Preparation method and application of core-shell structure high water permeable inorganic clay matrix coated calcium-based composite energy storage material

Abstract

This invention discloses a method for preparing and applying a core-shell structured, highly permeable inorganic clay matrix-coated modified calcium-based composite energy storage material. Step 1 involves dissolving a modified calcium-based and expanded graphite composite powder in ethanol, followed by ultrasonication, heat treatment, grinding, and spheroidization to form composite spherical particles with a diameter of 1.5–20 mm as the "core" structural material. Step 2 involves ball milling and high-temperature calcining an inorganic clay matrix powder based on a clay-based composite powder in ethanol to obtain the "outer shell" structural material. Step 3 involves coating the "outer shell" structural powder obtained in step 2 onto the surface of the "core" spheres obtained in step 1 using a spheroidization technique. This invention introduces pores and forms highly permeable mass transfer channels in the "core-shell" structured material through ultrasonic dispersion and heat treatment, thereby improving the material's thermochemical energy storage properties, such as resistance to sintering, crack resistance, stability, and energy storage density.

Description

Technical Field

[0001] This invention belongs to the field of thermochemical energy storage, specifically relating to a method for preparing and applying a core-shell structured, highly permeable inorganic clay matrix-coated, modified calcium-based composite energy storage material. Background Technology

[0002] Thermochemical thermal energy storage is an emerging thermal energy storage technology. Compared with sensible thermal energy storage and phase change thermal energy storage, it has a higher thermal energy storage density and can achieve long-term, lossless storage of thermal energy. The CaO / CaCO3 and CaO / Ca(OH)2 systems are typical thermochemical thermal energy storage systems. They are widely available in nature, inexpensive, and particularly suitable for storing medium- and high-temperature thermal energy. They have extremely broad application prospects in renewable energy utilization and industrial waste heat recovery.

[0003] Solar energy, as a renewable energy source, is one of the most promising low / zero carbon resources for the future. Furthermore, large-scale power generation can be achieved by integrating concentrated solar power (CSP) plants into the grid. However, to overcome the intermittency and instability of solar energy caused by regional and climatic differences, it is necessary to develop large-scale, long-term power generation and energy storage technologies. Among numerous energy storage technologies, thermochemical energy storage (TCES) is considered one of the most promising due to its high energy density, high operating temperature, and the possibility of indefinite energy storage. Compared to the immature molten salt energy storage, thermochemical energy storage is considered more efficient for current commercial systems. The reversible cyclic conversion between CaO and Ca(OH)2 / CaCO3, based on the reversible cyclic reaction between calcium oxide and calcium hydroxide / calcium carbonate, offers high energy density (theoretically approximately...). ), low cost (approximately The high reaction temperature (approximately 850℃) and abundant natural calcium-based materials (such as dolomite and limestone) have led to its extensive research. In the calcium cycle (CaL) process, the high energy density (-1044 kJ / kg Ca(OH)2 / -1780 kJ / kg CaCO3) allows for repeated cycles, meeting the medium requirements of reversible reaction technology in CSP (Cellular Solar Power) systems. Because this cyclic reaction system operates in a high-temperature region, it provides the conditions for subsequent thermochemical storage for efficient cyclic power generation.

