Method for manufacturing negative electrode material for secondary batteries using lignocellulose 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 particularly to a method for producing a negative electrode material for secondary batteries using lignocellulosic biomass, wherein trace amounts of metal components contained in the biomass used as raw material are removed, thereby contributing to improved performance and stability of secondary batteries when applied to secondary batteries. [Background technology]

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

[0003] In particular, research and development are active in hybrid and electric vehicles as alternatives to gasoline and diesel vehicles used for transportation, which are the main cause of air pollution, and in ESS (ENERGY STOREAGE SYSTEM) systems that can store large amounts of surplus electricity. A typical element used in the manufacture of such electrical energy systems is the secondary battery, and the demand for secondary batteries is rapidly increasing in portable devices such as telephones, laptops, cameras, and industrial tools.

[0004] Currently, lithium-ion batteries are the most commonly used example of such secondary batteries. A lithium-ion battery consists of a current collector coated with a positive electrode active material and a negative electrode active material, a porous separator membrane interposed between the current collectors, and a non-aqueous lithium salt electrolyte impregnated within the current collector.

[0005] In this context, the negative electrode active material uses expensive carbon-based and non-carbon-based materials. Among the non-carbon-based active materials, lithium metal, silicon (Si), and transition metal oxide systems are being studied, but commercialization has been delayed due to various drawbacks. The carbon-based negative electrode active material is broadly classified into graphitic and non-graphitic types. The non-graphitic type is further classified into soft carbon-based active materials that exhibit uniaxial orientation even at low temperatures, and hard carbon-based active materials that do not exhibit uniaxial orientation even at high temperatures.

[0006] On the other hand, graphite-based active materials have been used in most lithium-ion secondary batteries to date, thanks to their long electrode life characteristics resulting from the uniaxial orientation of the graphene layer and its highly reversible charge-discharge properties.

[0007] However, despite its many advantages, graphite's low theoretical capacity (372 mAh / g) is a major obstacle in the current demand for higher battery capacity. Furthermore, graphite can experience delamination during the charging process when lithium ions are inserted between the layers of its layered structure, as electrolyte salts are simultaneously inserted between the layers. To overcome this, graphite coated with non-graphite (amorphous) carbon is often used.

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

[0009] Currently, the demand for high-performance lithium-ion secondary batteries is surging. However, carbon materials used as anode active materials are extremely expensive globally and are mostly manufactured using coal or petroleum-based raw materials. Using these materials presents economic challenges and significant carbon dioxide emissions during disposal. As an alternative, research has recently been conducted on utilizing biomass-derived anode materials.

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

[0011] As a conventional technology using carbon materials derived from biomass as electrode materials, Korean Registered Patent No. 10-1545116 (published August 17, 2015) discloses a method for producing carbon materials for lithium-ion capacitor negative electrodes using charcoal derived from coconut shells as a carbonaceous precursor. However, this method has the problem that it requires heat treatment by a gas-phase deashification process, and metal-halogen composites generated in the deashification process must be collected and removed.

[0012] Furthermore, while Korean Patent No. 10-2442330 (published September 8, 2022) proposes a process for converting lignocellulose material into hard carbon material, it does not provide a process for removing metal components contained in the lignocellulose material. As a result, the carbon material has low crystallinity and micropore uniformity, which may lead to a decrease in battery performance. In particular, the decrease in crystallinity means that the material is converted only into hard carbon material and not into graphite-like carbon material.

[0013] Therefore, there is an even greater need to develop a novel, low-cost, biomass-derived negative electrode material for secondary batteries that uses lignocellulosic biomass, a material that can offer economic advantages, as a raw material, has a simple process, and produces an active material that overcomes the shortcomings of graphite-based and non-graphite-based materials, does not leach metal components, and is environmentally friendly. [Prior art documents] [Patent Documents]

[0014] [Patent Document 1] Korean Registered Patent No. 10-1545116 (Published August 17, 2015) [Patent Document 2] Korean Registered Patent No. 10-2442330 (Published September 8, 2022) [Overview of the Initiative] [Problems that the invention aims to solve]

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

[0016] Furthermore, the present invention aims to provide a secondary battery negative electrode composition containing the aforementioned negative electrode material, and a secondary battery containing the same. [Means for solving the problem]

[0017] To achieve the above objective, the present invention (a) adds acid to lignocellulosic biomass to hydrolyze at least a portion of the hemicellulose in the lignocellulosic biomass, and also converts at least a portion of the cellulose into cellulose microfibers (MFCs, Microfibrillated The present invention provides a method for producing a negative electrode material for a secondary battery using lignocellulose biomass as a raw material, comprising the steps of: (b) obtaining a hydrolysis reaction product containing a lignin-cellulose microfiber composite obtained by converting it to cellulose; (a) adding a basic aqueous 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) grinding the lignin-cellulose microfiber composite solid particles obtained from step (b) to obtain ground lignin-cellulose microfiber composite solid particles; and (d) heat-treating the ground 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.

