Graphite material, method for producing the graphite material, and use of the graphite material

Abstract

The present invention relates to a graphite material having the following characteristics: a) a pH of at least 5.4 as described herein, b) a Scott density of 0.11 g / cm as measured as described herein 3 as follows, and c) a Raman D / G intensity ratio measured with a laser having an excitation wavelength of 632.8 nm of 0.220 to 0.420.

Description

Technical Field

[0001] The present invention relates to a graphite material having an advantageous balance of low oxidizability and low electrical resistance, a method for manufacturing such a graphite material, and uses of the graphite material.

Background Art

[0002] Carbon-based conductive aids are used in various primary and secondary batteries, such as alkaline zinc / manganese dioxide batteries, zinc-carbon batteries, lithium primary batteries and rechargeable batteries, nickel-cadmium batteries, lead-acid batteries, nickel-metal hydride batteries, lithium-sulfur batteries, lithium-air batteries, metal-air batteries using metals such as zinc and iron, fuel cells, and capacitor systems. The conductive aid is applied to the electrodes of an electrochemical cell to reduce the electrode resistance. Carbonaceous powder materials are often selected as conductive aids because they are lightweight and inert to acidic and alkaline electrolytes. The conductive aid generally does not contribute to the electrochemical process of the electrode. This means that it is desirable to minimize the amount of conductive aid used for increasing the energy density of the cell. Typical carbon-based conductive aids used are graphite fine powder and conductive carbon black (see, for example, M.E. Spahr, Lithium-ion Batteries-Science and Technology, M. Yoshio, R.J. Brodd, A. Kozawa (Eds.), Springer, New York, 2009, Chapter 5).

[0003] Graphite is the most common allotrope of carbon and is characterized by good electrical, thermal, and lubricating properties. Graphite is widely used as a conductive aid in the above-described battery and fuel cell applications due to its good electrical conductivity, low density, and generally excellent chemical inertness. Lithium-ion batteries are used for household and industrial applications. A lithium-ion battery usually consists of a positive electrode, a negative electrode, an electrolyte, and a separator. The negative electrode active material used is natural graphite or synthetic graphite. Materials such as lithium cobalt oxide (LiCoO2) and manganese spinel (LiMn2O4) are mainly used as the positive electrode active material. Since the positive electrode active material has a high electrical resistance, the electrical resistance of the positive electrode is reduced by using a carbon-based conductive additive. Lead-acid batteries are used for household and industrial applications. A lead-acid battery usually consists of a positive electrode, a negative electrode, an electrolyte, and a separator. By adding a small amount of conductive carbon to the negative electrode of a lead-acid battery, for example, when applied to the use of a hybrid electric vehicle (HEV), the cycle life and charge acceptance when the battery operates in a high-rate partial state of charge (HRPSoC) are improved (see, for example, K. Nakamura, M. Shiomi, K. Takahashi, M. Tsubota, Journal of Power Sources 59 (1996) 153, M. Shiomi, T. Funato, K. Nakamura, K. Takahashi, M. Tsubota, Journal of Power Sources, 64 (1997), 147, and D. Pavlov, P. Nikolov, T. Rogachev, Journal of Power Sources 196 (2011), 5155-5167).

[0004] Alkaline batteries are used for household and industrial applications. Generally, a primary alkaline cell includes an anode, a cathode, a permeable electrolyte separator between the anode and the cathode, and an alkaline electrolyte generally composed of an aqueous solution of potassium hydroxide that contacts both the anode and the cathode. The cathode active material includes manganese dioxide or nickel oxyhydroxide, or a mixture thereof, and a conductive aid such as graphite to increase the electrical conductivity of the cathode. The cathode material of an alkaline battery is manganese dioxide (EMD electrolytic manganese dioxide). Fuel cells are used industrially. A fuel cell typically consists of a membrane, a catalyst layer, a gas diffusion layer, a microporous layer, and a bipolar plate. The bipolar plate is typically manufactured by molding a highly conductive graphite-polymer compound. Graphite needs to have high electrical conductivity and (especially at the cathode where oxygen gas is in direct contact with the bipolar plate) oxidation resistance. Also, since the gas diffusion layer and the microporous layer are in direct contact with oxygen, they need to be conductive. By using graphite with high oxidation resistance and high conductivity, the performance of the fuel cell system can be improved. One of the drawbacks of using a graphite material as a conductive aid is its limited stability in an oxidizing environment. This is particularly pronounced under harsh conditions such as those found in electrochemical systems. When used as a conductive aid, oxidation of the graphite material surface can reduce the electrical conductivity of the powder. Furthermore, the loss of graphite during oxidation can cause the system to lose its function. Additionally, as oxidation progresses further, gases such as CO and CO2 are significantly generated, potentially causing dangerous degradation to the system in which graphite is used.

