Electroactive materials having hard carbon-silicon dioxide nanocomposites from bioderived byproducts for electrochemical cells, methods for making and use thereof

Abstract

A method of making an electroactive nanocomposite material from a bioderived product comprising ash and char. The method includes removing silicon dioxide from a bioderived byproduct to form a silica-depleted bioderived byproduct having silicon dioxide at ≥ about 40% to ≤ about 65% by weight and hard carbon at ≥ about 35% to ≤ about 60% by weight. The method includes treating a surface of the silica-depleted bioderived byproduct in an inert environment to remove surface oxygenates to form an electroactive nanocomposite material comprising silicon dioxide and hard carbon. The method is free of any subsequent treatment at temperatures of greater than or equal to about 1,000°C after the treating. An electrode for an electrochemical cell includes an electroactive nanocomposite material comprising silicon dioxide and hard carbon formed by such methods derived from a silica-depleted bioderived byproduct.

Description

ELECTROACTIVE MATERIALS HAVING HARD CARBON-SILICON DIOXIDE NANOCOMPOSITES FROM BIODERIVED BYPRODUCTS FOR ELECTROCHEMICAL CELLS, METHODS FOR MAKING AND USE THEREOF CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional Application No. 63 / 651,465, filed May 24, 2024. The entire disclosure of the above application is incorporated herein by reference. GOVERNMENT SUPPORT

[0002] This invention was made with government support under 2103602 awarded by the National Science Foundation. The government has certain rights in the invention. FIELD

[0003] The present disclosure relates to methods of making electroactive nanocomposite materials comprising hard carbon and silicon dioxide from a silica-depleted bioderived byproduct comprising char and ash, batteries incorporating such electroactive materials, and methods for making and using the same. BACKGROUND

[0004] This section provides background information related to the present disclosure which is not necessarily prior art.

[0005] Electrochemical cells, like batteries, are used in a wide variety of applications, including transportation and vehicles, stationary (grid) energy storage for intermittent energy generation (e.g., wind / solar farms), unmanned aerial vehicles (UAVs), satellites, consumer goods, electronics, robotics, prosthetic devices, and the like. A continuing objective is to increase performance capabilities and efficiencies of electrochemical cells, like lithium-ion and sodium- ion batteries. Many different materials may be used to create electrodes for a lithium-ion or sodium-ion battery. For example, positive electrode materials for lithium-based batteries typically comprise an electroactive material that can be intercalated or reacted with lithium ions, such as lithium-transition metal oxides or mixed oxides, for example including LiMn2O4, LiCoO2, LiNiO2, LiMn1.5Ni0.5O4, LiNi(1-x-y)CoxMyO2(where 0<x<1, y<1, and M may be Al, Mn, or the like), or one or more phosphate compounds, for example including lithium iron phosphate or mixed lithium manganese-iron phosphate. The negative electrode typically includes a lithium (or sodium) insertion material or an alloy host material. One common electroactive material forforming a negative electrode / anode is graphite that serves as a lithium-graphite (LiC6) intercalation compound. Graphite is the commonly used negative electrode material because of its relatively high specific capacity (approximately 350 mAh / g).

[0006] However, finding new electroactive materials with higher specific capacities (mAh / g), higher energy capacities or densities or energy the battery can store with respect to its mass (watt-hours per kilogram (Wh / kg)), and / or higher power capacity / density or an amount of power that can be generated by the battery with respect to its mass (watts per kilogram (W / kg)) would be desirable. Thus, it would be desirable to develop new negative electroactive material for a negative electrode in an electrochemical cell that cycles lithium-ions or sodium-ions and exhibits higher specific capacity and / or higher energy capacity than currently available negative electroactive materials, like graphite. Further, it would be desirable if such active materials were environmentally friendly or circular products, for example, derived from biosources or from bioderived waste byproducts. SUMMARY

[0007] This section provides a general summary of the disclosure and is not a comprehensive disclosure of its full scope or all of its features.

[0008] In certain aspects the present disclosure relates to an electrode for an electrochemical cell. The electrode may include an electroactive layer comprising an electroactive nanocomposite material comprising silicon dioxide and hard carbon derived from a silica-depleted bioderived byproduct comprising char and ash. The electrode may also include a current collector on which the electroactive layer is disposed or with which the electroactive layer is in electrical contact.

[0009] In one aspect, the electroactive nanocomposite material is free of pyrolyzed carbon or carbothermal reaction products.

[0010] In one aspect, the electroactive nanocomposite material is free of silicon, silicon carbide, silicon nitride, silicon oxynitride, and combinations thereof.

[0011] In one aspect, the silica-depleted bioderived byproduct comprises a silica depleted rice hull ash product (SDRHA) comprising silicon dioxide at less than or equal to about 65% by weight and hard carbon at greater than or equal to about 35 % by weight.

[0012] In one aspect, the silica-depleted bioderived byproduct comprises a silica depleted rice hull ash product (SDRHA) that comprises silicon dioxide at greater than or equal to about 20% by weight to less than or equal to about 65% by weight and hard carbon at greater than or equal to about 35 % by weight to less than or equal to about 80% by weight.

[0013] In one further aspect, the silica-depleted bioderived byproduct comprises a silica depleted rice hull ash product (SDRHA) that comprises silicon dioxide at greater than or equal to about 40% by weight to less than or equal to about 65% by weight and hard carbon at greater than or equal to about 35 % by weight to less than or equal to about 60% by weight

[0014] In one aspect, the electroactive nanocomposite material has a treated surface to control surface oxygenates and minimize solid electrolyte interface (SEI) formation.

[0015] In one aspect, the electroactive nanocomposite material has an average surface area of greater than or equal to about 70 m2 / g (N2).

[0016] In one aspect, the electroactive nanocomposite material exhibits a specific capacity to the hard carbon mass of greater than or equal to about 400 mAh / gHC.

[0017] In one aspect, the electroactive nanocomposite material exhibits a specific capacity to a hard carbon mass of greater than or equal to about 700 mAh / gHC.

[0018] In one aspect, the electroactive nanocomposite material comprises at least one residual ion selected from a group consisting of: potassium ions, sodium ions, lithium ions, and combinations thereof.

[0019] In one aspect, the electroactive nanocomposite material comprises at least one residual ion comprising potassium ions, sodium ions, or both potassium and sodium ions.

[0020] In one aspect, the electroactive nanocomposite material comprises at least one residual ion comprising potassium ions.

[0021] In one aspect, the electroactive nanocomposite material defines a plurality of particles distributed into a polymeric matrix comprising a polymeric binder.

[0022] In one further aspect, the electrode further comprising a plurality of electrically conductive particles distributed in the polymeric binder.

[0023] In one aspect, the current collector comprises a metal selected from the group consisting of: copper, nickel, alloys, and combinations thereof.

[0024] In one aspect, the electroactive material layer further comprises a liquid electrolyte, a solid-state electrolyte, or combinations thereof.

[0025] In one aspect, the electroactive nanocomposite material comprises a matrix of hard carbon having surface regions at least partially coated with silicon dioxide.

[0026] In one aspect, the electroactive nanocomposite material comprises pores including carbon encapsulating silicon dioxide.

[0027] In further aspects, the present disclosure relates to an electrochemical cell comprising a first electrode comprising an electroactive layer comprising an electroactive nanocomposite material comprising silicon dioxide and hard carbon derived from a silica-depletedbioderived byproduct comprising char and ash and a current collector, along with a second electrode, and an electrolyte that cycles lithium ions or sodium ions.

[0028] In certain aspects, the first electrode is a negative electrode and the second electrode is a positive electrode.

[0029] In certain aspects, the electrochemical cell may comprise a separator disposed between the first electrode and the second electrode.

[0030] In one aspect, the electrochemical cell comprises two or more ions selected from a group consisting of: lithium ions, sodium ions, potassium ions, calcium ions, magnesium ions, and combinations thereof.

[0031] In one aspect, the electrochemical cell comprises two or more ions selected from a group consisting of: lithium ions, sodium ions, potassium ions, and combinations thereof.

[0032] In certain additional aspects, the present disclosure relates to a method of making an electroactive nanocomposite material from a bioderived byproduct. The method may comprise removing silicon dioxide from a bioderived byproduct comprising char and ash to form a silica- depleted bioderived byproduct having silicon dioxide at greater than or equal to about 20% by weight to less than or equal to about 65% by weight and hard carbon at greater than or equal to about 35% by weight to less than or equal to about 80% by weight. The method may further comprise treating a surface of the silica-depleted bioderived byproduct in an inert environment to selectively remove surface oxygenates to form an electroactive nanocomposite material comprising silicon dioxide and hard carbon. The method is free of any subsequent treatment at temperatures of greater than or equal to about 1,000°C after the treating.

[0033] In one aspect, the method further comprises lithiating the electroactive nanocomposite material with lithium ions or sodiating the electroactive material with sodium ions.

[0034] In one aspect, the bioderived byproduct is a rice hull ash and the silica-depleted bioderived byproduct is a silica-depleted rice hull ash.

[0035] In one aspect, the silica-depleted bioderived byproduct comprises a silica depleted rice hull ash product (SDRHA) that comprises silicon dioxide at greater than or equal to about 40% by weight to less than or equal to about 65% by weight and hard carbon at greater than or equal to about 35 % by weight to less than or equal to about 60% by weight.

[0036] In one aspect, the removing silicon dioxide from a bioderived byproduct occurs by reaction in the presence of a stoichiometric base to form the silica-depleted bioderived byproduct.

[0037] In one aspect, the stoichiometric base comprises tetramethylammonium hydroxide (TMAOH).

[0038] In one aspect, the removing silicon dioxide from a bioderived byproduct occurs by reaction with a hindered diol in the presence of a catalytic base to form the silica-depleted bioderived byproduct.

[0039] In one aspect, the hindered diol is selected from the group consisting of: 2-methyl- 2,4-pentanediol, 2,2,4-trimethyl-1,3-pentanediol, and combinations thereof.

[0040] In one aspect, the catalytic base is selected from the group consisting of: sodium hydroxide (NaOH), lithium hydroxide (LiOH), calcium hydroxide Ca(OH)2, potassium hydroxide (KOH), cesium hydroxide (CsOH), rubidium hydroxide (RbOH), and combinations thereof.

[0041] In one aspect, the hindered diol comprises 2-methyl-2,4-pentanediol and the catalytic base is selected from the group consisting of: sodium hydroxide (NaOH), potassium hydroxide (KOH), lithium hydroxide (LiOH), and combinations thereof.

[0042] In one aspect, the treating of the surface further comprises heating the silica-depleted bioderived byproduct to a temperature of greater than or equal to about 200°C to less than about 800°C.

[0043] In one aspect, the method further comprises after the removing silicon dioxide and prior to treating the surface of the silica-depleted bioderived byproduct, treating the silica-depleted bioderived product to have a target pH of greater than 7.

[0044] In one further aspect, the target pH is greater than or equal to about 9.

[0045] In one further aspect, the treating is a washing step.

[0046] In one aspect, the method further comprises after removing silicon dioxide, washing the silica-depleted bioderived byproduct with boiling water.

[0047] In one aspect, the electroactive nanocomposite material comprises a matrix of hard carbon having surface regions at least partially coated with silicon dioxide.

[0048] In one aspect, the electroactive nanocomposite material comprises pores including carbon encapsulating silicon dioxide.

[0049] In one aspect, the method further comprises prior to the removing silicon dioxide, milling the rice hull ash (RHA) byproduct with an acidic solution to yield a purified rice hull ash (RHA) byproduct.

[0050] In certain additional aspects, the present disclosure relates to a method of making an electroactive nanocomposite material from a bioderived byproduct. The method may comprise removing silicon dioxide from a bioderived byproduct comprising char and ash to form a silica- depleted bioderived byproduct having silicon dioxide at greater than or equal to about 20% by weight to less than or equal to about 65% by weight and hard carbon at greater than or equal to about 35% by weight to less than or equal to about 80% by weight. The method may furthercomprise adjusting a pH of the silica-depleted bioderived byproduct after removing silicon dioxide to greater than 7 to less than or equal to about 11. The method is free of any subsequent treatment at temperatures of greater than or equal to about 1,000°C after the treating.

[0051] In one aspect, the silica-depleted bioderived byproduct comprises a silica depleted rice hull ash product (SDRHA) that comprises silicon dioxide at greater than or equal to about 40% by weight to less than or equal to about 65% by weight and hard carbon at greater than or equal to about 35 % by weight to less than or equal to about 60% by weight.

[0052] In one aspect, the method further comprises after the adjusting the pH of the silica- depleted bioderived byproduct, further treating a surface of the silica-depleted bioderived byproduct in an inert environment to selectively remove surface oxygenates to form an electroactive nanocomposite material comprising silicon dioxide and hard carbon.

[0053] In one aspect, the method further comprises lithiating the electroactive nanocomposite material with lithium ions or sodiating the electroactive material with sodium ions.

[0054] In one aspect, the bioderived byproduct is a rice hull ash and the silica-depleted bioderived byproduct is a silica-depleted rice hull ash.

[0055] In one aspect, the removing silicon dioxide from a bioderived byproduct occurs by reaction in the presence of a stoichiometric base to form the silica-depleted bioderived byproduct.

[0056] In one aspect, the stoichiometric base comprises tetramethylammonium hydroxide (TMAOH).

[0057] In one aspect, the removing silicon dioxide from a bioderived byproduct occurs by reaction with a hindered diol in the presence of a catalytic base to form the silica-depleted bioderived byproduct.

[0058] In one aspect, the hindered diol is selected from the group consisting of: 2-methyl- 2,4-pentanediol, 2,2,4-trimethyl-1,3-pentanediol, and combinations thereof.

[0059] In one aspect, the catalytic base is selected from the group consisting of: sodium hydroxide (NaOH), lithium hydroxide (LiOH), calcium hydroxide Ca(OH)2, potassium hydroxide (KOH), cesium hydroxide (CsOH), rubidium hydroxide (RbOH), and combinations thereof.

[0060] In one aspect, the hindered diol comprises 2-methyl-2,4-pentanediol and the catalytic base is selected from the group consisting of: sodium hydroxide (NaOH), potassium hydroxide (KOH), lithium hydroxide (LiOH), and combinations thereof

[0061] In one aspect, after the adjusting the pH of the silica-depleted bioderived byproduct, further heating the silica-depleted bioderived byproduct to a temperature of greater than or equal to about 200°C to less than about 800°C.

[0062] In one aspect, the adjusting the pH of the silica-depleted bioderived byproduct further comprises at least one washing step.

[0063] In one further aspect, the at least one washing step comprises washing the silica- depleted bioderived byproduct with boiling water.

[0064] In one aspect, the electroactive nanocomposite material comprises a matrix of hard carbon having surface regions at least partially coated with silicon dioxide.

[0065] In one aspect, the electroactive nanocomposite material comprises pores including carbon encapsulating silicon dioxide.

[0066] In one aspect, the method further comprises prior to the removing silicon dioxide, milling the rice hull ash (RHA) byproduct with an acidic solution to yield a purified rice hull ash (RHA) byproduct.

[0067] In one aspect, the method further comprises lithiating the electroactive nanocomposite material with lithium ions or sodiating the electroactive material with sodium ions.

[0068] In one aspect, the bioderived byproduct is a rice hull ash and the silica-depleted bioderived byproduct is a silica-depleted rice hull ash.

[0069] In yet other aspects, the present disclosure relates to a method of operating an electrochemical cell. The method may comprise cycling lithium ions or sodium ions between a negative electrode and a positive electrode in the electrochemical cell that comprises the negative electrode, the positive electrode, and an electrolyte disposed therebetween. The negative electrode comprises a current collector and an electroactive layer comprising an electroactive nanocomposite material comprising silicon dioxide and hard carbon derived from a silica-depleted bioderived byproduct comprising char and ash.

[0070] In one aspect, the electroactive nanocomposite material is free of products of heating at greater than or equal to 1,000°C.

[0071] In one aspect, the electroactive nanocomposite material is free of silicon, silicon carbide, silicon nitride, silicon oxynitride, and combinations thereof.

[0072] In one aspect, the silica-depleted bioderived byproduct comprises a silica depleted rice hull ash product (SDRHA) comprising silicon dioxide at less than or equal to about 65% by weight and hard carbon at greater than or equal to about 20 % by weight.

[0073] In one aspect, the silica-depleted bioderived byproduct comprises a silica depleted rice hull ash product (SDRHA) comprises silicon dioxide at greater than or equal to about 20% by weight to less than or equal to about 65% by weight and hard carbon at greater than or equal to about 35 % by weight to less than or equal to about 80% by weight.

[0074] In one aspect, the silica-depleted bioderived byproduct comprises a silica depleted rice hull ash product (SDRHA) that comprises silicon dioxide at greater than or equal to about 40% by weight to less than or equal to about 65% by weight and hard carbon at greater than or equal to about 35 % by weight to less than or equal to about 60% by weight.

[0075] In one aspect, the electroactive nanocomposite material has a treated surface to control surface oxygenates and minimize formation of a solid electrolyte interface (SEI).

