Method for producing carbon materials 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 a carbon material 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 the method. The method comprises contacting lignin with a thermosetting resin. The present invention further relates to a negative electrode for a secondary battery comprising the carbon material as an active material. The present invention further relates to the use of the carbon material as an active material in a negative electrode for a secondary battery. [Background technology]

[0002] Secondary batteries, such as lithium-ion batteries, are batteries that can be charged and discharged multiple times, i.e., rechargeable batteries. In lithium-ion batteries, lithium ions flow from the negative electrode through an electrolyte to the positive electrode during discharge and back during charging. 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 positive electrode material, and carbon-rich materials are used as the negative electrode material.

[0003] Graphite (natural or synthetic) is currently utilized 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 (easily 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, an aromatic polymer that is the major component in, for example, wood and is one of the most abundant carbon sources on Earth. In recent years, with the development and commercialization of techniques to extract lignin in a highly purified, solid, particulate form from the pulp manufacturing process, lignin has attracted significant attention as a potential renewable alternative to the primarily aromatic chemical precursors currently supplied by the petrochemical industry. Amorphous carbon derived from lignin is typically non-graphitizable, i.e., hard carbon.

[0005] Lignin has a complex chemical structure that depends greatly on its origin, e.g., the type of plant or tree from which it is obtained. Lignin's properties, such as its glass transition temperature, vary greatly depending on the chemical structure, the composition of the lignin, and any impurities present. In particular, lignin obtained from hardwoods, such as eucalyptus, has a relatively lower glass transition temperature than lignin obtained from softwoods.

[0006] Today, the most commercially relevant source of lignin is kraft lignin, obtained from hardwood or softwood trees 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 WO2006031175A1. In this process, lignin is precipitated from alkaline black liquor, usually by adding carbon dioxide to lower the pH level of the black liquor, and then filtered. The lignin filter cake is then reslurried and washed under acidic conditions, usually using sulfuric acid. The precipitated, washed lignin can be used as is or further dried.

[0007] One problem with using lignin as a precursor to carbon-rich materials is that the direct use of lignin in the form of a fine powder is unsuitable due to its undesirable thermoplastic behavior as well as its strong tendency to form dust. During the thermal conversion of lignin powder to carbon-rich materials, lignin undergoes plastic deformation / melting, severe expansion, and foaming. This severely limits the processability of lignin on an industrially relevant scale in terms of equipment dimensions, process throughput, and the need for intermediate processing. Additionally, dust formation increases the risk of dust explosions during processing.

[0008] The above-mentioned problems with undesirable thermoplastic behavior are particularly pronounced when processing lignins with low glass transition temperatures, such as those obtained from hardwoods, where problems associated with melting, softening, and decomposition begin at relatively low temperatures.

[0009] Therefore, regardless of the source of lignin, there is still room for improvement in methods for producing carbon-rich materials from lignin. The method should avoid plastic deformation / melting, severe expansion, and foaming of the lignin during the heating step and when converting the lignin to the carbon-rich material. The method should also avoid dust formation during lignin processing. In addition, the method should be amenable to large-scale production. Summary of the Invention

[0010] It is an object of the present invention to provide an improved method for producing carbon-rich materials that allows for the use of renewable carbon sources and eliminates or mitigates at least some of the drawbacks of prior art methods.

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

[0012] It is a further object of the present invention to provide a method for producing carbon-rich materials from lignin that allows for heat treatment of the lignin while retaining its shape, regardless of the origin of the lignin.

[0013] A further object of the present invention is to provide a method for avoiding dust formation during processing of powdered lignin.

[0014] It is a further object of the present invention to provide a method for producing carbon-rich materials from lignin that is scalable and therefore suitable for large-scale production.

[0015] The above objectives, as well as other objectives that will be recognized by those skilled in the art in light of this disclosure, are achieved by various aspects of the present disclosure.

[0016] According to a first aspect, the present invention provides a method for producing a carbon material from lignin, comprising the steps of: a) providing lignin; b) providing at least one thermosetting resin; c) contacting the lignin with at least one thermosetting resin to obtain a lignin-thermosetting resin material; d) optionally drying the lignin-thermoset resin material; e) curing the lignin-thermoset resin material or the dried lignin-thermoset resin material to obtain a cured lignin-thermoset resin material; and f) subjecting the cured lignin thermoset material to a heat treatment at one or more temperatures ranging from 300°C to 3000°C to obtain a carbon material, wherein the heat treatment is carried out for a total time ranging from 30 minutes to 10 hours. The present invention relates to a method, comprising:

[0017] It has been surprisingly found that contacting lignin with a thermosetting resin results in a lignin-thermosetting resin material that can be heat-treated while retaining its shape after curing, avoiding melting / expansion and deformation. The method of the present invention also reduces dust formation during lignin processing. Contacting the lignin with a thermosetting resin can be carried out, for example, by coating the lignin with a thermosetting resin or by mixing the lignin with a thermosetting resin. In this way, the lignin-thermosetting resin material can be converted into a carbon-rich material while retaining its shape. Surprisingly, the method of the present invention also facilitates the heat treatment of lignins with low glass transition temperatures, such as lignins obtained from hardwoods.

