Composition for negative electrodes, negative electrode, and secondary battery

Abstract

The present invention provides a composition for negative electrodes of secondary batteries, the composition containing a silicon-based negative electrode active material and a dispersant, wherein: the dispersant contains a lignin component that contains a lignin derivative; the lignin derivative has a functional group represented by formula (1); and the S content in the functional group is 0.1 mass% to 7.0 mass%. formula (1): -SO3M (In the formula, M represents a hydrogen atom, a monovalent metal, or a divalent metal.)

Description

Negative electrode composition, negative electrode, and secondary battery

[0001] The present invention relates to a negative electrode composition used in the negative electrode of a secondary battery, a negative electrode using the same, and a secondary battery.

[0002] In recent years, the rapid spread of small portable devices such as smartphones and tablets, as well as stationary storage batteries, has led to an increasing demand for small, high-energy-density batteries to power them.

[0003] Generally, graphite-based materials are used for the negative electrodes of lithium-ion secondary batteries, and the theoretical capacity of graphite-based materials is 372 mAh / g (LiC ６ ) and is currently approaching its limit.

[0004] Furthermore, in order to improve the energy density of lithium-ion secondary batteries, it is necessary to select new materials. Therefore, materials made by alloying lithium with silicon, tin, etc., which have the second lowest potential and large specific capacity after carbon and lithium, are attracting attention.

[0005] Among these materials, silicon can absorb up to 4.4 lithium atoms per 1 silicon atom in molar ratio, theoretically providing approximately 10 times the capacity of graphite-based carbon materials. However, silicon particles expand in volume by approximately 3 to 4 times when they absorb lithium, leading to degradation and capacity loss with repeated charge / discharge cycles. Detailed analysis of this phenomenon has shown that when lithium is inserted into a silicon-containing active material, the volume expansion causes microcracks in the electrode, allowing the electrolyte to penetrate these microcracks and form a new coating (SEI layer). This results in irreversible capacity loss, resulting in a decrease in battery capacity. This phenomenon manifests itself in changes in charge / discharge efficiency during cycling. The decrease in cycle efficiency, especially during the early stages of cycling when volume change is significant, significantly impacts the battery's lifespan when combined with a positive electrode with high charge / discharge efficiency. Therefore, when using silicon-containing active materials, minimizing the adverse effects of changes in electrode structure due to this volume expansion is an important challenge.

[0006] Patent Document 1 describes a negative electrode produced by applying a negative electrode mixture slurry containing a silicon-containing electrode active material, a lignin sulfonate salt, and a conductive additive to a current collector and drying the slurry to form a coating film of the negative electrode mixture (negative electrode active material layer) on the current collector. It also describes that a battery using the negative electrode produced in this manner has excellent capacity characteristics.

[0007] However, the negative electrode mixture slurry described in the examples of Patent Document 1 contains too much components other than the active material (lignin, carboxymethyl cellulose, and conductive additive), and therefore, it is considered that the performance of a battery obtained by using a negative electrode prepared using this slurry is too low to withstand practical use.

[0008] EP 3544099

[0009] The silicon-based negative electrode active material contained in the negative electrode mixture slurry described in the examples of Patent Document 1 is about 60% on a solids basis. However, when the amount of silicon-based negative electrode active material mixed is large, there is a problem that satisfactory battery characteristics cannot be obtained because deterioration progresses due to repeated charge and discharge.

[0010] An object of the present invention is to provide a composition for a negative electrode that can suppress deterioration due to repeated charge and discharge in a negative electrode containing a silicon-based negative electrode active material, and that can provide a secondary battery with excellent battery performance such as capacity retention.

[0011] As a result of extensive research, the present inventors have found that the above-mentioned problems can be solved by incorporating a silicon-based negative electrode active material and a specific dispersant.

[0012] The present invention provides the following: (1) A composition for a negative electrode of a secondary battery, comprising a silicon-based negative electrode active material and a dispersant, the dispersant containing a lignin component containing a lignin derivative, the lignin component having a weight-average molecular weight of 6,000 to 35,000, a value obtained by dividing the weight-average molecular weight by the number-average molecular weight of 1.5 to 3.2, an amount of extractable components per solid content of the lignin component of 0.008 to 2.5 mass%, an amount of methoxy groups per solid content of the lignin component of 3 to 18 mass%, and a mass ratio of the amount of extractable components per solid content of the lignin component to the amount of methoxy groups of 0.0008 to 0.25, the lignin derivative having a functional group represented by the following formula (1), and an S content in the functional group of 0.1 to 7.0 mass%: Formula (1): -SO ３ M (wherein M represents a hydrogen atom, a monovalent metal, or a divalent metal). (2) The negative electrode composition according to (1), wherein a value obtained by dividing the weight-average molecular weight of the lignin component by the number-average molecular weight is 1.5 to 3.1. (3) The negative electrode composition according to (1) or (2), wherein the amount of extractable components per solid content of the lignin component is 0.01 to 2.5 mass%, and the mass ratio of the amount of extractable components per solid content of the lignin component to the amount of methoxy groups is 0.001 to 0.25. (4) The negative electrode composition according to (1) or (2), wherein the total yield of decomposition products by alkaline nitrobenzene oxidation per solid content of the lignin component is 15% or less. (5) A negative electrode for a secondary battery, comprising a negative electrode active material layer containing the negative electrode composition according to (1) or (2), a negative electrode binder, and a conductive additive. (6) A secondary battery comprising the negative electrode according to (5). (7) The negative electrode composition according to (1) or (2), wherein the secondary battery is a lithium ion battery.

[0013] According to the present invention, it is possible to provide a negative electrode composition that can suppress deterioration due to repeated charge and discharge in a negative electrode containing a silicon-based negative electrode active material, and that can obtain a secondary battery that has excellent battery performance such as capacity retention rate.

[0014] The present invention will be described in detail below. In the present invention, "to" includes the end values. That is, "X to Y" includes the values ​​X and Y at both ends.

[0015] <<Negative Electrode Composition>> The negative electrode composition of the present invention comprises a silicon-based negative electrode active material and a dispersant, the dispersant containing a lignin component including a lignin derivative, the lignin component having a weight-average molecular weight of 6,000 to 35,000, a value obtained by dividing the weight-average molecular weight by the number-average molecular weight of 1.5 to 3.2, an extractable component amount per solid content of the lignin component of 0.008 to 2.5 mass%, an extractable component amount per solid content of the lignin component of 3 to 18 mass%, a mass ratio of the extractable component amount to the methoxy group amount per solid content of the lignin component of 0.0008 to 0.25, and the lignin derivative having a functional group represented by the following formula (1), in which the sulfur content in the functional group is 0.1 to 7.0 mass%. ３ M (wherein M represents a hydrogen atom, a monovalent metal, or a divalent metal)

[0016] (Negative electrode active material) The negative electrode composition of the present invention contains a silicon-based negative electrode active material. Examples of the silicon-based negative electrode active material include silicon particles or silicon-based compounds such as silicon oxide particles. Silicon oxide particles are preferred from the viewpoint of a relatively small volume expansion rate during charge and discharge and high cycle characteristics. Note that the silicon oxide in the present invention refers to SiO ｘ (0<x≦2) In the present invention, from the viewpoint of imparting electrical conductivity, the negative electrode active material is more preferably a composite of a silicon-based compound and a graphite material such as graphite (natural graphite, artificial graphite, etc.), coke, or carbon fiber.

[0017] When the negative electrode active material is a composite of a silicon-based compound and a graphite material, the blending ratio of the graphite material to the silicon-based compound is preferably 10:90 to 90:10, more preferably 50:50 to 80:20.

[0018] The negative electrode composition of the present invention can also contain other active materials as the negative electrode active material in addition to the silicon-based negative electrode active material and the graphite material used as needed. Examples of other active materials include elements capable of forming an alloy with lithium, such as elements such as Al, Sn, Ag, Bi, Mg, Zn, In, Ge, Pb, and Ti; compounds containing elements capable of forming an alloy with lithium; composites of elements and compounds capable of forming an alloy with lithium and carbon and / or the graphite material, or nitrides containing lithium.

[0019] (Dispersant) The dispersant used in the present invention contains a lignin component including a lignin derivative, and the lignin derivative has a functional group represented by the following formula (1), and the S content in the functional group is 0.1 to 7.0 mass %. Formula (1): -SO ３ M (wherein M represents a hydrogen atom, a monovalent metal, or a divalent metal) In the present invention, the dispersant is mainly used for the purpose of dispersing the silicon-based negative electrode active material in the dispersion medium or the negative electrode mixture composition.

[0020] (Lignin Component) The dispersant used in the present invention contains a lignin component, and the lignin component includes at least a lignin derivative.

[0021] (Lignin Derivative) In this specification, the term "lignin derivative" refers to a decomposition product of lignin, a derivative of lignin, or a derivative of a decomposition product of lignin. The lignin derivative may be in powder or liquid form. The method for preparing a liquid lignin component is not particularly limited, but an example thereof includes a method in which a powdered lignin component is dissolved in an appropriate solvent (e.g., water, an aqueous sodium hydroxide solution, etc.) to obtain a liquid lignin component.

[0022] Lignin derivatives are usually derived from woody biomass and are classified into several types with different structures and physical properties depending on the processing method, such as lignin sulfonic acid, lignin sulfonate, kraft lignin, soda lignin, soda-anthraquinone lignin, organosolv lignin, explosive lignin, sulfuric acid lignin, and decomposition products thereof.

[0023] The lignin derivative is preferably modified from the viewpoint of improving the dispersibility of silicon-based negative electrode active materials. Examples of modifications include alkali treatment, alkaline oxygen treatment, oxidation treatment using active oxygen species such as ozone or hydrogen peroxide, and modification of aromatic nuclei by sulfomethylation. From the viewpoint of improving the dispersibility of silicon-based negative electrode active materials, modifications by alkali treatment, alkaline oxygen treatment, and sulfomethylation are preferred. Sulfomethylated lignin can be obtained by sulfomethylating raw lignin. Examples of raw materials that can be used include kraft lignin, soda lignin, soda-anthraquinone lignin, organosolv lignin, explosive lignin, lignin sulfonate, sulfuric acid lignin, and decomposition products thereof, as well as derivatives thereof. The lignin derivative may be one type or a combination of two or more types. Since the higher the degree of modification, the lower the total decomposition product yield by alkaline nitrobenzene oxidation. Therefore, the degree of modification can be determined by measuring the total decomposition product yield.

