Method for producing carbon-enriched materials

Abstract

A method for manufacturing a carbon-concentrating material comprises the following steps: a) providing lignin beads, wherein the lignin beads contain at least 80% by weight of lignin based on the dry weight of the lignin beads; b) optionally, heating the lignin beads at one or more temperatures in the range of 140 to 270 °C for at least 30 minutes to obtain thermally stabilized lignin beads; and c) optionally, carbonizing the thermally stabilized lignin beads at one or more temperatures in the range of 300 °C to 1500 °C for 30 minutes to 10 hours to obtain a carbon-concentrating material.

Description

Technology Field

[0001] The present invention relates to a method for producing a carbon-rich material using lignin beads as a starting material. Furthermore, the present invention relates to a carbon-rich material obtainable by the above method and a negative electrode for a non-aqueous secondary battery comprising the carbon-rich material as an active material. The present invention also relates to lignin beads comprising at least 80 weight% of lignin based on the dry weight of the lignin beads and using such lignin beads as a starting material for producing a carbon-rich material. Background Technology

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

[0003] Graphite (natural or synthetic graphite) is used as the negative electrode material in most lithium-ion batteries today. Alternatives to graphite are amorphous carbon materials such as hard carbon (non-graphitized amorphous carbon) and soft carbon (graphitized amorphous carbon), which lack long-range graphic regularity. Amorphous carbon can be used as a standalone active electrode material or in mixtures with graphite (and / or other active materials).

[0004] Amorphous carbon can be derived from the carbonization of lignin. Lignin is an aromatic polymer, a major component of wood, and one of the most abundant carbon sources on Earth. Recently, with the development and commercialization of technologies to extract lignin in high-purity, solidified, and specialized forms during the pulp manufacturing process, it is receiving significant attention as a renewable and viable alternative to the primarily aromatic chemical precursors currently supplied by the petrochemical industry. Amorphous carbon derived from the carbonization of lignin is generally carbon that does not graphitize, i.e., hard carbon.

[0005] Today, the most commercially relevant source of lignin is Kraft lignin obtained from hardwood or softwood through the Kraft process. Lignin can be separated from alkaline black liquor using, for example, membrane filtration or ultrafiltration. One common separation process is described in WO2006031175 A1. In this process, lignin is precipitated from the alkaline black liquor by adding acid, and then removed by filtration. In the next step, the lignin filter cake is slurried again under acidic conditions and washed before drying and grinding.

[0006] One problem with using lignin as a precursor for carbon-enriching materials is that using lignin directly in the form of fine powder is unsuitable because it exhibits undesirable thermoplastic behavior during the carbonization stage. During the thermal conversion of lignin powder into carbon-enriching materials, lignin undergoes plastic deformation / melting, aggressive swelling, and foaming. This severely limits the processability of lignin on an industrial scale in terms of equipment dimensions and process throughput, as well as the need for intermediate processing.

[0007] Inorganic additives, such as metal salts, have been used to partially reduce the melting and swelling of lignin during heat treatment. However, these metal salts also cause catalytic activation of the carbon structure during carbonization, and costly post-purification protocols are required to remove the metal salts from the final carbon-enriched material.

[0008] US6099990 A describes a method for manufacturing a carbon material comprising mixing lignin powder with a salt and then heating the mixture in several steps including a carbonization step.

[0009] Conventional processes that convert biomass into carbon-enriched intermediates often do not utilize powder. Consequently, lignin in the form of fine powder is not suitable for replacing conventional biomass in this field. To address this issue, lignin granulation has been considered. The granulation process involves applying mechanical pressure to lignin powder to form lignin flakes, which are then ground into irregularly shaped, angular granules typically smaller than 2 mm. Granules formed by this process may possess sharp, angular edges. These sharp edges, where the bonding between lignin powder particles is weak, can break during processing, generating dust and fine particles. The resulting dust can clog exhaust pipes and pose a risk of dust explosions during large-scale process operations.

[0010] To reduce the melting / expansion of lignin, the granules may undergo an intermediate thermal stabilization step before the carbonization process. Thermal stabilization is performed at a temperature lower than the carbonization temperature. The irregularly shaped granules formed by the granulation process make it more difficult to achieve uniform thermal stabilization of the granules.

[0011] Therefore, the method for producing carbon-enriched materials from lignin still has room for improvement. This method must prevent lignin from undergoing plastic deformation and melting, aggressive swelling and foaming, as well as the generation of dust and fine particles during heating when converting lignin into carbon-enriched materials. In addition, it must be applicable to large-scale manufacturing.