[0018] According to a second aspect, the present invention relates to a carbon material obtainable by the method according to the first aspect.

[0019] Surprisingly, we found that the lignin-thermoset resin material maintained its shape during heat treatment when converted into a carbon-rich material. The resulting carbon material is suitable for use in energy storage applications, such as the active material for the negative electrodes of secondary batteries.

[0020] According to a third aspect, the present invention relates to an anode for a secondary battery comprising, as active material, a carbon material obtainable by the method according to the first aspect.

[0021] 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 active material in the negative electrode of a secondary battery. DETAILED DESCRIPTION OF THE INVENTION

[0022] Step a) of the method according to the first aspect comprises providing lignin. Throughout this disclosure, the term "lignin" refers to any type of lignin that can be used as a carbon source to produce carbon-rich materials. Examples of lignin include, but are not limited to, lignin obtained from plant materials such as wood, for example, softwood lignin, hardwood lignin, and lignin derived from cyclic plants. Lignin can also be chemically modified.

[0023] Preferably, the lignin has been purified or separated before use in the process of the present invention. The lignin can be separated from the black liquor and optionally further purified before use in the process of the present invention. Purification is typically performed so that the lignin has a purity of at least 90%, preferably at least 95%, and more preferably at least 98%, based on the dry weight of the lignin material. Thus, the lignin material used in accordance with the process of the present invention preferably contains less than 10%, preferably less than 5%, and more preferably less than 2%, of impurities such as cellulose, carbohydrates, inorganic compounds, etc., based on the dry weight of the lignin material.

[0024] Lignin can be obtained by various extraction processes, such as organosolv or kraft processes. Preferably, the lignin used in the process of the present invention is kraft lignin, i.e., lignin obtained by the kraft process. Kraft lignin can be obtained from hardwood or softwood trees.

[0025] Kraft lignin is readily available as a by-product of kraft pulp production. Utilizing kraft lignin, which is typically discarded, is beneficial from a sustainability perspective. Therefore, utilizing kraft lignin allows for more sustainable methods. Kraft lignin can be extracted on an industrial scale by well-known and established processes that result in consistent lignin quality. Kraft lignin is therefore suitable for use in large-scale processing, where process reproducibility is crucial. Extracted kraft lignin can be easily chemically modified or crosslinked, facilitating further processing.

[0026] Lignin can be obtained by the process disclosed in WO2006031175A1, commonly referred to as the LignoBoost process. Typically, this process includes the steps of precipitating lignin from alkaline black liquor by acidification, separating the precipitated lignin, and reslurrying the lignin at least once under acidic conditions. The resulting lignin can be dried and ground to provide solid particles.

[0027] Preferably, the lignin provided in step a) of the method of the first aspect is in the form of a powder, agglomerated lignin, compacts, or a liquid solution.

[0028] In some embodiments, the lignin provided in step a) is in the form of a powder, agglomerated lignin, or compacts. In such embodiments, the lignin provided in step a) is preferably in a dry form. Providing the lignin in a dry form is advantageous because subsequent separation and drying steps are not required, and no solvents are required, thus facilitating processing.

[0029] In some embodiments, the lignin provided in step a) is in powder form. The particle size distribution of the powdered lignin can be such that at least 80% by weight of the particles have a particle size of less than 0.2 mm. The lignin powder can also have a moisture content of less than 45% by weight. Powdered lignin is readily available, for example, from the LignoBoost process, and therefore methods using lignin powder as a starting material do not require additional processing steps to prepare 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.

[0030] In the context of the present invention, the particle size of a particle is the equivalent spherical diameter of the particle if the particle is not spherical. The equivalent spherical diameter is the diameter of a sphere of equivalent volume.

[0031] In some embodiments, the lignin provided in step a) is in the form of agglomerated lignin. The agglomerated lignin can have a particle size distribution such that at least 80% by weight of the agglomerates have a particle size within the range of 0.2 mm to 5.0 mm. One method for obtaining such agglomerated lignin is described in WO2020183383A1.

