Electrode particles suitable for batteries

Abstract

To provide a method for forming a graphite anode material that achieves higher performance at lower cost.SOLUTION: A method for forming a graphite anode material for metal ion batteries, comprises: selecting and sizing a carbon precursor material into particles having a desired average particle size; combining the precursor material with a carbide-forming element at a ratio between 0.01% and 10% of the blend; graphitizing the combination at a temperature between about 2500°C and 3000°C in argon, helium or nitrogen gas to yield particles having a carbide compound on the surface and having a graphite core. The carbide compound comprises carbide-forming elements consisting of B and Ce.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] Relationship with Related Applications This is a PCT international patent application claiming the benefit and priority of all of U.S. Provisional Patent Application Nos. 62 / 875,299 and 62 / 875,315, both filed on July 17, 2019, and all of U.S. Patent Application Nos. 16 / 929,222, 16 / 929,233, and 16 / 929,248, all filed on July 15, 2020, each having the title "ELECTRODE PARTICLES SUITABLE FOR BATTERIES", which are hereby incorporated by reference in their entirety.

[0002] Field of the Invention This application relates to batteries, and more particularly to materials useful for making anodes for batteries, and even more particularly to materials useful for anodes of metal ion batteries.

Background Art

[0003] Background of the Invention Rechargeable lithium-ion batteries have been widely introduced into many portable systems and devices such as mobile phones, tablets, computers, portable hand-held tools, and new devices developed to rely on the power and weight advantages of lithium-ion batteries. These advantages are lightweight, high voltage, high electrochemical equivalence, and good electrical conductivity. The wide use and acceptance of lithium-ion batteries have achieved many advancements and developments. One area of development of lithium-ion batteries has focused on the anode, i.e., the negative electrode, of lithium-ion batteries, where much has been achieved.

[0004] For particularly portable devices, important considerations regarding the anode of a lithium-ion battery are high volumetric and weight specific capacity, and long battery life over multiple charge and discharge cycles. In prior research, anode materials have been produced with an initial coulombic efficiency reaching 95% due to long life via coated and graphitized carbon precursor materials. This is described in Patent Document 1 to Mao et al., where petroleum coke is ground to a suitable size, subjected to a solvent coating process, has a coating that is oxidatively stabilized at high temperature, then the entire particle is carbonized, and further graphitized at high temperature in an inert environment. The particles form a highly graphitized structure with a protective coating on the surface, and this coating protects the underlying graphite sheet from the battery's electrolyte. The protective coating protects the edges of the graphite sheet that are thought to be catalytically active in the battery's electrolyte. The electrolyte thus decomposes the graphite sheet during the charge cycle, and thereby rapidly and dramatically reduces the efficiency and storage capacity for the lithium ions of the anode. The coating created on the anode particles forms a more stable graphite with respect to catalytic decomposition from the electrolyte when carbonized with the remaining particles, but itself contains materials that cannot be graphitized so as to be suitable for the intercalation of lithium ions. However, lithium ions can easily pass through the coating and intercalate into a more organized graphite sheet. In fact, this is a very good material with good properties and good cycle life. However, its production requires the use of a significant volume of solvent with many continuous and separate heat treatments in different ambient environments, all of which are costly. However, for high-value applications where small space and minimum weight with high specific capacity are important, this anode is currently the most advantageous.

[0005] The most important parameters of the graphite negative electrode material of a lithium-ion battery are the initial coulombic efficiency and is the specific capacity. It is well known that highly crystalline graphite powder has a high specific capacity and very poor initial Coulombic efficiency and is not useful as an anode material for lithium-ion batteries. Through years of intensive research and development, sophisticated methods have been developed to mitigate problems related to specific capacity and initial Coulombic efficiency. The main solutions focus on graphitization at high temperatures and coating particles containing carbon that cannot be easily graphitized, and then graphitizing to provide protection of the graphite sheets inherent in the particles from the electrolyte. Since the mean average particle size of the graphite anode material is less than 30 microns and the individual particles must be uniformly coated with carbon that cannot be easily graphitized, the graphite anode material is currently manufactured through complex processing steps. As a result, the manufacturing cost is high, and some coating processes have a low yield.

