Carbon anode material

Abstract

The present invention relates to a carbon-containing anode material capable of inserting and extracting alkali metal ions and having a carbon structure including a core comprising one or more primary carbon-containing materials. The present invention further relates to the preparation of such a carbon-containing anode material.

Description

[Technical Field]

[0001] The present invention relates to a specific novel carbon-containing anode material, a novel process for producing such a carbon-containing anode material, an anode electrode having such a novel carbon-containing anode material, and the use of such an anode electrode in energy storage devices such as batteries (particularly rechargeable batteries), electrochemical devices, and electrochromic devices. [Background technology]

[0002] Sodium-ion batteries are similar in many ways to lithium-ion batteries, which are commonly used today; both are reusable secondary batteries that include a negative electrode, a positive electrode, and an electrolyte material, both can store energy, and both charge and discharge via similar reaction mechanisms. When a sodium-ion (or lithium-ion) battery is charged, Na is released from the positive electrode. + (or Li + Ions are extracted and inserted into the negative electrode. Meanwhile, charge balance electrons enter the negative electrode of the battery, passing from the positive electrode through an external circuit with a charger. During discharge, the same process occurs, but in the opposite direction.

[0003] Lithium-ion battery technology has attracted considerable attention in recent years, providing a preferred portable battery for most electronic devices used today; however, lithium is not an inexpensive metal to obtain and is considered too expensive for large-scale applications. In contrast, sodium-ion battery technology, while still in its relatively early stages, is seen as advantageous; sodium is far more abundant than lithium, and some researchers predict this will provide a cheaper and more durable method for energy storage in the future, particularly for large-scale applications such as storing energy in power grids. Nevertheless, much research is still needed before sodium-ion batteries can be commercialized.

[0004] While significant progress has been made in developing positive electrode materials with high charge storage and rate capabilities for both lithium-ion and sodium-ion batteries, one area that requires further attention is the development of more efficient and novel negative electrode materials.

[0005] Carbon, in the form of graphite, has long been preferred as a negative electrode material in lithium-ion batteries due to its high gravimetric and volumetric capabilities. Graphite electrodes achieve reversible capacities exceeding 360 mAh / g, comparable to a theoretical capacity of 372 mAh / g. In the electrochemical reduction process, Li is placed between the graphene layers. + Ions are inserted, and LiC6 is obtained. Unfortunately, however, graphite exhibits much lower electrochemical activity towards sodium, which, coupled with the fact that sodium has a considerably larger atomic radius compared to lithium, results in severely limited intercalation between graphene layers within the graphite anode in sodium ion cells.

[0006] On the other hand, negative electrodes made using hard carbon materials (such as those described in Patent Documents 1 to 4) have been shown to be far more advantageous in sodium ion cells.

[0007] Hard carbon has a disordered structure, overcoming many of the insertion problems for sodium ions. While the precise structure of hard carbon materials still needs to be elucidated, in general terms, hard carbon is described as a non-graphitizable carbon material lacking long-range crystalline order. Hard carbon has layers, but these are not neatly stacked over long distances, making it a microporous material. Although lacking a definitive crystallographic structure, hard carbon is isotropic at a macroscopic level. One reason why constructing a universal structural model of hard carbon is difficult is that short-range order, domain size, carbon layer proportion, and micropores depend on synthesis conditions such as the carbon source, carbonization, and thermal decomposition temperatures.

[0008] Furthermore, unlike graphite, which has a graphite crystal structure in which the planes of the carbon layers are stacked in layers, hard carbon has a random layer structure in which the planes of the carbon layers are stacked in a three-dimensionally shifted state. Therefore, even heat treatment of hard carbon at high temperatures (e.g., 3000°C) does not result in a transformation from the random layer structure to a graphite structure or the generation of graphite microcrystals. Thus, hard carbon is structurally completely different from graphite and can be said to contain one or more non-graphitizable domains and one or more non-graphitizable domains.

[0009] Conventional methods for producing hard carbon materials that can be used in electrodes for secondary battery applications include heating carbon-rich initiators, such as minerals like petroleum coke and pitch coke; plant-derived secondary materials such as sucrose and glucose; artificial organic materials such as polymeric hydrocarbons and smaller organic compounds such as resorcinol formaldehyde; animal-derived materials such as fertilizers; and plant-derived primary materials such as coconut shells, coffee beans, straw, bamboo, rice husks, and banana peels to temperatures exceeding 500°C in an oxygen-free atmosphere. When plant-derived and animal-derived materials are carbonized, "biocar" or biomass charcoal is produced, which can be further processed to obtain hard carbon materials.

[0010] On the other hand, soft carbon is a different form of carbon, structurally distinct from graphite, but it is a readily graphitizable form of carbon that can be altered at high temperatures (e.g., 3000°C) to contain domains of graphite structure. However, even after this heat treatment, a complete graphite structure is not produced by the alteration, so domains of non-graphitizable carbon material still exist. Therefore, it can be said that soft carbon contains one or more non-graphitizable domains, but it cannot be said that it contains one or more non-graphitizable domains.

[0011] A key characteristic of commercially useful negative electrode materials is the presence of a solid electrolyte interface (SEI) layer, which naturally forms as a result of the deposition of liquid electrolyte decomposition products at the interface between the electrolyte and the negative electrode surface during the first charge cycle of early alkali metal-ion batteries. This SEI layer has long been understood to be an essential component of alkali metal-ion batteries, primarily because it protects the negative electrode by inhibiting electron transfer from the negative electrode to the electrolyte, and secondly because it allows alkali metal ions to move from the electrolyte to the negative electrode; these two factors influence the battery's cycle life. Thus, an ideal SEI layer is both an ionic conductor and an electrical insulator. However, the formation of the SEI layer inevitably consumes a portion of the alkali metal ions extracted from the positive electrode during the first charge cycle, which then means they are not available for future charge / discharge cycles. Since isolated batteries have a fixed stock of charge carriers, this depletion of available alkali metal ions results in an irreversible loss of capacity. Recent research aims to maximize the ionic conductivity and electronic insulation properties and minimize irreversible specific capacitance by controlling the formation of the SEI layer (particularly by controlling the stability of the SEI layer).

[0012] As described below, the applicant designed the surface chemical properties, morphology, crystallography, thickness, and pore structure of the negative electrode material to control the stability and robustness of the SEI layer and thereby minimize the irreversible capacity of the first cycle loss.

[0013] Patent Document 5 discloses an anode material containing a hard carbon core, which is then coated with binchotan charcoal and heated to 1500°C. However, even at this high temperature, the hard carbon cannot chemically bond with the binchotan charcoal, so this process does not result in any design for the chemical properties of the hard carbon material's surface. [Prior art documents] [Patent Documents]

[0014] [Patent Document 1] PCT / GB2020 / 050872 [Patent Document 2] US2002 / 0192553A1 [Patent Document 3] US9,899,665B2 [Patent Document 4] US2018 / 0287153A1 [Patent Document 5] CN108963252A [Overview of the project] [Problems that the invention aims to solve]

[0015] Accordingly, the present invention provides novel carbon-containing anode materials having an outer surface treated to possess specific chemical and / or physical characteristics that can be used to establish an optimized, stabilized, and robust SEI layer while minimizing irreversible capacity. Furthermore, the present invention provides novel processes for preparing such surface-treated carbon-containing anode materials. Such processes are cost-effective, especially on a commercial scale, and utilize readily available reactants. The resulting surface-treated carbon-containing anode materials are useful in energy storage devices such as batteries (particularly secondary batteries (rechargeable batteries)), alkali metal ion cells (particularly sodium ion cells), electrochemical devices, and electrochromic devices. Importantly, these surface-treated carbon-containing anode materials yield excellent results in terms of reversible specific capacity, positive electrode specific energy, first positive electrode desodiumization specific capacity, and first discharge capacity efficiency (Coulomb efficiency calculated as the ratio of total charge extracted from the battery to total charge fed into the battery over the entire cycle), producing energy storage devices with significantly reduced irreversible capacity (first cycle loss). Furthermore, the novel surface-treated carbon-containing anode material of the present invention offers remarkably advantageous handling characteristics, including reduced moisture sensitivity and reduced viscosity of the slurry used in electrode preparation, compared to similar unsurface-treated carbon-containing anode materials, such as the anode material disclosed in Patent Document 5. [Means for solving the problem]

[0016] To achieve these objectives, the present invention provides a carbon-containing anode material having a carbon structure that allows for the insertion and extraction of alkali metal ions and comprises a core containing one or more primary carbon-containing materials and, preferably, an outer surface containing one or more carbide materials chemically bonded to one or more primary carbon-containing materials.