[0004] To form a durable "shell" for a calcium-based energy storage material under cycling conditions, several parameters were defined as limiting conditions. Therefore, the selected material must remain stable under cycling conditions, without undergoing any decomposition reactions, and must maintain chemical inertness to the thermal storage material. Furthermore, the "shell" must withstand the forces generated by the volume expansion of the "core" during hydration, as well as the collisions and abrasion between particles during cycling. To ensure cycling performance, the "shell" must have good permeability, allowing steam to diffuse through the shell during dehydration and rehydration. Therefore, clay materials containing organic matter are generally chosen as the "shell" for encapsulation, and these clay materials provide good permeability, thermal stability, and high mechanical stability after sintering. Through the ablation of organic compounds, a porous network is formed during sintering, allowing steam to smoothly permeate through the shell into the core. By adjusting the porosity of the shell material, the decoupling of power and capacity, the slowdown of reaction kinetics, and the reduction in material storage density can be easily compensated for. While most modified calcium-based energy storage materials show great promise in CSP (Continuous Suspension Processing) technology, pure calcium materials have a low Taman temperature, leading to severe sintering after continuous high-temperature cycling, resulting in decreased energy storage density and low cycle stability. Although existing technologies have conducted extensive research on anti-sintering and porosity optimization, most of the samples produced are in powder form, resulting in unsatisfactory anti-sintering performance and pore distribution, thus hindering their application in thermal energy storage. Summary of the Invention

[0005] Therefore, in view of the above-mentioned technical defects, the technical problem to be solved by the present invention is to overcome the low thermal conductivity of the existing calcium-based energy storage materials in the form of powder particles and the low energy storage density of the clay "shell", thereby providing a method for preparing and using an inorganic clay matrix-coated calcium-based composite energy storage material that can simultaneously achieve excellent calcium cycle stability, high energy storage density, high thermal conductivity and high water permeability.

[0006] This invention first provides a method for preparing core-structure modified calcium-based thermochemical energy storage material granules using a one-pot process, which is simple, inexpensive, and readily available. Secondly, this invention provides an inorganic clay matrix shell material with an outer shell structure to coat the core granules of calcium-based material, forming a core-shell structured, highly permeable inorganic clay-coated modified calcium-based composite energy storage material. This core-shell structure material exhibits excellent thermal cycling performance, high stability, good sintering resistance, and high hardness.

[0007] This invention is achieved by constructing a method for preparing a core-shell structured, highly permeable inorganic clay matrix-coated modified calcium-based composite energy storage material, characterized by the following steps: Step 1) The modified calcium-based and expanded graphite (EG) composite powder material is dissolved in ethanol, ultrasonically and heat-treated, ground and spherically shaped to form composite spherical particles with a diameter of 1.5 to 20 mm, thus obtaining a core structure modified calcium-based / EG composite particle sphere. Step 2) The ethanol solution based on the clay matrix composite powder is ball-milled and calcined at high temperature. After ball milling again, an inorganic clay matrix composite powder can be obtained. Step 3), add an adhesive. After mixing the shell structure powder obtained in Step 2 with the pore-forming agent using a high-speed mixing device, the shell structure particles are physically coated on the surface of the core spheres obtained in Step 1 using a spheroidization technique. Step 4) The core-shell structured particles obtained in Step 3) are calcined at 800℃-1300℃ under nitrogen atmosphere protection to obtain a core-shell structured high-permeability inorganic clay matrix-coated modified calcium-based composite energy storage material with good stability and sintering resistance.

[0008] Furthermore, the calcium-based material involved in step 1) is any one or more of calcium hydroxide (Ca(OH)2) and calcium carbonate (CaCO3); The modifier involved in step 1) is one of stearic acid, oleic acid and fatty acid; The expanded graphite involved in step 1) is used to improve the thermal conductivity of the material system. It is obtained by one of two expansion methods: microwave oven firing and high-temperature firing under a protective atmosphere. The core structure granules are obtained by adding an adhesive to improve their hardness. The adhesive is one of carboxymethyl cellulose (CMC), polyvinyl alcohol (PVA), and hydroxypropyl methylcellulose (HPMC). To improve the antioxidant properties of expanded graphite, an antioxidant needs to be added, which is one of phosphate, borate and silicate.

[0009] Further; in step 1), the mass ratio of the modifier to the calcium precursor used is 5:100 to 20:100; the mass ratio of the adhesive to the calcium precursor used is 0.5:100 to 1.5:100; the mass ratio of the antioxidant used for expanded graphite to the calcium precursor used is 5:100 to 30:100; and the mass ratio of the expanded graphite to the calcium precursor used is 0.5:100 to 10:100.

