Graphene and Silicon-Based Anodes for Lithium-Ion Batteries

Abstract

Described herein are composites comprising graphene and silicon, and methods for making the composites, which may be applied to energy storage devices, including anodes for Li-ion batteries. In some embodiments, the composites may include turbostratic graphene, which has graphene layers that are misoriented relative to one another.

Description

[Technical field]

[0001] The following relates to composite materials comprising graphene and silicon-based materials applicable to energy storage devices, including anodes for lithium-ion batteries, and methods for making such composite materials. [Background technology]

[0002] U.S. Patent No. 11,174,167 to Dhanabalan et al., published on November 11, 2021, describes "silicon carbon composites containing ultra-low Z." In this disclosure, the anode material is made from a nanoporous carbon scaffold, and Si is deposited within the pores of the carbon scaffold. A drawback of the porous carbon scaffold is that it lacks the strength and electrical conductivity of graphene nanoparticles and graphene materials.

[0003] US Patent No. 11,101,458 to Yushin et al., published on October 3, 2019, describes a "scaffold matrix with internal nanoparticles." In this disclosure, anode materials are prepared by deposition, solution infiltration, vapor infiltration, atomic layer deposition, and electroplating to form a porous, conductive scaffold matrix into which active materials are inserted. In another disclosed method, active nanoparticles are adsorbed onto a polymer precursor for carbon formation, and the polymer precursor is carbonized by heat treatment to form a nanocomposite shell containing active nanoparticles, carbon, and nanopores. A disadvantage of porous carbon scaffolds is that they lack the strength and electrical conductivity of graphene materials. A disadvantage of porous carbon scaffolds with embedded active materials (such as Si) is that they lack the strength and electrical conductivity of graphene materials.

[0004] U.S. Patent No. 8,673,502 to Petrat et al., published March 18, 2014, describes "Method of making coated carbon particles and use of the same in anode materials for lithium-ion batteries." In this disclosure, an anode material is claimed that is made by deposition of Si onto graphite particles and carbon black. The average particle size of the primary particles is preferably 20-60 nm. A disadvantage of Si-coated carbon black is that it lacks the strength and electrical conductivity of graphene nanoparticles.

[0005] Li, Y. et al., Growth of conformal graphene cages on micrometre-sized silicon particles as stable battery anode, Nat Energy 1, 15029 (2016) discloses silicon particles encapsulated with graphene. The disadvantage of this structure is that it requires an expensive process of depositing a Ni catalyst layer on the Si particles and then carbonizing them for a long time (about 8 hours) before forming the graphene using an expensive oven deposition system that requires inert gas to be kept flowing during deposition. Furthermore, the graphene in this disclosure is AB stacked rather than turbostratic. Furthermore, as is evident from Figure 2 in this disclosure (from the Raman 2D peaks and TEM images), the level of graphitization is very low, suggesting low crystallization graphene.

[0006] Sang Cheol Kim et al., Graphene coating on silicon anode enabled by thermal surface modification for high energy lithium ion batteries, MRS BULLETIN - VOLUME 47, February 2022, discloses graphene-coated microscopic silicon particles. The disadvantage of this structure is that it requires an expensive chemical vapor deposition process that requires a vacuum chamber and a constant flow of process gas during deposition. Furthermore, the graphene in this disclosure is AB-stacked. Furthermore, as is evident from Figures 1 and 4 of this disclosure (from Raman 2D peaks and TEM images), the level of graphitization is very low.

[0007] Son, I et al., Silicon carbide-free graphene growth on silicon for lithium-ion battery with high volumetric energy density, Nat Commun 6, 7393 (2015) discloses the growth of graphene on nanosilicon particles. The disadvantage of this structure is that it requires expensive chemical vapor deposition process and methane process gas. Furthermore, the graphene in this disclosure is AB stacked. Furthermore, as is evident from Figure 1 and S1, S2 in this disclosure (from TEM images and XRD analysis), the level of graphitization is very low.

[0008] The common approach to fabricate Si-based anodes by mixing graphene sheets with Si nanoparticles (including graphene sheets wrinkled into balls) has the disadvantages of poor electrical connection between graphene and Si nanoparticles, loose mobility of Si inside graphene sheets, and inability to prevent crushing of Si during lithiation / delithiation process. The small mass of Si relative to the mass of graphene is also a drawback of this approach. Summary of the Invention

[0009] Described herein is a composite material and a method for making the composite material, the material comprises graphene and silicon.The material can be applied to energy storage devices, including anodes for Li-ion batteries.In some embodiments, the material can comprise turbostratic graphene, where there is little order between the layers of graphene.

[0010] Disclosed herein is a composite material according to one embodiment, the material comprising graphene nanoparticles and at least partially coated with graphene silicon nanoparticles.

[0011] According to some embodiments, the graphene nanoparticles are turbostratic graphene nanoparticles.

[0012] According to some embodiments, the graphene nanoparticles are polyhedral graphene nanoparticles.

[0013] According to some embodiments, the graphene nanoparticles are spherical graphene nanoparticles.

[0014] According to some embodiments, the graphene nanoparticles are porous.

[0015] According to some embodiments, the pores of the graphene nanoparticles are at least partially filled with silicon.

[0016] According to some embodiments, the graphene nanoparticles comprise a hollow core.

[0017] According to some embodiments, the hollow core is at least partially filled with silicon.

[0018] According to some embodiments, the silicon coating is coated with carbon.

[0019] According to some embodiments, the silicon coating is coated with graphene.

[0020] According to some embodiments, the carbon coating is electrically conductive.

[0021] According to some embodiments, the silicon coating comprises a first layer of silicon and a second layer of silicon of a different composition.

[0022] According to some embodiments, the second layer is further coated with graphene.

[0023] According to some embodiments, the silicon coating comprises elemental silicon.

[0024] According to some embodiments, the silicon coating is SiO, SiO x or SiO 2 Includes.

[0025] According to some embodiments, the silicon coating comprises silicon carbide.

[0026] According to some embodiments, the material comprises a branched structure.

[0027] According to some embodiments, the graphene nanoparticles are doped with nitrogen.

[0028] According to some embodiments, the material is used as an anode in a battery.

[0029] According to some embodiments, the battery is a lithium ion battery.

[0030] According to some embodiments, the battery is a sodium ion battery.

[0031] According to one embodiment, a composite material is described herein, the material comprising silicon nanoparticles, the silicon nanoparticles being at least partially coated with turbostratic graphene.

[0032] According to some embodiments, the graphene coating is porous.

[0033] According to some embodiments, the graphene coating comprises polyhedral graphene.

[0034] According to some embodiments, the silicon nanoparticles are Si, SiO, SiO x , SiO 2 Or contains SiC.

[0035] According to some embodiments, the silicon nanoparticles include a first silicon layer and a second silicon layer of different composition.

[0036] According to some embodiments, the composite material comprises voids between the silicon nanoparticles and the graphene coating.

[0037] According to some embodiments, the silicon nanoparticles comprise elemental silicon.

[0038] According to some embodiments, the silicon nanoparticles have a diameter of between 5 nm and 50 μm.

[0039] According to some embodiments, the material is used as an anode in a battery.

[0040] According to some embodiments, the battery is a lithium ion battery.

[0041] According to some embodiments, the battery is a sodium ion battery.

[0042] A material according to one embodiment is described herein, which comprises empty shell turbostratic graphene particles.

[0043] According to some embodiments, the graphene particles are porous.

[0044] According to some embodiments, the graphene shell is doped with Li, Na, Sn, CO 2 or H 2 It is filled with.

[0045] According to some embodiments, the material is used as an anode in an electrochemical cell.

[0046] According to some embodiments, the battery is a lithium ion battery.

[0047] According to some embodiments, the battery is a sodium ion battery.

[0048] A method for producing a composite material according to one embodiment is described herein, the method comprising providing turbostratic graphene nanoparticles and coating the graphene nanoparticles with a silicon material.

[0049] According to some embodiments, the nanoparticles are coated by chemical vapor deposition.

[0050] According to some embodiments, the graphene nanoparticles are polyhedral graphene nanoparticles.

[0051] According to some embodiments, the graphene nanoparticles are spherical graphene nanoparticles.

[0052] According to some embodiments, the graphene nanoparticles are porous.

[0053] According to some embodiments, the pores are filled with silicon.

[0054] According to some embodiments, the graphene nanoparticles comprise a hollow core.

[0055] According to some embodiments, the hollow core is at least partially filled with silicon.

[0056] According to some embodiments, the method further comprises coating the silicon coating with carbon.

[0057] According to some embodiments, the carbon coating is electrically conductive.

[0058] According to some embodiments, the silicon coating comprises a first silicon layer and a second silicon layer of a different composition.

[0059] According to some embodiments, the silicon coating comprises elemental silicon.

[0060] According to some embodiments, the silicon coating is SiO, SiO x or SiO 2 Includes.

[0061] According to some embodiments, the silicon coating comprises silicon carbide.

[0062] According to some embodiments, the method further comprises forming the material into a branched structure.

[0063] According to some embodiments, the graphene nanoparticles are doped with nitrogen.

[0064] According to one embodiment, a method for producing a composite material is described herein, the method comprising the steps of providing silicon nanoparticles, coating the silicon nanoparticles with a carbon material, and joule heating the coated silicon nanoparticles to convert the carbon coating into graphene.

[0065] According to some embodiments, coating the silicon nanoparticles with a carbon material comprises direct carbon coating by thermal gas decomposition.

[0066] According to some embodiments, the direct carbon coating comprises nitrogen doped carbon.

[0067] According to some embodiments, the direct carbon coating comprises urea, melamine, glucosamine, cyanamide, amino acids, proteins, or chitin.

[0068] According to some embodiments, the step of coating the silicon nanoparticles with a carbon material comprises direct carbon coating by hydrothermal carbonization of carbohydrates.

[0069] In some embodiments, the carbohydrate comprises glucose, fructose, sucrose, or a combination thereof.

[0070] According to some embodiments, the carbon material comprises carbon black.

[0071] According to some embodiments, the silicon nanoparticles comprise elemental silicon.

[0072] According to some embodiments, the silicon nanoparticles are SiO, SiO x or SiO 2 Includes.

[0073] According to some embodiments, the silicon nanoparticles and the carbon coating comprise a weight ratio of 90:10 to 10:90.

[0074] According to some embodiments, the graphene coating is porous.

[0075] According to some embodiments, the graphene comprises polyhedral graphene.

[0076] According to some embodiments, the composite material comprises voids between the silicon nanoparticles and the graphene coating.

[0077] According to some embodiments, the silicon nanoparticles have a diameter of between 5 nm and 50 μm.

