Ultralow thermal conductive rubidium-silver-iodine-based superionic conductor porous material, preparation method and application thereof

Abstract

This invention relates to an ultra-low thermal conductivity rubidium silver iodine-based superionic conductor porous material, its preparation method, and its applications. The superionic conductor porous material has the chemical formula RbAg4I5, a density of 3.6%–100%, and a thermal conductivity of 6–130 mW / m⁻¹K in the temperature range of 300–400 K. Compared with existing technologies, this invention, based on the ultra-low intrinsic thermal conductivity of RbAg4I5, produces porous materials with excellent thermal insulation properties, which can be widely used in thermoelectric materials, thermal insulation coatings, and other fields.

Description

Technical Field

[0001] This invention relates to the field of thermal insulation materials technology, and in particular to an ultra-low thermal conductivity rubidium silver iodine-based superionic conductor porous material, its preparation method and application. Background Technology

[0002] With the development of industrialization, energy shortage has become one of the common problems facing the world. Under the advocacy of a dual-carbon, green environment, the rational use of thermal energy, a clean energy source, and the exploration of new and efficient thermal management materials are particularly important. Thermal insulation materials, which can resist heat flow across temperature gradients, have become a key component of modern thermal management systems. To explore the essence of thermal insulation performance, thermal conductivity is a key indicator for evaluating the effectiveness of thermal insulation materials.

[0003] Based on the mechanisms related to reducing the lattice thermal conductivity of materials, weakly bonded ionic conductors have the potential to become thermal insulation materials. These materials inherently possess low sound velocities and high scattering sources, making them more likely to form materials with low thermal conductivity. However, the lattice thermal conductivity of dense materials is limited by the inherent properties of atoms. Even the optimal system (such as high-entropy alloys) struggles to surpass the thermal insulation levels of porous materials like aerogels, and cannot simultaneously meet the requirements for lightweighting.

[0004] RbAg4I5 is a ternary metal halide compound with ultra-high ionic conductivity. It possesses a partially occupied complex crystal structure and a heavy element composition, and its properties in solid electrolytes have been extensively studied in recent years (e.g., US20250385250A1). However, there are currently no studies focusing on its thermal conductivity.

[0005] Therefore, there is an urgent need to develop novel thermal insulation materials based on RbAg4I5 superionic conductors and to reveal their potential in low thermal conductivity applications. Summary of the Invention

[0006] The purpose of this invention is to overcome the defects of the prior art and provide an ultra-low thermal conductivity rubidium silver iodine-based superionic conductor porous material, its preparation method and application.

[0007] This invention further prepares novel RbAg4I5-based thermal insulation materials with different densities and thermal conductivity by controlling the microstructure of rubidium silver iodine-based superionic conductor materials, especially by controlling the porosity.

[0008] The objective of this invention can be achieved through the following technical solutions: The first aspect of the present invention provides an ultra-low thermal conductivity rubidium silver iodine-based superionic conductor porous material, wherein the chemical formula of the superionic conductor porous material is RbAg4I5 and the density is 3.6%~100%; the thermal conductivity of the superionic conductor porous material is 6~130 mW / mK in the temperature range of 300~400K.

[0009] The second aspect of this invention provides a method for preparing a porous material of ultra-low thermal conductivity rubidium silver iodine-based superionic conductor.

[0010] When the density of the superionic conductor porous material is 3.6%~60%, it is prepared by the following solvent method: rubidium iodide and silver iodide are dispersed in an organic solvent and reacted under stirring to obtain an RbAg4I5 solution; a mixed solution of antisolvent tert-butanol and water is added dropwise to the RbAg4I5 solution to generate cross-linked flocculents, and then the porous material with a density of 3.6%~60% is obtained by freeze drying.

[0011] Furthermore, the stoichiometric ratio of silver iodide to rubidium iodide is 4:1.

[0012] Furthermore, in the solvent method, the organic solvent is any one or more of dimethyl sulfoxide, N-methylpyrrolidone, dimethylacetamide, and acetonitrile, preferably dimethyl sulfoxide.

[0013] Furthermore, in the solvent method, the reaction temperature is 50~70 °C, and the reaction time is 5~7 h.

[0014] Furthermore, in the solvent method, the volume ratio of tert-butanol to water is (1-2):(10-15), and the dropping rate is not less than 0.2 mL / s.

