Process for manufacturing phase-change composite materials

Abstract

Process for manufacturing phase-change composite materials The manufacturing process includes the steps of: a) Growing a ceramic material shell of determined thickness on nanoparticles comprising metal and / or carbon, so as to prepare core-shell nanoparticles, b) Integrating the core-shell nanoparticles by mixing into a solid-liquid phase-change material, for example by melting using a twin-screw extruder, so as to obtain the phase-change composite material.

Description

Title of the invention: Process for manufacturing phase-change composite materials

[0001] The present invention relates to the field of phase-change materials for thermal energy storage applications. In particular, the invention provides a method for producing a phase-change composite material configured to exhibit very good thermal conductivity while providing very good electrical insulation. According to a second aspect, the invention relates to the phase-change composite material obtained by said method.

[0002] In recent years, the energy crisis and concerns about greenhouse gas emissions have generated increasing interest in phase change materials (PCMs) for thermal energy storage applications.

[0003] Solid-liquid composite materials (SL composites) offer the advantages of high latent heat and easy availability, but they often exhibit low intrinsic thermal conductivity, which significantly reduces the efficiency of heat transfer within the material. This is a real problem because it affects the system's performance, and in particular induces a kinetic limitation on heat exchange, and therefore a limitation on the performance of the associated thermal storage. To overcome this limiting phenomenon, the integration of carbon or ceramic fillers has been proposed. The main advantage of ceramic fillers lies in their excellent electrical insulation properties, which allows these composites to be placed very close to electrically sensitive components to be cooled, such as battery cells.The electrical insulating properties of ceramic fillers eliminate the risk of electrical disturbances such as electromagnetic interference or short circuits. However, ceramic fillers have relatively low thermal conductivity (averaging between 20 and 80 W / mK) and very limited geometric form factors, meaning they are predominantly spherical or ovoid particles. This ultimately makes this type of filler inefficient for thermal management. It forces engineers to implement a very high filler density, which drastically increases the material's viscosity. Therefore, this solution is not really suitable for high-performance industrial applications.Just like metallic nanofillers (based on at least 50% by mass of Cu, Ag, Ni, Pd, Pt, or Al in particular), carbon-based fillers possess very interesting form factors (ff) such as 1D structures (nanotubes), 2D structures (sheets), and have excellent thermal conductivity. Unfortunately, their construction... chemically making them highly electrically conductive, which is therefore incompatible with thermal management applications in electrical and electronic systems.

[0004] One of the aims of the present invention is to overcome the aforementioned drawbacks. To this end, the invention proposes a process for manufacturing a solid-liquid phase-change composite material, comprising the steps of:

[0005] a) Growing a ceramic material shell of determined thickness on nanoparticles comprising metal and / or carbon, so as to prepare core-shell nanoparticles,

[0006] b) Integrate the core-shell nanoparticles by mixing into a solid-liquid phase change material (or SL PCM), for example by melting using a twin-screw extruder, so as to obtain the phase change composite material.

[0007] Thus, the process of the invention makes it possible to obtain a composite material exhibiting a combination of the properties desired for thermal management applications. The nanoparticles, whose core (also referred to as the core in this document) is thermally and electrically conductive, covered with a shell of a ceramic material that is a very good electrical insulator and thermal conductor, lead to the production of core-shell nanoparticles with a balanced mix of the advantages of each component, namely very good thermal conductivity and good electrical insulation.Integrating these nanoparticles into a phase-change material, which has the advantages of high latent heat but low thermal conductivity, makes it possible to obtain a composite material with a combination of the aforementioned advantages, namely very good enthalpy of fusion, electrical insulation and thermal conductivity, as illustrated in Table I below.

[0008] The expression "core-shell nanoparticles" is also known to those skilled in the art as "core-envelope nanoparticles".

[0009] According to one arrangement, the determined thickness of the ceramic material envelope is between 10 and 90 nm, and preferably between 20 and 60 nm. This thickness results from the search for a compromise allowing good electrical insulation without excessively impacting the thermal conductivity of the core.

[0010] According to one possibility, the nanoparticles have a non-zero shape factor, typically a 1D or 2D structure, allowing the creation of low-loading percolation domains that increase the performance of the resulting phase-change composite material.

[0011] The expression "1D or 2D structure" is also known to those skilled in the art as "one- or two-dimensional structure"

[0012] It is known to those skilled in the art that in 1D structure nanoparticles, at least one of the dimensions of the nanoparticle is 20 times greater than the larger of the other two, and for 2D structure nanoparticles at least one of the dimensions is at least 20 times smaller than the smaller of the other two dimensions, which promotes percolation.

