyzer at a gas flow rate of 50 mL / min. Heat from room temperature to 350 °C at a heating rate of 10 °C / min and hold for 10 min to remove moisture and impurity gases. Switch the gas to a mixture of CO₂ and N₂ (40 vol% CO₂ and 60 vol% N₂, gas flow rate 50 mL / min), and hold at 350 °C for 120 min (hold for 30 min in the cyclic stability test). Switch the gas to pure N₂ (gas flow rate 50 mL / min) and heat to 450 °C and hold for 10 min. Repeat this cycle to test the energy storage density and cyclic stability of the MgO-based adsorbent.

[0093] Perform microscopic morphology analysis and thermochemical energy storage density test on MgO-3 prepared in Comparative Example 3. Figure 11 Figure shows the microscopic morphology of MgO-3. It can be seen from the figure that the petal-like structure of the obtained product is damaged under high-temperature calcination, presenting irregular nanosheets, which is not conducive to reacting with CO₂. The test results of the energy storage density are as Figure 12 and Figure 13 shown. The energy storage density at 120 min is 971.48 kJ / kg. Under the condition of a 30-min carbonation reaction, the energy storage density decays by 55% after 10 rapid cycles, and the final energy storage density is 220.36 kJ / kg.

[0094] Comparative Example 4

[0095] In this comparative example, the raw materials used are exactly the same as those in Example 1, and the preparation method is also the same. The difference from Example 1 is that in step S2, the inorganic salt solution prepared from the alkali metal salt is not mixed with the filtration product in step S1. Only the filtration product is dried, and then the calcination in step S3 is continued. Therefore, no doped nitrate is added in this comparative example, and the obtained product is named MgO-4. The microscopic morphology of the prepared MgO-4 is as Figure 14 shown, presenting a disordered flaky aggregate. Using the same thermogravimetric analyzer as in Example 1 and the same experimental conditions to test the energy storage density of MgO-4, the results are as Figure 15 shown. It can be seen from the figure that the energy storage density is only 118.31 kJ / kg at 120 minutes, and the energy storage density is about 10 kJ / kg in the first 40 minutes.

[0096] Comparing Example 1 with Comparative Example 1, and Example 2 with Comparative Example 2, it shows that only by using the one-step calcination preparation method of the present invention can magnesium oxide-based thermochemical energy storage materials with higher energy density and higher cycle stability be obtained; comparing Example 1 with Comparative Example 4, within the same time, the energy storage density of Comparative Example 4 is very low, and the reaction rate is extremely low. The reaction rate of Comparative Example 4 is very low, while the reaction rate of Example 1 is very fast, and thus the energy storage density is large, indicating that doped nitrate can accelerate the reaction rate; comparing Example 1 with Comparative Example 3, by strictly controlling the calcination temperature, a higher energy storage density and cycle stability can be obtained; comparing Example 1 with Comparative Example 3 and 4, it can be seen that by simultaneously controlling the temperature and doped nitrate, a stable microscopic morphology as Figure 1 shown can be obtained. Therefore, through the one-step calcination preparation method of the present invention, magnesium oxide-based thermochemical energy storage materials with higher energy density and higher cycle stability can be obtained. Therefore, the magnesium-based thermochemical energy storage material obtained by the preparation method of the present invention not only improves the reaction rate of magnesium oxide, enhances the energy density and cycle stability, but also can greatly simplify the preparation process, reduce the energy loss in the preparation process, lower the cost, and effectively promote industrial production.

[0097] The embodiments of the present invention have been described in detail above with reference to the drawings, but the present invention is not limited to the above embodiments. Even if various changes are made to the present invention, provided that these changes fall within the scope of the claims of the present invention and their equivalent technologies, they still fall within the protection scope of the present invention.

Claims

1. A magnesium-based thermochemical energy storage material, characterized in that, The magnesium-based thermochemical energy storage material includes a magnesium oxide matrix and a dopant loaded on the magnesium oxide matrix. The microstructure of the magnesium-based thermochemical energy storage material is a nanoscale petal-like lamella. The dopant is a ternary alkali metal nitrate of LiNO3-NaNO3-KNO3. The molar ratio of LiNO3-NaNO3-KNO3 is 0.3:0.18:0.

52. The molar proportion of the dopant in the magnesium-based thermochemical energy storage material is 5%-20%. The preparation method of the magnesium-based thermochemical energy storage material includes the following steps: S1: Stir and mix the magnesium precursor solution and the carbonate solution, react, and then filter; S2: Stir and mix the nitrate solution with the filtration product of step S1, and dry the mixture; S3: Place the dried mixture in step S2 into a high-temperature furnace for calcination, where the calcination temperature is 400-450 °C.

2. The magnesium-based thermochemical energy storage material according to claim 1, characterized in that, The molar proportion of the dopant in the magnesium-based thermochemical energy storage material is 10%-20%.

3. The magnesium-based thermochemical energy storage material according to claim 1, characterized in that, In step S3, the mixture is heated to 450 °C at a heating rate of 5 °C / min in the high-temperature furnace and calcined for 4 hours.

4. A method for preparing a magnesium-based thermochemical energy storage material according to any one of claims 1-3, characterized in that, Including the following steps: S1: Stir and mix the magnesium precursor solution and the carbonate solution, react, and then filter; S2: Stir and mix the nitrate solution with the filtration product of step S1, and dry the mixture; S3: Place the dried mixture in step S2 into a high-temperature furnace for calcination, where the calcination temperature is 400-450 °C to obtain the magnesium-based thermochemical energy storage material; The magnesium-based thermochemical energy storage material includes a magnesium oxide matrix and a dopant loaded on the magnesium oxide matrix. The microstructure of the magnesium-based thermochemical energy storage material is a nanoscale petal-like lamella. The dopant is a nitrate.

5. The preparation method of the magnesium-based thermochemical energy storage material according to claim 4, characterized in that, In step S3, the mixture is heated to 450 °C at a heating rate of 5 °C / min in the high-temperature furnace.

6. The preparation method of the magnesium-based thermochemical energy storage material according to claim 4, characterized in that, The drying in step S2 is to place the mixture in 105-120 °C for 12-24 h for drying.

7. The preparation method of the magnesium-based thermochemical energy storage material according to claim 4 or 6, characterized in that, In step S2, weigh 5-20 mol% of the nitrate in the magnesium-based thermochemical energy storage material and prepare it into a nitrate solution.

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