[0012] Summary of the Invention

[0013] The object of the present invention is to provide an improved method for manufacturing a carbon-enriched material that allows the use of a renewable carbon source and eliminates or mitigates at least some of the disadvantages of the prior art method.

[0014] Another objective of the present invention is to provide a method for obtaining an improved carbon enrichment material suitable for use as a negative electrode active material for secondary batteries, such as lithium-ion batteries or sodium-ion batteries, using lignin as a starting material.

[0015] Another objective of the present invention is to provide a method for producing a carbon-rich material from lignin through the carbonization of lignin while maintaining its shape and dimensions.

[0016] Another objective of the present invention is to provide a method for improving the mechanical and thermal processability of lignin.

[0017] Another objective of the present invention is to provide a method for producing a carbon-rich material from lignin that is highly scalable and suitable for large-scale manufacturing.

[0018] In addition to the purposes mentioned above, other purposes to be realized by those skilled in the art in the context of this disclosure are achieved by various aspects of this disclosure.

[0019] According to the first aspect, the present invention relates to a method for producing a carbon-enriched material, the method comprising the following steps:

[0020] a) a step of providing lignin beads, wherein the lignin beads comprise at least 80 weight percent of lignin based on the dry weight of the lignin beads;

[0021] b) optionally, a step of heating the lignin beads at one or more temperatures in the range of 140 to 270 °C for at least 30 minutes to obtain thermally stabilized lignin beads; and

[0022] c) Optionally, a step of obtaining a carbon-concentrated material by carbonizing the thermally stabilized lignin beads at one or more temperatures in the range of 300 °C to 1500 °C for 30 minutes to 10 hours.

[0023] The present invention is based on the fact that using lignin beads, which are lignin particles having a substantially spherical or elliptical shape, as a starting material for the production of carbon-enriched materials provides several significant advantages, such as reduced generation of dust and fine particles and more uniform thermal stabilization. The spherical shape of the beads ensures excellent fluidity in a rotary kiln and minimizes contact with other beads, thereby preventing bead sticking or aggregation. Furthermore, it has been found that using lignin beads allows for the omission of the thermal stabilization step and enables the direct carbonization of the lignin beads without an intermediate thermal stabilization step.

[0024] According to a second aspect of the present invention, the invention relates to lignin beads comprising at least 80% by weight of lignin based on the dry weight of the lignin beads. Such lignin beads with a high lignin content are useful as starting materials for the method according to the first aspect.

[0025] According to a third aspect of the present invention, the present invention relates to a method for producing thermally stabilized lignin beads comprising the following steps:

[0026] a) a step of providing lignin beads, wherein the lignin beads comprise at least 80 weight percent of lignin based on the dry weight of the lignin beads; and

[0027] b) A step of obtaining thermally stabilized lignin beads by heating the lignin beads at one or more temperatures in the range of 140 to 270 °C for at least 30 minutes.

[0028] According to the fourth aspect, the present invention relates to thermally stabilized lignin beads that can be obtained by the method according to the third aspect.

[0029] Thermal stabilization enables heat-stabilized lignin beads to better maintain their shape and dimensions while preventing melting, expansion, and deformation during the carbonization process. The substantially spherical or elliptical shape of the lignin beads allows for more uniform cross-linking of the lignin across each bead through heating and reaction with oxidizing agents, thereby enabling uniform thermal stabilization. These thermally stabilized lignin beads are useful as intermediate products for carbon-enriching materials.

[0030] According to the fifth aspect, the present invention relates to a carbon-enriched material obtainable by a method according to the first aspect.

[0031] According to the sixth aspect, the present invention relates to a negative electrode for a non-aqueous secondary battery comprising a carbon-enriched material powder obtainable by the method according to the first aspect.

[0032] According to the seventh aspect, the present invention relates to the use of lignin beads comprising at least 80% by weight of lignin based on the dry weight of the lignin beads for the production of carbon-enriched materials. Brief explanation of the drawing

[0033] Figure 1 is a photograph of dried lignin beads. Figures 2a and 2b are scanning electron microscope (SEM) images of dried and ground lignin beads. Figure 3 is a photograph of dried lignin carbon beads. Figures 4a and 4b are scanning electron microscope (SEM) images of lignin carbon beads. Specific details for implementing the invention

[0034] Step a) of the method according to the first aspect of the present invention comprises providing lignin beads, wherein the lignin beads contain at least 80% by weight of lignin based on the dry weight of the lignin beads.