[0013] According to one possibility, the process as previously described includes before step a) a step i) of dispersing the nanoparticles in an aqueous phase comprising a water-soluble polymer, so as to obtain a thin conforming layer of water-soluble polymer covering the nanoparticles, in particular the thin layer having a thickness of between 0.5 and 5 nm, so as to facilitate the growth of the ceramic material envelope.

[0014] According to one arrangement, the nanoparticles have a non-zero form factor, typically nanoparticles with a 1D or 2D structure.

[0015] According to one possibility, the ceramic material envelope is made of silica and its growth is obtained by sol-gel method on the nanoparticles, in particular in hydroalcoholic medium and in the presence of tetraethyl orthosilicate (TEOS), in particular until reaching the determined envelope thickness of between 10 and 90 nanometers, and preferably between 20 and 60 nanometers.

[0016] According to one provision, the process includes, prior to step b), a step a') of functionalizing the ceramic material shell in the presence of a coupling agent, such as a silane or a phosphonic acid derivative, particularly in a solvent with a concentration ranging from 0.1 to 20 mmol.L-1, preferably 1 to 5 mmol.L-1, for example by stirring at room temperature for between 1 and 24 h, preferably between 4 and 14 h, so as to provide core-shell nanoparticles with surface functionalization. Functionalization is advantageous because the ceramic material, for example silica, naturally exhibits hydroxyl bonds on its surface, whereas the MCP has long, relatively nonpolar organic chains. Thus, the two surfaces have different surface energies, which is not optimal for bringing the two materials together and creating interactions.Using a functionalization modifies the surface energy of the ceramic in order to approach the polarity of the PCM.

[0017] According to one possibility, the functionalization step a') generates the grafting of alkyl chains onto the ceramic material, in particular the alkyl chains having at least three carbon atoms, or even at least six carbon atoms; in particular, the alkyl chains are at least partially fluorinated and, for example, the alkyl chains are perfluorinated. These alkyl chains with a length greater than three carbon atoms are less polar than the hydroxyl groups of the ceramic and bring them closer to the polarity of the MCP surface, promoting better interactions, as will be seen later.

[0018] According to one provision, step b) of integration includes the mixing of an organic MCP with functionalized core-shell nanoparticles or core-shell nanoparticles, in particular by melting using a twin-screw extruder.

[0019] According to one possibility, the process includes before step b) a step of ii) diluting the organic MCP in a polymer, in particular in polyethylene (PE) or polypropylene (PP), so as to form a polymeric matrix loaded with MCP.

[0020] The polymer matrix advantageously allows the MCP to be contained during its phase change.

[0021] According to one provision, the process includes, prior to step ii), a step of functionalizing the polymer intended to form the polymeric matrix with maleic anhydride (PEgMA). This involves chemically modifying the matrix by grafting a molecule, typically, for example, with maleic anhydride grafts.

[0022] According to a second aspect, the invention proposes a phase-change composite material comprising a plurality of core-shell nanoparticles integrated into an organic phase-change material, the nanoparticles comprising a metal or carbon forming the core and being covered by a ceramic material shell having a determined thickness.

[0023] According to other features, the phase-change composite material of the invention comprises one or more of the following optional features considered alone or in combination: - Metal-based nanoparticles or nuclei comprise at least 50% by weight of a metal, and in particular the metal is chosen from the group consisting of Cu, Ag, Ni, Pd, Pt, Al and an alloy of these metals. - The nanoparticles or the carbon-based core are chosen from the group consisting of carbon nanotubes, graphene derivatives such as graphene nanoplatelets, graphene sheets, possibly partially reduced graphene oxides, graphite and a mixture of these elements. - The ceramic material envelope is based on silica, alumina and / or boron nitride. - The phase-change material is an organic material. - The phase-change material is chosen from the group consisting of paraffins (sometimes referred to as PW, the English acronym for Paraffin) Wax), fatty acids, fatty esters, fatty alcohols, and a mixture of these materials. - The phase change material is preferably a compound comprising a hydrocarbon chain of C5 to C50. - The thin conformal layer of water-soluble polymer on the nanoparticles is obtained beforehand in step a), directly by the process of obtaining the nanoparticles. - The core-shell nanoparticles of the invention comprise covalent bonds between the core and the ceramic shell material.

