A method for producing a carbon enriched material

Abstract

A method for producing a carbon enriched material, said method comprising the steps of: a) providing lignin beads, wherein said lignin beads comprise at least 80 wt% of lignin based on the dry weight of the lignin beads; b) optionally heating the lignin beads to one or more temperatures in the range of from 140 to 270 °C for a period of at least 30 minutes so as to obtain thermally stabilized lignin beads; and c) subjecting the, optionally thermally stabilized, lignin beads to carbonization at one or more temperatures in the range of from 300 °C to 1500 °C, wherein the carbonization is carried out for a total time in the range of from 30 minutes to 10 hours, so as to obtain a carbon enriched material.

Description

[0001] A METHOD FOR PRODUCING A CARBON ENRICHED MATERIAL

[0002] Technical field

[0003] The present invention relates to a method for producing a carbon enriched material using lignin beads as starting material. The present invention also relates to a carbon enriched material obtainable the method, and a negative electrode for a non-aqueous secondary battery comprising said carbon enriched material as active material. The present invention further relates to lignin beads comprising at least 80 wt% of lignin based on the dry weight of the lignin beads and to the use of such lignin beads as a starting material for producing a carbon enriched material.

[0004] Secondary batteries, such as lithium-ion batteries, are electrical batteries which can be charged and discharged many times, i.e. they are rechargeable batteries. In lithium-ion batteries, lithium ions flow from the negative electrode through the electrolyte to the positive electrode during discharge, and back when charging. Typically, a lithium compound, in particular a lithium metal oxide such as lithium nickel manganese cobalt oxide (NMC) or alternatively a lithium iron phosphate (LFP), is utilized as material of the positive electrode and a carbon enriched material is utilized as material of the negative electrode.

[0005] Graphite (natural or synthetic graphite) is today utilized as material of the negative electrode in most lithium-ion batteries. An alternative to graphite is amorphous carbon materials, such as hard carbons (non-graphitizable amorphous carbons) and soft carbons (graphitizable amorphous carbons), which lack long-range graphitic order. Amorphous carbons can be used as sole active electrode materials or in mixtures with graphite (and / or other active materials).

[0006] Amorphous carbons can be derived by carbonization of lignin. Lignin is an aromatic polymer, which is a major constituent in e.g. wood and one of the most abundant carbon sources on earth. In recent years, with development and commercialization of technologies to extract lignin in a highly purified, solid and particularized form from the pulp-making process, it has attracted significant attention as a possible renewable substitute to primarily aromatic chemical precursors currently sourced from the petrochemical industry. Amorphous carbons derived by carbonization of lignin are typically non-graphitizable, i.e. hard carbons.

[0007] Today, the most commercially relevant source of lignin is Kraft lignin, obtained from hardwood or softwood through the kraft process. The lignin can be separated from alkaline black liquor using for example membrane- or ultrafiltration. One common separation process is described in W02006031175 A1 . In this process lignin is precipitated from alkaline black liquor by addition of acid and then filtered off. The lignin filter cake is in the next step re-slurried under acidic conditions and washed prior to drying and pulverization.

[0008] One problem with using lignin as a precursor for a carbon enriched material is that direct use of lignin, in the form of a fine powder, is not suitable since it exhibits undesired thermoplastic behavior in the carbonization step. During thermal conversion of lignin powder into carbon enriched materials, lignin undergoes plastic deformation / melting, aggressive swelling and foaming. This severely limits the processability of lignin in an industrially relevant scale, in terms of equipment dimensioning and process throughput as well as need of intermediate processing.

[0009] Inorganic additives, such as metal salts, has been used to partly reduce the melting / swelling behaviour of lignin during thermal processing. However, these metal salts are also causing catalytic activation of the carbon structure during carbonization and costly post-purification protocols are required in order to remove the metal salts from the final carbon enriched material.

[0010] US6099990 A describes a method of fabricating a carbon material, which involves the steps of mixing a lignin powder with a salt and then heating the mixture in several steps, involving a carbonization step.

[0011] In the conventional process of converting biomass into carbon enriched intermediates, powders are normally avoided. Therefore, lignin in fine powder form is not a suitable alternative to conventional biomass in this field. In an approach to overcome this problem, formation of granules of lignin has been contemplated. The granulation process involved applying mechanical pressure to the lignin powder to form lignin flakes, and then breaking up the flakes into irregular shaped angular granules typically of <2mm size. The granules formed by this process may contain angular and sharp edges. Along with poorly bonded lignin powder, these sharp edges break during processing and may lead to the formation of dust and fine particles. The dust produced would lead to clogging of off gas pipes and risk of dust explosion when the process is operated in large scale.