[0010] Furthermore; in step 2), the inorganic clay matrix composite powder of the shell structure is any two or more of clay, metal oxides, and fly ash; the pore-forming agent is used to improve the water permeability of the inorganic clay matrix material, and the mass ratio of the agent to the inorganic clay matrix composite powder is 10:240 to 100:240.

[0011] Furthermore, the inorganic clay matrix material is formed by spherical coating using a ball rolling machine.

[0012] Furthermore, the calcination temperature in step 2) is 1000–1400°C, and the time is 1–4 h.

[0013] Application of a core-shell structured, highly permeable inorganic clay matrix-coated modified calcium-based composite energy storage material prepared according to the above method in solar thermochemical energy storage.

[0014] The above method produces a core-shell structured, highly permeable inorganic clay matrix-coated modified calcium-based composite energy storage material. After multiple cycles, its heat storage capacity can reach over 1313 kJ / kg. This work has raised the development of this technology to a level closer to its industrial application.

[0015] The present invention has the following advantages: (1) Improve the thermal conductivity of calcium-based energy storage materials and prevent sintering and aggregation by performing multifunctional modification on pure calcium materials. Compared with pure calcium, this pure calcium material only needs to add 2-4 w% of expanded graphite (EG) to effectively improve the thermal conductivity of the core material, thereby improving the heat transfer efficiency of the heat storage and release process. This invention constructs a "core" structure particle ball system based on calcium-based materials coated with high thermal conductivity carbon materials by building a porous structure. Through its unique synthesis strategy, calcium-based particles are uniformly coated and filled in the gaps of expanded graphite (EG), and by controlling the EG content, a thermally conductive network is introduced into the calcium material, thereby improving the thermal conductivity of the composite calcium-based material.

[0016] (2) Improve the anti-oxidation and anti-sintering properties of calcium-based energy storage materials. This invention regulates the stability of the "heat-conducting network" built by calcium-based materials and porous expanded graphite (EG) by adding antioxidants. The antioxidants work synergistically with the porous EG to support the heat transfer channels, which can further provide a buffer space for the volume change of calcium-based materials during cycling, thereby reducing the sintering of the materials and improving the stability of the materials.

[0017] (3) To improve the cycle stability of calcium-based energy storage materials, an inorganic clay matrix with a "shell" structure is designed to coat the calcium-based material in the "core". This constructs a modified calcium-based composite energy storage material system with a "core-shell" structure and a highly permeable inorganic clay matrix. Furthermore, high-viscosity inorganic clay and solid waste materials such as fly ash, which are difficult to mold, are added, allowing for complementary advantages. This invention improves the single-form powder structure of the calcium-based material and the permeability of the clay material by introducing a pore-forming agent into the "shell", thereby enhancing the cycle stability of the calcium-based material's heat storage and release. Attached Figure Description

[0018] Figure 1 The thermal conductivity curve of the pure calcium-based energy storage material prepared in Comparative Example 1 is shown. Figure 2 The thermal conductivity curves of the "core" modified calcium-based energy storage materials prepared in Example 1 (expandable graphite EG) and Comparative Example 2 (general graphite and flake graphite) are shown. Figure 3 Images of particles with diameters of 1.6 mm and 2 mm, respectively, of the "core" modified calcium-based energy storage material prepared in Example 1; Figure 4 This is a comparison of the density change curves of the "core" modified calcium-based energy storage material prepared in Example 3 under different pressure-induced methods; Figure 5 This is a cross-sectional view of the inner and outer layers of a core-shell structured, highly permeable inorganic clay matrix-coated modified calcium-based composite energy storage material granules prepared in Example 3. Detailed Implementation

