Thermal energy storage media and system and methods of forming and using same

Abstract

Systems and methods are disclosed including a method of forming thermal energy storage media. An exemplary method includes the steps of, using additive manufacturing, forming a silicon-containing material core and forming a carbon-based shell that encapsulates the silicon-containing material core to form a printed medium, drying the printed medium to form a preform, and heating the preform to convert at least a portion of the carbon-based shell to silicon carbide. Other exemplary embodiments are disclosed herein.

Description

THERMAL ENERGY STORAGE MEDIA AND SYSTEM ANDMETHODS OF FORMING AND USING SAMECROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Provisional Application Number 63 / 631.352, entitled “THERMAL ENERGY STORAGE MEDIA AND SYSTEMS AND METHODS OF FORMING AND USING SAME,” and filed April 8. 2024, which is herein incorporated by this reference in its entirety.TECHNICAL FIELD

[0002] This disclosure relates generally to thermal energy storage media, to systems including the thermal energy storage media, and to methods of forming and using the thermal energy storage media and systems.BACKGROUND

[0003] There is often a gap between thermal energy availability and thermal energy demand, particularly for industrial processes. Roughly 70% of energy demand in the industrial sector is for heat. Demand for energy7is expected to increase up to 15% from 2022 levels by 2050. There is further a push to obtain energy from renewable sources due to global warming and climate change; however, the production of energy from renewable sources is often intermittent. The generation of electricity and thermal energy from solar energy7is highest during the day with peak sunlight and drops drastically at night. Accordingly, there is a drop in energy7load on a related grid. At the same time, there is typically an increase in energy demand on the grid in the evening as people return home and use energy in their homes. This puts stress on the grid to generate more energy and to accommodate an extreme shift in relative energy load and demand.

[0004] Thermal energy storage can store thermal energy7generated by, for example, renewable sources, during periods of peak energy7load and relatively low energy7demand and can discharge thermal energy7to be converted into electricity during periods of low energy7load and relatively high energy demand. Further, thermal energy storage may reduce the need toretrofit existing processes to be suitable for battery storage of electricity. However, there are often issues with cost, degradation, thermal energy storage capacity, toxicity, and corrosiveness associated with traditional methods of thermal energy storage.

[0005] Therefore, in view of the above, there is a need for improved thermal energy storage media that is relatively low cost, non-toxic, non-corrosive, and which has a long lifetime of use, is less subject to thermal degradation, and has a relatively high thermal energy storage capacity.

[0006] Any discussion, including discussion of problems and solutions, set forth in this section, has been included in this disclosure solely for the purpose of providing a context for the present disclosure, and should not be taken as an admission that any or all of the discussion was known at the time the invention was made or otherwise constitutes prior art.SUMMARY

[0007] This summary may introduce a selection of concepts in a simplified form, which may be described in further detail below. This summary is not intended to necessarily identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.

[0008] Various embodiments provide a method of forming thermal energy storage media, a system including thermal energy storage media, and methods of using and forming the same. While particular examples of how the present methods, systems, and articles of manufacture address the shortcomings of prior media, systems, and methods are described in more detail below, in general, the present methods, systems, and articles of manufacture provide an efficient, relatively low cost, non-toxic, non-corrosive thermal energy storage media which has a long lifetime of use, is less subject to thermal degradation, and has a relatively high thermal energy storage capacity, and is meant to store thermal energy.

[0009] In accordance with various embodiments, a method includes forming a silicon- containing material core and forming a carbon-based shell that encapsulates the silicon- containing material core to form a printed medium, using additive manufacturing. The method can further comprise drying the printed medium to form a preform and heating the preform to convert at least a portion of the carbon-based shell to silicon carbide.

[0010] In accordance with various examples, forming the carbon-based shell can comprise forming a suspension that can comprise a carbon material precursor, a thermosetting compound, and a dispersion medium. The thermosetting compound can comprise, for example,a phenol-formaldehyde resin or a lignin. The dispersion medium can, for example, comprise water. The suspension can comprise a binding agent. The binding agent can comprise one or more of polyvinyl alcohol, polyethyleneimine, sodium polyacrylate, or polyethylene oxide. An amount of binding agent in the dispersion medium can be from about 1 wt% to about 5 wt%, is from about 5 wt% to about 15 wt%, is from about 1 wt% to about 30 wt%, or is from about 5 wt% to about 30 wt%. The suspension can comprise from about 10 wt% to about 20 wt% or from about 20 wt% to about 45 wt% carbon material precursor, from about 5 wt% to about 15 wt% or from about 15 wt% to about 30 wt% thermosetting compound, and / or from about 40 wt% to about 50 wt% or from about 50 wt% to about 75 \\1% dispersion medium.

[0011] In various examples, the drying can comprise providing the preform in a humidity-controlled environment. The humidity can be between about 60% and about 80% or about 80% and about 99% relative humidity, or the like.

[0012] The heating can comprise a curing stage, a pyrolytic stage, and a vacuum infiltration stage. A temperature during the curing stage can be less than 300 °C, less than 250 °C, less than 200 °C or can be between about 70 °C and about 180 °C. A temperature during the pyrolytic stage can be greater than 200 °C, greater than 250 °C, greater than 300 °C, or can be between about 250 °C and about 1000 °C. A temperature during the vacuum infiltration stage can be greater than 1000 °C or between 1300 °C and 1900 °C.

[0013] The forming a silicon-containing material core can comprise forming a suspension which can comprise silicon-or doped silicon or silicon alloy solids, a binding agent, and a dispersion medium. The suspension can comprise about 5-30 wt%, about 10-20 wt%, or about 20-30 wt% binding agent.

[0014] Various embodiments can include an article of manufacture. The article of manufacture can be a heat storage device that can comprise the thermal energy media formed, for example, according to any of the methods disclosed herein. In various embodiments, the article of manufacture can comprise a silicon-containing material core and a shell that can comprise silicon carbide. The density of the silicon carbide shell can be greater than 80%, greater than 90%, greater than 95%, or between about 80% and about 99% of the theoretical density of the silicon carbide shell.

[0015] Various embodiments can include a system. The system can comprise an inner chamber, an outer chamber, thermal energy media, a heat transfer gas inlet tube, and a valve module. The outer chamber can encapsulate the inner chamber. The thermal energy’ media canbe within the inner chamber. The heat transfer gas inlet tube can be coupled to a top region of the inner chamber. The valve module can be coupled to a lower region of the inner chamber.

[0016] In various embodiments, the inner chamber can comprise a closed-end tube. The inner chamber can comprise a ceramic wall. The outer chamber can comprise a metal wall. The system can further comprise insulating material between the inner chamber and the outer chamber. The system can further comprise a cross tube, a suspension tube, and a cross pin. The cross tube can be disposed within a bore within a wall of the inner chamber. The suspension tube can be engaged with the cross tube. The cross pin can comprise a hollow center in fluid communication with the cross tube and the heat transfer gas inlet tube. The cross tube can intersect the wall of the inner chamber and can be fluidly coupled to an interior portion of the inner chamber. The thermal energy media can be formed according to any of the methods disclosed herein. The system can be configured to operation within a range of about 1000 °C to about 1500 °C.

[0017] For the purpose of summarizing the disclosure and the advantages achieved over the prior art, certain objects and advantages of the disclosure may have been described herein above. Of course, it is to be understood that not necessarily all such objects or advantages may be achieved in accordance with any particular embodiment. Thus, for example, one may recognize that the invention may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught or suggested herein without necessarily achieving other objects or advantages as may be taught or suggested herein.