[0024] The lignin derivative used in the present invention preferably has a functional group (sulfo group) represented by the following formula (1), and from the viewpoint of improving the adsorption to the silicon-based negative electrode active material, the S content in the functional group is 0.1 to 7.0 mass%, preferably 0.1 to 6.0 mass%, and more preferably 0.1 to 5.0 mass%. If the S content is too high, there is a risk that the adsorption of lignin to the silicon-based negative electrode active material will deteriorate. Formula (1): -SO ３ M (wherein M represents a hydrogen atom, a monovalent metal, or a divalent metal)

[0025] (S Content) Here, the S content in the functional group refers to the content of sulfur atoms contained in the functional group relative to the solid content of the lignin derivative. Specifically, it is a value calculated by the following formula (2). Formula (2): S content (mass%) = total S content (mass%) - inorganic S content (mass%) In formula (2), the total S content and inorganic S content of the lignin derivative both indicate the S content relative to the solid content of the lignin derivative. In formula (2), the total S content is the total S content contained in the lignin derivative, and can be quantified by ICP atomic emission spectroscopy. In addition, the inorganic S content is calculated by the SO quantified by ion chromatography. ３ Ion content, SO ４ Ion content and S ２ O ３ It can be calculated from the total amount of ion content.

[0026] (Weight-average molecular weight) The weight-average molecular weight of the lignin component used in the present invention is preferably 6,000 to 35,000, more preferably 6,000 to 30,000, and even more preferably 6,000 to 25,000. If the weight-average molecular weight is greater than the upper limit, the dispersibility of the silicon-based negative electrode active material may be deteriorated.

[0027] (Polydispersity (weight average molecular weight / number average molecular weight)) The value obtained by dividing the weight average molecular weight by the number average molecular weight of the lignin component used in the present invention (also referred to as "polydispersity") is 1.5 to 3.2, preferably 1.5 to 3.1, and more preferably 1.5 to 2.5. If the polydispersity is greater than the above upper limit, the dispersibility of the silicon-based negative electrode active material may deteriorate.

[0028] In the present invention, the weight-average molecular weight and number-average molecular weight are measured by gel permeation chromatography (GPC). The GPC measurement may be performed by a known method using pullulan equivalents under the following conditions: Measurement apparatus: manufactured by Tosoh Corporation; Column used: Shodex Column OH-pak SB-806HQ, SB-804HQ, SB-802.5HQ; Eluent: aqueous solution of 1.0% sodium tetraborate and 0.3% isopropyl alcohol; Eluent flow rate: 1.00 mL / min; Column temperature: 50°C; Measurement sample concentration: 0.2% by mass; Standard substance: pullulan (manufactured by Showa Denko KK); Detector: RI detector (manufactured by Tosoh Corporation); Calibration curve: pullulan standard

[0029] (Extractable Components) The lignin component preferably contains extractable components. In this specification, extractable components refer to extractable components of plants (e.g., plants used as pulp raw materials, preferably wood from plants of the genus Cedar, Chamaecyparis obtusa, Pinus spp., Larch spp., Abies spp., and Eucalyptus spp.). These are typically trace components that are measured and identified by extracting wood using organic solvents. Among extractable components, those with phenolic hydroxyl groups or carboxyl groups can also be obtained by extraction using alkali. Extractable components are typically determinants of wood properties such as color, odor, durability, adhesiveness, and biological activity, and are said to be the components that chemically characterize wood. After the skeleton is formed by the deposition of cellulose and hemicellulose and lignin, trees are finally completed as biological materials only after the accumulation of extractable components, which are linked to heartwood formation. Examples of organic solvents used to obtain extractable components include hexane, benzene, ether, acetone, and alcohol. The extractable component content relative to the wood is typically approximately 5% or less.

[0030] Extracted components typically contain low-molecular-weight compounds. Many of these are secondary metabolites with molecular weights of several thousand or less, and although they are generally extremely diverse, they can be broadly classified into aromatic extracted components and terpenoids. Examples of aromatic extracted components include flavonoids, tannins, lignans, and stilbenes. The extracted components contain at least one selected from these.

[0031] Flavonoids include diphenylpropane (C ６ -C ３ -C ６ ) skeleton, examples of which include flavones, flavanones, chalcones, aurones, isoflavones, catechins, and leucoanthocyanidins. Tannins may be either hydrolyzable tannins or condensed tannins. Hydrolyzable tannins are tannins having a structure in which a phenolic carboxylic acid such as gallic acid is ester-bonded to a nucleus such as glucose, examples of which include gallotannins and ellagitannins. Hydrolyzable tannins can be decomposed into simple fragments by hydrolysis with acids, alkalis, etc., and hydrolysis of gallotannins and ellagitannins yields gallic acid and ellagic acid, respectively. Condensed tannins include, for example, amorphous polymers whose precursors are catechins or leucoanthocyanidins.

[0032] Lignans include, for example, lignans and related substances. Lignans (resinols) are C phenylpropane units, which are the same structural units as lignin, bonded to each other via carbon-carbon bonds between the β-positions of their side chains. ６ -C ３ -C ３ -C ６ Unlike lignin, it has an asymmetric carbon in the molecule and is optically active. Examples of substances related to lignan include C ６ -C ３ -C ２ -C ６ The stilbenes may be any compounds having an α,β-diphenylethylene skeleton.

[0033] Terpenoids are composed of isoprene units (C ５ H ８The terpenoid may be a series of compounds in which two or more isoprenoid units are bonded in a chain or ring. Terpenoids consisting of 2, 3, 4, and 6 isoprenoid units are called monoterpenes (10 carbon atoms), sesquiterpenes (15 carbon atoms), diterpenes (20 carbon atoms: for example, abietic acid), and triterpenes (30 carbon atoms), respectively, and any of these may be used.

[0034] Extractives have a variety of physiological activities depending on their basic carbon skeleton and substituents, including, for example, biological activity against microorganisms, insects, and plants ("Resistance of wood to biodeterioration by extractives," Wood Conservation 34(2), 48-54, 2008), improved wood durability, adverse effects on human health, and adverse effects on chemical and physical processing of wood (e.g., pulping, bleaching, cement hardening).

[0035] (Extracted component / lignin component (mass ratio)) In the lignin component, the mass ratio of the amount of extracted component to the amount of methoxy groups per solid content of the lignin component is 0.0008 to 0.25, preferably 0.001 to 0.25, more preferably 0.005 to 0.2, and even more preferably 0.01 to 0.15, from the viewpoint of highly orienting the lignin and extracted component in the negative electrode. By having the mass ratio within the above range, the lignin and extracted component can be highly oriented in the negative electrode. If the mass ratio is too large, the amount of extracted component as an impurity increases, resulting in a decrease in battery performance, and if it is too small, the lignin and extracted component cannot be oriented in the negative electrode.

[0036] The extractables may affect the orientation of the negative electrode components, particularly lignin. Furthermore, since lignin generally contains methoxy groups bonded to aromatic nuclei in its structure, the amount of methoxy groups is an indicator of the lignin derivative content. Therefore, the mass ratio can be said to represent the balance required for highly oriented lignin and extractables within the negative electrode.

[0037] (Amount of extracted component) The amount of extracted component per solid content of the lignin component is 0.008 to 2.5 mass%, preferably 0.01 to 2.5 mass%, and more preferably 0.1 to 2.0 mass%, from the viewpoint of affecting the orientation of the negative electrode component, particularly with lignin.

[0038] (Methoxy Group Amount) The methoxy group amount per solid content of the lignin component is preferably 3 to 18 mass %, more preferably 5 to 15 mass %, from the viewpoint of using high-purity lignin. Since lignin generally has a methoxy group bonded to an aromatic nucleus in its structure, the methoxy group amount is an index of the content of lignin and lignin derivatives, i.e., the purity of the lignin and lignin derivatives.

[0039] The amount of methoxy groups can be measured by the quantitative determination of methoxy groups by the Viebock and Schwappach method (see "Lignin Chemistry Research Methods," pp. 336-340, 1994, published by Uni Publishing Co., Ltd.). The amount of extractable components can be measured by the measurement method for hexane extractable substances described in JIS K 0102:2019.

[0040] (Total Decomposition Product Yield) The total decomposition product yield of the lignin component by alkaline nitrobenzene oxidation (also simply referred to as "total decomposition product yield") is preferably 15% or less, more preferably 2% to 13%, from the viewpoint of improving the dispersibility of materials other than CMC contained in the negative electrode mixture composition. When the total decomposition product yield is within the above range, the dispersibility of materials other than CMC contained in the negative electrode mixture composition can be improved, thereby improving battery performance. If the total decomposition product yield is too high above the upper limit, there is a problem that the dispersibility of materials other than CMC contained in the negative electrode mixture composition in particular becomes insufficient, resulting in deterioration of battery performance. On the other hand, if the total decomposition product yield is too low below the lower limit, there is a problem that the degree of modification of the lignin is too high, resulting in the loss of the properties of lignin and the inability to exhibit various performances derived from lignin. Note that a lower total decomposition product yield means a higher degree of modification of lignin. Here, the total degradation product yield can be quantified by the method described in "Plant Cell Wall Experimental Methods" (see "Plant Cell Wall Experimental Methods," pp. 128-131, 2016, published by Hirosaki University Press). The total degradation product yield can be determined from the ratio (w / w%) of the total weight of the six degradation products (p-hydroxybenzaldehyde, p-hydroxybenzoic acid, vanillin, vanillic acid, syringaldehyde, and syringic acid) obtained by the measurement to the solid content of the sample.

[0041] (Lignosulfonic acid, lignosulfonate salts) Lignosulfonic acid and lignosulfonate salts are lignin derivatives having a sulfo group, which are prepared from lignocellulose raw materials via sulfite treatment. Examples of methods for preparing lignosulfonic acid and lignosulfonate salts include a method in which the lignocellulose raw materials or lignin itself is subjected to sulfite treatment, and preferably a method in which the lignocellulose raw materials or lignin itself is subjected to sulfite cooking.

[0042] (Lignocellulose Raw Material) The lignocellulose raw material is not particularly limited as long as it contains lignocellulose in its constituents. Examples include pulp raw materials such as wood and non-wood. Examples of wood include coniferous trees such as Yezo spruce, red pine, cedar, and cypress, and broadleaf trees such as white birch and beech. The age and location of the wood do not matter. Therefore, wood harvested from trees of different ages or from different locations on a tree may be used in combination. Examples of non-wood include bamboo, kenaf, reed, and rice. The lignocellulose raw material may be a single material or a combination of two or more materials. Lignin sulfonic acid and lignin sulfonate may be prepared from a material other than the lignocellulose raw material, such as lignin. Examples of lignin include naturally occurring lignin and artificially produced lignin (e.g., dehydrogenation polymerized products of hydroxycinnamic alcohol analogs), and both can be used. Lignosulfonic acid and lignosulfonate salts can be prepared from lignin, for example, by a method of decomposing and sulfonating lignin.

[0043] (Sulfite Treatment) The sulfite treatment can be carried out by contacting the lignocellulosic raw material with at least one of sulfurous acid and a sulfite salt. The conditions for the sulfite treatment are not particularly limited, as long as they allow a sulfo group to be introduced into the α-carbon atom of the side chain of lignin contained in the lignocellulosic raw material.