[0019] The following will be combined with the appendix Figures 1-5 This invention will be described in detail, and the technical solutions in the embodiments of this invention will be clearly and completely described. Obviously, the described embodiments are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0020] This invention provides a method for preparing and applying a core-shell structured, highly permeable inorganic clay matrix-coated, modified calcium-based composite energy storage material, which mainly includes the following steps: Step 1) The modified calcium-based and expanded graphite (EG) composite powder material is dissolved in ethanol, ultrasonically and heat-treated, ground and spherically shaped to form composite spherical particles with a diameter of 1.5 to 20 mm, thus obtaining a "core" structure modified calcium-based / EG composite particle sphere. Step 2) The ethanol solution based on calcium oxide-based composite powder is ball-milled, calcined at high temperature and quenched. After ball milling again, an inorganic clay matrix powder with a "shell" structure can be obtained. Step 3) Add some adhesives and other auxiliary agents, and use the spheroidization technique to physically coat the "shell" structure powder obtained in Step 2 onto the surface of the "core" sphere obtained in Step 1, thereby obtaining a "core-shell" structure high permeability inorganic clay matrix coated modified calcium-based composite energy storage material. Step 4) The modified calcium-based composite energy storage material with a core-shell structure and high permeability inorganic clay matrix obtained in Step 3) is first calcined under a protective atmosphere, and then cooled to room temperature to obtain a modified calcium-based composite energy storage material with a core-shell structure and high permeability inorganic clay matrix with good stability and sintering resistance.

[0021] In step 1), a type of "core" structure modified calcium-based / EG composite granules are described. The calcium-based material is one or more of calcium hydroxide (Ca(OH)2) and calcium carbonate (CaCO3). The modifier is one of stearic acid, oleic acid, and fatty acids. The expanded graphite is used to improve the thermal conductivity of the material system and is obtained by one of two expansion methods: microwave oven firing and high-temperature firing under atmosphere protection. The "core" structure granules require the addition of some adhesives to improve hardness. The adhesive is one of carboxymethyl cellulose (CMC), polyvinyl alcohol (PVA), and hydroxypropyl methylcellulose (HPMC). To improve the antioxidant properties of the expanded graphite, antioxidants are added. The antioxidants are one of phosphates, borates, and silicates.

[0022] Additionally, in step 1), the mass ratio of the modifier to the calcium precursor used in the modified calcium-based / EG composite spheres with a "core" structure is 5:100 to 20:100; the mass ratio of the adhesive to the calcium precursor used is 0.5:100 to 1.5:100; the mass ratio of the antioxidant used for expanded graphite to the calcium precursor used is 5:100 to 30:100; and the mass ratio of the expanded graphite to the calcium precursor used is 0.5:100 to 10:100. In step 2), the inorganic clay matrix powder of the "shell" structure is any two or more of clay, metal oxides, and fly ash; the additives and other auxiliary agents are used to improve the water permeability of the inorganic clay matrix material, and the mass ratio of the additives to the inorganic clay matrix composite powder is 10:240 to 100:240. In addition, the calcination temperature in step 2) is 1000-1400℃ and the time is 1-4h; the inorganic clay matrix material is formed by spherical coating using a ball rolling machine.

[0023] The present invention will be described in detail below with reference to specific examples. These specific examples are preferred embodiments. Those skilled in the art can extend the invention in similar and identical ways without departing from its spirit. Therefore, the disclosed embodiments should not be regarded as limitations on the present invention.

[0024] Example 1

[0025] First, 0.031 g of expanded graphite (EG) (mass ratio to calcium precursor 3:100), 0.022 g of boric acid (mass ratio to calcium precursor 2:100), 0.301 g of stearic acid (mass ratio to calcium precursor 30:100), and 0.031 g of carboxymethyl cellulose (CMC) (mass ratio to calcium precursor 3:100) were dissolved in 100 mL of ethanol solution. The mixture was then sonicated for 30 min to obtain an ethanol solution based on the expanded graphite (EG) composite material. 1.0 g of CaCO3 was added to the EG composite material ethanol solution and stirred for 30 min to ensure complete dissolution, yielding an ethanol solution of the "core" structure modified calcium-based composite energy storage material. During stirring, calcium carbonate powder was slowly added to the ethanol solution to ensure uniform mixing.

