Carbon anode material

Abstract

The present invention relates to a carbonaceous anode material which is capable of intercalating and deintercalating alkali metal ions and which has a carbon structure comprising a core containing one or more primary carbonaceous materials. The present invention also relates to the preparation of such a carbonaceous anode material.

Description

Field of the Invention

[0001] The present invention relates to certain novel carbon-containing anode materials, to new methods for preparing such carbon-containing anode materials, to anode electrodes comprising such novel carbon-containing anode materials, and to the use of such anode electrodes in energy storage devices such as, for example, batteries (especially rechargeable batteries), electrochemical devices, and electrochromic devices. Background of the Invention

[0003] Sodium-ion batteries are in many respects similar to the lithium-ion batteries commonly used today; they are both reusable secondary batteries comprising an anode (negative electrode), a cathode (positive electrode), and an electrolyte material, both are capable of storing energy, and they both charge and discharge via similar reaction mechanisms. When a sodium-ion (or lithium-ion) battery is charged, Na + (or Li + ) ions are deintercalated from the cathode and intercalated into the anode. At the same time, charge-balancing electrons pass from the cathode through an external circuit including a charger and into the anode of the battery. The same process occurs during discharge, but in the opposite direction.

[0004] Lithium-ion battery technology has received a lot of attention in recent years and provides the preferred portable batteries for most of the electronic devices used today; however, lithium is not an inexpensive source of metal and is considered too expensive for use in large-scale applications. In contrast, sodium-ion battery technology is still in its relatively infancy but is considered advantageous; sodium is much more abundant than lithium, and some researchers predict that this will provide a cheaper and more durable way to store energy in the future, especially for large-scale applications such as storing energy on the electrical grid. However, there is still a great deal of work to be done before sodium-ion batteries become a commercial reality.

[0005] Significant research progress has been made in developing cathode electrode materials with high charge storage capacity and rate performance for both lithium-ion batteries and sodium-ion batteries; however, one area that requires more attention is the development of new and more effective anode electrode materials.

[0006] Carbon in the form of graphite has been favored as an anode material in lithium-ion batteries for some time due to its high weight and volume capacity; graphite electrodes provide a reversible capacity of greater than 360 mAh / g, comparable to the theoretical capacity of 372 mAh / g. The electrochemical reduction process involves intercalating Li + ions between the graphene layers to produce LiC6. Unfortunately, however, graphite is much less electrochemically active towards sodium, and this, combined with the fact that sodium has a significantly larger atomic radius compared to lithium, results in severely limited intercalation between the graphene layers in a graphite anode in a sodium-ion battery.

[0007] On the other hand, it has been found that anodes made of hard carbon materials (such as those described in PCT / GB2020 / 050872, US2002 / 0192553A1, US9,899,665B2, US2018 / 0287153A1) perform much more favorably in sodium-ion batteries.

[0008] Hard carbon has a disordered structure, which overcomes many of the problems of sodium ion insertion. The exact structure of hard carbon materials remains to be resolved, but generally, hard carbon is described as a non-graphitizable carbon material lacking long-range crystal order. Hard carbon has layers, but these layers are not neatly stacked in the long range, and it is a microporous material. Despite the lack of a definite crystal structure, hard carbon is isotropic at the macroscopic level. One of the reasons it is difficult to construct a general structural model of hard carbon is that the short-range order, domain size, ratio of carbon layers and micropores depend on synthesis conditions such as carbon source, carbonization and pyrolysis temperature.

[0009] In addition, unlike graphite with a graphite crystal structure in which carbon layer planes are stacked layer by layer, hard carbon has a turbostratic structure in which carbon layer planes are stacked in a three-dimensionally staggered state. Therefore, heat treatment of hard carbon, even at high temperatures (such as 3000 °C), does not result in a transition from the turbostratic structure to a graphite structure or the development of graphite microcrystals. Therefore, hard carbon is structurally completely different from graphite and can be said to include one or more non-graphitizable regions and one or more irreversibly non-graphitizable regions.

[0010] A common method for preparing hard carbon materials that can be used in electrodes for secondary battery applications involves heating a carbon-rich starting material to a temperature above 500 °C in an oxygen-free atmosphere, the carbon-rich starting materials such as minerals like petroleum coke and pitch coke; secondary plant-based 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 manure; and primary plant-derived materials such as coconut shells, coffee beans, straw, bamboo, rice husks, banana peels, etc. In the case where plant-derived and animal-derived materials are carbonized, "biochar" or biomass char is produced, which can be further processed to obtain hard carbon materials.

[0011] On the other hand, soft carbon is another form of carbon, which is also structurally different from graphite, but it is a graphitizable form of carbon and can be transformed into regions including a graphite structure at high temperatures (such as 3000 °C). However, even after this heat treatment, regions of non-graphitizable carbon material will still exist because the transformation does not result in a complete graphite structure. Therefore, soft carbon can be said to include one or more non-graphitizable regions, but cannot be said to include one or more irreversibly non-graphitizable regions.

[0012] An important feature of a commercially useful anode material is the formation of a solid electrolyte interphase (SEI) layer that naturally occurs at the interface between the electrolyte and the anode surface during the first charge cycle of a pristine alkali metal ion battery due to the deposition of liquid electrolyte decomposition products. For some time, it has been recognized that this SEI layer is a necessary component of an alkali metal ion battery, firstly because it protects the anode by inhibiting the transfer of electrons from the anode to the electrolyte, and secondly because it allows the transfer of alkali metal ions from the electrolyte to the anode, and these two factors affect the battery cycle life. Thus, an ideal SEI layer is both an ionic conductor and an electrical insulator. However, the formation of the SEI layer necessarily consumes a portion of the alkali metal ions that are deintercalated from the cathode during the initial charge cycle, which in turn means that they cannot be used in future charge / discharge cycles. Since there is a fixed inventory of charge carriers in a sealed rechargeable battery, this loss of available alkali metal ions results in an irreversible loss of capacity. The present work aims to control the formation of the SEI layer (in particular, to control the stability of the SEI layer) in order to maximize its ionic conduction and electron insulation properties and to minimize the irreversible specific capacity.

[0013] As described below, the present applicant has designed the surface chemistry, morphology, crystallography, thickness, and pore structure of the anode electrode material in order to control the stability and robustness of the SEI layer and thereby minimize the irreversible capacity loss during the first cycle.

[0014] CN 108963252 A discloses an anode material comprising a hard carbon core, which is then coated with binchotan and heated to 1500 °C. However, this method does not result in any design of the surface chemistry of the hard carbon material because even at this high temperature, the hard carbon cannot be chemically bonded to the binchotan.

[0015] Accordingly, and in particular, the present invention provides novel carbonaceous anode materials having an outer surface designed to have specific chemical and / or physical properties, which can be used to establish an optimized, stable, and robust SEI layer while minimizing the irreversible capacity. In addition, the present invention provides a new method for preparing such surface-designed carbonaceous anode materials. This method will be cost-effective, especially on a commercial scale, and will use readily available reactants. The resulting surface-designed carbonaceous anode materials will be useful in energy storage devices such as batteries (especially secondary (rechargeable) batteries), alkali metal ion batteries (especially sodium ion batteries), electrochemical devices, and electrochromic devices. Importantly, these surface-designed carbonaceous anode materials will prepare energy storage devices that provide excellent results for reversible specific capacity, cathode specific energy, first cathode sodiation specific capacity, and first discharge capacity efficiency (Coulombic efficiency, calculated as the ratio of the total charge withdrawn from the battery over the entire cycle to the total charge input into the battery), as well as a significantly reduced irreversible capacity (first cycle loss). In addition, compared to similar non-surface-designed carbonaceous anode materials such as the anode materials disclosed in CN108963252 A, the novel surface-designed carbonaceous anode materials of the present invention will provide surprising and advantageous processing characteristics, including a reduced moisture sensitivity and a reduced slurry viscosity for preparing electrodes.

[0016] To achieve these objects, the present invention provides a carbonaceous anode material capable of intercalating and deintercalating alkali metal ions and having a carbon structure comprising a core containing one or more primary carbonaceous materials and an outer surface containing one or more carbonized materials, wherein the one or more carbonized materials are preferably chemically bonded to the one or more primary carbonaceous materials.