[0032] Briefly, purified, preferably dried, lignin powder is compacted, and the compacted lignin is pulverized to obtain agglomerated lignin. The compaction of lignin is preferably carried out by roll compaction. The compaction process produces an intermediate product. Here, fine lignin powder is typically fed through a hopper and conveyed by a horizontal or vertical feed screw to a compaction zone, where the material is compacted into flakes by compaction rollers with a defined gap. By controlling the feed screw speed and the pressure generated in the compaction zone, flakes of uniform density can be obtained. The pressure generated in the compaction zone is preferably monitored and can be controlled by the rotation speed of the compaction rolls. As the powder is drawn between the rollers, it enters a region called the nip region, where the density of the material increases, converting the powder into flakes or ribbons. The rolls used have cavities. The depth of each cavity used in roll compaction is 0.1 mm to 10 mm, preferably 1 mm to 8 mm, more preferably 1 mm to 5 mm or 1 mm to 3 mm. The specific pressure applied during compaction may vary depending on the equipment used for compaction, but may range from 1 kN / cm to 100 kN / cm. Equipment suitable for carrying out compaction is known in the art.

[0033] In the crushing step, the intermediate product from the compaction step is subjected to crushing or grinding, such as by a rotary granulator, cage mill, beater mill, hammer mill, or crusher mill, and / or combinations thereof. During this step, further intermediate products are produced.

[0034] After crushing, the crushed material is preferably subjected to a sieving process to remove fine materials. Additionally, larger materials, such as agglomerates with a particle size greater than 5.0 mm, may be removed and / or recycled to the crushing process.

[0035] Agglomeration of lignin results in agglomerated lignin with improved thermal properties, such as reduced tendency to melt / foam and deform during heating. The tendency to form dust during processing is also reduced by the agglomeration process. Thus, in embodiments where the lignin is provided in the form of agglomerated lignin, the combination of the lignin being in an agglomerated form and the presence of a thermoset resin improves the ability of the lignin-thermoset resin material to retain its shape during heat treatment.

[0036] 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 predetermined shape by thermal treatment or shaping of the lignin. Non-limiting examples of such shaped bodies include pellets, granules, sheets, fibers, rods, bars, tablets, etc. The size and dimensions of the shaped body are not limited. Thus, the method of the present invention can be applied to objects of various sizes and shapes.

[0037] In some embodiments, the lignin provided in step a) is in the form of a liquid solution. The lignin may be dissolved in any suitable solvent to form a liquid solution, such that the liquid solution comprises dissolved lignin and at least one solvent. The solvent can be, for example, an aqueous alkaline solution, a polar protic solvent such as dimethyl sulfoxide or dimethyltryptamine, or a polar aprotic solvent such as an alcohol or an amine. The lignin may also be dissolved in a polymer melt. The amount of lignin in the liquid solution preferably ranges from 10 to 95 wt. %, e.g., 10 to 70 wt. %, or 10 to 50 wt. %, or 10 to 30 wt. %, based on the total weight of the liquid solution. Providing the lignin in the form of a liquid solution can facilitate subsequent contact with a thermosetting resin, particularly in embodiments where the thermosetting resin is provided in liquid form. In some embodiments, the liquid solution comprises more than one solvent.

[0038] Step b) of the method of the first embodiment comprises providing at least one thermosetting resin. As used herein, the term "thermosetting resin" refers to a resin that is irreversibly hardened by curing. The term "thermosetting resin" is not intended to cover precursors of thermosetting resins, but only resins that are obtained by reaction of one or more precursors.

[0039] The type of thermosetting resin is not particularly limited, and any suitable thermosetting resin can be used in the method of the present invention. In some embodiments, the at least one thermosetting resin can be 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. Preferably, the thermosetting resin is a furan resin such as polyfurfuryl alcohol.

[0040] Preferably, at least one thermosetting resin is provided in solid and / or liquid form, for example, if more than one thermosetting resin is provided, one may be in solid form and another in liquid form.

[0041] In some embodiments, at least one thermosetting resin is provided in liquid form. Optionally, the liquid thermosetting resin may be diluted using a solvent. Dilution of the liquid thermosetting resin is preferred when the thermosetting resin has a high viscosity to facilitate subsequent contacting steps. Providing the thermosetting resin in liquid form reduces the tendency for dust formation during processing of the lignin after contacting the lignin with the thermosetting resin and facilitates handling.

[0042] In some embodiments, the at least one thermosetting resin is provided in a solid form, such as in the form of a powder. Providing the thermosetting resin in a solid form facilitates the process of mixing the thermosetting resin with the lignin powder. Dry mixing is advantageous from a cost perspective because it requires fewer process steps, as no solvent is required, and separation and drying of the lignin and / or thermosetting resin is not required.