[0024] According to a second aspect, the invention also relates to a phase-change composite material comprising a polymeric matrix, such as polyethylene or polypropylene, loaded with MCP and comprising core-shell nanoparticles. - The phase change composite material has an electrical resistivity greater than or equal to 1.109 Q.cm, and in particular greater than or equal to 1.1011 Q.cm. - The phase-change composite material has a thermal conductivity greater than or equal to 1 W / mK, for example greater than or equal to 1.50 W / mK and in particular greater than or equal to 1.60 W / mK - The phase change composite material exhibits increased thermal conductivity of more than 1W / mK compared to the phase change material used alone. - The phase change composite material has an enthalpy of fusion greater than or equal to 137 J / g, and in particular greater than or equal to 138 J / g. - The phase change composite material has a reduced enthalpy of fusion of less than 25% compared to that of the phase change material used alone.

[0025] Other features and advantages will become apparent from the detailed description below, several non-limiting implementation examples, and a comparative results table.

[0026] Step 1: Preparation of nanoparticles (step i of the process)

[0027] Metal- or carbon-based nanoparticles are dispersed in an aqueous phase containing a water-soluble polymer at a concentration of between 0.1 and 10 wt%, preferably between 1 and 5 wt%, for 5 to 60 min. After a filtration and drying step, the recovered nanoparticles are coated with a very thin conformal layer of the polymer so as to promote the subsequent growth of the ceramic material envelope. Preferred polymers are water-soluble, and by way of example and without restriction, the polymers are chosen from the group consisting of polyvinyl pyrrolidone, polyethylene glycol, cellulose derivatives, polyvinyl alcohol and a mixture of these polymers.

[0028] Step 2: Ceramic material casing (step a) of the process)

[0029] When the ceramic material is silica, the growth of the silica coating on the surface of the core, also called 'thermally conductive charge', is carried out according to the sol-gel process, well known to those skilled in the art and for example described in the document 'Chem. Review 1990, 90, pp33-72'.

[0030] For this purpose, TEOS (tetraethyl orthosilicate) is dissolved in an alcoholic or hydroalcoholic solvent, for example absolute ethanol, in a mass proportion of between 0.05 and 15% by weight, preferably between 0.1 and 7% by weight, in the presence of traces of acid catalyst (for example hydrochloric acid) or basic catalyst (for example ammonium hydroxide).

[0031] Then, the nanoparticles obtained in step 1 are introduced into the solution under stirring, until a mass concentration of between 0.01 and 10% by weight is reached, and preferably between 0.05 and 1% by weight.

[0032] The suspension is placed under magnetic stirring for a period of between 1 min and 15 h, preferably between 1 h and 4 h, at room temperature. The suspension is then filtered and rinsed between 1 and 10 times, preferably 3 times, using the solvent. The resulting powder is dried at 60°C for at least 4 h in an oven. A shell with a thickness of between 20 and 60 nm then covers the nanoparticles, forming core-shell nanoparticles.

[0033] The same process applied to an alumina precursor such as aluminium isopropoxide or boron nitride such as boric acid makes it possible to obtain an alumina or boronized shell on the nanoparticles.

[0034] Step 3: Functionalization of the silica envelope (optional - step a') of the process)

[0035] The third step consists of dissolving the core-shell nanoparticle powder obtained in step 2 in a degassed and dried solvent containing the coupling agent, selected from silane and / or phosphonic acid, at a concentration ranging from 0.1 to 20 mmol.L*, preferably from 1 to 5 mmol.L*. The solvent is selected, for example, from the group consisting of chloroform, toluene, tetrahydrofuran, and ethanol. The mixture is stirred at room temperature for between 1 and 24 hours, preferably between 4 and 14 hours. Once the reaction is complete, the functionalized core-shell nanoparticle powder is filtered and washed with absolute ethanol and then dried.

[0036] Step 4: Integration of core-shell-functionalized nanoparticles into an MCP material (step s ii) and b) of the process)

[0037] The filler (or nanoparticles) is then introduced into a pure organic PCM, or into a mixture of organic PCM with a polymer at a concentration of between 2% and 80% by volume, preferably between 10% and 70% by volume, and even more preferably between 15% and 60% by volume. The polymer is chosen from polypropylene and polyethylene. The filler can be incorporated by any means known to those skilled in the art, for example, by melting using a twin-screw extruder. When using pure organic PCM, the temperature of the mixture in the extruder varies between 20 and 120 °C, and preferably between 30 and 70 °C. When using a mixture of organic PCM and polymer, the temperature of the mixture in the extruder is higher due to the polymer's melting point. It is between 100 and 240°C, and preferably between 120 and 160°C.

