Graphene oxide liquid crystal regulated electrode composites for practical areal capacity energy storage and methods of preparing such composites

Abstract

Embodiments relate to graphene composite electrodes and methods of making thereof. The graphene electrode composites are formed from graphene oxide liquid crystal precursors and exhibit a scaffolding structure configured to host electrode active material. The graphene composite electrodes exhibit practical capacity retention, high Coulombic efficiency, and long cycling stability.

Description

GRAPHENE OXIDE LIQUID CRYSTAL REGULATED ELECTRODE COMPOSITES FOR PRACTICAL AREAL CAPACITY ENERGY STORAGE AND METHODS OF PREPARINGSUCH COMPOSITESCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present application claims priority to U.S. Provisional Patent Application No.63 / 519,570, filed on August 15, 2023. The entirety of this provisional patent application is incorporated by reference herein.FIELD

[0002] Embodiments relate to electrode composites and methods of making thereof. In particular, embodiments relate to graphene electrode composites formed from graphene oxide liquid crystal precursors and including a scaffolding structure configured to host electrode active material. In some embodiments, the formed electrode can be an anode or a cathode, for example.BACKGROUND

[0003] The increasing demand of electric vehicles requires high-energy density storage systems. Lithium-ion batteries, in particular, stand out among portable energy storage systems due to their high capacities and energy density. High-capacity anodes such as silicon anodes and other metal oxides are considered as potential candidates for high-performance lithium-ion batteries.However, they suffer from severe volume changes during the charge-discharge process and poor charge transfer properties, thus compromising the battery’s capacity and stability.

[0004] Over the past decade, intensive research on two-dimensional (2D) graphene has led to significant advancements. This single atomic layer of carbon with covalent bonding exhibitsexceptional electronic, thermal, mechanical, and optical characteristics within its 2D planes.Consequently, graphene has found applications in various fields such as high-performance composites, electronics, energy conversion, and storage. However, there are substantial scientific challenges in effectively translating the unique nanoscale features of 2D graphene into practical macroscopic forms.SUMMARY

[0005] Graphene oxide (GO), the oxidized form of graphene, has emerged as a promising precursor for bottom-up assembly into high-performance macroscopic structures. It offers advantages such as easy functionalization, hybridization, and processability due to the presence of oxygen-containing functional groups on the 2D carbon layer. Previous studies have demonstrated the versatility of hydrophilic GO as building blocks, enabling the assembly of various macroscopic forms, including ID fibers, 2D films, and 3D porous frameworks using solution-based approaches. For instance, layer-by-layer assembly of GO films can be achieved through vacuum filtration of dispersed GO in an aqueous solution. This approach improves the packing density and ordering, leading to enhanced electrical and mechanical properties of the graphene film after thermal reduction. Therefore, it may be crucial to regulate the arrangement and orientation in the assembled bulk forms to preserve the unique material properties for practical applications. Achieving controlled assembly of GO into macroscopic structures with tailored properties is essential for unlocking the full potential of graphene-based materials in various applications.

[0006] In a dilute dispersion, GO typically exhibits an isotropic phase. However, by increasing the concentration, GO can undergo a transition from an isotropic colloidal solution to a nematic liquid crystal (LC) phase in water and some polar solvents. In this LC phase, the GO sheets tend to align parallel (nematic ordering) to minimize excluded volume and achieve thermodynamic stability. Consequently, the LC phase enables enhanced alignment of GO sheets in macroscopic assemblies, leading to improved material properties compared to randomly oriented GOs in dilute solutions. The long-range ordered and tailored inter-sheet interactions based on the spontaneous structural alignment of LC domains hold significant promise in enhancing the material properties of self-assembled macroscopic forms using GO LCs.

[0007] The remarkable electrical conductivity, high surface area, good flexibility, and excellent thermal and chemical stability of 2D graphene make solution-processable GO-derived graphene an extensively studied matrix for hosting active electrode materials in high-performance battery electrodes, particularly for high-capacity electrodes like silicon and metal oxides. The assembled graphene network acts as a highly conductive matrix, effectively mitigating volume expansion and contraction during charge and discharge cycles. Significant progress has been made in developing GO / graphene-composite electrodes to address critical issues in lithium-ion batteries (LIBs) and other battery technologies. However, the exploration of favorable properties offered by GO LC phase-regulated structures has received minimal attention. The potential benefits of GO LC-regulated hierarchical structures, such as enhanced alignment, long-range ordering, and tailored inter-sheet interactions, have not been extensively studied in battery community. These structures hold promise for advancing the performance of battery electrodes by effectivelymanaging mechanical stress, improving electron transport pathways, and accommodating large volume changes.

[0008] We have found that GO LCs may enable the self-assembly of a 3D hierarchical structure that serves as a versatile scaffold. Secondary structures within the scaffold consist of graphene / GO sheets arranged in a cellular-like feature, creating a “parent crystal lattice structure.” This arrangement may effectively confine active material, or “secondary phase atoms,” within the graphene scaffold. The resulting artificial “parent crystal lattice” may not only facilitate expedited electron transport pathways due to the high in-plane electrical conductivity of 2D graphene sheets, but may also provide mechanically robust cellular walls in the secondary structure. These walls play a crucial role in mitigating the substantial volume changes experienced by the active material during prolonged charge and discharge cycles.

