Manganese-iron composite metal oxide heat storage material and preparation method thereof

Abstract

The application provides a manganese-iron composite metal oxide heat storage material and a preparation method thereof, and the preparation method comprises the following steps: mixing a manganese source, an iron source and a solvent, then adding a complexing agent and a pH regulator, stirring to obtain a gel solution; and sequentially performing drying, first calcination and second calcination on the gel solution to obtain the manganese-iron composite metal oxide heat storage material. The general formula of the manganese-iron composite metal oxide heat storage material is (Mn x Fe 1‑x )2O3, wherein 0.5 <= x <= 0.8. The manganese-iron composite metal oxide heat storage material prepared by the preparation method has high heat storage density, fast redox rate and excellent cyclic heat storage performance.

Description

Technical Field

[0001] This invention belongs to the field of thermal storage materials technology, and particularly relates to a manganese-iron composite metal oxide thermal storage material and its preparation method. Background Technology

[0002] To address global warming and the depletion of non-renewable resources, more and more countries are focusing on utilizing new energy sources. As the proportion of renewable energy in energy consumption gradually increases, the mismatch between supply and demand for renewable energy sources such as solar and wind power in time and space is becoming increasingly prominent. Developing new energy storage technologies is a key supporting technology for solving this problem. Thermochemical thermal energy storage has the advantages of high energy density, long storage period, and low heat loss.

[0003] The principle of thermochemical heat storage is to utilize reversible thermochemical reactions to achieve heat storage and release processes. High-temperature thermochemistry is mainly divided into metal hydride systems, carbonate systems, hydroxide systems, metal oxide systems, ammonia systems, and organic systems. Currently, metal oxide systems are the most studied. Metal oxide heat storage systems utilize the interconversion between metal oxides of different valence states to achieve energy storage and release.

[0004] Researchers have discovered that the Mn2O3 / Mn3O4 oxide system possesses advantages such as environmental friendliness, non-toxicity, and low production cost, making it a highly promising thermal storage material. However, under repeated high-temperature conditions, the manganese oxide particles in single Mn2O3 / Mn3O4 thermal storage materials exhibit significant grain growth and coarsening, leading to drawbacks such as poor redox kinetics and poor cycle performance, severely impacting the normal use of the material.

[0005] CN113736432B discloses a metal oxide thermal storage material, a metal oxide thermal storage unit, and a preparation method thereof, wherein the metal oxide material is Cu. 1.5 Mn 1.5 O4 composite metal oxide material, wherein Cu 1.5 Mn 1.5 The O4 composite metal oxide material is prepared by a hydrothermal method, in which the hydrothermal reaction product is calcined at a high temperature of 800℃-900℃ to obtain the Cu. 1.5 Mn 1.5 O4 composite metal oxide material, wherein Cu 1.5 Mn 1.5 O4 composite metal oxide materials have a hollow porous structure after multiple thermal storage cycles.

[0006] However, the cyclic thermal storage performance of copper-manganese metal oxide thermal storage materials still needs to be improved. There is an urgent need to develop a new type of manganese-based metal oxide thermal storage material to enhance its oxidation-reduction rate and cyclic thermal storage performance. Summary of the Invention

[0007] The purpose of this invention is to provide a manganese-iron composite metal oxide thermal storage material and its preparation method. The manganese-iron composite metal oxide thermal storage material prepared by the method has high thermal storage density, fast oxidation-reduction rate and excellent cyclic thermal storage performance.

[0008] To achieve this objective, the present invention adopts the following technical solution:

[0009] In a first aspect, the present invention provides a method for preparing a manganese-iron composite metal oxide thermal storage material, the method comprising the following steps:

[0010] (1) Mix manganese source, iron source and solvent, then add complexing agent and pH adjuster, stir to obtain gel solution;

[0011] (2) The gel solution described in step (1) is dried, calcined for the first time, and calcined for the second time in sequence to obtain the manganese-iron composite metal oxide thermal storage material.

[0012] In this invention, the first calcination and the second calcination are carried out in a muffle furnace under an air atmosphere.

[0013] The preparation method provided by this invention involves obtaining a precursor via a sol-gel method, followed by drying and two calcinations to obtain the final product. This preparation method is simple, highly efficient, and suitable for large-scale industrial production. The resulting manganese-iron composite metal oxide thermal storage material exhibits high thermal density, rapid redox rate, and excellent cyclic thermal storage performance.