[0038] Implementation: The phase change composite material thus formed is then implemented by the usual techniques in the field of plastics processing, for example by injection, hot pressing, or additive manufacturing. Comparative examples

[0039] Example 1: Fabrication of AgNW / PVP / SiO2 core-shell nanoparticles without functionalization - 1 g of PVP (Poly Vinyl Pyrrolidone) is dissolved in 500 mL of water deionized, then 5 g of silver nanowires purchased from Protavic International® are added and the mixture is treated in an ultrasonic bath for 5 min. - The solution is then continuously stirred for 1 hour at room temperature, then filtered and washed three times using deionized water cooled to 5°C. - The resulting powder (AgNW-PVP) is left in an oven at a controlled temperature of 60°C for approximately 12 hours. - The dried powder is dispersed in 500 mL of ethanol. - To 300 mg of silver nanowires (1D structure nanoparticles) in 150 mL of ethanol, 2.0% TEOS, 5 mL of ammonium hydroxide and 3 mL of deionized water are added. - The reaction is maintained for 14 hours under vigorous magnetic stirring. - The mixture is washed three times in absolute ethanol and then vacuum-filtered through a PTFE membrane.

[0040] The silver nanowires are thus coated with a 28 nm thick layer of silica. They are referred to as AgNW-SiO2 in the remainder of this document.

[0041] Yields are difficult to calculate with certainty, but it appears that more than 99.9% of silver nanowire is coated by silica.

[0042] The term AgNW is well known to those skilled in the art. It is an English acronym derived from the expression Ag NanoWires.

[0043] Example 2: Functionalization of core-shells with octadecylphosphonic acid.

[0044] The silica-coated AgNW-SiO2 nanoparticles obtained according to the protocol described in Example 1 are then functionalized. To do this, 0.600 g of nanoparticles are placed in a 103 mol.L-1 solution of octadecylphosphonic acid in THF (tetrahydrofuran) at 40°C for 24 h under gentle mechanical stirring so as to graft alkyl chains onto the silica. The functionalized nanoparticle powder is then filtered, rinsed thoroughly with absolute ethanol, and dried. After purification, 0.580 g of functionalized nanoparticles are obtained. These are referred to as Charges A in the remainder of this document.

[0045] Example 3: Functionalization of core-shells with acid 3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,11,11,12,12,12-fluorododecyl-phosphonic

[0046] 0.600 g of AgNW-SiO2 nanoparticles obtained according to the protocol described In Example 1, 3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,11,11,12,12,12-fluorododecylphosphonic acid is placed in a 103 mol / L solution of THF (tetrahydrofuran) at 40°C for 24 h under gentle mechanical stirring. The functionalized nanoparticle powder is then filtered, rinsed thoroughly with absolute ethanol, and dried. After purification, 0.595 g of core-shell-functionalized nanoparticles are obtained. These are referred to as Charge B in the remainder of this document.

[0047] Example 4: Functionalization of core-shells with trichloro(octadecyl)silane

[0048] 0.620 g of AgNW-SiO2 nanoparticles obtained according to the protocol described in Example 1 samples are placed in a 103 mol / L solution of trichloro(octadecyl)silane in anhydrous toluene at 45°C for 24 hours, under gentle mechanical stirring. The functionalized nanoparticle powder is then filtered, rinsed thoroughly with absolute ethanol, and dried. After purification, 0.615 g of functionalized nanoparticles are obtained. These are referred to as C-Charges in the remainder of this document.

[0049] Example 5: Manufacture of phase-change, thermally conductive and electrically insulating composite materials

[0050] a- Fabrication of the composite material from AgNW-SiO2: Approximately exactly 13.75 g of nanoparticles (from example 1) and 36.25 g of phase change material purchased from RubiTherm - Germany (paraffin RT44HC), are integrated into an internal mixer at a temperature of 60°C for 5 min.

[0051] b- Fabrication of the composite material from the Charges A, B and C: Approximately exactly 0.55 g of nanoparticles and 1.45 g of phase change material purchased from RubiTherm - Germany (paraffin RT44HC) are integrated into a glass pillbox, heated and mixed at 60°C using a heated magnetic stirrer for 5 min.

[0052] The two above-described mixing process variants were carried out on the paraffin + 15% vol AgNW material for comparison purposes. The results are identical regardless of the process. Thus, these two processes do not affect the final properties of the resulting composite material.

