Method for manufacturing negative electrode material for secondary battery from lignocellulosic biomass

Abstract

The present invention relates to a method for manufacturing a negative electrode material for a secondary battery from lignocellulosic biomass, and more specifically, to a method for manufacturing a negative electrode material for a secondary battery derived from lignocellulosic biomass such that metallic components contained in the biomass do not leach into the electrolyte, and when applied to a secondary battery material, it can contribute to improving the performance and stability of the secondary battery.

Description

Technology Field

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

[0002] Due to environmental pollution caused by the excessive use of fossil fuels, the demand for eco-friendly products and alternative energy sources is rapidly increasing. Furthermore, technological development in the fields of power generation and energy storage is actively underway to utilize electric energy as an alternative energy source.

[0003] In particular, research and development are active for hybrid and electric vehicles that can replace gasoline and diesel vehicles used for transportation, which are a major cause of air pollution, and for Energy Storage Systems (ESS) that can store large amounts of surplus electricity. A representative component used in the production of these electric energy systems is the secondary battery, and the demand for secondary batteries is surging in portable devices such as telephones, laptops, cameras, and industrial tools.

[0004] Currently, lithium secondary batteries are primarily used as a representative example of such secondary batteries. Lithium secondary batteries consist of a structure in which current collectors coated with positive and negative active materials, respectively, a porous separator interposed between the current collectors, and an electrolyte of a non-aqueous lithium salt are impregnated.

[0005] At this time, expensive carbon-based and non-carbon-based materials are used as negative electrode active materials. Regarding the non-carbon-based active materials, lithium metal, silicon (Si), and transition metal oxide series are being studied, but commercialization is being delayed due to various disadvantages. The carbon-based negative electrode active materials are broadly classified into graphitic and non-graphitic types. The non-graphitic type can be further divided into soft carbon-based (graphitizable carbon) active materials that exhibit uniaxial orientation even at low temperatures, and hard carbon-based (non-graphitizable carbon) active materials that are difficult to achieve uniaxial orientation even at high temperatures.

[0006] Meanwhile, graphite-based active materials are currently used in most lithium-ion secondary batteries due to their long electrode life characteristics resulting from highly reversible charge-discharge properties caused by the uniaxial orientation of the graphene layer.

[0007] However, the low theoretical capacity of graphite (372 mAh / g) is a major obstacle in the current situation where high capacity of batteries is required, despite its many advantages. Additionally, during the charging process, as lithium ions are inserted between the layered structures of graphite, salts from the electrolyte are simultaneously inserted between the layered structures, causing the layered structures to delaminate. To overcome this, graphite coated with non-graphite (amorphous) carbon is often used.

[0008] Generally, the capacity of cathode active materials made of non-graphite carbon is lower than that of graphite (crystalline) carbon, but their power characteristics are superior compared to graphite carbon.

[0009] Currently, with the surging demand for high-performance lithium-ion rechargeable batteries, carbon materials used as anode active materials worldwide are considerably expensive and are mostly manufactured using coal or petroleum-based raw materials. Since the use of these materials presents economic feasibility issues and causes significant carbon dioxide emissions upon disposal, recent research is being conducted on utilizing biomass-derived anode materials as an alternative.

[0010] However, due to metallic components such as potassium and sodium contained in biomass, metallic components remain in the carbon materials produced from biomass. When these are used as electrode active materials, they may leach into the electrolyte and cause electrochemical reactions, which can affect battery performance and safety, so they must be removed.

[0011] As a conventional technology using the above-mentioned biomass-based carbon material as an electrode material, Korean Registered Patent No. 10-1545116 (published on August 17, 2015) discloses a method for manufacturing a carbon material for a lithium-ion capacitor negative electrode by utilizing charcoal derived from coconut shells as a carbonaceous precursor, but this has the problem that heat treatment must be performed according to a vapor phase demineralization process and metal-halogen complexes generated during the demineralization process must be captured and removed.

[0012] Furthermore, Korean Registered Patent No. 10-2442330 (published September 8, 2022) proposes a process for converting lignocellulose material into a hard carbon-type carbon material; however, it does not present a process for removing metallic components contained in the lignocellulose material, and the low crystallinity and micropore uniformity of the carbon material can cause a degradation in battery performance. In particular, there is a problem in that the material is converted only into a hard carbon form rather than a graphite-like carbon material due to the reduced crystallinity.

[0013] Therefore, there is an increasingly urgent need to develop a method for manufacturing novel, low-cost anode materials for secondary batteries derived from eco-friendly biomass that uses lignocellulosic biomass—a material with economic advantages—as a raw material. This method involves a simple process, produces active materials that overcome the disadvantages of both graphite-based and non-graphite-based materials, and does not leach metallic components. Prior art literature

[0014] Korean Registered Patent No. 10-1545116 (Published on Aug. 17, 2015) Korean Registered Patent No. 10-2442330 (Published on Sep. 8, 2022) The problem to be solved

[0015] The objective of the present invention is to provide a method for manufacturing a negative electrode material for a secondary battery based on a carbon material having a highly crystalline graphite phase or based on an amorphous carbon material, using lignocellulosic biomass, which is an eco-friendly raw material, in a simple and economical manner, while having high specific capacity, charge / discharge capacity, and efficiency.

[0016] In addition, the present invention aims to provide a composition for a secondary battery negative electrode comprising the above-mentioned negative electrode material and a secondary battery comprising the same. means of solving the problem

[0017] To solve the above problem, the present invention comprises the steps of: (a) obtaining a hydrolysis reaction product comprising a lignin-cellulose microfiber composite obtained by adding an acid to lignocellulosic biomass to hydrolyze at least a portion of the hemicellulose in the lignocellulosic biomass and simultaneously modifying at least a portion of the cellulose into microfibrillated cellulose (MFC); (b) adding a basic aqueous solution to the hydrolysis reaction product comprising 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 solid particles of the lignin-cellulose microfiber composite; and (c) grinding the solid particles of the lignin-cellulose microfiber composite obtained from step (b) to obtain ground solid particles of the lignin-cellulose microfiber composite. The present invention provides a method for manufacturing a negative electrode material for a secondary battery using lignocellulosic biomass as a raw material, comprising: (d) heat-treating the pulverized lignin-cellulose microfiber composite solid particles obtained from step (c) above to modify at least a portion of the solid particles into a crystalline or amorphous carbon material.

