Process and apparatus for production of graphite

Abstract

A process for production of graphite. The process comprises providing a metallic melt; supplying a carbonaceous material to the metallic melt; subjecting the carbonaceous material to catalytic graphitization in the metallic melt; passing a gas through the metallic melt; and collecting a composition leaving the metallic melt, the composition comprising graphite carried by said gas. An apparatus (100) for production of graphite. The apparatus comprises a graphitization reactor (110); a heating element (120) heating the graphitization reactor; an inlet conduit (130) connecting a source (140) of carbonaceous material with the graphitization reactor; a gas conduit (150) connecting a source (160) of gas with a bottom part of the graphitization reactor; and an outlet conduit (170) connecting a top part of the graphitization reactor with a gas-solids separator (180).

Description

[0001] PROCESS AND APPARATUS FOR PRODUCTION OF GRAPHITE

[0002] Technical field

[0003] The present application relates to a process for production of graphite and an apparatus for production of graphite.

[0004] Background

[0005] Lithium-ion batteries are widely used in portable electronic devices and electric vehicles due to their high energy density and long cycle life. These batteries consist of an anode, cathode, separator, and electrolyte. The anode, typically made of graphite, plays a crucial role in storing and releasing lithium ions during charge and discharge cycles. Graphite has a relatively high specific capacity of 372 mAh / g and the lowest average de- / lithiation potential (i.e. , 0.2 V vs. Li / Li+).

[0006] As the rapid expansion of lithium-ion battery market, the demand for graphite is growing fast. It has been reported that the global production of graphite in 2022 was over 1.3 million metric tons. However, the reserve of natural graphite is quite limited and concentrated. In 2021 , 82 % of natural graphite was mined and exported from China whereas Europe only accounted for 3.3 %. Another concern for natural graphite extraction is environmental pollution, e.g., toxic dust in the air and water, polluted crops and damaged earth. As an alternative to natural graphite, graphite material can be artificially synthesized using fossil-based carbon materials. Nevertheless, the production cycle of artificial graphite is 14 days, including ultra-high temperatures between 2500 and 3500 °C for 1-2 days. Some research has verified that the production of synthetic graphite materials requires 4.0 x 104MJ / ton of energy and emits 5.3 ton CO2-eq / ton into the atmosphere.

[0007] Catalytic graphitization offers a promising solution for sustainable graphite production. It allows to convert renewable non-graphitizing carbon sources, such as biomass, biomass-derived biochar and other carbon-rich organic materials into graphitic carbon under a relatively low temperature between 800 and 2000 °C. The technology can tackle the existing challenges such as raw material supply constraints, high-energy consumption, and high CO2 emissions in traditional graphite production processes, aligning with the low-carbon development strategies being pursued globally. Several studies have been done to investigate and optimize the graphitization process. A variety of catalysts, such as Ni, Co, and Fe, have been introduced to decrease the temperature of graphitization for the preparation of nanostructured graphitic carbons. Recently, Wang et al. reported that rare earth metals including Pr, La, and Ce and additives (Ti, Ni, and B) could promote the graphitization of needle coke and pitch coke at 2800 °C. In these studies, hydrochloric acid, hydrofluoric acid and nitric acid were widely used to dissolve and remove catalyst residues in the obtained graphite.

[0008] Although catalytic graphitization is a promising technology for the mass production of synthetic graphite, its development is still in its infancy and has not yet been commercially applied because of multi-scale challenges. The bio-based graphite products that have been researched up to now do not exhibit electrochemical performance comparable to the commercial graphite currently in use. Lars Frankenstein et al. employed four different iron-based catalysts to graphitize coffee grounds. Specific delithiation capacities of up to 320 mAh g-1were achieved using Fe powder (Frankenstein, Lars, et al. “Revealing the Impact of Different Iron-Based Precursors on the ‘Catalytic’ Graphitization for Synthesis of Anode Materials for Lithium-Ion Batteries” ChemElectroChem 10.5 (2023): e202201073). Gomez-Martin et al. investigated ‘catalytic graphitization’ behavior of wood-based biomass precursors using FeCh as activator. Reversible capacities of 307 mAh g-1were achieved at 2000 °C using ~35 wt% FeCh (Gomez-Martin, Aurora, Zoe Schnepp, and Joaquin Ramirez-Rico. “Structural evolution in iron-catalyzed graphitization of hard carbons” Chemistry of Materials 33.9 (2021): 3087-3097). Wang Tao et al. conducted catalytic graphitization of anthracite based on boric acid (H3BO3), lanthanum oxide (La2Os), praseodymium oxide (PreOn), and cerium oxide (CeO2) at 2600 °C and 2800 °C. The specific capacities of the samples varied from 240.1 mAh g-1to 337.2 mAh g-1(Wang, Tao, et al. “Catalytic graphitization of anthracite as an anode for lithium ion batteries” Energy & Fuels 34.7 (2020): 8911-8918).