[0026] Place the mixed ethanol solution in 100... o The sample was dried in a vacuum drying oven (C) under vacuum for 2 hours, then cooled to room temperature to obtain a mixed block sample. The block sample was then ground in a crusher at speed 3 to obtain a mixed powder sample. The powder sample was then granulated into 2mm pellets using a ball mill at speed 4 and constant power to obtain sample A of the "core" structure modified calcium-based composite energy storage material pellets.

[0027] Preparation of highly permeable inorganic kaolin matrix: Kaolin, fly ash, and pore-forming agent (calculated at a mass ratio of 1:8 and a total mass ratio of 1:9 with the previously mixed inorganic powder) were dissolved in ethanol. After ultrasonic homogenization, the mixture was successively ball-milled, dried in an oven, and calcined in a high-temperature furnace at a rate of 5℃ / min to 1100℃ for 120min. Finally, the calcined sample was cooled, ground, ball-milled again in ethanol solution, and dried to obtain highly permeable inorganic kaolin matrix powder material B.

[0028] Preparation of a core-shell structured calcium-based composite energy storage material: A core-shell structured sample C was obtained by coating an inorganic clay matrix powder sample ("outer shell") with the modified calcium-based material spherical particles ("inner core") using a ball rolling mill. Sample C was then placed in a high-temperature furnace and heated to 1050℃ at a rate of 5℃ / min, and calcined once for 120min to form core-shell structured, highly permeable inorganic clay matrix-coated modified calcium-based composite energy storage material spherical particles.

[0029] Example 2

[0030] First, 0.031 g of expanded graphite (EG) (mass ratio to calcium precursor 3:100), 0.022 g of phosphoric acid (mass ratio to calcium precursor 2:100), 0.301 g of oleic acid (mass ratio to calcium precursor 30:100), and 0.031 g of polyvinyl alcohol (PVA) (mass ratio to calcium precursor 3:100) were dissolved in 100 mL of ethanol solution. The mixture was then sonicated for 30 min to obtain an ethanol solution based on the expanded graphite (EG) composite material. 1.0 g of Ca(OH)₂ was added to the EG composite material ethanol solution and stirred for 30 min to ensure complete dissolution, yielding an ethanol solution of the "core" structure modified calcium-based composite energy storage material. During stirring, calcium carbonate powder was slowly added to the ethanol solution to ensure uniform mixing.

[0031] Place the mixed ethanol solution in 100... o The sample was dried in a vacuum drying oven (C) under vacuum for 2 hours, then cooled to room temperature to obtain a mixed block sample. The block sample was then ground in a crusher at speed 3 to obtain a mixed powder sample. The powder sample was then granulated into 2mm pellets using a ball mill at speed 4 and constant power to obtain sample A of the "core" structure modified calcium-based composite energy storage material pellets.

[0032] Preparation of highly permeable inorganic terracotta matrix: Terracotta, metal oxides, and pore-forming agent (calculated at a mass ratio of 1:8 and a total mass ratio of 1:9 with the previously mixed inorganic powder) were dissolved in ethanol. After ultrasonic homogenization, the mixture was sequentially ball-milled, dried in an oven, and calcined in a high-temperature furnace at a rate of 5℃ / min to 1100℃ for 120 min. Finally, the calcined sample was quenched in deionized water, ball-milled again in an ethanol solution, and dried to obtain highly permeable inorganic terracotta matrix powder material B.

[0033] Preparation and application of a core-shell structured, highly permeable inorganic terracotta matrix-coated modified calcium-based composite energy storage material: An inorganic terracotta matrix powder sample was coated with the aforementioned core-shell modified calcium-based material spherical particles (sample A) using a ball rolling mill to obtain a core-shell structured sample C. Sample C was then placed in a high-temperature furnace and heated to 1050℃ at a rate of 5℃ / min, and calcined once for 120min to form core-shell structured, highly permeable inorganic terracotta matrix-coated modified calcium-based composite energy storage material spherical particles.