[0017] As used herein, the term “core” means the central part of the carbon structure.

[0018] Most preferably, the core is not composed of, or is essentially composed of, one or more primary carbon-containing materials selected from graphite and materials having a fully graphite structure. In one embodiment, the core may essentially consist of one or more primary carbon-containing materials, and more preferably of one or more primary carbon-containing materials.

[0019] As used herein, the term "chemically bonded" means that a chemical bond, such as a covalent bond, is formed between one or more primary carbon-containing materials and one or more carbide materials. Therefore, "strong bond" is included in the meaning of this term, but "weak bond," such as van der Waals interactions, is not included in the meaning of this term.

[0020] The carbide material is "chemically bonded" to the primary carbon-containing material, preferably by the use of chemical vapor deposition according to the present invention, which advantageously allows for surface treatment of the primary carbon-containing material. Furthermore, the carbide material of the present invention is thermally decomposed on one or more primary carbon-containing materials, and this "bottom-up synthesis approach" allows for the deposition of carbon atoms one by one on the outer surface of one or more primary carbon-containing materials.

[0021] As such, the carbon-containing anode material comprises one or more primary carbon-containing materials having outer surfaces treated to exhibit specific surface characteristics as described below, most ideally the carbon-containing anode material according to the present invention is determined using nitrogen gas BET analysis, 0m 2 / g to 5m 2 It comprises one or more primary carbon-containing materials having outer surfaces treated to exhibit a specific surface area of ​​open micropores of 0 m / g. Preferably, determined using nitrogen gas BET analysis, 0 m 2 / g to 5m 2 This is the specific surface area of ​​an open micropore exceeding / g.

[0022] Suitable primary carbon-containing materials are in any form of fine particles (e.g., granular or powdery) that allow for the insertion and extraction of sodium ions.

[0023] In one embodiment, the one or more primary carbon-containing materials may include a domain selected from the group consisting of a graphitization-resistant domain and a non-graphitized domain. As described above, the hard carbon material is an example of a carbon-containing material including a graphitization-resistant domain and a non-graphitized domain. The soft carbon material is an example of a carbon-containing material including a graphitizable domain and a non-graphitized domain.

[0024] In one embodiment, the one or more primary carbon-containing materials may include a graphitizable domain and / or a non-graphitized domain. An example of this is soft carbon.

[0025] In one embodiment, the one or more primary carbon-containing materials may include a graphitization-resistant domain and a non-graphitized domain. An example of this is hard carbon.

[0026] In one embodiment, the one or more primary carbon-containing materials include a disordered carbon-containing material, more preferably a conventional carbon negative electrode material (e.g., a hard carbon negative electrode material, etc.); a high-T hard carbon that is incompletely graphitized (e.g., when complete graphite is formed, a hard carbon annealed at a temperature exceeding 2000 °C but not exceeding 3000 °C, etc.); a composite material of carbon-metal, carbon-semimetal, or carbon-nonmetal (e.g., carbon-Sb, carbon-Sn, carbon-Si, carbon-Pb, carbon-Ti, and carbon-P, etc.) (a hard carbon analog of these materials is particularly preferred); a soft carbon material (e.g., pyrolytically pulverized carbon fiber, etc.); a carbon conductive additive mixture (e.g., a hard carbon-carbon black mixture, etc., and a suitable carbon black may be the Super C65 (trademark) material commercially available from Imerys); a carbon-oxide composite material (e.g., hard carbon-Fe2O 3、 Hard carbon-Sb oxide, hard carbon-Sn oxide, hard carbon-Sb / Sn oxide, etc.); a carbon-carbide composite material (e.g., a hard carbon-SiC composite material, etc.); and an activated carbon material (e.g., a BET surface area of >100 m 2The material comprises one or more materials selected from activated hard carbon, etc., which is 1 / g. Conveniently, primary carbon-containing materials may also be produced by the thermal decomposition (typically high-temperature treatment at temperatures ranging from 700°C to over 2500°C, typically in a non-oxidizing atmosphere containing one or more inert gases selected from nitrogen, carbon dioxide, another non-oxidizing gas, and argon) of carbon-based initiating materials such as plant materials, animal-derived materials (including "animal-derived waste materials" obtained after food has passed through the digestive tract of animals and been excreted therefrom), hydrocarbon materials (including fossil fuel materials such as coal, coal pitch, coal tar, petroleum pitch, petroleum tar, and oil), carbohydrate materials, and other carbon-containing organic materials. Preferably, the carbon-based initiator is purified, ideally before thermal decomposition, by charring (typically at temperatures from 150°C to ≤700°C), washing, decomposition, chemical digestion (e.g., using acidic and / or alkaline conditions), filtration, centrifugation, "heavy liquid separation" or "buoyancy separation," use of ion exchange materials, chromatographic separation techniques, electrophoretic separation techniques, use of complexing agents or chemical precipitation techniques, and milling (typically into particles of about 8-25 μm). 50 Unwanted non-carbon-containing materials (e.g., transition metals, alkali metals, or alkaline earth metals) and non-metal-containing ions (e.g., phosphorus, oxygen, hydrogen) are removed using a process step that may include one or more selected steps (filtering through a 15-25 μm sieve to the particle size to remove larger particles).

[0027] In one embodiment, the particle size distribution of one or more primary carbon-containing materials is approximately 1 nm to approximately 30 μm, preferably approximately 1 nm to approximately 20 μm. In particular, the applicant understands that the surface treatment of the present invention does not substantially alter the particle size distribution of one or more primary carbon-containing materials. Therefore, this range applies not only to the particle size distribution of one or more primary carbon-containing materials before the carbide material is chemically bonded to one or more primary carbon-containing materials, but also to the particle size distribution of one or more primary carbon-containing materials after the treatment has been performed.

[0028] In one embodiment, one or more primary carbon-containing materials have a d of about 0.01 μm to about 4 μm. 10 The particle size is different.

[0029] In one embodiment, one or more primary carbon-containing materials have a d of about 4 μm to about 15 μm. 50 It has a particle size. In another embodiment, one or more primary carbon-containing materials have a particle size of about 1 to about 25 μm, preferably about 8 to about 25 μm. 50 The particle size is different.

[0030] In one embodiment, one or more primary carbon-containing materials have a d of about 15 μm to about 30 μm. 90 The particle size is different.

[0031] Ideally, the primary carbon-containing material used in the carbon-containing anode material of the present invention includes hard carbon and / or soft carbon materials, and more ideally, this hard carbon and / or soft carbon material has an incomplete graphite structure, i.e., includes non-graphitized domains.

[0032] Other preferred primary carbon-containing materials include carbon (e.g., hard carbon, soft carbon, etc., as described above) in combination with one or more elements and / or compounds. Particularly preferred combinations include carbon / X materials, where X may be one or more elements such as antimony, tin, phosphorus, sulfur, boron, aluminum, gallium, indium, germanium, lead, arsenic, bismuth, titanium, molybdenum, selenium, tellurium, silicon, carbon, or magnesium. Carbon / Sb, carbon / Sn, carbon / Sb x Sn y、 Suitable carbon-containing materials include carbon / phosphorus, carbon / silicon, carbon / silicon carbide (HC / SiC), or carbon / sodium silicate. One or more hard carbon analogs among these materials are particularly preferred. A more preferred example of a combination includes a carbon / X material, where X may be an oxide of one or more elements selected from the group including antimony, tin, phosphorus, sulfur, boron, aluminum, gallium, indium, germanium, lead, arsenic, bismuth, titanium, molybdenum, selenium, tellurium, silicon, carbon, and magnesium.

[0033] In some embodiments, the primary carbon-containing material may have one or more metal and / or nonmetallic ions that can act as dopants in the final carbon-containing anode material. These metal and / or nonmetallic ions may be added to the primary carbon-containing material before treatment with the carbide material as described below, or they may be added to the carbon-based initiator used to produce the primary carbon-containing material before thermal decomposition. Alternatively, one or more metal and / or nonmetallic ions may be selectively retained in the carbon-based initiator before thermal decomposition and thus transported to the primary carbon-containing material.

[0034] The surface characteristics of the carbon-containing anode material according to the present invention are investigated using BET technique to determine the specific surface area of ​​open micropores, which are micropores with large openings formed on the surface of the carbon-containing anode material. In this specification, "surface" literally refers to the outside of the carbon-containing anode particles and has no depth into its interior. Pores referred to as "micropores" have a diameter of less than 2 nm and are distinguished from "mesopores," which have a diameter of approximately 2 nm to 50 nm.