[0018] In one embodiment, in step (a), the acid can be any of the following: 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; preferably, any of the hydrochloric acid, sulfuric acid, and nitric acid, or a mixture thereof, can be used.

[0019] As one embodiment, the hydrolysis step in the step (a) may 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 mixed, or iv) a biological degradation process using one or more cellulolytic enzymes.

[0020] As one embodiment, after the step (a), when an aqueous solution component exists in the hydrolysis reaction product containing the lignin-cellulose microfiber composite obtained from the step (a), the 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 microfiber composite may be further included.

[0021] As one embodiment, also, before the step (b), the step (a-2) of washing the hydrolysis reaction product containing the lignin-cellulose microfiber composite obtained from the step (a) with deionized water to obtain a hydrolysis reaction product containing a lignin-cellulose microfiber composite from which at least a part of the water-soluble metal components contained in the lignocellulosic biomass has been removed may be further included.

[0022] As one embodiment, the base used in the 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] In one embodiment, the lignin-cellulose microfiber solid particles obtained in step (b) above may have a hemicellulose content of 5% by weight (wt%) or less, based on the total of the components derived from lignin, cellulose, and hemicellulose.

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

[0025] In one embodiment, the particle size of the pulverized lignin-cellulose microfiber composite solid particles obtained in step (c) above 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 crystalline carbon material, in which case the method may further include the step of (e) acid-treating the solid particles obtained from step (d), in which at least a portion of the particles are crystalline carbon material, to obtain 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 portion of the particles obtained after the heat treatment may be amorphous carbon material.

[0029] Furthermore, the present invention can provide a negative electrode material for a secondary battery manufactured by the above manufacturing method, and can also provide a negative electrode composition for a secondary battery containing the above negative electrode material.

[0030] Furthermore, the present invention can provide a secondary battery comprising the above-mentioned secondary battery negative electrode composition. [Effects of the Invention]

[0031] The method for manufacturing 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 that is also the most abundant and inexpensive material on Earth, thus offering an economic advantage in terms of manufacturing costs. The process is simple, and it is possible to produce highly crystalline or amorphous carbon material from which residual metal components in the lignocellulosic biomass have been removed. Secondary batteries containing the negative electrode material produced by this method exhibit excellent specific capacity and charge / discharge characteristics, and have stable output characteristics.

[0032] Furthermore, the negative electrode material for secondary batteries of the present invention has the added advantage of being environmentally friendly, as it significantly reduces pitch and carbon dioxide emissions during manufacturing and incineration compared to carbon materials for negative electrodes manufactured using conventional technologies. [Brief explanation of the drawing]

[0033] [Figure 1] (a) This figure shows the hierarchical structure of biomass-derived cellulose, and (b) the structure of cellulose microfibers including crystalline and amorphous domains. [Figure 2] This is an electron microscope image of solid particles composed of lignin-cellulose microfiber bundles, cellulose microfiber bundles, and lignin, produced in Production Example 1 according to the present invention, before grinding. [Figure 3] a) is an electron microscope image of an amorphous hard carbon material obtained by heat treatment at 2500°C without a metal catalyst according to the present invention, and b) is an electron microscope image 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]These are electron microscope images of amorphous hard carbon-like carbon materials produced in Examples 2-1, 2-4, and 2-5 according to the present invention. [Figure 5] This figure shows the results of Raman spectroscopy (RAMANtouch, nanophoton Corp.) of the carbon materials produced in Example 1 and Example 2 of the present invention. [Figure 6] This figure shows the results of X-ray diffraction analysis (XRD) of the carbon materials produced in Example 1 and Example 2 according to the present invention. [Figure 7] This figure shows a graph (current rate: 0.1C) showing the measurement of a) specific capacity and initial coulomb efficiency (ICE) of the carbon material and b) cyclic performance of the coin cell using a coin cell to which the negative electrode carbon material manufactured in Example 1 of the present invention is applied. [Figure 8] This figure shows a graph (current rate) of the measured values ​​of a) specific capacity and initial coulomb efficiency (ICE) of the carbon material and b) cyclic performance of the coin cell, using a coin cell to which the amorphous carbon material manufactured in Example 2 of the present invention is applied. [Modes for carrying out the invention]

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

[0035] Furthermore, the dimensions and thicknesses of each component shown in the illustrations are arbitrary for the sake of explanation, and the present invention is not necessarily limited to those shown in the illustrations. Also, the thicknesses are shown enlarged in the drawings to clearly represent multiple layers and regions. In addition, in the drawings, the thicknesses of some layers and regions are exaggerated for the sake of explanation. When a part such as a layer, film, region, or plate is said to be "on top of" another part, this includes not only the case where it is "immediately on top of" another part, but also the case where there is another part between them.