[0043] In some embodiments, one thermosetting resin is provided in step b). In some embodiments, more than one thermosetting resin is provided in step b), for example, 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.

[0044] Step c) of the method of the first aspect comprises contacting lignin with at least one thermosetting resin to obtain a lignin-thermosetting resin material. As used herein, the term "lignin-thermosetting resin material" refers to a material comprising both lignin and at least one thermosetting resin. The lignin-thermosetting resin material may optionally include at least one additive. For example, the lignin may be coated or impregnated with the thermosetting resin, or the lignin and thermosetting resin may form a mixture.

[0045] The lignin-thermoset resin material of the present invention is a composite material comprising lignin and at least one thermosetting resin. The lignin is contacted with a thermosetting resin, but not with a precursor of the thermosetting resin. Thus, the lignin-thermoset resin material of the present invention is not a lignin-based thermosetting resin. Such a lignin-based thermosetting resin could be obtained, for example, by reacting lignin with a precursor of the thermosetting resin. In the present invention, the lignin is not modified by contacting it with the thermosetting resin, and the primary polymer structure of the lignin is not changed.

[0046] In one embodiment, the total amount of thermosetting resin in the lignin-thermoset resin material ranges from 1 wt % to 70 wt %, e.g., 1 wt % to 50 wt %, 1 wt % to 20 wt %, or 1 wt % to 10 wt %, based on the total dry weight of the lignin-thermoset resin material. By "total amount of thermosetting resin" is meant the total amount of all thermosetting resins present in the lignin-thermoset resin material.

[0047] In preferred embodiments, the total amount of thermosetting resin in the lignin-thermoset resin material ranges from 1 wt. % to 20 wt. %, or 1 wt. % to 10 wt. %, or 1 wt. % to 5 wt. %, based on the total weight of the lignin-thermoset resin material. Forming a lignin-thermoset resin material with a small amount of thermosetting resin is advantageous because the material is then primarily composed of materials from renewable resources, allowing for a more sustainable process. The cost of lignin is also typically lower than the cost of thermosetting resin. A small amount of thermosetting resin, such as 1 wt. % to 5 wt. %, based on the total weight of the lignin-thermoset resin material, is sufficient to improve the thermal properties of the material and prevent the lignin from melting / expanding during heat treatment.

[0048] In some embodiments, the thermoset resin may be derived from renewable resources. In such embodiments, the lignin-thermoset resin material may be completely renewable.

[0049] The lignin-thermoset resin material comprises 30 to 99 wt%, or 50 to 99 wt%, or 80 to 99 wt%, or 90 to 99 wt%, of lignin, based on the total weight of the lignin-thermoset resin material. Preferably, the lignin-thermoset resin material comprises 80 to 99 wt%, or 90 to 99 wt%, or 95 to 99 wt%, of lignin, based on the total weight of the lignin-thermoset resin material.

[0050] The lignin-thermoset resin material may include only lignin and a thermoset resin, or may include lignin, a thermoset resin, and at least one additive, the amount of the at least one additive being typically small, such as less than 5% by weight, or less than 2% by weight, based on the total weight of the lignin-thermoset resin material.

[0051] As used herein, the term "contacting" refers to a process of bringing lignin and at least one thermosetting resin into close proximity with one another, for example, 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 the thermosetting resin and reactive sites on the lignin during the contacting step.

[0052] In preferred embodiments of the present invention, the lignin-thermoset resin material comprises 80 to 99 wt. %, or 90 to 99 wt. %, or 95 to 99 wt. % lignin, based on the total weight of the lignin-thermoset resin material. In such embodiments, the amount of lignin is always significantly greater than the amount of thermoset resin in the contacting step. Thus, if any chemical reaction occurs between the thermoset resin and the lignin, only a small portion of the lignin in the agglomerated lignin-thermoset resin material reacts, while the majority of the lignin remains unchanged by the contacting step.

[0053] In some embodiments, the contacting step comprises coating or impregnating the lignin with at least one thermosetting resin. In such embodiments, the thermosetting resin is preferably in liquid form and the lignin is preferably in solid form, i.e., powder form, agglomerated lignin form, or compact form. Any suitable method known to those skilled in the art can be used, such as spray coating or dip coating. Coating or impregnating the lignin with a thermosetting resin results in an outer layer of thermosetting resin on the solid lignin. After curing, this provides a hard, protective layer on the solid lignin, reducing dust formation and also reducing the tendency of individual particles of the solid lignin to stick together due to surface melting / softening during subsequent heat treatment.