[0006] For all materials, it is always desirable (a driver) to achieve higher performance at a lower cost, and any progress in either performance or cost is highly desirable.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Summary of the Invention

[0008] The present invention relates to a graphite carbon powder comprising particles having an average particle size between 1 μm and 50 μm, wherein the particles have a modified surface comprising a carbide compound constituting at least 5 ppm and up to 1 wt% of the particles and comprising at least 90 wt% carbon graphite.

Brief Description of the Drawings

[0009] A more complete understanding of the present invention and its benefits can be obtained by referring to the following description in conjunction with the accompanying drawings.

Fig. 1

DETAILED DESCRIPTION OF THE INVENTION

[0010] Now, moving on to a detailed description of the preferred arrangement(s) of the present invention, it should be understood that the features and concepts of the present invention can be implemented in other arrangements as well, and the scope of the present invention is not limited to the embodiments described or illustrated. The scope of the present invention is limited only by the claims that follow.

[0011] First, turning to FIG. 1, a schematic battery is shown by arrow 10. The battery includes a number of particles of cathode material 20 and a number of particles of anode material on the opposite side of electrolyte separator 40. Each particle of cathode 20 and anode 30 is held in its respective metal electrode in an electrically conductive paste (not specifically shown). An electrical load such as a light or an electric motor shown at 50 can be connected to battery 10 by wiring shown at 51. When the battery 10 is charged, positive ions are stored in the anode particles 30. Due to the electro-chemical properties of the cathode and anode materials, the positive ions are driven (attracted and then repelled) to move from the anode 30 through the electrolyte separator 40 to the cathode. While the ions are moving through the electrolyte, electrons pass around the metal electrode 31 and move through wire 51 and load 50 to the cathode to balance the charge. In the process of electrons passing through the load, electrical work such as lighting a light bulb or turning an electric motor is performed. For a lithium-ion battery, the cathode is generally formed of a chemical structure with lithium, which forms lithium ions during charging of the battery that move across separator 40 and intercalate into the anode. The anode material has chemical complexity Low and high-performance anode materials can densely store lithium ions in a manner that easily releases the lithium ions to the cathode without permanently binding them to the anode. The present invention focuses on the configuration of anode materials used in batteries as shown in FIG. 1.

[0012] Carbon-coated anode materials have shown very attractive properties for high-value batteries where weight and size are important, but conversely have low utility for batteries where weight and size are not important. Such lower-value applications include power storage devices in fixed locations that require very high power capacity, such as standby power in switchboards.

[0013] With an eye towards batteries that meet such needs, research has been done to develop a battery design that uses a larger volume of uncoated graphitized petroleum coke material to compensate for the expected degradation of anode performance over multiple charge and discharge cycles. In the process of exploring the optimal graphitization level of the battery, several graphite nucleating agents were added to accelerate the formation of the graphite structure at low temperatures. However, the end result was a somewhat high-performance anode material, and further development research was immediately directed towards elucidating the properties of the new anode product and why it operates at a higher level than expected.

[0014] What is thought to have occurred in these tests is that rather than nucleating graphite formation, the nucleating agent reacted with the carbon surface of the particles to form carbide compounds or reacted with nitrogen gas to form nitride compounds on the surface of the particles. Carbide and nitride compounds are formed deep within the particles and do not appear to protect the bulk particles as crystalline graphite for ion intercalation. Carbides and nitrides clearly protect the graphite structure from the electrolyte within the metal ion battery, thereby preventing the electrolyte from interacting with the graphite. Generally, the electrolyte is known to decompose graphite at the anode, and furthermore, the thin thickness of this modified surface protected the graphite sheet in the present invention.

