Method for producing carbon-enriched materials from lignin

Abstract

The present invention relates to a method for producing a carbon-enriched material, the method comprising: a) providing lignin; b) mixing the lignin with a recycled carbon-enriched material fraction to obtain a lignin-carbon mixture; c) forming an aggregated lignin-carbon composite material comprising lignin, a recycled carbon-enriched material fraction, and optionally at least one additive; d) subjecting the aggregated lignin-carbon composite material to heat treatment at one or more temperatures in the range of 300 to 1500°C for a total time in the range of 30 minutes to 10 hours in order to obtain a carbon-enriched material; e) grinding the obtained carbon-enriched material in order to reduce the average particle size of the carbon-enriched material and to obtain at least a first fraction and a second fraction of the carbon-enriched material; and f) recycling at least a portion of the first fraction obtained in step e) to step b).

Description

[Technical Field]

[0001] The present invention relates to a method for producing a carbon-enriched material from lignin. This method includes a step of recycling at least a portion of the obtained carbon-enriched material and mixing it with lignin in an earlier step before converting lignin into the carbon-enriched material. The present invention relates to a negative electrode for a non-aqueous secondary battery containing the obtained carbon-enriched material as an active material, and to the use of the obtained carbon-enriched material as an active material in the negative electrode of a non-aqueous secondary battery. [Background technology]

[0002] Rechargeable batteries, such as lithium-ion batteries, are electric batteries that can be charged and discharged multiple times. In lithium-ion batteries, during discharge, lithium ions flow from the negative electrode through the electrolyte to the positive electrode, and during charging, they return to the negative electrode. Typically today, lithium compounds, particularly lithium metal oxides such as lithium nickel manganese cobalt oxide (NMC), or lithium iron phosphate (LFP) are used as the positive electrode material, and carbon-enriched materials are used as the negative electrode material.

[0003] Graphite (natural or synthetic graphite) is used today as the negative electrode material in most lithium-ion batteries due to its high energy density and stable charge / discharge performance over long periods. Alternatives to graphite include amorphous carbon materials such as hard carbon (non-graphitizable amorphous carbon) or soft carbon (graphitizable amorphous carbon), but these do not possess the long-range order of graphite. A common characteristic of graphite and amorphous carbon is their small volume change during charge and discharge. This results in improved mechanical stability of the electrode material and easier maintenance of cycle stability. Amorphous carbon can be used as a standalone active electrode material or in mixtures with graphite. Hard carbon often offers superior charge / discharge speed performance, desirable for rapid charging and high-power systems.

[0004] Amorphous carbon is obtained from lignin. Lignin is an aromatic polymer, a major component of wood and other materials, and one of the most abundant carbon sources on Earth. In recent years, technologies have been developed and put into practical use to highly purify lignin from the pulp manufacturing process and extract it in a solid and specialized form, attracting significant attention as a renewable alternative to the mainly aromatic chemical precursors currently supplied by the petrochemical industry. Lignin-derived amorphous carbon is typically non-graphitizable, i.e., hard carbon. Thus, lignin-derived hard carbon offers a more sustainable anode material option than graphite, which is typically used in today's secondary batteries.

[0005] Today, the most commercially available source of lignin is kraft lignin, obtained from hardwoods or softwoods via the krafting process. Lignin can be separated from alkaline black liquor, for example, by membrane filtration or ultrafiltration. One common separation process is described in International Publication No. 2006031175 A1. In this process, lignin is precipitated from alkaline black liquor by the addition of acid, and then filtered. The lignin filter cake is then reslurried under acidic conditions in the next step and washed before drying and pulverization.

[0006] One of the problems with using lignin as a precursor for carbon-enriched materials is that lignin exhibits undesirable thermoplastic behavior, making it unsuitable for direct use in the form of a fine powder. When lignin powder is thermally converted into a carbon-enriched material, the lignin undergoes plastic deformation / melting, expanding violently and foaming. This severely limits the possibility of processing lignin on an industrially appropriate scale in terms of equipment size, processing capacity, and the need for intermediate processing.

[0007] Thus, there is still room for improvement in the method for producing carbon-enriched materials from lignin. This method needs to avoid plastic deformation and melting, or violent expansion and foaming, of the lignin during heating and when converting it to carbon-enriched materials. Furthermore, it should be possible to use this method for large-scale production. To enable sustainable production, material waste in this method must be minimized. [Overview of the project]

[0008] 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.

[0009] A further object of the present invention is to provide a method for obtaining an improved carbon-enriched material starting from lignin, which is suitable for use as an active material in the negative electrode of secondary batteries such as lithium-ion batteries.

[0010] A further object of the present invention is to provide a method for producing a carbon-enriched material from lignin, the method enabling heat treatment of lignin while maintaining its shape and dimensions.

[0011] A further object of the present invention is to provide a method for improving the thermoworkability of lignin.

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

[0013] A further object of the present invention is to provide a method for producing carbon-enriched materials from lignin, in which material waste is reduced and a more sustainable method is possible.

[0014] 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.

[0015] According to a first aspect, the present invention is a method for producing a carbon-enriched material, a) A process of providing lignin; b) To obtain a lignin-carbon mixture, a step is taken to mix lignin with a recycled carbon-enriched material fraction; c) A step of forming an aggregated lignin-carbon composite material comprising lignin, a recycled carbon-enriched material fraction, and optionally at least one additive: d) A step of subjecting an aggregated lignin-carbon composite material 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 carried out for a total time in the range of 30 minutes to 10 hours; e) A step of grinding the obtained carbon-enriched material in order to reduce the average particle size of the carbon-enriched material and to obtain at least a first fraction of the carbon-enriched material and a second fraction of the carbon-enriched material; f) A step of recirculating at least a portion of the first fraction obtained in step e) back to step b) Regarding methods including

[0016] Surprisingly, it was found that mixing lignin with a carbon-enriched material and agglomerating the mixture improved the thermoprocessability of lignin. The carbon-enriched material disperses within the lignin matrix, forming an aggregated lignin-carbon composite. The carbon-enriched material reduces the melting / expansion behavior of lignin during heating, thereby improving the heat resistance of the aggregated lignin-carbon composite and, consequently, the processability of lignin on an industrial scale.