[0044] The sulfite treatment is preferably carried out by sulfite cooking, which allows for more quantitative sulfonation of lignin in lignocellulosic raw materials. The sulfite cooking method involves reacting lignocellulosic raw materials at high temperatures in a solution of at least one of sulfurous acid and a sulfite salt (e.g., an aqueous solution: cooking liquor). This method is industrially established and practiced as a method for producing sulfite pulp, and is therefore advantageous in terms of economy and ease of implementation.

[0045] When sulfite cooking is carried out, examples of sulfite salts include magnesium salts, calcium salts, sodium salts, and ammonium salts.

[0046] The sulfurous acid (SO2) concentration in the solution of at least one of sulfurous acid and sulfite salt is not particularly limited, but the ratio of the mass (g) of SO2 to 100 mL of reaction solution is preferably 1 g / 100 mL or more, and more preferably 2 g / 100 mL or more when sulfite cooking is performed. The upper limit is preferably 20 g / 100 mL or less, and more preferably 15 g / 100 mL or less when sulfite cooking is performed. The SO2 concentration is preferably 1 g / 100 mL to 20 g / 100 mL, and more preferably 2 g / 100 mL to 15 g / 100 mL when sulfite cooking is performed.

[0047] The pH value of the sulfite treatment is not particularly limited, but is usually 10 or less. When sulfite cooking is performed, it is preferably performed under acidic conditions, more preferably a pH of 5 or less, and even more preferably 3 or less. This allows lignin derivatives (e.g., lignin sulfonates) to be efficiently extracted, resulting in pulp of higher quality. The lower limit of the pH value is preferably 0.1 or more, and when sulfite cooking is performed, more preferably 0.5 or more. The pH value during the sulfite treatment is preferably 0.1 to 10, and when sulfite cooking is performed, more preferably 0.5 to 5, and even more preferably 0.5 to 3.

[0048] The temperature for the sulfite treatment is not particularly limited, but is preferably 170°C or lower, and more preferably 150°C or lower if sulfite cooking is performed. The lower limit is preferably 70°C or higher, and more preferably 100°C or higher if sulfite cooking is performed. The temperature conditions for the sulfite treatment are preferably 70 to 170°C, and more preferably 100 to 150°C if sulfite cooking is performed. The treatment time for the sulfite treatment is not particularly limited, and although it depends on the conditions for the sulfite treatment, 0.5 to 24 hours is preferred, and 1.0 to 12 hours is more preferred.

[0049] In the sulfite treatment, it is preferable to add a compound that supplies a counter cation (salt: containing the substituent M of the group represented by formula (1)). By adding a compound that supplies a counter cation, the pH value during the sulfite treatment can be maintained constant. Examples of compounds that supply counter cations include MgO, Mg(OH), CaO, Ca(OH), CaCO, NH, NHOH, NaOH, NaHCO, and NaCO. Calcium ions, magnesium ions, and sodium ions are preferred as counter cations.

[0050] When a solution of at least one of sulfurous acid and sulfite salts is used in the sulfite treatment, the solution may contain, in addition to SO, the above-mentioned counter cations (salts) and digestion penetrants (e.g., cyclic ketone compounds such as anthraquinone sulfonates, anthraquinone, and tetrahydroanthraquinone) as needed.

[0051] There are no limitations on the equipment used for the sulfite treatment, and for example, commonly known dissolving pulp manufacturing equipment can be used.

[0052] The intermediate product can be separated from the solution of at least one of sulfurous acid and sulfite salts by a conventional method, such as a method for separating the sulfite cooking effluent after sulfite cooking (e.g., filtration).

[0053] Another example of a method for producing lignosulfonic acid and lignosulfonates is the sulfonation of kraft lignin, which will be described later in this specification. The method for sulfonating kraft lignin may be similar to the sulfonation method using a conventional sulfite treatment or sulfite cooking treatment, but is not particularly limited and other methods may also be used.

[0054] The lignin sulfonic acid and lignin sulfonate salts obtained by the sulfite treatment (e.g., as the filtrate or filtration residue after filtering the insoluble matter in the sulfite solution, preferably as the filtrate) may be used as the active ingredient, i.e., as a lignin derivative, either directly or after concentration as necessary. Furthermore, if necessary, other treatments may be carried out. This allows the production of lignin derivatives with high purity and / or an appropriate degree of sulfonation (S content). Examples of such other treatments include alkali treatment, oxidation treatment, dialysis treatment, and combinations thereof.

[0055] (Alkaline Treatment) The alkali treatment is preferably performed on the filtration residue (insoluble matter) or filtrate after sulfite treatment, or on the treated product after dialysis. The alkali treatment can be performed by placing the target sample under alkaline conditions. Placing under alkaline conditions usually means placing the sample in an aqueous solution with a pH value of 8 or higher, preferably a pH value of 9 or higher. The upper limit of the pH value is usually 14.

[0056] In the alkali treatment, an alkaline substance is usually brought into contact with the sulfite-treated product. The alkaline substance is not particularly limited, but examples thereof include calcium hydroxide, magnesium hydroxide, sodium hydroxide, potassium hydroxide, sodium carbonate, and ammonia. Among these, sodium hydroxide and calcium hydroxide are preferred. The alkaline substance may be used alone or in combination of two or more.

[0057] Examples of methods for contacting the sulfite-treated product with an alkaline substance include a method in which a dispersion or solution (e.g., an aqueous dispersion or aqueous solution) of the sulfite-treated product is prepared and the alkaline substance is added to the dispersion or solution, and a method in which a solution or dispersion (e.g., an aqueous dispersion or aqueous solution) of the alkaline substance is added to the sulfite-treated product.

[0058] The temperature of the alkali treatment is not particularly limited, but is preferably 40° C. or higher, more preferably 60° C. or higher. The upper limit is preferably 150° C. or lower, more preferably 140° C. or lower, and even more preferably 130° C. or lower.

[0059] The amount of the alkaline substance in the alkali treatment is preferably 0.5 to 40 mass %, more preferably 1.0 to 30 mass %, relative to the mass of the solids content of the sulfite-treated product, or, when an aqueous solution or dispersion is prepared by dispersing the alkali-treated extract in an aqueous solvent (e.g., water), relative to the mass of the aqueous solution or dispersion.

[0060] The time for the alkali treatment is not particularly limited, but is preferably 0.1 hours or more, more preferably 0.5 hours or more, and is preferably 10 hours or less, more preferably 6 hours or less.

[0061] Prior to the alkali treatment, the sulfite-treated product may be dissolved, dispersed, or its concentration adjusted (prepared as a solution or dispersion in an aqueous solvent such as water) as needed. Dispersion can be carried out by passing the product through a disc refiner, adding it to a mixer or disperser, or by kneading it. The concentration can be adjusted, for example, using an aqueous solvent such as water.

[0062] (Oxidation Treatment) The oxidation treatment can be performed on the treated product obtained after the sulfite treatment (e.g., the filtrate after filtration) or the treated product after the alkali treatment. The oxidation treatment can be performed using an appropriate oxidizing agent. When the oxidizing agent is a gas, the oxidation treatment can be performed by bubbling the gas into the filtrate. When the oxidizing agent is a liquid, the oxidation treatment can be performed by adding the liquid to the filtration residue or the filtrate. The oxidizing agent is preferably air, oxygen, hydrogen peroxide, ozone, or a combination thereof. The oxidation treatment is preferably performed under alkaline conditions (alkaline oxidation treatment). The treatment pH of the alkaline oxidation treatment is usually 8 or higher, preferably 10 or higher, and more preferably 12 or higher. The temperature of the oxidation treatment is usually 20 to 200°C, preferably 50 to 180°C. The oxidation treatment time is usually preferably 0.1 hour or longer, more preferably 0.5 hour or longer. The upper limit is preferably 5 hours or shorter, more preferably 3 hours or shorter.

[0063] (Dialysis or UF Treatment) Dialysis can be performed on the treated product obtained after the sulfite treatment (e.g., the filtrate after filtration). Examples of dialysis membranes include cellulose-based membranes such as cellulose acetate, and synthetic polymer membranes such as ethylene vinyl alcohol, polyacrylonitrile, polymethyl methacrylate, polysulfone, and polyethersulfone, and the molecular weight cutoff is usually 5,000 to 100,000, preferably 7,000 to 80,000, and more preferably 10,000 to 50,000.

[0064] UF treatment can be used instead of dialysis treatment. Known UF membranes can be used. Examples include hollow fiber membranes, spiral membranes, tubular membranes, and flat membranes. Known UF membrane materials can be used. Examples include cellulose acetate, aromatic polyamide, polyvinyl alcohol, polysulfone, polyvinylidene fluoride, polyethylene, polyacrylonitrile, and ceramics. The UF membrane may be a commercially available product.

[0065] The molecular weight cutoff of the UF membrane is preferably 5,000 to 30,000, more preferably 10,000 to 25,000, and even more preferably 15,000 to 23,000. Using a UF membrane with a molecular weight cutoff of 5,000 or more can prevent the separation rate of the treatment liquid from becoming excessively slow. Furthermore, using a UF membrane with a molecular weight cutoff of 30,000 or less can prevent lignin from becoming unable to be separated from the treatment liquid.

[0066] The concentration ratio by UF treatment using a UF membrane can be set as desired. In other words, the UF treatment can be stopped when the outflow volume of the concentrated liquid reaches a desired volume. It is preferable to concentrate the liquid 2 to 6 times. Concentrating 2 to 6 times means that the volume of the raw liquid (black liquor) is reduced to 1 / 2 to 1 / 6.

[0067] The temperature of the treatment liquid during UF treatment is not particularly limited. For example, 20 to 80°C is preferred, and considering the heat resistance of the UF membrane material, 20 to 70°C is more preferred. The pH value of the treatment liquid during UF treatment is preferably 2 to 11. The solids concentration (w / w) of the black liquor during UF treatment is preferably 2 to 30%, more preferably 5 to 20%.

[0068] (Kraft lignin) Kraft lignin is also called thiolignin or sulfate lignin. Kraft lignin can be obtained, for example, by adding an acid to black liquor obtained by kraft cooking of a lignocellulose raw material, thereby causing precipitation.

[0069] Kraft cooking is a process in which wood chips, a lignocellulosic raw material, are cooked with caustic soda (NaOH) and sodium sulfide (Na ２ The wood chips can be placed in a pressure-resistant vessel together with a kraft cooking liquor containing sucrose. The liquor ratio of the wood chips to the cooking liquor can be, for example, 1.0 to 40 L / kg, preferably 1.5 to 30 L / kg, and more preferably 2.0 to 30 L / kg. In another aspect, the liquor ratio of the wood chips to the chemical solution can be, for example, 1.0 to 5.0 L / kg, preferably 1.5 to 4.5 L / kg, and more preferably 2.0 to 4.0 L / kg.