[0036] Furthermore, throughout the specification, when a part "includes" a certain component, this means that, unless otherwise stated, it does not exclude other components, but rather that it may include other components. Also, throughout the specification, "on top of" means located above or below the part in question, and does not necessarily mean located above the direction of gravity.

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

[0038] The present invention provides a method for producing a negative electrode material for secondary batteries from lignocellulosic biomass, which involves a) adding an acid to lignocellulosic biomass to hydrolyze at least a portion of the hemicellulose in the lignocellulosic biomass, and also hydrolyzing at least a portion of the cellulose into cellulose microfibers (MFCs, Microfibrillated The method includes: (b) obtaining a hydrolysis reaction product containing a lignin-cellulose microfiber composite obtained by converting it to cellulose; (a) adding a base aqueous 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) grinding the lignin-cellulose microfiber composite solid particles obtained from step (b) to obtain ground lignin-cellulose microfiber composite solid particles; and (d) heat-treating the ground 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 the first step of the manufacturing method according to the present invention, step (a) is a step of adding acid to lignocellulosic biomass, which is the raw material, to obtain a hydrolysis reaction product containing a lignin-cellulose microfiber composite obtained by hydrolyzing at least a portion of hemicellulose and converting at least a portion of the cellulose into cellulose microfibers (MFCs, microfibrillated cellulose) as a precursor for producing a carbon material for secondary battery negative electrode active material, in which the strong crystalline structure between lignin and cellulose in the biomass is destroyed by the addition of acid in step (a), at least a portion of the hemicellulose is hydrolyzed, and at least a portion of the cellulose fiber is 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, and even more preferably 95% or more of the cellulose component contained in the biomass is cellulose microfiber (microfibrillated cellulose). The lignin is converted to a cellulose form, and the acid treatment physically or chemically bonds the lignin and at least some of the cellulose microfibers (MFCs) to form a polymeric lignin-cellulose microfiber (MFC) composite.

[0040] In other words, the lignin-cellulose microfiber composite according to the present invention can function as a negative electrode active material for secondary batteries by subsequently heat-treating the cellulose microfibers (microfibrillated cellulose) and the hydrophobized lignin obtained by the acid treatment within the lignin-cellulose microfiber (MFC) composite, and thereby providing a negative electrode material for secondary batteries through a more environmentally friendly and economical process using components derived from lignocellulosic biomass, which is a low-cost bio-raw material.

[0041] Here, the cellulose contained in the lignocellulosic biomass is a fibrous material in which linear chains linked by β-glycosidic bonds of D-glucose units overlap. Referring to Figure 1(a), which shows the hierarchical structure of biomass-derived cellulose, a cellulose fiber includes a microfibril bundle composed of microfibrils, and these microfibrils include elementary fibrils, which are the lowest-level components.

[0042] In the present invention, microfibrillated cellulose (MFC) refers to microfibrillated cellulose fibers with 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, obtained when cellulose fibers contained in lignocellulosic biomass such as wood bulk are defibrated, and should be understood as a concept that includes microfibril bundles and microfibrils, as shown in Figure 1(a).

[0043] In this case, the cellulose microfiber (MFC) has a structure that includes a crystalline domain and an amorphous domain, as shown in Figure 1(b).

[0044] Furthermore, step (a) allows the metal components contained in the lignocellulosic biomass to be eluted in order to remove them, as the strong structure of the lignocellulosic biomass is broken down by the acid treatment, making it easier to dissolve the metal components contained in the biomass. That is, the metal components in the acid-treated biomass are converted into ionic substances, making them easier to remove in the subsequent dehydration and / or washing steps.

[0045] Here, the term "metallic component" should be understood as a concept encompassing one or more of the various metallic components contained in lignocellulosic biomass, alloys of the metallic 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 include biomass derived from herbaceous plants, woody plants such as conifers and broad-leaved trees (ordinary wood), or various other biomass such as rice straw, corn cobs, coconut husks, and sugarcane.

[0047] On the other hand, the lignocellulosic biomass used as a raw material in step (a) above can be one which has been dried and pulverized. In this case, in order to ensure uniformity in subsequent processes, the pulverization size is preferably 20 mm or less, and more preferably in the range of 10 to 0.001 mm.

[0048] After the pulverization step of the lignocellulosic biomass, a drying step may be taken to reduce the moisture content. The drying step preferably reduces 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 can be any method that can reduce the moisture content of the lignocellulosic biomass, such as oven drying, natural drying in a well-ventilated place, or hot air drying.

