Carbon aerogel-based cathode for lithium-air battery

Abstract

Nanoporous carbon-based scaffolds or structures, particularly carbon aerogels, and their manufacture and use. Embodiments include cathode materials in lithium-air batteries, in which the cathode is formed from a binder-free, monolithic polyimide-derived carbon aerogel. The carbon aerogel contains pores that improve oxygen transport properties for the electrolyte and improve lithium peroxide formation along the surface and / or within the pores of the carbon aerogel. The cathode and underlying carbon aerogel provide optimal properties for use in lithium-air batteries.

Description

Technical Field

[0001] Cross - reference to related applications This application claims the benefit of priority of U.S. Patent Application No. 16 / 826,223, filed Mar. 21, 2020, and U.S. Provisional Patent Application No. 62 / 822,710, filed Mar. 22, 2019, each of which is hereby incorporated by reference in its entirety and any definition of any term in this application is controlling.

[0002] Technical field The present invention generally relates to nanoporous carbon-based materials. More specifically, it relates to carbon aerogels suitable for use in an environment involving electrochemical reactions, such as as an electrode material in a lithium-air battery.

Background Art

[0003] An aerogel is a solid material that contains a highly porous network of micro-sized and meso-sized pores. Depending on the precursor materials used and the processing performed, the pores of an aerogel can frequently occupy more than 90% of the volume when the density of the aerogel is about 0.05 g / cc. Aerogels are generally created by removing the solvent from a gel (a solid network containing its solvent) such that the shrinkage of the gel can be minimized or not caused at all by capillary forces at its surface. Methods of solvent removal include, but are not limited to, supercritical drying (drying using a supercritical fluid such that the low surface tension of the supercritical fluid exchanges with the transient solvent within the gel), solvent exchange with a supercritical fluid, solvent exchange with a fluid that is subsequently converted to a supercritical state, subcritical or near-critical drying, and sublimation of the frozen solvent in a freeze-drying process. See, for example, PCT Patent Application Publication No. 2016127084 Pamphlet (A1). Note that drying under ambient conditions can cause shrinkage of the gel due to evaporation of the solvent and can result in the formation of a xerogel. Thus, the creation of an aerogel by the sol-gel method or other polymerization methods typically proceeds through the following series of steps: dissolution of the solute in a solvent, formation of a sol / solution / mixture, formation of a gel (which may include further crosslinking), and removal of the solvent by supercritical drying techniques or any other method that removes the solvent from the gel without causing pore collapse.

[0004] Aerogels can be formed from inorganic materials and / or organic materials. For example, when formed from organic materials such as phenol, resorcinol-formaldehyde (RF), phloroglucinol-formaldehyde (PF), polyacrylonitrile (PAN), polyimide (PI), polyurethane (PU), polybutadiene, polydicyclopentadiene, and their precursors or polymer derivatives, the aerogel can be carbonized (e.g., by pyrolysis) to form carbon aerogels that can have different or overlapping properties (e.g., pore volume, pore size distribution, morphology, etc.) depending on the precursor materials and methodologies used. However, in all cases, there were specific defects based on the material and application, such as low pore volume, broad pore size distribution, low mechanical strength, etc. In recent years, efforts have been devoted to the development and characterization of carbon aerogels as electrode materials with improved performance for applications in energy storage devices such as zinc-air / oxygen and lithium-air / oxygen batteries (collectively "Li-air batteries").

[0005] Li-air batteries are an increasingly attractive form of electrochemical energy storage and an alternative to lithium-ion batteries (LIBs) because they have the potential to achieve low cost, high reversible energy storage, and high cycling. A Li-air battery is a type of rechargeable battery in which lithium ions move from the anode to the cathode through a liquid or solid electrolyte during discharge and from the cathode to the anode during charging. Conventionally, in a Li-air system, the anode is formed of lithium metal and the active material of the cathode is not stored in the battery. Instead, the active material of the cathode is formed by the reduction of oxygen drawn from the ambient air to form lithium peroxide (Li2O2) during discharge. During charging, Li2O2 is oxidized to release oxygen, enabling lithium ions to return to the anode. Porous carbonaceous materials are commonly used in Li-air batteries because the carbon surface functions as a reaction site for Li2O2 formation during discharge. Li-air batteries can theoretically achieve very high capacities (exceeding 1,000 mAh / g) and energy densities (exceeding 500 Wh / kg) because they depend on the capacity of the cathode to form Li2O2. In order to form Li2O2 on the surface of the porous carbonaceous material containing the electrolyte, it is important that the electrolyte has very good oxygen transport properties, which means that oxygen can diffuse through the electrolyte and then move to the carbon surface. This means that.

[0006] Despite the opportunity to achieve high capacity and energy density with Li-air batteries, conventional Li-air batteries have not been widely commercially adopted like their LIB counterparts, which feature higher cycle life but lower energy density. General challenges and obstacles of Li-air batteries that need to be overcome to make them viable energy systems include behavior under variable humidity, oxygen availability to the reaction site (carbon surface), electrolyte composition, and the structure of the carbonaceous material itself. For example, water is a problematic species for Li-air batteries because it can react violently with lithium metal when it reaches the anode. Water can also react with Li2O2 in the cathode and subsequently with carbon dioxide to form Li2CO3, which ultimately leads to cathode blockage and loss of capacity. If Li2O2 is formed only within the porous carbon, the electrodes can become blocked, making it increasingly difficult to redissolve Li2O2 into the electrolyte and release oxygen during charging.

[0007] Therefore, what is needed is an improved nanoporous carbon material that includes a functional morphology and an optimal pore structure in which nano-sized Li2O2 can be formed and is available for redissolution back into a size-matched electrolyte (e.g., a narrow pore size distribution). However, considering the art as a whole at the time the present invention was made, it was not apparent to those of ordinary skill in the art of the present invention how to overcome the deficiencies of the prior art.

[0008] Certain aspects of the prior art have been discussed to facilitate the disclosure of the present invention, but the applicant does not in any way disclaim these technical aspects, and it is contemplated that the claimed invention may encompass one or more of the conventional technical aspects described herein, particularly in combination with the innovative aspects described herein.

[0009] The present invention can address one or more of the above-described technical problems and drawbacks. However, the present invention may be found to be useful for addressing other problems and deficiencies in several technical fields. Accordingly, the claimed invention is not necessarily limited to addressing any of the specific problems or deficiencies discussed herein. should not be construed as

[0010] In this specification, when a document, act, or item of knowledge is referenced or discussed, this reference or discussion does not admit that the document, act, or item of knowledge or any combination thereof constituted prior art under the applicable statutory provisions, was publicly available as of the priority date, was known to the public, or was part of common general knowledge, or was known to be relevant to any attempt to solve any problem with which this specification is concerned.

Prior Art Documents

Patent Documents

[0011]

Patent Document 1

Summary of the Invention

[0012] The long-standing but hitherto unmet need for improved nanoporous carbon materials is now met by a new useful and non-obvious invention.

[0013] A first general aspect relates to a cathode in a lithium air / oxygen or zinc air / oxygen battery, such as a nanoporous carbon cathode. The cathode includes Fibril a nanoporous carbon material having a pore structure including a morphology and a series of pores surrounding lithium peroxide particles.

[0014] In an exemplary embodiment, the cathode has a pore structure with a substantially uniform pore size distribution, and the pores correspond to the formation of lithium peroxide particles. In some embodiments, the cathode can have either or both a density of about 0.10 g / cc to about 1.5 g / cc, a Young's modulus of at least about 0.2 GPa, and a conductivity of at least about 1 S / cm.

[0015] In an exemplary embodiment, the nanoporous carbon material includes a carbon aerogel. For example, the carbon material can include a polyimide-derived carbon aerogel. In some embodiments, the carbon aerogel can be in monolithic or powder form. In some embodiments, the monolithic carbon aerogel can be substantially or completely binder-free. The monolithic carbon aerogel can have a thickness of about 10 μm to about 1000 μm.

[0016] In an exemplary embodiment, the pore structure of the carbon material is characterized by pores surrounding the lithium peroxide particles. In some embodiments, the pores of the carbon material form an interconnected structure around the lithium peroxide particles, characterized by a plurality of connection points between the lithium peroxide particles and the pore walls of each pore surrounded by the lithium peroxide particles.

