# US 2014/0197355 A1 · Method of encapsulating a phase change material with a metal oxide

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- Number: US 2014/0197355 A1
- Document ID: US20140197355A1
- Status: Published application
- Kind: A1
- Application number: 14/159,874
- Filed: 2014-01-21
- Published: 2014-07-17
- Earliest claimed: 2011-07-18
- Assignees: University of South Florida
- Inventors: Manoj Kumar Ram; Chand K. Jotshi; Elias K. Stefanakos; Dharendra Yogi Gaswami
- Web page: https://patentgrep.com/patent/US20140197355A1

## CPC

- C09K 5/063: {Materials absorbing or liberating heat during crystallisation; Heat storage materials}
- C08G 73/1035: {from tetracarboxylic acids or derivatives and diisocyanates}
- C08K 3/08: Metals
- C08K 3/10: Metal compounds
- C08K 3/16: Halogen-containing compounds
- C08L 79/08: Polyimides; Polyester-imides; Polyamide-imides; Polyamide acids or similar polyimide precursors
- C08K 3/28: Nitrogen-containing compounds
- C08K 2003/0862: {Nickel}
- C09K: MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
- C08G: MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
- C08K: Use of inorganic or non-macromolecular organic substances as compounding ingredients (paints, inks, varnishes, dyes, polishes, adhesives C09)
- C08L: COMPOSITIONS OF MACROMOLECULAR COMPOUNDS (compositions based on polymerisable monomers C08F, C08G; artificial filaments or fibres D01F; textile treating compositions D06)

## Abstract

Storage systems based on latent heat storage have high-energy storage density, which reduces the footprint of the system and the cost. However, phase change materials (PCMs), such as NaNO3, NaCl, KNO3, have very low thermal conductivities. To enhave the storage of PCMs, macroencapsulation of PCMs was performed using a metal oxide, such as SiO2 or a graphene-SiO2, over polyimide-coated or nickel-embedded, polyimide-coated pellets The macro encapsulation provides a self-supporting structure, enhances the heat transfer rate, and provides a cost effective and reliable solution for thermal energy storage for use in solar thermal power plants. NaNO3 was selected for thermal storage in a temperature range of 300° C. to 500° C. The PCM was encapsulated in a metal oxide cell using self-assembly reactions, hydrolysis, and simultaneous chemical oxidation at various temperatures.

## Claims

### Claim 1

A thermal energy storage material; comprising:
phase changing salt pellet, wherein the phase changing salt pellet is inorganic;
a polyimide coating disposed on the exterior surface of the phase changing salt pellet;
wherein the polyimide coating comprises polyimide and a surface roughener disposed in the polyimide coating, where the surface roughener is nickel, silicon carbide, or carbon; and
a encapsulant disposed on the exterior of the polyimide coating, wherein the encapsulant is metal oxide or a graphene-metal oxide composite.

### Claim 2 (depends on 1)

The thermal energy storage material of claim 1, wherein the phase changing salt pellet is aluminum phosphate, ammonium carbonate, ammonium chloride, caesium carbonate, caesium sulfate, calcium citrate, calcium carbonate, calcium chloride, calcium hydroxide, calcium oxide, calcium phosphate, calcium saccharate, calcium sulfate, cerium phosphate, chromic chloride, iron phosphate, lithium carbonate, lithium sulfate, magnesium chloride, magnesium sulfate, manganese chloride, manganese nitrate, manganese sulfate, potassium acetate, potassium carbonate, potassium chloride, potassium hydroxide, potassium phosphate, rubidium carbonate, rubidium sulfate, disodium tetraborate, sodium acetate, sodium bicarbonate, sodium bisulfate, sodium borate, sodium carbonate, sodium citrate, sodium chloride, sodium hydroxide, sodium nitrate, sodium percarbonate, sodium persulfate, sodium phosphate, sodium propionate, sodium selenite, sodium silicate, sodium sulfate, sodium tellurate, sodium tetraborate, sodium thiosulfate, strontium hydrophosphate, zinc acetate, zinc chloride, eutectic of Li2CO3 and Na2CO3, or a combination thereof.