[0018] In one embodiment, the acid in step (a) may be selected from 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 the inorganic acid; or a mixture of the organic acid and the mixture of inorganic acids; and preferably, any one selected from hydrochloric acid, sulfuric acid, and nitric acid, or a mixture thereof may be used.

[0019] In one embodiment, the hydrolysis step of step (a) may be carried out by i) heating and / or pressurizing while adding acid, or ii) steam explosion while adding acid, or iii) carrying out a process that combines the heating and pressurizing in i) and the steam explosion in ii), or iv) through biological degradation using one or more cellulose degrading enzymes.

[0020] As an example, after step (a), the method may additionally include: (a-1) a step of separating and removing at least some of the aqueous components in the hydrolysis reactant containing the lignin-cellulose microfiber composite obtained from step (a) when an aqueous component is present in the hydrolysis reactant containing the lignin-cellulose microfiber composite obtained from step (a).

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

[0022] In one embodiment, the base used in step (b) may be at least one selected from sodium hydroxide (NaOH), potassium hydroxide (KOH), ammonia (NH3), lithium hydroxide (LiOH), potassium carbonate (K2CO3), sodium carbonate (Na2CO3), potassium bicarbonate (KHCO3), magnesium hydroxide (Mg(OH)2), magnesium oxide (MgO), and sodium bicarbonate (NaHCO3), or a mixture thereof.

[0023] As one example, 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 sum of lignin, cellulose, and hemicellulose-derived components.

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

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

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

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

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

[0029] In addition, the present invention can provide a negative electrode material for a secondary battery manufactured from the above manufacturing method, and the present invention can also provide a composition for a secondary battery negative electrode comprising the above negative electrode material.

[0030] In addition, the present invention can provide a secondary battery using the above-described composition for a secondary battery negative electrode. Effects of the invention

[0031] The method for manufacturing a negative electrode material for a secondary battery according to the present invention utilizes lignocellulosic biomass, which is an eco-friendly material and the most abundant and inexpensive on Earth, thereby offering an economic advantage in manufacturing costs. By using lignocellulosic biomass as a raw material, it is possible to manufacture a highly crystalline or amorphous carbon material with residual metallic components removed from the lignocellulosic biomass through a simple process. A secondary battery containing the negative electrode material manufactured therefrom exhibits excellent specific capacity and charge / discharge characteristics, and has the effect of having stable output characteristics.

[0032] In addition, the negative electrode material for secondary batteries according to the present invention can have additional eco-friendly advantages, as carbon dioxide emissions are significantly reduced compared to pitch and carbon materials for negative electrodes manufactured according to conventional technology during manufacturing and incineration. Brief explanation of the drawing

[0033] FIG. 1 is a diagram showing (a) the hierarchical structure of biomass-derived cellulose and (b) a cellulose microfiber structure including crystalline and amorphous domains. Figure 2 is an electron microscope image of a solid particle composed of lignin and a cellulose microfibril bundle prepared in Example 1 according to the present invention before grinding. FIG. 3a) is an electron microscope image of an amorphous hard carbon material obtained by heat treatment at 2500 ℃ without a metal catalyst according to the present invention, and FIG. 3b) is an electron microscope image of a graphitized crystalline carbon material obtained by heat treatment at 2500 ℃ in the presence of a metal catalyst according to the present invention. FIG. 4 is an electron microscope image of a carbon material with amorphous hard carbon properties prepared in Examples 2-1, 2-4, and 2-5 according to the present invention. Figure 5 is a figure showing the Raman spectroscopy (RAMANtouch, nanophoton Corp.) results of the carbon materials prepared in Examples 1 and 2 of the present invention. Figure 6 is a figure showing the X-ray diffraction (XRD) analysis results of carbon materials prepared in Example 1 and Example 2 according to the present invention. FIG. 7 is a graph showing the measured a) specific capacity and initial Coulomb efficiency (ICE) and b) cyclic performance of the carbon material and the coin cell (current rate: 0.1 C) using a coin cell to which the carbon material for the cathode prepared in Example 1 according to the present invention is applied. Figure 8 is a figure showing the results of measuring a) specific capacity and initial Coulomb efficiency (ICE) and b) cyclic performance (current rate) of a carbon material and a coin battery (a) the cyclic performance of the coin battery using a coin battery to which the amorphous carbon material prepared in Example 2 according to the present invention is applied. Specific details for implementing the invention

[0034] The present invention will be described in more detail below. In each drawing of the present invention, the sizes or dimensions of the structures are depicted enlarged or reduced compared to the actual size for the sake of clarity of the invention, and known components are omitted to reveal characteristic configurations, so the invention is not limited to the drawings.

[0035] Furthermore, the size and thickness of each component shown in the drawings are depicted arbitrarily for convenience of explanation, and thus the present invention is not necessarily limited to what is illustrated. Additionally, thicknesses have been enlarged in the drawings to clearly represent various layers and regions. Moreover, in the drawings, the thickness of some layers and regions has been exaggerated for convenience of explanation. When a part such as a layer, film, region, or plate is described as being "on" another part, this includes not only cases where it is "immediately on" another part, but also cases where there is another part in between.

[0036] Furthermore, throughout the specification, when a part is described as "including" a certain component, this means that, unless specifically stated otherwise, it does not exclude other components but may include additional components. Also, throughout the specification, the term "on" means being located above or below the subject part, and does not necessarily mean being located on the upper side with respect to the direction of gravity.

[0037] The manufacturing method according to the present invention will be described in more detail below.

[0038] A method for manufacturing a negative electrode material for a secondary battery from lignocellulosic biomass according to the present invention comprises: a) a step of obtaining a hydrolysis reaction product comprising a lignin-cellulose microfiber composite obtained by adding an acid to lignocellulosic biomass to hydrolyze at least a portion of the hemicellulose in the lignocellulosic biomass and simultaneously modifying at least a portion of the cellulose into microfibrillated cellulose (MFC); (b) a step of adding a basic aqueous solution to the hydrolysis reaction product comprising the lignin-cellulose microfiber composite obtained from step (a), thereby further removing 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 solid particles of the lignin-cellulose microfiber composite; (c) a step of grinding the lignin-cellulose microfiber solid particles obtained from step (b) above to obtain ground lignin-cellulose microfiber solid particles; and (d) a step of heat-treating the ground lignin-cellulose microfiber composite solid particles obtained from step (c) above to modify at least a portion of the solid particles into a crystalline or amorphous carbon material; comprising