[0034] Example 3

[0035] First, 0.031g of expanded graphite (EG) (mass ratio to calcium precursor 3:100), 0.022g of silicic acid (mass ratio to calcium precursor 2:100), 0.301g of fatty acid (mass ratio to calcium precursor 30:100), and 0.031g of hydroxypropyl methylcellulose (HPMC) (mass ratio to calcium precursor 3:100) were dissolved in 100mL of ethanol solution and sonicated for 30 min to obtain an ethanol solution based on expanded graphite (EG) composite material. Then, 1.0g of Ca(OH)₂ was added to the EG composite material ethanol solution and stirred for 30 min to ensure complete dissolution, resulting in an ethanol solution of the "core" structure modified calcium-based composite energy storage material. During stirring, calcium carbonate powder was slowly added to the ethanol solution to ensure uniform mixing.

[0036] Place the mixed ethanol solution in 100... o The sample was dried in a vacuum drying oven (C) under vacuum for 2 hours, then cooled to room temperature to obtain a mixed block sample. The block sample was then ground in a crusher at speed 3 to obtain a mixed powder sample. The powder sample was then granulated into 2mm pellets using a ball mill at speed 4 and constant power to obtain sample A of the "core" structure modified calcium-based composite energy storage material pellets.

[0037] Preparation of highly permeable inorganic clay matrix: Clay, metal oxide (CaO, MgO, etc.) powders were dissolved in ethanol at a mass ratio of 1:2:6, and a pore-forming agent (calculated at a mass ratio of 1:9 with the total mass of the previously mixed inorganic powders) were dissolved. After ultrasonic homogenization, the mixture was successively ball-milled, dried in an oven, and calcined in a high-temperature furnace at a rate of 5℃ / min to 1100℃ for 120 min. Finally, the calcined sample was quenched in deionized water, ball-milled again in an ethanol solution, and dried to obtain highly permeable inorganic clay matrix powder material B.

[0038] Preparation and application of a core-shell structured, highly permeable inorganic terracotta matrix-coated modified calcium-based composite energy storage material: A core-shell structured sample C was obtained by coating the aforementioned core-shell modified calcium-based material spherical particles (sample A) with an outer shell inorganic terracotta matrix powder sample using a ball rolling mill. Sample C was then placed in a high-temperature furnace and heated to 1250℃ at a rate of 5℃ / min, and calcined once for 120min to form core-shell structured, highly permeable inorganic terracotta matrix-coated modified calcium-based composite energy storage material spherical particles.

[0039] Comparative Example 1: A comparison of the thermal conductivity of pure calcium-based (without expanded graphite (EG)) materials and those with expanded graphite (EG) was conducted on calcium-based energy storage materials. First, 0.301 g of stearic acid (30:100 mass ratio to calcium precursor) and 0.031 g of carboxymethyl cellulose (CMC) (3:100 mass ratio to calcium precursor) were dissolved in 100 mL of ethanol solution. The mixture was then sonicated for 30 min to obtain an ethanol solution based on the calcium-based composite material. 1.0 g of CaCO3 was added to the ethanol solution of the calcium-based composite material and stirred for 30 min to ensure complete dissolution, resulting in an ethanol solution of the "core" structure-modified calcium-based composite energy storage material. During stirring, calcium carbonate powder was slowly added to the ethanol solution to ensure uniform mixing.

[0040] Place the mixed ethanol solution in 100... o The sample was dried in a vacuum drying oven at C for 2 hours under vacuum. After cooling to room temperature, it was removed to obtain a mixed block sample. The block sample was then placed in a crusher and ground at speed 3 to obtain a mixed powder sample. The powder sample was then granulated into 2mm particles using a ball mill at speed 4 and constant power to obtain a particle sample of calcium-based composite energy storage material with a modified "core" structure.