[0017] As used herein, the term "core" refers to the central part of the carbon structure.

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

[0019] As used herein, the phrase "chemically bonded" refers to the formation of a chemical bond such as a covalent bond between one or more primary carbonaceous materials and one or more carbonized materials. Thus, "strong bonds" are included within the meaning of this phrase, but "weak bonds" such as van der Waals interactions are not included within the meaning of this phrase.

[0020] Since, according to the invention, the carbonized material is preferably "chemically bonded" to the primary carbonaceous material by using chemical vapor deposition, this advantageously allows for the surface design of the primary carbonaceous material. In addition, the carbonized material of the invention pyrolytically decomposes on one or more primary carbonaceous materials, and this "bottom-up synthesis method" allows carbon atoms to be deposited one by one on the outer surface of the one or more primary carbonaceous materials.

[0021] Thus, the carbonaceous anode material comprises one or more primary carbonaceous materials having an outer surface designed to exhibit specific surface properties as described below, and most desirably, the carbonaceous anode material according to the invention comprises one or more primary carbonaceous materials having an outer surface designed to exhibit an open micropore specific surface area of 0 m 2 / g to 5 m 2 / g as determined by nitrogen BET analysis. Preferably, the open micropore specific surface area determined by nitrogen BET analysis is greater than 0 m 2 / g to 5 m 2 / g.

[0022] Suitable primary carbonaceous materials are in any particulate (such as granular or powdered) form and are capable of intercalating and deintercalating sodium ions.

[0023] In one embodiment, the one or more primary carbonaceous materials may include regions selected from non-graphitizable regions and non-graphitic regions. As discussed above, hard carbon materials are examples of carbonaceous materials that include non-graphitizable regions as well as non-graphitic regions. Soft carbon materials are examples of carbonaceous materials that include graphitizable regions and non-graphitic regions.

[0024] In one embodiment, the one or more primary carbonaceous materials may include graphitizable regions and / or non-graphitic regions. An example thereof is soft carbon.

[0025] In one embodiment, the one or more primary carbonaceous materials may include non-graphitizable regions and non-graphitic regions. An example thereof is hard carbon.

[0026] In one embodiment, the one or more primary carbonaceous materials include disordered carbonaceous materials, and further preferably, they include one or more materials selected from conventional carbon anode materials (such as hard carbon anode materials); non-fully graphitized high-temperature hard carbon (e.g., hard carbon annealed to a temperature above 2000 °C but below 3000 °C when complete graphite formation occurs); carbon-metal, carbon-semimetal, or carbon-nonmetal composites (such as carbon-Sb, carbon-Sn, carbon-Si, carbon-Pb, carbon-Ti, and carbon-P, and the hard carbon analogues of these materials are particularly preferred); soft carbon materials (such as pyrolyzed ground carbon fibers); carbon-conductive additive mixtures (such as hard carbon-carbon black mixtures, and suitable carbon blacks can be Super C65 commercially available from Imerys TM materials); carbon-oxide composites (such as hard carbon-Fe2O3, hard carbon-Sb oxide, hard carbon-Sn oxide, hard carbon-Sb / Sn oxide); carbon-carbide composites (such as hard carbon-SiC composites); and activated carbon materials (such as activated hard carbon with a BET surface area > 100 m 2 / g). Conveniently, the primary carbonaceous materials can be prepared by pyrolysis (high-temperature treatment, generally greater than 700 °C to 2500 °C and generally in a non-oxidizing atmosphere comprising one or more selected from nitrogen, carbon dioxide, another non-oxidizing gas, and an inert gas such as argon) of a carbon-based starting material, such as plant-based materials, animal-derived materials (including "animal-derived waste" obtained after food has passed through the digestive tract of an animal and has been excreted from the digestive tract of the animal), 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, ideally before pyrolysis, the carbon-based starting material is purified using one or more method steps that can include carbonization (generally at a temperature of 150 °C to ≤700 °C), washing, decomposition, chemical digestion (e.g., using acidic and / or basic conditions), filtration, centrifugation, "heavy medium separation" or "sink-float separation method", using ion exchange materials, chromatographic separation techniques, electrophoretic separation techniques, using complexing agents or chemical precipitation techniques, and grinding (generally to a d 50 particle size of about 8 - 25 μm and filtering through a 15 - 25 μm sieve to exclude larger particles) to remove unwanted non-carbon-containing materials (such as metal-containing ions (such as transition metals, alkali metals, or alkaline earth metals) and non-metal-containing ions (such as phosphorus, oxygen, hydrogen)).

[0027] In one embodiment, the particle size distribution of the one or more primary carbonaceous materials ranges from about 1 nm to about 30 μm, preferably from about 1 nm to 20 μm. In particular, the applicant understands that the surface treatment of the present invention substantially does not change the particle size distribution of the one or more primary carbonaceous materials. Thus, this range applies to the particle size distribution of the one or more primary carbonaceous materials before the carbonaceous material is chemically bonded to the one or more primary carbonaceous materials and after the treatment occurs.

[0028] In one embodiment, the one or more primary carbonaceous materials have a d 10 particle size of from about 0.01 μm to about 4 μm.

[0029] In one embodiment, the one or more primary carbonaceous materials have a d 50 particle size of from about 4 μm to about 15 μm. In another embodiment, the one or more primary carbonaceous materials have a d 50 particle size of from about 1 to about 25 μm, preferably a d 50 particle size of from about 8 to about 25 μm.

[0030] In one embodiment, the one or more primary carbonaceous materials have a d 90 particle size of from about 15 μm to about 30 μm.

[0031] Desirably, the primary carbonaceous materials for the carbonaceous anode materials of the present invention comprise hard carbon and / or soft carbon materials, and further desirably, the hard carbon and / or soft carbon materials have a non-fully graphitic structure, i.e., they include non-graphitized regions.

[0032] Other preferred primary carbonaceous materials include carbon in combination with one or more elements and / or compounds (such as hard carbon, soft carbon as described above). Particularly preferred exemplary combinations include carbon / X materials, where X can 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 , carbon / phosphorus, carbon / silicon, carbon / silicon carbide (HC / SiC) or carbon / sodium silicate are suitable carbonaceous materials. Hard carbon analogs of one or more of these materials are particularly preferred. Further preferred exemplary combinations include carbon / X materials, where X can be one or more oxides of elements selected from 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 carbonaceous material may contain one or more metal ions and / or non-metal ions that can act as dopants in the final carbonaceous anode material. These metal ions and / or non-metal ions can be added to the primary carbonaceous material before treatment with the carbonized material as described below, or added to the carbon-based starting material used to prepare the primary carbonaceous material before pyrolysis. Alternatively, one or more metal ions and / or non-metal ions can be selectively retained in the carbon-based starting material before pyrolysis and will thus be carried into the primary carbonaceous material.

[0034] The surface properties of the carbonaceous anode material according to the invention have been studied using BET techniques to determine the specific surface area of open micropores, which are micropores having open entrances formed at the surface of the carbonaceous anode material. Herein, the word "surface" is literally on the outside of the carbonaceous anode particles and does not penetrate into the body of the carbonaceous anode particles. The pores designated as "micropores" are those having a diameter of less than 2 nm, and they are different from "mesopores" which are pores having a diameter of about 2 nm to 50 nm.

[0035] The applicant has found that in the case of an electrochemical cell using a surface-designed carbonaceous anode material according to the invention, significantly improved electrochemical performance can be achieved, the surface-designed carbonaceous anode material having a BET analysis using nitrogen greater than 0 m 2 / g up to a maximum value of 5 m 2 / g, preferably up to a maximum value of 0.9, particularly preferably up to a maximum value of 0.5 m 2 / g, highly preferably up to a maximum value of 0.3 m 2 / g, most preferably up to a maximum value of 0.15 m 2 / g of open micropore specific surface area.