[0005] Therefore, an important characteristic of the graphite material for such applications is its resistance to oxidation. As described in U.S. Patent No. 7,273,680, the oxidation resistance of a specific graphite is related to the specific surface area of the graphite particles, and it is considered that the smaller the surface area, the higher the oxidation resistance of the graphite. This document teaches that oxidation-resistant graphite can be produced by heat-treating high-purity synthetic or natural graphite at a high temperature of over 2500°C or over 3000°C in an inert atmosphere. When using a graphite material as a conductive aid, the electrical resistance of the material is another very important parameter. Electrical resistance is a material property related to the degree of resistance of the material to an electric current. A material with a low resistivity is a material that can easily conduct an electric current. Summary of the Invention Problems to be Solved by the Invention

[0006] The object of the present invention is to provide a novel graphite material having excellent properties as compared with conventional graphite materials. In particular, the object of the present invention is to provide a graphite material in which the balance between low oxidizability and low electrical resistance is improved, and products containing these graphite materials. Another object of the present invention is to provide a suitable method for manufacturing such a graphite material.

Means for Solving the Problems

[0007] The inventors have surprisingly found that by selecting an appropriate graphite starting material and carefully controlling the process parameters, a graphite material having excellent properties can be prepared. In particular, the inventors have surprisingly found that a graphite material having a pH of at least 5.4, a Scott density of 0.11 g / cm 3 or less, and a Raman D / G intensity ratio measured with a laser having an excitation wavelength of 632.8 nm in the range of 0.220 to 0.420 can achieve an optimal balance between low oxidizability and low electrical resistance. Furthermore, the present invention provides a method for manufacturing a graphite material, comprising: a) subjecting a graphite starting material to a surface modification process including heating to a temperature in the range of 300 to 1700 °C in the presence of an oxidizing process gas, such as, but not limited to, oxygen, air, oxygen-enriched air, carbon dioxide, ozone, steam, NO x (including but not limited to NO2, NO, N2O), or any combination thereof; and b) obtaining the graphite material described herein.

[0008] The present invention further relates to a battery containing the graphite material described herein, preferably a negative electrode or a positive electrode for incorporation into a battery containing the graphite material described herein as a conductive aid. The present invention further relates to a battery containing the graphite material described herein, which battery is preferably a lithium ion battery, a lead storage battery, an alkaline battery or a NiCd battery. The present invention further relates to a fuel cell containing the graphite material described herein. Furthermore, the present invention relates to the use of the graphite material described herein in any one of a lithium-ion battery, a lead-acid battery, an alkaline battery, a NiCd battery, and a fuel cell. The graphite material of the present invention can be advantageously used in a battery or a fuel cell. By using a graphite material having low oxidizability and low electrical resistance, there are advantages of extending the life of the battery or fuel cell, delaying the decrease in the efficiency of the battery or fuel cell, and improving safety by reducing the risk of decomposition of graphite into gas. Furthermore, when the electrical resistance is low, the amount of the conductive assistant used in the battery or fuel cell can be reduced, and as a result, the cell capacity can be increased.

Mode for Carrying Out the Invention

[0009] Definition In the context of the present invention, the term "electrical resistance" ρ, which may also be referred to as resistivity, volume resistivity, or specific electrical resistance, is a material property related to the degree of resistance of a material to an electric current, and is expressed in SI units as ohm·meter or ohm·centimeter (Ω·m or Ω·cm, respectively).

[0010] The volume resistivity can be measured by the following method. ● Prepare a mixture containing 95% electrolytic manganese dioxide and 5% by mass of graphite (when synthetic or natural graphite is used as the graphite starting material) or 3% by mass of graphite and 97% electrolytic manganese dioxide (when expanded graphite is used as the graphite starting material). ● Press 10 g of the obtained mixture at 180 Nm using a die having a length of 50 mm and a width of 12 mm to obtain a block. ● Measure the height (H) and width (W) of the block. ● Measure the electrical resistance (R) of the block with a four-probe probe. ● Calculate the resistivity as H×R / D. Here, D is the distance between the probe measurement pins.

[0011] A material having a low resistivity is a material that easily conducts an electric current. In the context of the present invention, the term "oxidizability" refers to the resistance of a material to oxidation. Oxidizability is measured by aging a material in an aqueous KOH solution and measuring the absorbance of the solution. In particular, the oxidizability of a graphite material can be measured by a method including the following steps. a) Preparing a mixture of 40% by mass of a graphite material and 60% by mass of electrolytic manganese dioxide; b) Pressing the mixture of step a) together and applying a pressure of 6.8 metric tons / cm 2 for 5 seconds to form a tablet; c) Aging the tablet in 20 mL of a 30% by mass KOH aqueous solution at 60°C to obtain an aging solution; d) Filtering the aging solution to obtain a filtered aging solution; e) Measuring the absorbance at 410 nm with a UV-Vis spectrophotometer; and f) Evaluating the oxidizability of the tested graphite material as the measured absorbance value.

[0012] Oxidizability is defined as the measured absorbance value. The lower the measured absorbance, the lower the oxidizability and the higher the oxidation resistance of the graphite material. In the context of the present invention, the term "conductive aid" refers to a material applied to the electrodes of an electrochemical cell to reduce the electrode resistance. Carbonaceous powder materials are often selected as conductive aids because they are lightweight and inert to acidic and alkaline electrolytes. Conductive aids generally do not contribute to the electrochemical process of the electrodes. This means that it is desirable to minimize the amount of conductive aid used for increasing the energy density of the cell. Typical carbon-based conductive aids used are graphite fine powder and conductive carbon black (see, for example, M.E. Spahr, Lithium-ion Batteries - Science and Technology, M. Yoshio, R.J. Brodd, A. Kozawa (Eds.), Springer, New York, 2009, Chapter 5). Hereinafter, the graphite material of the present invention and its properties will be described in more detail. All descriptions are also applicable to further aspects of the present invention, for example, the method of the present invention, the positive or negative electrode for incorporation into a battery including the graphite material, the battery or fuel cell including the graphite material, and the use of the graphite material.