[0015] The initial experiments started with boron as the nucleating agent. Since graphitization must be carried out in a non-oxygen environment or combustion where carbon forms carbon dioxide in principle, graphitization is generally carried out under a non-oxygen blanket gas. Under a nitrogen blanket gas, nitrides are also formed on the surface. However, there is a possibility that the nitride form in the nucleating agent may boil and not remain on the surface. Stable nitrides and / or carbides seem to be most formed when the graphitization temperature is above the melting point of the stable carbide or nitride molecules but below their boiling points. For nucleating agents that form stable nitrides boiling below the graphitization temperature, other inert blanket gases can be selected. Argon has been successfully used in those situations. Referring to Table 1, potential nucleating agents for each of the carbides and nitrides that can be formed during graphitization are shown. Referring to Table 2, the clone efficiency and specific capacity are shown respectively for each cell made using boron as a carbide or nitride forming agent.

Table 1

[0016] The carbide and nitride forming materials are blended with powdered coke at about 0.1 wt% to about 5 weight percent. It is believed that carbides and nitrides are formed on the surface of the particles when the inherent carbon forms a graphite structure therein. That is, the method of the present invention for making anode powder comprises preparing a graphite precursor to a desired size by milling or other methods, and adding by blending an appropriate amount of a carbide or nitride forming element together, and then subjecting the blended mixture to a graphitization temperature for a time sufficient to form the surface chemistry and the inherent graphite structure. For some coke materials, it is preferred to carbonize them to drive off heteroatoms and other non-oxygen atoms prior to graphitization by calcination. Carbonization is generally a heat treatment below the graphite temperature, but high enough such as between 900 °C and 1500 °C, and generally the carbon content of the coke in the calcination furnace is raised to at least 92%, or at least 97% such as 95%.

[0017] Preferably, the surface of the particles is continuous with either carbide or a mixture of carbide and nitride, and there is no graphite exposed to the electrolyte. Also, the surface of the particles is preferably as smooth as possible compared to rough or jagged. Most graphite materials have a jagged surface where the graphite sheets tend to be more fragmented when the particles are sized. A smooth surface is thought to be more resistant to electrolyte attack on the bulk graphite structure, and that has been achieved in the prior art by coating. The carbide surface can range from a few atomic layers thick, which results in a modified surface that is a few nanometers thick, depending on the selected carbide-forming compound(s) (one or more), but does not modify the jagged surface to a more desirable smooth surface. The content of such carbide-forming surface or elements in the graphitized powder can range from about 50 ppm to about 5000 ppm, also depending on the selected compound(s) (one or more). The types of coke and carbide-forming compounds have also been found to play an important role in the formation of the desired graphite anode material. The selected coke is preferably calcined or at least partially calcined at a temperature between 500 and 2000 °C prior to graphitization. Untreated coke, especially that containing high levels of volatile substances, can react with the selected carbide-forming compound to form volatile compounds, causing the evaporation of such elements before the formation of the appropriate carbide at the graphitization temperature. On the other hand, coke that is carbonized or graphitized at temperatures above 2000 °C is chemically more stable and has no chemical reactivity with the selected carbide-forming compounds such as salts and oxides, resulting in the evaporation of such additional salts or oxides during the temperature rise to graphitization.

[0018]

[0019] ​The atmosphere in which a mixture of coke and carbide-forming compounds is graphitized is a factor in selecting such carbide-forming compounds. Non-oxidizing gases such as argon, helium, and nitrogen are suitable for graphitization. However, in the case of a nitrogen gas atmosphere, some carbide-forming elements may react with nitrogen to form undesirable nitride compounds, particularly volatile nitride compounds that dilute or reduce the carbide content. Thus, the selection of carbide-forming compounds is limited to elements that form carbides and / or nitrides at high temperatures. For graphitization in argon or other non-reactive gases, suitable carbide-forming elements form carbides that are stable at temperatures above 2000 °C. In other words, the best results occur when the melting point of the carbide is higher than 2500 °C and preferably higher than 2700 °C.

[0020] Furthermore, the form of this anode material is not coated with a graphitization precursor (or carbon layer different from the bulk). The present invention modifies the existing surface to have carbide compounds or carbide and nitride compounds formed on the surface that protect the core of the particles through many charge and discharge cycles. Thus, there is no high degree of graphitization crystallinity on the surface that chemically reacts with the electrolyte, and the nitride or carbide or both on the surface substantially reduces or eliminates the degradation of the bulk graphite material, thereby reducing one mode of battery inactivity.