[0018] These and other embodiments will become readily apparent to those skilled in the art from the following detailed description of certain embodiments having reference to the attached figures, the invention not being limited to any particular embodiment(s) disclosed.BRIEF DESCRIPTION OF THE DRAWINGS

[0019] To facilitate further description of the embodiments, the following drawings are provided in which:

[0020] FIG. 1 illustrates a perspective view of a portion of a thermal energy storage media, according to an embodiment:

[0021] FIGs. 2A and 2B illustrate a cross-section view of a thermal energy storage media, according to an embodiment:

[0022] FIG. 3 illustrates an exemplary method of forming a thermal energy7storage media, according to an embodiment:

[0023] FIG. 4 illustrates an exemplary method of forming a thermal energy storage media, according to an embodiment:

[0024] FIG. 5 illustrates exemplary embodiments of a carbon shell material, having varying ratios of microcrystal line cellulose and phenol-formaldehyde resin, according to an embodiment;

[0025] FIG. 6A illustrates exemplary embodiments of a carbon shell material dried in air and dried in a humid environment, according to an embodiment;

[0026] FIG. 6B illustrates exemplary embodiments of a carbon shell material printed first and last in a respective batch of carbon shell material, according to an embodiment;

[0027] FIG. 7 illustrates exemplary7embodiments of a carbon shell material printed with and without a binding agent, according to an embodiment;

[0028] FIG. 8 illustrates measured distance distributions of exemplary embodiments of a carbon shell material with varying amounts of a binding agent, according to an embodiment;

[0029] FIG. 9 illustrates the median distance versus percent binding agent of the exemplary embodiments of FIG. 8, according to an embodiment;

[0030] FIG. 10 illustrates an exemplary method of carbonizing a carbon shell material, according to an embodiment;

[0031] FIG. 11 illustrates exemplary embodiments of a carbon shell material, according to an embodiment;

[0032] FIG. 12 illustrates an exemplary thermal energy storage media before and after carbonization and liquid silicon infiltration, according to an embodiment;

[0033] FIG. 13 illustrates an energy dispersive spectroscopy mapping of an exemplary thermal energy storage medium, according to an embodiment;

[0034] FIG. 14 illustrates the gelation and glass transition onsets during curing of an exemplary thermal energy storage medium, according to an embodiment;

[0035] FIG. 15 illustrates a glass transition temperature as a function of curing time at 100 °C of an exemplary thermal energy storage medium, according to an embodiment;

[0036] FIG. 16A illustrates a 3D reconstruction of a micro-CT scan of an exemplary carbon shell material, according to an embodiment;

[0037] FIG. 16B illustrates a cross section of the medium illustrated in FIG.16A, filtered to illustrate solids and pore space within the exemplary carbon shell material, according to an embodiment;

[0038] FIG. 17 illustrates porosity of an exemplary carbon shell material as a function of the curing time, according to an embodiment;

[0039] FIG. 18 illustrates weight loss as a function of time for microcrystalline cellulose pyrolysis at varying temperatures, particle sizes, and bed sizes, according to an embodiment;

[0040] FIG. 19 illustrates ion current curves as a function of time for an exemplary microcry stalline cellulose sample heated at less than about 300 °C. according to an embodiment;

[0041] FIG. 20 illustrates an exemplary unit of cellobiose, according to an embodiment;

[0042] FIG. 21 illustrates a carbon dioxide isotherm at 0 °C for an exemplary 600 mg microcrystalline cellulose sample after carbonization, according to an embodiment;

[0043] FIG. 22 illustrates a backscattered electron image of an exemplary carbon shell material after carbonization, according to an embodiment;

[0044] FIG. 23 illustrates a Raman spectra of graphite, glassy carbon, and char of an exemplary carbon shell material under slow and fast pyrolysis conditions, according to an embodiment;

[0045] FIG. 24 illustrates an exemplary7thermocline system, according to an embodiment;

[0046] FIG. 25 illustrates an exemplary thermocline system, according to an embodiment;

[0047] FIG. 26A illustrates an exemplary thermocline system mounted on a linear rail system, according to an embodiment;

[0048] FIG. 26B illustrates a side view of an exemplary thermocline sy stem mounted on a linear rail system, according to an embodiment;

[0049] FIG. 27 illustrates an internal schematic view of the exemplary thermocline system of FIG. 26A, according to an embodiment;

[0050] FIG. 28 illustrates an internal schematic view of a top portion of the thermocline of FIG. 26 A. according to an embodiment;

[0051] FIG. 29 illustrates an exemplary schematic view of a junction between a cross tube and a horizontal tube of an exemplary thermocline system, according to an embodiment;

[0052] FIG. 30 illustrates an exemplary schematic view of a top portion of the electric furnace of FIG. 26A, according to an embodiment;

[0053] FIG. 31 illustrates an exemplary thermocline system, according to an embodiment;

[0054] FIG. 32 illustrates a middle portion of the exemplary thermocline system of FIG. 31, according to an embodiment;

[0055] FIG. 33 illustrates a top portion of the exemplary thermocline system of FIG. 31 , according to an embodiment;

[0056] FIG. 34 illustrates a bottom portion of the exemplary thermocline system of FIG. 31 , according to an embodiment;

[0057] FIG. 35 illustrates a flowchart for a method of forming a thermal energy storage media, according to an embodiment:

[0058] It will be appreciated that elements in the figures are illustrated for simplicity7and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help improve understanding of illustrated embodiments of the present disclosure.DETAILED DESCRIPTION

[0059] Although certain embodiments and examples are disclosed below, it will be understood by those in the art that the disclosure extends beyond the specifically disclosed embodiments and / or uses of the disclosure and obvious modifications and equivalents thereof. Thus, it is intended that the scope of the disclosure should not be limited by the particular embodiments described herein.

[0060] Unless noted otherwise, illustrations presented herein are not necessarily meant to be actual views of any particular material, assembly, structure, or device, but are merely representations that are used to describe embodiments of the disclosure.

[0061] Disclosed herein are systems, methods, and articles of manufacture comprising thermal energy storage media. The thermal energy storage media may comprise Si-based encapsulated phase change materials (EPCMs). With reference to FIG. 1, a Si-based EPCM 100 may comprise a silicon core 105 and a silicon carbide (SiC) composite shell 110. The Si- based EPCM 100 may have a spherical, cylindrical, cubical, rectangular, triangular, ovular, or any other suitable geometry.

[0062] Silicon may be a desirable material for a high-temperature thermal energy storage media due to its low cost and high energy density. The Si-based EPCM 100 may utilize the heat release associated with the melt-to-metal phase transition of the Si core 105 above 1414°C for a high-temperature thermal energy storage media. Table 1 illustrates properties of Si as a thermal energy storage media compared to other thermal energy storage (TES) media materials.Table 1

[0063] FIG. 2A illustrates an exemplary' cross section of a Si-based EPCM precursor 201 having a colloidal silicon core 204 and a carbon-based material shell 214. The Si-based EPCM precursor 201 may undergo heat treatment and carbonization to convert the carbonbased material shell 214 to porous carbon and / or to convert the colloidal silicon core 204 to silicon. In this manner, the colloidal systems may be removed from the Si-based EPCM precursor 201. The Si-based EPCM precursor 201 may be formed by additive manufacturing, for example by direct ink writing. Direct ink writing may involve layer-by-layer deposition of solid suspensions, for example to fabricate complex-shaped parts. Direct ink writing may be desirable for one-step Si encapsulation. Dynamic mixing may be an example of additive manufacturing. For example, Si, for example Si in a spherical or pellet form, may be added to a dynamic mixer. A polymeric carbon precursor, such as microcrystalline cellulose (MCC), and / or a thermosetting material may be added to the dynamic mixer. The dynamic mixer may be operated to agglomerate the polymeric carbon precursor around the Si pellets. In this manner, the Si pellets may be encapsulated by the carbon-based material shell. Additional examples of additive manufacturing include, but are not limited to. powder bed fusion, vat photopolymerization, sheet lamination, direct energy deposition, and / or any other suitable technique of additive manufacturing.