[0041] Comparative Example 2: The addition of carbon-based materials, including general graphite and flake graphite (G), was compared with the addition of expanded graphite (EG) to improve the thermal conductivity of calcium-based energy storage materials: First, 0.031 g of general graphite or flake graphite (G) (mass ratio to calcium precursor 3:100), 0.022 g of boric acid (mass ratio to calcium precursor 2:100), 0.301 g of stearic acid (mass ratio to calcium precursor 30:100), and 0.031 g of carboxymethyl cellulose (CMC) (mass ratio to calcium precursor 3:100) were dissolved in 100 mL of ethanol solution and sonicated for 30 min to obtain an ethanol solution based on expanded graphite (EG) composite material. 1.0 g of CaCO3 was added to the above EG composite material ethanol solution and stirred for 30 min to ensure complete dissolution, obtaining an ethanol solution of calcium-based composite energy storage material with a "core" structure modification. During stirring, calcium carbonate powder was slowly added to the ethanol solution to ensure uniform mixing.

[0042] Place the mixed ethanol solution in 100... o The sample was dried in a vacuum drying oven at C for 2 hours under vacuum. After cooling to room temperature, it was removed to obtain a mixed block sample. The block sample was then placed in a crusher and ground at speed 3 to obtain a mixed powder sample. The powder sample was then granulated into 2mm particles using a ball mill at speed 4 and constant power to obtain a particle sample of calcium-based composite energy storage material with a modified "core" structure.

[0043] Figure 1 The thermal conductivity curve of the pure calcium-based energy storage material prepared in Comparative Example 1 shows that adding expanded graphite (EG) can improve the thermal conductivity of calcium-based materials. Depending on the mass ratio of EG added, the thermal conductivity of calcium-based materials can be increased by 3 to 7 times or more.

[0044] Figure 2 The thermal conductivity curves of the "core" modified calcium-based energy storage materials prepared in Example 1 (expandable graphite EG) and Comparative Example 2 (general graphite and flake graphite) under pressure compression are shown. This indicates that adding expanded graphite (EG) with a porous structure can improve the thermal conductivity of the calcium-based material by more than 7 times, while adding general graphite or flake graphite has the same thermal conductivity as the calcium-based material itself and does not significantly improve the thermal conductivity of the calcium-based energy storage material.

[0045] Figure 3 The density change curves of the "core" modified calcium-based energy storage material prepared in Example 1 under different pressure induction methods are shown in the following diagrams: Explanation 1 is to extrude a round sheet with a diameter of 25 mm and a fixed mass of 3.0 g using a tablet press. Explanation 2 is to extrude a flat round granular ball with a diameter of 2 mm using a roller extrusion method. The density of the calcium-based energy storage material granular ball is about 1.2 times that of the tablet density.

[0046] Figure 4 Images of spheres with diameters of 1.6 mm and 2 mm for the "core" modified calcium-based energy storage material prepared in Example 1: This illustrates that the ball rolling machine can be adjusted to prepare spheres with diameters ranging from 1.6 mm to 20 mm.

[0047] Figure 5 This is a cross-sectional view of the inner and outer layers of a core-shell structured, highly permeable inorganic clay matrix-coated modified calcium-based composite energy storage material particle sphere prepared in Example 3: illustrating that the inorganic clay matrix "outer shell" material is uniformly coated on the surface of the "core" modified calcium-based energy storage material particle sphere.

[0048] The stability of the energy storage materials obtained in the examples and comparative examples was tested. The energy storage density was characterized by chemical enthalpy, which was obtained by DSC heating. The results are shown in Table 1.