[0078] A method for producing a composite material is described herein, the method comprising the steps of providing silicon nanoparticles, coating the nanoparticles with an amorphous carbon material, heating the coated nanoparticles to pyrolyze the amorphous carbon material, and Joule heating the nanoparticles to convert the pyrolyzed carbon material into turbostratic graphene.

[0079] According to some embodiments, the method further comprises coating the silicon nanoparticles with a sacrificial layer prior to coating the nanoparticles with the amorphous carbon material, and etching the sacrificial layer after the Joule heating process to create voids between the silicon nanoparticles and the turbostratic graphene.

[0080] According to some embodiments, the method further comprises etching the silicon nanoparticles to create voids between the silicon nanoparticles and the pyrolyzed carbon.

[0081] According to some embodiments, the method further comprises etching the silicon nanoparticles prior to the Joule heating process to create voids between the silicon nanoparticles and the turbostratic graphene.

[0082] According to some embodiments, the method further comprises etching the silicon nanoparticles prior to the Joule heating process to create voids between the silicon nanoparticles and the pyrolyzed carbon.

[0083] According to some embodiments of the methods and materials described herein, turbostratic graphene includes graphene layers that are misoriented with respect to one another.

[0084] Aspects and features will become apparent to those of ordinary skill in the art upon review of the following description of several exemplary embodiments.

[0085] The drawings included herein are intended to illustrate various embodiments of the articles, methods, and apparatus herein. [Brief description of the drawings]

[0086] [Figure 1]Figure 1A is a cross-sectional schematic diagram of a hollow polyhedral graphene nanoparticle before coating, Figure 1B is a cross-sectional schematic diagram of a hollow polyhedral graphene nanoparticle of Figure 1A after coating with Si, and Figure 1C is a cross-sectional schematic diagram of a solid polyhedral graphene nanoparticle after coating with Si, according to one embodiment. [Diagram 2] Figure 2A is a cross-sectional schematic diagram of a hollow polyhedral graphene nanoparticle before coating, Figure 2B is a cross-sectional schematic diagram of a hollow polyhedral graphene nanoparticle of Figure 2A after coating with Si, and Figure 2C is a cross-sectional schematic diagram of a solid polyhedral graphene nanoparticle after coating with Si, according to one embodiment. [Diagram 3] Figure 3A is a cross-sectional schematic diagram of a hollow polyhedral graphene nanoparticle before filling and after coating with Si, according to one embodiment. Figure 3B is a cross-sectional schematic diagram of the hollow polyhedral graphene nanoparticle of Figure 3A after filling and coating with Si, according to one embodiment. [Figure 4] Figure 4A is a cross-sectional schematic diagram of a porous hollow polyhedral graphene nanoparticle before coating, Figure 4B is a cross-sectional schematic diagram of the porous hollow polyhedral graphene nanoparticle of Figure 4A after coating with Si, and Figure 4C is a cross-sectional schematic diagram of a solid porous polyhedral graphene nanoparticle after coating with Si, according to one embodiment. [Diagram 5] 5A and 5B are schematic cross-sectional views of the polyhedral graphene branched structure of FIG. 5A before and after coating with Si, according to one embodiment. [Figure 6] 6A and 6B are schematic cross-sectional views of a matrix of polyhedral graphene branched structures before and after coating with Si, according to an embodiment, respectively. [Figure 7]Figure 7A is a cross-sectional schematic diagram of a polyhedral graphene nanoparticle coated with an inner Si layer and an outer SiOx(x<2), SiO2 layer according to one embodiment. Figure 7B is a cross-sectional schematic diagram of a polyhedral graphene nanoparticle coated with an inner Si layer, a middle SiOx(x<2), SiO2 layer, and an outer carbon layer according to one embodiment. Figure 7C is a cross-sectional schematic diagram of a polyhedral graphene nanoparticle coated with an inner Si, SiOx(x<2), SiO2 layer, and an outer carbon layer according to one embodiment. [Figure 8] FIG. 8A is a cross-sectional schematic of a Si, SiOx(x<2), SiO2 nanoparticle before coating, according to one embodiment. FIG. 8B is a cross-sectional schematic of a Si, SiOx(x<2), SiO2 nanoparticle of FIG. 8A covered with carbon black nanoparticles, according to one embodiment. FIG. 8C is a cross-sectional schematic of a Si, SiOx(x<2), SiO2 nanoparticle of FIG. 8A coated with polyhedral graphene nanoparticles, according to one embodiment. FIG. 8D is a cross-sectional schematic of a Si nanoparticle core with a SiOx(x<2), SiO2 shell coated with polyhedral graphene nanoparticles, according to one embodiment. [Figure 9] Figure 9A is a SEM image of Si, SiOx (x<2), SiO2 nanoparticles coated with polyhedral graphene nanoparticles according to one embodiment. Figure 9B is a SEM image of clusters of Si, SiOx (x<2), SiO2 nanoparticles coated with polyhedral graphene nanoparticles according to one embodiment. [Figure 10] Figure 10A is an image of an EDX analysis of the sample of Figure 9A according to one embodiment, and Figure 10B is a cross-sectional schematic of an EDX analysis of the sample of Figure 9B according to one embodiment. [Figure 11A] FIG. 2 is a cross-sectional schematic diagram of Si, SiOx (x<2), SiO2 nanoparticles according to one embodiment. [Figure 11B] FIG. 11B is a cross-sectional schematic diagram of the carbon-coated Si, SiOx (x<2), SiO2 nanoparticles of FIG. 11A according to one embodiment. [Figure 11C]FIG. 11B is a cross-sectional schematic diagram of the Si, SiOx (x<2), SiO2 nanoparticles of FIG. 11A coated with pyrolyzed carbon, according to one embodiment. [Figure 11D] FIG. 11B is a cross-sectional schematic diagram of the Si, SiOx (x<2), SiO2 nanoparticles of FIG. 11A coated with turbostratic graphene, according to one embodiment. [Figure 11E] 1 is a TEM image of multiple graphene-covered Si nanoparticles with an average diameter of 100 nm, according to one embodiment. [Figure 11F] 1 is a TEM image at 44k magnification of individual graphene-covered Si nanoparticles, according to one embodiment. [Figure 11G] 1 is a TEM image at 270k magnification of individual graphene-covered Si nanoparticles, according to one embodiment. [Figure 11H] 1 is a Raman signature of pure Si nanoparticle powder according to one embodiment. [Figure 11I] FIG. 1 is a Raman signature of graphene-covered Si nanoparticle powder according to one embodiment. [Figure 11J] FIG. 11I is a magnified view of the Raman signature of FIG. 11I according to one embodiment. [Figure 11K] 1 is a SEM image and EDX measurements of an example Si-graphene composite structure according to an embodiment. [Figure 11L] 1 is a SEM image and EDX measurements of an example Si-graphene composite structure according to an embodiment. [Figure 11M] 1 is a SEM image and EDX measurements of an example Si-graphene composite structure according to an embodiment. [Figure 11N] 1 is a SEM image and EDX measurements of an example Si-graphene composite structure according to an embodiment. [Figure 11O] 1 is a TGA analysis plot of a Si-graphene composite powder according to an embodiment. [Figure 12A] FIG. 2 is a cross-sectional schematic diagram of Si, SiOx (x<2), SiO2 nanoparticles coated with a sacrificial layer and a carbon coating, according to one embodiment. [Figure 12B] FIG. 2 is a cross-sectional schematic diagram of Si, SiOx (x<2), SiO2 nanoparticles coated with a sacrificial layer and pyrolyzed carbon, according to one embodiment. [Figure 12C] FIG. 2 is a cross-sectional schematic diagram of Si, SiOx (x<2), SiO2 nanoparticles coated with a sacrificial layer and turbostratic graphene, according to one embodiment. [Figure 12D] FIG. 2 is a cross-sectional schematic diagram of a Si, SiOx (x<2), SiO2 nanoparticle coated with turbostratic graphene and having voids between the graphene and one or more nanoparticles, according to one embodiment. [Figure 12E] FIG. 2 is a cross-sectional schematic diagram of Si, SiOx (x<2), SiO2 nanoparticles coated with a pyrolyzed carbon coating, according to one embodiment. [Figure 12F] FIG. 12C is a cross-sectional schematic diagram of a Si, SiOx (x<2), SiO2 nanoparticle coated with a pyrolyzed carbon coating of FIG. 12E having voids between the carbon and one or more nanoparticles, according to one embodiment. [Figure 12G] FIG. 2 is a cross-sectional schematic diagram of a Si, SiOx (x<2), SiO2 nanoparticle coated with graphene and having voids between the graphene and one or more nanoparticles, according to one embodiment. [Figure 12H] 1 is a SEM image of an exemplary graphene shell made from a 1 μm average diameter Si sacrificial core, according to one embodiment. [Figure 12I] 1 is a SEM image and corresponding EDX map of an exemplary TG-shell according to one embodiment. [Figure 12J] 1 shows an SEM image and corresponding EDX trace of an exemplary TG-shell according to a further embodiment. [Figure 12K] FIG. 2 is a cross-sectional schematic diagram of Si, SiOx (x<2), SiO2 nanoparticles coated with a porous carbon coating according to one embodiment. [Figure 12L] FIG. 2 is a cross-sectional schematic diagram of porous graphene coated Si, SiOx (x<2), SiO2 nanoparticles according to one embodiment. [Figure 13]13A and 13B are schematic cross-sectional views of Si, SiOx (x<2), SiO2 nanoparticles covered with carbon particles and Si, SiOx (x<2), SiO2 nanoparticles coated with turbostratic graphene, respectively, according to one embodiment. [Figure 14] Figure 14A is a cross-sectional schematic of Si, SiOx (x<2), SiO2 nanoparticles covered with carbon particles and carbon black nanoparticles, and Figure 14B is a cross-sectional schematic of Si, SiOx (x<2), SiO2 nanoparticles coated with turbostratic graphene and polyhedral graphene nanoparticles, according to an embodiment. [Figure 15] Figure 15A is a TEM image of predominantly hollow polyhedral graphene nanoparticles according to one embodiment. Figure 15B is a high resolution TEM image of polyhedral graphene clusters according to one embodiment. Figure 15C is a very high resolution TEM image of polyhedral graphene according to one embodiment. Figure 15D is a TEM image of predominantly solid polyhedral graphene nanoparticles according to one embodiment. [Figure 16] Figure 16A is a high resolution TEM image of graphene flakes according to one embodiment, and Figure 16B is a very high resolution TEM image of graphene flakes according to one embodiment. [Figure 17] Figure 17A is a cross-sectional schematic diagram of a typical Li-ion battery in which the Si-graphene composite of the present invention may be used, Figure 17B is a cross-sectional schematic diagram of a Li-ion battery during a discharging operation according to one embodiment, and Figure 17C is an image of components of a Li-ion battery according to one embodiment. [Figure 18] 1 is a plot of cycle life and specific volume of Si-graphene composite, Si-pyrolytic carbon composite, and pure Si material according to one embodiment. [Figure 19] 1 is a flow chart illustrating a method for producing a silicon graphene composite material, according to one embodiment. [Figure 20] 1 is a flow chart illustrating a method for producing a silicon graphene composite material according to another embodiment. [Figure 21]1 is a flow chart illustrating a method for producing a silicon graphene composite material according to another embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0087] Various materials, devices, or processes are described below to provide examples of each of the claimed embodiments. The embodiments described below are not intended to limit the claimed embodiments, which may be directed to materials, processes, or devices different from those described below. The claimed embodiments are not limited to materials, devices, or processes having all of the features of any one device or process described below, or to features common to some or all of the materials or devices described below.

