Negative electrode for lithium-ion batteries, lithium-ion batteries, manufacturing method of negative electrode for lithium-ion batteries, and manufacturing method of lithium-ion batteries.

Abstract

[Technical Problem to be Solved]: To provide a negative electrode for lithium-ion batteries that improves battery characteristics such as high capacity and cycle performance. [Technical Means for Solving the Problem]: A negative electrode layer 1M containing a negative electrode binder is constructed as follows: the negative electrode binder includes a negative electrode active material, a binder, and hydrophobic cellulose. The negative electrode active material contains Si particles, and the binder is an organic solvent-based binder (e.g., polyimide or polyvinylidene fluoride), and a portion of the hydrophilic groups of the hydrophobic cellulose is replaced by hydrophobic groups. In this way, by using an organic solvent-based binder, the reaction between water and Si can be prevented, and electrode characteristics can be improved. Furthermore, under normal circumstances, using nano-Si requires increasing the amount of organic solvent-based binder added, and battery capacity and cycle performance (battery life) decrease; however, by adding hydrophobic CeNF, battery capacity and cycle performance (battery life) can be improved.

Description

Technical Field

[0001] This invention relates to a negative electrode for lithium-ion batteries, a lithium-ion battery, a method for manufacturing a negative electrode for lithium-ion batteries, and a method for manufacturing lithium-ion batteries. Prior Technology

[0002] The application of secondary batteries is expanding from electronic devices to automobiles, large-scale energy storage systems, and other fields. Among them, lithium-ion batteries (secondary batteries) that are small, lightweight, and have high energy density are attracting much attention.

[0003] The negative electrode of a lithium-ion battery consists of a current collector and a negative electrode binder layer disposed on top of it. In addition to the negative electrode active material, the negative electrode binder layer also contains binders and other materials.

[0004] For example, Patent Document 1 discloses an adhesive, which is a non-aqueous adhesive for lithium-ion battery electrodes composed of cellulose nanofibers and thermoplastic fluororesin; wherein the cellulose nanofibers have a fiber diameter of 0.002 μm or more and 1 μm or less, a fiber length of 0.5 μm or more and 10 mm or less, and an aspect ratio (fiber length of cellulose nanofibers / fiber diameter of cellulose nanofibers) of 2 or more and 100,000 or less.

[0005] [Previous Technical Documents] [Patent Literature] [Patent Document 1] International Publication No. 2019 / 064583 Summary of the Invention

[0006] [The problem the invention aims to solve] In the negative electrode of lithium-ion batteries, various materials are being explored for the purpose of increasing capacity. Among these, silicon (Si) has a higher theoretical capacity than graphite and is considered a promising negative electrode active material.

[0007] However, because the Si system expands in volume with the insertion of lithium, the negative electrode active material expands and contracts repeatedly due to repeated charging and discharging of the battery, making it easy for Si (particles) to be stripped from the electrode, resulting in a problem of lower cycle characteristics (shorter battery life).

[0008] To address these issues, the study investigated reducing the impact of volume expansion by nano-sizing (micro-refining) Si. On the other hand, a negative electrode was formed by adding a negative electrode active material or binder to a solvent to form a slurry, which was then coated onto a current collector. In this case, when Si is nano-sized (micro-refined), the surface area of ​​the Si nanoparticles (nano-Si) increases, and the amount of binder used to bind the nano-Si particles together increases. Furthermore, when Si reacts with water and an aqueous binder is used, hydrogen gas is generated, which degrades battery performance (Problem 1). Moreover, even when using organic binders, the increased amount of binder results in lower cycle performance (shorter battery life) (Problem 2).

[0009] Therefore, one embodiment of this specification aims to provide a negative electrode and a lithium-ion battery using the negative electrode, which can improve battery characteristics such as high capacity and cycle characteristics (battery life). Furthermore, it provides a method for manufacturing a negative electrode and a method for manufacturing a lithium-ion battery, which can improve battery characteristics such as high capacity and cycle characteristics (battery life).

[0010] The foregoing and other objectives of the present invention, as well as its novel features, will become apparent from the description and drawings herein.

[0011] [Solutions] The negative electrode for lithium-ion batteries disclosed in this case contains: a negative electrode compound, which includes: a negative electrode active material, binder and hydrophobic cellulose; the aforementioned negative electrode active material contains Si particles; and the aforementioned binder is an organic solvent-based binder; wherein, a portion of the hydrophilic cellulose groups of the aforementioned hydrophobic cellulose is replaced by hydrophobic groups.

[0012] The lithium-ion battery disclosed in this case comprises: a negative electrode, which includes: a current collector; and a negative electrode binder layer formed on the aforementioned current collector; a positive electrode; and an electrolyte; wherein the aforementioned negative electrode binder layer comprises: a negative electrode active material, a binder, and hydrophobic cellulose; and the aforementioned negative electrode active material contains Si particles; the aforementioned binder is an organic solvent-based binder; and a portion of the hydrophilic groups of the aforementioned hydrophobic cellulose is replaced by hydrophobic groups.

[0013] The method for manufacturing a negative electrode for lithium-ion batteries disclosed in this case includes: (a) mixing a negative electrode active material, a binder, and hydrophobic cellulose to form a negative electrode slurry; and (b) coating the aforementioned negative electrode slurry onto a current collector; wherein the aforementioned negative electrode active material contains Si particles; the aforementioned binder is an organic solvent-based binder; and a portion of the hydrophilic groups of the aforementioned hydrophobic cellulose is replaced by hydrophobic groups.

[0014] The method for manufacturing a lithium-ion battery disclosed in this case includes: (a) a step of preparing a negative electrode slurry; (b) a step of coating the aforementioned negative electrode slurry onto a current collector to form a negative electrode having the aforementioned current collector and a negative electrode binder layer; (c) a step of laminating the aforementioned negative electrode and a positive electrode through a separator to form an electrode assembly; (d) a step of housing the aforementioned electrode assembly in a battery container; and (e) a step of injecting an electrolyte into the aforementioned battery container after the aforementioned step (d); wherein, the aforementioned step (a) involves mixing a negative electrode active material, a binder, and hydrophobic cellulose to form a negative electrode slurry; and the aforementioned negative electrode active material contains Si particles; the aforementioned binder is an organic solvent-based binder; and a portion of the hydrophilic groups of the aforementioned hydrophobic cellulose is replaced by hydrophobic groups.

[0015] [Benefits of the Invention] The following is a brief explanation of the effects achieved by a representative embodiment of this specification.

[0016] The negative electrode for lithium-ion batteries disclosed in one embodiment of this specification can improve battery characteristics such as high capacity and cycle characteristics (battery life).

[0017] The lithium-ion battery disclosed in one embodiment of this specification can improve battery characteristics such as high capacity and cycle characteristics (battery life).

[0018] According to the method for manufacturing a negative electrode for lithium-ion batteries disclosed in one embodiment of this specification, a negative electrode can be manufactured that can improve battery characteristics such as high capacity and cycle characteristics (battery life).

