Method for producing granular carbon-silicon composite from lignin-silicon composite

Abstract

The present invention relates to a method for producing an agglomerated lignin-silicon composite material, the method comprising the steps of mixing lignin in powder form, at least one silicon-containing active material in powder form, and optionally at least one additive, compressing the mixture, and grinding the compressed composite material to obtain an agglomerated lignin-silicon composite material. The present invention also relates to a granular carbon-silicon composite material obtained by heat treating the agglomerated lignin-silicon composite material.

Description

[Technical field]

[0001] The present invention relates to a method for producing an agglomerated lignin-silicon composite material, and to an agglomerated lignin-silicon composite material obtainable by said method.The present invention further relates to a method for obtaining a granular carbon-silicon composite material from said agglomerated lignin-silicon composite material.The present invention further relates to a carbon-silicon composite powder obtainable from said downstream carbon-silicon composite material, and to an anode for a non-aqueous secondary battery comprising said carbon-silicon composite powder as an active material.The present invention further relates to the use of said carbon-silicon composite powder as an active material in 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. Today, 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] Graphite (natural or synthetic) is currently used as the anode material in most lithium-ion batteries due to its high energy density and stable charge / discharge performance over long periods of time. 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. What graphite and amorphous carbon have in common is their small volume change during charge and discharge. This enhances the mechanical stability of the electrode material and helps maintain good cycling stability. Amorphous carbon can be used as the sole active electrode material or in a mixture with graphite. Hard carbon often has good charge / discharge rate performance required for fast charging and high power systems.

[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] However, hard carbons typically have a lower usable energy density compared to graphite, which currently limits their widespread use as an anode material in lithium-ion batteries.

[0006] Silicon has a high specific charge capacity (theoretical capacity is 3579 mAh / g, corresponding to Li15Si4) compared to carbon (372 mAh / g, LiC6) and can therefore be used to increase the energy density of carbon-based (graphite and / or amorphous) anode materials. Thus, in principle, the addition of silicon could be used to compensate for the lower energy density of amorphous carbon (such as hard carbon) compared to graphite.

[0007] A drawback of silicon as an electrode material is the large volume expansion that occurs during charging and discharging of silicon. The large volume expansion of silicon poses challenges that lead to high irreversible capacity and poor cycling behavior. To alleviate this issue, it has been envisioned to encapsulate silicon within a carbon matrix to reduce the effect of volume expansion, thereby reducing irreversible capacity loss and improving charge / discharge cycling behavior.

[0008] Silicon is one of the three main forms of elemental silicon: silicon suboxide (SiO x Silicon may be used as a silicon-containing material or as a silicon alloy (e.g., SiMxCz, where M is the metal). Compounds containing silicon or silicon rich materials are generally referred to herein as silicon-containing materials or SiX.

[0009] Commercially available composites of carbon and SiX, such as graphite and SiX composites, are currently typically produced by processes that include one of the following steps: Mixing graphite and SiX prior to electrode preparation, e.g. using high energy mixing or grinding techniques Coating graphite with a thin layer of silicon-containing material, e.g. by chemical vapor deposition (CVD), to obtain a graphite / SiX core / shell material Coating the SiX particles with a thin carbon layer, for example by wet chemical methods, to obtain a SiX / carbon core / shell material Blending graphite with SiX during electrode preparation

[0010] The SiX component in the above method can be surface pre-oxidized or carbon coated to enhance stability, and the carbon / SiX composite can be further carbon coated to enhance its stability.

[0011] When utilized as an electrode material in secondary batteries, the graphite and SiX composite is typically provided in powder form and mixed with a binder to form an electrode.

[0012] US20140287315 A1 describes a method for producing a Si / C composite material, which includes providing a silicon-containing active material, providing lignin, contacting the active material with a lignin-containing C precursor, and carbonizing the active material by converting the lignin to carbon at a temperature of at least 400° C. in an inert gas atmosphere. The silicon-based active material can be ground together with the lignin or physically mixed with the lignin.

[0013] However, in graphite / carbon and SiX composites obtained by grinding, coating, and other methods as mentioned above, the individual components are usually adjacent to each other (SiX next to graphite / carbon) or on top of each other (SiX on the surface of graphite / carbon or graphite / carbon on the surface of SiX). Thus, the loading amount of SiX is limited while maintaining good and uniform dispersion of Si. Furthermore, if SiX or graphite / carbon and SiX composites are not carbon-coated, SiX will be in direct contact with the binder and electrolyte of the battery, which will cause problems in cycle stability. Therefore, special binders and electrolytes are required.

