Carbon particles and method for producing same

Abstract

The invention relates to a carbon particle comprising at least 97% by weight of carbon, up to 0.2% by weight of impurities, based on the total weight of the carbon particle, at least 0.08% by weight of boron, based on the total weight of the carbon particle, and up to 0.05% by weight of boron carbide, based on the total weight of the carbon particle. The invention also relates to a method for producing carbon particles, comprising a step of graphitization in an electric field. The invention also relates to the use of said carbon particles as an anode active material for batteries.

Description

[0001] Cross - reference to related applications

[0002] This application claims the priority of U.S. Provisional Application No. 63 / 406,932, filed on September 15, 2022, the entire content of which is incorporated herein by reference. Background of the Invention

[0003] The present invention relates to a carbon particle, a method for preparing the same, and its use as an active material for a battery anode.

[0004] Carbonaceous materials can electrochemically store and release lithium ions and have thus been studied as active materials for the anodes of lithium - ion batteries. Depending on their role during battery discharge, these electrodes are commonly referred to as anodes.

[0005] In particular, it has been found that graphite, a crystalline layered carbon allotrope, provides both a high specific capacity and a low discharge potential close to that of lithium metal, resulting in a high energy density for the battery. In addition, these graphite anode materials have been developed in various forms, making lithium - ion batteries commercially viable in terms of safety, shelf life, and charge - discharge cycle life. Thus, graphite is currently the most prominent active material in lithium - ion secondary batteries.

[0006] The distance between two adjacent layers in graphite is described by the d 002 value measured by powder X - ray diffraction. The d 002 value is commonly referred to as the interlayer distance. A lower d 002 value is generally associated with a higher specific capacity.

[0007] We use the form of Bragg's law:

[0008] 2*d hkl *sin(θ n ) = n*λ

[0009] Where:

[0010] ·d hkl = interplanar spacing

[0011] ·λ = X - ray wavelength

[0012] ·n = order of reflection

[0013] ·θ n = Bragg angle of the nth - order reflection

[0014] For graphite, the hexagonal crystal system is the main stacking variant, for which we have:

[0015] 1 / d hkl 2 = (4 / 3*(h 2 +k2 +h*k)+l 2 *(a / c) 2 )*1 / a 2

[0016] where c = 2*d 002 , and a is the diagonal length of the hexagon in the graphene layer, for which we have a = 2*d 110 .

[0017] Impurities in graphite and its precursor materials, especially sulfur and oxygen, usually have a negative impact on the specific capacity obtainable with a given graphite sample. In addition, the particle size and particle shape also affect the specific capacity obtainable with a given graphite sample, and the main aspect affected by the typical particle size is the rate performance of the anode.

[0018] To meet the requirements for high specific capacity in battery applications, natural graphite is shaped, sized, and purified. Synthetic graphite, which is usually produced from coke in a process called graphitization, is also used as the active material of the negative electrode. Graphitization is usually carried out at a high temperature above 1700 °C, preferably above 2500 °C, in an excluded oxidative atmosphere, in which the previously amorphous carbon crystallizes at least partially and some impurities can be removed. The high temperature is usually obtained by resistive heating of the carbonaceous material by passing a large current through it. Graphitization is considered to be achieved by long-term exposure to high temperatures, while at lower temperatures, the time required to achieve sufficient graphitization is unacceptable for any commercially viable process.

[0019] Historically, the so-called Acheson process was applied, which required batch processing and a large amount of energy. The disadvantages of the Acheson process include long cooling times, non-uniform product properties, limited atmosphere control, limited purification effect, and a large number of by-products. These disadvantages forced the use of very high processing temperatures for a long time.

[0020] The first charge of a lithium-ion secondary battery is usually called "formation". During the formation process of a lithium-ion secondary battery with an anode containing graphite as the active material, the non-aqueous solvent or additive in the electrolyte is reduced and decomposed on the graphite surface, thereby forming a solid electrolyte interface, namely the so-called SEI (solid electrolyte interface) layer. This process not only consumes organic molecules but also consumes lithium ions, which are irreversibly lost in the formation of various lithium salts in the SEI layer.

[0021] The stability of the SEI layer itself and the stability of the surface of the graphite particles themselves (and the resulting bulk) during multiple charge-discharge cycles and storage are one of the key properties of the commercial value of the battery system.

[0022] To reduce the extent of lithium loss in the first cycle and stabilize the SEI layer over multiple cycles, the graphite particles constituting the anode can be modified, for example, by controlling the chemical surface activity. Coating the particles with a more inert layer before exposure to the electrolyte has proven beneficial, where the application, post-treatment, and finishing of this coating (usually by secondary heat treatment at a lower temperature or by additional secondary coating via CVD or other techniques) must be carefully carried out to successfully integrate the particles into the overall battery system.

[0023] In the search for a material that can reconcile the diverse requirements of lithium-ion batteries in a reliable, simple, and cost-effective manner, various approaches have been taken. A very interesting concept is to dope carbon with the natural alloy partners of carbon, namely boron and nitrogen. However, the solutions proposed in the literature to date have been limited in terms of success.

[0024] One of the challenges of this approach is the distribution of the alloying element source, which is typically in the coke precursor and thus has an impurity effect on the graphitization potential similar to that of sulfur, for example, or via a separate powder, which can have a negative impact on the integrity of the graphite particles. Slow heating and cooling rates can lead to the formation of undesired structures, as described below.

[0025] An example of a coated carbon particle is described in US 6 869 546 B1, which describes a carbon material comprising a first carbon material as an inner core particle (having an outer surface) and a second carbon material coating on the outer surface of the first carbon material, the second carbon material containing at least 1 wt% to at most 15 wt% boron.

[0026] Boron and nitrogen can partially replace carbon in the graphite structure. Boron and nitrogen can be found in natural graphite (not necessarily in substitution positions within the graphite layers) and are sometimes intentionally added during the preparation of synthetic graphite because boron is reported to accelerate the crystallization of carbon to graphite during high-temperature treatment, thus allowing lower process temperatures.

[0027] Synthetic graphite carbon materials containing boron and / or nitrogen have been reported.

[0028] For example, US 5 358 805 A describes a secondary battery comprising a positive electrode, an electrolyte, and a negative electrode capable of reversibly intercalating lithium; wherein the negative electrode comprises a carbon compound having a graphite crystal structure, wherein carbon (C) is partially replaced by boron (B) and nitrogen (N), and the carbon compound has the formula BC 3 N.

[0029] In particular, it is assumed that placing boron and / or nitrogen on the surface of carbon particles improves the surface chemistry of the carbon particles. Adding boron and nitrogen during the graphitization process can purposefully incorporate said elements into the carbon surface, thereby improving the formation and stabilizing the SEI layer. However, this can lead to the formation of a boron nitride surface coating in addition to boron and nitrogen doping. The boron nitride coating can increase the chemical stability of graphite, but due to its insulating properties, this has a negative impact on the diffusion of lithium ions and the interaction between the SEI layer, the electrolyte, and the surface of the anode particles. Therefore, controlling and adjusting the amount of boron nitride is of great significance. In this regard, US2018 / 0337423 A1 describes a negative electrode active material comprising graphite including boron and nitrogen, and describes that the ratio of the peak area of boron bonded to nitrogen to the total boron can be observed using X-ray photoelectron spectroscopy (XPS), each considering the boron 1s spectrum.