[0019] According to the method for manufacturing a lithium-ion battery disclosed in an embodiment of this specification, a lithium-ion battery can be manufactured that improves battery characteristics such as high capacity and cycle characteristics (battery life). Simple Explanation of the Diagram

[0020] [Figure 1] is a schematic diagram showing the positive and negative electrodes of Embodiment 1 and the configuration of a lithium-ion battery using such a battery. [Figure 2] is a schematic diagram showing the positive and negative electrodes of Embodiment 1 and the configuration of the lithium-ion battery using such a battery. [Figure 3] is a diagram showing the modulation steps of hydrophobic CeNF (cellulose nanofibers) dispersed in a solvent. [Figure 4] is a diagram showing an example of the preparation steps for the negative electrode slurry. [Figure 5] is a schematic diagram showing the configuration of the negative electrode manufacturing apparatus of Embodiment 1. [Figure 6] is a perspective view of the appearance of the negative electrode slurry applied using a slotted die. [Figure 7] is a diagram showing an example of the preparation steps for the negative electrode slurry when using a water-based binder. [Figure 8] is a diagram showing the initial characteristics of a button cell battery. [Figure 9] is a graph showing the initial characteristics of a battery using an aqueous solvent. [Figure 10] is a graph showing the cycle characteristics of button batteries (samples 1, 2, 5, and 6). [Figure 11] is a graph showing the cycle characteristics of button cells with different amounts of hydrophobic CeNF added. [Figure 12] shows the cycle characteristics of a button cell with a graphite to nano-Si ratio of 8:2. [Figure 13] is a cross-sectional perspective view showing the structure of a cylindrical lithium-ion battery. [Figure 14] is a cross-sectional view showing the preparation method of negative electrode slurry using an extruder. [Figure 15] is a cross-sectional view showing the preparation method of positive electrode slurry using an extruder. [Figure 16] is a diagram showing the modulation steps of hydrophobic CeNF dispersed in an organic solvent. Implementation

[0021] The embodiments will now be described in detail based on examples and drawings. Furthermore, in all the drawings used to describe the embodiments, components with the same function will be represented by the same symbols, and repeated descriptions will be omitted. Additionally, in the following embodiments, when the range is represented as A~B, unless otherwise specified, it means A and above and B and below.

[0022] (Implementation Form 1) Figures 1 and 2 schematically show the negative and positive electrodes of this embodiment and the configuration of the lithium-ion battery using these electrodes. Figure 1(A) shows the configuration of the negative electrode, Figure 1(B) shows the configuration of the positive electrode, and Figure 1(C) shows the internal configuration of the lithium-ion battery.

[0023] As shown in Figure 1(A), the negative electrode is composed of a current collector 1S and a negative electrode flux layer 1M disposed on top of it; as shown in Figure 1(B), the positive electrode is composed of a current collector 2S and a positive electrode flux layer 2M disposed on top of it. Furthermore, as shown in Figure 1(C), the lithium-ion battery has a negative electrode, a positive electrode, and a separator disposed between them, with the negative and positive electrodes arranged opposite each other such that the negative electrode flux layer 1M and the positive electrode flux layer 2M are each in contact with the separator SP (see also Figure 2). Also, as shown in Figure 1(C), a portion of the current collector 1S of the negative electrode becomes the negative terminal 1T, and a portion of the current collector 2S of the positive electrode becomes the positive terminal 2T. The aforementioned stack of the negative electrode, positive electrode, and separator (also called an electrode assembly) is contained together with the electrolyte in a battery container (a bag, battery can, etc., made of stacked thin films), and sealed with the negative terminal 1T and the positive terminal 2T protruding (exposed).

[0024] By adding various electrode materials such as electrode active materials and binders to a solvent (organic solvents and aqueous solvents, etc.) to form a slurry, then coating this onto a current collector, and drying it, a negative electrode and a positive electrode are formed.

[0025] In this embodiment, nano-Si can be used as the negative electrode active material in the negative electrode binder layer. Furthermore, an adhesive is used in the negative electrode binder layer to bond the aforementioned negative electrode active material. Additionally, hydrophobic cellulose is used as an additive in the negative electrode binder layer.

[0026] By using such a negative electrode binder layer, battery characteristics such as high capacity and cycle life can be improved. In particular, even when using nano-Si and organic solvent-based binders, battery characteristics such as high capacity and cycle life can still be improved.

[0027] Next, the negative electrode, positive electrode, separator, and electrolyte of the lithium-ion battery in this embodiment will be described in sequence.

[0028] [negative electrode] The negative electrode (negative electrode plate, negative electrode sheet) is as described above, having a current collector and a negative electrode binder layer disposed on top of it. The negative electrode binder layer is disposed on top of the current collector and contains at least a layer of negative electrode active material. In this embodiment, the negative electrode active material contains nano-Si. Furthermore, the negative electrode binder layer contains an adhesive for bonding the aforementioned negative electrode active material. Next, the negative electrode binder layer contains hydrophobic cellulose as an additive. Moreover, other additives may also be included in the negative electrode binder layer, such as thickeners, dispersants, and conductive agents (also known as conductive additives).

[0029] For the current collector used as the negative electrode, a thin metal film can be used. For the metal material, copper, lithium (Li), stainless steel, etc., can be used. Alternatively, a plating of nickel or the like can be used on the surface of such a material.

[0030] (Negative electrode active material) As the negative electrode active material, nano-Si, a Si (silicon) based material, can be used. This nano-Si system is composed of nano-sized Si particles. Alternatively, SiO (SiOx) can be formed on the Si surface, or carbon can be used to coat the nano-Si. The thickness of the coating layer is preferably around 1 nm to 10 nm.

[0031] There are no limitations on the methods for miniaturizing (nano-sizing) Si. For example, Si microparticles can be obtained by vaporizing Si compounds and then cooling them. The average particle size (median particle size, D50) of nano-Si is preferably 10 nm to 500 nm, more preferably 20 nm to 200 nm. Generally, the finer the Si particle size, the higher the electrode capacity. However, on the other hand, due to the increased surface area of ​​Si, the amount of binder needs to be increased to prevent peeling due to expansion and contraction during charging and discharging. Therefore, it is preferable to select the particle size according to the desired battery capacity. The average particle size (median particle size, D50) of nano-Si can be determined by methods such as laser diffraction / scattering particle size distribution measurement. In addition, Si particles can be observed using electron microscopes such as SEM and TEM, and atomic force microscopes such as AFM and SPM, and the particle size can be determined by these observations.

[0032] Regarding the negative electrode active material, nano-Si and other materials can be used in combination. Carbon-based materials such as graphite, hard carbon (difficult-to-graphitize carbon), and soft carbon (easily-graphitize carbon) can be used as negative electrode active materials that can be used in combination with nano-Si. Additionally, lithium titanate (Li₄Ti₅O₁₂) can also be used. From the viewpoint of improving cycle performance, it is preferable to use a combination of carbon-based materials, especially graphite.

[0033] As mentioned above, theoretically, the capacity should increase by using nano-Si as the negative electrode active material. However, in reality, the battery capacity has not increased by much, and the cycle performance tends to decrease. This is believed to be because the nano-sizing of particles, designed to reduce the volume expansion of Si, increases the surface area of ​​the particles, leading to an increase in binder. However, in this embodiment, by adding hydrophobic CeNF, the decrease in battery capacity can be suppressed even with the increased binder, thus achieving the original effect of increasing battery capacity with Si. This is believed to be due to the combination of hydrophobic CeNF and binder, which suppresses the volume expansion of Si. Furthermore, this suppression of volume expansion is believed to inhibit the stripping of the negative electrode active material, thereby improving cycle performance (battery life).

[0034] (Adhesive) Adhesives serve to bond the negative electrode materials, such as the active electrode material, within the negative electrode adhesive layer together, and to bond the negative electrode material to the current collector. Adhesives used in electrode adhesive layers can be categorized into aqueous and organic solvent-based types.

[0035] As for water-based adhesives, materials such as styrene-butadiene copolymer rubber (SBR), polyvinyl alcohol, polyacrylic acid, and carboxymethyl cellulose can be used, and they can be used in a state of dispersion in an aqueous solvent (e.g., water).