[0035] As used herein, the term “lignin bead” refers to a lignin particle having a substantially spherical or elliptical shape. In some embodiments, the lignin bead provided in step a) has a spherical or elliptical shape. However, the lignin bead is not necessarily perfectly spherical or elliptical and may have a spherical or elliptical shape overall without sharp angles or edges.

[0036] It is desirable to select the size of the lignin beads so that handling and processing, for example, the carbonization process, is easy. In some embodiments, the diameter of the lignin beads provided in step a) is in the range of 0.1 mm to 5.0 mm, preferably in the range of 0.2 mm to 2.0 mm, and more preferably in the range of 0.3 mm to 0.5 mm.

[0037] In the present invention, the diameter of the bead refers to the equivalent spherical diameter of the bead when the bead is not a perfect sphere. The equivalent spherical diameter is the spherical diameter of the equivalent volume.

[0038] In some embodiments, at least 80% by weight, at least 90% by weight, or at least 95% by weight of the lignin beads provided in step a) have a diameter in the range of 0.1 mm to 5.0 mm, preferably in the range of 0.2 mm to 2.0 mm, more preferably in the range of 0.3 mm to 0.5 mm.

[0039] In some embodiments, the lignin beads provided in step a) comprise at least 90 weight%, preferably at least 95 weight%, of lignin based on the dry weight of the lignin beads. In some embodiments, the lignin beads provided in step a) of the method according to the first aspect of the invention comprise 80 to 99.9 weight% of lignin and 0.1 to 20 weight% of one or more additives based on the dry weight of the lignin beads.

[0040] As used herein, the term "lignin" refers to all types of lignin that can be used as a carbon source for manufacturing carbon-enriching materials. Examples of such lignin include, but are not limited to, lignin obtained from plant sources such as wood, e.g., coniferous lignin, hardwood lignin, and lignin from annular plants. Additionally, lignin may be chemically modified.

[0041] Preferably, lignin is purified or separated before being used in the method according to the present invention. Lignin can be separated from black liquor and optionally further purified before being used in the method according to the present invention. Purification is typically performed so that the purity of the lignin is at least 90%, preferably at least 95%. Accordingly, the lignin used according to the method of the present invention preferably contains less than 10%, more preferably less than 5%, impurities, e.g., cellulose, ash, and / or moisture.

[0042] Preferably, the lignin contains less than 1% ash, more preferably less than 0.5% ash.

[0043] Lignin can be obtained through various fractionation methods, such as organic solvent processes or Kraft processes. For example, lignin can be obtained using the process disclosed in WO2006031175 A1.

[0044] Preferably, the lignin used in the method according to the first aspect of the present invention is Kraft lignin, that is, lignin obtained through the Kraft process. Preferably, the Kraft lignin is obtained from hardwood or softwood, most preferably from softwood.

[0045] Depending on the method of manufacturing the lignin beads, the beads may contain one or more additional components in addition to lignin.

[0046] In some embodiments, the lignin beads provided in step a) further comprise 0.5 to 10 weight%, preferably 1 to 5 weight%, more preferably 1 to 3 weight% of a polymer binder based on the dry weight of the lignin beads. This polymer binder can improve the stability and structural integrity of the lignin beads and prevent crushing and dust generation.

[0047] The polymer binder may be any polymer component capable of improving the stability and structural integrity of lignin beads and preventing crushing and dust generation. One type of useful polymer binder is a gel-forming polymer, that is, a polymer capable of forming a gel network in a liquid medium. Thus, in some embodiments, the polymer binder comprises a gel-forming polymer. A particularly useful type of gel-forming polymer is a polymer that forms a gel through ionic crosslinking with divalent cations. Such polymers are often referred to as ionic gelling polymers. For example, divalent cations, such as calcium ions, crosslink polymer chains to form a gel network. Therefore, in some embodiments, the polymer binder comprises an ionic gelling polymer.

[0048] In some embodiments, the polymer binder comprises a polysaccharide or a polysaccharide derivative. In some embodiments, the polymer binder comprises a gel-forming polysaccharide. In some embodiments, the gel-forming polysaccharide is an ionic gelling polysaccharide, that is, a polysaccharide that forms a gel through ionic crosslinking with a divalent cation. Examples of ionic gelling polysaccharides include, but are not limited to, alginates, carrageenan, gellan gum, xanthan gum, pectin, and carboxymethylcellulose (CMC). In a preferred embodiment, the polymer binder comprises an alginate.