[0030] In addition, JP 2000 012020A describes a negative electrode material for a lithium secondary battery, which is graphitized carbon powder containing boron and nitrogen, wherein the 10% cumulative diameter (d 10 ) of the carbonaceous powder is 5 to 25 μm.

[0031] JP 2000 12021A describes a negative electrode material for a lithium secondary battery, comprising graphitized carbon powder containing boron and nitrogen, wherein the specific surface area calculated by nitrogen desorption of the carbon powder is 10 m 2 / g or less.

[0032] US2001 / 0051300 A1 describes a surface treatment after graphitization to obtain graphite powder containing 0.01 to 5.0% by weight of boron, and having a closed-loop structure at the end of the graphite c-plane layer on the powder surface, and the density of the gap plane portion between adjacent closed-loop structures is not less than 100 / μm and not greater than 1500 / μm.

[0033] Similar to boron nitride, boron carbide can be formed during the graphitization process, but is not limited to the particle surface. The disadvantage of boron carbide is that when particles containing boron carbide are coated on other surfaces (such as metal foils), it can act as an abrasive. In addition, boron carbide is basically non-reactive, thus reducing the weight and volume capacity of the particles.

[0034] In view of the prior art, an object of the present invention is to provide carbon particles that can be used in the anode of a lithium ion battery. The carbon particles should particularly produce an anode and / or a battery having a high shelf life and / or a high specific capacity and / or a high cycle life.

[0035] Another object of the present invention is to provide a method for manufacturing the carbon particles. The method should particularly allow the preparation of particles with customized properties, preferably excluding or at least limiting the tradeoffs of boron and nitrogen doping known from other methods.

[0036] Other and further objects, features and advantages will become more fully apparent from the following description. Summary of the Invention

[0037] The above - mentioned part or all of the objects are solved by the carbon particles according to claim 1, the method according to claim 12, the use according to claim 19, and the battery according to claim 20.

[0038] Without wishing to be bound by scientific theory, it is believed that impurities in the carbon particles can affect the electrochemical performance and the crystallinity of graphite. Therefore, removing these impurities during the graphitization process can be advantageous. In addition, impurities, especially of a metallic nature, carry the risk of promoting side reactions in the chemical battery system, thus posing risks to the control of the battery, its shelf life, and its cycle life.

[0039] On the other hand, boron can be beneficial to these properties, but it is believed that the formation of boron carbide clusters deactivates the boron, and macroscopic crystals are known to be abrasive. Therefore, the formation of boron carbide should be inhibited. Surprisingly, it has been found that granulating the carbonaceous particles with an organic binder, followed by carbonization and finally graphitization in an electric field, especially in an electro - thermal fluidized bed, and then de - agglomerating the granules, especially by gently mechanically decomposing the granules to recover the particles, allows the use of a wide range of precursor particle sizes and produces particles with a graphitized core and an unstructured carbon shell. In this way, many of the advantages of doping with boron and nitrogen can be united, while potential trade - offs known from other methods can be avoided or at least limited.

[0040] This process can allow for the controlled introduction of boron and nitrogen as dopants in the bulk and on the surface of the particles and may limit the formation of boron carbide and boron nitride. The carbon particles according to the invention can be used in lithium - ion secondary batteries, especially as the negative electrode active material in their negative electrodes. The resulting batteries can particularly exhibit a high shelf life and / or a high specific capacity and / or a high cycle life. Without wishing to be bound by scientific theory, it is believed that the carbon particles contain boron only in very small amounts of clusters, contributing to the achievement of an anode and / or a battery with ideal properties. Description of the Drawings

[0041] Figure 1 A graph showing the relationship between boron substitution and the degree of graphitization is shown.

[0042] Figure 2 A part of the XPS spectrum of natural flake graphite purified and boronated in an electro - thermal fluidized bed reactor in the presence of a boron source at a black - body radiation temperature of about 2300 °C in a nitrogen atmosphere is shown. The residence times for Examples 1 - 6 are described below. Boron nitride was mechanically removed from the surface using tape.

[0043] Figure 3Shows the particle size distribution of several kinds of particles. Detailed implementation

[0044] The embodiments of the present invention will be described in detail below. However, the present disclosure is not limited to these embodiments.

[0045] According to one embodiment, the BET surface area of the carbon particles is 0.5 to 50 m 2 / g, preferably 0.5 to 10 m 2 / g, more preferably 1 to 3 m 2 / g, even more preferably 1 to 2 m 2 / g. The BET surface area is preferably measured by the nitrogen adsorption - desorption method. The optimized specific surface area is very important for graphite as an active material in the anode of a lithium - ion battery because a higher specific surface area can be associated with a higher irreversible lithium loss during the SEI formation process, while a lower specific surface area can be associated with low conductivity and rate performance of the anode. Carbon particles with the BET surface area described herein can have a good balance particularly between lithium loss and conductivity.

[0046] According to another embodiment, the d 002 spacing of the carbon particles is from 0.3363 nm to 0.3355 nm, preferably from 0.3359 nm to 0.3355 nm, and / or the d 110 spacing is from 0.120 nm to 0.126 nm, preferably from 0.1229 nm to 0.1236 nm, more preferably from 0.123027 nm to 0.123244 nm. A lower d 002 can be associated with a higher specific capacity and can serve as a measure of the degree of graphitization and carbon crystallinity. The d 110 spacing is affected by boron doping, where the d 110 spacing within the specified range can indicate the uniform distribution of boron atoms in the graphite structure rather than the formation of clusters with a higher boron content.

[0047] According to one embodiment, the XPS spectrum of the carbon particles has a first peak at 184.0 eV to 188.0 eV, preferably 185.0 eV to 187.5 eV, more preferably 185.5 eV to 187.0 eV, and most preferably at about 186.5 eV, and / or a second peak at 188.5 eV to 192.0 eV, preferably 189.0 eV to 191.5 eV, more preferably 189.5 eV to 191.0 eV, and most preferably at about 190.3 eV, and / or substantially no peak at about 187.7 eV. Preferably, the intensity ratio of the first peak to the second peak in the XPS spectrum is from 0.25 to 6.0, preferably from 0.5 to 2, more preferably from 0.8 to 1.25. A high intensity ratio of the first peak to the second peak indicates the strong presence of B-N bonds, which is generally associated with the presence of boron nitride. The first peak and / or the second peak is preferably prominent in the XPS spectrum. The first peak in the XPS spectrum is preferably a B1s peak, indicating the presence of boron-carbon bonds on the surface of the carbon particles. The first peak in the XPS spectrum can also be referred to as the B1s(BC) peak. The second peak in the XPS spectrum is preferably a B1s peak, indicating the presence of boron-nitrogen bonds on the surface of the carbon particles. The second peak in the XPS spectrum can also be referred to as the B1s(BN) peak. The peak at 187.7 eV is preferably a B1s peak, indicating boron-boron bonds and / or boron-boron clusters. Preferably, the peak at 187.7 eV is below the detection limit.