[0036] Regarding organic solvent-based adhesives, materials such as polyvinylidene fluoride (PVdF) and polyimide (PI) can be used, and these can be added to an organic solvent. PVdF is known as a solvent-based adhesive, and it can be used when dissolved in organic solvents such as N-methyl-2-pyrrolidone (NMP). Polyimide (PI) is known as a reactive adhesive, and it can be used when the PI precursor is dissolved or dispersed in a solvent such as NMP. A cross-linking reaction is initiated through amide formation (dehydration and cyclization) by heat treatment, resulting in a tough PI.

[0037] In this embodiment, an organic solvent-based binder is used. When using an aqueous binder (described later), the reaction between water and Si produces hydrogen gas, which degrades the electrode characteristics (see Figure 9). Therefore, by using an organic solvent-based binder, the reaction between water and Si can be prevented, and the electrode characteristics can be improved.

[0038] Furthermore, generally speaking, using nano-Si requires increasing the amount of organic solvent-based binder, which reduces battery capacity and cycle characteristics (battery life). However, in this embodiment, by adding hydrophobic CeNF as an additive, battery capacity and cycle characteristics (battery life) can be improved even when using organic solvent-based binders (see Figures 10, 11, etc.).

[0039] (Hydrophobic cellulose) Cellulose (Cell-OH) is a carbohydrate that can be represented by (C 12H 20O 10)n. For example, it can be represented by the following chemical structural formula (Chemical Formula 1). In this chemical structural formula, n, which represents the average number of repetitions, is a number greater than or equal to 1, preferably 10 to 10000, and more preferably 50 to 2000.

[0040] [Chemical Formula 1]

[0041] Furthermore, as shown in the following chemical structural formula (Chemical Formula 2), a portion of the multiple hydroxyl groups of the carbohydrate represented by (C 12H 20O 10) n can be replaced with a group having hydroxyl groups (for example, -R-OH of -CH 2OH (R represents a divalent hydrocarbon group)).

[0042] [Chemical Formula 2]

[0043] As can be seen from the aforementioned chemical structural formulas (Formula 1 and Formula 2), cellulose possesses hydroxyl groups (hydrophilic groups). These hydroxyl groups (hydrophilic groups) are hydrophobically treated (oil-loving treated) using a hydrophobic agent (e.g., a carboxylic acid compound). That is, a portion of the hydroxyl group (-OH) in cellulose is replaced with a hydrophobic group. Specifically, a portion of the hydroxyl group in cellulose is esterified using a carboxylic acid compound (R-CO-OH). In other words, a portion of the hydroxyl group (-OH) in cellulose is formed into an ester bond (-O-CO-R, carboxyl group). Furthermore, it is not necessary to replace all the hydroxyl groups in cellulose with hydrophobic groups; only a portion needs to be replaced. An example of the esterification (hydrophobication) reaction of cellulose is represented by the following reaction formula.

[0044] [Chemical Formula 3]

[0045] Regarding hydrophobicating agents, any composition capable of imparting hydrophobic groups to the hydrophilic groups of cellulose is acceptable and is not particularly limited. For example, carboxylic acid compounds can be used. Among these, compounds having two or more carboxyl groups, acid anhydrides of compounds having two or more carboxyl groups, etc., are preferred. Among compounds having two or more carboxyl groups, compounds having two carboxyl groups (dicarboxylic acid compounds) are preferred.

[0046] Examples of dicarboxylic acid compounds with two carboxyl groups include malonic acid, butaneonic acid, pentaneonic acid, hexaneonic acid, 2-methylpropaneonic acid, 2-methylbutaneonic acid, 2-methylpentaneonic acid, 1,2-cyclohexanedicarboxylic acid, 2-butenedioic acid (maleic acid, trans-butenedioic acid), 2-pentenedioic acid, 2,4-hexadienoic acid, 2-methyl-2-butenedioic acid, 2-methyl-2-pentenedioic acid, 2-methylenebutaneonic acid (iconic acid), phenyl-1,2-dicarboxylic acid (phthalic acid), phenyl-1,3-dicarboxylic acid (isophthalic acid), phenyl-1,4-dicarboxylic acid (terephthalic acid), and ethanedioic acid (oxalic acid). Examples of acid anhydrides containing two carboxyl groups include dicarboxylic acid compounds such as maleic anhydride, succinic anhydride, phthalic anhydride, glutaric anhydride, adipic anhydride, itanic anhydride, pyrolithic anhydride, and 1,2-cyclohexanedicarboxylic anhydride, or acid anhydrides containing a plurality of carboxyl groups. Examples of derivatives of acid anhydrides containing two carboxyl groups include dimethylmaleic anhydride, diethylmaleic anhydride, and diphenylmaleic anhydride, where at least some of the hydrogen atoms are substituted with substituents (e.g., alkyl, phenyl, etc.). Among these, maleic anhydride, succinic anhydride, and phthalic anhydride are preferred from the viewpoint of ease of industrial application and easy vaporization.

[0047] Furthermore, the hydrophilic groups of cellulose can be hydrophobically modified (by carboxylic acid compounds), followed by a secondary treatment with the addition of alkylene oxides to improve hydrophilicity. In addition, two or more of the aforementioned hydrophobicating agents can be added.

[0048] Furthermore, defiberization can also be performed to micronize (nanoscale) cellulose. Defiberization (nanoscale processing) includes chemical and mechanical methods. A combination of these methods can be used. Through this defiberization (nanoscale processing), CeNF with a fiber length (L) of 3 nm or more and 10 μm or less, and an aspect ratio (length L / diameter D) of 0.005 or more and 10000 or less can be obtained. Cellulose fibers micronized to the nanoscale are thus called cellulose nanofibers (CeNF).

[0049] The micronization (nanoization) of cellulose, as described above, can be carried out before or after hydrophobication.

[0050] (Preparation method of hydrophobic CeNF dispersed in solvent) To prevent aggregation and improve dispersibility in slurries, hydrophobic CeNF is preferably used in a solvent-dispersed state.

[0051] Figure 3 is a diagram showing the preparation steps of hydrophobic CeNF dispersed in a solvent. For example, as shown in Figure 3, cellulose (solid, e.g., powder) and succinic anhydride (solid, e.g., plate) are mixed at a temperature above 100°C. For example, mixing is performed using a pressure kneader at 125°C for 20 minutes. The weight ratio of cellulose to succinic anhydride is, for example, 90 wt% (wt%, mass%) and 10 wt%.

[0052] As described above, an ester reaction occurs due to stirring under heating, and hydrophobic cellulose is generated. Afterwards, to remove unreacted succinic anhydride, the mixture is washed with acetone or the like.

[0053] Next, the generated hydrophobic cellulose is dispersed in an aqueous solvent (water and / or alcohols, in this case, water (H₂O)) and subjected to a micronization process (defibrillation, nanonization). For example, a micronization device (starburst) is used to perform a treatment at 245 MPa and 10 Pass to nanonize the cellulose. This allows the acquisition of hydrophobic CeNF dispersed in an aqueous solvent (e.g., water).

[0054] (Preparation steps for negative electrode slurry) Next, the preparation steps for the negative electrode slurry will be explained. The negative electrode slurry is prepared by adding the aforementioned negative electrode active material, organic solvent-based binder, and hydrophobic CeNF (dispersed in water) to an organic solvent. In addition to the above, other additives such as conductive agents and dispersants may also be added. Figure 4 shows an example of the preparation steps for the negative electrode slurry. Referring to Figure 4, an example of the preparation steps for the negative electrode slurry will be explained.

