Process for producing carbon material from lignin

Abstract

The present invention relates to a method for producing a carbon material, the method comprising the steps of providing lignin, providing at least one thermosetting resin, contacting the lignin with the at least one thermosetting resin to obtain a lignin-thermosetting resin material, curing the lignin-thermosetting resin material, and subjecting the cured lignin-thermosetting resin material to a heat treatment to obtain the carbon material. The obtained carbon material is suitable for use as an active material in a negative electrode of a secondary battery.

Description

Technical Field

[0001] The present invention relates to a method for producing a carbon material from lignin, and a carbon material obtainable by said method. The method involves contacting lignin with a thermosetting resin. The present invention further relates to a negative electrode for a secondary battery comprising said carbon material as an active material. The present invention further relates to the use of said carbon material as an active material in a negative electrode for a secondary battery. Background Art

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

[0003] Graphite (natural or synthetic graphite) is now used as the negative electrode material in most lithium-ion batteries. Alternatives to graphite are amorphous carbon materials, such as hard carbon (non-graphitizable amorphous carbon) and soft carbon (graphitizable amorphous carbon), which lack long-range graphitic order. Amorphous carbon can be used as the sole active electrode material or mixed with graphite (and / or other active materials).

[0004] Amorphous carbon can be derived from lignin. Lignin is an aromatic polymer that is, for example, the main component in wood and one of the most abundant carbon sources on Earth. In recent years, with the development and commercialization of technologies for extracting highly purified, solid and particularized forms of lignin from pulping processes, it has attracted great attention as a possible renewable alternative to the main aromatic chemical precursors currently derived from the petrochemical industry. Amorphous carbon derived from lignin is typically non-graphitizable, i.e., hard carbon.

[0005] Lignin has a complex chemical structure, which depends primarily on its source, such as the type of plant or tree from which the source of the lignin is obtained. The properties of lignin, such as its glass transition temperature, vary significantly depending on the chemical structure, the composition of the lignin, and any impurities present. In particular, the lignin obtained from hardwoods such as eucalyptus has a relatively lower glass transition temperature than the lignin obtained from softwoods.

[0006] Today, the most commercially relevant source of lignin is kraft lignin, which is obtained from hardwood or softwood by the kraft process. Lignin can be separated from alkaline black liquor using, for example, membrane filtration or ultrafiltration. A conventional separation process is described in WO2006031175 A1. In this process, lignin is precipitated from alkaline black liquor by reducing the pH level of the black liquor (usually by adding carbon dioxide) and then filtered out. In the next step, the lignin filter cake is re-pulped (usually using sulfuric acid) and washed under acidic conditions. The precipitated washed lignin can be used directly or further dried.

[0007] In the case of using lignin as a precursor for the material of carbon enrichment, a problem is that the direct use of the lignin in the form of fine powder is inappropriate because it shows undesirable thermoplastic behavior and a strong tendency for dust formation. During the conversion of lignin powder to the material of carbon enrichment, lignin undergoes plastic deformation / melting, violent expansion and foaming. From the perspective of equipment size and process output and the needs of intermediate processing, this seriously limits the processability of lignin in industrially relevant scales. In addition, dust formation increases the risk for dust explosion during processing.

[0008] The above-mentioned problems about undesirable thermoplastic behavior are particularly evident when processing lignin with a low glass transition temperature, such as lignin obtained from hardwood.For lignin with a low glass transition temperature, problems involving melting, softening and decomposition will begin at relatively low temperatures.

[0009] Therefore, no matter how the source of lignin is, there is still room for improving the method for producing carbon-enriched materials from lignin. The method should avoid plastic deformation / melting, severe expansion and foaming of lignin during any heating step and when converting lignin into carbon-enriched materials. The method should also avoid dust formation during the processing of lignin. In addition, the method should be used in large-scale manufacturing. Summary of the invention

[0010] It is an object of the present invention to provide an improved process for producing carbon-enriched materials which allows the use of renewable carbon sources and which obviates or mitigates at least some of the disadvantages of existing processes.

[0011] It is a further object of the present invention to provide a method for obtaining improved carbon-enriched materials starting from lignin, which carbon-enriched materials are suitable for use as active material in the negative electrode of secondary batteries, such as lithium-ion batteries.

[0012] A further object of the present invention is to provide a method for producing carbon-enriched materials from lignin, whatever the origin of the lignin, which method allows thermal treatment of the lignin with preservation of the shape.

[0013] It is a further object of the present invention to provide a method for avoiding dust formation during the processing of lignin in powder form.

[0014] It is a further object of the present invention to provide a method for producing carbon-enriched materials from lignin which is scalable and thus suitable for large-scale manufacturing.

[0015] The above-mentioned objects and other objects that will be recognized by those skilled in the art from the present disclosure are achieved by various aspects of the present disclosure.

[0016] According to a first aspect, the present invention relates to a method for producing a carbon material from lignin, the method comprising the following steps:

[0017] a) providing lignin;

[0018] b) providing at least one thermosetting resin;

[0019] c) contacting lignin with said at least one thermosetting resin to obtain a lignin-thermosetting resin material;

[0020] d) optionally drying the lignin-thermosetting resin material;

[0021] e) curing the lignin-thermosetting resin material or the dried lignin-thermosetting resin material to obtain a cured lignin-thermosetting resin material; and

[0022] f) subjecting the cured lignin-thermosetting resin material to heat treatment at one or more temperatures in the range from 300° C. to 3000° C., wherein the heat treatment is carried out for a total time in the range from 30 minutes to 10 hours, to obtain a carbon material.