[0053] c- Fabrication of the composite material with the MCP diluted in a polymer: Approximately exactly 13.75 g of nanoparticles and 36.25 g of phase change material comprising 50% by mass of paraffin (RubiTherm - Germany - paraffin RT44HC) and 50% by mass of polyethylene (ExxonMobil™ LLDPE LL 6101) are integrated into an internal mixer at a temperature of 160°C for 5 min.

[0054] It is understood in this document that the expression "approximately exactly" well known elsewhere by those skilled in the art, corresponds to the value indicated in grams "+ / - 0.05g" regardless of the weighing carried out in these examples.

[0055] For each manufacturing example, the phase-change composite material is recovered and then pressed at 60°C using a thermopress to obtain pellets for thermal and electrical analysis. The formed pellets measure 12.8 ± 0.05 mm in diameter and 1.2 ± 0.05 mm in thickness.

[0056] The performance of phase-change composite materials for thermal management is characterized by measurements of thermal conductivity and enthalpy of fusion. The method for measuring thermal conductivity is indirect: thermal conductivity is the product of thermal diffusivity, specific heat, and density. Enthalpy of fusion is measured by differential scanning calorimetry (DSC). Electrical resistivities are measured using a resistivity meter.

[0057] Specifically, the thermal conductivity values ​​(X) were calculated using the formula X = a*p*Cp, where a is the thermal diffusivity measured by a Netzsch LFA447 device, p is the apparent density measured by pycnometry (Micromeritics AccuPyc 1340) and Cp is the specific heat capacity measured by a microcalorimeter (Setaram Microcalvet).

[0058] Surface and volume electrical resistivities are measured using a UR-SS concentric double-ring probe mounted on a Hiresta-UX resistivity meter (MCP-HT800, Mitsubishi Chemical Analytech, Japan) for high resistivity samples (> 10⁴ Ω·cm). Lower resistivity samples (< 10⁶ Ω·cm) are measured using a 4-point PSP probe mounted on a Loresta-GX resistivity meter (MCP-T700, Mitsubishi Chemical Analytech, Japan). Results

[0059] The results of the measurements carried out on the phase change composite materials obtained as described in the preceding examples are recorded in Table I below. Input Materials Thermal conductivity (W / mK) Electrical resistivity (Ω·cm) Enthalpy of fusion (J / g) 1 PW 0.23 1lxO15 183 2 PW+LLDPE 0.23 1lxO15 146 3 PW + 15% vol AgNW 1.34 5.4lxO5 137 4 (PW+LLDPE) + 15% vol AgNW 1.36 5.2lxO5 131 5 PW + 15% vol AgNW-SiO2 1.41 4.5x10" 143 6 PW +15% vol Charges A 1.60 4.6x10" 138 7 PW +15% vol Charges B 1.66 8.1x10" 140 8 PW +15% vol Charges C 1.63 5.7x10" 141

[0061] Input 1 records the results of thermal conductivity, electrical resistivity and enthalpy of fusion of paraffin alone (paraffin RT44HC), which can serve as a reference.

[0062] Entry 2 indicates the results for said paraffin diluted in polyethylene according to example 5c). Only the enthalpy of fusion is impacted by this dilution.

[0063] Entry 3 indicates the results of the composite material comprising only the silver nanowires not encapsulated by a ceramic material. As expected, the thermal conductivity is increased by one unit and the electrical resistivity falls significantly below the values ​​of electrical insulators (1.109 Q.cm) while the enthalpy of fusion is further reduced compared to entry 2.

[0064] Entry 4 indicates the results for the composite material comprising only the Ag nanowires and the polyethylene matrix of the paraffin. The results vary little in the presence or absence of the polymer matrix.

[0065] Entry 5 indicates the results of the composite material comprising the Ag nanowires wrapped with silica (example 5a), which significantly improves the results: the thermal conductivity increases by almost 0.1 unit compared to the values ​​of entry 2. The enthalpy value is also improved, but the greatest benefit is to The introduction of a ceramic material results in electrical resistivity exceeding the value threshold of electrical insulators. Thus, the combination of core-shell nanoparticles made of ceramic material with a phase-change material represents a genuine advancement. The presence of the ceramic shell on the electrically conductive nanoparticles improves the enthalpy of fusion, thermal conductivity, and electrical resistivity of the phase-change composite material containing electrically and thermally conductive nanoparticles (Ag nanowires - entry 3).