[0054] In some embodiments, the contacting comprises mixing the lignin with at least one thermosetting resin. In such embodiments, the thermosetting resin can be in liquid or solid form, and the lignin can be in powder form, agglomerated lignin form, compact form, or liquid solution form. The mixing can be carried out using any method known to those skilled in the art. Both dry and wet mixing methods can be used. One example of a suitable method is a vertical mixer, such as a paddle, screw, or ribbon screw mixer, in batch or continuous mode. The mixing process can be carried out in low, medium, or high shear impact mode.

[0055] In embodiments where at least one thermosetting resin is provided in liquid form and the lignin is provided in dry form, the lignin is insoluble or only slightly soluble in the thermosetting resin.

[0056] In some embodiments, a solvent is present during the contacting step. The presence of the solvent facilitates contact between the lignin and the thermosetting resin and may facilitate further processing steps, such as forming a lignin-thermosetting resin material. Any solvent suitable for thermosetting resins can be used, such as water, tetrahydrofuran, or dichloromethane. The solvent can be added during contacting, e.g., before contacting with the thermosetting resin or during mixing. In embodiments where the lignin is provided in the form of a liquid solution, the solvent can be added to the liquid solution containing the dissolved lignin.

[0057] The lignin-thermoset resin material may optionally contain additives. Any suitable additive, such as a binder or lubricant, can be added to facilitate the subsequent forming or agglomeration process and / or to improve the density and mechanical properties of the lignin-thermoset resin material. In addition, additives that affect the properties of the final carbon material, such as additives that enhance functionality, can also be added. The total amount of additives is preferably less than 5 wt. %, e.g., less than 2 wt. %, based on the total dry weight of the additives and the lignin thermoset resin material. In one embodiment, the additives are added to the lignin-thermoset resin material before curing the lignin-thermoset resin material. The additives can also be added to the lignin and / or the thermoset resin before contacting the lignin with the thermoset resin.

[0058] In some embodiments, the method of the first aspect includes the additional step of forming the resulting lignin-thermoset resin material before curing. Forming can be performed by at least one means selected from the group consisting of molding, pressing, pelletizing, kneading, granulating, and extruding the lignin-thermoset resin material. The size and shape of the formed lignin-thermoset resin material vary depending on the means used for forming. The type, amount, and form of the at least one thermosetting resin provided in step b) can be selected depending on the means used to form the lignin-thermoset resin material. The forming means can also influence the choice of thermosetting resin. Conducting the contacting in step c) in the presence of a solvent can facilitate subsequent forming of the lignin-thermoset resin material. Forming the lignin-thermoset resin material can facilitate subsequent processing. Depending on the type of furnace used in the process, different shapes of the lignin-thermoset resin material are preferred. For rotary kilns, small granules or pellets are useful. For batch production furnaces, the lignin-thermoset resin material is preferably cylindrical or brick-shaped.

[0059] In some embodiments, the formed lignin-thermoset resin material may be crushed or ground prior to subsequent processing steps to reduce the size of the formed lignin-thermoset resin material. Crushing or grinding of the formed lignin-thermoset resin material is preferably performed when forming means such as molding, pressing, or kneading are used that result in the formation of large agglomerated pieces of the lignin-thermoset resin material. The large pieces are preferably crushed or ground to facilitate further processing into a carbonaceous material. Crushing or grinding may be performed after curing of the lignin-thermoset resin material or after partial curing of the lignin-thermoset resin material. If crushing or grinding is performed after partial curing, additional curing may be performed after crushing or grinding. Crushing or grinding may be performed using any suitable means known to those skilled in the art.

[0060] Step d) of the method of the first aspect optionally involves drying the resulting lignin-thermoset resin material. Drying can be carried out at room temperature and / or elevated temperature. Drying can be carried out using any suitable means known to those skilled in the art. Drying can be carried out under normal 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 one or more temperatures below 60°C, for example, in the range of 30°C to 60°C, for a time period ranging from 5 minutes to 10 hours. After drying, the dry content of the lignin-thermoset resin material is at least 50% by weight, for example, at least 70% by weight, or at least 80% by weight. The drying step is particularly important in embodiments where the thermoset resin is diluted with a solvent, to remove the solvent.

[0061] Step e) of the method of the first aspect comprises curing the lignin-thermoset resin material or the dried lignin-thermoset resin material to obtain a cured lignin-thermoset resin material. Curing can be carried out at room temperature and / or at an elevated temperature. Increasing the temperature will result in faster curing. The temperature required for curing will also vary depending on the type of thermoset resin.