[0023] Surprisingly, it has been found that by contacting lignin with a thermosetting resin, a lignin-thermosetting resin material is obtained, which can be heat treated while retaining its shape after solidification, avoiding melting / expansion and deformation. By the method of the present invention, dust formation during lignin processing is also reduced. The contact of lignin with a thermosetting resin can be carried out, for example, by coating lignin with a thermosetting resin or by mixing lignin with a thermosetting resin. Therefore, the lignin-thermosetting resin material can be converted into a carbon-enriched material while retaining its shape. Surprisingly, the method of the present invention is also conducive to the thermal processing of lignin with a low glass transition temperature such as the lignin obtained from hardwood.

[0024] According to a second aspect, the present invention relates to a carbon material obtainable by a method according to the first aspect.

[0025] Surprisingly, it has been found that when a lignin-thermosetting resin material is converted into a carbon-enriched material by heat treatment, the shape of the lignin-thermosetting resin material is maintained during the heat treatment. The resulting carbon material is suitable for use, for example, in energy storage applications, such as active materials in the negative electrode of a secondary battery.

[0026] According to a third aspect, the present invention relates to a negative electrode of a secondary battery comprising as active material a carbon material obtainable by the method according to the first aspect.

[0027] According to a fourth aspect, the present invention relates to the use of a carbon material obtainable by a method according to the first aspect as active material in a negative electrode of a secondary battery. DETAILED DESCRIPTION

[0028] Step a) of the method according to the first aspect involves providing lignin. Throughout this disclosure, the term "lignin" is intended to refer to any type of lignin that can be used as a carbon source for making carbon materials. Examples of the lignin are, but are not limited to, lignin obtained from plant raw materials such as wood, for example, softwood lignin, hardwood lignin, and lignin from annular plants. In addition, the lignin can be chemically modified.

[0029] Preferably, the lignin has been purified or separated before being used in the process according to the invention. The lignin may be separated from the black liquor and optionally further purified before being used in the process according to the invention. The purification typically results in a lignin purity of at least 90%, preferably at least 95%, more preferably at least 98%, based on the dry weight of the lignin material. Thus, the lignin material used in the process according to the 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 material.

[0030] Lignin can be obtained by different extraction methods, such as an organosolv process or a kraft process. Preferably, the lignin used in the method of the invention is kraft lignin, i.e. lignin obtained by the kraft process. Kraft lignin can be obtained from hardwood or softwood.

[0031] Kraft lignin is readily available as a by-product from pulp production by the kraft process. From a sustainability perspective, it is beneficial to utilize kraft lignin that would otherwise typically be discarded. Therefore, by utilizing kraft lignin, a more sustainable process can be achieved. Kraft lignin can be extracted on an industrial scale by well-known and established processes, resulting in lignin of consistent quality. Kraft lignin is therefore suitable for use in large-scale processing, where repeatability of the process is of high importance. The extracted kraft lignin can be easily chemically modified or cross-linked, which facilitates further processing.

[0032] Lignin can be obtained by the process disclosed in WO2006031175 A1, which is conventionally referred to as the LignoBoost process. Typically, the process involves the following steps: precipitation of lignin from alkaline black liquor by acidification; separation of the precipitated lignin; and re-slurrying the lignin at least once under acidic conditions. The obtained lignin can be dried and pulverized and thus provided as solid particles.

[0033] Preferably, the lignin provided in step a) of the method according to the first aspect is in the form of a powder, agglomerated lignin, a shaped body, or a liquid solution.

[0034] In some embodiments, the lignin provided in step a) is in the form of powder, agglomerated lignin or a shaped body. In such an embodiment, the lignin provided in step a) is preferably in dry form. Providing lignin in dry form is advantageous because subsequent separation and drying steps are not required, and solvents are not required. Therefore, it is conducive to processing.

[0035] In some embodiments, the lignin provided in step a) is in the form of a powder. The particle size distribution of the lignin in powder form can be such that at least 80% by weight of the particles have a diameter less than 0.2 mm. The lignin powder can also have a moisture content less than 45% by weight. Lignin in powder form is easily available, for example, from the LignoBoost process, and therefore the method using lignin powder as a starting material does not require additional processing steps for the preparation of the starting material. The lignin powder can also be provided in the form of a slurry, i.e., the lignin powder is mixed with a solvent, preferably water.

[0036] In the context of the present invention, if the particle is not spherical, the diameter of the particle is the equivalent spherical diameter of the particle. The equivalent spherical diameter is the diameter of a sphere of equivalent volume.

[0037] In some embodiments, the lignin provided in step a) is in the form of agglomerated lignin. The agglomerated lignin may have a particle size distribution such that at least 80% by weight of the agglomerates have a diameter in the range of from 0.2 mm to 5.0 mm. A method for obtaining such agglomerated lignin is described in WO2020183383 A1.

