Method for producing carbon-enriched materials from heat-treated lignin

Abstract

The present invention relates to a method for producing fully heat-stabilized aggregated lignin, the method comprising: a) providing aggregated lignin having an average particle size in the range of 50 to 500 μm; and b) heating the aggregated lignin to a temperature in the range of 140 to 300°C for at least 30 minutes to obtain fully heat-stabilized aggregated lignin. The present invention also relates to fully heat-stabilized aggregated lignin and a method for producing a carbon-enriched material obtained by subjecting the fully heat-stabilized aggregated lignin to heat treatment.

Description

Technical Field

[0001] The present invention relates to a method for producing completely thermally stabilized aggregated lignin and completely thermally stabilized aggregated lignin. This application relates to a method for producing a carbon-enriched material from the completely thermally stabilized aggregated lignin, a negative electrode for a non-aqueous secondary battery containing the carbon-enriched material as an active material, and the use of the carbon-enriched material as an active material in the negative electrode of a non-aqueous secondary battery.

Background Art

[0002] A secondary battery such as a lithium-ion battery is a rechargeable battery, that is, a battery that can be charged and discharged multiple times. In a lithium-ion battery, lithium ions flow from the negative electrode through the electrolyte to the positive electrode during discharge and return to the negative electrode during charging. Today, typically, a lithium compound, particularly a lithium metal oxide such as lithium nickel manganese cobalt oxide (NMC), or lithium iron phosphate (LFP) is used as the material for the positive electrode, and a carbon-enriched material is used as the material for the negative electrode.

[0003] Graphite (natural graphite or synthetic graphite) is currently used as the negative electrode material for most lithium-ion batteries due to its high energy density and stable charge-discharge performance over a long period. Instead of graphite, there are amorphous carbon materials such as hard carbon (non-graphitizable amorphous carbon) or soft carbon (graphitizable amorphous carbon), but these do not have the long-range order of graphite. What graphite and amorphous carbon have in common is that the volume change during charge and discharge is small. As a result, the mechanical stability of the electrode material is improved, and it becomes easier to maintain cycle stability. Amorphous carbon can be used as a single active electrode material or as a mixture with graphite. Hard carbon often has excellent charge-discharge rate performance desired for rapid charging and high-power systems.

[0004] Amorphous carbon is obtained from lignin. Lignin is an aromatic polymer and a main component such as in wood, and is one of the most abundant carbon sources on Earth. In recent years, technologies for highly purifying lignin from the pulp manufacturing process and extracting it in a solid and special form have been developed and put into practical use, and currently, it has attracted great attention as a renewable alternative to the main aromatic chemical precursors supplied from the petrochemical industry. Amorphous carbon derived from lignin is typically non-graphitizable, that is, hard carbon.

[0005] Today, the most commercial source of lignin is kraft lignin, which is obtained from hardwood or softwood through the kraft process. Lignin can be separated from the alkaline black liquor using, for example, membrane filtration or ultrafiltration. One common separation process is described in International Publication No. WO 2006 / 031175 A1. In this process, lignin is precipitated from the alkaline black liquor by the addition of an acid and then filtered. The lignin filter cake is reslurried under acidic conditions in the next step and washed before drying and micronization.

[0006] One of the problems when using lignin as a precursor for carbon-rich materials is that lignin exhibits undesirable thermoplastic behavior, so it is not suitable for direct use in the form of fine powder. When thermally converting lignin powder into a carbon-rich material, lignin undergoes plastic deformation / melting, expands violently, and foams. Combined with the strong tendency to generate dust during handling, the processability of lignin on an industrially appropriate scale is significantly limited in terms of the dimensions of the equipment, processing capacity, and the need for intermediate processing.

[0007] International Publication No. 2021250604 A1 describes a method for producing carbon from lignin, which includes compressing lignin powder and then crushing the compressed lignin to obtain aggregated lignin having a particle size distribution such that at least 80 wt% of the aggregates have a diameter in the range of 0.2 to 5.0 mm. The aggregated lignin is then heat-treated to obtain heat-stabilized aggregated lignin, which can be converted into a carbon-enriched material that avoids melting / expansion deformation and retains its shape and dimensions.

[0008] However, there remains a need for an improved method for obtaining carbon-enriched materials from lignin, which maintains its shape and dimensions while the lignin is converted into the carbon-enriched material, avoids melting / expansion deformation, and results in a carbon-enriched material with high capacity when used as the active material for the negative electrode of a secondary battery. [Overview of the Initiative]

[0009] An object of the present invention is to provide an improved method for producing carbon-enriched materials, the method enabling the use of renewable carbon sources, and the method eliminating or mitigating at least some of the drawbacks of prior art methods.

[0010] A further object of the present invention is to provide a method for producing an improved carbon-enriched material suitable for use as an active material in the anode of non-aqueous secondary batteries such as lithium-ion batteries and sodium-ion batteries, and in particular, the capacity of non-aqueous secondary batteries is improved by using the carbon-enriched material as an active material in the anode.

[0011] A further object of the present invention is to provide a method for producing a carbon-enriched material from lignin, which allows the use of lignin in powder form while avoiding the problem of dust formation during heat treatment to obtain the carbon-enriched material and maintaining the shape and dimensions of the lignin.

[0012] A further object of the present invention is to provide a method for producing carbon-enriched materials, the method being scalable and therefore suitable for large-scale production.

[0013] The purposes described above, as well as other purposes that a person skilled in the art would achieve in light of this disclosure, are achieved by various aspects of this disclosure.

[0014] According to a first aspect, the present invention is a method for producing fully heat-stabilized aggregated lignin, a) A step of providing aggregated lignin having an average particle size in the range of 50 to 500 μm; b) To obtain fully heat-stabilized aggregated lignin, the aggregated lignin is heated to a temperature in the range of 140-300°C for at least 30 minutes. Regarding methods including

[0015] Heating aggregated lignin ensures that melting / expansion deformation does not occur during subsequent heat treatment. Surprisingly, it has been found that heating aggregated lignin with an average particle size in the range of 50-500 μm yields completely heat-stabilized aggregated lignin. During heat stabilization, the aggregated lignin is crosslinked. The degree of crosslinking within the resulting completely heat-stabilized aggregated lignin is uniform or substantially uniform throughout the entire aggregate. Uniform crosslinking ensures that a carbon-enriched material with uniform properties is obtained from the heat-stabilized aggregated lignin. Because the size of the provided aggregated lignin is relatively small, the penetration of oxidizing species is promoted during the heat stabilization stage, ensuring that the resulting heat-stabilized aggregated lignin is completely crosslinked even in the core of the aggregate. In other words, uniform crosslinking within completely heat-stabilized aggregated lignin means that the material is homogeneous. Carbon-enriched materials obtained from homogeneous heat-stabilized aggregated lignin are also homogeneous in terms of structure.