[0076] In one aspect, the electroactive nanocomposite material has an average surface area of greater than or equal to about 70 m2 / g (N2).

[0077] In one aspect, the electroactive nanocomposite material exhibits a specific capacity to the hard carbon mass of greater than or equal to about 400 mAh / gHC.

[0078] In certain aspects, the electroactive nanocomposite material has an average surface area of greater than or equal to about 70 m2 / g (N2) and exhibits a specific capacity to the hard carbon mass (mAh / gHC) of greater than or equal to about 400 mAh.

[0079] In one aspect, the electroactive nanocomposite material exhibits a specific capacity to a hard carbon mass (mAh / gHC) of greater than or equal to about 700 mAh.

[0080] In one aspect, the electroactive nanocomposite material defines a plurality of particles distributed into a polymeric matrix comprising a polymeric binder.

[0081] In one further aspect, the electrode further comprising a plurality of electrically conductive particles distributed in the polymeric binder.

[0082] In one aspect, the current collector comprises a metal selected from the group consisting of: copper, nickel, alloys, and combinations thereof.

[0083] In one aspect, the electroactive material layer further comprises a liquid electrolyte, a solid -state electrolyte, or combinations thereof.

[0084] In one aspect, the silica-depleted bioderived byproduct forming the electroactive nanocomposite material comprises at least one residual ion selected from a group consisting of: potassium ions, sodium ions, lithium ions, and combinations thereof.

[0085] In one aspect, the cycling lithium ions or sodium ions further comprises cycling two or more ions selected from a group consisting of: lithium ions, sodium ions, potassium ions, and combinations thereof.

[0086] Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.DRAWINGS

[0087] The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations and are not intended to limit the scope of the present disclosure.

[0088] FIG.1 is an illustration of an example of an electrochemical cell having a negative electrode assembly including a negative electroactive layer (for example, incorporating an electroactive nanocomposite material comprising hard carbon and silicon dioxide) and a negative current collector prepared in accordance with certain aspects of the present disclosure, a separator, and a positive electrode assembly including a positive electroactive layer and a positive current collector component.

[0089] FIGS.2A–2E show a comparison of a rice hull ash (RHA) having 90 weight % of silica, 10 weight % of carbon and a silica-depleted rice hull ash (SDRHA60) having 60 weight % of silica, 40 weight % of carbon. FIG.2A shows TGA analyses for RHA and SDRHA60. FIG.2B shows an XPS survey scan for RHA and SDRHA60. FIG. 2C shows XRD and FIG. 2D shows SEM images of each RHA and SDRHA60, respectively. FIG.2E shows N2 adsorption-desorption isothermal plots and pore size distribution (inset) of RHA and SDRHA60.

[0090] FIGS.3A–3B show XRD and N2adsorption-desorption isothermal plots of RHA having 90 weight % of silica, 10 weight % of carbon and SDRHA40–65 having silica ranging from 40 to 65 weight % of silica and correspondingly 35 to 60 weight % of carbon. FIG. 3A shows XRDs for these materials, while FIG.3B shows N2adsorption-desorption isothermal plots with quantities adsorbed (cm3 / g) versus relative pressure (P / PO).

[0091] FIGS. 4A–4B show wide scan XPS and C 1s spectra of conventional graphite (commercially available from Superior Graphite, labeled as graphite or C-G) and conventional hard carbon (commercially available from MSE Corp., labeled as Hard carbon or C-HC) compared with SDRHA40–60 having silica ranging from 40 to 65 weight % of silica and correspondingly 60 to 35 weight % of carbon prepared in accordance with certain aspects of the present disclosure. FIG.4A shows wide scan XPS, while FIG.4B shows C 1 spectra.

[0092] FIG.5 shows Raman spectra and ID / IG ratios of SDRHA40,50,60 respectively having silica at 40, 50, and 60 weight % and correspondingly 60, 50, and 40 weight % of carbon prepared in accordance with certain aspects of the present disclosure versus hard carbon (C-HC) and graphite (C-G).

[0093] FIGS.6A–6B compare voltage profiles of SDRHA60 having silica at 60 weight % and correspondingly 40 weight % carbon prepared in accordance with certain aspects of thepresent disclosure (FIG. 6A) versus hard carbon (C-HC) (FIG.6B) tested in typical lithium half cells for 3 cycles at C / 10.

[0094] FIGS.7A–7B show specific capacities of SDRHA40,50,60 respectively having silica at 40, 50, and 60 weight % and correspondingly 60, 50, and 40 weight % of carbon prepared in accordance with certain aspects of the present disclosure versus hard carbon (C-HC) in lithium half cells. FIG. 7A shows Nyquist plots, while FIG. 7B shows cycling capabilities of SDRHA40,50,60and C-HC half-cells. Specific capacities are normalized to carbon contents in each sample.

[0095] FIGS.8A–8B show volumetric, specific energy and power densities normalized to carbon contents for SDRHA40,50,60respectively having silica at 40, 50, and 60 weight % and correspondingly 60, 50, and 40 weight % of carbon prepared in accordance with certain aspects of the present disclosure versus hard carbon (C-HC). FIG.8A is a Ragone plot of the volumetric (Energy density (Wh / L) versus Power (W / L)), while FIG. 8B is specific energy and power densities (Energy density (Wh / L) versus Power (W / L)) normalized to the carbon contents.

[0096] FIG. 9 shows XPS studies on SDRHA60 (having silica at 60 weight % and correspondingly 40 weight % of carbon prepared in accordance with certain aspects of the present disclosure versus hard carbon (C-HC) after 60 charge-discharge cycles in a lithium-ion cell.

[0097] FIG. 10 shows a comparison of average PEIS performance for all SDRHA sodium-ion battery (NIB) half-cell permutations tested.

[0098] FIG. 11 shows average rate capability for various SDRHA permutations in sodium-ion battery (NIB) half-cells.

[0099] FIG. 12 shows an average C / 10 static cycle life behavior across all sodium-ion battery (NIB) half-cell permutations.

[0100] FIG.13 shows a comparison of average PEIS performance for HG and TMAOH- derived SDRHA in a sodium-ion battery (NIB).

[0101] FIGS. 14A–14B show a comparison of half-cell Performance for TMAOH and HG-derived SDRHA sodium-ion batteries (NIBs). FIG. 14A shows an average rate capability. FIG.14B shows an average C / 10 static cycle life.

[0102] FIG. 15 shows a comparison of average PEIS performance for neutral and pH9 HG-50.

[0103] FIGS.16A–16B show a comparison of half-cell performance for neutral and pH9 HG-50 sodium-ion batteries (NIBs). FIG.16A shows an average rate capability. FIG.16B shows an average C / 10 static cycle life.

[0104] FIG.17 shows a comparison of average PEIS performance for HG-50 and HG-25 sodium-ion battery (NIB) half cells.

[0105] FIGS.18A–18B show a comparison of half-cell performance for HG-50 and HG- 25 NIBs. FIG.18A shows an average rate capability. FIG.18B shows an average C / 10 static cycle life.

[0106] FIG. 19 shows a comparison of average PEIS performance for heat-treated SDRHA.

[0107] FIGS. 20A–20B show a comparison of half-cell performance for heat treated SDRHA NIBs. FIG.20A shows an average rate capability. FIG.20B shows an average C / 10 static cycle life.

[0108] FIG. 21 shows a TEM microscopy image of SDRHA55made in accordance with certain aspects of the present disclosure by using tetramethylammonium hydroxide (TMAOH) during silicon dioxide removal. Scale bar: 200 micrometers.

[0109] FIGS. 22A–22B show galvanostatic cycling performance of an SDRHA25electroactive material prepared in accordance with certain aspects of the present disclosure cycled between 0.01 and 3 V (FIG.22A), along with the corresponding coulombic efficiency (FIG.22B). The average of 3 coin cells is provided. Specific capacities are normalized to the carbon components.

[0110] FIGS. 23A–23B show galvanostatic cycling performance of an SDRHA60 electroactive material prepared in accordance with certain aspect so the present disclosure including having a final basic pH of about 9 cycled between 0.01 and 3 V (FIG.23A), along with the corresponding coulombic efficiency (FIG. 23B). The average of 3 coin cells is provided. Specific capacities are normalized to the carbon components.

[0111] Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings. DETAILED DESCRIPTION

[0112] Example embodiments are provided so that this disclosure will be thorough, and will fully convey the scope to those who are skilled in the art. Numerous specific details are set forth such as examples of specific compositions, components, devices, and methods, to provide a thorough understanding of embodiments of the present disclosure. It will be apparent to those skilled in the art that specific details need not be employed, that example embodiments may be embodied in many different forms and that neither should be construed to limit the scope of thedisclosure. In some example embodiments, well-known processes, well-known device structures, and well-known technologies are not described in detail.

[0113] The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting. As used herein, the singular forms “a,” “an,” and “the” may be intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms “comprises,” “comprising,” “including,” and “having,” are inclusive and therefore specify the presence of stated features, elements, compositions, steps, integers, operations, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof. Although the open-ended term “comprising,” is to be understood as a non-restrictive term used to describe and claim various embodiments set forth herein, in certain aspects, the term may alternatively be understood to instead be a more limiting and restrictive term, such as “consisting of” or “consisting essentially of.” Thus, for any given embodiment reciting compositions, materials, components, elements, features, integers, operations, and / or process steps, the present disclosure also specifically includes embodiments consisting of, or consisting essentially of, such recited compositions, materials, components, elements, features, integers, operations, and / or process steps. In the case of “consisting of,” the alternative embodiment excludes any additional compositions, materials, components, elements, features, integers, operations, and / or process steps, while in the case of “consisting essentially of,” any additional compositions, materials, components, elements, features, integers, operations, and / or process steps that materially affect the basic and novel characteristics are excluded from such an embodiment, but any compositions, materials, components, elements, features, integers, operations, and / or process steps that do not materially affect the basic and novel characteristics can be included in the embodiment.

[0114] Any method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance. It is also to be understood that additional or alternative steps may be employed, unless otherwise indicated.

[0115] When a component, element, or layer is referred to as being “on,” “engaged to,” “connected to,” or “coupled to” another element or layer, it may be directly on, engaged, connected or coupled to the other component, element, or layer, or intervening elements or layers may be present. In contrast, when an element is referred to as being “directly on,” “directly engaged to,” “directly connected to,” or “directly coupled to” another element or layer, there may be no intervening elements or layers present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., “between” versus “directlybetween,” “adjacent” versus “directly adjacent,” etc.). As used herein, the term “and / or” includes any and all combinations of one or more of the associated listed items.

[0116] Although the terms first, second, third, etc. may be used herein to describe various steps, elements, components, regions, layers and / or sections, these steps, elements, components, regions, layers and / or sections should not be limited by these terms, unless otherwise indicated. These terms may be only used to distinguish one step, element, component, region, layer or section from another step, element, component, region, layer or section. Terms such as “first,” “second,” and other numerical terms when used herein do not imply a sequence or order unless clearly indicated by the context. Thus, a first step, element, component, region, layer or section discussed below could be termed a second step, element, component, region, layer or section without departing from the teachings of the example embodiments.

[0117] Spatially or temporally relative terms, such as “before,” “after,” “inner,” “outer,” “beneath,” “below,” “lower,” “above,” “upper,” and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. Spatially or temporally relative terms may be intended to encompass different orientations of the device or system in use or operation in addition to the orientation depicted in the figures.

[0118] Throughout this disclosure, the numerical values represent approximate measures or limits to ranges to encompass minor deviations from the given values and embodiments having about the value mentioned as well as those having exactly the value mentioned. Other than in the working examples provided at the end of the detailed description, all numerical values of parameters (e.g., of quantities or conditions) in this specification, including the appended claims, are to be understood as being modified in all instances by the term “about” whether or not “about” actually appears before the numerical value. “About” indicates that the stated numerical value allows some slight imprecision (with some approach to exactness in the value; approximately or reasonably close to the value; nearly). If the imprecision provided by “about” is not otherwise understood in the art with this ordinary meaning, then “about” as used herein indicates at least variations that may arise from ordinary methods of measuring and using such parameters. For example, “about” may comprise a variation of less than or equal to 5%, optionally less than or equal to 4%, optionally less than or equal to 3%, optionally less than or equal to 2%, optionally less than or equal to 1%, optionally less than or equal to 0.5%, and in certain aspects, optionally less than or equal to 0.1%.

[0119] In addition, disclosure of ranges includes disclosure of all values and further divided ranges within the entire range, including endpoints and sub-ranges given for the ranges.

[0120] Example embodiments will now be described more fully with reference to the accompanying drawings.

[0121] Recently, investigations into new electroactive materials for negative electrodes have focused on alternatives to commonly used graphite to enhance energy capabilities for electrochemical cells. Research has focused on testing alternative carbon-based materials. As background, elemental carbon can be found in many morphologies, including amorphous, hard carbon, graphite, carbon nanotubes, and diamond. Full graphitization typically occurs on heating most carbon sources to greater than 2,000°C. However, hard carbon (HC), which may also be referred to as non-graphitizing carbon or char, is a form of carbon that cannot be converted or transformed to graphite despite heat treatment at high temperatures. Hard carbon is typically produced by heating carbonaceous precursors to approximately 1,000 °C or greater in the absence of oxygen. Generally, hard carbon may be formed by heating amorphous carbon at such temperatures. Hard carbon may be characterized as small graphene islands distributed in amorphous regions with defects and nanopores present in the HC structures, while the bulk of the material does not convert to graphite when heated. The nongraphitizable nature of HC is suggested to be inherited from the precursors’ bonding features, such that the short range ordered graphene sheets restrictedly stack in bent, curved, or turbostratic, rather than flat, in a paralleled manner. Certain types of hard carbon have been used as negative electroactive materials for lithium-ion batteries (LIB) and sodium-ion batteries (NIB).

[0122] There has been further interest in forming such hard carbon materials from bioderived products, such as bioderived byproducts. Bioderived byproducts as used herein are derived from biological sources and have been burned or otherwise heated to form a byproduct comprising char (high content carbonaceous material remaining from incomplete burning), and ash (primarily inorganic constituents). Thus, various materials, such as bagasse, wood, nanocellulose, seeds (e.g., tamarind seeds), fibers (e.g., kapok fibers), hulls (e.g., rice hulls), straw (e.g., rice straw), stover (e.g., corn stover), grass, stems, husks (e.g., mustard husks, coconut husks), bagasse (e.g., sugar cane or sorghum waste), peels (e.g., banana peels, shaddock peels), shells (e.g., walnut shells), starch (e.g., potato starch, corn starch), pits (e.g., cherry pits), mushrooms, pinecones, and the like have been explored as bio-derived sources to form hard carbon for potential use as electroactive materials. In various processes, hard carbon was formed from such materials (e.g., bioderived products as carbon sources) by heating in oxygen-free environments at high temperatures, for example, greater than or equal to about 1,000 °C. It was believed that hard carbon would only be produced by heating such carbon sources in the absence of oxygen at high temperatures, for example, greater than or equal to about 1,000 °C, so thatpyrolysis, carbothermal reduction, hydrothermal reduction, and the like would occur. However, in accordance with various aspects of the present disclosure, it has been unexpectedly discovered that certain bioderived byproducts contain hard carbon without requiring high-temperature and oxygen-free treatment previously believed to be necessary, such that these materials may be processed at low temperatures to form advantageous negative electroactive materials. As used herein, a bioderived product means a product obtained from an organic source, such as a plant, by way of non-limiting example. Where the bioderived product has been burned or otherwise heated to relatively high temperatures, it forms a bioderived byproduct comprising char and ash. A bioderived byproduct may be an agricultural waste product or other ash product (e.g., the ash and char remaining after burning a raw agricultural waste product), such as rice hull ash ((RHA) formed when burning rice hulls that may also contain char).

[0123] The bioderived byproduct has silicon dioxide (SiO2), particularly amorphous silica / silicon dioxide, carbon, and impurities. Many plants, like grasses (e.g., rice, wheat, barley, oats), take up silica / silicon dioxide (SiO2) through their roots into their stalks, seed hulls, and the like. In various aspects, while the present disclosure contemplates rice hulls as a preferred source of silicon and carbon, other biogenic silica and carbon sources (e.g., biomass, bagasse, husks) including grasses (e.g., wheat, rice, corn, barley, oats, and the like) or other sources described above that take up SiO2 in the plant (for example, into the stems, stalks, seed hulls) may also be used and processed as described herein. Rice hulls (RH) have the highest silica content of all grasses. The resulting bioderived byproduct comprising char (e.g., biochar) and ash from, for example, rice hulls (RHA), corn stover (CSA), and bagasse (BA) can have silica contents as high as 90 wt. %. Notably, ashes of other biogenic sources are also contemplated in alternative variations. Bioderived byproducts are typically formed from a biogenic or bioderived source of material that is burned or combusted in an environment containing oxygen / oxidizing environment, typically for energy production. Such a combustion / burning process occurs in an environment with oxygen / oxidizing agents and may occur at 400°C to 800°C, although higher temperatures may be reached, by way of example.