[0035] A chemical battery utilizing the surface-treated carbon-containing anode material according to the present invention has been determined using nitrogen gas BET analysis to be 0 m 2 From / g up to 5m 2 Up to / g, preferably up to 0.9, particularly preferably up to 0.5m 2 Up to / g, very preferably up to 0.3m 2 Up to / g, most preferably a maximum of 0.15m 2 The applicant has found that significantly improved electrochemical performance can be achieved when the specific surface area of ​​an open micropore is up to / g.

[0036] As described above, the surface-treated carbon-containing anode material according to the present invention can be conveniently produced when one or more primary carbon-containing materials (solid, preferably particulate, granular, or powdery) are treated with a carbonizing material. Through this treatment, the carbonizing material is preferably chemically bonded to the primary carbon-containing material, and more preferably chemically deposited, by the use of chemical vapor deposition according to the present invention.

[0037] However, the present invention is not limited to the use of chemical vapor deposition. In fact, those skilled in the art are aware of alternative methods for chemically bonding materials to a primary substrate. Examples of these include plasma-enhanced deposition, atomic layer deposition, and physical vapor deposition.

[0038] Where used herein, “carbonized material” is preferably a carbon-rich solid species obtained from one or more secondary carbon-containing materials. Most specifically, the present invention utilizes such carbonized material as an extremely thin deposit on the outer surface of one or more primary carbon-containing materials. It is important to note that although the carbonized material is preferably deposited substantially uniformly on the surface of the internal core, the deposit does not necessarily have to be in the form of a complete layer or uniform coating (i.e., the primary carbon-containing materials and the deposited carbonized material do not necessarily have to be in a core / full-shell type arrangement). Nevertheless, the thickness of the deposited material is preferably 1 nm to less than 500 nm, more preferably 10 nm to less than 500 nm, and very preferably 10 nm to 250 nm. Ideally, 10% to 90% of the surface area of ​​the outer surface of one or more primary carbon-containing materials will be covered by the carbonized material obtained from one or more secondary carbon-containing materials. The mass of the deposit is also extremely small (typically 2.2 ± 0.8 wt per 30 minutes of deposit). Therefore, the carbonized material does not substantially alter the particle size distribution of one or more primary carbon-containing materials, as described above.

[0039] Preferably, a suitable secondary carbon-containing material from which a carbonized material can be obtained can be selected from one or more organic and / or hydrocarbon materials, such as alkanes, alkenes, alkynes, or arenes, and may be linear, branched, or cyclic. The secondary carbon-containing material itself can be obtained from coal or petroleum-based tar or pitch, oil or plant-based materials. General formula: C n H 2n+2 A secondary carbon-containing material containing one or more gaseous hydrocarbons (1 ≤ n ≤ 10) is particularly preferred.

[0040] In one embodiment, the secondary carbon-containing material from which a carbide material is preferably obtained may include a vapor phase and / or a liquid phase and / or a gas phase at at least one temperature from about 950°C or below. Preferably, it is a vapor phase and / or a liquid phase and / or a gas phase at at least one temperature from about 200°C or above to about 950°C or below.

[0041] It can be seen that the specific surface area of ​​open micropores in the carbon-containing anode material of the present invention is dramatically smaller than the specific surface area of ​​open micropores in primary carbon-containing material before treatment with a carbide material obtained from, for example, one or more secondary carbon-containing materials (as described above). This is thought to be because at least some of the openings of the open micropores (i.e., those on the surface) of the carbon-containing anode material are "masked" or "plugged" by the deposited carbide material. Preferably, the presence of chemically deposited carbide material obtained from one or more secondary carbon-containing materials reduces the surface area of ​​the surface micropores of the carbon-containing anode material by at least 40%, more preferably at least 50%, and particularly preferably at least 85%, compared to the surface area of ​​open micropores in primary carbon-containing material before treatment with the carbide material. The significant reduction in the surface area of ​​open micropores seems to support the applicant's current understanding that the deposited carbide material only clogs the surface (open) micropores, and this belief is further supported by the fact that a significant weight increase in primary carbon-containing material cannot be measured after treatment with the carbide material.

[0042] As described above, the present invention provides a carbon-containing anode material comprising a carbide material deposited or partially deposited on the outer surface of a primary carbon-containing material.

[0043] The carbonized material may be a "soft" carbon-containing species that is graphitized to some extent by the carbonization process, and the presence of graphitized material can be verified, for example, by Raman spectroscopy, X-ray diffraction, or high-resolution transmission electron microscopy. However, it is important to control the formation of the carbon-containing anode material so that the degree of graphitization is suitable for the chemical properties of the particular cell being used. For example, in the case of Na ion cells, it is very preferable that graphitization be limited to the level commonly seen in conventional hard carbon materials, that is, since graphite is far less electrochemically active to sodium, it is desirable to avoid highly graphitized soft carbon-containing species on the surface of primary carbon-containing materials for the purpose of reversible sodiumization. However, the opposite is true for lithium ion cells.

[0044] Highly graphitized domains catalyze various parasitic reactions (for example, when propylene carbonate (PC) is used in the electrolyte composition), and care must be taken to avoid their formation. Therefore, extreme annealing has been shown not to increase carbon anode efficiency. On the other hand, the surface treatment according to the present invention has been shown to systematically improve the efficiency of carbon-containing anode materials, regardless of the electrolyte system. However, the method of the present invention does not affect the volume of closed pores. This is evident from the fact that primary carbon-containing materials before and after treatment with the carbide material produce similar (de)sodium potential profiles.

[0045] Another preferred feature of the surface of the carbon-containing anode material according to the present invention is the extremely low degree of surface oxygenation. When compounds with oxygen-containing groups are present on the surface of a carbon-containing material (e.g., CO, C=O, and C(=O)OH functional groups), they are known to act as permanent anchor points for incoming charge carriers and as platforms for undesirable parasitic reactions; when these carbon-containing materials are used as anode materials, both of these factors can potentially contribute to first-cycle losses. Advantageously, the carbon-containing anode material according to the present invention has a surface oxygen content of 0 atomic percent (atm.%) to less than 2.5 atm.%, preferably 0 atm.% to less than 1.5 atm.%, and very preferably 0 atm.% to less than 1 atm.%, as measured using X-ray photoelectron spectroscopy (XPS). Therefore, treating one or more primary carbon-containing materials with a carbide material obtained, for example, from one or more secondary carbon-containing materials according to the present invention has the effect of reducing the surface oxygen content of the primary carbon-containing materials by at least 30 atm.%, preferably at least 50 atm.%, and more preferably at least 90 atm.%. In some embodiments, it is possible to reduce the surface oxygen atoms to nearly 100 atm.%.

[0046] Generally, the specific surface area of ​​the entire carbon-containing anode material is considered another useful factor influencing the degree of irreversible capacity of the first cycle loss; a larger specific surface area leads to greater sensitivity of the anode material, over-stabilizing the SEI layer and thereby increasing irreversible capacity. However, in the present invention, treating one or more primary carbon-containing materials with a carbide material obtained, for example, from one or more secondary carbon-containing materials does indeed reduce the specific surface area of ​​the carbon-containing anode material by about 30%, although this reduction is not as pronounced as the reduction in surface micropore surface area, which can be as much as 87%. All specific surface area values ​​given in this application are determined using BET N2 analysis. Figure 1 is discussed in detail in the following experimental section and illustrates the mechanism by which the surface of the carbon-containing anode material according to the present invention can result in a significant observed reduction in open (surface) micropore surface area while simultaneously recording a minimal reduction in overall surface area.

[0047] According to the present invention, by contacting one or more primary carbon-containing materials with a carbide material (for example, obtained from one or more secondary carbon-containing materials), one or more primary carbon-containing materials are treated with one or more secondary carbon-containing materials to achieve a desired surface-treated carbon-containing anode material.

[0048] Contact between a primary carbon-containing material and a carbide material can be achieved by any suitable method, such as directly contacting the primary carbon-containing material with the carbide material, or by contacting the primary carbon-containing material with one or more secondary carbon-containing materials, thereby facilitating the formation of a carbide material from one or more secondary carbon-containing materials.