[0014] It is worth noting that this invention employs a two-stage calcination process after obtaining the dried gel, resulting in superior product performance. First, a low-temperature calcination removes adsorbed water from the surface and oxidizes various alkoxy groups. Then, a high-temperature calcination removes organic groups from the gel material. Furthermore, during the heating process, the gel material continuously releases various gases. Compared to a single-calcination process, the two-stage calcination results in more uniform grain size, better redox rate, and improved cycle performance.

[0015] As a preferred technical solution of the present invention, the molar ratio of manganese source and iron source in step (1) is (1-5):1, for example, it can be 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1 or 4.5:1, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0016] It is worth noting that by adjusting the doping ratio of Mn and Fe, this invention enables iron oxide and manganese oxide to have a strong interaction, forming Mn-Fe composite metal oxide. The Mn-Fe composite metal oxide has a much better redox performance than single manganese oxide or iron oxide, and after multiple cycles, there is no high-temperature sintering phenomenon, and it can still maintain a high heat storage density.

[0017] Preferably, the manganese source in step (1) includes any one or a combination of at least two of manganese nitrates, acetates, chlorides or sulfates.

[0018] Preferably, the iron source in step (1) includes any one or a combination of at least two of iron nitrates, acetates, chlorides or sulfates.

[0019] Preferably, the solvent in step (1) includes water.

[0020] This invention does not impose a specific limit on the amount of solvent added, as long as the added solvent can dissolve the manganese source and the iron source.

[0021] Preferably, the mixing temperature in step (1) is 70-90℃, for example, it can be 72℃, 74℃, 75℃, 77℃, 79℃, 80℃, 82℃, 84℃, 85℃, 87℃ or 89℃, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0022] Preferably, the mixing in step (1) is carried out under stirring.

[0023] As a preferred technical solution of the present invention, the complexing agent in step (1) includes ethylenediaminetetraacetic acid (EDTA).

[0024] In this invention, the precursor is prepared by sol-gel method and ethylenediaminetetraacetic acid (EDTA) is selected as the complexing agent. EDTA can chelate a variety of metal ions. Its four carboxyl oxygen groups and two amino nitrogen groups can all act as coordinating atoms, serving as both tetradentate and hexadecanate ligands. It can form chelates with metal ions such as manganese and iron. When EDTA reacts with metal ions, it can form chelates with multiple five-membered rings, exhibiting high stability. Therefore, the complexation reaction has a high degree of completeness. Thus, EDTA can make manganese and iron ions evenly distributed in the solution in a short time.

[0025] Preferably, the ratio of the molar amount of the complexing agent in step (1) to the total molar amount of the manganese source and the iron source is (0.8-1.2):1, for example, it can be 0.85:1, 0.9:1, 0.95:1, 1:1, 1.05:1, 1.1:1 or 1.15:1, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0026] Preferably, the pH adjuster in step (1) includes ammonia.

[0027] Preferably, the pH adjuster in step (1) adjusts the pH of the system to 7-8, for example, it can be 7.1, 7.2, 7.3, 7.4, 7.5, 7.6, 7.7, 7.8 or 7.9, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0028] Preferably, the stirring temperature in step (1) is 70-90℃, for example, it can be 72℃, 74℃, 75℃, 77℃, 79℃, 80℃, 82℃, 84℃, 85℃, 87℃ or 89℃, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0029] Preferably, the stirring time in step (1) is 2-4 hours, for example, it can be 2.2 hours, 2.4 hours, 2.5 hours, 2.7 hours, 2.9 hours, 3 hours, 3.2 hours, 3.4 hours, 3.5 hours, 3.7 hours or 3.9 hours, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0030] As a preferred technical solution of the present invention, the drying temperature in step (2) is 170-200℃, for example, it can be 172℃, 175℃, 177℃, 179℃, 180℃, 182℃, 185℃, 187℃, 190℃, 192℃, 195℃, 197℃ or 199℃, etc., but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0031] Preferably, the drying time in step (2) is 4-6 hours, for example, it can be 4.2 hours, 4.4 hours, 4.5 hours, 4.7 hours, 4.9 hours, 5 hours, 5.2 hours, 5.4 hours, 5.5 hours, 5.7 hours or 5.9 hours, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0032] As a preferred technical solution of the present invention, the heating rate of the first calcination in step (2) is 3-7℃ / min, for example, it can be 3.5℃ / min, 4℃ / min, 4.5℃ / min, 5℃ / min, 5.5℃ / min, 6℃ / min or 6.5℃ / min, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0033] Preferably, the heating endpoint of the first calcination in step (2) is 350-450℃, for example, it can be 360℃, 370℃, 380℃, 390℃, 400℃, 410℃, 420℃, 430℃ or 440℃, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0034] Preferably, the heat preservation time for the first calcination in step (2) is 3-5h, for example, it can be 3.2h, 3.4h, 3.5h, 3.7h, 3.9h, 4h, 4.2h, 4.4h, 4.5h, 4.7h or 4.9h, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0035] Preferably, step (2) after the first calcination and before the second calcination, includes cooling to room temperature with the furnace.