### Claim 3 (depends on 2)

The thermal energy storage material of claim 2, wherein the phase changing salt pellet is sodium chloride or sodium nitrate.

### Claim 4 (depends on 1)

The thermal energy storage material of claim 1, wherein the surface roughener is nickel or silicon carbide.

### Claim 5 (depends on 1)

The thermal energy storage material of claim 1, wherein the metal oxide encapsulant is silicon dioxide, titanium dioxide, zinc oxide, calcium oxide, barium oxide, titanium dioxide-silicon dioxide composite, cerium dioxide, iron (III) trioxide, aluminum (III) oxide, magnesium oxide, lithium cobalt dioxide, lithium nickel dioxide, zinc oxide, zirconium dioxide, lithium, titanium oxide, lithium aluminum manganese oxide, lithium nickel manganese oxide, lithium dimanganese tetraoxide, indium tin oxide, or combinations thereof.

### Claim 6 (depends on 5)

The thermal energy storage material of claim 5, wherein the graphene-metal oxide composite is graphene-silicon dioxide.

### Claim 7 (depends on 1)

The thermal energy storage material of claim 1, wherein the phase changing salt pellet is surface functionalized, further comprising hexane and silane functionalization.

### Claim 8 (depends on 1)

The thermal energy storage material of claim 1, wherein the phase changing salt pellet is cylindrical, spherical or oblong.

### Claim 9 (depends on 8)

The thermal energy storage material of claim 8, wherein phase changing salt pellet is a cylindrical pellet having a porosity of 1% to 5% or a spherical pellet having a porosity of 22 to 29%.

### Claim 10 (depends on 1)

The thermal energy storage material of claim 1, further comprising a void space, disposed in the phase changing salt pellet.

### Claim 11 (depends on 10)

The thermal energy storage material of claim 10, wherein the void space is between about 15 to about 35% of the size of the phase changing salt pellet.

### Claim 12 (depends on 10)

The thermal energy storage material of claim 10, wherein the void space is evacuated of ambient air.

### Claim 13

A method of manufacturing a thermal energy storage material, comprising the steps:
providing a phase changing salt pellet, wherein the phase changing salt pellet is inorganic;
coating the exterior surface of the phase changing salt pellet in a polyimide coating;
wherein the polyimide coating comprises polyimide and a surface roughener disposed in the polyimide coating, where the surface roughener is nickel, silicon carbide, or carbon
curing the polyimide coating; and
encapsulating the exterior of the polyimide coating with a metal oxide or a graphene-metal oxide composite.

### Claim 14 (depends on 13)

The method of claim 13, wherein the phase changing salt pellet is aluminum phosphate, ammonium carbonate, ammonium chloride, caesium carbonate, caesium sulfate, calcium citrate, calcium carbonate, calcium chloride, calcium hydroxide, calcium oxide, calcium phosphate, calcium saccharate, calcium sulfate, cerium phosphate, chromic chloride, iron phosphate, lithium carbonate, lithium sulfate, magnesium chloride, magnesium sulfate, manganese chloride, manganese nitrate, manganese sulfate, potassium acetate, potassium carbonate, potassium chloride, potassium hydroxide, potassium phosphate, rubidium carbonate, rubidium sulfate, disodium tetraborate, sodium acetate, sodium bicarbonate, sodium bisulfate, sodium borate, sodium carbonate, sodium citrate, sodium chloride, sodium hydroxide, sodium nitrate, sodium percarbonate, sodium persulfate, sodium phosphate, sodium propionate, sodium selenite, sodium silicate, sodium sulfate, sodium tellurate, sodium tetraborate, sodium thiosulfate, strontium hydrophosphate, zinc acetate, zinc chloride, eutectic of Li2CO3 and Na2CO3, or a combination thereof.