[0013] Graphite material In a first aspect, the present invention has the following properties: a) The pH measured as described herein is at least 5.4, b) The Scott density measured as described herein is 0.11 g / cm 3 or less, and c) The Raman D / G intensity ratio measured with a laser having an excitation wavelength of 632.8 nm is 0.220 to 0.420. The present invention provides a graphite material having the above properties. The graphite material of the present invention has a pH of at least 5.4, preferably a pH of 5.4 to 12, a pH of 5.4 to 11, or a pH of 5.4 to 10. The pH of the graphite material can be measured by dispersing the material in water and measuring the pH using a pH meter. References to the pH of the graphite material herein relate to the pH of the graphite material dispersed in water.

[0014] Furthermore, the graphite material of the present invention has a Scott density of 0.11 g / cm 3 or less, preferably 0.10 g / cm 3 or less, or 0.09 g / cm 3 or less. The Scott density can be 0.001 to 0.11 g / cm 3 preferably 0.01 to 0.10 or 0.01 to 0.09 g / cm 3 and may be. In a preferred embodiment, the Scott density is 0.03 to 0.11 g / cm 3 for example 0.03 to 0.10 g / cm 3 or 0.03 to 0.09 g / cm 3 The Scott density can be measured using a pycnometer in accordance with ASTM B329-98(2003). Furthermore, when the graphite material of the present invention is measured with a laser having an excitation wavelength of 632.8 nm, the Raman D / G intensity ratio is 0.220 to 0.420, for example 0.230 to 0.420 or 0.220 to 0.400. In a preferred embodiment, the graphite material of the present invention has a Raman D / G intensity ratio of 0.230 to 0.400. The Raman D / G intensity ratio is based on the ratio of the intensities of the so-called D band and G band. These peaks are respectively at 1350 cm -1 and 1580 cm -1 and are characteristic peaks of carbon materials measured at these positions.

[0015] It will be further understood that the graphite material can be further defined by each pH value range, either independently or in addition to the range of the Scott density value and the range of the Raman D / G intensity ratio (of course, when they are not mutually exclusive). The graphite material of the present invention may have a pH of 5.4 to 12, a Scott density of 0.001 to 0.11 g / cm 3 , and a Raman D / G intensity ratio of 0.220 to 0.420. In a preferred embodiment of the present invention, the graphite material has a pH of 5.4 to 11, a Scott density of 0.03 and 0.11 g / cm 3 , and a Raman D / G intensity ratio of 0.220 to 0.400. In a preferred embodiment of the present invention, the graphite material has a pH of 5.4 to 11, a Scott density of 0.03 and 0.10 g / cm 3 , and a Raman D / G intensity ratio of 0.230 to 0.400. In a preferred embodiment of the present invention, the graphite material has a pH of 5.4 to 10, a Scott density of 0.03 and 0.09 g / cm 3 , and a Raman D / G intensity ratio of 0.230 to 0.400.

[0016] In some embodiments, the graphite material of the present invention is further characterized by a specific particle size distribution. The particle size distribution can be measured using a laser diffraction method. The particle size distribution is typically defined by values D10, D50, and D90, where 10 (volume) percent of the particle population has a particle diameter less than the D10 value, 50 (volume) percent of the particle population has a particle diameter less than the D50 value, and 90 (volume) percent of the particle population has a particle diameter less than the D90 value. In the graphite material of the present invention, D90 may be at least 5 μm, at least 6 μm, at least 7 μm, at least 11.0 μm, preferably at least 12 μm, or at least 13 μm. In the graphite material of the present invention, D90 may be 11 - 120 μm, 12 - 120 μm, or 13 - 120 μm. In certain embodiments using non-expanded graphite material as the starting material, a D90 value in the range of 11 - 50 μm, or 11 - 40 μm, or 11 - 30 μm is preferred. Similarly, the particle size distribution value D50 is in the range of 1 - 50 μm in some embodiments, but in certain embodiments using non-expanded graphite material as the starting material, a D50 value in the range of 5 - 20 μm, or 6 - 15 μm is preferred.

[0017] It will be further understood that the graphite material can be further defined independently or in addition to the range of D50 values (of course, if not mutually exclusive) by the range of each D90 value. In some embodiments using non-expanded graphite material as the starting material, the graphite material has a D90 value of 11 - 50 μm and a D50 value of 5 - 20 μm. In certain embodiments, the graphite material of the present invention is further characterized in that the oxygen concentration is at least 0.042% by mass based on the total mass of the graphite material. In preferred embodiments, the oxygen concentration is 0.042 - 1.0% by mass, or 0.042 - 0.9% by mass, or 0.042 - 0.7% by mass, or 0.042 - 0.6% by mass, or 0.042 - 0.5% by mass. The oxygen concentration can be measured by measuring the elemental oxygen content of the graphite material by elemental analysis. The oxygen concentration corresponds to the oxygen content of the graphite material. In a preferred embodiment of the present invention, the graphite material has a D90 of at least 11.0 μm and an oxygen concentration of at least 0.042% by mass based on the total mass of the graphite material.