[0048] In the XPS spectrum, to determine the presence of nitrogen in the hard carbon shell itself, boron nitride is removed by gentle treatment with caustic NaOH aq (10% NaOH, for 20 minutes in an Anton Paar Multiwave 7000 microwave digester at 250 °C, using a PTFE sample container, and then neutralized with nitric acid). The remaining B-N peak at about 190.3 eV indicates doped nitrogen in the carbon particle shell, which improves the surface properties of the particles.

[0049] According to yet another embodiment, the carbon particles contain at least 97.5 wt%, preferably at least 98 wt%, more preferably at least 98.5 wt% carbon, based on the total weight of the particles. A higher carbon content may indicate a higher proportion of the active material capable of intercalating lithium in the anode made of the active material, which may result in a higher specific capacity. In addition, a higher carbon content may indicate a lower content of impurities that may have various adverse effects.

[0050] According to a preferred embodiment, at least 85 wt%, more preferably at least 90 wt%, and most preferably at least 95 wt% of the carbon contained in the carbon particles is graphite carbon.

[0051] "Impurities" in this text preferably refer to the constituent elements in the particles other than carbon, boron, and nitrogen. Impurities can affect the properties of graphite, especially the crystallinity and layered structure of graphite. In addition, impurities, especially those of a metallic nature, can carry the risk of promoting side reactions in a chemical battery system, thereby posing risks to the control of the battery, its shelf life, and cycle life. The initially detected impurities can depend on the source and previous treatment of the carbonaceous material precursor. Preferably, the carbon particles disclosed herein contain a small amount of impurities. According to one embodiment, the carbon particles contain up to 0.1 wt%, preferably up to 0.05 wt%, more preferably up to 0.04 wt%, even more preferably up to 0.03 wt%, and most preferably up to 0.025 wt% of impurities, based on the total weight of the carbon particles.

[0052] According to yet another embodiment, the impurities are at least one impurity of a metallic nature, such as transition metals, especially vanadium and / or iron, oxygen, and sulfur, preferably at least one transition metal, especially vanadium and / or iron, oxygen, and sulfur. Preferably, the carbon particles contain up to 100 ppm of oxygen and 100 ppm of sulfur. The oxygen level and the total nitrogen content are determined using a Leco ONH836 gas analyzer, and the sulfur level is determined using a LECO SC-432 sulfur determination unit. Vanadium, iron, and other elements, especially metals, are determined using a Jobin Yvon Horiba Ultima 2 ICP-OES after nitric acid-sulfuric acid digestion (for vanadium and other metals) and hydrochloric acid digestion (for iron).

[0053] According to yet another embodiment, the carbon particles contain up to 0.03 wt%, preferably up to 0.02 wt%, more preferably up to 0.01 wt%, and most preferably up to 0.005 wt% of boron carbide, based on the total weight of the carbon particles, and / or wherein the carbon particles contain up to 0.5 wt%, preferably up to 0.3 wt%, more preferably up to 0.1 wt% of boron nitride, based on the total weight of the carbon particles. The carbon particles can also contain boron nitride in an amount of especially 0.05 wt% to 1 wt%, preferably 0.1 wt% to 0.8 wt%, based on the total weight of the carbon particles. If boron nitride is present, it is preferably located on the surface of the carbon particles. It has been found that for boron and / or nitrogen contained in the carbon particles in amounts within the above ranges, the formation of clusters and / or phases and / or particles and / or surfaces enriched with dopants can be reduced. Clusters and / or phases and / or particles and / or surfaces enriched with dopants can reduce the ability of the carbon particles to intercalate and deintercalate lithium, or can even promote the irreversible loss of lithium in side reactions. In addition, when a slurry containing the carbon particles is coated on a copper foil to manufacture a battery negative electrode, boron carbide can act as an abrasive. In addition, boron carbide is substantially non-reactive, thereby reducing the weight and volume capacity of the negative electrode.

[0054] Boron can exist in carbon particles in different forms. For example, boron can exist in the form of boron nitride. Boron nitride is preferably located at the surface of the carbon particles. Boron can also exist in the form of boron carbide.

[0055] The carbon particles can be treated to remove boron nitride by leaching with caustic (NaOH aq ) in an Anton Paar Multiwave 7000 microwave digester at up to 250 °C. The residue of the caustic treatment can be used as a method for quantifying boron nitride using ICP-OES for boron.

[0056] The upper limit of the amount of boron carbide can be determined as follows: During the XRD measurement of the graphitization degree, the boron carbide reflections in the diffraction pattern can be examined. Then, the boron carbide particles in the ash of the carbon particle sample (3 g sample, 780 - 800 °C for 8 hours in a muffle furnace, air) can be visually inspected. The ash is white, boron nitride stands out as white particles, and boron carbide stands out as grey to black particles (specs) in the ash. Then, the upper limit of boron carbide in the carbon particles can be determined by comparing the amount of grey to black boron carbide particles with the amount of white boron nitride particles in the ash, where the amount of boron nitride can be determined using ICP-OES as described herein. In addition, XRD analysis of the ash can be performed as an additional control.

[0057] In addition, instead of carbon atoms, boron can also be present. For example, if the carbon particles contain graphene sheets or graphite crystallites, or an amorphous carbon structure, boron atoms can be located at the lattice positions in the graphene sheets or graphite crystallites, replacing the carbon atoms at those positions, or boron atoms can replace the carbon atoms in the amorphous carbon structure. In this case, boron is also said to be in a substitutional position.

[0058] In particular, the amount of boron in the substitutional position in the carbon particles can be determined by the following steps:

[0059] First, a 3 g sample is ashed in a muffle furnace at 780 - 800 °C for 8 hours,

[0060] Second, boron oxide is leached from the ash in hot 2% nitric acid, and then boron nitride in the ash is filtered to obtain a nitric acid filtrate,

[0061] Third, the boron content in the nitric acid filtrate is determined using ICP-OES.

[0062] The carbon particles contain at least 0.08 wt% of boron, based on the total weight of the carbon particles. According to one embodiment, the carbon particles contain at least 0.1 wt%, preferably at least 0.15 wt%, more preferably at least 0.2 wt%, even more preferably at least 0.3 wt% of boron, based on the total weight of the carbon particles, and / or at most 2.3 wt%, preferably at most 2 wt%, more preferably at most 1.5 wt%, most preferably at most 1.3 wt% of boron, based on the total weight of the carbon particles. According to a preferred embodiment, the carbon particles contain from 0.1 wt% to 2 wt%, more preferably from 0.3 wt% to 1.5 wt% of boron. For boron in the substitutional position in the carbon particles, the boron content in the above carbon particles is preferred. Carbon particles having a boron content within the ranges described herein, particularly a boron content in the substitutional position, can inhibit the formation of by-products that do not participate in lithium ion intercalation or deintercalation and can maintain a high discharge specific capacity.