[0088] The description of an embodiment in which multiple components relate to one another does not imply that all such components are required, rather, a variety of optional components are described to illustrate the wide variety of possible embodiments of the present disclosure.

[0089] Additionally, although process steps, method steps, algorithms, and the like may be described (in this disclosure and / or claims) in a sequential order, such processes, methods, and algorithms may be configured to work in alternative orders. In other words, any order or sequence of steps that may be described does not necessarily indicate a requirement that the steps be performed in that order. Steps of processes described herein may be performed in any order that is practical. Additionally, some steps may be performed simultaneously.

[0090] It will be readily apparent that where a single device or article is described herein, multiple devices / articles (whether they cooperate or not) may be used in place of the single device / article. Similarly, where multiple devices or articles (whether they cooperate or not) are described herein, it will be readily apparent that a single device / article may be used in place of the multiple devices or articles.

[0091] The following relates generally to graphene and silicon based materials, and more particularly to graphene and silicon based materials used in or as anodes for lithium ion batteries.

[0092] A method for producing graphene by flash Joule heating is disclosed in Nature (Luong, DX, Bets, KV, Algozeeb, WA, Stanford, MG, Kittrell, C., Chen, W., Salvatierra, RV, Ren, M., McHugh, EA, Advincula, PA and Wang, Z., 2020). Additional details regarding the production of graphene by Joule heating are disclosed in International Application No. CA2022051406, filed September 21, 2022, which claims priority to U.S. Patent Application No. 63 / 246,424, and which is incorporated herein by reference. This disclosure describes the flash Joule heating process as one tool for producing graphene-silicon composites.

[0093] The term "graphene" refers to a material composed of crystalline layered sp2 bonded carbon atoms. In one embodiment, the graphene material comprises planar sheets one atom thick. In one embodiment, the graphene material comprises multiple layers of planar sheets one atom thick. The graphene material comprises sheets densely packed in a honeycomb crystal lattice and may further comprise an intact ring structure of carbon atoms and aromatic bonds throughout at least a majority of the internal sheets. The graphene material may lack significant oxidative modification of the carbon atoms. Graphene can be distinguished from graphene oxide in that it has a low degree of oxygen-containing groups such as OH, COOH, and epoxides.

[0094] In one embodiment, the graphene is comprised of two to several hundred individual graphene shells nested together. The nested graphene shells may be hollow cores or may be solid. The nested graphene shells may be three-dimensional polyhedral structures (like a soccer ball) or may be predominantly spherical. In some embodiments, the graphene is predominantly spherical with diameters ranging from 100 nanometers to tens of micrometers.

[0095] The term "graphene monolayer" refers to graphene that is a single layer of graphene. The term "very few layer graphene" refers to graphene that is one to three layers of graphene. The term "few layer graphene" refers to graphene that is two to five layers of graphene. The term "multilayer graphene" refers to graphene that is two to ten layers of graphene.

[0096] "Turmostratic graphene (TG)" refers to graphene with little order between the graphene layers. In one embodiment, turbostratic graphene has random order between the graphene layers. In one embodiment, turbostratic graphene has graphene sheets that are randomly twisted with respect to each other. Turmostratic graphene has graphene layers that are misoriented with respect to each other. The graphene layers in TG are not AB stacked (AB stacking is also called Bernal stacking). Instead, in turbostratic graphene, the orientation of adjacent graphene layers is misaligned with respect to each other. Other terms to describe the order between the graphene layers include misoriented, twisted, rotated, rotated fault, and weakly bonded.

[0097] The rotational stacking of turbostratic graphene helps relax the interlayer bonds and increase the interplanar spacing, resulting in superior physical properties compared to competing graphene structures when compared by weight. Subtle differences in the stacking orientation of adjacent layers can lead to important differences in product performance characteristics. An important performance advantage revealed by turbostratic graphene is that the multi-layer graphene structure is more prone to decomposing into a few individual graphene layers, and the graphene layers tend not to recoupling. The turbostratic nature of graphene can be observed and confirmed by Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected area electron diffraction (SAED), scanning transmission electron microscopy (STEM), energy dispersive X-ray spectroscopy (EDX), atomic force microscopy (AFM), and X-ray diffraction (XRD).

[0098] As a result of the Joule heating process, TG is mainly produced in two predominant morphologies: flake-like turbostratic graphene structures (FTG) and polyhedral turbostratic graphene structures (PG).

[0099] Polyhedral graphene is a closed form of graphene forming a polyhedral cage, with multiple cages nested within each other. Spherical cages are also possible. In some cases, polyhedral graphene nanoparticles are voided (hollow); in other cases, they are solid (void-free). Typical PG graphenes have sizes (diameter) between 20 nm and 200 nm, with layer thicknesses ranging from 2 layers to 100 layers or more. Polyhedral graphene nanoparticles can self-assemble in branched structures consisting of multiple PG nanoparticles with lengths ranging from a few nm to a few μm.

[0100] The term "carbon source" generally refers to any carbon-based material that can be converted to graphene material, preferably turbostratic graphene. The carbon source can be in any form, such as powdered or carbon-coated. Carbon sources include, but are not limited to, petroleum coke, tire carbon black, carbon black, metallurgical coke, plastic ash, plastic powder, ground coffee, anthracite, coal, corn starch, pine bark, polyethylene microwax, wax, cellulose, naphthenic oil, asphaltene, and gilsonite.

[0101] The term "silicon nanoparticles" refers to nanoparticles made primarily of silicon, silicon monoxide, silicon dioxide, or any combination thereof. SiO x Silicon-based materials, SiC, and Si-OC-based materials are also included. The SiC material may be β-SiC, which is known to have lithium storage capabilities and is used in battery applications. The silicon-based nanoparticles may be amorphous, crystalline, or a combination thereof. The silicon-based nanoparticles may be spherical or irregularly shaped. The silicon-based nanoparticles may be rod-shaped, nanowire-like, or two-dimensional structures. The silicon-based nanoparticles may be nanoporous, mesoporous, or microporous. Typical silicon-based nanoparticles used in lithium-ion battery anodes have diameters of 5 nm to several μm.

[0102] Referring to Figure 1A, there is shown a cross-sectional schematic diagram of a polyhedral graphene (PG) nanoparticle 101 according to one embodiment. The polyhedral graphene nanoparticle 101 is configured such that the cross-section of the polyhedral graphene nanoparticle is a polyhedral shape. The polyhedral graphene nanoparticle is composed of graphene, specifically turbostratic graphene.

[0103] Polyhedral graphene (PG) nanoparticles 101 can be obtained by a Joule heating process that converts carbon black nanoparticles into polyhedral turbostratic graphene nanoparticles 101. The polyhedral graphene can be hollow 101 or solid nanoparticles (121) after flash Joule heating, depending on the morphology and material composition of the initial CB feedstock.

[0104] 1B, there is shown a cross-sectional schematic diagram of a hollow PG-Si based composite 110, according to one embodiment. The hollow PG-Si composite 110 includes hollow polyhedral graphene nanoparticles 111. The hollow polyhedral graphene nanoparticles 111 can be the polyhedral graphene nanoparticles 101 of FIG. 1A.

[0105] The hollow polyhedral graphene nanoparticle 111 includes (is hollow) voids 114. The voids 114 are smaller in size than the hollow polyhedral graphene nanoparticle 111 such that the voids are inside the hollow polyhedral graphene nanoparticle 111. The hollow polyhedral graphene nanoparticle 111 is at least partially coated with silicon deposits 112 to form a hollow PG-Si-based composite 110. The hollow PG-Si-based composite 110 may be generally referred to as a PG-Si-based composite 110. The PG-Si-based composite 110 is suitable for use in an anode of a Li-ion battery.

[0106] The silicon deposition 112 is Si, SiO x (x<2) or SiO 2 When the silicon deposit 112 is Si, the PG-Si based composite material 110 may be referred to as a PG-Si composite material. Silicon, SiO, with controlled thickness, crystallinity and purity. x , and SiO 2The technique for depositing the coating is silicon, SiO x , and SiO 2 Chemical vapor deposition (CVD) of silicon is well known to those skilled in the art. In one example of Si deposition, silane gas is used as the process gas, and other carrier and doping gases may be added. Other deposition methods include plasma enhanced chemical vapor deposition (PECVD) processes. In this disclosure, silicon, SiO x , and SiO 2 The terms may be used interchangeably and without restriction.

[0107] 1C, there is shown a cross-sectional schematic diagram of a solid PG-Si based composite 120 according to one embodiment. The solid PG-Si based composite 120 includes solid polyhedral graphene nanoparticles 121. The solid polyhedral graphene nanoparticles 121 may be the polyhedral graphene nanoparticles 101 of FIG. 1A. The solid polyhedral graphene nanoparticles 121 do not include voids 114. The solid PG-Si based composite 120 is otherwise configured similarly to the hollow PG-Si based composite 110 of FIG. 1B. The solid PG-Si based composite 120 may be generally referred to as the PG-Si based composite 110.

[0108] 2A, there is shown a cross-sectional schematic diagram of a spherical graphene nanoparticle 201. The spherical graphene nanoparticle 201 is configured as a sphere. The spherical graphene nanoparticle 201 is otherwise configured similarly to the polygonal graphene nanoparticle 101.

[0109] Referring now to Figure 2B, there is shown a cross-sectional schematic diagram of a hollow SG-Si based composite 210. The hollow SG-Si based composite 210 includes hollow spherical graphene nanoparticles 211. The hollow spherical graphene nanoparticles 211 may be the spherical graphene nanoparticles 201 of Figure 2A. The spherical hollow SG-Si based composite 210 is otherwise configured similarly to the hollow PG-Si based composite 110 of Figure 1B. The hollow SG-Si based composite 210 may be generally referred to as the PG-Si based composite 110.