[0124] Previously, such bioderived byproduct / agricultural waste materials were heated to high temperatures in the absence of oxygen to generate biochar that comprised (depending on conditions), partially oxygenated amorphous carbon, or amorphous carbon with some turbostratic carbon (partially graphitized or hard carbon, HC) and if heated long / or hot enough, graphitic carbon. However, it was believed that heating to high temperatures (greater than or equal to about 1,000 °C) in inert and oxygen-free environments was required to generate such forms of carbon, including hard carbon. Thus, conventionally such bioderived byproducts would be further treatedby carbothermal reduction, hydrothermal reduction, pyrolysis, and the like, in an environment free of oxygen and / or oxidizing agents, at temperatures in excess of 1,000°C. Such treatment, like carbothermal reduction, could further be conducted in the presence of nitrogen or argon, such that products including SiC, Si3N4or Si2N2O could be formed in conjunction with hard carbon.

[0125] As noted above, it was unexpectedly discovered that hard carbon is present in bioderived byproducts which typically are not subjected to high-temperature processing (e.g., above 1,000°C) in an oxygen-free environment. Given that it was conventionally understood that hard carbon is typically produced by heating biomass products to greater than 1,000°C in a non- oxidizing / oxygen-free environment, a surprising discovery was made that hard carbon is in fact present in bioderived ash byproducts, like rice hull ash, which have not been treated at high- temperatures in inert environments. For example, the carbon in bioderived products, like RHA, appears to have been pyrolyzed during the combustion process. It is believed that during initial combustion of the bioderived product, the silica content ends up at the surface, as carbon is burned away, thus leaving a silica-enriched surface that encapsulates the remaining carbon.

[0126] In accordance with certain aspects of the present disclosure, beneficial reuse of bioderived byproducts as a waste starting material for fabricating a negative electroactive material can provide several advantages: (1) the environmental benefits related to a reduced carbon footprint; (2) the economical disposal of waste materials; (3) improved properties arising from reduction of product particle sizes enabled by initiating production using nanoscale mixtures, and (4) economization of energy and capital equipment costs due to decreases in processing temperatures and times.

[0127] In various aspects, the present disclosure contemplates a method of making an electroactive nanocomposite material from a bioderived byproduct comprising char and ash. In certain aspects, the method comprises removing silicon dioxide from a bioderived byproduct comprising ash and char to form a silica-depleted bioderived byproduct. In certain aspects, the process that removes silica reveals and exposes high surface area carbon previously masked by the silica (e.g., exposes underlying regions of high surface area carbon within the nanocomposite), making it available for use in a negative electrode. The silica-depleted bioderived byproduct may have silicon dioxide at greater than or equal to about 20% by weight to less than or equal to about 65% by weight and hard carbon at greater than or equal to about 35% by weight to less than or equal to about 80% by weight and optionally greater than or equal to about 40% by weight to less than or equal to about 65% by weight and hard carbon at greater than or equal to about 35 % by weight to less than or equal to about 60% by weight. It will be appreciated that at these massamounts, a volumetric amount of carbon is quite high, for example, volumetrically there is substantially more carbon than silica in the electroactive nanocomposite.

[0128] In other aspects, as described further herein, the method also comprises treating a surface of the silica-depleted bioderived byproduct to form an electroactive nanocomposite material comprising silicon dioxide and hard carbon. For example, the surface of the silica- depleted bioderived byproduct may be treated in an inert environment to control an extent of surface oxygenates, for example, by removing at least a portion of surface oxygenates, to form an electroactive nanocomposite material comprising silicon dioxide and hard carbon. In this manner, the formation of the solid electrolyte interface (SEI) can be minimized. The methods of making an electroactive nanocomposite material in accordance with various aspects of the present disclosure are low-temperature and free of any subsequent treatment at temperatures of greater than or equal to about 1,000°C after the treating and / or aside from the products from initial combustion, is free of products of heating at greater than or equal to 1,000°C, especially free of products of heating in an oxygen-free environment at temperatures of greater than or equal to 1,000°C. Stated in another way, after the initial combustion to form the bioderived product, the silica-depleted bioderived byproduct is not subjected to subsequent high-temperature treatments, like pyrolysis, carbothermal reduction, hydrothermal reduction, or the like. Further, any microwave or further high-energy reactions are not conducted on the electroactive nanocomposite material.

[0129] In the first step, silicon dioxide / silica is removed from a bioderived byproduct to form a silica-depleted bioderived byproduct. In certain aspects, the bioderived byproduct may be a rice hull ash (RHA), such as an acid-purified RHA, which is processed to have advantageously adjusted silica content in a silica depleted rice hull ash product (SDRHA). Silica in the byproduct is susceptible to base-promoted depolymerization and dissolution, for example, using either stoichiometric or catalytic base resulting in recovery of carbon-enriched ash or char. More specifically, the methods advantageously provide the ability to form a silica-depleted rice hull ash product (SDRHA) having advantageously adjusted silicon and carbon contents, without any need to add an external carbon source. The silicon dioxide / silica (SiO2) content in the silica depleted rice hull ash product (SDRHA) can be controlled to arrive at a SRDHA precursor having a sufficiently large carbon content and exposed high surface areas. In the past, in contrast to the present technology, carbon had to be added to carefully adjust the SiO2:C stoichiometry. Further, in conventional processes the particle size of the reactants was at a minimum micron sized, whereas in various aspects, the reactants used in the present disclosure may all be on the nanoscale,for example, having at least one spatial dimension that is less than about 1 micrometer (i.e., 1,000 nm).

[0130] Thus, rather than introducing extra carbon from an external source as has been required in the past, a ratio of SiO2:C is optimized by distillative removal of SiO2from RHA to produce SDRHA with different SiO2:C ratios, while also eliminating typical impurities. Thus, in certain aspects, the methods of the present disclosure contemplate methods of distillatively removing silica from bioderived byproducts / biochar as spirosiloxanes.

[0131] In various aspects, the methods of the present disclosure contemplate removing silicon dioxide from a bioderived byproduct by a reaction with a stoichiometric base or a catalytic base. For example, the stoichiometric base may be a Group I or II metal hydroxide or oxide including M(OH) or M2O, where M may be lithium (Li), sodium (Na), potassium (K), cesium (Cs), or mixtures thereof or M(OH)2 or MO, where M may be calcium (Ca), magnesium (Mg), barium (Ba), or mixtures thereof or a carbonate, for example, NaHCO3. The bases may be used in an aqueous or alcoholic solution, for example, where the alcohol is ROH where R may be a methyl group (Me), ethyl (Et) group, propyl (Pr), isopropyl group (iPr), or a diol including ethylene glycol, propylene glycol or butane 1,3 or 1,4 diol or hexylene glycol or a polyol, such as glycerol, for example. The reaction may be conducted at temperatures of about 25° to 250 °C. Spirosiloxane co-distills with water. This is followed by washing the silica-depleted bioderived byproduct / biochar with a simple alcohol or boiling water, until a target pH is reached, which may optionally be followed by further washing, for example, with a dilute acid.

[0132] Various silicon dioxide removal processes described herein, including removing silicon dioxide from a bioderived byproduct by a reaction with a stoichiometric base or a catalytic base, generally result in a high basic pH product, for example, having a pH of greater than or equal to about 12. After the desired amount of silica / silicon dioxide removal occurs, the high pH silica-depleted bioderived rice hull ash byproduct may be washed one or more times to reduce pH to a target level. In certain variations, the washing may occur until the pH is neutral or nearly neutral (e.g., about 7), which may be followed by washing with dilute acid. The washing with boiling water serves to remove surface basic silicates and unreacted base, inter alia. However, in certain other variations, the silica-depleted bioderived byproduct / biochar is washed so that a target pH is basic (e.g., greater than 7), for example, optionally greater than or equal to about 8, optionally greater than or equal to about 8.5, and in certain variations, optionally greater than or equal to about 9.

[0133] In certain aspects, the stoichiometric base is a tetraalkylammonium hydroxide (TAAOH), including for example, Me4NOH (where Me is methyl) or cholineNMe3OH, ortetramethylammonium hydroxide (TMAOH), or a related base using aqueous medium or aqueous alcoholic media at temperatures below the decomposition temperature of the alkylammonium hydroxide, with or without removal of water, followed by reacting for example with Me3SiCl or related chlorosilane to cap the [SiO1.5]6,8,106-,8-,10-anion followed by extraction with hexane as described in Asuncion et al., “The Selective Dissolution of Rice Hull Ash to Form [OSiO1.5]8[R4N]8(R = Me, CH2CH2OH) Octasilicates. Basic Nanobuilding Blocks and Possible Models of Intermediates Formed during Biosilicification Processes,” J. Mater. Chem., 15 (21), 2114 (2005) https: / / doi.org / 10.1039 / b502178b, the relevant portions of which are incorporated herein by reference.

[0134] In one particular variation, the SDRHA is formed from RHA by using a tetramethylammonium hydroxide (TMAOH).

[0135] In other aspects, the catalytic base for removing silica from the bioderived byproduct may include, for example, M(OH) or M2O, where M may be lithium (Li), sodium (Na), potassium (K), cesium (Cs), or mixtures thereof or M(OH)2or MO, where M may be calcium (Ca), magnesium (Mg), barium (Ba), or mixtures thereof, or carbonates (e.g., KHCO3) used in an alcoholic solution, where the alcohol is a diol such as ethylene glycol or 1,2- or 1,3-propylene glycol or 1,2- or 1,3- or 1,4-butanediol or mixtures thereof, and the reaction mixture is heated to temperatures of greater than or equal to about 100 °C to still water, but optionally 150°C, optionally up to 250 °C to drive the reaction faster.

[0136] In further aspects, the catalytic base is used with a hindered diol, such as hexylene glycol, and the reaction is run to first distill out product water and then to distill out a spirosiloxanes as detailed in Laine et al., “Avoiding Carbothermal Reduction: Distillation of Alkoxysilanes from Biogenic, Green, and Sustainable Sources,” Angew. Chem. Int. Ed. 55 (3), pp. 1065–1069 (2016), the relevant portions of which are incorporated herein. For example, product water is produced at temperatures above 100°C as the depolymerization of silica requires higher temperatures to be sufficiently rapid to be convenient, even under pressure at 220°C. Thereafter, the product is isolated by filtration and washing with alcohol and boiling water to a target pH. The length of reaction time determines the final SiO2 content as determined by removing samples at given times to determine the instant silica content SDRHAxx (where xx represents an amount of silica remaining in the SDRHA) typically by TGA in air.

[0137] In certain aspects, the methods of the present disclosure contemplate removing silicon dioxide from a bioderived byproduct by a reaction with a hindered diol in the presence of a catalytic base to form the silica-depleted bioderived byproduct. In certain variations, the presentdisclosure contemplates removing SiO2from rice hull ash (RHA) by forming distillable spirosiloxane per reaction (2):

[0138] For example, SiO2 can be extracted from RHA as spirosiloxane (shown above), {[(CH3)2C(O)CH2CH(O)CH3)]2Si}, an approximately 90:10 nanocomposite mixture of SiO2:C, to carefully control a mole ratio of C:SiO2 without any need to add extra carbon and as a mechanism to preserve the original nanocomposite structure. Notably, the extraction of SiO2 from RHA to form spirosiloxanes can also be achieved with other hindered glycols, such as, 2,2,4- trimethyl-1,3-pentanediol.

[0139] Suitable hindered diols for treating the RHA to adjust silicon and carbon contents may be selected from the group consisting of 2-methyl-2,4-pentanediol (hexylene glycol), 2,2,4- trimethyl-1,3-pentanediol, and combinations thereof. In certain aspects, a combination of hindered diols may be used, including those just listed above and optionally further including ethane-1,2- diol. In one aspect, the hindered diol comprises 2-methyl-2,4-pentanediol (hexylene glycol).

[0140] Suitable catalytic bases may include those selected from the group consisting of: sodium hydroxide (NaOH), lithium hydroxide (LiOH), calcium hydroxide Ca(OH)2, potassium hydroxide (KOH), cesium hydroxide (CsOH), rubidium hydroxide (RbOH), and combinations thereof.

[0141] In one variation, the SDRHA is formed from RHA by using a hindered diol comprising 2-methyl-2,4-pentanediol (hexylene glycol) for removing silicon dioxide by distilling spirosiloxane, followed by exposure to a stoichiometric base or a catalytic base to form the silica- depleted bioderived byproduct. The base may comprise sodium hydroxide (NaOH), potassium hydroxide (KOH), and / or lithium hydroxide (LiOH). In certain variations, the base may comprise at least one of sodium hydroxide (NaOH) or potassium hydroxide (KOH).

[0142] In certain other aspects, the methods of the present disclosure contemplate removing silicon dioxide from a bioderived byproduct by using a stoichiometric base, which then may be neutralized, where silica is precipitated and the silica-depleted bioderived byproduct is thus formed. By way of example only, suitable stoichiometric bases may include those selected from the group consisting of: sodium hydroxide (NaOH), lithium hydroxide (LiOH), calcium hydroxide Ca(OH)2, potassium hydroxide (KOH), cesium hydroxide (CsOH), rubidium hydroxide(RbOH), and combinations thereof. The recovered bioderived product may then be further processed to form an electroactive material, such as removing surface oxygenates.

[0143] In certain aspects, the methods of the present disclosure contemplate removing silicon dioxide from a bioderived byproduct by any of the reactions described above to form the silica-depleted bioderived byproduct. Prior to final treatment and washing, the reaction product has a highly basic pH, for example, greater than or equal to about 12. Thus, in certain variations, the removing of silicon oxide from the bioderived product includes treating (e.g., washing) the silica-depleted bioderived byproduct to reduce pH. In certain aspects, the treating (e.g., washing) and to achieve a final target pH of the silica-depleted bioderived byproduct / biochar to be basic and greater than 7, for example, controlling a pH of the silica-depleted bioderived byproduct / biochar to be greater than or equal to about 7.5, optionally greater than or equal to about 8, optionally greater than or equal to about 8.5, and in certain variations, optionally greater than or equal to about 9. In one aspect, the target pH may be greater than 7 to less than or equal to about 11, optionally greater than or equal to about 9 to less than or equal to about 11, and optionally greater than or equal to about 9 to less than or equal to about 10. This target pH may occur after completion of reaction (where typically the product has a high basic pH, for example, greater than or equal to about 12), after which washing of the silica-depleted bioderived byproduct occurs. The washing may occur with water, for example, boiling water, and / or an alcohol or other conventional washing compositions.

[0144] While not limiting the present disclosure to any particular theory, it is believed that by allowing the silica-depleted bioderived byproduct / biochar to remain at basic conditions, for example, at a pH of about 7 and more particularly above about 9, rather than processing the material to achieve neutral pH, certain cations, like potassium ions (K+) or sodium ions (Na+), remain present on and within the silica-depleted bioderived byproduct, which subsequently can enhance performance of the electroactive material. The presence of potassium results from the addition of potassium as a reactant, such as a catalytic base (e.g., potassium hydroxide (KOH). If a different base is used, such as sodium hydroxide (NaOH), sodium remains on the silica-depleted bioderived byproduct. Where the base includes alkaline earth metals, such as calcium (Ca), magnesium (Mg), barium (Ba), these ions may likewise remain on the silica-depleted bioderived byproduct. By way of example, when the silica-depleted bioderived byproduct / biochar has a basic pH (e.g., pH of greater than 7, optionally at least about 9) potassiation occurs from residual K+ions left on the SDRHA material surface. The presence of residual potassium (or other residual alkali metal ions) may facilitate a surface-driven charge storage behavior in the electroactive nanocomposite material. Thus, depending on the nature of the residual ions (e.g., potassium,sodium, or lithium), both lithiation and / or sodiation and / or potassiation can occur coincidentally or sequentially. Thus, the potassium (or other alkali metal ions) may enhance electrochemical performance of the electroactive nanocomposite material when used as an electroactive material of an electrode in an electrochemical cell. Thus, in certain aspects, the electroactive nanocomposite material formed from the silica-depleted bioderived byproduct comprises at least one residual ion from the silica depletion process that is selected from a group consisting of: potassium ions, sodium ions, lithium ions, and combinations thereof. In certain variations, the residual ion present in the silica-depleted bioderived byproduct forming an electroactive material comprises at least one residual ion from the silica depletion process that is selected from a group consisting of: potassium ions, sodium ions, and combinations thereof. In certain variations, the residual ion present in the silica-depleted bioderived byproduct forming an electroactive material comprises potassium (K+).