[0009] In an exemplary embodiment, a method of producing a graphene electrode composite comprises preparing a precursor solution comprising graphene oxide dispersed in a solvent; controlling a concentration of the dispersed graphene oxide to form a graphene oxide liquid crystal solution; mixing at least one nano active material with the graphene oxide liquid crystal solution to form an active material- graphene oxide mixture; and reducing the active materialgraphene oxide mixture to form the graphene electrode composite.

[0010] In some embodiments, the concentration of the dispersed graphene oxide is at least 3 mg mL'1.

[0011] In some embodiments, the concentration of the dispersed graphene oxide is between 4 and 10 mg mL'1.

[0012] In some embodiments, the at least one nano active material comprises a material selected from the group consisting of silicon, metal oxides, and mixtures thereof.

[0013] In some embodiments, the at least one nano active material is between 65 and 75 wt.% of the graphene oxide composite.

[0014] In some embodiments, the method further comprises washing the graphene oxide composite.

[0015] In some embodiments, annealing the graphene oxide composite.

[0016] In an exemplary embodiment, a graphene electrode composite made by a method comprising the steps of preparing a precursor solution comprising graphene oxide dispersed in a solvent; controlling a concentration of the dispersed graphene oxide to form a graphene oxide liquid crystal solution; mixing at least one nano active material with the graphene oxide liquid crystal solution to form an active material- graphene oxide mixture; and reducing the active material-graphene oxide mixture to form the graphene electrode composite.

[0017] In some embodiments, the composite exhibits 100% capacity retention over 200 cycles at a current density of 840 mA g’1.

[0018] In some embodiments, the composite exhibits elastic moduli between 20.5 and 25.6 kPa.

[0019] In some embodiments, the composite exhibits a steady modulus of 8.5 kPa at 150 cycles of repeated compression.

[0020] In some embodiments, the at least one nano active material comprises silicon nanoparticles.

[0021] In some embodiments, the at least one nano active material comprises polyvinylpyrrolidone-coated silicon nanoparticles.

[0022] In some embodiments, the graphene electrode composite comprises a plurality of stacked graphene sheets.

[0023] In some embodiments, the graphene sheets have an average thickness between 0.8 and 1.5 nm.

[0024] In some embodiments, the graphene sheets have an average lateral dimension between 5 and 30 pm.

[0025] In some embodiments, the composite has a high maximum areal capacity of between 4 and 8 mAh cm'2at 0.21 mA cm'2.

[0026] In some embodiments, the composite has an active material mass loading of between 2 and 6 mg cm'2.

[0027] In some embodiments, the composite has a coulombic efficiency of 99.5%.

[0028] In an exemplary embodiment, a graphene electrode composite comprises a graphene scaffold structure formed from a graphene oxide liquid crystal phase precursor, and at least one nano active material hosted within the graphene scaffold structure.

[0029] Further features, aspects, objects, advantages, and possible applications of the present invention will become apparent from a study of the exemplary embodiments and examples described below, in combination with the Figures, and the appended claims.BRIEF DESCRIPTION OF THE FIGURES

[0030] The above and other objects, aspects, features, advantages, and possible applications of the present invention will be more apparent from the following more particular description thereof, presented in conjunction with the following drawings. It should be understood that like reference numbers used in the drawings may identify like components.

[0031] FIG. 1 shows an exemplary method of producing exemplary graphene composites.

[0032] FIG. 2 shows a schematic illustration of exemplary hierarchical structures in graphene composites across multiple length scales.

[0033] FIG. 3 is an optical image of exemplary graphene oxide sheets.

[0034] FIG. 4 is a graph showing lateral size distribution of the exemplary graphene oxide sheets shown in FIG. 3.

[0035] FIG. 5 is a scanning electron microscope (SEM) image of the exemplary graphene oxide sheets shown in FIG. 3.

[0036] FIG. 6 is an atomic force microscopy (AFM) image of the exemplary graphene oxide sheets shown in FIG. 3.

[0037] FIG. 7 shows polarized optical microscopy (POM) observations of exemplary graphene oxide liquid crystal phases under various concentrations of 1,5, 3.0, 6.0, and 10.0 mg ml / 1.

[0038] FIG. 8 shows POM observations of exemplary silicon-graphene oxide composites at various Si concentrations of 50%, 60%, and 80%.

[0039] FIG. 9 is a digital photo of exemplary silicon-graphene oxide mixtures with various graphene oxide concentrations.

[0040] FIG. 10 is a digital photo of exemplary silicon-graphene nanocomposite hydrogels after chemical reduction.

[0041] FIG. 11 is a SEM image of an exemplary silicon-graphene nanocomposite (regulated by 4 mg mL'1graphene-oxide liquid crystals) after thermal annealing at a low magnification.

[0042] FIG. 12 shows SEM images of exemplary silicon-graphene nanocomposites mixing with graphene oxide dispersions at a concentration of 1 mg mL’1.

[0043] FIG. 13 shows SEM images of exemplary silicon-graphene nanocomposites mixing with graphene oxide dispersions at a concentration of 2 mg mL’1.

[0044] FIG. 14 shows SEM images of exemplary silicon-graphene nanocomposites mixing with graphene oxide dispersions at a concentration of 4 mg mL’1.

[0045] FIG. 15 shows SEM images of exemplary silicon-graphene nanocomposites mixing with graphene oxide dispersions at a concentration of 6 mg mL’1.

[0046] FIG. 16 shows SEM images of exemplary silicon-graphene nanocomposites at higher magnifications.