[0016] According to a second aspect, the present invention relates to fully thermally stabilized aggregated lignin having an average particle size in the range of 50 μm to 500 μm. Since the aggregated lignin is fully thermally stabilized, the degree of crosslinking of the fully thermally stabilized aggregated lignin is uniform throughout the fully thermally stabilized aggregated lignin.

[0017] According to a third aspect, the present invention is a method for producing a carbon-enriched material, 1) A step of providing fully thermally stabilized aggregated lignin that can be obtained by a method according to the first embodiment; 2) A step of subjecting stabilized aggregated lignin to heat treatment at one or more temperatures in the range of 300 to 1500°C in order to obtain a carbon-enriched material, wherein the heat treatment is performed for a total time in the range of 30 minutes to 10 hours; 3) A step of optionally pulverizing the obtained carbon-enriched material. Regarding methods including

[0018] Surprisingly, it was found that when fully thermally stabilized aggregated lignin is heat-treated, the resulting carbon-enriched material has a reduced amount of volatile substances compared to carbon-enriched materials obtained from only partially thermally stabilized aggregated lignin. This is important in terms of yield and process efficiency. The carbon-enriched material obtained by the method of the present invention also has a pore size distribution that is advantageous in that it provides a carbon-enriched material with high capacity when used as a negative electrode active material in non-aqueous secondary batteries.

[0019] According to a fourth aspect, the present invention relates to a negative electrode for a non-aqueous secondary battery comprising a carbon-enriched material as an active material obtained by the method according to the third aspect.

[0020] According to a fifth aspect, the present invention relates to the use of a carbon-enriched material obtained by the method according to the third aspect as an active material in the negative electrode of a non-aqueous secondary battery. [Modes for carrying out the invention]

[0021] Step a) of the method according to the first aspect of the present invention is to measure the average particle size (D) in the range of 50 to 500 μm, or 100 to 400 μm, or 200 to 500 μm. v50 The present invention provides aggregated lignin having )

[0022] In some embodiments, the aggregated lignin has an average particle size in the range of 50-500 μm, or 50-400 μm, or 50-300 μm, or 100-500 μm, or 100-400 μm, or 100-300 μm, or 200-500 μm, or 200-400 μm, or 300-500 μm.

[0023] In this application, the average particle size is defined as the volume-average particle size (D v50 ) is defined as the maximum particle size that occupies 50% of the sample volume. In this invention, particle size refers to the diameter of the particle. The average particle size can be determined, for example, by laser diffraction. In the context of this invention, the particle diameter is the equivalent spherical diameter of the particle if the particle is not spherical. The equivalent spherical diameter is the diameter of an equivolute sphere.

[0024] Throughout this disclosure, the term “lignin” is intended to refer to all types of lignin that can be used as a carbon source for producing carbon-enriched materials. Examples of such lignin include, but are not limited to, lignin obtained from plant-based raw materials such as wood, such as coniferous lignin, broadleaf lignin, and lignin from annelid plants. Lignin may also be chemically modified.

[0025] Preferably, the lignin is purified or isolated before use in the method according to the present invention. Lignin may be isolated from black liquor and optionally further purified before use in the method according to the present invention. Purification is typically carried out so that the purity of the lignin is at least 90%, preferably at least 95%, and more preferably at least 98%, based on the dry weight of the lignin material. Thus, the lignin material used by the method of the present invention preferably contains less than 10%, preferably less than 5%, and more preferably less than 2%, of impurities such as cellulose, carbohydrates, and inorganic compounds, based on the dry weight of the lignin material.

[0026] The lignin used in the method according to the present invention can be obtained by various extraction methods, such as the organosolve process or the Kraft process. Lignin can also be obtained from processes such as steam explosion or enzymatic hydrolysis following acidic pretreatment. Preferably, the lignin used in the method according to the present invention is Kraft lignin, i.e., lignin obtained by the Kraft process. Kraft lignin can be obtained from hardwoods or conifers. Lignin can usually be obtained by a process called the LignoBoost process, disclosed in International Publication No. 2006031175 A1. Typically, this process includes the steps of precipitating lignin from alkaline black liquor by acidification, separating the precipitated lignin, and restrush the lignin at least once under acidic conditions. The obtained lignin is dried and pulverized to be provided as solid particles.

[0027] As used herein, the term “aggregated lignin” refers to macroscopic particles containing clustered small particles of lignin. Providing lignin in an aggregated form results in a more compact and rigid material. The rigid aggregate is advantageous for subsequent processing because it can withstand physical shocks during processing. Furthermore, when lignin is provided in an aggregated form, the tendency to generate dust is reduced. The aggregated lignin of the present invention is prepared by a method that includes a step of compressing lignin. This means that the aggregated lignin is not in the form of secondary lignin particles that spontaneously aggregate, for example, during lignin precipitation.

[0028] The aggregated lignin provided in step a) is 0.4-0.8 g / cm³. 3 For example, 0.5~0.7 g / cm³ 3 It may have a bulk density within the range of [this range].

[0029] The aggregated lignin provided in step a) may or may not contain at least one additive. In the context of the present invention, an additive is a substance added to improve either the processing or functionality of the resulting material. Therefore, an additive is a substance that is not present in the lignin starting material but is added. Accordingly, water and other moisture, as well as other components already present in the lignin starting material, are not considered additives in the context of the present invention.

[0030] The total amount of additives is preferably less than 5 wt%, for example 0 to 5 wt%, or 0.1 to 5 wt%, or less than 2 wt%, for example 0 to 2 wt%, or 0.1 to 2 wt%, based on the total dry weight of the aggregated lignin. In this way, the aggregated lignin contains at least 95 wt%, for example at least 98%, of the total dry weight of the aggregated lignin.

[0031] Step b) of the method according to the first embodiment includes heating the aggregated lignin to a temperature in the range of 140 to 300°C for at least 30 minutes in order to obtain fully heat-stabilized aggregated lignin.