[0036] As described above, when one or more primary carbonaceous materials (which are in solid form and preferably in particulate, granular or powder form) are treated with a carbonized material, a surface-designed carbonaceous anode material according to the invention is conveniently prepared. This treatment results in a carbonized material preferably chemically bonded to the primary carbonaceous material, more preferably chemically deposited on the primary carbonaceous material, and preferably chemically deposited on the primary carbonaceous material by chemical vapor deposition according to the invention.

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

[0038] As used herein, the "carbonized material" is preferably a carbon-rich solid material derived from one or more secondary carbonaceous materials. Most particularly, the present invention uses such a carbonized material as an extremely thin deposit on the outer surface of one or more primary carbonaceous materials. Although the carbonized material is preferably deposited substantially uniformly on the inner core surface, it is important to note that the deposit need not be in the form of a complete layer or a uniform coating (i.e., the primary carbonaceous material and the deposited carbonized material need not be in a core / full-shell arrangement). However, the deposited material preferably has a thickness of from 1 nm to less than 500 nm, more preferably from 10 nm to less than 500 nm, and highly preferably from 10 nm to 250 nm. Ideally, 10% to 90% of the surface area of the outer surface of one or more primary carbonaceous materials will be covered by the carbonized material derived from one or more secondary carbonaceous materials. The mass of the deposit is also extremely small (generally 2.2 ± 0.8 wt% deposited every 30 minutes). Thus, the carbonized material substantially does not change the particle size distribution of the one or more primary carbonaceous materials as discussed above.

[0039] Suitable secondary carbonaceous materials from which the carbonized material is preferably derived can be selected from one or more organic and / or hydrocarbon materials such as alkanes, alkenes, alkynes or aromatic hydrocarbons, which can be straight-chain, branched-chain or cyclic. The secondary carbonaceous materials themselves can be derived from coal-based or petroleum-based tars or pitches, oils or plant-based materials. Particularly preferred are secondary carbonaceous materials comprising one or more gaseous hydrocarbons having the following general formula: C n H 2n+2 , where 1 ≤ n ≤ 10.

[0040] In one embodiment, the secondary carbonaceous materials from which the carbonized material is preferably derived can include a vapor phase and / or a liquid phase and / or a gas phase at at least one temperature of about 950 °C or lower. Preferably, a vapor phase and / or a liquid phase and / or a gas phase at at least one temperature of about 200 °C or higher to about 950 °C or lower.

[0041] It has been found that the specific surface area of the open micropores of the carbonaceous anode material of the present invention is significantly lower than that of the open micropores of the primary carbonaceous material before treatment with a carbonized material derived from, for example, one or more secondary carbonaceous materials (as described above). It is believed that this is due to the "masking" or "blocking" of the entrances of at least a portion of the open micropores of the carbonaceous anode material (i.e., the open micropores at the surface) by the deposited carbonized material. Preferably, the presence of the chemically deposited carbonized material derived from one or more secondary carbonaceous materials results in a reduction in the surface area of the surface micropores of the carbonaceous anode material of at least 40%, further preferably at least 50%, and particularly preferably at least 85% compared to the surface area of the open micropores of the primary carbonaceous material before treatment with the carbonized material. The highly reduced surface area of the open micropores seems to support the applicant's current understanding that the deposited carbonized material only blocks the surface (open) micropores. In addition, this view is further supported by the fact that no significant weight increase of the primary carbonaceous material is measured after treatment with the carbonized material.

[0042] As disclosed above, the present invention provides a carbonaceous anode material comprising a carbonized material deposited or partially deposited on the outer surface of a primary carbonaceous material.

[0043] The carbonized material can be a "soft" carbonaceous substance that will be graphitized to some extent during the carbonization process, and the presence of the graphitized material can be confirmed by, for example, Raman spectroscopy, X-ray diffraction, or high-resolution transmission electron microscopy. However, it is important to control the formation of the carbonaceous anode material such that it has a degree of graphitization suitable for the chemical properties of the particular battery for which it is used. For example, in the case of a Na-ion battery, the graphitization is highly preferably limited to the level often observed in conventional hard carbon materials, i.e., since graphite is much less electrochemically active towards sodium, for the purpose of reversible sodium intercalation, it is desirable to avoid highly graphitized soft carbonaceous substances on the surface of the primary carbonaceous material. However, for a lithium-ion battery, the situation will be the opposite.

[0044] Care must be taken to avoid the formation of highly graphitic regions as these catalyze various parasitic reactions (such as when propylene carbonate (PC) is used in the electrolyte composition). Thus, it has been found that extreme annealing does not improve the carbon anode efficiency. On the other hand, it has been found that the surface treatment according to the present invention systematically improves the efficiency of the carbonaceous anode material, regardless of the electrolyte system. However, the method of the present invention does not affect the volume of the closed pores. This is evident from the fact that the primary carbonaceous material before and after treatment with the carbonized material yields similar (de)intercalation potential curves for sodium.

[0045] Another preferred characteristic of the surface of the carbonaceous anode material according to the present invention is the extremely low degree of surface oxidation. The presence of compounds having oxygen-containing groups (such as C-O, C=O, and C(=O)OH functional groups) on the surface of carbonaceous materials is known to readily act as permanent anchor points for the introduced charge carriers and as platforms for unwanted parasitic reactions; both of these factors will potentially contribute to the first-cycle loss when these carbonaceous materials are used as anode materials. Advantageously, the carbonaceous anode material according to the present invention has a surface oxygen content measured by X-ray photoelectron spectroscopy (XPS) of from 0 atomic percent (atm.%) to less than 2.5 atm.%, preferably from 0 atm.% to less than 1.5 atm.%, and highly preferably from 0 atm.% to less than 1 atm.%. Thus, treating one or more primary carbonaceous materials with a carbonized material (such as derived from one or more secondary carbonaceous materials) according to the present invention has the effect of reducing the surface oxygen content of the primary carbonaceous materials by at least 30 atm.%, preferably at least 50 atm.%, and further preferably at least 90 atm.%. In some embodiments, the surface oxygen atoms can be reduced by nearly 100 atm.%.

[0046] The specific surface area of the carbonaceous anode material is generally also considered to be another useful factor affecting the degree of irreversible capacity of the first-cycle loss; the higher the specific surface area, the higher the sensitivity of the anode material to over-stabilizing the SEI layer, thereby increasing the irreversible capacity. However, in the case of the present invention, although treating one or more primary carbonaceous materials with a carbonized material (such as derived from one or more secondary carbonaceous materials) does reduce the specific surface area of the carbonaceous anode material by about 30%, this reduction is not as significant as the reduction in the surface micropore surface area, which can be as high as 87%. All specific surface area values given in this application are determined using BET N2 analysis. Figure 1 The mechanism by which the surface of the carbonaceous anode material according to the present invention can produce a significant reduction in the observed open (surface) micropore surface area while recording a minimal reduction in the total surface area is discussed in detail in the following experimental section.

[0047] According to the present invention, one or more primary carbonaceous materials are treated with one or more secondary carbonaceous materials by contacting the one or more primary carbonaceous materials with a carbonized material (such as derived from one or more secondary carbonaceous materials) to obtain a carbonaceous anode material with a desired surface design.

[0048] Contacting the primary carbonaceous material with the carbonized material can be achieved using any suitable method, such as directly contacting the primary carbonaceous material with the carbonized material or contacting the primary carbonaceous material with one or more secondary carbonaceous materials and then promoting the formation of the carbonized material from the one or more secondary carbonaceous materials.

[0049] Suitably, contacting a primary carbonaceous material with one or more secondary carbonaceous materials can involve a solvent-mediated step in which the solid primary carbon-based material is mixed with one or more solvents and / or other liquids in which the secondary carbonaceous material is dissolved / dispersed, and then the solvent / dispersant is removed prior to carbonization of the secondary carbonaceous material. Alternatively, prior to carbonization of the secondary carbonaceous material, a mechanochemical step can be used in which one or more primary and secondary carbonaceous materials are mixed together (without a solvent or other dispersant or with a reagent that aids mixing). Or further alternatively, a diffusion-based system is used in which one or more primary carbonaceous materials in solid form are contacted with one or more secondary carbonaceous materials in vapor and / or gaseous form, followed by heating to carbonize the secondary carbonaceous material.