[0047] FIG. 17 shows transmission electron miscopy (TEM) images of exemplary silicon- graphene nanocomposites.

[0048] FIG. 18 is a graph showing x-ray diffraction (XRD) patterns of exemplary silicon- graphene nanocomposites at various graphene oxide concentrations.

[0049] FIG. 19 is a graph showing thermogravimetric analysis (TGA) of exemplary silicon- graphene nanocomposites.

[0050] FIG. 20 is a digital photo demonstrating the compression and recovery of exemplary silicon-graphene composites (4 mg mL"1) at a strain rate of 30 mm min"1to an upper strain limit of 30%.

[0051] FIG. 21 is a graph showing stress-strain curves during cyclic compression to strain 30% at different strain rates of 2, 8, and 30 mm min"1for exemplary silicon-graphene composite electrodes (4 mg ml1).

[0052] FIG. 22 is a graph showing stress-strain curves during cyclic compression to strain 10%, 20%, and 30% at various silicon-graphene composite electrodes at a strain rate of 2 mm min"1.

[0053] FIG. 23 is a graph showing the elastic modulus of exemplary composite electrodes during a cyclic compression process under various strains.

[0054] FIG. 24 is a graph showing the elastic modulus of exemplary silicon-graphene composites (4 mg mL"1) during a cyclic compression process at a strain rate of 20 mm min"1for 150 cycles.

[0055] FIG. 25 is a graph showing the Nyquist plot of exemplary silicon-graphene nanocomposite electrodes in assembled half cells.

[0056] FIG. 26 is a graph showing the cyclic voltammetry (CV) curves of exemplary silicon- graphene nanocomposite electrodes in assembled half cells.

[0057] FIG. 27 is a graph showing the first two charge-discharge cycles of exemplary 4 mg mL"1graphene oxide liquid crystal-regulated silicon-graphene nanocomposite electrodes.

[0058] FIG. 28 is a graph showing the rate of performance of various silicon-graphene composite electrodes with a mass loading of around 4 mg cm"2.

[0059] FIG. 29 is a graph showing the long-term cycling of the silicon-graphene composite electrode 4 mg ml / 1at a mass loading of about 2.5 mg cm’2.

[0060] FIG. 30 is a graph showing N2 adsorption-desorption isotherms of exemplary silicon- graphene nanocomposites using various graphene oxide concentrations of 1, 2, 4, and 6 mg mL’1.

[0061] FIG. 31 is a graph showing the pore size distribution calculated by NLDFT and BJH (inset) methods of exemplary silicon-graphene nanocomposites using various graphene oxide concentrations of 1, 2, 4, and 6 mg mL-1.

[0062] FIG. 32 shows graphs of stress-strain curves during a cyclic compression to strain 30% at different strain rates of 2, 8, and 30 mm min-1for exemplary silicon-graphene composites.

[0063] FIG. 33 is a graph showing stress-strain curves during a cyclic compression to 10%, 20%, and 30% strains of various exemplary silicon-graphene composites at a strain rate of 30 mm min" 1

[0064] FIG. 34 shows graphs of CV curves of exemplary silicon-graphene nanocomposite electrodes prepared from various graphene oxide concentrations of 1, 2, 4, and 6 mg mL-1at scan rates of 0.1, 0.2, and 0.5 mV s’1.DETAILED DESCRIPTION OF THE INVENTION

[0065] The following description is of an embodiment presently contemplated for carrying out the present invention. This description is not to be taken in a limiting sense but is made merely for the purpose of describing the general principles and features of the present invention. The scope of the present invention should be determined with reference to the claims.

[0066] Embodiments relate to graphene electrode composites and methods of making thereof.Methods of preparing the graphene electrode composites may generally comprise forming the composites from a graphene oxide (GO) precursor. In particular, by selectively controlling GO dispersion concentration in a precursor solution, a liquid crystal (LC) phase with long range ordering may be formed. It is contemplated that GO in a LC phase may result in self-assembly of the graphene electrode composites into a defined, three-dimensional scaffolding structure that may load sufficient active materials.

[0067] As seen in FIG. 1, in exemplary embodiments, the method may comprise preparing a GO precursor solution. The precursor solution may be an aqueous solution comprising GO dispersed in a solvent, such as a water-containing solvent, polar solvents, or any other suitable solvent. The GO may be prepared by oxidizing graphite (e.g., graphite flakes). It is contemplated that GO is a carbon-based nanomaterial generally capable of being assembled into various macroscopic forms to create high-performance graphene-based structures.

[0068] The method may further comprise controlling the GO dispersion concentration in the precursor solution to form a GO LC phase. It is contemplated that in dilute dispersions, GO typically exhibits an isotropic phase. However, as the GO dispersion concentration within the solution increases, the solution may undergo a transition from an isotropic phase to a nematic LC phase, resulting in long range ordering of the GO. It is contemplated that other precursors, such as isotropic graphene oxide or reduced graphene oxide precursors, do not exhibit such properties. It is further contemplated that the GO concentration within the solution may be above 3.0 mg mL’1, such as between 4 and 10 mg mL’1, as concentrations in this range adequately results in thestable nematic LC phase. It is contemplated that the critical concentration for the formation of the LC phase is determined by the aspect ratio of GO sheets used according to the Onsager LC theory.