[0145] In this manner, by removing silicon dioxide from a bioderived byproduct, useful and highly dispersed mixtures of hard carbon and silica are provided as a nanocomposite. As noted above, the SDRHA has a nanocomposite structure after RHA is treated that is generally preserved forming a composite or nanocomposite product. More specifically, SDRHA is an amorphous SiO2 / carbon nanocomposite, where carbon-enriched materials contain a highly dispersed (nanocomposite) carbon / silica mixture. In certain variations, a nanocomposite is a structure that includes a primary phase or matrix with a secondary phase distributed therein. One or more of the primary phase or secondary phase may be in the form of a plurality of nanostructures distributed in the other phase. Nanostructures may include “nano-sized” or “nanometer-sized” particles having at least one spatial dimension that is less than about 1 micrometer (i.e., 1,000 nm), optionally less than about 0.5 micrometers (i.e., 500 nm), optionally less than about 0.4 micrometers (i.e., 400 nm), optionally less than about 0.3 micrometers (i.e., 300 nm), optionally less than about 0.2 micrometers (i.e., 200 nm), and in certain variations, optionally less than about 0.1 micrometers (i.e., 100 nm). Accordingly, a nanoparticle component has at least one spatial dimension that is greater than about 1 nm and less than about 1,000 nm (1 micrometer). It should be noted that so long as at least one dimension of the nanoparticle falls within the above-described nano-sized scale (for example, diameter), one or more other axes may well exceed the nano-size (for example, length and / or width). In certain variations, the nanocomposite includes a first phase comprising hard carbon and a second phase comprising silicon dioxide (SiO2).

[0146] While not limiting the present disclosure to any particular theory, it is believed that the bioderived byproduct like RHA has a nanocomposite structure, which may include at least a partially layered structure, where distributed hard carbon or hard carbon nanostructures have acoating of silicon dioxide / silica. The removal of silicon dioxide to form the silicon-depleted bioderived byproduct serves to remove a portion of the silica coating from surfaces of the hard carbon, such that regions of the underlying hard carbon (e.g., hard carbon layers, nanostructures, or matrix) are then exposed. In this manner, the present disclosure contemplates removing silicon dioxide as a means to generate a hard carbon-silica nanocomposite containing large amounts of accessible hard carbon.

[0147] The methods of the present disclosure thus contemplate in certain variations, adjusting the silicon and carbon content from an RHA to form a silica depleted rice hull ash (SDRHA) having predetermined range of silicon and carbon contents. In certain aspects, the treated silica depleted rice hull ash (SDRHA) comprises greater than or equal to about 20% by weight to less than or equal to about 80 % by weight of carbon for a total weight of the SDRHA, optionally greater than or equal to about 40 % by weight to less than or equal to about 80% by weight of carbon for a total weight of the SDRHA.

[0148] In certain variations, the silica-depleted biochar material comprises a silica depleted rice hull ash product (SDRHA) comprising silicon dioxide (SiO2) at less than or equal to about 65% by weight and hard carbon at greater than or equal to about 35 % by weight. In other variations, the silica-depleted biochar material comprises a silica depleted rice hull ash product (SDRHA) comprising silicon dioxide (SiO2) at greater than or equal to about 35% by weight to less than or equal to about 60% by weight and hard carbon at greater than or equal to about 40% by weight to less than or equal to about 55% by weight.

[0149] In yet other variations, the silica-depleted biochar material comprises a silica depleted rice hull ash product (SDRHA) comprising silicon dioxide (SiO2) at greater than or equal to about 40% by weight to less than or equal to about 65% by weight and hard carbon at greater than or equal to about 35 % by weight to less than or equal to about 60% by weight

[0150] As noted above, the carbon may be hard carbon may be characterized as a mixture of amorphous carbon with islands of graphite-like materials distributed therein (for example, by definition, turbostratic includes graphene like inclusions in an amorphous carbon matrix or linked by amorphous carbon). The treated SDRHA may thus have greater than or equal to about 20% by weight to less than or equal to about 65 % by weight silicon for a total weight of the SDRHA, optionally greater than or equal to about 45% by weight to less than or equal to about 80% by weight of carbon for a total weight of the SDRHA. In certain aspects, the silicon is present as silicon dioxide and more particularly, as amorphous silicon dioxide.

[0151] The silicon to carbon content can be reflected by a ratio of moles of silicon dioxide or silica (SiO2) to moles of carbon. The SiO2:C ratio can be adjusted by reacting the initial RHAmaterial with a hindered diol in the presence of catalytic base to distillatively remove excess SiO2to produce the treated SDRHA with the desired silica to carbon ratios. For example, the treated SDRHA may have a ratio of moles of SiO2 to carbon (SiO2:C) of about 1:8 to about 1:3, optionally about 2:15 to about 13:35, and in one variation, optionally about 1:5 (which comprises about 0.8 mole SiO2 and about 4 moles of carbon).

[0152] The RHA may first be washed in an acid. In one variation, rice hull ash (RHA) may be milled (e.g., with a milling or grinding media) with an acid for washing to remove impurities. The acid may be a dilute acid, such as hydrochloric acid, sulfuric acid, phosphoric acid, and combinations thereof. In one variation, a dilute hydrochloric acid may be used. In certain variations, a dilute acid may be one that is present in a solution at less than or equal to about 20 weight %, optionally less than or equal to about 12 weight %, optionally less than or equal to about 10 weight %, optionally greater than or equal to about 1 weight % to less than or equal to about 12 weight %, in one variation, optionally greater than or equal to about 1 weight % to less than or equal to about 10 weight % or in another variation, optionally greater than or equal to about 5 weight % to less than or equal to about 12 weight %.

[0153] The milled and acid washed RHA may then be washed with boiling water in at least one wash cycle, optionally multiple wash cycles. The acid and boiling water prewashing of RHA with milling provides an advantage in that it eliminates typical product impurities found in RHA, compared to those found in conventional agricultural waste precursors, which can provide highly pure products after conventional carbothermal reduction. Milling RHA in dilute acid followed by washing with boiling water provides SDRHA with very low impurity levels. In certain aspects, the SDRHA has less than or equal to about 1% by weight of undesired impurities, like minerals, multiple metals, boron, and aluminum, optionally less than or equal to about 0.5 % by weight, optionally less than or equal to about 0.1% by weight impurities and in certain variations, may be as low as about 0.01% by weight or less than about 1 ppm impurities.

[0154] After removing a portion of silicon dioxide, the silica-depleted byproduct may be treated to have a target pH that is basic and greater than 7, for example, optionally having a target pH of greater than or equal to about 8, optionally of greater than or equal to about 8.5, and in certain variations, optionally of greater than or equal to about 9. In certain aspects, the target pH may be greater than or equal to about 9 to less than or equal to about 11 and optionally the target pH may be greater than or equal to about 9 to less than or equal to about 10. The treating may include washing the silica-depleted byproduct, for example, with boiling water in at least one wash cycle, optionally multiple wash cycles, to remove any residual reagents or products from the silica removal reactions. Washing may also include a wash liquid comprising an acid, for example, likethose described above for the washing of RHA. However, the pH during washing desirably remains in basic conditions at the target pH described above.

[0155] The present methods thus provide a more environmentally- and economically- friendly approach that can advantageously adjust the silica (SiO2) content to enhance carbon content while preserving microstructures in the nanocomposite product formed. This material having adjusted silica content can then optionally be further treated to modify the surface for use as an electroactive material. For example, the washing after removal of silica can introduce various oxygen-containing species onto a surface of the silica-depleted bioderived byproduct. The presence of such surface oxygenates may reduce an ability to fully lithiate or sodiate the electroactive material and promote formation of an excessive solid-electrolyte interface (SEI) layer when used in a negative electrode of a battery.

[0156] Thus, the surface may be treated to form an electroactive nanocomposite material where surface oxygenates (e.g., hydroxyl-containing species) are minimized so as to control the extent of surface oxygenates present and to help reduce detrimental formation of an excessive solid electrolyte interface (SEI). The solid electrolyte interface (SEI) layer can form over the surface of a negative electrode, which is often generated by reaction products of electrolyte reduction, and / or lithium or sodium ion reduction. The formation of a thick solid-electrolyte interface layer (SEI) can occur because of conversion reactions on a negative electrode during a first cycle of the battery, as well as ongoing lithium or sodium loss due to, for example, continuous solid electrolyte interphase (SEI) growth and rebuilding, which results in permanent loss of lithium or sodium ions that can then decrease specific energy and power in the battery.

[0157] Thus, the methods of the present disclosure contemplate in certain aspects, treating a surface of the silica-depleted byproduct in an inert environment to control an extent of, for example, reducing or removing surface oxygenates, to form an electroactive nanocomposite material comprising silicon dioxide and hard carbon. By an inert or reducing atmosphere, it is meant that the gaseous atmosphere is generally free of reactive non-carbon containing oxidant species, such as oxygen containing species (e.g., O2, CO, NOx, and the like). Suitable inert or reducing atmospheres include nitrogen (N2), argon (Ar), and / or N2 / H2, by way of example. Heating in a controlled environment for certain lengths of time will first eliminate oxygenated carbon species that form carbon monoxide (CO) or carbon dioxide (CO2) and / or water (H2O) can be generated. In certain aspects, the silica-depleted bioderived byproduct is surface treated to minimize or remove surface oxygenates by heating the silica-depleted byproduct in a relatively low temperature process, for example, to a temperature of less than about 800°C, optionally greater than or equal to about 100°C to less than or equal to about 800°C, optionally greater thanor equal to about 200°C to less than or equal to about 800°C, optionally greater than or equal to about 300°C to less than or equal to about 800°C, optionally greater than or equal to about 400°C to less than or equal to about 800°C, optionally greater than or equal to about 400°C to less than or equal to about 700°C, and in certain aspects, optionally greater than or equal to about 400°C to less than or equal to about 600°C. As noted previously, this heating process remains well below 1,000°C, where changes in the carbon structure may occur. The methods are thus free of any subsequent treatment at temperatures of greater than or equal to about 1,000°C. Thus, no additional high-temperature heat treatments are conducted on the silica-depleted bioderived byproduct, such as pyrolysis, carbothermal reduction, hydrothermal reduction, or the like.

[0158] The silica-depleted byproduct may be subjected to these temperatures for a duration of greater than or equal to about 1 hour, optionally greater than or equal to about 2 hours, optionally greater than or equal to about 3 hours, optionally greater than or equal to about 4 hours, optionally greater than or equal to about 5 hours, optionally greater than or equal to about 6 hours, optionally greater than or equal to about 7 hours, optionally greater than or equal to about 8 hours, optionally greater than or equal to about 9 hours, and in certain variations, optionally greater than or equal to about 10 hours.

[0159] After the surface of the silica-depleted bioderived byproduct has been treated and the electroactive nanocomposite material comprising silicon dioxide and hard carbon is formed, the methods may include further steps. For example, the methods may include lithiating the electroactive nanocomposite material with lithium ions or sodiating the electroactive material with sodium ions. Lithiation, for example pre-lithiation, or sodiation, or pre-sodiation, of the electroactive materials prior to incorporation into the battery, may compensate for lithium or sodium losses during cycling. For example, reserved lithium can compensate for lithium lost during cycling, including during the first cycle, so as to decrease capacity loss over time. Thus, the electroactive composite material may be exposed to a lithium-source or a sodium-source that may contact the treated surface and infiltrate and infuse into the electroactive material / particles. By way of non-limiting example, the electroactive material can be heated with lithium or sodium metal powder, while milling in molten metal state, or alternatively treating with reagents such as lithium hydride (LiH) or sodium hydride (NaH). These treatments may be preceded by other treatments, such as treatment with thionyl chloride (SOCl2).

[0160] In certain aspects, the present disclosure contemplates chemical removal of silica from biochar / bioderived byproducts (e.g., derived from rice hulls and straw, wheat straw, coconut shells, corn stalks and stover, and bagasse) as exemplified by rice hull ash (RHA, which typically has about 90 wt. % SiO2) via various forms of base promoted silica depolymerization to multiplesilicon containing products, results in formation of silica depleted-greatly carbon enriched bioderived byproduct, e.g., RHA90 has 90 wt. % SiO2 (1.5 moles) and roughly 9 wt. % carbon (0.75 moles), SDRHA50 has 50 wt. % SiO2 (0.83 moles) and roughly 50 wt. % carbon (approximately 4.2 moles) with specific surface areas of 400 m2 / g. As discussed above, it was surprisingly found that when this material is treated to form a silica-depleted bioderived byproduct / biochar, depending on the initial heating conditions, it can contain considerable amounts of hard carbon (HC) as demonstrated above, which after silica depolymerization, can be quite porous with high surface area. As such, it offers exceptional potential for both lithium and sodium ion battery anode materials. Notably, without silica removal, access to the hard carbon (HC) for electrochemical devices is limited and because initially hard carbon represents just a small mass fraction of the starting biochar with limited surface exposure, for example, by being coated in silicon dioxide, and is thus not accessible for lithiation or sodiation. Furthermore, with the removal of the silica, pores are generated within the silica-depleted bioderived byproduct / biochar that provide excellent receptacles for lithium and sodium ions to associate with the surfaces, providing superior interfaces for intercalation for both LIBs and NIBs.

[0161] The bioderived ash / biochar has silica that is susceptible to base-promoted depolymerization and dissolution using either stoichiometric or catalytic base resulting in recovery of carbon-enriched biochar / ash, e.g., silica-depleted bioderived byproduct, as such as silica-depleted rice hull ash (SDRHA) with silica contents less than or equal to about 65 wt. % or the amounts specified above. After removing the silica from the bioderived byproduct, biochar, for example, by silica depolymerization, the material may be further heated in a low temperature process, where temperatures are less than 1,000°C, for example, greater than or equal to about 200 °C to less than about 1000 °C in an oxygen-free environment to control surface oxygenate contents as a prelude to use as anode materials for LIBs and NIBs without coincident significant production of silicon carbide, oxycarbide or silicon nitride or oxynitride. In this manner, electroactive nanocomposite materials with high surface areas are advantageously formed. For example, after removing silicon dioxide from a bioderived byproduct to form a silica-depleted byproduct (e.g., SDRHA), the material may be heated to between about 300°C to about 800 °C in an inert atmosphere to eliminate or control the surface oxygenate content to form the electroactive material, where electrochemical behavior is optimized, for example, improving the rates of Li+or Na+intercalation or deintercalation across the resulting restructured carbon interface.

[0162] In certain variations, the present disclosure contemplates an electroactive material for an electrode in an electrochemical cell, such as a lithium ion or a sodium ion battery, formed in accordance with certain aspects of the present disclosure.

[0163] As background, a rechargeable battery operates by reversibly passing ions (e.g., lithium ions or sodium ions) back and forth between the negative electrode and the positive electrode during charging and discharging. For example, ions may move from the positive electrode to the negative electrode during battery charging and in the opposite direction when discharging the battery. For example, a representative rechargeable battery 20 prepared in accordance with certain aspects of the present disclosure is shown in FIG. 1. The battery 20 includes a positive electroactive material layer or as referred to herein, a positive electrode 22 (e.g., cathode) and a negative electroactive material layer or as referred to herein, a negative electrode 24 (e.g., anode).

[0164] The electroactive material prepared in accordance with various aspects of the present teachings may be used in a negative electrode or anode. The negative electrode 24 may include a negative electroactive material in an electroactive layer. The negative electrode 24 may be a composite electrode that comprises a plurality of electroactive material particles distributed in a polymeric matrix (that may comprise an ionically conductive material), optionally further including electrically conductive particles distributed therein. The negative electrode assembly may also further include a negative current collector 34 on which the electroactive layer 22 is disposed or with which the electroactive layer 22 is in electrical contact.

[0165] In various aspects, a negative electroactive layer / negative electrode 24 may comprise an electroactive nanocomposite material comprising silicon dioxide and hard carbon derived from a silica-depleted bioderived byproduct formed as described above. In certain aspects, the silica-depleted bioderived byproduct forming the electroactive nanocomposite material may have less than or equal to about 65 weight % silica (silicon dioxide), optionally less than or equal to about 60 weight % silica, optionally less than or equal to about 55 weight % silica, and in certain variations, optionally less than or equal to about 50 weight % silica. Correspondingly, the silica- depleted bioderived byproduct forming the electroactive nanocomposite material may have greater than or equal to about 35 weight % carbon (hard carbon), optionally greater than or equal to about 40 weight % hard carbon, optionally greater than or equal to about 45 weight % hard carbon, optionally greater than or equal to about 50 weight % hard carbon, optionally greater than or equal to about 60 weight % hard carbon, optionally greater than or equal to about 70 weight % hard carbon, and in certain variations, optionally greater than or equal to about 80 weight % carbon.

