Method for producing negative electrode material for secondary batteries using lignocellulosic biomass

Abstract

To provide a method for producing a negative electrode material for a secondary battery from lignocellulosic biomass.SOLUTION: The present invention provides a method for producing a negative electrode material for secondary batteries using lignocellulosic biomass, which can contribute to improving the performance and stability of secondary batteries when applied to the secondary batteries by removing trace amounts of metal components contained in the raw material lignocellulosic biomass.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a method for producing a negative electrode material for secondary batteries from lignocellulosic biomass, and more specifically, to a method for producing a negative electrode material for secondary batteries using lignocellulosic biomass, which can contribute to improving the performance and stability of secondary batteries when applied to secondary batteries by removing trace amounts of metal components contained in the biomass as a raw material. [Background technology]

[0002] Due to the problem of environmental pollution caused by the excessive use of fossil fuels, there has been a sharp increase in demand for environmentally friendly products and alternative energy sources to petroleum. In addition, there has been active technological development in the fields of power generation and storage to utilize electrical energy as an alternative energy source.

[0003] In particular, there has been active research and development into hybrid and electric vehicles to replace gasoline and diesel vehicles, which are the main cause of air pollution, and energy storage systems (ESS) that can store large amounts of surplus electricity. A typical element used in the creation of such electric energy systems is the secondary battery, and the demand for secondary batteries is rapidly increasing in portable devices such as phones, laptops, cameras, and industrial tools.

[0004] Currently, a lithium secondary battery is widely used as a representative example of such secondary batteries. The lithium secondary battery is configured to include current collectors on which a positive electrode active material and a negative electrode active material are applied, and a porous separator interposed between the current collectors, and is impregnated with a non-aqueous lithium salt electrolyte.

[0005] In this case, expensive carbon-based and non-carbon-based materials are used as negative electrode active materials, and lithium metal, silicon (Si), and transition metal oxides have been researched as non-carbon-based active materials, but commercialization has been delayed due to various drawbacks. The carbon-based negative electrode active materials are broadly classified into graphitic and non-graphitic, and the non-graphitic is broadly classified into soft carbon-based (graphitizable carbon) active materials that have uniaxial orientation even at low temperatures and hard carbon-based (non-graphitizable carbon) active materials that do not easily have uniaxial orientation even at high temperatures.

[0006] Meanwhile, graphite-based active materials have been used in most lithium-ion secondary batteries up to now due to their long electrode life characteristics resulting from highly reversible charge and discharge characteristics due to the uniaxial orientation of the graphene layer.

[0007] However, despite its many advantages, graphite's low theoretical capacity (372mAh / g) is a major obstacle in the current situation where higher capacity batteries are required. In addition, when lithium ions are inserted between the layered structure of graphite during charging, electrolyte salt may also be inserted between the layered structure at the same time, causing the layered structure to peel off. To overcome this, graphite coated with non-graphitic (amorphous) carbon is often used.

[0008] Generally, the capacity of a negative electrode active material made of non-graphite-based carbon is lower than that of a negative electrode active material made of graphite-based (crystalline) carbon, but the power characteristics of a negative electrode active material made of non-graphite-based carbon are superior to those of a negative electrode active material made of graphite-based carbon.

[0009] Currently, as the demand for high-performance lithium-ion secondary batteries is rapidly increasing, carbon materials used worldwide as negative electrode active materials are very expensive and most are produced using coal or petroleum-based raw materials, which poses problems of economic viability and the emission of significant amounts of carbon dioxide upon disposal. As an alternative to this, methods of utilizing negative electrode materials derived from biomass have recently been researched.

[0010] However, due to metal components such as potassium and sodium contained in biomass, metal components remain in the carbon material produced from biomass. When these metal components are used as electrode active materials, they need to be removed because they may dissolve into the electrolyte and cause electrochemical reactions that may affect battery performance and safety.

[0011] As a conventional technique for using the carbon material using biomass as an electrode material, Korean Patent No. 10-1545116 (announced on August 17, 2015) discloses a method for manufacturing a carbon material for a lithium ion capacitor anode by using charcoal derived from coconut shells as a carbonaceous precursor. However, this method has problems in that it requires heat treatment through a gas phase demineralization process, and metal-halogen complexes generated during the demineralization process must be captured and removed.

[0012] In addition, Korean Patent No. 10-2442330 (announced on September 8, 2022) proposes a process for converting lignocellulose materials into carbon materials in the form of hard carbon, but does not propose a process for removing metal components contained in the lignocellulose materials. The crystallinity and micropore uniformity of the carbon material are low, which may cause a decrease in battery performance. In particular, there is a problem that the carbon material is converted only into a hard carbon form, rather than into a graphite-like carbon material, due to the decrease in crystallinity.

[0013] Therefore, there is an urgent need to develop a production method for a new, low-cost, environmentally friendly biomass-derived negative electrode material for secondary batteries that uses lignocellulosic biomass, a potentially economically advantageous material, as a raw material, has a simple process, yet can produce an active material that overcomes the drawbacks of graphite-based and non-graphite-based materials and does not leach metal components. [Prior art documents] [Patent documents]

[0014] [Patent Document 1] Korean Patent No. 10-1545116 (Announced on August 17, 2015) [Patent Document 2] Korean Patent No. 10-2442330 (Announced on September 8, 2022) Summary of the Invention [Problem to be solved by the invention]

[0015] The present invention aims to provide a method for producing a negative electrode material for secondary batteries based on a carbon material having highly crystalline graphite properties or a carbon material having amorphous properties, which has high specific capacity, charge / discharge capacity and efficiency, from lignocellulosic biomass, an environmentally friendly raw material, by a simple and economical method.

[0016] Another object of the present invention is to provide a composition for a secondary battery anode containing the anode material, and a secondary battery containing the same. [Means for solving the problem]

[0017] In order to achieve the above object, the present invention provides a method for producing a lignocellulosic biomass by hydrolyzing at least a part of the hemicellulose in the lignocellulosic biomass by adding an acid to the lignocellulosic biomass and converting at least a part of the cellulose into microfibrillated cellulose (MFC). (b) adding an aqueous base solution to the hydrolysis reaction product containing the lignin-cellulose microfiber composite obtained in step (a) to further remove residual acid components and water-soluble residual metal components contained in the lignin-cellulose microfiber composite, and then separating the aqueous solution components to obtain lignin-cellulose microfiber composite solid particles; (c) pulverizing the lignin-cellulose microfiber composite solid particles obtained in step (b) to obtain pulverized lignin-cellulose microfiber composite solid particles; and (d) heat-treating the pulverized lignin-cellulose microfiber composite solid particles obtained in step (c) to modify at least a portion of the solid particles into a crystalline or amorphous carbon material.

[0018] As one embodiment, in the step (a), the acid may be any one selected from the group consisting of an organic acid having 1 to 20 carbon atoms; or an inorganic acid selected from sulfuric acid, hydrochloric acid, phosphoric acid, and nitric acid, or a mixture thereof; a mixture of the organic acid and an inorganic acid; or a mixture of the organic acid and an inorganic acid; and preferably, any one selected from the group consisting of hydrochloric acid, sulfuric acid, and nitric acid, or a mixture thereof.