[0036] As a preferred technical solution of the present invention, the heating rate of the second calcination in step (2) is 3-7℃ / min, for example, it can be 3.5℃ / min, 4℃ / min, 4.5℃ / min, 5℃ / min, 5.5℃ / min, 6℃ / min or 6.5℃ / min, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0037] Preferably, the heating endpoint of the second calcination in step (2) is 750-850℃, for example, it can be 760℃, 770℃, 780℃, 790℃, 800℃, 810℃, 820℃, 830℃ or 840℃, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0038] Preferably, the heat preservation time for the second calcination in step (2) is 3-5h, for example, it can be 3.2h, 3.4h, 3.5h, 3.7h, 3.9h, 4h, 4.2h, 4.4h, 4.5h, 4.7h or 4.9h, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0039] As a preferred technical solution of the present invention, step (2) after the second calcination further includes cooling to room temperature in the furnace.

[0040] In this invention, after the second calcination is cooled to room temperature, grinding is also performed.

[0041] As a preferred technical solution of the present invention, the preparation method includes the following steps:

[0042] (1) Mix manganese source, iron source and solvent at a temperature of 70-90℃, then add complexing agent and pH adjuster, and stir at a temperature of 70-90℃ for 2-4 hours to obtain gel solution;

[0043] The molar ratio of the manganese source to the iron source is (1-5):1;

[0044] The complexing agent includes ethylenediaminetetraacetic acid; the molar ratio of the complexing agent to the total molar ratio of the manganese source and the iron source is (0.8-1.2):1;

[0045] The pH adjuster includes ammonia; the pH adjuster adjusts the pH of the system to 7-8.

[0046] (2) The gel solution described in step (1) is dried at a temperature of 170-200℃ for 4-6 hours, and then heated to 350-450℃ at a heating rate of 3-7℃ / min for the first calcination and held for 3-5 hours. Then it is cooled to room temperature with the furnace, and then heated to 750-850℃ at a heating rate of 3-7℃ / min for the second calcination and held for 3-5 hours. Then it is cooled to room temperature with the furnace to obtain the manganese-iron composite metal oxide heat storage material.

[0047] In a second aspect, the present invention provides a manganese-iron composite metal oxide thermal storage material, which is prepared by the preparation method described in the first aspect.

[0048] As a preferred technical solution of the present invention, the general formula of the manganese-iron composite metal oxide thermal storage material is (Mn x Fe 1-x )2O3, where 0.5≤x≤0.8, for example, it can be 0.52, 0.55, 0.57, 0.6, 0.62, 0.65, 0.67, 0.7, 0.72, 0.75, 0.77 or 0.79, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0049] This invention effectively improves the sintering and agglomeration phenomenon of manganese oxide by adding iron ions, and makes the oxidation-reduction rate of manganese-iron composite metal oxide thermal storage material faster and the cycle performance significantly improved.

[0050] It is worth noting that the control of manganese ion content in the composite metal oxide of this invention is particularly important. When the proportion of manganese ions is too small, the composite metal oxide only undergoes reduction reaction and not oxidation reaction during the redox process. When the proportion of manganese ions is too large, the mass of the composite metal oxide hardly changes during the redox process, and it can be considered that it does not participate in the reaction. Only when the proportion of manganese ions is controlled within the range of 0.5 to 0.8 can the composite metal oxide thermal storage material have good cycle performance and heat storage / release performance.

[0051] Compared with the prior art, the present invention has the following beneficial effects:

[0052] (1) The preparation method provided by the present invention obtains the precursor by sol-gel method, and then obtains the manganese iron composite metal oxide heat storage material by drying and calcining twice. The preparation method is simple, has high production efficiency, and is suitable for large-scale industrial production.