[0039] Herein, as the first step of the manufacturing method according to the present invention, the step (a) is a step of obtaining a hydrolysis reaction product comprising a lignin-cellulose microfiber composite obtained by adding acid to lignocellulosic biomass, which is a raw material, as a precursor for manufacturing a carbon material for a negative electrode active material of a secondary battery, by hydrolyzing at least a portion of hemicellulose and simultaneously modifying at least a portion of cellulose into microfibrillated cellulose (MFC); wherein, by adding acid according to the step (a), the rigid crystallization structure between lignin and cellulose in the biomass is destroyed, at least a portion of hemicellulose is hydrolyzed, and at least a portion of the cellulose fiber is preferably 10% or more, more preferably 20% or more, more preferably 30% or more, more preferably 40% or more, more preferably 50% or more, more preferably 60% or more, more preferably 70% or more, more preferably More than 80%, more preferably more than 90%, more preferably more than 95% is converted into the form of microfibrillated cellulose, and furthermore, by the acid treatment, lignin and at least some of the microfibrillated cellulose (MFC) are physically or chemically bonded to form a polymeric lignin-cellulose microfibrillated (MFC) complex.

[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) and the lignin modified by acid treatment within the lignin-cellulose microfiber (MFC) composite obtained by acid treatment. Through this, there is an advantage of being able to provide a negative electrode material for a secondary battery through a more eco-friendly and economical process using components derived from lignocellulose-based biomass, which is a low-cost bio-raw material.

[0041] Here, the cellulose included in the above lignocellulosic biomass is a fibrous material in which linear chains connected by beta-glycosidic bonds of monomer D-glucose are overlapped. Referring to Figure 1 (a), which shows the hierarchical structure of biomass-derived cellulose, the cellulose fiber includes a microfibril bundle composed of microfibrils, and the microfibrils include an elementary fibril as the lowest component.

[0042] Hereinafter, in the present invention, microfibrillated cellulose (MFC) refers to 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 defibrillated, and should be understood as a concept including microfibril bundles and microfibrils as illustrated in FIG. 1a).

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

[0044] In addition, step a) above can leach out the metallic components contained in the lignocellulosic biomass so that the rigid structure of the lignocellulosic biomass is dismantled by the acid treatment, making it easy to leach out the metallic components contained in the biomass—that is, so that the metallic components in the acid-treated biomass are converted into ionic substances and become easy to remove through subsequent dehydration and / or washing processes.

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

[0046] The lignocellulosic biomass in step (a) according to the present invention is a material that includes lignin and at least one of cellulose and hemicellulose, preferably may include all of lignin, cellulose, and hemicellulose, and such lignocellulosic biomass may be a woody biomass derived from herbaceous plants, conifers or deciduous trees (conventional wood), or various biomass such as rice straw, corn stalks, palm fruit shells, sugarcane, etc.

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

[0048] After the above-mentioned lignocellulosic biomass undergoes a crushing process, 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 without limitation using any method capable of reducing the moisture content of the lignocellulosic biomass, such as oven drying, natural drying in a well-ventilated area, or hot air drying.

[0049] In addition, the grinding and drying steps in the present invention may be performed regardless of the order. That is, the drying process may be performed after the grinding process of the lignocellulosic biomass, or the grinding process may be performed after the drying process. This may vary depending on the surrounding environment or the type and drying state of the lignocellulosic biomass. For example, if the biomass is very well dried, the drying process may be omitted. Preferably, drying the lignocellulosic biomass with a larger surface area after the grinding step may be preferred from the perspective of efficiency.

[0050] In addition, the acid used in step (a) of the present invention may be selected from an organic acid having 1 to 20 carbon atoms; any one inorganic acid selected from sulfuric acid, hydrochloric acid, phosphoric acid, and nitric acid, or a mixture thereof; a mixture of the organic acid and the inorganic acid; or a mixture of the organic acid and the mixture of inorganic acids.

[0051] At this time, the organic acid may be a carbon compound containing a carboxylic acid, and depending on the number of carboxylic acids, monocarboxylic acid, biscarboxylic acid, triscarboxylic acid, tetracarboxylic acid, etc. may be used, and depending on the number of carbon atoms, an organic acid having 1 to 20 carbon atoms, preferably 1 to 15 carbon atoms may be used, and more preferably, acetic acid, formic acid, propionic acid, etc. may be used.

[0052] In addition, 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 may be used, and the preferred acid concentration may be 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 crushed biomass and acid, and as a more preferred example, sulfuric acid may be used 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 crushed biomass and acid.

[0053] Here, regarding the content of the strong acid, if we look at the case where 75% (v / v) sulfuric acid is added as an example, the 75% (v / v) sulfuric acid is added, and the sulfuric acid concentration can be used in a range of 0.5 wt% to 70 wt% based on the final concentration (based on the total content of the crushed biomass and aqueous solution), and preferably, in a range of 0.6 wt% to 65 wt%. The above ratio can be used by varying the optimal conditions depending on the type of biomass, and even 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 aforementioned range.

[0054] In addition, the hydrolysis step of step (a) in the present invention may be carried out by i) heating and / or pressurizing while adding acid, or ii) steam explosion while adding acid, or iii) performing a process that combines the heating and pressurizing in i) and the steam explosion in ii), or iv) biological decomposition using one or more cellulose degrading enzymes.

[0055] Here, in the hydrolysis process of step (a) above, i) the process of heating and / or pressurizing while adding 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 atmospheric pressure or 10 atmospheres or less, and then filtering the solid by depressurizing; ii) the process of steam explosion while adding 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, and then reacting by instantaneously depressurizing; furthermore, in the biological degradation process iv) above, one or more known cellulose-degrading enzymes may be used without limitation, and at this time, the i) The concentration of acid introduced in the process to iv) can be introduced in a range of concentrations depending on conditions such as the type of acid and reaction temperature and pressure.

[0056] Meanwhile, the hydrolysis reactant comprising the lignin-cellulose microfiber composite obtained in step (a) according to the present invention may be in the state of a slurry comprising a solid lignin-cellulose microfiber composite, an acid, an eluted metal component, and a decomposed sugar component.

[0057] In addition, the present invention may further include, after step (a), a step of (a-1) separating and removing at least some of the aqueous components in the hydrolysis reactant when the hydrolysis reactant containing the lignin-cellulose microfiber composite obtained from step (a) is in a slurry state.

[0058] Here, the separation of the above aqueous solution components may be performed using known separation techniques without limitation, and may include, for example, dehydration by centrifugation, filtration, and decantation.