[0038] Briefly, the purified and preferably dried lignin powder is compacted, and the compacted lignin is broken to obtain agglomerated lignin. The compaction of lignin is preferably carried out by roller compaction. An intermediate product is generated in the compaction step. Here, fine lignin powder is usually fed by a feed hopper and conveyed to a compaction zone by a horizontal or vertical feed screw, where the material is compacted into flakes by a compaction roller with a defined gap in the compaction zone. By controlling the feed screw speed, the pressure development in the compaction zone, a flake with uniform density can be obtained. The pressure development in the compaction zone can preferably be monitored and controlled by the rotation speed of the compaction roller. As the powder is dragged between the rollers, it enters a region known as the nip area, where the density of the material increases and the powder is converted into flakes or ribbons. The roller used has a cavity. The depth of each cavity used in the roller compaction is from 0.1mm to 10mm, preferably from 1mm to 8mm, more preferably from 1mm to 5mm or from 1mm to 3mm. The specific pressure applied during compaction may vary, depending on the equipment used for compaction, but may range from 1 kN / cm to 100 kN / cm. Suitable equipment for performing compaction is known in the art.

[0039] In the crushing step, the intermediate product from the compacting step is subjected to crushing or grinding, such as by a rotary granulator, a cage mill, a beater mill, a hammer mill or a pulverizer mill and / or a combination thereof. During this step, further intermediate products are generated.

[0040] After crushing, the crushed material is preferably subjected to a screening step to remove fine material. In addition, large materials such as agglomerates with a diameter greater than 5.0 mm can be removed and / or recirculated back to the crushing step.

[0041] Agglomeration of lignin results in an agglomerated lignin with improved thermal properties, such as a reduced tendency towards melting / foaming and deformation during heating. The tendency for dust formation during processing is also reduced by the agglomeration process. Therefore, in embodiments in which the lignin is provided in the form of agglomerated lignin, the ability of the lignin-thermosetting resin material to retain its shape during thermal processing is improved by the combination of the presence of the lignin in agglomerated form and the thermosetting resin.

[0042] In some embodiments, the lignin provided in step a) is in the form of a shaped body. As used herein, the term "shaped body" refers to a solid lignin body that has been formed into a specific shape by thermal processing or casting of lignin. Non-limiting examples of such shaped bodies are pellets, granules, sheets, fibers, rods, strips, sheets, etc. The size and size of the shaped body are not limited. Therefore, the method of the present invention can be applied to objects of various sizes and shapes.

[0043] In some embodiments, the lignin provided in step a) is in the form of a liquid solution. Lignin can be dissolved in any suitable (one or more) solvents to form a liquid solution, so that the liquid solution contains dissolved lignin and at least one solvent. The solvent can be, for example, an alkaline aqueous solution, a polar protic solvent, such as dimethyl sulfoxide or dimethyltryptamine, or a polar aprotic solvent, such as an alcohol or an amine. Lignin can also be dissolved in a polymer melt. The amount of lignin in the liquid solution is preferably in the range of from 10 to 95% by weight, such as from 10 to 70% by weight or from 10 to 50% by weight or from 10 to 30% by weight, based on the gross weight of the liquid solution. By providing lignin in the form of a liquid solution, it can be beneficial to contact with a thermosetting resin subsequently, particularly in an embodiment in which a thermosetting resin is provided in liquid form. In some embodiments, the liquid solution contains more than one solvent.

[0044] Step b) of the method according to the first aspect involves providing at least one thermosetting resin. The term "thermosetting resin" as used herein refers to a resin that hardens irreversibly by curing. The term "thermosetting resin" is not intended to cover precursors of thermosetting resins, but only resins obtained by reaction of one or more precursors.

[0045] The type of thermosetting resin is not particularly limited, and any suitable thermosetting resin can be used in the method according to the present invention. In some embodiments, at least one thermosetting resin can be selected from: furan resins, such as polyfurfuryl alcohol, epoxy-based resins, phenolic resins, such as bakelite, vinyl esters, melamine resins and polyimides. Preferably, the thermosetting resin is a furan resin, such as polyfurfuryl alcohol.

[0046] Preferably, the at least one thermosetting resin is provided in solid form and / or in liquid form. For example, if more than one thermosetting resin is provided, one may be in solid form and one may be in liquid form.

[0047] In some embodiments, the at least one thermosetting resin is provided in liquid form. Optionally, the thermosetting resin in liquid form can be diluted with a solvent. If the thermosetting resin has a high viscosity, dilution of the liquid thermosetting resin is preferably performed to facilitate subsequent contacting steps. After contacting the lignin with the thermosetting resin, by providing the thermosetting resin in liquid form, the tendency for dust formation during the processing of the lignin is reduced and facilitated for handling.

[0048] In some embodiments, the at least one thermosetting resin is provided in solid form, such as in the form of a powder. By providing the thermosetting resin in solid form, the process of mixing the thermosetting resin with the lignin powder is facilitated. Dry mixing is advantageous from a cost perspective because no solvent is required, and because fewer process steps are required because separation and drying of the lignin and / or thermosetting resin is not required.

[0049] In some embodiments, one thermosetting resin is provided in step b). In some embodiments, more than one thermosetting resin is provided in step b), such as two different types of thermosetting resins, or three different types of thermosetting resins. The different types of thermosetting resins may also be in different forms, such as at least one in liquid form and at least one in solid form.