[0019] In one embodiment, the hydrolysis step in step (a) can be carried out by i) a process of heating and / or pressurizing while adding an acid, or ii) a process of steam explosion while adding an acid, or iii) a process in which the heating and pressurizing treatment in i) and the steam explosion in ii) are combined, or iv) a biological decomposition process using one or more cellulolytic enzymes.

[0020] In one embodiment, after the step (a), the method may further include a step (a-1) of separating and removing at least a portion of the aqueous solution component in the hydrolysis reaction product containing the lignin-cellulose microfibril composite obtained from the step (a), if the aqueous solution component is present in the hydrolysis reaction product containing the lignin-cellulose microfibril composite.

[0021] In one embodiment, the method may further include, prior to step (b), a step of (a-2) washing the hydrolysis reaction product containing the lignin-cellulose microfiber composite obtained in step (a) with desalted water to obtain a hydrolysis reaction product containing the lignin-cellulose microfiber composite from which at least a portion of the water-soluble metal components contained in the lignocellulosic biomass has been removed.

[0022] In one embodiment, the base used in step (b) is sodium hydroxide (NaOH), potassium hydroxide (KOH), ammonia (NH 3 ), lithium hydroxide (LiOH), potassium carbonate (K 2 CO 3 ), Sodium Carbonate (Na 2 CO 3 ), potassium bicarbonate (KHCO 3 ), magnesium hydroxide (Mg(OH) 2 ), magnesium oxide (MgO) and sodium bicarbonate (NaHCO 3 ) or a mixture thereof.

[0023] In one embodiment, the lignin-cellulose microfiber solid particles obtained in step (b) may have a hemicellulose content of 5 weight % (wt%) or less based on the total amount of components derived from lignin, cellulose and hemicellulose.

[0024] In one embodiment, the lignin-cellulose microfiber composite solid particles obtained in step (b) may contain 20 wt% to 80 wt% of lignin-derived components and further contain 20 wt% to 80 wt% of cellulose-derived components, based on the total of the lignin, cellulose and hemicellulose-derived components.

[0025] In one embodiment, the particle size of the pulverized lignin-cellulose microfiber composite solid particles obtained in step (c) may be 500 nm to 200 μm.

[0026] In one embodiment, the heat treatment temperature in step (d) may be in the range of 500 to 3000°C.

[0027] In one embodiment, the heat treatment in step (d) may be carried out in the presence of a metal catalyst, so that at least a portion of the particles obtained after the heat treatment are a crystalline carbon material. In this case, after step (d), the method may further include a step of (e) treating the solid particles, at least a portion of which is a crystalline carbon material obtained from step (d), with an acid to obtain a carbon material from which the metal catalyst has been removed.

[0028] In one embodiment, the heat treatment in step (d) may be carried out in the absence of a metal catalyst, so that at least a part of the particles obtained after the heat treatment is an amorphous carbon material.

[0029] The present invention also provides a negative electrode material for a secondary battery produced by the above-mentioned production method, and a composition for a secondary battery negative electrode including the above-mentioned negative electrode material for a secondary battery.

[0030] The present invention also provides a secondary battery including the composition for a secondary battery negative electrode. Effect of the Invention

[0031] The method for producing a negative electrode material for secondary batteries according to the present invention uses lignocellulosic biomass as a raw material, which is an environmentally friendly material and is therefore the most abundant and inexpensive material on earth, and therefore has an economic advantage in terms of production costs. The process is simple and it is possible to produce a highly crystalline or amorphous carbon material from which residual metal components in lignocellulosic biomass have been removed. A secondary battery containing the negative electrode material produced thereby has the effect of exhibiting excellent specific capacity and charge / discharge characteristics, and having stable output characteristics.

[0032] In addition, the negative electrode material for secondary batteries according to the present invention has an additional advantage of being environmentally friendly since it produces significantly less carbon dioxide during manufacture and incineration than pitch and carbon materials for negative electrodes manufactured by conventional techniques. [Brief description of the drawings]

[0033] [Figure 1] FIG. 1 shows (a) the hierarchical structure of biomass-derived cellulose and (b) the structure of cellulose microfibrils containing crystalline and amorphous domains. [Diagram 2] 1 is an electron microscope photograph of lignin-cellulose microfibril bundles and solid particles composed of cellulose microfibril bundles and lignin prepared in Preparation Example 1 according to the present invention before pulverization. [Diagram 3] a) is an electron microscope photograph of a carbon material having amorphous hard carbon properties obtained by heat treatment at 2500°C without a metal catalyst according to the present invention, and b) is an electron microscope photograph of a graphitized crystalline carbon material obtained by heat treatment at 2500°C in the presence of a metal catalyst according to the present invention. [Figure 4]2 is an electron microscope photograph of the carbon materials having amorphous hard carbon properties produced in Examples 2-1, 2-4, and 2-5 according to the present invention. [Diagram 5] FIG. 2 is a diagram showing the results of Raman spectroscopy (RAMANtouch, nanophoton Corp.) of the carbon materials produced in Examples 1 and 2 of the present invention. [Figure 6] FIG. 2 is a diagram showing the results of X-ray diffraction analysis (XRD) of the carbon materials produced in Examples 1 and 2 according to the present invention. [Figure 7] FIG. 1 is a graph showing a) specific capacity and initial coulomb efficiency (ICE) of a coin cell to which the carbon material for a negative electrode prepared in Example 1 according to the present invention is applied, and b) cyclic performance of the coin cell (current rate: 0.1C). [Figure 8] FIG. 1 is a graph showing a) specific capacity and initial Coulomb efficiency (ICE) of a coin battery using the amorphous carbon material prepared in Example 2 according to the present invention, and b) cyclic performance of the coin battery (current rate). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0034] The present invention will be described in more detail below. In each drawing of the present invention, the size and dimensions of structures are shown enlarged or reduced from the actual size in order to clarify the present invention, and known structures are omitted so that characteristic structures can be seen, and the present invention is not limited to the drawings.

[0035] In addition, the sizes and thicknesses of the components shown in the drawings are arbitrarily shown for the convenience of explanation, and the present invention is not necessarily limited to those shown in the drawings. Also, in the drawings, the thicknesses are enlarged to clearly show a plurality of layers and regions. Further, in the drawings, for the convenience of explanation, the thicknesses of some layers and regions are exaggerated. When a part such as a layer, film, region, or plate is said to be "on" another part, this includes not only the case where it is "immediately above" the other part but also the case where there are other parts between them.

[0036] Also, throughout the specification, when a part "includes" a certain component, this means that, unless otherwise stated to the contrary, it does not exclude other components but can further include other components. Also, throughout the specification, "on" means being located above or below the target part and does not necessarily mean being located on the upper side with reference to the direction of gravity.

[0037] Hereinafter, the manufacturing method according to the present invention will be described more specifically.

