Carbon aerogel electrode material and method for manufacturing the same

Abstract

To provide a carbon composition suitable for use in an environment including an electrochemical reaction.SOLUTION: A carbon composition includes: a carbon material having a porous structure; and a silicon-based material at least partially present in the porous structure of the carbon material, wherein the carbon composition contains more than about 10 wt.% of the silicon-based material, has a porosity between about 10% and about 80%, has a pore size at a maximum peak in a distribution of about 100 nm or less, and has a silicon utilization rate of at least about 20%.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] [Cross-reference of related applications] This application claims priority to U.S. Patent Application No. 16 / 803,348, filed on 27 February 2020, and U.S. Provisional Patent Application No. 62 / 811,230, filed on 27 February 2019, each of which is incorporated herein by reference in whole, and which are all governed by the definitions of terms herein.

[0002] [Technical field] This invention generally relates to nanoporous carbon-based materials. More specifically, it relates to carbon aerogels suitable for use in environments involving electrochemical reactions, for example, as electrode materials in lithium-ion batteries. [Background technology]

[0003] Aerogels are solid materials containing a highly porous network of micro- and meso-sized pores. Depending on the precursor material used and the processing performed, when the density of an aerogel is approximately 0.05 g / cc, the pores often account for more than 90% of the volume. Aerogels are generally prepared by removing the solvent from the gel (the solid network containing the solvent) in a manner that minimizes or prevents any shrinkage of the gel by capillary forces on the surface. Methods of solvent removal include, but are not limited to, supercritical drying (drying using a supercritical fluid, e.g., exchanging transient solvents in the gel with a supercritical fluid with low surface tension), solvent exchange with a supercritical fluid, solvent exchange with a fluid that is then converted to a supercritical state, subcritical or near-critical drying, and sublimation of the frozen solvent in freeze-drying processes, see, for example, PCT Patent Application Publication WO2016127084A1. It should be noted that drying under ambient conditions may cause gel shrinkage due to solvent evaporation, potentially leading to the formation of a xerogel. Therefore, the preparation of aerogels by the sol-gel method or other polymerization methods typically proceeds with the following steps: dissolution of solute in solvent, formation of sol / solution / mixture, formation of gel (which may include additional crosslinking), and solvent removal by supercritical drying or any other method that removes the solvent from the gel without disrupting the pores.

[0004] Aerogels can be formed from inorganic and / or organic materials. When aerogels are formed from organic materials such as phenol, resorcinol-formaldehyde (RF), phloroglucinol-fluoraldehyde (PF), polyacrylonitrile (PAN), polyimide (PI), polyurethane (PU), polybutadiene, polydicyclopentadiene, and their precursors or polymer derivatives, they can be carbonized (e.g., by thermal decomposition) to form a carbon aerogel, which may have different or overlapping properties (e.g., pore volume, pore size distribution, morphology, etc.) depending on the precursor material and method used. However, in all cases, there are specific drawbacks based on the material and application, such as low pore volume, broad pore size distribution, and low mechanical strength. In recent years, efforts have focused on the development and characterization of carbon aerogels as electrode materials with improved performance for applications in energy storage devices such as lithium-ion batteries (LIBs).

[0005] Lithium-ion batteries (LIBs) are widely used in a variety of applications, from portable electronic devices to automobiles. They are a type of rechargeable battery in which lithium ions move from the anode to the cathode during discharge and from the cathode to the anode during charging. Traditionally, the cathode is formed from a lithium metal oxide (e.g., cobalt, nickel, manganese), and the anode is formed from graphite, with lithium ions being inserted into the graphite layer during charging (energy storage). Graphite is widely used because it allows for higher lithium insertion than other known carbons.

[0006] With increasing demand for high-capacity anode and cathode materials, the main drawback of conventional LIBs is the limited capacity of graphite; in other words, graphite can only accommodate a limited amount of lithium. Silicon has a higher affinity for lithium than graphite (carbon) and can store significantly more lithium during charging than graphite, theoretically resulting in a higher capacity on the anode side of LIBs. For comparison, graphite, when combined with lithium, has a theoretical capacity of 372 mAh / g, while silicon has a theoretical capacity of 4200 mAh / g. These figures necessitate placing as much silicon as possible within the anode. However, a significant problem with silicon is that when fully lithified, its volume expands 3-4 times (often causing breakage or cracking), drastically limiting the amount of silicon that can be placed within the electrode.

[0007] Therefore, what is needed is an improvement of nanoporous carbon materials, including functional forms and optimal porous structures, while solving at least one of the problems described above. However, in light of the art considered as a whole at the time the present invention was made, it was not clear to those skilled in the art how the shortcomings of the prior art could be overcome.

[0008] While certain aspects of the prior art have been considered to facilitate the disclosure of the present invention, the applicant does not in any way reject these technical aspects, and believes that the claimed invention may encompass one or more of the aspects of the prior art considered herein, in particular in combination with the innovative aspects described herein.

[0009] The present invention can address one or more of the technical problems and shortcomings described above. However, we believe that the present invention may also prove useful in addressing other problems and shortcomings in many other areas of the art. Therefore, the claimed invention should not be construed as being limited to addressing the specific problems or shortcomings discussed herein.

[0010] Wherever a document, act, or item relating to knowledge is referenced or considered in this Specification, such reference or consideration is not deemed to mean that such document, act, or item relating to knowledge, or any combination thereof, was publicly available, known to the public, part of common sense, or constitutes prior art under applicable legal provisions on the priority date, nor is it deemed to be known to be relevant to an attempt to solve a problem relating to this Specification. [Overview of the project]

[0011] The improvement of nanoporous carbon materials has been needed for many years, but had not been achieved until now. This is now being realized through a new, useful, and non-trivial invention.

[0012] A first general embodiment relates to a carbon composition, which comprises a carbon material, such as a nanoporous carbon material, and a silicon-based material. The carbon material has a porous structure, the silicon-based material in the carbon composition exceeds about 10% by weight, and the silicon utilization rate is at least about 20%.

[0013] In exemplary embodiments, the carbon material comprises a fibrilous morphology and has one or more porous structures having a Young's modulus of at least about 0.2 GPa, an electrical conductivity of at least about 10 S / cm, and a density between about 0.15 g / cc and about 1.5 g / cc.

[0014] In another exemplary embodiment, the carbon composition comprises a silicon-doped nanoporous carbon material having a silicon utilization rate of at least about 20%, wherein the carbon material is doped with silicon in an amount exceeding about 25% by weight. Optionally, the conductivity of the carbon material may be at least about 10 S / cm. Optionally, the Young's modulus of the carbon material may be at least about 0.2 GPa.

[0015] In further exemplary embodiments, the carbon composition includes a silicon-doped nanoporous carbon material having a porous structure comprising a fibrilous morphology, a Young's modulus of at least about 0.2 GPa, a density between about 0.15 g / cc and about 1.5 g / cc, and a silicon utilization rate of at least about 20%. Optionally, the conductivity of the carbon material may be at least about 10 S / cm.

[0016] In another exemplary embodiment, the carbon composition comprises a silicon-doped nanoporous carbon material having a porous structure comprising a fibrilous morphology, an electrical conductivity of at least 10 S / cm, a density between about 0.15 g / cc and about 1.5 g / cc, and a silicon utilization rate of at least about 20%. Optionally, the Young's modulus of the carbon material may be at least about 0.2 GPa.

[0017] In any embodiment, the nanoporous carbon material may be a carbon aerogel, such as an imide-derived carbon aerogel, like a polyimide-derived carbon aerogel. In further embodiments, the carbon aerogel may take the form of a monolith or particulate form, such as a powder. When the carbon aerogel exists in monolithic form, the carbon material may be substantially binder-free or completely binder-free. Alternatively or additionally, the thickness of the monolithic carbon aerogel may be between about 10 micrometers and about 500 micrometers.

[0018] In exemplary embodiments where the carbon aerogel is in particulate form, the diameter of the particulate carbon aerogel can be about 1 micrometer to about 50 micrometers.

[0019] In any embodiment, the porous structure of the nanoporous carbon material may feature pores in the carbon material that partially, substantially, or completely surround a silicon-based material, such as forming an interconnection structure around silicon characterized by multiple connection points between silicon and the pore walls. For example, the silicon-based material may be present at least partially within the porous structure of the carbon material.

[0020] In any embodiment, the nanoporous carbon material may be doped with silicon in an amount of about 5% to 80% by weight of the carbon material. For example, the carbon material may comprise from about 25% to about 65% by weight of silicon, based on the carbon material.

[0021] In any embodiment, the pore volume of the nanoporous carbon material may be at least 0.3 cc / g.

[0022] In any embodiment, the prelithiation porosity of the nanoporous carbon material may be between about 10% and about 80%.

[0023] In any embodiment, residual nitrogen in the carbon material, e.g., the nanoporous carbon material, may be at least about 4% by weight.

[0024] In any embodiment, the capacity of the silicon-doped nanoporous carbon material may be at least about 800 mAh / g. For example, the capacity of the silicon-doped nanoporous carbon material may be up to about 2000 mAh / g.

[0025] In any embodiment, the full width at half maximum of the porous structure of the nanoporous carbon material may be about 50 nm or less (i.e., a narrow pore size distribution).

[0026] In any embodiment, the pore diameter at the maximum peak from the distribution of the porous structure of the nanoporous carbon material may be about 100 nm or less.

[0027] In any embodiment, the average strut width of the fibrillar morphology of the nanoporous carbon material may be from about 2 to 10 nm, or even more specifically from about 2 to 5 nm.

[0028] In exemplary embodiments, a collectorless, binderless interconnect anode material for lithium-ion batteries is provided. The anode material comprises a nanoporous carbon material (also called a CPI composite) derived from open-cell monolithic polyimide having a fibrilous network and an array of pores, wherein silicon particles are present in pores surrounded by the fibrilous network and are contained in amounts between approximately 20% and 80% by weight of the anode material. The average strut width of the fibrilous network is approximately 2 to 10 nm. The porosity of the carbon material is between approximately 20% and approximately 50%, and the porosity includes pores that can contain silicon particles in a non-lithified state and silicon particles in a lithified, volume-expanded state. The carbon aerogel has the following properties: a pore volume of approximately 0.1 cc / g or more, a substantially uniform pore size distribution with a full width at half maximum of approximately 50 nm or less, and a pore size with a maximum peak from a distribution of approximately 100 nm or less. The obtained anode material has the following properties: density between approximately 0.50 g / cc and approximately 1.5 g / cc, conductivity of approximately 10 S / cm or more, Young's modulus of approximately 0.5 GPa or more, and thickness between approximately 10 micrometers and approximately 200 micrometers.

[0029] In an exemplary embodiment, a collectorless, binderless anode material for lithium-based energy storage devices is provided. The anode material comprises an open-cell monolithic nanoporous carbon material having a fibrilous network and a pore array, wherein silicon particles are present in pores surrounded by the fibrilous network and constitute more than 0% and less than about 95% by weight of the anode material. The fibrilous network acts as a carbon coating for the silicon particles, which can protect the silicon particles from damage during lithiation, with an average strut width of about 2 to 10 nm. The porosity of the carbon material is about 80% or less, and the porosity includes pores that can surround silicon particles in the non-lithiated state and accommodate silicon particles in the lithiated volume-expanded state. The carbon aerogel has the following properties: a pore volume of about 0.3 cc / g or more, a substantially uniform pore size distribution with a full width at half maximum of about 50 nm or less, and a pore size with a maximum peak from a distribution of about 100 nm or less. The obtained anode material has the following properties: density between approximately 0.50 g / cc and approximately 1.5 g / cc, conductivity of approximately 10 S / cm or more, Young's modulus of approximately 0.5 GPa or more, and thickness between approximately 10 micrometers and approximately 4 cm.

[0030] Other embodiments relate to a binder-free composite comprising an open-cell porous carbon scaffold having a pore array, wherein electrochemically active species are located within the pore array of the carbon scaffold and in direct contact with the carbon scaffold, and the porosity of the carbon scaffold is about 90% or less. The electrochemically active species are present in an amount between about 5% and about 65% by weight of the composite material. The carbon aerogel has the following properties: a pore volume of about 0.3 cc / g or more, and a substantially uniform pore size distribution with a full width at half maximum of about 50 nm or less.

[0031] Other embodiments relate to composite materials comprising an open-cell nanoporous carbon network and electrochemically active species disposed within the pores of the nanoporous carbon network. The porosity of the carbon network is about 90% or less and has a substantially uniform pore size distribution with a full width at half maximum of about 50 nm or less. The composite material is formed as a monolith or powder. Optionally, the conductivity of the material is about 10 S / cm or more. Optionally, the Young's modulus of the material is about 0.5 GPa or more and the thickness is between 10 micrometers and about 500 micrometers.

[0032] In another embodiment, a silicon-containing monolithic imide-derived carbon aerogel composite is provided, which is formed from a nanoporous carbon material and does not contain a binder, wherein silicon particles are embedded within a monolithic polyimide-derived carbon aerogel composite.

[0033] In some cases, the composite may be pre-doped with a metal oxide selected from the group consisting of tin, sulfur, phosphorus, nickel, copper, cobalt, manganese, lithium, magnesium, iron, zinc, boron, titanium, aluminum oxide, titanium oxide, niobium oxide, molybdenum oxide, silica, and aluminosilicates.

[0034] In some cases, silicon particles may be pre-doped with a p-type acceptor selected from the group consisting of boron, aluminum, gallium, and indium. Alternatively, silicon particles may be pre-doped with an n-type donor selected from the group consisting of phosphorus, lithium, arsenic, antimony, and bismuth.

[0035] In some cases, carbon aerogels contain fibril-like structures with an average strut width of approximately 2-10 nm.

[0036] In further embodiments, an electrode comprising the nanoporous carbon material described herein is provided. This electrode may be an anode and may not include a separate current collector. In another embodiment, an electrochemical cell comprising the carbon composition, nanoporous carbon material and / or electrode described herein is provided. In further embodiments, an energy storage device, such as a battery, more specifically a lithium-ion battery, is provided, comprising the carbon composition, nanoporous carbon material and / or electrochemical cell described herein.

[0037] A further general embodiment relates to a method for forming or producing a carbon composition. In an exemplary embodiment, the method includes: supplying a mixture of a polyimide precursor and a silicon-based material; chemically or thermally imidizing the mixture, for example by adding an imidation catalyst or by heating; drying the imidized mixture to obtain a porous polyimide-silicon composite; and carbonizing the porous polyimide-silicon composite, for example by thermal decomposition, to obtain a carbon composition containing more than about 25% by weight of silicon and having a porosity between about 10% and about 90%. In some embodiments, the method further includes combining the mixture with an immiscible medium, such as a dispersion medium, to form droplets of the imidized mixture. For example, an emulsion can be formed with the imidized mixture as a dispersed phase. In an exemplary embodiment, the method further includes drying the droplets to form particles. In any embodiment, the carbon composition may include a carbon aerogel and may be formed as a monolith or particles.