[0062] In some embodiments, curing is carried out at one or more temperatures ranging from 20°C to 250°C, e.g., from 20°C to 200°C, or from 20°C to 150°C, or from 50°C to 150°C, for a total time of at least 30 minutes, i.e., the residence time of the lignin-thermoset resin material in the equipment used for curing is at least 30 minutes. The total curing time is preferably less than 24 hours. During curing, irreversible curing of the at least one thermoset resin occurs. After curing, a lignin-thermoset resin material is obtained that does not change shape during subsequent heat treatment. Additionally, the addition of a thermoset resin to the lignin reduces the melting / swelling behavior of the lignin during heating.

[0063] In preferred embodiments, curing is carried out for a total time of at least 30 minutes at one or more temperatures ranging from 20° C. to 150° C., or from 50° C. to 150° C. In such embodiments, the lignin exhibits no or only minimal melting / swelling behavior.

[0064] In embodiments in which the lignin is coated with at least one thermosetting resin, the inventors believe that, after curing, the cured thermosetting resin holds the lignin within the lignin-thermosetting resin material, preventing the lignin from melting / swelling during subsequent heat treatment at temperatures at which lignin normally exhibits melting / swelling behavior.

[0065] In embodiments where lignin is mixed with at least one thermosetting resin, it is believed that after curing a matrix of thermosetting resin is formed and the lignin is contained within the matrix, thereby preventing the lignin from melting / swelling during subsequent heat treatment at temperatures at which lignin normally exhibits melting / swelling behavior.

[0066] In some embodiments, lignin may react with the thermosetting resin during curing. In other embodiments, reactions occurring during curing are limited to within the thermosetting resin. In some embodiments, reactions between lignin polymer chains occur during curing. Thus, crosslinking reactions may occur within the thermosetting resin during curing, and may occur between the thermosetting resin and lignin, and / or between different lignin polymer chains. Crosslinking reactions between the lignin and thermosetting resin, as well as between different lignin polymer chains, reduce the melting / swelling behavior of the lignin during a subsequent heating step at temperatures where lignin normally exhibits melting / swelling behavior. Crosslinks within the thermosetting resin may create physical constraints that prevent the lignin from melting / swelling.

[0067] What reactions occur during curing, other than crosslinking of the thermosetting resin, depends, for example, on the temperature and the type of thermosetting resin used.

[0068] In some embodiments, curing is carried out using the same temperature throughout the curing process, for example, curing may be carried out at room temperature for a total time of at least 30 minutes.

[0069] In some embodiments, curing is carried out at various temperatures, such as using a stepwise temperature increase or using a temperature gradient. In some embodiments, curing is carried out in several steps at different temperatures. The temperature can be increased from one step to the next using a temperature ramp or gradient. For example, curing can be carried out by heating the lignin-thermoset material to a first temperature ranging from 20° C. to 250° C., such as from 20° C. to 200° C., or from 20° C. to 150° C., or from 0° C. to 150° C., followed by heating to a second temperature ranging 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., and holding at each selected temperature for a predetermined time, such as from 10 minutes to 3 hours. By carrying out curing in several steps at different temperatures, improved crosslinking of the cured lignin-thermoset material can be achieved. Additionally, the curing process can be carried out in a more controlled manner, reducing the risk of cracking of the lignin-thermoset material during curing.

[0070] In some embodiments, curing is immediately followed by a heat treatment. For example, curing can be carried out initially at one or more temperatures ranging from 20° C. to 250° C., e.g., 20° C. to 200° C., 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 temperature increase can be stepwise or can include a temperature ramp. Thus, in some embodiments, curing can be carried out in the same reactor as the subsequent heat treatment.

[0071] In some embodiments, an acid 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 the acid catalyst. The acid catalyst may be selected from sulfuric acid, maleic anhydride, or p-toluenesulfonic acid. The curing using the catalyst can be carried out at room temperature and / or at an elevated temperature. Curing is faster at elevated temperatures.

[0072] Curing can be achieved using both a catalyst and elevated temperature, or by catalyst alone, or elevated temperature alone.

[0073] If the lignin-thermoset material is not dried prior to curing at elevated temperatures, drying can occur simultaneously with curing.

[0074] Preferably, the method includes the additional step of grinding the cured lignin thermoset resin material. Grinding is performed to reduce the average particle size. Grinding can also be performed on the carbon material obtained after heat treatment of the cured lignin thermoset resin material. Grinding can be performed by methods such as impact grinding, hammer grinding, ball grinding, and jet grinding. Optionally, grinding can be followed by fine / coarse particle separation by classification and / or sieving.

[0075] The method of the first aspect may include multiple grinding steps. For example, if the lignin-thermoset resin material has been formed into large agglomerated pieces, an initial crushing or grinding step may be followed by subsequent grinding steps. Grinding may be performed both after curing and after heat treatment.