[0110] Referring now to Figure 2C, there is shown a cross-sectional schematic diagram of a solid SG-Si based composite 220, according to one embodiment. The solid SG-Si based composite 220 includes solid spherical graphene nanoparticles 221. The spherical graphene nanoparticles 221 may be the spherical graphene nanoparticles 201 of Figure 2A. The solid SG-Si based composite 220 is otherwise configured similarly to the solid PG-Si based composite 120 of Figure 1C. The solid SG-Si based composite 220 may be generally referred to as the PG-Si based composite 110.

[0111] A powder of multiple PG-Si based composite nanoparticles 110 is suitable for use in a Li-ion battery anode. Any PG-Si based composite 110 or combination of multiple PG-Si based composites 110, such as hollow PG-Si based composites 110, solid PG-Si based composites 120, hollow SG-Si based composites 210, and solid SG-Si based composites 220, may be used as a Li-ion battery anode. In the figures of this disclosure, the illustrations of spherical and hexagonal or hollow and solid polyhedral graphene morphology may be used interchangeably without any limitation.

[0112] One advantage of using the PG-Si based composite 110 as an anode material for Li-ion batteries is the high mechanical strength of the polyhedral graphene nanoparticles compared to similar samples made from graphite, carbon or carbon black. High particle strength is necessary to prevent the destruction of the silicon coating, which expands by 200-300% during the anode lithiation process. Another advantage of the PG-Si based composite 110 as an anode material for Li-ion batteries is the high electrical conductivity of the crystalline polyhedral graphene nanoparticles compared to that of amorphous carbon or carbon black.

[0113] Referring to Figure 3A, there is shown a cross-sectional schematic diagram of a hollow polyhedral graphene nanoparticle 300 according to one embodiment. The hollow polyhedral graphene nanoparticle 301 is configured similarly to the hollow polyhedral graphene nanoparticle 101 of Figure 1A.

[0114] 3B, there is shown a cross-sectional schematic diagram of a filled PG-Si based composite 310 according to a further embodiment. A hollow polyhedral graphene nanoparticle 301 is filled and coated with a silicon deposit 302 to form the PG-Si based composite 310. In some examples, the hollow polyhedral graphene nanoparticle 301 is only partially filled with the silicon deposit 302. In other examples, the polyhedral graphene nanoparticle 301 is only partially coated with the silicon deposit 302. The PG-Si based composite 310 is otherwise configured similarly to the hollow PG-Si based composite 110 of FIG. 1B. The filled PG-Si based composite 300 may be generally referred to as the PG-Si based composite 110. Alternately, the SiO x (x<2) or SiO 2 The filled PG-Si based composite material is also generally referred to as PG-Si based composite material 110.

[0115] Standard and modified chemical vapor deposition techniques for silicon deposition can be used, such as the choice of deposition rate, deposition temperature, carrier gas, etc., to achieve silicon filling. One method to enable silicon filling in the voids of PG is to partially open polyhedral graphene nanoparticles with the help of selective carbon activation.

[0116] Referring to Figure 4A, there is shown a cross-sectional schematic diagram of a hollow polyhedral graphene nanoparticle 401 according to one embodiment. The graphene shell 403 of the porous polyhedral graphene nanoparticle 401 includes pores 405. The pores 405 can be shallow pores that do not penetrate the graphene shell 403. Additionally, the pores 405 can be deep pores that penetrate the graphene shell 403 and partially communicate with the voids of the graphene nanoparticle 401. The porous polyhedral graphene nanoparticle 401 is otherwise configured similarly to the polyhedral graphene nanoparticle 101 of Figure 1A.

[0117] 4B and 4C, cross-sectional schematic diagrams of porous coated PG-Si-based composites 410, 420 according to further embodiments are shown. The porous coated PG-Si-based composites 410, 420 include silicon deposits 402 deposited in the pores 405 and on the surface of the porous polyhedral graphene nanoparticles 401 to form the porous coated PG-Si-based composites 400. The silicon deposits 402 are configured similarly to the silicon deposits 112 of FIG. 1B. In some examples, the pores 405 of the porous polyhedral graphene nanoparticles 401 are only partially filled with silicon. In other examples, the outer surface of the graphene nanoparticles 401 are only partially coated with silicon. The porous polyhedral graphene nanoparticles 401 may be hollow, as in the porous coated PG-Si-based composite 410, or solid 421, as in the porous coated PG-Si-based composite 420. The porous and coated PG-Si based composites 410, 420 are generally referred to as the PG-Si based composite 110.

[0118] In one embodiment, the porous graphene shells 403 may be obtained by direct chemical or physical activation of polyhedral graphene nanoparticles 401 to generate pores 405 on the graphene. In another embodiment, the porous surface may be obtained by first making carbon black nanoparticles porous using a chemical or physical activation process, and then converting the porous carbon black nanoparticles into porous polyhedral graphene nanoparticles 401 in a Joule heating process.

[0119] The chemical activation of carbon and graphene materials to obtain porosity is generally carried out using CO 2 and CO gas by using NaOH, KOH, H 3 PO 4 , ZnCl 2 , or FeCl 3The nanopores 405 are created by a physical activation process known to generate pores 405 in carbon or graphene materials. 2 , or O 2 At temperatures ranging from about 300 to 900 °C depending on the chemical. In some cases, it may be necessary to first oxidize the graphene surface to create defects where activation works more efficiently. Another method of producing porous carbon and graphene materials uses an oxidizing liquid in a hydrothermal process reaction. Yet another method of producing porous carbon and graphene materials uses mechanical comminution, such as ball milling techniques.

[0120] A favorable raw material for the production of polyhedral graphene has an oil absorption capacity (OAN) in cc / 100 g and m 2 Carbon blacks are carbon blacks with a variety of branched structures measured in surface area per gram. Most, if not all, carbon blacks have a spherical morphology, with diameters between 20 nm and 300 nm, and typically form branched structures that range from smaller to more complex, and from single CB nanoparticles to structures several micrometers in length. The bonds between the CB nanoparticles are structural and are not easily broken by most industrial milling tools. Figure 15B, described further below, shows one such example.

[0121] Referring to FIG. 5A, a cross-sectional schematic diagram of a branched structure 500 according to one embodiment is shown. The polyhedral graphene nanoparticles 502 of the branched structure are structurally joined together. One way to obtain the branched structure 500 of polyhedral graphene nanoparticles 502 can be by a Joule heating process that converts the branched carbon black nanoparticle structure into a branched polyhedral turbostratic graphene nanoparticle structure with a shape and morphology similar to the starting CB material. The polyhedral graphene nanoparticles 502 can be the polyhedral graphene nanoparticles 101, 201, 301 and 401 of FIGS. 1A-4A. The polyhedral graphene nanoparticles 502 of the branched structure 500 act as a single mechanical structure. The branched structure 500 has electrical conductivity between the individual nanoparticles. For illustrative purposes, the polyhedra are depicted as spheres.

[0122] Referring to FIG. 5B, a cross-sectional schematic diagram of a branched PG-Si composite 504 is shown, according to one embodiment. The branched PG-Si composite 504 comprises a branched structure 500. The branched PG-Si composite 504 further comprises silicon deposits 502 deposited on an outer surface 503 of the branched structure 500. The structure of the branched PG-Si composite 504 is beneficial for forming an anode that is mechanically more stable and has better electrical conductivity than an aggregate of individual carbon or graphene nanoparticles. The polyhedral graphene nanoparticles 502 may be hollow or solid, porous or not, and may be formed of Si or SiO x (x<2) or SiO 2 Or it may be coated with any combination thereof.

[0123] 6A, a cross-sectional schematic diagram of a conductive matrix 600 according to one embodiment is shown. The conductive matrix 600 includes a plurality of branched structures 500. The plurality of branched structures 500 of the conductive matrix 600 function as a single mechanical structure. The conductive matrix 600 may be formed by the intermingling and entanglement of a number of branched structures 500. In some examples, the matrix may be compressed to form a better entanglement of the branched structures 500. In some examples, a metal-based or polymer-based bond may be applied to bond the branched structures 500 to the matrix 600.

[0124] Referring now to FIG. 6B, there is shown a cross-sectional schematic diagram of a PG-Si composite matrix 610 according to one embodiment. The PG-Si composite matrix 610 includes silicon deposits 602 deposited on a surface 603 of a conductive matrix 600. Due to the randomness of the branched structures 500, the matrix is ​​macroporous in nature to allow for the free flow of ions. The PG-Si composite matrix 610 can be compressed to further densify the battery anode without compromising the flow of electrons and ions. The nanoparticles shown in FIG. 6 may be hollow or solid, porous or not, and may be made of Si or SiO x (x<2) or SiO 2 and any combination thereof.

[0125] Silicon has a theoretical capacity of 4200mAh g -1 ) is a very promising alternative anode material. However, during the lithiation / delithiation process, silicon undergoes extreme volume changes of up to 300%, which tends to destroy silicon. The incorporation of the disclosed PG-Si composite material reduces or eliminates the problems associated with the expansion. However, SiO and SiO 2 Either compromise the high specific capacitance of Si for the low material expansion of SiO and SiO 2 In the design of battery anodes, SiO and SiO are used to trade off better resistance to unwanted solid electrolyte interphase (SEI) formation with2 There are advantages to using alternative silicon materials such as SiO 2 / C Anode Materials for Lithium-Ion Batteries.J.Electron.Mater.50,6667-6687(2021).https: / / doi.org / 10.1007 / s11664-021-09187-x). SiO 2 has a smaller expansion volume (100%) and a higher theoretical capacity (1965mAh / g) than Si (300%). SiO has an expansion volume of 150% and a theoretical capacity of 2400mAh / g. Therefore, Si, SiO, and SiO x (x<2), SiO 2 There is a need for composite material design that incorporates this.

[0126] Referring to FIG. 7A, a PG-Si-SiO 2 A composite material 700 is shown. PG-Si-SiO 2 The composite material 700 includes a Si active layer 702 and a SiO x (x<2) or SiO 2 The PG core 701 is coated with a protective layer 704 of SiO x (x<2) and SiO 2 Layer 704 can be formed by oxidizing or thermally annealing Si layer 702, or by forming another SiO 2 Or SiO x This may be achieved by a deposition process.

[0127] Referring to FIG. 7B, a PG-Si-SiO 2 A cross-sectional schematic of a PG-Si composite 710 is shown. One potential problem with PG-Si composite nanoparticles is that the contact between two PG-Si composite nanoparticles is silicon-to-silicon or SiO 2 SiO 2This contact reduces the electrical conductivity between the nanoparticles. 2 The -C composite 710 is the PG-Si-SiO 2 It is composed similarly to composite material 700. PG-Si-SiO 2 The -C composite material 710 further includes a conductive carbon film 712. The conductive carbon film 712 is made of SiO x (x<2) or SiO 2 The carbon film 712 at least partially coats the outer surface 713 of the protective layer 704 of PGSi-SiO 2 This beneficially improves electrical conductivity between the nanoparticles.