[0015] When the density of the superionic conductor porous material is 60%~100%, it is prepared by the following hot pressing method: silver iodide and rubidium iodide are mixed in a vacuum quartz tube, melted at high temperature and annealed to obtain a pure phase RbAg4I5 ingot; the RbAg4I5 ingot is ground and then hot-pressed and sintered to obtain a porous material with a density of 60%~100%.

[0016] Furthermore, the stoichiometric ratio of silver iodide to rubidium iodide is 4:1.

[0017] Furthermore, in the hot pressing method, the high-temperature melting temperature is 650~750 ℃, and the high-temperature melting time is 3~5 h.

[0018] Furthermore, in the hot pressing method, the annealing temperature is 120~180 ℃, and the annealing time is 36~60 h.

[0019] Furthermore, in the hot pressing method, the hot pressing sintering temperature is 120~200 ℃, and the hot pressing sintering pressure is 0~80 MPa.

[0020] The third aspect of this invention provides the application of an ultra-low thermal conductivity rubidium silver iodine-based superionic conductor porous material in the fabrication of low thermal conductivity devices.

[0021] The fourth aspect of this invention provides the application of an ultra-low thermal conductivity rubidium silver iodine-based superionic conductor porous material in the fabrication of thermoelectric cooling devices.

[0022] Furthermore, the density of the rubidium silver iodine-based superionic conductor porous material is 3.6%~12%.

[0023] Compared with the prior art, the present invention has the following technical advantages: (1) The present invention innovatively uses hot pressing and solution method to porous RbAg4I5 low thermal conductivity matrix to further reduce its thermal conductivity, and finally obtains a series of new thermal insulation materials with density from 3.6% to 100% and room temperature thermal conductivity not higher than 130 mW / mK.

[0024] (2) Based on the ultra-low intrinsic thermal conductivity of RbAg4I5, the porous material prepared by this invention has excellent thermal insulation properties. At room temperature, the thermal conductivity of the dense material is only 0.13 W / mK. The thermal conductivity of the porous material can be lower than that of air, and it can be widely used in various thermal insulation materials such as thermal insulation coatings.

[0025] (3) The present invention also made a breakthrough discovery that low-density porous materials can be used to fill thermoelectric devices to reduce heat loss and improve thermoelectric performance in non-vacuum environments.

[0026] (4) The porousing method of the present invention can be widely applied to all inorganic materials. A series of porous materials with different densities can be prepared by simply using hot pressing technology and solvent adjustment. It is a new way to study new ultra-low thermal conductivity materials.

[0027] (5) The RbAg4I5 material of the present invention uses non-toxic Ag ions to replace lead and retains the perovskite structure, and there are no longer organic cations in the framework. Compared with similar pure inorganic perovskites, it further reduces the toxicity to the environment. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the preparation process of the high-density RbAg4I5 porous material of the present invention.

[0029] Figure 2 This is a schematic diagram of the preparation process of the low-density RbAg4I5 porous material of the present invention.

[0030] Figure 3 The X-ray image of the RbAg4I5 porous material powder provided in Example 1.

[0031] Figure 4 The X-ray photoelectron spectrum of the RbAg4I5 porous material provided in Example 2 is shown.

[0032] Figure 5 The graph shows the test results of the thermal conductivity of the RbAg4I5 porous materials provided in Examples 1 and 2 as a function of temperature.

[0033] Figure 6 This invention relates to the relationship between the density and thermal conductivity of the RbAg4I5 porous material.

[0034] Figure 7 The diagram shows the cooling temperature difference and power generation efficiency before and after filling the thermoelectric device in Example 3. Detailed Implementation

[0035] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0036] The purpose of this invention is to provide a method for preparing RbAg4I5 material with low thermal conductivity and its series of porous materials. The RbAg4I5 material prepared through porousification exhibits extremely low thermal conductivity at room temperature, reaching or below that of air. Furthermore, RbAg4I5 material does not undergo a phase change from room temperature to its melting point, possessing excellent structural stability and can be widely used in thermoelectric materials, thermal insulation materials, and other fields requiring efficient thermal management. This invention also provides an application scenario for thermal insulation filling in thermoelectric devices and can be widely used in other thermal insulation fillings.