[0017] In the method of the present invention, the carbon-enriched material mixed with lignin in step b) is recycled from step e). After the grinding step, at least two fractions of the carbon-enriched material are obtained. The at least two fractions of the carbon-enriched material may have different average particle sizes. By recycling at least a portion of the first fraction, process material waste is minimized and yield is improved because carbon-enriched material that would otherwise be discarded, such as carbon fine powder, is reintroduced into the process. This increases the profitability of the process and reduces the environmental footprint. Thus, a more sustainable process is possible. The second fraction of the carbon-enriched material may be further processed to the final product.

[0018] Typically, after grinding, fractions of carbon-enriched material with an average particle size in the range of 2–4 μm (i.e., fine fractions) are discarded, while fractions of carbon-enriched material with larger particle sizes are further processed to the final product. The discarded fractions can be used for various purposes, for example, as an energy source or as a substitute for carbon supplied by the petrochemical industry. Recycling the fine fractions instead reduces material waste in the process and enables a more sustainable process.

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

[0020] According to a third aspect, the present invention relates to the use of a carbon-enriched material obtained by the method according to the first 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 involves providing lignin. Throughout the present disclosure, the term "lignin" is intended to refer to any kind of lignin that can be used as a carbon source for producing carbon-enriched materials. Examples of said lignin include, but are not limited to, lignin obtained from vegetable raw materials such as wood, for example softwood lignin, hardwood lignin and lignin from cyclic plants. Also, the lignin may be chemically modified.

[0022] The lignin used in the present invention can be obtained by various extraction methods such as the organosolv process or the kraft process. Lignin can also be obtained from processes such as enzymatic hydrolysis following steam explosion or acidic pretreatment. Preferably, the lignin used in the method of the present invention is kraft lignin, that is, lignin obtained by the kraft process. Kraft lignin is obtained from hardwood or softwood. Lignin can usually be obtained by the process disclosed in International Publication No. WO 2006 / 031175 A1, which is commonly referred to as the LignoBoost process. Typically, this process includes a step of precipitating lignin from alkaline black liquor by acidification, a step of separating the precipitated lignin, and a step of re-slurrying the lignin at least once under acidic conditions. The obtained lignin is dried and micronized and provided as solid particles in powder form.

[0023] Preferably, the lignin is purified or isolated before being used in the method according to the present invention. Lignin can be isolated from black liquor and optionally further purified before being used in the method according to the present invention. The purification is typically carried out such that the purity of the lignin is at least 90%, preferably at least 95%, more preferably at least 98% based on the dry weight of the lignin. Therefore, the lignin used in the process of the present invention preferably contains less than 10%, preferably less than 5%, more preferably less than 2% of impurities such as cellulose, carbohydrates and inorganic compounds based on the dry weight of the lignin.

[0024] In one embodiment, the lignin provided in step a) is in powder form. The particle size distribution of the lignin in powder form may be such that at least 80 wt% of the particles have a diameter of less than 0.2 mm. The lignin in powder form preferably has a water content of less than 45 wt%, or less than 25 wt%, or less than 10 wt%, or less than 8 wt%. In the context of the present 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.

[0025] In one embodiment, the lignin in step a) is provided in powder form. As used herein, the term “slurry” refers to solid lignin particles suspended in a liquid, preferably an aqueous solution. For example, the lignin slurry provided in step a) may be a process flow in a lignin extraction method such as the LignoBoost process. In embodiments where the lignin is provided in slurry form, the lignin must be dried before agglomeration in step c). After drying, the lignin may also be pulverized to obtain lignin powder.

[0026] In one embodiment, the lignin provided in step a) is dissolved in a solution. The lignin may be dissolved in any suitable solvent capable of dissolving lignin. For example, lignin may be dissolved in black liquor. In embodiments where the lignin is dissolved in a solution, the lignin needs to be isolated from the solution and dried, for example by precipitation, before aggregation in step c). After drying, the lignin may also be ground to obtain lignin powder.

[0027] Thus, the lignin provided in step a) may be in solid or dissolved form. In step c), the lignin must be in powder form.

[0028] Step b) of the method according to the first aspect of the present invention comprises mixing lignin with a recycled carbon-enriched material fraction to obtain a lignin-carbon mixture. As used herein, the terms “recycle” and “recycled” refer to a process in which the fraction of the generated material is recovered and introduced early in the process. The recycled carbon-enriched material fraction is thus recycled so that it is generated by heat treatment at a later stage of the process, recovered, and introduced again into the earlier process in which it is mixed with lignin.

[0029] As used herein, the term “lignin-carbon mixture” refers to a mixture of lignin and a carbon-enriched material, the carbon-enriched material being recycled. The recycled carbon-enriched material fraction is in the form of a solid powder and is mixed with lignin by any suitable mixing means. The mixing means may be selected depending on the form in which the lignin is provided. In aggregated lignin-carbon composite materials, it is important that the distribution of the carbon-enriched material within the lignin matrix is ​​uniform. This is ensured by sufficient mixing time and mixing rate in the process of mixing lignin with the recycled carbon-enriched material fraction.

