Method for producing granular carbon-carbon composites from lignin-carbon composites

Abstract

The present invention relates to a method for producing a thermally stabilized agglomerated lignin-carbon composite, the method comprising the steps of providing an agglomerated lignin-carbon composite comprising lignin and at least one carbon additive, and heating the agglomerated lignin-carbon composite to obtain a thermally stabilized agglomerated lignin-carbon composite. The present invention also relates to a granular carbon-carbon composite obtained by heat treating the thermally stabilized agglomerated lignin-carbon composite.

Description

[Technical field]

[0001] The present invention relates to a method for producing a thermally stabilized agglomerated lignin-carbon composite material. The present invention also relates to a thermally stabilized lignin-carbon composite material. Furthermore, the present invention relates to a method for producing a granular carbon-carbon composite material and a granular carbon-carbon composite material obtained by said method, the granular carbon-carbon composite material being produced from said thermally stabilized agglomerated lignin-carbon composite material. Furthermore, the present invention relates to a carbon-carbon composite powder obtained from said granular carbon-carbon composite material and an anode for a non-aqueous secondary battery comprising said carbon-carbon composite powder as an active material. The present invention further relates to the use of said carbon-carbon composite powder as an active material for an anode of a non-aqueous secondary battery. [Background technology]

[0002] Secondary batteries, such as lithium-ion batteries, are electric cells that can be charged and discharged many 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 to the positive electrode during charging. Typically, lithium compounds, in particular lithium nickel manganese cobalt oxide (NMC) or alternatively lithium metal oxides such as lithium iron phosphate (LFP), are used as the positive electrode material and carbon-rich materials are used as the negative electrode material.

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

[0004] Amorphous carbon is produced from lignin, an aromatic polymer that is the main component of wood and one of the most abundant carbon sources on Earth. In recent years, the development and commercialization of techniques to extract highly purified, solid, particulate lignin from the pulp manufacturing process has attracted considerable attention as a renewable alternative to the primarily aromatic chemical precursors currently supplied by the petrochemical industry. Lignin-derived amorphous carbon is typically non-graphitizable, i.e., it is a hard carbon.

[0005] Currently, 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 WO2006031175 A1. In this process, lignin is precipitated from alkaline black liquor by adding acid and then filtered. The lignin filter cake is then reslurried under acidic conditions and washed before drying and grinding.

[0006] One of the problems with using lignin as a precursor for carbon-enriched materials is that the direct use of lignin in the form of a fine powder is unsuitable due to its undesirable thermoplastic behavior. 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 industrial scale in terms of equipment dimensions and process throughput as well as the need for intermediate processing.

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

[0008] US 6099990 A describes a method for producing a carbon material which comprises mixing lignin powder with salt and then heating the mixture in multiple steps, including a carbonization step.

[0009] Therefore, there is still room for improvement in the method of producing carbon-rich materials from lignin. The method should avoid the plastic deformation of lignin, which causes melting, or the severe expansion and foaming during heating and conversion of lignin into carbon-enriched substances. Furthermore, 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-enriched materials that allows for the use of renewable carbon sources and eliminates or mitigates at least some of the disadvantages 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-enriched material suitable for use as active material in the negative electrodes of secondary batteries, such as lithium-ion batteries.

[0012] It is a further object of the present invention to provide a method for producing carbon rich materials from lignin that allows the lignin to be heat treated while retaining its shape and size.

[0013] It is a further object of the present invention to provide a method for improving the mechanical and thermal processability of lignin.

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

[0015] The above objectives, as well as other objectives which will be realized by one skilled in the art in light of the present disclosure, are accomplished by various aspects of the present disclosure.

[0016] According to a first aspect, the present invention relates to a method for producing a thermally stabilized agglomerated lignin-carbon composite material, comprising: a) providing an agglomerated lignin-carbon composite material having a particle size distribution such that at least 80% by weight of the agglomerates have a diameter within the range of 0.2 mm to 5.0 mm, the agglomerated lignin-carbon composite material comprising lignin and at least one carbon additive; b) heating the agglomerated lignin-carbon composite to a temperature of 140-250° C. for at least 30 minutes to obtain a thermally stabilized agglomerated lignin-carbon composite.

[0017] Surprisingly, it has been found that lignin, agglomerated into macroscopic particles and thermally stabilized, can be heat treated while avoiding melting / expansion and deformation and retaining its shape and dimensions.

[0018] Surprisingly, it has also been found that the mechanical and thermal processability of the agglomerated lignin is improved by the addition of at least one carbon additive. At least one carbon additive is dispersed within the lignin matrix to form an agglomerated lignin-carbon composite. The carbon additive improves the heat resistance of the agglomerated lignin-carbon composite by reducing the melting / expansion behavior upon heating, thereby improving its processability on an industrial scale. The processability of the lignin is further improved by combining thermal stabilization with the addition of a carbon additive.

[0019] According to a second aspect, the present invention relates to a thermally stabilized agglomerated lignin-carbon composite material having a particle size distribution such that at least 80% by weight of the agglomerates have a diameter in the range of 0.2 mm to 5.0 mm, the thermally stabilized agglomerated lignin-carbon composite material comprising lignin and at least one carbon additive. The thermally stabilized agglomerated lignin-carbon composite material of the second aspect is obtainable by the method according to the first aspect.

[0020] According to a third aspect, the present invention provides a method for producing a granular carbon-carbon composite material, comprising the steps of: 1) providing a thermally stabilized agglomerated lignin-carbon composite material obtainable by a method according to the first aspect; 2) subjecting the thermally stabilized agglomerated lignin-carbon composite material to a heat treatment at one or more temperatures in the range of 300° C. to 1500° C., the heat treatment being carried out for a total period in the range of 30 minutes to 10 hours, so as to obtain a granular carbon-carbon composite material; The present invention relates to a method comprising the steps of:

[0021] Surprisingly, it has been found that providing lignin in the form of a thermally stabilized agglomerated lignin-carbon composite facilitates the production of carbon-enriched materials from lignin because the thermally stabilized agglomerated lignin-carbon composite retains its dimensional integrity during further processing into a carbon-enriched material.