[0050] In a second aspect, the present invention provides a method for preparing a carbonaceous anode material capable of intercalating and deintercalating alkali metal ions and having a carbon structure, the method comprising: contacting a core comprising one or more primary carbonaceous materials in solid form with a carbonizing material at a temperature of up to 950 °C, thereby producing a carbonaceous anode material having an open micropore specific surface area of 0 m 2 / g to 5 m 2 / g as determined by nitrogen BET analysis.

[0051] In one embodiment, the outer surface can be designed to exhibit an open micropore specific surface area of greater than 0 m 2 / g to 5 m 2 / g as determined by nitrogen BET analysis.

[0052] Desirably, the core does not consist of or is not substantially composed of one or more primary carbonaceous materials selected from graphite and materials having a fully graphitic structure. In one embodiment, the core can be substantially composed of the one or more primary carbonaceous materials and preferably can consist of the one or more primary carbonaceous materials.

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

[0054] The heating conditions will be selected to i) (in the case where the carbonized material is pre-formed before contacting the primary carbonaceous material) promote the vapor deposition of the carbonized material on the surface of the primary carbonaceous material, or ii) promote the carbonization of one or more secondary carbonaceous materials already on the surface of the primary carbonaceous material, or iii) promote the carbonization of one or more secondary carbonaceous materials and subsequent deposition of the resulting carbonized material on the surface of the primary carbonaceous material.

[0055] In each case, the end result will be the formation of chemical bonds such as covalent bonds between one or more primary carbonaceous materials and one or more carbonized materials. Thus, one or more carbonized materials will be chemically bonded to the surface of one or more primary carbonaceous materials, preferably chemically deposited on the surface of one or more primary carbonaceous materials.

[0056] Preferably, the temperature used is lower than the temperature that would cause excessive graphitization of the carbonized material, especially (as discussed above) when the resulting carbonaceous anode material is used in a sodium-ion battery. However, importantly, the temperature used in the method according to the present invention will cause the carbonized material to be chemically bonded to the primary carbonaceous material.

[0057] As described above, therefore, the secondary carbonaceous material from which the carbonized material is preferably derived can include a vapor phase and / or a liquid phase and / or a gas phase at at least one temperature of about 950 °C or lower. Preferably, a vapor phase and / or a liquid phase and / or a gas phase at at least one temperature of about 200 °C or higher to about 950 °C or lower.

[0058] A maximum temperature of 930 °C is preferred, a maximum temperature of 900 °C is highly preferred, and a maximum temperature of 880 °C is particularly preferred. The minimum heating temperature is any temperature at which carbonization can occur, and it will depend on the secondary carbonaceous material used. A minimum temperature of 200 °C is generally sufficient, but lower temperatures may also be possible if a catalyst or other reagent is used to lower the activation energy required for the thermal catalytic decomposition and carbonization of the secondary carbonaceous material. 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 carbonaceous materials from which the carbonized material is preferably derived can be selected from one or more organic and / or hydrocarbon materials such as alkanes, alkenes, alkynes or arenes, which can be straight-chain, branched-chain or cyclic. The secondary carbonaceous material itself can be derived from coal-based or petroleum-based tar or pitch, oil or plant-based materials. Secondary carbonaceous materials containing one or more gaseous hydrocarbons having the following general formula are particularly preferred: C n H 2n+2 , where 1 ≤ n ≤ 10.

[0060] In a preferred method of the present invention, when a primary carbonaceous material is contacted with a secondary carbonaceous material of a fluid (liquid, vapor or gas) or a preformed carbonized material of a fluid (liquid, vapor or gas), the total pressure, total flow rate, and individual partial pressures and individual flow rates of the reactants are optimized to ensure that the correct amount of carbonized material is deposited on the primary carbonaceous material. The preferred total pressure, total flow rate, and individual partial pressures and individual flow rates of the secondary carbonaceous material are respectively in the ranges of 10 -6 to 3×10 7 Pa, 0.001 to 1000 L / min, 10 -6 to 3×10 7 Pa and 0.001 to 1000 L / min, and more preferably in the ranges of 10 4 to 10 6 Pa, 0.01 to 100 L / min, 10 4 to 10 6 Pa and 0.01 to 100 L / min, and highly preferably respectively in the ranges of 5×10 4 to 5×10 5 Pa, 0.1 to 10 L / min, 5×10 4 to 5×10 5 Pa and 0.1 to 10 L / min.

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

[0062] In a further preferred method of the present invention, the concentration of the carbonized material used to contact one or more primary carbonaceous materials and / or the concentration of one or more secondary carbonaceous materials are preferably in the range of 0.001 - 100 vol%, preferably 0.01 - 10 vol%, more preferably 0.01 to 5 vol% and highly preferably 0.05 - 0.1 vol% in the carrier gas for the gaseous secondary carbonaceous material, and preferably in the range of 0.001 - 100 vol% in the solvent or carrier liquid for the liquid and semi-solid (such as pitch, tar, oil) secondary carbonaceous materials.

[0063] In another further 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 more likely the carbonized material is to be over-graphitized; and ii) ensure that it is long enough to chemically deposit enough carbonized material to block at least a portion of the open micropores, as discussed above.

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

[0065] An annealing time of from 5 minutes to 120 minutes is preferred, and an annealing time of from 30 minutes to 90 minutes is particularly preferred. The annealing time is the time 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 bringing one or more primary carbon-containing materials in solid form into contact with the carbonized material is carried out using any method required to ensure that at least a portion of the surface of each particle of the primary carbon-containing material is in contact with the carbonized material. Suitable methods include: stirring or agitating the primary carbon-containing material when in contact with the carbonized material, spraying the particles of the primary carbon-containing material into an atmosphere containing the vaporized carbonized material, and spreading the primary carbon-containing material on a flat plate or wide-mouth reaction vessel prior to the introduction of the carbonized material.

[0067] Furthermore, in a particularly preferred method of the present invention, it is desirable to carry out the step of bringing one or more primary carbon-containing materials in solid form into contact with the carbonized material in the final stage of the method of the present invention. More particularly, it is highly desirable to carry out this step after any grinding treatment (such as milling, grinding, crushing, etc.) of the one or more primary carbon-containing materials. This advantageously avoids disturbing the outer surface of one or more carbonized materials that are chemically bonded to the one or more primary carbon-containing materials. For example, a post-surface treatment including a grinding treatment can cause the passivated surface to crack and expose micropores.

[0068] To avoid any doubt, within the meaning of this phrase, post-surface treatment steps such as mixing an active material with a binder, electrode printing (such as coating), and electrode calendering (such as rolling) are not considered to be "grinding treatments".

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

[0070] In a third aspect, the present invention provides an alkali metal ion battery comprising at least one negative electrode (anode) as described above. Preferably, the negative electrode (anode) has an open micropore specific surface area determined using nitrogen BET analysis of from greater than 0 m 2 / g to 5 m 2 / g.

[0071] The alkali metal ion battery will further include a positive electrode (cathode) which preferably comprises one or more positive electrode active materials capable of intercalating and deintercalating alkali metals, and which is preferably selected from oxide-based materials, polyanion materials, and Prussian blue analogue-based materials. Particularly preferably, the one or more positive electrode active materials comprise one or more selected from alkali metal-containing oxide-based materials and alkali metal-containing polyanion materials, wherein the alkali metal is one or more alkali metals selected from sodium and / or potassium, and optionally combined with lithium. Certain positive electrode active materials contain lithium as a minor alkali metal component, i.e., the amount of lithium is less than 50% by weight of the total alkali metal content, preferably less than 10% by weight of the total alkali metal content, and desirably less than 5% by weight of the total alkali metal content.