[0009] Another challenge for catalytic graphitization is that metal needs to be removed from graphite after the catalytic graphitization as battery requires an ultra-high material purity. Nowadays, strong inorganic acids such as nitric acid and hydrochloric acid are utilized to remove metal catalysts after catalytic graphitization. Hongtao Li et al. use HCI and HF to purify the graphite products after catalytic graphitization (Li, Hongtao, et al. “Catalytic graphitization of coke carbon by iron: Understanding the evolution of carbon Structure, morphology and lattice fringes” Fuel 279 (2020): 118531). Nathan A. Banek et al. performed acid leaching on obtained graphite products by using HCI and HNO3 (Banek, Nathan A., et al. “Sustainable conversion of biomass to rationally designed lithium-ion battery graphite” Scientific Reports 12.1 (2022): 8080). Some studies have verified the acid washing step using HNO3 might also create some oxygen-surface groups that influence electrochemical performance (Gomez-Martin, Aurora, et al. “Binder-free supercapacitor electrodes: Optimization of monolithic graphitized carbons by reflux acid treatment” Fuel Processing Technology 199 (2020): 106279).

[0010] Excessive consumption of inorganic acid is not only a substantial expense but also a huge burden on the environment. Compared to natural graphite with a price of 743-829 $ / ton, green graphite is not cost-effective. Therefore, green graphite is not competitive in the market.

[0011] Summary of the invention

[0012] It is an object of the present invention to alleviate one or more of the challenges or deficiencies mentioned above. Another object is to facilitate production of batteryuse graphite from various resources. These and other objects, which will become apparent to a skilled person studying the description, are achieved by a process for production of graphite and an apparatus for production of graphite, as set out in the appended clams. The present invention thus allows for high-quality battery-use graphite production while avoiding the use of strong inorganic acids for graphite and metal catalyst separation after the catalytic graphitization process is complete.

[0013] The process for production of graphite comprises

[0014] - providing a metallic melt;

[0015] - combining a carbonaceous material with the metallic melt;

[0016] - subjecting the carbonaceous material to catalytic graphitization in the metallic melt;

[0017] - passing a gas through the metallic melt; and

[0018] - collecting a composition leaving the metallic melt, the composition comprising graphite carried by said gas.

[0019] It has thus been found that graphite-containing particles formed during the catalytic graphitization may be removed from the metallic melt by a gas passing through the metallic melt. The need for subsequent separation of graphite from metal catalyst is thus reduced. In other words, the gas may be passed into the metallic melt and through the metallic melt. The gas is preferably passed into a lower part of the metallic melt. Thereby, graphite-containing particles formed in the metallic melt may be driven out of the metallic melt.

[0020] The metallic melt may comprise a melt of metal or a melt of metal salt. The term “metallic melt” thus refers to a melt comprising one or more metallic element(s). The melt of metal or the melt of metal salt may comprise one or more element(s) selected from the group consisting of Fe, Co, Ni, Mg, Mn, Ti and Zr. Said elements catalyse the graphitization of carbonaceous material. An additional catalyst or graphitization agent, such as Si, is not necessary. The catalytic graphitization may thus occur in the absence or substantial absence of Si. The metallic melt may be free or substantially free from Si. In other words, Si may be present in the metallic melt in trace amounts. Accordingly, the process may occur without addition of Si to the metallic melt. The melt of metal or melt of metal salt may further comprise one or more melting point lowering elements. It is preferred that the melt of metal comprises or consists of cast iron.

[0021] A nucleating agent, such as one or more of SiSr, BiFe, SiFe and BiFe, is not necessary. The catalytic graphitization may thus occur in the absence of or substantial absence of a nucleating agent, such as one or more of SiSr, BiFe, SiFe and BiFe. The metallic melt may be free or substantially free from a nucleating agent, such as one or more of SiSr, BiFe, SiFe and BiFe. Accordingly, the process may occur without addition of a nucleating agent, such as one or more of SiSr, BiFe, SiFe and BiFe.

[0022] A spheroidizing agent, such as Mg or a combination of a rare earth metal and Mg, is not necessary. The catalytic graphitization may thus occur in the absence of or substantial absence of a spheroidizing agent, such as Mg or a combination of a rare earth metal and Mg. The metallic melt may be free or substantially free from a spheroidizing agent, such as Mg or a combination of a rare earth metal and Mg. Accordingly, the process may occur without addition of a spheroidizing agent, such as Mg or a combination of a rare earth metal and Mg.