[0070] In the present invention, kraft cooking is carried out using caustic soda (NaOH), sodium sulfide (Na ２ In addition to the above, various cooking aids may be used in combination. For example, an alkaline cooking liquor containing 0.01 to 5% by mass of a quinone compound per bone-dry chip may be added to the digester.

[0071] The quinone compound used is a quinone compound, a hydroquinone compound, or a precursor thereof known as a cooking aid, and at least one compound selected from these compounds can be used. Examples of these compounds include anthraquinone, dihydroanthraquinone (e.g., 1,4-dihydroanthraquinone), tetrahydroanthraquinone (e.g., 1,4,4a,9a-tetrahydroanthraquinone, 1,2,3,4-tetrahydroanthraquinone), methylanthraquinone (e.g., 1-methylanthraquinone, 2-methylanthraquinone), methyldihydroanthraquinone (e.g., 2-methyl-1,4-dihydroanthraquinone), methyltetrahydroanthraquinone (e.g., 1-methyl-1,4,4a,9a-tetrahydroanthraquinone, 2-methyl-1,4,4a,9a-tetrahydroanthraquinone), and the like. and hydroquinone compounds such as anthrahydroquinone (generally 9,10-dihydroxyanthracene), methylanthrahydroquinone (e.g., 2-methylanthrahydroquinone), dihydroanthrahydroanthraquinone (e.g., 1,4-dihydro-9,10-dihydroxyanthracene) or alkali metal salts thereof (e.g., disodium salt of anthrahydroquinone, disodium salt of 1,4-dihydro-9,10-dihydroxyanthracene), and precursors such as anthrone, anthranol, methylanthrone, and methylanthranol. These precursors have the potential to be converted into quinone compounds or hydroquinone compounds under cooking conditions.

[0072] The cooking liquor can have an active alkali addition rate (AA) of 8 to 55% by mass, preferably 8 to 20% by mass, based on the mass of bone-dry wood chips. If the active alkali addition rate is less than 8% by mass, the removal of lignin and hemylulose becomes insufficient, and if it exceeds 55% by mass, a decrease in yield and a decrease in quality occur. Here, the active alkali addition rate refers to the amount of NaOH, Na ２ The addition rate of S is Na ２ This is converted into the addition rate of O, and by multiplying the addition rate of NaOH by 0.775, Na ２The sulfidity is preferably in the range of 15 to 40%. In the sulfidity range of less than 15%, the delignification property decreases, the pulp viscosity decreases, and the dregs rate increases.

[0073] Kraft cooking is preferably carried out at a temperature in the range of 120 to 180°C, more preferably 140 to 160°C. If the temperature is too low, delignification (reduction in kappa number) will be insufficient, while if the temperature is too high, the degree of polymerization (viscosity) of cellulose will decrease. Furthermore, the cooking time in the present invention is the time from when the cooking temperature reaches its maximum temperature until the temperature starts to decrease, and the cooking time is preferably 60 minutes or more and 600 minutes or less, more preferably 120 minutes or more and 360 minutes or less. If the cooking time is less than 60 minutes, pulping will not proceed, and if it exceeds 600 minutes, pulp production efficiency will decrease, which is undesirable.

[0074] After kraft cooking, the kraft lignin is filtered and the resulting alkaline black liquor (filtrate) is precipitated with an acid to produce acid-precipitated kraft lignin, as described, for example, in the methods for preparing powdered acid-precipitated kraft lignin (WO 2006 / 038863, WO 2006 / 031175, and WO 2012 / 005677).

[0075] Alternatively, for example, carbon dioxide may be passed through the resulting alkaline black liquor to lower the pH of the black liquor to about 10, the precipitated lignin particles may be separated by filtration, the separated lignin particles may be resuspended, sulfuric acid may be added to lower the pH to about 2, the resulting precipitate may be separated by filtration, and the precipitate may be further washed with water, dried, etc., to obtain kraft lignin.

[0076] (Soda Lignin) Soda lignin can be obtained by adding an acid to black liquor obtained by soda cooking a lignocellulose raw material, and then precipitating the black liquor.

[0077] Soda cooking can be carried out by placing wood chips, which are lignocellulose raw materials, in a pressure-resistant vessel together with soda cooking liquor (aqueous sodium hydroxide solution). The liquor ratio of wood chips to cooking liquor can be, for example, 1.0 to 40 L / kg, preferably 1.5 to 30 L / kg, and more preferably 2.0 to 30 L / kg. In another aspect, the liquor ratio of wood chips to cooking liquor can be, for example, 1.0 to 5.0 L / kg, preferably 1.5 to 4.5 L / kg, and more preferably 2.0 to 4.0 L / kg.

[0078] In the present invention, soda cooking can also use various cooking aids in addition to caustic soda (NaOH). For example, it is preferable to add an alkaline cooking liquor containing 0.01 to 5 mass% of a quinone compound per bone-dry chip to the digester. If the amount of quinone compound added is less than 0.01 mass%, the effect of the quinone compound as an aid cannot be fully exerted. On the other hand, if the amount of quinone compound added exceeds 5 mass%, the aid remains significantly in the pulp, affecting the quality and safety of paper produced from the pulp. Note that the quinone compound can be the same as that described for kraft cooking.

[0079] The cooking liquor may contain 1 to 50% by mass of caustic soda, preferably 10 to 30% by mass, based on the mass of bone-dry wood chips. If the caustic soda content is less than 1% by mass, lignin and hemylulose are not sufficiently removed, whereas if the caustic soda content exceeds 50% by mass, the yield and quality decrease.

[0080] Soda cooking is preferably carried out at a temperature in the range of 120 to 180°C, more preferably 140 to 160°C. If the temperature is too low, delignification (reduction in kappa number) will be insufficient, while if the temperature is too high, the degree of polymerization (viscosity) of cellulose will decrease. Furthermore, the cooking time in the present invention is the time from when the cooking temperature reaches its maximum temperature to when the temperature starts to decrease, and the cooking time is preferably 60 minutes or more and 600 minutes or less, more preferably 120 minutes or more and 360 minutes or less. If the cooking time is less than 60 minutes, pulping will not proceed, and if it exceeds 600 minutes, pulp production efficiency will decrease, which is undesirable.

[0081] After soda cooking, filtration is performed, and the resulting alkaline black liquor (filtrate) is precipitated with acid to prepare acid-precipitated soda lignin. For example, sulfuric acid is added to the alkaline black liquor to lower the pH to about 2, and the resulting precipitate is separated by filtration, washed with water, dried, etc., to obtain soda lignin.

[0082] The kraft lignin and soda lignin obtained as described above may be further purified as needed to be used as a lignin derivative with increased purity. Furthermore, other treatments may be performed as needed. The derivatization of lignin is not particularly limited, and for example, sulfomethylation may be performed.

[0083] (Sulfomethylated Lignin) Kraft lignin, soda lignin, soda-anthraquinone lignin, organosolv lignin, explosive lignin, lignin sulfonate, sulfate lignin, etc., preferably kraft lignin and soda lignin, more preferably kraft lignin, can be derivatized by introducing a sulfo group into the aromatic nucleus via carbon by sulfomethylation and used as sulfomethylated lignin.

[0084] In the sulfomethylation reaction of kraft lignin, the C of lignin is generally ６ -C ３ A sulfo group is introduced into the aromatic nucleus of the unit via a carbon atom at the position shown in the following general formula (1). General formula (1) represents the C ６ -C ３ The units shown are: In the reaction indicated by the arrow on the left, a sulfo group is introduced at the α-position, which is generally called sulfonation; on the other hand, in the reaction indicated by the arrow on the right, a sulfo group is introduced at the 5-position of the aromatic nucleus via formaldehyde, in addition to the α-position.

[0085] (In general formula (1), M represents a hydrogen atom, a monovalent metal, or a divalent metal.)

[0086] The sulfomethylated lignin may be produced by a known method, for example, by reacting kraft lignin or soda lignin with a sulfite and an aldehyde.

[0087] An example of a method for sulfomethylating lignin is disclosed in U.S. Patent No. 2,680,113. In this method, the sulfomethylation reaction of lignin is carried out at a temperature ranging from 50 to 200° C., preferably from 80 to 170° C., and more preferably from 90 to 160° C. Furthermore, the pH during the sulfomethylation reaction is preferably 8 or higher.

[0088] The amount of sulfite to be added is preferably 1 to 50% by mass relative to lignin, from the viewpoint of efficiently carrying out the reaction and preventing unreacted substances from remaining when an excess amount is added.

[0089] As the aldehyde, formaldehyde is preferred. The amount of aldehyde to be added is preferably 0.25 to 12.5% ​​by mass relative to lignin. When the amount of formaldehyde is within this range, the reaction indicated by the arrow on the right side of the general formula (1) proceeds smoothly, and a sulfo group is introduced via formaldehyde.

[0090] (Optional Components) The lignin component may contain components other than the extracted components that are mixed in from the raw materials when the lignin derivative is prepared (for example, during sulfite cooking), such as inorganic salts such as sodium sulfate, sodium sulfite, sodium chloride, magnesium sulfate, magnesium sulfite, magnesium chloride, calcium sulfate, calcium sulfite, calcium chloride, ammonium sulfate, ammonium sulfite, ammonium chloride, and sodium hydroxide.

[0091] In the negative electrode composition of the present invention, the ratio of the silicon-based negative electrode active material to the dispersant is preferably 0.1 to 5 parts by mass, more preferably 0.3 to 4.5 parts by mass, and even more preferably 0.5 to 4 parts by mass, based on the solid content, from the viewpoint of adding a necessary and sufficient amount of dispersant to disperse the silicon-based negative electrode active material. Furthermore, as long as the negative electrode composition of the present invention contains a silicon-based negative electrode active material and a dispersant, it may be used as the negative electrode composition in a state where it is dispersed in a dispersion medium.

[0092] (Negative Electrode) The negative electrode of the present invention is used in a secondary battery, and includes a negative electrode active material layer containing the negative electrode composition of the present invention, a negative electrode binder, and a conductive additive.

[0093] The content of the negative electrode composition in the negative electrode active material layer is preferably 10 to 99 mass %, more preferably 90 to 99 mass %, based on the solid content.

[0094] The content of the silicon-based negative electrode active material in the negative electrode active material layer is preferably 1 to 99 mass%, more preferably 10 to 99 mass%, still more preferably 50 to 99 mass%, particularly preferably 60 to 99 mass%, and most preferably 65 to 99 mass%, based on the solid content.

[0095] When a silicon-based negative electrode active material is used in combination with another negative electrode active material, the total content of the negative electrode active materials in the negative electrode active material layer is preferably 90 to 99 mass%, more preferably 91 to 99 mass%, even more preferably 92 to 99 mass%, still more preferably 95 to 99 mass%, particularly preferably 96 to 99 mass%, and most preferably 98 to 99 mass%, based on the solid content.