[0038] In exemplary embodiments, the method involves forming or producing a continuous porous carbon-silicon composite, such as a carbon aerogel. For example, imide precursors, such as diamines and dianhydrides, each containing aromatic and / or aliphatic groups, are mixed in a suitable solvent (e.g., a polar, aprotic solvent). Additives, such as silicon particles in this embodiment, are mixed with the imide precursors in the solvent medium before adding the imidation catalyst. The imidation catalyst is then added to initiate imidation. In alternative embodiments, imidation can be achieved by thermal imidation. A gel is formed in which the additive particles, such as silicon particles, are uniformly dispersed. The resulting mixture is then dried to obtain a continuous porous polyimide-silicon composite, which may be carried out using subcritical and / or supercritical carbon dioxide. Optionally, the polyimide-silicon composite may be densified. For example, the polyimide-silicon composite can preferably be compressed uniaxially (e.g., to 95% strain) to increase its density, which can be adjusted to about 1.5 g / cc based on the amount of compression. Whether or not compression is performed, the polyimide-silicon composite is thermally decomposed to obtain a continuous porous carbon-silicon composite, the resulting composite containing more than 0% by weight and less than about 95% by weight of silicon, with a porosity between about 5% and 99%. In certain embodiments, the thermal decomposition is carried out at a maximum temperature between about 750°C and about 1600°C, and optionally the graphitization may be carried out between about 1600°C and about 3000°C.

[0039] Another embodiment provides a method for forming or producing continuous porous silicon-carbon composites such as carbon aerogels. Polyimide precursors, such as diamines and dianhydrides, each containing aromatic and / or aliphatic groups, are mixed in a suitable solvent (e.g., a polar, aprotic solvent). A silicate (e.g., silicon dioxide, aluminosilicate, and / or halloysite) and a reducing agent (e.g., magnesium, lithium, sodium, potassium, aluminum, calcium, or a combination thereof) are mixed with the polyimide precursor in the solvent before adding an imidation catalyst. The imidation catalyst is then added. In an alternative embodiment, imidation can be achieved by thermal imidation. The resulting mixture is then dried to obtain a continuous porous polyimide silicate and reducing agent composite, where drying may be carried out using subcritical and / or supercritical carbon dioxide. Optionally, the polyimide silicate and reducing agent composite can be preferably compressed uniaxially (e.g., to 95% strain) to increase its density, which can be adjusted to about 1.5 g / cc based on the amount of compression. Regardless of whether compression is performed, a composite of polyimide silicate and a reducing agent is heated under thermal decomposition and reducing environmental conditions to produce a continuous porous carbon-silicon composite, the resulting composite containing more than 0% by weight and less than about 95% by weight of silicon, with a porosity between about 5% and 99%. In certain embodiments, thermal decomposition is carried out at a maximum temperature between about 750°C and about 1600°C, and optionally graphitization may be carried out between about 1600°C and about 3000°C. Furthermore, the silicate and reducing agent may be reacted with hydrogen gas at temperatures above about 700°C under inert conditions to form silicon within the carbon composite.

[0040] In further embodiments, a method for forming or producing porous silicon-carbon composites, such as silicon-doped carbon aerogels, is provided. Polyimide precursors, such as diamines and dianhydrides, each containing aromatic and / or aliphatic groups, are mixed in a suitable solvent (e.g., a polar, aprotic solvent). An imidation catalyst is then added. In alternative embodiments, imidation can be achieved by thermal imidation. The resulting mixture is then dried to obtain a continuous porous polyimide, which may be carried out under subcritical conditions and / or using supercritical carbon dioxide.

[0041] In some cases, the polyimide can be preferably compressed uniaxially (for example, to 95% strain) to increase its density, which can be adjusted to about 1.5 g / cc based on the amount of compression. Whether or not compression has occurred, the polyimide is thermally decomposed to obtain continuous porous carbon. Silicon is then deposited on or in the silicon to obtain a continuous porous silicon composite containing more than 0 wt% and less than about 95 wt% silicon, with a porosity between about 5% and 99%. In certain embodiments, the thermal decomposition is carried out at a maximum temperature between about 750°C and about 1600°C, and optionally graphitization may be carried out between about 1600°C and about 3000°C.

[0042] In some cases, silicon may be deposited by immersing porous carbon in a silicon-forming silane precursor, followed by heating under inert conditions to decompose the silane and form a conformal silicon coating within the porous carbon. This immersion treatment can be repeated multiple times, increasing the thickness and silicon content up to approximately 95% by weight. In other embodiments, silicon can be deposited by atomic layer deposition or chemical vapor deposition (CVD).

[0043] In any of the above methods for producing a carbon composition, such as a continuous porous silicon-carbon composite, the carbon composition may optionally be a monolith or a self-supporting structure, may be prepared with or without a substrate, may be formed as beads, or may be pulverized into a powder. Furthermore, the composite may be reinforced with or without nonwoven or woven materials (e.g., fibers, foams, etc.).

[0044] These and other important objectives, advantages, and features of the present invention will become apparent as this disclosure progresses.

[0045] Accordingly, the present invention includes structural features, combinations of elements, and arrangements of parts as illustrated in the disclosure described below, and the scope of the present invention is set forth in the claims.

[0046] To fully and clearly understand the present invention, the following detailed description should be referred to in conjunction with the accompanying drawings. [Brief explanation of the drawing]

[0047] [Figure 1] This is a flowchart illustrating the formation of carbon aerogel for use in battery applications. [Figure 2] This figure shows the discharge capacity over several cycles, comparing silicon-doped monoliths with silicon particles incorporated by conventional slurry processing methods. [Figure 3] This is a flowchart illustrating the formation of carbon aerogel derived from polyimide. [Figure 4] The density of the polyimide carbide (CPI) composite is shown as a function of the compressed thickness (initial thickness of approximately 250 micrometers). [Figure 5] The density of the CPI composite is shown as a function of the compressed thickness (initial thickness is approximately 580 micrometers). [Figure 6A] This is a scanning electron microscope (SEM) image of silicon-doped uncompressible PI aerogel (LS1). [Figure 6B]This is a SEM image of silicon-doped compressed PI aerogel (LS2). [Figure 7] This shows the discharge capacity per dopant (silicon, LS2; graphite, LG2) compressed composite (half-cell battery test, 0.1°C rate). [Figure 8] The surface area and micropore area function of silicon content in CPI monoliths are shown. [Figure 9] This shows the pore size distribution of a Si-doped CPI monolith. [Figure 10] The discharge capacity of the CPI composite as a function of Si content at cycle 5 is shown. [Figure 11A] This is a SEM image of a CPI composite with a Si load of 27% Si. [Figure 11B] This is a SEM image of a CPI composite with a Si load of 46% Si. [Figure 11C] This is a SEM image of a CPI composite with a Si load of 64% Si. [Figure 12A] The cycle capacity is shown based on a 27% Si content (S27). [Figure 12B] This shows the electrode-based cycle capacity compared to Figure 12A. [Figure 12C] The cycle capacity is shown based on a 46% Si content (S46). [Figure 12D] This shows the electrode-based cycle capacity compared to Figure 12C. [Figure 12E] The cycle capacity is shown based on the 64% Si content (S64). [Figure 12F] This shows the electrode-based cycle capacity compared to Figure 12E. [Figure 13A] This is a SEM image of a CPI composite with a thickness of approximately 337 micrometers. [Figure 13B] This is a SEM image of a CPI composite with a thickness of approximately 180 micrometers. [Figure 14A] This shows the discharge capacity based on the electrode weight (thickness approximately 323 μm). [Figure 14B] This shows the discharge capacity based on the electrode weight (thickness approximately 170 μm). [Figure 15A] This is an SEM image (C45) of a CPI composite prepared without a dispersant, before thermal decomposition. [Figure 15B] This is an SEM image of the composite material shown in Figure 15A after thermal decomposition. [Figure 16A] This is an SEM image of a CPI complex (C45-control) prepared without a dispersant. [Figure 16B] This is an SEM image of a CPI composite (B45) prepared using BYK384. [Figure 16C] This is an SEM image of a CPI complex (P45) prepared using Pluronic® F87 dispersant. [Figure 17A] Figure 16A shows the discharge capacity of the C45 composite material. [Figure 17B] Figure 16B shows the discharge capacity of the B45 composite material. [Figure 17C] Figure 16C shows the discharge capacity of the P45 composite material. [Figure 18] The density of the P45 CPI composite as a function of thickness is shown. [Figure 19] The conductivity of CPI composites doped with various Si concentrations is shown as a function of density. [Figure 20] This is a schematic diagram illustrating the formation of polyamic acid. [Figure 21] The isotherms of the four CPI samples are shown. [Figure 22] Figure 21 shows the pore size distribution of the CPI sample. [Figure 23] This is an SEM image of MT material (uncompressible). [Figure 24] This is an SEM image of MTC material (compressed). [Figure 25A] The Si content (left) and cycle capacity (right) of the compressed CPI sample are shown. [Figure 25B] The Si content (left) and cycle capacity (right) of the uncompressible CPI sample are shown. [Figure 26A] For a compressed CPI sample containing 29% by weight of silicon per total solids, the cycle capacity based on Si content (left) and electrode (right) is shown. [Figure 26B] For an uncompressible CPI sample containing 29% by weight of silicon per total solids, the cycle capacity based on Si content (left) and electrode (right) is shown. [Figure 27] The properties and micrographs of carbon / Si impregnated into carbon fiber (10 g / m2) are shown. [Figure 28] The properties and micrographs of carbon / Si impregnated into carbon fiber (4g / m2) are shown. [Figure 29] The properties and micrographs of carbon / Si impregnated into carbon fiber (2g / m2) are shown. [Figure 30] This shows the cycle capacity of carbon fiber-reinforced C / Si based on Si content (left) and electrodes (right). [Figure 31] This shows the cycle capacity of cellulose fiber-reinforced C / Si based on Si content (left) and electrodes (right). [Figure 32] This is an SEM image of a thick composite material (approximately 0.6 mm thick) obtained by mixing Si and PI for 16 hours. [Figure 33] This is an SEM image of a thin composite material (approximately 0.12 mm thick) obtained by mixing Si and PI for 16 hours. [Figure 34] This is an SEM image of a monolithic sample in which Si and PI were mixed for 16 hours. [Figure 35] These are SEM cross-sectional images of a C / Si monolith. The image on the left shows Si and PI mixed for 16 hours, while the image on the right shows Si and PI mixed for 4-6 minutes. [Figure 36] These are SEM cross-sectional images of C / Si composites. The image on the left shows Si and PI mixed for 16 hours, while the image on the right shows Si and PI mixed for 4-6 minutes. [Figure 37] The cycle capacity of incompressible C / Si (mixed 16 hours) is shown based on Si content (left) and electrode (right). [Figure 38] The cycle capacity of compressed C / Si (mixed for 16 hours) is shown based on Si content (left) and electrode (right). [Figure 39]This shows a compressed circular Si / C electrode fabricated using a die cutter on aerogel. [Figure 40] The cycle capacity of an incompressible circular C / Si aerogel is shown based on Si content (left) and electrode (right). [Figure 41] This shows the cycle capacity of compressed circular C / Si aerogel based on Si content (left) and electrode (right). [Figure 42] This shows a C / Si aerogel sample obtained from PF / Si aerogel. [Figure 43] The image shows an SEM image of C / Si aerogel (obtained from PF / Si aerogel). [Figure 44] This shows the cycle capacity of a PF aerogel composite containing Si based on electrodes. [Figure 45] This shows the effect of silicon content on the Young's modulus of samples tested by nanoindentation. [Figure 46] This shows the effect of density on Young's modulus, as tested by nanoindentation. [Figure 47] This is an SEM image of a particle C / Si aerogel sample according to the embodiments disclosed herein. [Figure 48] The cycling performance of electrodes containing CPI silicon beads according to embodiments disclosed herein is shown. [Modes for carrying out the invention]

[0048] The following detailed description of the present invention will refer to the accompanying drawings illustrating specific embodiments that form part of the present invention and can be used to carry it out. It should be understood that other embodiments may be utilized and structural modifications may be made without departing from the scope of the present invention.

[0049] As used herein and in the appended claims, the singular forms “a,” “an,” and “the” refer to multiple subjects unless the content clearly indicates otherwise. As used herein and in the appended claims, the term “or” is generally used to mean “and / or” unless otherwise explicitly indicated herein.

[0050] As used herein, “approximately” means nearly or almost, and means ±15% of the given number or range. In one embodiment, the term “approximately” may include conventional rounding by significant figures of a number. Also, “approximately 'x' to 'y'” includes “approximately 'x' to approximately 'y'.”

[0051] In this disclosure, the terms “aerogel” or “aerogel material” mean a gel containing a framework of interconnected structures and a corresponding network of interconnected pores incorporated within the framework, and containing a gas such as air as a dispersed interstitial medium, and the following physical and structural properties attributable to aerogels (as determined by nitrogen porosimetry testing): (a) average pore size in the range of approximately 2 nm to approximately 100 nm, (b) porosity of at least 80%, and (c) approximately 20 m 2 It is characterized by a surface area of ​​1 / g or more. It is understood that the inclusion of additives such as reinforcing materials or electrochemically active species may reduce the porosity of the resulting aerogel composite. Furthermore, densification may also reduce the porosity of the resulting aerogel composite. This will become clearer later in this specification.

[0052] Therefore, the aerogel materials of this disclosure include any aerogel or other open-cell compound that satisfies the defining elements described in the preceding paragraph, including compounds that can be classified elsewhere, such as xerogels, cryogels, ambigels, and microporous materials.

[0053] In this disclosure, the terms “framework” or “framework structure” refer to a network of interconnected oligomers, polymers, or colloidal particles that form a solid structure in a gel or aerogel. The diameter of the polymers or particles constituting the framework structure is typically about 100 angstroms. However, the framework structures in this disclosure may also include networks of interconnected oligomers, polymers, or colloidal particles of all diameter sizes that form a solid structure within a gel or aerogel.

[0054] In this disclosure, the term “aerogel composition” means any composite material that includes an aerogel material as a component of the composite. Examples of aerogel compositions include, but are not limited to, fiber-reinforced aerogel composites, aerogel composites containing additives such as opacifiers and electrochemically active species, aerogel-foam composites, aerogel-polymer composites, and composite materials that incorporate aerogel particles, particles, granules, beads, or powders into a solid or semi-solid material such as a binder, resin, cement, foam, polymer, or similar solid material.

[0055] In this disclosure, the term “reinforced aerogel composition” means an aerogel composition that includes a reinforcing phase within an aerogel material, which may be modified to be covalently bonded to the aerogel framework or not part of the aerogel skeleton. The reinforcing phase may be any material that improves the flexibility, resilience, conformability, or structural stability of the aerogel material. Examples of well-known reinforcing materials include, but are not limited to, open-cell foam reinforcing materials, closed-cell foam reinforcing materials, open-cell membranes, honeycomb reinforcing materials, polymer reinforcing materials, and fibrous reinforcing materials such as discrete fibers, woven materials, nonwoven materials, battings, webs, mats, and felts. Furthermore, the reinforcing material may be combined with one or more other reinforcing materials and may be continuously oriented in preferred parts of the composition, in whole or in part. In other embodiments, if the aerogel material and / or aerogel framework is structurally stable (i.e., self-supporting) on ​​its own, no reinforcing phase may be used at all. This self-supporting nature of certain carbon aerogels will become clearer later in this specification.

[0056] In this disclosure, the term “wet gel” refers to a gel in which the mobile pore phase within an interconnected network of pores consists primarily of a liquid phase, such as a conventional solvent, a liquefied gas, such as liquid carbon dioxide, or a combination thereof. Aerogels generally require the initial formation of a wet gel, followed by processing and extraction to replace the mobile pore liquid phase in the gel with air or another gas. Examples of wet gels include, but are not limited to, alcohol gels, hydrogels, ketogels, carbonogels, and any other wet gels known to those skilled in the art.

[0057] In this disclosure, the terms “additive” or “additive element” refer to materials that can be added to a composition before, during, or after the production of the composition. Additives may be added, for example, to alter or improve desirable properties in an aerogel composition, or to counteract or mitigate undesirable properties in an aerogel composition. Additives are generally added to the aerogel composition before or during gelation. Additives may also be added to the aerogel composition by atomic layer deposition or chemical vapor deposition (CVD). Specific examples of additives are silicon, such as electrochemically active species such as silicon particles.