[0050] Step c) of the method according to the first aspect involves contacting lignin with the at least one thermosetting resin to obtain a lignin-thermosetting resin material. The term "lignin-thermosetting resin material" as used herein refers to a material comprising both lignin and at least one thermosetting resin. The lignin-thermosetting resin material may optionally comprise at least one additive. The lignin may, for example, be coated with or impregnated with a thermosetting resin, or the lignin and the thermosetting resin may form a mixture.

[0051] The lignin-thermosetting resin material of the present invention is a composite material comprising lignin and at least one thermosetting resin. Lignin is in contact with the thermosetting resin and is not in contact with the precursor of the thermosetting resin. Therefore, the lignin-thermosetting resin material of the present invention is not a thermosetting resin based on lignin. For example, if lignin reacts with a precursor of a thermosetting resin, such a thermosetting resin based on lignin will be obtained. In the present invention, lignin is not modified by contact with a thermosetting resin, and the main polymer structure of lignin is not changed.

[0052] In one embodiment, the total amount of thermosetting resin in the lignin-thermosetting resin material is in the range of from 1 wt % to 70 wt %, such as from 1 wt % to 50 wt %, or from 1 wt % to 20 wt %, or from 1 wt % to 10 wt %, based on the total dry weight of the lignin-thermosetting resin material. By "total amount of thermosetting resin" is meant the total amount of all thermosetting resins present in the lignin-thermosetting resin material.

[0053] In a preferred embodiment, the total amount of thermosetting resin in the lignin-thermosetting resin material is in the range of from 1 wt % to 20 wt %, or from 1 wt % to 10 wt %, or from 1 wt % to 5 wt %, based on the total weight of the lignin-thermosetting resin material. Advantageously, a lignin-thermosetting resin material comprising a low amount of thermosetting resin is formed, because in this case the material mainly comprises materials from renewable resources, enabling a more sustainable method. The cost of lignin is also typically lower than the cost of thermosetting resins. A low amount of thermosetting resin (such as from 1 wt % to 5 wt %) based on the total weight of the lignin-thermosetting resin material will fully improve the thermal properties of the material to avoid melting / expansion of lignin during thermal treatment.

[0054] In some embodiments, the thermosetting resin(s) may be derived from renewable resources. In such embodiments, the lignin-thermosetting resin material may be completely renewable.

[0055] The lignin-thermosetting resin material comprises from 30 to 99 wt %, or from 50 to 99 wt %, or from 80 to 99 wt %, or from 90 to 99 wt %, based on the total weight of the lignin-thermosetting resin material. Preferably, the lignin-thermosetting resin material comprises from 80 to 99 wt %, or from 90 to 99 wt %, or from 95 to 99 wt % of lignin, based on the total weight of the lignin-thermosetting resin material.

[0056] The lignin-thermosetting resin material may comprise only lignin and a thermosetting resin, or may comprise lignin, a thermosetting resin, and at least one additive. The amount of the at least one additive is typically small, such as below 5 wt %, or below 2 wt %, based on the total weight of the lignin-thermosetting resin material.

[0057] As used herein, the term "contacting" refers to the process of bringing lignin and at least one thermosetting resin into close proximity with each other, such as by coating or mixing. In some embodiments, no or substantially no chemical reaction occurs between the lignin and the at least one thermosetting resin during the contacting step. In other embodiments, some chemical reaction may occur between reactive sites of the thermosetting resin and the lignin during the contacting step.

[0058] In a preferred embodiment of the invention, the lignin-thermosetting resin material comprises from 80 to 99 wt %, or from 90 to 99 wt %, or from 95 to 99 wt % lignin, based on the total weight of the lignin-thermosetting resin material. In such an embodiment, the amount of lignin in the contacting step is always significantly higher than the amount of thermosetting resin. Therefore, if some chemical reaction occurs between the thermosetting resin and the lignin, only a small portion of the lignin in the lignin-thermosetting resin material will react, while most of the lignin will remain unchanged by the contacting step.

[0059] In some embodiments, the step of contacting involves coating or impregnating lignin with the at least one thermosetting resin. In such an embodiment, the thermosetting resin is preferably in liquid form and the lignin is preferably in solid form, i.e. in the form of a powder, in the form of agglomerated lignin or in the form of a shaped body. Any suitable method known to those skilled in the art can be used, such as spray coating or dip coating. By coating or impregnating lignin with a thermosetting resin, an outer layer of a thermosetting resin is obtained on solid lignin. After solidification, this provides a hard protective layer for solid lignin, which reduces the formation of dust, and any tendency for individual particles of solid lignin to stick together due to melting / softening of the surface during subsequent thermal treatment.

[0060] In some embodiments, contacting involves mixing lignin and at least one thermosetting resin. In such an embodiment, the thermosetting resin can be in the form of a liquid or solid, and the lignin can be in the form of a powder, in the form of agglomerated lignin, in the form of a shaped body, or in the form of a liquid solution. Any method known to those skilled in the art can be used to mix. Both dry mixing and wet mixing methods can be used. An example of a suitable method is a vertical mixer, such as a paddle, screw or ribbon mixer performed in batch or continuous mode. The mixing process can be performed in low, medium or high shear impact mode.

[0061] In embodiments where at least one thermosetting resin is provided in liquid form and the lignin is provided in dry form, the lignin is not soluble or is soluble only to a minor extent in the thermosetting resin.