[0166] In certain aspects, the electroactive nanocomposite material comprises a matrix of hard carbon having surface regions at least partially coated with silicon dioxide (where other uncoated surface regions of the hard carbon are exposed). Further, in certain aspects, theelectroactive nanocomposite material comprises pores including carbon encapsulating silicon dioxide, where the pores have not been exposed to a base during the silica removal reaction. In certain aspects, the silica-depleted bioderived byproduct / biochar material that forms the electroactive nanocomposite material comprises a silica depleted rice hull ash product (SDRHA) comprising silicon dioxide at less than or equal to about 65% by weight and hard carbon at greater than or equal to about 35 % by weight. In certain further aspects, the silica-depleted bioderived product / biochar material that forms the electroactive nanocomposite material comprises silicon dioxide at greater than or equal to about 35% by weight to less than or equal to about 65% by weight, optionally greater than or equal to about 45% by weight to less than or equal to about 55% by weight, and hard carbon at greater than or equal to about 35% by weight to less than or equal to about 60% by weight, optionally greater than or equal to about 45% by weight to less than or equal to about 55% by weight. In one variation, the electroactive nanocomposite material comprises silicon dioxide at about 50% by weight and hard carbon at about 50% by weight. Such a variation may be formed from SDRHA50having 50 weight % SiO2and 50 weight % carbon, which comprises about 0.8 mole SiO2 and about 4 moles of carbon. Volumetrically there is much more carbon than SiO2. This carbon offers properties superior to graphite used in lithium-ion batteries and further can be used in sodium ion batteries (NIBs) for energy storage.

[0167] In various aspects, the electroactive nanocomposite material has a treated surface to carefully control the extent of surface oxygenates (notably some minimal surface oxygenates may remain) and minimize solid electrolyte interface (SEI). As noted above, the electroactive nanocomposite material is not further treated at high temperatures. The electroactive nanocomposite material is thus substantially free of or fully free of various species, including carbothermal reaction products or other species formed after being subject to pyrolysis, including silicon (Si), silicon carbide (SiC), silicon nitride (Si3N4), or silicon oxynitride (Si2N2O), and any combinations thereof.

[0168] In various aspects, the electroactive nanocomposite material formed in accordance with various aspects of the present disclosure has a total surface area measured via the Brunauer- Emmett-Teller (BET) method using nitrogen (N2) of greater of greater than or equal to about 70 m2 / g, optionally greater than or equal to about 100 m2 / g, optionally greater than or equal to about 150 m2 / g, optionally greater than or equal to about 200 m2 / g, and in certain aspects, optionally greater than or equal to about 250 m2 / g.

[0169] Further, in various aspects, the electroactive nanocomposite material exhibits a specific capacity to the hard carbon mass (mAh / gHC) of greater than or equal to about 200 mAh at 1C (Coulombs) discharge rate, optionally greater than or equal to about 250 mAh at 1C, optionallygreater than or equal to about 300 mAh at 1C, optionally greater than or equal to about 350 mAh at 1C, optionally greater than or equal to about 400 mAh at 1C, optionally greater than or equal to about 450 mAh at 1C, optionally greater than or equal to about 500 mAh at 1C, optionally greater than or equal to about 550 mAh at 1C, optionally greater than or equal to about 600 mAh at 1C, optionally greater than or equal to about 650 mAh at 1C, optionally greater than or equal to about 700 mAh at 1C, optionally greater than or equal to about 750 mAh at 1C, optionally greater than or equal to about 800 mAh at 1C, optionally greater than or equal to about 850 mAh at 1C, and in certain aspects, optionally greater than or equal to about 900 mAh at 1C. In certain variations, the electroactive nanocomposite material exhibits a specific capacity to the hard carbon mass (mAh / gHC) of greater than or equal to about 400 mAh or greater than or equal to about 700 mAh at 1C.

[0170] The negative electroactive materials formed in accordance with certain aspects of the present disclosure may be particulates or powder compositions. In certain variations, the electrode may be a porous composite electrode where the electroactive material and optional additional solid components may be mixed with and distributed in a polymeric binder to provide further mechanical integrity to the electrode. Thus, the negative electroactive materials may be intermingled with an optional electrically-conductive material (e.g., electrically-conductive particles that provide an electron conduction path) and a polymeric binder.

[0171] The polymeric binder may hold together the negative electroactive material particles, as well as providing ionic conductivity to the negative electrode 24. Thus, in certain variations, the negative electroactive particles may be optionally intermingled with one or more electrically conductive materials and / or a polymeric binder material as a matrix for the solid-state particles.

[0172] Electrically conductive materials may include, for example, carbon-based materials, nickel powder or other metal particles, or a conductive polymer. Examples of carbon- based particles may include, for example, graphite, acetylene black (such as KETCHEN™black or DENKA™black), graphene, carbon fibers and nanotubes, and the like. Examples of a conductive polymer may include polyaniline, polythiophene, polyacetylene, polypyrrole, and the like. In certain aspects, mixtures of the conductive materials may be used. In certain variations, the additional electrically conductive particulate materials may be carbon-containing materials, like carbon black or graphite.

[0173] The polymeric binder materials may include polyvinylidene difluoride (PVdF), polytetrafluoroethylene (PTFE), polyethylene oxide (PEO), poly(vinyl alcohol) (PVA), ethylene propylene diene monomer (EPDM) rubber, nitrile butadiene rubber (NBR),poly(diallyldimethylammonium chloride) (PDDA), styrene-butadiene rubber (SBR), polychlorotrifluoroethylene, polyamic acid, polyamide, polyimide, polysulfone, carboxymethyl cellulose (CMC), lithium alginate, and / or sodium alginate, polyacrylic acid (PAA), lithium polyacrylate (LiPAA), and / or sodium polyacrylate (NaPAA) binders, by way of example.

[0174] The negative electrode 24 may include greater than or equal to about 50 wt.% to less than or equal to about 95 wt.%, optionally greater than or equal to about 65 wt.% to less than or equal to about 90 wt.%, and in certain aspects, optionally greater than or equal to about 70 wt.% to less than or equal to about 90 wt.% of the electroactive materials. The negative electrode 24 may include greater than or equal to about 0 wt.% to less than or equal to about 25 wt.%, optionally greater than or equal to about 0 wt.% to less than or equal to about 15 wt.%, and in certain aspects, optionally greater than or equal to about 0 wt.% to less than or equal to about 15 wt.% of the one or more electrically conductive additives and greater than or equal to about 0 wt.% to less than or equal to about 20 wt.%, optionally greater than or equal to about 0 wt.% to less than or equal to about 15 wt.%, and in certain aspects, optionally greater than or equal to about 0 wt.% to less than or equal to about 15 wt.% of the one or more binders. In one example, an electroactive material may be present in the negative electrode 24 at about 70 wt.% with about 15 wt.% electrically conductive carbon particles, and about 15 wt.% binder.

[0175] As will be described further herein, the electroactive material layer forming the negative electrode 24 optionally further comprises a liquid electrolyte, a solid-state electrolyte, or combinations thereof.

[0176] The positive electrode 22 includes a positive electroactive material. The positive electrode 22 may be a composite electrode like that described above in the context of the negative electrode 24 that comprises a plurality of electroactive material particles distributed in a polymeric matrix (that may comprise an ionically conductive material), optionally further including electrically conductive particles distributed therein.

[0177] Thus, the positive electrode 22 may be formed from a lithium-based or sodium- based electroactive material that can undergo lithium or sodium cycling (e.g., plating and depleting or intercalation and deintercalation) while functioning as the positive terminal of the battery 20. By way of non-limiting example, the positive electrode 22 may be formed of a positive electroactive material used for a traditional lithium-ion battery that is one of a layered-oxide cathode, a spinel cathode, or a polyanion cathode. For example, such positive electroactive particles may comprise one or more positive electroactive materials selected from the group consisting of: LiMn2O4, LiNixMn1.5O4, LiCoO2, LiNixMnyCo1-x-yO2 (where 0 ≤ x ≤ 1 and 0 ≤ y ≤ 1), LiNixMn1-xO2(where 0 ≤ x ≤ 1), Li1+xMO2(where 0 ≤ x ≤ 1), LiFePO4, LiVPO4,LiV2(PO4)3, Li2FePO4F, Li3Fe3(PO4)4, Li3V2(PO4)F3, LiFeSiO4, NaCoO2, NaNixMnyCo1-x-yO2(where 0 ≤ x ≤ 1 and 0 ≤ y ≤ 1), NaNixMn1-xO2 (where 0 ≤ x ≤ 1), Na1+xMO2 (where 0 ≤ x ≤ 1), NaMn2O4, NaNixMn1.5O4, NaFePO4, NaVPO4, NaV2(PO4)3, Na2FePO4F, Na3Fe3(PO4)4, Na3V2(PO4)F3, NaFeSiO4, and combinations thereof. Like the negative electroactive materials, the positive electroactive materials may be particulates or powder compositions, which may be intermingled with an optional electrically-conductive material (e.g., electrically-conductive particles that provide an electron conduction path) and a polymeric binder in the amounts described above in the context of the negative electrode 24.

[0178] As recognized by those of skill in the art, the electrochemical cell may further comprise a negative current collector in electrical communication with the negative electrode, positive electrode, a positive current collector in electrical communication with the positive electrode, an electrolyte, and an optional separator (in the case that the electrolyte comprises a liquid electrolyte), among other components.

[0179] More specifically, a separator layer 26 may be disposed between the positive electrode 22 and negative electrode 24. The separator layer 26 prevents physical contact and electrically isolates the positive electrode 22 and negative electrode 24 — and further is suitable for conducting ions (e.g., lithium or sodium ions). The separator layer 26 may be a conventional polymeric separator used in lithium-ion or sodium-ion batteries, for example, a polyolefin-based microporous separator. Conventional ion-conducting membranes include those based on polyolefins that are commercially available from Celgard as CELGARDTMseparators. By way of non-limiting example, triple layer CELGARDTMmembranes, those with polypropylene sheets sandwiched between two sheets of polyethylene, are commonly used because they are compatible with current manufacturing requirements of roll-to-roll (R2R) processing.

[0180] Both the positive electrode 22 and the separator layer 26 may be porous or have voids defined therein. The open pores may define a network through each electrode interconnected with open pores defined in the porous separator 26. At least a portion of the pores of the separator layer 26, and optionally of the positive electrode 22 and / or negative electrode 24, are filled with an electrolyte, which may be a liquid electrolyte or a solid-state electrolyte particle, which helps to transport ions therethrough. Where the electrolyte is a solid electrolyte, it may be the polymeric separator layer 26 may be omitted. Where the electrolyte is liquid, it may be imbibed into pores of the separator layer 26.

[0181] In certain aspects, the electrolyte may be a non-aqueous liquid electrolyte solution that includes one or more lithium salts dissolved in an organic solvent or a mixture of organic solvents. In certain aspects, the electrolyte may include a lithium salt dissolved in an organicsolvent or a mixture of organic solvents. For example, a non-limiting list of lithium salts that may be dissolved in an organic solvent to form the non-aqueous liquid electrolyte solution include lithium hexafluorophosphate (LiPF6), lithium iodide (LiI), lithium bromide (LiBr), lithium perchlorate (LiClO4), lithium tetrachloroaluminate (LiAlCl4), lithium thiocyanate (LiSCN), lithium tetrafluoroborate (LiBF4), lithium tetraphenylborate (LiB(C6H5)4), lithium bis(oxalato)borate (LiB(C2O4)2) (LiBOB), lithium difluorooxalatoborate (LiBF2(C2O4)), lithium hexafluoroarsenate (LiAsF6), lithium trifluoromethanesulfonate (LiCF3SO3), lithium bis(trifluoromethane)sulfonylimide (LiN(CF3SO2)2), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and combinations thereof. For example, a non-limiting list of sodium salts that may be dissolved in an organic solvent to form the non- aqueous liquid electrolyte solution include sodium hexafluorophosphate (NaPF6), sodium perchlorate (NaClO4), sodium tetraborate (NaBF4), sodium trifluoromethanesulfonimide (NaTFSI), and combinations thereof.

[0182] These and other similar lithium salts may be dissolved in a variety of non-aqueous aprotic organic solvents, including but not limited to, various alkyl carbonates, aliphatic carboxylic esters, ethers, sulfur compounds, equivalents and combinations thereof. Alternatively, the electrolyte may be replaced with a solid-state electrolyte (not shown) that functions as both an electrolyte and separator 26. The solid-state electrolyte may be disposed between the positive electrode 22 and negative electrode 24. The solid-state electrolyte may be a solid-state inorganic compound or a solid-state polymer electrolyte, including garnets or other similar compounds, such as Li7La3Zr2O12, Li3xLa2 / 3-xTiO3, Li3PO4, Li3N, LiTi2(PO4)3, LiGe2(PO4)3, Li4GeS4, Li10GeP2S12, Li2S-P2S5, Li6PS5Cl, Li6PS5Br, Li6PS5I, Li3OCl, polymers, such as polyacrylonitrile (PAN), polyalkylene oxide (PAO) based polymers, equivalents and combinations thereof.

[0183] A composite electrode may be made by slurry casting, where the electrode active material, such as an electroactive nanocomposite material comprising silicon dioxide and hard carbon prepared in accordance with certain aspects of the present disclosure, is formed into a slurry by combining it with a polymeric binder compound, a liquid, such as a non-aqueous solvent, optionally a plasticizer, and optionally electrically conductive particles. The slurry can be mixed and then cast, for example, by being thinly applied to a substrate (e.g., via a doctor blade). The substrate can be a functional substrate, such as a current collector (such as a foil, metallic grid, or mesh layer) attached to one side of the electrode film. In one variation, heat, radiation, or negative pressure can be applied to evaporate the solvent from the electrode film, leaving a solid residue. The electrode film may be further consolidated, where heat and pressure are applied to the film to sinter and calendar it. In other variations, the film may be air-dried at moderate temperatures. Invariations where the substrate is removable rather than functional, it is removed from the electrode film that is then further laminated to a current collector. With either type of substrate, it may be necessary to extract or remove the remaining plasticizer prior to incorporation into the battery cell.

[0184] In solid-state batteries, the solid-state electrolyte may be solid state particles disposed between solid-state electrodes (positive electrode 22 and negative electrode 24), where the solid-state electrolyte serves as the separator 26 layer that physically separates the respective electrodes and can thus serve as both separator and ionic conductor, so that a distinct conventional polymeric separator is not required. In other variations, the electrolyte may be a non-aqueous liquid electrolyte solution that includes a salt, such as a lithium salt, dissolved in an organic solvent or a mixture of organic solvents.

[0185] A positive electrode current collector 32 may be in electrical communication with the positive electrode 22 and thus positioned adjacent to or near the positive electrode 22. The positive electrode current collector 32 and the positive electroactive layer / positive electrode 22 together may be considered to form a positive electrode assembly. The positive electrode current collector 32 may be formed from aluminum (Al) or any other suitable electrically conductive material known to those of skill in the art.

[0186] Likewise, a negative electrode current collector 34 may be in electrical communication with the negative electrode 24 and thus positioned adjacent to or near the negative electrode 24. The negative current collector 34 may be formed of copper (Cu), nickel (Ni), alloys thereof, or any other suitable electrically conductive material known to those of skill in the art. The positive electrode current collector 32 and the negative electrode current collector 34 move free electrons to and from an external circuit 38 that may include a load device 40. For example, the battery 20 can generate an electric current during discharge when electrochemical reactions occur. The chemical potential difference between the positive electrode 22 and the negative electrode 24 drives electrons produced at the negative electrode 24 through the external circuit 38 towards the positive electrode 22.

[0187] Ions, which are also produced at the negative electrode 24, are concurrently transferred through the separator 26 and electrolyte towards the positive electrode 22. Electric current passing through the external circuit 38 can be harnessed and directed to a device 40 until the reaction in the negative electrode 24 is depleted or completed and the capacity of the battery 20 is diminished. In various aspects, an electrochemical cell incorporating the negative electrodes having the electroactive nanocomposite material comprising silicon dioxide and hard carbon and having a positive electrode cycles lithium ions, sodium ions, or sodium salts, by way of non- limiting example.

[0188] In certain variations according to the present disclosure, the battery 20 may comprise two or more ions selected from a group consisting of: lithium ions, sodium ions, potassium ions, calcium ions, magnesium ions, and combinations thereof. In one aspect, the battery 20 may comprise two or more ions selected from a group consisting of: lithium ions, sodium ions, potassium ions, and combinations thereof.

[0189] The battery 20 may be rechargeable and capable of undergoing reversible electrochemical reactions, where the rechargeable battery can be charged or reenergized by connecting to an external power source (for example, a charging device) to reverse the electrochemical reactions that occur during battery discharge. The connection of the external power source to the battery 20 causes a reaction at the positive electrode 22 to produce electrons and ions. The electrons, which flow back towards the negative electrode 24 through the external circuit 38, and the ions, which move across the electrolyte and / or separator 26 back towards the negative electrode 24 combine at the negative electrode 24 to replenish it for reaction during the next battery discharge cycle. Each discharge and charge event is considered to be a cycle in a rechargeable battery, where ions are cycled between the positive electrode 22 and the negative electrode 24.

[0190] In many of the configurations of the battery 20, each of the negative electrode current collector 34, the negative electrode 24, the separator 26, the electrolyte, the positive electrode 22, and the positive electrode current collector 32 are prepared as thin layers (for example, from several microns to a millimeter or less in thickness) and assembled in layers electrically connected in parallel or series arrangements (e.g., in a stack) to provide greater voltage output, energy, or power as required. The battery 20 may include a variety of other components not shown in FIG. 1, such as gaskets, casings, terminal caps, and any other conventional components or materials that may be situated within the battery 20. The battery 20 can be used to provide electrical energy to a variety of known electrically-powered devices, including by way of non-limiting example, transportation, vehicles, robots, drones, satellites, prosthetic devices, consumer products (e.g., wearable electronics, laptops, mobile devices, cellular phones), power tools, appliances, and the like.