[0049] Table 1

[0050] As can be seen from the above embodiments and comparative examples, the "core-shell" structure high permeability inorganic clay matrix-coated modified calcium-based composite energy storage material of the present invention can not only improve the cycle stability of calcium cycle thermochemical energy storage materials, thereby improving the heat storage and release effect.

[0051] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a core-shell structured, highly permeable inorganic clay matrix-coated modified calcium-based composite energy storage material. Its features are: Includes the following steps: Step 1) The calcium-based material, modifier and expanded graphite (EG) composite powder material is dissolved in ethanol, ultrasonically and heat-treated, ground and spherically shaped to form composite spherical particles with a diameter of 1.5 to 20 mm, thus obtaining a core structure modified calcium-based / EG composite particle sphere. Step 2) The ethanol solution based on the clay matrix composite powder is ball-milled and calcined at high temperature. After ball milling again, an inorganic clay matrix composite powder can be obtained. Step 3), add an adhesive. After mixing the shell structure powder obtained in Step 2 with the pore-forming agent using a high-speed mixing device, the shell structure particles are physically coated on the surface of the core spheres obtained in Step 1 using a spheroidization technique. Step 4) The core-shell structured particles obtained in Step 3) are calcined at 800℃-1300℃ under nitrogen atmosphere protection to obtain a core-shell structured high-permeability inorganic clay matrix-coated modified calcium-based composite energy storage material with good stability and sintering resistance.

2. The preparation method of a core-shell structured, highly permeable inorganic clay matrix-coated modified calcium-based composite energy storage material according to claim 1, characterized in that: The calcium-based materials involved in step 1) are any one or more of calcium hydroxide (Ca(OH)2) and calcium carbonate (CaCO3); The modifier involved in step 1 is one of stearic acid, oleic acid, and fatty acid. The expanded graphite involved in step 1 is used to improve the thermal conductivity of the material system. It is obtained by one of two expansion methods: microwave oven firing and high-temperature firing under atmosphere protection. In step 3, obtaining the core structure granular spheres requires the addition of some adhesive to improve hardness. The adhesive is one of carboxymethyl cellulose (CMC), polyvinyl alcohol (PVA), and hydroxypropyl methylcellulose (HPMC). To improve the antioxidant properties of expanded graphite, an antioxidant needs to be added, which is one of phosphate, borate and silicate.

3. The preparation method of a core-shell structured, highly permeable inorganic clay matrix-coated modified calcium-based composite energy storage material according to claim 1, characterized in that: In step 1), the mass ratio of the modifier to the calcium-based material used is 5:100 to 20:100; the mass ratio of the adhesive to the calcium precursor used is 0.5:100 to 1.5:100; the mass ratio of the antioxidant used for expanded graphite to the calcium precursor used is 5:100 to 30:100; and the mass ratio of expanded graphite to the calcium precursor used is 0.5:100 to 10:

100.

4. The preparation method of a core-shell structured, highly permeable inorganic clay matrix-coated modified calcium-based composite energy storage material according to claim 1, characterized in that: The inorganic clay matrix composite powder for the outer shell structure mentioned in step 2) is a mixture of any two or more of clay, metal oxides, and fly ash; the pore-forming agent is used to improve the water permeability of the inorganic clay matrix material, and the mass ratio of the agent to the inorganic clay matrix composite powder is 10:240 to 100:

240.

5. The preparation method of a core-shell structured, highly permeable inorganic clay matrix-coated modified calcium-based composite energy storage material according to claim 4, characterized in that: The inorganic clay matrix material is formed by spherical rolling and encapsulation using a ball rolling machine.

6. The preparation method of a core-shell structured, highly permeable inorganic clay matrix-coated modified calcium-based composite energy storage material according to claim 1, characterized in that: The calcination temperature in step 2) is 1000–1400℃, and the time is 1–4 hours.

7. The application of a core-shell structured, highly permeable inorganic clay matrix-coated modified calcium-based composite energy storage material prepared by any one of the preparation methods described in claims 1 to 6 in solar thermochemical energy storage.

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