[0062] In some embodiments, there is a solvent during the step of contacting. The presence of a solvent may facilitate the contact between lignin and the thermosetting resin, and may also facilitate further processing steps, such as the formation (molding) of a lignin-thermosetting resin material. Any suitable solvent for a thermosetting resin may be used, such as water, tetrahydrofuran or methylene chloride. The solvent may be added before contacting, such as being added to the thermosetting resin, or added during contacting, such as being added during mixing. In an embodiment in which lignin is provided in the form of a liquid solution, a solvent may be added to a liquid solution comprising dissolved lignin.

[0063] Lignin-thermosetting resin material can optionally include additives. Any suitable additives such as adhesives or lubricants can be added to facilitate any subsequent molding or agglomeration process and / or improve the density and mechanical properties of lignin-thermosetting resin material. In addition, additives having an impact on the properties of the final carbon material can be added, such as functional enhancement additives. The total amount of (one or more) additives is preferably less than 5 weight %, such as less than 2 weight %, based on the total dry weight of additives and lignin-thermosetting resin material. In one embodiment, additives are added to lignin-thermosetting resin material before the solidification of lignin-thermosetting resin material. Additives can also be added to lignin and / or added to thermosetting resin before lignin is contacted with thermosetting resin.

[0064] In some embodiments, the method according to the first aspect includes an additional step of molding the obtained lignin-thermosetting resin material before curing. Molding can be performed by at least one method selected from the following: casting, pressing, granulation, kneading, granulation, and extrusion of lignin-thermosetting resin material. The size and shape of the molded lignin-thermosetting resin material vary according to the method used for molding. The type, amount and form of the at least one thermosetting resin provided in step b) can be selected according to the method used to mold the lignin-thermosetting resin material. The molding method may also affect the selection of thermosetting resins. By carrying out the contact in step c) in the presence of a solvent, the subsequent molding of the lignin-thermosetting resin material can be facilitated. By molding the lignin-thermosetting resin material, subsequent processing can be facilitated. Depending on the type of furnace used in the process, lignin-thermosetting resin materials of different shapes are preferred. Small particles or pellets are useful for rotary furnaces. For batch production furnaces, it is preferred that the lignin-thermosetting resin material is in the shape of a cylinder or a brick.

[0065] In some embodiments, the molded lignin-thermosetting resin material may be crushed or ground before subsequent processing steps to reduce the size of the molded lignin-thermosetting resin material. The crushing or grinding of the molded lignin-thermosetting resin material is preferably carried out when using a molding method such as casting, pressing or kneading, which results in the formation of large coherent pieces of the lignin-thermosetting resin material. In order to facilitate further processing into a carbon material, the large pieces are preferably crushed or ground. The crushing or grinding can be carried out after the solidification of the lignin-thermosetting resin material, or after the partial solidification of the lignin-thermosetting resin material. If the crushing or grinding is carried out after partial solidification, additional solidification can be carried out after the crushing or grinding. The crushing or grinding can be carried out using any suitable method known to those skilled in the art.

[0066] Step d) of the method according to the first aspect involves optionally drying the obtained lignin-thermosetting resin material. Drying can be carried out at room temperature and / or at an elevated temperature. Drying can be carried out using any suitable means known to those skilled in the art. Drying can be carried out under ambient pressure, reduced pressure or vacuum. In some embodiments, drying is carried out at room temperature for at least 10 hours. In some embodiments, drying is carried out at a temperature below 60°C, such as at one or more temperatures in the range of from 30°C to 60°C, for a period of time in the range of from 5 minutes to 10 hours. After drying, the dry content of the lignin-thermosetting resin material is at least 50% by weight, such as at least 70% by weight, or at least 80% by weight. The drying step is of particular importance in embodiments in which the thermosetting resin has been diluted with a solvent to remove the solvent.

[0067] Step e) of the method according to the first aspect involves curing the lignin-thermosetting resin material or the dried lignin-thermosetting resin material to obtain a cured lignin-thermosetting resin material. Curing can be carried out at room temperature and / or at an elevated temperature. By increasing the temperature, curing becomes faster. The temperature required for curing also depends on the type of thermosetting resin.

[0068] In some embodiments, curing is carried out at one or more temperatures in the range of from 20°C to 250°C, such as from 20°C to 200°C, or from 20°C to 150°C, or from 50°C to 150°C for a period of at least 30 minutes, i.e., the residence time of the lignin-thermosetting resin material inside the device for curing is at least 30 minutes. The total time for curing is preferably less than 24 hours. During curing, irreversible hardening of the at least one thermosetting resin occurs. After curing, a lignin-thermosetting resin material that does not change its shape during subsequent heat treatment is obtained. In addition, adding a thermosetting resin to lignin reduces the melting / expansion behavior of the lignin during heating.

[0069] In a preferred embodiment, curing is carried out at one or more temperatures in the range from 20 to 150° C. or 50 to 150° C. for a total time of at least 30 minutes. In such embodiments, the lignin exhibits no or only slight melting / expansion behavior.

[0070] In embodiments where the lignin is coated or impregnated with the at least one thermosetting resin, the inventors believe that the hardened thermosetting resin, after curing, will retain the lignin within the lignin-thermosetting resin material such that melting / expansion of the lignin is prevented during any subsequent thermal treatment at temperatures at which the lignin would normally exhibit melting / expansion behavior.