[0063] According to one embodiment, the carbon particles contain both boron nitride and boron, preferably in a weight ratio of at least 0.0005 wt% boron nitride per wt% boron to at most 2.5 wt% boron nitride per wt% boron, more preferably at least 0.001 wt% boron nitride per wt% boron to at most 1 wt% boron nitride per wt% boron, even more preferably at least 0.002 wt% boron nitride per wt% boron to at most 0.1 wt% boron nitride per wt% boron.

[0064] According to one embodiment, the carbon particles contain both boron nitride and boron, preferably in a weight ratio of at least 0.02 (wt% boron nitride / wt% boron) to at most 12.5 (wt% boron nitride / wt% boron), more preferably at least 0.05 (wt% boron nitride / wt% boron) to at most 1 (wt% boron nitride / wt% boron), even more preferably at least 0.07 (wt% boron nitride / wt% boron) to at most 0.3 (wt% boron nitride / wt% boron).

[0065] According to yet another embodiment, the carbon particles contain nitrogen. Advantageously, the carbon particles particularly contain at least 0.005 wt%, preferably 0.01 to 0.05 wt%, more preferably 0.015 to 0.04 wt%, most preferably 0.02 to 0.03 wt% of nitrogen, based on the total weight of the carbon particles. The above nitrogen content in the carbon particles is preferably determined after removing boron nitride from the surface of the carbon particles. Nitrogen doping within the ranges described herein can contribute to reducing the formation of by-products that do not participate in lithium ion intercalation or deintercalation and maintaining a high discharge specific capacity. After removing boron nitride, the nitrogen in the carbon particles can be determined by XPS.

[0066] According to a preferred embodiment, the carbon particles contain boron and nitrogen. Advantageously, the carbon particles comprise:

[0067] at least 97 wt% of carbon, based on the total weight of the carbon particles,

[0068] Up to 0.2% by weight of impurities, based on the total weight of the carbon particles,

[0069] At least 0.08% by weight of boron, based on the total weight of the carbon particles,

[0070] Up to 0.05% by weight of boron carbide, based on the total weight of the carbon particles, and

[0071] Nitrogen.

[0072] Boron is preferably in a substitutional position in the carbon particles.

[0073] According to another preferred embodiment, the carbon particles comprise:

[0074] At least 97% by weight of carbon, based on the total weight of the carbon particles,

[0075] Up to 0.2% by weight of impurities, based on the total weight of the carbon particles,

[0076] At least 0.15% by weight of boron, based on the total weight of the carbon particles,

[0077] Up to 0.05% by weight of boron carbide, based on the total weight of the carbon particles.

[0078] Boron is preferably in a substitutional position in the carbon particles.

[0079] According to another preferred embodiment, the carbon particles comprise:

[0080] At least 97% by weight of carbon, based on the total weight of the carbon particles,

[0081] Up to 0.2% by weight of impurities, based on the total weight of the carbon particles,

[0082] At least 0.15% by weight of boron, based on the total weight of the carbon particles,

[0083] Up to 0.05% by weight of boron carbide, based on the total weight of the carbon particles, and

[0084] Nitrogen.

[0085] According to another preferred embodiment, the carbon particles comprise:

[0086] At least 97% by weight of carbon, based on the total weight of the carbon particles,

[0087] Up to 0.2% by weight of impurities, based on the total weight of the carbon particles,

[0088] At least 0.15% by weight of boron, based on the total weight of the carbon particles,

[0089] Up to 0.05% by weight of boron carbide, based on the total weight of the carbon particles, and

[0090] At least 0.0003% nitrogen and at most 1% nitrogen.

[0091] According to another preferred embodiment, the carbon particles comprise:

[0092] At least 97 wt% carbon, based on the total weight of the carbon particles,

[0093] At most 0.2 wt% impurities, based on the total weight of the carbon particles,

[0094] At least 0.15 wt% boron, based on the total weight of the carbon particles,

[0095] At least 0.0001 wt% to at most 0.05 wt% boron carbide, based on the total weight of the carbon particles, and

[0096] Nitrogen,

[0097] And the carbon particles are preferably core - shell particles, especially with a hard carbon shell.

[0098] According to another preferred embodiment, the carbon particles comprise:

[0099] At least 97 wt% carbon, based on the total weight of the carbon particles,

[0100] At most 0.2 wt% impurities, based on the total weight of the carbon particles,

[0101] At least 0.08 wt% boron, based on the total weight of the carbon particles,

[0102] At most 0.05 wt% boron carbide, based on the total weight of the carbon particles,

[0103] Nitrogen,

[0104] And boron nitride,

[0105] Wherein the weight ratio of boron nitride contained therein to boron is at least 0.0005 wt% boron nitride per wt% boron to 2.5 wt% boron nitride per wt% boron.

[0106] According to another preferred embodiment, the carbon particles comprise:

[0107] At least 97 wt% carbon, based on the total weight of the carbon particles,

[0108] At most 0.2 wt% impurities, based on the total weight of the carbon particles,

[0109] At least 0.08 wt% boron, based on the total weight of the carbon particles,

[0110] At most 0.05 wt% boron carbide, based on the total weight of the carbon particles,

[0111] Nitrogen,

[0112] and boron nitride,

[0113] and having a weight ratio of boron nitride / boron of at least 0.02 (wt% boron nitride / wt% boron) to at most 12.5 (wt% boron nitride / wt% boron).

[0114] According to yet another embodiment, the particle size distribution d of the carbon particles 50 is from 3 to 30 μm, preferably from 4 to 25 μm, more preferably from 5 to 20 μm. Advantageously, the particle size distribution d of the carbon particles 10 is from 1 to 25 μm, preferably from 1.5 to 20 μm, more preferably from 2 to 15 μm. Advantageously, the particle size distribution d of the carbon particles 90 is from 6 to 50 μm, preferably from 8 to 45 μm, more preferably from 10 to 35 μm. Although particles smaller than those specified above may irreversibly consume too much lithium due to SEI formation and may exhibit a lower specific capacity, particles larger than the above range may have the disadvantage of slow lithium intercalation and deintercalation, resulting in low anode rate performance. Particles outside the specified size distribution may also have a negative impact on the anode manufacturing process and result in anodes of poor manufacturing quality.

[0115] All particle size distributions described herein are preferably volume distributions, determined by wet dispersion laser diffraction using a Microtrac S3500 after dispersion by ultrasound in a Branson 3510 ultrasonic bath using a Branson Sonifier 250 - ultrasonic probe and the surfactant "Triton X100".