[0128] Conductive carbon film was heated with acetylene gas to form PG-Si-SiO 2 Coating on composite material 700, PG-Si-SiO 2 A PG-Si-SiO 3 composite material 710 can be formed using a carbon source (carbon, graphene, PG, carbon nanotubes). 2 Mechanical ball milling of the composite material 700 is another method of conductive carbon coating. Other methods of carbon coating are possible.

[0129] Referring now to Figure 7C, there is shown a cross-sectional schematic of a PG-Si-C composite 720 according to one embodiment. An outer silicon surface 723 of the PG-Si composite is at least partially coated with a conductive carbon film 712 to form the PG-Si-C composite 720. The conductive carbon film beneficially improves electrical conductivity between the PG-Si nanoparticles. The conductive carbon film 712 can also be implemented with the processes and composites described in Figures 1A-6B.

[0130] Referring to Figure 8A, a cross-sectional schematic diagram of a Si nanoparticle 801 according to one embodiment is shown. The Si nanoparticle 801 is made of Si, SiO x (x<2), or SiO 2The starting Si nanoparticles 801 have a diameter of 5 nm to several μm. Preferably, the Si nanoparticles are greater than 50 nm and less than 500 nm. The Si nanoparticles 801 can be spherical or irregular in shape, as seen in nanoparticles and microparticles.

[0131] Referring to Figure 8B, there is shown Si nanoparticles 801 at least partially covered with carbon black (CB) nanoparticles 802. Preferably, the diameter of the CB nanoparticles 802 is smaller than the diameter of the Si nanoparticles 801. More preferably, the diameter of the CB nanoparticles 802 is 5-10 times smaller than the diameter of the Si nanoparticles 801. Covering may be achieved by mechanical mixing of the dry powders, such as by ball milling or blade / disk grinding.

[0132] 8B and 8C, there is shown a Si-PG composite 810 according to one embodiment. The Si-PG composite 810 further includes a polyhedral graphene coating 812. The polyhedral graphene coating 812 is on the Si nanoparticles 801. The polyhedral graphene coating 812 is achieved by a Joule heating process.

[0133] The Joule heating process involves Joule heating of a bulk powder mixture of Si and CB, such as Si nanoparticles 801 covered with carbon black (CB) nanoparticles 802. In the bulk powder mixture, some of the CB 802 cover the Si nanoparticles 801 and some are in the vicinity of the Si nanoparticles 801. In the flash Joule heating process, the mixture of CB 802 and Si nanoparticles 801 is rapidly heated to over 2000°C. This heating converts the CB nanoparticles 802 into polyhedral graphene nanoparticles 812. Some of the PG 812 at least partially coat the Si nanoparticles 801, forming a Si-PG composite 810. Other PG 812 remains unattached in the mixture. The unattached PG 812 acts as a conductive filler. The proportion of the attached PG 812 depends on the mass ratio of Si 801 to CB 802. The mass ratio of Si 801:CB 802 is preferably 80:20 to 20:80. The Si core 801 in this embodiment is made of SiO, SiO x (x<2) or SiO 2 Or any combination thereof.

[0134] 8D, a Si-PG composite 820 according to a further embodiment is shown. The Si core 821 of the Si-PG composite 820 is made of SiO, SiO x (x<2) or SiO 2 A composite of a Si core 801 with a layer 822. Such a construction can be used in conjunction with the above-mentioned SiO and SiO 2 This provides the advantage of the following characteristics:

[0135] One advantage of using the Si-PG composite 820 as an anode material for Li-ion batteries is that the polyhedral graphene shell covering the Si has high mechanical strength compared to similar shell coatings made from carbon or carbon black. Another advantage is the high electrical conductivity of graphene compared to carbon or carbon black. Another advantage of the disclosed Si-PG composite 820 over known composites with Si nanoparticles loosely dispersed on graphene sheets is that the Si and PG are bonded together and can expand and contract together.

[0136] Referring to FIG. 9A, an exemplary SiO 2 -SEM images of composite material 900 are shown. 2 The composite material 900 is the SiO 2 -An example of a composite material 810. SiO 2 - Composite material 900 is SiO 2 -PG composite single particle. 2 Nanoparticles 901 are 500 nm and SiO 2 The average diameter of the PG 902 covering the nanoparticles 901 is 40 nm to 60 nm.

[0137] Now referring to FIG. 9B, cluster SiO 2 -PG composite 910 is shown. 2 Cluster 903 is composed of several SiO 2 Contains nanoparticles 901. SiO 2 The cluster 910 of the -PG composite is a CB as in FIG. 8B, with unclear SiO 2 This is obtained by coating clusters of nanoparticles 903 with SiO 2 Clusters of -PG nanoparticles 910 are further obtained by converting CB via a Joule heating process as in FIG. 8C.

[0138] 10A and 10B, the individual SiO 2 -PG composite 900 and cluster SiO in FIG. 9B 2 10A and 10B show the results of EDX analysis of the SiO -PG composite material 910, respectively. The EDX results indicate the presence of Si, C, and O with approximate atomic masses of Si:C:O=65:20:15 for the analysis in FIG. 10A and Si:C:O=80:15:5 for the analysis in FIG. 10B, with the predominant atomic mass being silicon. This result is due to the consumption of some of the oxygen during the joule flushing process, resulting in the SiO -PG composite material 910 being the predominant atomic mass. 2 This indicates that a part of the SiC was converted into Si and SiC.

[0139] Referring to FIG. 11A, a cross-sectional schematic diagram of a starting Si nanoparticle 1101 according to one embodiment is shown. The Si nanoparticle 1101 can be the Si nanoparticle 801 of FIG. 8A. The Si nanoparticle 1101 of this embodiment can have a diameter of 10-100 nm, or 100-1000 nm, or 1 μm-20 μm. The silicon nanoparticle 1101 of this embodiment can be in the shape of a sphere, an irregular particle, a rod, a nanowire, or a two-dimensional structure. The silicon nanoparticle 1101 of the present invention can be an isolated particle or a collection of nanoparticles with a branched structure that can range in size from 100 nm to several μm. The surface 1103 of the Si nanoparticle 1101 can be smooth, nanoporous, or microporous.

[0140] Referring to FIG. 11B, a cross-sectional schematic diagram of a carbon-coated Si nanoparticle 1110 is shown. The Si nanoparticle 1101 is coated with a layer of carbon 1112 on top of the Si nanoparticle 1101. Depending on the carbon deposition method, the layer of carbon 1112 is mainly amorphous. Amorphous carbon may refer to carbon with a low crystalline structure and / or a high proportion of sp3 carbon. The layer of carbon 1112 serves as the feedstock for a subsequent flash Joule heating process that can convert the carbon into graphene. To be suitable for the Joule heating process, the amorphous carbon layer 1112 may be further processed to increase its electrical conductivity, as shown in FIG. 11C. However, if the carbon layer 1112 is sufficiently conductive, it may already be suitable for Joule heating.

[0141] In one example, the coating process step can be accomplished by forming carbon 1112 directly on the Si nanoparticles 1101. An example of direct carbon coating on the Si nanoparticles 1101 is by acetylene gas in a tube oven or rotary oven. Other carbon deposition processes involving pyrolysis of carbon from other hydrocarbons or alcohols are also applicable. Another example of direct carbon coating is the use of hydrothermal carbonization of glucose (or sucrose or fructose or other carbohydrates) in an aqueous solution in the presence of the Si nanoparticles 1101 in a reactor. In a typical reaction, 5 g of glucose is dissolved in 100 mL of water containing 4% by weight of Si nanoparticles and heated at 180° C. for 2 hours in a Teflon-lined hydrothermal reactor. The free liquid is removed, the sludge is filtered, and the powder is dried, resulting in a powder of carbon-coated Si nanoparticles 1110.

[0142] In another example, the carbon coating 1112 can be achieved indirectly by coating a high carbon material on the Si nanoparticles 1101 and then converting the high carbon material to carbon. In some examples, the high carbon material can include any material with a carbon content greater than 10%, including other materials such as oxygen, hydrogen, and nitrogen. Other intermediate process steps to convert the high carbon material to carbon can include liquid and solid dispersions, spray coating, spin coating, deposition (high vacuum, low vacuum, chemical or physical), drying or oven heating. One example of a high carbon coating is a film of a polymer or monomer on the Si nanoparticles. One such polymer is acrylic. The coating can be done by spin coating or spray coating.

[0143] Referring now to FIG. 11C, a cross-sectional schematic diagram of pyrolyzed carbon coated Si nanoparticles 1120 is shown according to one embodiment. A subsequent pyrolysis process is required to make the carbon coated Si nanoparticles 1110 of FIG. 11B suitable for a Joule heating process in which the predominantly amorphous carbon is converted to predominantly graphene. The subsequent pyrolysis process enhances the electrical conductivity of the carbon coating 1112 of FIG. 11B and / or removes non-carbon impurities, organic impurities, inorganic impurities, and hydrocarbons. In some instances, the pyrolysis process can increase the carbon content of the coating to a greater amount than before the pyrolysis process was performed. The carbon coating 1112 covering the Si nanoparticles 1101 is pyrolyzed at 600-900° C. for several hours in an inert atmosphere to obtain a conductive carbon coating 1122. The preferred resistivity of carbon-coated Si powder suitable for Joule heating is in the range of 0.3 to 700 ohm*cm, as described in further detail in the Patent Cooperation Treaty Application by Mancevski et al., International Application No. PCT / CA2022 / 051406, having an international filing date of September 21, 2022, which is incorporated herein by reference in its entirety. The electrical conductivity of the carbon coating 1122 can be controlled by the thickness of the carbon layer 1112 prior to pyrolysis, and the temperature and time of pyrolysis. It is understood that if the electrical conductivity of the carbon layer 1112 is within the parameters required for Joule heating, then the carbon-coated Si nanoparticles 1110 of FIG. 11B may not be pyrolyzed.

[0144] Referring now to FIG. 11D, a cross-sectional schematic diagram of a silicon-turbostratic graphene (Si-TG) composite 1130 is shown. The Si-TG composite 1130 is obtained by Joule heating a bulk powder of conductive carbon coated Si nanoparticles 1120 of FIG. 11C. Joule heating converts the pyrolyzed carbon layer 1122 of FIG. 11C into a turbostratic graphene (TG) layer 1132 covering the surface of the Si nanoparticles 1101 to produce the Si-TG composite 1130. The TG layer 1132 may be a single continuous layer or multiple overlapping layers. The thickness of the TG layer 1132 depends on the thickness of the pyrolyzed carbon layer 1122 of FIG. 11C. The TG layer 1132 may be a single layer of graphene, few layers of graphene or multi-layers of graphene with wall thicknesses of <1 nm to 100 nm. Furthermore, the TG layer 1132 may be a single domain crystal or a multi-domain crystal.