[0064] In various embodiments, the colloidal silicon core 204 may comprise or consist essentially of Si particles, with or without other metal particles, and / or a suspension medium. The suspension medium may be an aqueous medium, i.e. it may comprise water. The suspension medium may include one or more binding agents and / or dispersing agents such as, for example, polyvinyl alcohol, polyethyleneimine, polyethylene oxide, sodium polyacrylate, and / or any other suitable binding agent and / or dispersing agent. An amount of the binding agent in the dispersion medium is from about 1 wt% to about 5 wt%, is from about 5 wt% to about 15 wt%, is from about 1 wt% to about 30 wt%, or is from about 5 wt% to about 30 wt%. The Si particles may be agglomerated in a solvent-free method, such as pressing, with or without binding agents and / or dispersing agents. As defined herein, binding agents and dispersing agents may refer to the same or similar groups of agents.

[0065] In various embodiments, the carbon-based material shell 214 may comprise or consist essentially of polymeric carbon precursors. The polymeric carbon precursors may comprise microcrystalline cellulose (MCC) and / or any other suitable polymeric carbon precursor. The polymeric carbon precursors may be selected such that the polymeric carbon precursors carbonize to form solid, porous char (carbon) which can be infiltrated by molten Siand thus converted to silicon carbide. One or more thermosetting materials, such as, for example, phenol-formaldehyde resin (PF) and / or lignin may be added to the polymeric carbon precursors. In various embodiments, one or more materials may be both a polymeric carbon precursor and a thermosetting material. Stated another way, there may be some overlap between the suitable polymeric carbon precursor materials and the suitable thermosetting materials. In this manner, mechanical stability' of the porous carbon shell after heat treatment may be improved. With momentary reference to FIG. 11. Image A of FIG. Il represents a MCC-PF printed material, and Image C represents the same material after carbonization. Image B of FIG. 11 represents a MCC-Lignin material, and Image D represents the same material after carbonization. The shape of the print in Images A and B is retained after carbonization, as illustrated by Images C and D. With momentary reference to FIG. 5, exemplary carbonbased material shells 214 (FIG. 2A) having varying ratios of MCC to PF are provided. Carbonbased shell materials 506, 507, and 508 have MCC:PF ratios of 100:0, 60:40, and 0: 100 respectively. Altering the ratio of MCC to PF may vary the resulting porous carbon pore size distribution. Returning now to FIG. 2A, in various embodiments, MCC and / or PF may be used in additive manufacturing with the addition of only water. In various embodiments, the carbonbased material shell 214 may additionally comprise one or more binding agents and / or dispersing agents, such as, for example, polyvinyl alcohol, polyethyleneimine, polyethylene oxide, sodium polyacrylate, and / or any other suitable binding agent and / or dispersing agent. In various embodiments, the polymeric carbon precursors may be agglomerated in a solvent-free method, such as pressing, with or without binding agents and / or dispersing agents. A suspension including the polymeric carbon precursors, the thermosetting materials, and a dispersion medium may include about 10 wt% to about 20 wt% or from about 20 wt% to about 45 wt% polymeric carbon precursor, from about 5 wt% to about 15 wt% or from about 15 wt% to about 30 wt% thermosetting compound, and from about 40 wt% to about 50 wt% or from about 50 wt% to about 75 wt% dispersion medium. The dispersion medium may comprise water.

[0066] With reference to FIG. 3 and FIG. 10, an exemplary process flow for MCC 1002 and phenol-formaldehyde resin (PF) 1001 carbonization is provided. A particle level depiction of a carbon-based material shell 314 is provided. The carbon-based material shell may undergo dehydration, for example at about 100 °C, to remove water. The PF 1001 may undergo a series of cross-linking reactions during dehydration above its gelation temperature of about 65 °C, releasing water while forming a dense polymer network around the MCC particles 1002.Removal of water may reduce or prevent gasses becoming trapped in the carbon-based shell material during curing. Such trapped gasses would present as undesirable large pores in the carbon which may hinder control over Si infiltration. Accordingly, it may be desirable to select the dehydration phase such that water is effectively able to diffuse out of the carbon-based shell material prior to vitrification.

[0067] The carbon-based material shell 314 may then undergo curing, for example at less than 300 °C, less than 250 °C, less than 200 °C, at 170 °C, or between about 70 °C and 180 °C. During curing, the PF 1001 may undergo vitrification above its glass transition temperature of about 170 °C, and may thereby act as a carbon-rich glue for the MCC 1002 particles. The carbon-based material shell 314 may then undergo pyrolysis, for example at above 200 °C, above 250 °C, above 300 °C, or between about 250 °C and 1000 °C. The molecular mobility' of PF 1001 will decrease as cross-linking proceeds during dehydration and curing, resulting in an increase in the glass transition temperature. With reference to FIG. 14, differential scanning calorimetry was used to determine changes in heat flow as a carbon-based shell material is thermally treated. The onset of gelation may occur at about 63 °C. The initial glass transition temperature of PF after negligible curing may be about 166 °C. The degree of curing of PF may reach a practical maximum indicated by an increase in the glass transition temperature to an asymptotic maximum, as illustrated by FIG. 15, which provides the glass transition temperature as a function of the curing time at 100 °C. The asymptotic maximum glass transition temperature of about 188 °C may indicate a near-complete cure. Low temperature heating of the carbon-based material shell below the glass transition temperature, with an increasing dwell temperature as the degree of curing and glass transition temperature increase, can cure PF in a minimal amount of time while sufficiently outgassing the carbon-based material shell.

[0068] With reference to FIG. 16A, a micro-CT scan of PF cured for 15 hours at 100 °C is provided. A filtered cross section illustrating the pore space and solids space of the embodiment of FIG. 16A is provided in FIG. 16B. With reference to FIG. 17, the decreasing resin porosity as a function of time at 100 °C, with no asymptotic maximum or minimum shown, indicates that outgassing of water and other curing byproducts occurs over a longer timescale than the curing reaction. Accordingly, a ramped cure, such as one provided in Table 4 (below), may be used to accelerate curing and outgassing as compared to heating at a constant temperature. A carbon-based material shell subjected to a 10 hour ramped cure exhibited a 45% reduction in porosity as compared to vitrification after negligible curing, and a 25% reduction in porosity as compared to a carbon-based material shell cured for 50 hours at 100 °C.

[0069] Returning now to FIG. 10, during pyrolysis, the MCC and the PF may decompose to yield char (carbon). The char may be a high surface area char 1026 and may have a number of roughly 1 pm pores to facilitate Si infiltration. Pyrolysis at or about the low- temperature pyrolytic region of about 250 °C may be desirable as char-forming reactions of MCC are preferential to higher temperature tar-forming reactions which may result in the loss of carbon. Image A of FIG. 18 illustrates weight loss as a function of time for MCC pyrolysis performed at a low temperature of 250 °C 1810, 260 °C 1820, and 275 °C 1830 for 60 mg of MCC in a 6.2 mm bed of a crucible with a 7.8 mm outside diameter, compared to a 60 mg sample in a 0.9 mm bed of a crucible with a 20.3 mm outside diameter at 255 °C 1840. Each sample had a particle size of approximately 20 pm. There may be a relatively minor energy barrier to formation of polyfuranic structures from R-ends within the carbon-based shell material and / or the charring matrix, minimizing variation in the prevalence of these reactions in the range of about 250 °C and about 280 °C. The occurrence of acid-catalyzed dehydration of R-ends may be proportional to a concentration of water and a concentration of endogenous acids in the carbon-based shell material and / or charring matrix. The diffusivity of water and endogenous acids does not vary significantly in the range of about 250 °C to about 280 °C. An increase in intermediate char observed at lower temperatures may result from increased formation of branched polysaccharide structures, which may readily fragment upon high temperature treatment and may result in little final char.