[0096] The content of the dispersant in the negative electrode active material layer is preferably 0.05 to 10 mass %, more preferably 0.1 to 5 mass %, based on the solid content.

[0097] (Negative Electrode Binder) The negative electrode binder used in the present invention is not particularly limited as long as it is a binder generally used for negative electrodes. However, when preparing a negative electrode in an aqueous system, it is preferable to use carboxymethyl cellulose or a salt thereof from the viewpoint of high performance. In addition, the negative electrode binder may contain other binders other than carboxymethyl cellulose or a salt thereof. Examples of other binders include synthetic rubber binders.

[0098] (Carboxymethylcellulose and / or its salt) Carboxymethylcellulose and / or its salt (hereinafter sometimes abbreviated as "CMC") has a structure in which the hydroxyl group in the glucose unit constituting cellulose is substituted with a carboxymethyl ether group. Carboxymethylcellulose may be in the form of a salt. Examples of the salt of carboxymethylcellulose include metal salts such as carboxymethylcellulose sodium salt.

[0099] In the present invention, cellulose refers to a polysaccharide having a structure in which D-glucopyranose units (also simply referred to as "glucose units" or "anhydroglucose") are linked together through β,1-4 bonds. Cellulose is generally classified into native cellulose, regenerated cellulose, fine cellulose, microcrystalline cellulose (which is cellulose obtained by removing the amorphous region), etc., based on its origin and manufacturing method.

[0100] Examples of natural cellulose include bleached or unbleached pulp, purified linters, and cellulose produced by microorganisms such as acetic acid bacteria. The raw materials for bleached or unbleached pulp are not particularly limited, and examples include wood, cotton, straw, bamboo, etc. The method for producing bleached or unbleached pulp is also not particularly limited, and examples include mechanical methods, chemical methods, and methods that combine mechanical and chemical methods. Examples of bleached or unbleached pulp include mechanical pulp, chemical pulp, groundwood pulp, sulfite pulp, kraft pulp, and papermaking pulp. Another example of bleached or unbleached pulp is dissolving pulp, which is chemically refined and used primarily by dissolving it in chemicals, and is used as a main raw material for artificial fibers, cellophane, etc.

[0101] Examples of regenerated cellulose include regenerated cellulose obtained by dissolving cellulose in a solvent such as a cuprammonium solution, a cellulose xanthate solution, or a morpholine derivative, and then spinning the resulting solution.

[0102] Examples of fine cellulose include fine cellulose obtained by depolymerizing cellulosic materials such as natural cellulose and regenerated cellulose through acid hydrolysis, alkali hydrolysis, enzymatic decomposition, blasting treatment, vibrating ball mill treatment, etc., and fine cellulose obtained by mechanically treating cellulosic materials.

[0103] For producing CMC, a known CMC production method can be applied. For example, CMC can be produced by treating cellulose with a mercerizing agent (alkali) to prepare mercerized cellulose (alkali cellulose), and then adding an etherifying agent to the mercerized cellulose to cause an etherification reaction.

[0104] The cellulose raw material can be any of the above-mentioned celluloses without any particular limitations, but cellulose with high purity is preferred, and dissolving pulp or linter is more preferred. By using these, CMC with high purity can be obtained.

[0105] Examples of the mercerizing agent include alkali metal hydroxides such as sodium hydroxide, potassium hydroxide, etc. Examples of the etherifying agent include monochloroacetic acid, sodium monochloroacetate, etc.

[0106] In a typical method for producing water-soluble carboxymethyl cellulose, the molar ratio of the mercerizing agent to the etherifying agent (mercerizing agent / etherifying agent) is generally 2.00 to 2.45 when monochloroacetic acid is used as the etherifying agent. A ratio of 2.00 or more allows the etherification reaction to proceed sufficiently, preventing unreacted monochloroacetic acid from being wasted. A ratio of 2.45 or less prevents the side reaction of excess mercerizing agent and monochloroacetic acid from progressing and producing an alkali metal glycolate, which is economical. In the present invention, the CMC may be a commercially available product. An example of a commercially available product is "Sunrose" manufactured by Nippon Paper Industries Co., Ltd.

[0107] (Degree of substitution of carboxymethyl groups) The degree of substitution of carboxymethyl groups per anhydroglucose unit of CMC (hereinafter sometimes referred to as DS value) is 0.5 to 1.2. A DS value of 0.5 or more can maintain good solubility in water and suppress the generation of undissolved matter. Furthermore, a DS value of 1.2 or less can suppress an increase in spinnability of the liquid and maintain easy handling. Therefore, the DS value of the CMC of the present invention is 0.5 to 1.2, preferably 0.5 to 1.0, and more preferably 0.6 to 1.0.

[0108] The degree of substitution of carboxymethyl groups is measured as follows: Approximately 2.0 g of sample is weighed out and placed in a 300 mL Erlenmeyer flask with a stopper. 100 mL of a solution of 100 mL of concentrated nitric acid added to 1000 mL of methanol is added, and the mixture is shaken for 3 hours to convert the carboxymethyl cellulose salt (CMC) into H-CMC (hydrogen-form carboxymethyl cellulose). 1.5 to 2.0 g of the bone-dry H-CMC is weighed out and placed in a 300 mL Erlenmeyer flask with a stopper. The H-CMC is moistened with 15 mL of 80% methanol, 100 mL of 0.1 N NaOH is added, and the mixture is shaken at room temperature for 3 hours. Phenolphthalein is used as an indicator, and the 0.1 N H ２ SO ４ The excess NaOH is back-titrated with 0.01% NaOH, and the degree of carboxymethyl substitution (DS value) is calculated using the following formula: A = [(100 × F' - 0.1N - H ２ SO ４ (mL) × F) × 0.1] / (bone dry mass (g) of H-CMC) Degree of carboxymethyl substitution = 0.162 × A / (1 - 0.058 × A) F': 0.1N-H ２ SO ４ F: Factor of 0.1N-NaOH

[0109] (Viscosity) The viscosity of a 1% by mass aqueous solution of CMC, measured at 25°C using a Brookfield viscometer (30 rpm), is preferably 1,000 to 20,000 mPa·s, more preferably 1,000 to 15,000 mPa·s, and even more preferably 1,000 to 10,000 mPa·s. If this viscosity is too high, there are problems such as the inability to mix well with the active material and conductive additive when preparing the slurry, and problems such as poor fluidity when applying the slurry to a current collector, making it impossible to apply. If the viscosity is too low, there are problems such as the slurry flowing off the current collector when applied to the current collector, making it difficult to apply, and the possibility of migration of the active material occurring after application.

[0110] The viscosity was measured as follows: CMC was weighed into a 1000 mL glass beaker and dispersed in 900 mL of distilled water to prepare an aqueous dispersion with a solids content of 1% (w / v). The aqueous dispersion was stirred at 600 rpm for 3 hours at 25°C using a stirrer. Thereafter, the viscosity was measured after 3 minutes at 30 rpm using a B-type viscometer (manufactured by Toki Sangyo Co., Ltd.) in accordance with the method of JIS-Z-8803.

[0111] The CMC may be one type, or a combination of two or more types of CMC with different DS values, viscosities, molecular weights, etc.

[0112] (Synthetic Rubber Binder) As the synthetic rubber binder, one or more selected from the group consisting of styrene butadiene rubber (SBR), nitrile butadiene rubber, methyl methacrylate butadiene rubber, chloroprene rubber, carboxy-modified styrene butadiene rubber, and latexes of these synthetic rubbers can be used. Among these, styrene butadiene rubber (SBR) is preferred.

[0113] Here, the average particle size (D50) of the SBR is preferably 50 to 300 nm, and more preferably 50 to 200 nm. If the average particle size (D50) of the SBR is too large, the SBR will not adhere uniformly to the active material, reducing its binder function and resulting in a problem of high electrical resistance. If the average particle size (D50) of the SBR is too small, the SBR will cover the active material, resulting in a problem of high electrical resistance.

[0114] The glass transition temperature (Tg) of the SBR is preferably −50° C. to 50° C. When the glass transition temperature (Tg) is within the above range, the SBR mixes well with the carboxymethyl cellulose and / or a salt thereof contained in the negative electrode mixture composition and the negative electrode composition of the present invention, and has appropriate flexibility when formed into a negative electrode layer, so that the electrical resistance is less likely to be high.

[0115] When CMC and SBR are used in combination as the negative electrode binder, it is preferable to use 50 to 500 parts by mass of SBR per 100 parts by mass of CMC on a solids basis, from the viewpoint of obtaining optimal binder performance.

[0116] The content ratio of the negative electrode binder in the negative electrode active material layer and the dispersant contained in the negative electrode composition is preferably 1 to 100 parts by mass, and more preferably 2 to 50 parts by mass, of the dispersant per 100 parts by mass of the negative electrode binder, based on the solid content, from the viewpoint of containing the dispersant in a balanced manner in amounts necessary and sufficient to exhibit the respective effects.

[0117] (Conductive Aid) The negative electrode active material layer contains a conductive aid. Examples of the conductive aid include conductive carbon such as carbon black, acetylene black, and ketjen black. The content of the conductive aid in the negative electrode active material layer is usually 0.01 to 20 mass %, and preferably 0.1 to 10 mass %, based on the solid content.

[0118] (Method for Producing Negative Electrode) The negative electrode of the present invention can be obtained, for example, by obtaining a slurry-like negative electrode mixture composition containing the negative electrode composition of the present invention, a negative electrode binder, a conductive auxiliary, and other auxiliary agents used as needed, and a solvent, and then applying the slurry to a current collector and drying the mixture. This gives a negative electrode having a negative electrode active material layer formed on the current collector.

[0119] The method for producing the negative electrode mixture composition is not particularly limited. For example, a method can be used in which the negative electrode composition of the present invention and the negative electrode binder are dissolved or dispersed in a solvent, and other materials used in the negative electrode mixture composition are added thereto, and the mixture is mixed while stirring as needed. Alternatively, a method can be used in which the negative electrode composition of the present invention, the negative electrode binder, the conductive auxiliary, and other auxiliary agents used as needed are first mixed, and then a solvent is added thereto, and the mixture is mixed while stirring as needed. The properties of the negative electrode mixture composition are also not particularly limited. For example, the negative electrode mixture composition can be in a liquid, paste, slurry, or other form, and any of these may be used.

[0120] The solvent used in the negative electrode mixture composition is preferably an aqueous solvent. The type of aqueous solvent is not particularly limited, but is preferably water, a water-soluble organic solvent, or a mixed solvent thereof, and more preferably water.

[0121] The water-soluble organic solvent is an organic solvent that dissolves in water, and examples thereof include methanol, ethanol, 2-propanol, butanol, glycerin, acetone, methyl ethyl ketone, 1,4-dioxane, N-methyl-2-pyrrolidone, tetrahydrofuran (THF), N,N-dimethylformamide (DMF), N,N-dimethylacetamide, dimethyl sulfoxide (DMSO), acetonitrile, methyl succinate triglycol diester, acetic acid, and combinations thereof.