[0021] This suggests that an anode material comprising coke, whether derived from petroleum or coal tar, can be sized by any number of methods to obtain an average particle size such that most particles are between about 3 microns and up to about 30 microns, and this can then be graphitized to about 3100 °C in an inert atmosphere.

[0022] The measurement of particle size serves many perspectives. In a preferred invention, the particle size can be tailored to the battery application or the specifications of the battery manufacturer. Ideally, the particles are substantially the same size, taking into account the variability of milling, sieving, and other sizing techniques. And the fact that the particles are not spherical adds an additional complexity. Fortunately, it is not necessary for the particle size measurement to be overly complex. Laser diffraction or imaging systems manufactured by Malvern or Horiba, which generally use volume-based calculations, provide adequate accuracy for the purpose of providing such anode powders for use in lithium-ion batteries. And from these measurements, the average particle size in the useful powder is generally between 1 and 50 microns, and more typically within a narrower range.

[0023] Accordingly, the present invention provides a novel graphite electrode material for lithium-ion batteries and also provides a convenient method suitable for the manufacture of such electrode materials. In one aspect regarding the graphite anode material, the graphite particles contain metal or non-metal carbide and nitride components on the particle surface, and such carbide or nitride content is between 5 ppm and 1 wt%, preferably between 50 ppm and 2000 ppm, more preferably less than about 1500 ppm, and even more preferably between about 100 ppm and 1000 ppm. The carbides and nitrides can be a single element or a mixture of different elements. The amount blended into the carbon precursor is between about 500 ppm and 10 weight percent, more preferably between 1000 ppm and 3 weight percent. The average particle size of the anode particles is between 3 and 30 microns, and preferably between 3 and 25 microns.

[0024] The process for generating a graphite material involves two main steps: milling a graphitizable carbon precursor to a specific particle size and then graphitizing the resulting powder with carbide and nitride forming materials within a specific temperature range. More specifically, the carbon precursor is selected from petroleum and coal tar coke. Untreated coke is preferred. The selected carbon precursor is milled into a powder having an average particle size of less than 30 μm depending on the requirements of a particular battery by any mechanical milling method such as ball mills, knife mills, impact mills, and jet mills. The general average particle size ranges from 3 μm to 25 μm. Optionally, the milled powder is carbonized in a non-oxygen environment to remove non-carbon elements. Since graphitization makes the particles more brittle, more jagged, and irregular in shape, which are more vulnerable to catalytic decomposition of the graphite sheet structure, sieving is preferred before graphitization.

[0025] The milled powder (carbonized or untreated) is combined with carbide and nitride forming compounds and graphitized at a temperature higher than 2650 °C, preferably between 2800 °C and 3000 °C, in an inert environment such as nitrogen, argon, helium, or a combination thereof. The carbide and nitride forming compounds can be fibrous metals, non-metals, rare earth metals, and combinations thereof. The amount of carbide or nitride forming compound used is between 100 ppm and 10 wt% of the total mass, more preferably between 0.05 wt% and 2 wt%.

Example

[0026] Description of Embodiment The usefulness of such a generated material is evaluated as a negative electrode material (lithium intercalation) of a coin-type battery containing lithium metal as a counter electrode. The preparation procedure is described below:

[0027] Preparation of Electrodes - Each electrode was fabricated through the following steps: Step 1) Approximately 2 g of graphitized powder, 0.043 g of carbon black, and 0.13 g of polyvinylidene difluoride (PVDF) (in a 10 wt% solution in N-methylpyrrolidone (NMP)) were placed in a 25 ml plastic vial and shaken in a mill with approximately 3 g of 1 / 8” steel balls for 10 minutes to form a homogeneous paste. Additional NMP was added to give the mixture the required fluidity. Step 2) A thin film of the resulting paste was cast onto a copper foil or aluminum foil using a doctor blade coater. The obtained film was dried on a hot plate at 120 °C for at least 2 hours. Step 3) The dried film was cut into 5 cm wide strips and compressed through a roller press. Step 4) Three disks (1.5 cm in diameter) of each film were punched out as electrodes using a die cutter. The electrode weight was measured by subtracting the weight of the disk substrate from the total weight of each disk. The electrode composition was 92 wt% graphite, 6 wt% PVDF, and 2 wt% carbon black, and the mass loading was approximately 10 mg / cm2.