[0072] The most preferred positive electrode active material is a compound of the following general formula:

[0073] A 1±δ M 1 V M 2 W M 3 X M 4 Y M 5 Z O 2-c

[0074] where

[0075] A is one or more alkali metals selected from sodium, potassium, and lithium;

[0076] M 1 comprises one or more redox-active metals in the +2 oxidation state,

[0077] M 2 comprises metals with an oxidation state greater than 0 to less than or equal to +4;

[0078] M 3 comprises a metal in the +2 oxidation state;

[0079] M 4 comprises metals with an oxidation state greater than 0 to less than or equal to +4;

[0080] M 5 comprises a metal in the +3 oxidation state;

[0081] where

[0082] 0 ≤ δ ≤ 1;

[0083] V > 0;

[0084] W ≥ 0;

[0085] X ≥ 0;

[0086] Y ≥ 0;

[0087] At least one of W and Y > 0

[0088] Z ≥ 0;

[0089] C is in the range of 0 ≤ C < 2;

[0090] wherein V, W, X, Y, Z, and C are selected to maintain electrochemical neutrality.

[0091] For the avoidance of doubt, the term "one or more alkali metals selected from sodium, potassium, and lithium" shall be construed to include: Na, K, Li, Na+K, Na+Li, K+Li, and Na+K+Li.

[0092] Ideally, metal M 2 comprises one or more transition metals and is 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 comprises one or more transition metals, preferably selected from manganese, titanium, and zirconium; and M 5 is preferably one or more selected from aluminum, iron, cobalt, tin, molybdenum, chromium, vanadium, scandium, and yttrium. A cathode active material having any crystal structure can be used, and preferably the structure will be O3 or P2 or a derivative thereof, but specifically, it is also possible that the cathode material will comprise a mixture of phases, i.e., it will have a non-uniform structure composed of several different crystal forms.

[0093] Highly preferred positive electrode active materials include transition metal-containing compounds containing sodium and / or potassium, and sodium transition metal nickelate compounds are 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, oxymetallates Prussion blue analogs, and Prussioan whiteanalogs. Specific examples include O3 / P2-A 0.833 Ni 0.317 Mn 0.467 Mg 0.1 Ti 0.117 O2, 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-A2 / 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)3A3V2(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, wherein "A" is one or more alkali metals selected from Li, Na and K, preferably Na and / or K, most preferably Na.

[0094] Advantageously, the alkali metal ion battery according to the present invention can use an electrolyte in any form, i.e., a solid, liquid or gel composition can be used, and suitable examples include; 1) liquid electrolytes such as > 0 to 10 moles of alkali metal salts such as NaPF6, NaBF4, sodium bis(oxalato)borate (NaBOB), sodium trifluoromethanesulfonate (NaOTf), LiPF6, LiAsF6, LiBF4, LiBOB, LiClO4, LiFSi, LiTFSi, lithium trifluoromethanesulfonate and mixtures thereof, which are in one or more solvents selected from ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), (preferably in a ratio of 1:2:1 weight / weight of EC:DEC:PC as a mixture), γ - butyrolactone (GBL) sulfolane, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, dimethyl sulfoxide (DMSO), dioxolane and mixtures thereof, all of which may or may not have 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)); 2) gel electrolytes based on any one of the following matrix materials used alone or in combination with each other; or 3) solid electrolytes such as: NASICON - type such as Na3Zr2Si2PO 12 of the NASICON type, sulfide - based such as Na3PS4 or Na3SbS4, such as Na2B 10 H 10 -Na2B 12 H 12Hydride-based or β-alumina-based such as Na2O.(8-11)Al2O3 or related β"-alumina-based such as Na2O.(5-7)Al2O3). Known electrolyte additives such as 1,3-propylene glycol cyclic sulfate (PCS), P123 surfactant, tris(trimethylsilyl) phosphite (TMSP), tris(trimethylsilyl) borate (TMSB), 1-propene-1,3-sultone, 1,3-propane sultone may also be included in the electrolyte, and binders such as polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), poly(methyl methacrylate) (PMMA), sodium carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) may also be included in the electrolyte.

[0095] It should be noted that in addition to being an excellent anode material, the surface-designed carbon-containing material of the present invention also offers additional commercial advantages.

[0096] The first of these advantages relates to improved moisture sensitivity. Due to the extremely low level of open microporosity of the surface-designed carbon-containing anode material of the present invention, the surface-designed carbon-containing anode material of the present invention absorbs significantly less atmospheric moisture upon exposure than non-surface-designed primary carbon materials. This not only makes it easier to handle the applicant's anode material during anode preparation, but also reduces the moisture content of the resulting anode coating and the finished battery.

[0097] The second unexpected advantage relates to the improvement of the viscosity of the electrode slurry containing the carbon-containing anode material according to the present invention. During battery preparation, the viscosity of the electrode slurry should not be overlooked, as this will make an important difference to the smooth running of the process and the quality control of the resulting electrode. The electrode materials (active material, binder, and additive) are generally mixed and dispersed in an organic or aqueous solvent so that they can be coated on the current collector. During the coating process, the solvent evaporates and leaves the dry components. Insufficient viscosity results in a too-soft slurry, and this may lead to misaligned coating edges; meanwhile, an overly viscous slurry will cause process problems as the slurry will not run as smoothly as it should. This adversely affects the quality of the dried coating. Generally, electrode materials with a reduced surface area require less solvent to achieve a given optimal viscosity. From a cost perspective, this is advantageous. Therefore, due to the lower microporous surface area of the surface-designed carbon-containing anode material according to the present invention, the surface-designed carbon-containing anode material according to the present invention exhibits a lower viscosity for the same solid content, and this results in a smoother surface morphology and a purer surface chemistry. Cost can be saved by using less solvent to obtain electrodes of good quality.

[0098] As demonstrated in the specific examples discussed below, the use of the carbonaceous anode material according to the present invention enables advantageous improvements in electrochemical performance, which can be summarized as follows: i) The irreversible capacity and the first-cycle loss of the Na-ion full cell characterized by the carbonaceous material are as low as 25.2 mAh / g and 8.6%, respectively. This is a significant reduction compared to the values of 54.9 mAh / g and 16.8% obtained from the reference cells characterized by conventional hard carbon anodes and other identical chemistries and compositions; ii) The Na-ion full cell characterized by the carbonaceous anode material of the present invention shows significantly improved capacity retention and cycling stability at faster charge and discharge rates up to ±3C; iii) The carbonaceous anode materials according to the present invention have a reduced water adsorption rate, and the Na-ion full cells characterized by these carbonaceous anode materials have improved cycling stability due to their reduced total water content. Brief Description of the Drawings

[0100] The present invention will now be described with reference to the following drawings, in which:

[0101] Figure 1 Schematic representations showing the particles of the pristine primary carbonaceous material and the particles of the surface-engineered carbonaceous anode material according to the present invention.

[0102] Figure 2 Flow chart showing the preferred method of the present invention.

[0103] Figure 3 Bar graph showing the amount of surface oxygen (atm.%) present on the pristine hard carbon material compared to the same hard carbon material treated with a carbonizing material according to the present invention.

[0104] Figure 4 Bar graph showing the BET specific surface area (m 2 2 / g) of the pristine hard carbon material compared to the same hard carbon material treated with a carbonizing material according to the present invention.

[0105] Figure 5 Bar graph showing the BET micropore surface area (m 2 2 / g) of the pristine hard carbon material compared to the same hard carbon material treated with a carbonizing material according to the present invention.

[0106] Figure 6 Representative T-curve of sample material 8 according to the present invention.

[0107] Figure 7 Graph showing the voltage versus Na + + / Na capacity curve obtained for a Na-ion half cell using the carbonaceous anode material 3 according to the present invention.

[0108] Figure 8 Shows the voltage obtained for a Na-ion half-cell using the carbonaceous anode material 8 according to the present invention relative to Na + / Na capacity curve.

[0109] Figure 9 Shows the voltage obtained for a Na-ion half-cell using the carbonaceous anode material 4 (control) relative to Na + / Na capacity curve.

[0110] Figure 10 Shows the voltage obtained for a three-electrode full cell using the carbonaceous anode material 7 according to the present invention relative to the capacity curve.

[0111] Figure 11 Shows the voltage obtained for a three-electrode full cell using the carbonaceous anode material 8 according to the present invention relative to the capacity curve.