[0049] Furthermore, the grinding and drying steps in the present invention can be performed in any order. That is, the drying step can be performed after the grinding step of the lignocellulosic biomass, or the grinding step can be performed after the drying step. This can be changed depending on the surrounding environment or the type and drying state of the lignocellulosic biomass. For example, if the drying is done very well, the drying step can be omitted. Preferably, from the viewpoint of efficiency, it is preferable to dry the lignocellulosic biomass with a larger surface area after the grinding step.

[0050] Furthermore, the acid used in step (a) of the present invention 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 an inorganic acid; or a mixture of the organic acid and an inorganic acid.

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

[0052] Furthermore, preferred examples of the acid component used as the inorganic acid include hydrochloric acid, sulfuric acid, and nitric acid, or mixtures thereof. 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, taking the case of adding 75% (v / v) sulfuric acid as an example, the addition of 75% (v / v) sulfuric acid allows the sulfuric acid concentration to be used in a range of 0.5 wt% to 70 wt%, preferably in a range of 0.6 wt% to 65 wt%, based on the final concentration standard (based on the total content of crushed biomass and aqueous solution). 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 if a mixture of sulfuric acid and hydrochloric acid is used, the amount of strong acid to be added can be appropriately determined based on the above range.

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

[0055] Here, in the hydrolysis step of step (a) above, i) the step of heating and / or pressurizing while adding acid may include a step 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 reducing the pressure to filter out the solids; ii) the step of steam explosion while adding acid may include a step 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 reducing the pressure; and in the iv) biological decomposition step, one or more known cellulose-degrading enzymes can be used without limitation, and in this case, the acid in steps i) to iv) above can be added at concentrations in a range of various types depending on the type of acid and conditions such as reaction temperature and pressure.

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

[0057] Furthermore, the present invention may further include, after step (a), (a-1) if the hydrolysis reaction product containing the lignin-cellulose microfiber composite obtained from step (a) is in a slurry state and contains aqueous solution components, a step of separating and removing at least a portion of the aqueous solution components from the hydrolysis reaction product.

[0058] Here, the separation of the aqueous solution components can be carried out using any known separation technique without limitation, and may include, for example, dehydration by centrifugation, filtration, and decantation.

[0059] On the other hand, step (b) in the present invention is a step to obtain lignin-cellulose microfiber composite solid particles by adding a basic aqueous solution to the hydrolysis reaction product containing the lignin-cellulose microfiber composite obtained from step (a) to react with or dissolve residual acid components and water-soluble residual metal components contained in the lignin-cellulose microfiber composite in the aqueous solution, and then separating and removing the aqueous solution components. This corresponds to a step to remove residual acid components and residual metal components because if residual acid components and water-soluble residual metal components are not removed from the hydrolysis reaction product obtained in step (a), it may adversely affect the physical properties of the negative electrode material for secondary batteries and the performance of secondary batteries in subsequent steps.

[0060] In this case, the step of separating the aqueous solution components obtained after adding a basic aqueous solution to the hydrolysis reaction product can be performed using any known separation technique without limitation, and may include, for example, dehydration by centrifugation, filtration, and decantation.

[0061] Furthermore, 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. 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) can be used without limitation.

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

[0063] In other words, step (a-2) has the advantage of reducing the amount of basic aqueous solution added in step (b) by washing the acidic components remaining in the modified lignin-cellulose microfiber (MFC) composite obtained through step (a) with desalinated water before adding the basic aqueous solution in step (b). This allows for the removal of components that can dissolve in aqueous solution, such as water-soluble substances containing residual sugar components derived from biomass, substances derived from the acid addition process, substances derived from the base addition process, acidic components, and water-soluble metal components, or a mixture thereof.

[0064] Furthermore, in addition, the present invention allows for the removal of water-soluble components, including metal components and residual base components, contained within the solid particles by further washing the lignin-cellulose microfiber composite solid particles obtained from step (b) with desalinated water after step (b), thereby separating the aqueous solution containing water-soluble components through washing.

[0065] As a result, after removing a certain amount of polysaccharides hydrolyzed by the acid component, the solid particles obtained through step (b) can be converted to solid particles in which 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 or more of lignocellulosic biomass is converted, based on the total weight of the obtained solid particles relative to the dry weight of the input biomass.

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

[0067] In other words, the solid particles obtained through steps (a) and (b) above mainly consist of lignin and cellulose microfibers (MFCs), which form a lignin-cellulose microfiber (MFC) complex and serve as a precursor for the negative electrode active material.

[0068] On the other hand, the solid particles obtained through step (b) above 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%, based on the total amount of components derived from lignin, cellulose, and hemicellulose.

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

[0070] Furthermore, the solid particles obtained through step (b) may 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 amount of components derived from lignin, cellulose, and hemicellulose.

[0071] Furthermore, in addition, the present invention allows for the removal of water-soluble components, including metal components and residual base components, contained within the solid particles by (b-1) further washing the lignin-cellulose microfiber composite obtained from step (b) with desalinated water to separate the aqueous solution containing these water-soluble components.