[0018] In a preferred embodiment of the present invention, the graphite material of the present invention has a D90 of 11 to 120 μm, a D50 of 1 to 50 μm, and an oxygen concentration of 0.042 to 1.0% by mass based on the total mass of the graphite material. In a preferred embodiment, the graphite material has a pH of 5.4 to 11, a Scott density of 0.03 and 0.11 g / cm 3 , a Raman D / G intensity ratio of 0.220 to 0.400, a D90 of 12 to 120 μm, and an oxygen concentration of 0.042 to 1.0% by mass based on the total mass of the graphite material. In a preferred embodiment, the graphite material has a pH of 5.4 to 11, a Scott density of 0.03 to 0.10 g / cm 3 , a Raman D / G intensity ratio of 0.230 to 0.400, a D90 of 13 to 120 μm, and an oxygen concentration of 0.042 to 0.6% by mass based on the total mass of the graphite material. In a preferred embodiment, the graphite material has a pH of 5.4 to 10, a Scott density of 0.03 and 0.09 g / cm 3 , a Raman D / G intensity ratio of 0.230 to 0.400, a D90 of 13 to 120 μm, and an oxygen concentration of 0.042 to 0.6% by mass based on the total mass of the graphite material.

[0019] The graphite material of the present invention may further be characterized by a relatively large BET surface area of at least 5.5 m 2 / g. The BET surface area can be measured based on the procedure proposed by Brunauer, Emmet and Teller (Adsorption of Gases in Multimolecular Layers, J. Am. Chem. Soc., 1938, 60, 309 - SI 9). The ash content is less than 0.3% by mass, preferably less than 0.2% by mass, more preferably less than 0.1% by mass, still more preferably less than 0.08% by mass, still more preferably less than 0.06% by mass, for example less than 0.05% by mass, and most preferably less than 0.04% by mass. The ash content can be measured according to ASTM C561. The graphite material of the present invention may have an oxidizability of 0.19 or less and an electric resistance of 600 mΩ·cm or less, preferably 400 mΩ·cm or less, and most preferably 285 mΩ·cm or less. The graphite material preferably may have an oxidizability of 0.18 or less, 0.17 or less, 0.16 or less, or 0.15 or less.

[0020] The oxidizability is determined by the following steps: a) preparing a mixture of 40% by mass of the graphite material and 60% by mass of electrolytic manganese dioxide; b) pressing the mixture of step a) together and applying a pressure of 6.8 metric tons / cm 2 for 5 seconds to form tablets; c) aging the tablets in 20 mL of a 30% by mass KOH aqueous solution at 60 °C to obtain an aging solution; d) filtering the aging solution to obtain a filtered aging solution; e) measuring the absorbance of the filtered aging solution at 410 nm with a UV-Vis spectrophotometer, and f) evaluating the oxidizability of the tested graphite material as the measured absorbance value. It is defined as the measured absorbance value (absorbance intensity ratio) by a method including the above steps. Furthermore, the graphite material has an electric resistance of 260 mΩ·cm or less, or 255 mΩ·cm or less, or 250 mΩ·cm or less. Generally, the graphite material of the present invention characterized by the above parameters is obtained by subjecting a graphite starting material to an oxidation process gas such as, but not limited to, oxygen, air, oxygen-enriched air, carbon dioxide, ozone, steam, NO xObtained by subjecting to a process that includes heating to a temperature in the range of 300 to 1700 °C, preferably 500 to 1400 °C, most preferably 700 to 1100 °C, in the presence of (including but not limited to NO2, NO, N2O) or any combination thereof. The graphite material of the present invention can be manufactured by the method described in detail below.

[0021] Method In a second aspect, the present invention provides a method for treating a graphite starting material in order to obtain the graphite material of the present invention with improved oxidizability and electrical resistance. In particular, a method for manufacturing a graphite material, comprising: a) subjecting the graphite starting material to a surface modification process that includes heating to a temperature in the range of 300 to 1700 °C in the presence of an oxidizing process gas, such as, but not limited to, oxygen, air, oxygen-enriched air, carbon dioxide, ozone, steam, NO x (including but not limited to NO2, NO, N2O), or any combination thereof; and b) obtaining the graphite material of the present invention. A method is provided. The inventors have found that, in order to obtain a graphite material characterized by the parameters described herein, by carefully selecting the starting material and adjusting the main process parameters such as residence time, oxidizing process gas flow rate, temperature, etc., a graphite material with improved oxidizability and electrical resistance can be obtained. In a preferred embodiment, step a) includes heating to a temperature in the range of 500 to 1400 °C, preferably 700 to 1100 °C. The graphite starting material can be natural graphite, synthetic graphite, expanded graphite, or a mixture thereof. The graphite starting material is not coated with a carbon coating.