[0070] Image B of FIG. 18 illustrates weight loss as a function of time for MCC pyrolysis at an approximately equal temperature of a 100 mg sample of MCC in a 2.2 mm bed of a crucible with an outside diameter of 20.3 mm and a particle size of approximately 20 pm 1850; a 100 mg sample of MCC in a 2.2 mm bed of a crucible with an outside diameter of 20.3 mm and a particle size of approximately 50 pm 1860; a 600 mg sample of MCC in a 5.7 mm bed of a crucible with an outside diameter of 20.3 mm and a particle size of approximately 20 pm 1870; and a 600 mg sample of MCC in a 5.7 mm bed of a crucible with an outside diameter of 20.3 mm and a particle size of approximately 50 pm 1880. FIG. 18 illustrates that char yield is primarily increased by promotion of secondary reactions by inter- and intra- particles masstransfer limitations, such as for example, use of large sample sizes and / or particle sizes. Increasing the sample size and / or particle size may limit the bulk diffusion of water and endogenous acids out of the carbon-based shell material and / or charring matrix, which may increase the yield of polyfuranic structures in the intermediate char. Polyfuranic structures may be more thermostable than branched polysaccharide structures due to the aromatic structure ofpolyfuranic structures. High temperature treatment may result in polyfuranic structures condensing to clusters of benzene rings with 5 -membered incorporations at a greater rate than branched polysaccharides. As a result, the final char yield may increase with limitations on bulk diffusion of water and endogenous acids out of the carbon-based shell material and / or the charring matrix.

[0071] Table 2 provides the respective carbon wt%, oxygen wt%, and hydrogen wt% for a 60 mg sample of MCC and a 600 mg sample of MCC after low temperature treatment (LTT) at less than about 300 °C and after low temperature treatment at less than about 300 °C followed by high temperature treatment (HTT). The oxygen wt% after LTT for the 60 mg and the 600 mg samples, about 30%, is consistent with the elemental composition of a hydrochar product of hydrothermal carbonization of cellulose that is known to proceed through a polyfuranic intermediate and that leads to desirably high final char yields of between about 30 wt% and about 50 wt%.Table 2

[0072] With respect to FIG. 19, Image A illustrates ion current curves in an inert carrier gas at m / z = 40 and general product peaks such as the M+peak of CO at m / z = 28, the M+peak of water at m / z = 18, the [HCO]+fragment of aliphatic aldehydes at m / z = 29, the M+peak of CO2 at m / z = 44, the characteristic peak of furan at m / z = 68. and a primary’ fragment of glucose and levoglucosan at m / z = 73 at a temperature under 300 °C. Image B of FIG. 19 provides a comparison of the aliphatic aldehyde fragment, expected of most light oxygenates produced by decomposition reactions) and the main signal for CO2 at m / z = 44, at a temperature under 300 °C, illustrating that CO2 may be generated in a low -temperature channel separate from CO and other light oxygenates. Image C of FIG. 19 provides the M1signal for formic acid at m / z = 46,the M+signal for acetic acid at m / z = 60, and the M+signal for [COOH]+at m / z = 45 which may be common to acids and other endogenous acids, at a temperature under 300 °C, illustrating that endogenous acids may be present to catalyze the reactions leading to polyfuranic structures. Image D of FIG. 19 provides that while the M+signal of hydroxymethylfurfural (HMF) at m / z = 126 1910 is relatively stable, the M+ / M+-l signals at m / z = 98 1920 and m / z = 97 1930 show that HMF's main thermal decomposition product, furfuryl alcohol, is in the system at a temperature under 300 °C. Further, the M7 M+-l signals at m / z = 96 1940 and m / z = 95 1950 show that furfural is in the system, and the M+peak at m / z = 68 1960 shows that stable furans from all furan-type compounds are in the system. The illustrated results provide that addition reactions leading to relatively high char-yielding polyfuranic regions in the MCC are present. Stated another way, the examples illustrated in FIG. 19 provide that heating the MCC at a temperature under about 300 °C may lead to the formation of thermostable furan-type intermediate structures in the intermediate char. Such furan-type intermediate structures may be resistant to fragmentation upon heating to high temperatures during pyrolysis and may transition to benzene units that form char particles at a desirably high rate.

[0073] With respect to FIG. 20, an exemplary unit of cellobiose is provided. Cellobiose is a repeating unit of cellulose and may comprise two glucose groups linked by a glycosidic bond. The boxed OH indicates a hydroxyl group to be removed by dehydration, and the boxed O indicates a (1-4) glycosidic linkage to be removed by scission. Scission is not expected to occur until about 300 °C or higher. Therefore, inter / intramolecular condensation reactions leading to the elimination of oxygen as water are expected to dominate deoxygenations pathways at least below 300 °C. The molecular weight of cellulose is approximately 162 g / mol glucose, or 324 g / mol cellobiose. If all eight non (1-4) glycosidic oxygens are removed during heat treatment as water, a 44% weight reduction leading to a 56% residual mass is expected. However, the thermochemical equilibrium limit for carbon yield is approximately 27.7%. The primary byproduct of cellulose conversion below 220 °C is water, with increasing CO2 and CO prominence as temperatures are increased to 250 °C.

[0074] With respect to FIG. 21, the specific surface area of the final char of a 600mg sample of MCC is provided, calculated using CO2 physisorption. The specific surface area of the final char may affect the reactivity with Si. A high specific surface area, for example, 500 m2 / g. is desirable for conversion of carbon to silicon carbide. The shape of the isotherm of FIG. 21 demonstrates a highly microporous material. The specific surface area of the final charresulting from full carbonization of the 600mg sample was 592 +- 12 m2 / g according to fitting the adsorption isotherm to a Langmuir model. The high Langmuir surface area may indicate a high concentration of sites on the carbon surface which are available for direct contact with the Si melt. FIG. 22 illustrates a back-scattered electron microscopy image of the char particles. The roughly 10pm diameters of the carbon microfibrils, as compared to the roughly 20pm diameters of the starting MCC powder, indicate a porous medium which may be infiltrated by Si and converted to silicon carbide. FIG. 22 also illustrates that at least a 50% reduction in volume of the Si-based EPCM precursor 201 (FIG. 2A) should be expected during the carbonization process due to particle shrinkage, with further reduction in volume due to the removal of water and compaction of particles during degassing.

[0075] An exemplary carbonization schedule for an Si-based EPCM precursor 201 (FIG. 2A) is provided by Table 3.Table 3

[0076] PF-coated MCC may carbonize to char with a high degree of sp2-bonding character and a short-range order, which may result in a high chemical potential for reaction with molten Si. The dissolution of carbon in molten Si is affected by the carbon’s bonding character, with sp2-hybridized carbon atoms having higher affinity to Si than sp3-hybridized carbon atoms. Atomic disorder, such as bonding imperfections and small crystallites, may alsoincrease the concentration of active sites for dissolution of carbon by molten Si. Cellulose, as well as other polymers, carbonizes to materials with high sp2character due to its hydrogen backbone. Further, the absence of a viscous transition during carbonization of cellulose may result in low-density, amorphous carbon compared with polymers that melt before carbonizing to high-density, glassy carbon. The retention of interparticle spacing during the process may give rise to pm-scale pores in the carbon, which may facilitate Si infiltration. Therefore, carbonization of MCC may yield a char with high sp2-bonding character and atomic disorder that is readily dissolvable by molten Si. Varying the carbonization schedule may vary the carbon porosity and reactivity7, which may vary7the time-dependent change of permeability as pore choking during Si infiltration occurs and may vary Si infiltration depth. For example, when the MCC:PF ratio is held constant, the pm-scale porosity of the resulting carbon is primarily affected by the degree of outgassing during the curing stage. Therefore, a design of the curing stage where gelation time is kept sufficiently long for the curing byproducts, such as water, to evolve and diffuse out of the system, may be desirable.