[0112] Figure 12 Shows the voltage obtained for a three-electrode full cell using the carbonaceous anode material 6 according to the present invention relative to the capacity curve.

[0113] Figure 13 Describes the cathode specific capacity, cycle life performance, and Coulombic efficiency of a full sodium-ion battery including the carbonaceous anode material 8 during rapid discharge.

[0114] Figure 14 Describes the cathode specific capacity, cycle life performance, and Coulombic efficiency of a full sodium-ion battery including the carbonaceous anode material 8 during rapid discharge.

[0115] Figure 15 Describes the cathode specific capacity, cycle life performance, and Coulombic efficiency of a full sodium-ion battery including the carbonaceous anode materials 6 and 8 during rapid discharge.

[0116] Figure 16 Describes the cathode specific capacity of a full sodium-ion battery including the carbonaceous anode material 8 during rapid charging.

[0117] Figure 17 Shows a graph of moisture content versus air exposure time to illustrate the reduced moisture sensitivity exhibited by the carbonaceous anode materials of materials 6, 7, 8, 9, and 10 prepared according to the present invention compared to material 4 (control).

[0118] Figure 18 Is a bar graph to illustrate the moisture sensitivity of electrodes prepared using the carbonaceous anode materials 7, 8, and 10 prepared according to the present invention compared to material 4 (control).

[0119] Figure 19 Shows various particle size distributions obtained using laser diffraction of a hard carbon material once.

[0120] Figure 20 Shows a scanning electron micrograph of a hard carbon material once.

[0121] Detailed Description

[0122] Model Proposed for the Structure of the Carbon-Containing Anode Material According to the Invention

[0123] Figure 1 Shows a schematic representation of a particle of a pristine carbonaceous material including a core containing a first carbonaceous material 1. Figure 1 Further shows a schematic representation of a particle of a carbonaceous anode material 10 (i.e., non - pristine) according to the surface design of the present invention, including a core containing a first carbonaceous material 1 and an outer surface 15 containing a carbonized material 35 chemically bonded to the first carbonaceous material 1. More particularly, Figure 1 Provides assistance in explaining the proposed mechanism for explaining how the carbonaceous anode material 10 according to the surface design of the present invention may exhibit a significantly reduced open micropore surface area while recording a minimal reduction in the total surface area. Figure 1 Can also help explain how the carbonaceous anode material 10 according to the surface design of the present invention has a greater resistance to moisture adsorption compared to the pristine carbonaceous material including a core containing a first carbonaceous material 1.

[0124] As Figure 1 Depicted, a representative particle of a pristine carbonaceous material including a core containing a first carbonaceous material 1 having open porosity has an irregular and non - uniform outer surface 15 formed by a plurality of open mesopores 20 and a plurality of open micropores 25. After treating a pristine carbonaceous material including a core containing a first carbonaceous material 1, for example, by the method according to the present invention, an uneven, incomplete, and extremely thin layer 30 of particles of a carbonized material 35 (e.g., derived from a secondary carbonaceous material) is deposited on the outer surface 15 of the pristine carbonaceous material including a core containing a first carbonaceous material 1 to prepare a carbonaceous anode material 10 according to the surface design of the present invention.

[0125] As Figure 1 Shown, the entrances of many of the open micropores 25 are blocked by the deposited particles of the carbonized material 35 forming the extremely thin layer 30. In Figure 1 , the blocked micropores on the surface - designed carbonaceous anode material 10 are denoted by 55. It should be understood that the extreme thinness of the uneven, incomplete layer 30 will make it highly unlikely that the entrances of the larger mesopores 20 are sufficiently covered / blocked, but the layer 30 may instead partially coat the interior of the mesopores, which may reduce the surface area of these pores, but only slightly.

[0126] The increased hydrophobicity of the carbonaceous anode material according to the surface design of the present invention can also be explained by the fact that the number of water molecules 40a that can enter the blocked or obstructed micropores 55 is reduced compared to the number of water molecules 40 that can enter the open micropores 25 in the original primary carbonaceous material 1, such that the carbonaceous material 10 according to the surface design of the present invention is more resistant to moisture than the non-surface-designed material. This is studied below.

[0127] General Method for Preparing the Carbon-Containing Anode Material According to the Invention

[0128] Figure 2 A schematic flowchart illustrating a general method of the present invention is provided. In a general method, one or more primary carbonaceous materials in particulate form are treated with a carbonizing material at 200 to 950 °C for 30 - 120 minutes. As discussed above, the carbonizing material can be a pre-prepared carbonizing material, or it can be a carbonizing material derived from one or more secondary carbonaceous materials. Ideally, the treatment process is carried out in an inert gas atmosphere. Further ideally, one or more secondary carbonaceous materials are provided at a desired concentration (as discussed above), and the gaseous secondary carbonaceous material is preferably provided in a carrier gas (preferably an inert carrier gas), and the liquid secondary carbonaceous material is preferably provided in a carrier solvent or other carrier liquid.

[0129] Details of the carbonaceous anode materials tested are given in Table 1 below:

[0130] Table 1

[0131]

[0132]

[0133] Measurement of the Sizes of the Primary Carbon Materials

[0134] Size measurements of the primary hard carbonaceous materials are carried out using laser diffraction and scanning electron microscopy. The results obtained are shown respectively in Figure 19 and 20 below. The results show the following preferred particle size distributions of the primary carbonaceous materials:

[0135] Parameters Preferred Lower Endpoint Preferred Upper Endpoint D10 [μm] 0.01 4 D50 [μm] 4 15 D90 [μm] 15 30

[0136] When the one or more primary carbonaceous materials include one or more carbon composites represented by (carbon)-X, as disclosed herein, in some cases, the particle size distribution can be different from those indicated above. This is because the size of some composites can be in the nanometer range. Thus, in one embodiment, the particle size distribution of the primary carbonaceous materials of the present invention ranges from about 1 nm to about 30 μm, preferably from about 1 nm to about 20 μm.

[0137] As far as the applicant is aware, the surface treatment of the present invention substantially does not change the particle size distribution of the primary carbonaceous material. In one example of the present invention, it was found that the mass deposition of the secondary carbonaceous material is very small (2.2 ± 0.8 wt% deposition per 30 minutes). Therefore, the particle size distribution of the primary carbonaceous material after surface treatment can be considered to be substantially the same as that of the primary carbonaceous material before surface treatment.

[0138] Measurement of the Patterned Characteristics of the Carbon-Containing Anode Material According to the Invention

[0139] As discussed above, it is important to control the graphitization level of the carbonaceous material deposited on the outer surface of the primary carbonaceous material to match the requirements of the battery chemistry using the anode material. Table 3 below compares the graphitization characteristics (graphite spacing and crystallite size in the stacking (Lc) and in-plane (La) directions) of the carbonaceous anode material designed according to the surface of the present invention with those of the non-surface-designed primary carbonaceous material (i.e., the starting material used to prepare the primary carbonaceous material).

[0140] From the results in Table 3, it can be seen that the presence of the surface design according to the present invention has no significant effect on the degree of graphitization. Therefore, it is expected that anode materials 3, 6 - 11, and 14 are highly suitable for sodium ion batteries.

[0141] Measurement of the Surface Oxygen Content (atm.%)

[0142] The amount of oxygen present on the surface of i) the carbonaceous anode material according to the present invention and ii) the primary carbonaceous material before contact with the carbonaceous material was measured using XPS, and the analysis specifications are summarized in Table 2 below. The surface oxygen content results are shown in Figure 3 in.

[0143] Table 2

[0144]

[0145] Measurement of BET surface area (m 2 / g)

[0146] BET analysis was carried out using a Micromeritics Gemini VII 2390 surface area analyzer with nitrogen as the adsorbate at liquid nitrogen temperature. Before analysis, all samples were degassed overnight at 250 °C under flowing nitrogen. The results obtained are shown in Figure 4 in.