[0030] The lignin-carbon mixture may be a powder mixture or a mixture in which the carbon-enriched material is dispersed in a solution in which lignin is dispersed or dissolved. Thus, the recycled carbon-enriched material fraction can be returned to the process at any appropriate stage. For example, the recycled carbon-enriched material fraction can be introduced after the lignin has been isolated and dried, i.e., outside the lignin isolation plant, for example, outside the LinoBoost plant. In another example, the recycled carbon-enriched material fraction can be introduced inside a lignin isolation plant, such as inside the LinoBoost plant. When introduced inside a lignin isolation plant, the recycled carbon-enriched material can be introduced into the process flow before or after the isolation of lignin from the black liquor.

[0031] In embodiments where lignin is provided in powder form, the recycled carbon-enriched material fraction and the lignin powder can be mixed by a dry mixing method. By providing lignin in powder form, the mixing with the recycled carbon-enriched material fraction is simplified because both materials are dry and the mixing takes place outside the lignin isolation plant.

[0032] In embodiments where lignin is provided in the form of a slurry, the recycled carbon-enriched material fraction can be mixed with the lignin by adding the carbon-enriched material to the lignin slurry. Thus, the slurry will contain both lignin particles and carbon-enriched material particles. The lignin-carbon mixture can be separated from the solution by, for example, filtration or any other suitable separation means. The lignin-carbon mixture is then dried before agglomeration in step c). In embodiments where the lignin slurry is the process flow of a LignoBoost plant, the recycled carbon-enriched material fraction can be introduced into the process at any suitable stage after precipitation of lignin from the black liquor.

[0033] In embodiments where lignin is provided dissolved in a slurry solution, the recycled carbon-enriched material fraction can be mixed with the lignin by adding the carbon-enriched material to the solution in which the lignin is dissolved. Thus, the solution will contain dissolved lignin and dispersed carbon-enriched material. The lignin must be isolated from the solution by, for example, precipitation or any other suitable means before agglomeration in step c). Once the lignin is in a solid form, the lignin-carbon mixture can be separated from the solution by, for example, filtration or any other suitable separation method. The lignin-carbon mixture is then dried before agglomeration in step c). In embodiments where the solution is black liquor, the recycled carbon-enriched material fraction must be introduced into the black liquor before the lignin is precipitated from the black liquor. For example, the carbon-enriched material can be introduced into the black liquor before or when the black liquor is introduced into the LignoBoost plant.

[0034] Mixing recycled carbon-enriched material with lignin may be advantageous because the interaction between the carbon-enriched material and lignin can be improved when lignin is in the form of a slurry or dissolved in a solution.

[0035] Step c) of the method according to the first aspect of the present invention includes forming an aggregated lignin-carbon composite material comprising lignin, a recycled carbon-enriched material fraction, and optionally at least one additive.

[0036] As used in the present invention in phrases such as "aggregated lignin-carbon composite material" and "thermal-stabilized aggregated lignin-carbon composite material," the term "lignin-carbon composite material" refers to a composite material comprising lignin and a carbon-enriched material. The term "lignin-carbon composite" further refers to a material that essentially consists only of lignin and a carbon-enriched material, wherein, based on the dry weight of the lignin-carbon composite, at least 95 wt%, or at least 98 wt%, of the lignin-carbon composite consists of lignin and the carbon-enriched material. The lignin-carbon composite may optionally also contain small amounts of at least one additive, such as less than 5 wt%, or less than 2 wt%. In the lignin-carbon composite, the carbon-enriched material is uniformly dispersed within the lignin matrix.

[0037] As used herein, the term “aggregated lignin-carbon composite material” refers to macroscopic particles containing clustered lignin particles, with carbon-enriched material particles dispersed within the lignin matrix. Optionally, small amounts of at least one additive may be present in the aggregated lignin-carbon composite material.

[0038] The aggregated lignin-carbon composite material comprises, based on the total weight of the aggregated lignin-carbon composite material, 1 to 50 wt%, or 1 to 40 wt%, or 1 to 30 wt%, or 5 to 30 wt%, recycled carbon-enriched material; 50 to 99 wt%, or 60 to 99 wt%, or 70 to 95 wt%, or 70 to 99 wt%, of lignin; and optionally, less than 5 wt%, or less than 2 wt%, of at least one additive.

[0039] The aggregated lignin-carbon composite material may have an average particle size in the range of 0.05 to 5.0 mm, or 0.05 to 1.0 mm, or 0.2 to 1.0 mm, or 0.2 to 5.0 mm, or 0.5 to 2.0 mm. A preferred average particle size is in the range of 0.5 to 2.0 mm. In this application, the average particle size is defined as the volume-average particle diameter (D v50 This value is defined as the largest particle size that occupies 50% of the sample's volume. In this invention, particle size refers to the diameter of the particle. The particle size distribution can be determined, for example, using laser diffraction.

[0040] Aggregated lignin-carbon composite material has a concentration of 0.4-0.8 g / cm³. 3 It has a bulk density in the range of [value]. The bulk density of aggregated lignin-carbon composite material increases compared to the lignin-carbon mixture before the aggregation of the material.

[0041] Forming aggregated lignin-carbon composites yields more compact and rigid materials. These rigid aggregates are advantageous for subsequent processing because they can withstand physical shocks during machining. In aggregated composites, the proximity of particles enhances interparticle interactions, such as between lignin and carbon-enriched materials. A further advantage is the reduced tendency to generate dust when lignin is provided in an aggregated form.