[0028] Each coin-type cell was subjected to an electrochemical test. Each coin consisted of a bottom can, lithium metal as the counter electrode, a separator, a disk electrode, a stainless steel disk spacer, a wave spring, and a top can. These components were sequentially placed on the bottom can. After the electrolyte was added to the separator, the disk electrode was stacked on top. A 1 M LiPF6 electrolyte in a mixture of 40 vol% ethylene carbonate, 30 vol% dimethyl carbonate, and 30 vol% diethylene carbonate was used. After the top can was dropped onto the stack, the assembly was transferred to a coin-type cell compression bench and crimped together.

[0029] The electrochemical tests were conducted on an electrochemical test station as follows using different charge / discharge test programs for the anode and cathode materials respectively:

[0030] As a negative electrode material for a lithium-ion battery - A) Charge to 0.0 V at a constant current of 1.0 mA, B) Further charge at 0.0 volts for 1 hour, C) Discharge at 1 mA until the voltage reaches 2.0 volts, and D) Repeat steps A to C 5 times or 5 cycles. The charge passing through each cycle during charging and discharging was recorded and used to calculate the specific capacity and Coulombic efficiency. All tests were conducted at ambient temperature, and the batteries were tested in a glove box with oxygen and humidity levels below 3 ppm.

[0031] Analysis of Carbide and Nitride Forming Element Content After graphitization, the powder was dissolved in an acid solution and analyzed for elemental content by standard inductively coupled plasma mass spectrometry.

Example

[0032] Example Set 1 Two samples of petroleum raw coke were obtained from different suppliers and dried, crushed, and milled to an average particle size of 5 μm. The first sample was from the Phillips 66 refinery in Ponca City, Oklahoma, and the second sample was from the second Phillips 66 refinery in Lake Charles, Louisiana. Each powder was blended with 1 wt% and 2 wt% of the elements boron (<1 μm average particle size) and compared with a sample of the boron-free powder. The mixtures were graphitized at 2900 °C in an argon environment and subsequently evaluated as negative electrode materials for lithium-ion batteries. For comparison, these anode powders were graphitized under the same conditions. Table 2 lists the discharge specific capacity and initial Coulombic efficiency for such graphitized powders. Without boron, the initial Coulombic efficiency is very low (<40%), and the discharge capacity is also low (-300 mAh / g). Such materials are not suitable for use as negative electrode materials for lithium-ion batteries. When boron is included, the graphitized powders exhibit excellent properties as negative electrode materials for lithium-ion batteries (high capacity >350 mAh / g and initial Coulombic efficiency >91%).

Table 2

Example

[0033] Example Set 2 Additional coke sample powder of coke sample 1 from Example Set 1 was graphitized together with a blend of several carbide and nitride forming elements of boron and others. Six examples were created, each containing 1.5 wt% of the blend. The blend consisted of three different boron-to-cerium ratios of boron and cerium at 1:10, 10:1, and 1:1. These carbide and nitride forming compounds were selected from metal and non-metal chemicals and graphitized at 2900 °C in a nitrogen atmosphere. The graphitized powder was evaluated in the same manner as Example Set 1. Table 3 lists the discharge specific capacity and initial coulombic efficiency for such graphitized powders. The fourth and fifth columns show the elemental content of the carbide and nitride forming elements in the powder after graphitization. The first three samples exhibited an initial coulombic efficiency higher than 91% and a specific capacity greater than 335 mAh / g, demonstrating that high-performance anode graphite powder can be economically produced according to the present invention.

[0034] Referring to Table 3 below, at a graphitization temperature of 2900 °C, the carbide forming elements cause a physical difference in the resulting electrodes, which is extremely obvious in providing a huge enhancement to the initial coulombic efficiency. The carbide forming elements have a high melting point and seem to form carbide crystals on the surface carbon or accept (accommodate) nitride crystals on the surface, both of which facilitate the passage of ions in and out of the graphite and at the same time enable the protection of the graphite from the electrolyte.