[0053] (2) The manganese-iron composite metal oxide thermal storage material provided by the present invention effectively improves the sintering and agglomeration phenomenon of single manganese oxide. The resulting manganese-iron composite metal oxide thermal storage material has high thermal storage density, fast oxidation-reduction rate and excellent cycle thermal storage performance. Attached Figure Description

[0054] Figure 1 The thermogravimetric curves of the manganese-iron composite metal oxide thermal storage material prepared in Example 1 are compared with those of commercially available pure manganese oxide.

[0055] Figure 2 The image shows the TG-DSC curve of the manganese-iron composite metal oxide thermal storage material prepared in Example 1.

[0056] Figure 3 The X-ray diffraction pattern of the manganese-iron composite metal oxide thermal storage material prepared in Example 1 is shown below.

[0057] Figure 4 The thermogravimetric curves of the manganese-iron composite metal oxide thermal storage material prepared in Example 1 after different cycles are shown. Detailed Implementation

[0058] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0059] Example 1

[0060] This embodiment provides a method for preparing a manganese-iron composite metal oxide thermal storage material, the method comprising the following steps:

[0061] (1) Manganese nitrate, ferric nitrate and water were mixed at 80°C, and then ethylenediaminetetraacetic acid and ammonia were added. The mixture was stirred at 80°C for 3 hours to obtain a gel solution.

[0062] The molar ratio of manganese nitrate to ferric nitrate is 4:1;

[0063] The molar ratio of the ethylenediaminetetraacetic acid to the total molar ratio of manganese nitrate and ferric nitrate is 1:1.

[0064] The ammonia solution adjusts the pH of the system to 7.5;

[0065] (2) The gel solution described in step (1) is dried at 180°C for 5 hours, then heated to 400°C at a heating rate of 5°C / min for the first calcination and held for 4 hours. After that, it is cooled to room temperature in the furnace, then heated to 800°C at a heating rate of 5°C / min for the second calcination and held for 4 hours. After that, it is cooled to room temperature in the furnace, and finally ground for 15 minutes to obtain the manganese-iron composite metal oxide heat storage material.

[0066] The manganese-iron composite metal oxide thermal storage material prepared in this embodiment was characterized for its material properties:

[0067] (1) Thermogravimetric analysis and reaction enthalpy were measured and analyzed using a STA-449F3 synchronous thermal analyzer manufactured by German company Chine. The test procedure was to heat the sample from room temperature to 1050℃, hold it for 5 min, and then cool it down to 700℃ to remove impurities and interference factors for the first time. The air flow rate was set to 50 mL / min, nitrogen was used as the protective gas, and the nitrogen flow rate was set to 20 mL / min. Then, the cycle was repeated and the data was recorded.

[0068] (2) X-ray diffraction analysis was performed using a Rigaku SmartLab X-ray diffractometer from Rigaku Corporation of Japan, with a step size of 0.01°.

[0069] Figure 1 This is a comparison chart of the thermogravimetric curves of the manganese-iron composite metal oxide thermal storage material prepared in this embodiment and commercially available pure manganese oxide. Figure 1 It is known that commercially available manganese oxide particles only undergo a reduction reaction after the first high-temperature exposure, losing their oxidizing ability. The manganese-iron composite metal oxide prepared in this embodiment has good redox cycle capability. During the redox process, the sample weight loss and weight gain are normal, and the sample loss rate is low when heating is stopped, exhibiting excellent heat storage / exothermic performance.

[0070] Figure 2 This is the TG-DSC curve of the manganese-iron composite metal oxide thermal storage material prepared in this embodiment. Figure 2 It is known that the reduction enthalpy of the manganese-iron composite metal oxide is 261.8 J / g, and the oxidation enthalpy is 262.6 J / g. The reduction temperature of the manganese-iron composite metal oxide is 998℃, and the oxidation temperature is 819℃. This indicates that the manganese-iron composite metal oxide prepared by the method provided in this invention has a large oxidation enthalpy and a high heat storage density.

[0071] Figure 3 The image shows the X-ray diffraction pattern of the manganese-iron composite metal oxide thermal storage material prepared in this embodiment. Figure 3 It can be seen that manganese nitrate and ferric nitrate raw materials generate a new crystal phase from two crystal phases, and the resulting manganese-iron composite oxide is the main substance participating in the redox process.