[0049] Appropriately, contacting a primary carbon-containing material with one or more secondary carbon-containing materials may involve a solvent-mediated procedure in which a solid primary carbon-containing material is mixed with one or more solvents and / or other liquids in which the secondary carbon-containing material is dissolved / dispersed, and then the solvent / dispersant is removed before carbonization of the secondary carbon-containing material. Alternatively, a mechanochemical procedure may be used in which one or more primary carbon-containing materials and secondary carbon-containing materials are mixed together (without using a solvent or other dispersant, or with an agent to aid mixing) before carbonization of the secondary carbon-containing material. Alternatively, a diffusion-based system may be used in which one or more solid primary carbon-containing materials are contacted with one or more secondary carbon-containing materials in vapor and / or gaseous form, and then heated to carbonize the secondary carbon-containing material.

[0050] In a second embodiment, the present invention provides a method for preparing a carbon-containing anode material having a carbon structure, which allows for the insertion and extraction of alkali metal ions, the method comprising: contacting a core containing one or more solid primary carbon-containing materials with a carbonized material at a temperature up to 950°C, thereby obtaining a carbon atom determined using nitrogen gas BET analysis, 0m 2 / g to 5m 2 The process includes obtaining a carbon-containing anode material having a specific surface area of ​​open micropores of 1 / g.

[0051] In one embodiment, the outer surface was determined using nitrogen gas BET analysis, and the temperature was 0m 2 / g to 5m 2 The material can be processed to exhibit a specific surface area of ​​open micropores exceeding / g.

[0052] Ideally, the core is not composed of, or is essentially composed of, one or more primary carbon-containing materials selected from graphite and materials having a fully graphite structure. In one embodiment, the core may be essentially composed of one or more primary carbon-containing materials, preferably one or more primary carbon-containing materials.

[0053] As described above, one or more solid primary carbon-containing materials are preferably in any particulate form (e.g., granules or powder). In one embodiment, the particle size distribution of one or more primary carbon-containing materials is also as described above, from about 1 nm to about 30 μm. Suitable primary carbon-containing materials used in the method of the present invention are those described above with reference to the carbon-containing anode material according to the present invention.

[0054] The heating conditions will be selected to: i) facilitate the vapor phase deposition of the carbide material onto the surface of the primary carbon-containing material (when the carbide material is pre-formed before contact with the primary carbon-containing material); ii) facilitate the carbonization of one or more secondary carbon-containing materials already present on the surface of the primary carbon-containing material; or iii) facilitate the carbonization of one or more secondary carbon-containing materials and the subsequent deposition of the resulting carbide material onto the surface of the primary carbon-containing material.

[0055] In either case, the final result is that chemical bonds, such as covalent bonds, are formed between one or more primary carbon-containing materials and one or more carbide materials. Therefore, one or more carbide materials are chemically bonded to the surface of one or more primary carbon-containing materials, and preferably chemically deposited.

[0056] Preferably, the temperature used is below the temperature that would lead to excessive graphitization of the carbonized material, especially when the resulting carbon-containing anode material is to be used in a sodium ion cell (as described above). However, it is important that the temperature used according to the method of the present invention leads to the carbonized material chemically bonding with the primary carbon-containing material.

[0057] As described above, the secondary carbon-containing material from which a carbide material is preferably obtained may therefore include a vapor phase and / or a liquid phase and / or a gas phase at at least one temperature from about 950°C or below. Preferably, the vapor phase and / or liquid phase and / or gas phase at at least one temperature from about 200°C or above to about 950°C or below.

[0058] A maximum temperature of 930°C is preferred, a maximum temperature of 900°C is very preferred, and a maximum temperature of 880°C is particularly preferred. The minimum heating temperature is any temperature at which carbonization occurs, and it depends on the secondary carbon-containing material being used. Lower temperatures may be possible if a catalyst or other reagent is used to reduce the activation energy required to thermally decompose and carbonize the secondary carbon-containing material, but a minimum temperature of 200°C is usually sufficient. Possible catalysts include small amounts of one or more metal compounds or metal oxide compounds, such as transition metals or transition metal oxides.

[0059] As described above, suitable secondary carbon-containing materials from which carbide materials can preferably be obtained can be selected from one or more organic and / or hydrocarbon materials that may be linear, branched, or cyclic, such as alkanes, alkenes, alkynes, or arenes. The secondary carbon-containing material itself can be obtained from coal or petroleum-based tar or pitch, oil, or plant-based materials. General formula: C n H 2n+2 A secondary carbon-containing material containing one or more gaseous hydrocarbons (1 ≤ n ≤ 10) is particularly preferred.

[0060] In the preferred method of the present invention, the total pressure, total flow rate, and individual partial pressures and individual flow rates of the reagent when the primary carbon-containing material is in contact with a fluid (liquid, vapor, or gaseous) secondary carbon-containing material or a fluid (liquid, vapor, or gaseous) pre-formed carbonized material are optimized to ensure that a precise amount of carbonized material is deposited on the primary carbon-containing material. The preferred total pressure, total flow rate, and individual partial pressures and individual flow rates of the secondary carbon-containing material are, respectively, 10 -6 From 3x10 7 Pa, 0.001 to 1000 L / min, 10 -6 From 3x10 7 Pa, and in the range of 0.001 to 1000 L / min, more preferably 10 4 from 10 6 Pa, 0.01 to 100 L / min, 10 4 from 10 6Pa, and in the range of 0.01 to 100 L / min, very preferably 5 × 10 4 From 5x10 5 Pa, 0.1 to 10 L / min, 5 × 10 4 From 5x10 5 The pressure is Pa, and the flow rate is in the range of 0.1 to 10 L / min.

[0061] Injection carbon vapor deposition (CVD) systems and aerosol-assisted reactors are examples of devices that can control the pressure and flow rate of individual fluid precursors.

[0062] In a more preferred method of the present invention, the concentration of the carbide material used to contact one or more primary carbon-containing materials and / or the concentration of one or more secondary carbon-containing materials is preferably in the range of 0.001 to 100 vol.%, preferably 0.01 to 10 vol.%, more preferably 0.01 to 5 vol.%, and very preferably 0.05 to 0.1 vol.%, in a carrier gas for the gaseous secondary carbon-containing material, and preferably in the range of 0.001 to 100 vol.%, in a solvent or carrier liquid for the liquid and semi-solid (e.g., pitch, tar, oil, etc.) secondary carbon-containing materials.

[0063] In another, more preferred method of the present invention, the duration of the heating step (annealing time) is also preferably adjusted to i) minimize, and preferably prevent, excessive graphitization of the carbonized material; the longer the heating time, the greater the likelihood of excessive graphitization of the carbonized material. Furthermore, ii) it is adjusted to ensure that it is long enough to chemically deposit enough carbonized material to block at least a portion of the open micropores, as described above.

[0064] As described above, the method of the present invention is not limited to the use of chemical vapor deposition. In fact, those skilled in the art are aware of alternative methods for chemically bonding materials to a primary substrate, and these fall within the scope of the present invention. Examples of these may include plasma-enhanced deposition, atomic layer deposition, and physical vapor deposition.

[0065] An annealing time of 5 to 120 minutes is preferred, and an annealing time of 30 to 90 minutes is particularly preferred. The annealing time is the period required for the carbonized material to deposit on the primary carbon-containing material.

[0066] In a particularly preferred method of the present invention, the step of contacting one or more solid primary carbon-containing materials with a carbonizing material is performed using any means necessary to ensure that at least a portion of the surface of each particle of the primary carbon-containing material is in contact with the carbonizing material. Suitable means include: mixing or stirring the primary carbon-containing material when contacting it with the carbonizing material; spraying the particles of the primary carbon-containing material into an atmosphere containing evaporated carbonizing material; and spreading the primary carbon-containing material on a plate or wide-mouthed reaction vessel before introducing the carbonizing material.

[0067] Furthermore, in a particularly preferred method of the present invention, it is desirable that the step of contacting one or more solid primary carbon-containing materials with the carbide material be performed in the final step of the method of the present invention. In particular, it is highly desirable that this step be performed after any abrasive treatment (e.g., milling, polishing, or grinding) of one or more primary carbon-containing materials. This is advantageous because it avoids the prevention of the outer surface containing one or more carbide materials from chemically bonding to one or more primary carbon-containing materials. For example, post-surface treatments including abrasive treatments may pry open the deactivated surface and expose micropores.

[0068] To avoid any doubt, post-surface treatment steps such as mixing the active material with the binder, electrode printing (e.g., coating), and electrode calendering (e.g., rolling) are not considered "polishing" in the sense of this term.

[0069] The carbon-containing negative electrode material according to the present invention is suitable for use as an electrode active material in secondary battery applications, particularly in alkali metal ion cells, and especially in sodium ion cells.