[0055] First, mixture 1 is prepared by mixing an organic solvent-based binder, an organic solvent, and hydrophobic CeNF (dispersed in water). Other additives, such as conductive agents and dispersants, may also be added at this time. Mixture 1 is stirred (e.g., at 1000 rpm for approximately 1 minute). A high-speed mixer (e.g., a homogenizer) can be used for stirring.

[0056] Next, graphite and nano-Si were added to mixture 1 as negative electrode active materials. Then, CNTs and acetylene black (AB) were added as conductive agents, and the mixture was stirred to prepare mixture 2. The mixture was stirred using a high-speed mixer (e.g., a homogenizer), for example at 3000 rpm for about 30 minutes.

[0057] Next, alcohol is added to mixture 2 and stirred to prepare mixture 3. The mixture is stirred using a high-speed mixer (e.g., a homogenizer), for example at 3000 rpm for about 1 minute.

[0058] In this way, a negative electrode slurry can be obtained. The viscosity of the obtained negative electrode slurry is 6200 mPas (35°C), and no air bubbles can be visually observed, unlike the negative electrode slurry 4 described later. Furthermore, the coatability is good; for example, when forming the negative electrode binder layer using the apparatus described later, it was confirmed that there are no defects in the layer caused by air bubbles. Considering coatability, the viscosity of the negative electrode slurry is preferably 3000~5000 mPas.

[0059] As described above, in this embodiment, by using an organic solvent-based binder, it is possible to reduce the bubbles generated in the negative electrode slurry and improve the properties of the negative electrode binder layer.

[0060] Furthermore, in addition to AB and CNT, other conductive agents used as the aforementioned additives can include Ketjen black, carbon nanofibers, etc. Additionally, surfactants can be used as dispersants. Besides dispersants, thickeners and other additives can also be used.

[0061] (Steps for forming the negative electrode) The aforementioned negative electrode slurry is applied to the surface of a current collector (e.g., steel foil) and dried to form a negative electrode mixture layer. In this way, a negative electrode having a current collector (e.g., steel foil) and a negative electrode mixture layer can be formed (see Figure 1(A)).

[0062] The coating method for the negative electrode slurry is not limited; for example, a die-coating machine can be used. Then, by drying the coating layer, a negative electrode flux layer can be formed on the surface of the substrate S. In this way, a negative electrode having a substrate (e.g., steel foil as a current collector) S and a negative electrode flux layer can be formed.

[0063] Figure 5 is a schematic diagram showing the configuration of the negative electrode manufacturing apparatus of this embodiment. The manufacturing apparatus shown in Figure 5 includes: a roll-out section (transfer section) UW for winding out a substrate (current collector) S; and a winding section (transfer section) WD for winding the substrate (current collector) S. The substrate (current collector) S is continuously arranged between the roll-out section UW and the winding section WD. A negative electrode mixture layer (coating layer of negative electrode slurry SL) 1M is formed on the surface (first surface) of the substrate S between the roll-out section UW and the winding section WD, and the negative electrode is completed. According to this manufacturing apparatus, the rolled (strip) substrate S can be continuously processed, and the negative electrode can be formed efficiently. In this specification, the roll-out section UW side is sometimes referred to as the upstream side, and the winding section WD is sometimes referred to as the downstream side.

[0064] Specifically, at least one coating section 20 and a drying section (drying oven) 30 are arranged between the roll-out section UW and the winding section WD. The substrate S is guided by a plurality of rollers (guide rollers) R and processed in each processing section to form a negative electrode mixture layer (a coating layer of negative electrode slurry SL) 1M on its surface. Detailed description follows.

[0065] The substrate S, rolled out from the roll-out section UW, is guided by a plurality of rollers R and conveyed to the coating section 20. The coating section 20 is equipped with a coating liquid tank T, a pump P, and a slit mold D. The negative electrode slurry SL, which serves as the coating liquid, is supplied from the coating liquid tank T to the slit mold D via the pump P. Furthermore, a valve B is provided between the supply pipe of the negative electrode slurry SL and the coating liquid tank T. Figure 6 is a perspective view showing the appearance of the negative electrode slurry coated using the slit mold. As shown in Figure 6, the negative electrode slurry SL is coated onto the substrate S from a manifold inside the slit mold D through a slit (ejection section) at the front end of the mold, forming a coating layer (SL).

[0066] The substrate S with the coating layer (SL) formed is guided by roller R and conveyed to the drying section 30. In the drying section 30, heated air is introduced through a nozzle (not shown). The temperature of the heated air is controlled by a heating element (heater, etc., not shown). The temperature of the drying section 30 is below 100°C, for example, around 70°C. In the drying section 30, the liquid components of the coating layer (SL) vaporize, forming a negative electrode binder layer 1M.

[0067] In this way, by using the aforementioned negative electrode paste SL, a high-precision negative electrode can be formed efficiently. In particular, the aforementioned negative electrode paste SL has few bubbles and good coatability, and a good negative electrode can be formed even when the substrate S is transported at a speed of 10 m / min or higher.

[0068] Furthermore, a rolling section can be provided downstream of the drying section 30. For example, the coating layer can be rolled by passing the laminate of the substrate S and the coating layer through a narrow gap between two rollers. The rolling section can be provided between the coating section 20 and the drying section 30.

[0069] In addition, a gravure coating machine can be used instead of a die coating machine. Furthermore, the negative electrode paste SL can also be coated on both sides of the substrate S. In this case, the negative electrode paste SL can be sequentially coated onto the substrate S side by side, or the negative electrode paste SL can be coated onto both sides of the substrate S during the processing shown in Figure 5.

[0070] Figure 7 shows an example of the preparation steps for the negative electrode slurry when using a water-based binder. As shown in Figure 7, a mixture 1 is prepared by mixing a water-based binder and water. At this time, other additives such as conductive agents and dispersants may also be added. This mixture 1 is stirred (for example, at 1000 rpm for about 1 minute). A high-speed mixer (e.g., a homogenizer) can be used for stirring.

[0071] Next, graphite, nano-Si, and other negative electrode active materials (e.g., acetylene black (AB)) are added to mixture 1 and stirred to prepare mixture 2. The mixture is stirred using a high-speed mixer (e.g., a homogenizer) for approximately 30 minutes at 1000–4000 rpm.

[0072] Next, alcohol is added to mixture 2 and stirred to prepare mixture 3. The mixture is stirred using a high-speed mixer (e.g., a homogenizer) for about 1 minute, for example at 1000-4000 rpm.

[0073] [positive electrode] The positive electrode (positive plate, positive electrode sheet) is as described above, having a current collector and a positive electrode flux layer disposed on top of it. The positive electrode flux layer is disposed on top of the current collector and contains at least a layer of positive electrode active material.

[0074] Regarding the positive electrode active material, examples include ternary lithium metal oxides such as NCA (lithium-nickel-cobalt-aluminum oxide, lithium nickel-cobalt-aluminum oxide (Li(Ni, Co, Al)O 2)) and NCM (lithium-nickel-cobalt-manganese oxide, lithium nickel-cobalt-manganese oxide (Li(Ni, Co, Mn)O 2)). Furthermore, the positive electrode binder layer contains an adhesive for bonding the aforementioned positive electrode active material. As an adhesive, a plastic fluoropolymer binder such as polyvinylidene fluoride (PVdF) can be used, for example. Additionally, the positive electrode binder layer may contain conductive agents, thickeners, dispersants, etc., similar to those in the negative electrode.