[0071] In embodiments where lignin is mixed with the at least one thermosetting resin, it is believed that a matrix of the thermosetting resin may be formed after curing, wherein the lignin is contained within the matrix such that melting / expansion of the lignin is prevented during any subsequent thermal treatment at temperatures at which the lignin would normally exhibit melting / expansion behavior.

[0072] In some embodiments, lignin can react with thermosetting resin during curing. In other embodiments, the only reaction that occurs during curing is within the thermosetting resin. In some embodiments, there will be reactions between lignin polymer chains during curing. Therefore, crosslinking reactions will occur within the thermosetting resin during curing, and crosslinking reactions between the thermosetting resin and lignin and / or between different lignin polymer chains may also occur. The crosslinking reactions between lignin and thermosetting resin and between different lignin polymer chains will reduce the melting / expansion behavior of lignin during any subsequent heating step at a temperature at which lignin would normally exhibit melting / expansion behavior. Crosslinking within the thermosetting resin can produce physical restrictions that prevent the melting / expansion of lignin.

[0073] Besides the crosslinking of the thermosetting resin, the reactions which occur during curing depend, for example, on the temperature and the type of thermosetting resin used.

[0074] In some embodiments, curing is performed using the same temperature throughout the curing step. For example, curing can be performed at room temperature for a total time of at least 30 minutes.

[0075] In some embodiments, curing is carried out at different temperatures, such as using a stepwise increase in temperature or using a temperature gradient. In some embodiments, curing is carried out in multiple steps at different temperatures. The temperature can be increased from one step to a subsequent step by a temperature ramp or gradient. For example, curing can be carried out by: the lignin-thermosetting resin material is heated to a first temperature in the range of from 20°C to 250°C, such as from 20°C to 200°C, or 20°C to 150°C, or 50°C to 150°C, and then heated to a second temperature from 20°C to 250°C, such as from 20°C to 200°C, or 20°C to 150°C, or 50°C to 150°C, and at each selected temperature, a certain amount of time is maintained, such as in the range of from 10 minutes to 3 hours. By curing in multiple steps at different temperatures, the improved crosslinking of the cured lignin-thermosetting resin material is achieved. In addition, the risk of cracking of the lignin-thermosetting resin material during curing is reduced because the curing process can be carried out in a more controlled manner.

[0076] In some embodiments, the heat treatment is directly performed after curing. For example, curing can be first performed at one or more temperatures in the range of from 20°C to 250°C, such as from 20°C to 200°C, or 20°C to 150°C, or 50°C to 150°C, and the temperature can then be increased to the temperature used during the heat treatment. The increase in temperature can be gradual or can include a temperature ramp. Therefore, curing can be performed in the same reactor as the subsequent heat treatment in some embodiments.

[0077] In some embodiments, an acidic catalyst is added to the at least one thermosetting resin material provided in step b), and the curing of the lignin-thermosetting resin material in step e) is catalyzed by an acidic catalyst. The acidic catalyst may be selected from sulfuric acid, maleic anhydride or p-toluenesulfonic acid. Curing using a catalyst may be carried out at room temperature and / or at an elevated temperature. Curing is faster at an elevated temperature.

[0078] Curing can be achieved using both a catalyst and elevated temperature, or by a catalyst alone, or by elevated temperature alone.

[0079] If the lignin-thermoset resin material is not dried prior to curing at elevated temperatures, drying may occur simultaneously with curing.

[0080] Preferably, the method comprises the additional step of grinding the solidified lignin-thermosetting resin material. Grinding is performed so that the average particle size is reduced. Grinding can also be performed on the carbon material obtained after the heat treatment of the solidified lignin-thermosetting resin material. Grinding can be performed by methods such as impact grinding, hammer milling, ball milling and jet milling. Optionally, fine / coarse particle selection can be performed by classification and / or screening after grinding.

[0081] The method according to the first aspect may involve multiple grinding steps. For example, if the lignin-thermosetting resin material has been formed into large coherent blocks, a first step of crushing or grinding may be followed by a subsequent grinding step. Grinding may also be performed after curing and after heat treatment.

[0082] Step f) of the method according to the first aspect involves subjecting the solidified lignin-thermosetting resin material to a heat treatment at one or more temperatures in the range from 300° C. to 3000° C. The heat treatment is carried out for a total time in the range from 30 minutes to 10 hours, i.e. the residence time of the lignin-thermosetting resin material inside the equipment for heat treatment is in the range from 30 minutes to 10 hours, to obtain a carbon material.

[0083] As used herein, the term "heat treatment" refers to the process of heating a lignin-thermosetting resin material at one or more temperatures and for a sufficient amount of time so that the carbon content of the lignin-thermosetting resin material increases and the lignin-thermosetting resin material is converted into a carbon material. Depending on the temperature during the heat treatment, different types of carbon materials such as charcoal or hard carbon can be obtained from the lignin-thermosetting resin material.

[0084] As used herein, the terms "carbon material" and "carbon-enriched material" both refer to a material that is primarily composed of carbon, such as at least 80% by weight, or at least 90% by weight, or at least 95% by weight, and is obtained by carbonization of an organic compound.