[0069] The method may further comprise mixing at least one nano active material with the GO LC solution to produce an active material-GO mixture. As described in further detail below, the nano active material may include any suitable active material, such as silicon, tin oxide, cobalt (II, III) oxide, sulfur, etc.

[0070] In exemplary embodiments, the method further comprises reducing the active material- GO mixture to produce a (reduced) graphene electrode composite. The active material-GO mixture may be reduced via chemical reduction and / or thermal reduction. For example, the active material-GO mixture may be chemically reduced by adding a reduction agent (e.g., sodium ascorbate) to the mixture. It is contemplated that chemical reduction of GO refers to the process of converting the GO into reduced graphene oxide (rGO) through the removal of oxygen-containing functional groups. Additionally, the active material-GO mixture may be thermally reduced by subjecting the mixture to high temperatures in an inert atmosphere (e.g., argon gas). In preferred embodiments, the active material-GO mixture may first undergo chemical reduction followed by thermal reduction. Such embodiments may further remove the oxygen-containing functional groups remaining after chemical reduction and restore sp2 carbon networks, converting the GO into reduced graphene oxide (rGO). This may occur in a controlled environment, such as a furnace or oven, where the oxygen-containing groups on the GO may bethermally decomposed and reduced, which may lead to the restoration of electrical, thermal, and mechanical properties of the graphene.

[0071] It is contemplated that the nano active material may be around 70+5 wt% of the graphene electrode composites. Accordingly, the composites demonstrate high active material loading.

[0072] In some embodiments, the method may optionally comprise washing the graphene electrode composite. It is contemplated that washing the composite may remove excess compositions from the composite.

[0073] In some embodiments, the method may optionally comprise annealing the graphene electrode composite. It is contemplated that annealing the composite may enhance the electrical conductivity of the graphene.

[0074] As seen in FIG. 2, the graphene electrode composite may have a long-range ordered, three-dimensional scaffold structure. As noted above, by selectively controlling GO dispersion concentration in a precursor solution, a liquid crystal (LC) phase with long range ordering may be formed. Notably, this long range ordering is maintained in the graphene electrode composites themselves. The scaffold structure may be a cellular structure with hierarchical pores ranging from mesopores (2-50 nm) to macropores (5-20 pm) and wall thickness of approximately 4.3 nm corresponding to 13 stacked graphene layers in unit building block, such that the scaffold structure may resemble an artificial parent crystal lattice configured to host and confine active electrode materials.

[0075] It is contemplated that the architecture of graphene electrode composite may facilitate an expedited electron transport pathway due to high in-plane electrical conductivity of the graphene.For example, the composite may demonstrate excellent electrochemical and mechanical cycling stability, exhibiting 100% capacity retention over 200 cycles at a current density of 840 mA g’1. The composite may also facilitate mechanically robust cellular walls within the scaffold structure, which may play a critical role in mitigating substantial volume changes during chargedischarge cycles. The composite may exhibit elastic behavior by reverting to its original shape after compression. For example, the composite may exhibit elastic moduli between 20.5 and 25.6 kPa. Moreover, the composite may demonstrate a steady modulus of 8.5 kPa at 150 cycles of repeated compression.

[0076] The graphene electrode composite may have at least one nano active material loaded within the scaffold structure. In particular, the nano active material may be hosted and confined within the electrode composites via electrostatic interactions, as the graphene and nano active material may be in close proximity. The nano active material may comprise silicon, tin oxide, cobalt (II, III) oxide, sulfur, and mixtures thereof. It is contemplated that the nano active material may be in the form of nanoparticles. In one embodiment, the nano active material may be polyvinylpyrrolidone (PVP)-coated silicon nanoparticles. It is contemplated that the presence of oxygen-containing groups in the GO may facilitate the formation of hydrogen bonds between the GO and the PVP, which contains carbonyl and amino groups. These hydrogen bonds may play an important role in reducing the isotropic-to-nematic transition to a lower GO concentration.

[0077] It is contemplated that the nano active material may be between 65-75 wt. % of the graphene electrode composites.

[0078] It is contemplated that the graphene electrode composites may comprise a plurality of stacked graphene sheets. The graphene sheets may exhibit a wrinkled morphology and have an average thickness between 0.8 and 1.5 nm (see FIG. 6). The graphene sheets may have an average lateral dimension between 5 and 30 pm, preferably between 10 and 25 pm, and more preferably between 15 and 20 pm (see FIGS. 3 and 4). Accordingly, the graphene sheets may have a high aspect ratio (e.g., over 16,000). It is contemplated that a high aspect ratio may result in a lower critical concentration for the formation of the LC phase in the precursor solution.

[0079] Due to the LC phase, the graphene sheets tend to align parallel (nematic ordering) to minimize excluded volume and achieve thermodynamic stability. Accordingly, the graphene sheets are advantageously aligned in comparison with randomly oriented graphene sheets.

[0080] It is contemplated that the composite may have an active material mass loading of 2-6 mg cm"2, leading to a high areal capacity of 4-8 mAh cm'2at 0.21 mA cm'2. This may help save energy storage spaces in electric vehicles. The composite may further maintain a practical capacity of 4.2 mAh cm'2at 1.68 mA cm'2. As noted above, the composite may further demonstrate excellent cycling stability and exhibit a coulombic efficiency of 99.5% and nearly 100% capacity retention over 200 cycles.