[0076] Step f) of the method according to the first aspect comprises subjecting the cured lignin-thermoset resin material to a heat treatment at one or more temperatures in the range of from 300° C. to 3000° C. The heat treatment is carried out for a total time in the range of from 30 minutes to 10 hours so as to obtain a carbon material, i.e. the residence time of the lignin-thermoset resin material in the equipment used for the heat treatment is in the range of from 30 minutes to 10 hours.

[0077] As used herein, the term "heat treatment" refers to a process in which a lignin-thermoset resin material is heated at one or more temperatures for a sufficient time to increase the carbon content of the lignin-thermoset resin material and convert it into a carbon material. Depending on the temperature during heat treatment, different types of carbon materials, such as charcoal or hard carbon, can be obtained from the lignin-thermoset resin material.

[0078] The terms "carbon material" and "carbon-rich material" are both used herein to denote a material that consists primarily of carbon, such as at least 80% by weight, or at least 90% by weight, or at least 95% by weight, and that is obtained by carbonization of an organic compound.

[0079] The heat treatment may be carried out at the same temperature throughout the heat treatment, or at varying temperatures, such as by increasing the temperature stepwise or using a temperature gradient. The heat treatment may include a temperature ramp from a starting temperature to a target temperature. The heating rate may be 1 to 100°C / min. For example, the heat treatment may include several intermediate temperatures with temperature ramps between them before reaching the target temperature required for carbonization of the lignin-thermoset resin material. The heat treatment may be carried out as a batch or continuous process. Any suitable reactor may be used, such as a rotary kiln, a moving bed furnace, a pusher furnace, or a rotary hearth furnace. The heat treatment is preferably carried out under an inert atmosphere, preferably a nitrogen atmosphere.

[0080] Preferably, the heat treatment includes a preheating step, preferably followed by a final heating step. The preheating step is preferably carried out at one or more temperatures in the range of 300°C to 800°C, for example 500°C to 700°C. The preheating step is preferably carried out under an inert atmosphere, preferably a nitrogen atmosphere. The duration of the preheating step is at least 30 minutes, preferably less than 10 hours. The surface area of ​​the carbon material obtained after the preheating step is typically between 300 and 700 m, measured as BET using nitrogen gas. 2 / g range.

[0081] The final heating step is preferably carried out at one or more temperatures in the range of 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, preferably less than 10 hours. After a final heating step carried out at 1000°C or above, the surface area of ​​the resulting carbon material is typically 50 m 2 / g or less.

[0082] The preliminary and final heating steps can be performed as separate steps or directly in succession as a single step. The preliminary and final heating steps can include heating at one or more temperatures, as discussed above for heat treatment. For example, preliminary heating can begin at about 300°C, and the temperature can then be increased to about 500°C. The final heating step is preferably performed at a temperature between 900°C and 1300°C, e.g., about 1000°C.

[0083] The preliminary and final heating steps 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. The preliminary and final heating steps can be carried out in the same reactor or in separate reactors.

[0084] If milling is performed, it can be performed between the pre-heating step and the final heating step, or after the final heating step.

[0085] After heat treatment, the resulting carbon material may be subjected to further processing, such as carbon coating by chemical vapor deposition (CVD), pitch coating, thermal and / or chemical refining, further heat treatment, particle size adjustment, and blending with other electrode materials, for example, to further improve its electrochemical performance.

[0086] According to a second aspect, the present invention relates to a carbon material obtainable by the method according to the first aspect. The carbon material obtainable by the method according to the first aspect is suitable for use in energy storage applications, for example as an active material in the negative electrode of a secondary battery. The carbon material according to the second aspect may be further defined as set out above with reference to the first aspect.

[0087] The carbonaceous 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 manufacture such a negative electrode, any suitable method for forming such a negative electrode can be utilized. In forming the negative electrode, the carbon-rich material can be processed with additional components. Such additional components can include, for example, one or more binders for forming the carbon-rich material into an electrode, a conductive material, such as carbon black, carbon nanotubes, or a metal powder, and / or an additional Li-storage material, such as graphite or lithium. For example, the binder can be selected from, but is not limited to, poly(vinylidene fluoride), poly(tetrafluoroethylene), carboxymethyl cellulose, natural butadiene rubber, synthetic butadiene rubber, polyacrylate, poly(acrylic acid), alginate, etc., or a combination thereof. Optionally, a solvent, such as 1-methyl-2-pyrrolidone, 1-ethyl-2-pyrrolidone, water, or acetone, is utilized during processing.

[0088] According to a third aspect, the present invention relates to an anode 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 anode according to the third aspect may be further defined as described above with reference to the first aspect.