[0014] One strategy to overcome these issues is to embed SiX in a carbon precursor and convert it into a carbon-rich material to create a C / SiX composite.

[0015] As mentioned above, hard carbon can be obtained from lignin as a raw material. 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.

[0016] 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.

[0017] Therefore, there is still room for improvement in the method for producing carbon-silicon composites with high silicon content as well as good and uniform distribution of silicon in the carbon matrix. The method should allow the use of powdered lignin, thereby avoiding the plastic deformation / melting, severe expansion and foaming of the lignin upon heating to obtain the carbon-silicon composite. Furthermore, the method should be amenable to large-scale production. Summary of the Invention

[0018] It is an object of the present invention to provide an improved process for producing carbon-silicon composite materials that allows for the use of renewable carbon sources and eliminates or mitigates at least some of the disadvantages of the prior art processes.

[0019] It is a further object of the present invention to provide a method for producing an improved carbon-silicon composite material suitable for use as the negative electrode active material in secondary batteries, such as lithium ion batteries.

[0020] It is a further object of the present invention to provide a method for producing carbon-silicon composite materials having a high silicon content as well as good and uniform dispersion of silicon in the carbon matrix.

[0021] It is a further object of the present invention to provide a method for producing carbon-silicon composite materials that allows for the use of lignin in powder form while maintaining the shape and dimensions of the lignin during subsequent heat treatment.

[0022] It is a further object of the present invention to provide a method for producing carbon-silicon composites from lignin that is scalable and therefore suitable for large-scale production.

[0023] 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. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] According to a first aspect, the present invention relates to a method for producing an agglomerated lignin-silicon composite material, said method comprising the steps of: a) providing lignin in powder form; b) providing at least one silicon-containing active material in powder form; c) mixing lignin powder, at least one silicon-containing active material powder, and optionally at least one additive to obtain a lignin-silicon powder mixture; d) compressing the lignin-silicon powder mixture obtained in step c) to obtain a lignin-silicon composite material; e) grinding the lignin-silicon composite material obtained in step d) to obtain an agglomerated lignin-silicon composite material; f) optionally sieving the agglomerated lignin-silicon composite material obtained in step e) to remove particles with a size less than 100 μm, thereby obtaining an agglomerated lignin-silicon 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; Includes.

[0025] It has surprisingly been found that the silicon-containing active material can be directly dispersed within the lignin matrix by mixing, followed by compaction and agglomeration, resulting in an agglomerated lignin-silicon composite material having a high silicon content as well as a uniform distribution of silicon within the lignin matrix.

[0026] Furthermore, it has been surprisingly found that lignin compressed and agglomerated into macroscopic particles can be heat treated while avoiding melting / expansion and deformation and retaining its shape and dimensions. Thus, the agglomerated lignin-silicon composite has good heat treatability and is suitable as a precursor for industrial-scale production of carbon-silicon composites.

[0027] According to a second aspect, the present invention relates to an agglomerated lignin-silicon composite material obtainable by the method according to the first aspect.

[0028] According to a third aspect, the present invention provides a method for producing a granular carbon-silicon composite material comprising the steps of: i) providing an agglomerated lignin-silicon composite material obtained by the method according to the first aspect; ii) subjecting the agglomerated lignin-silicon 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-silicon composite material.

[0029] Surprisingly, it has been found that the production of carbon-silicon composites using lignin as a carbon precursor is facilitated by providing the lignin-silicon composite in the form of an agglomerated lignin-silicon composite, as the agglomerated lignin-silicon composite maintains its dimensional integrity during further heat treatment to obtain the carbon-silicon composite.

[0030] Furthermore, the uniform distribution of silicon within the agglomerated granular silicon composite is maintained after conversion to a carbon-enriched material, and thus the resulting granular carbon-silicon composite also has a uniform distribution of silicon, making it suitable for further processing into the active material of the negative electrode of a secondary battery.

[0031] According to a fourth aspect, the present invention relates to a granular carbon-silicon composite material obtainable by the method according to the third aspect.

[0032] According to a fifth aspect, the present invention relates to a carbon-silicon composite powder obtainable by grinding a granular carbon-silicon composite material obtained by the method according to the third aspect.

[0033] The uniform distribution of silicon within the carbon is maintained after pulverization, and the resulting carbon-silicon composite powder is suitable for use as the negative electrode active material in secondary batteries.

[0034] 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-silicon composite powder according to the fifth aspect.

[0035] According to a seventh aspect, the present invention relates to the use of a carbon-silicon composite powder according to the fifth aspect as an active material in the negative electrode of a non-aqueous secondary battery.