[0023] Any additional catalyst or graphitizing agent, nucleating agent and / or spheroidizing agent may end up as an impurity in the formed graphite. By avoiding or minimizing the presence of such catalysts and / or agents, less effort needs to be spent on removal of impurities from the formed graphite. As an example, acid leaching of graphite-containing particles removed from the metallic melt may be dispensed with or may consume less acid than acid leaching of less pure particles.

[0024] The carbonaceous material may comprise carbon, coal, char, biocarbon, biocoal or biochar. Herein, the terms “carbon”, “coal” and “char”, including the terms “biocarbon”, “biocoal” and “biochar”, are used interchangeably to represent a carbon- rich material, which for example may have been obtained by pyrolysis of organic matter, such as biomass. Specifically, the terms “biocarbon”, “biocoal” and “biochar” refer to such material of biological or renewable origin. It is preferred that the carbonaceous material originates from biological or renewable sources, such as biomass or waste. The carbonaceous material is typically a particulate material, preferably a material having a largest particle size of less than 100 pm, such as less than 50 pm. The combination of the carbonaceous material with the metallic melt may be achieved by supplying the carbonaceous material to the metallic melt or by supplying the carbonaceous material to the metallic material before melting thereof.

[0025] The gas is typically an inert gas, suitably a noble gas, such as Ar.

[0026] The metallic melt may have a first temperature during the catalytic graphitization and a second temperature during the collection of the composition leaving the metallic melt, the second temperature being lower than the first temperature. The first, higher, temperature may allow carbon of the carbonaceous material to dissolve into the metal of the metallic melt and convert carbon to graphite. Lowering of the temperature of the metallic melt may facilitate phase separation, or precipitation, of graphite, promoting a high graphite content in graphite-containing particles leaving the metallic melt. The second temperature is typically more than 100 °C, such as more than 200 °C, lower than the first temperature. When the metallic melt comprises or consists of cast iron, the first temperature may be above 1600 °C, such as in the range of 1610 to 1800 °C or 1650 to 1800 °C, and the second temperature may be below 1500 °C, such as in the range of 1200 to 1490 °C or 1200 to 1450 °C. It is understood that the metallic melt remains in a liquid state. A sequence of such first temperature catalytic graphitization, followed by second temperature collection of the composition leaving the metallic melt, may be repeated one or more times.

[0027] Any remnant of the metallic melt may be considered as an impurity in the formed graphite. By facilitating phase separation, or precipitation, of graphite, less effort needs to be spent on removal of impurities from the formed graphite. As an example, acid leaching of graphite-containing particles removed from the metallic melt may be dispensed with or may consume less acid than acid leaching of less pure particles.

[0028] The metallic melt may have a temperature in the range of 600 to 2800 °C, preferably in the range of 1200 to 1800 °C, during the catalytic graphitization. It is understood that the metallic melt is in a liquid state. When the metallic melt comprises or consists of cast iron, the metallic melt may have a temperature above 1600 °C, such as in the range of 1610 to 1800 °C or 1650 to 1800 °C, during the catalytic graphitization. The catalytic graphitization at said temperatures typically lasts for more than 1 hour, preferably more than 2 hours or more than 3 hours, such as in the range of 1 to 6 hours, such as 2 to 6 hours or 3 to 6 hours. As a result, graphite having a highly crystalline structure may be obtained. The metallic melt is suitably stirred during the catalytic graphitization, such as by gas stirring, mechanical stirring or induction stirring. The gas used for gas stirring is typically an inert gas, suitably a noble gas, such as Ar.

[0029] The process for production of graphite may be a continuous or semi-continuous process. In other words, carbonaceous material may be continuously or intermittently supplied to the metallic melt and the composition leaving the metallic melt may be continuously or intermittently collected.

[0030] The process may further comprise separating the graphite from the gas of said composition. Alternatively or additionally, the process may further comprise preparing the carbonaceous material to be supplied to the metallic melt by pyrolysis of biomass.

[0031] The apparatus for production of graphite comprises

[0032] - a graphitization reactor;

[0033] - a heating element heating the graphitization reactor;

[0034] - an inlet conduit connecting a source of carbonaceous material with the graphitization reactor;

[0035] - a gas conduit connecting a source of gas with a bottom part of the graphitization reactor; and

[0036] - an outlet conduit connecting a top part of the graphitization reactor with a gas-solids separator.

[0037] It has thus been found that graphite-containing particles may be collected by, and separated from, a gas passing through the graphitization reactor. In other words, graphite-containing particles may be driven through the graphitization reactor by a gas that is passed into the bottom part of the graphitization reactor.