[0059] Meanwhile, step (b) in the present invention is a step of obtaining solid particles of the lignin-cellulose microfiber composite by adding a basic aqueous solution to a hydrolysis reactant containing the lignin-cellulose microfiber composite obtained from step (a), reacting the residual acid component and water-soluble residual metal component contained in the lignin-cellulose microfiber composite with or dissolving them in the aqueous solution, and separating and removing the aqueous solution component. This corresponds to a process for removing residual acid component and residual metal component, as if the residual acid component and water-soluble residual metal component in the hydrolysis reactant obtained from step (a) are not removed, it may adversely affect the properties of the negative electrode material for secondary batteries and the performance of the secondary battery in subsequent processes.

[0060] In this case, the step of separating the aqueous solution component obtained after adding a basic aqueous solution to the hydrolysis reactant may apply known separation techniques without limitation and may include, for example, dehydration by centrifugation, filtration, and decantation.

[0061] Additionally, the base used in step (b) above may be at least one selected from sodium hydroxide (NaOH), potassium hydroxide (KOH), ammonia (NH3), lithium hydroxide (LiOH), potassium carbonate (K2CO3), sodium carbonate (Na2CO3), potassium bicarbonate (KHCO3), magnesium hydroxide (Mg(OH)2), magnesium oxide (MgO), and sodium bicarbonate (NaHCO3), or a mixture thereof; however, any base that neutralizes the acid component without forming a sparingly soluble salt and does not remain in the solid particles produced in step (b) may be used without limitation.

[0062] Additionally, prior to step (b), the present invention may further include a step (a-2) of washing the hydrolysis reaction product containing the lignin-cellulose microfiber composite obtained from step (a) with deionized water to obtain a hydrolysis reaction product containing the lignin-cellulose microfiber composite, in which at least a portion of the water-soluble metal component contained in the lignocellulosic biomass is removed; wherein the residual acid component obtained after washing with deionized water can be recovered and reused.

[0063] That is, the above step (a-2) has the advantage of being able to remove components soluble in an aqueous solution, selected from water-soluble substances containing residual sugar components derived from biomass, substances derived from the acid addition process, substances derived from the base addition process, acid components, and water-soluble metal components, or a mixture thereof, by washing the residual acid components in the modified lignin-cellulose microfiber (MFC) composite obtained through the above step (a) with deionized water before adding the basic aqueous solution in the above step (b), thereby reducing the content of the basic aqueous solution added in the above step (b).

[0064] In addition, the present invention allows for the additional removal of water-soluble components, including metal components and residual basic components, contained within the solid particles by, after step (b), (b-1) additionally washing the lignin-cellulose microfiber composite solid particles obtained from step (b) with deionized water and separating the aqueous solution containing water-soluble components resulting from the washing.

[0065] As a result, when a certain amount of polysaccharides hydrolyzed by an acid component are removed from the solid particles obtained through step b) above, a solid particle modified from lignocellulosic biomass can be obtained, with at least 30% by weight, preferably 40% by weight, more preferably 50% by weight, more preferably 60% by weight, and more preferably 70% by weight, based on the total weight of the solid particle obtained and the dry weight of the input biomass.

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

[0067] That is, the solid particles obtained through steps (a) and (b) above contain lignin and cellulose microfibers (MFCs) as major components, and these form a lignin-cellulose microfiber (MFC) complex and serve as a precursor for the cathode active material.

[0068] Meanwhile, the solid particles obtained through step (b) above may contain 1 wt% to 99 wt% of lignin-derived components based on the total sum of lignin, cellulose, and hemicellulose-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 lignin-derived components.

[0069] In addition, the solid particles obtained through step (b) above may contain 1 wt% to 99 wt% of cellulose-derived components based on the total sum of lignin, cellulose, and hemicellulose-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.

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

[0071] In addition, the present invention can further remove water-soluble components, including metal components, residual basic components, etc., contained within the solid particles by, after step (b), (b-1) washing the solid particles of the lignin-cellulose microfiber composite obtained from step (b) with deionized water and separating the aqueous solution containing these water-soluble components.

[0072] Meanwhile, step (c) in the present invention is a step of grinding the lignin-cellulose microfiber composite solid particles obtained from step (b) to obtain ground solid particles. The ground solid particles in powder form are easy to handle, enable uniform heat treatment during the subsequent heat treatment step (d), and can also improve the dispersibility of the metal catalyst in the subsequent process, thereby having the advantage of improving physical properties such as crystallinity of the finally manufactured cathode carbon material.

[0073] Here, the grinding method of step (c) above may apply any known grinding method including ball milling, spex milling, and nano milling without limitation, and the particle size of the solid particles obtained after grinding may 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 performed prior to the grinding of step (c) above, and through the drying step, the moisture content in the solid particles can be reduced to less than 5 weight%, preferably less than 3 weight%.

[0075] Meanwhile, 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; wherein if the lignin-cellulose microfiber solid particles pulverized 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 crystalline carbon material with graphite properties, and furthermore, if the solid particles are heat-treated in the absence of the metal catalyst, at least a portion of the solid particles may be converted into a hard carbonized amorphous carbon material.

[0076] Here, the crystalline carbon material obtained by heat treatment in the presence of the metal catalyst is the ratio of the intensity of the D band to the G band in the Raman spectroscopic spectrum (I) as an indicator representing the degree of defects in graphite. D / I GIt is characterized by being 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) according to the present invention may have at least 50 wt% of the total weight of the solid particles as a crystalline carbon material, more preferably at least 60 wt% as a crystalline carbon material, more preferably at least 70 wt% as a crystalline carbon material, more preferably at least 80 wt% as a crystalline carbonized material, more preferably at least 90 wt% as a crystalline carbon material, and more preferably at least 95 wt% as a crystalline carbon material.

[0078] In addition, the particles obtained by heat treatment in the absence of a metal catalyst in step (d) according to the present invention may have at least 60 wt% of the total solid particle weight as an amorphous carbon material, more preferably at least 70 wt% as an amorphous carbon material, more preferably at least 80 wt% as an amorphous carbon material, more preferably at least 90 wt% as an amorphous carbon material, and more preferably at least 95 wt% as an amorphous carbon material.

[0079] At this time, the heat treatment in step (d) above can be performed in a temperature range of 500 to 3,000 ℃, preferably in a range of 1,000 to 2,700 ℃, and more preferably in a range of 1,500 to 2,500 ℃.