[0049] In some embodiments, the lignin beads provided in step a) further comprise 0.5 to 10 weight%, preferably 1 to 5 weight%, more preferably 1 to 3 weight% of a surfactant based on the dry weight of the lignin beads. In some embodiments, the surfactant is a nonionic surfactant, preferably a polysorbate, and more preferably Tween 80.

[0050] One method of manufacturing lignin beads is as follows:

[0051] i) a step of preparing an aqueous mixture comprising at least 80 weight% of lignin, 0.5 to 10 weight% of an ionic gelling polymer, and 0.5 to 10 weight% of a nonionic surfactant, based on the total dry weight of the aqueous mixture;

[0052] ii) a step of obtaining lignin beads by adding the above mixture drop by drop to an aqueous solution containing divalent metal ions, preferably calcium ions; and

[0053] iii) A step of recovering the obtained lignin beads and optionally washing them.

[0054] In some embodiments, the ionic gelling polymer is selected from the group consisting of alginate, carrageenan, gellan gum, xanthan gum, pectin, and carboxymethylcellulose (CMC), and more preferably is alginate.

[0055] The divalent metal ion can be any divalent cation, but calcium ions are preferred. An aqueous solution containing the divalent metal ion can be obtained by dissolving a salt of the divalent metal ion, such as calcium chloride (CaCl2), in water. The divalent metal ion reacts with an ionic gelling polymer through ion exchange polymerization or crosslinking reactions to form lignin beads.

[0056] Lignin beads formed by this method contain, in addition to lignin, an ionic gelling polymer as a polymer binder. The ionic gelling polymer within the lignin beads may be in the form of a gel, such as calcium alginate gel.

[0057] Depending on the type of surfactant and the degree of washing, the lignin beads provided in step a) may additionally contain 0.5 to 10 weight%, preferably 1 to 5 weight%, and more preferably 1 to 3 weight% of a surfactant based on the dry weight of the lignin beads. In some embodiments, the surfactant is a nonionic surfactant, preferably a polysorbate, and more preferably Tween 80.

[0058] In some embodiments, the lignin beads provided in step a) are porous lignin beads. For example, the lignin beads obtained by the method for manufacturing ionic gelling polymer-based lignin beads are porous. Porous beads are desirable because the thermal stabilization of the beads is more uniform, as the cross-linking of lignin through heating and reaction with an oxidizing agent can occur more uniformly throughout each bead. Additionally, using porous beads allows active or inactive fillers or additives to be easily incorporated into the pores of the beads.

[0059] In some embodiments, the lignin beads provided in step a) have a bulk density in the range of 0.2 to 1 g / cm³, preferably in the range of 0.5 to 0.7 g / cm³.

[0061] In some embodiments, the lignin beads provided in step a) have a glass transition temperature (T) of 140 °C or higher g has ).

[0062] To reduce the melting / expansion phenomenon of lignin, the beads may undergo an intermediate thermal stabilization step prior to the carbonization process. In this specification, "thermal stabilization" refers to a process of thermally stabilizing lignin beads by heating them to a temperature lower than that required for carbonization. Through thermal stabilization, the lignin beads are stabilized and hardened, allowing them to maintain their shape during the subsequent carbonization process. Thermal stabilization is preferably performed under oxidizing conditions, for example, in an environment where oxygen or other oxidizing substances are present, preferably in air. While not bound by specific scientific theories, it is believed that the thermal stabilization of lignin beads can be promoted by the cross-linking of lignin through reaction with oxidizing substances. Thermal stabilization occurs at the glass transition temperature (T) of the lignin beads g Increases ) By performing thermal stabilization, lignin beads can be heat-treated while maintaining their shape and dimensions, while avoiding melting / swelling and deformation.

[0063] In addition, it has been found that using lignin beads allows the heat stabilization step to be omitted in some cases and the lignin beads to be carbonized directly without an intermediate heat stabilization step. For example, it has been found that the polymer binder present in the lignin beads helps maintain the shape of the beads and prevents melting or swelling during the carbonization process. Therefore, the heat stabilization step of the method of the present invention is optional.

[0064] When performing the heat stabilization process, the lignin beads are heated to a temperature lower than the temperature used in the subsequent carbonization process.

[0065] Optional step b) of the method according to the first embodiment of the present invention comprises heating the lignin beads to one or more temperatures in the range of 140 to 270°C, preferably to a temperature in the range of 180 to 250°C, to obtain thermally stabilized lignin beads.