[0145] In one embodiment, the Si nanoparticles 1101 and the TG layer 1132 of the Si-TG composite 1130 are bonded together such that they can expand and contract together. In another configuration, the Si nanoparticles 1101 and the TG layer 1132 are not bonded together such that the Si nanoparticles 1101 can move relative to the TG layer 1132.

[0146] The TG layer 1132 can be doped with nitrogen to enhance its electrical conductivity. Nitrogen doping can be achieved directly by performing Joule heating in a nitrogen rich environment. Such a nitrogen rich environment is N 2 , N.H. 3 , N 2 O, NO, NO xor other gaseous atmosphere of gaseous nitro compounds. The environment can be pure, a mixture of different nitro compounds, or a mixture of nitro compounds with other inert gases such as Ar or He. By adjusting the concentration of nitrogen gas in the inert gas, the nitrogen doping level in the TG layer 1132 can be adjusted. Nitrogen doping can also be achieved by incorporating materials in the carbon coating 1122 of FIG. 11C that produce nitrogen upon decomposition at high temperatures. One such material is glucosamine as a source of N-doped carbon, which can be used in hydrothermal carbonization to coat the Si nanoparticles 1101 with a high-nitrogen carbon layer. Other examples can be urea, melamine, cyanamide, amino acids, proteins, chitin, etc.

[0147] 11E, 11F, and 11G, TEM microscopy images of the exemplary Si-TG composite nanoparticles 1130 of FIG. 11D according to one embodiment are shown. The exemplary Si-TG composite nanoparticles 1130 were produced as described above. In this example, 100 nm diameter Si nanoparticles were coated with carbon by hydrothermal carbonization of table sugar as described above. The Si-carbon composite was pyrolyzed in an oven at 850° C. for 1 hour. The resulting Si pyrolytic carbon was Joule heated in a quartz tube to convert the carbon to graphene. Details of the Joule heating process are disclosed in PCT / CA2022 / 051406 to Mancevski et al. The resulting Si-TG composite includes Si nanoparticles (not directly visible due to the graphene layer covering them) and graphene layers 1140 (which can be seen in cross section at the edge of the composite particle). The graphene layers 1140 are shown to include approximately 10 graphene layers 1142. The graphene layer 1140 uniformly coats the Si nanoparticles. Close inspection of the graphene layer at 1142 shows light and dark lines representing each of the 10 graphene layers and the gaps between them. The light and dark lines at 1144 indicate the graphene crystallinity and number of graphene layers.

[0148] 11H, 11I, and 11J, Raman plots verifying the crystal structure of Si and graphene in the Si-TG composites are shown. Raman microscopy was used to confirm the crystal structure of the exemplary Si-TG composites in FIGS. 11E, 11F, and 11G.

[0149] FIG. 11I is a Raman plot of the Si-graphene sample, showing the presence of graphene peaks (2D peaks indicative of a well-defined graphene structure) 1152, the presence of Si peaks 1154, and the presence of SiC peaks 1156 and SiO 2 The Raman signature shows the presence of peak 1158. The G peak 1160 in the Raman signature is the primary form of graphene and graphite. The G peak 1160 represents the planar sp2 bonded carbon that constitutes graphene. The D peak 1162 in the Raman signature is known as the disorder band or defect band. The D peak 1162 represents the presence of defects in graphene. The Raman peaks 1152, 1154, 1156, and 1158 confirm the unique structure of the Si-TG composite in this example. SiC and SiO 2 were formed during the Joule heating process. Figure 11J shows a magnified overlay of Raman peaks 1152, 1154, 1156, 1158, 1160, 1162 of three different material samples. Figure 11H shows the Raman signature of pure Si nanoparticles before processing.

[0150] 11K-11N, which are SEM images with EDX analysis results of exemplary Si-TG composites prepared by steps of the disclosed process according to further embodiments. The starting Si nanoparticles in this example have an average diameter of 1 μm. The SEM images show that the Si-TG composites can be individual nanoparticles (FIG. 11M) or form an aggregate of branched structures (FIGS. 11K, 11L, and 11N). The EDX results show the presence of Si, C, and O, with carbon loadings ranging from 43-63% for the branched structures and about 84% for the individual composites. In the average Si-TG composite of this example, the Si loadings were 35-41% for the branched structures and about 9% for the individual composites. The presence of O indicates the presence of SiO in the structure of the composites. 2indicates the existence of Referring now to FIG. 11O, a thermogravimetric analysis (TGA) plot of an exemplary Si-TG composite prepared by the steps of the disclosed process is shown. TGA uses thermogravimetric analysis (TGA) to determine the composition of the Si-TG composite. The starting Si nanoparticles in this example have an average diameter of 1 μm. The results show that the loading of Si was 81% and graphene was 19%. The disclosed process procedure allows the production of Si-TG composites with Si loadings ranging from less than 5% to 95%. The advantage of this high Si loading is that battery anodes can be constructed with very high Si loadings. This loading is beneficially higher than that achievable by current state-of-the-art techniques for Si battery anode production, such as the production of mixed Si nanoparticles and loose graphene sheets.

[0151] One advantage of the Si-TG composite as an anode material for lithium-ion batteries is the higher mechanical strength of the graphene layer covering Si compared to a similar shell coating made of amorphous carbon. Another advantage is the higher electrical conductivity of graphene compared to carbon and carbon black. Another advantage of the disclosed Si-TG composite compared to known composites with loosely dispersed Si nanoparticles on graphene sheets is that the TG coating protects the Si from degradation due to repeated SEI formation and electrical contact loss.

[0152] One of the problems that can occur during the formation of graphene coatings (PG or TG) is the formation of a SiC layer at the interface between Si and graphene due to the exposure of Si nanoparticles to high temperatures of 900 °C to over 2000 °C generated by the Joule heating process. This layer can reduce the electrical conductivity of the Si-graphene composite. However, if the resulting SiC material is β-SiC, which is known to have lithium storage capacity, the composite is suitable for battery applications. If the core particles contain SiO instead of Si, 2If the SiC is nanoparticles, the formation of SiC may be reduced. Another means of reducing the presence of SiC in the present invention is the use of CO, which has been shown to suppress the formation of SiC during the growth of graphene by prior art CVD methods. 2 The method involves Joule heating of a carbon source in the presence of CO gas. 2 can be injected into the Joule heated reactor as a gas or decomposed at high temperatures to produce CO 2 One such material is calcium acetate (Ca(OAc) 2 ) at high temperatures and CO 2 The calcium acetate simultaneously makes the carbon or graphene in the Si-carbon or Si-graphene composites porous.

[0153] 12A, a cross-sectional schematic diagram of a coated Si nanoparticle 1200 according to one embodiment is shown. The coated Si nanoparticle 1200 includes a Si nanoparticle 1201. The Si nanoparticle is configured similarly to the Si nanoparticle 801 of FIG. 8A. The coated Si nanoparticle 1200 further includes a sacrificial layer 1202. The sacrificial layer 1202 is disposed proximate to and in contact with the Si nanoparticle 1201. The sacrificial layer is configured and arranged to prevent Si of the Si nanoparticle 1200 from interacting with carbon at elevated temperatures. The coated Si nanoparticle 1200 further includes a carbon layer 1204. The carbon layer 1204 coats the coated Si nanoparticle 1200 with carbon. The carbon layer 1204 is disposed outside the sacrificial layer 1202 such that the sacrificial layer 1202 is disposed between the Si nanoparticle 1201 and the carbon layer 1204. In one example, the sacrificial layer 1202 is silicon oxide on the silicon nanoparticle 1201. In a further example, the sacrificial layer 1202 is plasma treated on the surface of the Si nanoparticles 1201 to produce an oxidized surface. The sacrificial layer can also be a metal such as nickel that can be deposited by electroless means onto the Si nanoparticles 1201. Other sacrificial layers 1201 include dielectric or inorganic coatings.

[0154] Referring to Figure 12B, a cross-sectional schematic diagram of pyrolyzed carbon coated Si nanoparticles 1210 is shown according to one embodiment. The pyrolyzed carbon coated Si nanoparticles 1210 include a pyrolyzed carbon layer 1212 on a sacrificial layer 1202. The pyrolyzed carbon layer 1212 is conductive carbon. The pyrolyzed carbon layer 1212 is obtained by pyrolyzing the carbon layer 1204 of Figure 12A. The pyrolyzed carbon coated Si nanoparticles 1210 are otherwise constructed similarly to the coated Si nanoparticles 1200.

[0155] 12B and 12C, there is shown a cross-sectional schematic diagram of a turbostratic graphene coated Si nanoparticle 1220 according to one embodiment. The turbostratic graphene coated Si nanoparticle 1220 comprises a turbostratic graphene layer 1222. The turbostratic graphene layer 1222 is obtained by Joule heating a pyrolyzed carbon coated Si nanoparticle 1210 to convert the pyrolyzed carbon layer 1212 into a turbostratic graphene layer 1222 that covers the outer surface of a sacrificial layer (SL) 1202. The turbostratic graphene coated Si nanoparticle 1220 is otherwise configured similarly to the pyrolyzed carbon coated Si nanoparticle 1210.

[0156] 12D, a cross-sectional schematic diagram of a Si-void-TG nanoparticle 1230 according to one embodiment is shown. The Si-void-TG nanoparticle 1230 includes a void 1232. The void 1232 is a space that does not contain solid material. The void is located between the turbostratic graphene layer 1222 and the Si nanoparticle 1201. In some configurations, the void does not have to be complete and there is some contact between the graphene layer 1222 and the Si nanoparticle 1201. The void 1232 is obtained by washing the sacrificial layer 1202 of FIG. 12C to remove the sacrificial layer 1202. Depending on the chemical nature of the sacrificial layer 1202, the sacrificial layer 1202 is washed with a base, acid or solvent. In one example, SiO 2The sacrificial layer 1202 is removed by immersion in 2M NaOH solution for 1 hour with stirring. In another example, the Ni sacrificial layer is removed with dilute hydrochloric acid. The voids help the Si nanoparticles 1201 to expand without imparting excessive stress to the graphene layer 1222 during the lithiation / delithiation process.

[0157] 12E, there is shown a cross-sectional schematic diagram of pyrolyzed carbon coated Si nanoparticles 1240 according to one embodiment, which are configured similarly to pyrolyzed carbon coated Si nanoparticles 1120 of FIG.