[0075] Regarding the current collector used for the positive electrode, a thin metal film can be used. As for the metal material, aluminum, stainless steel (SUS), etc., can be used. Furthermore, a surface plated with nickel or the like can be used. In the embodiments described later, a half-cell with the positive electrode omitted (the counter electrode is Li metal) is used for evaluation.

[0076] [Septum] For the diaphragm, resins such as polypropylene (PP), polyethylene (PE), and polyethylene terephthalate (PET) can be used; as well as glass fiber and non-woven fabrics.

[0077] Electrolyte The electrolyte is composed of an electrolyte salt and an electrolyte solvent. Lithium salts can be used as the electrolyte salt. Among these, at least one of the following groups can be used: lithium hexafluorophosphate (LiPF6), lithium perchlorate (LiClO4), lithium tetrafluoroborate (LiBF4), lithium trifluoromethanesulfonate (LiCF3SO4), lithium bis(SO2CF3)2, lithium bis(SO2C2F5)2, lithium bis(SO4)borate (LiBC4O8), etc. Regarding electrolyte solvents, examples include at least one from the following group: propylene carbonate (PC), ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC), diphenyl carbonate, γ-butyrolactone (GBL), γ-valerolactone, methyl formate (MF), 2-methyltetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, dimethoxyethane (DME), 1,2-diethoxyethane, diethyl ether, cyclobutane, tetrahydrofuran (THF), methylcyclobutane, nitromethane, N,N-dimethylformamide, dimethyl sulfide, vinylene carbonate (VC), ethylene ethylene carbonate (EVC), fluoroethylene carbonate (FEC), and cyclothioethane (ES). In particular, it is preferable to use a mixture of the aforementioned cyclic carbonates such as EC and PC with cyclic carbonates such as DMC, DEC, and EMC. In such mixing ratios, for example, the proportion of cyclic carbonates can be adjusted in the range of 10 to 90% by volume. Preferably, VC is used, or EVC, FEC, or ES are added.

[0078] [Example] The present invention will not be limited to the following embodiments, although the embodiments described in detail below are examples.

[0079] <Sample 1> (Preparation of negative electrode paste 1) Prepare the negative electrode paste according to the aforementioned "Preparation Steps for Negative Electrode Paste".

[0080] First, using a homogenizer, the binder (PI dissolved in NMP, 11 wt%) and hydrophobic CeNF (dispersed in water, solids concentration 0.5 wt%, acid value: 76.5 mg / g) were mixed at a rotation speed of 1000 rpm. For the hydrophobic CeNF, the one dispersed in water with an acid value of 76.5 mg / g was used. Furthermore, regarding the amount of hydrophobic CeNF added, the amount of the aqueous dispersion was adjusted so that the proportion in the solids of the negative electrode slurry 1 (i.e., the portion that becomes the negative electrode binder) was 0.5 wt%. The concentration of hydrophobic CeNF in the aqueous dispersion was 4 wt%. The acid value is expressed as the number of mg of potassium hydroxide required to neutralize the acidic components contained in 1 g of the sample, and can be adjusted, for example, within the range of 30 to 300 mg / g.

[0081] Next, graphite and nano-Si, as the negative electrode active materials, were added at a weight ratio of 9:1, along with carbon nanotubes (CNTs), another negative electrode active material. The mixture was then stirred for 24 minutes at 3000 rpm using a homogenizer. The added amounts of graphite, nano-Si, and CNTs were 78.3 wt%, 8.7 wt%, and 2 wt%, respectively. Afterward, alcohol was added, and the mixture was stirred for 1 minute to obtain negative electrode slurry 1. The amounts of negative electrode materials added are shown in Table 1.

[0082] Furthermore, here, carbon-coated nano-Si (average particle size 45 nm, coating thickness 2-3 nm) is used as the nano-Si. As the graphite, one with an average particle size of 22 μm is used.

[0083] (Making of negative electrode 1) The negative electrode is fabricated according to the aforementioned "formation steps of the negative electrode". The negative electrode is coated onto the current collector with slurry 1 using a die coater and dried in a drying oven at 70°C. For the current collector, Ni-plated steel foil is used.

[0084] (Making Battery 1) A half-cell button cell (sample 1) was fabricated by combining a negative electrode 1, a counter electrode of Li metal, and a glass fiber (separator) with a thickness of 100 μm. The electrolyte used was 1 mol / L LiPF6 (EC:DEC = 1:1 Vol%, VC: 1 wt%). In the button cell, the positive electrode, as shown in Figures 1 and 2, is composed of Li metal. This laminate of Li metal, negative electrode, and separator (also called the electrode assembly) is housed inside a button-shaped container, and after the electrolyte is injected, the container is capped and sealed. For example, the above laminated system is configured such that the Li metal is in contact with the bottom of the container, and the negative electrode is in contact with the back of the cap.

[0085] <Sample 2> (Preparation of negative electrode paste 2) Except for changing the binder (PI dissolved in NMP) of the aforementioned negative electrode slurry 1 from 11wt% to 5wt%, and adjusting the reduced difference to a graphite to nano-Si ratio of 9:1, negative electrode slurry 2 is manufactured in the same manner as negative electrode slurry 1.

[0086] (Making of negative electrode 2) The negative electrode 2 is manufactured in the same manner as the aforementioned negative electrode 1.

[0087] (Making Battery 2) Using the negative electrode 2, battery 2 is manufactured in the same manner as battery 1 described above.

[0088] <Sample 3> (Preparation of negative electrode paste 3) Except for adjusting the ratio of graphite to nano-Si in the aforementioned negative electrode paste 1 to be 8:2, negative electrode paste 3 is prepared in the same manner as negative electrode paste 1.

[0089] (Making of negative electrode 3) The negative electrode 3 is manufactured in the same manner as the aforementioned negative electrode 1.

[0090] (Making Battery 3) Using the negative electrode 3, battery 3 is manufactured in the same manner as battery 1 described above.

[0091] <Sample 4> (Preparation of negative electrode paste 4) The binder in the aforementioned negative electrode slurry 1 was changed to an aqueous system (referring to SBR dispersed in water, 4.5 wt%), and hydrophobicated CeNF was not added to prepare negative electrode slurry 4. Furthermore, since it is difficult to add large amounts of nano-Si when using an aqueous binder, a portion of the nano-Si was replaced with SiO to prepare negative electrode slurry 4. Specifically, the nano-Si was set at 4 wt%, SiO at 8.5 wt%, graphite at 81 wt%, and acetylene black (AB), as another negative electrode active material, at 2 wt%. Air bubbles were observed in negative electrode slurry 4.

[0092] (Making of negative electrode 4) The negative electrode 4 is manufactured in the same manner as the aforementioned negative electrode 1.

[0093] (Making Battery 4) Using the negative electrode 4, battery 4 is manufactured in the same manner as battery 1 described above.

[0094] <Sample 5> (Preparation of negative electrode paste 5) Except for changing the binder (PI dissolved in NMP) of the aforementioned negative electrode slurry 1 from 11wt% to 7wt%, and adjusting the reduced difference to a graphite to nano-Si ratio of 9:1, negative electrode slurry 5 is manufactured in the same manner as negative electrode slurry 1.

[0095] (Making of the negative electrode 5) The negative electrode 5 is manufactured in the same manner as the aforementioned negative electrode 1.

[0096] (Making Battery 5) Using the negative electrode 5, battery 5 is manufactured in the same manner as battery 1 described above.