[0081] In exemplary uses, the graphene electrode composites may be assembled as free-standing working electrodes. It is contemplated that the graphene electrode composites can be applied to anode and / or cathode materials. For example, it is contemplated that the composites may be used to address critical issues in lithium ion batteries and other battery technologies. However, itshould be understood that the above are only exemplary uses for the described composites, and uses and applications of the composites are not limited to these listed examples.EXAMPLES

[0082] Below are examples of specific embodiments for carrying out the present application.The examples are offered for illustrative purposes only, and are not intended to limit the scope of the present application in any way. Efforts have been made to ensure accuracy with respect to numbers used (e.g., amounts, temperatures, etc.), but some experimental error and deviation should, of course, be allowed for.

[0083] Graphene oxide (GO) was prepared by oxidizing natural graphite flakes (50 mesh; Sigma-Aldrich) using the modified Hummers’ method. The resulting GO solution (3.6 mg mL'1) was stored in a refrigerator. To obtain GO LC samples, centrifugation was performed at the speed of 11,000 rpm. for 1 hour, followed by redispersion in varying volumes of water. This process yielded GO LCs at concentrations of 4, 6, and 10 mg mL’1, while low concentrations GO solutions at 1 and 2 mg mL’1were prepared as control samples.

[0084] To prepare Si-GO composites, 50 mg of silicon nanoparticles (>99%, 50 nm) and 175 mg of polyvinylpyrrolidone (PVP; molecular weight of ~55 000; Sigma) were mixed and dispersed in 25 mL of deionized (DI) water using sonication bath for 1 hour. Excess PVP was eliminated through three cycles of centrifugation, washing, and redispersion. The resulting PVP-coated Si NPs were then mixed with either a diluted GO solution or concentrated GO LCs to achieve different concentrations of GO in the Si-GO mixtures (1, 2, 4, and 6 mg mL’1). Excess sodium ascorbate was added, and the mixtures were heated at 95°C for 2 hours in an oven to reduce GOin Si-based composites. The prepared composites were washed four times with D.I. water to remove excess sodium ascorbate. Subsequently, freeze-drying was performed, and the samples were annealed at 600°C under argon flow with a heating rate of 10 °C min-1for three hours to enhance the electrical conductivity of the graphene frameworks.

[0085] Although silicon active material is used in the example described herein, it is contemplated that the described composites may contain any suitable active material.

[0086] LC Phases of GOs and Si-GO Nanocomposites: As detailed above, large-sized GO sheets were synthesized by oxidizing natural graphite flakes. The morphology of the GO sheets and their lateral size distribution were characterized, as shown in FIGS. 3 and 4, respectively, revealing an average lateral dimension of approximately 18.0 pm. The GO nanosheets exhibited a wrinkled morphology (FIG. 5) and had a measured thickness of about 0.8-1.5 nm, as determined by atomic force microscopy (AFM) (FIG. 6). Thus, the GO sheets possessed a high aspect ratio of over 16,000, resulting in a lower critical concentration (1.6 mg mL"1) for the formation of the LC phase, in accordance with the Onsager LC theory. Polarized optical microscopy (POM) observations between crossed polarizers were conducted to investigate GO dispersions with increasing concentrations ranging from 1.5 to 10.0 mg mL"1(FIG. 7). As the concentration increased, the GO dispersions underwent a transition from an isotropic solution to a nematic phase. At approximately 1.5 mg mL"1, a clear phase separation between the isotropic and nematic phases was observed (FIG. 7), consistent with the calculated critical concentration. The critical concentration of our GO LCs was found to be much lower than previously reported value due to the presence of large-sized GO building blocks. Above 3 mg mL"1, the dispersionsexhibited a uniform orientational ordering, as indicated by the vivid Schlieren texture, which is characteristics of a stable nematic phase (FIG. 7). At a concentration of 10.0 mg mL’1, aligned bands were observed in certain regions of the textures.

[0087] Furthermore, as noted above, Si-GO nanocomposites were prepared by mixing GO LCs with poly(N- vinylpyrrolidone) (PVP) grafted Si NPs. The presence of oxygen-containing groups on the GO sheets may facilitate the formation of hydrogen bonds between the GO sheets and the PVP, which contains carbonyl and amino groups. These hydrogen bonds may play a crucial role in reducing the isotropic-to-nematic transition to a lower GO concentration. FIG. 8 shows the Si- GO nanocomposite with varying weight percentages of Si (ranging from 50% to 80%) when mixed with GO LCs (4 mg mL"1). The LC phase was still observed in the Si-GO mixture in the polarized image compared to the unpolarized image (FIG. 8) in the same region. Agglomeration of Si NPs may partially disrupt the localized ordering of GO LCs. However, SEM imaging of the freeze-dried samples confirmed the maintenance of long-range ordering in the Si- GO nanocomposites.