[0072] On the other hand, 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 powdered solid particles are easy to handle, allow for uniform heat treatment in the subsequent step (d), and improve the dispersibility of the metal catalyst in the subsequent step, thus improving the physical properties such as crystallinity of the negative electrode carbon material that is ultimately produced.

[0073] Here, the grinding method in step (c) above can be any known grinding method, including ball milling, speck milling, and nanomilling, and the particle size of the solid particles obtained after grinding may be in the range of 500 nm to 200 μm.

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

[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, wherein when the pulverized lignin-cellulose microfiber composite solid particles obtained 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 graphite-like crystalline carbon material, and when the heat treatment is performed 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 heat treatment in the presence of the metal catalyst has an intensity ratio of the D band (I) to the G band in the Raman spectroscopic spectrum, which is an indicator of the degree of defects in graphite. D / I G Its distinguishing feature is that its θ 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 consist of 50 wt% or more of crystalline carbon material, more preferably 60 wt% or more of crystalline carbon material, more preferably 70 wt% or more of crystalline carbon material, more preferably 70 wt% or more of crystalline carbon material, more preferably 80 wt% or more of crystalline carbonized material, more preferably 90 wt% or more of crystalline carbon material, and more preferably 95 wt% or more of crystalline carbon material.

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

[0079] In this case, the heat treatment in step (d) can 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] Furthermore, the catalyst used in the heat treatment in step (d) in the presence of a metal catalyst is not limited to any type as long as it is a known graphitization catalyst. 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 such metals, can be used. For example, as a metal-containing catalyst, a catalyst containing one selected from Fe, Co, Mn, Ni, and Zn, or a mixture thereof, can be used. As a metal salt, a catalyst containing any of Fe(NO3)3, Fe2O3, FeCl3, Ni(NO3)3, ZnO, or a mixture thereof can be used.

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

[0082] On the other hand, the present invention may further include the step of (e) after the heat treatment in the presence of a metal catalyst in step (d), 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. This is to prevent the secondary battery negative electrode active material from containing metal components, as discussed in step (a), and the metal components derived from the residual metal catalyst are converted into the form of water-soluble metal salts through the acid treatment, which can then be easily removed by washing with water or the like.

[0083] At this time, the type, concentration, amount, and method of treatment of the acid used to remove the residual metal catalyst component can be appropriately modified by an ordinary technician, referring to what has been described for the acid added in step (a). For example, when hydrochloric acid is used, the equivalent amount of the acid can be determined and added 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 of washing the crystalline carbon material obtained from step (e) with demineralized water, thereby enabling more efficient removal of metal components derived from the metal catalyst.

[0085] Furthermore, the present invention may, after step (e), perform the step of (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 can be any known grinding method, including ball milling, speck milling, and nanomilling, as in the solid particle grinding method of step (c), and the particle size of the solid particles 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 secondary batteries manufactured by the manufacturing method described above. Specifically, the crystalline carbon material produced from lignocellulosic biomass by the manufacturing method of the present invention has high specific capacity and charge / discharge performance, making it suitable for use as a negative electrode material for secondary batteries.

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

[0088] The present invention will be described in more detail below through examples to aid in understanding the present invention. However, the examples described herein are subject to various modifications, 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 further detail to those who are ordinary in the art.

[0089] [Manufacturing Example 1: Production of acid-treated lignin-cellulose microfiber composite solid particles] In Production Example 1, a deashification process was performed in which an acid aqueous solution was treated to remove metal components contained in lignocellulosic biomass, thereby producing lignin-cellulose microfiber composite solid particles.

[0090] 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, it was dried at 100°C for 2 hours to a moisture content of 5 wt%, preparing the lignocellulosic biomass powder that would be the raw material.

[0091] Subsequently, the pulverized biomass powder and water were added to the reactor in a mass ratio of 1.4:1.0 and heated to 90°C while stirring. Then, 95% sulfuric acid was added to achieve a final concentration of 10 wt%, and the temperature was raised to 120°C for 1 hour while stirring. The mixture was then reacted for 60 minutes to hydrolyze the hemicellulose component and convert at least some of the cellulose component into cellulose microfibers (MFCs, microfibrillated cellulose), obtaining a hydrolysis reaction product containing a solid lignin-cellulose microfiber composite. This product was filtered to separate and remove the aqueous solution component.

[0092] The resulting hydrolysis reaction product was neutralized to a pH of 7.0 using a 0.1N ammonium hydroxide solution, and residual acid and metal components within the lignin-cellulose microfiber complex were further removed. After dehydration, the aqueous solution components were separated and removed.