[0066] Entries 6 to 8 indicate the results obtained from the composite materials of Examples 5b), comprising the phase-change material blended with Ag nanowires wrapped in functionalized silica (Charges A, B, and C). Functionalization provides a thermal conductivity improvement of 0.2 units compared to the unfunctionalized material of Entry 5. Electrical resistivity remains stable, and the enthalpy of fusion is improved compared to that of the silica-free material in Entry 3. Thus, functionalization provides a clear advantage with regard to thermal conductivity, undoubtedly due to better surface compatibility between the silica and the PCM. Without being bound by any theory, it is possible that the presence of the grafted chains increases the number of Van der Waals-type bonds with the PCM, leading to better thermal conductivity within the composite material.The best results in terms of thermal conductivity and electrical resistivity are obtained with B charges which exhibit functionalization based on fluorinated alkyl chains.

[0067] In conclusion, the addition of conductive nanoparticles wrapped by a thermally conductive and electrically insulating material to a PCM allows a notable gain in thermal conductivity without significantly altering the enthalpy of fusion of the PCM while remaining electrically resistive.

[0068] Surface functionalization of the shell material also improves the thermal conductivity of the final composite material and provides an improvement in electrical insulation. These analyses demonstrate the advantages of both unfunctionalized and functionalized core-shell nanoparticles in the MCP matrices of the present invention for improving thermal management while remaining within the range of electrical insulators. This clearly demonstrates its strong potential as a new material for the thermal management of electrical and electronic systems.

Claims

Demands

1. A method for preparing a phase-change composite material, comprising the steps of: a) Growing a ceramic material shell of determined thickness on nanoparticles comprising metal and / or carbon, so as to prepare core-shell nanoparticles, b) Integrating the core-shell nanoparticles by mixing into a solid-liquid phase-change material (or SL PCM), for example by melting using a twin-screw extruder, so as to obtain the phase-change composite material.

2. A method for producing a phase-change composite material according to claim 1, which includes prior to step a) a step i) of dispersing the nanoparticles in an aqueous phase comprising a water-soluble polymer, so as to obtain a thin conforming layer of water-soluble polymer covering the nanoparticles, in particular the thin layer having a thickness of between 0.5 and 5 nm, so as to facilitate the growth of the ceramic material shell.

3. A method for producing a phase-change composite material according to claim 1 or 2, wherein the nanoparticles have a non-zero shape factor, typically nanoparticles with a 1D or 2D structure.

4. A method for developing a phase-change composite material according to any one of claims 1 to 3, wherein the ceramic material shell is made of silica and its growth is obtained by sol-gel method on nanoparticles, in particular in a hydroalcoholic medium and in the presence of tetraethyl orthosilicate (TEOS), in particular until reaching the determined shell thickness of between 10 and 90 nanometers, and preferably between 20 and 60 nanometers.

5. A method for producing a phase-change composite material according to any one of claims 1 to 4, wherein prior to step b) a step a') of functionalizing the ceramic material shell in the presence of a coupling agent, such as a silane or a phosphonic acid derivative, particularly in a solvent with a concentration ranging from 0.1 to 20 mmol.L-1, preferably 1 to 5 mmol.L-1, for example by stirring at temperature ambient between 1 and 24 h, preferably between 4 and 14 h, so as to provide core-shell-surface functionalized nanoparticles.

6. A method for producing a phase-change composite material according to the preceding claim, wherein the functionalization step a') generates the grafting of alkyl chains onto the ceramic material, in particular the alkyl chains have at least three carbon atoms, or even at least six carbon atoms, in particular, the alkyl chains are at least partially fluorinated and for example the alkyl chains are perfluorinated.

7. A method for preparing a phase-change composite material according to any one of claims 1 to 6, wherein the integration step b) comprises mixing an organic PCM with functionalized core-shell nanoparticles or core-shell nanoparticles, in particular by melting using a twin-screw extruder.

8. A method for producing a phase-change composite material according to the preceding claim, which includes prior to step b) a dilution step ii) of the organic MCP in a polymer, in particular in polyethylene (PE) or polypropylene (PP), so as to form a polymeric matrix loaded with MCP.

9. A method for developing a phase-change composite material according to the preceding claim, which includes, prior to step ii) a step of functionalizing the polymer intended to form the polymer matrix, with maleic anhydride (PEgMA).

10. Phase-change composite material comprising a plurality of core-shell nanoparticles embedded in an organic phase-change material, the nanoparticles comprising a metal or carbon forming the core and being covered by a ceramic material shell of a determined thickness.