[0088] LC Phase-Induced Long-Range Ordering of Si-Graphene Nanocomposites: The Si nanocomposites regulated by GO LCs may exhibit a hierarchical structure spanning multiple length scales from the macroscopic scale of the backbone scaffold to the atomic scale of the interspacing between restacked graphene building blocks (FIG. 2). Here, freestanding Si-G nanocomposites were fabricated by mixing PVP-coated Si NPs with GO LCs at different concentrations (1, 2, 4, 6 mg mL"1) and subsequently subjecting them to chemical reduction- induced self-assembly (FIGS. 9 and 10). Prior to chemical reduction, the viscosity of the mixtureincreased with GO concentration from 1 to 6 mg mL"1, becoming highly viscous at 6 mg mL"1, preventing flow when the vials were inverted (FIG. 9). After the chemical reduction, the selfassembled Si-GO nanocomposites floated on the water surface (FIG. 10). Upon freeze-drying and thermal treatment at 600°C, the Si-G nanocomposite (regulated by 4 mg mL'1GO LCs) illustrates a backbone scaffold comprising thick walls and large pores (FIG. 11). Examination of the wall region revealed perfectly aligned, long-range ordered graphene building blocks organized into cellular-like secondary structures within the backbone scaffold (FIGS. 12-15) These secondary structures acted as a matrix for hosting active Si NPs. The long-range ordering of graphene networks resembled a “parent crystal lattice structure” that constrained the Si NPs as “secondary phase atoms.” As the GO concentration increased from 1 to 6 mg mL"1, the interconnected cellular secondary structures transitioned from isotropic to elongated anisotropic cellular structures. The “interspacing” within GO LCs-regulated cellular structure, a crucial parameter of the “parent crystal lattice,” decreased as the GO concentration increased (from 1 to 6 mg mL"1) during the self-assembly process (FIGS. 12-15). Notably, higher GO concentrations above 4 mg mL"1yielded more anisotropic cellular structures with long-range ordering, indicating the inheritance of nematic structures from the oriented GO LCs (FIGS. 14 and 15).

[0089] Upon scaling down to the submicron and nanoscale levels, the graphene-based backbone structure provides numerous sites for anchoring Si NPs through successful wrapping facilitated by electrostatic interactions (FIG. 16). TEM images reveal the presence of wrinkled graphene sheets and Si NPs in close proximity (FIG. 17). The high-resolution TEM image further confirms the clear Si lattice structure (FIG. 17), with no noticeable crystallite of SiOx phase, in agreementwith the X-ray diffraction (XRD) pattern (FIG. 18). All the Si-G nanocomposites with similar graphene content (e.g., around 30+5 wt% in FIG. 19) illustrate the diffraction patterns of pristine Si phase without any impurities. More importantly, we further investigated the structural characteristics of Si-G nanocomposites at atomic and molecular scales using XRD. Specifically, the (002) graphene peak at approximately 25.8° confirms an atomic-scale interspacing of 3.44 A, representing the molecular orientation of graphene building blocks. Moreover, the intensity of the graphene peak increases with higher concentrations of GO LCs dispersion, indicating a higher degree of graphene sheet restacking. For instance, the (002) graphene peak is barely discernible in the Si-G composite with a dilute GO solution (1 mg niL'1). However, when GO LCs are concentrated to 6 mg mL’1, the resulting Si-G nanocomposite exhibits a pronounced graphene diffraction peak, indicating increased restacking of graphene sheets, consistent with the more densely packed anisotropic cellular structure observed in the SEM image. The calculated restacked crystallite height in the Si-G composite (6 mg mL’1) using the Scherrer equation is approximately 4.3 nm, corresponding to 13 stacked graphene layers within the graphitic domains.

[0090] Mechanical Characterizations: The incorporation of increased GO concentration in the chemical-induced assembly of Si-G composites may result in a more mechanically robust matrix that can effectively constrain the large volume experienced by Si active materials during chargedischarge cycling, as compared to counterparts derived from dilute GO solutions. To validate the regulation of mechanical properties induced by GO concentration, we conducted comparative analysis of mechanical behaviors of our GO-derived Si-G nanocomposites. The cycliccompression behaviors of the various Si-G composites are displayed in FIG. 20 and FIGS. 30 and 31. For example, the Si-G composite with 4 mg mL"1GO, when compressed to a strain of 30% at a high strain rate of 30 mm min"1, exhibits elastic behavior by bouncing back to its original shape (FIG. 20), indicating superior compressive elasticity. Furthermore, the cyclic compressive mechanical tests conducted at different strain rates of 2, 8, and 30 mm min"1(FIG. 21) and under various upper strain limits of 10%, 20%, and 30% (FIG. 22) confirm the resilient nature of our Si-G nanocomposites.

[0091] Taking 30% strain measurements as an example, the initial compressive stress-strain curve demonstrates a linear elasticity response (s < 10-15%) followed by a bump-up plateau (15% < s < 30%), corresponding to the elastic deformation region and buckling of the assembled hierarchical structures, respectively (FIG. 21 and FIGS. 30-32). The larger hysteresis observed during the first compression and recovery cycles indicates permanent deformations. Si-G composites derived from higher GO concentrations show enhanced mechanical properties compared to those derived from lower GO concentrations during the chemical-induced assembly (FIG. 23). For example, Si-G composites derived from highly concentrated GO LC phases (4 and 6 mg mL"1) reveal elastic moduli of 20.5 and 25.6 kPa, respectively, during 10% compression measurements, which are higher than the moduli of 14.6 and 12.5 kPa for composites derived from dilute GO solutions (1 and 2 mg mL"1). Furthermore, the Si-G composite prepared from 4 mg mL"1GO LC can undergo more than 150 cycles of compression, maintaining a steady modulus of around 8.5 kPa at a compression strain rate of 20 mm min-1 (FIG. 24).