[0058] In this disclosure, the term “silicon particles” means silicon or silicon-based materials having a particle size range suitable for use with the aerogel compositions disclosed herein. The silicon particles in this disclosure may be nanoparticles, for example, two-dimensional or three-dimensional particles in the range of about 1 nm to about 150 nm. The silicon particles in this disclosure may be fine particles, for example, two-dimensional or three-dimensional micron-sized particles, for example, substantially spherical particles with a diameter in the range of about 150 nm to about 10 micrometers or more. For example, the silicon particles in this disclosure are two-dimensional or three-dimensional particles, for example, substantially spherical particles with a diameter of about 10 nm, 50 nm, 100 nm, 150 nm, 200 nm, 500 nm, 1 micrometer, 1.5 micrometers, 2 micrometers, 3 micrometers, 5 micrometers, 10 micrometers, 20 micrometers, 40 micrometers, 50 micrometers, 100 micrometers, or in the range of any two of these values. In some embodiments, the silicon particles may be monodisperse or substantially monodisperse. In other embodiments, silicon particles may have a particle size distribution. In this disclosure, the dimensions of silicon particles are provided based on the median of the particle size distribution, i.e., D50. The silicon particles of this disclosure may include silicon wire, crystalline silicon, amorphous silicon, silicon alloys, silicon oxide (SiOx), coated silicon, such as carbon-coated silicon, and any combination of the silicon particle materials disclosed herein.

[0059] In this disclosure, the term “self-supporting” refers to the ability of an aerogel material or composition to be flexible and / or elastic, primarily based on the physical properties of the aerogel. The self-supporting aerogel materials or compositions of this disclosure can be distinguished from other aerogel materials, such as coatings, which rely on a substrate or reinforcing material to impart flexibility and / or elasticity to the material.

[0060] In this disclosure, the term “density” refers to a measured mass per unit volume of an aerogel material or composition. The term “density” typically refers to true density for aerogel materials and bulk density for aerogel compositions. Density is generally expressed in kg / m³. 3 Alternatively, the density may be recorded in g / cc. The density of aerogel materials or compositions can be measured by methods known in the art, including, but not limited to, the standard test methods for the dimensions and density of preformed block and board-type insulation materials (ASTM C303, ASTM International, West Conshohocken, Pa.), the standard test methods for the thickness and density of blanket or butt insulation materials (ASTM C167, ASTM International, West Conshohocken, Pa.), and the measurement of the apparent density of preformed pipe insulation materials (ISO 18098, International Organization for Standardization, Switzerland). In this disclosure, unless otherwise specified, density measurements are obtained in accordance with the ASTM C167 standard. The density of the aerogel material or composition of this disclosure is preferably about 1.50 g / cc or less, about 1.40 g / cc or less, about 1.30 g / cc or less, about 1.20 g / cc or less, about 1.10 g / cc or less, about 1.00 g / cc or less, about 0.90 g / cc or less, about 0.80 g / cc or less, about 0.70 g / cc or less, about 0.60 g / cc or less, about 0.50 g / cc or less, about 0.40 g / cc or less, about 0.30 g / cc or less, about 0.20 g / cc or less, about 0.10 g / cc or less, or in the range between any two of these values, for example, between about 0.15 g / cc and 1.5 g / cc, or more specifically 0.50 g / cc and 1.5 g / cc.

[0061] The production of aerogels, according to a particular embodiment, typically includes the following steps: i) forming a solution containing a gel precursor, ii) forming a gel from the solution, and iii) extracting a solvent from the gel material to obtain a dry aerogel material. The production of aerogel beads, according to a particular embodiment, follows a normal process for the production of aerogels and typically includes the following steps: i) forming a solution containing a gel precursor, ii) dispersing the gel precursor in a medium immiscible with the gel precursor, iii) forming gel beads from the gel precursor solution in the immiscible medium, iv) removing the gel beads from the medium, and v) extracting a solvent from the gel beads to obtain a dry aerogel material. These methods are described in more detail below, particularly in relation to the formation of organic aerogels such as polyimide aerogels. However, the specific examples and figures provided herein are not intended to limit this disclosure to any particular type of aerogel and / or preparation method. This disclosure may include any aerogel formed by any relevant preparation method known to those skilled in the art.

[0062] Exemplary solutions for producing silica aerogels are formed by combining at least one gelling precursor with a solvent. Other solvents known to those skilled in the art may also be used as solvents suitable for solution formation, including lower alcohols having 1 to 6 carbon atoms, preferably 2 to 4. Examples of useful solvents include, but are not limited to, methanol, ethanol, isopropanol, ethyl acetate, acetate acetate, acetone, dichloromethane, and tetrahydrofuran. Multiple solvents may also be combined to achieve a desired level of dispersion or to optimize the properties of the gel material. Therefore, the selection of the optimal solvent for the polymerization and gelling processes depends on the specific precursors, fillers, and additives incorporated into the solution, as well as the target processing conditions for gelation and liquid-phase extraction, and the desired properties of the final aerogel material.

[0063] Exemplary solutions for producing polyimide aerogels are formed by combining at least one diamine and at least one dianhydride in a common polar aproton solvent. Further details regarding polyimide gel / aerogel formation can be found in Rhine et al., U.S. Patent Nos. 7,074,880 and 7,071,287; Suzuki et al., U.S. Patent No. 6,399,669; Leventis et al., U.S. Patent No. 9,745,198; Leventis et al., Polyimide Aerogels by Ring-Opening Metathesis Polymerization (ROMP), Chem. Mater. 2011, 23, 8, 2250-2261; Leventis et al., Organic Aerogels Derived from Isocyanates: Polyurea Polyimide, polyamide, MRS treatment, 1306 (2011), Mrsf10-1306-bb03-01.doi:10.1557 / opl.2011.90; Chidambareswarapattar et al., One-step room-temperature synthesis of fibrous polyimide aerogels from anhydrides and isocyanates and conversion to isocarbon, J.Mater.Chem.2010,20,9666-9678; Guo et al., Crosslinked polyimide aerogels with amine-functionalized polyoligomer silsesquioxane, ACS Appl.Mater.Interfaces 2011, 3, 546-552; Nguyen et al., Development of High-Temperature Flexible Polyimide Aerogels, Proceedings of the American Chemical Society, 2011; Meador et al., Mechanically Strong Flexible Polyimide Aerogels Crosslinked with Aromatic Triamines, ACS Appl.Mater.Interfaces, 2012, 4(2), pp536-544; Meador et al., Polyimide Aerogels with Amide Crosslinking: A Low-Cost Alternative to Mechanically Strong Polymer Aerogels, ACS Appl.Mater.Interfaces 2015, 7, 1240-1249; Pei et al., Preparation and Characterization of Polyimide-Based Highly Crosslinked Polyimide Aerogels Containing Trimethoxysilane Side Chain Groups, Langmuir 2014, 30, 13375-13383, each of which is incorporated herein by reference in whole. To optimize the properties of the gel material, triamines, tetraamines, pentamines, hexamines, etc., can be used instead of or in addition to diamines or combinations thereof.To optimize the properties of the gel material, trianhydrous, tetraanhydrous, pentanhydrous, and hexanhydrous compounds can be used instead of or in addition to dianhydrous compounds or combinations thereof. Dehydrating agents and catalysts can be incorporated into the solution for the initiation and progression of imidation.

[0064] The solution may contain additional co-gelling precursors along with the filler material and other additives. The filler material and other additives may be added to the solution at any point before or during gel formation. Alternatively, the filler material and other additives may be incorporated into the gel material after gelation by various techniques known to those skilled in the art. The solution containing the gelling precursor, solvent, catalyst, water, filler material, and other additives is preferably a homogeneous solution capable of effective gel formation under appropriate conditions.

[0065] Once the solution is formed and optimized, the gel-forming components in the solution can be transferred to the gel material. The process of transferring the gel-forming components to the gel material includes an initial gel-forming step in which the gel solidifies to the gelation point of the gel material. The gelation point of the gel material can be considered as the point in which the gelling solution exhibits flow resistance and / or forms a substantially continuous polymer framework over its entire volume. Various gel-forming techniques are known to those skilled in the art. Examples include, but are not limited to, maintaining the mixture at rest for a sufficient time, adjusting the concentration of the catalyst, adjusting the temperature of the solution, exposing the mixture to a type of energy (ultraviolet, visible light, infrared, microwave, ultrasonic, particle radiation, electromagnetic), or a combination thereof.

[0066] The process of forming gel beads from a gel solution may involve combining the solution with an immiscible medium, such as a dispersion medium. Examples of dispersion media include silicone oil and mineral oil. The gel solution can be added, for example, by pouring, or otherwise combined with an immiscible dispersion medium. Before or during the process of transferring the gel-forming components to the gel material, the combined dispersion medium and gel precursor can be agitated, such as by mixing, to facilitate the formation of bead-like droplets. For example, by combining a dispersion medium and a gel precursor, an emulsion can be formed with the gel precursor solution as the dispersed phase. An exemplary method for producing gel beads is described in U.S. Patent Application Publication 2006 / 0084707 by Ou et al., which is incorporated herein by reference in its entirety.

[0067] Due to interfacial tension, spherical droplets of gel precursors are formed in the dispersion medium. The droplets gel and strengthen within the dispersion medium, such as silicone oil. Stirring the mixture is generally done to prevent droplet aggregation. Additionally, heat or radiation can be applied to the dispersion medium to induce or enhance droplet gelation, strengthening the gel beads to be strong enough to withstand impacts. The ability to generate gel beads in a given space depends on precise control of the droplet gelation process.

[0068] The process further includes removing the gel beads from a dispersion medium such as silicone oil. The gel beads are filtered from the dispersion medium and then washed or rinsed with a fluid, such as an alcohol such as ethanol, methanol, isopropanol, or a higher alcohol. The rinsing solution is essentially required to be able to remove the oil (or other dispersion medium) without chemically reacting with the gel. After removing the excess silicone oil, the gel beads can be placed in a solvent for aging, as will be discussed in more detail below. For example, the gel beads can be aged in ethanol. As described herein, the gel beads are suitable for crevice solvent removal using a supercritical fluid drying method. They can also be dried under ambient conditions to produce xerogels. As will be described in more detail below, dried gel beads such as aerogels or xerogel beads are suitable for heat treatment and carbonization. In exemplary embodiments, the gel beads are substantially spherical.

[0069] Furthermore, the process of transferring gel-forming components to the gel material may include an aging step (also called curing) before liquid-phase extraction. Aging the gel material after it reaches its gelation point increases the number of crosslinks within the network, thereby further strengthening the gel framework. By adjusting the duration of gel aging, various properties within the resulting aerogel material can be controlled. This aging procedure can be useful in preventing potential volume loss and shrinkage during liquid-phase extraction. Aging methods include maintaining the gel in a static state for a long period (before extraction), maintaining the gel at a high temperature, adding crosslinking-promoting compounds, or any combination thereof. Preferred temperatures for aging are generally between approximately 10°C and 200°C. Aging of the gel material generally continues until liquid-phase extraction of the wet gel material.

[0070] The time required to transfer the gel-forming material to the gel material includes both the duration of initial gel formation (from the start of gelation to the gelation point) and the duration of any subsequent curing and aging of the gel material before liquid-phase extraction (from the gelation point to the start of liquid-phase extraction). The total time required to transfer the gel-forming material to the gel material is generally between about 1 minute and several days, preferably about 30 hours or less, about 24 hours or less, about 15 hours or less, about 10 hours or less, about 6 hours or less, about 4 hours or less, about 2 hours or less, about 1 hour or less, about 30 minutes or less, or about 15 minutes or less.

[0071] The resulting gel material may be washed in a suitable secondary solvent to replace the primary reaction solvent present in the wet gel. Examples of such secondary solvents include linear monohydric alcohols having one or more aliphatic carbon atoms, dihydric alcohols having two or more carbon atoms, branched alcohols, cyclic alcohols, alicyclic alcohols, aromatic alcohols, polyhydric alcohols, ethers, ketones, cyclic ethers, or derivatives thereof.

[0072] After forming and processing a gel material, the liquid phase of the gel can then be extracted, at least partially, from the wet gel using extraction methods, including processing and extraction methods, to form an aerogel material. In particular, liquid phase extraction plays a crucial role in manipulating the properties of aerogels, such as porosity and density, and related properties such as thermal conductivity. Typically, aerogels are obtained by extracting the liquid phase from the gel in a manner that causes low shrinkage of the porous network and framework of the wet gel.

[0073] Aerogels are typically formed by removing the liquid mobile phase from a gel material at temperatures and pressures near or above the critical point of the liquid mobile phase. When the critical point is reached (near critical) or exceeded (supercritical) (i.e., the pressure and temperature of the system reach or exceed the critical pressure and temperature, respectively), a new supercritical phase distinct from the liquid or gas phase appears in the fluid. The solvent can then be removed without causing any associated mass transfer limitations related to the liquid-vapor interface, capillary pressure, or generally the liquid-vapor boundary. Furthermore, the supercritical phase is usually more miscible with organic solvents and therefore has better extraction capabilities. Co-solvents and solvent exchanges are also commonly used to optimize the supercritical fluid drying process.

[0074] When evaporation or extraction occurs below the supercritical point, capillary forces resulting from liquid evaporation can cause shrinkage and pore collapse within the gel material. Such adverse effects of capillary forces can be mitigated by maintaining the mobile phase near or above the critical pressure and temperature during the solvent extraction process. In certain embodiments of this disclosure, using near-critical conditions just below the critical point of the solvent system enables the production of aerogel materials or compositions with sufficiently low shrinkage, thereby producing commercially viable end products.

[0075] Various different methods for using supercritical fluids in aerogel drying, as well as several additional aerogel extraction methods, including ambient drying methods, are known in the art. For example, Kistler (J. Phys. Chem. (1932) 36:52-64) describes a simple supercritical extraction process in which the gel solvent is maintained above its critical pressure and critical temperature, thereby reducing the evaporative capillary force and maintaining the structural integrity of the gel network. U.S. Patent No. 4,610,863 describes an extraction method in which the gel solvent is replaced with liquid carbon dioxide, and then extracted under conditions in which the carbon dioxide is in a supercritical state. U.S. Patent No. 6,670,402 teaches that aerogels can be produced by rapidly exchanging the solvent and extracting the liquid phase from the gel by injecting supercritical (not liquid) carbon dioxide into an extractor that is substantially preheated and pre-pressurized to a supercritical state or higher. U.S. Patent No. 5,962,539 describes a method for obtaining an aerogel from a polymer material in sol-gel form in an organic solvent by replacing the organic solvent with a fluid whose critical temperature is below the polymer decomposition temperature and by supercritical extraction of the fluid / sol-gel. U.S. Patent No. 6,315,971 discloses a method for producing a gel composition, comprising drying a wet gel containing a gel solid and a desiccant, and removing the desiccant under drying conditions sufficient to reduce the shrinkage of the gel during drying. U.S. Patent No. 5,420,168 describes a method for producing a resorcinol / formaldehyde aerogel using a simple air-drying method. U.S. Patent No. 5,565,142 describes a drying technique for modifying the gel surface to be stronger and more hydrophobic so that the gel framework and pores can withstand collapse during atmospheric drying or subcritical extraction. Other examples of extracting the liquid phase from aerogel materials are found in U.S. Patents No. 5,275,796 and No. 5,395,805.