Table 3

Examples

[0035] Example Set 3 Samples of untreated anode-grade petroleum coke commonly used in the production of anodes for aluminum refining were dried at 100 °C, crushed in a roller mill, and pulverized to an average particle size of 5 μm in a laboratory jet mill. The coke samples had 12 weight percent volatile matter and were divided into six separate samples. The first three samples were blended with boron and cerium, and the remaining three samples were blended with silicon, manganese, and yttrium at about 1.5 weight percent. Each group in separate small crucibles was placed in a large graphite container and graphitized in an argon gas environment at 2900 °C for 15 minutes.

[0036] The graphitized powders were evaluated as described above as anode materials for lithium-ion batteries of coin-type cells. The important parameters were specific discharge capacity and initial coulombic efficiency, and the results are listed in Table 4. The contents of carbide-forming elements in the graphitized samples are listed in Table 9. Graphitized samples containing sufficient carbide-forming element contents yielded excellent initial coulombic efficiencies (>92%) and specific capacities, and those with non-detectable contents of carbide-forming elements showed poor initial coulombic efficiencies (<60%) and low specific capacities.

Table 4

Example

[0037] Example Set 4 A set of the same mixture as in Example Set 3 was similarly graphitized at a temperature of 2900 °C, but in a nitrogen gas environment. The resulting graphitized powders were evaluated as in Example Set 3. The specific capacities and initial coulombic efficiencies obtained for these samples are listed in Table 5 below. The measured properties were similar to those of Example Set 3, except for yttrium, which showed decreased performance in initial coulombic efficiency. The carbide-forming material also forms nitrides with nitrogen gas that evaporates at a temperature lower than the graphitization temperature, and the surface treatment does not retain the particles, making them unsuitable as anode materials for metal-ion batteries.

Table 5

[0038] These examples show that the graphitized powder exhibits excellent properties as an anode material for lithium-ion batteries in the presence of carbide-forming elements, and does not have desirable properties (low coulombic efficiency) without such a content of carbide-forming elements.

Examples

[0039] Example Set 5 In Set 5 of the examples, three grades of untreated petroleum coke were dried at 100 °C, crushed in a roller mill, and ground in a laboratory jet mill to average particle sizes of 5, 8, 11, and 15 μm, respectively. The resulting coke powder was heated in nitrogen gas at 950 °C for 2 hours to remove volatile substances. These coke powders were labeled A, B, and C in the examples described below, where A is an aluminum anode grade of petroleum coke, B is a premium grade of petroleum coke of the type used as an anode for making recycled steel in an electric arc furnace, and C is a lower premium grade of petroleum coke that has been used as a precursor for making anodes in metal ion batteries with high volatile content.

[0040] Samples of various coke particles containing 11-μm powder of Coke A, 5- and 8-μm powders of Coke B, and 15-μm powder of Coke C, together with two carbide-forming compounds (the elements boron and cerium oxide) at weight contents of 0.5% and 1.5% were blended. The resulting mixtures were graphitized under the same conditions as in Example 4 and tested as anode materials for lithium-ion batteries. The graphitized samples were labeled A5, B5, B8, and C15 in this example, respectively. The test results are listed in Table 6 below.

Table 6

[0041] Comparative Example Set 1 The 5-μm powder of coke A and the 5- and 8-micrometer powders of coke B were graphitized in a nitrogen gas environment under the same conditions as in Set 4 of the examples without any carbide-forming elements. The graphitized powders were evaluated as anode materials for lithium-ion batteries in the same manner as in the above examples. These samples were labeled A5, B5, and B8, respectively, in this example. The test results are also listed in Table 7 in Comparative Example 1 below.