[0038] The method for producing a negative electrode material for a secondary battery from lignocellulosic biomass according to the present invention includes the steps of: (a) adding an acid to lignocellulosic biomass to hydrolyze at least a part of the hemicellulose in the lignocellulosic biomass and converting at least a part of the cellulose into microfibrillated cellulose (MFC); (b) adding an aqueous base solution to the hydrolysis reaction product containing the lignin-cellulose microfiber composite obtained from step (a) to further remove residual acid components and water-soluble residual metal components contained in the lignin-cellulose microfiber composite, and then separating the aqueous solution components to obtain lignin-cellulose microfiber composite solid particles; (c) pulverizing the lignin-cellulose microfiber composite solid particles obtained from step (b) to obtain pulverized lignin-cellulose microfiber composite solid particles; and (d) heat-treating the pulverized lignin-cellulose microfiber composite solid particles obtained from step (c) to modify at least a portion of the solid particles into a crystalline or amorphous carbon material.

[0039] Here, as a first step of the production method according to the present invention, the step (a) is a step of adding an acid to lignocellulosic biomass as a raw material to hydrolyze at least a part of hemicellulose as a precursor for producing a carbon material for a secondary battery negative electrode active material, and obtaining a hydrolysis reaction product containing a lignin-cellulose microfibrillated composite obtained by converting at least a part of the cellulose into cellulose microfibrillated cellulose (MFC), and this is a step in which the addition of acid in the step (a) destroys the strong crystallization structure between the lignin and cellulose in the biomass, at least a part of the hemicellulose is hydrolyzed, and at least a part of the cellulose fiber is converted into cellulose microfibrillated cellulose (MFC), preferably 10% or more of the cellulose component contained in the biomass, more preferably 20% or more, even more preferably 30% or more, even more preferably 40% or more, even more preferably 50% or more, even more preferably 60% or more, even more preferably 70% or more, even more preferably 80% or more, even more preferably 90% or more, even more preferably 95% or more The cellulose is converted to a lignin-cellulose microfibril (MFC) form, and the lignin and at least a portion of the cellulose microfibril (MFC) are physically or chemically bound to each other by the acid treatment to form a lignin-cellulose microfibril (MFC) complex in a polymeric form.

[0040] That is, the lignin-cellulose microfiber composite according to the present invention can function as a negative electrode active material for a secondary battery by subsequently heat-treating the cellulose microfibers (microfibrillated cellulose) in the lignin-cellulose microfiber (MFC) composite obtained by the acid treatment and the lignin that has been hydrophobized by the acid treatment. This has the advantage that a negative electrode material for a secondary battery can be provided through a more environmentally friendly and economical process using components derived from lignocellulose-based biomass, which is a low-cost biomaterial.

[0041] Here, the cellulose contained in the lignocellulosic biomass is a fibrous material in which linear chains linked by β-glycosidic bonds of the unit D-glucose overlap each other. Referring to FIG. 1(a) showing the hierarchical structure of biomass-derived cellulose, the cellulose fiber includes microfibril bundles made up of microfibrils, and the microfibril includes elementary fibrils, which are the lowest level components.

[0042] Hereinafter, in the present invention, microfibrillated cellulose (MFC) means microfibrillated cellulose fibers having a fiber width (thickness) of 1 μm or less, preferably 100 nm or less, more preferably 50 nm or less, and even more preferably 30 nm or less, which are obtained when cellulose fibers contained in lignocellulosic biomass such as wood bulk are defibrated, and should be understood as a concept including microfibril bundles and microfibrils, as shown in FIG. 1(a).

[0043] At this time, the cellulose microfibrillated (MFC) has a structure including a crystalline domain and an amorphous domain, as shown in FIG. 1(b).

[0044] In addition, in step (a), the strong structure of the lignocellulosic biomass is broken down by the acid treatment, and the metal components contained in the biomass are easily eluted, i.e., the metal components in the acid-treated biomass are converted into ionic substances, making them easier to remove in the subsequent dehydration and / or water washing processes, thereby allowing the metal components to be removed. This allows the metal components contained in the lignocellulosic biomass to be eluted.

[0045] Here, the metal component should be understood as a concept including one or more of various metal components contained in lignocellulosic biomass, alloys of the metal components, metal ions, and metal compounds.

[0046] The lignocellulosic biomass in step (a) of the present invention is a material containing lignin and at least one of cellulose and hemicellulose, and preferably contains all of lignin, cellulose and hemicellulose. Such lignocellulosic biomass can be biomass derived from herbaceous plants, woody plants such as coniferous trees and broad-leaved trees (normal wood), or various biomass such as rice straw, corn cobs, palm husks, and sugar cane.

[0047] Meanwhile, the lignocellulosic biomass used as a raw material in step (a) may be pulverized after a drying process. In this case, in order to ensure uniformity in the subsequent processes, the pulverized size is preferably 20 mm or less, and more preferably in the range of 10 to 0.001 mm.

[0048] After the pulverization process of the lignocellulosic biomass, a drying process may be performed to reduce the moisture content. The drying process is preferably performed to reduce the moisture content of the lignocellulosic biomass to 30% by weight or less, preferably 20% by weight or less, and more preferably 10% by weight or less. The drying process may be performed by any method capable of reducing the moisture content of the lignocellulosic biomass, such as oven drying, natural drying in a well-ventilated place, or hot air drying, without any limitation.

[0049] In addition, the grinding and drying steps in the present invention may be performed in any order. That is, the drying step may be performed after the grinding step of the lignocellulosic biomass, or the grinding step may be performed after the drying step. This may vary depending on the surrounding environment or the type and drying state of the lignocellulosic biomass. For example, if the drying is performed very well, the drying step may be omitted, and preferably, it is preferable from the viewpoint of efficiency to dry the lignocellulosic biomass whose surface area has increased after the grinding step.

[0050] The acid used in step (a) in the present invention can be selected from the group consisting of an organic acid having 1 to 20 carbon atoms; an inorganic acid selected from sulfuric acid, hydrochloric acid, phosphoric acid, and nitric acid, or a mixture thereof; a mixture of the organic acid and an inorganic acid; or a mixture of the organic acid and an inorganic acid.

[0051] In this case, in the case of the organic acid, a monocarboxylic acid, a biscarboxylic acid, a triscarboxylic acid, a tetracarboxylic acid, or the like can be used as the carbon compound containing a carboxylic acid depending on the number of the carboxylic acid, and an organic acid having 1 to 20 carbon atoms, preferably an organic acid having 1 to 15 carbon atoms, can be used depending on the number of carbon atoms, and more preferably, acetic acid, formic acid, propionic acid, or the like can be used.

[0052] As a preferred example of the acid component used as the inorganic acid, any one selected from hydrochloric acid, sulfuric acid, and nitric acid, or a mixture thereof, can be used. The preferred acid concentration is in the range of 0.5 to 70 wt%, more preferably 0.6 to 65 wt%, and even more preferably 0.7 to 60 wt%, based on the total content of the aqueous solution containing the pulverized biomass and the acid. As a more preferred example, sulfuric acid in the range of 0.5 to 70 wt%, more preferably 0.6 to 65 wt%, and even more preferably 0.7 to 60 wt%, based on the total content of the aqueous solution containing the pulverized biomass and the acid, can be used.