[0076] A preferred embodiment for extracting the liquid phase from a wet gel involves using supercritical conditions for carbon dioxide, for example, first substantially replacing the primary solvent present in the gel's pore network with liquid carbon dioxide, then heating the wet gel (typically in an autoclave) above the critical temperature of carbon dioxide (about 31.06°C), and increasing the system pressure to a pressure higher than the critical pressure of carbon dioxide (about 1070 psig). Slight variations in the pressure around the gel material can facilitate the removal of the supercritical carbon dioxide fluid from the gel. To facilitate the continuous removal of the primary solvent from the wet gel, the carbon dioxide can be recirculated through the extraction system. Finally, the temperature and pressure are slowly returned to ambient conditions to produce a dry aerogel material. The carbon dioxide can also be pre-treated to a supercritical state before being injected into the extraction chamber. In other embodiments, extraction can be carried out by any suitable mechanism, e.g., by changing the pressure, timing, and solvent as described above.

[0077] In certain embodiments of this disclosure, the dried polyimide aerogel composition is 3 hours or more, between 10 seconds and 3 hours, between 10 seconds and 2 hours, between 10 seconds and 1 hour, between 10 seconds and 45 minutes, between 10 seconds and 30 minutes, between 10 seconds and 15 minutes, between 10 seconds and 5 minutes, between 10 seconds and 1 minute, between 1 minute and 3 hours, between 1 minute and 1 hour, between 1 minute and 45 minutes, between 1 minute and 30 minutes, between 1 minute and 15 minutes, between 1 minute and 5 minutes, and between 10 minutes and 3 hours. It can be subjected to one or more heat treatments for durations between 10 minutes and 1 hour, between 10 minutes and 45 minutes, between 10 minutes and 30 minutes, between 10 minutes and 15 minutes, between 30 minutes and 3 hours, between 30 minutes and 1 hour, between 30 minutes and 45 minutes, between 45 minutes and 3 hours, between 45 minutes and 90 minutes, between 45 minutes and 60 minutes, between 1 hour and 3 hours, between 1 hour and 2 hours, between 1 hour and 90 minutes, or any two of these values.

[0078] In certain embodiments, the present invention includes the formation and application of nanoporous carbon-based scaffolds or structures, such as carbon aerogels, as electrode materials in energy storage devices, for example, as primary anode materials in LIBs. The pores of the nanoporous scaffold are designed, organized, and structured to accommodate silicon, other metalloids, or metal particles, and the expansion of said particles during lithiation, for example, in LIBs. Alternatively, the pores of the nanoporous scaffold may be filled with sulfides, hydrides, any suitable polymer, or other additives, if it is beneficial to contact additives with the conductive material (i.e., the scaffold / aerogel) to provide a more effective electrode. A typical process utilizing silicon-doped carbon aerogels in battery applications is shown in Figure 1.

[0079] To further extend exemplary applications within LIBs, when carbon aerogel material is utilized as a primary anode material, as in a particular embodiment of the present invention, the aerogel nanoporous structure has a narrow pore size distribution, high conductivity, high mechanical strength, and a morphology and sufficient pore volume (at final density) that accommodates a high weight percent of silicon particles and their expansion. A particular embodiment of the present invention has a fibril-like morphology structurally having a strut size that results in, among other things, the narrow pore size distribution, high pore volume, and improved connectivity described above.

[0080] In additional or alternative embodiments, the carbon aerogel itself functions as a current collector due to its conductivity and mechanical strength, and therefore, in a preferred embodiment, a separate current collector is not required on the anode side (when the anode is formed of carbon aerogel). It should be noted that in conventional LIBs, copper foil is bonded to the anode as its current collector. However, depending on the application of the carbon aerogel, removing one or both of these components creates additional space for more electrode material, further increasing the capacity of the cell / individual electrodes and the overall energy density of the packaged battery system. However, in certain embodiments, the existing current collector can be integrated with the anode material of various other embodiments to enhance the current collecting ability or capacity of the copper or aluminum foil.

[0081] In certain embodiments, a nanoporous carbon-based scaffold or structure, specifically a carbon aerogel, can be used as a conductive network or current collector on the anode side of an energy storage device. The fully interconnected carbon aerogel network is filled with electrochemically active species, which are in direct contact with or physically connected to the carbon network. The load of electrochemically active species is adjusted with respect to pore volume and porosity for high stable capacity and improved safety of the energy storage device. When used on the anode side, examples of electrochemically active species include silicon, graphite, lithium, or other metalloids or metals. In yet another embodiment, the anode may include a nanoporous carbon-based scaffold or structure, specifically a carbon aerogel.

[0082] In this disclosure, the term “collectorless” means that there is no separate current collector directly connected to the electrode. As described above, in conventional LIBs, copper foil is typically coupled to the anode as its current collector. According to embodiments of the present invention, electrodes formed from a nanoporous carbon scaffold or structure (e.g., carbon aerogel) may be self-supporting structures, or otherwise have the ability to be collectorless, as the scaffold or structure itself functions as a current collector due to its high conductivity. Within an electrochemical cell, collectorless electrodes can be coupled to form a circuit by embedding solid, mesh, or woven tabs during a dissolution process to produce continuous porous carbon, or by soldering, welding, or metal deposition of leads to a portion of the porous carbon surface. Other mechanisms for bringing carbon into contact with the rest of the system are also intended herein. In alternative embodiments, the nanoporous carbon scaffold or structure, specifically the carbon aerogel, may be placed on or otherwise communicated with a dedicated current collector substrate (e.g., copper foil, aluminum, etc.). In this method, the carbon aerogel is attached to a solid current collector using a conductive adhesive and subjected to varying amounts of pressure.

[0083] Furthermore, this specification also intends that nanoporous carbon-based scaffolds or structures, in particular carbon aerogels, can take the form of monolithic structures. When essentially monolithic, carbon aerogels do not require any binder; in other words, the anode can be binderless. As used herein, the term “monolithic” means an aerogel material in which the majority (by weight) of the aerogel contained in an aerogel material or composition is in the form of a single continuous interconnected aerogel nanostructure. Monolithic aerogel materials include aerogel materials that are initially formed to have a single interconnected gel or aerogel nanostructure but can subsequently be cracked, fractured, or segmented into non-single aerogel nanostructures. Monolithic aerogels can take the form of self-supporting structures or reinforced (fiber or foam) materials. Using silicon lithiation as an example for comparison, silicon incorporated into a monolithic aerogel can be utilized more effectively in terms of theoretical capacity compared to the same amount of silicon incorporated into a slurry using a conventional process (see Figure 2).

[0084] Monolithic aerogel materials are distinguished from granular aerogel materials. The term "granular aerogel material" refers to an aerogel material in which the majority (by weight) of the aerogel contained therein is in the form of fine particles, particles, granules, beads, or powder, which can be mixed together (i.e., via a binder such as a polymer binder) or compressed together, but there are no interconnected aerogel nanostructures between the individual particles. Collectively, this form of aerogel material is said to have a powder or particulate form (as opposed to a monolithic form). Note that although the individual particles of the powder have a single structure, these individual particles are not considered monoliths in this specification. The integration of aerogel powder into an electrochemical cell generally involves the preparation of a paste or slurry from the powder, casting onto a substrate and drying, and may optionally involve calendering.

[0085] Particulate aerogel materials, such as aerogel beads, offer certain advantages. For example, particulate materials according to the embodiments disclosed herein can be used as direct substitutes for other materials, such as graphite in LIB anodes and anode manufacturing processes. Furthermore, particulate materials according to the embodiments disclosed herein can result in improved lithium ion diffusion rates due to shorter diffusion pathways within the particulate material. In addition, particulate materials according to the embodiments disclosed herein can achieve electrodes with optimized packing density by, for example, adjusting particle size and packing arrangement. Moreover, fine particle materials according to the embodiments disclosed herein offer improved acceleration to silicon due to inter- and intra-particle porosity.

[0086] In this disclosure, the terms “binderless” or “binder-free” (or their derivatives) refer to materials that substantially do not contain a binder or adhesive for holding the materials together. For example, monolithic nanoporous carbon materials do not contain a binder because their framework is formed as a single continuous interconnected structure. Advantages of being binderless include, for example, avoiding the effects of a binder on conductivity and pore volume. Aerogel particles, on the other hand, require a binder to hold them together in order to form larger functional materials, and such larger materials are not considered monolithic in this specification. Furthermore, the term “binder-free” does not exclude the use of binders in all cases. For example, a binder or adhesive may be placed on the main surface of an aerogel material to fix a monolithic aerogel according to the present invention to another monolithic aerogel or non-aerogel material. In this way, the binder is used to fabricate a laminated composite, but the binder does not have the function of maintaining the stability of the monolithic aerogel framework itself.

[0087] Furthermore, the monolithic polymer aerogel material or composition of this disclosure may be compressed to a strain of up to 95% without significantly damaging or fracturing the aerogel framework, while densifying the aerogel and minimizing the reduction in porosity. In certain embodiments, the compressed polymer aerogel material or composition is subsequently carbonized using various methods described herein to form a nanoporous carbon material. It is understood that the amount of compression affects the thickness of the resulting carbon material, and that the thickness affects the volume, which will become clearer later in this specification. The examples described below show various thicknesses formed and intended in the invention, and the thickness is adjustable based on compression. Thus, the thickness of the composite (generally compressed) can be about 10 to 1000 micrometers or any narrower range therein, based on the advantages required for the final composite. The invention also intends for powder or particle forms of carbon aerogel when a binder is required and particle size is optimized. The particle size range can be about 1 to 50 micrometers.

[0088] Nanoporous carbon materials according to the present invention, such as carbon aerogels, can be formed from any suitable organic precursor material. Examples of such materials include, but are not limited to, RF, PF, PI, polyamides, polyacrylates, polymethyl methacrylates, acrylate oligomers, polyoxyalkylenes, polyurethanes, polyphenols, polybutadienes, trialkoxysilyl-terminated polydimethylsiloxanes, polystyrene, polyacrylonitriles, polyfurfural, melamine-formaldehyde, cresol-formaldehyde, phenol-furfural, polyethers, polyols, polyisocyanates, polyhydroxybenz, polyvinyl alcohol dialdehyde, polycyanurates, polyacrylamides, various epoxies, agaroses, chitosans, and combinations and derivatives thereof. Any precursor of these materials may be used to prepare and use the resulting materials. In exemplary embodiments, carbon aerogels are formed from pyrolysis / carbonization polyimide aerogels, i.e., polymerization of polyimides. More specifically, polyimide aerogels can be produced using one or more methods described in U.S. Patents No. 7,071,287 and 7,074,880 by Rhine et al., for example, by imidation of a poly(amidic) acid and drying of the resulting gel using a supercritical fluid. Other suitable methods for producing polyimide aerogels (and carbon aerogels derived therefrom) include, for example, U.S. Patent No. 6,399,669 by Suzuki et al.; U.S. Patent No. 9,745,198 by Leventis et al.; Leventis et al., Polyimide Aerogels by Ring-Opening Metathesis Polymerization (ROMP), Chem. Mater. 2011, 23, 8, 2250-2261; Leventis et al., Organic Aerogels Derived from Isocyanates: Polyurea, Polyimide, Polyamide, MRS Method, 1306 (2011), Mrsf10-1306-bb03-01.doi:10.1557·opl.2011.90; Chidambareswarapattar et al., One-step room-temperature synthesis of fibrous polyimide aerogels from anhydrides and isocyanates and conversion to isomorphic carbons, J.Mater.Chem., 2010, 20, 9666-9678; Guo et al., Crosslinked polyimide aerogels with amine-functionalized polyoligomer silsesquioxanes, ACS Appl.Mater.Interfaces 2011, 3, 546-552; Nguyen et al., Development of high-temperature flexible polyimide aerogels, American Chemical Society, proceedings, 2011; Meador et al., Mechanically strong flexible polyimide aerogels crosslinked with aromatic triamines, ACS Appl.Mater.Interfaces, 2012, 4(2), pp536-544; Meador et al., Polyimide aerogels with amide crosslinking: A low-cost alternative for mechanically strong polymer aerogels, ACS The methods described herein are also intended, as described in Appl. Mater. Interfaces 2015, 7, 1240-1249; and Pei et al., Preparation and Characterization of Highly Crosslinked Polyimide Aerogels Based on Polyimide-Containing Trimethoxysilane Side Chain Groups, Langmuir 2014, 30, 13375-13383. The resulting polyimide aerogel is then thermally decomposed to form a polyimide-derived carbon aerogel.

[0089] The residual nitrogen content of a carbon aerogel according to an exemplary embodiment of the present disclosure, for example, a carbon aerogel derived from polyimide, may be at least about 4% by weight. For example, the residual nitrogen content of a carbon aerogel according to an embodiment disclosed herein may be at least about 0.1% by weight, at least about 0.5% by weight, at least about 1% by weight, at least about 2% by weight, at least about 3% by weight, at least about 4% by weight, at least about 5% by weight, at least about 6% by weight, at least about 7% by weight, at least about 8% by weight, at least about 9% by weight, at least about 10% by weight, or in the range of any two of these values.

[0090] In certain embodiments of this disclosure, for the carbonization of an organic (e.g., polyimide) aerogel, a dry polymer aerogel composition may be subjected to a processing temperature of 200°C or higher, 400°C or higher, 600°C or higher, 800°C or higher, 1000°C or higher, 1200°C or higher, 1400°C or higher, 1600°C or higher, 1800°C or higher, 2000°C or higher, 2200°C or higher, 2400°C or higher, 2600°C or higher, 2800°C or higher, or in the range of any two of these values. While not bound by theory, this specification assumes that the conductivity of the aerogel composition increases as the carbonization temperature increases.

[0091] In this disclosure, the term “conductivity” means a measure of a material’s ability to conduct electric current or otherwise allow electrons to pass through or flow through it. Conductivity is specifically measured as the electrical conductivity / susceptance / admittance of a material per unit size. This is commonly recorded as S / m (siemens per meter) or S / cm (siemens per centimeter). The conductivity or resistivity of a material can be measured by methods known in the art, including, but not limited to, the four-point series resistivity method (using the dual-configuration test method of ASTM F84-99). In this disclosure, unless otherwise specified, the conductivity measurement is obtained according to the ASTM F84 resistivity (R) measurement, which is obtained by measuring the voltage (V) and dividing it by the current (I). In certain embodiments, the conductivity of the aerogel material or composition of the Disclosure is approximately 10 S / cm or more, 20 S / cm or more, 30 S / cm or more, 40 S / cm or more, 50 S / cm or more, 60 S / cm or more, 70 S / cm or more, 80 S / cm or more, or in the range of any two of these values.

[0092] In this disclosure, the term “electrochemically active species” refers to additives that can accept and release ions within an energy storage device. Using a lithium-ion battery (LIB) as an example, electrochemically active species in the anode accept lithium ions during charging and release lithium ions during discharging. Electrochemically active species can be stabilized within the anode by direct / physical connection with nanoporous carbon. In certain embodiments, the nanoporous carbon network forms an interconnected structure around the electrochemically active species. The electrochemically active species binds to the nanoporous carbon at multiple points. An example of an electrochemically active species is silicon, which, as previously mentioned, may expand, crack, or break during lithiation. However, because silicon has multiple connection points with the nanoporous carbon (aerogel), even if fracture or cracking occurs, it remains active, retained within the nanoporous structure, for example, in pores, or surrounded by the structure.