[0072] Figure 4 This is a thermogravimetric curve of the manganese-iron composite metal oxide thermal storage material prepared in this embodiment after different cycles. Figure 4 It can be seen that after the ferromanganese composite metal oxide underwent 50, 100, 150, and 200 redox cycles in a tube furnace, its redox capacity was tested. The ferromanganese composite metal oxide maintained good redox capacity even after 200 cycles, and both the weight loss and weight gain rates were within the normal range, with no significant weight loss or gain. This indicates that the ferromanganese composite metal oxide prepared by the method provided in this invention has good redox capacity.

[0073] Based on the above characterization results, the manganese-iron composite metal oxide thermal storage material prepared in this embodiment has high thermal storage density, fast oxidation-reduction rate, and excellent cyclic thermal storage performance; at the same time, it also has high purity, good crystallinity, and uniform particle size.

[0074] Example 2

[0075] This embodiment provides a method for preparing a manganese-iron composite metal oxide thermal storage material, the method comprising the following steps:

[0076] (1) Manganese chloride, ferric chloride and water were mixed at 70°C, and then ethylenediaminetetraacetic acid and ammonia were added. The mixture was stirred at 70°C for 4 hours to obtain a gel solution.

[0077] The molar ratio of manganese chloride to ferric chloride is 1:1;

[0078] The molar ratio of the ethylenediaminetetraacetic acid to the total molar ratio of manganese chloride and ferric chloride is 0.8:1;

[0079] The ammonia solution adjusts the pH of the system to 7.

[0080] (2) The gel solution described in step (1) is dried at 170°C for 6 hours, then heated to 350°C at a heating rate of 3°C / min for the first calcination and held for 5 hours. After that, it is cooled to room temperature in the furnace, then heated to 750°C at a heating rate of 3°C / min for the second calcination and held for 5 hours. After that, it is cooled to room temperature in the furnace, and finally ground for 15 minutes to obtain the manganese-iron composite metal oxide heat storage material.

[0081] Example 3

[0082] This embodiment provides a method for preparing a manganese-iron composite metal oxide thermal storage material, the method comprising the following steps:

[0083] (1) Manganese nitrate, ferric nitrate and water were mixed at 90°C, and then ethylenediaminetetraacetic acid and ammonia were added. The mixture was stirred at 90°C for 2 hours to obtain a gel solution.

[0084] The molar ratio of manganese nitrate to ferric nitrate is 5:1;

[0085] The molar ratio of the ethylenediaminetetraacetic acid to the total molar ratio of manganese nitrate and ferric nitrate is 1.2:1;

[0086] The ammonia solution adjusts the pH of the system to 8.

[0087] (2) The gel solution described in step (1) is dried at 200°C for 4 hours, then heated to 450°C at a heating rate of 7°C / min for the first calcination and held for 3 hours. After that, it is cooled to room temperature in the furnace, then heated to 850°C at a heating rate of 7°C / min for the second calcination and held for 3 hours. After that, it is cooled to room temperature in the furnace, and finally ground for 15 minutes to obtain the manganese-iron composite metal oxide heat storage material.

[0088] Example 4

[0089] This embodiment provides a method for preparing a manganese-iron composite metal oxide thermal storage material. Except for the molar ratio of manganese nitrate and iron nitrate in step (1) being 0.5:1, all other conditions are the same as in Example 1.

[0090] Example 5

[0091] This embodiment provides a method for preparing a manganese-iron composite metal oxide thermal storage material. Except for the molar ratio of manganese nitrate and iron nitrate in step (1) being 6:1, all other conditions are the same as in Example 1.

[0092] Example 6

[0093] This embodiment provides a method for preparing a manganese-iron composite metal oxide thermal storage material. Except for the ratio of the molar amount of ethylenediaminetetraacetic acid to the total molar amount of manganese nitrate and iron nitrate in step (1) being 0.5:1, all other conditions are the same as in Example 1.

[0094] Example 7

[0095] This embodiment provides a method for preparing a manganese-iron composite metal oxide thermal storage material. Except for the ratio of the molar amount of ethylenediaminetetraacetic acid to the total molar amount of manganese nitrate and iron nitrate in step (1) being 2:1, all other conditions are the same as in Example 1.

[0096] Example 8

[0097] This embodiment provides a method for preparing a manganese-iron composite metal oxide thermal storage material. Except for replacing "ethylenediaminetetraacetic acid" with "citric acid" in step (1), all other conditions are the same as in Example 1.