[0077] With reference to FIG. 23, a Raman spectra of graphite, glassy carbon, and chars derived from MCC under slow pyrolysis and rapid pyrolysis (900 °C) is illustrated. The peak at 1580 cm'1for graphite arises due to the in-plane bond-stretching motion of all pairs of sp2- hybridized carbon atoms. This band is prominent in MCC char due to the hydrogen-bonded chains which hold together as parallel stacks and carbonize to graphene-like sheets with short- range order. The second prominent band at about 1350 cm’1appears in disordered carbons, such as those with point defects or crystallite edges. Increases in this band are indicative of defection or clustenng, and broadening of this band is associated with increased variation in the size and ordering of clusters. The narrower peaks observed for MCC under slow pyrolysis as compared to rapid pyrolysis indicate longer-range order in the char consistent with aligned cellulosic chains carbonizing through inter- and intra- molecular condensation reactions to a char with local orientation. The broader peaks observed for rapid pyrolysis are consistent with a higher concentration of char that has formed from repolymerized or recondensed fragments. Variability of secondary7char is also consistent with the observed peak broadening.

[0078] An exemplary7carbonization schedule for Si-based EPCMs is provided by Table 4.Table 4

[0079] With reference to FIG. 12, an Si-based EPCM precursor 1201 is provided prior to carbonization and reactive melt infiltration (RMI). An Si-based EPCM 1200 is also provided. The Si-based EPCM precursor 1201 may be the same as Si-based EPCM precursor 201 (FIG. 2A) or may be a different embodiment. The Si-based EPCM 1200 may be the same as Si-based EPCM 200 (FIG. 2B) or may be a different embodiment. Micro-CT scans of a cross section of the Si-based EPCM precursor 1201 and the Si-based EPCM are provided, illustrating the change in the envelopment of the Si core during thermal treatment. With respect to FIG. 13, an energy dispersive spectroscopy image of the Si-based EPCM 1200 (FIG. 12) is provided, illustrating a near-uniform infiltration of Si 1340 to approximately a 200 pm depth. The infiltration of Si into the carbon shell may be a function of the carbon shell’s initial porous architecture.

[0080] With reference to FIG. 6B, a decrease in print quality over time may indicate that carbon-based material shells 214 without one or more binding agents and / or dispersing agents may suffer from low long-term stability, as evidenced in the difference in quality between first print 609 and last print 613. With reference to FIG. 7, a carbon-based material shell 717 having 10 wt% polyvinyl alcohol (PVA) in water as a solvent is illustrated compared to a carbon-based material shell 718 having water as a solvent. As evidenced, inclusion of one or more binding agents and / or dispersing agents may increase the quality of the carbon-based material shell 214. Carbon-based material shell 717 exhibited a solids loading of 39.5% while carbon-based material shell 718 exhibited a solids loading of 33.5%, indicating that addition of one or more binding agents and / or dispersing agents may increase solids loading of the carbon-based material shell 214.

[0081] FIG. 8 illustrates the distance distributions of several carbon-based material shells 214 having varying a wt% of PVA. The distance distribution for each was calculated by printing the carbon-based material shell 214 according to a model point cloud, drying the carbon-based material shell 1 214, and 3D scanning the carbon-based material shell 214 toproduce an actual point cloud. The distance between the model and actual positions of each point was calculated and signed based on whether the point was inside (-) or outside (+) the model shape. PVA wt%s of 1.21% PVA 820, 1.92% PVA 821, 3.63% PVA 822, 5.33% PVA 823, and 6.04% PVA 824 are illustrated. The median of each distribution is illustrated by a respective dashed line. FIG. 9 illustrates the median of the distance distribution of each embodiment illustrated in FIG. 8 as a function of the wt% of PVA in the embodiment. As illustrated by FIG. 9, an increase in the wt% of PVA in the carbon-based material shell 214 may be associated with a decrease in the deviation of the distance distribution. Stated another way, print shape defection may decrease with an increase in PVA wt%. The error bars illustrate the range of distance distribution medians for all prints produced from a single batch of ink with a specified PVA wt%. The dashed line indicates the minimum PVA wt% where an entire batch could be printed without clogging or ink separation.

[0082] An exemplars' protocol for direct ink writing of Si-based EPCM precursors 201 with less than 30 vol% deviation is provided by Table 5.Table 5

[0083] Returning now to FIG. 2A, in various embodiments, where an aqueous medium is used in the Si-based EPCM precursor 201, the Si-based EPCM precursor 201 may be dried in a humidity chamber. In this manner, water may be removed from the Si-based EPCMprecursor 201 slowly, which may prevent or reduce cracking of the Si-based EPCM precursor 201. For example, drying the Si-based EPCM precursor 201 in humidity may decrease the rate of dehydration, which may increase drying uniformity and / or quality. With reference to FIG. 6A, an Si-based EPCM precursor 611 dried in air is illustrated compared to an Si-based EPCM precursor 612 dried in a humid environment (75% relative humidity), such as a humidity chamber. The Si-based EPCM precursor 201 may be dried in an environment having about 60% to about 80% relative humidity, about 80% to about 99% relative humidity, and / or any other suitable humidity.

[0084] FIG. 2B illustrates an exemplary cross section of a Si-based EPCM 200 having a silicon core 205, a silicon carbide composite shell 210, and a carbon shell 215. The Si-based EPCM 200 may undergo reactive melt infiltration (RMI) to cause the silicon core 205 to melt and for the molten Si to move into the pores of the carbon shell 215, thereby converting at least a portion of the carbon shell 215 to a silicon carbide shell 210. Si infiltration depth into the carbon shell 215 may be a function of the carbon shell 215 pore size distribution. In this manner, manipulation of the pore size distribution, such as by altering the ratio of MCC to PF in the carbon-based material shell 214 (FIG. 2A), may be used to achieve a specific Si infiltration depth. RMI may be performed at temperatures above the melting point of Si, 1414°C, and at vacuum or low-pressure conditions. RMI may cause a time-dependent reduction in the pore size of the carbon shell 215. In this manner, the remaining Si melt may be encapsulated in the core, with the melt path choked off by the silicon carbide shell 210. The density of the silicon carbide shell 210 may be greater than 90% of the theoretical density of silicon carbide. The porosity of the Si-based EPCM 200 may be between about 0% and about 5% or between about 5% and about 15% or between about 0% and about 15%.

[0085] FIG. 3 illustrates an exemplary process flow for converting an Si-based EPCM precursor 301 into an Si-based EPCM 300. An Si-based EPCM precursor 301 comprising a colloidal silicon core 304 and a carbon-based material shell 314 may undergo carbonization311 to form a heat-treated Si-based EPCM precursor 302 comprising a silicon core 305 and a porous carbon shell 316. The heat-treated Si-based EPCM precursor 302 may undergo RMI312 to form an Si-based EPCM 300 comprising a silicon core 305 and a silicon carbide shell 310. FIG. 4 illustrates the process flow of FIG. 3 using an Si-based EPCM precursor 301 formed by additive manufacturing, for example direct ink writing 403. The specific molar volumes (m3 / kmol) of Si, C. and SiC within the Si-based EPCM 300 are provided.