[0042] It has been found that using carbon-enriched materials together with lignin, such as in agglomerated lignin-carbon composite materials, improves the thermoprocessability of lignin. Compared to agglomerated lignin without the addition of carbon-enriched materials, agglomerated lignin-carbon composite materials exhibit improved heat resistance by reducing melting / expansion behavior during heating. This makes it easier to process lignin on an industrial scale and improves processability.

[0043] The aggregated lignin-carbon composite material may contain at least one additive, or it may not contain any additives. In the context of this invention, an additive is a substance added to improve either the processability or functionality of the resulting material. Therefore, an additive is a substance that is not present in the lignin starting material but is added. Consequently, water and other moisture, as well as other components already present in the lignin starting material, are not considered additives in the context of this invention. Recycled carbon-enriched material is not considered an additive in the context of this invention.

[0044] 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-carbon composite material. In this way, the aggregated lignin-carbon composite material contains at least 95 wt%, for example at least 98%, of lignin and carbon-enriched material, based on the total dry weight of the aggregated lignin-carbon composite material.

[0045] In embodiments in which the aggregated lignin-carbon composite material includes at least one additive, the additive may be added to the lignin-carbon mixture at any time. The additive may be added to the lignin or the recycled carbon-enriched material fraction before the lignin is mixed with the recycled carbon-enriched material fraction. The additive may be added at any stage during the formation of the aggregated lignin-carbon composite material. Any suitable additives, such as binders or lubricants, may be added to facilitate the subsequent compression process and to improve the density and mechanical properties of the resulting lignin-carbon composite material. Furthermore, additives that affect the properties of the final material, such as functional enhancement additives, may be added.

[0046] Aggregated lignin-carbon composite materials can be formed by any suitable method. For example, lignin-carbon composite materials can be formed by compressing a dry lignin-carbon mixture and crushing the compressed material, or by, for example, a pellet press.

[0047] In a preferred embodiment, the aggregated lignin-carbon composite material is formed by a method comprising compression and crushing. The steps for forming the aggregated lignin-carbon composite material are as follows: - A process of selectively drying a lignin-carbon mixture; - A step of compressing a lignin-carbon mixture to obtain a lignin-carbon composite material; and - A step of crushing the lignin-carbon composite material in order to obtain an aggregated lignin-carbon composite material. It may include.

[0048] A first step in forming an aggregated lignin-carbon composite material optionally includes drying the lignin-carbon mixture. In embodiments where a recycled carbon-enriched material fraction is mixed with lignin in a solution or slurry, the lignin-carbon mixture must be dried before compression. In embodiments where a recycled carbon-enriched material fraction is mixed with lignin in powder form, the lignin-carbon mixture may be dried before compression. Preferably, the moisture content of the lignin-carbon mixture before compression is less than 45 wt%, or less than 25 wt%, or less than 10 wt%, or less than 8 wt%. Preferably, the moisture content is at least 1 wt%, for example, at least 5 wt%. Drying is carried out using methods and apparatus known in the art. The temperature during drying is preferably in the range of 80 to 160°C, more preferably in the range of 100 to 120°C. The lignin-carbon mixture may also be pulverized before compression.

[0049] A second step in forming an aggregated lignin-carbon composite material includes compressing the lignin-carbon mixture to obtain the lignin-carbon composite material. Since the lignin-carbon mixture is dried before compression, the lignin-carbon mixture is preferably in powder form at the start of compression. Compression of the lignin-carbon powder mixture is preferably carried out by roll compression. Roll compression of the lignin-carbon powder mixture can be achieved by a roller compactor for pressing the lignin-carbon powder mixture into a composite material.

[0050] In the compression process, a compressed lignin-carbon composite material is produced. Here, the lignin-carbon powder mixture is typically supplied through a hopper and transported to the compression zone by a horizontal or vertical feed screw. In the compression zone, the material is compressed into flakes by compression rollers with a constant gap. By controlling the feed 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 rotation 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 performing compression is known in the art.

[0051] In a preferred embodiment, the temperature of the lignin-carbon powder mixture is kept below 150°C, for example, below 100°C, during the compression process.

[0052] In one embodiment of roll compression, the roll configuration is such that the first roll has an annular rim, and the lignin-carbon powder mixture in the nip region is sealed axially along the roller surface.

[0053] 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, the loss of lignin-carbon powder at both axial ends of the roller is minimized compared to a fully cylindrical nip roller.

[0054] During compression, lignin particles and carbon-enriched material particles are pressed together by mechanical pressure to form a lignin-carbon composite material. The dispersion of the carbon-enriched material and lignin is improved by pressing the particles of each powder in close proximity to each other. It has been found that the carbon-enriched material can facilitate the compression process by reducing internal friction between lignin particles.

[0055] Compression can also act to enhance the interaction between lignin particles and carbon-enriched material in the composite material through primary particle rearrangement and plastic deformation induced by mechanical forces. Compression further acts to ensure that the uniform distribution achieved in the mixing process is maintained until the lignin-carbon composite material is further stabilized, i.e., until it is stabilized by the thermal stabilization process.

[0056] Compression may be performed on lignin-carbon powder mixtures without additives. Alternatively, it may be performed on lignin-carbon powder mixtures containing small amounts of at least one additive, such as less than 5 wt% or less than 2 wt%, based on the total dry weight of the lignin-carbon powder mixture.

[0057] A second step in forming an aggregated lignin-carbon composite material includes crushing the lignin-carbon composite material to obtain the aggregated lignin-carbon composite material. In the crushing step, the compressed lignin-carbon composite from the compression step is subjected to crushing or grinding by means such as a rotary granulator, cage mill, beater mill, hammer mill or crusher mill and / or a combination thereof. During this step, the compressed lignin-carbon composite material is crushed into aggregates, thereby producing the aggregated lignin-carbon composite material.