[0037] Specifically, such as Figure 1 As shown, this invention first provides a method for preparing a high-density rubidium silver iodine-based superionic conductor porous material (density ≥ 60%), comprising the following steps: S1. The raw materials are reacted and melted by high temperature, and the product is crystallized and homogenized by low temperature annealing to eliminate impurities and obtain a uniform RbAg4I5 ingot.

[0038] S2. The above-mentioned homogeneous RbAg4I5 ingot is ground into fine powder. Using hot pressing technology, the pressure setting range of the hot pressing process is adjusted from 0-80 MPa, and the hot pressing sintering temperature is 120-200 ℃ to prepare porous materials with a density ranging from 100% to 60%. The density is mainly adjusted by the hot pressing pressure and pressing time, and the sintering temperature is appropriately increased under low pressure.

[0039] like Figure 2 As shown, the present invention also provides a method for preparing a low-density rubidium silver iodine-based superionic conductor porous material (density as low as 3.6%), comprising the following steps: S1. The raw material is dissolved using dimethyl sulfoxide (DMSO), a common perovskite solvent, and the reaction occurs under temperature and stirring to obtain an RbAg4I5 solution. S2. Cross-linked flocculents are generated by rapidly adding a mixture of antisolvent tert-butanol and distilled water to a RbAg4I5 solution under kinetic drive.

[0040] S3. Pre-cooling during stirring generates cross-linked flocs. Freeze-drying is used to dehydrate the flocs and retain their porous structure, resulting in porous materials with a density ranging from 60% to 3.6%.

[0041] Thirdly, the present invention provides an application of a low-density rubidium silver iodine-based superionic conductor porous material, which reduces heat loss by filling thermoelectric devices to improve thermoelectric performance in non-vacuum environments.

[0042] Unless otherwise specified, the reagents, methods, instruments, and equipment used in this invention are conventional in the art. Unless otherwise specified, the reagents and materials used in the following examples are all commercially available.

[0043] The thermal conductivity involved in the following embodiments k Refrigeration temperature difference (△) T ) and power generation efficiency ( η The results, such as those obtained using conventional measurement methods in the art, can all be obtained. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the scope of the invention.

[0044] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0045] Example 1: This embodiment provides a RbAg4I5 porous material with a density of approximately 78.9%, and its preparation method specifically includes the following steps: (1) Rubidium iodide (99.99%) and silver iodide (99.99%) powders were loaded into a quartz tube at a stoichiometric ratio of 1:4 and sealed under vacuum conditions (<5 Pa). The tube was melted at 800 °C and held for 4 hours, and then cooled to 150 °C for annealing for 48 hours.

[0046] (2) Grind the obtained RbAg4I5 ingot into fine powder, put the RbAg4I5 powder into a graphite mold, place the thermocouple inside the graphite sleeve, heat to the sintering temperature of 150 ℃, apply an axial pressure of 30 MPa and maintain the pressure for 5 min, release the pressure and keep warm for 30 min.

[0047] (3) The pressure was then released and cooled to obtain a non-dense sheet (density of about 78.9%).

[0048] (4) The non-dense sheet and the hot-pressed powder precursor were characterized by X-ray diffraction (XRD, Rigaku SmartLab, Cu-K) to confirm their uniform composition (see Figure 3 ).

[0049] Example 2: This embodiment provides a RbAg4I5 porous material with a density of 12.8%, and its preparation method specifically includes the following steps: (1) Weigh 1.9882 g of rubidium iodide (99.99%) and 8.7918 g of silver iodide (99.99%) (in accordance with the stoichiometric ratio of 1:4) and add them to a 10 mL dimethyl sulfoxide solution. Stir the mixture at a constant temperature of 60 °C for 6 h.

[0050] (2) After the solution has been completely reacted, it is ultrasonically dispersed again for 20 min. Then, while stirring, the prepared mixture of tert-butanol and distilled water (volume ratio 1:10) is rapidly added dropwise at a rate of 1 mL / s.

[0051] (3) Pre-cool the solution after rapid addition of antisolvent in a -50 ℃ cold trap.

[0052] (4) After cooling is complete, the flocculent is dehydrated and the porous structure is preserved by freeze drying. The final structure will collapse by 50% of its volume, resulting in a porous block material with a density of 12.8%.