[0017] In an exemplary embodiment. For example, the nanoporous carbon material of the cathode includes lithium peroxide particles on a weight basis of about 5% to 90% of the carbon material. In an exemplary embodiment, the carbon material can have any one of a pore volume of at least 0.3 cc / g, a porosity of about 10% to about 90%, and / or a capacity of at least about 800 mAh / g. In an exemplary embodiment, the pore structure of the carbon material can include a full width at half maximum of about 50 nm or less, a pore diameter at the maximum peak from a distribution of about 100 nm or less, and / or an average strut width of about 2 to 10 nm.

[0018] Another general aspect relates to a carbon aerogel composite derived from monolithic polyimide formed of a nanoporous carbon material. In an exemplary embodiment, the composite is binder-free, lithium peroxide particles are disposed along the surface of or within the pores of the carbon aerogel composite derived from monolithic polyimide, and the carbon aerogel composite forms the cathode of a lithium air / oxygen or zinc air / oxygen battery.

[0019] A further general aspect relates to a current collector None for a lithium air / oxygen or zinc air / oxygen battery None and an interconnected cathode material of a binder. In an exemplary embodiment, the cathode material comprises Fibril a continuous cellular monolithic polyimide-derived nanoporous carbon aerogel having a network and a series of pores. In some embodiments, the lithium peroxide particles are disposed along the surface of or within the pores of the carbon aerogel.

[0020] Another general aspect relates to an electrochemical cell or a lithium air / oxygen or zinc air / oxygen battery comprising the nanoporous carbon material or carbon aerogel of any of the embodiments disclosed herein. For example, a lithium air / oxygen or zinc air / oxygen battery can comprise an electrochemical cell disclosed herein.

Brief Description of the Drawings

[0021] To better understand the present invention, reference should be made to the following detailed description in connection with the accompanying drawings.

[0022]

Figure 1A

Figure 1B

Modes for Carrying Out the Invention

[0023] In the following detailed description of the invention, reference is made to the accompanying drawings, which form a part hereof, and which illustrate by way of example specific embodiments in which the invention can be practiced. It is to be understood that other embodiments may be utilized and structural changes may be made without departing from the scope of the present invention.

[0024] As used in this specification and the appended claims, the singular forms "a", "an", and "the" include plural referents unless the content clearly dictates otherwise. As used in this specification and the appended claims, the term "or" is generally used in the sense of "and / or" unless the context clearly indicates otherwise.

[0025] As used herein, "about" means approximately or nearly and, in the context of a recited numerical value or range, means ±15% of the numerical value. In embodiments, the term "about" can include conventional rounding based on the significant digits of the numerical value. Also, the phrase "about 'x' to 'y'" includes "about 'x' to about 'y'".

[0026] In the context of the present disclosure, the term "aerogel" or "aerogel material" refers to a gel that includes a skeleton of interconnected structures, a corresponding network of interconnected pores incorporated within the skeleton, and a dispersed interstitial medium that includes a gas such as air: the following physical and structural properties resulting from the aerogel (by nitrogen porosimetry testing): (a) an average pore diameter in the range of about 2 nm to about 100 nm; (b) a porosity of at least 80% or more, and (c) a surface area of about 20 m 2 / g or more. It can be understood that including additives such as reinforcing materials or electrochemically active species may reduce the porosity of the resulting aerogel composite. This will become clearer as the specification continues.

[0027] Thus, the aerogel materials of the present disclosure include any aerogel or other open-cell compound that meets the defining elements described in the previous paragraph and includes compounds that can be classified as xerogels, cryogels, ambigels, microporous materials, and the like.

[0028] In the context of the present disclosure, the terms "skeleton" or "skeletal structure" refer to a network of interconnected oligomers, polymers, or colloidal particles that form the solid structure of a gel or aerogel. The polymers or particles that make up the skeletal structure typically have a diameter of about 100 angstroms. However, the skeletal structures of the present disclosure may also include networks of interconnected oligomers, polymers, or colloidal particles of all diameter sizes that form a solid structure within the gel or aerogel.

[0029] In the context of the present disclosure, the term "aerogel composition" refers to any composite material that includes an aerogel material as a component of the composite. Examples of aerogel compositions include Fiber fiber-reinforced aerogel composites; aerogel composites that include additive elements such as opacifiers and electrochemically active species; aerogel-foam composites; aerogel-polymer composites; and composites that incorporate aerogel microparticles, particles, granules, beads, or powders into a solid or semi-solid material such as a binder, resin, cement, foam, polymer, or similar solid material, but are not limited thereto.

[0030] In the context of the present disclosure, the term "reinforced aerogel composition" refers to an aerogel composition that includes a reinforcing phase within the aerogel material, and the aerogel composition may or may not be part of the aerogel skeleton or may be modified to covalently bond to the aerogel skeleton. The reinforcing phase may be any material that imparts high flexibility, elasticity, compatibility, or structural stability to the aerogel material. Examples of well-known reinforcing materials include open-cell foam reinforcements, closed-cell foam reinforcements, open-cell membranes, honeycomb reinforcements, polymer reinforcements, and discrete Fiber fibers, textile materials, non-woven materials, batting, webs, mats, and felts, among others. FiberReinforcing materials are included, but not limited to these. Further, the reinforcing materials may be combined with one or more of other reinforcing materials and can be continuously oriented throughout the entire composition or a limited preferred portion thereof. In other embodiments, when the aerogel material and / or the aerogel framework is structurally stable by itself (i.e., self-supporting), no reinforcing phase may be used at all. This self-supporting property of certain carbon aerogels will become clearer as the present specification continues.

[0031] In the context of the present disclosure, the term "wet gel" refers to a gel in which the mobile interstitial phase within the network of interconnected pores is mainly composed of a liquid phase such as a conventional solvent, a liquefied gas such as liquid carbon dioxide, or a combination thereof. An aerogel typically requires an initial formation of a wet gel and subsequent processing and extraction to replace the mobile interstitial liquid phase in the gel with air or another gas. Examples of wet gels include, but are not limited to, alcogels, hydrogels, ketogels, carbogels, and any other wet gels known to those skilled in the art.

[0032] In the context of the present disclosure, the term "additive" or "additive element" refers to a material that can be added to the composition before, during, or after the manufacture of the composition. Additives can be added, for example, to modify or improve desirable properties in the aerogel composition or to counteract or mitigate undesirable properties in the aerogel composition. Additives are typically added to the aerogel composition before or during gelation. A specific example of an additive is a sacrificial porogen that can decompose in situ to provide a hierarchical pore structure.

[0033] In the context of the present disclosure, the term "self-supporting" refers to the ability of an aerogel material or composition to become flexible and / or elastic, mainly based on the physical properties of the aerogel. The self-supporting aerogel materials or compositions of the present disclosure can be distinguished from other aerogel materials such as coatings that rely on a substrate or reinforcing material below to impart flexibility and / or elasticity to the material.

[0034] In the context of the present disclosure, the term "density" refers to a measure of the mass per unit volume of an aerogel material or composition. The term "density" generally refers to the true density of the aerogel material and the bulk density of the aerogel composition. Density is typically recorded as kg / m 3 or g / cc. The density of an aerogel material or composition can be determined by methods known in the art, including but not limited to Standard Test Method for Dimensions and Density of Preformed Block and Board-Type Thermal Insulation (ASTM C303, ASTM International, West Conshohocken, Pa.); Standard Test Methods for Thickness and Density of Blanket or Batt Thermal Insulations (ASTM C167, ASTM International, West Conshohocken, Pa.); or Determination of the apparent density of preformed pipe insulation (ISO 18098, International Organization for Standardization, Switzerland). In the context of the present disclosure, unless otherwise specified, density measurements are obtained in accordance with the specifications of ASTM C 167. Preferably, the aerogel material or composition of the present disclosure has a density of 1.50 g / cc or less, 1.40 g / cc or less, 1.30 g / cc or less, 1.20 g / cc or less, 1.10 g / cc or less, 1.00 g / cc or less, 0.90 g / cc or less, 0.80 g / cc or less, 0.70 g / cc or less, 0.60 g / cc or less, 0.50 g / cc or less, 0.40 g / cc or less, 0.30 g / cc or less, 0.20 g / cc or less, 0.10 g / cc or less, or in the range between any two of these values.

[0035] The production of aerogels according to certain embodiments generally involves the following steps: i) forming a solution containing a gel precursor; ii) forming a gel from the solution; and iii) extracting the solvent from the gel material to obtain a dry aerogel material. This process is described in more detail below, particularly in the context of the formation of organic aerogels such as polyimide aerogels. However, the specific examples and illustrations provided herein are not intended to limit the present disclosure to any particular type of aerogel and / or method of making. The present disclosure can include any aerogel formed by any related method of making known to those skilled in the art.