[0022] By appropriately selecting the at least one carbon additive, e.g., with respect to particle size and amount, the processability of the lignin-carbon composite and the functionality of the resulting carbon enriched material, i.e., granular carbon-carbon composite, can be fine-tuned.

[0023] The granular carbon-carbon composite material obtained by the method according to the third aspect may also be used in applications such as activated carbon and biochar.

[0024] According to a fourth aspect, the present invention relates to a granular carbon-carbon composite material obtainable by the method according to the third aspect.

[0025] According to a fifth aspect, the present invention relates to a carbon-carbon composite powder obtainable by grinding a granular carbon-carbon composite material obtained by the method according to the third aspect.

[0026] According to a sixth aspect, the present invention relates to a negative electrode for a non-aqueous secondary battery comprising the carbon-carbon composite powder according to the fifth aspect.

[0027] According to a seventh aspect, the present invention relates to the use of the carbon-carbon composite powder according to the fifth aspect as an active material in the negative electrode of a non-aqueous secondary battery. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] Step a) of the method according to the first aspect of the present invention comprises providing an agglomerated lignin-carbon composite material having 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, preferably from 0.5 mm to 2.0 mm, said agglomerated lignin-carbon composite comprising lignin and at least one carbon additive.

[0029] In the context of the present invention, the diameter 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.

[0030] Providing the lignin-carbon composite in an agglomerated form results in a more compact and harder material. Hard particles are advantageous for subsequent processing since they can withstand physical impacts during processing. Additionally, the particles are closer together in the agglomerated composite, enhancing interactions between the particles within the composite.

[0031] In one embodiment of the method according to the first aspect, the bulk density of the agglomerated lignin-carbon composite material is between 0.4 and 0.7 g / cm 3 , preferably 0.5 to 0.7 g / cm 3 is in the range.

[0032] The term "lignin" as used herein refers to any type of lignin that can be used as a carbon source to produce carbon-enriched materials. Examples of said lignin include, but are not limited to, lignins obtained from plant sources such as wood, e.g., coniferous lignin, hardwood lignin, and lignins from annular plants. Lignin can also be chemically modified.

[0033] Preferably, the lignin is purified or isolated prior to use in the method according to the present disclosure. The lignin is isolated from the black liquor and may optionally be further purified prior to use in the method according to the present disclosure. Purification is typically carried out such that the purity of the lignin is at least 90%, preferably at least 95%. Thus, the lignin used according to the method of the present invention preferably contains less than 10%, more preferably less than 5%, of impurities such as cellulose, ash, and / or moisture.

[0034] Preferably, the lignin contains less than 1% ash, more preferably less than 0.5% ash.

[0035] Lignin can be obtained by various fractionation methods such as the organosolv process or the Kraft process. For example, lignin can be obtained using the method disclosed in WO2006031175 A1.

[0036] Preferably, the lignin used in the process according to the first aspect of the invention is kraft lignin, i.e. lignin obtained by the kraft process. Preferably, the kraft lignin is obtained from hardwoods or softwoods, most preferably from softwoods.

[0037] The term "carbon" as used herein in phrases such as "lignin-carbon composite" and "carbon-carbon composite" refers to carbon derived from any type of carbon additive that is added during the processing of lignin into a carbon enriched material and forms a composite with the lignin. The carbon can be produced from any type of carbon additive that can be used as a functional enhancer for the lignin-derived carbon enriched material. The term also includes carbon derived from any type of carbon additive that can be used to form a lignin-carbon composite, improving the thermal and mechanical processability of the composite when preparing a carbon-rich material starting from a lignin-carbon composite.

[0038] The term "carbon additive" as used herein includes carbonaceous materials such as graphite, graphene, carbon nanotubes, charcoal, biochar, hard carbon, soft carbon, carbon black, carbon fiber, conductive carbon, etc. The carbon content in the carbon additive is at least 80% by weight, such as at least 90% by weight, or at least 95% by weight. The term "carbon additive" as used herein does not refer to carbon atoms themselves.

[0039] The term "lignin-carbon composite" as used herein in terms such as "agglomerated lignin-carbon composite" and "thermally stabilized agglomerated lignin-carbon composite" refers to a composite material comprising lignin and one or more carbon additives, such as a composite material comprising lignin and graphite, a composite material comprising lignin and hard carbon, or a composite material comprising lignin, graphite, and hard carbon. The term "lignin-carbon composite" further refers to a material that essentially comprises lignin and one or more carbon additives, where at least 95% by weight, or at least 98% by weight, of the lignin-carbon composite is made up of lignin and one or more carbon additives, based on the dry weight of the lignin-carbon composite. The lignin-carbon composite may also optionally comprise a small amount, such as less than 5% by weight, or less than 2% by weight, of at least one additive. In the lignin-carbon composite, the one or more carbon additives are uniformly dispersed within the lignin matrix.