[0093] In this disclosure, the terms “compressive strength,” “flexural strength,” and “tensile strength” refer to the resistance of a material to fracture or cracking under compressive, flexural, and tensile forces, respectively. These strengths are specifically measured as the amount of load / force per unit area resisting the load / force. This is generally recorded as pounds per square inch (psi), megapascals (MPa), or gigapascals (GPa). In particular, the compressive, flexural, and tensile strengths of a material contribute collectively to the structural integrity of the material, which is beneficial, for example, to withstand the volume expansion of silicon particles during lithiation in LIBs. Specifically, referring to Young's modulus, an indicator of mechanical strength, the modulus of elasticity may be measured by methods known in the art, such as, for example, Standard Test Practice for Instrumented Indentation Testing (ASTM E2546, ASTM International, West Conshocken, PA), or Standardized Nanoindentation (ISO14577, International Organization for Standardization, Switzerland). In this disclosure, Young's modulus measurements are obtained in accordance with ASTM E2546 and ISO14577 unless otherwise specified. In certain embodiments, the Young's modulus of the aerogel material or composition of this disclosure is about 0.2 GPa or greater, 0.4 GPa or greater, 0.6 GPa or greater, 1 GPa or greater, 2 GPa or greater, 4 GPa or greater, 6 GPa or greater, 8 GPa or greater, or in the range of any two of these values.

[0094] In this disclosure, the term “pore size distribution” refers to the statistical distribution or relative quantity of each pore size within a sample volume of a porous material. A narrower pore size distribution refers to a relatively large proportion of pores within a narrow range of pore sizes, thus optimizing the amount of pores that can enclose electrochemically active species and maximizing the use of pore volume. Conversely, a wider pore size distribution refers to a relatively small proportion of pores within a narrow range of pore sizes. Therefore, the pore size distribution is generally measured as a function of pore volume and recorded as the unit size of the full width at half maximum of the main peak in the pore size distribution chart. The pore size distribution of a porous material may be measured by methods known in the art, including, but not limited to, surface area and porosity analyzers by nitrogen adsorption and desorption that can calculate the pore size distribution. In this disclosure, measurements of the pore size distribution are obtained according to these methods unless otherwise specified. In certain embodiments, the relatively narrow pore size distribution (full width at half maximum) of the aerogel material or composition of the present disclosure is in the range of approximately 50 nm or less, 45 nm or less, 40 nm or less, 35 nm or less, 30 nm or less, 25 nm or less, 20 nm or less, 15 nm or less, 10 nm or less, 5 nm or less, or any two of these values.

[0095] In this disclosure, the term “pore volume” means the total volume of pores in a sample of porous material. Specifically, pore volume is measured as the volume of void space within the porous material, which may be measurable and / or measurable by another material, such as electrochemically active species, such as silicon particles. This is generally expressed in cubic centimeters / gram (cm³). 3The volume is recorded as ( / g or cc / g). The pore volume of porous materials may be measured by methods known in the art, including, but not limited to, surface area and porosity analyzers by nitrogen adsorption and desorption that can calculate the pore volume. In this disclosure, pore volume measurements are obtained according to this method unless otherwise specified. In certain embodiments, the relatively large pore volumes of the aerogel materials or compositions of this disclosure (without incorporating electrochemically active species such as silicon) are in the range of about 1 cc / g or more, 1.5 cc / g or more, 2 cc / g or more, 2.5 cc / g or more, 3 cc / g or more, 3.5 cc / g or more, 4 cc / g or more, or any two of these values. In other embodiments, the pore volume of the aerogel material or composition of the present disclosure (incorporating an electrochemically active species such as silicon) is approximately 0.3 cc / g or more, 0.6 cc / g or more, 0.9 cc / g or more, 1.2 cc / g or more, 1.5 cc / g or more, 1.8 cc / g or more, 2.1 cc / g or more, 2.4 cc / g or more, 2.7 cc / g or more, 3.0 cc / g or more, 3.3 cc / g or more, 3.6 cc / g or more, or in the range of any two of these values.

[0096] In this disclosure, the term “porosity” refers to the pore volume ratio that does not include other materials (e.g., electrochemically active species such as silicon) bonded to the pore walls. For clarification and illustrative purposes, it should be noted that in certain embodiments of silicon-doped carbon aerogel as the primary anode material in a LIB, porosity refers to the void space after the inclusion of silicon particles. Thus, the porosity may be, for example, about 10% to 70% when the anode is in a pre-lithiation state (to accommodate ion transport and silicon expansion), and about 1% to 50% when the anode is in a post-lithiation state (to accommodate ion transport). More generally, porosity may be measured by methods known in the art, such as, for example, the ratio of the pore volume to the bulk density of the aerogel material, and is not limited to these methods. In this disclosure, porosity measurements are obtained according to these methods unless otherwise specified. In certain embodiments, the porosity of the aerogel material or composition of the Disclosure is about 80% or less, 70% or less, 60% or less, 50% or less, 40% or less, 30% or less, 20% or less, 10% or less, or in the range of any two of these values.

[0097] It should be noted that pore volume and porosity are different measures of the same property of porous structures, namely the "empty space" within the porous structure. For example, when silicon is used as the electrochemically active species contained within the pores of a nanoporous carbon material, pore volume and porosity refer to the "empty" space, i.e., the space not utilized by silicon or carbon. As will be seen later, densification of pre-carbonized nanoporous materials, for example by compression, can affect pore volume and porosity, among other things.

[0098] In this disclosure, the term “pore size at the maximum peak from the distribution” means the value at an identifiable peak on a graph showing the pore size distribution. Specifically, the pore size at the maximum peak from the distribution is measured as the pore size that is formed most frequently. This is generally recorded in any unit length of pore size, such as micrometers or nm. The pore size at the maximum peak from the distribution is measured by methods known in the art, including, but not limited to, a surface area and porosity analyzer by nitrogen adsorption and desorption that can calculate the pore size distribution and measure the pore size at the maximum peak. In this disclosure, unless otherwise specified, measurements of the pore size at the maximum peak from the distribution are obtained according to these methods. In certain embodiments, the pore size at the maximum peak from the distribution of the aerogel material or composition of the present disclosure is approximately 150 nm or less, 140 nm or less, 130 nm or less, 120 nm or less, 110 nm or less, 100 nm or less, 90 nm or less, 80 nm or less, 70 nm or less, 60 nm or less, 50 nm or less, 40 nm or less, 30 nm or less, 20 nm or less, 10 nm or less, 5 nm or less, 2 nm or less, or in the range of any two of these values.

[0099] In this disclosure, the term “strut width” means the average diameter of nanostruts, nanorods, nanofibers, or nanofilaments that form an aerogel having a fibril-like morphology. This is generally recorded as any unit length such as micrometers or nm. Strut width is measured by methods known in the art, including, but not limited to, scanning electron microscopy image analysis. In this disclosure, strut width measurements are obtained according to this method unless otherwise specified. In certain embodiments, the strut width of the aerogel material or composition of this disclosure is about 10 nm or less, 9 nm or less, 8 nm or less, 7 nm or less, 6 nm or less, 5 nm or less, 4 nm or less, 3 nm or less, 2 nm or less, or in the range of any two of these values. An exemplary range of strut widths seen in the following examples (particularly in the ESM images in the figures) is about 2 to 5 nm. Smaller strut widths such as these allow a greater quantity of struts to be present in the network and thus in contact with electrochemically active species, and subsequently allow more electrochemically active species to be present in the composite. This improves conductivity and mechanical strength.

[0100] In this disclosure, the term “fibrilary morphology” refers to structural morphologies of nanoporous carbon (e.g., aerogels) that include struts, rods, fibers, or filaments. For example, in one embodiment, the choice of solvent, such as dimethylacetamide (DMAC), may affect the generation of such morphologies. Furthermore, in certain embodiments, when the carbon aerogel is derived from polyimide, crystalline polyimide is produced from the polyimide that forms the linear polymer. As will become clearer in the following examples, in certain embodiments, surprisingly, fibrilary morphologies have been observed to be included as interconnected polymer structures, where long linear structures were expected based on the known behavior of polyimide precursors. In comparison, the product morphology of nanoporous carbon may instead be essentially granular or powdery, in which the fibrilary morphology of the carbon aerogel persists. As will become apparent later in this specification, the fibrilary morphology may offer certain advantages over the granular morphology, such as mechanical stability / strength and conductivity, particularly when nanoporous carbon is provided for specific applications, such as as an anode material in LIBs. It should be noted that this fibrilous morphology is observed in both monolithic and powdery forms of nanoporous carbon; in other words, monolithic carbon can have s, and aerogel powder / particles can have fibrilous morphology. Furthermore, in certain embodiments, if the nanoporous carbon material contains additives such as silicon, the fibrilous nanostructure inherent to the carbon material is preserved and functions as a bridge between the additive particles.

[0101] In this disclosure, the term “cycle life” means the number of complete charge / discharge cycles that an anode or battery (e.g., a LIB) can withstand before its capacity drops to less than about 80% of its original rated capacity. Cycle life may be affected by various factors that are not significantly affected over time, such as the mechanical strength of the substrate (e.g., carbon aerogel), the connectivity of silicon particles within the aerogel, and the maintenance of the interconnectivity of the aerogel. It should be noted that the fact that these factors actually remain relatively unchanged over time is a remarkable aspect of certain embodiments of the invention. Cycle life can be measured by methods known in the art, including, but not limited to, a cycle test in which a battery cell undergoes repeated charge / discharge cycles at a given current rate and operating voltage. In this disclosure, measurements of cycle life are obtained according to these methods unless otherwise specified. In certain embodiments of this disclosure, the cycle life of an energy storage device such as a battery, or its electrodes, is approximately 25 cycles or more, 50 cycles or more, 75 cycles or more, 100 cycles or more, 200 cycles or more, 300 cycles or more, 500 cycles or more, 1000 cycles or more, or in the range of any two of these values.

[0102] In this disclosure, the term “capacity” means the amount of specific energy or charge that a battery can store. Specifically, capacity is measured as the discharge current that a battery can supply over time per unit mass. This is generally recorded as ampere-hours or milliampere-hours per gram of total electrode mass, Ah / g or mAh / g. The capacity of a battery (and in particular the anode) can be measured by methods known in the art, such as, for example, applying a fixed constant current load to a fully charged cell until the cell voltage reaches the end of the discharge voltage value, the time to reach the end of the discharge voltage multiplied by the constant current being the discharge capacity, and measuring the specific capacity and volumetric capacity by dividing the discharge capacity by the weight or volume of the electrode material. In this disclosure, capacity measurements are obtained according to these methods unless otherwise specified. In certain embodiments, the capacity of the aerogel material or composition of the Disclosure is approximately 200 mAh / g or more, 300 mAh / g or more, 400 mAh / g or more, 500 mAh / g or more, 600 mAh / g or more, 700 mAh / g or more, 800 mAh / g or more, 900 mAh / g or more, 1000 mAh / g or more, 1200 mAh / g or more, 1400 mAh / g or more, 1600 mAh / g or more, 1800 mAh / g or more, 2000 mAh / g or more, 2400 mAh / g or more, 2800 mAh / g or more, 3200 mAh / g or more, or in the range of any two of these values. Unless otherwise specified, when the current nanoporous carbon material is used in a battery, the capacity is reported in 10 battery cycles.

[0103] In this disclosure, the term “silicon utilization” refers to the difference between the theoretical capacity of silicon to be lithified and the measured capacity of the electrode based on silicon weight. Specifically, silicon utilization is measured as the silicon utilization efficiency within the electrode. In this specification, it is recorded as a percentage using the following formula.

number

[0104] To calculate the silicon utilization rate, the electrode capacity and silicon capacity are measured as described above. In certain embodiments, the silicon utilization rate of the aerogel material or composition of this disclosure is in the range of about 20% or more, 30% or more, 40% or more, 50% or more, 60% or more, 70% or more, 80% or more, 90% or more, or any two of these values, where a higher percentage indicates a better or more efficient silicon utilization rate. Unless otherwise specified, when the nanoporous carbon material is used in a battery, the silicon utilization rate is reported in battery cycle 10.

[0105] In one embodiment, the present invention is an anode of a lithium-ion battery (LIB) comprising a silicon-doped polyimide-derived carbon aerogel, where silicon particles are at least partially contained within the pores of the carbon aerogel. The usual reactions and processes for developing a polyimide-derived carbon aerogel (i.e., silicon-free) are shown in Figure 3. As will be seen later, the structure of the carbon aerogel pores can be tuned to have different properties (e.g., pore volume, pore size distribution) based on requirements (e.g., electrode size or capacity in the LIB). In another embodiment, the present invention is an electrode in a LIB or its electrochemical cell comprising such an anode. Further embodiments also include a device or system incorporating such an energy storage device. Examples include, but are not limited to, electric vehicles and electronic devices (e.g., mobile devices and drones).

[0106] In certain embodiments, the present invention relates to a method for forming or producing continuous porous silicon-carbon composites such as carbon aerogels. Polyimide precursors, such as diamines and dianhydrides, which may contain aromatic and / or aliphatic groups, respectively, are mixed in a suitable solvent (e.g., a polar, aprotic solvent). Silicon particles are mixed with the polyimide precursors in the solvent before the addition of an imidation gelling catalyst. The imidation gelling catalyst is then added to initiate the gelation of the mixture. In alternative embodiments, imidation can be achieved by thermal imidation, with any suitable temperature and time range being considered (e.g., heating at about 100°C to 200°C for about 20 minutes to about 8 hours, followed by heating at about 300°C to 400°C for about 20 minutes to about 1 hour). The gelled mixture is then dried to obtain a continuous porous polyimide-silicon composite, where drying can be carried out using subcritical and / or supercritical carbon dioxide. In some cases, the polyimide-silicon composite can be compressed, preferably uniaxially (for example, to 95% strain) to increase its density, which can be adjusted to about 1.5 g / cc based on the amount of compression. In exemplary embodiments, the polyimide-silicon composite can be compressed to more than 80% strain before the thermal decomposition of the composite. Whether or not compression has been performed, the polyimide-silicon composite can be thermally decomposed to obtain a continuous porous carbon-silicon composite, the resulting composite containing more than 0% by weight and less than 95% by weight of silicon, with a porosity between about 5% and 99%. In certain embodiments, thermal decomposition can be carried out at a maximum temperature between about 750°C and about 1600°C, and optionally graphitization can be carried out from about 1600°C to about 3000°C.

[0107] In certain embodiments, the silicon-carbon composite may be a monolith or a self-supporting structure, may be prepared on or off a substrate, may be pulverized into a powder, or may be prepared as a particulate material such as beads. Furthermore, the composite may be reinforced with or without nonwoven or woven materials (e.g., fibers, foams, etc.). Optionally, the composite may be pre-doped with a metal or metal oxide, such as, but not limited to, tin, sulfur, phosphorus, nickel, cobalt, manganese, lithium, magnesium, iron, zinc, boron, titanium, aluminum oxide, titanium oxide, niobium oxide, molybdenum oxide, silica, and aluminosilicates. Furthermore, the silicon particles may be pre-doped with a p-type acceptor (e.g., boron, aluminum, gallium, and indium) or an n-type donor (e.g., phosphorus, lithium, arsenic, antimony, bismuth).

[0108] In alternative embodiments, porous carbon-silicon composites may be formed or produced using the above method, except that instead of mixing silicon particles into a mixture of polyimide precursors in a solvent, silicates (e.g., silicon dioxide, aluminosilicate, and / or halloysite) and reducing agents (e.g., magnesium, lithium, sodium, potassium, aluminum, calcium, or a combination thereof) are mixed with a mixture of polyimide precursors in a solvent. Upon drying, a continuous porous polyimide silicate and reducing agent composite is formed, which can optionally be compressed to adjust its density. In this case (i.e., when silicates and reducing agents are used), the silicates and reducing agents react with hydrogen gas under inert conditions at temperatures above about 700°C to form silicon within the carbon composite.