[0036] The solution is formed by combining at least one gelling precursor with a solvent. Solvents suitable for use in forming the solution include lower alcohols having 1 to 6, preferably 2 to 4 carbon atoms, although other solvents can also be used as known to those skilled in the art. Examples of useful solvents include, but are not limited to, methanol, ethanol, isopropanol, ethyl acetate, ethyl acetoacetate, acetone, dichloromethane, tetrahydrofuran, and the like. Multiple solvents can also be combined to achieve a desired level of dispersion or to optimize the properties of the gel material. Thus, the selection of the solvent optimal for the polymerization and gel formation steps 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.

[0037] The solution for producing a polyimide aerogel comprises at least one diamine and at least one in a common polar aprotic solvent AcidIt is formed by combining dianhydrides. Further details regarding the formation of polyimide gels / aerogels can be found in U.S. Patent Nos. 7,074,880 and 7,071,287 to Rhine et al.; U.S. Patent No. 6,399,669 to Suzuki et al.; U.S. Patent No. 9,745,198 to Leventis et al.; Leventis et al., Polyimide Aerogels by Ring-Opening Metathesis Polymerization (ROMP), Chem. Mater. 2011, 23, 8, 2250-2261; Leventis et al., Isocyanate-Derived Organic Aerogels: Polyureas, Polyimides, Polyamides, MRS Proceedings, 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., Polyimide Aerogels Cross-Linked through Amine Functionalized Polyoligomeric Silsesquioxane, ACS Appl. Mater. Interfaces 2011, 3, 546-552; Nguyen et al., Development of High Temperature, Flexible Polyimide Aerogels, American Chemical Society, proceedings published 2011; Meador et al., Mechanically Strong, Flexible Polyimide Aerogels Cross-Linked with Aromatic Triamine, ACS Appl. Mater.Interfaces, 2012, 4(2), pp 536 - 544; Meador et al., Polyimide Aerogels with Amide Cross - Links: A Low Cost Alternative for Mechanically Strong Polymer Aerogels, ACS Appl. Mater. Interfaces 2015, 7, 1240 - 1249; Pei et al., Preparation and Characterization of Highly Cross - Linked Polyimide Aerogels Based on Polyimide Containing Trimethoxysilane Side Groups, Langmuir 2014, 30, 13375 - 13383. Each of these is hereby incorporated by reference in its entirety. 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,. Acid Instead of, or in addition to, dianhydrides or combinations thereof, Acid trianhydrides, Acid tetraanhydrides, Acid pentaanhydrides, Acid hexaanhydrides can also be used. A dehydrating agent and a catalyst are incorporated into the solution to initiate and drive imidization.

[0038] The solution can include additional co - gelling precursors, as well as filler materials and other additives. The filler materials and other additives may be dispensed into the solution at any point before or during the formation of the gel. The filler materials and other additives may also be incorporated into the gel material after gelation by various techniques known to those skilled in the art. Preferably, the solution containing the gelling precursor, solvent, catalyst, water, filler materials, and other additives is a homogeneous solution capable of forming an effective gel under appropriate conditions.

[0039] 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 where the gel solidifies to the gelation point of the gel material. The gelation point of the gel material can be considered as the point where the gelling solution exhibits resistance to flow and / or forms a substantially continuous polymer backbone throughout its volume. Various gel-forming techniques are known to those skilled in the art. Examples include, but are not limited to, maintaining the mixture in a static state for a sufficient period; adjusting the concentration of the catalyst; regulating the temperature of the solution; directing forms of energy at the mixture (ultraviolet, visible light, infrared, microwave, ultrasonic, particle radiation, electromagnetic); or combinations thereof.

[0040] The process of transferring the gel-forming components to the gel material can also include an aging step (also called curing) prior to liquid phase extraction. Aging the gel material after reaching the gelation point can further strengthen the gel backbone by increasing the number of crosslinks within the network. The duration of gel aging can be adjusted to control various properties within the resulting aerogel material. This aging procedure can be useful in preventing potential volume loss and shrinkage during liquid phase extraction. Aging can include maintaining the gel in a static state for an extended period (prior to extraction); maintaining the gel at an elevated temperature; adding crosslinking promoting compounds; or any combination thereof. The preferred temperature for aging is typically from about 10°C to about 200°C. Aging of the gel material typically continues until liquid phase extraction of the wet gel material.

[0041] The time for transferring the gel-forming material to the gel material includes both the duration of the initial gel formation (from the start of gelation to the gelation point) and the subsequent duration of any hardening and aging of the gel material prior to liquid phase extraction (from the gelation point to the start of liquid phase extraction). The total time for transferring the gel-forming material to the gel material is typically between about 1 minute and several days, preferably less than about 30 hours, less than about 24 hours, less than about 15 hours, less than about 10 hours, less than about 6 hours, less than about 4 hours, less than about 2 hours, less than about 1 hour, less than about 30 minutes, or less than about 15 minutes.

[0042] The resulting gel material can be washed in a suitable secondary solvent to replace the primary reaction solvent present in the wet gel. Such secondary solvents can be linear monohydric alcohols having one or more aliphatic carbon atoms, dihydric alcohols having two or more carbon atoms, branched alcohols, cyclic alcohols, cycloaliphatic alcohols, aromatic alcohols, polyhydric alcohols, ethers, ketones, cyclic ethers or derivatives thereof.

[0043] Once the gel material has been formed and processed, an extraction method including treatment and extraction techniques can then be used to at least partially extract the liquid phase of the gel from the wet gel to form an aerogel material. Liquid phase extraction plays an important role in manipulating properties of the aerogel such as porosity and density, as well as related properties such as thermal conductivity, among other factors. Generally, an aerogel is obtained when the liquid phase is extracted from the gel in a manner that causes low shrinkage of the porous network and skeleton of the wet gel.

[0044] An aerogel is generally formed by removing a liquid mobile phase from a gel material at a temperature and pressure near or above the critical point of the liquid mobile phase. When the critical point is reached or exceeded (i.e., the pressure and temperature of the system are above the critical pressure and critical temperature, respectively), a new supercritical phase different from the liquid or gas phase appears in the fluid. The solvent can then be removed without introducing a liquid-vapor interface, capillary pressure, or any associated mass transfer limitations typically associated with the liquid-vapor boundary. Furthermore, the supercritical phase is generally more miscible with organic solvents and thus has better extraction ability. Solvent and co-solvent exchange are also commonly used to optimize the supercritical fluid drying process.

[0045] When evaporation or extraction occurs below the critical point, the capillary forces generated by the evaporation of the liquid can cause shrinkage and pore collapse within the gel material. By maintaining the mobile phase near or above the critical pressure and critical temperature during the solvent extraction process, the adverse effects of such capillary forces are reduced. In certain embodiments of the present disclosure, using a near-critical state just below the critical point of the solvent system enables the production of aerogel materials or compositions with sufficiently low shrinkage, and thus a commercially viable final product can be manufactured.

[0046] Several additional aerogel extraction techniques are known in the art, including a range of different approaches for using supercritical fluids in the drying of aerogels. 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 temperature, thereby reducing evaporative capillary forces and maintaining the structural integrity of the gel network. U.S. Patent No. 4,610,863 describes an extraction process in which the gel solvent is exchanged with liquid carbon dioxide and then extracted in a state where the carbon dioxide is in a supercritical state. U.S. Patent No. 6,670,402 teaches extracting the liquid phase from the gel via rapid solvent exchange by injecting supercritical (rather than liquid) carbon dioxide into an extractor that is preheated and pre-pressurized substantially above the supercritical state, thereby producing an aerogel. U.S. Patent No. 5,962,539 describes a method for obtaining an aerogel from a polymer material in the form of a sol-gel in an organic solvent by exchanging the organic solvent with a fluid having a critical temperature below the polymer decomposition temperature and supercritically extracting the fluid / sol-gel. U.S. Patent No. 6,315,971 discloses a method for producing a gel composition that includes drying a wet gel containing a gel solid and a desiccant and removing the desiccant under drying conditions sufficient to reduce shrinkage of the gel during drying. U.S. Patent No. 5,420,168 describes a method by which a resorcinol / formaldehyde aerogel can be produced using a simple air-drying procedure. 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 skeleton and pores can withstand collapse during ambient drying or subcritical extraction. Other examples of extracting the liquid phase from an aerogel material can be found in U.S. Patent Nos. 5,275,796 and 5,395,805.