[0032] As used herein, the term “thermal stabilization” refers to the process of heating aggregated lignin at a temperature lower than the temperature required for carbonization. By performing thermal stabilization, the resulting thermally stabilized aggregated lignin can be heat-treated while maintaining its shape and dimensions, and melting / expansion and deformation during subsequent heat treatment can be avoided. Thermal stabilization is preferably carried out in an oxidizing atmosphere. Crosslinking of lignin occurs during thermal stabilization by both oxidation and heat. Crosslinking is promoted by the combination of oxidation and heat. Crosslinking hardens the lignin within the aggregate and prevents melting / expansion during subsequent heat treatment. Lignin aggregates before thermal stabilization behave as thermoplastics, while lignin aggregates after thermal stabilization behave as thermosettings instead. Both the terms “thermal stabilization” and “heating” are used throughout this disclosure to define a method for obtaining thermally stabilized aggregated lignin.

[0033] As used herein, the term "fully thermal-stabilized" in expressions such as "fully thermal-stabilized aggregated lignin" refers to aggregated lignin that has been thermally stabilized to such an extent that the same or substantially the same degree of crosslinking is achieved throughout the material. Thus, the degree of crosslinking is uniform or substantially uniform throughout the fully thermal-stabilized aggregated lignin. This means that material properties such as structure and hardness will be the same throughout the fully thermal-stabilized aggregated lignin. For example, the core of fully thermal-stabilized aggregated lignin will have the same hardness and degree of crosslinking as the shell. Fully thermal-stabilized aggregated lignin has a homogeneous structure. Fully thermal-stabilized aggregated lignin is also called fully crosslinked aggregated lignin.

[0034] The glass transition temperature (Tg) of lignin typically increases after a heating process; therefore, the Tg of heat-stabilized aggregated lignin is higher than that of aggregated lignin before heating. The Tg of fully stabilized aggregated lignin is typically higher than that of aggregated lignin before heating, and also typically higher than that of partially heat-stabilized aggregated lignin.

[0035] Carbon-enriched materials obtained from fully thermally stabilized aggregated lignin will have improved properties, for example, in terms of pore size distribution.

[0036] The heating in step b) for producing fully heat-stabilized aggregated lignin is preferably carried out in an oxidizing atmosphere. Such an oxidizing atmosphere contains oxidizing species that can react to crosslink the lignin. The heating may be carried out in the presence of, for example, oxygen, iodine, ozone, nitrogen dioxide, nitrobenzene, hydrogen peroxide, or peracetic acid. Preferably, the heating is carried out in air. Alternatively, suitable oxidizing species may be supplied in a nitrogen atmosphere.

[0037] By providing aggregated lignin having an average particle size in the range of 50 to 500 μm, the penetration of oxidizing species is promoted, and after heating, the aggregated lignin is completely thermally stabilized.

[0038] Instead, if, for example, at least 80 wt% of the aggregated lignin has a relatively large particle size, such that it has a diameter in the range of 0.2 to 5.0 mm (corresponding to an average particle size in the range of 0.8 to 2.0 mm), the aggregated lignin will only be partially thermally stabilized after heat treatment. Therefore, the degree of crosslinking will not be uniform throughout the thermally stabilized aggregated lignin. While the outer shell of the thermally stabilized aggregated lignin becomes fully crosslinked and hard, the core remains mostly uncrosslinked and soft. Thus, the resulting thermally stabilized aggregated lignin is only partially crosslinked or partially thermally stabilized. The uncrosslinked core may foam / expand during subsequent heat treatment, which will affect the structure of the carbon-enriched material obtained from such lignin. The resulting carbon-enriched material will have a different structure on the surface compared to the core, which is undesirable in terms of performance.

[0039] As used herein, the term "partially thermal-stabilized" refers to agglomerated lignin that is partially crosslinked during thermal stabilization. The degree of crosslinking is non-uniform, with some parts (e.g., the shell) being fully crosslinked and others (e.g., the core) not being crosslinked. In other words, the shell is fully thermal-stabilized, while the core is not, retaining its thermoplastic behavior. Partially crosslinked, thermal-stabilized, agglomerated lignin is structurally heterogeneous. Partially thermal-stabilized, agglomerated lignin is also called partially crosslinked agglomerated lignin.

[0040] The aggregated lignin provided in step a) may be uncrosslinked (i.e., unheat-treated) or partially crosslinked (i.e., partially heat-stabilized), depending on the method used to prepare the aggregated lignin.

[0041] The heating in step b) for producing fully heat-stabilized aggregated lignin may be carried out continuously or in batch mode. The heating may be carried out using methods known in the art, preferably in a rotary furnace, a moving bed furnace or a rotary hearth furnace.

[0042] Heating for producing fully heat-stabilized aggregated lignin is carried out so that the aggregated lignin is heated to a temperature in the range of 140–300°C, preferably 180–260°C. The heating is carried out for at least 30 minutes, i.e., the residence time of the aggregated lignin in the apparatus used for heating is at least 30 minutes. In one embodiment, the heating is carried out for at least 1 hour, or at least 1.5 hours. Preferably, the heating is carried out for less than 12 hours. The heating may be carried out at the same temperature throughout the heating stage, or it may be carried out while changing the temperature, such as by gradually increasing the temperature or utilizing a temperature gradient. More preferably, the heating is carried out so that the aggregated lignin is first heated to a temperature in the range of 140–175°C for at least 15 minutes, and then heated to a temperature in the range of 175–300°C for at least 15 minutes.

[0043] Compared to the aggregated lignin before heating to obtain a completely heat-stabilized material, there may be a slight weight loss during heating. The weight loss is typically less than 15 wt% and is mainly due to the evaporation of water and the loss of volatile components due to the decomposition of lignin during heating.

[0044] By controlling and optimizing parameters such as temperature and time during the heating process, fully thermally stabilized aggregated lignin can be obtained, maintaining its shape and dimensions without melting or expanding during subsequent processing. This described process, due to the mechanical stability and relatively short residence time of the aggregated lignin, is well-suited to typical process requirements for continuous production, such as using a rotary furnace. This is particularly important for realizing economical, large-scale industrial processes for producing carbon-enriched materials. Since the average particle size of the aggregated lignin is in the range of 50–500 μm, the time required for complete thermal stabilization is typically short, which is beneficial from a process efficiency standpoint.

[0045] Completely heat-stabilized aggregated lignin is present in a concentration of 0.4-0.8 g / cm³. 3 For example, 0.5~0.7 g / cm³ 3 It may have a bulk density within this range. Upon heating, the bulk density may increase or decrease slightly compared to the aggregated lignin before heating. However, the bulk density of fully heat-stabilized aggregated lignin preferably remains within the same range as before the heating process.