[0070] In a third embodiment, the present invention provides an alkali metal ion cell comprising at least one negative electrode (anode) as described above. Preferably, the anode is determined using nitrogen gas BET analysis. 2 / g to 5m 2 It has a specific surface area of ​​open micropores of / g.

[0071] The alkali metal ion cell also includes a positive electrode (cathode), which preferably contains one or more positive electrode active materials selected from oxide-based materials, polyanionic materials, and Prussian blue-like system materials, and which can insert and extract alkali metals. Particularly preferably, the one or more positive electrode active materials include one or more selected from alkali metal-containing oxide-based materials and alkali metal-containing polyanionic materials, where the alkali metal is one or more alkali metals selected from sodium and / or potassium, and optionally combined with lithium. A particular positive electrode active material contains lithium as a trace alkali metal component, i.e., the amount of lithium is less than 50% by weight, preferably less than 10% by weight, and ideally less than 5% by weight of the total alkali metal content.

[0072] The most preferred positive electrode active material is given by the following general formula: A 1±δ M 1 V M 2 W M 3 X M 4 Y M 5 Z O 2-c It is a compound of, Here, A is one or more alkali metals selected from sodium, potassium, and lithium; M 1 It contains one or more redox-active metals in oxidation state +2; M 2 This includes metals in oxidation states from 0 to +4 or less; M 3 This includes metals in oxidation state +2; M 4 This includes metals in oxidation states from 0 to +4 or less; M 5 This includes metals in oxidation state +3; Here, 0 ≤ δ ≤ 1; V is > 0; W is ≥ 0; X is ≥ 0; Y is ≥ 0; At least one of W and Y is > 0; Z is ≥ 0; C lies in the range 0 ≤ c < 2; Here, V, W, X, Y, Z, and C are chosen to maintain electrochemical neutrality.

[0073] To avoid any doubt, the term "one or more alkali metals selected from sodium, potassium, and lithium" will be interpreted to include: Na, K, Li, Na+K, Na+Li, K+Li, and Na+K+Li.

[0074] Ideally, metal M 2 It comprises one or more transition metals, preferably selected from manganese, titanium, and zirconium; M 3 is preferably one or more selected from magnesium, calcium, copper, tin, zinc, and cobalt; M 4 It preferably comprises one or more transition metals selected from manganese, titanium, and zirconium; further, M 5 The positive electrode active material is preferably one or more selected from aluminum, iron, cobalt, tin, molybdenum, chromium, vanadium, scandium, and yttrium. Any crystalline structure of the positive electrode active material can be used, preferably O3 or P2 or a derivative thereof, but specifically, the positive electrode material may also have a heterogeneous structure consisting of a mixture of phases, i.e., several different crystalline forms.

[0075] A highly preferred cathode active material includes a sodium and / or potassium-containing transition metal-containing compound, with a sodium transition metal nickelate compound being particularly preferred. Particularly advantageous examples include alkali metal layered oxides, single-phase and mixed-phase O3, P2, and P3 alkali metal layered oxides, alkali metal-containing polyanion materials, oxymetallate Prussian blue analogs, and Prussian white analogs. Specific examples include O3 / P2-A 0.833 Ni 0.317 Mn 0.467 Mg 0.1 Ti 0.117 O 2、 O3-A 0.95 Ni 0.3167 Mn 0.3167 Mg 0.1583 Ti 0.2083 O2, P2-type A 2 / 3 Ni 1 / 3 Mn 1 / 2 Ti 1 / 6 O2, P2-A 2 / 3 (Fe 1 / 2 Mn 1 / 2 )O2, P´2-A 2 / 3 MnO2, P3 or P2-A 0.67 Mn 0.67 Ni 0.33 O2, A3V2(PO4)3, AVPO4F, AVPO4F, A3V2(PO4)3, A3V2(PO4)2F3, A3V2(PO4)2F3, A x Fe y Mn y (CN) 6. nH2O (0 ≦ x, y, z ≦ 2; 0 ≦ n ≦ 10), O3, P2, and / or P3-A x Mn y Ni z O2 (0 ≦ x ≦ 1 and 0 ≦ y, z ≦ 1), A2Fe2(SO4) 3、 A2Ni2SbO6, and A3Ni2SbO6 are included, where "A" is one or more alkali metals selected from Li, Na, and K, preferably Na and / or K, and most preferably Na.

[0076] Advantageously, the alkali metal ion cell according to the present invention can use any form of electrolyte, that is, a solid, liquid or gel composition can be used, and suitable examples include the following: 1) All, with or without diluents such as HFE (1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether) or D2 (1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether), ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC) (preferably as an EC:DEC:PC mixture in a ratio of 1:2:1 wt. / wt.), gamma-butyrolactone (GBL) sulfolane, diglyme, triglyme, tetraglyme, dimethyl sulfoxide (DMSO), dioxolane, and one or more solvents selected from mixtures thereof, NaPF6, NaBF4, sodium bis(oxalate) (NaBOB), sodium triflate (NaOTf), LiPF6, LiAsF6, LiBF4, LiBOB, LiClO4, LiFSi, LiTFSi, Li-triflate and mixtures thereof, etc., a liquid electrolyte such as an alkali metal salt of >0 to 10 moles; 2) A gel electrolyte based on any one of the following matrix materials used alone or in combination with each other; or 3) Na3Zr2Si2PO 12 NASICON-type such as, sulfide-based such as Na3PS4 or Na3SbS4, Na2B 10 H 10 -Na2B 12 H 12Solid electrolytes such as hydrogen compounds, β-alumina systems such as Na2O.(8-11)Al2O3, or related β''alumina systems such as Na2O.(5-7)Al2O3. Known electrolyte additives such as 1,3-propanediol cyclic sulfate (PCS), P123 surfactants, tris(trimethylsilyl) phosphate (TMSP), tris(trimethylsilyl) borate (TMSB), 1-propene-1,3-sultone, and 1,3-propanesultone can also be included in the electrolyte, as can binders such as polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), poly(methyl methacrylate) (PMMA), sodium carboxymethylcellulose (CMC), and styrene-butadiene rubber (SBR).

[0077] It should be noted that, in addition to being an excellent anode material, the surface-treated carbon-containing material of the present invention also offers further commercial advantages.

[0078] The first of these relates to improved moisture sensitivity. Due to its extremely low level of open microporosity, the surface-treated carbon-containing anode material of the present invention adsorbs considerably less moisture from the atmosphere upon exposure than unsurface-treated primary carbon-containing materials. This not only makes the anode material of the present invention easier to handle during anode manufacturing, but also reduces the moisture content of the resulting anode coating and the finished cell.

[0079] A second unexpected benefit relates to the improvement in the viscosity of electrode slurries containing the carbon-containing anode material according to the present invention. During cell manufacturing, the viscosity of the electrode slurry should not be overlooked, as it makes a significant difference to the smooth operation of the process and the resulting electrode quality control. Electrode materials (activators, binders, additives) are typically mixed and dispersed in organic or aqueous solvents so that they can be coated on a current collector. During the coating process, the solvent evaporates, leaving behind the dried components. Insufficient viscosity results in a slurry that is too low in viscosity, which can cause the coating edge to shift; on the other hand, a slurry that is too high in viscosity does not flow as smoothly as required, raising process problems. This negatively impacts the quality of the dry coating. Typically, electrode materials with reduced surface area require less solvent to achieve a given optimal viscosity. This is advantageous from a cost standpoint. Thus, the surface-treated carbon-containing anode material according to the present invention exhibits lower viscosity for the same solid content as a result of a lower micropore surface area, thereby obtaining a smoother surface morphology and purer surface chemistry. Costs can be reduced by achieving high-quality electrodes using less solvent.