[0047] One preferred embodiment of extracting the liquid phase from the wet gel uses supercritical conditions of carbon dioxide. For example, first substantially exchanging the primary solvent initially present in the pore network of the gel with liquid carbon dioxide; and then heating the wet gel (usually in an autoclave) above the critical temperature of carbon dioxide (about 31.06 °C) and raising the pressure of the system to a pressure higher than the critical pressure of carbon dioxide (about 1070 psig). The pressure around the gel material can be slightly varied to 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, carbon dioxide can be recycled through the extraction system. Finally, the temperature and pressure are slowly returned to ambient conditions to produce the dry aerogel material. Carbon dioxide can also be pretreated to the supercritical state before being injected into the extraction chamber. In other embodiments, the extraction can be performed by changing any suitable mechanism, such as the pressure, timing, and solvent described above.

[0048] In certain embodiments of the present disclosure, the dry carbon aerogel composition can be subjected to one or more heat treatments for a duration of 3 hours or more, 10 seconds to 3 hours, 10 seconds to 2 hours, 10 seconds to 1 hour, 10 seconds to 45 minutes, 10 seconds to 30 minutes, 10 seconds to 15 minutes, 10 seconds to 5 minutes, 10 seconds to 1 minute, 1 minute to 3 hours, 1 minute to 1 hour, 1 minute to 45 minutes, 1 minute to 30 minutes, 1 minute to 15 minutes, 1 minute to 5 minutes, 10 minutes to 3 hours, 10 minutes to 1 hour, 10 minutes to 45 minutes, 10 minutes to 30 minutes, 10 minutes to 15 minutes, 30 minutes to 3 hours, 30 minutes to 1 hour, 30 minutes to 45 minutes, 45 minutes to 3 hours, 45 minutes to 90 minutes, 45 minutes to 60 minutes, 1 hour to 3 hours, 1 hour to 2 hours, 1 hour to 90 minutes.

[0049] In certain embodiments, the present invention involves the formation and use of nanoporous carbon-based scaffolds or structures, such as carbon aerogels, as electrode materials within an energy storage device, for example, as a primary cathode host for Li2O2 formation in a Li-air battery. The pores of the nanoporous scaffold are designed, woven, and structured to accommodate the formation and dissolution of consistent nano-sized Li2O2 particles. Alternatively, the pores of the nanoporous scaffold can be filled with catalysts or scavengers for species that can contribute to minimizing side reactions, such as, but not limited to, water and CO2.

[0050] To further expand on exemplary uses within a Li-air battery, when a carbon aerogel material, as in certain embodiments of the present invention, is utilized as a conductive cathode host for Li2O2 formation, the nanoporous structure of the aerogel has a narrow pore size distribution and is equipped with a high conductivity, high mechanical strength, and morphology and sufficient pore volume (at final density) to accommodate a high weight percentage of Li2O2. Structurally, certain embodiments of the present invention have strut sizes that produce, among other characteristics, the narrow pore size distribution and high pore volume described above. Fibril have a morphology.

[0051] As further discussed below, the surface of the carbon aerogel may be modified by chemical, physical, or mechanical means in order to enhance performance through the formation of consistent nano Li2O2 particles within the pores of the carbon aerogel. For example, additives such as MoS2 nanoflakes can be added to the carbon aerogel to catalyze the formation and dissolution of Li2O2. As another example, sacrificial agents can be used as additives to provide bimodal porosity to the carbon aerogel. Finally, the interconnected porous carbon aerogel surface provides reaction sites for the Li-oxygen reaction, and the carbon aerogel can be surface modified to facilitate the formation and confinement of Li2O2 species. Regardless of the presence or absence of surface modification, the carbon aerogel is structured and can further function as a host to improve the oxygen transport properties of the electrolyte. Specifically, the electrolyte diffuses through the pores of the carbon aerogel, and thereafter, the availability of oxygen is determined by its diffusion in the electrolyte within the carbon aerogel and its dissolution in the electrolyte (i.e., Li2O2 species are not formed only at the interface between the electrolyte and oxygen). Thus, the improved oxygen transport properties of the electrolyte increase the availability of oxygen to react with lithium to form Li2O2, and thus benefit the function of the electrode and the Li-air battery as a whole.

[0052] In additional or alternative embodiments, it is contemplated that the material of an existing current collector can be made porous, such as a mesh, and integrated with the cathode material (carbon aerogel) to enhance the current collecting ability or capacity of the aluminum foil. Note that in a conventional LIB, the aluminum foil is bonded to the cathode as its current collector. In the absence of a separate porous current collector, since the cathode of the Li-air battery is typically physically accessible to external air, the carbon aerogel itself also functions as a current collector due to the necessary structure of the Li-air battery with its high conductivity and mechanical strength.

[0053] In certain embodiments, a nanoporous carbon-based scaffold or structure, particularly a carbon aerogel, can be used as a conductive network or current collector on the cathode side of an energy storage device. The fully interconnected carbon aerogel network is filled with electrochemically active species such as the formation of Li2O2 during discharge, and the electrochemically active species are in direct contact with or physically connected to the carbon network. The filling of the capacity of the electrochemically active species is adjusted with respect to the pore volume and porosity for high stable capacity and improved safety of the energy storage device. In yet another embodiment, the cathode can include a nanoporous carbon-based scaffold or structure, particularly a carbon aerogel.

[0054] In the context of the present disclosure, the term "current collector" None refers to the absence of a separate current collector directly connected to the electrode. As described above, in a conventional LIB, an aluminum foil is typically bonded to the cathode as its current collector. According to an embodiment of the present invention, an electrode formed from a nanoporous carbon-based scaffold or structure (e.g., a carbon aerogel) can be a stand-alone structure or otherwise have the function of a current collector because the scaffold or structure itself functions as a current collector due to its high conductivity. None In an electrochemical cell, a current collector can connect the current collector-less electrode to form a circuit by embedding a solid, mesh, fabric tab during the solution process of manufacturing continuous porous carbon, or by soldering, welding, or metal depositing a lead to a portion of the porous carbon surface. Other mechanisms for contacting the carbon to the rest of the system are also contemplated herein. In an alternative embodiment, the nanoporous carbon-based scaffold or structure, specifically a carbon aerogel, may be disposed on or otherwise in communication with a dedicated current collector substrate (such as a copper foil, an aluminum foil, etc.). In this scenario, the carbon aerogel is attached to a solid or porous or mesh current collector using a conductive adhesive and various amounts of pressure can be applied. None

[0055] Furthermore, in this specification, it is contemplated that the nanoporous carbon-based scaffold or structure, particularly carbon aerogel, can take the form of a monolithic structure or a powder form. When essentially monolithic, the carbon aerogel eliminates the need for any binder. In other words, the cathode can be the binder None . As used herein, the term "monolithic" refers to an aerogel material in which most (by weight) of the aerogel contained in the aerogel material or composition is in the form of a single continuous interconnected aerogel nanostructure. Monolithic aerogel materials are initially formed to have an integrally interconnected gel or aerogel nanostructure, but can subsequently include aerogel materials that are cracked, broken, or segmented into non-integral aerogel nanostructures. Monolithic aerogels can take the form of a self-standing structure or a reinforcing ( Fiber fiber or foam) material. In comparison, when using a Li-air battery as an example, uniform Li2O2 nanoparticles are formed within the monolithic aerogel. These can be utilized more effectively during formation and dissolution.

[0056] Monolithic aerogel materials are distinguished from particulate aerogel materials. The term "particulate aerogel material" refers to an aerogel material in which most (by weight basis) of the aerogel contained in the aerogel material is in the form of fine particles, particles, granules, beads, or powder, which can be combined together (i.e., via a binder such as a polymer binder) or compressed together, but lack an interconnected aerogel nanostructure between individual particles. Collectively, this form of aerogel material is called having a powder form (in contrast to the monolithic form). It should be noted that although individual particles of a powder having a single structure, the individual particles are not considered monoliths herein. The integration of aerogel powder into an electrochemical cell typically requires calendaring from a paste / slurry, resulting in dilution of the active surface area.