[0122] When the mixed solvent is used as the aqueous solvent, the amount of the water-soluble organic solvent in the mixed solvent is preferably 10% by mass or more, more preferably 50% by mass or more, and even more preferably 70% by mass or more. There is no upper limit to this amount, but it is preferably 95% by mass or less, more preferably 90% by mass or less. Furthermore, the aqueous solvent may contain a water-insoluble organic solvent as long as the effects of the invention are not impaired.

[0123] Examples of methods for applying the negative electrode mixture composition to the current collector include blade coating, bar coating, and die coating, with blade coating being preferred. For example, blade coating can be achieved by casting the negative electrode mixture composition onto the current collector using a coating device such as a doctor blade. The coating method is not limited to the specific example described above, and can also be achieved by discharging the negative electrode mixture composition from an extrusion-type injector having a slot nozzle onto a running current collector wound around a backup roll. In blade coating, after casting, if necessary, drying can be performed by heating (for example, at a temperature of 80 to 120°C, for example, for 4 to 12 hours) or applying pressure by a roll press or the like to obtain a negative electrode active material layer.

[0124] The shape of the electrode is not particularly limited, but is usually a sheet. The thickness of a sheet-shaped electrode plate (the thickness of the negative electrode active material layer formed from the negative electrode mixture composition, excluding the current collector portion) is difficult to specify because it depends on the composition and production conditions of the composition, but is usually 30 to 150 μm.

[0125] (Current Collector for Negative Electrode) Any electrical conductor that does not cause a fatal chemical change in the electrode or battery can be used as the current collector.

[0126] Examples of materials for the negative electrode current collector include stainless steel, nickel, copper, titanium, carbon, and copper or stainless steel surfaces treated with carbon, nickel, titanium, or silver. Among these, copper or a copper alloy is preferred, and copper is more preferred. Examples of the shape of the current collector include mesh, punched metal, foam metal, and foil processed into a plate shape, with foil processed into a plate shape being preferred.

[0127] (Lithium-ion battery) The secondary battery including the above-described negative electrode of the present invention is preferably a lithium-ion battery (lithium-ion secondary battery). A lithium-ion secondary battery may have a structure in which positive electrodes and negative electrodes are alternately stacked with separators interposed therebetween and wound many times. A lithium-ion secondary battery can be obtained by placing a stack of the wound positive electrode, separator, and negative electrode many times into a battery container, injecting a nonaqueous electrolyte, and sealing the container.

[0128] (Positive Electrode) The positive electrode has, for example, a positive electrode current collector and a positive electrode active material layer.

[0129] The positive electrode active material layer contains one or more positive electrode active materials capable of absorbing and releasing lithium ions, and may contain other materials such as a positive electrode binder, a positive electrode conductive additive, and a dispersant as necessary. In this case, details regarding the positive electrode binder and the positive electrode conductive additive are the same as those for the negative electrode binder and the negative electrode conductive additive already described. Examples of the positive electrode binder include carboxymethyl cellulose and / or its salt, synthetic rubber binders, and polytetrafluoroethylene (PTFE), which are listed as negative electrode binders.

[0130] (Positive electrode active material) The positive electrode active material is LiFePO ４ , LiMe ｘ O ｙ (Me represents a transition metal including at least one of Ni, Co, and Mn, and x and y represent arbitrary numbers.)-based positive electrode active materials are preferred.

[0131] (Positive Electrode Current Collector) Examples of materials for the positive electrode current collector include metals such as aluminum and stainless steel, with aluminum being preferred.

[0132] (Separator) The separator may be, for example, a microporous membrane or nonwoven fabric made of polyolefin such as polyethylene or polypropylene, and may be impregnated with a nonaqueous electrolyte.

[0133] (Non-aqueous electrolyte) The non-aqueous electrolyte usually contains a lithium salt and a non-aqueous solvent. Examples of the lithium salt include LiPF ６ , LiAsF ６ , LiBF ４ , LiClO4, etc. Examples of the non-aqueous solvent include ethylene carbonate, diethyl carbonate, dimethyl carbonate, propylene carbonate, butylene carbonate, and methyl ethyl carbonate. One type of non-aqueous solvent may be used alone, or two or more types may be used in combination. The concentration of the lithium salt in the non-aqueous electrolyte is usually 0.5 to 2.5 mol / L.

[0134] The shape of the lithium ion secondary battery is not particularly limited, and may be cylindrical, prismatic, flat, coin, button, sheet, etc. The material of the battery container is not particularly limited as long as it can prevent moisture from entering the battery, and examples thereof include metals, laminates of aluminum, etc.

[0135] The negative electrode composition of the present invention contains a lignin component containing a specific lignin derivative, thereby providing excellent dispersibility for silicon-based negative electrode active materials. A negative electrode obtained by adding this negative electrode composition has uniform dispersion of the silicon-based negative electrode active material, forming an effective conductive path. Therefore, lithium-ion batteries using the negative electrode of the present invention are prevented from irreversible capacity loss associated with electrical discontinuity due to volumetric changes in the negative electrode active material during charge / discharge cycles, resulting in excellent battery performance, such as capacity retention.

[0136] Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited to these examples.

[0137] <Measurement and Evaluation Methods> In the Examples, Comparative Examples, and Reference Examples, measurements and evaluations were carried out as follows.

[0138] (Average Particle Diameter of SiOx) In the Examples and Comparative Examples, the average particle diameter of SiOx in the SiOx dispersions obtained in Active Material Dispersibility Tests 1 and 2 was measured using a Zetasizer 3000HSA (manufactured by Malvern). The measurement sample was prepared by placing 2 mL of water in a 4.5 mL polystyrene cuvette, adding 20 μL of the SiOx dispersion, and diluting by gently stirring.

[0139] (Methoxy Group Amount) The methoxy group amount of the lignin derivatives produced in each production example was measured by the methoxy group quantification method according to the Viebock and Schwappach method (see "Lignin Chemical Research Methods," pp. 336-340, 1994, published by Uni Publishing Co., Ltd.).

[0140] (Amount of Extractable Components) The amount of extractable components was measured by the method for measuring hexane extractable substances described in JIS K 0102:2019.

[0141] (S content) The sulfo group (—SO ) of the lignin derivative produced in each production example ３ The S content of the lignin sample (M) was calculated using the following formula: S content (mass%) = total S content (mass%) - inorganic S content (mass%) (The S content in the formula indicates the S content relative to the solid content of the lignin sample.) In the formula, the total S content was determined by ICP atomic emission spectroscopy. The inorganic S content was calculated using SO 2 determined by ion chromatography. ３ Ion content, SO ４ Ion content and S ２ O ３ The total ionic content was used in the calculation.

[0142] (Total Decomposition Product Yield by Alkaline Nitrobenzene Oxidation) The total decomposition product yield by alkaline nitrobenzene oxidation of the lignin derivatives produced in each Production Example was measured by the method described in "Plant Cell Wall Experimental Methods" (see "Plant Cell Wall Experimental Methods," pp. 128-131, 2016, published by Hirosaki University Press). The total decomposition product yield was calculated as the ratio (w / w%) of the total weight of the six decomposition products (p-hydroxybenzaldehyde, p-hydroxybenzoic acid, vanillin, vanillic acid, syringaldehyde, and syringic acid) obtained in the measurement to the solid content of the sample.

[0143] (Weight-average molecular weight, polydispersity index) The weight-average molecular weight and polydispersity index of the lignin derivatives produced in each production example were measured / calculated by the methods described in the specification.

[0144] (Discharge Capacity (Charge / Discharge Rate Test)) The charge / discharge rate test for the coin-type lithium-ion secondary batteries prepared in the Examples and Comparative Examples was performed using a Nagano Corporation BTS2004 in a thermostatic chamber at 25°C. The coin-type lithium-ion secondary batteries were subjected to 52 cycles, with one cycle consisting of a charge treatment followed by a discharge treatment. The charge treatment conditions were a constant current / constant voltage (CC-CV) method (CC current 0.2 C, CV voltage 4.2 V, and end current 0.02 C) for all cycles. The end voltage for the discharge treatment was set to 3.0 V. The first cycle was performed at a constant current of 0.2 C, and the discharge capacity (mAh / g) after one cycle was measured. From then until the 52nd cycle, the constant current for the discharge treatment was set as follows, and the discharge capacity (mAh / g) was measured after each cycle. (Constant current for discharge treatment in each cycle) 2 to 10 cycles: Constant current for discharge treatment of 0.2 C 11 to 20 cycles: Constant current for discharge treatment of 1 C 21 cycle: Constant current for discharge treatment of 0.2 C 22 to 31 cycles: Constant current for discharge treatment of 2 C 32 cycle: Constant current for discharge treatment of 0.2 C 33 to 42 cycles: Constant current for discharge treatment of 3 C 43 to 52 cycles: Constant current for discharge treatment of 0.2 C

[0145] (Capacity Retention Rate) The capacity retention rate was calculated from the discharge capacity (mAh / g) in each cycle test described above using the formula "Capacity Retention Rate = Discharge Capacity after 52 Cycles (mAh / g) / Discharge Capacity after 1 Cycle (mAh / g) × 100." The results are shown in Table 2.

[0146] (Production Example 1) (Production of Highly Modified Lignin Derivative A) Wood chips (Radiata pine) were subjected to a sulfite treatment based on the sulfite cooking method. ２ A sodium sulfite solution with a concentration of 4 g / 100 mL was used, and the treatment was carried out at 140°C, pH 2, and for 4 hours. The intermediate composition was then filtered and dehydrated to obtain filtrate 1 and pulp (sulfite-treated product). The pulp was then suspended in 5% by mass of NaOH (relative to the pulp solids) and subjected to an alkali treatment. The pulp was then filtered to separate the alkali-treated pulp and the alkali-treated extract, yielding alkali-treated extract 1 as a filtrate. The alkali treatment was carried out by contacting the pulp with 5% by mass of NaOH (relative to the pulp solids) and treating at 100°C for 2 hours.

[0147] The obtained filtrate 1 and alkali-treated extract 1 were mixed at a solids mass ratio of 9:1 (filtrate 1 / alkali-treated extract 1), to obtain raw material 1. The obtained raw material 1 was concentrated using a rotary evaporator until the solids content reached 50%. The pH of the solution was then adjusted to 4.5 with NaOH and powdered using a spray dryer. The obtained powder was dissolved in water to prepare an aqueous solution with a solids content of 25%, adjusted to pH 13 with 40% NaOH, and then subjected to alkaline air oxidation at 160°C for 120 minutes. 70% sulfuric acid was then added to adjust the pH to 3, and the precipitate was separated and precipitated. The obtained precipitate was washed with water until the filtrate became neutral, and 20 parts of the precipitate was suspended in 80 parts of water. The suspension was heated to 60°C, and 40% NaOH was added with stirring until the pH reached 9, to completely dissolve the precipitate. The resulting solution was powdered using a spray dryer to obtain highly modified lignin derivative A (methoxy group content: 11.9% by mass, extractable component content: 0.7% by mass, extractable component content / methoxy group content: 0.06, S content of sulfo groups: 1.6% by mass, total decomposition product yield by nitrobenzene oxidation: 7.1%).