[0093] Subsequently, the lignin-cellulose microfiber composite solid particles were finally obtained by washing and dewatering two to three times with a sufficient amount of desalinated water to remove residual metal ions and other ionic compound components to the greatest extent possible.

[0094] The solid particles were dried at 100°C for 6 hours, and then pulverized to an average particle size of 20 μm to obtain pulverized lignin-cellulose microfiber composite solid particles, which serve as a carbon precursor for conversion into a carbon material for secondary battery negative electrodes. Figure 2 shows electron microscope images of the solid particles composed of lignin-cellulose microfiber bundles, cellulose microfiber bundles, and lignin produced in Production Example 1, before pulverization.

[0095] [Comparative Manufacturing Example 1: Production of Acid-Free Lignin-Cellulose Microfiber Solid Particles] Grinding of lignin-cellulose microfiber composite solid particles was obtained by the same method as in Production Example 1, except that the reaction solution was not treated with sulfuric acid.

[0096] Table 1 below shows the results of an analysis of the amount of metal components contained in the crushed lignin-cellulose microfiber composite solid particles obtained by the above-mentioned Production Example 1 and Comparative Production Example 1.

[0097] [Table 1]

[0098] Considering the results of the analysis of residual metal content in lignin-cellulose microfiber composite solid particles with and without acid treatment for Production Example 1 and Comparative Production Example 1 according to the present invention, as shown in Table 1, it can be confirmed that, as a result of the acid treatment demineralization process, no metal components were observed at the detection limit (2-10 mg / kg) in the lignin-cellulose microfiber composite solid particles of Production Example 1, while various metal components were detected in the lignin-cellulose microfiber composite solid particles of Comparative Production Example 1.

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

[0100] The heat-treated powder was placed in a 1M aqueous HCl solution to remove the metal catalyst, filtered to remove the aqueous solution components, neutralized with a 1M ammonium hydroxide solution, and then washed with demineralized 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%. The carbon materials of Examples 1-1 to 1-3 were confirmed to be free of residual Fe by ICP-MS (detection limit 5 mg / kg).

[0101] [Examples 2-1 to 2-5: Production of amorphous carbon material for secondary battery anodes by heat treatment without metal catalyst] Carbon materials for secondary battery negative electrodes were manufactured using the same methods as in Examples 1-1 to 1-3, except that only solid particles were placed in a furnace without the addition of the metal catalyst Fe, and heat treatment was performed for 4 hours each 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] Photographs of the carbon materials of Examples 1-3 and the carbon material particles of Examples 2-3 (2,500 °C) taken with an electron microscope (FE-SEM, JSM-7100F, JEOL Ltd) are shown in FIGS. 3(a) and 3(b). More specifically, FIG. 3(a) shows an amorphous hard carbon-like carbon material obtained by heat treatment without a metal catalyst, and FIG. 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-like 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 FIGS. 4(c), 4(d), and 4(e), respectively.

[0104] [Raman Spectroscopy] Analysis In the case of graphite, the G peak located at 1585 cm 2 due to the sp -1 bond of carbon atoms and the 2D peak located at 2680 cm -1 due to multiple scattering typically appear. Also, the D peak band at a wavelength of 1350 cm -1 appearing in graphite is observed. This is a peak that appears due to defects within the crystal. In the case of graphite, since it has a structure in which multiple layers of graphene overlap, the probability of having relative defects is high, so the intensity of the D peak tends to appear large. The F peak (1430 cm -1 ) is due to the C-C stretching mode composed of 5,6-membered rings, and the G * peak (~2445 cm -1 ) is due to turbostratic graphite.

[0105] Figure 5 shows the results obtained by Raman spectroscopy (RAMANtouch, nanophoton Corp.) of carbon materials produced in Examples 1 and 2 of the present invention. Referring to the Raman spectra at different heat treatment temperatures for the carbon material heat-treated without a metal catalyst in Example 2 (Figure 5a)) and the carbon material heat-treated in the presence of a metal catalyst in Example 1 (Figure 5b)), in the case of Example 1 (with metal catalyst) in Figure 5b), it can be observed 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 observed to be very weak, and the G peak, which is proportional to the degree of crystallinity, appears strongly, indicating that it was converted very well 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 ratio is an indicator of the degree of defects in graphite, and is the ratio of the carbon material in Example 1 of Figure 5b). D / I G The value is 0.04, which confirms that it exhibits a higher degree of crystallinity than the generally known 0.05 for natural graphite.

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

[0107] More specifically, in Figure 5(c), L-HC-1000 (heat-treated at 1000°C) is the result of Example 2-1, L-HC-1250 (heat-treated at 1250°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 intensity of the D and F bands associated with defects decreases, while the intensity of the G* and 2D bands increases. The 2D band was observed only in L-HC-1500, which means that the L-HC-1500 sample contains a crystalline structure similar to graphite among the amorphous hard carbon. The intensity ratios of each band are shown in Table 2 below.