[0191] Various embodiments of the inventive technology can be further understood by the specific examples contained herein. Specific examples are provided for illustrative purposes of how to make and use the compositions, devices, and methods according to the present teachings.

[0192] Examples

[0193] As noted above, when processing bioderived byproducts, it was assumed that hard carbon (HC) was only produced at high temperatures well above 1,000°C, for example, as part ofthe carbothermal reduction process that also generates silicon carbide (SiC), silicon nitride (Si3N4), or silicon oxynitride (Si2N2O). More specifically, it was not believed that hard carbon would be produced in rice hull ash formed coincidentally with the combustion of rice hulls in an oxidizing environment. Thus, no extensive characterization of silica-depleted rice hull ash (SDRHA) carbon, with typical methods of identifying hard carbon (e.g., XPS, Raman FTIR, TEM) had previously been investigated. These forms of analyses were never used to characterize any SDRHAxxpreviously produced.

[0194] As shown in FIGS.2A–2E, a rice hull ash (RHA) having 90 weight % of silica, 10 weight % of carbon and silica-depleted rice hull ash (SDRHA60) having 60 weight % of silica, 40 weight % of carbon are comparatively characterized. FIG.2A shows TGA analysis. Samples were tested at 800°C with a ramp rate of 10°C min-1in the presence of O2(60 mL min-1). FIG. 2B shows an XPS survey scan, measured on a Kratos Axis Ultra system at room temperature under 3.1×10−8Pa using monochromatic Al source (14 kV and 8 mA). FIG.2C shows XRD, acquired with Cu-Kα radiation (k = 0.154 nm). FIG.2D shows SEM images of each RHA and SDRHA60respectively. FIG.2E shows N2 adsorption-desorption isothermal plots and pore size distribution (inset) of RHA and SDRHA60. Samples were degassed at 300 °C / 6 h prior to analyses by N2 physisorption at -196 °C (77 K). BET method using 10 data multipoint with relative pressures of 0.05-1 was applied. The pore volume was calculated based on the Barret–Joyner–Halenda (BJH) model. These previously-published analyses in “Adjusting SiO2 : C mole ratios in rice hull ash (RHA) to control carbothermal reduction to nanostructured SiC, Si3N4or Si2N2O composites” do not identify hard carbon (HC) as the coproduct of the generation of RHA rather than one that arises from high temperature treatment, like carbothermal reduction, of SDRHA.

[0195] FIGS.3A–3B show XRD and N2 adsorption-desorption isothermal plots of RHA having 90 weight % of silica, 10 weight % of carbon and SDRHA40–65having silica ranging from 40 to 65 weight % of silica and correspondingly 60 to 35 weight % of carbon. As can be seen, the quantity absorbed and thus surface area is greater as the amount of silica decreases in the silica- depleted rice hull ash. BET analysis are the same and standard using nitrogen.

[0196] FIGS. 4A–4B show XPS in a wide scan and C 1s spectra of graphite and hard carbon compared with SDRHA40–65 having silica ranging from 40 to 65 weight % of silica and correspondingly 60 to 35 weight % of carbon. FIGS.4A and 4B present deconvolution peak fitting of SDRHA40-60, commercial graphite and hard carbon C 1 spectra. C 1s spectra of graphitic carbon are characterized by an asymmetric peak at a binding energy typically reported as 284.5 eV and a characteristic π-π* shake-up structure centered at approximately 291 eV. In contrast, HC and the SDRHA40-60samples C 1s spectra show broad, predominantly C-C / C=C sp2peaks at 284.8 eVwith C-H / C=C sp3peaks at 285–285.5 eV without asymmetry, as expected for disordered and defective carbon. Peaks at 286-287 eV, 287.5-288.5 eV, and 288.5-290 eV are ascribed to C-O- C / C-OH, C=O, and O-C=O bonds, respectively.

[0197] The symmetric C-H / C=C sp3peaks of SDRHA40-60are broader and stronger than the commercial HC, indicating more defect structures and C-O species. Meanwhile, the C-O peaks shift towards high-bond energies (BEs) with higher carbon contents in SDRHA, suggesting stronger C-O bonding in samples where more SiO2has been extracted (SDRHA40). This is not unexpected given that much higher surface areas are found for these samples per Table 1. Table 1. SDRHAxx specific surface areas and Raman D:G (D band: G band) ratios

[0198] Overall, SDRHA40-60XPS results suggest more disordered and defective carbon than commercial HC, but still analyze as hard carbon (HC). The more evident C-O bonding in SDRHA is expected given the high specific surface areas (SSAs) and presence of nano silica (SiO2). To further understand the ordered / disordered structures in SDRHA carbon (compared to widely defined hard and soft carbon), Raman spectroscopy (FIG.4B) is especially useful. Raman identifies two peaks 1580 (G band) and 1340 cm-1(D band). The ratio of D:G band intensities (ID / IG) is a common parameter to estimate structural order. A low ID / IG value suggests higher graphitization (Table 1), see also FIG.5.

[0199] To further understand the ordered / disordered structures in SDRHA carbon (compared to widely defined hard carbon and soft carbon, both amorphous), Raman spectra of SDRHA40,50,60, carbon – hard carbon (C-HC), and carbon-graphitic (C-G) were collected using a Bruker Bravo spectrometer with a 532 nm excitement laser to understand the structural defects and degree of graphitization. The spectra over the 1000-1800 cm−1region with baseline correction in FIGS.4A and 4B all exhibit two major feature peaks: the G-band and the D-band.

[0200] The G-band appears at approximately 1580 cm-1and is associated with the in-plane bending motion of sp2carbon configurations, representing graphitic carbon. The G-band is sharp in C-G given its high degree of crystallinity. In comparison, this band broadens in the C-HC and SDRHA40,50,60samples, indicating increased disorder. Meanwhile, the disorder-induced D-band is located at approximately 1340 cm-1, arising from a ring breathing mode for doubly bonded carbon atoms. In principle, the D-band first increases with the disorder then decreases and overlaps with other bands until it nearly disappears in highly amorphous carbon samples.

[0201] The ratio of D-band and G-band intensities (ID / IG) is a commonly adopted parameter to estimate the level of structural order. A low ID / IG value suggests a higher graphitization degree; a high ID / IGmaterial has more disorder and defects in its structure. Accordingly, the D-band and G-band were fitted with Voigt shape peaks, area for each was used to calculate the ID / IG due to the broadened nature of band and width changes. As compared in FIG. 5 and Table 1, the ID / IG ratios of SDRHA40, 50, 60 (ID / IG of about 0.6) are relatively higher than C- HC (ID / IGof about 0.5). Nonetheless, the measured D-band and ID / IGratios are close to the C-HC sample indicating the presence of ordered graphitic structures in SDRHA40,50,60.

[0202] Another useful but indirect analytical method is electrochemical capacity. FIGS. 6A–6B compares SDRHA40-60versus hard carbon (C-HC) tested in typical lithium half cells. The electrodes were prepared with 80 wt. % SDRHA40-60 or C-HC, 5 wt. % C65, and 15 wt. % poly(vinylidene fluoride) (PVDF) binder (5 wt. % solution in NMP) using a speed mixer. The uniform slurries were then coated onto a copper foil (16 μm thick) using a 150 μm gap die at a controlled speed of 50^mm / s. After drying at 80 °C / vacuum / 2 h, it was punched into 18 mm electrodes. Half-cells were assembled with the SDRHA and commercial material electrodes, with lithium (Li) metal used as the counter electrode in the format of 2023 coin cells. The metallic Li (16 mm) was scraped to remove the oxide layer and expose a clean surface before cell assembly. CELGARD 2400™ (19 mm) was used as a separator and 1.2 M LiPF6 in EC:DMC (3:7weight ratio) as the electrolyte. FIG.6A shows voltage profiles of SDRHA60, while FIG.6B shows carbon in hard carbon form (C-HC) for 3 cycles at C / 10. It has been reported that the discharge potential profile for HC through its characteristic sloping lithiation starts at a potential greater than 1 V versus Li / Li+without clear plateaus. The disordered carbon layers (e.g., disorderly-stacked carbon layers) have higher interplanar spacings eliminating staging transitions as seen in graphite. The disordered nature provides additional pore volume that can be filled by Li+(or Na+) providing additional capacity as an electroactive material. Thus, SDRHA lithiation or sodiation (not shown) also suggests C-HC-like Li+electrochemical behavior indicative of the presence of HC in the SDRHA.

[0203] SDRHA60in FIG.6A shows higher slope shapes at greater than 1 V compared to C-HC in FIG.6B, indicating more capacitive contribution in the total capacities, consistent with previous CV results.

[0204] Impedance spectroscopic measurements were conducted after the above 3 cycles at C / 10. The semi-circles shown in the FIG.7A Nyquist plots at less than about 10 Hz are assigned to RSEI. The higher RSEI in SDRHA60 (44 Ω) suggests a thicker SEI formed than the C-HC (29 Ω), resulting from the high surface areas. In accordance with various aspects of the present disclosure, this may be eliminated or greatly reduced by heating SDRHA at low temperatures in an oxygen-free or inert environment, for example, between approximately 200° and 800 °C, to reduce the surface oxygenates, as such species have been found to interfere with lithiation under some conditions.

[0205] FIGS.7A–7B show Nyquist plots (FIG.7A) and rate cycling capabilities (FIG.7B) of SDRHA 40,50,60 and C-HC half-cells. Specific capacities are normalized to carbon contents in each sample. FIG. 7B compares rate capabilities of SDRHA40, 50, 60, and C-HC half-cells after 3 cycles at C / 10. The discharge capacities for SDRHA60 are 360, 290, 225, 192, 170, and 130 mAh / gcarbon after 10 cycles at C / 2, 1C, 2C, 3C, 4C, 5C, respectively (1C = 300 mAh is used for both SDRHA60and C-HC). The discharge capacities for SDRHA50are 405, 330, 280, 250, 220, and 210 mAh / gcarbon after 10 cycles at C / 2, 1C, 2C, 3C, 4C, 5C, respectively (1C = 300 mAh). Again, only carbon mass (50 wt. % of the active material loadings) was used to calculate the specific capacities. For the SDRHA40, rate capability tests show that at 1C, 2C, 3C, 4C, and 5C, SDRHA40shows 340, 280, 240, 220, and 200 mAh / gcarbon, respectively.

[0206] As summarized in Table 2, SDRHA50 appears to deliver the highest capacities at all C rates based on testing conducted.

[0207] Table 2. Comparison of specific capacities of SDRHA40, 50, 60and HC at different C rates.

[0208] Using the above results, volumetric and specific energy and power densities for SDRHA40,50,60 and C-HC were assessed by Ragone plots in FIGS.8A–8B. C-HC generally showshigher volumetric energy / power regions (FIG. 8A) while SDRHA samples exceed this performance when evaluated solely by carbon content (FIG. 8B). These observations are as expected due to the porous structures and, consequently, lower SDRHA densities. It is also worth noting that the loadings on SDRHA40,50electrodes are lower than for SDRHA60and HC. This could also affect the cycling results, especially for rate capabilities and the calculated energy / power densities.

[0209] The C-HC sample shows 160, 140, 130, 120, and 110 mAh / g at C / 2, 1C, 2C, 3C, 4C, and 5C, respectively. On returning to C / 10 the capacities of SDRHA60 returns to 480-500 mAh / g whereas the HC material rises only to 230 mAh / g. It should be noted that only carbon mass was used to calculate the specific capacities, which represent 40 wt. % of the total loading on the electrodes.

[0210] After cycling for 60 cycles one SDRHA60 cell and one HC cell were removed from cycling, taken into a glovebox, decrimped, washed to remove electrolyte and dried to for XPS studies with the following results shown in FIG 9. The significant peaks in FIG. 9 at 284.8 eV, 532.8 eV, 103.8 eV, and 687 eV are assigned to C 1s, O 1s, Si 2p, and F 1s, respectively. Core peaks Li 1s and P 2p centered at 54.8 and 132.8 eV, respectively, ascribing to the LiPF6 electrolyte salt formed SEI on the electrode. The F peak is ascribed to the PVDF binder in addition to the electrolyte decomposition.

[0211] Deconvolution of the C 1s core scans reveals peaks at 284.8 eV, 285.2 eV, and 287.1 eV that are attributed to sp2-hybridized C–C / C-H bonding, C-O, and C=O, respectively, in both cycled SDRHA60and hard carbon electrodes. Meanwhile, -CH2- and -CF2- species in PVDF also contribute to the peaks at approximately 286.2 eV and approximately 288.5 eV in both electrodes. The HC sample shows additional peaks at approximately 290.2 eV and approximately 283.5 eV, for both Li2CO3and lithiated carbon C-Li. The latter signal is not seen in SDRHA60.

[0212] The O 1s XPS core-level spectra of cycled SDRHA60 electrodes show a main peak at approximately 533.3 eV attributed to O in Si-O-Si bonds. Another dominant peak at approximately 531.8 eV is attributed to overlapping LixSiOy, (Li)-C-O, and P-O bonding. The weaker peak at approximately 533.4 eV is assigned to Si-O, C-O, and C=O bonding. In comparison, the hard carbon electrode shows a more intense peak at 534.6 eV originating from Li2CO3, consistent with the above C 1s results.

[0213] The main peak fitted in Si 2p spectra for cycled SDRHA60electrodes peak is ascribed to Si-O-Si bonds at 102.3 eV, while a small peak at approximately 104.6 eV is probably associated with Si-O-C bonds, where both Si are in a +4 valence state. Meanwhile, the appearance of an additional peak at lower binding energies of approximately 101 eV indicates lower valencestates. This observation agrees with the lithiation of some SiO anodes previously reported, likely due to the formation of silicates. It should be noted that Si0(approximately 99 eV) and LixSi (approximately 96 eV) typically show peaks at lower energy ranges and are not observed in the Si 2p spectra for cycled SDRHA60.

[0214] Further examples forming silica-depleted bioderived rice hull ash byproduct (SDRHAxx) are provided herein.

[0215] In this example, the silica-depleted bioderived rice hull ash byproduct (SDRHAxx) is prepared by a silicon dioxide removal reaction using hexylene glycol (HG).

[0216] First, the rice hull ash (RHA) is prepared as follows. As-received rice hull ash is weighed out to 200 g. A solution having 3.7 wt.% HCl is prepared by combining 200 mL of 37% HCl diluted in 1800 mL DI water. Then, the 3.7 wt. % HCl solution is mixed with 200 g (or more) raw rice hull ash in 2 L bottle, with 200 g of milling media (Yttria stabilized zirconia, 3 mm dia. spheres). The RHA is milled for 48 hours. To recover RHA, suction filtration through a Buchner funnel is used. Some RHA will pass through filter paper, but this can be recovered by filtering again or centrifugation. The recovered RHA is then boiled with 1L DI water in a 2 L glass flask equipped with a stir bar and a reflux condenser. The suspension is boiled for 3 days before separation by filtration through a Buchner funnel. Boiling and filtering is repeated until the pH of the filtrate reaches target value, for example, typically 7. Thereafter, the RHA is dried at 80 °C in a vacuum oven overnight and stored as the clean RHA for further use.

[0217] Next, a mixture of 1 L hexylene glycol (HG) and 16.8 g KOH (300 mmol) is prepared by first heating to 190 °C in a 3L three-neck flask equipped with a stir bar and distillation setup (under N2 is desirable) to distill off water for at least 3 hours. Dried RHA powder (approximately 200 or 300 g) is added to the HG and KOH solution. The mixture is heated to 200°C and a first 100 mL HG is distilled off, another 100 mL HG (equal vol) is then added and the process repeated until 1 L HG has distilled out coincident with water during silica depolymerization.

[0218] After approximately four weeks, 40–50 wt.% of the silica is extracted as spirosiloxane from the rice hull ash to form silica-depleted bioderived rice hull ash byproduct (SDRHAxx). Spirosiloxane is recovered by using a separatory funnel to mix the distillate thoroughly with hexane and DI water (equal vol of the distillate), and let it stand for stratification. The upper clear liquid is the product of spirosiloxane dissolved in hexane. Hexane was evaporated by vacuum rotary evaporation at 80°C and white crystals were precipitated after standing for 24 hours.

[0219] The silica removal / dissolution progress is checked each week, as follows to determine the extent of reaction. A 2 mL of mixture is pipetted from the reaction flask, then transfer it into a glass tube, where the sample is washed with hexane and methanol 3 times each. Hexane / methanol is added into the tube and fully mixed with SDRHA and the solvent. The mixture is centrifuged for 3 minutes permitting the SDRHA to settle to the bottom. The solvent is removed and then added again. After that, the SDRHA is boiled in DI water 2-3 times, and the pH of the upper layer of DI water is checked. Next, a TGA test is conducted from room temperature (RT - approximately 21°C) 800oC in air, and the mass loss corresponds to the carbon content of SDRHAxx.