[0053] Here, the content of the strong acid is, for example, when 75% (v / v) sulfuric acid is added, the sulfuric acid concentration can be in the range of 0.5 wt% to 70 wt%, preferably 0.6 wt% to 65 wt%, based on the final concentration (based on the total content of the pulverized biomass and the aqueous solution) by adding 75% (v / v) sulfuric acid. The above ratio can be used by changing the optimal conditions in various ways depending on the type of biomass, and if hydrochloric acid is used, a similar range of moles can be calculated and used, and even if a mixture of sulfuric acid and hydrochloric acid is used, the amount of strong acid added can be appropriately determined based on the above range.

[0054] In addition, the hydrolysis step of step (a) of the present invention can be carried out by i) a process of heating and / or pressurizing while adding an acid, or ii) a process of steam explosion while adding an acid, or iii) a process in which the heating and pressurizing treatment in i) and the steam explosion in ii) are combined, or iv) a biological decomposition process using one or more cellulolytic enzymes.

[0055] Here, in the hydrolysis process of step (a), i) the process of heating and / or pressurizing while adding an acid may include a process of reacting a mixture containing lignocellulosic biomass and an aqueous acid solution at 80 to 250° C., preferably 90 to 150° C., for 2 minutes to 2 days, preferably 5 minutes to 5 hours, at normal pressure or below 10 atmospheres, followed by depressurizing and filtering the solid matter; ii) the process of steam explosion while adding an acid may include a process of reacting a mixture containing lignocellulosic biomass and an aqueous acid solution using steam at 100 to 250° C., preferably 120 to 190° C., for 5 minutes to 5 hours, preferably 10 minutes to 1 hour, followed by instantaneous depressurization; and iv) the biological degradation process may use one or more known cellulolytic enzymes without any restrictions, and the acid in steps i) to iv) may be added in various concentrations depending on the type of acid and conditions such as reaction temperature and pressure.

[0056] Meanwhile, the hydrolysis reaction product containing the lignin-cellulose microfibril composite obtained in step (a) according to the present invention may be in a slurry state of an aqueous solution containing a solid lignin-cellulose microfibril composite, an acid, eluted metal components and decomposed sugars.

[0057] In addition, the present invention may further include, after the step (a), a step (a-1) of separating and removing at least a part of the aqueous solution component in the hydrolysis reaction product containing the lignin-cellulose microfibril composite obtained in the step (a) when the hydrolysis reaction product is in a slurry state and an aqueous solution component is present.

[0058] Here, the separation of the aqueous solution components can be performed by using a known separation technique without any restrictions, and examples thereof include dehydration by centrifugation, filtration, and decantation.

[0059] On the one hand, in the step (b) of the present invention, a basic aqueous solution is added to the hydrolysis reaction product containing the lignin-cellulose microfiber composite obtained from the step (a) to react with or dissolve in the aqueous solution the residual acid component and the water-soluble residual metal component contained in the lignin-cellulose microfiber composite, and the aqueous solution component is separated and removed to obtain lignin-cellulose microfiber composite solid particles. This corresponds to the step of removing the residual acid component and the water-soluble residual metal component in the hydrolysis reaction product obtained in the step (a), because if the residual acid component and the water-soluble residual metal component are not removed, they may have an adverse effect on the physical properties of the negative electrode material for secondary batteries and the performance of secondary batteries in subsequent processes.

[0060] In this case, for the step of separating the aqueous solution component obtained after adding the basic aqueous solution to the hydrolysis reaction product, known separation techniques can be applied without limitation. For example, it can include dehydration by centrifugation, filtration, and decantation.

[0061] Also, the base used in the step (b) can be at least one selected from sodium hydroxide (NaOH), potassium hydroxide (KOH), ammonia (NH 3 ), lithium hydroxide (LiOH), potassium carbonate (K 2 CO 3 ), sodium carbonate (Na 2 CO 3 ), potassium bicarbonate (KHCO 3 ), magnesium hydroxide (Mg(OH) 2 ), magnesium oxide (MgO), and sodium bicarbonate (NaHCO 3 ) or a mixture thereof, but any base that does not form a poorly soluble salt while neutralizing the acid component and does not remain in the solid particles produced in the step (b) can be used without limitation.

[0062] In addition, the present invention may further include a step (a-2) prior to step (b), of washing the hydrolysis reaction product containing the lignin-cellulose microfiber composite obtained from step (a) with desalted water to obtain a hydrolysis reaction product containing the lignin-cellulose microfiber composite from which at least a portion of the water-soluble metal components contained in the lignocellulosic biomass has been removed, and in this case, the residual acid components obtained after the desalted water washing may be recovered and reused.

[0063] In other words, in the (a-2) step, before the basic aqueous solution is added in the (b) step, the acid components remaining in the modified lignin-cellulose microfiber (MFC) composite obtained through the (a) step are washed with demineralized water to remove components that can be dissolved in an aqueous solution, such as any one or a mixture of water-soluble substances including residual sugar components derived from the biomass, substances derived from the acid addition process, substances derived from the base addition process, acid components, and water-soluble metal components, which are selected from these. This has the advantage that the content of the basic aqueous solution added in the (b) step can be reduced.

[0064] In addition, in the present invention, after the step (b), (b-1) the lignin-cellulose microfiber composite solid particles obtained in the step (b) are further washed with desalted water, and the aqueous solution containing the water-soluble components obtained by washing can be separated, thereby further removing water-soluble components including metal components, residual base components, etc. contained in the solid particles.

[0065] As a result, when a certain amount of polysaccharides hydrolyzed by the acid component is removed from the solid particles obtained through step (b), solid particles can be obtained in which at least 30% by weight, preferably 40% by weight or more, more preferably 50% by weight or more, even more preferably 60% by weight or more, and even more preferably 70% by weight or more of lignocellulosic biomass is converted, based on the total weight of the solid particles obtained, relative to the dry weight of the input biomass.

[0066] In this case, the lignin-cellulose microfiber composite solid particles obtained from step (b) may have a hemicellulose content of 5 weight % (wt%) or less, preferably 3 weight % (wt%) or less, and more preferably 2 weight % (wt%) or less, based on the total of the components derived from lignin, cellulose and hemicellulose.

[0067] That is, the solid particles obtained through steps (a) and (b) contain lignin and cellulose microfiber (MFC) as main components, which form a lignin-cellulose microfiber (MFC) complex and serve as a precursor of the negative electrode active material.

[0068] On the other hand, the solid particles obtained through step (b) may contain 1 wt% to 99 wt% of lignin-derived components, preferably 20 wt% to 80 wt%, more preferably 30 wt% to 70 wt%, and even more preferably 40 wt% to 60 wt%, of the lignin-derived components, based on the total of the lignin-, cellulose- and hemicellulose-derived components.

[0069] Furthermore, the solid particles obtained through step (b) can contain 1 wt% to 99 wt% of cellulose-derived components, preferably 20 wt% to 80 wt%, more preferably 25 wt% to 75 wt%, and even more preferably 30 wt% to 70 wt% of cellulose-derived components, based on the total of the components derived from lignin, cellulose and hemicellulose.