[0085] Heat treatment can be carried out at the same temperature throughout the heat treatment or can be carried out at different temperatures, such as gradually increasing the temperature or using a temperature gradient. Heat treatment can include a temperature ramp from a starting temperature to a target temperature. The heating rate can be 1-100 ° C / min. For example, before reaching the target temperature required for the carbonization of the lignin-thermosetting resin material, heat treatment can involve multiple intermediate temperatures with a temperature ramp between them. Heat treatment can be carried out as a batch process or a continuous process. Any suitable reactor can be used, such as a rotary kiln, a moving bed furnace, a pusher furnace or a rotary hearth furnace. Heat treatment is preferably carried out in an inert atmosphere, preferably under a nitrogen atmosphere.

[0086] Preferably, the heat treatment comprises a preliminary heating step, preferably followed by a final heating step. The preliminary heating step is preferably carried out at one or more temperatures in the range from 300°C to 800°C, such as from 500°C to 700°C. The preliminary heating step is preferably carried out under an inert atmosphere, preferably a nitrogen atmosphere. The duration of the preliminary heating step is at least 30 minutes and preferably less than 10 hours. The surface area of ​​the carbon material obtained after the preliminary heating step is typically in the range from 300 to 700 m 2The range of 1.1777 W / g is 1.177 W / g, which is measured using nitrogen gas according to BET.

[0087] The final heating step is preferably carried out at one or more temperatures in the range from 800° C. to 3000° C. The final heating step is preferably carried out under an inert atmosphere, preferably a nitrogen atmosphere. The duration of the final heating step is at least 30 minutes and preferably less than 10 hours. After the final heating step at 1000° C. or higher, the surface area of ​​the obtained carbon material is typically 50 m 2 / g or less.

[0088] The preliminary heating step and the final heating step may be performed as discrete steps or as a single step performed in direct sequence. The preliminary heating step and the final heating step may involve heating at one or more temperatures, as discussed above for thermal treatment. For example, the preliminary heating begins at about 300°C and then the temperature is increased to about 500°C. The final heating step is preferably performed between 900°C and 1300°C, for example at about 1000°C.

[0089] The preliminary heating step and the final heating step can be carried out as a batch process or as a continuous process. Any suitable reactor can be used, such as a rotary kiln, a moving bed furnace, a pusher furnace or a rotary hearth furnace. The preliminary heating step and the final heating step can be carried out in the same reactor or in separate reactors.

[0090] If grinding is performed, it may be performed between the preliminary heating step and the final heating step, or after the final heating step.

[0091] After the heat treatment, the obtained carbon can undergo further processing, such as, for example, carbon coating by chemical vapor deposition (CVD), pitch coating, thermal and / or chemical purification, further (one or more) heat treatments, particle size adjustment, and blending with other electrode materials to, for example, further improve its electrochemical properties.

[0092] According to a second aspect, the present invention relates to a carbon material obtainable by a method according to the first aspect. The carbon material obtainable by the method according to the first aspect is suitable for use, for example, in energy storage applications, such as active materials in the negative electrode of a secondary battery. The carbon material according to the second aspect may be further defined as described above with respect to the first aspect.

[0093] The carbon material obtainable by the method according to the first aspect is preferably used as an active material in the negative electrode of a non-aqueous secondary battery such as a lithium ion battery. When used to produce such a negative electrode, any suitable method can be used to form such a negative electrode. In the formation of the negative electrode, the carbon-enriched material can be processed together with other components. Such other components may include, for example, one or more adhesives to shape the carbon-enriched material into an electrode, a conductive material such as carbon black, carbon nanotubes or metal powders and / or other Li storage materials such as graphite or lithium. For example, the adhesive may be selected from, but not limited to, poly(vinylidene fluoride), poly(tetrafluoroethylene), carboxymethyl cellulose, natural butadiene rubber, synthetic butadiene rubber, polyacrylate, poly(acrylic acid), alginate, etc., or selected from a combination thereof. Optionally, a solvent such as, for example, 1-methyl-2-pyrrolidone, 1-ethyl-2-pyrrolidone, water or acetone is used during processing.

[0094] According to a third aspect, the present invention relates to a negative electrode of a secondary battery comprising as active material a carbon material obtainable by the method according to the first aspect. The carbon material of the negative electrode according to the third aspect may be further defined as set out above with respect to the first aspect.

[0095] According to a fourth aspect, the present invention relates to the use of a carbon material obtainable by the method according to the first aspect as an active material in a negative electrode of a secondary battery. The carbon material of the fourth aspect may be further defined as set out above in relation to the first aspect.

[0096] Example

[0097] Example 1

[0098] Softwood or hardwood lignin powder obtained from the LignoBoost process is mixed with liquid polyfurfuryl alcohol to obtain a mixture. The amount of polyfurfuryl alcohol added is 10% by weight, based on the dry weight of lignin. Water (25% by weight, based on the amount of polyfurfuryl alcohol) is added to the mixture to form a dough-like material. The dough-like material is cast or pelletized into smaller objects, which are dried at room temperature for 12 hours. After drying, curing is carried out in a step-by-step sequence, wherein the material is heated at 50°C for 1 hour, at 70°C for 1 hour, at 90°C for 1 hour, and at 150°C for 1 hour. The material gradually darkens during the curing process. After curing, the smaller objects are crushed and ground into particle sizes ranging from 0.5 mm to 2 mm. After crushing and grinding, the material is carbonized at a temperature ranging from 500°C to 1400°C under an inert atmosphere. For both lignin obtained from hardwood and softwood, no melting, fusion or expansion was observed during the heat treatment, and the material retained its shape after carbonization.