[0109] In further alternative embodiments, the above method may be utilized, except that instead of adding silicon or silicate + reducing agent to the polyimide precursor, a continuous porous carbon is first formed (i.e., polyimide precursor, imidation using a catalyst or heat, drying and thermal decomposition), and then silicon is deposited on or within the porous carbon. In this case, silicon is deposited by immersion coating of the porous carbon onto the silicon-forming silane precursor, followed by heating under inert conditions to decompose the silane and form a conformal silicon coating within the porous carbon. This immersion treatment can be performed multiple times, increasing the thickness and silicon content up to approximately 95% by weight. In other embodiments, silicon can be deposited by atomic layer deposition or CVD.

[0110] Furthermore, this specification assumes that pore size can be adjusted as needed. There are five main methods for adjusting pore size as taught herein. First, pore size can be adjusted by the amount of solids, specifically the amount of polyimide precursor monomers (e.g., aromatic or aliphatic diamines and aromatic or aliphatic dianhydrides). Smaller pore sizes result from a larger amount of solid per unit volume of fluid, as there is less available space for tighter interconnections. It should be noted that strut width does not change to a certain extent regardless of the amount of solids used. The amount of solids is more related to the density of the network.

[0111] Another method for adjusting pore size is to apply radiation (e.g., radio waves, microwaves, infrared rays, visible light, ultraviolet rays, X-rays, gamma rays) to the composite in either the polyimide or carbon state. Radiation has an oxidizing effect, resulting in an increase in surface area, an increase in pore size, and a broadening of the pore size distribution. Thirdly, pore size is affected by macroscopic compression of the polyimide composite. As demonstrated in the following examples, pore size decreases with compression.

[0112] Another method for adjusting pore size is ionic bombardment of the composite in either the polyimide or carbon state. The effect of ionic bombardment depends on the method used. For example, there is additive ionic bombardment (e.g., CVD), where something is added and the pore size decreases. There is also destructive ionic bombardment, which increases the pore size. Finally, pore size can be adjusted (increased or decreased) by heat treatment under different gas environments, such as the presence of carbon dioxide or carbon monoxide, a chemically active environment, or a hydrogen-reducing environment. It is well known that a carbon dioxide environment can produce activated carbon, for example, where, in the case of activation, mass is removed, increasing the pore size and surface area.

[0113] While each of the above methods for adjusting pore size is conceivable, this disclosure focuses on changes in the solid content (polyimide precursor) and compression of the polyimide composite before carbonization. [Examples]

[0114] The following examples are provided for illustrative purposes only and are not intended to limit the scope of the various embodiments of the present invention.

[0115] Example 1: Low-level doping CPI complex A. CPI having a 9% dopant dispersed in polyimide PI gels were prepared from pyromellitic dianhydride (PMDA) and 1,4-phenylenediamine (PDA) in DMAC solvent at a target density of 0.06 g / cc and a molar ratio of 1:1. The precursors were mixed at room temperature for 3 hours, then acetic anhydride (AA) was added to the PMDA at a molar ratio of 4.3, and the solution was mixed for 2 hours. Powder dopants such as graphite CNGT0112 with a thickness of approximately 40 nm and a length of approximately 400-600 nm and silicon BASIC005 with spherical particles of approximately 30 nm in diameter were obtained from ACS MATERIALS. The solution was doped with 4.5% graphite or silicon (Si) per total solids. The graphite was mixed with the solution for 10 minutes by stirring with a magnetic rod, and the doped mixture and imidation were catalyzed with pyridine (Py). Based on visual evaluation, the graphite dispersed well. When silicon was stirred with the polyimide solution for 10 minutes, the dispersion appeared visually inferior in quality (i.e., evidence of sedimentation and / or particle aggregation in solution), and the mixture was sonicated for a further 3 minutes. Once the dispersion quality was improved, a pyridine catalyst was added to the mixture. The molar ratio of Py to PMDA was 4.0.

[0116] To prepare the PI composites, the solution was cast between glass plates with spacers at the edges to control the thickness. Other suitable methods for casting the solution are also intended herein. The spacers were made from 200 micrometer thick aluminum foil. Monoliths with a diameter of approximately 2 inches were also cast in Teflon® containers. The gelation time at ambient temperature was approximately 11.5 minutes for the graphite-doped samples and approximately 15.5 minutes for the silicon-doped samples. The gels were cured overnight at room temperature, and then subjected to three ethanol exchanges at 68°C before supercritical CO2 extraction. The PI aerogel composites were compressed to various thicknesses from approximately 250 micrometers and thermally decomposed and carbonized at 1050°C for 2 hours under an inert atmosphere to form CPI composites. The dopant percentage in the CPI was calculated to be approximately 9%, based on the amount of dopant in the formulation and the weight of the composite retained after thermal decomposition.

[0117] The density of compressed CPI composites with a thickness of approximately 80 to 50 micrometers ranged from approximately 0.24 to 0.36 g / cc (Table 1 and Figure 4).

[0118] [Table 1]

[0119] Porosity was calculated based on the actual density and skeletal density of the CPI composites. Since the density of amorphous carbon is in the range of approximately 2.0–2.3 g / cc and the density of silicon or graphite is approximately 2.3 g / cc, the skeletal density used in these calculations was approximately 2.2 g / cc for all composites. High porosity of 84–89% was calculated for these low-density composites.

[0120] B. CPI containing 9% dopant dispersed in the solvent by mixing. Similar experiments were conducted using a polyimide solution with a target density of 0.10 g / cc. In this case, the dopant was mixed with a portion of the DMAC for 10 minutes and added to the mixture before the catalyst. A 500 micrometer thick Teflon® spacer was used for casting. The molar ratio of Py to PMDA was 2.0. The gelation time was approximately 2.5 minutes for the graphite-doped sample and approximately 4.0 minutes for the silicon-doped sample. The gel was extracted using supercritical CO2. The PI aerogel composites were compressed to various thicknesses from approximately 580 micrometers and thermally decomposed and carbonized at 1050°C for 2 hours to form CPI composites.

[0121] The properties of the CPI composites are shown in Table 2. As expected, the more compressed composites showed slightly lower porosity.

[0122] [Table 2]

[0123] The density of the compressed CPI composites (at a thickness of approximately 115–80 micrometers) ranged from approximately 0.57–0.87 g / cc. The density of the silicon-doped CPI composites was slightly lower compared to the graphite-doped samples (Figure 5).

[0124] Table 3 shows the density and shrinkage of doped PI aerogel monoliths after thermal decomposition. The density of the uncompressible monoliths (LS1 and LG1) was lower compared to the density of the compressed composites (LS2 and LG2).

[0125] [Table 3]

[0126] SEM images of silicon-doped pyrolysis composites are shown in Figures 6A-6B, where Figure 6B shows the fibrillary morphology of the silicon-doped CPI composite. The silicon aggregates and silicon nanowire pockets were embedded in the carbon matrix. Figure 7 shows the anode discharge capacity per dopant content in the half-cell tests. The initial capacity of silicon was significantly higher compared to the graphite dopant. Although the initial capacity decreased with cycling, its reversible capacity was still dramatically higher than graphite alone, as was the case with conventional anodes. Furthermore, the capacity degradation may be attributable to the foil electrodes used in these half-cell tests, as the electrodes were unable to operate at the high capacity of the silicon-containing electrodes.

[0127] Example 2: CPI composite with high PI solids content and high silicon doping A. 27% silicon-doped CPI dispersed by ultrasonic treatment in a solvent. A PI gel was prepared using a target density of 0.10 g / cc. PMDA precursor and PDA precursor were mixed at room temperature for 3 hours. Separately, silicon powder with a particle size of 30 nm was sonicated in DMAC solvent for 20 seconds and added to the mixture at 15.0% of the total solids content, and stirred for 15 minutes. AA was added to the mixture doped at a 4.3 molar ratio relative to PMDA and mixed for 2 hours. Pyridine was used to catalyze the mixture at a 2.0 molar ratio relative to PMDA. The composite was cast between glass plates using a 500 micrometer thick Teflon® spacer. A 2-inch diameter monolith was also cast in a Teflon® container. The gelation time at ambient temperature was approximately 3.5 minutes. The gel was cured overnight at room temperature, followed by three ethanol exchanges at 68°C before supercritical CO2 extraction. The PI aerogel composite was compressed and thermally decomposed and carbonized at 1050°C for 2 hours to form a CPI composite.

[0128] B. 46% and 64% silicon-doped CPI dispersed by sonication in a solvent A PI gel was prepared with a target density of 0.08 g / cc. PMDA precursor and PDA precursor were mixed at room temperature for 4 hours. Then, AA was added and mixed with the solution for 2 hours. Separately, silicon powder with a particle size of 30 nm was sonicated in DMCA solvent for 1 minute and added to the mixture 5 minutes before adding the pyridine catalyst. Silicon was added at approximately 29.7% and 49.6% of the total solids content. The doped mixture was catalyzed with Py at a 3.2 molar ratio to PMDA. The composite was cast using a spacer with a thickness of 500 micrometers. The gelation time at ambient temperature was approximately 6.5 minutes. After processing and extraction, the PI aerogel composite was compressed and thermally decomposed and carbonized at 1050°C for 2 hours to form a CPI composite.

[0129] Table 4 and Figure 8 show a comparison of the surface area and porosimetry of pyrolysis-incompressible monoliths doped with different amounts of silicon. Surface area, micropore area, and pore volume decreased as the silicon content in the CPI increased.

[0130] [Table 4]

[0131] The pore size distribution at the maximum peak depended on the silicon content and the silicon dispersion pattern (Figure 9). Generally, increasing the silicon content shifted the pore size at the maximum peak from the distribution to larger sizes. As the Si content increased from approximately 9% to approximately 46% and then to approximately 64%, a shift in the main peak in the maximum size distribution was observed from approximately 23 nm to approximately 26 nm and then to approximately 34 nm. The basal pore size distribution broadened with increasing silicon content.

[0132] However, when comparing the Td 0.10 g / cc samples, the 27% Si monolith prepared by adding silicon before AA and mixing with the solution for a long time showed a pore size shift of approximately 15 nm for the main peak of the 9% Si monolith prepared by short-term Si mixing with the solution, compared to approximately 23 nm for the 9% Si monolith. The 27% Si-doped sample showed a bimodal pore size distribution, with another small broadband centered at approximately 30 nm. This may be due to the incomplete dispersion of silicon in the high target density, high viscosity mixture. This was also true for samples with a higher silicon content (64%) in this series, which also showed a bimodal pore size distribution.

[0133] The compressed pyrolysis composites exhibited higher densities, as well as smaller surface area and pore volume, compared to their uncompressed monolithic counterparts (Table 5). Densities were calculated as the average of six samples.

[0134] [Table 5]

[0135] Half-cell units (2032 coin cells) were fabricated using CPI composites as electrodes, lithium foil as counter electrodes, and CELGARD2500 as a microporous separator between the electrodes. The electrolyte used was 1.0 M LiPF6 with an EC:EMC (3:7) weight ratio. Unless otherwise specified, all cells were tested using an ARBIN BT2043 tester at a charge / discharge rate of 0.1C. Table 6 shows the discharge capacity of the compressed CPI composites after 5 cycles.

[0136] [Table 6]

[0137] As shown in Figure 10, the optimal performance of these samples was obtained with a Si content of 30-50% per CPI.

[0138] SEM images of high-Si-content doped composites are shown in Figures 11A-11C, which also show the fibrillary morphology of the composites. In samples with higher doping concentrations, silicon (bright regions) is more compressed. In all samples, Si nanowires can be observed at high magnification. As can be seen from the figures, there is direct contact and interpenetration between silicon and the carbon porous structure (dark regions).

[0139] The cycle capacities based on Si and electrode content are shown in Figures 12A-12F, and the raw data is shown in Table 7. Increasing the Si load of the CPI composite resulted in a faster decrease in capacity due to cycling. However, the capacity decrease may be due to the foil electrodes used in these half-cell tests, as the electrodes were unable to operate at the high capacities of silicon-containing electrodes.

[0140] [Table 7]

[0141] As shown in Table 7, the silicon utilization rate can be calculated to be approximately 20% to 90%, or more optimally, approximately 50% to 90%, depending on the amount of silicon incorporated into the electrode. A narrower range is also intended herein, based on the advantages required for the final composite (e.g., the desired amount of silicon). Overall, this wider range is significantly higher than that seen in the prior art. Furthermore, the capacity in cycle 10 can be beneficially approximately 800 mAh / g or more, but can vary depending on the silicon concentration.

[0142] Example 3: Silicon-doped CPI composite containing low PI solids A. 66% silicon-doped CPI dispersed in a solvent by ultrasonic treatment A PI gel was prepared with a target density of 0.05 g / cc. PMDA precursor and PDA precursor were mixed at room temperature for 3 hours. Then, AA was added and mixed with the solution for 2 hours. Separately, silicon powder with a particle size of approximately 30 nm was sonicated in DMAC solvent for 2 minutes and added to the mixture 30 minutes before the addition of the pyridine catalyst. Approximately 60.5% silicon was added per total solid content. The Py / PMDA molar ratio was 7.5. The gelation time at ambient temperature was approximately 5.5 minutes. The composite was cast using a spacer with a thickness of 500 micrometers. After processing and extraction, the PI aerogel composite was compressed and thermally decomposed and carbonized at 1050°C for 2 hours to form a CPI composite. The Si content per CPI was 66%.

[0143] CPI composites compressed to different thicknesses were examined by SEM, and the fibril-like morphology of the CPI composites is shown in Figures 16A-16B. No silicon nanowires were observed in these images. The properties of low-compression (LC) and high-compression (MC) composites tested in half-cells are shown in Table 8.

[0144] [Table 8]

[0145] Figures 14A-14B show that thickness plays a role in anode performance. By reducing the thickness by approximately half, the electrode capacity essentially doubled, with electrodes 170 micrometers thick exhibiting a discharge capacity exceeding 1500 mAh / g after four cycles. While these high-capacity CPI composites, filled with a large amount of silicon (66%), were not stable over multiple cycles, the capacity degradation may be attributable to the foil electrodes used in these half-cell tests, as the electrodes were unable to operate at the high capacity of silicon-containing electrodes.

[0146] B. 45% silicon-doped CPI mixed and dispersed in a solvent with and without a dispersant. A PI gel was prepared at a target density of 0.05 g / cc. PMDA precursor and PDA precursor were mixed at room temperature for 17 hours. Then, AA was added and mixed with the solution for 3 hours. Separately, silicon powder with a particle size of 30 nm was mixed in a DMAC solvent with or without a dispersant for 20 hours. Control sample C45 was prepared in the absence of a dispersant. BYK384 was used as a dispersant in sample B45 at 20% by weight of Si. Pluronic® F87 was used as a nonionic surfactant in sample P45 at 20% by weight of Si. The dispersion was added to the mixture 30 minutes before the addition of the pyridine catalyst. Silicon was added at 27.3% of the total solids. The Py / PMDA molar ratio was 7.0. The gelation time at ambient temperature was approximately 11 minutes. The composite was cast using a 500 micrometer thick spacer. After processing and extraction, the PI aerogel composite was compressed and thermally decomposed at 1050°C for 2 hours to carbonize it, forming a CPI composite. The Si content per CPI was approximately 45%.

[0147] SEM images of compressed C45 polyimide composites before and after thermal decomposition are shown in Figures 15A-15B, with Figure 15B also showing the fibrillary morphology of the CPI composite. In the case of Si nanowires, no non-thermal decomposition composites were observed only in the CPI composite. SEM images of CPI composites with and without dispersant are shown in Figures 16A-16C. The properties of the CPI composites used in battery testing are shown in Table 9. The conductivity of these samples was approximately 26-27 S / cm.