[0116] According to yet another embodiment, the carbon particles are core - shell particles, comprising a substantially non - graphitizable (especially hard carbon) shell and at least partially graphitized carbon core, which carbon core may still contain graphitizable portions (especially soft carbon). Without wishing to be bound by scientific theory, it is believed that the hard carbon shell reduces SEI formation and / or irreversible lithium loss due to side reactions, and can protect the inner surface of the particle core from similar side reactions, especially co - intercalation of the electrolyte that can cause particle deterioration. At the same time, it is believed that the shell is conductive to lithium ions, thus not affecting the lithium storage performance of the core.

[0117] For the core - shell particles, the core preferably accounts for 91 wt% to 99 wt% of the total weight of the carbon particles, more preferably 92 wt% to 99 wt%, most preferably 94 wt% to 98.5 wt%, and the shell accounts for 1 wt% to 9 wt% of the total weight of the carbon particles, preferably 1 wt% to 8 wt%, more preferably 1.5 wt% to 6 wt%.

[0118] The shell is preferably formed from a carbonized binder.

[0119] Another aspect of the present invention relates to a method for preparing the carbon particles described herein, wherein:

[0120] In the granulation step, carbonaceous particles are granulated using a binder to obtain carbonaceous granules (granule).

[0121] In the carbonization step, the carbonaceous granules are heated to a temperature of at least 1000 °C to obtain carbonized granules.

[0122] In the graphitization step, the carbonized granules are introduced into an electric field for graphitization of the carbonized granules, thereby obtaining graphitized granules.

[0123] In the deagglomeration step, the graphitized granules are deagglomerated, thereby obtaining carbon particles.

[0124] Wherein at least one of the granulation step, the carbonization step and the graphitization step is carried out in the presence of a boron source.

[0125] After the graphitization step, the graphitized granules preferably comprise carbon particles adhered to each other. In the deagglomeration step, it is preferred to break the particle-particle contact of the carbon particles in the graphitized granules to deagglomerate the graphitized granules. Preferably, the carbon particles themselves are not substantially broken into smaller carbon particles. The deagglomeration step of the graphitized granules is preferably achieved mainly by shear force. The deagglomeration step can also be referred to as a mechanical decomposition step.

[0126] In one embodiment, the particle size distribution d of the carbonaceous particles 50 is from 3 to 30 μm, preferably from 4 to 25 μm, more preferably from 5 to 20 μm. Advantageously, the particle size distribution d of the carbonaceous particles 10 is from 1 to 25 μm, preferably from 1.5 to 20 μm, more preferably from 2 to 15 μm. Advantageously, the particle size distribution d of the carbonaceous particles 90 is from 6 to 50 μm, preferably from 8 to 45 μm, more preferably from 10 to 35 μm.

[0127] Preferably, the carbonaceous particles are selected from green petroleum coke particles, calcined petroleum coke particles, spherical flake graphite particles, spherical natural graphite particles, recycled anode powder particles, petroleum coke, pitch coke, carbonized wood, needle coke, sponge coke, shot coke, metallurgical coke, coal tar-based carbon, medium carbon, anthracite, synthetic graphite, natural graphite, expanded graphite, carbonized polymers, carbon black and mixtures thereof, preferably selected from green petroleum coke particles, calcined petroleum coke particles, spherical flake graphite particles, spherical natural graphite particles, recycled anode powder particles and mixtures thereof. The method can allow the use of a wide range of precursor particle sizes, because granules of particles and binders are formed in the granulation step, which can result in particles having an appropriate particle size distribution for processing in subsequent steps and subsequent applications, especially as an active material for anodes of lithium-ion batteries. Similarly, the method can tolerate a wide range of precursor materials, because impurities can be removed during the process.

[0128] According to yet another embodiment, the binder comprises at least one starch, modified starch, phenolic resin, modified Kraft lignin, styrene-butadiene rubber (SBR), and latex. Preferably, the binder comprises or consists of starch and / or modified starch. These materials are widely available, inexpensive, and due to their composition, can be carbonized in the carbonization step described above. At the same time, the granulation step can be carried out with these binders under favorable conditions, preferably using water as the solvent. However, the present invention is not dependent on the specific choice of these binders. The binder preferably promotes the agglomeration of the fine carbonaceous powder, particularly the formation of carbon granules. Advantageously, each carbonaceous particle obtains a binder coating. Preferably, the particles are bound together by the binder to form granules. In this way, the carbon granules can produce carbonized granules after the carbonization step, which are preferably strong enough to pass through the electrothermal fluidized bed reactor with substantially no mechanical decomposition, but allow for de-agglomeration by gentle mechanical treatment. Additionally, in this way, the individual carbon particles preferably retain a complete carbonized coating, particularly a hard carbon shell. Binders suitable for this purpose include, but are not limited to: binders containing starch, modified starch, phenolic resin, modified Kraft lignin, styrene-butadiene rubber (SBR), or latex.

[0129] Preferably, the amount of the binder is 3 to 25 wt%, more preferably 5 to 20 wt%, based on the total weight of the carbonaceous particles and the binder.

[0130] If a solvent (such as water) is used, the amount of the solvent is 10 to 30 wt%, more preferably 15 to 25 wt%, based on the total weight of the binder and the carbonaceous particles.

[0131] According to yet another embodiment, in the carbonization step, the carbon granules are heated to a first temperature of 30°C to 700°C, preferably 30°C to 300°C, in a first heating step, and then to a second temperature of 300°C to 1400°C, preferably 300°C to 1300°C, more preferably 300°C to 1100°C, in a second heating step. This step may require careful calcination, consistent with prior art procedures for preparing graphitizable carbon, for optimized yield and process performance in the process. The two heating steps can be carried out batchwise or continuously, and can be carried out in one or more furnaces, whether or not the granules are pretreated.

[0132] According to yet another embodiment, the carbonaceous feedstock is heated to a first temperature for a period of 0.1 to 20 hours, preferably 0.25 to 12 hours, and / or heated to a second temperature for a period of 0.1 to 20 hours, preferably 0.25 to 12 hours. The carbonization time can depend on the furnace used for heating. If a rotary kiln is used, it is preferred to heat the carbonaceous feedstock to the first and / or second temperature for a period of 0.1 to 2 hours, preferably 0.5 to 1.5 hours. If a furnace (such as a debinding furnace or a sintering furnace) is used, it is preferred to heat the carbonaceous feedstock to the first and / or second temperature for a period of 5 to 20 hours, preferably 10 to 15 hours, more preferably 10 to 12 hours. Under these carbonization conditions, the resulting carbonized feedstock can exhibit advantageous properties, particularly with respect to graphitization properties in subsequent steps. The carbonization step can be carried out in a directly or indirectly heated rotary kiln under a reducing atmosphere having less than 2% vol oxygen, or in a directly or indirectly heated furnace chamber under a reducing atmosphere having less than 2% vol oxygen, or in other suitable equipment.

[0133] The graphitization step can be carried out batchwise or continuously, preferably continuously.