[0036] According to a first aspect, the present invention relates to a method for producing an agglomerated lignin-silicon composite material, wherein step a) of the method according to the first aspect of the invention comprises providing lignin in the form of a powder.

[0037] The term "lignin" as used herein refers to any type of lignin that can be used as a carbon source for producing carbonized granular carbon-silicon composites. Examples of said lignin include, but are not limited to, lignin obtained from plant materials such as wood, for example, softwood lignin, hardwood lignin, and lignin from annular plants. Lignin can also be chemically modified.

[0038] 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.

[0039] Preferably, the carbon-containing precursor contains less than 1% ash, more preferably less than 0.5% ash.

[0040] 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.

[0041] Preferably, the lignin provided in step a) of the process according to the first aspect is a Kraft lignin, i.e. a lignin obtained by a Kraft process. Preferably, the Kraft lignin is obtained from hardwoods or softwoods, most preferably from softwoods.

[0042] The lignin in powder form provided in step a) is preferably dried before being mixed with at least one silicon-containing active material. Drying of the lignin powder is carried out by methods and devices known in the art. In one embodiment, the moisture content of the lignin in powder form used in step a) is less than 45% by weight. Preferably, the moisture content of the lignin before being mixed with at least one silicon-containing active material 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 at least one silicon-containing active material 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.

[0043] In one embodiment, the particle size distribution of the lignin in powder form is such that at least 80% by weight of the particles have a diameter of less than 0.2 mm. The lignin powder obtained after drying has a broad particle size distribution ranging from 1 μm to 2 mm, which is heavily biased towards the micrometer range, meaning that a significant proportion of the particles have a diameter in the range of 1 to 200 μm.

[0044] In one embodiment, 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 less than 0.2 mm and the moisture content is less than 45% by weight.

[0045] The lignin powder preferably has a density of 0.3 g / cm before being mixed with the at least one silicon-containing active material. 3 ~0.4g / cm 3 The bulk density ranges from 0.01 to 0.01.

[0046] Step b) of the method according to the first aspect comprises providing at least one silicon-containing active material in the form of a powder.

[0047] The term "silicon-containing active material" (SiX) as used herein refers to silicon-containing materials that can be used as (battery) capacity enhancing materials in carbon-silicon composites and thus can be used to make carbonized carbon-silicon composites.

[0048] The term "silicon-containing active materials" (SiX) as used herein encompasses both pure elemental Si and Si-rich compounds. The Si-rich compounds include silicon dioxide (SiO2), Si suboxides (SiOx, where 0≦x≦2), Si alloys (such as SiFex, SiFexAly, or SiFexCy), and other Si-rich compounds such as silicates. Various models have been proposed to explain the structure of SiOx. Most commonly, SiOx is described as a mixture of Si and SiO2 interdispersed on the nanometer scale. The silicon-containing active materials (SiX) described above can be provided in crystalline or amorphous form, and can further be surface pre-oxidized or carbon-coated to enhance stability.

[0049] At least one form-containing active material in particulate form is mixed with lignin in powder form. In some embodiments, each silicon-containing active material utilized is selected from the group of elemental silicon, silicon suboxide, silicon-metal alloy, or silicon-metal carbon alloy. Silicon suboxide can be SiOx, where 0≦x≦2. Silicon-metal alloy can be any suitable silicon-metal alloy, such as, for example, SiFex or SiFexAly. Silicon-metal carbon alloy can be, for example, SiFexCy.

[0050] In some embodiments, one silicon-containing active material is utilized, i.e., the step of providing at least one silicon-containing active material includes providing one silicon-containing active material.

[0051] In some embodiments, one or more silicon-containing active materials are utilized, i.e., providing at least one silicon-containing active material includes providing two, three, four, or more silicon-containing active materials, each of which can be selected from the silicon-containing active materials described above.

[0052] The silicon-containing active material is provided in the form of a powder, and preferably, the silicon-containing active material is micro-sized or nano-sized. In this specification, "micro-sized" means that the silicon-containing active material is in a particulate form, and the average particle size of the particles is in the micrometer range, for example, 1 to 50 μm. In this specification, "nano-sized" means that the silicon-containing active material is in a particulate form, and the average particle size of the particles is in the nanometer range, for example, 1 to 999 nm.

[0053] Typically, the average particle size of the silicon-containing active material in powder form is in the range of 5 nm to 5 μm.