[0012] To reduce the melting / swelling behaviour of the lignin, the granules may also be subjected to an intermediate thermal stabilization step before being subjected to carbonization. The thermal stabilization is performed at a lower temperature than the carbonization. The irregular shaped granules formed by the granulation process also makes it more difficult to achieve a uniform thermal stabilization of the granules.

[0013] Thus, there is still room for improvements of methods for producing a carbon enriched material from lignin. The method should avoid that lignin undergoes plastic deformation and melting, aggressive swelling and foaming during heating, as well as the formation of dust and fine particles when converting lignin to a carbon enriched material. In addition, it should be possible to use the method in large-scale manufacturing.

[0014] Summary of the invention

[0015] It is an object of the present invention to provide an improved method for producing a carbon enriched material, which method allows use of a renewable carbon source, and which method eliminates or alleviates at least some of the disadvantages of the prior art methods.

[0016] It is a further object of the present invention to provide a method that obtains an improved carbon enriched material starting from lignin, which carbon enriched material is suitable for use as active material in a negative electrode of a secondary battery, such as a lithium-ion battery or sodium-ion battery. It is a further object of the present invention to provide a method for producing a carbon enriched material from lignin, which method allows carbonization of lignin while retaining shape and dimension.

[0017] It is a further object of the present invention to provide a method for improving the mechanical and thermal processability of lignin.

[0018] It is a further object of the present invention to provide a method for producing a carbon enriched material from lignin, which method is scalable and thus suitable for large-scale manufacturing.

[0019] The above-mentioned object, as well as other objects as will be realized by the skilled person in the light of the present disclosure, are achieved by the various aspects of the present disclosure.

[0020] According to a first aspect, the present invention relates to a method for producing a carbon enriched material, said method comprising the steps of: a) providing lignin beads, wherein said lignin beads comprise at least 80 wt% of lignin based on the dry weight of the lignin beads; b) optionally heating the lignin beads to one or more temperatures in the range of from 140 to 270 °C for a period of at least 30 minutes so as to obtain thermally stabilized lignin beads; and c) subjecting the, optionally thermally stabilized, lignin beads to carbonization at one or more temperatures in the range of from 300 °C to 1500 °C, wherein the carbonization is carried out for a total time in the range of from 30 minutes to 10 hours, so as to obtain a carbon enriched material.

[0021] The present invention is based on the realization that using lignin beads, i.e. lignin particles having a substantially spherical or spheroidal shape, as a starting material for the production a carbon enriched material provides several important advantages, including less formation of dust and fine particles and more uniform thermal stabilization. The spherical shape of the beads ensures good flow properties in a rotary kiln and minimum contact with other beads, which prevents sticking or agglomeration of the beads. With the use of lignin beads it has also been found that thermal stabilization may be dispensed with, and the lignin beads may be directly subjected to carbonization, without an intermediate thermal stabilization step.

[0022] According to a second aspect, the present invention relates to lignin beads comprising at least 80 wt% of lignin based on the dry weight of the lignin beads. The lignin beads having such high content of lignin are useful as a starting material in the method according to the first aspect.

[0023] According to a third aspect, the present invention relates to a method for producing thermally stabilized lignin beads, comprising the steps of: a) providing lignin beads, wherein said lignin beads comprise at least 80 wt% of lignin based on the dry weight of the lignin beads; and b) heating the lignin beads to one or more temperatures in the range of from 140 to 270 °C for a period of at least 30 minutes so as to obtain thermally stabilized lignin beads.

[0024] According to a fourth aspect the present invention relates to thermally stabilized lignin beads obtainable by the method according to the third aspect.

[0025] Thermal stabilization allows for the thermally stabilized lignin beads to be subjected to carbonization with better retained shape and dimensions, avoiding melting / swelling and deformation. The substantially spherical or spheroidal shape of the lignin beads provides for a uniform thermal stabilization as heating and possible cross-linking of lignin by reaction with oxidizing species may be effected more uniformly throughout each bead. The thermally stabilized lignin beads are useful as an intermediate product for the production a carbon enriched material. According to a fifth aspect, the present invention relates to a carbon enriched material obtainable by the method according to the first aspect.