[0086] A thermocline is an energy storage system that uses a tank or a body, a heat transfer fluid (HTF), and thermal energy storage media (TSM). It may be desirable for a TSM to absorb, store, and release heat efficiently. For example, materials with high thermal conductivity may increase the rate of charging and discharging the TSM. Materials with high thermal and chemical stability may increase the lifetime of the TSM. A high density may allow utilization of a smaller overall system, which may be desirable. For sensible heat, the specific heat capacity may desirably be sufficiently high such that the TSM may store a large amount of energy. For latent heat and / or phase change materials (PCMs), the specific latent heat may desirably be large. For thermochemical heat storage, the heat of reaction may desirably be large. PCMs may desirably have a small change in volume between phases, which may allow for a smaller system. Materials may desirably be low cost, non-toxic. and non-corrosive.

[0087] The use of latent heat may allow for a greater amount of energy stored within a phase change as compared to sensible heat, for example, latent heat may be around 50 to 100 times greater than sensible heat, resulting in a smaller volume of TSM needed. For a sensible and latent heat system, the temperature drop of an HTF outflow over a discharge time may be less than a sensible heat only system due to the phase change at a single temperature, while a sensible material will continue to decrease in temperature during discharging. PCMs typically have low thermal conductivities, however, the impregnation of porous materials and / or dispersion of high conductivity particles within a porous material may improve the thermal conductivity of PCMs. Stated another way, the Si-based EPCM described above may provide a greater thermal conductivity than a typical PCM, and as such, may greatly improve thermocline operation. Si has a very high heat of fusion, 1800 kJ / kg, resulting in Si being able to store a very large amount of energy.

[0088] In various embodiments, the HTF may be a gas with a suitably high rate of heat transfer. The HTF may be a radiation absorbing gas. In this manner, the HTF may transfer a greater energy to a thermocline as compared to a non-radiation absorbing gas, such as an inert gas. For example, the HTF may be CO2 and / or steam. In various embodiments, the HTF may be N2.

[0089] With respect to FIG. 24. an exemplary embodiment of a thermocline system 2800 is illustrated. The system 2800 may include a thermocline 2850, a heat source 2855, and a heat sink 2860. The system 2800 may further include a pump 2865 and valves VI, V2, V3, V4. During charging of the thermocline 2850, an HTF may be delivered to the heat source 2855 and may flow to the thermocline 2850. Heat may be transferred from the HTF to a TSMcontained with the thermocline 2850, causing the temperature gradient to shift down, or, stated another way, the hotter temperature may be present within a greater region of the thermocline 2850. Valves V2 and VI may be open to recycle the HTF through pump 2865 to the heat source 2855 for further charging of the thermocline 2850. During discharging of the thermocline 2850, valves VI and V2 may be closed and valves V3 and V4 may be opened. The HTF may be pumped up the thermocline 2850 causing the HTF to increase in temperature, causing the temperature gradient to shift up, or, stated another way, the colder temperature is present within a greater region of the thermocline 2850. The HTF may flow to the heat sink 2860 which may absorb heat, cooling the HTF. The HTF may be pumped by pump 2865 back through the thermocline 2850 for further discharging of the thermocline 2850. In various embodiments, the heat source 2855 may be an electric furnace, a combustion furnace, a solar concentration plant, and / or any other suitable system or apparatus for generating heat.

[0090] With respect to FIG. 25. an exemplary embodiment of a thermocline system 2900 using CO2 and N2 is illustrated. During charging of the thermocline, CO2 may be flowed into the system 2900, through the heat source 2855, and to thermocline 2850. CO2 may further be pumped back through pump 2865 to further and / or continuously charge the thermocline 2850. To discharge the thermocline 2850, the CCh may be purged, and N2 may be flowed into the system. The N2may flow through the thermocline 2850 and to heat sink 2860. The N2 may further be pumped back through pump 2865 to further and / or continuously discharge the thermocline 2850. To charge the thermocline 2850, the IShmay be purged, and the process maybe repeated.

[0091] FIG. 26A provides an exemplary embodiment of a thermocline system 3000 mounted on a linear rail system 3002. The thermocline 2850, the heat source 2855, and the heat sink 2860 may be mounted on linear rail 3070. The heat sink 2860 may be a thermo-chemical reactor. The heat source 2855 may be an electric furnace. Each of the thermocline 2850, the heat source 2855, and the heat sink 2860 may be individually mounted to the linear rail 3070, such that each module may thermally expand both horizontally and vertically as they heat and cool. FIG. 26B illustrates a side view of the system 3000 illustrated in FIG. 26A.

[0092] FIG. 27 provides an exemplary- internal schematic view of the system 3000 of FIG. 26A. The system 3000 may include a TSM 3171 and a cool down zone 3172 within the thermocline 2850 (FIG. 26A), a redox material 3174 within the heat sink 2860 (FIG. 26A), a thermocouple 3173 and an O-ring 3178 seal within the heat source 2855 (FIG. 26A), a purge gas outlet 3175, a pin 3176, a steam hose 3177, and / or valves 3179. Each of the thermocline2850, the heat source 2855, and the heat sink 2860 may be constructed using dual walls. An inner wall may contain the HTF. reactant gasses, and TSM, while an outer wall may provide a leak-tight pressure enclosure to the atmosphere configured to prevent a leak of any of the HTF, the reactant gasses, and the TSM.

[0093] FIG. 28 provides a close-up view of the top of the thermocline 2850 (FIG. 26A) of the exemplary7system of FIG. 27. The inner wall 3204 of the thermocline may be a closed- one-end ceramic tube 3280. The outer wall 3206 may be a stainless steel shell 3281. An upper portion of the ceramic tube 3280 may have a bore, which may be configured to accept a cross tube 3282. The cross tube 3282 may engage a suspension tube 3283. The suspension tube may be pinned to the linear rail system 3070 by pin 3176. The cross tube 3282 may be a tight fit to the bore in the inner tube, such that it is leak resistant. The cross tube 3282 may have a central hole, configured to allow an HTF to flow into and out of the thermocline 2850 (FIG. 26 A). The outer wall for the horizontal tubes connecting the thermocline 2850, the heat source 2855, and the heat sink 2860 may be a steam hose 3177.

[0094] FIG. 29 provides a schematic view of the junction 3308 between the cross tube 3282 and the horizontal tube 3310. The horizontal tube 3310 may be ceramic and may have a spherical ball detail 3312 on an end of the horizontal tube 3310. The ball detail 3312 may be configured to interface with the cross tube 3282 and may accommodate both horizontal and angular misalignment as well as differential thermal growth while maintaining a leak resistant coupling between the horizontal tube 3310 and the cross tube 3282. A nominal amount of leakage is expected between the cross tube 3282 and the horizontal tube 3310, through the ball detail 3312. To accommodate nominal leakage, the insulation chamber 3207 (FIG. 28) between the inner wall 3204 and outer wall 3206 may be purged with inert gas. The inert gas may be maintained slightly above or below the process pressure, depending on the chemistry' of the process, oxidation, reduction, and heat transport gasses.

[0095] FIG. 30 provides a close-up view of the top of the heat source 2855 (FIG. 26A) of the exemplary' system of FIG. 27. A cross tube 3482 and horizontal tube 3410 junction 3408 may be configured similarly to the junction 3308 (FIG. 29) for the thermocline 2850 (FIG. 26A). A thermocouple 3173 may be used to monitor a gas temperature within or exiting the heat source 2855. In this manner, the heat source 2855 may be maintained within operating limits. An O-ring 3178 may maintain inert gas containment between the cross tube 3482 and the heat source tube 3480.