[0054] At least one silicon-containing active material is preferably dried before being mixed with lignin in powder form.The drying of silicon-containing active material is carried out by the method and device known in the art.In one embodiment, the moisture content of the silicon-containing active material used in step b) is less than 20% by weight, for example less than 10% by weight.

[0055] Step c) of the method according to the first aspect comprises mixing lignin powder, at least one silicon-containing active material powder, and optionally at least one additive to obtain a lignin-silicon powder 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. To facilitate the subsequent compaction process and improve the density and mechanical properties of the resulting lignin-silicon composite material, suitable additives such as binders or lubricants can be added. 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-silicon powder mixture.

[0058] In some embodiments, the mixing is carried out for at least 1 minute, or at least 10 minutes, or at least 15 minutes. In some embodiments, the 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 silicon-containing active material 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 the dispersion of the at least one silicon-containing active material within the lignin matrix.

[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 at least one silicon-containing active material in the lignin matrix can be improved by both sufficient mixing time, appropriate mixing speed, and appropriate mixing temperature to achieve uniform distribution of at least one silicon-containing active material in the lignin matrix. The uniform dispersion of the mixture of lignin and silicon powder ensures uniform dispersion in the formed aggregate after compression.

[0062] The degree of dispersion of the at least one silicon-containing active material in the lignin matrix can be controlled by appropriately selecting the amount of the at least one silicon-containing active material added to the lignin powder, the particle size of the at least one silicon-containing active material, and mixing parameters such as mixing speed, mixing time, mixing temperature, etc. For example, when using nano-sized silicon-containing active materials, the particles of the silicon-containing active material may be strongly aggregated. Therefore, a high mixing speed is required to break the aggregates and disperse the silicon-containing active material in the lignin matrix.

[0063] The uniform dispersion of the mixture of lignin and silicon powder ensures uniform dispersion in the formed aggregates after compression. The dispersion of the silicon-containing active material is maintained after conversion to carbon-enriched material, resulting in a granular carbon-silicon composite material with a uniform dispersion of the silicon-containing active material in the carbon matrix. After pulverization, this material is suitable for use as an active material in the negative electrode of a secondary battery. The use of a carbon-silicon composite material with a uniform dispersion of the silicon-containing active material in the carbon matrix as an active material in the negative electrode of a secondary battery is advantageous because the uniform dispersion means that more uniform properties of the active material, and therefore the electrode, are obtained compared to using a material in which the silicon-containing active material is not uniformly distributed. For example, a uniform dispersion of the silicon-containing active material in the carbon matrix may result in a more uniform volume change of the electrode during charging and discharging.

[0064] In one embodiment, the lignin powder is mixed with at least one silicon-containing active material in powder form while simultaneously grinding the powder to reduce the particle size of the powder particles. Grinding can be performed by methods such as impact milling, hammer milling, ball milling, jet milling, etc.

[0065] The mixing of lignin powder and at least one silicon-containing active material in powder form can be carried out using any suitable device known in the art.For example, when a particularly high level of mixing is required, a high-impact dry blending machine suitable for high shear mixing, such as mechanical chemical processing or hybridization, can be used to simultaneously deagglomerate and break down the particles of lignin particles and silicon-containing active material and reform them into hybrid particles.

[0066] In one embodiment, the mixing is performed by dry mixing. The term "dry mixing" as used herein refers to a 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 silicon-containing active material are in the form of dry powders during the mixing process. The lignin-silicon mixture thus obtained is in the form of a dry powder.

[0067] Dry mixing provides a simple process for mixing the lignin powder with the at least one silicon-containing active material powder, which can be easily integrated with subsequent processing steps.

[0068] In one embodiment, the lignin-silicon powder mixture has a bulk density of 0.3 to 0.5 g / cm 3 The range is.

[0069] Step d) of the method according to the first aspect comprises compressing the lignin-silicon powder mixture obtained in step c) to obtain a lignin-silicon composite material.

[0070] The term "lignin-silicon composite" as used herein refers to a composite material comprising lignin and one or more silicon-containing active materials, such as a composite material comprising lignin and elemental silicon, a composite material comprising lignin and one or more silicon-rich compounds, or a composite material comprising lignin, elemental silicon, and one or more silicon-rich compounds. The term "lignin-silicon composite" further refers to a material essentially comprising lignin and one or more silicon-containing active materials, where at least 95% by weight, or at least 98% by weight, of the lignin-silicon composite material is composed of lignin and one or more silicon-containing active materials, based on the dry weight of the lignin-silicon composite material. The lignin-silicon composite material can also optionally contain a small amount of at least one additive, less than 5% by weight, or less than 2% by weight, based on the dry weight of the lignin-silicon composite material. In the lignin-silicon composite material, one or more silicon-containing active materials are uniformly dispersed within the lignin matrix.