[0026] According to a sixth aspect, the present invention relates to a negative electrode for a non-aqueous secondary battery comprising a carbon enriched material powder obtainable by the method according to the first aspect.

[0027] According to a seventh aspect, the present invention relates to the use of lignin beads, wherein said lignin beads comprise at least 80 wt% of lignin based on the dry weight of the lignin beads, for producing a carbon enriched material.

[0028] Brief description of the drawings

[0029] Figure 1 is a photograph of the dried lignin beads.

[0030] Figures 2a and 2b are scanning electron microscope (SEM) images of dried and crushed lignin beads.

[0031] Figure 3 is a photograph of the dried carbonized lignin beads.

[0032] Figures 4a and 4b are scanning electron microscope (SEM) images of carbonized lignin beads.

[0033] Detailed

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

[0035] The term “lignin beads” used herein refers to lignin particles having a substantially spherical or spheroidal shape. In some embodiments, the lignin beads provided in step a) have a spherical or spheroidal shape. However, the lignin beads are not necessarily perfectly spherical or elliptical in shape but may have an overall spherical or elliptical appearance without sharp angles or edges.

[0036] The size of the lignin beads is preferably selected so that handling and treatment, e.g. carbonization, is facilitated. In some embodiments, the lignin beads provided in step a) have a diameter in the range of from 0.1 mm to 5.0 mm, preferably in the range of 0.2 mm to 2.0 mm, and more preferably in the range of 0.3 mm to 0.5 mm.

[0037] In the context of the present invention, the diameter of a bead is the equivalent spherical diameter of the bead, if the bead is not perfectly spherical. The equivalent spherical diameter is the diameter of a sphere of equivalent volume.

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

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

[0040] The term “lignin” as used herein, refers to any kind of lignin which may be used as the carbon source for making a carbon enriched material. Examples of said lignin are, but are not limited to, lignin obtained from vegetable raw material such as wood, e.g. softwood lignin, hardwood lignin, and lignin from annular plants. Also, lignin can be chemically modified.

[0041] Preferably, the lignin has been purified or isolated before being used in the process according to the present disclosure. The lignin may be isolated from black liquor and optionally be further purified before being used in the process according to the present disclosure. The purification is typically 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 disclosure preferably contains less than 10%, more preferably less than 5%, impurities such as e.g. cellulose, ash, and / or moisture. Preferably, the lignin contains less than 1% ash, more preferably less than 0.5% ash.

[0042] The lignin may be obtained through different fractionation methods such as an organosolv process or a Kraft process. For example, the lignin may be obtained by using the process disclosed in W02006031175 A1 .

[0043] Preferably, the lignin used in the method according to the first aspect of the present invention is Kraft lignin, i.e. lignin obtained through the Kraft process. Preferably, the Kraft lignin is obtained from hardwood or softwood, most preferably from softwood.

[0044] Depending on the method used for producing the lignin beads, the beads may comprise one or more additional components, besides lignin.

[0045] In some embodiments, the lignin beads provided in step a) further comprise in the range of 0.5 to 10 wt%, preferably in the range of 1 to 5 wt%, and more preferably in the range of 1 to 3 wt%, of a polymeric binder based on the dry weight of the lignin beads. The polymeric binder may improve the stability and structural integrity of the lignin beads and prevent breaking and dust formation.

[0046] The polymeric binder may be any polymeric component capable of improving the stability and structural integrity of the lignin beads and preventing breaking and dust formation. One useful group of polymeric binders are gel forming polymers, i.e. polymers capable of forming a gel network in a liquid medium. Thus, in some embodiments, the polymeric binder comprises a gel forming polymer. One particularly useful group of gel forming polymers are polymers that form gels through ionic cross-linking with divalent cations. Such polymers are often referred to as ionotropic gelling polymers. The divalent cations, for example calcium ions, cross-link the polymer chains, leading to the formation of a gel network. Thus, in some embodiments, the polymeric binder comprises an ionotropic gelling polymer.

[0047] In some embodiments, the polymeric binder comprises a polysaccharide or a polysaccharide derivative. In some embodiments, the polymeric binder comprises a gel forming polysaccharide. In some embodiments, the gel forming polysaccharide is an ionotropic gelling polysaccharide, i.e. a polysaccharide that forms gels through ionic cross-linking with divalent cations. Examples of ionotropic gelling polysaccharides include, but are not limited to alginate, carrageenan, gellan gum, xanthan gum, pectin, and carboxymethylcellulose (CMC). In a preferred embodiment the polymeric binder comprises alginate.