[0096] The use of a thermocline 2850 may be desirable over a typical heat storage system using a dual tank, molten salt HTF configuration. A thermocline 2850 may use a single tank, rather than two, may use a lower cost filler material, and a lower cost HTF, such as air, than a molten salt. Thermal ratcheting may lead to degradation of the thermocline 2850 over time due to deformation of the tank material under cyclic thermal loading, temperature gradient decrease, heat losses, thermal conduction losses, and natural convection. Thermal degradation may be reduced with the use of a PCM with a melting temperature close to the discharging temperature of the HTF. Further, a smaller particle size of the TSM may be lead to better heat transfer and an increased thermal storage efficiency. For example, the user of a higher thermal conductivity material, such as a metal, may reduce thermal degradation. By encapsulating the high thermal conductivity material, concerns related to corrosion and toxicity may be reduced or eliminated. For example, the Si-based EPCMs described herein may provide an encapsulated PCM with a high thermal conductivity, a high latent heat, a small volume change upon phase change, are low cost, and are non-toxic and non-corrosive due to the encapsulation. Additionally, the Si-based EPCMs may be sufficiently small such that greater heat transfer and increased thermal storage efficiency are achieved as compared to conventional PCMs.

[0097] FIG. 31 provides an exemplary schematic view of a thermocline 3600. depicted in more detail in FIGs. 37-39. The exemplary thermocline 3600 uses an existing three-zone furnace 3614 capable of operation at 1600 °C.

[0098] FIG. 32 provides an exemplary schematic view of a middle portion 3700 of the thermocline 3600 of FIG. 31. The middle portion 3700 may include a redox material 3789, a TSM 3790, an inert material 3791, a thermocline transition zone 3792, one or more thermocouples 3793. and one or more electric heaters 3794. The one or more electric heaters 3794 may be positioned proximate to the redox material 3789, the TSM 3790, and / or the inert material 3791. A ceramic disk may separate each of redox material 3789, TSM 3790 and / or inert material 3791. The inert material 3791 may gather heat energy from the one or more electric heaters 3794 and may pass the heat energy’ to the TSM 3790. The TSM 3790 may then discharge by passing heat energy' to the redox material 3789. A thermocouple 3793 may move about within the electric furnace as controlled by a thermocouple positioner 3795 (FIG. 33), which may be an actuator. In this manner, the thermocouple 3793 may measure a temperature proximate to any of redox material 3789, TSM 3790, and / or inert material 3791.

[0099] FIG. 33 provides an exemplary schematic view of a top portion 3800 of the thermocline 3600 of FIG. 31. The top portion 3800 may include a thermocouple positioner3795, which may be configured to control a position of a thermocouple 3793 within the thermocline. The top portion 3800 may include part of one or more thermocouples 3793. The top portion 3800 may include a thermocouple 3796, configured to measure a temperature of the redox material 3789 (FIG. 32). The top portion 3800 may include a compression spring 3797, configured to hold a ceramic gas dispersion disk in contact with the redox material 3789. The compression spring may be. for example, a helical coil compression spring.

[0100] FIG. 34 provides an exemplary schematic view of a bottom portion 3900 of the thermocline 3600 of FIG. 31. The bottom portion 3900 may have a bottom end cap 3798. The bottom end cap 3798 may be free to float up or down for thermal expansion. The thermocline tube may be sealed by the bottom end cap 3798. The bottom end cap 3798 may be configured to accommodate the one or more thermocouples 3793.

[0101] FIG. 35 illustrates a flow chart for a method 4000, according to an embodiment. Method 4000 is merely exemplary and is not limited to the embodiments presented herein. Method 4000 can be employed in many different embodiments or examples not specifically depicted or described herein. In some embodiments, the activities of method 4000 can be performed in the order presented. In other embodiments, the activities of method 4000 can be performed in any suitable order. In still other embodiments, one or more of the activities of method 4000 can be combined or skipped.

[0102] In many embodiments, method 4000 can comprise a step 4001 of forming a silicon-containing material core. The silicon-containing material core may be formed using additive manufacturing in combination with step 4002. Step 4001 may comprise forming a suspension comprising silicon, doped silicon, or silicon alloy solids, a binding agent, and / or a dispersion medium - e.g., as described above. The suspension may comprise about 5-30 wt%, about 10-20 wt%, or about 20-30 wt% binding agent.

[0103] In many embodiments, method 4000 can comprise a step 4002 of forming a carbon-based shell. The carbon-based shell may be formed using additive manufacturing in combination with step 4001. The carbon-based shell may encapsulate the silicon-containing material core. Encapsulation of the silicon-containing material core by the carbon-based shell may form a printed medium. Step 4002 may comprise forming a suspension comprising a carbon material precursor, a thermosetting material, and / or a dispersion medium - e.g., as described above. The thermosetting material may comprise a phenol-formaldehyde resin or a lignin. The dispersion medium may comprise water. The suspension may comprise a bindingagent. The binding agent may comprise one or more of polyvinyl alcohol, polyethyleneimine, sodium polyacrylate, or polyethylene oxide. An amount of the binding agent in the dispersion medium may be from about 1 wt% to about 5 wt%, is from about 5 wt% to about 15 wt%, is from about 1 wt% to about 30 wt%, or is from about 5 \\1% to about 30 wt%. The suspension may comprise from about 10 wt% to about 20 wt% or from about 20 wt% to about 45 wt% carbon material precursor, from about 5 wt% to about 15 wt% or from about 15 wt% to about 30 wt% thermosetting compound, and from about 40 wt% to about 50 wt% or from about 50 wt% to about 75 wt% dispersion medium.

[0104] In various embodiments, the additive manufacturing may comprise direct ink writing. For example, the silicon-containing material core and / or the carbon-based shell may be deposited layer-by-layer as a solid suspension. In this manner, the silicon-containing material core may be encapsulated by the carbon-based shell.

[0105] In various embodiments, the additive manufacturing may comprise dynamic mixing. For example, the silicon-containing material core, for example silicon in spherical or pellet form, may be added to a dynamic mixer. A carbon material precursor, such as MCC, and / or a thermosetting material may be added to the dynamic mixer. The dynamic mixer may be used to agglomerate the carbon material precursor and / or the thermosetting material around the silicon-containing material core. In this manner, the silicon-containing material core may be encapsulated by the carbon-based shell. In various embodiments, the additive manufacturing can comprise any method or combinations of methods of additive manufacturing described herein.

[0106] In many embodiments, method 4000 can comprise a step 4003 of drying the printed medium. Drying the printed medium may form a preform. The dry ing may comprise providing the preform in a humidity -controlled environment. The humidity in the humidity - controlled environment may be between about 60% and about 80% or between about 80% and about 99% relative humidity. Further exemplar}’ examples of drying are described above.

[0107] In many embodiments, method 4000 can comprise a step 4004 of heating the preform. Heating the preform may convert at least a portion of the carbon-based shell to silicon carbide. The heating may comprise a curing stage, a pyrolytic stage, and a vacuum infiltration stage. A temperature during the curing stage may be less than 300 °C. less than 250 °C, less than 200 °C or may be between about 70 °C and about 180 °C. A temperature during the pyrolytic stage may be greater than 200 °C, is greater than 250 °C, is greater than 300 °C, ormay be between about 250 °C and about 1000 °C. A temperature during the vacuum infiltration stage may be greater than 1000 °C or may be between 1300 °C and 1900 °C. In this manner, the silicon within the silicon containing core may be melted and may infiltrate the pores of the carbon-based shell.