[0070] In addition, the solid particles obtained through step (b) preferably contain 20 wt% to 80 wt% of lignin-derived components and 20 wt% to 80 wt% of cellulose-derived components, based on the total of the lignin-, cellulose- and hemicellulose-derived components.

[0071] In addition, in the present invention, after the step (b), (b-1) the lignin-cellulose microfiber composite obtained in the step (b) can be further washed with desalted water to separate the aqueous solution containing these water-soluble components, thereby further removing water-soluble components contained in the solid particles, including metal components, residual base components, etc.

[0072] Meanwhile, in the step (c) of the present invention, the lignin-cellulose microfiber composite solid particles obtained in the step (b) are pulverized to obtain pulverized solid particles. The pulverized powder-like solid particles are easy to handle, can be uniformly heat-treated in the subsequent heat treatment step (d), and can improve the dispersibility of the metal catalyst in the subsequent step, thereby improving the physical properties such as the crystallinity of the negative electrode carbon material finally produced.

[0073] Here, the pulverization method in step (c) can be any known pulverization method including ball milling, speck milling, and nano milling without limitation, and the particle size of the solid particles obtained after pulverization can be in the range of 500 nm to 200 μm.

[0074] In addition, a step of drying the moisture in the solid particles may be carried out prior to the grinding in step (c), and the moisture content in the solid particles may be reduced to less than 5% by weight, preferably less than 3% by weight, through the drying step.

[0075] On the other hand, step (d) in the present invention is a step of heat-treating the pulverized lignin-cellulose microfiber composite solid particles obtained from step (c) to modify at least a portion of the solid particles into a crystalline or amorphous carbon material. When the pulverized lignin-cellulose microfiber composite solid particles in step (c) are heat-treated in the presence of a metal catalyst, at least a portion of the solid particles are graphitized and converted into a graphitic crystalline carbon material, and when the solid particles are heat-treated in the absence of the metal catalyst, at least a portion of the solid particles can be converted into a hard-carbonized amorphous carbon material.

[0076] Here, the crystalline carbon material obtained by the heat treatment in the presence of the metal catalyst has a Raman spectrum having a D band intensity ratio (I D / I G ) is lower than that of natural graphite (0.05).

[0077] The solid particles obtained by heat treatment in the presence of a metal catalyst in step (d) of the present invention may be 50 wt% or more of crystalline carbon material, more preferably 60 wt% or more of crystalline carbon material, even more preferably 70 wt% or more of crystalline carbon material, even more preferably 70 wt% or more of crystalline carbon material, even more preferably 80 wt% or more of crystalline carbonized material, even more preferably 90 wt% or more of crystalline carbon material, even more preferably 95 wt% or more of crystalline carbon material, based on the total weight of the solid particles.

[0078] Furthermore, the particles obtained by heat treatment in the absence of a metal catalyst in step (d) according to the present invention can be 60 wt% or more of amorphous carbon material, more preferably 70 wt% or more of amorphous carbon material, even more preferably 80 wt% or more of amorphous carbon material, even more preferably 90 wt% or more of amorphous carbon material, and even more preferably 95 wt% or more of amorphous carbon material, based on the total weight of the solid particles.

[0079] At this time, the heat treatment in the step (d) may be carried out at a temperature in the range of 500 to 3,000°C, preferably in the range of 1,000 to 2,700°C, and more preferably in the range of 1,500 to 2,500°C.

[0080] In addition, the catalyst used in the heat treatment in the presence of a metal catalyst in step (d) may be any known graphitization catalyst, and may be used without any particular type. For example, a catalyst containing one or more metals selected from Fe, Co, Mn, Ni, Zn, Mg, Si, Ca, Cu, Ge, Al, Ti, V, Cr, Mo, and Pb, or a metal salt containing the metal may be used. For example, the catalyst containing the metal may be a catalyst containing one or a mixture of Fe, Co, Mn, Ni, and Zn, and the metal salt may be Fe(NO 3 ) 3 , Fe 2 O 3 , FeCl 3 , Ni(NO 3 ) 3 Catalysts containing either ZnO or a mixture of these components can be used.

[0081] In this case, the metal catalyst may be added in a range of 5 to 60 wt %, preferably 10 to 20 wt %, based on the total weight of the crushed solid particles. If the metal catalyst is added in an amount less than 5 wt %, the catalytic function may be insignificant and the content of the crystalline carbon material may be low, whereas if the amount exceeds the above range, there may be a problem that the residual amount of the metal component is excessive.

[0082] Meanwhile, the present invention may further include a step (e) of treating the crystalline carbon material obtained from step (d) with an acid after the heat treatment in the presence of a metal catalyst in step (d) to obtain a crystalline carbon material from which the metal catalyst components have been removed. This is for the purpose of preventing metal components from being included in the secondary battery negative electrode active material, as discussed in step (a). Through the acid treatment, the metal components derived from the residual metal catalyst are converted into the form of a water-soluble metal salt, which can be easily removed by washing with water, for example.

[0083] In this case, the type, concentration, input amount and treatment method of the acid used for removing the remaining metal catalyst component can be appropriately changed by a person skilled in the art with reference to the description of the acid added in step (a). For example, when hydrochloric acid is used, the acid can be added in an amount within a range of 0.3 equivalents to 50 equivalents based on the content of the metal catalyst used in step (d).

[0084] Furthermore, the present invention may further include, after step (e), a step (e-1) of washing the crystalline carbon material obtained from step (e) with desalted water, thereby making it possible to more efficiently remove metal components derived from the metal catalyst.

[0085] In addition, in the present invention, after the step (e), a step (f) of drying and pulverizing the crystalline carbon material from which the metal catalyst has been removed, obtained in the step (e), can be carried out. In this case, the pulverization method can be a known pulverization method including ball milling, speck milling, and nano milling, without limitation, like the solid particle pulverization method in the step (c), and the particle size of the solid particles finally obtained after pulverization can be in the range of 0.1 to 200 μm.

[0086] The present invention can provide a negative electrode material for secondary batteries produced by the above-mentioned production method. That is, the crystalline carbon material produced from lignocellulosic biomass by the production method of the present invention has high specific capacity and charge / discharge performance, and can be used as a negative electrode material for secondary batteries.

[0087] The present invention also provides a composition for a secondary battery negative electrode, which contains the negative electrode material for a secondary battery, and a secondary battery, which contains the negative electrode composition.

[0088] The present invention will be described in more detail below through examples to help the understanding of the present invention. However, the examples described in the present invention can be modified in various conditions, and therefore the scope of the present invention is not limited to the following examples. The following examples of the present invention are intended to provide a more detailed explanation to those skilled in the art.

[0089] [Production Example 1: Production of acid-treated lignin-cellulose microfiber composite solid particles] In Preparation Example 1, a deashing process was carried out by treating the lignocellulosic biomass with an acid aqueous solution to remove metal components contained in the lignin-cellulose microfiber composite solid particles.

[0090] Pine and oak were mixed in equal weight ratios, and the biomass was then crushed to a particle size of less than 10 mesh. After crushing, the biomass was dried at 100°C for 2 hours to a moisture content of 5 wt% to prepare the raw lignocellulosic biomass powder.