[0057] In the context of this disclosure, "binder NoneThe term "binder-free" or "free of binder" (or a derivative thereof) refers to a material that substantially does not contain a binder or adhesive for holding the material together. For example, a monolithic nanoporous carbon material does not contain a binder because its framework is formed as an integral continuous interconnected structure. The binder None The advantages of being such include avoiding any adverse effects of the binder on conductivity and pore volume, etc. On the other hand, aerogel powder requires a binder to be held together to form a larger functional material. Such a larger material is not considered to be a monolith in this specification. Furthermore, the term "binder-free" does not exclude all use of binders. For example, a monolithic aerogel according to the present invention can be fixed to another monolithic aerogel or non-aerogel material by disposing a binder or adhesive on the main surface of the aerogel material. In this way, the binder is used to make a laminated composite, but the binder does not have the function of maintaining the stability of the monolithic aerogel framework itself.

[0058] Furthermore, the monolithic polymer aerogel materials or compositions of the present disclosure can be compressed with up to 95% strain without significant destruction or fragmentation of the aerogel framework while densifying the aerogel and minimizing the 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. The amount of compression affects the thickness of the resulting carbon material, and it can be understood that the thickness affects the volume, which will become clearer as the specification continues. The examples described below show various thicknesses formed and contemplated by the present invention, and the thickness can be adjusted based on compression. Thus, the thickness of the composite (typically compressed) can be about 10 - 1000 μm, or any narrower range therein, based on the advantages required for the final composite. The present invention also contemplates forms of carbon aerogel powder or particles that require a binder and have an optimized particle size. The particle size range can be about 5 - 50 μm.

[0059] The nanoporous carbon such as carbon aerogel according to the present invention can be formed from any suitable organic precursor material. Examples of such materials include, but are not limited to, RF, PF, PI, polyamide, polyacrylate, polymethyl methacrylate, acrylate oligomer, polyoxyalkylene, polyurethane, polyphenol, polybutadiene, trialkoxysilyl-terminated polydimethylsiloxane, polystyrene, polyacrylonitrile, polyfurfural, melamine-formaldehyde, cresol-formaldehyde, phenol-furfural, polyether, polyol, polyisocyanate, polyhydroxybenzes, polyvinyl alcohol dialdehyde, polycyanurate, polyacrylamide, various epoxies, agar, agarose, chitosan, as well as combinations and derivatives thereof. Any precursor of these materials can be used to produce and use the resulting material. In an exemplary embodiment, the carbon aerogel is formed from the pyrolysis / carbonization of a polyimide-based aerogel, i.e., from the polymerization of polyimide. Even more specifically, the polyimide-based aerogel can be produced using one or more methodologies described in U.S. Patent Nos. 7,071,287 and 7,074,880 to Rhine et al., for example, by imidization of poly(amic) acid and drying of the resulting gel using supercritical fluid. Other suitable methods for producing polyimide aerogels (and carbon aerogels derived therefrom) are also contemplated herein, for example, U.S. Patent No. 6,399,669 to Suzuki et al.; U.S. Patent No. 9,745,198 to Leventis et al.; Leventis et al., Polyimide Aerogels by Ring-Opening Metathesis Polymerization (ROMP), Chem. Mater. 2011, 23, 8, 2250-2261; Leventis et al., Isocyanate-Derived Organic Aerogels: Polyureas, Polyimides, Polyamides, MRS Proceedings, 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.,Polyimide Aerogels Cross-Linked through Amine Functionalized Polyoligomeric Silsesquioxane,ACS Appl.Mater.Interfaces 2011,3,546-552;Nguyen et al.,Development of High Temperature,Flexible Polyimide Aerogels,American Chemical Society,proceedings published 2011;Meador et al.,Mechanically Strong,Flexible Polyimide Aerogels Cross-Linked with Aromatic Triamine,ACS Appl.Mater.Interfaces,2012,4(2),pp 536-544;Meador et al.,Polyimide Aerogels with Amide Cross-Links:A Low Cost Alternative for Mechanically Strong Polymer Aerogels,ACS Appl.Mater.Interfaces 2015,7,1240-1249;Pei et al.,Examples include those described in Langmuir 2014, 30, 13375-13383, "Preparation and Characterization of Highly Cross-Linked Polyimide Aerogels Based on Polyimide Containing Trimethoxysilane Side Groups". Subsequently, the obtained polyimide aerogel is thermally decomposed to form a carbon aerogel derived from polyimide.

[0060] In certain embodiments of the present disclosure, the dry polymer aerogel composition can 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 between any two of these values for the carbonization of the organic (e.g., polyimide) aerogel. Without being bound by theory, it is contemplated herein that the conductivity of the aerogel composition increases with the carbonization temperature.

[0061] In the context of the present disclosure, the term "conductivity" refers to a measure of the ability of a material to conduct an electric current or otherwise enable electrons to flow through or within it. Conductivity is specifically measured as the conductivity / susceptance / admittance of the material per unit size of the material. This is typically recorded as S / m (Siemens / meter) or S / cm (Siemens / centimeter). The conductivity or resistivity of a material can be determined by methods known in the art, including, but not limited to, for example, the four-point resistivity in series (using the double-configuration test method of ASTM F84-99). In the context of the present disclosure, unless otherwise specified, the measured value of conductivity is obtained in accordance with the ASTM F84-resistivity (R) measurement obtained by dividing the voltage (V) by the current (I). In certain embodiments, the aerogel material or composition of the present disclosure has a conductivity of about 1 S / cm or greater, about 5 S / cm or greater, about 10 S / cm or greater, 20 S / cm or greater, 30 S / cm or greater, 40 S / cm or greater, 50 S / cm or greater, 60 S / cm or greater, 70 S / cm or greater, 80 S / cm or greater, or in the range between any two of these values. It should be noted that highly conductive carbon enables reactions at the surface of the carbon and thus facilitates the formation of Li2O2 on such carbon surfaces.

[0062] In the context of the present disclosure, the term "electrochemically active species" refers to a material capable of accepting and releasing ions within an energy storage device. Using a Li-air battery as an example, the electrochemically active species within the cathode accepts lithium ions during discharge (and thus undergoes conversion to Li2O2 species) and releases lithium ions during charge. The electrochemically active species can be stabilized within the cathode by having a direct / physical bond with the pore walls of the nanoporous carbon. In certain embodiments, Li2O2 nanoparticles of uniform particle size are formed on the surface and / or within the pores of the nanoporous carbon network. The electrochemically active species is bonded to the nanoporous carbon at multiple points. The amount of Li2O2 that can be formed, i.e., the capacity of the cathode, is determined by the surface area, pore volume, and pore diameter of the nanoporous carbon material. In certain embodiments, the aerogel material or composition of the present disclosure has the capacity to form between about 5 wt% and about 90 wt% of the cathode, or any range between these two values, of Li2O2.

[0063] In the context of the present disclosure, the terms "compressive strength," "bending strength," and "tensile strength" refer, respectively, to the resistance of a material to breakage or failure under compressive force, bending or flexing force, and tensile or pulling force. These strengths are specifically measured as the amount of load / force per unit area that resists the load / force. This is typically recorded as pounds per square inch (psi), megapascal (MPa), or gigapascal (GPa). In particular, the compressive strength, bending strength, and tensile strength of a material collectively contribute to the structural integrity of the material, which is beneficial in Li-air batteries. Specifically referring to the Young's modulus, which is an indicator of mechanical strength, this modulus of elasticity can be determined by methods known in the art, including, for example, but not limited to, Standard Test Practice for Instrumented Indentation Testing (ASTM E2546, ASTM International, West Conshocken, PA); or Standardized Nanoindentation (ISO 14577, International Organization for Standardization, Switzerland). In the context of the present disclosure, the measured value of Young's modulus is obtained in accordance with ASTM E2546 and ISO 14577 unless otherwise specified. In certain embodiments, the aerogel material or composition of the present disclosure has a Young's modulus of about 0.2 GPa or more, 0.4 GPa or more, 0.6 GPa or more, 1 GPa or more, 2 GPa or more, 4 GPa or more, 6 GPa or more, 8 GPa or more, or in a range between any two of these values.

[0064] In the context of the present disclosure, the term "pore size distribution" refers to the statistical distribution or relative amount of each pore size within the 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, and thus optimizes the amount of pores that can surround electrochemically active species and maximizes the use of the pore volume. Conversely, a wider pore size distribution refers to a relatively small proportion of pores within a narrow range of pore sizes. Thus, the pore size distribution is typically measured as a function of the pore volume and is recorded as the size in units of the full width at half maximum of the main peak of the pore size distribution chart. The pore size distribution of a porous material can be determined by methods known in the art, including but not limited to surface area and porosity analyzers by nitrogen adsorption / desorption capable of calculating the pore size distribution. In the context of the present disclosure, the measured value of the pore size distribution is obtained according to this method unless otherwise specified. In certain embodiments, the aerogel material or composition of the present disclosure has a relatively narrow pore size distribution (full width at half maximum) in the range of about 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 between any two of these values.