[0066] Heating for producing thermally stabilized lignin beads is performed by heating the lignin beads to a temperature in the range of 140 to 270°C, preferably in the range of 180 to 250°C. Heating is performed for at least 30 minutes, which means that the residence time of the lignin beads in the equipment used for heating is at least 30 minutes. In one embodiment, it is preferable that heating be performed for at least 1 hour, or at least 1.5 hours. Preferably, heating is performed for less than 12 hours.

[0067] Thermal stabilization is preferably carried out under oxidizing conditions, for example, in an environment where oxygen or other oxidizing substances are present, preferably in air. Although there is no need to be bound by specific scientific theories, it is believed that the thermal stabilization of lignin beads can be promoted by the cross-linking of lignin through reaction with oxidizing substances. Accordingly, in some embodiments, the heating of step b) to obtain thermally stabilized lignin beads is carried out under oxidizing conditions, for example, in the presence of oxygen or other oxidizing substances, preferably in air.

[0068] Heating may be performed at a constant temperature throughout the entire heating step, or at varying temperatures, such as by using a stepwise increase in temperature or a temperature gradient. In some embodiments, the process of heating the lignin beads in step b) is performed by first heating the lignin beads to a temperature in the range of 140 to 175°C for at least 15 minutes, and then heating them to a temperature in the range of 175 to 270°C for at least 15 minutes. More preferably, heating is performed such that the lignin beads are first heated to a temperature of 140 to 175°C for at least 15 minutes and then heated to a temperature of 175 to 250°C for at least 15 minutes.

[0069] The lignin bead heating step for producing thermally stabilized lignin beads can be performed in a continuous or batch manner. Heating can be performed using methods known in the art and can be performed in the presence of air or under a completely or partially inert gas. Preferably, heating is performed in a rotary furnace or other suitable heating device.

[0070] Thermally stabilized lignin beads preferably have a bulk density in the range of 0.5 g / cm³ to 0.7 g / cm³. Thermal stabilization may slightly increase or decrease the bulk density of the lignin beads. However, the bulk density is preferably maintained within the same range as the density of the lignin beads prior to thermal stabilization.

[0071] Compared to the lignin beads before heating to obtain a thermally stabilized material, there may be a small weight loss during heating. The weight loss is generally less than 15 weight percent and is mainly caused by the evaporation of moisture and the loss of volatile substances due to the decomposition of lignin during heating.

[0072] By controlling and optimizing parameters such as temperature and time during the thermal stabilization process, thermally stabilized lignin beads can be obtained that maintain their shape and dimensions without fusion or swelling during subsequent processes. The described process is highly suitable for general process requirements for continuous production, for example using rotary kilns, due to the mechanical stability of the lignin beads and their relatively short residence time. This is particularly important for achieving an economical large-scale industrial process for producing carbon-enriched materials.

[0073] The lignin beads provided in step a) or optionally the thermally stabilized lignin beads in step b) are carbonized at one or more temperatures ranging from 300°C to 1500°C, and this carbonization treatment is carried out for a total of 30 minutes to 10 hours to obtain a carbon-rich material.

[0074] As used herein, the term “carbonization” refers to a process of converting lignin into carbon by heating the lignin beads provided in step a) or optionally the thermally stabilized lignin beads in step b) at one or more temperatures for a sufficient amount of time. Depending on the temperature during the carbonization process, various types of carbon, such as charcoal or hard carbon, can be obtained from the lignin in the lignin beads.

[0075] As described above, during the carbonization process, the lignin in the lignin beads is converted into carbon. Thus, a carbon-rich material is obtained. In some embodiments, the obtained carbon-rich material has an elemental carbon content of at least 70 wt%, preferably at least 85 wt%, more preferably at least 90 wt% or at least 95 wt% based on dry weight.

[0076] In some embodiments, the carbonization process includes a preheating step and a final heating step. The preheating step is preferably performed at a temperature between 300 and 800°C, for example, between 500 and 700°C. The preheating step is preferably performed in an inert atmosphere, preferably a nitrogen atmosphere. The duration of the preheating step is at least 30 minutes, preferably less than 10 hours. The preheating step and the final heating step may be performed as separate steps or as a single step in a direct sequence.

[0077] The final heating step is preferably performed at a temperature of 800°C to 1500°C. The final heating step is preferably performed under an inert atmosphere, preferably a nitrogen atmosphere. The duration of the final heating step is 30 minutes or more, preferably less than 10 hours.