[0134] According to yet another embodiment, in the graphitization step, the carbonized feedstock is introduced into an electrothermal fluidized bed reactor. Suitable electrothermal fluidized bed reactors are described, for example, in US 3 684 446 or US 3 807 961. In such a reactor, the particles can be rapidly and directly heated under local plasma conditions. Compared to other reactor types, particularly the Acheson process, the electrothermal fluidized bed reactor can have advantages in terms of energy consumption per unit of product, product uniformity due to mixing during the fluidization process (especially when considering boron content), continuous operation (as opposed to batch operation), throughput, and / or controllability of the residence time.

[0135] According to another embodiment, the graphitization step is carried out at a temperature of at least 2000 °C, preferably at least 2300 °C, more preferably at least 2400 °C, and most preferably at least 2550 °C. The above temperatures are particularly the blackbody radiation temperatures. The graphitization step is preferably carried out at a temperature of at most 3500 °C, more preferably at most 3200 °C, and most preferably at most 3000 °C. If the graphitization step is carried out within the above temperature range, the formation of boron nitride can be reduced.

[0136] According to yet another embodiment, the average residence time of the carbonized feedstock in the electric field during graphitization is 5 to 120 minutes, preferably 10 to 90 minutes, more preferably 15 to 60 minutes, and most preferably 20 to 45 minutes. These specified average residence times can ensure high graphitization and purification, boron diffusion, and uniform particle properties, while still enabling high throughput of the reactor.

[0137] According to yet another embodiment, the graphitized pellets are cooled to a temperature of 500 °C or lower within a time of 5 to 90 minutes, preferably 10 to 60 minutes, more preferably 15 to 45 minutes, and most preferably 20 to 30 minutes after the graphitization step. It is believed that rapid cooling prevents the formation of boron clusters (such as boron carbide) and the loss of boron from the graphite lattice.

[0138] According to yet another embodiment, in the deagglomeration step, the particle-particle contacts of the carbon particles in the graphitized pellets are broken, advantageously by shear forces. Preferably, in the deagglomeration step, a mill (in particular a mill selected from ball mills, jet mills, hammer mills, and cone mills, preferably a jet mill) is used to deagglomerate the graphitized pellets. The deagglomerated pellets result in particles within a preferred particle size distribution range for subsequent applications, in particular as the active material of an anode of a lithium-ion battery. The length of the crushing step and the choice of mill can be adjusted according to the particle properties and application specifications. The above mills, in particular jet mills, are well-suited for breaking the particle-particle contacts between carbon particles.

[0139] According to yet another embodiment, the boron source is selected from boron oxide, boric acid, elemental boron, and mixtures thereof, preferably boron oxide. Advantageously, the boron source is added in the granulation step or the graphitization step, preferably in the graphitization step, in particular as a separate powder for mixing and evaporation. The choice of boron source and the boron introduction step can affect the boron content in the resulting particles and / or shells, especially when comparing boron introduction in binder formulations with introduction in a fluidized bed. In addition, the reaction time to achieve the desired boron distribution can be affected.

[0140] According to yet another embodiment, the graphitization step is carried out in the presence of a nitrogen source, preferably in the presence of nitrogen. Nitrogen can serve as a process gas for fluidization and prevention of oxidation, or as a nitrogen source for doping. When nitrogen doping through a fluidizing gas is not required, argon can be used instead of nitrogen. In this case, the nitrogen source can be added, for example, in the form of urea powder in the graphitization step.

[0141] Another aspect of the present invention relates to the use of the carbon particles described herein as the active material of the negative electrode of a battery (in particular a lithium-ion secondary battery). An anode can be prepared from the active material or a mixture of active materials by coating a current collector with a mixture of the active material, a binder, an additive, and (if necessary) a solvent.

[0142] Another aspect of the present invention relates to a battery, in particular a lithium-ion secondary battery, which comprises the carbon particles described herein, in particular as the active material of the negative electrode.

[0143] The battery can be assembled from the above negative electrode and further comprises a cathode, which particularly comprises an active material capable of reversibly intercalating and deintercalating lithium, including but not limited to lithium iron phosphate LiFePO 4, lithium cobalt oxide LiCoO 2 , lithium nickel oxide LiNiO 2 , lithium manganese oxide LiMn 2 O 4 , and related materials, such as the so-called NCM material LiNi x Mn y Co z O 2 (x + y + z = 1), or spinel structures such as LiNi 0.5 Mn 1.5 O 4 . In addition, the battery may include a polymer or fiberglass separator and an electrolyte composed of one or more organic solvents and a lithium salt, including but not limited to lithium hexafluorophosphate LiPF 6 , lithium perchlorate LiClO 4 or lithium tetrafluoroborate LiBF 4 . The electrolyte may also include other additives, including but not limited to organic molecules (such as vinylene carbonate or fluoroethylene carbonate) and / or salts (such as lithium difluorophosphate). The use and combination of the electrolyte and additives can be selected according to the performance of the anode and cathode active materials. Detailed implementation mode

[0145] Use an aqueous starch solution as a binder to granulate different carbonaceous particles in a drum granulator. The amount of starch is 7 wt%, based on the total weight of the carbonaceous particles and the starch binder.

[0146] After dispersion by ultrasound using a Branson Sonifier 250 ultrasonic probe and the surfactant "Triton X100" in a Branson 3510 ultrasonic bath, the particle size distribution is measured by laser scattering using a Microtrac S3500.

[0147] The carbonaceous particles used are as follows:

[0148] Carbonaceous particle 1: Sponge coke I, d 10 : 1.7 μm; d 50 : 8.7 μm; d 90 : 23.2 μm, sulfur content 3.55 wt%;

[0149] Carbonaceous particle 2: Sponge coke II, d 10 : 2.5 μm; d 50 : 10.0 μm; d 90 : 21.8 μm, sulfur content: 0.85 wt%;

[0150] Carbonaceous particle 3: Needle coke I, d 10 : 6.5 μm; d 50: 19.0 μm; d 90 : 40.7 μm, sulfur content: 0.47 wt%;

[0151] Carbonaceous particle 4: needle coke II, d 10 : 2.9 μm; d 50 : 9.1 μm; d 90 : 18.7 μm, sulfur content: 0.6 wt%.

[0152] After heat-treating the obtained carbonaceous material of sponge coke I + II in a rotary kiln to 300 °C (total residence time is 45 minutes), and then heating to 1100 °C in the rotary kiln with a total residence time of 45 minutes. The needle coke I + II is heat-treated in a batch furnace to a peak temperature of 650 °C within 12 hours, and then heated to 1100 °C in another batch furnace with a total batch time of 12 hours.