[0022] Natural graphite is mined from mines where the typical content in the ore is 3 to 10% by mass. The ore is crushed, and graphite flakes are separated from the rock by flotation and centrifugation. The resulting graphite typically has a purity of 85 to 96% by mass. To obtain higher purity, the graphite can be chemically treated with a high-concentration KOH solution, followed by acid treatment with acids such as concentrated HCl, H2SO4, and HF, depending on the desired final purity. The obtained graphite can be further crushed to the desired particle size according to the end use. Synthetic graphite is produced by treating natural or petroleum-derived carbon precursors in a high-temperature process to convert amorphous carbon into more structured carbon. Synthetic graphite is typically produced by heat-treating a carbonaceous precursor material in an Acheson furnace (described in U.S. Patent No. 933,944). In this furnace, a high current is passed through the carbonaceous material placed between two electrodes. This material is heated by resistive heating (Joule effect) and heat conduction at temperatures above 2000 °C, and graphitization occurs. The resulting graphite, like natural graphite, is further crushed to the desired particle size according to the end use.

[0023] Expanded graphite is graphite in exfoliated form. The method for producing expanded graphite is described, for example, in European Patent No. 0,981,659. The manufacturing process is based on the thermal exfoliation of a graphite intercalation compound formed by treating graphite flakes with a strong acid in the presence of an oxidizing agent, such as a mixture of concentrated sulfuric acid and nitric acid. The intercalated graphite is then rapidly heated to a temperature of about 850 to 1000 °C to undergo a thermal shock, decomposing the guest anions and acid molecules between the graphite layers into gases and exfoliating the graphite layers. As an alternative, microwave radiation can also be used in the exfoliation process. Finally, the graphite is crushed, which further exfoliates and separates the expanded graphite. In a preferred embodiment, the starting graphite raw material is crushed before being subjected to the surface modification process. The starting graphite raw material may be a mixture of 10 to 90% by mass of natural or synthetic graphite and 90 to 10% by mass of expanded graphite. Increasing the amount of expanded graphite increases the electrical conductivity but also increases the material cost accordingly.

[0024] Oxidation is achieved by heating the graphite starting material in the presence of an oxidation process gas, such as, but not limited to, oxygen, air, oxygen-enriched air, carbon dioxide, ozone, steam, NO x (including but not limited to NO2, NO, N2O), or any combination thereof. In a preferred embodiment, the oxidation is carried out in the presence of an oxidation process gas containing at least one of oxygen, CO2, ozone, steam, and / or NO x (including but not limited to NO2, NO, N2O), by heating the graphite starting material in a high-temperature furnace suitable for powder treatment for a predetermined time. This process can be carried out as a continuous process. However, a batch process or a semi-continuous process can also be used. The furnace to be used is preferably, for example, a fixed-bed furnace, a fluidized-bed furnace, a roller hearth kiln, a belt furnace, a rotary kiln, a continuous stirred reactor, an autogenous furnace or a flash calciner multi-stage furnace, or a modified or combined form thereof. The process can be gas-fired or electrically heated.

[0025] The oxidation process gas used may be oxygen, air, oxygen-enriched air, carbon dioxide, ozone, steam, and NO x (including but not limited to NO2, NO, N2O), but is not limited thereto. It will be understood that the oxidation process gas may be any combination of the aforementioned gases, optionally mixed with an inert carrier gas such as nitrogen or argon. In a preferred embodiment, the oxidation process gas used is air or CO2. Generally, it will be understood that the higher the oxygen concentration, that is, the higher the partial pressure of oxygen in the oxidation process gas, the faster the oxidation process. The amount of the oxidation process gas depends on the amount of the graphite starting material in order to maintain a certain C / O ratio for better process efficiency. The residence time of step a) required to obtain a graphite material characterized by the specific properties described herein varies depending on process conditions such as the type of reactor selected, temperature, carbon amount, oxygen amount, etc. In the case of a batch process, the residence time can be adapted to any time required to reach the final properties of the graphite material described herein. In the case of a continuous process (e.g., rotary kiln, roller hearth kiln, etc.), process parameters such as temperature or carbon throughput may need to be adapted according to the maximum possible residence time. In the case of a roller hearth kiln, the maximum residence time can be (by design) more than 5 hours. In a rotary kiln, the maximum residence time used can be several hours.

[0026] In one embodiment, a batch process with a residence time of 30 minutes to 120 minutes is used. In another embodiment, a continuous process with a residence time of 15 minutes to 45 minutes is used. In both embodiments, it is necessary to keep in mind that the furnace design and carbon mass loading have a great influence on the process parameters. When using different starting materials, temperatures, and oxygen partial pressures, it may be necessary to adapt the processing time to obtain a graphite material with the desired parameters defined herein. The flow rate of the oxidation process gas varies depending on the size of the apparatus. A person skilled in the art can adapt the flow rate according to the type of oxidation process gas, processing temperature, and residence time in the furnace to obtain the graphite material of the present invention.

[0027] The process parameter of the ratio of the oxidation process gas to carbon (kg / kg) is defined herein as the ratio of the oxidation process gas (kg) to solid carbon (kg). The term "solid carbon" means elemental carbon contained in the graphite material to be processed. The ratio of the oxidation process gas to carbon strongly depends on the technology used and other process parameters such as residence time and temperature. The ratio of the oxidation process gas to carbon is usually in the range of 25 kg / kg to 0.005 kg / kg, preferably in the range of 15 kg / kg to 0.01 kg / kg, and more preferably in the range of 5 kg / kg to 0.2 kg / kg.