[0148] [Table 9]

[0149] The half-cell test results showed that the P45 composite had a higher discharge capacity and lower irreversible capacity loss compared to the other two samples (Figures 17A-17C). The capacity reduction may also be due to the foil electrodes used in these half-cell tests, as the electrodes were unable to operate at the higher capacity of the silicon-containing electrodes.

[0150] P45 composites were cast at three different thicknesses: 780 microns, 580 microns, and 370 microns. Each of these PI batches was divided into approximately 0.5 × 0.5 square inch sections of composite material, which were compressed at three different levels using a hydraulic press and then pyrolyzed. The results are shown in Table 10 and Figure 18.

[0151] [Table 10]

[0152] The density of the Si-doped CPI composite varied between 0.3 and 1.0 g / cc at thicknesses of approximately 50 to 130 micrometers (Figure 18). The density increased with increasing initial thickness of the PI composite. Porosity ranged from approximately 50 to 90%.

[0153] Electrical conductivity of silicon-doped CPI composites. The electrical conductivity of CPI composites doped with various concentrations of silicon and thermally decomposed at 1050°C was measured using a Keithley 4-point probe instrument. The conductivity of the samples varied in the range of approximately 5–80 S / cm (Table 11). The conductivity of the undoped carbon composite was approximately 13.6 S / cm, which, as known in the art, is within the expected range for amorphous carbon. The reported conductivity of silicon is 1.6 × 10⁻⁶. -5 While the conductivity is S / cm, silicon nanowires can exhibit conductivity three orders of magnitude higher (0.03 S / cm) (Sabar D. Hutagalung, Mohammed M. Fadhali, Raed A. Areshi and Fui D. Tan, Optical and Electrical Properties of Silicon Nanowires Prepared by Electroless Etching, Nanoscale Research Letters, 2017, 12:425).

[0154] [Table 11]

[0155] Typically, electrical conductivity increased with increasing density. However, at silicon concentrations exceeding 60%, conductivity was lower than expected (Figure 19). At this high silicon content, the connectivity of the carbon network was broken, resulting in decreased conductivity. Samples doped with 27 wt% Si per CPI showed the highest conductivity, suggesting that there is an optimal dispersion of silicon for the purpose of high conductivity. A broader optimal range for Si is found to be between approximately 5% and 80 wt% per CPI, or more specifically, between approximately 5% and 50 wt% Si per CPI. As can be seen in Tables 9 and 11, conductivity can be adjusted up to approximately 80 S / cm by varying the silicon content. Thus, conductivity can exceed approximately 5 S / cm, 10 S / cm, 15 S / cm, 25 S / cm, 50 S / cm, and 75 S / cm, where a wider range and more precise conductivity are considered tunable based on silicon content.

[0156] Example 4: Carbide polyimide aerogel with high pore volume and narrow pore size distribution A PI gel is prepared by reacting 6 g of PMDA with 3 g of PDA at room temperature for 2 to 24 hours to form a polyamic acid in 100 mL of DMCA. Subsequently, 8.86 g of AA is added to the polyamic acid solution as a chemical imidization reagent (see Figure 20). The acidified polyamide solution is mixed vigorously for at least 2 hours. The resulting mixture is diluted with DMAC to the desired target density of the PI aerogel. 1 to 4 g of Py per 100 mL of mixture is added to the final solution to promote gelation, which occurs in 4 to 25 minutes. Before gelation, the mixture is cast into the desired form (e.g., film, monolith, reinforcing fiber, etc.). The resulting gel is then aged in an oven at 65 to 70°C and washed / rinsed several times with ethanol before supercritical drying. The PI aerogel is converted to a carbon aerogel by thermal decomposition at 1050°C for 2 hours under an inert environment (nitrogen gas flow). While not bound by theory, the physical and structural properties of carbide-PI aerogels depend on the precursor mixing time and the amount of Py.

[0157] Table 12 reports the structural properties of four CPI aerogels tested by nitrogen adsorption-desorption. The four samples differed in mixing time and amount of Py. The target density was fixed at 0.05 g / cc. Interestingly, all samples showed relatively similar surface BET, but the pore size distribution and pore volume appeared to be affected by the synthesis parameters.

[0158] [Table 12]

[0159] Example 5: Si-supported polyimide carbide aerogel Si particles (30 nm) were added to polyamic acid solutions at different concentrations. The synthesis of the solutions was the same as described in Example 4. However, in this composite system (PI / Si), the silicon particles were first dispersed in DMAC for at least 2 hours before being mixed with the polyamic acid solution. To avoid Si sedimentation, the gelation time of the Si / polyamic acid solution was kept relatively short (4-6 minutes). For this purpose, a mixture of 4 g pyridine / 100 mL was used to achieve the target gelation time. Before gelation, the mixture was cast into the desired form (e.g., film, monolith, or reinforcing fiber). The resulting gel was then aged in an oven at 65-70°C and washed / rinsed several times with ethanol before supercritical drying.

[0160] A. 22-25% by weight of silicon in polyimide carbon aerogel composite The target density of the composite was fixed at 0.06 g / cc, and the Si loading during the polymerization process was approximately 11.88 wt%. Since weight loss of more than 50% was recorded in all samples, the silicon content was adjusted after thermal decomposition of the polyimide aerogel at 1050°C for 2 hours. Four different thicknesses of composites were prepared. MT (medium thickness composite approx. 0.3~0.4mm) T (thick composite material approximately 0.6-0.8 mm) MTC (Medium-thickness compressed composite material, approximately 0.07-0.09 mm) TC (thick compressed composite material, approximately 0.12-0.16 mm thick)

[0161] Different PI / Si samples were thermally decomposed at 1050°C for 2 hours and then subjected to battery testing. The physical properties of each sample are shown in Table 13. [Table 13]

[0162] Figure 23 shows an SEM image of a pyrolysis composite (MT material) doped with approximately 25% Si. The SEM image shows high magnification the aggregation of Si and silicon nanowires embedded in the carbon matrix.

[0163] Figures 25A and 25B show the cycle capacities of MTC5 and MT5 samples based on Si and electrode content. MTC5 (compressed CPI aerogel) was tested up to 400 cycles, and MT5 (uncompressed CPI aerogel) up to 150 cycles. The two samples exhibited different behaviors. MTC5 showed relatively stable capacity discharge up to 200 cycles, followed by a decrease in capacity, which, as mentioned earlier, is thought to be due to the foil electrodes in the half-cell test.

[0164] B. 39% by weight of silicon in polyimide carbon aerogel composite In the following synthesis route, the Si content was increased to 39% by weight in anticipation of a reduction in capacity loss during the initial discharge. A polyimide gel was prepared at a target density of 0.05 g / cc. A polyamic acid solution was prepared by mixing PMDA precursors and PDA precursors in DMAC for 16 hours. Separately, silicon powder was dispersed in DMAC for 2 hours and then added to the polyamic acid solution before adding pyridine. After adding pyridine, the composite was prepared between Teflon® plates using a 500 micron spacer. The aerogel composite was compressed and then thermally decomposed at 1050°C for 2 hours. The silicon content was 39% by weight of the total solids.

[0165] Table 14 shows the properties of the compressed (PISi1NC(C)) and uncompressed (PISi7NC) composites tested with half-cells.

[0166] [Table 14]

[0167] Figures 26A and 26B show the discharge capacity as a function of cycles for anodes fabricated using the two materials reported in Table 14. A clear improvement in discharge capacity based on the anode is evident when the silicon content is increased from 25 wt% (previous materials, i.e., MT5 and MYC5) to 39 wt%.

[0168] Example 6: Fiber-reinforced C / Si aerogel Different surface densities (2, 4, 10 g / m²) 2 Three different carbon fiber reinforcements were tested as reinforcements for C / Si aerogel. The synthesis and processing of the PI / Si aerogel were the same as described above, with one exception. During the gelation process, the mixture was cast into the fibers. After supercritical drying, the carbon fiber-reinforced PI / Si composite was cut into 15 mm (inner diameter (ID)) circular samples using a dye cutter and thermally decomposed at 1050°C for 2 hours. Figures 27-29 show the properties and micrographs of the carbide PI / Si / carbon fiber samples.

[0169] After thermal decomposition, 2 and 4 g / m 2 The carbon fiber-reinforced sample showed increased shrinkage and strengthening compared to the carbon aerogel. Figures 28-29 show high voids that characterize these two types of materials as particularly unsuitable for battery testing. In Figure 27, 10 g / m 2 The carbon fiber-reinforced C / Si exhibited a better microstructure with no evidence of voids. However, the Si content was low (approximately 21%) and the fiber density was high (>30 wt%). The charge and discharge capacities of this composite were tested in the system. Based on the Si and electrode content, the cycle capacities of the samples shown in Figure 27 are reported in Figure 30.

[0170] In another experiment, cellulose fibers were also tested as a reinforcing material for C / Si. The synthesis route was the same as that used for carbon fibers. Cellulose fibers constituted 68% (by weight) of the C / Si composite, but much of these fibers decomposed after thermal decomposition, because the percentage of Si increased from 6% to 24% after thermal decomposition. The physical properties of C / Si reinforced with cellulose fibers are reported in Table 15.

[0171] [Table 15]

[0172] The cycle capacity of cellulose fiber-reinforced C / Si based on Si and electrode content is reported in Figure 31. The performance of this material is similar to that of carbon fiber-reinforced C / Si.

[0173] Example 7: Improvement of silicon dispersion in PI aerogel PI composites and monolithic gels supporting 47% silicon at a target density of 0.05 g / cc were prepared. To avoid aggregation, a pathway was used to better disperse silicon within the polyimide matrix. Silicon was dispersed and mixed with PMDA and PDA from the start of the solution synthesis. The polyamic acid solution + silicon was mixed for 16 hours. Acetic acid was added and mixed with the solution for 4 hours. Rapid gelation (approximately 4 minutes) was ensured by adding an appropriate amount of Py to the acidified polyimide / Si mixture. Composites and thick monoliths with a thickness of approximately 200-300 microns were cast. After supercritical drying, the PI / Si aerogel composites were compressed and then thermally decomposed at 1050°C for 2 hours.

[0174] Next, several different samples (e.g., compressed, incompressible, monolith, etc.) were analyzed by SEM to evaluate the dispersion of silicon in the carbon matrix. Figure 32 shows three cross-sectional SEM images of a thick, incompressible composite (0.60 mm). At low magnification (left image), uniform and well-distributed silicon is shown. Large clusters of silicon are also visible. At higher magnification (right image), it can be seen that high-density silicon is well embedded in the carbon matrix. Figure 33 shows three cross-sectional SEM images of a thin composite (0.12 mm). The same observations are obtained, namely good Si dispersion and proper impregnation into the carbon matrix. In the cross-sectional SEM image of the monolith (Figure 34), the same structure as shown in the thick and thin composites is clearly confirmed.

[0175] Figures 35-36 show a parallel comparison of two types of C / Si composites treated differently. The image on the left (in both figures) is for monoliths and composites cast from a Si / polyamic acid solution mixed for 16 hours (long contact). The image on the right is for monoliths and composites prepared from a Si / polyamic acid solution mixed for 4-6 minutes (short contact). The silicon distribution is observed to differ between the two processes. Indeed, longer contact resulted in better Si dispersion than shorter contact.

[0176] Half-cell tests were performed on compressed and uncompressible C / Si composites. In both PISi3 (uncompressible) and PISi6C (compressed) samples, Si was well dispersed in the carbon aerogel matrix. The physical properties of both samples are reported in Table 16.

[0177] [Table 16]

[0178] The charge-discharge cycles of the two samples are shown in Figures 37 and 38. The samples performed remarkably well, and the compressed sample (PISi6C) showed stable cycle performance.

[0179] Example 8: Fabrication of a C / Si circular electrode In the previous embodiment, the shape of the C / Si electrode was square (approximately 1 cm). 2 The battery performance of a circular battery (ID=15mm) was tested. To obtain higher efficiency and more reliable test results, testing of circular C / Si electrodes is necessary. Therefore, circular electrodes were fabricated using a die cutter.

[0180] A PI aerogel composite with a target density of 0.13 g / cc (using a 16-hour mixture) and 31.4% Si content was prepared. After extraction, the density of the final aerogel was measured to be approximately 0.213 g / cc. Multiple circular aerogel composites with an inner diameter of 15 mm were prepared using a die cutter (see Figure 39). The thickness of the samples was approximately 0.43 mm. After compressing some of the samples, they were thermally decomposed at 1050°C for 2 hours. The characteristics of the thermally decomposed circular electrodes are as follows. Weight loss: about 41% Uncompressed sample: approximately 0.261 g / cc (inner diameter 1.1 cm, thickness 0.38 mm) Compressed sample: Approximately 0.652 g / cc (inner diameter 1.35 cm, thickness 0.11 mm)

[0181] The performance of compressed and uncompressed half-cells is shown in Figures 40 and 41. The capacity of the uncompressed sample appears to be higher than that of the compressed sample, but the capacity of the uncompressed sample was also more unstable.

[0182] Example 9 Si-filled carbide PF aerogel Regarding the production of C / Si aerogel electrodes, carbon aerogels produced from PF are also contemplated herein. In the case of PF systems, aerogels with a high target density (>0.7 g / cc) can be achieved depending on the synthetic route. There is no need to compress the obtained aerogel. There is no need to compress the obtained aerogel. The high-density PF gel composite was prepared as follows. 22 g of phloroglucinol was dissolved in 100 mL of ethanol, and 44 mL of 2-furaldehyde was added to the phloroglucinol solution. The resulting solution was mixed for 30 minutes. 5 wt% of silicon was added to the mixture, followed by further vigorous mixing for 30 minutes. The PF mixture can be gelled with a base (diamine or triamine), and the gelation time is about 20 to 40 minutes depending on the concentration of the base. In this case, in the presence of silicon, the gelation time should be shortened (less than 1 minute) to avoid sedimentation of silicon during gelation. Hydrochloric acid (HCl) was used to catalyze the gelation of PF with a short gelation time of 20 seconds. Therefore, concentrated HCl at a concentration of 0.012 g per 100 mL of the mixture was added to the mixture, mixed for 20 seconds, and cast between Teflon® plates to prepare a gel. After aging and solvent exchange, the PF gel composite was dried with supercritical CO₂. The properties of the obtained PF / Si aerogel are as follows. Thicknesses of the two composites: about 0.2 mm and about 0.1 mm Final density of the aerogel: about 0.7 g / cc

[0183] After pyrolysis under inert gas at 1050°C for 2 hours, the density of the obtained C / Si aerogel was adjusted to 0.77 g / cc, and the Si content was adjusted to 10% by weight. Precut sample (1 cm 2 ) (see Figure 42) was prepared.

[0184] The surface area of the C / Si aerogel tested by liquid nitrogen adsorption-desorption is 541 m 2The volume was high at / g, and the pore volume was 0.32 cc / g. Interestingly, the micropore area accounted for 80% of the total surface area, confirming the dense and compact structure shown in the SEM image (see Figure 43). Furthermore, the Si-containing carbon aerogel composite sample, in which the carbon originated from PF, showed high volume loss after the first cycle and a very low overall volume (see Figure 44). These results highlight the unique properties of Si, which functions better in a fibrillary morphology, as seen in nanoporous carbon / carbon aerogels derived from polyimide.