[0080] In addition, the catalyst used for heat treatment in the presence of a metal catalyst in step (d) above may be any catalyst known as a graphitization catalyst, without being limited to any specific type. For example, a catalyst comprising 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 comprising said metal, may be used. For example, the catalyst comprising said metal may be a catalyst comprising one selected from Fe, Co, Mn, Ni, and Zn, or a mixture thereof. Furthermore, as said metal salt, Fe(NO3)3, Fe2O3, FeCl3, A catalyst containing one of Ni(NO3)3, ZnO, or a mixture thereof may be used.

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

[0082] Meanwhile, the present invention may additionally include the step of (e) acid-treating the crystalline carbon material obtained from step (d) to obtain a crystalline carbon material from which the metal catalyst component has been removed, after heat treatment in the presence of a metal catalyst in step (d); this is intended to prevent the inclusion of a metal component in the negative electrode active material of a secondary battery, as described in step (a); and through the acid treatment, the metal component derived from the residual metal catalyst is converted into a water-soluble metal salt form so that it can be easily removed by washing with water, etc.

[0083] At this time, the type, concentration, amount of acid, and treatment method of the acid used to remove the residual metal catalyst component can be appropriately modified by a person skilled in the art by referring to the description of the acid added in step (a). For example, when hydrochloric acid is used, the acid can be added by determining the equivalent range of the acid within the range of 0.3 equivalents to 50 equivalents based on the content of the metal catalyst used in step (d).

[0084] In addition, the present invention may further include, after step (e), a step (e-1) of washing the crystalline carbon material obtained from step (e) using deionized water, thereby enabling more efficient removal of metal components derived from the metal catalyst.

[0085] In addition, the present invention may perform, after step (e), (f) drying and grinding the crystalline carbon material from which the metal catalyst has been removed obtained from step (e); in this case, the grinding method may apply any known grinding method including ball milling, spex milling, and nano milling, such as the solid particle grinding method of step (c), without limitation, and the particle size of the solid particle finally obtained after grinding may be in the range of 0.1 to 200 μm.

[0086] The present invention can provide a negative electrode material for a secondary battery manufactured by the manufacturing method described above. That is, the crystalline carbon material manufactured from lignocellulosic biomass through the manufacturing method of the present invention has the advantage of high specific capacity and charge / discharge performance, and thus can be utilized as a negative electrode material for a secondary battery.

[0087] In addition, the present invention can provide a composition for a secondary battery negative electrode comprising the negative electrode material for the secondary battery, and the present invention can also provide a secondary battery comprising the negative electrode composition.

[0088] Hereinafter, the present invention will be described in more detail through examples to aid in understanding. However, various conditions may be changed in the embodiments described in the present invention, and therefore, the scope of the present invention is not limited to the following examples. The following examples of the present invention are merely intended to provide a more detailed explanation to those with average knowledge in the art.

[0089] [Preparation Example 1: Preparation of Acid-Treated Lignin-Cellulose Microfiber Composite Solid Particles]

[0090] In Preparation Example 1 below, lignin-cellulose microfiber composite solid particles were prepared by performing a demineralization process using an aqueous acid solution to remove metallic components contained in lignocellulosic biomass.

[0091] Pine and oak were mixed in equal weight ratios, and then the biomass was ground to a particle size of less than 10 mesh. After grinding, the raw material, lignocellulosic biomass powder, was prepared by drying at 100°C for 2 hours until the moisture content was 5 wt%.

[0092] Subsequently, the crushed biomass powder and water were introduced into a reactor in a mass ratio of 1.4:1.0 and stirred while raising the temperature to 90°C. Then, 95% sulfuric acid was added to achieve a final concentration of 10 wt% and stirred while raising the temperature to 120°C for 1 hour. Afterward, the reaction was carried out for 60 minutes to hydrolyze the hemicellulose component and, at the same time, transform at least some of the cellulose component into microfibrillated cellulose (MFC), thereby obtaining a hydrolysis reaction product containing a solid lignin-cellulose microfibrillation composite. The product was then filtered to separate and remove the aqueous component.

[0093] The obtained hydrolysis reaction product was neutralized to a pH of 7.0 using a 0.1 N ammonium hydroxide solution to further remove residual acidic components and residual metallic components within the lignin-cellulose microfiber composite, and then dehydrated to separate and remove the aqueous components.

[0094] Afterwards, the residual metal ions and other ionic compound components were removed as much as possible by washing and dehydrating 2 to 3 times with a sufficient amount of deionized water to finally obtain lignin-cellulose microfiber composite solid particles.

[0095] The above solid particles were dried at 100°C for 6 hours and then ground to an average particle size of 20 μm to obtain ground lignin-cellulose microfiber composite solid particles as a carbon precursor for conversion into a carbon material for a secondary battery negative electrode, and Figure 2 shows an electron microscope image before grinding of the solid particles composed of lignin and cellulose microfibril bundles prepared in Preparation Example 1.

[0096] [Comparative Manufacturing Example 1: Preparation of Acid-Untreated Lignin-Cellulose Microfiber Solid Particles]

[0097] A ground lignin-cellulose microfiber composite solid particle was obtained by performing the same method as in Preparation Example 1 above, except that sulfuric acid was not applied to the reaction solution.

[0098] The results of analyzing the amount of metallic components contained in the ground lignin-cellulose microfiber composite solid particles obtained according to the above Manufacturing Example 1 and Comparative Manufacturing Example 1 are listed in Table 1 below.

[0099] metal Residual metal content (mg / kg) in lignin-cellulose microfiber composite Residual Metal Content Evaluation Agency (Test Method) * Preparation Example 1 Comparative Example 1 K ND 70.4 ICP (Self-Assessment) Ca ND 166.7 ICP (Self-Assessment) Mg ND 19.1 ICP (Self-Assessment) Na ND ND ICP (Self-Assessment) Fe ND 55.6 ICP (Self-Assessment) Mn ND 8.4 ICP (Self-Assessment) Mo ND 3.8 ICP (Self-Assessment) CD ND 0.1 Korea Institute of Construction & Living Environment Testing (ISO 8124-3:2010) Cr ND 1.9 Korea Institute of Construction & Living Environment Testing (ISO 8124-3:2010) Cu ND ND ICP (Self-Assessment) Ni ND 2.5 ICP (Self-Assessment) Pb ND ND Korea Institute of Construction & Living Environment Testing (ISO 8124-3:2010) Zn ND 6.5 ICP (Self-Assessment) As ND ND Korea Institute of Construction & Living Environment Testing (ISO 8124-3:2010) Hg ND ND Korea Institute of Construction & Living Environment Testing (ISO 8124-3:2010) * Concentration after neutralization and washing (detection limit by ISO method (2-10 mg / kg)

[0100] Looking at the analysis results of residual metal content in solid particles of the lignin-cellulose microfiber composite according to the presence or absence of acid treatment in Preparation Example 1 and Comparative Preparation Example 1 according to the present invention in Table 1 above, it can be confirmed that no metallic components were observed at the detection limit (2~10 mg / kg) level as a result of the acid treatment demineralization process in the solid particles of the lignin-cellulose microfiber composite of Preparation Example 1, whereas various metallic components were detected in the solid particles of the lignin-cellulose microfiber composite of Comparative Preparation Example 1.