[0038] The graphitization reactor may be configured to hold a metallic melt or may hold a metallic melt. Thus, graphite-containing particles may be driven out of the metallic melt by a gas that passed into the bottom part of the graphitization reactor. The graphitization reactor may typically be a graphite crucible. The gas-solids separator may be a cyclone. The apparatus may be further defined as mentioned above in respect of the process for production of graphite.

[0039] Brief description of the drawings

[0040] Fig. 1 is a schematic illustration of an apparatus for production of graphite.

[0041] Fig. 2 is an XRD pattern for the raw material of Example 1.

[0042] Fig. 3 is an XRD pattern for sample G-1600-1 h-11 of Example 1.

[0043] Fig. 4 is an XRD pattern for sample G-1600-1 h-31 of Example 1.

[0044] Fig. 5 is an XRD pattern for sample G-1600-1 h-51 of Example 1.

[0045] Fig. 6 is an XRD pattern for sample G-1600-1 h-101 of Example 1. Fig. 7 is a Raman spectrum for sample G-1600-1 h-11 of Example 1.

[0046] Fig. 8 is a Raman spectrum for sample G-1600-1 h-31 of Example 1.

[0047] Fig. 9 is a Raman spectrum for sample G-1600-1 h-51 of Example 1.

[0048] Fig. 10 is a Raman spectrum for sample G-1600-1h-101 of Example 1.

[0049] Fig. 11 is an SEM image of sample G-1600-1h-101 of Example 1.

[0050] Fig. 12 shows specific capacity and coulombic efficiency of sample G-1600-1 h- 11 of Example 1.

[0051] Fig. 13 shows specific capacity and coulombic efficiency of sample G-1600-1 h- 31 of Example 1.

[0052] Fig. 14 shows specific capacity and coulombic efficiency of sample G-1600-1 h- 51 of Example 1.

[0053] Fig. 15 shows specific capacity and coulombic efficiency of sample G-1600-1 h- 101 of Example 1.

[0054] Fig. 16 shows long-term specific capacity and coulombic efficiency of sample G-1600-1h-101 of Example 1.

[0055] Fig. 17 shows the specific capacity of the sample G-1600-1 h-101 of Example 1.

[0056] Fig. 18 is a photo of sample 1 of Example 2.

[0057] Fig. 19 is a photo of sample 3 of Example 2.

[0058] Fig. 20 is a TGA curve for sample 1 of Example 2.

[0059] Fig. 21 is a TGA curve for sample 2 of Example 2.

[0060] Fig. 22 is a TGA curve for sample 3 of Example 2.

[0061] Fig. 23 present Raman patterns of the graphite samples collected from 20 min to 210 min in Example 3.

[0062] Fig. 24 shows a SEM image and a corresponding EDS characterization of the graphite sample collected between 180-210 min in Example 3.

[0063] Fig. 25 shows an XPS pattern of the ash compounds in the graphite sample collected between 180-210 min in Example 3.

[0064] Detailed description

[0065] Fig. 1 schematically shows an apparatus 100 for production of graphite. The apparatus 100 comprises a graphitization reactor 110 in the form of a graphite crucible. A heating element 120 in the form of a copper coil surrounds and heats the graphitization reactor 110. An inlet conduit 130 connects a source 140 of carbonaceous material with the graphitization reactor 110. A gas conduit 150 connects a source 160 of gas with a bottom part of the graphitization reactor 110. An outlet conduit 170 connects a top part of the graphitization reactor 110 with a gas-solids separator 180 in the form of a cyclone. The graphitization reactor 110 holds a metallic melt 190.

[0066] In a process for production of graphite, a metallic melt 190 is provided in a graphitization reactor 110. Particulate carbonaceous material is supplied from a source 140 of carbonaceous material, via an inlet conduit 130, to the metallic melt 190. In the metallic melt 190, the carbonaceous material is subject to catalytic graphitization. For stirring of the metallic melt during catalytic graphitization, gas is supplied at a low rate from a source 160 of gas, via a gas conduit 150, to the metallic melt 190. Graphitecontaining particles formed by catalytic graphitization travel upwards through the metallic melt 190 due to gravity. For removal of graphite-containing particles from the metallic melt 190, gas is supplied at a high rate from the source 160 of gas, via the gas conduit 150, to the metallic melt 190. The gas carries graphite containing particles up through and out of the metallic melt 190. At a top part of the graphitization reactor 110, a composition of graphite-containing particles and gas is collected in an outlet conduit 170 and led to a gas-solids separator 180.