[0097] <Sample 6> (Preparation of negative electrode paste 6) Except for changing the binder (PI dissolved in NMP) of the aforementioned negative electrode slurry 1 from 11wt% to 9wt%, and adjusting the reduced difference to a 9:1 ratio of graphite to nano-Si, negative electrode slurry 6 is manufactured in the same manner as negative electrode slurry 1.

[0098] (Making of negative electrode 6) The negative electrode 6 is manufactured in the same manner as the aforementioned negative electrode 1.

[0099] (Making Battery 6) Using the negative electrode 6, battery 6 is manufactured in the same manner as battery 1 described above.

[0100] <Sample 7> (Preparation of negative electrode paste 7) Except for changing the hydrophobic CeNF (dispersed in water, acid value: 76.5 mg / g) in the aforementioned negative electrode slurry 1 from 0.5 wt% to 0.3 wt%, negative electrode slurry 7 is prepared in the same manner as negative electrode slurry 1. Furthermore, since the hydrophobic CeNF content is 1 wt% or less, it is not calculated as a solid component, but the solid component containing hydrophobic CeNF can be calculated as 100 wt%.

[0101] (Making of the negative electrode 7) The negative electrode 7 is manufactured in the same manner as the aforementioned negative electrode 1.

[0102] (Making Battery 7) Using the negative electrode 7, battery 7 is manufactured in the same manner as battery 1 described above.

[0103] <Sample 8> (Preparation of negative electrode paste 8) Except for changing the hydrophobic CeNF (dispersed in water, acid value: 76.5 mg / g) in the aforementioned negative electrode slurry 1 from 0.5 wt% to 0.25 wt%, negative electrode slurry 8 is prepared in the same manner as negative electrode slurries 1 and 7.

[0104] (Making of the negative electrode 8) The negative electrode 8 is manufactured in the same manner as the aforementioned negative electrode 1.

[0105] (Making Battery 8) Using the negative electrode 8, battery 8 is manufactured in the same manner as battery 1 described above.

[0106] <Sample 9> (Preparation of negative electrode paste 9) Except for replacing the hydrophobic CeNF of the aforementioned negative electrode slurry 1 with unhydrophobic CeNF (also known as untreated CeNF), negative electrode slurry 9 is made in the same manner as negative electrode slurry 2.

[0107] (Making of the negative electrode 9) The negative electrode 9 is manufactured in the same manner as the aforementioned negative electrode 1.

[0108] (Making Battery 9) Using the negative electrode 9, battery 9 is manufactured in the same manner as battery 1 described above.

[0109] <Sample 10> (Preparation of negative electrode paste 10) Except for the absence of hydrophobic CeNF in the aforementioned negative electrode paste 1, negative electrode paste 10 is prepared in the same manner as negative electrode paste 2.

[0110] (Making of the negative electrode 10) The negative electrode 10 is manufactured in the same manner as the aforementioned negative electrode 1.

[0111] (Making Battery 10) Using the negative electrode 10, battery 10 is manufactured in the same manner as battery 1 described above.

[0112] <Sample 11> (Preparation of negative electrode paste 11) Except for adjusting the ratio of graphite to nano-Si in the aforementioned negative electrode paste 1 to be 8:2, negative electrode paste 11 is prepared in the same manner as negative electrode paste 6.

[0113] (Making of the negative electrode 11) The negative electrode 11 is manufactured in the same manner as the negative electrode 1 described above.

[0114] (Making Battery 11) Using the negative electrode 11, battery 11 is manufactured in the same manner as battery 1 described above.

[0115] [Table 1] negative electrode graphite Nano Si conductive agent Hydrophobic CeNF Adhesive collector Design capacity AB CNT Sample 1 78.3wt% 8.7wt% 0wt% 2wt% 0.5wt% Pl: 11wt% Nickel plating steel foil 600mAh / g Sample 2 83.7wt% 9.3wt% 0wt% 2wt% 0.5 wt% Pl: 5wt% Sample 3 69.6 wt% 17.4 wt% 0 wt% 2wt% 0.5 wt% Pl: 11wt% 800mAh / g Sample 4 81 wt% Si 4wt% SiO 8.5wt% 2wt% 0 wt% 0 wt% Water-based SBR: 4.5wt% Kyoho steel foil 500mAh / g Sample 5 81.9 wt% 9.1 wt% 0 wt% 2wt% 0.5 wt% Pl:7wt% Kyoho steel foil 600mAh / g Sample 6 80.1 wt% 8.9 wt% Pl:9wt% Sample 7 83.7 wt% 9.3 wt% 0.3 wt% Pl: 5wt% Sample 8 0.25 wt% Sample 9 unknown CeNF 0.5 wt% Sample 10 0 wt% Sample 11 71.2 wt% 17.8wt% 0.5wt% Pl: 9wt% 800mAh / g

[0116] (Initial characteristics) For the manufactured batteries, the initial characteristics of button batteries (samples 1, 2, 5, and 6) were investigated at a constant current of 0.46 mA under an environment of 30°C and a battery voltage range of 1 mV to 1 V. Figure 8 shows the initial characteristics of button batteries (samples 1, 2, 5, and 6). The horizontal axis represents capacity (mAh / g), and the vertical axis represents voltage (E, V).

[0117] As shown in Figure 8, each sample exhibited good initial characteristics. Next, we found that as the amount of binder (PI dissolved in NMP) increased from 5 wt% → 7 wt% → 9 wt% → 11 wt%, the capacity also increased. Generally, as the amount of binder increases, the capacity tends to decrease. In contrast, in the samples of this embodiment, the opposite trend was observed. Therefore, by using both the binder (PI dissolved in NMP) and hydrophobic CeNF (dispersed in water), the expansion and contraction of nano-Si during charging and discharging were suppressed, and an increase in battery capacity was observed. Furthermore, Figure 9 shows the initial characteristics of battery 4 using an aqueous solvent. In the case of battery 4 using this aqueous binder, its battery capacity was lower than any of the samples 1, 2, 5, and 6 mentioned above. Also, in battery 4, portions of the coating layer without visible defects were used.

[0118] (Cyclic Characteristics) For the manufactured batteries, the cycle characteristics of button cell batteries (samples 1, 2, 5, and 6) were investigated at a constant current of 0.46 mA under an environment of 30°C and a battery voltage range of 1mV to 1V. Figure 10 shows the cycle characteristics of button cell batteries (samples 1, 2, 5, and 6). The horizontal axis represents the number of cycles, and the vertical axis represents the discharge capacity (mAh / g).

[0119] As shown in Figure 10, all samples (samples 1, 2, 5, and 6) exhibited good discharge capacity even with increased cycle count. Furthermore, compared to sample 10 without CeNF, all samples (samples 1, 2, 5, and 6) showed good discharge capacity. Additionally, there was no significant difference in cycle characteristics when the binder (PI dissolved in NMP) addition amount was 5 wt% and 7 wt%, but the cycle characteristics were better at 11 wt% addition compared to 9 wt%, and among samples 1, 2, 5, 6, and 10, the sample with 11 wt% addition exhibited the best cycle characteristics. Here, because samples with 0.5 wt% hydrophobic CeNF addition were compared, it was observed that a more efficient battery can be obtained by adjusting the ratio of binder (PI dissolved in NMP) to hydrophobic CeNF.

[0120] Figure 11 shows the cycling characteristics of button cells (samples 2, 7, and 8) with different amounts of hydrophobic CeNF added. The horizontal axis represents the number of cycles, and the vertical axis represents the discharge capacity (mAh / g).