[0148] (Production Example 2) (Production of Highly Modified Lignin Derivative B) Wood chips (Radiata pine) were subjected to a sulfite treatment based on the sulfite cooking method. ２ A sodium sulfite solution with a concentration of 2.5 g / 100 mL was used, and the treatment temperature was 140°C, pH 3, and treatment time was 4 hours. Next, the intermediate composition was filtered and dehydrated to obtain filtrate 2 and pulp (sulfite-treated product). Subsequently, the pulp was suspended in 5% by mass of NaOH (relative to the pulp solids) and subjected to an alkali treatment. The pulp was then filtered to separate the alkali-treated pulp and the alkali-treated extract, and alkali-treated extract 2 was obtained as a filtrate. The alkali treatment was carried out under conditions of contact with 5% by mass of NaOH (relative to the pulp solids) and treatment at 100°C for 2 hours.

[0149] The obtained filtrate 2 and alkali-treated extract 2 were mixed at a solids mass ratio of filtrate 2 / alkali-treated extract 2 of 9 / 1 to obtain raw material 2. The obtained raw material 2 was concentrated using a rotary evaporator until the solids content reached 50%. The pH of the solution was then adjusted to pH 4.5 with NaOH and powdered using a spray dryer. The obtained powder was dissolved in water to prepare an aqueous solution with a solids content of 25%. The pH was adjusted to 12 with 40% NaOH and then subjected to alkaline air oxidation at 150°C for 120 minutes. 70% sulfuric acid was then added to adjust the pH to 3, and the precipitate was separated and precipitated. The obtained precipitate was washed with water until the filtrate became neutral, and 20 parts of the precipitate was suspended in 80 parts of water. The suspension was heated to 60°C and 40% NaOH was added with stirring until the pH reached 9, and the precipitate was completely dissolved. The resulting solution was powdered using a spray dryer to obtain highly modified lignin derivative B (methoxy group content: 11.8% by mass, extractable component content: 1.1% by mass, extractable component content / methoxy group content: 0.10, S content of sulfo groups: 2.7% by mass, total decomposition product yield by nitrobenzene oxidation: 8.9%).

[0150] (Production Example 3) (Production of Highly Modified Lignin Derivative C) Raw material 1 containing alkali-treated extract 1 prepared in Production Example 1 was concentrated using a rotary evaporator until the solid content reached 50%. The pH of the solution was then adjusted to 4.5 with NaOH and powdered using a spray dryer. The resulting powder was dissolved in water to prepare an aqueous solution with a solid content of 25%. This was then dialyzed for 3 days using a dialysis membrane (molecular weight cutoff: 20,000, Spectra / Por cellulose ester dialysis tubing). The solution in the dialysis tubing was collected, concentrated until the original volume reached 25%, and powdered using a spray dryer to obtain dialyzed product 1. The following materials, including dialyzed product 1, were charged in predetermined amounts into a 3-L autoclave equipped with a stirrer and temperature controller. Dialyzed product 1: 500 g, sodium hydroxide: 75 g, water: 1,500 g.

[0151] The mixture was heated to 140°C under stirring and maintained at this temperature for 2 hours. Then, it was cooled to 70°C, and air was blown into it at 500 mL / min for 3 hours. The resulting solution was powdered using a spray dryer to obtain highly modified lignin derivative C (methoxy group content: 9.7% by mass, extractable component content: 0.2% by mass, extractable component content / methoxy group content: 0.02, sulfur content in sulfo groups: 5.6% by mass, total decomposition product yield by nitrobenzene oxidation: 7.1%).

[0152] (Production Example 4) (Production of Highly Modified Lignin Derivative D) Wood chips (radiata pine) were alkali-treated using the Kraft cooking method. The alkali treatment was carried out using a rotary reactor under the following conditions: active alkali (relative to bone-dry chips): 20%, sulfidity: 25%, liquor ratio: 3.2 L / kg, reaction temperature: 165°C, reaction time: 180 minutes. The reaction solution used in the alkali treatment was prepared by dissolving sodium hydroxide and sodium sulfide in water to an active alkali concentration of 50 g / L. After the reaction, filtration was carried out to obtain alkali-treated extract 3 as the filtrate. Carbon dioxide was passed through alkali-treated extract 3 to lower the pH of the black liquor to 10, and primary filtration was carried out. The precipitate obtained by primary filtration was dispersed in ion-exchanged water, and sulfuric acid was added dropwise to lower the pH to 2, followed by secondary filtration. The precipitate obtained by secondary filtration was washed with water and then dried to obtain filtered precipitate 1. Thermometer, stirrer, 1 L separable flask equipped with a reflux condenser, 500 parts of a solution of dried filtered precipitate 1 dissolved in 40% NaOH to a pH of 10 so as to have a solids content of 17%, 17 parts of sodium sulfite, 12 parts of a 37% formaldehyde solution were charged, and the mixture was reacted for 24 hours under stirring at 95 ° C. After cooling to room temperature, the resulting solution was powdered with a spray dryer to obtain a highly modified lignin derivative D (methoxy group amount: 10.1 mass%, extractable component amount: 1.0 mass%, extractable component amount / methoxy group amount: 0.10, sulfo group S content: 4.4 mass%, total decomposition product yield by nitrobenzene oxidation: 4.7%).

[0153] (Production Example 5) (Production of Highly Modified Lignin Derivative E) Wood chips (radiata pine) were alkali-treated based on the soda cooking method. The alkali treatment was carried out using a rotary reactor under the following conditions. Sodium hydroxide and anthraquinone were added to the rotary reactor containing the chips so that the amount was 25 wt% (based on the solid content of the chips) and 0.02 wt% (based on the solid content of the chips), respectively, and ion-exchanged water was added to a liquid ratio of 5.0 L / kg. Steam was then blown into the mixture while rotating, and the mixture was heated to 160°C and reacted for 4 hours. After the reaction, filtration was carried out to obtain alkali-treated extract 4 as the filtrate. Sulfuric acid was added dropwise to alkali-treated extract 4 to lower the pH to 2, and filtration was carried out. The precipitate obtained by filtration was washed with water and then dried to obtain filtered precipitate 2. Thermometer, stirrer, 1 L separable flask equipped with a reflux condenser, 500 parts of a solution of dried filtered precipitate 2 dissolved in 40% NaOH to a pH of 10 so as to have a solids content of 17%, 8.5 parts of sodium sulfite, 6.0 parts of a 37% formaldehyde solution were charged and reacted for 24 hours under stirring at 95 ° C. After cooling to room temperature, the resulting solution was powdered with a spray dryer to obtain a highly modified lignin derivative E (methoxy group amount: 10.6% by mass, extractable component amount: 1.0% by mass, extractable component amount / methoxy group amount: 0.09, sulfo group S content: 3.0% by mass, total decomposition product yield by nitrobenzene oxidation: 3.7%).

[0154] (Production Example 6) (Production of highly modified lignin derivative F) A thermometer, a stirrer, and a reflux condenser were attached to a 1 L separable flask. 500 parts of a solution obtained by dissolving the same dried filtered precipitate 2 obtained in Production Example 5 in 40% NaOH to a pH of 10 so that the solid content was 17%, 2.1 parts of sodium sulfite, and 1.5 parts of a 37% formaldehyde solution were added, and the mixture was reacted for 24 hours under stirring at 95 ° C. After cooling to room temperature, the resulting solution was powdered with a spray dryer to obtain a highly modified lignin derivative F (methoxy group amount: 11.2 mass%, extractable component amount: 1.1 mass%, extractable component amount / methoxy group amount: 0.10, sulfo group S content: 0.4 mass%, total decomposition product yield by nitrobenzene oxidation: 3.5%).

[0155] (Production Example 7) (Production of Lignosulfonate A) The filtrate 1 obtained in Production Example 1 was concentrated using a rotary evaporator to a solids content of 50%. The pH of the solution was then adjusted to 4.5 with NaOH and powdered using a spray dryer. The resulting powder was dissolved in water to prepare an aqueous solution with a solids content of 25%. This solution was then dialyzed for 3 days using a dialysis membrane (molecular weight cutoff: 20,000, Spectra / Por cellulose ester dialysis tubing). The solution in the dialysis tubing was collected and concentrated to a concentration of 25%. The concentrate was then powdered using a spray dryer to obtain Lignosulfonate A (methoxy group content: 11.1% by mass, extractable component content: 0.03% by mass, extractable component content / methoxy group content: 0.003, sulfur content in sulfo groups: 6.7% by mass, total decomposition product yield by nitrobenzene oxidation: 16.0%).

[0156] (Production Example 8) (Production of Lignin Sulfonate B) Lignin sulfonate B was obtained in the same manner as in Production Example 7, except that the number of days for dialysis treatment was changed from 3 days to 2 days (amount of methoxy groups: 9.8% by mass, amount of extracted components: 0.008% by mass, amount of extracted components / amount of methoxy groups: 0.0008, S content in sulfo groups: 6.9% by mass, total yield of decomposition products by nitrobenzene oxidation: 16.2%).

[0157] (Example 1) (Active Material Dispersibility Test 1) The highly modified lignin derivative A obtained in Production Example 1 was added to water to a solids content of 0.17% by mass. Subsequently, SiOx (manufactured by Shin-Etsu Chemical Co., Ltd., product name: KSC-1064) as a silicon-based negative electrode active material was added to a concentration of 3.2% by mass, and the mixture was stirred at 2500 rpm for 30 minutes using a homodisper to obtain a dispersion. The average particle size of the SiOx in the dispersion was measured using a Zetasizer 3000HSA (manufactured by Malvern). The measurement results of the average particle size and the dispersion state immediately after stirring are shown in Table 1.

[0158] (Examples 2 to 8) Active material dispersibility test 1 was performed in the same manner as in Example 1, except that the highly modified lignin derivatives B to F or lignin sulfonates A and B obtained in Production Examples 2 to 8 were used instead of the highly modified lignin derivative A obtained in Production Example 1.

[0159] Comparative Example 1 Active material dispersibility test 1 was performed in the same manner as in Example 1, except that carboxymethyl cellulose (MAC500LC, manufactured by Nippon Paper Industries Co., Ltd.) (DS value: 0.65 mol / C6, 1% viscosity: 4700 mPa·s) was used instead of the highly modified lignin derivative A obtained in Production Example 1.