[0046] During heating, the structure of lignin changes due to crosslinking. Surprisingly, it has been found that the degree of thermal stabilization of lignin affects the pore size distribution of carbon-enriched materials obtained from thermally stabilized lignin. In carbon-enriched materials obtained from fully thermally stabilized aggregated lignin, the pore size distribution is such that high capacity can be obtained when the carbon-enriched material is used as a negative electrode active material in secondary batteries. The pore size distribution of carbon-enriched materials obtained from fully thermally stabilized aggregated lignin typically features a wide range of pore sizes, including a large number of relatively small pores. Conversely, in carbon-enriched materials obtained from partially thermally stabilized aggregated lignin, the pore size distribution is less favorable in terms of capacity. The pore size distribution of carbon-enriched materials obtained from partially thermally stabilized aggregated lignin typically features a narrow range of pore sizes, with most pores being relatively large.

[0047] The color of the heat-stabilized aggregated lignin is different from the color of the aggregated lignin before heat stabilization. The color can be determined, for example, using a spectrophotometer and reported according to the CIELAB color space. In the CIELAB color space, the color can be reported as lightness (L * ), green-red (a * ), and blue-yellow (b * ) components. Preferably, the lightness (L * ) of the surface of the completely heat-stabilized aggregated lignin is in the range of 34 to 39. The lightness of the surface of the aggregated lignin before heat stabilization exceeds 44 and is, for example, in the range of 44 to 52. Therefore, the lightness of the aggregated lignin decreases during heat stabilization.

[0048] Preferably, the sum of the absolute values of the CIELAB green-red component (a * ) and the CIELAB blue-yellow component (b * ) of the surface of the completely heat-stabilized aggregated lignin is less than 5.0, i.e., |a * | + |b * | < 5.0. More preferably, the sum of the absolute values of the CIELAB green-red component (a * ) and the CIELAB blue-yellow component (b * ) of the surface of the completely heat-stabilized aggregated lignin is less than 3.0. The sum of the absolute values of the CIELAB green-red component (a * ) and the CIELAB blue-yellow component (b * ) of the surface of the completely heat-stabilized aggregated lignin can be in the range of 0.5 to 5.0, or 0.5 to 3.0. The absolute value of the CIELAB green-red component (a * ) of the surface of the completely heat-stabilized aggregated lignin is preferably less than 3.0, or less than 2.0. The absolute value of the CIELAB blue-yellow component (b * ) of the surface of the completely heat-stabilized aggregated lignin is preferably less than 3.0, or less than 2.0. <​​The core color of heat-stabilized aggregated lignin can be measured by first crushing the aggregate to obtain smaller lignin particles. Since the smaller lignin particles represent all parts of the aggregate, i.e., both the core and the surface, they can be used to obtain an average color value for heat-stabilized aggregated lignin.

[0050] In the case of fully thermally stabilized aggregated lignin, the surface of the lignin particles obtained by crushing the aggregated lignin is the same as the L measured on the surface of the aggregated lignin. * a * and b * It has the same or very similar value as [the other value].

[0051] In the case of partially heat-stabilized aggregated lignin, L * a * and b * The L values ​​differ between the surface and the core of the aggregate. The surface of partially thermally stabilized aggregated lignin is fully thermally stabilized, and the L values ​​are in the same range as described above for fully thermally stabilized aggregated lignin. * a * and b * It has a value of . After crushing, the brightness of the surface of the obtained lignin particles may be 40-44, and the CIELAB green-red component (a * ) and CIELAB blue-yellow component (b * The sum of the absolute values ​​of |a * |+|b * |<10. CIELAB green-red component (a) on the surface of lignin particles. * The absolute value of ) may be less than 5.0. CIELAB blue-yellow component (b) on the surface of lignin particles * The absolute value of ) can be less than 5.0.

[0052] Therefore, L measured on the surface of crushed aggregated lignin * a * and b * The value can be used to evaluate and monitor the degree of thermal stabilization obtained during heating of aggregated lignin, and therefore the degree of crosslinking.

[0053] The aggregated lignin provided in step a) can be obtained by compressing lignin powder and crushing the resulting lignin powder to obtain aggregated lignin having an average particle size in the range of 50 to 500 μm. Two embodiments of the method for obtaining aggregated lignin will now be described in detail.

[0054] In the first embodiment, the aggregated lignin provided in step a) is as follows: - A step of providing lignin in powder form; - A process of compressing lignin powder to obtain compressed lignin; - A step of crushing compressed lignin in order to obtain aggregated lignin having an average particle size in the range of 50 to 500 μm and It is obtained by a method that includes the following.

[0055] The lignin powder is preferably dried before compression. The drying of the lignin powder is carried out by methods and apparatus known in the art. The moisture content of the lignin in powder form is less than 45 wt%. Preferably, the moisture content of the lignin before compression is less than 25 wt%, preferably less than 10 wt%, and more preferably less than 8 wt%. The moisture content of the lignin before compression may be at least 1 wt%, for example, at least 5 wt%. The temperature during drying is preferably in the range of 80 to 160°C, more preferably in the range of 100 to 120°C.

[0056] The particle size distribution of the lignin powder is preferably such that 80 wt% of the particles have a diameter of less than 0.2 mm.

[0057] The lignin powder obtained after drying has a wide particle size distribution ranging from 1 μm to 2 mm, with a significant bias towards the micrometer range. This means that a considerable proportion of the particles have a diameter in the range of 1 to 200 μm. The lignin powder is preferably 0.3 to 0.4 g / cm³. 3 It has a bulk density within the range of [value].

[0058] Lignin compression is preferably carried out by roll compression. Roll compression of lignin can be achieved by agglomerating lignin particles with a roller compressor.

[0059] In the compression process, intermediate products are generated. Here, fine lignin powder is typically supplied through a hopper and transported to the compression zone by a horizontal or vertical supply screw. In the compression zone, the material is compressed into flakes by compression rollers with a constant gap. By controlling the supply screw speed and the pressure generated in the compression zone, flakes of uniform density can be obtained. Preferably, the pressure generated in the compression zone can be monitored and controlled by the rotational speed of the compression rolls. As the powder is drawn between the rollers, it enters a section called a nip, where the density of the material increases and the powder changes into flakes or ribbons. The rolls used have cavities. The depth of each cavity used for roll compression is 0.1 mm to 10 mm, preferably 1 mm to 8 mm, more preferably 1 mm to 5 mm or 1 mm to 3 mm. The specific pressing force exerted during compression may vary depending on the equipment used for compression, but can range from 1 kN / cm to 100 kN / cm. Apparatus suitable for carrying out compression is known in the art.