[0058] After crushing, the crushed material is preferably subjected to a sieving process to remove fine material, which can then be recycled and returned to the compression process. Furthermore, larger material, such as aggregates with a diameter greater than 2.0 mm or 5.0 mm, can be removed and / or recycled and returned to the crushing process.

[0059] In the sieving step, the aggregated lignin-carbon composite material from the crushing step is screened by a physical fractionation means such as sieving (also called screening) to obtain a product which is an aggregated lignin-carbon composite material having a particle size determined by the pore size of the sieve or screen in this step. The sieve or screen is selected so that most particles with a diameter of less than 50 μm, less than 200 μm, or less than 500 μm pass through the screen and are rejected, preferably returned to the compression step, while most particles with a diameter greater than 50 μm, greater than 200 μm, or greater than 500 μm are retained and subjected to subsequent steps of the method according to the present invention. Sieving can be carried out in multiple steps. That is, sieving can be carried out so that the crushed material from the crushing step passes sequentially through multiple screens, sieves, or classifiers.

[0060] During the compression process, the materials are strongly pressed against each other, increasing their bulk density. In one embodiment, the bulk density of the aggregated lignin-carbon composite material is 0.5-0.8 g / cm³. 3 This is within the range. During the preparation of aggregated lignin-carbon composites, the bulk density of the lignin-carbon powder mixture increases as pressure is applied to the powder. This means that the bulk density of aggregated lignin-carbon composites is higher than that of the lignin-carbon powder mixture. Since aggregated lignin-carbon composites have been found to retain their shape and dimensions without melting or expanding, the more compact material can be beneficial during subsequent processing of carbon-enriched materials. Aggregated lignin-carbon composites also exhibit relatively high hardness after compression. Hard aggregates are advantageous for subsequent processing because they can withstand physical shocks during processing. As mentioned above, carbon-enriched materials also improve the thermoworkability of lignin.

[0061] In a preferred embodiment, the method according to the first aspect includes an additional step of preheating the aggregated lignin-carbon composite material to a temperature in the range of 140 to 300°C for at least 30 minutes in order to obtain a heat-stabilized aggregated lignin-carbon composite material.

[0062] As used herein, the term “thermally stabilized” refers to a material obtained by a process of preheating an aggregated lignin-carbon composite material to a temperature lower than the temperature required for carbonization. By performing such preheating, also called thermal stabilization, the resulting thermally stabilized aggregated lignin-carbon composite material can be heat-treated at high temperatures while maintaining its shape and dimensions, thus avoiding melting / expansion and deformation during subsequent carbonization. The thermally stabilized aggregated lignin-carbon composite material is crosslinked.

[0063] In one embodiment, preheating is performed in an oxidizing atmosphere. Lignin crosslinking occurs during preheating through both oxidation and heat. Crosslinking is promoted by the combination of oxidation and heat. Crosslinking hardens the lignin within the aggregates, preventing melting / expansion during subsequent carbonization. Lignin aggregates before preheating behave as thermoplastics, but lignin aggregates after heat stabilization instead behave as thermosettings.

[0064] Such an oxidizing atmosphere contains oxidizing species that can react to crosslink lignin. Preheating can be carried out in the presence of, for example, oxygen, iodine, ozone, nitrogen dioxide, nitrobenzene, hydrogen peroxide, or peracetic acid. Preferably, heating is carried out in air. Alternatively, suitable oxidizing species may be supplied in a nitrogen atmosphere.

[0065] Preferably, preheating is performed so that the aggregated lignin-carbon composite material is fully thermally stabilized, i.e., fully crosslinked. As used herein, the term “fully thermally stabilized” refers to an aggregated lignin-carbon composite material that is thermally stabilized to such an extent that the same degree of crosslinking is achieved throughout the material. This means that material properties such as structure and hardness will be the same throughout the fully thermally stabilized aggregated lignin-carbon composite material. For example, the core of a fully thermally stabilized aggregated lignin-carbon composite material will have the same hardness and degree of crosslinking as the shell. A fully thermally stabilized aggregated lignin-carbon composite material is thus structurally homogeneous. A fully thermally stabilized aggregated lignin-carbon composite material can be obtained by providing a relatively small-sized aggregated lignin-carbon composite material having an average particle size in the range of 50 μm to 1.0 mm, and / or by preheating the aggregated lignin-carbon composite material for a sufficient amount of time.

[0066] Preheating is performed so that the aggregated lignin-carbon composite material is heated to a temperature in the range of 140 to 300°C, preferably 180 to 260°C. Preheating is performed for at least 30 minutes, i.e., the residence time of the aggregated lignin in the apparatus used for preheating is at least 30 minutes. In one embodiment, preheating is performed for at least 1 hour, or at least 1.5 hours. Preferably, preheating is performed for less than 12 hours. Preheating may be performed at the same temperature throughout the entire preheating stage, or it may be performed while changing the temperature, such as by gradually increasing the temperature or utilizing a temperature gradient. More preferably, preheating is performed so that the aggregated lignin-carbon composite material is first heated to a temperature in the range of 140 to 175°C for at least 15 minutes, and then heated to a temperature in the range of 175 to 300°C for at least 15 minutes.

[0067] The thermal workability of lignin is improved by a combination of providing lignin in the form of aggregated lignin, mixing lignin with a carbon-enriched material to obtain a lignin-carbon composite, and preheating the lignin to ensure thermal stabilization. Thus, the thermally stabilized aggregated lignin-carbon composite can be subjected to further heat treatment to carbonize the material without melting / expansion behavior. This improves processability on an industrial scale. Depending on the amount and particle size distribution of the carbon-enriched material present in the aggregated lignin-carbon composite, sufficient processability may be obtained even without preheating.