[0040] The carbon in the agglomerated lignin-carbon composite is in the form of at least one carbon additive. In some embodiments, the amount of the at least one carbon additive in the agglomerated lignin-carbon composite is in the range of 0.1-60 wt%, or 0.1-30 wt%, or 0.1-10 wt%, based on the dry weight of the agglomerated lignin-carbon composite. In some embodiments, the amount of the at least one carbon additive in the agglomerated lignin-carbon composite is in the range of 10-60 wt%, or 10-40 wt%, or 20-40 wt%, based on the dry weight of the agglomerated lignin-carbon composite. The amount of the at least one carbon additive may depend on the type of carbon additive and its desired function in the composite. For certain carbon additives, such as carbon nanotubes and graphene, the amount of the carbon additive in the agglomerated lignin-carbon composite is preferably low, for example, in the range of 0.1-5 wt%, based on the dry weight of the agglomerated lignin-carbon composite. For other carbon additives, such as graphite, the range of application of the amount of carbon additive in the agglomerated lignin-carbon composite may be greater, such as 0.1 to 60 weight percent, based on the dry weight of the agglomerated lignin-carbon composite.

[0041] In some embodiments, the amount of lignin in the agglomerated lignin-carbon composite is in the range of 40 to 99.9 weight percent, based on the dry weight of the agglomerated lignin-carbon composite.

[0042] In one embodiment, the at least one carbon additive is selected from the group of graphite, graphene, carbon nanotubes, charcoal, biochar, hard carbon, soft carbon, carbon black, carbon fiber, and conductive carbon.

[0043] In some embodiments, each carbon additive utilized is selected from the group of graphite, graphene, carbon nanotubes, charcoal, biochar, hard carbon, soft carbon, carbon black, carbon fiber, and conductive carbon.

[0044] In some embodiments, only one carbon additive is present in the agglomerated lignin-carbon composite. Preferably, the carbon additive is selected from the group of graphite, charcoal, hard carbon, or soft carbon.

[0045] In some embodiments, multiple carbon additives are present in the aggregate lignin-carbon composite. In a preferred embodiment using two carbon additives, the carbon additives are graphite and hard carbon.

[0046] In some embodiments, the carbon additive is a conductive carbon, such as conductive carbon black, conductive graphite, conductive graphene, or conductive carbon nanotubes. The conductive carbon may be the only carbon additive or may be present together with at least one other carbon additive.

[0047] The use of lignin in combination with carbon additives has been shown to improve the mechanical and thermal processability of lignin, such as in agglomerated lignin-carbon composites, which have improved heat resistance by reducing the melting / expansion behavior upon heating, improving processability on an industrial scale.

[0048] As used herein, the term "agglomerated lignin-carbon composite" refers to macroscopic particles that include clustered smaller particles of lignin and at least one carbon additive.

[0049] In a preferred embodiment of the method according to the first aspect, the agglomerated lignin-carbon composite material used in step a) of the method of the invention comprises i) providing lignin in the form of a powder, the particle size distribution of the powdered lignin being such that at least 80% by weight of the particles have a diameter less than 0.2 mm and a moisture content of less than 45% by weight; ii) providing at least one carbon additive in the form of a powder, the particle size distribution of the carbon additive in the form of a powder being such that at least 80% by weight of the particles have a diameter of less than 0.1 mm; iii) mixing the lignin powder, at least one carbon-additive powder, and optionally at least one additive to obtain a lignin-carbon mixture; iv) compressing the lignin-carbon mixture obtained in step iii) to obtain a lignin-carbon composite material; v) grinding the lignin-carbon composite material obtained in step iv) to obtain an agglomerated lignin-carbon composite material; vi) optionally sieving the agglomerated lignin-carbon composite material obtained in step v) to remove particles having a size less than 100 μm, thereby obtaining an agglomerated lignin-carbon composite material having a particle size distribution such that at least 80% by weight of the agglomerates have a diameter within the range of 0.2 mm to 5.0 mm; The present invention is produced by a method comprising the steps of:

[0050] The lignin in powder form provided in step i) is preferably dried before being mixed with the at least one carbon additive. Drying of the lignin powder is carried out by methods and devices known in the art. The moisture content of the lignin in powder form used in step i) is less than 45% by weight. Preferably, the moisture content of the lignin before being mixed with the at least one carbon additive according to the invention is less than 25% by weight, preferably less than 10% by weight, more preferably less than 8% by weight. In one embodiment, the moisture content of the lignin before being mixed with the at least one carbon additive according to the invention is at least 1% by weight, for example at least 5% by weight. The temperature during drying is preferably in the range of 80°C to 160°C, more preferably in the range of 100°C to 120°C.

[0051] The lignin powder obtained after drying has a broad particle size distribution ranging from 1 μm to 2 mm, with a strong bias towards the micrometer range, meaning that a significant proportion of the particles have diameters in the range of 1 to 200 μm. The lignin powder preferably has a density of 0.3 g / cm3 to 0.4 g / cm3. 3 The bulk density ranges from 0.01 to 0.01.

[0052] The at least one carbon additive provided in step ii) is in the form of a powder. The at least one carbon additive is preferably dried before mixing with the lignin. Preferably, the carbon additive has a moisture content of less than 20% by weight, preferably less than 10% by weight, more preferably less than 5% by weight. In one embodiment, the carbon additive has a moisture content in the range of 0-20% by weight, such as 0-10% by weight or 0-5% by weight. In one embodiment, the carbon additive has a moisture content in the range of 0.1-20% by weight, such as 0.1-10% by weight or 0.1-5% by weight.

[0053] The at least one carbon additive provided in step ii) preferably has a particle size smaller than that of the lignin. Preferably, the particle size distribution of the at least one carbon additive in powder form is such that at least 80% by weight of the particles have a diameter of less than 0.1 mm. In one embodiment, the particle size distribution of the at least one carbon additive in powder form is such that at least 80% by weight of the particles have a diameter in the range of 5 nm to 20 μm.

[0054] In some embodiments, one carbon additive is utilized, i.e., the step of providing at least one carbon additive comprises providing one carbon additive. In some embodiments, one or more carbon additives are utilized, i.e., the step of providing at least one carbon additive comprises providing two, three, four, or more carbon additives. Each carbon additive can be selected from the carbon additives described above.