[0091] The pulverized biomass powder and water were then added to a reactor in a mass ratio of 1.4:1.0 and heated to 90°C while stirring, after which 95% sulfuric acid was added to a final concentration of 10 wt%, and the temperature was raised to 120°C for 1 hour while stirring. The reaction was then carried out for 60 minutes to hydrolyze the hemicellulose components and convert at least a portion of the cellulose components into cellulose microfibers (MFC, Microfibrillated cellulose), thereby obtaining a hydrolysis reaction product containing a solid lignin-cellulose microfiber complex, which was then filtered to separate and remove the aqueous solution components.

[0092] The resulting hydrolysis reaction product was neutralized to pH 7.0 using 0.1 N ammonium hydroxide solution to further remove residual acid components and residual metal components in the lignin-cellulose microfiber composite, and then dehydrated to separate and remove the aqueous solution components.

[0093] Thereafter, the mixture was washed and dehydrated 2-3 times with a sufficient amount of desalted water to remove residual metal ions and other ionic compound components to the maximum extent, and finally, lignin-cellulose microfiber composite solid particles were obtained.

[0094] The solid particles were dried at 100°C for 6 hours and then crushed to an average particle size of 20 μm to obtain crushed lignin-cellulose microfibril composite solid particles as a carbon precursor for conversion to a carbon material for a secondary battery anode. Figure 2 shows an electron microscope photograph of the lignin cellulose microfibril bundles and the solid particles composed of cellulose microfibril bundles and lignin produced in Production Example 1 before crushing.

[0095] [Comparative Production Example 1: Production of lignin-cellulose microfiber solid particles not treated with acid] Pulverized lignin-cellulose microfiber composite solid particles were obtained by carrying out the same method as in Production Example 1, except that the reaction liquid was not treated with sulfuric acid.

[0096] The amount of metal components contained in the pulverized lignin-cellulose microfiber composite solid particles obtained in Preparation Example 1 and Comparative Preparation Example 1 was analyzed. The results are shown in Table 1 below.

[0097] [Table 1]

[0098] Considering the results of the analysis of the amount of residual metals in the lignin-cellulose microfiber composite solid particles with and without acid treatment in Preparation Example 1 of the present invention and Comparative Preparation Example 1 in Table 1, it can be confirmed that, as a result of the acid treatment de-ashing process, no metal components are observed at the detection limit (2 to 10 mg / kg) in the lignin-cellulose microfiber composite solid particles of Preparation Example 1, whereas various metal components are detected in the lignin-cellulose microfiber composite solid particles of Comparative Preparation Example 1.

[0099] [Examples 1-1 to 1-3: Production of crystalline carbon material for secondary battery negative electrode by heat treatment in the presence of metal catalyst] As a carbon precursor for a secondary battery negative electrode, 100 g of the lignin-cellulose microfiber composite solid particles of Preparation Example 1 and 20 g of Fe catalyst (Sigma Aldrich, product number: 12310, ≧99%, reduced, powder (fine)) were put into a blender and mixed. The powder containing the mixed solid particles and catalyst was put into a furnace (Asiltech) and converted into a carbon material by heat treatment for 4 hours each under conditions of 1,500°C (Example 1-1), 2,000°C (Example 1-2), and 2,500°C (Example 1-3). At this time, the temperature was raised by 60°C per minute while supplying nitrogen gas at 10 L per minute into the furnace.

[0100] The heat-treated powder was put into a 1M HCl aqueous solution to remove the metal catalyst, and the aqueous solution components were removed by filtration. The powder was then neutralized with a 1M ammonium hydroxide solution, and then washed with desalted water and dried (120°C, 1 hour) to obtain a crystalline carbon material for secondary battery negative electrodes with a moisture content of less than 0.01%. It was confirmed by ICP-MS that no residual Fe was detected in the carbon materials of Examples 1-1 to 1-3 (detection limit 5 mg / kg).

[0101] [Examples 2-1 to 2-5: Preparation of amorphous carbon material for secondary battery negative electrode heat-treated without metal catalyst] Carbon materials for secondary battery negative electrodes were produced in the same manner as in Examples 1-1 to 1-3, except that the metal catalyst Fe was not added, and only the solid particles were added to the furnace, and heat-treated for 4 hours under the conditions of 1,500°C (Example 2-1), 2,000°C (Example 2-2), 2,500°C (Example 2-3), 1,000°C (Example 2-4), and 1,250°C (Example 2-5).

[0102] Electron microscope (FE-SEM, JSM-7100F, JEOL Ltd) photographs of the carbon material of Example 1-3 and the carbon material particles of Example 2-3 (2,500°C) are shown in Figures 3(a) and 3(b). More specifically, Figure 3(a) shows a carbon material with amorphous hard carbon properties obtained by heat treatment without a metal catalyst, and Figure 3(b) shows graphitized crystalline carbon material particles obtained by heat treatment in the presence of a metal catalyst.

[0103] In addition, electron microscope photographs of the amorphous hard carbon carbon materials of Example 2-4 (1,000°C; L-HC-1000), Example 2-5 (1,250°C; L-HC-1250), and Example 2-1 (1,500°C; L-HC-1500) are shown in Figures 4(c), 4(d), and 4(e), respectively.

[0104] [Raman spectroscopy] analysis In the case of graphite, the sp of carbon atom 2 1585cm resulting from the bond -1The G peak located at 2680 cm due to heavy scattering and -1 A 2D peak typically appears at a wavelength of 1350 cm -1 The D peak band is observed, but this is a peak that appears due to defects in the crystal. In the case of graphite, since the structure is made up of multiple layers of graphene stacked together, the probability of defects being relatively high, and the intensity of the D peak tends to be large. -1 ) is due to the CC stretching mode consisting of 5,6-membered rings, and G * Peak (~2445cm -1 ) is due to turbostratic graphite.

[0105] FIG. 5 shows the results of Raman spectroscopy (RAMANtouch, nanophoton Corp.) of the carbon materials prepared in Examples 1 and 2 of the present invention. Referring to the Raman spectra for the carbon material heat-treated without a metal catalyst in Example 2 (FIG. 5a) and the carbon material heat-treated in the presence of a metal catalyst in Example 1 (FIG. 5b), which are shown for each heat treatment temperature, in the case of Example 1 (presence of a metal catalyst) in FIG. 5b), it can be seen that the intensity of the D peak tends to decrease as the heat treatment temperature increases. In particular, at 2500°C, the D peak is very weak and the G peak, which is proportional to the degree of crystallinity, is strong, indicating that the material has been very well converted into crystalline graphite with almost no defects. In particular, the intensity ratio of the D peak to the G peak (I D / I G The I ratio of the carbon material in Example 1 in FIG. 5b) is an index relating to the degree of defects in graphite. D / I G It can be confirmed that the crystallinity is 0.04, which is higher than the 0.05 of commonly known natural graphite.

[0106] 5(c) shows the results of Raman spectroscopy of the carbon materials produced in Examples 2-1, 2-4, and 2-5 of the present invention. Specific values ​​are shown in Table 2 below.