[0101] [Examples 1-1 to 1-3: Preparation of crystalline carbon material for secondary battery negative electrode heat-treated in the presence of a metal catalyst]

[0102] As a carbon precursor for a secondary battery negative electrode, 100 g of solid particles of the lignin-cellulose microfiber composite of Preparation Example 1 and an Fe catalyst 20 g (Sigma Aldrich, Product No.: 12310, ≥99%, reduced, powder (fine)) was added to a blender and mixed. The powder mixed with the solid particles and catalyst was introduced into a furnace (Asiltech) and heat-treated for 4 hours each under conditions of 1,500 ℃ (Example 1-1), 2,000 ℃ (Example 1-2), and 2,500 ℃ (Example 1-3) to convert it into a carbon material, at which time 10 L of nitrogen gas was supplied into the furnace at a rate of 60 ℃ per minute.

[0103] The above heat-treated powder was added to a 1M HCl aqueous solution to remove the metal catalyst, and after removing the aqueous components by filtration, it was neutralized with a 1M ammonium hydroxide solution, washed with deionized water, and dried (120 ℃, 1 hour) to obtain a crystalline carbon material for a secondary battery negative electrode with a moisture content of less than 0.01%. It was confirmed that no residual Fe was detected in the carbon materials of Examples 1-1 to 1-3 using ICP-MS (detection limit 5 mg / kg).

[0104] [Examples 2-1 to 2-5: For a secondary battery negative electrode heat-treated without a metal catalyst non-determinacy Carbon material manufacturing

[0105] A carbon material for a secondary battery negative electrode was prepared by performing the same method as in Examples 1-1 to 1-3, respectively, except that only solid particles were introduced into a furnace without adding a metal catalyst Fe and heat-treated for 4 hours each under conditions of 1,500 ℃ (Example 2-1), 2,000 ℃ (Example 2-2), 2,500 ℃ (Example 2-3), 1,000 ℃ (Example 2-4), and 1,250 ℃ (Example 2-5).

[0106] Figures 3(a) and 3(b) show electron microscope (FE-SEM, JSM-7100F, JEOL Ltd) images of the carbon material of Examples 1-3 and the carbon material particles of Examples 2-3 (2,500 ℃). More specifically, Figure 3(a) shows an amorphous hard carbon material 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.

[0107] In addition, electron microscope images of the amorphous hard carbon carbon materials of Examples 2-4 (1,000 ℃; L-HC-1000), 2-5 (1,250 ℃; L-HC-1250), and 2-1 (1,500 ℃; L-HC-1250) are shown in FIG. 4(c), FIG. 4(d), and FIG. 4(e), respectively.

[0108] [Raman spectroscopy] analysis

[0109] In the case of graphite, the sp of carbon atoms 2 1585 cm resulting from the combination -1 2680 cm due to the G peak located at and mid-scatter -1 The 2D peak appearing at is typically present, and also the 1350 cm⁻¹ peak appearing in graphite. -1 A D-peak band is observed at this wavelength; this peak appears due to intracrystalline defects, and in the case of graphite, since it has a structure of multiple overlapping graphene layers, the probability of defects existing is relatively high, so the intensity of the D-peak tends to appear large. F-peak (1430 cm⁻¹)-1 ) originates from the CC stretching mode composed of 5,6-membered rings, and G * Peak (~2445 cm) -1 ) originates from turbostratic graphite.

[0110] Figure 5 shows the results obtained by Raman spectroscopy (RAMANtouch, nanophoton Corp.) of the carbon materials prepared in Examples 1 and 2 of the present invention. Referring to the Raman spectra according to heat treatment temperature 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), in the case of Example 1 (with a metal catalyst) in Fig. 5b), a tendency for the intensity of the D peak to decrease as the heat treatment temperature increases can be observed. In particular, at 2500 °C, the D peak is observed to be very weak, and the G peak, which is proportional to the degree of crystallinity, appears strongly, indicating that the material has been very well converted into crystalline graphite with almost no defects. In particular, the ratio of the intensity of the D peak to the G peak (I D / I G The ratio) is an indicator regarding the degree of defects in graphite, and is the carbon material I in Example 1 of Fig. 5b). D / I G It can be confirmed that the degree of crystallization is 0.04, which is higher than the generally known 0.05 of natural graphite.

[0111] In addition, Fig. 5c) shows the results obtained by Raman spectroscopy of the carbon materials prepared in Examples 2-1, 2-4, and 2-5 of the present invention, and the specific values ​​are shown in Table 2 below.

[0112] More specifically, L-HC-1000 (heat treated at 1,000 ℃) in Fig. 5c is the result according to Example 2-4, L-HC-1250 (heat treated at 1,250 ℃) is the result according to Example 2-5, and L-HC-1500 (heat treated at 1,500 ℃) is the result according to Example 2-1. It can be observed that as the treatment temperature increases, the D-band and F-band intensities associated with defects decrease, while the G* and 2D band intensities increase. The 2D band was observed only in the L-HC-1500, which means that the L-HC-1500 sample contains a crystalline structure similar to graphite between the amorphous hard carbons. The ratios of each band intensity are shown in Table 2 below.

[0113] Sample I F / I G I D / I G I 2D / I G L-HC-1000 0.42 1.26 0.19 L-HC-1250 0.38 1.13 0.15 L-HC-1500 0.17 1.13 0.53 Graphene reference 0.01 0.04 0.47

[0114] [XRD Analysis (X-ray diffraction)]

[0115] FIG. 6 is a figure showing the results of X-ray diffraction (XRD; Rigaku Ultima IV) analysis of carbon materials prepared in Example 1 and Example 2 according to the present invention. When referring to the XRD analysis by heat treatment temperature 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 heat-treated in the presence of a metal catalyst, peaks (002) and (004) representing the interlayer structure of graphite are clearly observed, and peaks (100) representing the planar structure of graphite and (101) representing the hexagonal structure can be observed.