[0055] In step iii), the lignin in powder form is mixed with at least one carbon additive and optionally at least one additive in powder form to obtain a lignin-carbon mixture.

[0056] Mixing is carried out by methods and equipment known in the art. One suitable method is a vertical mixer such as a paddle, screw, ribbon screw mixer, in batch or continuous mode. The mixing process can be carried out in low, medium, or high shear impact mode.

[0057] In some embodiments, at least one additive can be added during or before mixing. Suitable additives, such as binders or lubricants, can be added to facilitate the subsequent compaction process and to improve the density and mechanical properties of the resulting lignin-carbon composite material. In addition, additives that affect the properties of the final material, such as functionality-enhancing additives, can be added. The total amount of additives is preferably less than 5 wt%, for example 0-5 wt%, or 0.1-5 wt%, or less than 2 wt%, for example 0-2 wt%, or 0.1-2 wt%, based on the total dry weight of the lignin-carbon powder mixture.

[0058] In some embodiments, mixing is carried out for at least 1 minute, or at least 10 minutes, or at least 15 minutes. In some embodiments, mixing is carried out for a period ranging from 1 to 60 minutes, 1 to 30 minutes, or 1 to 10 minutes. Increasing the mixing time improves the dispersion of the at least one carbon additive within the lignin.

[0059] In some embodiments, mixing is performed at a mixing speed of at least 100 rpm, such as at least 200 rpm or at least 300 rpm. In some embodiments, the mixing speed is in the range of 100-3000 rpm, or 100-1500 rpm, or 100-1000 rpm. Increasing the mixing speed improves dispersion of the at least one carbon additive within the lignin.

[0060] During mixing, friction may cause the temperature of the mixture to increase. In one embodiment, the temperature of the powders during mixing is maintained in the range of 20-100° C. The temperature may be maintained by heating or cooling the equipment used for mixing.

[0061] As mentioned above, the dispersion of the at least one carbon additive within the lignin matrix is ​​enhanced by both sufficient mixing time, appropriate mixing speed, and appropriate mixing temperature, which results in a uniform distribution of the at least one carbon additive within the lignin matrix. The uniform dispersion of the lignin and carbon powder mixture ensures uniform dispersion in the formed aggregates after compaction.

[0062] In one embodiment, the mixing is performed by dry mixing. The term "dry mixing" as used herein refers to the process of mixing ingredients that are all in a dry state, i.e., not in a dispersion, slurry, or other type of solution. The ingredients in the mix may have a moisture content of less than 10% by weight. In a preferred embodiment, both the lignin and the carbon additive are in the form of dry powders during the mixing process. The lignin-carbon mixture thus obtained is in the form of a dry powder.

[0063] In one embodiment, the lignin powder is mixed with at least one carbon additive in powder form at the same time as the milling of the powder to reduce the size of the powder particles. The milling can be performed by impact milling, hammer milling, ball milling, jet milling, or other methods. In one embodiment, the milling of the powder is performed immediately before mixing. By performing the mixing by dry mixing, a simple process of mixing the lignin powder with at least one carbon additive powder is obtained. The dry mixing process can be easily integrated with subsequent processing steps.

[0064] The mixing of the lignin powder with the at least one carbon additive in powder form can be carried out using any suitable equipment known in the art, for example, if a particularly high level of mixing is desired, a high impact dry blending machine suitable for mechanochemical processing or hybridization can be used.

[0065] The uniform distribution of the at least one carbon additive in the agglomerated lignin-carbon composite also ensures its uniform distribution in the granular carbon-carbon composite obtained from the agglomerated lignin-carbon composite. Superior functionality of the granular carbon-carbon composite is achieved by the uniform distribution of the carbon additive.

[0066] In one embodiment, the lignin-carbon powder mixture has a bulk density of 0.3 to 0.5 g / cm 3 The range is.

[0067] In step iv), the lignin-carbon powder mixture is compressed to obtain a lignin-carbon composite material. The compression of the lignin-carbon powder mixture is preferably performed by roll compaction. The roll compaction of the lignin-carbon powder mixture is achieved by a roller compactor, which compresses the lignin-carbon powder mixture into a composite material.

[0068] In the compression step, a compressed lignin-carbon composite is produced. Here, a mixture of fine lignin and carbon powders is typically fed from a hopper and conveyed by a horizontal or vertical feed screw to the compression zone, where the material is compressed into flakes by compression rollers with a constant gap. By controlling the speed of the feed screw and the pressure generation in the compression zone, flakes of uniform density are obtained. The pressure generation in the compression zone can be preferably monitored and controlled by the rotation speed of the compression rolls. As the powder is pulled between the rollers, it enters an area called the nip region, where the density of the material increases and the powder turns into flakes or ribbons. The rolls used have cavities. The depth of each cavity used for roll compression is 0.1 mm to 10 mm, preferably 1 mm to 8 mm, more preferably 1 mm to 5 mm or 1 mm to 3 mm. The specific applied pressure during compression may vary depending on the equipment used for compression, but may be in the range of 1 kN / cm to 100 kN / cm. Suitable equipment for carrying out compression is known in the art.

[0069] In a preferred embodiment, the temperature of the lignin-carbon powder mixture is maintained below 150°C, such as below 100°C, during the compaction process.

[0070] In one embodiment of roll compaction, the roll configuration is such that the first roll has an annular rim in such a configuration that the lignin-carbon powder mixture in the nip region is axially sealed along the roller surface.

[0071] In one embodiment, the roll configuration is such that the nip area is sealed axially along the roller surface with a static plate. Ensuring a sealed nip area minimizes loss of lignin-carbon powder at the axial ends of the roller compared to fully cylindrical nip rollers.