[0053] (5) The porous bulk material with a density of 12.8% was characterized by X-ray photoelectron spectroscopy (XPS, Al-K radiation, Thermo Fisher ESCALAB 250Xi). By comparing with known standard peak values, it was verified that its internal valence state remained unchanged, indicating that it was a pure phase with no organic residue (see [link to standard X-ray photoelectron spectroscopy]). Figure 4 ).

[0054] Figure 4 a is the XPS full spectrum, indicating that the sample contains three core elements: Ag, Rb, and I, and its chemical composition is consistent with that of RbAg4I5. Figure 4 b is the high-resolution spectrum of Rb. The spin-orbit splitting double peaks at ~109.95 eV and Rb at ~111.41 eV indicate that rubidium is in a +1 valence (Rb). + It exists, and there is no other valence state. Figure 4 The c-spin-orbit splitting bimodal pattern also conforms to Ag. + The characteristic peak of . Similarly, iodine in Figure d has a valence of -1 (I - The presence of impurity peaks containing high-valence iodine is not observed. All of the above indicate a single chemical environment where all elements are in a single valence state, with no impurity valence states or oxidation / reduction products, suggesting high phase purity of the material.

[0055] Based on the successful preparation of the samples in Examples 1 and 2, this invention further investigated the thermal transport properties of the prepared samples. The thermal conductivity of the samples from Examples 1 and 2 was tested and analyzed, and plotted based on the test data. Figure 5 The temperature-dependent thermal conductivity curve is shown.

[0056] Through precise testing and calculation using the laser scintillation method, the results showed that the thermal conductivity of the high-density porous material in Example 1 at 300 K was 101.4 mW / mK, while that of the low-density porous material in Example 2 at 300 K was 21.5 mW / mK. Furthermore, within a wide temperature range of 300–400 K, the thermal conductivity of both samples with different densities did not fluctuate drastically with temperature, remaining at a low level across a broad testing temperature range, exhibiting excellent and stable low thermal conductivity behavior.

[0057] Figure 6 For the thermal conductivity test data at different densities and the model of thermal conductivity variation with density, the thermal conductivity model of porous materials can be regarded as gas thermal conductivity ( ) and solid thermal conductivity ( It consists of two parts: Total thermal conductivity = density × solid thermal conductivity + porosity × gas thermal conductivity, density + porosity = 100%.

[0058] The thermal conductivity of gases in aerogels is calculated using a widely used formula derived by Kaganer in this paper. Journal of Non-Crystalline Solids 186 (1995) 264-270; Energy 90 (2015) 701-721 and Int J Thermophys (2009) 30:1357–1371): .

[0059] Kn is defined as the ratio of the gas mean free path to the pore size: ; constant β Defined as: ; in The thermal conductivity of air is taken as 26 mW / mK. The mean free path of air is 74 nm. The thermal adaptability coefficient is 1 and The thermal conductivity of air is 1.4. The upper limit treats the thermal conductivity of air as that of a gas, while the lower limit assumes a hollow cubic structure with a minimum wall thickness of 1 nm and pores larger than the average diameter of an air molecule (3.34 nm). In this case, air molecules are confined within the pores, resulting in a gas thermal conductivity lower than that of air. As shown in the figure, the thermal conductivity is approximately 55–130 mW / mK in the 60%–100% range, primarily influenced by microstructure factors such as pore size.

[0060] Based on the above test results, it can be seen that both Example 1 and Example 2 successfully prepared rubidium silver iodine-based superionic conductor porous materials with extremely low thermal conductivity. They have significant advantages in application scenarios with stringent requirements for thermal insulation and thermal insulation performance. The excellent low thermal conductivity characteristics also lay a good performance foundation for their practical application in related fields.

[0061] Example 3: This embodiment provides a thermoelectric device filled with RbAg4I5 porous material with a density of approximately 4%. The preparation method is similar to that in Embodiment 2, and is as follows: (1) Weigh 1.1134 g of rubidium iodide (99.99%) and 4.9234 g of silver iodide (99.99%) (in accordance with the stoichiometric ratio of 1:4) and add them to a 10 mL dimethyl sulfoxide solution. Stir the mixture at a constant temperature of 60 °C for 6 h.

[0062] (2) After the reaction is complete, the solution is ultrasonically dispersed again for 20 min. While stirring, the prepared mixture of tert-butanol and distilled water (volume ratio 1:10) is rapidly added dropwise at a rate of 1 mL / s.