[0153] The obtained carbonized material is cooled to room temperature, and then 150 kg of the carbonized material is introduced into an electrothermal fluidized bed (EFB) reactor as described in US 3,684,446. The EFB reactor operates at a temperature of 2400 °C to 2700 °C and contains nitrogen as an inert gas. The average residence time of the carbonized material in the EFB reactor is about 60 minutes and is converted into graphitized material. During the graphitization process, depending on the expected boron doping, 4.5 kg to 8.5 kg of dry boron oxide is added to the EFB reactor. The graphitized material is cooled to less than 500 °C within about 60 minutes after leaving the EFB reactor. Subsequently, the cooled graphitized material is introduced into a jet mill, and the agglomerated material is deagglomerated in the jet mill to obtain carbon particles.

[0154] The carbon particles have the following properties:

[0155] Table 1: Properties of carbon particles

[0156]

[0157] Sample number = Example number n / d = not determined

[0158] The degree of graphitization is calculated by the following formula:

[0159] Degree of graphitization = (0.344 nm - d 002 ) / (0.344 nm - 0.3354 nm)

[0160] d 002 is the distance between two adjacent layers in graphite determined by X-ray.

[0161] Figure 1 Shows the relationship between boron substitution and the degree of graphitization.

[0162] Figure 2 Shows the B-C (186.5 eV) and B-N (190.3 eV) bond XPS peaks of a carbon particle sample made of natural flake graphite treated in an EFB furnace at a boron oxide dosage and at a blackbody radiation temperature of 2300 °C in a nitrogen atmosphere after removal of boron nitride from the surface using tape stripping, and no B-B bonds are present. The residence time, cooling time, and deflocculation conditions of the flake graphite sample are as described in Examples 1-6. The peak ratio of the peak at 190.3 eV to the peak at 186.5 eV is approximately 1.1. According to XPS measurements, the carbon particles contain boron nitride. In addition, the absence of a peak for the boron-boron bond indicates that there is substantially no boron present as boron clusters.

[0163] Figure 3 Shows the volume particle size distribution of the reference sample and the deflocculated carbon particles of spherical natural flake graphite powder agglomerated and treated using the above carbonization and EFB heat treatment processes and then deflocculated, thus showing the recovery of the particle size distribution during the deflocculation step. Deflocculation is carried out using an air jet mill.

[0164] Table 2 gives the metal impurity, oxygen, and sulfur contents of the deflocculated sample.

[0165] Table 2: Purity of Carbon Particles

[0166] Needle coke I Needle coke II Sponge coke II Example # 6 7 5 Oxygen % 0.008 0.006 0.007 Sulfur % <0.005 <0.005 <0.005 Element ppm ppm ppm Co <0.6 <0.6 <0.6 Ni <0.6 <0.6 <0.6 Si 1.1 1.0 1,8 Mn <0.6 <0.6 <0.6 Fe 0.66 3.1 2.2 Mo <0.6 <0.6 <0.6 Cr <0.6 <0.6 <0.6 V 2,9 9.3 24.9 Cu <0.6 0.7 <0.6 Al <0.6 <0.6 0.9

[0167] In addition, the carbon particles of all examples exhibit impurities (including the above metals as well as oxygen and sulfur) of less than 0.2 wt%, based on the total weight of the carbon particles.

[0168] In addition, the carbon particles of all examples exhibit less than 0.05 wt% of boron carbide, based on the total weight of the carbon particles.

[0169] The carbon particles also contain at least 97 wt% of carbon, based on the total weight of the carbon particles.

[0170] The amount of impurity (oxygen) is determined using a Leco ONH836 gas analyzer.

[0171] The amount of impurity (sulfur) is determined using a LECO SC-432 sulfur determination unit.

[0172] The amount of impurity (metallic nature, see above) is determined using a Jobin Yvon Horiba Ultima2 ICP-OES.

[0173] By using up to 250 °C caustic (NaOH) in an Anton Paar Multiwave 7000 microwave digester aq)The carbon particles are treated by leaching, and the amount of boron nitride is determined by using ICP-OES to analyze the residue of the caustic treatment for boron.

[0174] The amount of boron is determined by the following steps:

[0175] First, 3 g of the sample is ashed in a muffle furnace at 780 - 800 °C in air for 8 hours.

[0176] Secondly, boron oxide is leached from the ash in hot 2% nitric acid, and then boron nitride in the ash is filtered to obtain a nitric acid filtrate.

[0177] Thirdly, the boron content in the nitric acid filtrate is determined using ICP-OES.

[0178] The content of boron carbide is determined using the above visual inspection method.

[0179] The following are the preliminary results of the electrochemical tests to illustrate the feasibility of the particles described herein. The capacity and the first cycle loss are obtained from the powder by preparing such an anode slurry: PVDF 9300 Kureha: 5 - 7%, carbon black: Super C65 Imerys: 2%, NMP: Alpha, graphite: 91 - 93%. The anode is inserted into a 2032 coin half-cell. The tests of the half-cell are carried out on an Arbin 24-channel cycler, and the test sequence is as follows: 2 C / 20 cycles, 2 C / 5 cycles, and then at a constant voltage of 5 mV until < 10% of the initial current. The capacity and the first cycle loss are the average values of five unit cells.

[0180]

Claims

1. Carbon particles, comprising: At least 97% by weight of carbon, based on the total weight of the carbon particles; At most 0.2% by weight of impurities, based on the total weight of the carbon particles; At least 0.08% by weight of boron, based on the total weight of the carbon particles; At most 0.05% by weight of boron carbide, based on the total weight of the carbon particles.

2. The carbon particles according to claim 1, wherein the BET specific surface area of the carbon particles is 0.5 to 50 m 2 / g, preferably 0.5 to 10 m 2 / g, more preferably 1 to 3 m 2 / g, even more preferably 1 to 2 m 2 / g; and / or wherein the d of the carbon particles 002 spacing is from 0.3363 nm to 0.3355 nm, preferably from 0.3359 nm to 0.3355 nm; and / or d 110 spacing is from 0.120 nm to 0.126 nm, preferably from 0.1229 nm to 0.1236 nm, more preferably from 0.123027 nm to 0.123244 nm.

3. The carbon particles according to claim 1 or 2, wherein the XPS spectrum of the carbon particles has a first peak at 184.0 eV to 188.0 eV, preferably at 185.0 eV to 187.5 eV, more preferably at 185.5 eV to 187.0 eV, and most preferably at about 186.5 eV; and / or wherein the XPS spectrum of the carbon particles has a second peak at 188.5 eV to 192.0 eV, preferably at 189.0 eV to 191.5 eV, more preferably at 189.5 eV to 191.0 eV, and most preferably at about 190.3 eV; and / or wherein the XPS spectrum of the carbon particles has substantially no peak at about 187.7 eV, In particular, wherein the intensity ratio of the first peak to the second peak in the XPS spectrum is 0.25 to 6.0, preferably 0.5 to 2, more preferably 0.8 to 1.

25.

4. The carbon particles according to any one of the preceding claims, wherein the carbon particles comprise at least 97.5% by weight, preferably at least 98% by weight, more preferably at least 98.5% by weight of carbon, based on the total weight of the carbon particles; and / or At most 0.1% by weight of impurities, preferably at most 0.05% by weight, more preferably at most 0.04% by weight, even more preferably at most 0.03% by weight, and most preferably at most 0.025% by weight of impurities, based on the total weight of the carbon particles.