[0028] When air is used as the oxidation process gas, the ratio of the oxidation process gas to carbon is usually in the range of 25 kg / kg to 0.02 kg / kg, preferably in the range of 15 kg / kg to 0.04 kg / kg, and more preferably in the range of 10 kg / kg to 0.06 kg / kg. When oxygen is used as the oxidation process gas, the ratio of the oxidation process gas to carbon is usually in the range of 5 kg / kg to 0.005 kg / kg, preferably in the range of 3 kg / kg to 0.01 kg / kg, and more preferably in the range of 2 kg / kg to 0.02 kg / kg. When steam is used as the oxidation process gas, the ratio of the oxidation process gas to carbon is usually in the range of 7 kg / kg to 0.005 kg / kg, preferably in the range of 5 kg / kg to 0.01 kg / kg, and more preferably in the range of 3 kg / kg to 0.02 kg / kg. When ozone is used as the oxidation process gas, the ratio of the oxidation process gas to carbon is usually in the range of 18 kg / kg to 0.015 kg / kg, preferably in the range of 15 kg / kg to 0.02 kg / kg, and more preferably in the range of 10 kg / kg to 0.03 kg / kg. When CO2 is used as the oxidation process gas, the ratio of the oxidation process gas to carbon is usually in the range of 20 kg / kg to 0.01 kg / kg, preferably in the range of 15 kg / kg to 0.02 kg / kg, and more preferably in the range of 10 kg / kg to 0.05 kg / kg. When NO2 is used as the oxidation process gas, the ratio of the oxidation process gas to carbon is usually in the range of 8 kg / kg to 0.005 kg / kg, preferably in the range of 7 kg / kg to 0.01 kg / kg, and more preferably in the range of 6 kg / kg to 0.02 kg / kg. When using N2O as the acidification process gas, the ratio of the acidification process gas to carbon is usually in the range of 16 kg / kg to 0.01 kg / kg, preferably in the range of 14 kg / kg to 0.02 kg / kg, more preferably in the range of 10 kg / kg to 0.04 kg / kg.

[0029] Further aspect In a third aspect, the present invention provides a negative electrode or a positive electrode for incorporation into a battery including the graphite material of the present invention. In a preferred embodiment, the electrode includes a graphite material as a conductive aid. By using the graphite material having low oxidizing property and low electrical resistance described in this specification in a battery or a fuel cell, there are advantages of extending the life of the battery or the fuel cell, delaying the decrease in the efficiency of the battery or the fuel cell, and improving the safety by reducing the risk of the graphite decomposing into gas. Further, when the electrical resistance is low, a battery or fuel cell manufacturer can reduce the addition of a conductive aid, and as a result, can increase the cell capacity. In a fourth aspect, the present invention provides a battery including the graphite material of the present invention. In a preferred embodiment, the battery includes an electrode including a graphite material as a conductive aid.

[0030] The battery may be a lithium ion battery, a lead storage battery, an alkaline battery, or a NiCd battery, preferably a lithium ion battery. In a preferred embodiment, the battery is a lithium ion battery or an alkaline battery and includes a positive electrode including a graphite material as a conductive aid. In a preferred embodiment, the battery is a lead storage battery and includes a negative electrode including a graphite material as a conductive aid. In a fifth aspect, the present invention provides a fuel cell including the graphite material of the present invention. In a sixth aspect, the present invention provides the use of the graphite material of the present invention in any one of a lithium ion battery, a lead storage battery, an alkaline battery, a NiCd battery, and a fuel cell. In a preferred embodiment, the graphite material is used as a conductive aid. In a preferred embodiment, the graphite material is used as a conductive aid in the electrodes of a lithium-ion battery.

[0031] In summary, as described above, the subject matter of the present invention enables the advantageous optimization of both the oxidizability and the electrical resistance in the graphite material. All matters contained in the above description are intended to be construed as illustrative and not in a limiting sense. Accordingly, certain modifications can be made to the above compositions, uses, and methods without departing from the scope of the present invention. The present invention is further illustrated by the following examples, which exemplify the preparation of the graphite material and the corresponding properties of the material without limiting the invention.

Examples

[0032] Measurement method pH value Disperse 1 g of graphite powder in 49 ml of distilled water, add 2 drops of ethanol, and measure with a pH meter equipped with a calibrated pH electrode. Scott density According to ASTM B329-98(2003), measure the Scott density by passing dry carbon powder through a bulk density meter. Recover the powder in a 1 / 3 container (equivalent to 16.39 cm 3 ), and measure the mass with an accuracy of 0.1 mg. The ratio of mass to volume corresponds to the Scott density. It is necessary to measure 3 times and calculate the average value. The bulk density of graphite is calculated from the mass of 250 ml of the sample in a calibrated glass cylinder. Raman analysis Raman analysis is performed using a LabRAM-ARAMIS Micro-Raman Spectrometer from HORIBA Scientific and a 632.8 nm HeNeLASER. The ratio ID / IG is based on the ratio of the intensities of the bands called band D and band G. These peaks are 1350 cm -1 and 1580 cm -1 respectively, and are characteristic peaks of carbon materials measured at these wavelengths.