[0071] The compaction of the lignin-silicon powder mixture is preferably carried out by roll compaction. The roll compaction of the lignin-silicon powder mixture is achieved by a roller compactor, which causes the lignin-silicon powder mixture to agglomerate.

[0072] In the compression step, a compressed lignin-silicon intermediate is produced. Here, a mixture of fine lignin and silicon 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.

[0073] 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 powder in the nip region is sealed axially along the roller surface.

[0074] In one embodiment, the roll configuration is such that the nip area is sealed axially along the roller surface with a static plate. By ensuring that the nip area is sealed, powder loss at the axial ends of the roller is minimized compared to fully cylindrical nip rollers.

[0075] During compaction, the powdered material is compressed by mechanical pressure to form a lignin-silicon composite, with the powder particles compressed closer together and entering a plastic phase that improves the dispersion of the silicon within the lignin matrix.

[0076] Compaction may also act to enhance the interactions between the lignin particles and the silicon-containing active material 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-silicon composite is further stabilized, i.e., stabilized by a thermal stabilization step.

[0077] Compaction can be performed on a lignin and silicon powder mixture without the addition of any additives, or alternatively, on a lignin-silicon 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-silicon powder mixture.

[0078] Step e) of the method according to the first aspect comprises comminuting the lignin-silicon composite material obtained in step d) to obtain an agglomerated lignin-silicon composite material.

[0079] In the grinding step, the compressed lignin-silicon obtained in the compacting step is subjected to grinding or attrition, such as by a rotary granulator, a cage mill, a beater mill, a hammer mill, a crusher mill, and / or a combination thereof. During this step, an agglomerated lignin-silicon composite material is produced.

[0080] As used herein, the term "agglomerated lignin-silicon composite" refers to macroscopic particles that include clustered smaller particles of lignin and at least one silicon-containing active material.

[0081] In some embodiments, the agglomerated lignin-silicon composite material comprises in the range of 0.5 to 30 weight percent, or 2 to 20 weight percent, of a silicon-containing active material based on the dry weight of the agglomerated lignin-silicon composite material.

[0082] In some embodiments, the agglomerated lignin-silicon composite material comprises in the range of 70-99.5 wt% lignin, based on the dry weight of the agglomerated lignin-silicon composite material.

[0083] In one embodiment, the agglomerated lignin-silicon composite material comprises 70-99.5 wt.% lignin, 0.5-30 wt.% of at least one silicon-containing active material, and 0-5 wt.% of at least one additive, based on the dry weight of the agglomerated lignin-silicon composite material.

[0084] As the lignin-silicon powder mixture is compressed during the production of the agglomerated lignin-silicon composite, the bulk density of the lignin-silicon powder mixture increases when pressure is applied to the powder. This means that the bulk density of the agglomerated lignin-silicon composite is higher than that of the lignin-silicon powder mixture. The agglomerated lignin-silicon 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-silicon composite has a relatively high hardness even after compression. The hard particles are advantageous for subsequent processing because they can withstand physical impacts during processing.

[0085] The agglomerated lignin-silicon composite material preferably has a bulk density of 0.5 g / cm 3 ~0.7g / cm 3 In the process of agglomeration, the bulk density of the material increases as it is compressed.

[0086] Step f) of the method according to the first aspect comprises optionally sieving the agglomerated lignin-silicon composite material obtained in step e) to remove particles with a size less than 100 μm, thereby obtaining an agglomerated lignin-silicon 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. Includes.

[0087] 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.

[0088] In the sieving step, the agglomerated lignin-silicon composite material from the grinding step is sieved by physical separation, such as sieving, also called screening, to obtain a product that is an agglomerated lignin-silicon 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 of less than 100 (or 500) μm pass through the screen and are rejected, preferably returned to the compression step, while most of the particles with a diameter of more than 100 (or 500) μm are retained and subjected to the subsequent processing steps 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.

[0089] In a preferred embodiment, after the sieving step, an agglomerated lignin-silicon composite material is obtained 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, preferably 0.5 to 2.0 mm.

[0090] The agglomerated lignin-silicon composite material preferably 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.

[0091] In one embodiment, the method according to the first aspect comprises an additional step g) comprising heating the agglomerated lignin-silicon composite material to a temperature in the range of 140-250°C for at least 30 minutes to obtain a thermally stabilized agglomerated lignin-silicon composite material.