[0072] During compaction, the materials are compressed by mechanical pressure to form the lignin-carbon composite. The particles of each powder are compressed closer to each other, improving the dispersion of the at least one carbon additive and the lignin. It has been found that the at least one carbon additive can facilitate the compaction process by reducing the internal friction between the lignin particles.

[0073] Compaction may also act to enhance the interactions between the lignin particles and the carbon additive particles in the composite due to the rearrangement and plastic deformation of the primary particles induced by the mechanical forces. Compaction further acts to ensure that the uniform distribution achieved in the mixing step is maintained until the lignin-carbon composite is further stabilized, i.e., by a thermal stabilization step.

[0074] Compaction can be performed on a powder mixture of lignin and carbon without the addition of any additives, or alternatively, on a lignin-carbon powder mixture that also contains a small amount, such as less than 5% by weight, of at least one additive, based on the total dry weight of the lignin-carbon powder mixture.

[0075] Compression is preferably followed by crushing, in which the compressed lignin-carbon composite obtained in the compression step is subjected to crushing or grinding, such as by a rotary granulator, a cage mill, a beater mill, a hammer mill, a crusher mill, and / or a combination thereof, in which the compressed lignin-carbon composite is separated into aggregates, thus producing an agglomerated lignin-carbon composite.

[0076] After grinding, the ground material is preferably subjected to a sieving step to remove fine materials. Additionally, larger materials, such as agglomerates with a diameter of more than 5.0 mm, may be removed and / or recycled to the grinding step.

[0077] In the sieving step, the agglomerated lignin-carbon composite material from the grinding step is sieved by physical separation, such as sieving, also called screening, to obtain a product which is an agglomerated lignin-carbon composite material with a defined particle size distribution set by the porosity of the sieve or screen of this step. The sieve or screen is selected such that most of the particles with a diameter less than 100 (or 500) μm pass through the screen and are rejected, preferably returned to the compaction step, while most of the particles with a diameter greater than 100 (or 500) μm are retained and subjected to the subsequent heating step of the method according to the invention. Sieving can be carried out in several steps, i.e. sieving can be carried out such that the ground material from the grinding step passes through several screens or sieves in sequence.

[0078] During compression, the bulk density of the material increases as the material is compressed tightly together. In one embodiment, the bulk density of the agglomerated lignin-carbon composite material is between 0.5 and 0.7 g / cm. 3 The bulk density of the lignin-carbon powder mixture increases when pressure is applied to the powder because the lignin-carbon powder mixture is compressed during the production of the agglomerated lignin-carbon composite. This means that the bulk density of the agglomerated lignin-carbon composite is higher than that of the lignin-carbon powder mixture. The agglomerated lignin-carbon composite has been found to maintain its shape and dimensions without dissolving or expanding, so the more compact material may be beneficial during subsequent processing of the carbon enriched material. The agglomerated lignin-carbon composite has a relatively high hardness even after compression. Hard particles are advantageous for subsequent processing because they can withstand physical impacts during processing. As explained above, the carbon additive also improves the mechanical and thermal processability of the lignin. The carbon additive can also increase the stability of the agglomerated lignin-carbon composite by reducing inter-particle friction.

[0079] The agglomerated lignin-carbon composite has a particle size distribution such that at least 80% by weight of the particles have a diameter in the range of 0.2 mm to 5.0 mm. Preferably, the particle size distribution is such that at least 90% by weight, more preferably at least 95% by weight of the particles have a diameter in the range of 0.2 mm to 5.0 mm. More preferably, at least 90% by weight, more preferably at least 95% by weight of the particles have a diameter in the range of 0.5 mm to 2 mm.

[0080] In one embodiment, the agglomerated lignin-carbon composite provided in step a) of the method according to the first aspect comprises from 40 to 99.9 wt.% lignin, from 0.1 to 60 wt.% of at least one carbon additive, and from 0 to 5 wt.% of at least one additive, based on the dry weight of the agglomerated lignin-carbon composite.

[0081] Step b) of the method according to the first aspect of the present invention comprises heating the agglomerated lignin-carbon composite to a temperature of from 140 to 250° C. for at least 30 minutes to obtain a thermally stabilized agglomerated lignin-carbon composite.

[0082] As used herein, the term "heat stabilization" refers to the process of heating an agglomerated lignin-carbon composite material at a temperature below that required to carbonize the material, which allows the agglomerated lignin-carbon composite material to be heat treated while avoiding melting / expansion and distortion and retaining its shape and dimensions.

[0083] Thermal stabilization stabilizes and hardens the outer surface of the aggregated lignin-carbon composite, allowing it to retain its shape and dimensions. The interior of the aggregate is also heated, softening / melting the lignin and promoting the dispersion of carbon within the lignin matrix.

[0084] The thermally stabilized agglomerated lignin-carbon composite preferably has a bulk density of 0.5 g / cm 3 ~0.7g / cm 3Heat stabilization may slightly increase or decrease the bulk density of the agglomerated lignin-carbon composite material. However, it is preferred that the bulk density be maintained within the same range as the bulk density of the agglomerated lignin-carbon composite material prior to heat stabilization.

[0085] The step of heating the agglomerated lignin-carbon composite to produce a thermally stabilized agglomerated lignin-carbon composite can be carried out continuously or in a batch mode. Heating can be carried out using methods known in the art and can be carried out in the presence of air or fully or partially under an inert gas. Preferably, heating is carried out in a rotary kiln, a moving bed furnace, or a rotary hearth furnace.