[0089] 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 the negative electrode of a secondary battery. The carbon material of the fourth aspect may be further defined as described above with reference to the first aspect. [Example]

[0090] Example 1 Softwood or hardwood lignin powder obtained from the LignoBoost process was mixed with liquid polyfurfuryl alcohol to obtain a mixture. The amount of polyfurfuryl alcohol added was 10 wt.% based on the dry weight of the lignin. Water (25 wt.% based on the amount of polyfurfuryl alcohol) was added to the mixture to form a dough-like material. The dough-like material was molded or pelletized into smaller objects and dried at room temperature for 12 hours. After drying, a stepwise curing process was carried out, where the material was heated at 50°C for 1 hour, 70°C for 1 hour, 90°C for 1 hour, and 150°C for 1 hour. During the curing process, the material gradually darkened. After curing, the small objects were crushed and pulverized to particle sizes ranging from 0.5 mm to 2 mm. After crushing and grinding, the material was carbonized at temperatures ranging from 500°C to 1400°C under an inert atmosphere. For both hardwood and softwood derived lignins, no melting, fusion, or expansion was observed during the heat treatment, and the materials retained their shape after carbonization.

[0091] Example 2 Softwood or hardwood lignin powder obtained from the LignoBoost process was mixed with Bakelite powder or cryo-ground polyfurfuryl alcohol to obtain a mixture. The amount of resin (e.g., Bakelite or polyfurfuryl alcohol) added was 10 wt% based on the dry weight of the lignin. A homogeneous mixture of two powders (e.g., lignin and resin) was obtained. The powder mixture was pressed into large bodies or pellets. After pressing, curing was carried out in stages, with the material heated at 50°C for 1 hour, 70°C for 1 hour, 90°C for 1 hour, and 150°C for 1 hour. The material gradually darkened during the curing process. After curing, the bodies or pellets were crushed and pulverized to particle sizes ranging from 0.5 mm to 2 mm. After crushing and grinding, the material was carbonized at temperatures ranging from 500°C to 1400°C under an inert atmosphere. For both hardwood and softwood derived lignins, no melting, fusion, or expansion was observed during the heat treatment, and the materials retained their shape after carbonization.

[0092] Example 3 - Comparative Example Softwood or hardwood lignin powder obtained from the LignoBoost process was carbonized in an inert atmosphere at temperatures ranging from 500 to 1400°C. The lignin powder melted and foamed during carbonization, resulting in a single foam-like solid after carbonization.

[0093] It should be apparent that other modifications and variations will be apparent to those skilled in the art in view of the above detailed description of the invention, and that such other modifications and variations can be made without departing from the spirit and scope of the invention.

Claims

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

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

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

4. 4. The method according to claim 1, 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. 5. The method of claim 1, wherein the at least one thermosetting resin is provided in solid and / or liquid form.

6. 6. The method of any one of claims 1 to 5, wherein the total amount of thermosetting resin in the lignin-thermoset resin material is in the range of 1 to 70 wt%, based on the total dry weight of the lignin-thermoset resin material.

7. 7. The method of any one of claims 1 to 6, wherein the contacting step comprises coating or impregnating the lignin with at least one thermosetting resin.

8. 7. The method of claim 1, wherein the contacting step comprises mixing the lignin with at least one thermosetting resin.

9. 9. The method of claim 1, wherein a solvent is present during the contacting step.

10. 10. The method of any one of claims 1 to 9, including the additional step of forming a lignin-thermoset resin material before curing.

11. 11. The method of claim 10, wherein the step of forming the lignin-thermoset resin material is carried out by at least one means selected from the group consisting of molding, pressing, pelletizing, kneading, granulating, or extruding the lignin-thermoset resin material.

12. 12. The method of any one of claims 1 to 11, wherein curing is carried out at one or more temperatures in the range of 20°C to 250°C for a total time of at least 30 minutes.

13. 13. The method of any one of claims 1 to 12, wherein an acidic catalyst is added to the at least one thermosetting resin provided in step b), and the curing of the lignin-thermosetting resin material in step e) is catalyzed by the acidic catalyst.

14. 14. The method of any one of claims 1 to 13, comprising the additional step of grinding the cured lignin-thermoset resin material.

15. 15. The method according to any one of claims 1 to 14, wherein the heat treatment in step f) comprises a pre-heating step followed by a final heating step.

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

17. 17. The method of claim 15 or 16, wherein the preheating step is carried out under an inert atmosphere.

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

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

20. 20. A carbon material obtainable by the method 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. 20. Use of a carbon material obtainable by the method according to any one of claims 1 to 19 as active material in the negative electrode of a secondary battery.

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