[0092] The heat stabilization treatment further improves the heat processability of the agglomerated lignin-silicon composite material, thus both the formation of aggregates and the heat stabilization of the formed aggregates improves the processability of the lignin-silicon composite material in terms of avoiding melting / expansion and retaining shape and dimensions during heating.

[0093] As used herein, the term "heat stabilization" refers to the process of heating an agglomerated lignin-silicon composite material at a temperature below that required to carbonize the material, which allows the agglomerated lignin-silicon composite material to be heat treated while avoiding melting / expansion and deformation and retaining its shape and dimensions.

[0094] Thermal stabilization stabilizes and hardens the outer surface of the agglomerated lignin-silicon 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 silicon within the lignin matrix.

[0095] The thermally stabilized agglomerated lignin-silicon composite material preferably has a bulk density of 0.5 g / cm 3 ~0.7g / cm 3 Heat stabilization may slightly increase or decrease the bulk density of the lignin. However, it is preferred that the bulk density remains in the same range as before heat stabilization.

[0096] The step of heating the agglomerated lignin-silicon composite to produce a thermally stabilized agglomerated lignin-silicon 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.

[0097] Heating to produce a thermally stabilized agglomerated lignin-silicon composite is carried out such that the agglomerated lignin-silicon 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-silicon composite in the device 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-silicon composite is first heated to a temperature of 140-175°C for at least 15 minutes, and then to a temperature of 175-250°C for at least 15 minutes.

[0098] The thermally stabilized agglomerated lignin-silicon composite material comprises lignin, at least one silicon-containing active material, and optionally at least one additive. There may be some weight loss during heating compared to the agglomerated lignin-silicon 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 the evaporation of water and loss of volatile substances due to the decomposition of lignin during heating.

[0099] By controlling and optimizing parameters such as temperature and time during the thermal stabilization process, it is possible to obtain a thermally stabilized agglomerated lignin-silicon composite that retains its shape and dimensions without fusing or expanding during subsequent processing. The described method has excellent compatibility with typical process requirements for continuous production, for example using rotary kilns, due to the mechanical stability and relatively short residence time of the agglomerated lignin-silicon composite. This is particularly important for realizing an economical large-scale industrial-scale process for producing carbon-silicon composites.

[0100] According to a second aspect, the present invention relates to an agglomerated lignin-silicon composite material obtainable by the method according to the first aspect. The agglomerated lignin-carbon composite material according to the second aspect may be further defined as set out above with reference to the first aspect.

[0101] According to a third aspect of the invention, the present invention relates to a method for producing a granular carbon-silicon composite material, comprising heat treating an agglomerated lignin-silicon composite material obtainable by the method according to the first aspect of the invention to obtain a granular carbon-silicon composite material.

[0102] Step i) of the method according to the third aspect comprises providing an agglomerated lignin-silicon composite material obtainable by the method according to the first aspect.

[0103] By providing the lignin-silicon composite in an agglomerated form, a more compact and harder material is achieved. Hard particles are advantageous for subsequent processing as they can withstand physical impacts during processing. The agglomerated lignin-silicon composite is further defined as described above with reference to the first embodiment.

[0104] Step ii) of the method according to the third aspect comprises subjecting the agglomerated lignin-silicon composite material to a heat treatment at one or more temperatures in the range of from 300°C to 1500°C, the heat treatment being carried out for a total time period of from 30 minutes to 10 hours, so as to obtain a granular carbon-silicon composite material.

[0105] The term "heat treatment" as used herein refers to the process of heating the thermally stabilized agglomerated lignin-silicon composite at one or more temperatures for a time sufficient to convert the lignin to carbon. After heat treatment, the carbon content of the non-silicon portion of the composite is 80% by weight or more, or 90% by weight or more, or 95% by weight or more. Depending on the temperature during heat treatment, different types of carbon can be obtained from the lignin in the lignin-silicon composite, such as charcoal or hard carbon.

[0106] During the heat treatment, the components of the composite are fully cross-linked and carbon is enriched through carbonization of the lignin to produce a granular carbon-silicon composite.

[0107] As used herein, the term "carbon-silicon composite" as used in expressions such as "granular carbon-silicon composite" and "carbon-silicon composite powder" refers to a composite comprising lignin-derived carbon and at least one silicon-containing active material. The carbon-silicon composite is obtained by heat treating the agglomerated lignin-silicon composite described herein. In the carbon-silicon composite, at least one silicon-containing active material is uniformly dispersed within the carbon matrix.

[0108] 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.

[0109] 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.