[0048] In some embodiments, the lignin beads provided in step a) further comprise in the range of 0.5 to 10 wt%, preferably in the range of 1 to 5 wt%, and more preferably in the range of 1 to 3 wt%, of a surfactant based on the dry weight of the lignin beads. In some embodiments, the surfactant is a nonionic surfactant, preferably a polysorbate, and more preferably Tween 80.

[0049] One method for producing the lignin beads comprises: i) preparing an aqueous mixture comprising at least 80 wt% of lignin, 0.5 to 10 wt% of ionotropic gelling polymer, and 0.5 to 10 wt% of a nonionic surfactant, based on the total dry weight of the aqueous mixture; ii) adding the aqueous mixture dropwise into an aqueous solution comprising divalent metal ions, preferably calcium ions, so as to obtain lignin beads; and iii) recovering, and optionally washing, the formed lignin beads.

[0050] In some embodiments, the ionotropic gelling polymer is selected from the group consisting of alginate, carrageenan, gellan gum, xanthan gum, pectin, and carboxymethylcellulose (CMC), and more preferably alginate.

[0051] The divalent metal ions may be any divalent cations, but calcium ions are preferred. The aqueous solution comprising divalent metal ions may for example be provided by dissolving a salt of the divalent metal ion, for example calcium chloride (CaCh) in water. The divalent metal ions react with the ionotropic gelling polymer by an ion exchange polymerization or crosslinking reaction, and lignin beads are formed. The lignin beads formed by such a method will, besides lignin, also comprise ionotropic gelling polymer as a polymeric binder. The ionotropic gelling polymer in the lignin beads may be in the form of a gel, such as a calcium alginate gel.

[0052] Depending on the type of surfactant and the extent of washing, the lignin beads provided in step a) may further comprise in the range of 0.5 to 10 wt%, preferably in the range of 1 to 5 wt%, and more preferably in the range of 1 to 3 wt%, of a surfactant based on the dry weight of the lignin beads. In some embodiments, the surfactant is a nonionic surfactant, preferably a polysorbate, and more preferably Tween 80.

[0053] In some embodiments, the lignin beads provided in step a) are porous lignin beads. For example, the lignin beads obtained by the ionotropic gelling polymer based method for producing the lignin beads will be porous. Porous beads are preferred since this allows for a more uniform thermal stabilization of the beads as heating and possible cross-linking of lignin by reaction with oxidizing species may be effected more uniformly throughout each bead. Also, with porous beads active or passive fillers or additives can be easily incorporated in the pores of the beads.

[0054] In some embodiments, the lignin beads provided in step a) have a bulk density in the range of 0.2 to 1 g / cm3, preferably in the range of 0.5 to 0.7 g / cm3.

[0055] In some embodiments, the lignin beads provided in step a) have a Tgabove 140 °C.

[0056] To reduce the melting / swelling behaviour of the lignin, the beads may also be subjected to an intermediate thermal stabilization step before being subjected to carbonization. The term “thermal stabilization” as used herein, refers to a process of heating the lignin beads at a temperature lower than the temperature required for carbonization of the material. By thermal stabilization, the lignin beads are stabilized so that they become hard and can retain their shape during subsequent carbonization. The thermal stabilization is preferably performed under oxidizing conditions, for example in the presence of oxygen or other oxidizing species, preferably in air. Without wishing to be bound to any specific scientific theory, it is believed that the thermal stabilization of the lignin beads may be assisted by cross-linking of lignin by reaction with oxidizing species. The thermal stabilization increases the Tgof the lignin beads. By performing a thermal stabilization, the lignin beads can be heat treated with retained shape and dimension, avoiding melting / swelling and deformation.

[0057] With the use of lignin beads it has also been found that thermal stabilization may in some instances be dispensed with, and the lignin beads may be directly subjected to carbonization, without an intermediate thermal stabilization step. For example, it has been found that a polymeric binder present in the lignin beads may help retain the shape of the beads, and prevent melting or swelling, during carbonization Thus, the thermal stabilization step of the inventive method is optional.

[0058] When performed, the thermal stabilization involves heating the lignin beads to a lower temperature than the temperature used for the subsequent carbonization.

[0059] The optional step b) of the method according to the first aspect of the present invention involves heating the lignin beads to one or more temperatures in the range of from 140 to 270 °C for a period of at least 30 minutes so as to obtain thermally stabilized lignin beads.