[0147] Measurement of BET micropore surface area (m 2 / g)

[0148] By applying the model, the surface area of the micropores (open micropores, also known as the micropores on the surface of the carbonaceous anode material) into which the gas can enter can be estimated from the volume of the gas adsorbed by the material, and is calculated as the micropore surface area per gram of the carbonaceous anode material (or, in the case of the control sample, the original hard carbon-containing material). This is obtained from the 't-curve' analysis. The general t-curve consists of the amount of gas adsorbed at standard temperature and pressure relative to the thickness (nm) statistically calculated by Harkins and Jura according to the Harkins and Jura thickness equation (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 as follows. The representative t-curve of Material 8 is shown in Figure 6 as follows.

[0149] Measurement of the Moisture Content (ppm)

[0150] The moisture content of the active material and the anode electrode (coating) is measured using a CA-200 type moisture meter (coulometric titration) from MITSUBISHI CHEMICAL ANALYTECH titrator without any exposure (0 minutes) and after 30 and 60 minutes of exposure to an atmosphere with 20 - 50% relative humidity.

[0151] Results

[0152] Table 3 below summarizes the results of the graphitization characteristics, surface oxygen content, BET surface area, micropore surface area, and moisture content obtained as described above.

[0153] Table 3

[0154]

[0155] Product Analysis Using XRD

[0156] X-ray diffraction analysis is carried out using a Siemens (RTM) D5000 powder diffractometer to confirm that the required target material has been prepared, to determine the phase purity of the product material, and to determine the types of impurities present. From this information, the lattice parameters of the unit cell can be determined.

[0157] The general XRD operating conditions for analyzing the material are as follows:

[0158] Slit size: 1 mm

[0159] Range: 2θ = 10° - 60°

[0160]

[0161] Speed: 1.0 second / step

[0162] Increment: 0.025°

[0163] Electrochemical Results

[0164] An anode comprising a carbon material prepared according to the present invention is prepared by solvent casting a slurry comprising an experimental carbon material (as described above), a binder, and a solvent in a weight ratio of 92:6:2. Conductive carbon such as C5 TM carbon (Timcal) (RTM) can be included in the slurry. PVdF and styrene-butadiene rubber / carboxymethyl cellulose (SBR / CMC) are suitable binders, and N-methyl-2-pyrrolidone (NMP) or water can be used as the solvent. The slurry is then cast onto a current collector foil (such as the original carbon-coated aluminum foil) and heated until most of the solvent evaporates and an electrode film is formed. The anode electrode is then further dried under dynamic vacuum at about 120 °C and calendared to the desired thickness.

[0165] Cell Tests

[0166] For half-cell testing, the experimental carbon anode electrode is paired with a sodium metal disk as the reference and counter electrode. Glass fiber GF / A is used as the separator, and a suitable electrolyte is also used. Any suitable Na-ion electrolyte can be used, preferably it can contain one or more salts, such as NaPF6, NaAsF6, NaClO4, NaBF4, NaSCN, and sodium trifluoromethanesulfonate, in combination with one or more organic solvents, such as EC, PC, DEC, DMC, EMC, ethylene glycol dimethyl ether, esters, acetates, etc. Other additives such as vinylene carbonate and fluoroethylene carbonate can also be added. The preferred electrolyte composition contains 0.5 M NaPF6 / EC:PC:DEC.

[0167] All cells are allowed to stand for 24 hours before cycling. For three-electrode testing, the carbon anode material according to the present invention is used as the negative electrode, a standard oxide material is used as the positive electrode, and a piece of sodium is used as the reference, and all three electrodes are wetted by the same electrolyte. Two 24.5-μm thick polyethylene films are used as the separator.

[0168] The half-cell is tested using a constant current cycling technique, and the three-electrode cell is tested using a constant current-constant voltage technique.

[0169] The cells are cycled at a given current density between preset voltage limits. A commercial battery cycler from MTI Inc. (Richmond, CA, USA) or Maccor (Tulsa, OK, USA) is used. During charging, alkali ions are intercalated into the carbon anode material. During discharge, alkali ions are deintercalated from the anode and reintercalated into the cathode active material.

[0170] Results

[0171] Electrochemical testing of the experimental carbonaceous anode material 3 - half cell (versus Na + / Na)

[0172] Figure 7 The anodic sodium intercalation and deintercalation potential curves are shown as a function of the anodic specific capacity. Using the experimental carbonaceous anode material 3 according to the present invention as an example, a reversible deintercalation capacity of 315 mAh / g, an irreversible specific capacity of 36.0 mAh, and a first-cycle Coulombic efficiency of 89.8% can be achieved.

[0173] Electrochemical testing of the experimental carbon-containing anode material 8-half cell (versus Na + / Na)

[0174] Figure 8 The anodic sodium intercalation and deintercalation potential curves are shown as a function of the anodic specific capacity. Using the experimental carbonaceous anode material 8 according to the present invention as an example, a reversible specific capacity of greater than 330 mAh / g, an irreversible specific capacity of 29.1 mAh, and a first-cycle Coulombic efficiency of 91.9% can be achieved.

[0175] Electrochemical tests of the control anode material 4 (control) - half cell (versus Na + / Na)

[0176] Figure 9 The anodic sodium intercalation and deintercalation potential curves are shown as a function of the anodic specific capacity. Using the control anode material 4 according to the present invention as an example, a reversible specific capacity of 281 mAh / g, an irreversible specific capacity of 58.6 mAh, and a first-cycle Coulombic efficiency of 82.8% are obtained. Comparing these values with those of the experimental carbonaceous anode material 8 ( Figure 7 relative to Figure 8 ), it is evident that the surface treatment according to the present invention results in significantly improved electrochemical performance.

[0177] Electrochemical Tests of the Three-Electrode Full Cells of the Experimental Carbon-Containing Anode Materials 6, 7, and 8

[0178] Figures 10 - 12 The anodic and cathodic sodium intercalation and deintercalation potential curves and the cell voltage as a function of the cell capacity are shown in three voltage windows: 1.0 - 4.2 V, 1.0 - 4.1 V, and 1.0 - 4.0 V. The cells are characterized by the experimental carbonaceous anode materials 7, 8, and 6, respectively. The purpose of the three-electrode full-cell study is to measure the anodic potential with the maximum charge and to investigate the possibility of dendrite formation on the anode surface. The fact that the anodic potential with the maximum charge is safely positive in all voltage windows indicates that Na-ion batteries characterized by carbonaceous materials have no risk of dendrite formation. Since there is a Na metal reference between the anode and the cathode, this three-electrode full-cell design is not optimal for achieving the highest first-cycle Coulombic efficiency. Therefore, the carbonaceous anode materials are further tested in 0.1 Ah full-cells to verify the true first-cycle Coulombic efficiency values.

[0179] Electrochemical Tests of the Full Cells of the Experimental Carbon-Containing Anode Materials 6 - 11 and 4 (Control)

[0180] Figure 13 and 14 shows the Coulombic efficiency and the cathode discharge specific capacity as a function of the number of cycles for two comparable cells featuring an experimental carbonaceous anode material 8 as the anode. After four formation cycles of charging and discharging at C / 10, Figure 13 the cells in Figure 14 are charged at C / 5 and discharged at various rates from C / 5 up to 3C, while the cells in

[0181] Figure 15 are charged at various rates from C / 5 to 3C and discharged at C / 5 according to the same formation protocol. Both cells have a first cycle efficiency >90% and exhibit a capacity retention >98% after fast charge / discharge cycles. This indicates that the carbonaceous anode material according to the present invention has excellent fast charging and fast discharging capabilities. This may be due to the enhanced charge carrier properties of the material of the present invention.

[0182] Table 4 summarizes the FCL, the anodic irreversible specific capacity, and the cathodic reversible specific capacity of full cells featuring various experimental carbonaceous anode materials.

[0183] Table 4

[0184]

[0185] To understand the true performance improvement (reduced anodic irreversible specific capacity and first cycle loss), four comparable baseline full cells featuring a carbonaceous anode material 4 (control) are charged and discharged according to the same protocol as used for the full cells featuring experimental carbonaceous anode materials 6 - 11. The first cycle loss, anodic irreversible specific capacity, and cathodic reversible specific capacity values are summarized in Table 4.