[0098] Example 9

[0099] This embodiment provides a method for preparing a manganese-iron composite metal oxide thermal storage material. Except for changing "adding ethylenediaminetetraacetic acid and ammonia water" in step (1) to "adding citric acid and ethylene glycol", all other conditions are the same as in Example 1.

[0100] Example 10

[0101] This embodiment provides a method for preparing a manganese-iron composite metal oxide thermal storage material. Except for the first calcination heating endpoint of 300°C in step (2), all other conditions are the same as in Example 1.

[0102] Example 11

[0103] This embodiment provides a method for preparing a manganese-iron composite metal oxide thermal storage material. Except for the heating endpoint of the first calcination in step (2) being 550°C, all other conditions are the same as in Example 1.

[0104] Example 12

[0105] This embodiment provides a method for preparing a manganese-iron composite metal oxide thermal storage material. Except for the second calcination temperature endpoint of 700°C in step (2), all other conditions are the same as in Example 1.

[0106] Example 13

[0107] This embodiment provides a method for preparing a manganese-iron composite metal oxide thermal storage material. Except for the second calcination heating endpoint of 950°C in step (2), all other conditions are the same as in Example 1.

[0108] Comparative Example 1

[0109] This comparative example provides a method for preparing a manganese-iron composite metal oxide thermal storage material. Except for not performing the second calcination in step (2), all other conditions are the same as in Example 1.

[0110] The manganese-iron composite metal oxide thermal storage materials prepared in the above examples and comparative examples were subjected to cyclic thermal storage performance tests. The test procedure was as follows: heating from room temperature to 1050℃, holding at that temperature for 5 min, and then cooling to 700℃ to remove impurities and interfering factors. The air flow rate was set to 50 mL / min, nitrogen was used as the protective gas, and the nitrogen flow rate was set to 20 mL / min. This cycle was then repeated 50 times. The test results are shown in Table 1.

[0111] Table 1

[0112]

[0113]

[0114] As shown in Table 1:

[0115] (1) The preparation method provided by the present invention produces a manganese-iron composite metal oxide thermal storage material with characteristics such as fast oxidation-reduction rate and excellent cyclic thermal storage performance; wherein, the reduction conversion rate is ≥3.4% and the re-oxidation rate is ≥3.2%.

[0116] (2) Comparing Examples 1 and 4-5, it can be seen that when the proportion of manganese nitrate in the metal raw material is too small, the product contains a small amount of manganese-iron composite metal oxide, and most of it is iron oxide. The redox temperature of iron oxide is higher than that of manganese-iron composite metal oxide. Therefore, only a portion of the manganese-iron composite oxide undergoes redox reaction. When the proportion of manganese nitrate in the metal raw material is too large, the product contains only a small amount of manganese-iron composite metal oxide and a large amount of manganese oxide. Because the redox ability of manganese oxide is weak, only a small amount of manganese-iron composite metal oxide participates in the reaction.

[0117] (3) A comparison of Examples 1 and 6-7 shows that when the amount of ethylenediaminetetraacetic acid (EDTA) added is too small, some metal ions do not coordinate and no composite metal oxide is formed, resulting in poor redox performance of the prepared manganese-iron composite metal oxide. When the amount of EDTA added is too large, more ammonia water needs to be added for neutralization, which has little impact on the results but increases the cost and makes subsequent processing cumbersome. A comparison of Examples 1 and 8-9 shows that when citric acid is used instead of EDTA, the complexing effect of EDTA is better than that of citric acid, resulting in a manganese-iron composite metal oxide with better specific surface area, better particle size uniformity, and better redox performance.

[0118] (4) A comparison of Examples 1 and 10-11 shows that when the temperature of the first calcination is too low or too high, the organic impurities cannot volatilize, affecting the polymerization of the material in the next high-temperature step, resulting in poor redox performance of the obtained manganese-iron composite metal oxide; a comparison of Examples 1 and 12-13 shows that when the temperature of the second calcination is too low, the material does not polymerize and sinter at high temperature, resulting in poor redox performance of the obtained manganese-iron composite metal oxide; when the temperature of the second calcination is too high, the material undergoes large-scale sintering, affecting the entry and exit of oxygen in the redox process, resulting in poor redox performance of the obtained manganese-iron composite metal oxide.