[0060] After compression, crushing is preferably performed. In the crushing step, the intermediate product from the compression step is subjected to crushing or grinding using means such as a rotary granulator, cage mill, beater mill, hammer mill or crusher mill and / or a combination thereof.

[0061] After crushing, the crushed material is subjected to a sieving process to remove even finer particles. Furthermore, larger particles may be removed and / or recycled and returned to the crushing process.

[0062] In the sieving step, intermediate products from the crushing step are screened by a physical fractionation means such as sieving (also called screening) to obtain a product which is aggregated lignin having a particle size distribution determined by the pore size of the sieve or screen in this step. The sieve or screen is selected such that small particles, such as fine powder, pass through the screen and are rejected, preferably returned to the compression step. In other embodiments, the sieve may be selected such that most particles with a diameter of less than 50 μm or less than 100 μm pass through the screen and are rejected, preferably returned to the compression step. Particles with a diameter too large to pass through the sieve are retained and subjected to subsequent processing steps according to the present invention. The sieve may be selected such that most particles with a diameter greater than 50 μm or greater than 100 μm are retained. Sieving can be carried out in multiple steps. That is, sieving can be carried out such that the crushed material from the crushing step passes through multiple screens or sieves sequentially.

[0063] In one embodiment of roll compression, the roll configuration is such that the first roll has an annular rim, and the powder in the nip region is sealed axially along the roller surface.

[0064] In one embodiment, the roll configuration is such that the nip region is sealed axially along the roller surface by a stationary plate. By ensuring that the nip region is sealed, powder loss at both ends of the roller in the axial direction is minimized compared to a fully cylindrical nip roller.

[0065] Compression of lignin powder during the preparation of aggregated lignin increases the bulk density of lignin as pressure is applied to the lignin powder. This means that the bulk density of aggregated lignin is higher than that of lignin powder. Since compact lignin particles have been found to retain their shape and dimensions without melting or expanding, more compact lignin particles can be beneficial in subsequent processing of carbon-enriched materials. Aggregated, compressed lignin particles also exhibit relatively high hardness after compression. Hard aggregates are advantageous for subsequent processing because they can withstand physical shocks during processing. Furthermore, using hard, compressed particles avoids processing problems that may arise from the presence of lignin dust on the particle surface. This is particularly important in large-scale processes, as dust can form explosive mixtures with air or cause blockages inside processing equipment.

[0066] In the second embodiment, the aggregated lignin provided in step a) is as follows: - A step of providing lignin in powder form; - A process of compressing lignin powder to obtain compressed lignin; - A step of crushing compressed lignin in order to obtain aggregated lignin having an average particle size in the range of 0.8 to 2.0 mm; - To obtain partially heat-stabilized aggregated lignin, the obtained aggregated lignin is heated to a temperature in the range of 140-250°C for at least 1.5 hours; - In order to obtain aggregated lignin having an average particle size in the range of 50 to 500 μm, the obtained partially heat-stabilized aggregated lignin is crushed. It is obtained by a method that includes the following.

[0067] Compared with the method of the first embodiment, the method of the second embodiment includes first preparing aggregated lignin having an average particle size in the range of 0.8 to 2.0 mm, which is heated in a first heating step to obtain partially heat-stabilized aggregated lignin. The obtained partially heat-stabilized aggregated lignin is crushed into aggregated lignin having an average particle size in the range of 50 μm to 500 μm.

[0068] The steps of providing lignin powder and compressing lignin powder are defined as detailed above for the first embodiment. The first crushing step is carried out as detailed above for the first embodiment, except that lignin aggregates having an average particle size in the range of 0.8 to 2.0 mm are obtained. In an optional sieving step, a sieve or screen is selected such that most particles with a diameter of less than 100 μm (or 500 μm) pass through the screen, and most particles with a diameter greater than 100 μm (or 500 μm) are retained. Furthermore, larger particles are preferably removed.

[0069] The equipment used in the compression and crushing processes is the same regardless of the particle size of the resulting aggregates. Instead, an appropriate sieve or screen is selected depending on the desired aggregate size.

[0070] After the first crushing step, the resulting aggregated lignin having an average particle size in the range of 0.8 to 2.0 mm is subjected to heating. Heating is carried out in the same manner as the thermal stabilization step described above. Because the particle size is relatively large, partially thermally stabilized aggregated lignin is obtained. In the second crushing step, the partially thermally stabilized aggregated lignin is crushed to obtain lignin aggregates with a size in the range of 50 to 500 μm. The second crushing step is carried out as described above for the first embodiment. After heating of the aggregated lignin with an average particle size in the range of 0.8 to 2.0 mm, a partially thermally stabilized material is obtained. Therefore, the aggregated lignin with a particle size in the range of 50 to 500 μm obtained after the second crushing step is thermally stabilized to varying degrees depending on its position within the aggregate before the second crushing step. Such aggregated lignin is collectively referred to as "partially thermally stabilized" even after the second crushing step.

[0071] The advantage of the first embodiment is that it involves fewer steps compared to the second embodiment. Fewer steps are beneficial from a cost perspective. However, the first embodiment involves handling small lignin aggregates. Small size can lead to clogging problems in the process equipment and also increases the risk of dust explosions during handling. Furthermore, small lignin aggregates tend to melt during thermal stabilization before crosslinking.

[0072] However, this problem can sometimes be overcome by carefully selecting the process equipment. If melting is severe during stabilization, it is also possible to perform an additional crushing step on the fully heat-stabilized, aggregated lignin to obtain the desired particle size.

[0073] In the method according to the second embodiment, the drawbacks of the first embodiment are avoided. Since relatively large aggregates are handled, clogging and dust explosions are avoided. When the aggregated lignin is partially thermally stabilized, subsequent handling becomes easier even after crushing to further reduce the particle size, and aggregated lignin with an average particle size in the range of 50 to 500 μm is obtained. Melting during the thermal stabilization of small-sized aggregated lignin is not a problem if the aggregated lignin is already partially thermally stabilized before being crushed to a smaller size.

[0074] Both the first and second embodiments involve the following additional steps: - A step of providing at least one additive; and - A step of mixing lignin powder with at least one additive. It may include.