### Claim 15 (depends on 13)

The method of claim 13, wherein phase changing salt pellet are made either by using power press or a pelletizer.

### Claim 16 (depends on 13)

The method of claim 13, wherein the polyimide coating is cured at up to 250° C. for 2 hours.

### Claim 17 (depends on 16)

The method of claim 16, wherein the polyimide coating is cured at a temperature of between about 220° C. and about 250° C. for 2 hours.

### Claim 18 (depends on 13)

The method of claim 13, wherein the polyimide coating is coated further comprising the steps:
mixing the polyimide with N-methyl 2-pyrrolidinone and a plasticizer organic solvent;
applying a thin layer of the NMP+polyimide mixture onto the phase changing salt pellet by dip coating, spray coating, or brushing; and
curing the polyimide layer.

### Claim 19 (depends on 16)

The method of claim 16, further comprising heating the phase changing salt pellets up to 250° C. for 2 hours at 4° C./min.

### Claim 20 (depends on 13)

The method of claim 13, further comprising:
adding an additive to the polyimide prior to coating the exterior surface of the phase changing salt pellet in a polyimide,
wherein the additive is nickel powder, silicon carbide, or carbon.

### Claim 21 (depends on 13)

The method of claim 13, wherein the metal oxide encapsulant is silicon dioxide, titanium dioxide, zinc oxide, calcium oxide, barium oxide, titanium dioxide-silicon dioxide composite, cerium dioxide, iron (III) oxide, aluminum (III) oxide, magnesium oxide, lithium cobalt dioxide, lithium nickel dioxide, zinc oxide, zirconium dioxide, lithium, titanium oxide, lithium aluminum manganese oxide, lithium nickel manganese oxide, lithium dimanganese tetraoxide, indium tin oxide, or combinations thereof.

### Claim 22 (depends on 21)

The method of claim 21, wherein the exterior of the polyimide coating is encapsulated in silicon dioxide or a graphene-silicon dioxide composite, further comprising the steps:
obtaining a sol-gel silicon dioxide precursor, wherein the sol-gel silicon dioxide precursor is tetraethyl orthosilicate or tetraethyl orthosilicate containing graphene;
mixing the tetraethyl orthosilicate with 3-aminopropyltriethoxy silane to form a silicate precursor;
placing the polyimide-coated phase changing salt pellets into the silicate precursor;
heating the silicate precursor;
adding ethanol and hydrochloric acid to the silicate precursor;
permitting the silicate precursor to hydrolyze for about 5 to about 10 minutes;
neutralizing the silicate precursor with sodium hydroxide; and
permitting the sol-gel silicon dioxide precursor to encapsulate the polyimide coated phase changing salt pellet.

### Claim 23 (depends on 22)

The method of claim 22, wherein the sol-gel graphene-silicon dioxide precursor is cured at 250° C. at a rate of 4° C./minute for two hours.

### Claim 24 (depends on 13)

The method of claim 13, further comprising:
forming a void space in the phase changing salt pellet prior to polyimide coating,
wherein the void space is formed by drilling, briquetting, or die casting the pellet with a void space.

### Claim 25 (depends on 24)

The method of claim 24, further comprising:
reducing the pressure in the void space, comprising:
inserting a metal wire into the phase changing salt pellet during fabrication of the pellet;
heating the phase changing salt pellet;
removing the metal wire from the phase changing salt pellet;
permitting heated gases to escape from the void space; and
applying the polyimide coating to the phase changing salt pellet to seal the void space.

### Claim 26 (depends on 13)

The method of claim 13, further comprising functionalizing the surface of the phase changing salt pellet, comprising:
soaking the phase changing salt pellet in a solution of hexane and silane for 24 hours prior to applying the polyimide coating to the phase changing salt pellet.