[0121] As shown in Figure 11, all samples exhibited good discharge capacity compared to sample 10 without CeNF and sample 9 using untreated CeNF. Furthermore, as the amount of hydrophobic CeNF added increased from 0.25 wt% → 0.3 wt% → 0.5 wt%, the capacity also increased, and the decrease in discharge capacity with increasing cycle number was minimal.

[0122] In addition, in the above-mentioned samples (samples 2, 7, and 8), the proportion of nano-Si was set to 10%, and the cycle characteristics of samples 3 and 11, in which the proportion of nano-Si was set to 20%, were investigated.

[0123] Figure 12 shows the cycle characteristics of a button cell (samples 3 and 11) with a graphite to nano-Si ratio of 8:2. The horizontal axis represents the number of cycles, and the vertical axis represents the discharge capacity (mAh / g).

[0124] As shown in Figure 12, compared to sample 10 without CeNF and sample 9 using untreated CeNF, all samples showed good discharge capacity. Furthermore, the sample with a higher proportion of nano-Si exhibited improved discharge capacity. Also, in samples 3 and 11, it was confirmed that the capacity increased as the amount of binder (PI dissolved in NMP) increased from 9 wt% to 11 wt%.

[0125] (Discussion) Based on the above embodiments and other experiments conducted by the inventors, a preferred composition for the negative electrode slurry is discussed below.

[0126] For anode pastes containing nano-Si, it is preferable to use hydrophobic CeNF and organic solvent-based binders.

[0127] Regarding the amount of hydrophobic CeNF added, a preferred amount of 0.25 wt% or more was found, and good results were obtained even within the range of 0.25 to 0.5 wt%. Furthermore, this hydrophobic CeNF can be dispersed in an aqueous solvent. As mentioned earlier, nano-Si can react with water, but for example, if the amount of hydrophobic CeNF added is less than that of the binder, the amount of this solvent (dispersion medium) is also less. Therefore, water in the hydrophobic CeNF dispersed in water will not have an adverse effect. The concentration of hydrophobic CeNF in the aqueous dispersion is, for example, 0.05 to 1 wt%. Moreover, relative to the total solvent volume of 100 ml of the negative electrode slurry, this added amount is approximately 0.05 to 1 ml, and preferably less than 1 wt% of the total solvent volume of the negative electrode slurry.

[0128] The content of hydrophobic CeNF in the negative electrode slurry is preferably 0.01 wt% or more, and more preferably 0.02 wt% or more, relative to its solid components (total amount of negative electrode active material and binder).

[0129] Furthermore, good results were also obtained when the ratio of graphite to nano-Si in the negative electrode slurry was 9:1 to 8:2. Thus, it was found that even when the proportion of nano-Si in the negative electrode active material is 10% to 20% (8.7% to 17.8 wt% in the above examples), good results can still be obtained.

[0130] Furthermore, even when the amount of organic solvent-based binder added is 5 to 11 wt% of the solid component (negative electrode binder) of the negative electrode slurry, good results can still be obtained.

[0131] The above embodiments all involve forming the slurry, electrodes, and battery under atmospheric pressure. Here, as previously mentioned, trace amounts of aqueous solvents can be used, and the process is less susceptible to the effects of atmospheric moisture. Therefore, the formation of the slurry, electrodes, and battery in this embodiment does not require a drying oven with strict humidity and temperature control, but can be carried out under atmospheric pressure, which is extremely useful.

[0132] (Implementation Form 2) In the embodiment of Embodiment 1, although a button-type battery is fabricated, it is not limited to the battery structure applicable to the negative electrode described in Embodiment 1. For example, it can be used as the negative electrode of a cylindrical battery. Figure 13 is a cross-sectional perspective view showing the structure of a cylindrical lithium-ion battery. The lithium-ion battery shown in Figure 13 has a cylindrical can 106, in which an electrode assembly is housed, wherein a strip-shaped positive electrode 101 and a negative electrode 103 are wound together with a separator SP in between. For example, the strip-shaped positive electrode 101 and negative electrode 103 form electrode flux layers on both sides of the current collector. In addition, the positive current collector sheet on the upper end face of the electrode assembly is joined to the positive electrode cap. The negative current collector sheet on the lower end face of the electrode assembly is joined to the bottom of the can 106. Furthermore, an insulating coating layer (not shown) is provided on the outer peripheral surface of the can 106. In addition, an electrolyte solution (not shown) is injected into the can 106. Furthermore, although a cylindrical battery is used as an example here, a square battery could also be used.

[0133] Furthermore, although polyimide (PI) is used as the adhesive in the above embodiments, other organic solvent-based adhesives can also be used. From the viewpoint of improving the adhesion of nano-Si, the above-mentioned polyimide (PI) or polyvinylidene fluoride (PVdF) is preferred as an organic solvent-based adhesive.

[0134] (Implementation Form 3) In Embodiment 1, although the negative electrode slurry is prepared by using a mixer such as a homogenizer, it can also be prepared by an extruder.

[0135] Figure 14 is a cross-sectional view showing a method for preparing negative electrode slurry using an extruder. As shown in Figure 14, the extruder has a barrel 111 and a screw SC disposed inside the barrel 111. A screw drive unit (not shown) is connected to the screw SC. The barrel 111 has three supply ports 113a, 113b, and 113c on its upstream side. In addition, a discharge nozzle 119 is provided at the front end of the barrel 111.

[0136] For example, a negative electrode active material (such as graphite, nano-Si, or other negative electrode active materials) is added through supply port 113a and mixed while being rotated by the screw SC. An organic solvent-based binder, an organic solvent, and hydrophobic CeNF (dispersed in water) are added through supply port 113b. Next, an alcohol (for preparation) is added through supply port 113c and mixed while being rotated by the screw SC. This prepares the negative electrode slurry, which is then dispensed from the discharge nozzle 119.

[0137] Furthermore, the same extruder can be used to prepare the cathode slurry. Figure 15 is a cross-sectional view showing the preparation method of the cathode slurry using an extruder. For example, a binder and additives are added through the feed port 113a and mixed by the rotation of the screw SC, while an organic solvent (e.g., NMP) is added through the feed port 113b. Next, the cathode active material is further added through the feed port 113c and mixed by the rotation of the screw SC. In this way, the cathode slurry is prepared and discharged from the discharge nozzle 119.

[0138] (Implementation Form 4) In Embodiment 1, although an aqueous solvent (water and / or alcohols, in this case, water (H₂O)) is used as the dispersion solvent for hydrophobic CeNF, an organic solvent can also be used. As mentioned above, since hydrophobic CeNF can prevent aggregation and improve its dispersibility in the slurry, it is preferable to use it in a solvent-dispersed state. Here, a method for obtaining hydrophobic CeNF dispersed in an organic solvent by replacing the aqueous solvent of hydrophobic CeNF dispersed in an aqueous solvent with an organic solvent will be described.

[0139] (Preparation method of hydrophobic CeNF dispersed in organic solvent) Figure 16 is a diagram showing the preparation steps of hydrophobic CeNF dispersed in an organic solvent. Here, a method for preparing NMP-dispersed hydrophobic CeNF is described in the case of a carboxylic acid compound using NMP as the organic solvent and succinic anhydride as the hydrophobicating agent.

[0140] As shown in Figure 16(A), cellulose (solid, e.g., powder) and succinic anhydride (solid, e.g., sheet) are mixed at a temperature above 100°C. For example, a pressure kneader is used to mix at 125°C for 20 minutes. The weight ratio of cellulose to succinic anhydride is, for example, 90 wt% and 10 wt%.

[0141] By stirring under heating as described above, an esterification reaction occurs, producing hydrophobic cellulose. Afterwards, to remove unreacted succinic anhydride, the mixture is washed with acetone or similar solvents.