[0107] More specifically, in FIG. 5(c), L-HC-1000 (heat-treated at 1000°C) is the result of Example 2-1, L-HC-1250 (heat-treated at 1,250°C) is the result of Example 2-5, and L-HC-1500 (heat-treated at 1500°C) is the result of Example 2-1. It can be seen that as the treatment temperature increases, the intensities of the D band and F band related to defects decrease, while the intensities of the G* and 2D bands increase. The 2D band is observed only in the L-HC-1500, which means that the L-HC-1500 sample contains a crystalline structure similar to graphite between amorphous hard carbon. The intensity ratio of each band is shown in Table 2 below.

[0108] [Table 2]

[0109] [XRD analysis (X-ray diffraction)] FIG. 6 shows the results of X-ray diffraction (XRD; Rigaku Ultima IV) analysis of the carbon materials prepared in Examples 1 and 2 according to the present invention. Referring to the XRD analysis at different heat treatment temperatures of the carbon material heat-treated without a metal catalyst in Example 2 (FIG. 6a)) and the carbon material heat-treated in the presence of a metal catalyst in Example 1 (FIG. 6b), in the case of Example 1, which was heat-treated in the presence of a metal catalyst, the (002) and (004) peaks indicating the interlayer structure of graphite are clearly observed, and the (100) peak indicating the planar structure of graphite and the (101) peak indicating a hexagonal structure can be observed.

[0110] Also, unlike Example 2 which was heat-treated without a metal catalyst (FIG. 6a), the 2Θ position of the (002) peak is observed as a single sharp and strong peak at 26 degrees, confirming that it was well converted to crystalline graphite.

[0111] FIG. 6c) shows the results of XRD analysis of the carbon materials produced at each temperature in Example 2. The 23-25° and 43.5° 2θ (two-theta) peaks in FIG. 6c) indicate the (002) and (001) diffraction planes of graphite. The broad shape of each peak indicates that all hard carbon structures are amorphous, regardless of the treatment temperature. The position of the (002) plane peak shifts to a slightly higher 2θ (two-theta) value as the treatment temperature increases, which means that the disorder of the local structure increases.

[0112] [Example 3: Production of coin batteries from negative electrode material for secondary batteries and evaluation of their characteristics] Coin batteries were manufactured to evaluate the electrochemical properties of the negative electrode crystalline carbon material prepared in Example 1-3 and the amorphous carbon materials prepared in Examples 2-1, 2-4, and 2-5.

[0113] First, 0.5 g of a mixture of the crystalline carbon material prepared in Example 1-3, acetylene black as a conductive material, and PVDF (Polyvinylidene fluoride) as a binder in a weight ratio of 80:10:10 was dispersed in a solvent NMP (1-methyl-2-pyrrolidone, 1.25 ml) to obtain a secondary battery negative electrode slurry. The obtained negative electrode slurry was applied to a copper foil (Cu-foil) with an average loading density of 3.5 mg / cm. -2After coating with ZnO to form a thin electrode plate, it was dried at 100℃ for more than 5 hours, pressed, and then dried a second time in a vacuum dryer to produce a negative electrode plate with a thickness of 40μ.

[0114] In addition, the negative electrode plates containing the amorphous carbon material prepared in Examples 2-1, 2-4, and 2-5 were also prepared under the same conditions as the negative electrode plates containing the crystalline carbon material described above, except that the amorphous carbon material was used instead of the crystalline carbon material.

[0115] The electrolyte is LiPF for the crystalline carbon material. 6 A mixed solvent of diethyl carbonate (DEC) and ethylene carbonate (EC) (DEC:EC = 1:1 vol%) in which lithium hexafluorophosphate (LiHxA) was dissolved at a concentration of 1M was used, and a porous polypropylene film manufactured by Celgard was used as the separation membrane.

[0116] In addition, NaPF 6 A mixed solvent of ethylene carbonate (EC) (DEC:EC=1:1 vol%) in which DEC was dissolved at a concentration of 1 M was used, and a porous polypropylene film manufactured by Celgard was used as the separation membrane.

[0117] Thereafter, a half cell of a lithium coin battery and a half cell of a sodium coin battery of size 2023 were fabricated by using the fabricated negative electrode plate as a working electrode, a metallic lithium foil (metal Li) as a counter electrode of the negative electrode plate made of a crystalline carbon material, and a metallic sodium foil (metal Na) as a counter electrode of the negative electrode plate made of an amorphous carbon material. The entire process of fabricating the coin battery was carried out in a glove box under an argon gas atmosphere.

[0118] A charge / discharge test of the coin battery produced in Example 3 was carried out using WBCS3000 manufactured by WonATech Co., Ltd. For convenience, the intercalation reaction of lithium (or sodium) into the graphite layer (or hard carbon) of the working electrode is defined as "charging", and the deintercalation reaction of lithium (or sodium) from the graphite layer (or hard carbon) is defined as "discharging".

[0119] The initial charge / discharge efficiency of the lithium coin battery prepared in Example 3 was tested by applying a current of 37.2 mA / g, and the initial charge / discharge efficiency of the sodium coin battery was tested by applying a current of 20.0 mA / g. The value obtained by dividing the amount of electricity supplied by the weight of the carbon material of the electrode is defined as the specific capacity of the carbon material.

[0120] FIG. 7 is a graph showing a) specific capacity and initial coulomb efficiency (ICE) of the carbon material and b) cyclic performance (current rate) of the coin battery using the coin battery to which the carbon material for anode prepared in Example 1 according to the present invention is applied. FIG. 7a) is a graph showing average values ​​of specific capacity values ​​of the carbon material measured by preparing three lithium coin batteries according to Example 3 and using them for charge / discharge evaluation. The charge capacity was 431.47 mA / g, the discharge capacity was 348.2 mA / g, and the charge / discharge efficiency was 80.7%.

[0121] FIG. 7b) is a graph showing the cycle characteristics of the coin battery of Example 3. The charge and discharge was performed in CC (constant current) mode. As shown in FIG. 7b), the battery maintained 102% of its initial capacity even after 80 cycles, and it was confirmed that the battery maintained stable output characteristics.

[0122] When comparing the characteristics of the battery using the crystalline carbon material of the present invention with those of the conventional technology, the evaluation results of a battery using a carbonaceous material obtained from biomass in Korean Patent Publication No. 10-2021-0060754 as the conventional technology show that the present invention shows 431 mAh / g compared to the initial specific capacity of 350 mAh / g presented in Experimental Example 2 of the conventional technology document, and that the capacity after 80 cycles is at the level of 150 to 250 mAh / g in the conventional technology document (see Figure 3 of the conventional technology document), whereas the present invention shows 350 mAh / g (see Figure 7 of the present invention), demonstrating excellent characteristics.

[0123] Meanwhile, FIG. 8 shows the results of measuring a) specific capacity and initial coulomb efficiency (ICE) of the amorphous carbon material according to the present invention and b) cyclic performance of the coin battery (charge / discharge rate) using the coin battery in which the amorphous carbon material for negative electrode prepared in Examples 2-1, 2-4, and 2-5 according to the present invention is applied. FIG. 8a) is a graph showing the average of the specific capacity values ​​of the carbon material according to the present invention, which is measured by using three sodium coin batteries manufactured at each treatment temperature in Example 3 for charge / discharge evaluation. The charge capacities were measured as 388.4 mA / g, 441.7 mA / g, and 417.8 mA / g for L-HC-1000, L-HC-1250, and L-HC-1500, respectively, the discharge capacities were measured as 241.3 mA / g, 281.6 mA / g, and 256.9 mA / g, respectively, and the charge / discharge efficiencies were measured as 62.12%, 63.75%, and 61.48%, respectively.