[0119] (5) Comparing Example 1 and Comparative Example 1, it can be seen that when the second calcination is not performed, the material is only heat-treated at a low temperature from the dried gel. The material does not undergo complete condensation-polymerization and sintering processes, resulting in the manganese-iron composite metal oxide containing more impurities. During the heating process, mass loss will occur at the low temperature stage, and the amount of substances participating in the oxidation-reduction process will decrease at the high temperature stage.

[0120] The applicant declares that the detailed structural features of the present invention are illustrated through the above embodiments, but the present invention is not limited to the above detailed structural features, that is, it does not mean that the present invention must rely on the above detailed structural features to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions for the components selected in the present invention, additions of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

[0121] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0122] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

[0123] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. A method for preparing a manganese-iron composite metal oxide thermal storage material, characterized in that, The preparation method includes the following steps: (1) Mix manganese source, iron source and solvent, then add complexing agent and pH adjuster, stir to obtain gel solution; The complexing agent in step (1) includes ethylenediaminetetraacetic acid; The molar ratio of the complexing agent in step (1) to the total molar ratio of the manganese source and the iron source is (0.8-1.2):1; The molar ratio of manganese source to iron source in step (1) is (1-5):1 The pH adjuster described in step (1) adjusts the pH of the system to 7-8; (2) The gel solution described in step (1) is dried, calcined for the first time, and calcined for the second time in sequence to obtain the manganese-iron composite metal oxide heat storage material; The first and second calcinations are carried out in a muffle furnace under an air atmosphere; Step (2) The heating endpoint of the first calcination is 350-450℃; Step (2) The endpoint of the second calcination is 750-850℃; Step (2) After the first calcination and before the second calcination, the furnace is cooled to room temperature.

2. The preparation method according to claim 1, characterized in that, The manganese source in step (1) includes any one or a combination of at least two of manganese nitrates, acetates, chlorides or sulfates.

3. The preparation method according to claim 1, characterized in that, The iron source in step (1) includes any one or a combination of at least two of iron nitrates, acetates, chlorides or sulfates.

4. The preparation method according to claim 1, characterized in that, Step (1) The solvent includes water.

5. The preparation method according to claim 1, characterized in that, The mixing temperature in step (1) is 70-90℃.

6. The preparation method according to claim 1, characterized in that, The mixing in step (1) is carried out under stirring.

7. The preparation method according to claim 1, characterized in that, The pH adjuster in step (1) includes ammonia.

8. The preparation method according to claim 1, characterized in that, The stirring temperature in step (1) is 70-90℃.

9. The preparation method according to claim 1, characterized in that, The stirring time in step (1) is 2-4 hours.

10. The preparation method according to claim 1, characterized in that, The drying temperature in step (2) is 170-200℃.

11. The preparation method according to claim 1, characterized in that, The drying time in step (2) is 4-6 hours.

12. The preparation method according to claim 1, characterized in that, In step (2), the heating rate of the first calcination is 3-7℃ / min.

13. The preparation method according to claim 1, characterized in that, Step (2) The heat preservation time for the first calcination is 3-5 hours.

14. The preparation method according to claim 1, characterized in that, In step (2), the heating rate of the second calcination is 3-7℃ / min.

15. The preparation method according to claim 1, characterized in that, Step (2) The heat preservation time for the second calcination is 3-5 hours.

16. The preparation method according to claim 1, characterized in that, Step (2) The second calcination also includes cooling to room temperature in the furnace.

17. The preparation method according to claim 1, characterized in that, The preparation method includes the following steps: (1) Mix manganese source, iron source and solvent at a temperature of 70-90℃, then add complexing agent and pH adjuster, and stir at a temperature of 70-90℃ for 2-4 hours to obtain gel solution; The molar ratio of the manganese source to the iron source is (1-5):1; The complexing agent includes ethylenediaminetetraacetic acid; the molar ratio of the complexing agent to the total molar ratio of the manganese source and the iron source is (0.8-1.2):1; The pH adjuster includes ammonia; the pH adjuster adjusts the pH of the system to 7-8; (2) The gel solution described in step (1) is dried at a temperature of 170-200℃ for 4-6 hours, then heated to 350-450℃ at a heating rate of 3-7℃ / min for the first calcination and held for 3-5 hours, then cooled to room temperature with the furnace, and then heated to 750-850℃ at a heating rate of 3-7℃ / min for the second calcination and held for 3-5 hours, and then cooled to room temperature with the furnace to obtain the manganese-iron composite metal oxide heat storage material.

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