[0060] The heating to produce the thermally stabilized lignin beads is carried out such that the lignin beads are heated to a temperature in the range of from 140 to 270°C, preferably from 180 to 250°C. The heating is carried out for at least 30 minutes, i.e. the residence time of the lignin beads inside the equipment used for the heating is at least 30 minutes. In one embodiment, the heating is carried out for at least 1 hour, or at least 1 .5 hours. Preferably, the heating is carried out for less than 12 hours.

[0061] The thermal stabilization is preferably performed under oxidizing conditions, for example in the presence of oxygen or other oxidizing species, preferably in air. Without wishing to be bound to any specific scientific theory, it is believed that the thermal stabilization of the lignin beads may be assisted by cross-linking of lignin by reaction with oxidizing species. Thus, in some embodiments, the heating in step b) to obtain thermally stabilized lignin beads is carried out under oxidizing conditions, for example in the presence of oxygen or other oxidizing species, preferably in air.

[0062] The heating may be carried out at the same temperature throughout the entire heating stage or may be carried out at varying temperature, such as a stepwise increase of the temperature or using a temperature gradient. In some embodiments, the heating of the lignin beads in step b) is performed by first heating the lignin beads to a temperature in the range of from 140 to 175 °C for a period of at least 15 minutes and subsequently heating the lignin beads to a temperature in the range of from 175 to 270 °C for at least 15 minutes. More preferably, the heating is carried out such that the lignin beads are first heated to a temperature in the range of from 140 to 175°C for a period of at least 15 minutes and subsequently heated to a temperature in the range of from 175 to 250°C for at least 15 minutes.

[0063] The step of heating the lignin beads to produce the thermally stabilized lignin beads can be carried out continuously or in batch mode. The heating can be carried out using methods known in the art and can be carried out in the presence of air or completely or partially under inert gas. Preferably, the heating is carried out in a rotary kiln or other suitable heating apparatus.

[0064] The thermally stabilized lignin beads preferably have a bulk density in the range of from 0.5 g / cm3to 0.7 g / cm3. The thermal stabilization might lead to a slight increase or decrease in bulk density of the beads. The bulk density will however preferably remain within the same range as that of the lignin beads prior to the thermal stabilization.

[0065] Compared to the lignin beads prior to heating to obtain the thermally stabilized material, there may be a small weight loss during the heating. The weight loss typically amounts to less than 15 wt% and is mainly due to evaporation of moisture and loss of volatiles due to decomposition of lignin during heating. By controlling and optimizing parameters such as temperature and time during the thermal stabilization process, a thermally stabilized lignin beads that retains its shape and dimensions with no fusing or swelling during subsequent processing can be obtained. The described process has an excellent compatibility with the typical process requirements for continuous production, using rotary kiln for example, due to mechanical stability of the lignin beads and a relatively short residence time. This is of particular importance for achieving an economical large industry-scale process for producing carbon enriched materials.

[0066] The lignin beads as provided in step a) or optionally as thermally stabilized in step b) are then subjected to carbonization at one or more temperatures in the range of from 300 °C to 1500 °C, wherein the carbonization is carried out for a total time in the range of from 30 minutes to 10 hours, so as to obtain a carbon enriched material.

[0067] The term “carbonization” as used herein, refers to a process of heating the lignin beads as provided in step a) or optionally as thermally stabilized in step b) at one or more temperatures and for a sufficient time so that the lignin is converted to carbon. Depending on the temperature during the carbonization, different types of carbon, such as charcoal or hard carbon, can be obtained from the lignin in the lignin beads.

[0068] As described above, during carbonization the lignin in the lignin beads will be converted to carbon. Thus, a carbon enriched material is obtained. In some embodiments, the obtained carbon enriched material has an elemental carbon content of at least 70 wt%, preferably at least 85 wt%, and more preferably at least 90 wt%, or at least 95 wt%, based on the dry weight of the carbon enriched material.

[0069] In some embodiments, the carbonization comprises a preliminary heating step, followed by a final heating step. The preliminary heating step is preferably carried out at a temperature of between 300 and 800 °C, such as between 500 and 700 °C. The preliminary heating step is preferably carried out in inert atmosphere, preferably nitrogen atmosphere. The duration of the preliminary heating step is at least 30 minutes and preferably less than 10 hours. The preliminary and final heating steps may be carried out as discrete steps or as one single step in direct sequence.