[0075] Any suitable additives may be provided. For example, at least one additive may be selected from any suitable type of binder or lubricant, which may facilitate the subsequent compression process and improve the density and mechanical properties of the resulting aggregated lignin. At least one additive may be a functional additive that affects the carbon-enriched material obtained from the aggregated lignin. Examples of such functional additives include carbon additives and silicon-containing additives. Carbon additives may be selected from at least one of graphite, graphene, carbon nanotubes, charcoal, biochar, hard carbon, soft carbon, carbon black, and conductive carbon. Silicon-containing additives may be selected from at least one of elemental silicon, silicon dioxide, silicon-metal alloys, and silicon-metal-carbon alloys. Silicon dioxide may be SiOx (0 ≤ x ≤ 2). Silicon-metal alloys may be any suitable silicon-metal alloy, such as SiFex or SiFexAly. A silicon-metal alloy is, for example, SiFexCy.

[0076] The total amount of additives is preferably less than 5 wt%, for example 0 to 5 wt%, or 0.1 to 5 wt%, or less than 2 wt%, for example 0 to 2 wt%, or 0.1 to 2 wt%, based on the total dry weight of the lignin-additive powder mixture.

[0077] The mixing of lignin powder and at least one additive is carried out by methods and apparatus known in the art. An example of a suitable method is a vertical mixer such as a paddle, screw, or ribbon screw mixer in batch mode or continuous mode. The mixing process may be carried out in low, medium, or high shear impact mode.

[0078] In embodiments where at least one additive is present, the compression step is carried out as described above, even when at least one additive is present. At least one additive is compressed together with the lignin powder. At least one additive is dispersed within the resulting aggregated lignin.

[0079] A second aspect of the present invention relates to fully heat-stabilized aggregated lignin having an average particle size in the range of 50 μm to 500 μm. The degree of crosslinking is not uniform throughout the heat-stabilized aggregated lignin. The fully heat-stabilized aggregated lignin according to the second aspect can be prepared by the method according to the first aspect. The fully heat-stabilized aggregated lignin may be further defined as described above with reference to the first aspect.

[0080] In particular, fully thermally stabilized aggregated lignin has a cross-linked structure throughout the material. Thermally stabilized aggregated lignin is hard, dark in color, and retains its shape and dimensions without melting or expanding during subsequent heat treatment. The structure of fully thermally stabilized aggregated lignin makes it suitable as a starting material for obtaining carbon-enriched materials with a pore size distribution suitable for use as a high-capacity anode material.

[0081] A third aspect of the present invention relates to a method for producing a carbon-enriched material by heat treatment of fully thermally stabilized aggregated lignin according to the first aspect. The method according to the third aspect may thus include carrying out the method according to the first aspect.

[0082] As used herein, the term “heat treatment” refers to the process of heating fully heat-stabilized aggregated lignin at one or more temperatures for a sufficient amount of time so that the lignin is converted into a carbon-enriched material. This process may also be called “carbonization” or “calcination.” After heat treatment, the carbon content is greater than 80 wt%, greater than 90 wt%, greater than 95 wt%, or greater than 98 wt%. Depending on the temperature during heat treatment, various types of carbon, such as charcoal and hard carbon, can be obtained from the heat-stabilized aggregated lignin.

[0083] As used herein, the term “carbon-enriched material” refers to a carbon material obtained by heat treatment of fully thermally stabilized aggregated lignin. The carbon content of the carbon-enriched material is greater than 80 wt%, greater than 90 wt%, greater than 95 wt%, or greater than 98 wt%. The carbon-enriched material may also contain heteroatoms such as oxygen atoms, hydrogen atoms, nitrogen atoms, or sulfur atoms, inorganic impurities, and functional additives. The carbon-enriched material of the present invention is amorphous (i.e., non-crystalline) carbon, preferably hard carbon.

[0084] Step 1) of the method according to the third embodiment includes providing fully thermally stabilized aggregated lignin, which can be obtained by the method according to the first embodiment. As described above, the fully thermally stabilized aggregated lignin is fully crosslinked. Due to the crosslinking, the lignin retains its shape and dimensions without melting / expanding during the heat treatment for conversion into a carbon-enriched material. Thus, the resulting carbon-enriched material has the same shape as the fully thermally stabilized aggregated lignin.

[0085] Step 2) of the method according to the third embodiment includes subjecting fully thermally stabilized aggregated lignin to a heat treatment at one or more temperatures in the range of 300 to 1500°C, wherein the heat treatment is performed for a total time in the range of 30 minutes to 10 hours, in order to obtain a carbon-enriched material.

[0086] The heat treatment may be carried out at the same temperature throughout the entire heat treatment process, or it may be carried out while varying the temperature, such as by gradually increasing the temperature or utilizing a temperature gradient. The heat treatment may include a temperature rise from the starting temperature to the target temperature. The heating rate may be 1 to 100°C / min. For example, the heat treatment may include several intermediate temperatures and temperature increases in between before reaching the target temperature required for the complete carbonization of the heat-stabilized aggregated lignin. The heat treatment may be carried out as a batch process or as a continuous process. A suitable reactor may be used, such as a rotary furnace, moving bed furnace, pusher furnace, or rotary hearth furnace. The heat treatment is preferably carried out in an inert atmosphere, more preferably in a nitrogen atmosphere.

[0087] Preferably, the heat treatment includes a preheating step, preferably followed by a final heating step. The preheating step is preferably carried out at one or more temperatures in the range of 300 to 800°C, for example, 500 to 700°C. The preheating step is preferably carried out in an inert atmosphere, preferably in a nitrogen atmosphere. The duration of the preheating step is at least 30 minutes, preferably less than 10 hours. The surface area of ​​the carbon-enriched material obtained after the preheating step is measured by the BET method using nitrogen gas and is usually 300 to 700 m². 2 It is within the range of / g.

[0088] The final heating step is preferably carried out at one or more temperatures in the range of 800 to 3000°C. The final heating step is preferably carried out under an inert atmosphere, preferably under a nitrogen atmosphere. The duration of the final heating step is at least 30 minutes, preferably less than 10 hours. After the final heating step, which is carried out at 1000°C or higher, the surface area of ​​the resulting carbon-enriched material is typically 50 m². 2 It is less than / g.

[0089] The preheating and final heating steps may be performed as separate steps or as a single, direct step. The preheating and final heating steps may include heating at one or more temperatures, as described above for the heat treatment. For example, preheating may begin at approximately 300°C, and then the temperature may rise to approximately 500°C. The final heating step is preferably performed at a temperature between 900°C and 1300°C, for example, approximately 1000°C.

[0090] The preheating and final heating processes may be carried out as batch processes or as continuous processes. Any suitable reactor may be used. The preheating and final heating processes may be carried out in the same reactor or in separate reactors.