[0108] [Table 2]

[0109] [XRD Analysis (X-ray Diffraction)] Figure 6 shows the results of X-ray diffraction analysis (XRD; Rigaku Ultima IV) of carbon materials produced in Example 1 and Example 2 according to the present invention. Referring to the XRD analysis at different heat treatment temperatures for the carbon material heat-treated without a metal catalyst in Example 2 (Figure 6a) and the carbon material heat-treated in the presence of a metal catalyst in Example 1 (Figure 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 can be clearly observed, and the (100) peak indicating the planar structure of graphite and the (101) peak indicating the hexagonal structure can be observed.

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

[0111] Furthermore, Figure 6c) shows the results obtained by XRD analysis of carbon materials produced at different temperatures in Example 2. The 23-25° and 43.5° 2θ (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 carbon is amorphous, regardless of the processing temperature. The shift of the (002) plane peak to a slightly higher 2θ (two-theta) value as the processing temperature increases means that the disorderiness of the local structure increases.

[0112] [Example 3: Manufacturing and characterization of coin cell batteries from negative electrode materials for secondary batteries] Coin cells were manufactured to evaluate the electrochemical properties of the crystalline carbon material for the negative electrode produced in Examples 1-3 and the amorphous carbon material produced in Examples 2-1, 2-4, and 2-5.

[0113] First, 0.5 g of a mixture prepared by mixing the crystalline carbon material produced in Examples 1-3 with acetylene black as a conductive material and PVDF (Polyvinylidene fluoride) as a binder in a weight ratio of 80:10:10 was dispersed in 1.25 ml of solvent NMP (1-methyl-2-pyrrolidone) to obtain a secondary battery negative electrode slurry. The obtained negative electrode slurry was then placed on copper foil (Cu-foil) at an average loading density of 3.5 mg / cm³. -2 After coating the material to form a thin electrode plate, it was dried at 100°C for more than 5 hours, then pressed, and finally dried again in a vacuum dryer to produce a 40μm thick negative electrode plate.

[0114] Furthermore, the electrode plates containing the amorphous carbon material for the negative electrode, manufactured in Examples 2-1, 2-4, and 2-5, were manufactured 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.

[0115] For the electrolyte, a mixed solvent of diethyl carbonate (DEC) and ethylene carbonate (EC) containing LiPF6 (Lithium hexafluorophosphate) at a concentration of 1 M was used (DEC:EC = 1:1 vol%) for the crystalline carbon material, and a porous polypropylene film manufactured by Celgard was used as the separation membrane.

[0116] Furthermore, a mixed solvent of ethylene carbonate (EC) in which NaPF6 was dissolved at a concentration of 1M (DEC:EC=1:1 vol%) was used for the amorphous carbon material, and a porous polypropylene film manufactured by Celgard was used as the separation membrane.

[0117] Subsequently, using the fabricated negative electrode plate as the working electrode, metallic lithium foil (metal Li) was used as the counter electrode for the negative electrode plate made of crystalline carbon material, and metallic sodium foil (metal Na) was used as the counter electrode for the negative electrode plate made of amorphous carbon material, to fabricate half-cells of 2023 size lithium coin batteries and half-cells of sodium coin batteries, respectively. The entire manufacturing process of the coin batteries was carried out in a glove box under an argon gas atmosphere.

[0118] The coin cell manufactured in Example 3 above was subjected to charge-discharge testing using a WBCS3000 manufactured by WonATech. 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 manufactured 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. In this case, the specific capacity of the carbon material was defined as the amount of electricity supplied divided by the weight of the carbon material of the electrode.

[0120] Figure 7 shows a graph (current rate) of the measured values ​​of a) specific capacity and initial coulomb efficiency (ICE) of the carbon material and b) cyclic performance of the coin cell, using a coin cell to which the negative electrode carbon material manufactured in Example 1 of the present invention was applied. Figure 7a) is a graph showing the average of the specific capacity values ​​of the carbon material measured by using three lithium coin cells from Example 3, which were manufactured and used for charge-discharge evaluation. The measured charge capacity was 431.47 mA / g, the discharge capacity was 348.2 mA / g, and the coulombic efficiency was 80.7%.

[0121] Furthermore, Figure 7b) is a graph evaluating the cycle characteristics of the coin cell battery of Example 3. Charge and discharge were performed using the CC (constant current) mode, and as shown in Figure 7b), it can be confirmed that the battery maintains 102% of its initial capacity even after 80 cycles, demonstrating stable output characteristics.