[0080] As demonstrated in the specific examples discussed below, the ability to achieve advantageous improvements in electrochemical performance using the carbon-containing anode material according to the present invention can be summarized as follows: i) The irreversible capacity and first-cycle losses of Na-ion full cells featuring the carbon-containing material are low, at 25.2 mAh / g and 8.6%, respectively. This is a significant decrease compared to the values ​​obtained from benchmark cells featuring conventional hard carbon anodes, at 54.9 mAh / g and 16.8%, respectively, for otherwise identical chemical properties and composition. ii) Na-ion full cells featuring the carbon-containing anode material of the present invention demonstrate significantly improved capacity retention and cycle stability at faster charge and discharge rates up to ±3C. iii) The carbon-containing anode material according to the present invention reduces the moisture adsorption rate, and Na-ion full cells featuring these carbon-containing anode materials improve cycle stability due to the reduced overall moisture content. [Brief explanation of the drawing]

[0081] Next, the present invention will be described with reference to the following figures. [Figure 1] This is a schematic diagram of particles of the primary carbon-containing material in its original state and particles of the carbon-containing anode material surface-treated according to the present invention. [Figure 2] This flowchart illustrates a preferred method of the present invention. [Figure 3] This figure shows a bar graph illustrating the amount of surface oxygen (atm.%) present on the original hard carbon-containing material compared to the same hard carbon-containing material treated with a carbide material according to the present invention. [Figure 4] This figure shows a bar graph illustrating the BET specific surface area (m2 / g) of the original hard carbon-containing material compared to the same hard carbon-containing material treated with a carbide material according to the present invention. [Figure 5] This figure shows a bar graph illustrating the BET micropore surface area (m2 / g) of the original hard carbon-containing material compared to the same hard carbon-containing material treated with a carbide material according to the present invention. [Figure 6] This figure shows a typical T-plot for sample material 8 according to the present invention. [Figure 7] This figure shows the voltage vs. Na+ / Na capacitance curve obtained for a Na ion half cell using the carbon-containing negative electrode material 3 according to the present invention. [Figure 8] This figure shows the voltage vs. Na+ / Na capacitance curve obtained for a Na ion half cell using the carbon-containing negative electrode material 8 according to the present invention. [Figure 9] This figure shows the voltage vs. Na+ / Na capacitance curve obtained for a Na ion half-cell using the carbon-containing negative electrode material 4 (control) according to the present invention. [Figure 10] This figure shows the voltage-capacitance curve obtained for a three-electrode full cell using the carbon-containing negative electrode material 7 according to the present invention. [Figure 11] This figure shows the voltage-capacitance curve obtained for a three-electrode full cell using the carbon-containing negative electrode material 8 according to the present invention. [Figure 12] This figure shows the voltage-capacitance curve obtained for a three-electrode full cell using the carbon-containing negative electrode material 6 according to the present invention. [Figure 13] This figure illustrates the positive electrode specific capacity, cycle life performance, and Coulomb efficiency of a sodium ion full cell containing carbon-containing negative electrode material 8 during high-speed discharge. [Figure 14] This figure illustrates the positive electrode specific capacity, cycle life performance, and Coulomb efficiency of a sodium ion full cell containing carbon-containing negative electrode material 8 during high-speed discharge. [Figure 15] This figure illustrates the positive electrode specific capacity, cycle life performance, and Coulomb efficiency of a sodium ion full cell containing carbon-containing negative electrode materials 6 and 8 during high-speed discharge. [Figure 16] This figure illustrates the positive electrode specific capacity of a sodium ion full cell containing carbon-containing negative electrode material 8 during high-speed discharge. [Figure 17]This figure shows a graph of moisture content versus air exposure time to illustrate the reduced sensitivity to moisture exhibited by the carbon-containing anode materials 6, 7, 8, 9, and 10, which were prepared according to the present invention, compared to material 4 (control). [Figure 18] This figure shows a bar graph illustrating the sensitivity of electrodes fabricated using carbon-containing negative electrode materials 7, 8, and 10, prepared according to the present invention, to moisture, compared to material 4 (control). [Figure 19] This figure shows various particle size distributions obtained using laser diffraction on first-grade hard carbon-containing materials. [Figure 20] This figure shows a scanning electron microscope image of a first-grade hard carbon-containing material. [Modes for carrying out the invention]

[0082] Proposed model for the structure of carbon-containing anode material according to the present invention Figure 1 shows a schematic diagram of the particles of the carbon-containing material in its original state, including a core containing primary carbon-containing material 1. Figure 1 further shows a schematic diagram of the particles of the surface-treated carbon-containing anode material 10 according to the present invention (i.e., not in its original state), including a core containing primary carbon-containing material 1 and an outer surface 15 containing a carbide material 35 chemically bonded to the primary carbon-containing material 1. More specifically, Figure 1 contributes to illustrating the proposed mechanism by which the surface-treated carbon-containing anode material 10 according to the present invention may be able to exhibit a significantly reduced open micropore surface area while recording the minimum reduction in overall surface area. Figure 1 may also contribute to illustrating how the surface-treated carbon-containing anode material 10 according to the present invention has greater resistance to moisture adsorption compared to the carbon-containing material in its original state, including a core containing primary carbon-containing material 1.

[0083] As shown in Figure 1, a typical particle of the original carbon-containing material, including a core containing a primary carbon-containing material 1 having open porosity, has an irregular and non-uniform outer surface 15 formed of multiple open mesopores 20 and multiple open micropores 25. For example, according to the method of the present invention, after processing the original carbon-containing material including a core containing a primary carbon-containing material 1, an extremely thin, non-uniform and imperfect layer 30 of carbide material 35 particles (e.g., obtained from a secondary carbon-containing material) is deposited on the outer surface 15 of the original carbon-containing material including the primary carbon-containing material 1 to produce a surface-treated carbon-containing anode material 10 according to the present invention.

[0084] As shown in Figure 1, the entrances to many of the open micropores 25 are blocked by particles of deposited carbide material 35, which form an extremely thin layer 30. The blocked micropores are shown as 55 on the surface-treated carbon-containing anode material 10 in Figure 1. While the extreme thinness of the non-uniform and incomplete layer 30 makes it highly unlikely that it will be sufficient to cover / block the entrances to larger mesopores 20, it should be understood that the layer 30 can instead partially cover the interior of the mesopores, which can slightly reduce the surface area of ​​these pores.

[0085] The increased hydrophobicity of the surface-treated carbon-containing anode material according to the present invention can also be explained by the fact that the number of water molecules 40a that can enter the plugged or blocked micropores 55 is reduced compared to the number of water molecules 40 that can enter the open micropores 25 of the original primary carbon-containing material 1, thereby making the surface-treated carbon-containing material 10 according to the present invention more resistant to moisture than the untreated material. This is investigated below.

[0086] General preparation method for carbon-containing anode materials according to the present invention Figure 2 provides a schematic flowchart illustrating a typical method according to the present invention. In a typical method, one or more particulate primary carbon-containing materials are treated with a carbonizing material at 200°C to 950°C for 30–120 minutes, the carbonizing material may be a pre-prepared carbonizing material as described above, or a carbonizing material obtained from one or more secondary carbon-containing materials. Ideally, the treatment process is carried out in an inert gas atmosphere. More ideally, one or more secondary carbon-containing materials are provided at the required concentration (as described above), gaseous secondary carbon-containing materials are preferably provided with a carrier gas (preferably an inert carrier gas), and liquid secondary carbon-containing materials are preferably provided with a carrier solvent or other carrier liquid. Details of the tested carbon-containing anode materials are shown in Table 1 below:

[0087] [Table 1] TIFF0007905021000002.tif59161 Measurement of the size of primary carbon-containing materials The size of first-grade hard carbon-containing materials was measured using laser diffraction and scanning electron microscopy. The results are shown in Figures 19 and 20, respectively. These results indicate the following preferred particle size distribution for first-grade carbon-containing materials.

[0088] [Table 2] As disclosed herein, when one or more primary carbon-containing materials include one or more carbon composite materials represented by :(carbon)-X, the particle size distribution may differ from that described above. This is because some of the sizes of the composite materials may be in the nanoscale range. Accordingly, in one embodiment, the particle size distribution of the primary carbon-containing materials of the present invention is from about 1 nm to about 30 μm, preferably from about 1 nm to about 20 μm.

[0089] To the best of the applicant's knowledge, the surface treatment of the present invention does not substantially alter the particle size distribution of the primary carbon-containing material. In one example of the present invention, it was found that the mass deposition of the secondary carbon-containing material was very small (2.2 ± 0.8 wt.%) per 30 minutes of deposition. Therefore, it can be considered that the particle size distribution of the primary carbon-containing material after surface treatment is essentially the same as the particle size distribution of the primary carbon-containing material before surface treatment.

[0090] Measurement of graphitization characteristics of carbon-containing anode material according to the present invention As described above, it is important to control the level of graphitization of the carbide material deposited on the outer surface of the primary carbon-containing material to match the chemical property requirements of the cell in which the anode material is used. Table 4 below compares the graphitization characteristics (scale spacing distance and size of microcrystalline graphitization in the stacking (Lc) and in-plane (La) directions) of the surface-treated carbon-containing anode material according to the present invention with those of the unsurface-treated primary carbon-containing material (i.e., the initiating material used to make the primary carbon-containing material).