[0186] As can be seen from Table 4, the FCL and the anodic irreversible specific capacity of the reference full cell (control) characterized by the carbonaceous anode material 4 are significantly and systematically higher than those observed in the full cells characterized by the experimental carbonaceous anode materials 6 - 10. Compared with the cathodic reversible specific capacity values seen in the cells characterized by the experimental carbonaceous anode materials 6 - 9, the higher FCL results in the control cell showing a cathodic reversible specific capacity value that is approximately 10 mAh / g less.

[0187] The experimental carbonaceous anode material 11 did not exhibit FCL and anodic irreversible specific capacity values as low as those obtained with the experimental carbonaceous anode materials 6 - 10. However, the results for anode material 11 were still lower than those of the control sample 4. It is believed that surface treatment of the primary carbonaceous material up to a maximum of 900 °C is most advantageous to avoid graphitization of the carbonaceous material to an extent that inhibits reversible (de)intercalation of sodium. In summary, maximum efficiency is shown when the primary carbonaceous material is treated according to the present invention at a temperature of 780 - 900 °C.

[0188] The full cell including an anode characterized by experimental material 8 was gradually charged from C / 5 to 10C at a constant discharge rate of C / 5. A discharge capacity retention rate greater than 60% was demonstrated throughout the test. After completion of the rapid charge test, a rated capacity close to 100% was obtained, i.e., the cathodic discharge capacity when the cell was charged and discharged at C / 5. The results are summarized in Table 5 and Figure 16 in.

[0189] Table 5

[0190]

[0191] *Approximate

[0192] Experiment Demonstrating the Reduced Moisture Sensitivity of the Carbon-Containing Anode Material According to the Invention

[0193] It is highly preferred to reduce the residual moisture content of all cell components including the electrodes, separator, and electrolyte. A key advantage of the carbonaceous anode materials according to the present invention (experimental materials 6 - 11) is that they have been found to be significantly less sensitive to moisture exposure than the raw primary carbonaceous materials (experimental material 4 (control)) that have not been treated with carbonized materials.

[0194] The moisture contents of the experimental carbonaceous anode materials 6 - 11 and the control material 4 at different exposure durations are detailed in Table 3 and Figure 17 in. Clearly, the control material 4 adsorbs a large amount of moisture upon exposure, while the carbonaceous anode materials according to the present invention have a significantly reduced moisture adsorption rate. As described above, it is believed that this reduced moisture adsorption is due to the reduced availability of surface micropores after treatment of the primary hard carbon material in the presence of the carbonized material.

[0195] Figure 18 The residual moisture contents of the anode electrodes (coatings) characterized by the control material 4 and the anode electrodes (coatings) characterized by the carbon-containing materials according to the present invention (experimental materials 7 - 10) are shown. The anode electrode (coating) containing the experimental carbon material 10 exhibits the lowest (most favorable) residual moisture content.

Claims

1. A carbonaceous anode material capable of intercalating and deintercalating alkali metal ions and having a carbon structure comprising a core containing one or more primary carbonaceous materials and an outer surface of carbonized material containing one or more chemically bonded and substantially uniformly deposited on the one or more primary carbonaceous materials, wherein the carbonaceous anode material has an open micropore specific surface area of 0 m 2 / g to 0.9 m 2 / g as determined by nitrogen BET analysis, and wherein the core does not consist of or is not substantially composed of one or more primary carbonaceous materials selected from graphite and materials having a fully graphitic structure.

2. The carbonaceous anode material according to claim 1, wherein the one or more primary carbonaceous materials include graphitizable regions and non-graphitizable regions.

3. The carbonaceous anode material according to claim 1, wherein the one or more primary carbonaceous materials include non-graphitizable regions and non-graphitizable regions.

4. The carbonaceous anode material according to claim 1, wherein the one or more primary carbonaceous materials are derived from the pyrolysis of plant-based materials, animal-derived materials, hydrocarbon materials, carbohydrate materials, and other carbonaceous organic materials.

5. The carbonaceous anode material according to claim 1, wherein the one or more primary carbonaceous materials include one or more carbon composite materials represented by (carbon)-X, wherein X is one or more elements selected from antimony, tin, phosphorus, sulfur, boron, aluminum, gallium, indium, germanium, lead, arsenic, bismuth, titanium, molybdenum, selenium, tellurium, silicon, carbon, and magnesium; or wherein X is an oxide of one or more elements selected from antimony, tin, phosphorus, sulfur, boron, aluminum, gallium, indium, germanium, lead, arsenic, bismuth, titanium, molybdenum, selenium, tellurium, silicon, carbon, and magnesium.

6. The carbonaceous anode material according to claim 1, wherein the carbonized material is derived from one or more secondary carbonaceous materials selected from organic and hydrocarbon materials.

7. The carbonaceous anode material according to claim 1, which contains at most 2.5 atomic percent oxygen on the outer surface of the carbonaceous anode material.

8. The carbonaceous anode material according to claim 1, which has at most 50 parts per million of moisture as measured using the Karl Fischer titration technique and after exposure to the ambient atmosphere for at most one hour.

9. The carbonaceous anode material according to claim 1, wherein the one or more primary carbonaceous materials have a particle size ranging from 1 nm to 30 μm.

10. The carbonaceous anode material according to any one of claims 1 to 9, wherein the one or more primary carbonaceous materials include hard carbon.

11. A method for preparing a carbonaceous anode material capable of intercalating and deintercalating alkali metal ions and having a carbon structure, the method comprising: At a temperature of up to 950 °C, a core containing one or more primary carbonaceous materials in solid form is brought into contact with a carbonized material by one or more of chemical vapor deposition, plasma enhanced deposition, atomic layer deposition, and physical vapor deposition, thereby producing a carbonaceous anode material having one or more chemical bonds and a carbonized material deposited substantially uniformly on the outer surface of the one or more primary carbonaceous materials, and wherein the carbonaceous anode material has an open micropore specific surface area of 0 m 2 / g to 0.9 m 2 / g as determined by nitrogen BET analysis, and wherein the core does not consist of or is not substantially composed of one or more primary carbonaceous materials selected from graphite and materials having a fully graphitic structure.

12. The method according to claim 11, wherein the step of bringing the primary carbonaceous material into contact with the carbonized material is achieved by bringing the primary carbonaceous material into contact with one or more secondary carbonaceous materials and then promoting the formation of the carbonized material from the one or more secondary carbonaceous materials.

13. The method according to claim 12, wherein the one or more secondary carbonaceous materials include a vapor phase and / or a liquid phase and / or a gas phase at at least one temperature of 950 °C or lower.

14. A sodium-ion battery, which includes a cathode electrode, an anode electrode, and an electrolyte, wherein the anode electrode contains the carbonaceous anode material according to any one of claims 1 to 10.

15. The sodium ion battery according to claim 14, wherein the electrolyte comprises one or more selected from the following: 0 to 10 moles of a sodium metal salt selected from NaPF6, NaBF4, sodium bis(oxalate) (NaBOB), sodium trifluoromethanesulfonate (NaOTf), in one or more solvents selected from ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), γ-butyrolactone (GBL), sulfolane, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, dimethyl sulfoxide (DMSO), dioxolane, and mixtures thereof; NASICON-type electrolytes, sulfide-based electrolytes, hydride-based electrolytes, β-aluminum-based electrolytes, and β''-aluminum-based electrolytes.

16. A lithium ion battery comprising a cathode electrode, an anode electrode, and an electrolyte, wherein the anode electrode comprises a carbon-containing anode material according to any one of claims 1 to 10.

17. The lithium ion battery according to claim 16, wherein the electrolyte comprises LiPF6, LiAsF6, LiBF4, LiBOB, LiClO4, LiFSi, LiTFSi, lithium trifluoromethanesulfonate, and mixtures thereof, and one or more solvents selected from ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), γ-butyrolactone (GBL), sulfolane, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, dimethyl sulfoxide (DMSO), dioxolane, and mixtures thereof.

18. An alkali metal ion battery comprising an anode electrode, the anode electrode comprising one or more materials according to any one of claims 1 to 10, the material having a moisture content of less than 200 parts per million as measured using Karl Fischer titration technique.

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