[0142] Next, the generated hydrophobic cellulose is dispersed in an aqueous solvent (water and / or alcohol, here water (H₂O)) and subjected to a micronization process (defibrillation, nanonization). For example, a micronization device (starburst) is used to perform a 245 MPa, 10-pass treatment to nanonize the cellulose. Up to this point, it is the same as the preparation method of hydrophobic CeNF dispersed in the aqueous solvent described with reference to FIG3. In this way, hydrophobic CeNF can be obtained. Here, the hydrophobic CeNF at this stage is dispersed in an aqueous solvent, and the aqueous solvent is replaced with NMP (organic solvent). For example, as shown in FIG16(B), a rotary evaporator is used to gradually replace the aqueous solvent (here water (H₂O)) with an organic solvent (here NMP).

[0143] First, an organic solvent (e.g., NMP) is added to an aqueous solvent in which hydrophobic CeNF is dispersed to form a mixed solution. Then, when the solvent content is 100 wt%, the mixed solution is prepared such that the hydrophobic CeNF (solid component) is 0.1–20 wt%. In this way, CeNF dispersed in an organic solvent (e.g., NMP) can be obtained.

[0144] Next, while stirring the above mixed solution, the aqueous solvent (water (H2O)) is removed from the mixed solution by evaporation, which can increase the concentration of organic solvent (e.g., NMP).

[0145] The invention described above is based on the specific embodiments and examples. However, the invention is not limited to the above embodiments or examples. Naturally, various changes can be made without departing from the spirit of this invention.

[0146] 20: Coating Section 30: Drying section 101: Positive electrode 103: Negative electrode 106: Can 111: Cylinder 113a: Supply Port 113b: Supply Port 113c: Supply port 119: Discharge nozzle 1M: Negative electrode mixture layer 1S: Current collector 1T: Negative extreme particle 2M: Positive electrode mixture layer 2S: Collector 2T: Positive extreme particle B: Valve D: Slot mold T: Coating tank P: Pump R: Roller S: Substrate SC: Screw SL: Negative electrode slurry SP: Diaphragm UW: Volume Out WD: Winding section

Claims

1. A negative electrode for a lithium-ion battery, comprising: a negative electrode binder, which is composed of graphite, a negative electrode active material, a conductive agent, a binder, and hydrophobic cellulose; wherein the aforementioned negative electrode active material is nano-sized Si particles; and the aforementioned binder is an organic solvent-based binder, and the aforementioned organic solvent-based binder is polyimide or polyvinylidene fluoride; wherein, In the aforementioned hydrophobic cellulose, a portion of the hydrophilic groups of the cellulose are replaced by hydrophobic groups.

2. The negative electrode for a lithium-ion battery as described in claim 1, wherein, The average particle size of the aforementioned Si particles is greater than 10 nm and less than 500 nm.

3. The negative electrode for a lithium-ion battery as described in claim 1, wherein, The aforementioned hydrophobic cellulose is hydrophobized by carboxylic acid compounds.

4. The negative electrode for a lithium-ion battery as described in claim 3, wherein, The aforementioned hydrophobic cellulose particles have a length of 3 nm or more and 10 µm or less, and an aspect ratio (length / diameter) of 0.01 or more and 10,000 or less.

5. A lithium-ion battery comprising: a negative electrode, which includes: Current collector; and the negative electrode binder layer formed on the aforementioned current collector; positive electrode; The electrolyte; wherein the aforementioned negative electrode binder layer is composed of graphite, negative electrode active material, conductive agent, binder and hydrophobic cellulose; and the aforementioned negative electrode active material is nano-sized Si particles; the aforementioned binder is an organic solvent-based binder, and the aforementioned organic solvent-based binder is polyimide or polyvinylidene fluoride; a portion of the hydrophilic groups of the aforementioned hydrophobic cellulose is replaced by hydrophobic groups.

6. The lithium-ion battery as described in claim 5, wherein, The average particle size of the aforementioned Si particles is greater than 10 nm and less than 500 nm.

7. The lithium-ion battery as described in claim 6, wherein, The aforementioned hydrophobic cellulose is hydrophobized by carboxylic acid compounds.

8. The lithium-ion battery as described in claim 7, wherein, The aforementioned hydrophobic cellulose particles have a length of 3 nm or more and 10 µm or less, and an aspect ratio (length / diameter) of 0.01 or more and 10,000 or less.

9. A method for manufacturing a negative electrode for a lithium-ion battery, comprising: (a) mixing graphite, a negative electrode active material, a conductive agent, a binder, and hydrophobic cellulose to form a negative electrode slurry; and (b) coating the aforementioned negative electrode slurry onto a current collector; wherein, The aforementioned negative electrode active material is nano-sized Si particles; the aforementioned adhesive is an organic solvent-based adhesive, and the aforementioned organic solvent-based adhesive is polyimide or polyvinylidene fluoride; a portion of the hydrophilic groups of the aforementioned hydrophobic cellulose is replaced by hydrophobic groups.

10. A method for manufacturing a negative electrode for a lithium-ion battery as described in claim 9, wherein, The aforementioned step (b) includes: (b1) applying a negative electrode paste to the first side of the substrate removed from the transfer section; (b2) Step: A negative electrode paste layer is formed on the first surface of the aforementioned substrate by drying the negative electrode paste on the aforementioned substrate; (b3) Step: The aforementioned substrate on which the aforementioned negative electrode paste layer is formed is moved into the moving part.

11. A method for manufacturing a negative electrode for a lithium-ion battery as described in claim 10, wherein, The average particle size of the aforementioned Si particles is greater than 10 nm and less than 500 nm.

12. A method for manufacturing a negative electrode for a lithium-ion battery as described in claim 11, wherein, The aforementioned hydrophobic cellulose is hydrophobized by carboxylic acid compounds.

13. A method for manufacturing a lithium-ion battery, comprising: (a) preparing a negative electrode slurry; (b) coating the aforementioned negative electrode slurry onto a current collector to form a negative electrode having the aforementioned current collector and a negative electrode mixture layer; (c) laminating the aforementioned negative electrode and a positive electrode together with a separator to form an electrode assembly; (d) housing the aforementioned electrode assembly in a battery container; and (e) after step (d), injecting an electrolyte into the aforementioned battery container; wherein, The aforementioned step (a) involves mixing graphite, anode active material, conductive agent, binder, and hydrophobic cellulose to form a slurry for the anode; the aforementioned anode active material is nano-sized Si particles; the aforementioned binder is an organic solvent-based binder, and the aforementioned organic solvent-based binder is polyimide or polyvinylidene fluoride; a portion of the hydrophilic groups of the aforementioned hydrophobic cellulose is replaced by hydrophobic groups.

14. A method for manufacturing a lithium-ion battery as described in claim 13, wherein, The aforementioned step (b) includes: (b1) applying a negative electrode paste to the first side of the substrate removed from the transfer section; (b2) Step: A negative electrode paste layer is formed on the first surface of the aforementioned substrate by drying the negative electrode paste on the aforementioned substrate; (b3) Step: The aforementioned substrate on which the aforementioned negative electrode paste layer is formed is moved into the moving part.

15. A method for manufacturing a lithium-ion battery as described in claim 14, wherein, The average particle size of the aforementioned Si particles is greater than 10 nm and less than 500 nm.

16. A method for manufacturing a lithium-ion battery as described in claim 15, wherein, The aforementioned hydrophobic cellulose is hydrophobized by carboxylic acid compounds.

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