[0063] (3) After the solution after rapid addition of antisolvent is added to the Yamato Thermomagnetic 9501 / 017 / 030 B commercial thermoelectric refrigeration device, it is pre-cooled in a cold trap at -61 ℃.

[0064] (4) After cooling is complete, the flocculent material is dehydrated and the porous structure is preserved by freeze drying. Since commercial devices provide support for the porous material, the final structure will experience about 70% volume collapse, resulting in a porous material-filled thermoelectric device with a density of 4%.

[0065] (5) The filled device is subjected to thermoelectric power generation test and cooling test.

[0066] Figure 7 a shows schematic diagrams of thermoelectric devices with and without filler and with 4% density porous RbAg4I5. Figure 7 b represents the refrigeration performance test results of the thermoelectric device before and after filling. The refrigeration temperature difference in the air is 7.6 K higher after filling than before filling. Figure 7 c represents the power generation performance test of the thermoelectric device, specifically the maximum power generation efficiency. η max Compared to a 10% improvement in thermoelectric performance in an air environment, it is very close to the thermoelectric performance in a vacuum environment.

[0067] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. An ultra-low thermal conductivity Rb-Ag-I based superionic conductor porous material, characterized in that, The chemical formula of the superionic conductor porous material is RbAg4I5, and the density is 3.6%~100%. The superionic conductor porous material has a thermal conductivity of 6~130 mW / mK in the temperature range of 300~400 K.

2. A method of producing the ultra-low thermal conductivity Rb-Ag-I based superionic conductor porous material of claim 1, characterized in that, When the density of the superionic conductor porous material is 3.6%~60%, it is prepared using the following solvent method: Rubidium iodide and silver iodide are dispersed in an organic solvent and reacted under stirring to obtain an RbAg4I5 solution. A mixture of antisolvent tert-butanol and water is added dropwise to the RbAg4I5 solution to generate cross-linked flocculents, which are then freeze-dried to obtain a porous material with a density of 3.6% to 60%. When the density of the superionic conductor porous material is 60%~100%, it is prepared by the following hot pressing method: Silver iodide and rubidium iodide are mixed in a vacuum quartz tube, melted at high temperature, and annealed to obtain a pure phase RbAg4I5 ingot; the RbAg4I5 ingot is ground and then hot-pressed and sintered to obtain a porous material with a density of 60%~100%.

3. The method for preparing the ultra-low thermal conductivity rubidium silver iodine-based superionic conductor porous material according to claim 2, characterized in that, The stoichiometric ratio of silver iodide to rubidium iodide is 4:

1.

4. The method for preparing the ultra-low thermal conductivity rubidium silver iodine-based superionic conductor porous material according to claim 2, characterized in that, In the solvent method, the organic solvent is any one or more of the following: dimethyl sulfoxide, N-methylpyrrolidone, dimethylacetamide, and acetonitrile. The reaction temperature is 50~70 ℃, and the reaction time is 5~7 h.

5. The method for preparing the ultra-low thermal conductivity rubidium silver iodine-based superionic conductor porous material according to claim 2, characterized in that, In the solvent method, the volume ratio of tert-butanol to water is (1-2):(10-15), and the dropping rate is not less than 0.2 mL / s.

6. The method for preparing the ultra-low thermal conductivity rubidium silver iodine-based superionic conductor porous material according to claim 2, characterized in that, In the hot pressing method, the high-temperature melting temperature is 650~750 ℃, and the high-temperature melting time is 3~5 h.

7. The method for preparing the ultra-low thermal conductivity rubidium silver iodine-based superionic conductor porous material according to claim 2, characterized in that, In the hot pressing method, the annealing temperature is 120~180 ℃ and the annealing time is 36~60 h.

8. The method for preparing the ultra-low thermal conductivity rubidium silver iodine-based superionic conductor porous material according to claim 2, characterized in that, In the hot pressing method, the hot pressing sintering temperature is 120~200 ℃, and the hot pressing sintering pressure is 0~80 MPa.

9. The application of the ultra-low thermal conductivity rubidium silver iodine-based superionic conductor porous material as described in claim 1 in the fabrication of low thermal conductivity devices.

10. The application of the ultra-low thermal conductivity rubidium silver iodine-based superionic conductor porous material according to claim 1 in the fabrication of thermoelectric cooling devices, characterized in that, The density of the rubidium silver iodine-based superionic conductor porous material is 3.6%~12%.

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