[0160] Reference Example 1 Active material dispersibility test 1 was carried out in the same manner as in Example 1 except that no dispersant was used. However, due to separation, it was not possible to measure the average particle size.

[0161]

[0162] As shown in Table 1, the dispersants of Examples 1 to 8 successfully dispersed SiOx in water. The highly modified lignin derivatives and lignin sulfonates of each Example were introduced with sulfo groups at a predetermined sulfo group S content, maintaining high water solubility. It is presumed that these highly modified lignin derivatives and lignin sulfonates efficiently adsorbed to SiOx in water, thereby exhibiting excellent dispersibility. The carboxymethyl cellulose of Comparative Example 1 also exhibited dispersibility in SiOx, but the average particle size of the SiOx was larger than that of Examples 1 to 8. Carboxymethyl cellulose is used to improve the dispersibility of the negative electrode active material and to impart a certain viscosity to the active material slurry, thereby efficiently bonding the active material and the current collector. However, it was found that the highly modified lignin derivatives A to F and lignin sulfonates A and B were more suitable as dispersants for SiOx, a silicon-based negative electrode active material.

[0163] Example 9 (Production of a negative electrode mixture composition) SiOx (manufactured by Shin-Etsu Chemical Co., Ltd., product name: KSC-1064) as a silicon-based negative electrode active material and acetylene black (manufactured by Stream Chemical Co., Ltd., 50% acetylene black) as a conductive additive were mixed to prepare a negative electrode mixture composition. Compressed), carboxymethyl cellulose (manufactured by Nippon Paper Industries Co., Ltd., MAC500LC) (DS value: 0.65 mol / C6, 1% viscosity: 4700 mPa s), and the highly modified lignin derivative A (methoxy group amount: 11.9 mass%, extractable component amount: 0.7 mass%, extractable component amount / methoxy group amount: 0.06, sulfo group S content: 1.6 mass%, total decomposition product yield by nitrobenzene oxidation: 7.1%) obtained in Production Example 1 as a dispersant, and styrene butadiene rubber (SBR, manufactured by ENEOS Materials Co., Ltd., product number TRD104A) were mixed so that the solid content mass ratio was 97: 0.5: 0.67: 0.33: 1.5, water was added so that the slurry concentration was 45.6 mass%, and the mixture was stirred well using Mazerustar (manufactured by Kurabo Industries, KK-250S) to obtain a slurry negative electrode mixture composition.

[0164] (Preparation of Negative Electrode Plate) This slurry-like negative electrode mixture composition was applied to a copper foil (NC-WS, manufactured by Furukawa Electric Co., Ltd.) measuring 320 mm in length, 170 mm in width, and 17 μm in thickness using an applicator, and the coating was air-dried for 30 minutes. After that, the coating was dried in a dryer at 60° C. for 30 minutes. The coating was then pressed using a small tabletop roll press (SA-602, manufactured by Tester Sangyo Co., Ltd.) under conditions of 5 kN and a roll peripheral speed of 50 m / min to produce a negative electrode plate with a coating weight of 19.7 g / m. ２ A negative electrode plate with an effective discharge capacity of 2100 mAh / g was obtained.

[0165] (Fabrication of a coin-type lithium-ion secondary battery) The obtained negative electrode plate and LiCoO ２ Positive electrode plate (manufactured by NEI, basis weight 20.56 mg / cm ２ , capacity 3mAh / cm ２) was punched out to a circle with a diameter of 16 mm, and the punched negative and positive plates were vacuum dried at 120 ° C for 12 hours. Similarly, a separator (manufactured by CS Tech, a 20 μm thick polypropylene separator) was punched out to a circle with a diameter of 17 mm and vacuum dried at 60 ° C for 12 hours. Thereafter, the negative plate was placed in a stainless steel circular dish-shaped container with a diameter of 20.0 mm, and then the separator, positive plate, spacer (diameter 15.5 mm, thickness 1 mm), and stainless steel washer (manufactured by Hosen Co., Ltd.) were stacked in this order, and then the circular dish-shaped container was filled with an electrolyte (1 mol / L LiPF ６ 300 μL of a mixture of ethylene carbonate and diethyl carbonate (volume ratio of 1:1) was added to the container, which was then covered with a stainless steel cap via a polypropylene packing and sealed using a coin battery crimping machine (Hosen Co., Ltd.) to obtain a coin-type lithium ion secondary battery.

[0166] The resulting battery was subjected to a charge / discharge rate test, and the discharge capacity was measured and the capacity retention rate was calculated.

[0167] (Examples 10 to 16) Negative electrode mixture compositions were produced, negative electrode plates were fabricated, and coin-type lithium ion secondary batteries were fabricated in the same manner as in Example 9, except that highly modified lignin derivatives B to F or lignin sulfonates A and B were used instead of the highly modified lignin derivative A obtained in Production Example 1. The resulting batteries were also evaluated.

[0168] (Comparative Example 2) In the production of the negative electrode mixture composition, a negative electrode mixture composition was produced in the same manner as in Example 9, except that the highly modified lignin derivative A was not added. SiOx (manufactured by Shin-Etsu Chemical Co., Ltd., product name: KSC-1064) as a silicon-based negative electrode active material, acetylene black (manufactured by Stream Chemical Co., Ltd., 50% compressed) as a conductive additive, carboxymethyl cellulose (manufactured by Nippon Paper Industries Co., Ltd., MAC500LC) (DS value: 0.65 mol / C6, 1% viscosity: 4700 mPa s), and styrene butadiene rubber (SBR, manufactured by ENEOS Materials Co., Ltd., product number TRD104A) were mixed so that the solid content mass ratio was 97:0.5:1.0:1.5. Using this, a negative electrode plate was prepared in the same manner as in Example 9, and a coin-type lithium ion secondary battery was prepared. The resulting battery was also evaluated.

[0169]

[0170] As shown in Table 2, the capacity retention rate of the batteries in Examples 9 to 16, which used a dispersant containing a lignin component, was clearly improved compared to the battery in Comparative Example 2. In Examples 9 to 16, it is presumed that the SiOx negative electrode active material was uniformly dispersed within the electrode, and the other components effectively buffered the volume change of the negative electrode active material during cycling, thereby suppressing irreversible capacity loss due to electrical interruption.

[0171] As shown in Table 2, compared to the batteries using the highly modified lignin derivatives A to F of Examples 9 to 14, which had low sulfur content in the sulfo groups, high extractable component content, and low total decomposition product yield due to nitrobenzene oxidation, the battery using lignin sulfonate A of Example 15, which had high sulfur content in the sulfo groups, low extractable component content, and high total decomposition product yield due to nitrobenzene oxidation, showed a lower capacity retention rate. The battery using lignin sulfonate B of Example 16, which had a lower amount of extractable component content than lignin sulfonate A, showed a slight further decrease in capacity retention rate. To investigate the cause of the different degrees of battery performance improvement in each example, the differences in the active material dispersion performance of the highly modified lignin derivatives A to F and lignin sulfonates A and B were compared in detail using a Zetasizer. To approximate the composition of the negative electrode mixture composition, carboxymethyl cellulose (MAC500LC, manufactured by Nippon Paper Industries Co., Ltd.) (DS value: 0.65 mol / C6, 1% viscosity: 4700 mPa·s) was also used.

[0172] (Example 17) (Active Material Dispersibility Test 2) An aqueous solution was prepared containing carboxymethyl cellulose (manufactured by Nippon Paper Industries Co., Ltd., MAC500LC) (DS value: 0.65 mol / C6, 1% viscosity: 4700 mPa·s) at a solids content of 0.17% by mass, and the highly modified lignin derivative A obtained in Production Example 1 at a solids content of 0.12% by mass. SiOx (manufactured by Shin-Etsu Chemical Co., Ltd., product name: KSC-1064) was then added to the solution to a solid content of 3.2% by mass, and the solution was stirred at 2500 rpm for 30 minutes using a homodisper to obtain a dispersion. The average particle size of the SiOx in the dispersion was measured using a Zetasizer 3000HSA (manufactured by Malvern). The results of the average particle size measurement and the dispersion state immediately after stirring are shown in Table 3.

[0173] (Examples 18 to 24) Active material dispersibility test 2 was performed in the same manner as in Example 17, except that the highly modified lignin derivatives B to F or lignin sulfonates A and B obtained in Production Examples 2 to 8 were used instead of the highly modified lignin derivative A obtained in Production Example 1.

[0174]

[0175] As shown in Table 3, Examples 23 and 24, which used lignin sulfonate in combination with CMC and at a dispersant addition rate of 3.5% by mass relative to SiOx, had larger SiOx particle sizes than Examples 17 to 22, which used highly modified lignin derivatives. The lignin sulfonate used in Examples 23 and 24 had a higher sulfur content in the sulfo group than the highly modified lignin derivatives used in Examples 17 to 22. While the detailed mechanism is unclear, it is presumed that lignin derivatives with a lower sulfur content in the sulfo group are more adsorbed to SiOx and exhibit higher dispersibility. For these reasons, it is presumed that Examples 15 and 16, which used lignin sulfonate, had a relatively small effect on improving capacity retention, as shown in Table 2.

Claims

1. A composition for a negative electrode of a secondary battery, comprising a silicon-based negative electrode active material and a dispersant, the dispersant containing a lignin component containing a lignin derivative, the lignin component having a weight average molecular weight of 6,000 to 35,000, the weight average molecular weight divided by the number average molecular weight being 1.5 to 3.2, the amount of an extractable component per solid content of the lignin component being 0.008 to 2.5 mass%, the amount of a methoxy group per solid content of the lignin component being 3 to 18 mass%, the mass ratio of the amount of an extractable component per solid content of the lignin component to the amount of a methoxy group being 0.0008 to 0.25, the lignin derivative having a functional group represented by the following formula (1), the S content in the functional group being 0.1 to 7.0 mass%. Formula (1): -SO ３ M (wherein M represents a hydrogen atom, a monovalent metal, or a divalent metal) 2. The negative electrode composition according to claim 1, wherein the weight average molecular weight of the lignin component divided by the number average molecular weight is 1.5 to 3.

1.

3. The negative electrode composition according to claim 1 or 2, wherein the amount of extractable components per solid content of the lignin component is 0.01 to 2.5 mass%, and the mass ratio of the amount of extractable components per solid content of the lignin component to the amount of methoxy groups is 0.001 to 0.

25.

4. The negative electrode composition according to claim 1 or 2, wherein the total yield of decomposition products by alkaline nitrobenzene oxidation per solid content of the lignin component is 15% or less.

5. A negative electrode for a secondary battery comprising a negative electrode active material layer containing the negative electrode composition according to claim 1 or 2, a negative electrode binder, and a conductive assistant.

6. A secondary battery comprising the negative electrode according to claim 5.

7. The negative electrode composition according to claim 1 or 2, wherein the secondary battery is a lithium ion battery.

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