[0033] Particle Size Distribution (PSD) by Laser Diffraction Diffraction occurs when particles are present in a coherent light beam. The dimensions of the diffraction pattern are correlated with the particle size. A parallel beam of a low-power laser is used to illuminate a cell containing a sample suspended in water. The beam emerging from the cell is focused by an optical system. Subsequently, the distribution of light energy at the focal plane of the system is analyzed. The electrical signal obtained from the optical detector is converted into a particle size distribution by a computer. In this method, the ratio of the total volume of particles to the individual number of particle size classes is obtained, which forms the volume particle size distribution (PSD). The particle size distribution is defined by the values D10, D50, and D90, where 10 (volume) percent of the particle population has a particle size less than the D10 value, 50 (volume) percent of the particle population has a particle size less than the D50 value, and 90 (volume) percent of the particle population has a particle size less than the D90 value. The particle size distribution data by laser diffraction cited in this specification were measured using a MALVERN Mastersizer S. To measure the PSD, a small amount of graphite material sample is mixed with a few drops of wetting agent and a small amount of water. The sample thus prepared is introduced into the storage container of the apparatus (MALVERN Mastersizer S), ultrasonicated at 100% intensity for 5 minutes, and after setting the pump and stirrer speeds to 40%, the measurement is carried out.

[0034] Reference: ISO 13320(2009) / ISO 14887 Oxygen Concentration / Oxygen Content The oxygen concentration in the graphite material is evaluated using the principle of inert gas fusion or solid carrier gas thermal extraction. The sample is placed in a graphite crucible and inserted into an electrode furnace. The crucible is maintained between the upper and lower electrodes of an impulse furnace. After purging with an inert gas (He or Ar), a high current is passed through the crucible to raise the temperature (above 2500 °C). The gas generated in the furnace is released into the flowing inert gas stream. The gas stream is sent to an appropriate infrared (O as CO by NDIR) or thermal conductivity (N and H by TCD) detector and measured. The calibration of the instrument is performed using known reference materials.

[0035] Electrical Resistance The electrical resistance is measured in the following steps. The volume resistivity can be measured by the following method. ● Prepare a mixture containing 95% electrolytic manganese dioxide and 5% by mass of graphite (when synthetic or natural graphite is used as the graphite starting material) or 3% by mass of graphite and 97% electrolytic manganese dioxide (when expanded graphite is used as the graphite starting material). ● Press 10 g of the obtained mixture at 180 Nm using a die with a length of 50 mm and a width of 12 mm to obtain a block. ● Measure the height (H) and width (W) of the block. ● Measure the electrical resistance (R) of the block with a four-probe probe. ● Calculate the resistivity as H×R / D. Here, D is the distance between the probe measurement pins.

[0036] BET specific surface area This method is based on the measurement of the adsorption isotherm of liquid nitrogen in the range of p / p0 = 0.04 - 0.26 at 77 K. The adsorption of nitrogen gas was carried out with an Autosorb-1 manufactured by Quantachrome. The monolayer capacity can be determined according to the procedure proposed by Brunauer, Emmet and Teller (Adsorption of Gases in Multimolecular Layers, J. Am. Chem. Soc., 1938, 60, 309 - SI 9). The specific surface area can be calculated based on the cross-sectional area of nitrogen molecules, the monolayer capacity, and the mass of the sample. To evaluate the pore size distribution, micro and mesopore volumes, and areas, the isotherm measured at 77 K in the pressure range p / p0 0.01 - 1 can be processed by DFT calculation. Reference: Ravikovitch, P., Vishnyakov, A., Russo, R., Neimark, A., Langmuir 16 (2000) 2311 - 2320; Jagiello, J., Thommes, M., Carbon 42 (2004) 1227 - 1232 X-ray diffraction X-ray diffraction (XRD) data were collected using a combination of a PANalytical X’Pert PRO diffractometer and a PANalytical X’Celerator detector. The instrument data and measurement parameters of the diffractometer used are shown in Table 1. The instrument data and measurement parameters for XRD measurement are as follows.

Table 1

[0037] Interlayer spacing c / 2 The interlayer spacing c / 2 is determined by X-ray diffraction method. The angular positions of the peak maxima of the

[0002] and

[0004] reflection profiles are determined. By applying Bragg's equation, the interlayer spacing is calculated (Klug and Alexander, X-ray diffraction Procedures, John Wiley & Sons Inc., New York, London (1967)). To avoid problems due to the low absorption coefficient of carbon, instrument adjustment, and non-planarity of the sample, silicon powder, which is an internal standard substance, is added to the sample, and the graphite peak position is recalculated based on the position of the silicon peak. The graphite sample is mixed with the silicon standard powder by adding a mixture of polyglycol and ethanol. The resulting slurry is then applied to a glass plate at intervals of 150 μm using a blade and dried.