[0068] Step d) of the method according to the first aspect of the present invention relates to subjecting an aggregated lignin-carbon composite material to heat treatment at one or more temperatures in the range of 300 to 1500°C, wherein the heat treatment is carried out for a total time in the range of 30 minutes to 10 hours, in order to obtain a carbon-enriched material. In embodiments in which the aggregated lignin-carbon composite material is preheated to obtain a heat-stabilized aggregated lignin-carbon composite material, it is the heat-stabilized aggregated lignin-carbon composite material that is subjected to heat treatment.

[0069] As used herein, the term “heat treatment” refers to the process of heating an aggregated lignin-carbon composite material at one or more temperatures for a sufficient amount of time so that the lignin in the composite material is converted into a carbon-enriched material. This process may also be called carbonization or calcination. After heat treatment, the carbon content of the material 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 or hard carbon, can be obtained from lignin.

[0070] As used herein, the term “carbon-enriched material” refers to a carbon material obtained by the heat treatment of 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 O and N, inorganic impurities, and functional additives. The carbon-enriched material of the present invention is amorphous (i.e., non-crystalline) carbon, preferably hard carbon. The carbon-enriched material obtained in step d) of the method according to the first embodiment includes both recycled carbon-enriched material and carbon-enriched material obtained by the heat treatment of lignin, wherein the recycled material includes carbon-enriched material obtained in the previous heat treatment of lignin. Once the lignin is completely converted into carbon-enriched material (for example, at a temperature of at least about 1000°C), it is impossible to distinguish between recycled carbon-enriched material and freshly obtained carbon-enriched material.

[0071] 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 carbonization of the aggregated lignin-carbon composite material. 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.

[0072] 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.

[0073] 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.

[0074] 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.

[0075] The conversion of lignin to carbon-enriched material begins at approximately 250°C. The amount of lignin converted to carbon depends primarily on the temperature and time during the heat treatment. The properties of the resulting carbon-enriched material also depend on the temperature and time during the heat treatment. Therefore, the carbon-enriched material obtained after the preheating process may differ from the carbon-enriched material obtained after the final heating process. For example, the carbon content may be higher after the final heating process, and the carbon structure in the carbon-enriched material may differ.

[0076] 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.

[0077] The carbon-enriched material is preferably 0.2 g / cm³. 3 ~0.4g / cm 3 It has a bulk density in the range of [value missing]. This is lower than the bulk density of aggregated lignin-carbon composite materials, mainly due to mass loss during heat treatment.

[0078] The obtained carbon-enriched material preferably has a helium true density in the range of 1.4 g / cm 3 ~2.1 g / cm 3 , for example, 1.7~2.0 g / cm 3 . The helium true density can be measured using a pycnometer known to those skilled in the art. It is important that the helium true density is in the range of 1.4~2.1 g / cm 3 . Otherwise, the doping capacity and dedoping capacity of the carbon-enriched material when used as the active material of the negative electrode of a non-aqueous secondary battery may decrease, and the irreversible capacity of the battery may increase. If the density of the carbon-enriched material is too low, the energy density of the electrode may also decrease.

[0079] By providing lignin in an aggregated form and mixing it with the recycled carbon-enriched material fraction, it is ensured that the lignin does not melt / expand during the heat treatment performed to convert the lignin into a carbon-enriched material. By performing a preheating step before the heat treatment, the dimensional stability of the lignin is further improved, and thus the risk of melting / expansion can be further reduced. Depending on the amount of recycled carbon-enriched material mixed with the lignin and the particle size distribution of the recycled fraction, preheating may not be necessary to reduce the melting / expansion of the lignin during the heat treatment.

[0080] Step e) of the method according to the first aspect of the present invention includes pulverizing the obtained carbon-enriched material in order to reduce the average particle size of the carbon-enriched material and, at least, to obtain a first fraction and a second fraction of the carbon-enriched material. The pulverization can be performed using any suitable device, such as the use of a cutting mill, a blade mixer, a ball mill, an impact mill, a hammer mill, and / or a jet mill. The pulverization may also be referred to as, for example, micronization, crushing, or grinding. The first fraction of the carbon-enriched material may have a first average particle size, and the second fraction of the carbon-enriched material may have a second average particle size.

[0081] The first fraction of the carbon-enriched material may have an average particle size in the range of 1 to 100 μm, 1 to 80 μm, 1 to 50 μm, or 1 to 20 μm. The second fraction of the carbon-enriched material may have an average particle size in the range of 1 to 100 μm, 1 to 80 μm, 1 to 50 μm, or 1 to 20 μm.

[0082] The average particle sizes of the first and second fractions of the carbon-enriched material may be the same or different. For example, the average particle size of the first fraction may be smaller than that of the second fraction.

[0083] The first fraction can be separated from the second fraction by any suitable means, such as classification and / or sieving. Such processing may be carried out after and / or during grinding. Suitable apparatus that may be used to separate the first and second fractions may include air classifiers such as gravity, centrifugal, cyclonic, and / or swirling air classifier systems, and sieving devices such as tumbling and / or vibrating screening devices. Separation may be carried out in several steps.

[0084] The resulting carbon-enriched material is ground to reduce the average particle size, thereby facilitating its use as an active material for the negative electrode of a secondary battery. During grinding, large-span particles are produced. Typically, small particles (often called carbon nanoparticles) are removed and discarded, while particles with a desired particle size range are further processed. However, depending on the application, it may be interesting to utilize small particles such as carbon nanoparticles. For example, using a small-particle active material can improve electrode density. Also, using a small-particle active material can improve the charge-discharge rate performance of the electrode because it allows for faster metal diffusion. Therefore, the particle sizes of the first and second fractions are selected according to the end application of the carbon-enriched material produced by the method according to the present invention.