[0078] Preferably, carbonization is performed in stages. Preferably, preheating starts at about 300°C and is then increased to about 500°C. The final heating step is preferably performed between 900°C and 1300°C, such as about 1000°C.

[0079] In some embodiments, the obtained carbon-enriched material, i.e., the carbonized material which is the product of step c), has a bulk density in the range of 0.5 to 1 g / cm³, preferably in the range of 0.7 to 1 g / cm³.

[0080] Although the size of the beads may decrease slightly during the carbonization process, the bead sizes generally maintain the same size order. It is desirable that the shape of the beads be maintained during the carbonization process, and shrinkage is generally substantially uniform. Accordingly, in some embodiments, the carbon-rich material obtained in step c) comprises carbonized lignin beads having a diameter in the range of 0.1 mm to 5.0 mm, preferably in the range of 0.2 mm to 2.0 mm, and more preferably in the range of 0.3 mm to 0.5 mm. In some embodiments, at least 80 weight%, at least 90 weight%, or at least 95 weight% of the carbon-rich material obtained in step c) comprises carbonized lignin beads having a diameter in the range of 0.1 mm to 5.0 mm, preferably in the range of 0.2 mm to 2.0 mm, and more preferably in the range of 0.3 mm to 0.5 mm.

[0082] The obtained carbon-rich material is useful as a precursor for, for example, biochar or activated carbon.

[0083] In some embodiments, this method further includes an additional step of grinding the obtained carbon-concentrated material to obtain a carbon-concentrated material powder.

[0084] Grinding can be performed by any suitable process using, for example, a cutting mill, a blade mixer, an impact mill, a ball mill, a hammer mill, and / or a jet mill. Optionally, fine / coarse particle selection by classification and / or sieving can be performed after grinding.

[0085] The grinding of the above carbon-enriched material and the selective fine / large particle selection are, for example, the average particle size (D) measured by laser diffraction. v 50) This is done to obtain a carbon-concentrated material powder containing powder particles having a size of 1 to 25 μm.

[0086] In some embodiments, one or more steps of grinding or crushing may be performed. Additionally, the carbon-enriched material powder may undergo processing such as coating or additional heat treatment.

[0087] According to a second aspect of the invention, the invention relates to lignin beads comprising at least 80% by weight of lignin based on the dry weight of the lignin beads. Lignin beads with a very high lignin content have been found to be particularly useful as starting materials in the method according to the first aspect. Lignin beads according to the second aspect may be further defined as described above with reference to the lignin beads provided in step a) of the method according to the first aspect.

[0088] According to a third aspect of the present invention, the present invention relates to a method for producing thermally stabilized lignin beads comprising the following steps:

[0089] a) a step of providing lignin beads, wherein the lignin beads comprise at least 80 weight percent of lignin based on the dry weight of the lignin beads; and

[0090] b) A step of obtaining thermally stabilized lignin beads by heating the lignin beads at one or more temperatures in the range of 140 to 270 °C for at least 30 minutes.

[0091] According to the fourth aspect, the present invention relates to thermally stabilized lignin beads that can be obtained by the method according to the third aspect.

[0092] Thermal stabilization enables thermally stabilized lignin beads to better maintain their shape and dimensions while preventing melting / expansion and deformation during the carbonization process. The substantially spherical or elliptical shape of the lignin beads provides uniform thermal stability. These thermally stabilized lignin beads are useful as intermediate products for carbon-enriching materials.

[0093] The method according to the third aspect may be further defined as described above by referring to the method according to the first aspect.

[0094] According to the fifth aspect, the present invention relates to a carbon-enriched material obtainable by a method according to the first aspect.

[0095] According to the sixth aspect, the present invention relates to a non-aqueous secondary battery comprising a carbon-enriched material obtained by the method according to the first aspect.

[0096] The carbon-enriched material obtained by the method according to the first aspect is preferably used as an active material in the negative electrode of a water-insoluble secondary battery, such as a lithium-ion battery. When used to manufacture such a negative electrode, any suitable method for forming such a negative electrode may be utilized. In forming the negative electrode, the carbon-enriched material may be processed together with additional components. These additional components may include, for example, one or more binders for forming the carbon-enriched material into an electrode, conductive materials such as carbon black, carbon nanotubes, or metal powder, and / or additional 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), alginate, etc. Optionally, solvents such as 1-methyl-2-pyrrolidone, 1-ethyl-2-pyrrolidone, water, or acetone are used during treatment.

[0097] According to the seventh aspect, the present invention relates to the use of lignin beads comprising at least 80% by weight of lignin based on the dry weight of the lignin beads for the production of carbon-enriched materials.