[0070] 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 in inert atmosphere, preferably nitrogen atmosphere. The duration of the final heating step is at least 30 minutes and preferably less than 10 hours.

[0071] Preferably, the carbonization is carried out stepwise. Preferably, the preliminary heating starts at about 300 °C and is subsequently increased to about 500 °C. The final heating step is preferably carried out between 900 °C and 1300 °C, such as at about 1000 °C.

[0072] In some embodiments, the obtained carbon enriched material, i.e. the carbonized material which is the product of step c), has a bulk density in the range of 0.5 to 1 g / cm3, preferably in the range of 0.7 to 1 g / cm3.

[0073] The dimensions of the beads may be slightly reduced during the carbonization, but the size of the beads typically remains on the same order of magnitude. The shape of the beads is preferably retained during carbonization and the shrinkage is typically substantially uniform. Thus, in some embodiments, the carbon enriched material obtained in step c) comprises carbonized lignin beads having a diameter in the range of from 0.1 mm to 5.0 mm, preferably in the range of 0.2 mm to 2.0 mm, and more preferably in the range of 0.3 mm to 0.5 mm. In some embodiments, at least 80 wt%, at least 90 wt% or at least 95 wt% of the carbon enriched material obtained in step c) comprises carbonized lignin beads having a diameter in the range of from 0.1 mm to 5.0 mm, preferably in the range of 0.2 mm to 2.0 mm, and more preferably in the range of 0.3 mm to 0.5 mm.

[0074] The obtained carbon enriched material is useful for example as biochar, or as a precursor to activated carbon. In some embodiments, the method further comprises an additional step of pulverizing the obtained carbon enriched material so as to obtain a carbon enriched material powder.

[0075] The pulverization may be performed by any suitable process, using for example a cutting mill, blade mixer, impact mill, ball-mill, hammer mill and / or jet-mill. Optionally, fine / coarse particle selection by classification and / or sieving may be performed subsequent to the pulverization.

[0076] The pulverization of the carbon enriched material and optional fine / coarse particle selection may be performed so as to obtain a carbon enriched material powder comprising powder particles having an average particle size (Dv50) in the range of from 1 to 25 pm, as measured, for instance, by laser diffraction.

[0077] In some embodiments, more than one step of pulverizing or crushing is performed. In addition, the carbon enriched material powder may be subjected to treatments such as coating or further heat treatments.

[0078] According to a second aspect, the present invention relates to lignin beads comprising at least 80 wt% of lignin based on the dry weight of the lignin beads. Lignin beads having such high content of lignin have been found to be especially useful as a starting material in the method according to the first aspect. The lignin beads according to the second aspect may be further defined as set out above with reference to the lignin beads provided in step a) of the method according to the first aspect.

[0079] According to a third aspect, the present invention relates to a method for producing thermally stabilized lignin beads, comprising the steps of: a) providing lignin beads, wherein said lignin beads comprise at least 80 wt% of lignin based on the dry weight of the lignin beads; and b) heating the lignin beads to one or more temperatures in the range of from 140 to 270 °C for a period of at least 30 minutes so as to obtain thermally stabilized lignin beads.

[0080] According to a fourth aspect the present invention relates to thermally stabilized lignin beads obtainable by the method according to the third aspect.

[0081] Thermal stabilization allows for the thermally stabilized lignin beads to be subjected to carbonization with better retained shape and dimensions, avoiding melting / swelling and deformation. The substantially spherical or spheroidal shape of the lignin beads provides for a uniform thermal stabilization. The thermally stabilized lignin beads are useful as an intermediate product for the production a carbon enriched material.

[0082] The method according to the third aspect may be further defined as set out above with reference to the method according to the first aspect.

[0083] According to a fifth aspect, the present invention relates to a carbon enriched material obtainable by the method according to the first aspect.

[0084] According to a sixth aspect, the present invention relates to a non-aqueous secondary battery comprising the carbon enriched material obtained by the method according to the first aspect.

[0085] The carbon enriched material obtained by the method according to the first aspect is preferably used as an active material in a negative electrode of a non-aqueous secondary battery, such as a lithium-ion battery or sodium-ion battery. When used for producing such a negative electrode, any suitable method to form such a negative electrode may be utilized. In the formation of 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 to form the carbon enriched material into an electrode, conductive materials, such as carbon black, carbon nanotubes or metal powders, and / or further Li storage materials, such as graphite or lithium. For example, the binders may be selected from, but are not limited to, poly(vinylidene fluoride), poly(tetrafluoroethylene), carboxymethylcellulose, natural butadiene rubber, synthetic butadiene rubber, polyacrylate, poly(acrylic acid), alginate, etc., or from combinations thereof. Optionally, a solvent such as e.g. 1-methyl-2-pyrrolidone, 1 -ethyl-2-pyrrolidone, water, or acetone is utilized during the processing.