[0091] The color of carbon-enriched materials may differ slightly from the color of fully thermally stabilized aggregated lignin. The color can be determined, for example, using a spectrophotometer and reported according to the CIELAB color space. In the CIELAB color space, color is expressed in terms of lightness (L). * ), green-red (a * ), blue-yellow (b * ) may be reported as a component. Preferably, the brightness (L) of the surface of the carbon-enriched material. * ) is in the range of 34-39.

[0092] Preferably, the CIELAB green-red component (a) on the surface of the carbon-enriched material. * ) and CIELAB blue-yellow component (b * The sum of the absolute values ​​of |a| is less than 2.0 or less than 1.0, i.e., |a| * |+|b * |<1.0, or |a * |+|b * |<2.0. CIELAB green-red component (a) on the surface of carbon-enriched material. * The absolute value of (b) is preferably less than 1.5 or less than 1.0. CIELAB blue-yellow component (b) on the surface of the carbon-enriched material * The absolute value of ) is preferably less than 1.5 or less than 1.0. In some embodiments, the CIELAB green-red component (a) on the surface of the carbon-enriched material * ) and CIELAB blue-yellow component (b *The sum of the absolute values ​​of ) is zero. In some embodiments, the CIELAB green-red component (a) on the surface of the carbon-enriched material * ) and CIELAB blue-yellow component (b * The sum of the absolute values ​​of ) can be in the range of 0 to 2.0 or 0 to 1.0.

[0093] a on the surface of carbon-enriched material * and b * The absolute value of is the a of the surface of the fully heat-stabilized aggregated lignin before carbonization. * and b * It can be lower than the absolute value of a. * and b * The value may be approximately the same on the surface of the carbon-enriched material and on the surface of fully thermally stabilized aggregated lignin.

[0094] The carbon-enriched material is preferably 0.2 to 0.4 g / cm³. 3 It has a bulk density in the range of [value missing]. This is lower than the bulk density of aggregated lignin and fully heat-stabilized lignin, mainly due to mass loss during heat treatment.

[0095] The carbon-enriched material is preferably 1.4 to 2.1 g / cm³. 3 For example, 1.7-2.0 g / cm³ 3 It has a true helium density in the range of 1.4 to 2.1 g / cm³. The true helium density can be measured using a pycnometer known to those skilled in the art. 3 It is important that the material is within this range. Otherwise, the doping and dedoping capacities of the carbon-enriched material when used as the active material for the negative electrode of a non-aqueous secondary battery may decrease, potentially leading to an increase in the irreversible capacity of the battery. If the density of the carbon-enriched material is too low, the energy density of the electrode may also decrease.

[0096] The carbon-enriched material of the present invention is suitable for use as an active material in the negative electrode of a secondary battery because it has a high capacity obtained by a favorable pore size distribution. The carbon-enriched material is obtained from fully thermally stabilized aggregated lignin, because the pore size distribution correlates with the degree of crosslinking of the lignin. As a result of crosslinking, the structure of the lignin becomes suitable for forming an appropriate pore size distribution when converted into a carbon-enriched material.

[0097] The carbon obtained as a product of step 2) may be useful, for example, as biochar or as a precursor for activated carbon.

[0098] Step 3) of the method according to the third embodiment optionally includes pulverizing the obtained carbon-enriched material. In many applications, the particle size of the carbon-enriched material obtained in step 2) needs to be reduced before use to obtain carbon powder. For example, when the carbon-enriched material of the present invention is used as an active material in the negative electrode of a secondary battery, it is preferable to reduce the particle size.

[0099] Micronization can be carried out by any suitable process, for example, using a cutting mill, blade mixer, ball mill, impact mill, hammer mill and / or jet mill. Optionally, after micronization, sorting of fine / coarse particles may be performed by classification and / or sieving.

[0100] The micronization of carbon-enriched materials and the selective selection of fine / coarse particles may be carried out to obtain carbon powder containing powder particles having an average particle size in the range of 1 to 25 μm.

[0101] It is also possible to perform pulverization or crushing in multiple steps. Furthermore, the carbon powder may be subjected to further treatments such as coating or heat treatment.

[0102] A fourth aspect of the present invention relates to a negative electrode for a non-aqueous secondary battery, comprising a carbon-enriched material as an active material obtained by the method according to the third aspect.

[0103] The carbon-enriched material (preferably in powder form) of the present invention is preferably used as an active material in the negative electrode of non-aqueous secondary batteries such as lithium-ion batteries and sodium-ion batteries. When used in the manufacture of such negative electrodes, any suitable method for forming such negative electrodes may be utilized. In forming the negative electrode, the carbon-enriched material may be processed together with further components. Such further components include, for example, one or more binders for forming the carbon-enriched material into an electrode, a conductive material (such as carbon black, carbon nanotubes, or metal powder), and / or further Li storage materials (such as graphite or lithium). For example, the binder may be selected from, but is not limited to, poly(vinylidene fluoride), poly(tetrafluoroethylene), carboxymethylcellulose, natural butadiene rubber, synthetic butadiene rubber, polyacrylate, poly(acrylic acid), alginic acid, or a combination thereof. Optionally, solvents such as 1-methyl-2-pyrrolidone, 1-ethyl-2-pyrrolidone, water, or acetone may be used during processing.

[0104] A fifth aspect of the present invention relates to the use of a carbon-enriched material obtained by the method according to the third aspect as an active material in the negative electrode of a non-aqueous secondary battery. [Examples]

[0105] Example 1 - Comparison Aggregated lignin with an average particle size of 1.25 mm was subjected to thermal stabilization in air at 250°C for 2 hours. After thermal stabilization, a partially thermally stabilized material was obtained. The obtained lignin aggregates had a black, insoluble shell. The Tg of lignin increased from 148°C (for unthermally stabilized lignin) to 158°C after thermal stabilization. The color of the aggregated lignin after thermal stabilization was measured using a spectrophotometer, and L * =38, |a * |=0.5 and |b *A value of |=0.1 was obtained. After crushing the aggregated lignin to reduce the particle size, the resulting material exhibited a dark brown color. This indicates that the thermal stabilization of the lignin aggregate core is not complete. Rather, the core is hardly stable and remains soft. When the color of the crushed material was measured with a spectrophotometer, L * =43, |a * |=3.7 and |b * The value obtained was |=6.2.