[0098] The lignin beads used in the seventh aspect can be further defined as described above by referring to the lignin beads provided in step a) of the method according to the first aspect.

[0099] Generally, the products, polymers, materials, and processes described herein may be described as "comprising" various components or steps, but such products, polymers, materials, and processes may also be described as "essentially composed of" or "consisting of" various components and steps.

[0100] Although the present invention has been described with reference to various exemplary embodiments, those skilled in the art will understand that various modifications are possible and components may be replaced with equivalents without departing from the scope of the invention. Furthermore, various modifications are possible to apply the principles of the invention to specific situations or materials without departing from the essential scope of the invention. Accordingly, the present invention should not be interpreted as being limited to the specific embodiments disclosed as optimal embodiments for implementing the invention, but should be interpreted as including all embodiments included within the scope of the appended claims.

[0101] Example 1 - Preparation of Lignin Beads

[0102] A lignin slurry was prepared with the following formulation:

[0103] - Softwood Kraft Lignin 25g

[0104] 100g of deionized water

[0105] - Twin 80 1.2g

[0106] - Sodium alginate 0.6g

[0107] The lignin / alginate slurry was thoroughly stirred using a magnetic stirrer.

[0108] 10g of calcium chloride (CaCl₂) was dissolved in 1000g of deionized water in a separate beaker.

[0109] Lignin slurry was added drop by drop to a calcium chloride solution using a syringe with a 1.1 mm needle.

[0110] Spherical lignin / alginate beads were formed when lignin / alginate slurry droplets came into contact with calcium ions in the solution. The resulting beads were washed under running water and dried overnight at 50°C.

[0111] The obtained dried lignin beads exhibited high sphericity, high porosity, and mechanical stability. A photograph of the dried beads is shown in Fig. 1. The bulk density of the obtained beads was 0.4 g / cm³, and the diameter was less than 5 mm. The internal structure of the dried beads was studied by observing them using a scanning electron microscope (SEM) after grinding. The SEM images in Fig. 2a (1000x magnification) and Fig. 2b (5000x magnification) show that the beads have a porous structure with porosity in the range of 5–50% (estimated from the SEM images).

[0112] Example 2 - Thermal stabilization of lignin beads

[0113] The lignin beads obtained in Example 1 were heat-stabilized by heating them in air at 250 °C for 2 hours.

[0114] The obtained stabilized lignin beads retained their high sphericity, porosity, and mechanical stability.

[0115] Example 3 - Carbonization of Lignin Beads

[0116] The stabilized lignin beads obtained in Example 2 were carbonized by heating at 1050 °C for 2 hours under a nitrogen atmosphere.

[0117] The obtained stabilized lignin beads maintained high sphericity and porosity. A photograph of the carbonized beads is shown in Fig. 3. The obtained carbonized lignin beads were observed using a scanning electron microscope (SEM). The internal structure of the dried beads was studied by observing them using a scanning electron microscope (SEM) after grinding the beads. The SEM images show that the porosity observed in the dried lignin beads of Example 1 was maintained in the carbonized lignin beads as well. Figs. 4a (1000x magnification) and 4b (5000x magnification) show that the beads have a porous structure with porosity in the range of 5–50% (estimated from the SEM images).