[0065] In the context of the present disclosure, the term "pore volume" refers to the total volume of pores within a sample of a porous material. The pore volume is specifically measured as the volume of the void space within the porous material, which void space may be measurable and / or accessible by the formation of, for example, Li2O2 on a carbon surface having available oxygen. This is typically in cubic centimeters per gram (cm 3It is recorded as ( / g or cc / g). The pore volume of the porous material can be determined by methods known in the art, including but not limited to surface area and porosity analyzers by nitrogen adsorption / desorption that can calculate the pore diameter volume. In the context of the present disclosure, the measured value of the pore volume is obtained according to this method unless otherwise specified. In certain embodiments, the aerogel material or composition (before Li2O2 formation) of the present disclosure has a relatively large pore volume 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 in the range between any two of these values. In other embodiments, the aerogel material or composition (after Li2O2 formation) of the present disclosure has a pore volume of about 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 between any two of these values.

[0066] In the context of the present disclosure, the term "porosity" refers to the volume ratio of pores that do not contain another material (e.g., Li2O2) bonded to the pore walls. For purposes of clarification and illustration, it should be noted that in a particular embodiment of sulfur-doped carbon aerogel as a host for Li2O2 formation in a Li-air battery, porosity refers to the void space after Li2O2 formation. Porosity can be determined by methods known in the art, including but not limited to the ratio of the pore volume of the aerogel material to its bulk density. In the context of the present disclosure, the measured value of porosity is obtained according to this method unless otherwise specified. In certain embodiments, the aerogel material or composition of the present disclosure has a porosity of 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 between any two of these values.

[0067] It should be noted that the pore volume and porosity are different measures for the same property of the pore structure, i.e., the "empty space" within the pore structure. For example, when Li2O2 is formed within the pores of a nanoporous carbon material, the pore volume and porosity refer to the "empty" space, i.e., the space not occupied by carbon or Li2O2. As can be seen, the compression of the pre-carbonized nanoporous material affects, among other properties, the pore volume and porosity.

[0068] In the context of the present disclosure, the term "pore diameter at the maximum peak from the distribution" refers to the value at a distinguishable peak on a graph showing the pore diameter distribution. The pore diameter at the maximum peak from the distribution is specifically measured as the pore diameter at which the largest percentage of pores are formed. This is typically recorded in any unit length of pore diameter, such as μm or nm. The pore diameter at the maximum peak from the distribution can be determined by methods known in the art, including, but not limited to, a surface area and porosity analyzer by nitrogen adsorption / desorption that can calculate the pore diameter distribution and determine the pore diameter at the maximum peak. In the context of the present disclosure, the measured value of the pore diameter at the maximum peak from the distribution is obtained according to this method unless otherwise specified. In certain embodiments, the aerogel material or composition of the present disclosure has a pore diameter at the maximum peak from the distribution of about 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 a range between any two of these values.

[0069] In the context of the present disclosure, the term "strut width" Fibril nanostruts, nanorods, nano Fiber、or refers to the average diameter of the nanofilaments. This is typically recorded as any unit length, such as μm or nm. The strut width can be determined by methods known in the art, including, for example, but not limited to, scanning electron microscope image analysis. In the context of the present disclosure, the measured value of the strut width is obtained according to this method unless otherwise specified. In certain embodiments, the aerogel material or composition of the present disclosure has a strut width of 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 between any two of these values. Smaller strut widths, such as in the range of about 2 - 5 nm, allow for a greater amount of struts to be present within the network, thus enabling contact with electrochemically active species and, in turn, allowing for a greater amount of electrochemically active species to be present within the composite. This improves conductivity and mechanical strength.

[0070] In the context of the present disclosure, " Fibril morphology" refers to the structural morphology of nanoporous carbon (e.g., aerogel) including struts, rods, Fiber fibers, or filaments. For example, in embodiments, the choice of solvent, such as dimethylacetamide (DMAC), can affect the formation of such morphology. Further, in certain embodiments, when the carbon aerogel is derived from polyimide, the crystalline polyimide results from polyimides that form linear polymers. As will become more apparent in the following examples, certain embodiments have surprisingly been observed to include Fibril morphologies as interconnected polymer structures, in which long linear structures were expected based on the known behavior of polyimide precursors. In comparison, the product morphology of the nanoporous carbon may instead be a particulate nature or powder in which the Fibril morphology of the carbon aerogel persists. As will become apparent as the present specification continues, especially when the nanoporous carbon is implemented as a cathode material in specific applications, such as Li-air batteries, FibrilThe morphology can provide certain advantages beyond particulate morphology such as mechanical stability / strength and electrical conductivity. This Fibril morphology can be found in both monolithic and powder forms of nanoporous carbon, i.e., monolithic carbon can Fibril have the morphology, and aerogel powder / particles can Fibril have the morphology. It should be noted that in certain embodiments, when the nanoporous carbon material contains additives or forms compounds such as Li2O2, the Fibril nanostructure inherent to the carbon material is preserved and functions as a crosslink between additive particles.

[0071] In the context of the present disclosure, the term "cycle life" refers to the number of complete charge / discharge cycles that a cathode or a battery (e.g., a Li-air battery) can support before its capacity drops below about 80% of its original rated capacity. Cycle life can be affected by various factors that do not vary significantly over time, such as the mechanical strength of the underlying substrate (e.g., carbon aerogel), the formation / connectivity and dissolution of Li2O2 within and from the aerogel, and the maintenance of the aerogel's interconnectivity. It should be noted that the fact that these factors actually remain relatively unchanged over time is a surprising aspect of certain embodiments of the present invention. Cycle life can be determined by methods known in the art, such as, but not limited to, cycle testing, in which a battery cell undergoes repeated charge / discharge cycles at a predetermined current rate and operating voltage. In the context of the present disclosure, measured cycle life values are obtained according to this method unless otherwise specified. In certain embodiments of the present disclosure, an energy storage device, such as a battery, or its electrodes have a cycle life of about 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 a range between any two of these values.

[0072] In the context of the present disclosure, the term "capacity" refers to the amount of specific energy or charge that a battery can store. Capacity is specifically measured as the discharge current that a battery can supply over time per unit mass. This is typically recorded as ampere-hours or milliampere-hours per gram of total electrode mass, Ah / g or mAh / g. The capacity of a battery (and particularly the cathode) can be determined by methods known in the art, including, but not limited to, 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 until the end of the discharge voltage multiplied by the constant current is the discharge capacity; and dividing the discharge capacity by the weight or volume of the electrode material to determine the specific capacity and the volumetric measured capacity. In the context of the present disclosure, measured values of capacity are obtained according to this method unless otherwise specified. In certain embodiments, the aerogel material or composition of the present disclosure has a capacity of about 500 mAh / g or more, 1000 mAh / g or more, 1500 mAh / g or more, 2000 mAh / g or more, 3000 mAh / g or more, 4000 mAh / g or more, 5000 mAh / g or more, 6000 mAh / g or more, 7000 mAh / g or more, 8000 mAh / g or more, 9000 mAh / g or more, 10,000 mAh / g or more, or in a range between any two of these values.

[0073] In certain embodiments, the present invention is a PI-derived nanoporous carbon material (e.g., carbon aerogel) having a series of pores surrounding, containing, or encapsulating Li2O2. The nanoporous carbon material functions as an ideal host for Li2O2 due to its optimal pore structure, functional pore morphology, and high mechanical integrity. The nanoporous carbon material (carbon aerogel) is characterized by a narrow pore size distribution, resulting in a consistent behavior of oxygen and Li2O2 species throughout the interconnected network. The carbon material itself helps to overcome a major drawback of conventional Li-air batteries, namely the resistivity of Li2O2 species, with its high conductivity. It is characterized in that. The above characteristics of the current nanoporous carbon materials, individually and in combination, provide certain advantages that increase the cycle life and cell life of the resulting Li-air system or its cathode.