[0067] Example 1. Catalytic graphitization of biocarbon

[0068] Production of biocarbon

[0069] Biomass pyrolysis was performed in an auger reactor heated by a resistive electric heating element at a temperature of 550 °C by using softwood sawdust as raw biomass to produce biocarbon and, in the process of condensation, raw biooil and waste gases. Produced biocarbon was then used as a raw material for catalytic graphitization process to produce graphite powders. Elemental compositions of biomass and biocarbon are summarized in Table 1.

[0070] Table 1. Elemental analysis of biomass and biocarbon Preparation of catalyst and biocarbon

[0071] The biocarbon particles derived from pyrolysis were ground, broken down, and sieved. Specifically, the particles were ground by using a pestle and mortar. Only the finest biocarbon particles smaller than 32 pm were screened out and utilized. Cast iron powder (3.0-3.7 % carbon) was used as catalyst in batch catalytic graphitization experiments. Designed various cases, including catalyst loading amounts and the sample names, are referred in Table 2. Each case utilized 20 grams of biocarbon, with the catalyst loading defined as the mass ratio of the cast iron powder to biocarbon. The biocarbon powder and casting iron powder were loaded into a zirconia jar with zirconia balls. Afterward, the jar was installed in a planetary ball mill (QM-3SP2, manufactured by Henan Lanphan Technology Co., Ltd) and mixed at 600 rpm for 15 min.

[0072] Table 2. Graphitization samples

[0073] Catalytic graphitization of biocarbon

[0074] The resulting mixture (cast iron and biocarbon powders) was subsequently graphitized at high temperature. An induction furnace (MJ 120 F, manufactured by SinterCast International Ltd.) was used for the graphitization. Mixture powders were put into a graphite crucible and then moved to the induction furnace. A refractory brick cover made of aluminum oxide was wrapped around the graphite crucible to reduce the heat loss during the heat treatment. Argon, with a flow rate of 500 mL / min, was used as a protective gas. A type B thermocouple was used to detect the real-time temperature of the crucible from above. The crucible was heated up to 1600 °C for 1 hour to achieve graphitization.

[0075] Acid washing

[0076] Following the graphitization, the catalysts residues present in the produced graphite samples were removed through acid washing. Hydrochloric acid (1 mol / L) was utilized for an acid leaching process. Initially, the graphite samples were placed into a beaker containing 0.6 L of the hydrochloric acid solution, where they were subjected to washing. A magnetic stirring heater and a magnetic bar were utilized to maintain the temperature at 70 °C and stirring speed at 400 rpm, respectively. After 4 hours of stirring and heating, the graphite powders were separated from the waste liquid by filtration.

[0077] Afterwards, the ash content in the leached samples was determined by thermogravimetric analysis (TGA). The samples were weighed into 100 pL aluminum cups with pierced lids (the hole had approx. 0.4 mm diameter). Dry oxygen gas (50 mL / min) was flushed during the analysis. The samples were heated from 25 to 900 °C at a ramping rate of 10 °C / minute. Iron content (catalyst residues in graphite powders) was calculated based on the residual weight percentage.

[0078] XRD

[0079] XRD patterns for the biochar and the resulting graphitized samples are shown in Figs. 2 to 6. Graphite is shown most distinctly by the (002) peak near 20 = 26.55° which can be seen obviously in all treated samples, while the other peaks for the (100), (101), (004), and (110) planes are relatively weak. In the control sample, which was not treated by catalyst, a broad band with no distinct peak at 20 = 26.55° is observed, representing high amounts of disordered carbon. For the catalytically treated samples, the sharp band from 26.2° to 26.55° represent graphitic structure.

[0080] Table 3 summaries the crystallite size of the graphite in nanometers for each sample (La and Lc), calculated using the Scherrer equation (A. Oya and H. Marsh, “Phenomena of catalytic graphitization”, Journal of Materials Science, vol. 17, no. 2, pp. 309-322, 1982), based on the position of (002) peak. From this, the interlayer spacing (d002) was calculated, and used to find the graphitization degree parameter (G%), used by Maldonado-Hodar et al (F. Maldonado-Hodar, C. Moreno-Castilla, J. Rivera- Utrilla, Y. Hanzawa, and Y. Yamada, “Catalytic graphitization of carbon aerogels by transition metals”, Langmuir, vol. 16, no. 9, pp. 4367-4373, 2000).