[0158] Referring now to FIG. 12F, a cross-sectional schematic diagram of a pyrolyzed carbon void Si nanoparticle 1250 according to one embodiment is shown. The pyrolyzed carbon void Si nanoparticle 1250 includes a void 1252. The void 1252 is a space that is free of solid material. The void 1252 is located between the Si nanoparticle 1251 and the pyrolyzed carbon layer 1253. The void 1252 is obtained by etching the pyrolyzed carbon coated Si nanoparticle 1240 of FIG. 12E to reduce the diameter of the Si core 1251. This reduction in diameter leaves a space of the void 1252 between the Si nanoparticle 1251 and the pyrolyzed carbon shell 1253. In some configurations, the void need not be complete and there is some contact between the pyrolyzed carbon shell 1253 and the Si nanoparticle 1251. The pyrolyzed carbon void Si nanoparticle 1250 is otherwise configured similarly to the pyrolyzed carbon coated Si nanoparticle 1240 of FIG. 12E. One way to etch the Si cores 1251 is to etch with a 2M NaOH solution for a fixed time. This time can be used to control the size of the new Si nanoparticles 1251 and therefore the size of the voids 1252.

[0159] Referring now to FIG. 12G, a cross-sectional schematic diagram of a Si-void-TG nanoparticle 1260 according to one embodiment is shown. The Si-void-TG nanoparticle 1260 is constructed similarly to the Si-void-TG nanoparticle 1230 of FIG. 12D. The Si-void-TG nanoparticle 1260 is obtained by converting the pyrolyzed carbon coating 1253 into a graphene layer by Joule heating. The voids help to reduce the formation of SiC on the Si nanoparticle 1251 during the Joule heating process. The voids between the Si and graphene of the Si-void-TG composite help the Si to expand during the lithiation / delithiation process.

[0160] In one embodiment, the Si nanoparticle core 1251 is completely etched away. In this embodiment, the void 1252 includes the entire space previously occupied by the Si nanoparticle 1251. The graphene structure of the pyrolyzed carbon layer 1253 now forms an empty shell of pyrolyzed carbon 1250. For clarity, empty is understood to mean substantially absent of solid matter. In some embodiments, the empty pyrolyzed carbon shell 1250 can be converted to an empty TG shell 1260 by a Joule heating process.

[0161] Referring to FIG. 12H, an SEM image of an exemplary empty graphene shell 1270 according to one embodiment is shown. The graphene shell 1270 is a void-TG shell such as Si-void-TG nanoparticle 1260 where the Si nanoparticle core 1251 has been completely etched away. The exemplary graphene shell 1270 is made from a sacrificial Si nanoparticle core with an average diameter of 1 μm, not shown in the photograph. While removing the Si core, it may be coated with carbon, pyrolytic carbon, or graphene to form a shell structure. If the shell is carbon or pyrolytic carbon, an additional step of Joule heating converts the carbon to graphene.

[0162] 12I, there is shown an SEM image 1272 of an exemplary TG-shell and corresponding EDX map 1274 according to one embodiment. The EDX map 1274 shows that the presence of C and O is measured, and that Si is present at <1%.

[0163] 12J, there is shown an SEM image 1276 and corresponding EDX trace 1278 of an exemplary TG-shell structure according to one embodiment. The EDX trace 1278 shows very little Si, and the presence of C and some O. In one embodiment, the empty TG shells are filled with Li, Na, Sn, or other metals, or CO. 2 , H 2 or other gases. In further embodiments, the sacrificial core can be composed of a metal or oxide. In one implementation, the empty TG shells can be backfilled with Li, Na, Sn, or other metals, or CO. 2 , H 2 or other gas. In a further embodiment, the core of the sacrificial material may be composed of a metal or an oxide.

[0164] 12K, pyrolyzed carbon coated Si nanoparticles 1280 are shown according to one embodiment. The pyrolyzed carbon coated Si nanoparticles 1280 include a pyrolyzed carbon coating 1282. The pyrolyzed carbon coating 1282 includes pores 1285. The pyrolyzed carbon coated Si nanoparticles 1280 are otherwise configured similarly to the pyrolyzed carbon coated Si nanoparticles 1120 of FIG. 11C. The pyrolyzed carbon coated Si nanoparticles 1280 are prepared by pyrolyzing the pyrolyzed carbon coating 1282 with a pyrolyzed carbon solution containing NaOH, KOH, H 3 PO 4 , ZnCl 2 , FeCl 3 , or Ca(OAc) 2 The porous carbon can be made porous by a chemical activation process, typically performed at 450-900° C. in the presence of an activator such as CrNbO4 or other activators well known in the activated carbon industry.

[0165] Referring now to FIG. 12L, a Si-porous-graphene (Si-pTG) composite 1290 is shown. The Si-pTG composite 1290 includes a graphene layer 1292. The graphene outer layer 1292 includes pores 1295. The Si-pTG composite 1290 is otherwise configured similarly to the pyrolyzed carbon coated Si nanoparticles 1280 of FIG. 12K. In one embodiment, the Si-pTG composite 1290 is obtained by converting the porous carbon coating 1282 of FIG. 12K into porous graphene 1292 by a Joule heating process. In a further embodiment, the Si-pTG composite 1290 is obtained by subjecting the Si-TG composite 1130 of FIG. 11D to a chemical activation process to form pores 1295 in the graphene. The pores 1295 may be nanopores, mesopores, or micropores. The presence of pores in graphene facilitates the transport of Li from the electrolyte to Si and vice versa.

[0166] Another way to impart porosity to the graphene layers 1292 of the Si-graphene composite 1290 is by mechanical methods such as ball milling (vertical or horizontal mill) or speed mixer grinding (with balls, powder alone). Ball milling requires the use of small hard balls mixed with the ground powder in a closed jar, and the amount of damage to the surface where pores form depends on the grinding time, ball to powder ratio, and loading ratio. For speed mixers, the use of balls is optional, and the powder itself can be used to damage the composite surface and form pores. Mechanical pore formation results in the formation of shallow pores. To form deeper pores, a chemical activation treatment can be performed after mechanical milling.

[0167] Referring to Figure 13A, there is shown a cross-sectional schematic diagram of a starting mixture 1300 according to one embodiment. The starting mixture 1300 includes Si nanoparticles 1301 and carbon particles 1302. The starting mixture 1300 is otherwise configured similarly to and as the Si nanoparticles 801 covered with carbon black (CB) nanoparticles 802 of Figure 8B.

[0168] The size of the carbon particles 1302 is preferably smaller than the Si nanoparticles 1301, but not required. Examples of carbon particles 1302 include MetCoke, PetCoke, biochar, plastic char, and other common carbon sources used in Joule heating, which are likely to produce flake-like graphene morphology. The starting mixture 1300 can be achieved by mechanical mixing of dry powders, such as ball milling or blade / disk grinding.

[0169] Now referring to FIG. 13B, a cross-sectional schematic diagram of a silicon and flake turbostratic graphene (Si-FTG) composite 1310 according to one embodiment is shown. The Si-FTG composite 1310 is obtained by applying a flash Joule heating process to the bulk powder 1300 of FIG. 13A. When flash Joule heating is applied, the mixture is rapidly heated to above 2000° C., and the carbon particles 1302 are converted into flaky graphene 1312. Some FTG 1312 at least partially coat the Si nanoparticles 1301, forming a Si-FTG composite 1310. When some FTG 1312 remains unattached in the mixture, the unattached FTG functions as a conductive filler. The ratio of attached FTG 1312 to unattached FTG 1312 depends on the ratio of Si 1301 to carbon chunks 1302 of FIG. 13A. It is preferred that the mass ratio of Si:C is 80:20 to 20:80. The Si core 1301 in this embodiment is SiO, SiO x (x<2) or SiO 2 Or any combination thereof.

[0170] 14A, there is shown a further starting mixture 1400 according to one embodiment. Starting mixture 1400 includes Si nanoparticles 1401, carbon blacks (CBs) 1402, and carbon particles such as coke or char 1403. Starting mixture 1400 is otherwise configured similarly to starting mixture 1300 and is configured as such.

[0171] Referring to Figure 14B, a cross-sectional schematic diagram of a silicon and polyhedral and flake turbostratic graphene (Si-PG-FTG) composite 1410 according to one embodiment is shown. The Si-PG-FTG composite 1410 is obtained by applying a flash Joule heating process to the bulk powder starting mixture 1400 of Figure 14A. The carbon particles 1403 are transformed into FTG 1413 and the CB nanoparticles 1402 are transformed into PG 1412. A portion of the FTG 1413 and PG 1412 at least partially coats the Si nanoparticles 1401.

[0172] 15A, 15B, and 15C, high resolution TEM images of exemplary hollow polyhedron-like graphene nanoparticles according to various embodiments are shown. The hollow polyhedron-like graphene nanoparticles include 3-50 layers of graphene. As shown in FIG. 15A, the polyhedron-like graphene nanoparticles can self-assemble into branched structures consisting of multiple PG nanoparticles with lengths ranging from a few nm to a few μm.

[0173] Referring to Figure 15D, a high resolution TEM image of solid polyhedral graphene nanoparticles according to one embodiment is shown, which do not include voids in the nanoparticles.

[0174] 16A and 16B, TEM images of an example of flake graphene according to various embodiments are shown. Typical FTG graphene has a lateral size of 100 nm to 2 μm and a thickness of 2 to more than 10 layers. Polyhedral graphene is a closed form of graphene that forms polyhedral cages, with multiple cages nested within each other. Spherical cages are also possible. In some cases, polyhedral graphene nanoparticles can be voided (hollow) or solid (void-free). Typical PG graphene has a (diameter) size of 20 nm to 200 nm and a wall thickness of 2 to more than 50 layers.

[0175] 17A and 17B, cross-sectional schematic diagrams are shown of a Li-ion battery 1700 according to various embodiments. Figure 17B shows the Li-ion battery 1700 during a discharging operation.

[0176] The lithium ion battery 1700 includes an outer housing 1702. The outer housing 1702 may be a metal housing or a polymer casing, depending on the type of battery. The outer housing 1702 houses the remaining components, which are described further below.

[0177] The lithium ion battery 1700 further includes an aluminum foil current collector 1704 and a cathode material 1706. The cathode material 1706 is disposed on the aluminum foil 1704 (i.e., the cathode electrode 1707). The cathode 1707 is typically made of lithium cobalt oxide (LiCoO 2 ), Li(Ni 0.6 Mn 0.2 Co 0.2 )O 2 It is made from lithium metal oxide materials such as (NMC622).

[0178] The lithium ion battery further includes a copper foil current collector 1708 and an anode material 1710. The anode material 1710 is disposed on the copper foil (i.e., anode electrode 1711). The material of the anode material 1710 is a Si-graphene composite material as disclosed herein. Known anodes 1711 are made of graphite or composite materials such as silicon-carbon, tin-carbon, etc. The anode 1711 of the present disclosure is made of a Si-graphene composite material as disclosed herein.

[0179] The lithium ion battery 1700 further includes a separator 1712. The separator 1712 is disposed between the electrodes 1707, 1711. The separator 1712 electrically separates the anode 1711 and the cathode 1707 while allowing the lithium ions 1709 to pass through the separator 1712. The separator 1712 is a porous polymer membrane. The separator 1712 is made of a single layer or multiple layers of a polymer such as polypropylene, polyethylene, etc.