[0085] In one preferred embodiment, the first fraction of the carbon-enriched material has an average particle size in the range of 1 to 4 μm. This corresponds to carbon microparticles. By recycling the carbon microparticles, process material waste is reduced by the amount of carbon microparticles that would normally be discarded. Thus, a more sustainable process is possible, while also improving the thermoworkability of the aggregated lignin-carbon composite material. In such an embodiment, the second fraction of the carbon-enriched material may have an average particle size in the range of 4 to 100 μm, or 4 to 80 μm, or 4 to 50 μm, or 4 to 20 μm. Such a fraction can be obtained, for example, by simultaneously grinding and sorting such that most particles with particle sizes less than 100 μm, less than 80 μm, less than 50 μm, or less than 20 μm pass through the first sorting unit. Larger particles remain in the grinding unit until their particle size becomes even smaller. The particles that have passed through the first sorting unit are further sorted in the second sorting unit, and the first fraction is separated from the second fraction. Here, a first fraction of carbon-enriched material with a small average particle size, such as less than 4 μm, passes through a sorting unit and is recycled. A second fraction of carbon-enriched material with a larger average particle size, such as greater than 4 μm, may proceed to a subsequent process or be recovered as the final product.

[0086] In another embodiment, the first fraction of the carbon-enriched material may have an average particle size in the range of 1 to 100 μm, 1 to 80 μm, 1 to 50 μm, or 1 to 20 μm. The second fraction of the carbon-enriched material may also have an average particle size in the range of 1 to 100 μm, 1 to 80 μm, 1 to 50 μm, or 1 to 20 μm. Thus, in such an embodiment, the first and second fractions may contain carbon-enriched material having the same average particle size. Therefore, carbon particles may be present in both the first and second fractions. Thus, in this embodiment, recycling is performed not to reduce material loss in the process, but to improve the processability of the resulting aggregated lignin-carbon composite material.

[0087] In another embodiment, the first fraction of the carbon-enriched material may have an average particle size in the range of 4-100 μm, 4-80 μm, 4-50 μm, or 4-20 μm, so the carbon particles are mainly present in the second fraction. In such an embodiment, the second fraction of the carbon-enriched material may have an average particle size in the range of 1-20 μm. In such an embodiment, the recycled fraction may contain carbon-enriched material with an average particle size larger than the average particle size of the final product. If the desired average particle size of the final product is small, such as in the range of 1-5 μm, large-scale grinding, which leads to high energy consumption, is required to bring all the carbon-enriched material to the desired particle size. For example, if sufficient grinding is not possible due to equipment limitations, the carbon-enriched material with excessively large particle sizes is discarded. Instead, by recycling the carbon-enriched material with large particle sizes, as in the method of the present invention, less grinding is required, energy consumption is reduced, and material loss is also reduced. In addition, recycling the carbon-enriched material improves the thermoprocessability of the resulting aggregated lignin-carbon composite material, as described above.

[0088] In embodiments where the heat treatment in step d) includes a final heating step following a preheating step, the grinding step is preferably performed after the preheating step and before the final heating step. Thus, the first fraction is recycled after the preheating step, and the second fraction is subjected to the final heating step.

[0089] Step f) of the method according to the present invention includes recirculating at least a portion of the first fraction obtained in step e) back to step b). For example, at least 80% of the first fraction is recirculated. Preferably, at least 90% is recirculated, and more preferably at least 98%. This preferably means that the entire first fraction is recirculated so as to be mixed with lignin. In embodiments in which the first fraction is discarded, recirculating the entire first fraction or a large portion of the first fraction reduces material loss, thus enabling a more sustainable process. Furthermore, yield is improved because all or almost all of the lignin entering the process is converted to carbon, which constitutes the final product.

[0090] The method according to the present invention may be a batch process or a continuous process. In a batch process, recirculation includes recovering a first fraction and storing it until it is mixed with lignin in the next batch. In a continuous process, the first fraction recovered after the grinding step is continuously recirculated to the mixing step, where it is introduced into the lignin process flow.

[0091] In a preferred embodiment, the heat treatment includes a preheating step and a final heating step, and grinding is performed after the preheating step and before the final heating step. In such an embodiment, the first fraction is preferably recycled after the preheating step, and the second fraction is subjected to the final heating step.

[0092] During heat treatment, lignin is converted into a carbon-enriched material. The properties of the carbon-enriched material depend, for example, on the temperature and time of the heat treatment. Heating at high temperatures exceeding 1000°C results in a hard material. Thus, the carbon-enriched material obtained after the final heating step is harder than the carbon-enriched material obtained after the preheating step due to the temperature-dependent change in the carbon structure during heat treatment. It has been found that if grinding is performed after the preheating step and the resulting first fraction is recycled before the final heating step, the carbon-enriched material in the recycled fraction is softer, thus promoting mixing of the recycled fraction with lignin. Furthermore, the interaction between lignin and the carbon-enriched material is improved, promoting the formation of aggregated lignin-carbon composite materials.