[0086] Heating to produce a thermally stabilized agglomerated lignin-carbon composite is carried out such that the agglomerated lignin-carbon composite is heated to a temperature in the range of 140-250°C, preferably 180-230°C. Heating is carried out for at least 30 minutes, i.e. the residence time of the agglomerated lignin-carbon composite in the equipment used for heating is at least 30 minutes. In one embodiment, heating is carried out for at least 1 hour, or at least 1.5 hours. Preferably, heating is carried out for less than 12 hours. Heating can be carried out at the same temperature throughout the heating stage, or at varying temperatures, such as by increasing the temperature stepwise or using a temperature gradient. More preferably, heating is carried out such that the agglomerated lignin-carbon composite is first heated to a temperature of 140-175°C for at least 15 minutes, and subsequently heated to a temperature of 175-250°C for at least 15 minutes.

[0087] The thermally stabilized agglomerated lignin-carbon composite material includes lignin, at least one carbon additive, and optionally at least one additive. There may be some weight loss during heating compared to the agglomerated lignin-carbon composite material before heating to obtain the thermally stabilized material. The weight loss is typically less than 15% by weight and is mainly due to evaporation of water and loss of volatiles due to decomposition of the lignin during heating.

[0088] By controlling and optimizing parameters such as temperature and time during the thermal stabilization process, it is possible to obtain thermally stabilized agglomerated lignin-carbon composites that retain their shape and dimensions without fusing or expanding during subsequent processing. The described method has excellent compatibility with typical process requirements for continuous production using, for example, rotary kilns, due to the mechanical stability and relatively short residence time of the agglomerated lignin-carbon composites. This is particularly important for realizing an economical large-scale industrial-scale process for producing carbon enriched materials.

[0089] According to a second aspect, the present invention relates to a thermally stabilized agglomerated lignin-carbon composite having a particle size distribution such that at least 80% by weight of the agglomerates have a diameter in the range of 0.2 mm to 5.0 mm, the thermally stabilized agglomerated lignin-carbon composite comprising lignin and at least one carbon additive. The thermally stabilized agglomerated lignin-carbon composite according to the second aspect is obtainable by the method according to the first aspect. The thermally stabilized agglomerated lignin-carbon composite according to the second aspect may be further defined as set out above with reference to the first aspect.

[0090] In a method according to the third aspect of the invention, a thermally stabilised agglomerated lignin-carbon composite according to the first aspect of the invention is heat treated to obtain a granular carbon-carbon composite material.

[0091] Step 1 of the method according to the third aspect comprises providing a thermally stabilized agglomerated lignin-carbon composite material obtainable by the method according to the first aspect.

[0092] Providing the lignin-carbon composite in the form of a thermally stabilized agglomerated lignin-carbon composite provides a material that retains its shape and dimensions while avoiding melting / expansion and deformation during subsequent heat treatments.

[0093] Step 2) of the method according to the third aspect comprises subjecting the thermally stabilized agglomerated lignin-carbon composite material to a heat treatment at one or more temperatures in the range of 300°C to 1500°C for a total time in the range of 30 minutes to 10 hours, so as to obtain a granular carbon-carbon composite material.

[0094] The term "heat treatment" as used herein refers to the process of heating the thermally stabilized agglomerated lignin-carbon composite at one or more temperatures for a time sufficient to convert the lignin to carbon. Depending on the temperature during heat treatment, different types of carbon can be obtained from the lignin in the lignin-carbon composite, such as charcoal or hard carbon.

[0095] The term "carbon-carbon composite," as used herein in phrases such as "granular carbon-carbon composite" and "carbon-carbon composite powder," refers to a composite containing at least two different carbon materials, one derived from lignin and the other a carbon additive. The carbon-carbon composite is obtained by heat treating the thermally stabilized agglomerated lignin-carbon composite material described herein.

[0096] As mentioned above, during the heat treatment, the lignin in the thermally stabilized aggregated lignin-carbon composite is converted to carbon. In this way, a carbon-carbon composite is obtained. The total carbon content of the carbon-carbon composite (i.e., including contributions from both carbon additives and carbon derived from lignin) is preferably at least 90% by weight, or at least 95% by weight, based on the dry weight of the carbon-carbon composite. In one embodiment, the carbon-carbon composite comprises hard carbon (derived from lignin) and graphite (as a carbon additive). In one embodiment, the carbon-carbon composite comprises charcoal (derived from lignin) and graphite (as a carbon additive). In another embodiment, the carbon-carbon composite comprises hard carbon (derived from lignin) and hard carbon (as a carbon additive), i.e., the composite comprises two distinguishable hard carbon materials.

[0097] At least one carbon additive may also be altered by the heat treatment. Possible changes include conversion of one type of carbon to another (such as conversion of charcoal to hard carbon), changes in crystal and molecular structure, etc. Thus, the hard carbon formed during heat treatment of the lignin portion in the heat stabilized lignin-carbon composite may differ from the hard carbon provided as the carbon additive after heat treatment.

[0098] Preferably, the heat treatment comprises a pre-heating step, preferably followed by a final heating step. The pre-heating step is preferably carried out at a temperature between 300 and 800°C, for example between 500 and 700°C. The pre-heating step is preferably carried out under an inert atmosphere, preferably a nitrogen atmosphere. The duration of the pre-heating step is at least 30 minutes, preferably less than 10 hours. The pre-heating and final heating steps can be carried out as separate steps or directly in succession as a single step. The surface area of ​​the product obtained after the pre-heating step is typically between 300 and 700 m2, measured by the BET method with nitrogen gas. 2 / g.

[0099] The final heating step is preferably carried out at a temperature between 800° C. and 1500° C., the final heating step is preferably carried out under an inert atmosphere, preferably a nitrogen atmosphere, and the duration of the final heating step is at least 30 minutes and preferably less than 10 hours.

[0100] Preferably, the heat treatment is carried out in stages. Preliminary heating preferably starts at about 300°C and is then increased to about 500°C. The final heating step is preferably carried out between 900°C and 1300°C, for example at about 1000°C. After the final heating step carried out above 1000°C, the surface area of ​​the resulting product is typically greater than 10 m2. 2 / g or less.