[0108] For simplicity and clarity of illustration, the drawing figures illustrate the general manner of construction, and descriptions and details of some features and techniques may be omitted to avoid unnecessarily obscuring the present disclosure. Additionally, elements in the drawing figures are not necessarily drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help improve understanding of embodiments of the present disclosure. The same reference numerals in different figures denote the same elements.

[0109] The terms “first,” “second,” “third,” “fourth,” and the like in the description and in the claims, if any, are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It is to be understood that the terms so used are interchangeable under appropriate circumstances such that the embodiments described herein are, for example, capable of operation in sequences other than those illustrated or otherwise described herein. Furthermore, the terms “include,” and “have,” and any variations thereof, are intended to cover anon-exclusive inclusion, such that a process, method, system, article, device, or apparatus that comprises a list of elements is not necessarily limited to those elements, but may include other elements not expressly listed or inherent to such process, method, system, article, device, or apparatus. In some cases, the terms including, having, or comprising encompass consisting essentially of and consisting of.

[0110] The terms “left,” “right,” “front,” “back,” “top,” “bottom,” “over,” “under,” and the like in the description and in the claims, if any, are used for descriptive purposes and not necessarily for describing permanent relative positions. It is to be understood that the terms so used are interchangeable under appropriate circumstances such that the embodiments of the apparatus, methods, and / or articles of manufacture described herein are, for example, capable of operation in other orientations than those illustrated or otherwise described herein.[OHl] The terms “couple,” “coupled,” “couples,” “coupling,” and the like should be broadly understood and refer to connecting two or more elements mechanically and / or otherwise. Two or more electrical elements may be electrically coupled together, but not be mechanically or otherwise coupled together. Coupling may be for any length of time, e.g.,permanent or semi-permanent or only for an instant. “Electrical coupling” and the like should be broadly understood and include electrical coupling of all types. The absence of the word “removably,” “removable,” and the like near the word “coupled,” and the like does not mean that the coupling, etc. in question is or is not removable.

[0112] As defined herein, two or more elements are “integral” if they are comprised of the same piece of material. As defined herein, two or more elements are “non-integral” if each is comprised of a different piece of material.

[0113] As defined herein, “approximately” can, in some embodiments, mean within plus or minus ten percent of the stated value. In other embodiments, “approximately” can mean within plus or minus five percent of the stated value. In further embodiments, “approximately” can mean within plus or minus three percent of the stated value. In yet other embodiments, “approximately” can mean within plus or minus one percent of the stated value.

[0114] Although systems and methods for thermal energy storage media and system and methods of forming and using same have been described with reference to specific embodiments, it will be understood by those skilled in the art that various changes may be made without departing from the spirit or scope of the disclosure. Accordingly, the disclosure of embodiments is intended to be illustrative of the scope of the disclosure and is not intended to be limiting. It is intended that the scope of the disclosure shall be limited only to the extent required by the appended claims. For example, to one of ordinary' skill in the art, it will be readily apparent that any element of FIGs. 1-35 may be modified, and that the foregoing discussion of certain of these embodiments does not necessarily represent a complete description of all possible embodiments. For example, one or more of the procedures, processes, or activities of FIG. 35 may include different procedures, processes, and / or activities and be performed by many different modules, in many different orders.

[0115] Benefits, other advantages, and solutions to problems have been described with regard to specific embodiments. The benefits, advantages, solutions to problems, and any element or elements that may cause any benefit, advantage, or solution to occur or become more pronounced, however, are not to be construed as critical, required, or essential features or elements of any or all of the claims, unless such benefits, advantages, solutions, or elements are stated in such claim.

Claims

CLAIMSWhat is claimed is:

1. A method of forming thermal energy storage media, the method comprising the steps of: using additive manufacturing: forming a sili con-containing material core; and forming a carbon-based shell that encapsulates the silicon-containing material core to form a printed medium; drying the printed medium to form a preform; and heating the preform to convert at least a portion of the carbon-based shell to silicon carbide.

2. The method of claim 1, wherein the step of forming the carbon-based shell comprises: forming a suspension comprising a carbon material precursor, a thermosetting compound, and a dispersion medium.

3. The method of claim 2, wherein the thermosetting compound comprises a phenolformaldehyde resin or a lignin.

4. The method of claim 3, wherein the dispersion medium comprises water.

5. The method of claim 2, wherein the suspension comprises a binding agent.

6. The method of claim 5, wherein the binding agent comprises one or more of polyvinyl alcohol, polyethyleneimine, sodium polyacrylate, or polyethylene oxide.

7. The method of claim 6, wherein an amount of binding agent in the dispersion medium is from about 1 wt% to about 5 wt%, is from about 5 wt% to about 15 wt%, is from about 1 wt% to about 30 wt%, or is from about 5 wt% to about 30 wt%.

8. The method of claim 2, wherein the suspension comprises from about 10 wt% to about 20 wt% or from about 20 wt% to about 45 wt% of the carbon material precursor, from about 5 wt% to about 15 wt% or from about 15 wt% to about 30 wt% of the thermosettingcompound, and from about 40 wt% to about 50 wt% or from about 50 wt% to about 75 wt% of the dispersion medium.

9. The method of claim 1, wherein the step of drying comprises providing the preform in a humidity-controlled environment.

10. The method of claim 9, wherein a humidity is between about 60% and about 80% or about 80% and about 99% relative humidity.

11. The method of claim 1 , wherein the step of heating comprises a curing stage, a pyrolytic stage, and a vacuum infiltration stage.

12. The method of claim 11, wherein a temperature during the curing stage is less than 300 °C, less than 250 °C, less than 200 °C or is between about 70 °C and about 180 °C.

13. The method of claim 11. wherein a temperature during the pyrolytic stage is greater than 200 °C, is greater than 250 °C, is greater than 300 °C, or is betw een about 250 °C and about 1000 °C.

14. The method of claim 11. wherein a temperature during the vacuum infiltration stage is greater than 1000 °C or is between 1300 °C and 1900 °C.

15. The method of claim 1, wherein the step of forming the silicon-containing material core comprises forming a suspension comprising silicon-or doped silicon or silicon alloy solids, a binding agent, and a dispersion medium.

16. The method of claim 15, wherein the suspension comprises about 5-30 wt%, about 10-20 wt%, or about 20-30 wt% of the binding agent.

17. A heat storage device comprising the thermal energy storage media formed according to any of claims 1-16.

18. A thermal energy storage media comprising: a silicon-containing material core; anda shell comprising silicon carbide, wherein a density of the shell is greater than 90% of a theoretical density of the silicon carbide.

19. A system comprising: an inner chamber; an outer chamber encapsulating the inner chamber; thermal energy storage media within the inner chamber; a heat transfer gas inlet tube coupled to a top region of the inner chamber; and a valve module coupled to a lower region of the inner chamber.

20. The system of claim 19, wherein the inner chamber comprises a closed-end tube.

21. The system of claim 19, wherein the inner chamber comprises a ceramic wall.

22. The system of claim 19, wherein the outer chamber comprises a metal wall.

23. The system of claim 19, further comprising insulating material between the inner chamber and the outer chamber.

24. The system of claim 19, further comprising: a cross tube disposed within a bore within a wall of the inner chamber; a suspension tube engaged with the cross tube; and a cross pin comprising a hollow center in fluid communication with the cross tube and the heat transfer gas inlet tube, wherein the cross tube intersects the wall of the inner chamber and is fluidly coupled to an interior portion of the inner chamber.

25. The system of claim 19, wherein the thermal energy storage media is formed according to any of claims 1-15.

26. The system of claim 19, wherein the system is configured to operate within a range of about 1000 °C to about 1500 °C.

Images