[0081] The G% values quantitatively characterize the degree of order for graphene layer stacking and degree of conversion from turbostratic carbon to graphitic carbon. The d002 value of the sample G-1600-1h-101 is quite smaller than other treated samples, and its G% value is as high as 96.83%, indicating that the graphitic structure in this sample is very close to pure graphite (d002 = 0.3354 nm). Table 3. Crystallite size of the graphite

[0082] Raman

[0083] Figs. 7 to 10 present first-order Raman spectra of the graphite samples. The spectra are characterized by two peaks: the disorder-induced peak (D band) at wavelength around 1350 cm-1and the graphite peak (G band) at around 1580 cm-1. The intensities of the D peak and the G peak are related to the ordering of the graphitic structure (M. Dresselhaus, G. Dresselhaus, and M. Hofmann, “The big picture of Raman scattering in carbon nanotubes”, Vibrational Spectroscopy, vol. 45, no. 2, pp. 71-81 , 2007; A. C. Ferrari, “Raman spectroscopy of graphene and graphite: Disorder, electron-phonon coupling, doping and nonadiabatic effects”, Solid state communications, vol. 143, no. 1-2, pp. 47-57, 2007). The ratio of the intensities of the D band and the G band, Id / lg, is a measure of the degree of order where a lower ratio indicates a lower disorder and higher amounts of graphite. The Id / lg ratio of G-1600- 1 h-101 is 0.0452, which implies that the presence of a catalyst promotes the reordering of the carbon structure at lower temperature. Another evidence of the graphitic structure can be found in the broad band around 2700 cm-1. This band is a result of second order resonance from the D band, and can be called the G', 2D or D* band which is characteristic of stacked graphene layers. These results suggest almost 100 % graphitization occurred during the process. The Raman spectra agrees with the results shown by the XRD patterns, indicating superior graphitic structure of G-1600- 1 h-101. The results are comparable with artificial graphite materials derived directly from biomass (I. Major, J.-M. Pin, E. Behazin, A. Rodriguez-Uribe, M. Misra, and A. Mohanty, “Graphitization of Miscanthus grass biocarbon enhanced by in situ generated FeCo nanoparticles”, Green Chemistry, vol. 20, no. 10, pp. 2269-2278, 2018.)

[0084] SEM

[0085] Scanning electron microscope was used to observe the morphology of the sample G-1600-1 h-101 , as shown in Fig. 11. The image reveals that approximately 20 pm diameter plate-like graphite materials are homogeneously distributed on the matrix. In fact, the morphology of the G-1600-1 h-101 flakes look very similar to commercial artificial flake graphite.

[0086] Electrochemical characterization

[0087] The electrochemical lithium (de)intercalation properties of the four graphite samples were examined with the coin-type (CR2032) half-cell setup. Composite carbon electrodes were prepared with a composition of 80 wt% active material, 10 wt% sodium alginate binder as the binder and 10 wt% water. The mixture was ground to fine particles and blended together. The prepared paste was cast on a Cu foil and dried at 100 °C for 10 hours. The loading mass of the carbon electrode was controlled between 1.5 and 2.0 mg cm"2. Afterward, the electrodes were transferred inside an argon-filled glovebox. The electrolyte was a solution of 1 M LiPF6 in dimethyl carbonate : ethylene carbonate : ethyl methyl carbonate = 1 :1 :1 vol% with 1 % vinylene carbonate. A commercial lithium foil was used as the counter electrode and glass fiber was used as the separator. The discharge and charge tests of half-cells were carried out on a CT3002A battery test system (Wuhan, China) in a voltage range of 0-3 V. Cyclic voltammetry was measured by an electrochemistry workstation (CHI 700E) between 0.01 and 3 V at a scan rate of 1 mV s’1. The Electrochemical Impedance Spectroscopy (EIS) test was measured by AC impedance analysis (Zahner, Zennium pro). Figs.12 to 15 indicate the specific capacities (lower set of data points) and coulombic efficiencies (upper set of data points) of G-1600-1h-11 , G-1600-1 h-31 , G-1600-1 h-51 and G-1600- 1 h-101 in a half-cell at 0.5 C. It turns out that the G-1600-1 h-101 provided the highest initial specific capacity (392.7 mAhg-1) and initial coulombic efficiency (71.7 %). This half-cell also delivers a high capacity of 520 mAhg-1and a high coulombic efficiency of 99.43 % after 200 cycles. The specific capacity is even better than commercial synthetic graphite from fossil-based carbon feedstock, suggesting its excellent electrochemical properties.