[0124] FIG. 8b) is a graph evaluating the cycle characteristics of the sodium coin battery of Example 3, and charging and discharging were performed in a CC (constant current) mode.

[0125] As shown in FIG. 8b), even at 100 cycles, the capacities of L-HC-1000, L-HC-1250, and L-HC-1500 were 214.4 mA / g, 247.72 mA / g, and 213.33 mA / g, respectively, which were 95.7%, 94.1%, and 91.6% of the initial capacity, respectively, confirming that the output characteristics were stably maintained.

[0126] Furthermore, when comparing the characteristics of the battery using the amorphous carbon material of the present invention with the evaluation results of a sodium battery using a carbonaceous material obtained from biomass in U.S. Patent Publication No. 2021-0376321 as the prior art, it can be seen that the present invention shows an initial specific capacity of 388 to 441 mAh / g compared to 323 to 337 mAh / g presented in Table 1 (Examples 1 to 9) of the prior art document, demonstrating superior characteristics.

[0127] As shown in the results of the characteristic evaluation, the negative electrode material for secondary batteries derived from lignocellulosic biomass according to the present invention is a highly crystalline carbon material from which residual metal components have been removed, and it has been confirmed that the secondary battery manufactured from the carbon material exhibits excellent specific capacity and charge / discharge characteristics and has stable output characteristics, and therefore has high applicability as a negative electrode active material for secondary batteries.

Claims

1. (a) adding an acid to lignocellulosic biomass to hydrolyze at least a portion of the hemicellulose in the lignocellulosic biomass and convert at least a portion of the cellulose into cellulose microfibrillates (MFCs) to obtain a hydrolysis reaction product containing a lignin-cellulose microfibrillated composite; (b) adding a basic aqueous solution to the hydrolysis reaction product containing the lignin-cellulose microfiber composite obtained in step (a) to further remove residual acid components and water-soluble residual metal components contained in the lignin-cellulose microfiber composite, and then separating the aqueous solution component to obtain lignin-cellulose microfiber composite solid particles; (c) grinding the lignin-cellulose microfibril composite solid particles obtained from step (b) to obtain ground lignin-cellulose microfibril composite solid particles; (d) heat-treating the pulverized lignin-cellulose microfiber composite solid particles obtained in step (c) to modify at least a portion of the solid particles into a crystalline or amorphous carbon material.

2. 2. The method for producing a secondary battery negative electrode material according to claim 1, wherein in step (a), the acid is selected from the group consisting of an organic acid having 1 to 20 carbon atoms; an inorganic acid selected from sulfuric acid, hydrochloric acid, phosphoric acid, and nitric acid, or a mixture thereof; a mixture of the organic acid and an inorganic acid; or a mixture of the organic acid and a mixture of an inorganic acid.

3. 2. The method of claim 1, wherein the acid in step (a) is any one selected from hydrochloric acid, sulfuric acid, and nitric acid, or a mixture thereof.

4. 2. The method for producing a negative electrode material for a secondary battery according to claim 1, wherein the hydrolysis step in step (a) is carried out by: i) a process of heating and / or pressurizing the material while adding an acid; ii) a process of steam explosion while adding an acid; iii) a process in which the heating and pressurizing treatment in step i) and the steam explosion in step ii) are mixed; or iv) a biological decomposition process using one or more cellulose decomposition enzymes.

5. 2. The method for producing a negative electrode material for a secondary battery according to claim 1, further comprising the step of: (a-1) separating and removing at least a part of the aqueous solution component in the hydrolysis reaction product containing the lignin-cellulose microfiber composite obtained in step (a) if the aqueous solution component is present in the hydrolysis reaction product containing the lignin-cellulose microfiber composite obtained in step (a).

6. 2. The method for producing a negative electrode material for a secondary battery according to claim 1, further comprising, prior to step (b), a step (a-2) of washing the hydrolysis reaction product containing the lignin-cellulose microfiber composite obtained in step (a) with desalted water to obtain a hydrolysis reaction product containing the lignin-cellulose microfiber composite from which at least a portion of the water-soluble metal components contained in the lignocellulosic biomass has been removed.

7. The base used in step (b) is sodium hydroxide (NaOH), potassium hydroxide (KOH), ammonia (NH ３ ), lithium hydroxide (LiOH), potassium carbonate (K ２ CO ３ ), sodium carbonate (Na ２ CO ３ ), potassium bicarbonate (KHCO ３ ), magnesium hydroxide (Mg(OH) ２ ), magnesium oxide (MgO) and sodium bicarbonate (NaHCO ３ 2. The method for producing a negative electrode material for a secondary battery according to claim 1, wherein the negative electrode material is at least one selected from the group consisting of fluorine, arsenic, ...

8. 2. The method for producing a negative electrode material for a secondary battery according to claim 1, wherein the lignin-cellulose microfiber composite solid particles obtained in step (b) have a hemicellulose content of 5% by weight (wt%) or less based on the total amount of components derived from lignin, cellulose, and hemicellulose.

9. 2. The method for producing a negative electrode material for a secondary battery according to claim 1, wherein the lignin-cellulose microfiber composite solid particles obtained in step (b) contain 20 wt % to 80 wt % of a lignin-derived component and 20 wt % to 80 wt % of a cellulose-derived component, based on the total amount of the lignin-, cellulose- and hemicellulose-derived components.

10. 2. The method for producing a negative electrode material for a secondary battery according to claim 1, wherein the particle size of the pulverized lignin-cellulose microfiber composite solid particles obtained in step (c) is 500 nm to 200 μm.

11. 2. The method for producing a secondary battery negative electrode material according to claim 1, wherein the heat treatment temperature in step (d) is in the range of 500 to 3000° C.

12. 2. The method for producing a secondary battery negative electrode material according to claim 1, wherein the heat treatment in step (d) is carried out in the presence of a metal catalyst, so that at least a part of the particles obtained after the heat treatment is a crystalline carbon material.

13. After the step (d), 13. The method for producing a secondary battery negative electrode material according to claim 12, further comprising: (e) treating the solid particles obtained in step (d), at least a part of which is a crystalline carbon material, with an acid to obtain a carbon material from which the metal catalyst has been removed.

14. 2. The method for producing a secondary battery negative electrode material according to claim 1, wherein the heat treatment in step (d) is carried out in the absence of a metal catalyst, so that at least a part of the particles obtained after the heat treatment is an amorphous carbon material.

15. A negative electrode material for a secondary battery produced by the method according to any one of claims 1 to 14.

16. A composition for a secondary battery negative electrode, comprising the negative electrode material for a secondary battery according to claim 15.

17. A secondary battery comprising the composition for a secondary battery negative electrode according to claim 16.

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