[0116] In addition, unlike Example 2, which was heat-treated without a metal catalyst in Fig. 6a), the 2Θ position of the (002) peak is observed as a single sharp, strong peak at 26 degrees, confirming that it was successfully converted into crystalline graphite.

[0117] In addition, Figure 6c) shows the results obtained by XRD analysis of carbon materials prepared at each temperature in Example 2, where the 23-25° and 43.5° two-theta peaks in Figure 6c) represent the (002) and (001) diffraction planes of graphite. The broad shape of each peak indicates that the structure of all hard carbons is amorphous regardless of the processing temperature. The shift of the (002) plane peak to slightly higher two-theta values ​​as the processing temperature increases implies an increase in the disorder of the local structure.

[0118] [Example 3: Preparation of Coin Battery from Negative Electrode Material for Secondary Battery and Evaluation of Characteristics]

[0119] A coin cell was prepared to evaluate the electrochemical properties of the crystalline carbon material for the cathode prepared in Examples 1-3 and the amorphous carbon material prepared in Examples 2-1, 2-4, and 2-5.

[0120] First, a secondary battery negative electrode slurry was obtained by dispersing 0.5 g of a mixture of the crystalline carbon material prepared in Examples 1-3, acetylene black as a conductive material, and PVDF (Polyvinylidene fluoride) as a binder in a weight ratio of 80:10:10 in the solvent NMP (1-methyl-2-pyrrolidone, 1.25 ml). The obtained negative electrode slurry was placed on copper foil (Cu-foil) with an average loading density of 3.5 mg / cm² -2 A cathode plate with a thickness of 40 μm was manufactured by coating it to form a thin electrode plate, drying it at 100°C for more than 5 hours, pressing it, and then drying it a second time in a vacuum dryer.

[0121] In addition, the electrode plates containing the amorphous carbon material for the cathode prepared in Examples 2-1, 2-4, and 2-5 were also prepared under the same conditions as the electrode plates containing the crystalline carbon material described above, except that they contained the amorphous carbon material instead of the crystalline carbon material.

[0122] For the above-mentioned crystalline carbon material, the electrolyte was a mixed solvent of diethyl carbonate (DEC) and ethylene carbonate (EC) (DEC:EC = 1:1 vol%) in which LiPF6 (Lithium hexafluorophosphate) was dissolved at a concentration of 1 M, and for the separator, a porous polypropylene film from Celgard was used.

[0123] In addition, for the above-mentioned amorphous carbon material, a mixed solvent of ethylene carbonate (EC; ethylene carbonate) in which NaPF6 is dissolved at a concentration of 1 M (DEC:EC = 1:1 vol%) was used, and a porous polypropylene film from Celgard was used as the separator.

[0124] Subsequently, using the above-mentioned negative electrode plates as working electrodes, a 2023 size lithium coin battery half cell and a sodium coin battery half cell were fabricated by using a metal lithium foil (metal Li) as the counter electrode for the negative electrode plate made of crystalline carbon material and a metal sodium foil (metal Na) as the counter electrode for the negative electrode plate made of amorphous carbon material. The entire coin battery manufacturing process was carried out in a glove box under an argon gas atmosphere.

[0125] The charge and discharge test of the coin battery prepared in Example 3 above was performed using Wonatech’s WBCS3000. Here, for convenience, the intercalation reaction of lithium (or sodium) into the graphite layer (or hard carbon) of the working electrode is defined as “charge,” and the deintercalation reaction of lithium (or sodium) from the graphite layer (or hard carbon) is defined as “discharge.”

[0126] The initial charge-discharge efficiency using 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 using the sodium coin battery was tested by applying a current of 20.0 mA / g, and the value obtained by dividing the supplied amount of electricity by the weight of the carbon material of the electrode is defined as the specific amount of the carbon material.

[0127] FIG. 7 is a graph showing the specific capacity and initial Coulomb efficiency (ICE) and cyclic performance of the carbon material and the coin battery, respectively, using a coin battery prepared in Example 1 of the present invention. FIG. 7a) is a graph showing the average of the specific capacity values ​​of the carbon material measured by preparing three lithium coin batteries of Example 3 and using them for charge / discharge evaluation. The charge capacity was measured to be 431.47 mA / g, the discharge capacity to be 348.2 mA / g, and the coulombic efficiency to be 80.7%.

[0128] In addition, Figure 7b) is a graph evaluating the cycle characteristics of the coin battery of Example 3, where the CC (constant current) mode was applied for charging and discharging, and as seen in Figure 7b), it can be confirmed that the output characteristics are maintained stably, maintaining 102% of the initial capacity even after 80 cycles.

[0129] When comparing the characteristics of a battery using a crystalline carbon material according to the present invention with those of the prior art, and when comparing the evaluation results of a battery using a carbonaceous material obtained from biomass in the prior art published patent No. 10-2021-0060754, the present invention shows 431 mAh / g compared to the initial specific capacity of 350 mAh / g presented in Experimental Example 2 of the prior art literature. Furthermore, while the capacity after 80 cycles is at the level of 150~250 mAh / g in the prior art literature (see Fig. 3 of the prior art literature), the present invention shows 350 mAh / g (see Fig. 7 of the present invention), indicating that it exhibits superior characteristics.

[0130] Meanwhile, FIG. 8 is a graph showing the average of the measured specific capacity values ​​of the carbon material according to the present invention, obtained by fabricating three sodium coin batteries of Example 3 at each processing temperature and using them for charge / discharge evaluation. The results of measuring a) specific capacity and Initial Coulomb Efficiency (ICE) and b) cyclic performance of the coin battery using the amorphous carbon material for the cathode prepared in Examples 2-1, 2-4, and 2-5 according to the present invention (a figure showing the charge / discharge rate (current rate); more specifically, FIG. 8a) is a graph showing the average of the measured specific capacity values ​​of the carbon material according to the present invention. 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, and the discharge capacities were 241.3 mA / g and 281.6 It was measured at mA / g and 256.9 mA / g, respectively, and the coulombic efficiency was measured at 62.12%, 63.75%, and 61.48%, respectively.

[0131] In addition, Figure 8b) above is a graph evaluating the cycle characteristics of the sodium coin battery of Example 3, and the charge / discharge was performed using the CC (constant current) mode.