5. The carbon particles according to any one of the preceding claims, wherein the impurities are at least one metallic impurity, such as a transition metal, in particular vanadium and / or iron, oxygen and sulfur, in particular oxygen and sulfur, preferably at most 100 ppm of oxygen and 100 ppm of sulfur.

6. The carbon particles according to any one of the preceding claims, wherein the carbon particles comprise at least 0.1% by weight, preferably at least 0.15% by weight, more preferably at least 0.2% by weight, even more preferably at least 0.3% by weight of boron, preferably boron in substitutional positions, based on the total weight of the carbon particles; and / or At most 2.3% by weight, preferably at most 2% by weight, more preferably at most 1.5% by weight, and most preferably at most 1.3% by weight of boron, preferably boron in substitutional positions, based on the total weight of the carbon particles.

7. The carbon particles according to any one of the preceding claims, wherein the carbon particles contain nitrogen, in particular at least 0.005% by weight, preferably 0.01 to 0.05% by weight, more preferably 0.015 to 0.04% by weight, and most preferably 0.02 to 0.03% by weight of nitrogen, based on the total weight of the carbon particles, preferably determined after removing boron nitride from the surface of the carbon particles.

8. The carbon particles according to any one of the preceding claims, wherein the carbon particles comprise at most 0.03% by weight, preferably at most 0.02% by weight, more preferably at most 0.01% by weight, and most preferably at most 0.005% by weight of boron carbide, based on the total weight of the carbon particles; and / or wherein the carbon particles comprise at most 0.5% by weight of boron nitride, preferably at most 0.3% by weight of boron nitride, more preferably at most 0.1% by weight of boron nitride, based on the total weight of the carbon particles.

9. The carbon particles according to any one of the preceding claims, wherein the particle size distribution d of the carbon particles 50 is from 3 to 30 µm, preferably from 4 to 25 µm, more preferably from 5 to 20 µm; and / or The particle size distribution d 10 is from 1 to 25 µm, preferably from 1.5 to 20 µm, more preferably from 2 to 15 µm; and / or Particle size distribution d 90 is from 6 to 50 μm, preferably from 8 to 45 μm, more preferably from 10 to 35 μm.

10. The carbon particles according to any one of the preceding claims, wherein the carbon particles are core - shell particles, which comprise a shell of substantially non - graphitizable, in particular hard carbon, and a carbon core which is at least partially graphitized, and the carbon core may still contain graphitizable, in particular soft carbon, portions.

11. The carbon particles according to claim 10, characterized in that: the core accounts for 91% to 99% by weight, preferably 92% to 99% by weight, more preferably 94% to 98.5% by weight of the total weight of the carbon particles; and the shell accounts for 1% to 9% by weight, preferably 1% to 8% by weight, more preferably 1.5% to 6% by weight of the total weight of the carbon particles.

12. A method for preparing the carbon particles according to any one of claims 1 to 11, wherein: in the granulation step, carbonaceous particles are granulated using a binder to obtain carbonaceous pellets; in the carbonization step, the carbonaceous pellets are heated to a temperature of at least 1000 °C to obtain carbonized pellets; in the graphitization step, the carbonized pellets are introduced into an electric field to effect graphitization of the carbonized pellets, thereby obtaining graphitized pellets; and in the de - agglomeration step, the graphitized pellets are de - agglomerated to obtain the carbon particles, wherein at least one of the granulation step, the carbonization step and the graphitization step is carried out in the presence of a boron source.

13. The method according to claim 12, wherein the particle size distribution d of the carbonaceous particles 50 is from 3 to 30 µm, preferably from 4 to 25 µm, more preferably from 5 to 20 µm; and / or The particle size distribution d 10 is from 1 to 25 µm, preferably from 1.5 to 20 µm, more preferably from 2 to 15 µm; and / or Particle size distribution d 90 is from 6 to 50 μm, preferably from 8 to 45 μm, more preferably from 10 to 35 μm; and / or wherein the carbonaceous particles are selected from green petroleum coke particles, calcined petroleum coke particles, spherical flake graphite particles, spherical natural graphite particles, recycled anode powder particles, petroleum coke, pitch coke, carbonized wood, needle coke, sponge coke, metallurgical coke, coal - based carbon, medium carbon, anthracite, synthetic graphite, natural graphite, expanded graphite, carbonized polymers, carbon black and mixtures thereof, preferably selected from green petroleum coke particles, calcined petroleum coke particles, spherical flake graphite particles, spherical natural graphite particles, recycled anode powder particles and mixtures thereof.

14. The method according to claim 12 or 13, wherein the binder comprises at least one of starch, modified starch, phenolic resin, modified Kraft lignin, styrene - butadiene rubber (SBR), latex, preferably comprises and / or consists of starch and / or modified starch.

15. The method according to any one of claims 12 - 14, wherein in the carbonization step, the carbonaceous pellets are heated to a first temperature of 30 - 700 °C, preferably 30 - 300 °C in a first heating step; and then heated to a second temperature of 300 - 1400 °C, preferably 300 - 1300 °C, more preferably 300 - 1100 °C in a second heating step.

16. The method according to claim 15, wherein the carbonaceous feedstock is heated to a first temperature for a time of 0.1 - 20 hours, preferably 0.25 - 12 hours, and / or heated to a second temperature for a time of 0.1 - 20 hours, preferably 0.25 - 12 hours.

17. The method according to any one of claims 12 - 16, wherein the carbonized granules are introduced into an electrothermal fluidized bed reactor in the graphitization step; and / or wherein during the graphitization process, the average residence time of the carbonized granules in the electric field is 5 - 120 minutes, preferably 10 - 90 minutes, more preferably 15 - 60 minutes, and most preferably 20 - 45 minutes; and / or wherein after the graphitization step, the graphitized granules are cooled to a temperature below 500 °C within a time of 5 - 90 minutes, preferably 10 - 60 minutes, more preferably 15 - 45 minutes, and most preferably 20 - 30 minutes; wherein in the deflocculation step, a mill, in particular a mill selected from a ball mill, a jet mill, a hammer mill, and a conical mill, preferably a jet mill, is used to deflocculate the graphitized granules.

18. The method according to any one of claims 12 - 17, wherein the boron source is selected from boron oxide, boric acid, elemental boron, and mixtures thereof, preferably boron oxide; and / or wherein the boron source is added in the granulation step or the graphitization step, preferably in the graphitization step, in particular as a separate powder for mixing and evaporation; wherein the graphitization step is carried out in the presence of a nitrogen source, preferably in the presence of nitrogen.

19. Use of the carbon particles according to any one of claims 1 - 11 as a negative electrode active material for a battery, in particular a lithium ion secondary battery.

20. A battery, in particular a lithium ion secondary battery, comprising the carbon particles according to any one of claims 1 - 11, in particular as a negative electrode active material.

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