[0110] 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 at between 900°C and 1300°C, for example at about 1000°C. After the final heating step carried out at 1000°C or higher, the surface area of ​​the resulting product is typically greater than 10 m2. 2 / g or less.

[0111] The heat treated material, i.e. the product of step ii), a granular carbon-silicon composite material, preferably has a bulk density of 0.2 g / cm 3 ~0.7g / cm 3 Depending on the amount and type of silicon-containing active material in the agglomerated lignin-silicon composite, the bulk density may remain in the same range or may decrease (due to mass loss) after carbonization to a granular carbon-silicon composite.

[0112] Since the shape and dimensions of the agglomerated lignin-silicon composite material are retained during heat treatment, it is preferred that the granular carbon-silicon composite material 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.

[0113] The heat-treated material, i.e. the granular carbon-silicon composite material that is the product of step ii) of the method according to the third aspect, is useful, for example, as biochar or as a precursor to activated carbon.

[0114] In one embodiment, the method according to the third aspect includes an additional step of grinding the granular carbon-silicon composite material to obtain a carbon-silicon composite powder. The pulverization can be carried out by any suitable process, such as using, for example, a cutting mill, a blade mixer, a ball mill, an impact 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.

[0115] The choice of fine powder and optional fine / coarse particles of the carbon-silicon 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-silicon composite powder containing powder particles in the range of 5 to 25 μm.

[0116] In one embodiment, the grinding or pulverizing step is carried out multiple times. Further, the carbon-silicon composite powder may be subjected to processing such as coating or further heat treatment.

[0117] According to a fourth aspect, the present invention relates to a granular carbon-silicon composite material obtainable by the method according to the third aspect. The granular carbon-silicon composite material according to the fourth aspect may be further defined as set out above with reference to the third aspect.

[0118] Because the agglomerated lignin-silicon composite has a high content of at least one silicon-containing active material and a uniform distribution of the at least one silicon-containing active material within the lignin matrix, the granular carbon-silicon composite obtained from heat treatment of the agglomerated lignin-silicon composite also benefits from a high content and uniform distribution of the at least one silicon-containing active material within the carbon matrix.

[0119] According to a fifth aspect, the present invention relates to a carbon-silicon composite powder obtainable by grinding a granular carbon-silicon composite material obtainable by the method according to the third aspect. The carbon-silicon composite powder may be further defined as set out above with reference to the third aspect.

[0120] The uniform distribution of silicon within the carbon matrix is ​​maintained after pulverization, and the resulting carbon-silicon composite powder is suitable for use as the active material in the negative electrodes of secondary batteries, battery-capacitor hybrid systems, or other material applications.

[0121] 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-silicon composite powder according to the fifth aspect.

[0122] The carbon-silicon composite powder obtained by pulverizing the granular carbon-silicon composite material is suitable for use as an anode active material in non-aqueous secondary batteries such as lithium ion batteries. When used to manufacture such anodes, any suitable method for forming such anodes may be utilized. In forming the anode, the carbon-enriched material may be processed together with additional components. Such additional components may include, for example, one or more binders for forming the carbon-enriched material into an electrode, conductive materials such as carbon black, carbon nanotubes, metal powders, and / or additional 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.

[0123] According to a seventh aspect, the present invention relates to the use of a carbon-silicon composite powder according to the fifth aspect as an active material in the negative electrode of a non-aqueous secondary battery. EXAMPLES

[0124] Example 1 The lignin powder obtained from the LignoBoost process was mixed with 3 wt.% nanosilicon powder with an average primary particle size of 0.5 μm using a V-mixer (200 rpm, 15 min). No additional additives were added. The mixture was then compacted and agglomerated by roller compaction at 50 kN and crushed / sieved into agglomerates with a size distribution of 0.5–1.5 mm and a bulk density of 0.55 g / cm. 3 Agglomerated lignin-silicon composites of 1000g were obtained.

[0125] The agglomerated lignin-silicon composite was further thermally stabilized by heating in a rotary kiln in air at 235 °C for 2 h to obtain a thermally stabilized agglomerated lignin-silicon composite. During this process, the agglomerated lignin-silicon composite did not exhibit melting behavior and completely retained 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-silicon composite was 0.59 g / cm. 3 It was.

[0126] This thermally stabilized agglomerated lignin-silicon composite was then heat treated at 500 °C for 1 h under an inert atmosphere to carbonize the material. This resulted in a shape / size-retained granular carbon-silicon composite. The bulk density of the granular carbon-silicon composite was 0.58 g / cm. 3 It was.