[0088] Based on G-1600-1h-101 , a lithium ion full cell was constructed using lithiated graphite materials as the negative electrode and LiFePO4 as the positive electrode in a CR2032 coin-type cell. The N / P ratio was controlled to 1.20. The full cells were charged and discharged in a voltage range of 2.7-3.9 V at different current rates. The specific capacity (lower set of data points) and coulombic efficiency (upper set of data points) at 0.5 C is shown in Fig. 16. The full cell delivers a high discharge specific capacity of 141.5 mAh g-1with an ICE of 85.7 %. Even after 500 cycles, it maintains a discharge capacity of 124.1 mAhg-1, demonstrating superior stability, and highly reliable cycling performance. Fig. 17 shows the rate ability of the full-cell battery. As the current density increases from 0.2 C to 5 C, the full cells discharge specific capacities of 144.5 (0.2C), 137.6 (0.5C), 128.4 (10), 121.9 (1.5C), 115.1 (20), 102.6 (30) and 80.0 mAh g"1(5C), respectively. All these values are significantly higher than those of batteries made of LiFePC>4 and commercial graphite 26, indicating fast reaction kinetics during the Li storage process.

[0089] Example 2. Phase separation of carbon and iron in batch catalytic graphitization tests During the graphitization process of Example 1 , a clear iron separation was observed in the sample G-1600-1 h-101. Therefore, the G-1600-1 h-101 case was repeated to verify the physical separation and evaluate the separation efficiency. To elaborate, a sample was prepared in the same way as in Example 1. In a first stage, the prepared sample was heated to 1300 °C and held at such temperature for 6 hours in the induction furnace, with argon used as the protective gas. After heat treatment and subsequent cooling to room temperature, iron separation was observed (Fig. 18). A few small iron balls were detected. The iron balls and powder were manually separated by sieving. In a second stage, the powder derived after the first stage was heated to 1600 °C and maintained for 4 hours. After heat treatment and cooling to room temperature, a clear iron separation was observed and a lump of iron appeared. Similarly, the powder was separated by sieving. In a third stage, the same heat treatment program as in the second stage was applied to the powder derived from the second stage. After heat treatment and subsequent cooling to room temperature, a clear iron separation was again observed (Fig. 19) and the powder was separated by sieving.

[0090] TGA

[0091] Thermogravimetric analysis (TGA) was carried out on the powders obtained after the first, second and third heat treatment stages to determine the iron content in the powders. TGA was performed on a Mettler TGA / DSC 3+ Stare system, equipped with a Huber minichiller 600 cooler. The samples were weighed into 100 pL aluminum cups with pierced lid (the hole had approx. 0.4 mm diameter), and dry oxygen gas (50 ml / min) was flushed during the analysis. The samples were heated from 25 to 900 °C, with a ramping rate of 10 °C / minute. Figs. 20 to 22 show the TGA curves of the powders obtained from first (sample 1), second (sample 2) and third (sample 3) heat treatment stages. Table 4 presents the mass ratios of carbon to iron for samples 1 to 3. Table 4. Mass ratios of carbon to iron

[0092] It turns out that the first stage heat treatment leads to an increase in the atomic ratio of the C to Fe in the carbon-rich sample from 0.47 to 1.91 , which equals a decrease in iron content from 91 wt% to 71 wt%. Visual observation indicated no clear separation between graphite and iron after first heat treatment. The second heat treatment results in an increased atomic ratio of C to Fe in the sample to 2.45. This indicates a lower iron content of 66 wt% in the resulting sample 2. This result agrees with the visual observation of separated iron lump and graphite powder in crucible. The third heat treatment further leads to an increased atomic ratio of C to Fe in the sample to 3.11 , equalling an iron content of 60 wt% in the resulting sample 3.

[0093] SEM and EDS

[0094] Scanning electron microscope (SEM) photos and corresponding energy- dispersive X-ray spectroscopy (EDS) elemental mapping photos for C and Fe were obtained of the sample before heat treatment and of sample 3, respectively. The EDS elemental mapping photo of sample 3 indicates a significant reduction in iron content. Conversely, the EDS elemental mapping photos of the original sample reveal a well- mixed iron and carbon, with well-dispersed iron covering whole particles. This result aligns with the TGA result, indicating an effective phase separation of carbon and iron in batch catalytic graphitization tests.

[0095] Example 3. Direct separation of carbon from molten iron

[0096] Production of biocarbon

[0097] Biomass pyrolysis was performed in an auger reactor heated by a resistive electric heating element at a temperature of 550 °C by using softwood sawdust as raw biomass to produce biocarbon and, in the process of condensation, raw biooil and waste gases. Produced biocarbon was then used as a raw material for catalytic graphitization process to produce graphite powders. Preparation of biocarbon

[0098] Before the test, the biocarbon particles were ground, broken down, and sieved. The particles were ground by using a pestle and mortar. Only the finest biocarbon particles smaller than 32 pm were screened out and utilized.