[0185] Example 10: Nanoindentation as a measure of mechanical strength Multiple CPI composite samples were prepared using the method described above, where the variables within the samples were silicon content and density. The Young's modulus of each sample was measured using nanoindentation to test the hardness of the material. More specifically, 20 indentations were made across the sample surface. Approximately 8–10 indentations were selected to obtain the mean data and standard deviation for each mechanical property. The indentation locations were selected under a microscope, the surface was relatively clean and smooth, and there were few surface features, thus providing more reliable data. Since samples 1 and 2 were softer than the other samples, a maximum load of 50 mN was selected. An indentation load of 300 mN was used for samples 3–7. The results and other properties are shown in Table 18. Figure 45 shows the modulus of elasticity as a function of density, and Figure 46 shows the modulus of elasticity as a function of density.

[0186] [Table 17]

[0187] Example 11: CPI beads doped with 45% silicon PI gel beads were prepared at a target density of 0.10 g / cc. PMDA precursor and PDA precursor were mixed in DMAC solvent at room temperature for 3 hours. Then, AA was added and mixed with the solution for 2 hours. Separately, silicon powder with a particle size of 30 nm was sonicated in DMAC solvent for 1 minute and added to the mixture 5 minutes before adding the pyridine catalyst. Silicon was added at approximately 24% of the total solid content. The doped mixture was catalyzed with Py at a 3.2 molar ratio to PMDA. Before gelation, the catalyst sol containing silicon particles was poured into a container containing previously stirred silicone oil as a dispersion medium (silicone oil:catalyst sol volume ratio of 10:1). The gelled PI beads were isolated from the silicone oil by filtration, followed by rinsing with ethanol, and then dried by supercritical CO2 extraction. Next, the PI aerogel-silicon composite beads were thermally decomposed at 1050°C for 2 hours to form CPI silicon composite beads with a tap density of 0.7 g / cc and a D50 of 15 μm.

[0188] Example 12: Electrode prepared from CPI beads Using CPI silicon composite beads prepared according to Example 11, an anode electrode was prepared on a Cu foil as a current collector by mixing a slurry containing 80 wt% CPI silicon composite beads, 10 wt% polyacrylic acid (PAA) binder, and 10 wt% hard carbon conductive additive (C65) in water at a total solids content of approximately 36 wt%. The slurry was cast onto the Cu foil using a doctor blade. After drying and calendering, a load of 3.1 mg / cm was applied. 2 An electrode with a density of 0.7 g / cc was obtained.

[0189] Example 13: Half-cell unit manufactured from CPI electrodes Half-cell units (2032 coin cells) were fabricated using CPI composite electrodes prepared according to Example 12, with lithium foil as the counter electrode and CELGARD2500 as a microporous separator between the electrodes. The electrolyte was 1.0 M LiPF6 in ethylene carbonate (EC) / ethyl methyl carbonate (EMC) (3:7 wt ratio) and 5 wt% fluoroethylene carbonate (FEC). All batteries were tested with an ARBIN BT2043 tester. The battery test protocol included four formation cycles at a charge / discharge rate of C / 20. Subsequent cycles were performed at various rates between C / 20 and 5C. Figure 48 shows the half-cell cycle characteristics of a CPI composite electrode containing 30 wt% silicon particles, prepared as an electrode from a slurry containing 80 wt% CPI silicon composite beads, 10 wt% polyacrylic acid (PAA) binder, and 10 wt% hard carbon conductive additive (C65). The graph in Figure 48 shows the discharge capacity (mAh / g based on the total weight of the electrodes) and Coulomb efficiency as a function of cycles for 1.0 M LiPF6 in ethylene carbonate (EC) / ethyl methyl carbonate (EMC) (weight ratio 3:7) and 5 wt% fluoroethylene carbonate (FEC).

[0190] Example 14: Alternative method for producing PI aerogel The earlier embodiments discussed herein teach a specific method for forming PI aerogels. In certain embodiments, the present invention also intends to provide alternative methods for forming PI aerogels. Hereinafter, a non-exclusive and non-limiting set of such alternative methods are discussed.

[0191] For example, U.S. Patent No. 6,399,669 by Suzuki et al. teaches four related methods for producing PI dry gels (aerogels). In the first method, a PI precursor is synthesized, followed by the formation of an imide from the PI precursor to produce a polyimide. A PI solution or swollen bulk is prepared, and the solution / swollen bulk is gelled to produce a PI wet gel. This wet gel is dried to obtain a PI dry gel (aerogel). In the second method, a PI precursor is synthesized, followed by the preparation of a PI precursor solution or swollen bulk. The solution / swollen bulk is gelled to produce a PI precursor wet gel. Then, an imide is formed from the PI precursor to form a PI wet gel. This wet gel is dried to obtain a PI dry gel (aerogel). In the third method, a PI precursor is synthesized, followed by the preparation of a PI precursor solution or swollen bulk. Then, an imide is formed from the PI precursor while gelling to form a PI wet gel. In the third method, a PI precursor is synthesized, followed by the preparation of a PI precursor solution or swollen bulk. The solution / swelled bulk is gelled to produce a PI precursor wet gel. This wet gel is then dried to produce a PI precursor dry gel. Next, an imide is formed from the PI precursor dry gel to form a PI dry gel (aerogel).

[0192] As a further example, Leventis et al. [Polyimide Aerogels by Ring-Opening Metathesis Polymerization (ROMP), Chem. Mater. 2011, 23, 8, 2250~2261] investigated the formation of PI aerogels using the ROMP method. Low molecular weight imidized oligomers with polymerizable groups end-bound are provided and mixed with a polymerization (e.g., ROMP) catalyst. Polymerization is then initiated, producing crosslinked polyimides. These polyimides are gelled and dried to form PI aerogels. Furthermore, Leventis et al. [U.S. Patent No. 9,745,198; Chidambareswarapattar et al., One-Step Room Temperature Synthesis and Conversion to Isocaust of Fibrous Polyimide Aerogels from Anhydrides and Isocyanates, J.Mater.Chem., 2010, 20, 9666~9678] teach that PI aerogels are formed by mixing a dianhydride (e.g., PMDA) with an isocyanate (e.g., 4,4'-diisocyanatodiphenylmethane or methylenediparaphenyldiisocyanate) to form a sol-gel material. The sol-gel material is then dried to produce the PI aerogel. Furthermore, Leventis et al. [Isocyanate-derived organic aerogels: polyurea, polyimide, polyamide, MRS method, 1306 (2011), Mrsf10-1306-bb03-01.doi:10.1557 / opl.2011.90] note that DESMODUR N 3300A, DESMODUR RE, and MONDUR CD (all available from Bayer) can be used as isocyanates.

[0193] Another approach, described by Guo et al. [Amine-functionalized polyoligomers crosslinked with silsesquioxane polyimide aerogels, ACS Appl. Mater. Interfaces 2011, 3, 546-552], involves the formation of PI aerogels by the reaction of aminosilsesquioxane with polyamic acid oligomers terminally sealed with anhydride groups. The product is imidized with pyridine (thermal imidization is also possible), gelled, and then dried to obtain a PI aerogel. Nguyen et al. [Development of high-temperature flexible polyimide aerogels, American Chemical Society, minutes published in 2011] describes the production of branched polyimides by mixing a diamine and a dianhydride, imidizing them, and then reacting them with a multi-amino compound (e.g., 1,3,5-tris(4-aminophenoxybenzene)). This product is then reacted with 4,4'-methylene diisocyanate and dried to form a PI-urea aerogel.

[0194] In another embodiment, Meador et al. [Mechanically strong flexible polyimide aerogels crosslinked with aromatic triamines, ACS Appl. Mater. Interfaces, 2012, 4(2), pp536~544] investigated the formation of PI gels by crosslinking polyamic acid oligomers, which are terminally sealed with anhydride groups, with aromatic triamines in solution, followed by imidation. The resulting wet material was dried to form a PI aerogel. Furthermore, Meador et al. [Polyimide aerogels with amide crosslinking: A low-cost alternative to mechanically strong polymer aerogels, ACS Appl. Mater. Interfaces 2015, 7, 1240-1249] investigated the formation of PI gels by crosslinking amine-bound oligomers with 1,3,5-benzenetricarbonyl trichloride. The resulting gel was dried to form a PI aerogel.

[0195] In yet another embodiment, Pei et al. [Preparation and Characterization of Highly Crosslinked Polyimide Aerogels Containing Trimethoxysilane Side Chain Groups] Langmuir 2014, 30, 13375~13383] prepared a PI aerogel from a polyimide containing trimethoxysilane side chain groups, which is a condensation product of a polyimide containing an acid chloride side chain group and 3-aminopropyltrimethoxysilane. The resulting gel was dried to form a PI aerogel.

[0196] In any of these methods, a graphene suspension can be added (see Zhang et al., Graphene / Carbon Aerogel Derived from Graphene-Crosslinked Polyimide as Electrode Material for Supercapacitors, RSC Adv., 2015, 5, 1301).

[0197] Each of these methods can yield a polyimide aerogel, and the present invention intends any suitable method for producing such a polyimide aerogel. According to certain embodiments of the present invention, regardless of which method is used to produce the PI aerogel, the resulting PI aerogel can be thermally decomposed to form a PI-derived carbon aerogel. According to certain embodiments discussed herein, additives such as silicon can also be introduced.

[0198] All referenced publications are incorporated herein by reference in their entirety. Furthermore, if there is any conflict or inconsistency between the definition or use of a term in a reference incorporated herein by reference and the definition of that term provided herein, the definition provided herein shall apply, and the definition in the reference shall be disregarded.

[0199] The advantages described above, and those evident from the above description, are achieved efficiently. Since specific modifications can be made to the above configuration without departing from the scope of the invention, all matters included in the above description or shown in the accompanying drawings should be construed as illustrative and not as limiting.

[0200] It should also be understood that the following claims are intended to cover all of the general and specific features of the invention described in the present specification, and all descriptions of the scope of the invention that may be said to lie between them as a matter of language. Some embodiments of the present invention are shown below. [Embodiment 1] A carbon material having a porous structure, A silicon-based material located at least partially within the porous structure of the carbon material, A carbon composition comprising, A carbon composition containing more than approximately 10% by weight of silicon-based material, having a porosity between approximately 10% and approximately 80%, a pore diameter at the maximum peak from the distribution being approximately 100 nm or less, and a silicon utilization rate of at least approximately 20%. [Embodiment 2] The carbon composition according to Embodiment 1, wherein the carbon material has a porous structure comprising fibril-like morphology, a Young's modulus of at least about 0.2 GPa, and a density between about 0.15 g / cc and about 1.5 g / cc. [Embodiment 3] The carbon composition according to Embodiment 1, wherein the carbon material has a porous structure comprising fibril-like morphology, having an electrical conductivity of at least about 10 S / cm, and a density between about 0.15 g / cc and about 1.5 g / cc. [Embodiment 4] The carbon composition according to any one of Embodiments 1 to 3, wherein the carbon material includes a carbon aerogel. [Embodiment 5] The carbon composition according to Embodiment 4, wherein the carbon material comprises a carbon aerogel derived from polyimide. [Embodiment 6] The carbon composition according to any one of Embodiments 1 to 3, wherein the carbon material contains at least about 4% by weight of residual nitrogen. [Embodiment 7] The carbon composition according to any one of Embodiments 1 to 3, wherein the carbon composition is in a monolithic form. [Embodiment 8] The carbon composition according to Embodiment 7, wherein the monolithic carbon aerogel is binder-free. [Embodiment 9] The carbon composition according to Embodiment 8, wherein the thickness of the monolithic carbon aerogel is between approximately 10 micrometers and approximately 500 micrometers. [Embodiment 10] The carbon composition according to any one of Embodiments 1 to 3, wherein the carbon composition is in the form of particles. [Embodiment 11] The carbon composition according to Embodiment 10, wherein the diameter of the particulate carbon composition is about 1 micrometer to about 50 micrometers. [Embodiment 12] The carbon composition according to any one of Embodiments 1 to 3, wherein the carbon material contains approximately 25% to 65% by weight of silicon in the carbon material. [Embodiment 13] A carbon composition according to any one of Embodiments 1 to 3, having a capacity of at least about 800 mAh / g. [Embodiment 14] An electrode comprising the carbon composition described in any of Embodiments 1 to 3. [Embodiment 15] An energy storage device comprising the carbon composition described in any of Embodiments 1 to 3. [Embodiment 16] The energy storage device according to Embodiment 15, wherein the energy storage device is a lithium-ion battery. [Embodiment 17] A step of supplying a mixture of a polyimide precursor and a silicon-based material, A step of chemically or thermally imidizing the mixture, A step of drying the imidized mixture to obtain a porous polyimide silicon composite, A method for forming a carbon composition, comprising the step of carbonizing the porous polyimide silicon composite to obtain a carbon composition, A method for forming a carbon composition, wherein the carbon composition contains more than about 10% by weight of silicon, has a porosity between about 10% and about 80%, and has a pore diameter of about 100 nm or less at the maximum peak from the distribution, and wherein the silicon-based material is at least partially contained within the porous structure of the carbon material. [Embodiment 18] The method according to Embodiment 17, wherein the carbon composition comprises a carbon aerogel. [Embodiment 19] The method according to Embodiment 17, wherein the carbon composition is formed as a monolith. [Embodiment 20] The method according to Embodiment 17, further comprising the step of mixing the mixture with a medium that is immiscible with the mixture to form droplets of the imidized mixture. [Embodiment 21] The method according to Embodiment 20, further comprising the step of drying the droplets to form particles. [Embodiment 22] The method according to Embodiment 21, wherein the diameter of the particles is approximately 1 micrometer to approximately 50 micrometers. [Embodiment 23] The method according to Embodiment 17, wherein the maximum thermal decomposition temperature is between approximately 750°C and approximately 1600°C. [Embodiment 24] The method according to any one of embodiments 17 to 23, wherein the capacity of the carbon composition is at least about 800 mAh / g. [Embodiment 25] The method according to any one of Embodiments 17 to 23, wherein the silicon utilization rate of the carbon composition is at least about 20%. [Embodiment 26] The method according to any one of embodiments 17 to 23, wherein the carbon composition comprises a carbon aerogel.

Claims

1. A method for forming a carbon composition, The supply of a mixture of polyimide precursor and silicon-based material, The mixture is imidized chemically or thermally, The imidized mixture is dried to obtain a porous polyimide silicon composite, To obtain a carbon composition containing a carbon material that includes more than 10% by weight of silicon and has a fibril-like form, by carbonizing the porous polyimide-silicon composite. Includes, The fibril-like morphology includes a plurality of interconnected carbon struts, The plurality of interconnected carbon struts define a plurality of pores, A method wherein the carbon composition is characterized by a Young's modulus of at least 0.2 GPa and a density of 0.15 g / cc to 1.5 g / cc.

2. The method according to claim 1, wherein the carbon composition comprises a carbon aerogel.

3. The method according to claim 1, wherein the carbon composition is formed as a monolith.

4. The method according to claim 1, further comprising combining the mixture with a medium that is immiscible with the mixture to form droplets of an imidized mixture.

5. The method according to claim 4, further comprising drying the droplets to form particles.

6. The method according to claim 5, wherein the particles have a diameter of 1 micrometer to 50 micrometers.

7. The method according to any one of claims 1 to 6, wherein the maximum thermal decomposition temperature is 750°C to 1600°C.

8. The method according to any one of claims 1 to 7, wherein the silicon-based material is at least partially present within the porous structure of the carbon material.

9. The method according to any one of claims 1 to 8, wherein the carbon composition has a volume of at least 800 mAh / g.

10. The method according to any one of claims 1 to 9, wherein the carbon composition has a silicon utilization rate of at least 20%.

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