[0122] Comparing the characteristics of the battery using crystalline carbon material according to the present invention with those of the prior art, and comparing them with the evaluation results of a battery using carbonaceous material obtained from biomass in Korean Published Patent No. 10-2021-0060754, the present invention exhibits an initial specific capacity of 431 mAh / g compared to the 350 mAh / g presented in Experimental Example 2 of the prior art document. Furthermore, while the capacity after 80 cycles is at the level of 150-250 mAh / g in the prior art document (see Figure 3 of the prior art document), the present invention exhibits 350 mAh / g (see Figure 7 of the present invention), demonstrating superior characteristics.

[0123] On the other hand, Figure 8 shows the results of measuring a) specific capacity and initial coulomb efficiency (ICE) and b) cyclic performance of the coin cell using a coin cell to which the amorphous carbon material for the negative electrode manufactured in Examples 2-1, 2-4, and 2-5 according to the present invention was applied (charge / discharge rate (current)). Figure 8a) is a graph showing the average values ​​of the specific capacity of the carbon material according to the present invention, measured by manufacturing three sodium coin batteries of Example 3 at different processing temperatures and using them 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. The charge-discharge efficiency (coulombic efficiency) was measured as 62.12%, 63.75%, and 61.48%, respectively.

[0124] Furthermore, Figure 8b) is a graph evaluating the cycle characteristics of the sodium coin battery of Example 3, with charge and discharge performed using the CC (constant current) mode.

[0125] As shown in Figure 8b), even after 100 cycles, the L-HC-1000, L-HC-1250, and L-HC-1500 maintained their initial capacities of 214.4 mA / g, 247.72 mA / g, and 213.33 mA / g, respectively, confirming that they maintain stable output characteristics at 95.7%, 94.1%, and 91.6% of their initial capacities.

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

[0127] As shown in the above characteristic evaluation results, the lignocellulosic biomass-derived negative electrode material for secondary batteries according to the present invention is a highly crystalline carbon material from which residual metal components have been removed. Secondary batteries manufactured from this carbon material exhibit excellent specific capacity and charge / discharge characteristics, and can be confirmed to have stable output characteristics. Therefore, it can be seen that it has high potential for application 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 converting at least a portion of the cellulose into cellulose microfibers (MFCs) to obtain a hydrolysis reaction product containing a lignin-cellulose microfiber composite, (b) Adding a basic aqueous 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) A step of grinding the lignin-cellulose microfiber composite solid particles obtained from step (b) above to obtain ground lignin-cellulose microfiber composite solid particles, A method for producing a negative electrode material for a secondary battery using lignocellulose biomass as a raw material, comprising the 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.

2. The method for producing a negative electrode material for a secondary battery according to claim 1, characterized in that in step (a) above, the acid used is selected from 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; or a mixture of the organic acid and an inorganic acid; or a mixture of the organic acid and an inorganic acid.

3. The method for producing a negative electrode material for a secondary battery according to claim 1, characterized in that the acid in step (a) is selected from hydrochloric acid, sulfuric acid, and nitric acid, or a mixture thereof.

4. The method for producing a negative electrode material for a secondary battery according to claim 1, characterized in that the hydrolysis step of step (a) is carried out by i) a step of heating and / or pressurizing while adding an acid, or ii) a step of steam explosion while adding an acid, or iii) a step of a mixture of the heating and pressurizing step in i) and the steam explosion step in ii), or iv) a biological decomposition step using one or more cellulose-degrading enzymes.

5. A method for producing a negative electrode material for a secondary battery according to claim 1, further comprising the step of (a-1) if, after step (a), aqueous solution components are present in the hydrolysis reaction product containing the lignin-cellulose microfiber composite obtained from step (a), separating and removing at least a portion of the aqueous solution components in the hydrolysis reaction product containing the lignin-cellulose microfiber composite.

6. The method for producing a negative electrode material for a secondary battery according to claim 1, further comprising the step of (a-2) washing the hydrolysis reaction product containing the lignin-cellulose microfiber composite obtained from step (a) with desalting 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, prior to step (b).

7. The base used in step (b) above is sodium hydroxide (NaOH), potassium hydroxide (KOH), ammonia (NH₃). 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 (NaHCO3) ３ A method for producing a negative electrode material for a secondary battery according to claim 1, characterized in that it is at least one selected from among the following or a mixture thereof.

8. The method for producing a negative electrode material for a secondary battery according to claim 1, characterized in that 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. The method for producing a negative electrode material for a secondary battery according to claim 1, characterized in that 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 amount of components derived from lignin, cellulose, and hemicellulose.

10. A method for producing 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.

11. A method for manufacturing a negative electrode material for a secondary battery according to claim 1, characterized in that the heat treatment temperature in step (d) is in the range of 500 to 3000°C.

12. The method for producing a negative electrode material for a secondary battery according to claim 1, characterized in that the heat treatment in step (d) is 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.

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

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

15. A negative electrode material for a secondary battery manufactured by the manufacturing method described in 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 described in claim 15.

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

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