Claims

Claim 1 A method for manufacturing a carbon-concentrating material comprising the following steps: a) providing lignin beads, wherein the lignin beads contain at least 80% by weight of lignin based on the dry weight of the lignin beads; b) optionally, heating the lignin beads at one or more temperatures in the range of 140 to 270 °C for at least 30 minutes to obtain thermally stabilized lignin beads; and c) optionally, carbonizing the thermally stabilized lignin beads at one or more temperatures in the range of 300 °C to 1500 °C for 30 minutes to 10 hours to obtain a carbon-concentrating material. Claim 2 A method according to claim 1, wherein the lignin beads provided in step a) have a spherical or elliptical shape. Claim 3 A method according to any one of the prior claims, wherein the diameter of the lignin beads provided in step a) is in the range of 0.1 mm to 5.0 mm, preferably in the range of 0.2 mm to 2.0 mm, and more preferably in the range of 0.3 mm to 0.5 mm. Claim 4 A method according to any one of the prior claims, wherein the lignin beads provided in step a) comprise at least 90 weight%, preferably at least 95 weight%, of lignin based on the dry weight of the lignin beads. Claim 5 A method according to any one of the prior claims, wherein the lignin is Kraft lignin. Claim 6 A method according to any one of the prior claims, wherein the lignin beads provided in step a) further comprise 0.5 to 10 weight%, preferably 1 to 5 weight%, more preferably 1 to 3 weight% of a polymer binder based on the dry weight of the lignin beads. Claim 7 In claim 6, the polymer binder comprises a gel-forming polymer, preferably an ionic gelling polymer, more preferably an ionic gelling polysaccharide, and more preferably an alginate. Claim 8 A method according to any one of the prior claims, wherein the lignin beads provided in step a) further comprise a surfactant in an amount of 0.5 to 10 weight%, preferably 1 to 5 weight%, more preferably 1 to 3 weight% based on the dry weight of the lignin beads. Claim 9 In claim 8, the surfactant is a nonionic surfactant, preferably a polysorbate, and more preferably Tween 80. Claim 10 A method according to any one of the prior claims, wherein the lignin beads provided in step a) are prepared by a method comprising: i) preparing an aqueous mixture comprising, based on the total dry weight of the aqueous mixture, at least 80 weight% of lignin, 0.5 to 10 weight% of an ionic gelling polymer, and 0.5 to 10 weight% of a nonionic surfactant; ii) adding the mixture dropwise to an aqueous solution containing divalent metal ions to obtain lignin beads; and iii) recovering the obtained lignin beads and optionally washing them. Claim 11 In any one of the prior claims, the lignin beads provided in step a) have a glass transition temperature (T) of 140 °C or higher g A method of having ). Claim 12 A method according to any one of the prior claims, wherein the lignin beads provided in step a) are porous lignin beads. Claim 13 A method according to any one of the prior claims, wherein the lignin beads provided in step a) have a bulk density in the range of 0.2 to 1 g / cm³, preferably in the range of 0.5 to 0.7 g / cm³. Claim 14 A method according to any one of the prior claims, wherein the process of heating the lignin beads in step b) is performed by first heating the lignin beads to a temperature in the range of 140 to 175°C for at least 15 minutes, and then heating them to a temperature in the range of 175 to 270°C for at least 15 minutes. Claim 15 A method according to any one of the prior claims, wherein the carbonization of step c) comprises a preheating step and a subsequent final heating step. Claim 16 In claim 15, a method in which a preheating step is performed at a temperature of 300 to 800°C for at least 30 minutes. Claim 17 A method according to any one of claims 15 to 16, wherein the preheating step is performed in an inert atmosphere. Claim 18 A method according to any one of claims 15 to 17, wherein the final heating step is performed at a temperature of 800°C to 1500°C for at least 30 minutes. Claim 19 A method according to any one of claims 15 to 18, wherein the final heating step is performed in an inert atmosphere. Claim 20 A method according to any one of the prior claims, wherein the obtained carbon-enriched material has an elemental carbon content of at least 70 weight%, preferably at least 85 weight%, based on dry weight. Claim 21 A method according to any one of the prior claims, wherein the obtained carbon enrichment material has a bulk density in the range of 0.5 to 1 g / cm³, preferably in the range of 0.7 to 1 g / cm³. Claim 22 A method according to any one of the prior claims, comprising the additional step of grinding the obtained carbon-concentrated material to obtain a carbon-concentrated material powder. Claim 23 Lignin beads comprising at least 80 weight percent of lignin based on the dry weight of the lignin beads. Claim 24 In paragraph 23, lignin beads additionally defined in any one of paragraphs 2 through 13. Claim 25 A method for producing thermally stabilized lignin beads comprising the following steps: a) providing lignin beads, wherein the lignin beads contain at least 80% by weight of lignin based on the dry weight of the lignin beads; and b) heating the lignin beads at one or more temperatures in the range of 140 to 270 °C for at least 30 minutes to obtain thermally stabilized lignin beads. Claim 26 In paragraph 25, a method additionally defined in any one of paragraphs 2 through 14. Claim 27 Thermally stabilized lignin beads obtainable by a method according to any one of claims 25 to 26. Claim 28 A carbon-enriched material obtainable by a method according to any one of paragraphs 1-22. Claim 29 A negative electrode for a non-aqueous secondary battery comprising, as an active material, a carbon-enriched material obtainable by a method according to any one of claims 1-22. Claim 30 Use of lignin beads containing at least 80 weight% lignin based on the dry weight of the lignin beads for the production of carbon-enriched materials. Claim 31 In paragraph 30, lignin beads are used for any of the additional uses defined in paragraphs 2 through 13.

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