[0101] The heat treated material, i.e. the product of step 2), the granular carbon-carbon composite material, preferably has a bulk density of 0.2 g / cm 3 ~0.7g / cm 3In the case where the amount of lignin in the thermally stabilized agglomerated lignin-carbon composite is relatively high, the bulk density of the resulting granular carbon-carbon composite is reduced compared to the bulk density of the thermally stabilized agglomerated lignin-carbon composite before the heat treatment, mainly due to the mass loss of lignin during the heat treatment. Alternatively, in the case where the amount of the at least one carbon additive in the thermally stabilized agglomerated lignin-carbon composite is relatively high, the bulk density of the resulting granular carbon-carbon composite is not reduced as much because the mass loss in the at least one carbon additive is not as large. Thus, the bulk density of the granular carbon-carbon composite will be highly dependent on the amount of carbon additive in the thermally stabilized agglomerated lignin-carbon composite.

[0102] Because the shape and dimensions of the agglomerated lignin-carbon composite are retained during heat treatment, it is preferred that the granular carbon-carbon composite have a particle size distribution such that at least 80% by weight of the particles have a diameter within the range of 0.2 mm to 5.0 mm.

[0103] The heat-treated material, i.e. the granular carbon-carbon composite material that is the product of step 2) of the method according to the third embodiment, is useful, for example, as biochar or as a precursor to activated carbon.

[0104] In one embodiment, the method includes the additional step of pulverizing the granular carbon-carbon composite material to obtain a carbon-carbon composite material. The pulverization can be carried out by any suitable process, such as, for example, using a cutting mill, a blade mixer, an impact mill, a ball mill, a hammer mill, and / or a jet mill. Optionally, the pulverization can be followed by fine / coarse particle selection by classification and / or sieving.

[0105] The choice of fine powder and optional fine / coarse particles of the carbon-carbon composite material can be determined, for example, by the average particle size (D v 50) can be carried out so as to obtain a carbon-carbon composite powder containing powder particles in the range of 5 to 25 μm.

[0106] In one embodiment, the grinding or pulverizing process is performed multiple times. Further, the carbon-carbon composite powder may be subjected to processing such as coating or further heat treatment.

[0107] According to a fourth aspect, the present invention relates to a granular carbon-carbon composite material obtainable by the method according to the third aspect. The granular carbon-carbon composite material according to the fourth aspect may be further defined as set out above with reference to the third aspect.

[0108] The granular carbon-carbon composite material obtained by the method according to the third aspect may also be used in applications such as activated carbon and biochar.

[0109] According to a fifth aspect, the present invention relates to a carbon-carbon composite powder obtained by grinding a granular carbon-carbon composite material obtained by the method according to the third aspect. The carbon-carbon composite powder may be further defined as set out above with reference to the third aspect.

[0110] According to a sixth aspect, the present invention relates to a negative electrode for a non-aqueous secondary battery comprising as active material the carbon-carbon composite powder according to the fifth aspect.

[0111] The carbon-carbon composite powder obtained by the method according to the third aspect is suitable for use as an active material for 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 may be utilized. In forming the negative electrode, the carbon-enriched material may be processed together with further components. Such further components may include, for example, one or more binders for forming the carbon-enriched material into an electrode, conductive materials such as carbon black, carbon nanotubes, metal powders, and / or further Li-storage materials such as graphite and lithium. For example, the binder may 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, and the like, or combinations thereof. Optionally, a solvent is utilized during processing, such as, for example, 1-methyl-2-pyrrolidone, 1-ethyl-2-pyrrolidone, water, or acetone.

[0112] According to a seventh aspect, the present invention relates to the use of the carbon-carbon composite powder according to the fifth aspect as an active material in the negative electrode of a non-aqueous secondary battery.

[0113] Working Example Example 1 Lignin powder from the LignoBoost process was mixed with 5, 10, or 20 wt.% carbon additive in the form of hard carbon with an average particle size of 6 μm using a conical screw mixer (200 RPM, 15 min). No additional additives were added. The mixture was then compacted using a Lab Compactor with roller compaction at 50 kN to obtain a composite, which was then crushed using a flake crusher and sieved into granules with a size distribution of 0.5-1.5 mm. The bulk density of the agglomerated lignin-carbon composites is: 0.55 g / cm 3 (5% by weight carbon additive); 0.56 g / cm 3 (10 wt.% carbon additive); and 0.54 g / cm 3 (20% by weight carbon additive).

[0114] The agglomerated lignin-carbon composite was further thermally stabilized by heating to 235 °C in a rotary kiln in air for 2 hours. During this process, the agglomerated lignin did not exhibit melting behavior and maintained its original shape. It was found that the individual agglomerates did not fuse and remained free-flowing. During the process the material gradually darkened and eventually became completely black and odorless. The bulk density of the thermally stabilized agglomerated lignin-carbon composite was 0.63 g / cm. 3 (5% by weight carbon additive); 0.62 g / cm 3 (10 wt.% carbon additive); and 0.61 g / cm 3 (20% by weight carbon additive).

[0115] This thermally stabilized agglomerated lignin-carbon composite was then heat treated at 500 °C for 1 hour under an inert atmosphere to carbonize the material. This resulted in a granular carbon-carbon composite with no melting or fusion of the granules and with retained shape / size compared to the thermally stabilized agglomerated lignin-carbon composite before carbonization. The bulk density of the resulting granular carbon-carbon composite was 0.47 g / cm. 3 (5% by weight carbon additive); 0.47 g / cm 3 (10 wt.% carbon additive); and 0.58 g / cm 3 (20% by weight carbon additive).