[0086] According to a seventh aspect, the present invention relates to the use of lignin beads, wherein said lignin beads comprise at least 80 wt% of lignin based on the dry weight of the lignin beads, for producing a carbon enriched material.

[0087] The lignin beads used in the seventh aspect may be further defined as set out above with reference to the lignin beads provided in step a) of the method according to the first aspect.

[0088] Generally, while the products, polymers, materials, and processes herein may be described in terms of “comprising” various components or steps, the products, polymers, materials, and processes can also “consist essentially of” or “consist of” the various components and steps.

[0089] While the invention has been described with reference to various exemplary embodiments, it will be understood by those skilled in the art that various changes can be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.

[0090] 1 - Preparation of liqnin beads

[0091] A lignin slurry was prepared according to the following recipe: - 25 g softwood kraft lignin - 100 g deionized water

[0092] - 1 .2 g Tween 80

[0093] - 0.6 g sodium alginate

[0094] The lignin / alginate slurry was stirred well using a magnetic stirrer.

[0095] In a separate beaker 10 g of CaCl2 was dissolved in 1000 g deionized water.

[0096] The lignin slurry was added dropwise into the CaCl2 solution using a syringe with a needle size of 1.1 mm.

[0097] When the drops of lignin / alginate slurry contact the calcium ions in solution, spherical lignin / alginate beads are formed. The formed beads were washed under running water and then dried at 50 °C overnight.

[0098] The obtained dried lignin beads exhibited high sphericity, high porosity, and were mechanically stable. A photograph of the dried beads is shown in Fig. 1 . The obtained beads had a bulk density of 0.4 g / cm3and a diameter of < 5mm. The internal structure of the dried beads was studied by crushing the beads and studying the crushed beads by scanning electron microscopy (SEM). SEM images Fig 2a (1000X magnification) and 2b (5000X magnification) show that the beads are porous with a porosity in the range of 5-50% (as estimated from the SEM images).

[0099] Example 2 - Thermal stabilization of lion in beads

[0100] The lignin beads obtained in Example 1 were subjected to thermal stabilization by heating the lignin beads at 250 °C in air for 2 hours.

[0101] The obtained stabilized lignin beads had retained their high sphericity, porosity, and mechanical stability. Example 3 - Carbonization of lignin beads

[0102] The stabilized lignin beads obtained in Example 2 were subjected to carbonization by heating the lignin beads at 1050 °C under nitrogen for 2 hours.

[0103] The obtained stabilized lignin beads had retained their high sphericity and porosity. A photograph of the carbonized beads is shown in Fig. 3. The obtained carbonized lignin beads were studied by scanning electron microscopy (SEM). The internal structure of the dried beads was studied by crushing the beads and studying the crushed beads by scanning electron microscopy (SEM). SEM images show that the porosity observed in the dried lignin beads in Example 1 remains in the carbonized lignin beads. Fig 4a (1000X magnification) and 4b (5000X magnification) show that the beads are porous with a porosity in the range of 5- 50% (as estimated from the SEM images).

Claims

CLAIMS1 . A method for producing a carbon enriched material, said method comprising the steps of: a) providing lignin beads, wherein said lignin beads comprise at least 80 wt% of lignin based on the dry weight of the lignin beads; b) optionally heating the lignin beads to one or more temperatures in the range of from 140 to 270 °C for a period of at least 30 minutes so as to obtain thermally stabilized lignin beads; and c) subjecting the, optionally thermally stabilized, lignin beads to carbonization at one or more temperatures in the range of from 300 °C to 1500 °C, wherein the carbonization is carried out for a total time in the range of from 30 minutes to 10 hours, so as to obtain a carbon enriched material.

2. The method according to claim 1 , wherein the lignin beads provided in step a) have a spherical or spheroidal shape.

3. The method according to any one of the preceding claims, wherein the lignin beads provided in step a) have a diameter in the range of from 0.1 mm to 5.0 mm, preferably in the range of 0.2 mm to 2.0 mm, and more preferably in the range of 0.3 mm to 0.5 mm.