[0091] As can be seen from the results in Table 4, the presence of surface engineering according to the present invention does not significantly affect the degree of graphitization, and therefore, anode materials 3, 6-11, and 14 are expected to be very suitable for use in sodium ion cells.

[0092] Measurement of surface oxygen content (atm.%) i) The amount of oxygen present on the surface of the carbon-containing anode material according to the present invention, and ii) the amount of oxygen present on the surface of the primary carbon-containing material before contact with the carbide material, was measured using XPS according to the analytical specifications summarized in Table 3 below. The results for the surface oxygen content are shown in Figure 3.

[0093] [Table 3] BET surface area (m 2 Measurement of g / g BET analysis was performed using a Micromeritics Gemini VII 2390 surface area analyzer with nitrogen adsorbed at liquid nitrogen temperature. All samples were degassed overnight at 250°C while flowing nitrogen before analysis. The results are shown in Figure 4.

[0094] BET micropore surface area (m 2 Measurement of g / g By applying a model to the volume of gas adsorbed by the material, it is possible to estimate the surface area of ​​gas-reachable micropores (open micropores known as micropores on the surface of the carbon-containing anode material) per gram of carbon-containing anode material (or, in the case of a control sample, the original hard carbon-containing material). This was achieved from a "t-Plot" analysis. A typical t-Plot consists of the amount of gas adsorbed at standard temperature and pressure versus the Harkins and Jura statistical thickness (nm) according to the Harkins and Jura thickness formula (t=[13.99 / (0.034-log(p / p°))]^0.5). The difference between the external surface area and the BET (total) surface area is the estimated micropore surface area. The results obtained are shown in Figure 5. A t-Plot for representative material 8 is shown in Figure 6.

[0095] Measurement of moisture content (ppm) After no exposure (0 minutes) and exposure to air at a relative humidity of 20-50% for 30 minutes and 60 minutes, the moisture content of the active substance and the negative electrode (coating) was measured using a Moisture Meter (Coulometric Titration) Model CA-200 from a MITSUBISHI CHEMICAL ANALYTECH titrator.

[0096] result The graphitization characteristics, surface oxygen content, BET surface area, micropore surface area, and moisture content obtained as described above are summarized in Table 4 below.

[0097] [Table 4] Product analysis using TIFF0007905021000006.tif88170XRD X-ray diffraction analysis is performed using a Siemens (RTM) D5000 powder diffractometer to confirm that the desired target material has been prepared, to establish the phase purity of the product material, and to determine the types of impurities present. From this information, it is possible to determine the lattice constant of the unit cell.

[0098] The following are typical XRD operating conditions used for material analysis:

[0099] Slit size: 1mm Range: 2θ = 10° to 60° X-ray wavelength = 1.5418 A (angstrom) (Cu Kα) Speed: 1.0 seconds / step Increment: 0.025°.

[0100] Electrochemical results A negative electrode containing a carbon-containing material prepared according to the present invention is prepared by solvent casting a slurry containing the experimental carbon-containing material (mentioned above), a binder, and a solvent in a weight ratio of 92:6:2. The slurry may contain conductive carbon such as C65® carbon (Timcal) (RTM). Suitable binders are PVdF and styrene-butadiene rubber / carboxymethylcellulose (SBR / CMC), and the solvent can be N-methyl-2-pyrrolidone (NMP) or water. The slurry is then cast onto a current collector foil (e.g., aluminum foil in its original state or coated with carbon) and heated until most of the solvent has evaporated and an electrode film has formed. The negative electrode is then further dried under dynamic vacuum at approximately 120°C and calendered to the desired thickness.

[0101] Cell Test In a half-cell test, an experimental carbon-containing negative electrode is paired with a single disc of metallic sodium as a counter electrode to the reference electrode. Glass fiber GF / A is used as a separator, and a suitable electrolyte is also utilized. Any suitable Na-ion electrolyte can be used, preferably containing one or more salts, such as NaPF6, NaAsF6, NaClO4, NaBF4, NaSCN, and Na triflate, in combination with one or more organic solvents, such as EC, PC, DEC, DMC, EMC, glycerides, esters, acetates, etc. Further additives such as vinylene carbonate and fluoroethylene carbonate may also be incorporated. An electrolyte composition containing 0.5 M NaPF6 / EC:PC:DEC is preferred.

[0102] All cells were allowed to rest for 24 hours before cycling. In the three-electrode test, the carbon-containing negative electrode material according to the present invention was used as the negative electrode, a standard oxide material was used as the positive electrode, and a sodium piece was used as the reference. All three electrodes were moistened with the same electrolyte. Two polyethylene films with a thickness of 24.5 μm were used as separators.

[0103] Half-cells are tested using constant-current cycling technology, while three-electrode cells are tested using constant-current-constant-voltage technology.

[0104] The cell is cycled at a given current density between preset voltage limits. A commercially available battery cycler from MTI Inc. (Richmond, CA, USA) or Maccor (Tulsa, OK, USA) was used. During charging, alkaline ions are inserted into the carbon-containing negative electrode material. During discharge, alkaline ions are extracted from the negative electrode and reinserted into the positive electrode active material.

[0105] result Experimental carbon-containing anode material 3-half cell (against Na + Electrochemical test of Na) Figure 7 shows the potential curves for sodiumization and desodiumization of the anode as a function of the anode specific capacity. Using the experimental carbon-containing anode material 3 according to the present invention as an example, it is possible to achieve a reversible desodiumization capacity of 315 mAh / g with an irreversible specific capacity of 36.0 mAh and a Coulomb efficiency of 89.8% in the first cycle.

[0106] Experimental carbon-containing anode material 8-half cell (against Na + Electrochemical test of Na) Figure 8 shows the potential curves for sodiumization and desodiumization of the anode as a function of the anode specific capacity. Using the experimental carbon-containing anode material 8 according to the present invention as an example, it is possible to achieve a reversible specific capacity exceeding 330 mAh / g with an irreversible specific capacity of 29.1 mAh and a Coulomb efficiency of 91.9% in the first cycle.

[0107] Control anode material 4 (control) - half cell (against Na + Electrochemical test of Na) Figure 9 shows the potential curves of sodiumization and desodiumization of the anode as a function of the anode specific capacity. Using the control anode material 4 according to the present invention as an example, an irreversible specific capacity of 58.6 mAh and a reversible specific capacity of 281 mAh / g were obtained with a Coulomb efficiency of 82.8% in the first cycle. Comparing these values ​​with those of the experimental carbon-containing anode material 8 (Figure 7 vs. Figure 8), it is clear that the electrochemical performance is significantly improved by the surface treatment according to the present invention.

[0108] Electrochemical testing of three-electrode full cells using experimental carbon-containing negative electrode materials 6, 7, and 8. Figures 10–12 show the sodiumization and desodiumization potential curves of the negative and positive electrodes, along with the cell voltage as a function of cell capacitance in three voltage windows: 1.0–4.2V, 1.0–4.1V, and 1.0–4.0V. The cells feature experimental carbon-containing negative electrode materials 7, 8, and 6, respectively. The objective of the three-electrode full-cell study was to measure the negative electrode potential at the top of the charge and investigate the possibility of dendrite formation on the negative electrode surface. The fact that the negative electrode potential at the top of the charge was safely positive in all voltage windows indicates that Na ion cells featuring carbon-containing materials have no risk of dendrite formation. Such a three-electrode full-cell design is not optimal for achieving the best first-cycle Coulomb efficiency due to the presence of a Na metal reference between the negative and positive electrodes. Therefore, the carbon-containing negative electrode materials were further tested in a 0.1Ah full cell to verify the true first-cycle Coulomb efficiency value.

[0109] Electrochemical testing of full cells of experimental carbon-containing anode materials 6-11 and 4 (control). Figures 13 and 14 show the Coulomb efficiency and positive electrode relative discharge capacity of two comparable cells featuring experimental carbon-containing negative electrode material 8 as the negative electrode, as a function of the number of cycles. After four formation cycles of charging and discharging at C / 10, the cell in Figure 13 was charged at C / 5 and discharged at various rates from C / 5 to 3C, while the cell in Figure 14 was charged at various rates from C / 5 to 3C and discharged at C / 5, following the same formation protocol. Both cells exhibited a first-cycle efficiency of >90% and showed >98% capacity retention after the fast charge / discharge cycles. This demonstrates that the carbon-containing negative electrode material according to the present invention has excellent fast charge and discharge capabilities. This is likely due to the enhanced electron charge carrier characteristics of the material according to the present invention.