[0038] Crystallite size Lc The crystallite size is measured by determining the width of the peak profile at the half-width through the analysis of the diffraction profiles of

[0002] and

[0004] . The broadening of the peak should be affected by the crystallite size, as proposed by Scherrer (P. Scherrer, Gottinger Nachrichten 2, 98 (1918)). However, the broadening is also affected by other factors such as X-ray absorption, Lorentz polarization, and atomic scattering factor. To account for these effects, several methods have been proposed that use an internal silicon standard and apply a correction function to Scherrer's equation. In the present invention, the method proposed by Iwashita (N. Iwashita, C. Rae Park, H. Fujimoto, M. Shiraishi and M. Inagaki, Carbon 42, 701-714 (2004)) was used. The sample preparation is the same as the c / 2 measurement described above.

[0039] Ash content The ash content is evaluated by gravimetric loss. A low-wall ceramic crucible is heated to 800 °C in a muffle furnace and cooled to room temperature in a desiccator. A 10 g (accurate to 0.1 mg) sample of the dry powder is weighed in the low-wall ceramic crucible. The powder is burned at a temperature of 810 °C (for at least 8 hours) until a constant mass is reached. The residue corresponds to the ash content and is reported as a percentage of the initial mass of the sample. Reference: ASTM C561 Standard Test Method for Ash in a Graphite Sample

[0040] (Example 1) Different graphite starting materials were treated in a rotary furnace or a continuous stirred reactor using air or CO2 in the temperature range of 600 - 900 °C. The treatment conditions used to prepare different graphite materials are listed in Table 1. [Table 2] The pH, Scott density, Raman D / G intensity ratio, and various other parameters of the obtained graphite material were measured (Table 2). Furthermore, the oxidizability and electrical resistance of the material were measured. The same series of measurements were also carried out for the starting materials before treatment and for further comparative examples. The results are shown in Tables 3 and 4.

[0041] As can be seen from the comparison of the data, the materials having the combination of parameters described in the claims have an improved balance of low oxidizability and low electrical resistance.

Table 3

Table 4

Table 5

Claims

1. The following characteristics: a) The pH described herein is at least 5.4, b) Scott density of 0.11 g / cm³ as measured as described herein 3 The following are, and c) The Raman D / G intensity ratio measured with a laser at an excitation wavelength of 632.8 nm is 0.220 to 0.

420. A graphite material having [a certain characteristic].

2. The graphite material according to claim 1, wherein the pH is 5.4 to 12, preferably 5.4 to 11, or 5.4 to 10.

3. Scott density is 0.10 g / cm³ 3 Preferably, the concentration is 0.09 g / cm³. 3 The graphite material according to claim 1, which is as follows:

4. The graphite material according to claim 1, wherein the Raman D / G intensity ratio is 0.23 to 0.

40.

5. The following characteristics: d) The D90 measured by laser diffraction is at least 11.0 μm. e) The oxygen concentration measured by elemental analysis is at least 0.042% by mass based on the total mass of the graphite material. The graphite material according to claim 1, further comprising at least one of the following.

6. The graphite material according to claim 1, wherein the D90 measured as described herein is at least 5 μm.

7. The graphite material according to claim 1, wherein the oxygen concentration is 1.0% by mass or less, 0.9% by mass or less, 0.7% by mass or less, 0.6% by mass or less, or 0.5% by mass or less.

8. Furthermore, the BET specific surface area measured as described herein is at least 5.5 m². 2 The graphite material according to claim 1, wherein the weight is / g.

9. Furthermore, i) the oxidizing properties measured as described herein are 0.19 or less, and ii) The electrical resistance measured as described herein is 600 mΩ·cm or less, preferably 400 mΩ·cm or less, most preferably 285 mΩ·cm or less. The graphite material according to claim 1.

10. i) The oxidizing properties are 0.18 or less, 0.17 or less, 0.16 or less, or 0.15 or less, and / or ii) The electrical resistance is 260 mΩ·cm or less, 255 mΩ·cm or less, or 250 mΩ·cm or less. The graphite material according to claim 9.

11. A method for producing a graphite material according to any one of claims 1 to 10, wherein the graphite starting material is an oxidation process gas, for example, but not limited to, oxygen, air, oxygen-enriched air, carbon dioxide, ozone, vapor, NO x (NO 2 NO, N 2 A method comprising the step of subjecting a surface to a surface modification process, which includes heating to a temperature in the range of 300 to 1700°C in the presence of (but not limited to) or any combination thereof.

12. The method according to claim 11, wherein the ratio of oxidation process gas to carbon in graphite is in the range of 25 kg / kg to 0.005 kg / kg.

13. The method according to claim 11, wherein step a) includes heating to a temperature in the range of 500 to 1400°C, preferably 700 to 1100°C.

14. Preferably, a negative or positive electrode for incorporation into a battery, comprising a graphite material according to any one of claims 1 to 10 as a conductive additive.

15. A battery comprising the graphite material according to any one of claims 1 to 10, wherein the battery is preferably a lithium-ion battery, a lead-acid battery, an alkaline battery, or a NiCd battery.

16. A fuel cell comprising the graphite material according to any one of claims 1 to 10.

17. Use of the graphite material according to any one of claims 1 to 10 in any one of lithium-ion batteries, lead-acid batteries, alkaline batteries, NiCd batteries, or fuel cells.