[0127] Example 2 The same experimental details as in Example 1 were used, except that the lignin powder was mixed with 3 wt.% silicon oxide powder with an average primary particle size of 0.5 μm. No additional additives were added. The resulting agglomerated lignin-silicon composite had a particle size distribution of 0.5-1.5 mm and a mass fraction of 0.56 g / cm. 3 The bulk density was 1.01 g / g.

[0128] After heating, 0.59g / cm 3 The thermally stabilized agglomerated lignin-silicon composite was then carbonized to obtain a bulk density of 0.42 g / cm. 3 A granular carbon-silicon composite material having a bulk density of 1000 g / g was obtained.

[0129] Example 3 - Comparative Example In this experiment, the thermal conversion of conventional lignin powder was performed. The lignin powder was not agglomerated before the heat treatment.

[0130] Lignin powder from the LignoBoost process was heated at 200°C for up to 12 hours. After heating, the lignin was found to have melted / fused into a black, odorless solid.

[0131] 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 an agglomerated lignin-silicon composite material, comprising: a) providing lignin in the form of a powder; b) providing at least one silicon-containing active material in powder form; c) mixing lignin powder, at least one silicon-containing active material powder, and optionally at least one additive to obtain a lignin-silicon powder mixture; d) compressing the lignin-silicon powder mixture obtained in step c) to obtain a lignin-silicon composite material; e) grinding the lignin-silicon composite material obtained in step d) to obtain an agglomerated lignin-silicon composite material; f) optionally sieving the agglomerated lignin-silicon composite material obtained in step e) to remove particles having a particle size of less than 100 μm and to obtain an agglomerated lignin-silicon 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; A method comprising:

2. 2. The method of claim 1, wherein the particle size distribution of the lignin in powder form is such that at least 80% by weight of the particles have a diameter of less than 0.2 mm and the moisture content is less than 45% by weight.

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

4. The method of claim 1 or 2, wherein the at least one silicon-containing active material is microsized or nanosized.

5. 3. The method of claim 1 or 2, wherein the mixing step is carried out for at least 1 minute.

6. 3. The method of claim 1 or 2, wherein the mixing is carried out at a mixing speed of at least 100 rpm.

7. 3. The method according to claim 1 or 2, wherein the mixing is carried out by dry mixing.

8. The bulk density of the obtained agglomerated lignin-silicon composite material is 0.5 to 0.7 g / cm ３ The method according to claim 1 or 2, wherein the range is:

9. 3. The method of claim 1 or 2, wherein the agglomerated lignin-silicon composite material comprises in the range of 0.5 to 30 wt. % of the at least one silicon-containing material, based on the dry weight of the agglomerated lignin-silicon composite material.

10. 3. The method of claim 1 or 2, wherein the silicon-containing active material in the agglomerated lignin-silicon composite material is selected from the group of elemental silicon, silicon suboxide, silicon-metal alloy, or silicon-metal carbon alloy.

11. Additional steps: g) heating the agglomerated lignin-silicon composite material to a temperature in the range of 140-250°C for at least 30 minutes to obtain a thermally stabilized agglomerated lignin-silicon composite material.

3. The method of claim 1 or 2, comprising:

12. 12. The method of claim 11, wherein the step of heating the agglomerated lignin-silicon composite material is carried out by first heating the agglomerated lignin-silicon composite material to a temperature in the range of from 140 to 175°C for at least 15 minutes, and subsequently heating the agglomerated lignin-silicon composite material to a temperature in the range of from 175 to 250°C for at least 15 minutes.

13. 1. A method for producing a granular carbon-silicon composite material, comprising: i) providing an agglomerated lignin-silicon composite material obtained by the method according to claim 1 or 2; ii) subjecting the agglomerated lignin-silicon 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 time in the range of 30 minutes to 10 hours, to obtain a granular carbon-silicon composite material; A method comprising:

14. 14. The method of claim 13, wherein step ii) comprises a preheating step followed by a final heating step.

15. 15. The method of claim 14, wherein the preheating step is carried out at a temperature between 400 and 800°C for at least 30 minutes.

16. 15. The method of claim 14, wherein the preheating step is carried out in an inert atmosphere.

17. 15. The method of claim 14, wherein the final heating step is carried out at a temperature between 800°C and 1500°C for at least 30 minutes.

18. 15. The method of claim 14, wherein the final heating step is performed in an inert atmosphere.

19. 14. The method of claim 13, comprising the additional step of pulverizing the granular carbon-silicon composite material to obtain a carbon-silicon composite powder.