[0110] Figure 15 compares the cycle stability of three cells featuring experimental carbon-containing anode materials 6 and 8 at three different voltage windows. After four formation cycles of charging and discharging at C / 10, all three cells were charged and discharged at C / 5 and C / 2 (four cycles each), and then charged and discharged at 1C. All three cells had a first-cycle efficiency of approximately 89%. Cells cycled at 1.0–4.0V and 1.0–4.1V featured experimental carbon-containing anode material 6. Cells cycled at 1.0–4.2V featured experimental carbon-containing anode material 8.

[0111] Table 5 summarizes the FCL, irreversible ratio negative electrode capacity, and reversible ratio positive electrode capacity of full cells featuring various experimental carbon-containing negative electrode materials.

[0112] [Table 5] To properly understand the true performance improvement (reduction in anode irreversible ratio capacity and first-cycle losses), four similar benchmark full cells featuring carbon-containing anode material 4 (control) were charged and discharged according to the same protocol used for full cells featuring experimental carbon-containing anode materials 6–11. The first-cycle losses, anode irreversible ratio capacity, and cathode reversible ratio capacity values ​​are summarized in Table 5.

[0113] As can be seen from Table 5, the FCL and irreversible negative electrode ratio capacity of the benchmark full cell featuring carbon-containing negative electrode material 4 (control) were significantly and systematically higher than those observed in the full cells featuring experimental carbon-containing negative electrode materials 6-10. The higher FCL resulted in the control cell showing a positive electrode reversible ratio capacity value approximately 10 mAh / g lower compared to that observed in cells featuring experimental carbon-containing negative electrode materials 6-9.

[0114] Although experimental carbon-containing anode material 11 did not exhibit FCL and anode irreversible ratio capacity values ​​as low as those obtained for experimental carbon-containing anode materials 6-10, the results for anode material 11 were still lower than those for control sample 4. Surface treatment of primary carbon-containing materials up to 900°C is considered most preferable to avoid graphitization of carbon species to the extent that it inhibits reversible (de)sodiumization. In conclusion, it has been shown that maximum efficiency is obtained when primary carbon-containing materials are treated according to the present invention and at temperatures of 780-900°C.

[0115] A full cell containing the negative electrode, characterized by experimental material 8, was gradually charged from C / 5 to 10C at a constant discharge rate of C / 5. Throughout the test, the retention of over 60% of the discharge capacity was demonstrated. Near 100% of the rated capacity (i.e., the positive electrode discharge capacity when the cell is charged and discharged at C / 5) was obtained after the fast-charging test. The results are summarized in Table 6 and Figure 16.

[0116] [Table 6] Experiment to demonstrate the reduction in moisture sensitivity of the carbon-containing anode material according to the present invention It is highly preferable to reduce the residual moisture content of all cell components, including the electrodes, separators, and electrolytes. A key advantage of the carbon-containing negative electrode materials according to the present invention (experimental materials 6-11) is that they were found to be significantly less susceptible to moisture exposure than the original primary carbon-containing material (experimental material 4 (control)) that was not treated with a carbonizing material.

[0117] The moisture content of experimental carbon-containing anode materials 6-11 and control material 4 at different exposure durations is shown in detail in Table 4 and Figure 17. It is clear that the carbon-containing anode materials according to the present invention exhibit a significantly reduced moisture adsorption rate, while control material 4 adsorbs a large amount of moisture upon exposure. As mentioned above, this decrease in moisture absorption is thought to be due to a reduction in the usability of surface micropores after processing the first-grade hard carbon material in the presence of a carbide material.

[0118] Figure 18 shows the residual moisture content of a negative electrode (coating) characterized by control material 4, and a negative electrode (coating) characterized by the carbon-containing material according to the present invention (experimental materials 7-10). The negative electrode (coating) with experimental carbon-containing material 10 showed the lowest (most preferred) residual moisture content.

Claims

1. A carbon-containing anode material having a carbon structure comprising a core containing one or more primary carbon-containing materials including hard carbon, and an outer surface containing one or more carbide materials chemically bonded to and substantially uniformly deposited on the one or more primary carbon-containing materials, wherein the carbon-containing anode material is determined using nitrogen gas BET analysis, and the carbon structure is 0 m ２ / g to 0.9m ２ The core has a specific surface area of ​​open micropores of 1 / g, and the core is not composed of, or is essentially composed of, one or more primary carbon-containing materials selected from graphite and materials having a completely graphite structure. The carbon-containing anode material is a carbon-containing anode material having a maximum moisture content of 50 ppm, determined using Karl Fischer titration techniques after exposure to ambient air at 30% relative humidity for 30 minutes.

2. The carbon-containing anode material according to claim 1, wherein the one or more primary carbon-containing materials include easily graphitizable domains and non-graphitizable domains.

3. The carbon-containing anode material according to claim 1, wherein the one or more primary carbon-containing materials are obtained from the thermal decomposition of plant-derived materials, animal-derived materials, hydrocarbon materials, carbohydrate materials, and other carbon-containing organic materials.

4. The aforementioned one or more primary carbon-containing materials include one or more carbon composite materials represented by (carbon)-X, Here, X is one or more elements selected from the group including antimony, tin, phosphorus, sulfur, boron, aluminum, gallium, indium, germanium, lead, arsenic, bismuth, titanium, molybdenum, selenium, tellurium, silicon, carbon, and magnesium, or Here, X is an oxide of one or more elements selected from the group including antimony, tin, phosphorus, sulfur, boron, aluminum, gallium, indium, germanium, lead, arsenic, bismuth, titanium, molybdenum, selenium, tellurium, silicon, carbon, and magnesium. A carbon-containing anode material according to any one of claims 1 to 3.

5. The carbon-containing anode material according to any one of claims 1 to 4, wherein the carbonized material is obtained from one or more secondary carbon-containing materials selected from organic and hydrocarbon materials.

6. A carbon-containing anode material according to any one of claims 1 to 5, wherein the outer surface contains up to 2.5 atomic percent of oxygen.

7. The carbon-containing anode material according to any one of claims 1 to 6, wherein the one or more primary carbon-containing materials have a particle size of 1 nm to 30 μm.

8. A method for preparing a carbon-containing anode material having a carbon structure, which allows for the insertion and extraction of sodium ions, the method comprising the step of contacting a core containing one or more primary carbon-containing materials, including solid hard carbon, with a carbonized material at a temperature up to 950°C, thereby obtaining a carbon-containing anode material having one or more carbonized materials chemically bonded and substantially uniformly deposited on the outer surface of the one or more primary carbon-containing materials, wherein the carbon-containing anode material is determined using nitrogen gas BET analysis, 0 m ２ / g to 0.9m ２ The core has a specific surface area of ​​open micropores of 1 / g, and the core is not composed of, or is essentially composed of, one or more primary carbon-containing materials selected from graphite and materials having a completely graphite structure. A method for preparing a carbon-containing anode material having a maximum moisture content of 50 ppm, determined by using Karl Fischer titration techniques and exposure to ambient air at 30% relative humidity for 30 minutes.

9. The method according to claim 8, wherein the step of bringing the primary carbon-containing material into contact with the carbide material is achieved by bringing the primary carbon-containing material into contact with one or more secondary carbon-containing materials, and then facilitating the formation of a carbide material from the one or more secondary carbon-containing materials.

10. The method according to claim 9, wherein the one or more secondary carbon-containing materials include a vapor phase and / or a liquid phase and / or a gas phase at at least one temperature starting from 950°C.

11. A sodium ion cell comprising a positive electrode, a negative electrode, and an electrolyte, wherein the negative electrode comprises a carbon-containing negative electrode material according to any one of claims 1 to 7.

12. The electrolyte is NaPF in one or more solvents selected from ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), dimethyl carbonate (DMC), ethylmethyl carbonate (EMC), gamma-butyrolactone (GBL) sulfolane, diglyme, triglyceride, tetraglyceride, dimethyl sulfoxide (DMSO), dioxolane, and mixtures thereof. ６ NaBF ４ The sodium ion cell according to claim 11, comprising >0 to 10 moles of a sodium metal salt selected from sodium bis(oxalic acid) (NaBOB) and sodium triflate (NaOTf), one or more selected from NASICON-type electrolytes, sulfide-based electrolytes, hydrogen compound-based electrolytes, β-alumina-based electrolytes, and β''-alumina-based electrolytes.

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