[0093] Therefore, in a preferred embodiment, the method according to the present invention is as follows: a) A process of providing lignin; b) A step of mixing lignin with a recycled carbon-enriched material fraction to obtain a lignin-carbon mixture; c) A step of forming an aggregated lignin-carbon composite material comprising lignin, a recycled carbon-enriched material fraction, and optionally at least one additive: d) Optionally, an additional step of preheating the aggregated lignin-carbon composite material to a temperature in the range of 140-300°C for at least 30 minutes in order to obtain a heat-stabilized aggregated lignin-carbon composite material; e) To obtain a carbon-enriched material, the process involves subjecting an aggregated lignin-carbon composite material or a heat-stabilized aggregated lignin-carbon composite material to a preheating step at one or more temperatures in the range of 400 to 800°C for at least 30 minutes; f) A step of grinding the obtained carbon-enriched material in order to reduce the average particle size of the carbon-enriched material and to obtain at least a first fraction of the carbon-enriched material and a second fraction of the carbon-enriched material; g) A step of recirculating at least a portion of the first fraction obtained in step f) back to step b) h) The second fraction obtained in step f) is subjected to a final heating step at one or more temperatures in the range of 800°C to 1500°C for at least 30 minutes. Includes. [Examples]

[0094] Example 1 Lignin powder (coniferous kraft lignin) from the LignoBoost process was mixed with 5 wt% carbon-enriched material powder using a conical screw mixer (200 RPM, 15 min). The carbon-enriched material powder was heated at 500°C for 1 hour in a nitrogen atmosphere to collect the aggregated lignin, and then D v50 The mixture was recycled from the previous batch after being pulverized to a particle size of 5 μm. No other additives were added. This mixture was compressed using a Lab Compactor with a roller compression of 50 kN to obtain a composite material, which was then crushed using a Flake crusher and sieved into aggregates with a particle size distribution of 0.5 to 1.5 mm.

[0095] The aggregated lignin-carbon composite was further thermally stabilized by heating it in a rotary furnace at 235°C in air for 2 hours. During this process, the aggregated lignin did not exhibit melting behavior and maintained its original shape. It was found that the individual aggregates did not fuse together and maintained their fluidity. The material gradually turned black during processing, eventually becoming completely black and odorless.

[0096] This heat-stabilized, aggregated lignin-carbon composite material was heat-treated at 500°C for 1 hour under an inert atmosphere to carbonize it. As a result, compared to the heat-stabilized, aggregated lignin-carbon composite material before carbonization, a granular carbon-carbon composite material was obtained in which the shape and size of the granules were maintained without melting or fusing.

[0097] 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 carbon-enriched materials, comprising the following steps: a) A step of providing lignin; b) A step of mixing lignin with a recycled carbon-enriched material fraction in order to obtain a lignin-carbon mixture; c) A step of forming an aggregated lignin-carbon composite material comprising lignin, a recycled carbon-enriched material fraction, and optionally at least one additive; d) A step of subjecting an aggregated lignin-carbon composite material 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; e) A step of grinding the obtained carbon-enriched material in order to reduce the average particle size of the carbon-enriched material and to obtain at least a first fraction of the carbon-enriched material and a second fraction of the carbon-enriched material; f) A step of recirculating at least a portion of the first fraction obtained in step e) back to step b) Methods that include...

2. The method according to claim 1, wherein the lignin is kraft lignin.

3. The method according to claim 1 or 2, wherein the lignin provided in step a) is in the form of a powder.

4. The method according to claim 1 or 2, wherein the lignin provided in step a) is in the form of a slurry.

5. The method according to claim 1 or 2, wherein the lignin provided in step a) is dissolved in a solution.

6. The method according to any one of claims 1 to 5, wherein the first fraction of the carbon-enriched material has an average particle size in the range of 1 to 100 μm.

7. The method according to any one of claims 1 to 6, wherein the first fraction of the carbon-enriched material has an average particle size in the range of 1 to 4 μm.

8. The method according to any one of claims 1 to 7, wherein the aggregated lignin-carbon composite material comprises, based on the total weight of the aggregated lignin-carbon composite material, 1 to 50 wt% of recycled carbon-enriched material; 50 to 99 wt% of lignin; and optionally, at least one additive in less than 5 wt%.

9. The process for forming aggregated lignin-carbon composite material is as follows: - A step of selectively drying a lignin-carbon mixture; - A step of compressing a lignin-carbon mixture in order to obtain a lignin-carbon composite material; and - A process of crushing the lignin-carbon composite material in order to obtain an aggregated lignin-carbon composite material. The method according to any one of claims 1 to 8, including the method described in any one of claims 1 to 8.

10. The method according to any one of claims 1 to 9, further comprising the additional step of preheating an aggregated lignin-carbon composite material to a temperature in the range of 140 to 300°C for at least 30 minutes in order to obtain a heat-stabilized aggregated lignin-carbon composite material.

11. The method according to claim 10, wherein preheating is performed in an oxidizing atmosphere.

12. The method according to claim 10 or 11, wherein preheating is performed by first heating the aggregated lignin-carbon composite material to a temperature in the range of 140 to 175°C for at least 15 minutes, and then heating the aggregated lignin-carbon composite material to a temperature in the range of 175 to 300°C for at least 15 minutes.

13. The method according to any one of claims 1 to 12, wherein the heat treatment in step d) is performed in an inert atmosphere.

14. The method according to any one of claims 1 to 13, wherein the heat treatment in step d) includes a preheating step and a subsequent final heating step.

15. The method according to claim 14, wherein the preheating step is performed at a temperature between 400°C and 800°C for at least 30 minutes.

16. The method according to claim 15 or 16, wherein the final heating step is performed at a temperature between 800°C and 1500°C for at least 30 minutes.

17. The method according to any one of claims 14 to 16, wherein the grinding step is performed after the preheating step and before the final heating step.

18. The method according to claim 17, wherein at least a portion of the first fraction of the carbon-enriched material is recycled before the final heating step.

19. 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 1 to 18.

20. Use of a carbon-enriched material obtained by the method of any one of claims 1 to 18 as an active material in the negative electrode of a non-aqueous secondary battery.

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