[0099] Direct separation of carbon from molten iron

[0100] A 75 kW induction furnace (3 kHz, Inductotherm 75 KW in Elkem, Norway) was used for the direct separation of carbon from molten iron. The graphite crucible used for the induction furnace had a maximum capacity of 15 liters, equivalent to approximately 90 kg of iron. To prevent the combustion of produced graphite and oxidation of iron, Ar was injected from the bottom of the crucible using a gas lance during the graphitization process. In this experiment, 5 L (approximately 30 kg) cast iron powders and 5 L (approximately 5 kg) biocarbon powders were loaded. Specifically, biocarbon powders were placed at the bottom of the crucible, with the casting iron powders layered on top of them. To ensure a complete melting of iron powders, the furnace was heated to 1600 °C at a rate of 50 °C / min and maintained for 4 hours. Eight type C thermocouples were employed in the furnace to monitor the realtime temperature. During the graphitization, glass wool was used to wrap the outlet of crucible and capture floated graphite powders that were carried along with the gas. Samples of captured graphite powder were collected on the glass wool wrap at regular intervals, i.e. , every 20 minutes during the first hour and subsequently every 30 minutes.

[0101] Raman

[0102] The Raman patterns for the graphitized samples obtained from 20 min to 210 min are shown in Fig. 23. The D peak of the Raman spectra is much lower in the sample collected between 40-60 minutes compared to those collected between 0- 20 minutes and 20-40 minutes. As the test progresses, the continuous graphitization effect is still visible, with negligible D peak being detected in samples collected between 150-180 minutes and 180-210 minutes.

[0103] HRTEM

[0104] High-resolution transmission electron microscopy (HRTEM) was used to study morphologies of the graphite sample collected between 180-210 min. HRTEM images and the corresponding selected area electron diffraction (SAED) pattern reveal graphitic domains with well-organized crystal structures in the sample collected between 180-210 minutes. This result indicates that a molten iron pool is ideal for the graphitization of biocarbon. SEM and EDS

[0105] Samples collected between 180-210 minutes were characterized by SEM equipped with EDS elemental mapping analysis to detect the elemental distribution, as shown in Fig. 24. There is no obvious iron element observed, and the only element detected (excluding carbon) is calcium, which originates from the glass wool filter.

[0106] XPS

[0107] The 180-210 min sample was calcinated and the residues were analysed by X- ray photoelectron spectroscopy (XPS). As shown in Fig. 25, the results are consistent with the SEM and EDS analysis result, with no iron element being detected. The result indicates that obtaining pure graphite samples without any iron residues is possible by directly extracting graphite from molten iron.

Claims

CLAIMS1. A process for production of graphite, the process comprising- providing a metallic melt;- combining a carbonaceous material with the metallic melt;- subjecting the carbonaceous material to catalytic graphitization in the metallic melt;- passing a gas through the metallic melt; and- collecting a composition leaving the metallic melt, the composition comprising graphite carried by said gas.

2. The process according to claim 1 , wherein the metallic melt comprises a melt of metal or a melt of metal salt.

3. The process according to claim 1 or 2, wherein the metallic melt comprises Fe, Co, Ni, Mg, Mn, Ti or Zr.

4. The process according to any one of the preceding claims, wherein the carbonaceous material comprises carbon, coal, char, biocarbon, biocoal or biochar.

5. The process according to any one of the preceding claims, wherein the gas is an inert gas.

6. The process according to any one of the preceding claims, wherein the metallic melt has a first temperature during the catalytic graphitization and a second temperature during the collection of the composition leaving the metallic melt, the second temperature being lower than the first temperature.

7. The process according to any one of the preceding claims, wherein the metallic melt has a temperature in the range of 600 to 2800 °C during the catalytic graphitization.

8. The process according to any one of the preceding claims, further comprising- separating the graphite from the gas of said composition.

9. The process according to any one of the preceding claims, further comprising- preparing the carbonaceous material to be supplied to the metallic melt by pyrolysis of biomass.10 The process according to any one of the preceding claims, wherein the gas is passed into the metallic melt and through the metallic melt.

11. An apparatus for production of graphite, the apparatus comprising- a graphitization reactor;- a heating element heating the graphitization reactor;- an inlet conduit connecting a source of carbonaceous material with the graphitization reactor;- a gas conduit connecting a source of gas with a bottom part of the graphitization reactor; and- an outlet conduit connecting a top part of the graphitization reactor with a gas-solids separator.

12. The apparatus according to claim 11, wherein the graphitization reactor is configured to hold a metallic melt.

13. The apparatus according to claim 11 or 12, wherein the graphitization reactor holds a metallic melt.

14. The apparatus according to any one of claim 11 to 13, wherein the gas-solids separator is a cyclone.

15. The apparatus according to any one of claims 11 to 14, further defined as in any one of claims 2 to 10.

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