[0099] Example 2

[0100] Softwood or hardwood lignin powder obtained from the LignoBoost process is mixed with bakelite powder or frozen and pulverized polyfurfuryl alcohol to obtain a mixture. The amount of resin (e.g. bakelite or polyfurfuryl alcohol) added is 10% by weight, based on the dry weight of lignin. A homogeneous mixture of the two powders (e.g. lignin and resin) is obtained. The powder mixture is pressed into large blocks or pellets. After pressing, curing is carried out in a stepwise sequence, wherein the material is heated at 50°C for 1 hour, at 70°C for 1 hour, at 90°C for 1 hour, and at 150°C for 1 hour. The material gradually darkens during the curing process. After curing, the blocks or pellets are crushed and ground into a particle size in the range of from 0.5mm to 2mm. After crushing and grinding, the material is carbonized at a temperature in the range of from 500°C to 1400°C under an inert atmosphere. For both lignin obtained from hardwood and softwood, no melting, fusion or expansion was observed during the thermal treatment and the material retained its shape after carbonization.

[0101] Example 3 - Comparison

[0102] The softwood or hardwood lignin powder obtained from the LignoBoost process is carbonized under an inert atmosphere at a temperature in the range from 500° C. to 1400° C. The lignin powder melts and foams during carbonization, and a single foamy solid block is obtained after carbonization.

[0103] In view of the above detailed description of the invention, other modifications and variations will become apparent to those skilled in the art. However, it should be apparent that such other modifications and variations can be implemented without departing from the spirit and scope of the invention.

Claims

1. A method for producing a carbon material from lignin, the method comprising the following steps: a) providing lignin; b) providing at least one thermosetting resin; c) contacting lignin with said at least one thermosetting resin to obtain a lignin-thermosetting resin material; d) optionally drying the lignin-thermosetting resin material; e) curing the lignin-thermosetting resin material or the dried lignin-thermosetting resin material to obtain a cured lignin-thermosetting resin material; and f) subjecting the cured lignin-thermosetting resin material to heat treatment at one or more temperatures in the range from 300° C. to 3000° C., wherein the heat treatment is carried out for a total time in the range from 30 minutes to 10 hours, to obtain a carbon material.

2. The method according to claim 1, wherein the lignin provided in step a) is kraft lignin.

3. The method according to any one of claims 1-2, wherein the lignin provided in step a) is in the form of powder, agglomerated lignin, a shaped body, or a liquid solution.

4. The method according to any one of the preceding claims, wherein the at least one thermosetting resin is selected from the group consisting of furan resins, such as polyfurfuryl alcohol, epoxy-based resins, phenolic resins, such as bakelite, vinyl esters, melamine resins and polyimides.

5. The method according to any of the preceding claims, wherein the at least one thermosetting resin is provided in solid form and / or in liquid form.

6. The method according to any one of the preceding claims, wherein the total amount of thermosetting resin in the lignin-thermosetting resin material is in the range from 1 to 70 wt. %, based on the total dry weight of the lignin-thermosetting resin material.

7. A method according to any one of the preceding claims, wherein the step of contacting involves coating or impregnating the lignin with the at least one thermosetting resin.

8. The method according to any one of claims 1 to 6, wherein the step of contacting involves mixing lignin and the at least one thermosetting resin.

9. A method according to any preceding claim, wherein a solvent is present during the step of contacting.

10. A method according to any one of the preceding claims, wherein the method comprises the further step of shaping the lignin-thermosetting resin material prior to curing.

11. The method according to claim 10, wherein the step of shaping the lignin-thermosetting resin material is performed by at least one manner selected from the group consisting of casting, pressing, pelletizing, kneading, granulating, or extruding the lignin-thermosetting resin material.

12. A method according to any preceding claim, wherein curing is carried out at one or more temperatures in the range from 20°C to 250°C for a total time of at least 30 minutes.

13. The method according to any one of the preceding claims, wherein an acidic catalyst is added to the at least one thermosetting resin provided in step b), and wherein the curing of the lignin-thermosetting resin material in step e) is catalyzed by the acidic catalyst.

14. A method according to any one of the preceding claims, wherein the method comprises the further step of grinding the cured lignin-thermosetting resin material.

15. The method according to any one of the preceding claims, wherein the heat treatment in step f) comprises a preliminary heating step followed by a final heating step.

16. The method of claim 15, wherein the preliminary heating step is performed at one or more temperatures in the range from 400°C to 800°C for at least 30 minutes.

17. The method according to any one of claims 15 or 16, wherein the preliminary heating step is carried out under an inert atmosphere.

18. The method according to any one of claims 15-17, wherein the final heating step is carried out at one or more temperatures in the range from 800°C to 3000°C for at least 30 minutes.

19. The method according to any one of claims 15 to 18, wherein the final heating step is performed under an inert atmosphere.

20. Carbon material obtainable by a process according to any one of claims 1 to 19.

21. A negative electrode for a secondary battery comprising, as an active material, a carbon material obtainable by the method according to any one of claims 1 to 19.

22. Use of a carbon material obtainable by a process according to any one of claims 1 to 19 as active material in a negative electrode of a secondary battery.