[0092] Electrochemical Performance of LC-regulated Si-G Nanocomposite Electrodes: TheSi-G nanocomposite electrodes were compressed and directly assembled into freestanding electrodes in coin cells without the use of binders, conductive agents, and current collectors for electrochemical characterizations. The electrochemical impedance spectroscopy (EIS) measurements were performed to study the charge transport kinetics within the frequency range of 100kHz to 100 mHz. The Nyquist plot (FIG. 25) displays similar impedance spectra for all four samples, exhibiting a depressed semicircle in the medium-to-high-frequency region and a linear tail in the low-frequency region, consistent with previously reported silicon anodes. By fitting the Nyquist curves using an equivalent circuit, resistance parameters (Table 1) were obtained.Table 1: Surface Area and Pore Volume of Prepared Si-G Nanocomposites

[0093] The 4 mg mL’1GO LC- derived Si-G nanocomposite electrode exhibited a lower charge transfer resistance (Rct) of 311 Q and the Warburg resistance (Wo) of 163 Q compared to thenanocomposite electrodes derived from dilute solution or highly concentrated GO LC building blocks. The hierarchical structures of the assembled Si-G composite may influence the charge transport kinetics for both electrons and ions. The increased number of restacked graphene layers with long-range ordering may lead to reduced electric resistance due to the larger cross-sectional area for electric current and reduced contact interfaces. Moreover, the long-range ordering of the graphene framework may also improve ion transport. However, excessive restacking, such as with the 6 mg mL-1GO concentration, can adversely impede ion diffusion into the Si active materials, resulting in increased charge transfer resistance (FIG. 25).

[0094] The cyclic voltammetry (CV) profiles of the nanocomposite electrodes exhibited comparable redox peaks within the potential range of 0.01 to 1.0 V versus Li / Li+at scan rates of 0.1, 0.2, and 0.5 mV s-1(FIG. 26). The diffusion kinetics of lithium ions were determined using the Randles-Sevcik equation (Eq. (1)), which involves fitting the peak current and the square root of the scan rate to obtain the slope of the linear relationship.

[0095] where the R, T, and F represent the gas constant, temperature, and Faraday constant, respectively, and A, C, and n denote the electrode area, lithium-ion concentration, and the charge of transfer electrons. D, ip, and v represent the lithium-ion diffusion coefficient, peak current, and voltage scan rate, respectively. As shown in FIGS. 26 and 33, the slope of the linear fitting for the Si-G nanocomposite derived from 4 mg mL'1GO is higher than other electrodes derived from either lower or higher GO concentrations (e.g., 3.0 vs. 2.5, 2.3, and 2.9), indicating a higherlithium-ion diffusion coefficient. The CV curves at scan rates of 0.1-0.5 mV s’1demonstrate that the Si-G nanocomposite electrode regulated by 4 mg mL’1GO LC exhibits a larger peak area and lower redox overpotential compared to other composite electrodes derived from either dilute or concentrated GO. The first two charge-discharge curves for the 4 mg mL'1GO LC derived Si-G nanocomposite electrode (FIG. 27) show a plateau below 0.1 V during the first discharge process, corresponding to reduction peaks below 0.25 V in the CV curve. In the second discharge process, the plateau slightly increases, corresponding to the appearance of the reduction peak at 0.18 V in the CV curve. The plateau at 0.43 V during the charging process corresponds to the oxidation peaks at 0.36 and 0.53 V in the CV curves.

[0096] The rate performance of Si-G nanocomposite electrodes with a high mass loading of 4 mg cm'2prepared using various concentrations of GO (1, 2, 4, and 6 mg mL'1) was evaluated. The composite anodes were subjected to charge and discharge cycles at different areal current densities (0.21, 0.42, 0.84, 1.68, and 3.36 mA cm'2) for various cycling (1, 2, 3, 5, and 65 cycles), followed by 15 cycles at a current density of 0.84 mA cm'2(FIG. 28). The Si-G composite anode derived from 4 mg mL'1GO LCs exhibited higher areal capacities of 8.1, 7.2, 6.0, 4.2, and 2.3 mAh cm’2at the corresponding current densities compared to other composite electrodes. Additionally, the optimized GO LC-regulated Si-G composite electrode with a mass loading of around 2.5 mg cm’1demonstrated long cycling performance, maintaining a high specific capacity of 800 mAh g’1after 200 cycles at a high current density of 840 mA g’1, indicating a durable electrode structure during repeated expansion-contraction (FIG. 29).Therefore, the GO LC-regulated hierarchical structure provides an effective solution to balancefast charge transport kinetics and mechanical robustness of the “parent crystal lattice” by manipulating key “lattice parameters.” This approach leads to improved gravimetric and areal performance compared to previously reported Si-based composite anodes (Table 2).Table 2: Fitting Results from the Equivalent Circuit of the Nyquist Plots

[0097] Material Characterization: The morphology and structure of the materials were characterized through scanning electron microscopy (SEM, Zeiss Supra 40VP) and transmission electron microscopy (TEM, Titan S / TEM FEI). X-ray diffraction (XRD) analysis was conducted using a Panalytical X’Pert Pro X-ray Powder Diffractometer. Thermogravimetric analysis (TGA) was performed in an air atmosphere, covering a temperature range from room temperature to 750°C at a heating rate of 10°C min"1. The mechanical properties of the Si-G composite electrodes were investigated using dynamic mechanical analysis (DMA) (Anton Paar MCR 702e MultiDrive). The composites were compressed under different strain rates of 2, 8, and 30 mm min"1for 5 repeated cycles under different upper strain limits of 10%, 20%, and 30%, respectively.