[0074] In an embodiment, the present invention is a cathode of a Li-air battery comprising a carbon aerogel derived from polyimide, in which elemental oxygen enters the aerogel from the external environment or another oxygen source. The oxygen reacts with lithium from the anode to form Li2O2 along the surface of and / or within the pores of the carbon aerogel (see FIGS. 1A - 1B). As can be seen, the structure of the carbon aerogel pores can be adjusted to have different characteristics (e.g., pore volume, pore diameter, pore diameter distribution, and surface area) based on the requirements (e.g., the size or capacity of the electrode in a Li-air battery). In another embodiment, the present invention is an electrode of a Li-air battery or its electrochemical cell comprising such a cathode. In a Li-air battery, a cathode such as those described herein as nanoporous carbon materials or carbon aerogels are most commonly paired with a lithium anode in order to achieve a balanced capacity and lithium ions for reaction with oxygen. In yet a further embodiment, the present invention is a device or system incorporating such an energy storage device.

[0075] In a particular embodiment, the present invention is a method of forming or manufacturing a continuous porous carbon composite such as a carbon aerogel. A diamine that can each contain aromatic groups and / or aliphatic groups and AcidA polyimide precursor such as a dianhydride is mixed in a suitable solvent (e.g., a polar, aprotic solvent). Then, an imidization gelation catalyst is added to initiate mixing for gelation. In an alternative embodiment, imidization can be achieved by thermal imidization, in which case any suitable temperature and time ranges are contemplated (e.g., heating at about 100 °C to 200 °C for about 20 minutes to about 8 hours, and then 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 composite, where the drying can be carried out using subcritical and / or supercritical carbon dioxide. Optionally, the polyimide composite can be compressed to increase its density, which can be adjusted up to about 1.5 g / cc based on the amount of compression. Whether or not compression is performed, the polyimide composite is pyrolyzed to yield continuous porous carbon, and the carbon contains a porosity between about 5% and 99%. In certain embodiments, pyrolysis can be carried out at a maximum temperature of about 750 °C to about 1600 °C, optionally using graphitization at about 1600 °C to about 3000 °C. Following carbonization and implementation in a Li-air battery, oxygen is incorporated into the porous carbon network from the external environment or another oxygen source and reacts with lithium to form Li2O2.

[0076] In certain embodiments, the carbon composite may be in the form of a monolith or self-supporting structure, may be created on or outside a substrate, or may be micronized into a powder form. Further, the composite can be reinforced with or without non-woven or woven materials (e.g., Fiber fibers, foams, etc.).

[0077] Optionally, water is a problematic species for Li-air batteries due to its detrimental reaction with the lithium metal in the anode and / or Li2O2 in the cathode. As such, as described above, the carbon aerogel may be laminated with a hydrophobic silica aerogel, and the silica aerogel is typically disposed between the carbon aerogel and the external environment or another oxygen source. In this scenario, any suitable hydrophobic aerogel can be utilized. Further, any suitable mechanism for fixing the hydrophobic aerogel to the carbon aerogel is contemplated, including, by way of non-limiting example, organic and inorganic adhesives, non-adhesive bonds such as needle punching, and the like.

[0078] Furthermore, it is contemplated herein that the pore size can be adjusted as needed. There are five main ways to adjust the pore size taught herein. First, the amount of solids, specifically the amount of polyimide precursor monomers (e.g., aromatic or aliphatic diamines and aromatic or aliphatic Acid diacids) can be used to adjust the pore size. Smaller pore sizes result from a greater amount of solids per unit volume of fluid because there is less available space for more closely interconnected pathways. Note that the strut width does not measurably change regardless of the amount of solids used. The amount of solids is related to the density of the network.

[0079] Another way to adjust the pore size is to use radiation (e.g., radio waves, microwaves, infrared, visible light, ultraviolet light, X-rays, gamma rays) on the composite in either the polyimide state or the 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. Third, the pore size is affected by macroscopic compression of the polyimide composite. As demonstrated in the examples below, the pore size decreases with compression.

[0080] Yet another way to adjust the pore size is ion bombardment of the composite either in the polyimide state or the carbon state. The effect of ion bombardment depends on the specified method. For example, there is additional ion bombardment (e.g., CVD) where something is added, resulting in a decrease in pore size. There is also destructive ion bombardment where the pore size increases. Finally, the 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, a hydrogen reduction environment, etc. For example, a carbon dioxide environment where mass is removed during activation, the pore size increases, and the surface area increases is known to produce activated carbon. Alternative methods for producing PI aerogels

[0081] The prior examples discussed herein teach a particular methodology for forming PI aerogels. In certain embodiments, the present invention also contemplates alternative methods for forming PI aerogels. A non-exhaustive and non-limiting set of examples of such alternative methodologies will now be discussed.

[0082] For example, U.S. Patent No. 6,399,669 to Suzuki et al. teaches four related methods for making PI dry gels (aerogels). In the first method, after synthesizing the PI precursor, an imide is formed from the PI precursor to produce a polyimide. A PI solution or swollen bulk is created, 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, after synthesizing the PI precursor, a PI precursor solution or swollen bulk is created. 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, after synthesizing the PI precursor, a PI precursor solution or swollen bulk is created. Then, while gelling the PI precursor to produce a PI wet gel, an imide is formed from the PI precursor. In the third method, after synthesizing the PI precursor, a PI precursor solution or swollen bulk is created. The solution / swollen bulk is gelled to produce a PI precursor wet gel. Then, this wet gel is dried to produce a PI precursor dry gel. Then, an imide is formed from the PI precursor dry gel to form a PI dry gel (aerogel).

[0083] As a further example, Leventis et al. [Polyimide Aerogels by Ring-Opening Metathesis Polymerization (ROMP), Chem. Mater. 2011, 23, 8, 2250-2261] discuss the formation of PI aerogels using the ROMP method. A low molecular weight imidized oligomer end-capped with polymerizable groups is obtained and mixed with a polymerization (e.g., ROMP) catalyst. Polymerization is thus initiated, and a cross-linked polyimide is produced. This polyimide is gelled and dried to form a PI aerogel. Leventis et al. [U.S. Patent No. 9,745,198; 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] also Acid teach the formation of PI aerogels by mixing dianhydrides (e.g., PMDA) with isocyanates (e.g., 4,4'-diisocyanatodiphenylmethane or methylene diparaphenyl diisocyanate) to form a sol-gel material. The sol-gel material is then dried to produce a PI aerogel. Leventis et al. [Isocyanate-Derived Organic Aerogels: Polyureas, Polyimides, Polyamides, MRS Proceedings, 1306 (2011), Mrsf10-1306-bb03-01. doi:10.1557 / opl.2011.90] also note that DESMODUR N 3300A, DESMODUR RE, and MONDUR CD (all available from BAYER CORP) can be utilized as isocyanates.

[0084] In another methodology, Guo et al. [Polyimide Aerogels Cross-Linked through Amine Functionalized Polyoligomeric Silsesquioxane, ACS Appl. Mater. Interfaces 2011, 3, 546 - 552] discuss the formation of PI aerogels by reacting aminosilsesquioxane with Acid polyamic acid oligomers end-capped with anhydride groups. The product is imidized using pyridine (although thermal imidization is also conceivable), gelled, and subsequently dried to obtain the PI aerogel. Nguyen et al. [Development of High Temperature, Flexible Polyimide Aerogels, American Chemical Society, proceedings published 2011] describe the production of branched polyimides by mixing diamines and Acid dianhydrides, imidizing, and then reacting with multi-amino compounds (e.g., 1,3,5-tris(4-aminophenoxy)benzene). This product is then reacted with 4,4'-methylenediisocyanate and dried to form a PI-urea aerogel.

[0085] In other embodiments, Meador et al. [Mechanically Strong, Flexible Polyimide Aerogels Cross-Linked with Aromatic Triamine, ACS Appl. Mater. Interfaces, 2012, 4(2), pp 536 - 544] AcidThe formation of PI gels by crosslinking anhydride-based end-capped polyamic acid oligomers with aromatic triamines in solution followed by imidization is discussed. The resulting wet material is dried to form PI aerogels. Further, Meador et al. [Polyimide Aerogels with Amide Cross-Links: A Low Cost Alternative for Mechanically Strong Polymer Aerogels, ACS Appl. Mater. Interfaces 2015, 7, 1240-1249] discussed the formation of PI gels by crosslinking amine-capped oligomers with 1,3,5-benzenetricarbonyl trichloride. The resulting gel was dried to form a PI aerogel.

[0086] In yet another embodiment, Pei et al. [Preparation and Characterization of Highly Cross-Linked Polyimide Aerogels Based on Polyimide Containing Trimethoxysilane Side Groups, Langmuir 2014, 30, 13375-13383] produced PI aerogels from polyimides containing trimethoxysilane side groups, which were condensation products of polyimides containing acid chloride side groups and 3-aminopropyltrimethoxysilane. The resulting gel was dried to form a PI aerogel.