[0220] The reaction is then stopped and then the flask is allowed to cool down. A suction filter, using hexane first and then methanol, is used to wash the filter cake. The filter cake of silica-depleted bioderived rice hull ash byproduct (SDRHAxx) is recovered and transferred into a 2 L flask, where 1 L of DI water is added.

[0221] Reflux at 100oC for 2 to 5 days (according to experience, longer time should reduce the pH more efficiently). Next, the material may be filtered and a pH of the filtrate is determined (e.g., pH of approximately 12). A filter cake may be recovered and transferred to a 2 L flask, where 1 L DI water is added. Reflux at 100oC for 2 to 5 days may then be conducted (according to experience, a longer time should reduce the pH more efficiently). Next, a pH of the filtrate is determined again, which may be a pH of approximately 10 to 9. If the pH of the filtrate is about 9, the filter cake may be collected. Next, the powder is dried in a vacuum oven at 80oC. A mass of the SDRHAxx generated is measured and product stored in vials.

[0222] Table 3. Specific capacities for SDRHAxx coin cells.Ref. [1]: Yu, M.; Wang, M.; Indris, S.; Manassa, J.; Stangel, A.; Hovden, R.; Laine, R. M. An Unexpected Source of Hard Carbon, Rice Hull Ash, Provides Unexpected Li⁺ Storage Capacities.Adv. Sustainable Syst. 2024, 9 (2), 2400667. https: / / doi.org / 10.1002 / adsu.202400667, the relevant portions of which are incorporated herein by reference. a) Only carbon mass used to calculate specific capacities

[0223] In this example, the silica-depleted bioderived rice hull ash byproduct (SDRHAxx) (where xx represents an amount of silica remaining in the SDRHA) is prepared by a silicon dioxide removal reaction using a strong base, such as tetramethyl ammonium hydroxide (TMAOH).

[0224] First, the rice hull ash (RHA) is prepared as follows. As-received rice hull ash is weighed out to 200 g. A solution having 3.7 wt.% HCl is prepared by combining 200 mL of 37% HCl diluted in 1800 mL DI water. Then, the 3.7 wt. % HCl solution is mixed with 200 g (or more) raw rice hull ash in 2 L bottle, with 200 g of milling media (Yttria stabilized zirconia, 3 mm dia. spheres). The RHA is milled for 48 hours. To recover RHA, suction filtration through a Buchner funnel is used. Some RHA will pass through filter paper, but this can be recovered by filtering again or centrifugation. The recovered RHA is then boiled with 1L DI water in a 2 L glass flask equipped with a stir bar and a reflux condenser. The suspension is boiled for 3 days before separation by filtration through a Buchner funnel. Boiling and filtering is repeated until the pH of the filtrate reaches target value, for example, typically 7. Thereafter, the RHA is dried at 80 °C in a vacuum oven overnight and stored as the clean RHA for further use.

[0225] To remove silicon dioxide, clean RHA (50 g) is mixed with TMAOH (400 mL, 25% solution in methanol) using a magnetic stir bar in a round bottom flask. A condenser is placed over the round bottom flask. The mixture is then refluxed at 80oC. The reaction pH and ceramic yield are then monitored.

[0226] The silica removal / dissolution progress is checked each week, as follows to determine the extent of reaction. A 2 mL of mixture is pipetted from the reaction flask, then transferred into a glass tube, where the sample is washed with methanol 5 times each. Methanol is added into the tube and fully mixed with SDRHA and the solvent. The mixture is centrifuged for 3 to 5 minutes permitting the SDRHA to settle to the bottom. The solvent is removed and then the process is repeated 4 more times. The SDRHA is collected and dried.

[0227] Next, a TGA test is conducted from room temperature (RT - approximately 21°C) 800oC in air, and the mass loss corresponds to the carbon content of SDRHAxx.

[0228] The reaction is then stopped when the target product is obtained (desired amount of silica removal) and then the flask is allowed to cool down. A suction filter, using methanol, is used to wash the filter cake several times. The filter cake of silica-depleted bioderived rice hull ash byproduct (SDRHAxx) is recovered and transferred into a 1 L flask, where 500 mL of DI water is added.

[0229] Reflux occurs at 100oC for 2 to 5 days. Next, the material may be suction filtered and a pH of the filtrate is determined (e.g., pH of approximately 12). A filter cake may be recovered and transferred to a 1L flask, where 500 mL DI water is added. Reflux at 100oC for 2 to 5 days may then be conducted. Next, a pH of the filtrate is determined again, which may be at a target pH. If the pH of the filtrate is about 7, the filter cake may be collected. Next, the powder is dried in a vacuum oven at 80oC. A mass of the SDRHAxx generated is measured and product stored in vials.

[0230] FIG. 21 shows an SDRHA55 made by using TMAOH during silicon dioxide removal, where 200 to 300 nm oblong carbon nanoparticles are formed with groups of approximately 10 to 40 spherical particles having 10 to 20 nm diameters.

[0231] Sodium-Ion Battery (NIB) Cell Design

[0232] Half-cells utilized for sodium ion batteries (NIBs) are prepared as follows. Unless noted otherwise, the following applies to all NIB coin half-cells fabricated and tested, as discussed herein.

[0233] Coin cells are fabricated within a glove box, comprised of a standard CR2032 button cell chassis (top and bottom); a spring; a sodium metal chip placed flush against an aluminum spacer serving as a counter electrode; a CELGARDTMseparator punched to a diameter of 19 mm; and an 18 mm diameter anode electrode comprised of various types of SDRHAxx (silica depleted rice hull ash, content denoted as subscript “xx”) coated onto a foil current collector.

[0234] Copper has been used as the current collector foil for all NIB electrodes, driven primarily by a desire to share electrodes between both LIB (lithium-ion battery) and NIB half- cells, as necessary. Slurries created and calendared onto the electrodes share the same materials and process. Each slurry is an 80:5:15 wt. ratio of anode active material (SDRHA):Conductive Material (C65 Carbon Black):Binder (PVDF), dissolved with sufficient NMP solvent to reach a consistent, honey-like viscosity prior to coating.

[0235] The electrolyte used is sodium hexafluorophosphate, NaPF6, in a solvent blend of ethylene carbonate (EC): diethyl carbonate (DEC): ethyl methyl carbonate (EMC) 2:2:6 + 10% wt. fluorinated ethylene carbonate (FEC). This electrolyte is prepared manually within a glovebox in about 1 mL batches as needed. The electrolyte is stored in a sealed glass vial within the glovebox on a stir plate to prevent separation, wrapped in foil to block light induced degradation until use.

[0236] Half-Cell Performance

[0237] Coin half-cells are evaluated through a standard test template that is only adjusted to a desired voltage maximum, and to reflect the appropriate theoretical C-rates indicative of the theoretical capacities of each of cell. Initial testing was conducted with an upper voltage limit of 2.5 V, but after some experimentation to 3.0 V and finding that many healthy half-cells exhibited Open Current Voltages (OCVs) more than 2.5 V prior to formation, all further NIB half cells were tested under a voltage window of 0 to 3.0 V.

[0238] Coin cells move through testing in four main phases.

[0239] In a first formation phase, formation protocols for all half-cells includes three cycles of constant current (CC) C / 10 charge and discharge, with the charge step including a constant voltage (CV) C / 20 taper at the maximum voltage. First and second cycle capacities are captured and recorded to calculate the Initial Coulombic Efficiency of each half cell.

[0240] In a second phase, potentio-electrochemical impedance spectroscopy (PEIS) testing is conducted in a 10 kHz to 10 mHz frequency range, averaging 2 measurements per frequency and over 6 points per decade. This testing is conducted immediately after formation to quantify the beginning of life (BOL) resistance and impedance characteristics of the cell.

[0241] In a third phase, rate capability testing is a walk of increasing C-rates, starting at C / 2 and moving to 1C through 5C at 1C increments. Specific Charge and Discharge capacities are recorded over ten cycles at each C-rate, and each charge cycle includes a CV C / 20 taper at Vmax.

[0242] In a fourth and final stage of testing, static cycle life evaluation is conducted, in which the half-cell is simply allowed to cycle between its voltage limits at a CC-C / 10 rate, also with a CV-C / 20 taper at Vmax during the charge step. This cycling characterizes the aging behavior of the cell and the stability of its capacity. The cell is allowed to cycle for up to 500 cycles or until it reaches its end-of-life (EOL) capacity, which is defined as approximately 70% of its original capacity. Occasionally, some cell were removed before satisfying either of those conditions at the discretion of the tester.

[0243] NIB testing conducted has been done through a loose design-of-experiment structure aimed at exploring the impact of different properties of the SDRHAxx anode material on the overall NIB half-cell performance. Error! Reference source not found., below, summarizes t he build of all NIB half-cells. All materials should have the same structure: SDRHAXX-Derivation-pH-Heat Treat-ID.

[0244] Thus, the materials denote SDRHAXX (where xx represents an amount of silica remaining in the SDRHA) and method of formation (derivation, for example, silica removal with TMAOH, HG, and / or KOH / NaOH). Derivation indicates if the material was produced usinghexylene glycol (HG) / tetramethylammonium hydroxide (TMAOH) (Denoted TMAOH), HG / KOH (Denoted HG), or HG / NaOH (Denoted as HG / NaOH). Where pH is designated, it was controlled to be a basic pH of about 9, otherwise, the pH was neutral (7). Heat Treat indicates the temperature at which heat treatment in nitrogen atmosphere was conducted. If not listed, no heat treatment was performed. Finally, the ID is an alphanumeric designation to distinguish cells having the same material from one another. Coin cells were produced in batches of three to demonstrate reproducibility and minimize risk of outlier half-cells skewing the data.

[0245] Table 4. Sodium-Ion Battery (NIB) Half-Cell Properties.

[0246] With the exception of Cells C1, C2, C4, and C5, all other cells were cycled to an upper voltage limit of 3.0 V. Note that despite very similar total electrode mass values(approximately 30 mg), the theoretical capacity increases with decreasing residual silica content. This is due to the assumption that a greater mass fraction (or higher SSA) of the carbon is accessible in the anode, and that any residual silica provides no capacity benefits, which likely results in an underestimation of the true theoretical capacity of these anode electrodes.

[0247] For ease of comparison, the above cells are condensed and averaged in their performance and behavior by their build group. The formation results of these groups can be reviewed in Error! Reference source not found., below, which highlights the average first and s econd cycle specific discharge capacities for each cell group.

[0248] Table 5. NIB Half-Cell Average 1st and 2nd Cycle Specific Discharge Capacities at 3.0V by Group.

[0249] Major takeaways from this data in Table 5 suggest that initial capacity loosely correlates with decreasing residual silica content, which can be attributed to the greater porosity (SSAs) in the SDRHA material providing ample surface area for SEI formation and ion storage / transfer. Initial coulombic efficiencies across all half-cell permutations are low, averaging about 24% for the entire population. This appears to be largely independent of any of the factors tested and more an intrinsic behavior resulting from the compatibility with the selected electrolyte formulation.

[0250] In FIG.10, the results of PEIS testing for the eight permutations are averaged and plotted to show relative performance. Internal resistances within the NIB half-cells are large, witheven the lowest resistance cells still exhibiting charge-transfer and capacitance resistance in excess of hundreds of ohms. Solution resistance is consistent, although also high at approximately 40 ohm average, across all cells, which is to be expected as all 24 cells tested used an identical electrolyte formulation and amount. Again, there appears to be a correlation between the residual silica content of the SDRHA powder and decreasing resistance within the cell. However, given the comparative size of the resistances reported compared to LIB systems, and the high amount of solution resistance present, electrolyte optimization may be the best source of reduction in cell internal resistance.

[0251] A comparison of rate capability amongst the half-cell population in FIG.11 shows a bias towards TMAOH-derived SDRHA samples in terms of advantageous performance. Despite the lowest overall cell resistance per PEIS measurements, the HG-25 batch of cells have by far the lowest rate capability of the samples, especially beyond 2C rates.

[0252] Finally, a comparison of the status-to-date of C / 10 static cycle life testing can be reviewed in FIG. 12. An obvious behavior across most of the NIB cell groups is a fairly sharp decline in specific capacity over the first 50 cycles of C / 10 charge / discharge, which is only not present in the heat-treated samples and the untreated HG-50 batch of cells. Moreover, the initial C / 10 capacity across all cell groups tends to cluster in the 130 to 180 mAh / g range, and has a slight negative relationship with decreasing silica content. It is important to note that the Static Cycle life testing is conducted after cells have finished Rate Capability testing, and so any damage a cell may have sustained under the high C-rates would likely negatively impact the C / 10 performance.

[0253] Effects of SDRHA Derivation Species

[0254] Two chemical species have proven to be particularly effective for the process of producing SDRHA, namely depleting silicon dioxide content – Hexylene Glycol (HG), and Tetramethyl Ammonium Hydroxide (TMAOH). In LIB systems, HG derived SDRHA has provided extremely promising results, so much focus has been on investigating SDRHA materials derived using HG. Table 6 summarizes the average first and second capacities of two batches of three cells each, as well as their corresponding Initial Coulombic Efficiency (ICE).

[0255] Table 6. Average Initial NIB Capacity Characteristics of HG and TMOAH derived SDRHA Half-Cells.

[0256] Though there is some noise due to the differing silica content (40 % versus 50%) between the two batches of cells, TMAOH-derived SDRHA appears to produce greater initial capacities for sodium ion batteries (NIB) compared to HG-derived SDRHA. The ICE of HG- derived material is slightly greater, with an average of 26% versus the average 21% ICE of TMAOH, although the 31% greater initial capacity results in TMAOH having greater 2nd cycle capacity despite the lower efficiency.

[0257] A simple comparison of cell resistance in the PEIS results plotted in FIG.13 show a clear advantage for TMAOH-derived SDRHA species, with a 40% lower overall resistance. Granted, cell resistances calculated here are still high, but TMAOH seems to provide a distinct improvement towards cell performance.

[0258] In FIG.14A, the rate capabilities of HG and TMAOH cells are provided. TMAOH- 40 outperforms HG-50 across all C-rates, with an 80% greater capacity at C / 2 (+75 mAh / g), and doubling the capacity at 5C (+15 mAh / g). At C / 10, TMAOH-40 reported the greatest average specific capacity of all cells tested at approximately 230 mAh / g, a full 75 mAh / g greater than HG- 50. However, as can be seen in FIG.14B, TMAOH lacked stability, and within 100 cycles rapidly decayed to just 40% of its initial capacity. HG-50, however, has shown an almost linear decay, reaching end-of-life (EOL) 70% capacity in just 150 cycles and 40% capacity at 300 cycles.

[0259] Effects of pH on SDRHA

[0260] Under normal circumstances, in certain variations, silica is removed through reaction with HG / TMAOH and a base, typically KOH, and then washed to neutralize the pH. SDRHA50was synthesized using HG and NaOH as an alternative base, and then the washing step was forgone resulting in a basic final product of approximately pH of 9. Table 7 compares formation data for the two batches.

[0261] Table 7. Average Initial Capacity Characteristics of neutral and pH9 HG-50 Half- Cells.

[0262] Though there is some noise due to the differing silica content (40 versus 50%) between the two batches of cells, TMAOH-derived SDRHA appears to produce greater initial capacities for NIB compared to HG-derived SDRHA. The ICE of HG-derived material is slightly greater, with an average of 26% versus the average 21% ICE of TMAOH, although the 31%greater initial capacity results in TMAOH having greater 2nd cycle capacity despite the lower efficiency.

[0263] Average resistance information collected from PEIS assessment in FIG.15 shows very small changes in average cell resistance, with the more basic HG-50-pH9 batch having a slightly greater overall charge transfer resistance by approximately 100 Ohms. This would suggest that the pH of the resulting SDRHA has a very small effect, if any, on the overall compatibility with the electrolyte solution and the resulting SEI that is formed is similar in properties to neutral HG-50.

[0264] Reviewing FIGS.16A–16B, a much starker contrast between the two cell batches can be seen. The basic pH HG-50-pH9 batch demonstrates poor rate capability, particularly at C- rates beyond 2C. Average capability of neutral HG-50 is 20 to 40 mAh / g greater than that of the pH9 batch. Static Cycle life performance is similarly disappointing, with the pH9 samples decaying to approximately 33% of initial capacity within 50 cycles. Based on these results, it appears that the washing step to reduce SDRHA pH to neutral relates to the longevity and ultimate performance of the anode.

[0265] Effects of SDRHA residual silica Content

[0266] In addition to derivation methodology, the impact of the amount of residual silica contained within the SDRHA anode material was investigated. Synthesis methodology remained identical between batches, but the HG-25 SDRHA material was allowed to react for a longer period to reach a lower residual silica content, confirmed via TGA. Initial capacity characteristics are shown in Table 8.

[0267] Table 8. Average Initial Capacity Characteristics of HG-50 and HG-25 SDRHA Half-Cells.