[0116] Example 2 - Comparative Example In this experiment, conventional thermal conversion of lignin powder was performed. The lignin powder was not agglomerated with a carbon additive.

[0117] The lignin powder obtained from the LignoBoost process was heated at 200°C for up to 12 hours. After heating, it was found that the lignin melted / fused into a solid black cake with no odor.

[0118] In view of the above detailed description of the invention, other modifications and variations will be apparent to those skilled in the art, but it is apparent that such other modifications and variations can be made without departing from the spirit and scope of the invention.

Claims

1. 1. A method for producing a thermally stabilized agglomerated lignin-carbon composite, comprising: a) providing an agglomerated lignin-carbon composite material having a particle size distribution such that at least 80% by weight of the agglomerates have a diameter within the range of 0.2 mm to 5.0 mm, said agglomerated lignin-carbon composite material comprising lignin and at least one carbon additive; b) heating the agglomerated lignin-carbon composite to a temperature of 140-250°C for at least 30 minutes to obtain a thermally stabilized agglomerated lignin-carbon composite; A method comprising:

2. The agglomerated lignin-carbon composite material used in step a) is i) providing lignin in the form of a powder, wherein the particle size distribution of the lignin in the form of a powder is such that at least 80% by weight of the particles have a diameter of less than 0.2 mm and a moisture content of less than 45% by weight; ii) providing at least one carbon additive in the form of a powder, wherein the particle size distribution of the carbon additive in the form of the powder is such that at least 80% by weight of the particles have a diameter of less than 0.1 mm; iii) mixing lignin powder, at least one carbon-added powder, and optionally at least one additive to obtain a lignin-carbon mixture; iv) compressing the lignin-carbon mixture obtained in step iii) to obtain a lignin-carbon composite material; v) grinding the lignin-carbon composite material obtained in step iv) to obtain an agglomerated lignin-carbon composite material; vi) optionally sieving the agglomerated lignin-carbon composite material obtained in step v) to remove particles having a particle size of less than 100 μm, thereby obtaining an agglomerated lignin-carbon composite material having a particle size distribution such that at least 80% by weight of the agglomerates have a diameter in the range of 0.2 mm to 5.0 mm; 10. The method of claim 1, wherein the polymer is produced by a process comprising:

3. 3. The method of claim 2, wherein the mixing in step iii) is performed by dry mixing.

4. The agglomerated lignin-carbon composite material provided in step a) has a mass of 0.5 to 0.7 g / cm ３ 4. The method of claim 1, wherein the granules have a bulk density in the range of

5. 3. The method of claim 1 or 2, wherein the amount of the at least one carbon additive in the agglomerated lignin-carbon composite material is in the range of 0.1 to 60 wt %, based on the dry weight of the agglomerated lignin-carbon composite material.

6. 3. The method of claim 1 or 2, wherein the carbon additive is selected from the group consisting of graphite, graphene, carbon nanotubes, charcoal, biochar, hard carbon, soft carbon, carbon black, carbon fiber, and conductive carbon.

7. 3. The method of claim 1 or 2, wherein the lignin is kraft lignin.

8. 3. The method of claim 1 or 2, wherein heating the agglomerated lignin-carbon composite material in step b) is carried out by first heating the agglomerated lignin-carbon composite material to a temperature in the range of 140 to 175°C for at least 15 minutes, and subsequently heating the agglomerated lignin-carbon composite material to a temperature in the range of 175 to 250°C for at least 15 minutes.

9. 1. A thermally stabilized agglomerated lignin-carbon composite material having a particle size distribution such that at least 80% by weight of the agglomerates have a diameter within the range of 0.2 mm to 5.0 mm, the thermally stabilized agglomerated lignin-carbon composite material comprising lignin and at least one carbon additive.

10. 10. The thermally stabilized agglomerated lignin-carbon composite of claim 9, wherein the amount of the at least one carbon additive in the thermally stabilized agglomerated lignin-carbon composite is in the range of 0.1 to 60 wt %, based on the dry weight of the thermally stabilized agglomerated lignin-carbon composite.

11. 11. The thermally stabilized agglomerated lignin-carbon composite material of claim 9 or 10, wherein the carbon additive is selected from the group of graphite, graphene, carbon nanotubes, charcoal, biochar, hard carbon, soft carbon, carbon black, carbon fiber, and conductive carbon.

12. 11. The thermally stabilized agglomerated lignin-carbon composite material of claim 9 or 10, wherein the lignin is kraft lignin.

13. The thermally stabilized agglomerated lignin-carbon composite material has a density of 0.5 to 0.7 g / cm ３ 11. The thermally stabilized agglomerated lignin-carbon composite material of claim 9 or 10, having a bulk density in the range of

14. 1. A method for producing a granular carbon-carbon composite material, comprising: 1) Providing a thermally stabilized agglomerated lignin-carbon composite material obtainable by the method of claim 1 or 2; 2) subjecting the thermally stabilized agglomerated lignin-carbon composite to a heat treatment at one or more temperatures ranging from 300°C to 1500°C for a total time ranging from 30 minutes to 10 hours to obtain a granular carbon-carbon composite material; A method comprising:

15. 15. The method of claim 14, wherein step 2) comprises a preheating step followed by a final heating step.

16. 16. The method of claim 15, wherein the preheating step is carried out at a temperature between 400 and 800°C for at least 30 minutes.

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

18. 16. The method of claim 15, wherein the final heating step is carried out at a temperature between 800°C and 1500°C for at least 30 minutes.

19. 16. The method of claim 15, wherein the final heating step is performed in an inert atmosphere.

20. 15. The method of claim 14, comprising the additional step of pulverizing the granular carbon-carbon composite material to obtain a carbon-carbon composite powder.