[0180] The cathode electrode 1707, the anode electrode 1711, and the separator membrane 1712 are immersed in a solvent that functions as the electrolyte. A typical liquid electrolyte for a lithium-ion battery includes lithium hexafluorophosphate (LiPF ) in an organic solvent, such as a mixture of ethylene carbonate, dimethyl carbonate, and diethyl carbonate. 6 ) and other lithium salts. Additional electrolyte additives such as fluoroethylene carbonate (FEC) are added to obtain a good solid electrolyte interface (SEI) layer for long-term stability.

[0181] During the charging process (i.e., charging the battery), lithium ions 1709 migrate through the electrolyte from the cathode 1707 to the anode 1711. The lithium ions are stored in the anode 1711 via different mechanisms, such as intercalation (graphite anodes) or alloying (silicon-based anodes).

[0182] During the discharging process (i.e., the battery 1700 supplies power to a load), lithium ions flow through the electrolyte from the anode 1711 back to the cathode 1707. This movement of lithium ions 1709 causes electrons 1714 to move in the opposite direction in an external electrical circuit, providing power to a load. Charging a lithium-ion battery is the reverse of the discharging process described above. During charging, an external voltage forces the lithium ions 1709 back to the anode 1711, and the electrons 1714 move back to the anode 1711 through the external electrical circuit.

[0183] In known electrode fabrication, the anode 1711 and cathode 1707 electrodes are fabricated from pouring a slurry onto corresponding current collectors. For example, a typical anode slurry contains active material (e.g., graphite, silicon-carbon composite), binder (e.g., polyvinylidene fluoride, carboxymethyl cellulose), conductive carbon (e.g., Super P), and solvent (e.g., water, n-methyl-2-pyrrolidone). The coated film is dried in an oven at 60°C to 80°C for 12 hours. Coin cells are typically fabricated in the 2032 type (button cell). The cells are assembled in an argon-filled glove box with low water and oxygen content (e.g., below 1 ppm).

[0184] 17C, there is shown an image of an example of a Li-ion battery 1750 of the present invention. The Li-ion battery 1750 was tested in a half-cell configuration.

[0185] The half-cell includes a lithium metal foil 1752 configured as a pseudo reference electrode in place of the cathode electrode. The coin cells were cycled (charged and discharged) between 1.5 V and 0.005 V at different C-rates (current densities). Additional electrochemical measurements were also performed at times to further evaluate the cell performance.

[0186] Referring to FIG. 18, a plot 1800 of an example of the results of testing the Si-graphene composite 1130 of FIG. 11D is shown. The average diameter of the Si particles 1101 of FIG. 11D was 1 μm. The plot 1800 compares the performance of the Si-graphene composite 1130 with a Si-hydrolyzed carbon composite and a pure Si material. In this test, the cell was operated at C / 2 for the first 50 cycles and at a rate of 1C for the next 50 cycles (1C=4.2mA / mg Si). The cell with the Si-graphene composite showed a stable capacity of ~600mAh / g at C / 2 and ~500mAh / g at 1C. For comparison, the cell with the Si-pyrolytic carbon composite started with a capacity of 600mAh / g, but dropped to ~250mAh / g at C / 2 and further to ~200mAh / g at 1C. The Si-only cell had a first cycle capacity of ~1400 mAh / g, which rapidly declined to ~100 at C / 2 and ~10 at 1C, disappearing after 100 cycles. This result demonstrates the advantage of graphene-coated Si in preventing the decomposition of Si particles.

[0187] The composites disclosed herein are also suitable for use as performance enhancing additives in cement and concrete applications, rubber and tire composite manufacturing, plastic and polymer composite manufacturing, and lubricant manufacturing. For some applications, such as rubber and tires, the preferred composite is silica-graphene.

[0188] Although the disclosed invention has been described with silicon-based nanoparticles, other non-silicon particles may be used to practice the disclosed invention. The other non-silicon particles may be anode materials such as titanium oxide, vanadium oxide, niobium oxide, molybdenum oxide, tungsten oxide, or transition metal carbides such as titanium carbide, vanadium carbide, niobium carbide, molybdenum carbide, tungsten carbide, or metals that alloy with Li, such as aluminum, bismuth, cadmium, magnesium, tin, antimony, etc. Other non-silicon particles include lithium cobalt oxide (LiCoO 2 )-LCO, Lithium Manganese Oxide (LiMn 2 O 4)-LMO, Lithium Nickel Manganese Cobalt Oxide (LiNiMnCoO 2 )-NMC, lithium iron phosphate (LiFePO 4 )-LFP, lithium aluminum nickel cobalt oxide (LiNiCoAlO 2 )-NCA, lithium titanate (Li 2 TiO 3 Other non-silicon particles may be cathodic materials such as, but not limited to, Pt, Pd, Ru, Au, Ir, Rh, Co, Fe, Cu, Ni, Zn, Bi, or other transition or main group metals; Pt(acac) 2 , AuCl 3 , AgNO 3 or other metal precursors; TiO 2 , Al 2 O 3 , SiO 2 or other oxides; or any combination of the above. The other non-silicon particles may be Fe, Co, Ni, Cu, or other transition metals; iron acetate, iron chloride, iron acetylacetonate, or other metal salts; iron oxide, cobalt oxide, or other transition metal oxides; iron hydroxide, nickel hydroxide, or other transition metal hydroxides; TiO 2 , Al 2 O 3 , SiO 2 or other oxides; or a combination of any of the above.

[0189] 19, a flow chart illustrating a method 1900 of producing a silicon graphene composite material, according to an embodiment, is shown. Method 1900 includes steps 1902 and 1904. Method 1900 can be used to produce composite materials, such as those shown in FIGS. 1-10.

[0190] In 1902, turbostratic graphene nanoparticles are provided.

[0191] In 1904, graphene nanoparticles are coated with a silicon material.

[0192]

[0023] Referring now to Figure 20, there is shown a flow chart illustrating a method 2000 of producing a silicon graphene composite material, according to one embodiment. Method 2000 comprises steps 2002, 2004 and 2006. Method 2000 can be used to produce composite materials such as those shown in Figures 11, 12K, 12L, 13 and 14.

[0193] In 2002, silicon nanoparticles are provided.

[0194] In 2004, silicon nanoparticles are coated with a carbon material.

[0195] In 2006, coated silicon nanoparticles were Joule heated to convert the carbon coating into graphene.

[0196] 21, a flow chart illustrating a method 2100 of manufacturing a silicon graphene composite material according to one embodiment is shown. Method 2100 comprises steps 2102, 2106, and 2110. According to some embodiments, method 2100 may further comprise steps 2108, 2104, and 2112, and / or step 2114. Method 2100 may be used to manufacture composite materials, such as those shown in Figures 12A-12G, for example.

[0197] At 2102, silicon nanoparticles are provided.

[0198] At 2104, the silicon nanoparticles are coated with a sacrificial layer.

[0199] At 2106, the nanoparticles are coated with an amorphous carbon material.

[0200] At 2108, the coated nanoparticles are heated to pyrolyze the amorphous carbon material. The pyrolysis process may increase the crystallinity and / or electrical conductivity of the amorphous carbon.

[0201] In 2110, the nanoparticles are Joule heated to convert the carbon material from step 2106 or step 2108 into turbostratic graphene.

[0202] At 2112, the sacrificial layer is etched to create voids between the silicon nanoparticles and the turbostratic graphene.

[0203] In 2114, the silicon nanoparticles are etched to create voids between the silicon nanoparticles and the turbostratic graphene. In some examples, the silicon may be etched prior to performing step 2110.

[0204] Although the above description provides examples of one or more devices, methods, or systems, it will be understood that other devices, methods, or systems may be included within the scope of the claims as interpreted by one of ordinary skill in the art.

Claims

1. A composite material comprising graphene nanoparticles at least partially coated with silicon.

2. The graphene nanoparticles are Turbostratic graphene nanoparticles, the turbostratic graphene nanoparticles having graphene layers that are misoriented with respect to one another; Polyhedral graphene nanoparticles; Spherical graphene nanoparticles; are porous, the pores of the graphene nanoparticles being at least partially filled with silicon; and a hollow core, said hollow core being at least partially filled with silicon 2. The composite material of claim 1, wherein the composite material is at least one of:

3. The silicon coating is coated with carbon; and Coated with graphene 2. The composite material of claim 1, wherein the composite material is at least one of:

4. 4. The composite material of claim 3, wherein the carbon coating is electrically conductive.

5. 10. The composite material of claim 1, wherein the silicon coating comprises a first layer of silicon and a second layer of silicon of a different composition.

6. 6. The composite material of claim 5, wherein the second layer is further coated with graphene.

7. The silicon coating is is the element silicon; SiO, SiO x or SiO 2 ; and It is silicon carbide 10. The composite material of claim 1, comprising at least one of:

8. 10. The composite material of claim 1 used as an anode in a battery.

9. The battery comprises: is a lithium-ion battery; and It is a sodium-ion battery 9. The composite material according to claim 8, wherein the composite material is at least one of:

10. 1. A composite material comprising silicon nanoparticles at least partially coated with turbostratic graphene, the turbostratic graphene having graphene layers that are misoriented relative to one another.

11. The turbostratic graphene coating is Porous; and Contains polyhedral graphene 11. The composite material of claim 10, wherein the composite material is at least one of:

12. The silicon nanoparticles are Si, SiO, SiO ｘ , SiO ２ or containing SiC; comprising a first silicon layer and a second silicon layer of a different composition; Contains the element silicon; and Diameter is 5 nm to 50 μm 11. The composite material of claim 10, wherein the composite material is at least one of:

13. 11. The composite material of claim 10, comprising voids between the silicon nanoparticles and the graphene coating.

14. 11. The composite material of claim 10 for use as an anode in a battery.

15. The battery comprises: is a lithium-ion battery; and It is a sodium-ion battery 15. The composite material of claim 14, wherein the composite material is at least one of:

16. providing turbostratic graphene nanoparticles having graphene layers that are misoriented with respect to one another; coating the turbostratic graphene nanoparticles with a silicon material; A method for manufacturing a composite material comprising:

17. The method of claim 16, wherein the turbostratic graphene nanoparticles are coated by chemical vapor deposition.

18. The turbostratic graphene nanoparticles are Polyhedral graphene nanoparticles; Spherical graphene nanoparticles; Porous; and Contains a hollow core The method for producing a composite material according to claim 16, wherein the method is at least one of the following:

19. 20. The method of claim 18, wherein the pores are filled with silicon.

20. 20. The method of claim 18, wherein the hollow core is at least partially filled with silicon.

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