[0132] As shown in Figure 8b above, it can be confirmed that L-HC-1000, L-HC-1250, and L-HC-1500 maintain stable output characteristics even after 100 cycles, maintaining 95.7%, 94.1%, and 91.6% of the initial capacity, respectively, with values ​​of 214.4 mA / g, 247.72 mA / g, and 213.33 mA / g.

[0133] In addition, when comparing the characteristics of the battery using an amorphous carbon material according to the present invention with the prior art, and when comparing it with the evaluation results of a sodium battery using a carbonaceous material obtained from biomass in U.S. Patent Publication No. 2021-0376321 as prior art, the present invention shows 388 to 441 mAh / g compared to the initial specific capacity of 323 to 337 mAh / g presented in Table 1 (Examples 1 to 9) of the prior art literature, it can be seen that the present invention exhibits superior characteristics.

[0134] As shown in the above characteristic evaluation results, the negative electrode material for a secondary battery derived from lignocellulosic biomass according to the present invention is a highly crystalline carbon material from which residual metallic components have been removed. It can be confirmed that the secondary battery manufactured from said carbon material exhibits excellent specific capacity and charge / discharge characteristics, and possesses stable output characteristics, indicating a high potential for application as a negative electrode active material for secondary batteries.

Claims

Claim 1 (a) a step of obtaining a hydrolysis reaction product comprising a lignin-cellulose microfiber composite obtained by adding an acid to lignocellulosic biomass to hydrolyze at least a portion of the hemicellulose in the lignocellulosic biomass and simultaneously modifying at least a portion of the cellulose into microfibrillated cellulose (MFC); (b) a step of obtaining solid particles of the lignin-cellulose microfiber composite by adding a basic aqueous solution to the hydrolysis reaction product comprising the lignin-cellulose microfiber composite obtained from step (a), thereby further removing residual acid components and water-soluble residual metal components contained in the lignin-cellulose microfiber composite, and then separating the aqueous solution components; (c) a step of obtaining solid particles of the lignin-cellulose microfiber composite obtained from step (b) by grinding the solid particles of the lignin-cellulose microfiber composite to obtain ground solid particles of the lignin-cellulose microfiber composite; A method for manufacturing a negative electrode material for a secondary battery using lignocellulosic biomass as a raw material, comprising: (d) a step of heat-treating the pulverized lignin-cellulose microfiber composite solid particles obtained from step (c) above to modify at least a portion of the solid particles into a crystalline or amorphous carbon material; wherein the hydrolysis step of step (a) is performed by i) heating and / or pressurizing while adding acid, or ii) steam explosion while adding acid, or iii) performing a process that combines the heating and pressurizing in i) and the steam explosion in ii), or iv) biological degradation using one or more cellulose-degrading enzymes. Claim 2 A method for manufacturing a negative electrode material for a secondary battery according to claim 1, wherein in step (a), the acid is selected from 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 the inorganic acid; or a mixture of the organic acid and the mixture of inorganic acids. Claim 3 A method for manufacturing a negative electrode material for a secondary battery according to claim 1, wherein the acid in step (a) is selected from hydrochloric acid, sulfuric acid, and nitric acid, or a mixture thereof. Claim 4 delete Claim 5 A method for manufacturing a negative electrode material for a secondary battery, characterized in that, in the first step (a), after the above step (a), (a-1) a step of separating and removing at least a portion of the aqueous component in the hydrolysis reactant containing the lignin-cellulose microfiber composite obtained from the above step (a) when an aqueous component is present in the hydrolysis reactant containing the lignin-cellulose microfiber composite obtained from the above step (a). Claim 6 A method for manufacturing a negative electrode material for a secondary battery according to claim 1, further comprising, prior to step (b), (a-2) a step of washing the hydrolysis reaction product containing the lignin-cellulose microfiber composite obtained from step (a) with deionized water to obtain a hydrolysis reaction product containing the lignin-cellulose microfiber composite from which at least a portion of the water-soluble metal component contained in the lignocellulosic biomass is removed. Claim 7 A method for manufacturing a negative electrode material for a secondary battery according to claim 1, wherein the base used in step (b) is at least one selected from sodium hydroxide (NaOH), potassium hydroxide (KOH), ammonia (NH3), lithium hydroxide (LiOH), potassium carbonate (K2CO3), sodium carbonate (Na2CO3), potassium bicarbonate (KHCO3), magnesium hydroxide (Mg(OH)2), magnesium oxide (MgO), and sodium bicarbonate (NaHCO3), or a mixture thereof. Claim 8 A method for manufacturing a negative electrode material for a secondary battery according to claim 1, wherein the lignin-cellulose microfiber composite solid particles obtained in step (b) above have a hemicellulose content of 5 weight (wt%) or less based on the total sum of components derived from lignin, cellulose, and hemicellulose. Claim 9 A method for manufacturing 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 lignin-derived components and 20 wt% to 80 wt% of cellulose-derived components based on the total sum of lignin, cellulose, and hemicellulose-derived components. Claim 10 A method for manufacturing a negative electrode material for a secondary battery according to claim 1, characterized in that the particle size of the pulverized lignin-cellulose microfiber composite solid particles obtained in step (c) is 500 nm to 200 μm. Claim 11 A method for manufacturing a negative electrode material for a secondary battery, characterized in that, in claim 1, the heat treatment temperature of step (d) is in the range of 500 to 3000 ℃. Claim 12 A method for manufacturing a negative electrode material for a secondary battery according to claim 1, wherein the heat treatment of step (d) is performed in the presence of a metal catalyst, so that at least some of the particles obtained after heat treatment are crystalline carbon materials. Claim 13 A method for manufacturing a negative electrode material for a secondary battery according to claim 12, further comprising, after step (d), (e) acid-treating solid particles, of which at least a portion is a crystalline carbon material, to obtain a carbon material from which a metal catalyst has been removed. Claim 14 A method for manufacturing a negative electrode material for a secondary battery according to claim 1, wherein the heat treatment in step (d) is performed in the absence of a metal catalyst, so that at least some of the particles obtained after heat treatment are amorphous carbon materials. Claim 15 A negative electrode material for a secondary battery manufactured from any one of the manufacturing methods of paragraphs 1 to 3 and paragraphs 5 to 14. Claim 16 A composition for a secondary battery negative electrode comprising the negative electrode material for a secondary battery of claim 15. Claim 17 A secondary battery comprising the composition for a negative electrode of claim 16.

Images