[0087] In any of these methods, a suspension of graphene can be added (see Zhang et al., Graphene / carbon aerogels derived from graphene crosslinked polyimide as electrode materials for supercapacitors, RSC Adv., 2015, 5, 1301).

[0088] Each of these methods can result in a polyimide aerogel, and the present invention contemplates any suitable method for manufacturing such a polyimide aerogel. According to a particular embodiment of the present invention, regardless of the method utilized to manufacture the PI aerogel, the resulting PI aerogel can be pyrolyzed to form a PI-derived carbon aerogel.

[0089] All publications referenced are hereby incorporated by reference in their entirety. Further, if the definition or use of a term in a reference incorporated by reference herein conflicts with or is contrary to the definition of that term provided herein, the definition of that term provided herein shall apply and the definition of that term in the reference shall be disregarded.

[0090] The advantages described above, and those that become apparent from the above description, are efficiently achieved. Since specific changes can be made to the above configuration without departing from the scope of the present invention, all matters included in the above description or shown in the accompanying drawings should be construed as illustrative and not in a limiting sense.

[0091] It should also be understood that the following claims are intended to cover all general and specific features of the invention described herein, 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 invention related to the present invention are shown below. [Embodiment 1] A cathode in a lithium air / oxygen or zinc air / oxygen battery, wherein the cathode comprises a nanoporous carbon material, and the nanoporous carbon material has a pore structure comprising a fibril form and a series of pores surrounding lithium peroxide particles. [Embodiment 2] A nanoporous carbon cathode for a lithium air / oxygen or zinc air / oxygen battery, having a pore structure comprising a fibril form with a substantially uniform pore size distribution corresponding to the formation of lithium peroxide particles, a Young's modulus of at least about 0.2 GPa, and a density of about 0.10 g / cc to about 1.5 g / cc The nanoporous carbon cathode. [Embodiment 3] A nanoporous carbon cathode for a lithium air / oxygen or zinc air / oxygen battery, having a pore structure comprising a fibril form with a substantially uniform pore size distribution corresponding to the formation of lithium peroxide particles, a conductivity of at least about 1 S / cm, and a density of about 0.10 g / cc to about 1.5 g / cc The nanoporous carbon cathode. [Embodiment 4] The nanoporous carbon material according to claim 1 or claim 2, wherein the carbon material has a conductivity of at least about 1 S / cm. [Embodiment 5] The nanoporous carbon material according to claim 1 or claim 3, wherein the carbon material has a Young's modulus of at least about 0.2 GPa. [Embodiment 6] The nanoporous carbon material according to any one of claims 1 - 5, wherein the nanoporous carbon material comprises a carbon aerogel. [Embodiment 7] The nanoporous carbon material according to claim 6, wherein the carbon material comprises a carbon aerogel derived from polyimide. [Embodiment 8] The nanoporous carbon material according to any one of claims 6 and 7, wherein the carbon aerogel is in the form of a monolith or powder. [Embodiment 9] The nanoporous carbon material according to claim 8, wherein the monolithic carbon aerogel is substantially or completely binder - free. [Embodiment 10] The monolithic carbon aerogel has a thickness of about 10 μm to about 1000 μm, and the nanoporous carbon material according to any one of claims 6 and 7. [Embodiment 11] The nanoporous carbon material according to any one of claims 1 to 10, wherein the pore structure is characterized by pores surrounding the lithium peroxide particles. [Embodiment 12] The nanoporous carbon material according to claim 11, wherein the pores form an interconnected structure around the lithium peroxide particles, and are characterized by a plurality of connection points between the lithium peroxide particles and the pore walls of each pore surrounded by the lithium peroxide particles. [Embodiment 13] The nanoporous carbon material according to any one of claims 1 to 12, wherein the cathode contains about 5% to 90% by weight of the lithium peroxide particles of the carbon material. [Embodiment 14] The nanoporous carbon material according to any one of claims 1 to 13, wherein the carbon material has a pore volume of at least 0.3 cc / g. [Embodiment 15] The nanoporous carbon material according to any one of claims 1 to 14, wherein the carbon material has a porosity of about 10% to about 90%. [Embodiment 16] The nanoporous carbon material according to any one of claims 1 to 15, wherein the carbon material has a capacity of at least about 800 mAh / g. [Embodiment 17] The nanoporous carbon material according to any one of claims 1 to 16, wherein the pore structure includes a full width at half maximum of about 50 nm or less. [Embodiment 18] The nanoporous carbon material according to any one of claims 1 to 17, wherein the pore structure includes a pore diameter at the maximum peak from a distribution of about 100 nm or less. [Embodiment 19] The nanoporous carbon material according to any one of claims 1 to 18, wherein the fibril form of the nanoporous carbon material includes an average strut width of about 2 to 10 nm. [Embodiment 20] A monolithic polyimide-derived carbon aerogel composite formed of a nanoporous carbon material, wherein the composite is binder-free, lithium peroxide particles are arranged along the surface or in the pores of the monolithic polyimide-derived carbon aerogel composite, and the carbon aerogel composite forms a cathode of a lithium air / oxygen or zinc air / oxygen battery, a monolithic polyimide-derived carbon aerogel composite. [Embodiment 21] A current collector-free, binder-free interconnected cathode material for lithium-air / oxygen or zinc-air / oxygen batteries, comprising a fibril network and a continuous bubble having a series of pores, a monolithic, polyimide-derived nanoporous carbon aerogel, and lithium peroxide particles disposed along the surface of the carbon aerogel or within the pores. [Embodiment 22] An electrochemical cell comprising the nanoporous carbon material or carbon aerogel according to any one of claims 1 to 21. [Embodiment 23] A lithium-air / oxygen or zinc-air / oxygen battery comprising the nanoporous carbon material or carbon aerogel according to any one of claims 1 to 21. [Embodiment 24] A lithium-air / oxygen or zinc-air / oxygen battery comprising the electrochemical cell according to claim 22.

Claims

1. A nanoporous carbon cathode for a lithium air / oxygen or zinc air / oxygen battery, wherein the nanoporous carbon cathode comprises a nanoporous carbon material containing a carbon aerogel derived from polyimide, and the nanoporous carbon material has a pore structure including a fibril form and a series of pores having a pore diameter distribution with a full width at half maximum of 50 nm or less, and the pores correspond to the formation of lithium peroxide particles, a Young's modulus of at least 0.2 GPa, and a density of 0.10 g / cc to 1.5 g / cc having a nanoporous carbon cathode.

2. The nanoporous carbon cathode according to claim 1, wherein the carbon material has a conductivity of at least 1 S / cm.

3. The nanoporous carbon cathode according to claim 1 or 2, wherein the carbon aerogel is in the form of a monolith or powder.

4. The nanoporous carbon cathode according to claim 3, wherein the monolithic carbon aerogel does not contain a binder.

5. The nanoporous carbon cathode according to any one of claims 3 and 4, wherein the monolithic carbon aerogel has a thickness of 10 μm to 1000 μm.

6. The nanoporous carbon cathode according to claim 1, wherein the series of pores form an interconnected structure around the lithium peroxide particles, and a plurality of connection points between the lithium peroxide particles and the pore walls of each pore surrounded by the lithium peroxide particles are characterized.

7. The nanoporous carbon cathode according to any one of claims 1 to 6, wherein the nanoporous carbon material has a pore volume of at least 0.3 cc / g.

8. The nano-porous carbon cathode according to any one of claims 1 to 7, wherein the nano-porous carbon material has a porosity of 10% to 90%.

9. The nano-porous carbon cathode according to any one of claims 1 to 8, wherein the nano-porous carbon material has a capacity of at least 800 mAh / g.

10. The nano-porous carbon cathode according to any one of claims 1 to 9, wherein the pore structure includes a full width at half maximum of 50 nm or less.

11. The nano-porous carbon cathode according to any one of claims 1 to 10, wherein the pore structure includes a pore diameter at the maximum peak from a distribution of 100 nm or less.

12. The nano-porous carbon cathode according to any one of claims 1 to 11, wherein the fibril form of the nano-porous carbon material includes an average strut width of 2 to 10 nm.

13. An electrochemical cell including the nano-porous carbon cathode according to any one of claims 1 to 12.

14. A lithium air / oxygen or zinc air / oxygen battery including the nano-porous carbon cathode according to any one of claims 1 to 12.

15. A lithium air / oxygen or zinc air / oxygen battery including the electrochemical cell according to claim 13.

Images