[0106] Example 2 - Complete Thermal Stabilization The partially heat-stabilized lignin granules from Example 1 were crushed to obtain a powder with an average particle size of less than 500 μm. This powder was subjected to heat stabilization in air at 250°C for 2 hours. After heat stabilization, a fully heat-stabilized material was obtained. The obtained lignin aggregates were black in color, indicating complete heat stabilization. After the second heat stabilization step, the Tg increased from 158°C to 173°C. The color of the aggregated lignin after heat stabilization was measured using a spectrophotometer, and L * =37.5, |a * |=0.5 and |b * A value of |=0.2 was obtained. The lignin aggregates were also hard and possessed closed porosity.

[0107] Example 3 - Carbonization The fully thermally stabilized aggregated lignin from Example 2 and the partially thermally stabilized aggregated lignin from Example 1 were further carbonized in a nitrogen atmosphere at a temperature of 1050°C for a residence time of 2 hours. The resulting carbon-enriched material was ground to an average particle size of 10 μm. The color of the resulting carbon-enriched material was very similar to that of the fully thermally stabilized aggregated lignin obtained in Example 2.

[0108] Example 4 - Volume Measurement An electrode was prepared from the carbon-enriched material of Example 3 and PVDF (6 wt%), and the loading density of the carbon-enriched material was set to approximately 6 mg / cm³. 2The half-cell was assembled into a PAT cell (EL-CELL) in the glove box, with lithium metal as the counter electrode, glass fiber as the separator, and 1M LiPF6 in ethylene carbonate:diethyl carbonate (1:1, vol:vol) as the electrolyte. Constant current charge-discharge tests were performed using an Arbin cycler system. The discharge test was first performed at 0V and 1.5V (vs. Li / Li). + The charging process was performed with a constant current of C / 5 between 0V and 1.5V (vs. Li / Li). + The experiment was conducted with a constant current of C / 5 between ) and ). Carbon-enriched materials obtained from fully thermally stabilized aggregated lignin had a reversible capacity 30-50 mAh / g higher than carbon-enriched materials obtained from partially stabilized aggregated lignin.

[0109] Example 5 - Pore Size Distribution The pore size distribution of the carbon-enriched material in Example 3 was evaluated using CO2 isotherms obtained from porosimulation using a DFT model. As a result, it was found that the carbon-enriched material obtained from partially thermally stabilized aggregated lignin had a narrow pore size distribution with relatively large pores, while the carbon-enriched material obtained from completely thermally stabilized aggregated lignin had a broad pore size distribution with numerous small pores.

[0110] Considering the embodiments for carrying out the above invention of the present invention, other modifications and variations will become apparent to those skilled in the art. However, it will be clear that such other modifications and variations are possible without departing from the spirit and scope of the present invention.

Claims

1. A method for producing fully heat-stabilized aggregated lignin, comprising the following steps: a) A step of providing aggregated lignin having an average particle size in the range of 50 to 500 μm; b) To obtain fully heat-stabilized aggregated lignin, the aggregated lignin is heated to a temperature in the range of 140 to 300°C for at least 30 minutes. Methods that include...

2. The aggregated lignin provided in step a) is then processed in the following steps: - A step of providing lignin in powder form; - A process of compressing lignin powder to obtain compressed lignin; - A step of crushing compressed lignin in order to obtain aggregated lignin having an average particle size in the range of 50 to 500 μm and The method according to claim 1, manufactured by a method comprising:

3. The aggregated lignin provided in step a) is then processed in the following steps: - A step of providing lignin in powder form; - A process of compressing lignin powder to obtain compressed lignin; - A step of crushing compressed lignin in order to obtain aggregated lignin having an average particle size in the range of 0.8 to 2.0 mm; - To obtain partially heat-stabilized aggregated lignin, the process involves heating the obtained aggregated lignin to a temperature in the range of 140 to 300°C for at least 30 minutes; - In order to obtain aggregated lignin having an average particle size in the range of 50 to 500 μm, the obtained partially heat-stabilized aggregated lignin is crushed. The method according to claim 1, manufactured by a method comprising:

4. The method for producing aggregated lignin includes the following additional steps: - A step of providing at least one additive; and - A step of mixing lignin powder with at least one additive. The method according to claim 2 or 3, including the method described in claim 2 or 3.

5. The aggregated lignin provided in step a) is 0.5 to 0.7 g / cm³. ３ The method according to any one of claims 1 to 4, having a bulk density in the range of .

6. The method according to any one of claims 1 to 5, wherein the lignin is kraft lignin.

7. The method according to any one of claims 1 to 6, wherein the heating of the aggregated lignin in step b) is carried out by first heating the aggregated lignin to a temperature in the range of 140 to 175°C for at least 15 minutes, and then heating the aggregated lignin to a temperature in the range of 175 to 300°C for at least 15 minutes.

8. The method according to any one of claims 1 to 7, wherein the heating of the aggregated lignin in step b) is carried out in an oxidizing atmosphere.

9. Fully heat-stabilized aggregated lignin with an average particle size in the range of 50 μm to 500 μm.

10. The fully heat-stabilized aggregated lignin according to claim 9, which is Kraft Lignin.

11. A method for producing carbon-enriched materials, comprising the following steps: 1) A step of providing fully heat-stabilized aggregated lignin that can be obtained by the method of any one of claims 1 to 8; 2) A step of subjecting fully heat-stabilized aggregated lignin to heat treatment at one or more temperatures in the range of 300 to 1500°C in order to obtain a carbon-enriched material, wherein the heat treatment is performed for a total time in the range of 30 minutes to 10 hours; 3) A step of optionally pulverizing the obtained carbon-enriched material. Methods that include...

12. The method according to claim 11, wherein step 2) includes a preheating step and a subsequent final heating step.

13. The method according to claim 12, wherein the preheating step is performed at a temperature between 400°C and 800°C for at least 30 minutes.

14. The method according to claim 12 or 13, wherein the preheating step is performed in an inert atmosphere.

15. The method according to any one of claims 12 to 14, wherein the final heating step is carried out at a temperature between 800°C and 1500°C for at least 30 minutes.

16. The method according to any one of claims 12 to 15, wherein the final heating step is carried out in an inert atmosphere.

17. The carbon-enriched material obtained in step 2) is 1.7 to 2.0 g / cm³. ３ The method according to any one of claims 11 to 16, having a true density in the range of .

18. A negative electrode for a non-aqueous secondary battery comprising a carbon-enriched material as an active material, which can be obtained by the method described in any one of claims 11 to 17.

19. Use of a carbon-enriched material obtained by the method of any one of claims 11 to 17 as an active material in the negative electrode of a non-aqueous secondary battery.

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