[0098] Electrochemical Characterization: The Si-G nanocomposite anodes, with an areal mass loading of 4 or 2.5 mg cm'2, were compressed and directly assembled as working electrodes into 2032 coin cells without the use of binders, conductive agents, and current collectors. The assembly process was performed inside an argon-filled glovebox with water and oxygen content below 0.1 ppm. The electrolyte used was a mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC) with 1.0 M lithium hexafluorophosphate (LiPF6) (EC / DMC, 1:1 volume ratio, BASF, USA). Celgard 2340 was utilized as the separator in the coin cells. Galvanostatic charge / discharge cycling was conducted in a multichannel battery testing system (LAND CT2001A). Cyclic voltammetry and electrochemical impedance spectroscopy (EIS) were carried out using a VersaSTAT 4 from Princeton Applied Research. Cyclic voltammetry tests were measured at scan rates of 0.1, 0.2, and 0.5 mV s'1within a voltage window of 0.01-1V. EIS measurements were performed at open circuit potential, applying a sinusoidal signal over a frequency range of 10 kHz to 100 mHz with an amplitude of 10 mV.

[0099] It should be understood that the disclosure of a range of values is a disclosure of every numerical value within that range, including the end points. It should also be appreciated that some components, features, and / or configurations may be described in connection with only one particular embodiment, but these same components, features, and / or configurations can be applied or used with many other embodiments and should be considered applicable to the other embodiments, unless stated otherwise or unless such a component, feature, and / or configuration is technically impossible to use with the other embodiment. Thus, the components, features,and / or configurations of the various embodiments can be combined together in any manner and such combinations are expressly contemplated and disclosed by this statement.

[0100] It will be apparent to those skilled in the art that numerous modifications and variations of the described examples and embodiments are possible considering the above teachings of the disclosure. The disclosed examples and embodiments are presented for purposes of illustration only. Other alternate embodiments may include some or all of the features disclosed herein.Therefore, it is the intent to cover all such modifications and alternate embodiments as may come within the true scope of this invention, which is to be given the full breadth thereof.

[0101] It should be understood that modifications to the embodiments disclosed herein can be made to meet a particular set of design criteria. Therefore, while certain exemplary embodiments of the apparatus and methods of using and making the same disclosed herein have been discussed and illustrated, it is to be distinctly understood that the invention is not limited thereto but may be otherwise variously embodied and practiced within the scope of the following claims.

Claims

WHAT IS CLAIMED IS:

1. A method of producing a graphene electrode composite, comprising: preparing a precursor solution comprising graphene oxide dispersed in a solvent; controlling a concentration of the dispersed graphene oxide to form a graphene oxide liquid crystal solution; mixing at least one nano active material with the graphene oxide liquid crystal solution to form an active material- graphene oxide mixture; and reducing the active material-graphene oxide mixture to form the graphene electrode composite.

2. The method of claim 1, wherein the concentration of the dispersed graphene oxide is at least 3 mg mL’1.

3. The method of claim 1, wherein the concentration of the dispersed graphene oxide is between 4 and 10 mg mL'1.

4. The method of claim 1, wherein the at least one nano active material comprises a material selected from the group consisting of silicon, metal oxides, and mixtures thereof.

5. The method of claim 1 , wherein the at least one nano active material is between 65 and75 wt.% of the graphene oxide composite.

6. The method of claim 1, further comprising: washing the graphene oxide composite.

7. The method of claim 1, further comprising: annealing the graphene oxide composite.

8. A graphene electrode composite made by a method comprising the steps of: preparing a precursor solution comprising graphene oxide dispersed in a solvent; controlling a concentration of the dispersed graphene oxide to form a graphene oxide liquid crystal solution; mixing at least one nano active material with the graphene oxide liquid crystal solution to form an active material- graphene oxide mixture; and reducing the active material-graphene oxide mixture to form the graphene electrode composite.

9. The graphene electrode composite of claim 8, wherein the composite exhibits 100% capacity retention over 200 cycles at a current density of 840 mA g’1.

10. The graphene electrode composite of claim 8, wherein the composite exhibits elastic moduli between 20.5 and 25.6 kPa.

11. The graphene electrode composite of claim 8, wherein the composite exhibits a steady modulus of 8.5 kPa at 150 cycles of repeated compression.

12. The graphene electrode composite of claim 8, wherein the at least one nano active material comprises silicon nanoparticles.

13. The graphene electrode composite of claim 12, wherein the at least one nano active material comprises polyvinylpyrrolidone-coated silicon nanoparticles.

14. The graphene electrode composite of claim 8, wherein the graphene electrode composite comprises a plurality of stacked graphene sheets.

15. The graphene electrode composite of claim 14, wherein the graphene sheets have an average thickness between 0.8 and 1.5 nm.

16. The graphene electrode composite of claim 15, wherein the graphene sheets have an average lateral dimension between 5 and 30 pm.

17. The graphene electrode composite of claim 8, wherein the composite has a high maximum areal capacity of between 4 and 8 mAh cm'2at 0.21 mA cm'2.

18. The graphene electrode composite of claim 8, wherein the composite has an active material mass loading of between 2 and 6 mg cm’2.

19. The graphene electrode composite of claim 8, wherein the composite has a coulombic efficiency of 99.5%.

20. A graphene electrode composite, comprising: a graphene scaffold structure formed from a graphene oxide liquid crystal phase precursor, and at least one nano active material hosted within the graphene scaffold structure.

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