4. The method according to any one of the preceding claims, wherein the lignin beads provided in step a) comprise at least 90 wt%, preferably at least 95 wt%, of lignin based on the dry weight of the lignin beads.

5. The method according to any one of the preceding claims, wherein the lignin is Kraft lignin.

6. The method according to any one of the preceding claims, wherein the lignin beads provided in step a) further comprise in the range of 0.5 to 10 wt%,preferably in the range of 1 to 5 wt%, and more preferably in the range of 1 to 3 wt%, of a polymeric binder based on the dry weight of the lignin beads.

7. The method according to claim 6, wherein the polymeric binder comprises a gel forming polymer, preferably an ionotropic gelling polymer, more preferably an ionotropic gelling polysaccharide, and more preferably alginate.

8. The method according to any one of the preceding claims, wherein the lignin beads provided in step a) further comprise in the range of 0.5 to 10 wt%, preferably in the range of 1 to 5 wt%, and more preferably in the range of 1 to 3 wt%, of a surfactant based on the dry weight of the lignin beads.

9. The method according to claim 8, wherein the surfactant is a nonionic surfactant, preferably a polysorbate, and more preferably Tween 80.

10. The method according to any one of the preceding claims, wherein the lignin beads provided in step a) are produced by a method comprising: i) preparing an aqueous mixture comprising at least 80 wt% of lignin, 0.5 to 10 wt% of ionotropic gelling polymer, and 0.5 to 10 wt% of a nonionic surfactant, based on the total dry weight of the aqueous mixture; ii) adding the aqueous mixture dropwise into an aqueous solution comprising divalent metal ions so as to obtain lignin beads; and iii) recovering, and optionally washing, the formed lignin beads.1 1 . The method according to any one of the preceding claims, wherein the lignin beads provided in step a) have a Tgabove 140 °C.

12. The method according to any one of the preceding claims, wherein the lignin beads provided in step a) are porous lignin beads.

13. The method according to any one of the preceding claims, wherein thelignin beads provided in step a) have a bulk density in the range of 0.2 to 1 g / cm3, preferably in the range of 0.5 to 0.7 g / cm3.

14. The method according to any one of the preceding claims, wherein the heating of the lignin beads in step b) is performed by first heating the lignin beads to a temperature in the range of from 140 to 175 °C for a period of at least 15 minutes and subsequently heating the lignin beads to a temperature in the range of from 175 to 270 °C for at least 15 minutes.

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

16. The method according to claim 15, wherein the preliminary heating step is carried out at a temperature of between 300 and 800 °C for at least 30 minutes.

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

18. The method according to any one of claims 15-17, wherein the final heating step is carried out at a temperature between 800 °C and 1500 °C for at least 30 minutes.

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

20. The method according to any one of the preceding claims, wherein the obtained carbon enriched material has an elemental carbon content of at least 70 wt%, preferably at least 85 wt% based on the dry weight of the carbon enriched material.21 . The method according to any one of the preceding claims, wherein the obtained carbon enriched material has a bulk density in the range of 0.5 to 1 g / cm3, preferably in the range of 0.7 to 1 g / cm3.

22. The method according to any one of the preceding claims, wherein the method comprises an additional step of pulverizing the obtained carbon enriched material so as to obtain a carbon enriched material powder.

23. Lignin beads comprising at least 80 wt% of lignin based on the dry weight of the lignin beads.

24. The lignin beads according to claim 23, further defined as in any one of claims 2-13.

25. A method for producing thermally stabilized lignin beads, comprising the steps of: a) providing lignin beads, wherein said lignin beads comprise at least 80 wt% of lignin based on the dry weight of the lignin beads; and b) heating the lignin beads to one or more temperatures in the range of from 140 to 270 °C for a period of at least 30 minutes so as to obtain thermally stabilized lignin beads.

26. The method according to claim 25, further defined as in any one of claims 2- 14.

27. Thermally stabilized lignin beads obtainable by a method according to any one of claims 25-26.

28. A carbon enriched material obtainable by the method according to claim any one of claims 1 -22.

29. A negative electrode for a non-aqueous secondary battery comprising the carbon enriched material obtainable by the method according to claim any one of claims 1 -22 as active material.

30. Use of lignin beads, wherein said lignin beads comprise at least 80 wt% of lignin based on the dry weight of the lignin beads, for producing a carbon enriched material. 31 . Use according to claim 30, wherein the lignin beads are further defined as in any one of claims 2-13.

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