Table 7

[0042] Comparative Example Set 2 The 5- and 8-micrometer powders of coke B were coated with 8 wt% and 6 wt% pitch using the solution-phase precipitation method described in U.S. Patent No. 7,323,120. The pitch coating method involves several steps, which include a) dispersing the coke powder in an organic solvent, b) dissolving the selected pitch in an organic solvent, c) heating both the coke and pitch solutions to a high temperature, d) mixing the two solutions, and then cooling the mixture under continuous stirring such that the specific heavy portion of the dissolved pitch precipitates as a solid film onto the coke particles, e) separating the pitch-coated coke particles from the solution by filtration, f) washing out the residual pitch solution on the coated coke particles using an additional organic solvent, and finally drying the pitch-coated particles. The pitch-coated powders were further treated by oxidation in air at a high temperature (less than 350 °C) such that the resulting powders were non-fusible and the coated pitch was rendered non-graphitizable compared to the core of the bulk coke. This process is generally named stabilization. After pitch coating and stabilization, the powders were graphitized under the same conditions as in Set 4 of the examples. The graphitized powders were evaluated as anode materials for lithium-ion batteries as described above, and the results are listed in Table 8 under Comparative Example 2 below.

Table 8

[0043] Sample sets 3 and 4 were subjected to an analytical test to measure their components after graphitization. The amounts of carbide and nitride forming elements in the anode material after the test are shown in Table 9. They were essentially at a low level, and not all samples could be measured considering the capabilities of the in-house test equipment. [Table 9]

[0044] In sample set 5, the anode samples were created by combining boron and another carbide or nitride forming element in a 1:3 ratio, with 8 μm premium coke graphitized at 2900 in nitrogen gas and a nitrogen environment for 15 minutes. The weight was measured before graphitization. The results are shown in Table 10. [Table 10]

[0045] The above examples show that the graphite powder produced according to the present invention exhibits excellent specific capacity and good initial coulombic efficiency compared to those made via state-of-the-art methods, and moreover, the process is simple and the obtained graphite powder has a different chemical composition from either the particle surface or the bulk derived from those made by the prior art.

[0046] Finally, it should be noted that any discussion of reference documents, especially any reference documents that may have a publication date after the priority date of this application, is not an admission that it is prior art to the present invention. At the same time, all the following claims are hereby incorporated herein as additional aspects of the present invention into this detailed description or specification.

[0047] Although the systems and methods described herein have been described in detail, it should be understood that various changes, substitutions, and modifications can be made without departing from the spirit and scope of the invention as defined by the following claims. Those skilled in the art can experiment with suitable embodiments and can identify other ways to practice the invention that are not precisely described herein. The inventors intend that changes and equivalents of the invention be within the scope of the claims and that the description, summary, and drawings not be used to limit the scope of the invention. The invention is particularly intended to be as broad as the following claims and their equivalents.

Claims

1. Graphitic carbon powder comprising particles having an average particle size between 1 μm and 50 μm, the particles having a modified surface comprising carbide compounds constituting at least 5 ppm and not more than 1% by weight of the particles, the graphitic carbon powder comprising at least 99% by weight carbon graphite.

2. 2. The graphitic carbon powder of claim 1, wherein the particles have an average particle size between 3 μm and 30 μm.

3. 3. The graphitic carbon powder of claim 2, wherein the particles have an average particle size between 3 μm and 25 μm.

4. Graphitic carbon powder according to any of the preceding claims, wherein the particles are at least 99.5% by weight carbon graphite and at least 50 ppm carbide compounds.

5. Graphitic carbon powder according to any of the preceding claims, wherein the particles are at least 99.9% by weight carbon graphite.

6. Graphitic carbon powder according to any of the preceding claims, wherein the particles are at least 99.99% by weight carbon graphite.

7. Graphitic carbon powder according to any of the preceding claims, wherein the particles further comprise at least 5 ppm of a nitride compound.

8. 8. The graphitic carbon powder of claim 7, wherein the particles have a core and an outer surface, and the core comprises graphite and the outer surface comprises carbide and nitride compounds in the form of crystals, the crystals being along at least the outer edge or surface of the particles and comprising at least 50 ppm by weight and no more than 2000 ppm by weight of the powder.

9. Graphitic carbon powder according to any of the preceding claims, wherein the carbide compound comprises at least one selected from Ti, Y, Zr, Nb, Mo, La, Ce, B and combinations thereof.

Images