[0268] Reduction of silica content from 50% to 25% has a notable benefit in the form of substantially improved initial capacity, as show in Table 8.While an average of 50% greater than HG-50, the initial capacity of HG-25 is not as well retained as HG-50, with only a 23% ICE. Though this still results with HG-25 having greater average capacity, the extent of the disparity is diminished, at just approximately 40 mAh / g or approximately 30% greater specific capacity.

[0269] FIG. 17 compares average PEIS performance for an HG-50 and HG-25 sodium- ion battery (NIB) battery. The HG-25 sample of cells showed the lowest overall average cell resistance via PEIS, with charge transfer resistance on the order of 350 Ohms, roughly one-third of the average resistance figures reported by HG-50 cells. This could perhaps be attributed to increased pore volume of HG-25, as more of the residual silica is removed, allowing for more facile ion transfer through reduced kinetic bottlenecks.

[0270] Unfortunately, HG-25 cells seem to exhibit very poor rate capability and stability over life as shown in FIGS. 18A–18B. While poor rate capability at high C-rates is somewhat expected of NIBs due to the much larger ion size of Na+, HG-25’s average capability plummets after 1C, and effectively loses capacity beyond 2C. At low C-rates, its capability is slightly lower than what HG-50 shows, which points to a bottleneck in ion movement at high C-rates, perhaps due to Na+ions becoming trapped in the porous structure and unable to deintercalated at increased rates.

[0271] This could also explain HG-25’s life performance, which shows rapid capacity degradation to well below EOL capacities within 100 cycles. It is theorized that perhaps damage to the SEI and anode structure sustained from high C-rate cycling may have compromised the integrity of the anode material in such a way to accelerate its decay once C / 10 cycling began. The storage and release mechanisms for sodium ions appears to very different than lithium ions and this must be understood to design optimized anode materials to support NIB development.

[0272] Effects of Heat Treatment

[0273] TMAOH-40, HG-50-pH9, and HG-25 samples of SDRHA were each subjected to heat treatment at 600-800°C / N2 / 2 hour. This was to explore the impact that the surface morphology and present chemical species has on overall NIB half-cell performance. Confirmed by BET surface area analysis, the heat treatment temperatures have only minimal impact on the overall pore volume of the SDRHA powder, so all impacts should be due to surface-level changes brought on by the heat treatment process.

[0274] Table 9

[0275] As reflected in Table 9, in both the HG-25 and HG-50-pH9 cases, heat treatment at 600°C under N2 enabled gains in initial capacity, 30% and 10% over their base materials, respectively. Of these two, the HG-50-pH9 batch did not retain its capacity after the first cycle, as an ICE of 21% dropped capacity to 147 mAh / g, 32 mAh / g lower than its base equivalent.

[0276] The TMAOH-40 batch was split in two and one heat treated to 600°C and the other to 800°C / N2 / 2 h. Initial capacities dropped with respect to the base material, with TMAOH-40- 600 averaging approximately 70 mAh / g lesser and TMAOH-40-800 averaging approximately 28 mAh / g lesser. However, TMAOH-40-600 exhibited greater ICE than both other samples, which resulted in the greatest 2nd cycle capacity among the group.

[0277] The plotted PEIS results in FIG.19, are grouped to each individual species group. Overall, the heat-treated species saw a rise in overall resistance from the PEIS testing, though it was much less pronounced for HG-25 (approximately 10% increase) than it was for TMAOH-40 (approximately 50% increase). This can perhaps be attributed to the heat treatment removing surface species that would otherwise impede SEI formation or creating altered surface morphology that encourage thicker SEI growth, resulting in increases in charge transfer resistance.

[0278] Once again, the results in FIGS. 20A–20B are grouped according to the base SDRHA species. Overall, heat treatment once again had a largely positive impact on cell performance. Comparing the species groups to one another to begin, TMAOH-40 samples substantially outperform any HG-derived sample across all C-rates and heat treatments. Looking at the HG-50-pH9 results, the heat-treated samples exhibit substantially improved rate capability at 1 to 4C, gaining approximately 15-25 mAh / g under 1C to 3C regions and approximately 5 mAh / g under 4C and 5C regions.

[0279] The HG-25 heat treated samples show very similar behavior to the base material, though with the curve shifted slightly to the right. Gains are made in rate capability at 1C and 2C, as well as in 3C and beyond, although capacities are still low.

[0280] TMAOH-40 samples showed more varied results. The batch treated to 800°C has the worst rate capability of the group, though it is still 14-30 mAh / g greater in specific capacitycompared to the next best performing batch of cells. On average, the TMAOH-40-800 has approximately 10-60 mAh / g reduced capacity compared to the base material, with the greater delta correlating with lower C-rates. The batch treated to 600°C is still outperformed by the base material at low C-rates, but at rates 2C and above, the TMAOH-40-600 shows an improvement in rate capability that widens with increasing C-rate, making it the highest-performing cell at 5C with an average specific capacity of 46 mAh / g.

[0281] Batches are tested at each of various stages of C / 10 static cycle life in sodium-ion batteries, but there are a few notable trends worth discussing. The HG-50-pH9 group of cells appears to have identical behavior, showing sharp capacity fade within just 50 cycles, suggesting that heat treatment alone is not sufficient to address longevity issues native to the HG-50-pH9 material. The TMAOH-40 group, however, has very different behaviors among each batch. The base material shows similar behavior to HG-25 and HG-50-pH9, strong initial capacity that rapidly decays to EOL values (less than about 70% initial capacity) within 100 cycles. Heat treatment of this material to 800°C seems to stabilize it, reducing the initial capacity by approximately 70 mAh / g but substantially reducing the slope of the decay. An inflection point is reached around the 150th cycle, at which point the slope increases sharply and the cell decays to sub-50 mAh / g capacity by cycle 300. TMAOH-40-600, however, has a much flatter curve, having lost only 15% of its average initial capacity by 250 cycles. Assuming this trend continues and extrapolating to 500 cycles, the TMAOH-40-600 batch of cells would hit 70% EOL capacity by its 500th cycle.

[0282] In these examples, a variety of design parameters have been investigated in NIB Half-cells. NIB systems incorporating electroactive materials with silica-depleted bioderived rice hull ash byproduct seem to perform better, across all metrics except impedance, when derived by using TMAOH to remove silica. Further, SDRHA powder that has not been neutralized sufficiently exhibits lower rate and life performance than those that have been neutralized. Additionally, lower residual silica seems to correlate to greater initial capacities and lower impedance, but does not perform nearly as well as higher residual silica SDRHA in terms of rate capability and life. This may be due to changes in porosity of the material rather than a direct interaction of the residual silica itself. Further, heat treatment under nitrogen generates improvements in virtually all areas of NIB half-cell performance, especially in terms of rate capability. Life of NIB cells seems to be positively impacted by heat treatment, but results are inconsistent across species tested, indicating that heat treatment alone may not alone be enough to enable longer life.

[0283] In a further example, SDRHA25was prepared by using hexylene glycol and potassium hydroxide and its cycling performance in coin cells is discussed herein and shown in FIGS.22A–22B.

[0284] In this example, the silica-depleted bioderived rice hull ash byproduct (SDRHAxx) is prepared by a silicon dioxide removal reaction using hexylene glycol (HG) and potassium hydroxide (KOH). The SDRHA25 was made in accordance with the procedures in the examples described above using hexylene glycol and potassium hydroxide. The procedure for processing the rice hull ash (RHA) is the same as described above. The silicon dioxide removal process is the same, except that extraction of silica occurs for approximately 8 weeks, rather than the 4 weeks specified above to result in silica removal such that only 25 % silica remains (to form silica- depleted bioderived rice hull ash byproduct (SDRHA25)). The material is analyzed to have a BET surface area of approximately 530 m2 / g.

[0285] R2032-type coin cells were assembled using anodes formed from SDRHA25, and lithium foil was used as the cathode in an argon-filled glovebox. Three coin cells made from SDRHAxx are cycled on the Biologic Instrument, first at 0.1 C for 3 times (formation), following a PEIS test. The rate capabilities were tested at 0.5 C, 1 C, 2 C, 3 C, 4 C, and 5 C for 10 cycles each, within a voltage range of 0.01 V to 3 V. Meanwhile, the cycling performance is tested at 0.1C for 500 cycles within the same voltage range. The carbon in SDRHAxx (HG) was considered the only active material for the anode, with a theoretical specific capacity of 300 mAh / g.

[0286] Table 10. Specific capacities for SDRHA25pH about 7 (0.01-3V).

[0287] Only carbon mass was used to calculate specific capacities. At the 93rd cycle, the average capacity of SDRHA25 coin cells is about 630 mAh / gcarbon. It shows a decrease in capacity after 85th cycle.

[0288] In a further example, SDRHA60was prepared by using hexylene glycol and potassium hydroxide and its cycling performance in coin cells is discussed herein and shown in FIGS.23A–23B. See also, test results in Table 3. In this example, the silica-depleted bioderived rice hull ash byproduct (SDRHAxx) is prepared by a silicon dioxide removal reaction using hexylene glycol (HG) and potassium hydroxide (KOH) as described above, where the pH at the end of the silica removal process is maintained to a target pH this is basic and around 9. The SDRHA25was made in accordance with the procedures in the examples described above using hexylene glycol and potassium hydroxide. The procedure for processing the rice hull ash (RHA) is the same as described above. The SDRHA60 electroactive material is processed in the same coin cells as described above, where an average of performance in three coin cells is shown. The rate capabilities were tested at 0.5 C, 1 C, 2 C, 3 C, 4 C, and 5 C for 10 cycles each, within a voltage range of 0.01 V to 3 V. Meanwhile, the cycling performance is tested at 0.1C for 100 cycles within the same voltage range. At about the 100th cycle, the average capacity of SDRHA60coin cells is about 1,000 mAh / gcarbon.

[0289] The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.

Claims

CLAIMS What is claimed is:

1. An electrode for an electrochemical cell, the electrode comprising: an electroactive layer comprising an electroactive nanocomposite material comprising silicon dioxide and hard carbon derived from a silica-depleted bioderived byproduct comprising char and ash; and a current collector on which the electroactive layer is disposed or with which the electroactive layer is in electrical contact.

2. The electrode of claim 1, wherein the electroactive nanocomposite material is free of products of heating at greater than or equal to 1,000°C.

3. The electrode of claim 1, wherein the electroactive nanocomposite material is free of silicon, silicon carbide, silicon nitride, silicon oxynitride, and combinations thereof.

4. The electrode of claim 1, wherein the silica-depleted bioderived byproduct comprises a silica depleted rice hull ash product (SDRHA) comprising silicon dioxide at less than or equal to about 65% by weight and hard carbon at greater than or equal to about 35 % by weight.

5. The electrode of claim 1, wherein the silica-depleted bioderived byproduct comprises a silica depleted rice hull ash product (SDRHA) comprising silicon dioxide at greater than or equal to about 40% by weight to less than or equal to about 65% by weight and hard carbon at greater than or equal to about 35 % by weight to less than or equal to about 60% by weight.

6. The electrode of claim 1, wherein the electroactive nanocomposite material has a treated surface to control surface oxygenates and minimize solid electrolyte interface (SEI).

7. The electrode of claim 1, wherein the electroactive nanocomposite material has an average surface area of greater than or equal to about 70 m2 / g (N2).

8. The electrode of claim 1, wherein the electroactive nanocomposite material exhibits a specific capacity to a hard carbon mass of greater than or equal to about 400 mAh / gHC.

9. The electrode of claim 1, wherein the electroactive nanocomposite material exhibits a specific capacity to a hard carbon mass of greater than or equal to about 700 mAh / gHC.

10. The electrode of claim 1, wherein the electroactive nanocomposite material comprises at least one residual ion selected from a group consisting of: potassium ions, sodium ions, lithium ions, and combinations thereof.

11. The electrode of claim 1, wherein the electroactive nanocomposite material defines a plurality of particles distributed into a polymeric matrix comprising a polymeric binder.

12. The electrode of claim 11, further comprising a plurality of electrically conductive particles distributed in the polymeric binder.

13. The electrode of claim 1, where the current collector comprises a metal selected from the group consisting of: copper, nickel, alloys, and combinations thereof.

14. The electrode of claim 1, wherein the electroactive layer further comprises a liquid electrolyte, a solid state electrolyte, or combinations thereof.

15. The electrode of claim 1, wherein the electroactive nanocomposite material comprises a matrix of hard carbon having surface regions at least partially coated with silicon dioxide.

16. An electrochemical cell incorporating the electrode of claim 1 as a negative electrode, wherein the electrochemical cell further comprises a positive electrode and an electrolyte that cycles lithium ions or sodium ions.

17. The electrochemical cell of claim 16, comprising two or more ions selected from a group consisting of: lithium ions, sodium ions, potassium ions, and combinations thereof.

18. A method of making an electroactive nanocomposite material from a bioderived byproduct, the method comprising: removing silicon dioxide from a bioderived byproduct comprising char and ash to form a silica-depleted bioderived byproduct having silicon dioxide at greater than or equal to about 40% by weight to less than or equal to about 65% by weight and hard carbon at greater than or equal to about 35% by weight to less than or equal to about 60% by weight; and treating a surface of the silica-depleted bioderived byproduct in an inert environment to remove surface oxygenates to form an electroactive nanocomposite material comprising silicon dioxide and hard carbon, wherein the method is free of any subsequent treatment at temperatures of greater than or equal to about 1,000°C after the treating.

19. The method of claim 18, further comprising lithiating the electroactive nanocomposite material with lithium ions or sodiating the electroactive material with sodium ions.

20. The method of claim 18, wherein the bioderived byproduct is a rice hull ash and the silica-depleted bioderived byproduct is a silica-depleted rice hull ash.

21. The method of claim 18, wherein the removing silicon dioxide from the bioderived byproduct occurs by a reaction in the presence of a stoichiometric base to form the silica-depleted bioderived byproduct.

22. The method of claim 21, wherein the stoichiometric base comprises tetramethylammonium hydroxide (TMAOH).

23. The method of claim 18, wherein the removing silicon dioxide from a bioderived byproduct occurs by reaction with a hindered diol in the presence of a catalytic base to form the silica-depleted bioderived byproduct.

24. The method of claim 23, wherein the hindered diol is selected from the group consisting of: 2-methyl-2,4-pentanediol, 2,2,4-trimethyl-1,3-pentanediol, and combinations thereof.

25. The method of claim 23, wherein the catalytic base is selected from the group consisting of: sodium hydroxide (NaOH), lithium hydroxide (LiOH), calcium hydroxide Ca(OH)2, potassium hydroxide (KOH), cesium hydroxide (CsOH), rubidium hydroxide (RbOH), and combinations thereof.

26. The method of claim 23, wherein the hindered diol comprises 2-methyl-2,4- pentanediol and the catalytic base is selected from the group consisting of: sodium hydroxide (NaOH), potassium hydroxide (KOH), lithium hydroxide (LiOH), and combinations thereof.

27. The method of claim 18, wherein the treating the surface further comprises heating the silica-depleted bioderived byproduct to a temperature of greater than or equal to about 200°C to less than about 800°C.

28. The method of claim 18, further comprising after the removing silicon dioxide, washing the silica-depleted bioderived byproduct with boiling water.

29. The method of claim 18, further comprising after the removing silicon dioxide and prior to treating the surface of the silica-depleted bioderived byproduct, treating the silica-depleted bioderived product to have a target pH of greater than or equal to 9.

30. The method of claim 29, wherein the silica-depleted bioderived byproduct comprises at least one residual ion selected from a group consisting of: potassium ions, sodium ions, and combinations thereof.

31. The method of claim 18, further comprising prior to the removing silicon dioxide, milling a rice hull ash (RHA) byproduct with an acidic solution to yield a purified rice hull ash (RHA) byproduct.

32. A method of operating an electrochemical cell, the method comprising: cycling lithium ions or sodium ions between a negative electrode and a positive electrode in the electrochemical cell that comprises the negative electrode, the positive electrode, and an electrolyte disposed therebetween, wherein the negative electrode comprises a current collector and an electroactive layer comprising an electroactive nanocomposite material comprising silicon dioxide and hard carbon derived from a silica-depleted bioderived byproduct comprising char and ash.

33. The method of claim 32, wherein the electroactive nanocomposite material has an average surface area of greater than or equal to about 70 m2 / g (N2) and exhibits a specific capacity to a hard carbon mass (mAh / gHC) of greater than or equal to about 400 mAh.

34. The method of claim 32, wherein the electroactive nanocomposite material exhibits a specific capacity to a hard carbon mass (mAh / gHC) of greater than or equal to about 700 mAh.

35. The method of claim 32, wherein the electroactive nanocomposite material comprises at least one residual ion selected from a group consisting of: potassium ions, sodium ions, and combinations thereof.

36. The method of claim 32, wherein the cycling lithium ions or sodium ions further comprises cycling two or more ions selected from a group consisting of: lithium ions, sodium ions, potassium ions, and combinations thereof.

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