JP2015088472A - Electrode for power storage device, and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrode for a power storage device superior in charge and discharge characteristics and productivity, which never causes the worsening of charge and discharge characteristics owing to a manufacturing process.SOLUTION: An electrode for a power storage device comprises: a collector; and an electrode active material layer on the collector. The electrode active material layer includes: an electrode active material (A); and acetyl cellulose (B), of which the total acetyl group substitution degree is 0.4-1.2. In the electrode for a power storage device, composition distribution index (CDI) of the acetyl cellulose (B) is preferably 1.0-2.0.

Description

  The present invention relates to an electrode (an electrode for an electricity storage device) used for an electricity storage device such as an electric double layer capacitor (nonaqueous electric double layer capacitor) using a lithium ion battery or a nonaqueous electrolyte, a method for producing the electrode, and the above electrode. It is related with the electrical storage device which has (a lithium ion battery, a non-aqueous electric double layer capacitor, etc.).

An electrode in an electricity storage device such as a lithium ion battery (lithium ion secondary battery) or a non-aqueous electric double layer capacitor has a configuration in which an active material (electrode active material) is fixed on the surface of a current collector such as a metal foil. Electrodes are known. For example, as a lithium ion battery, a negative electrode using a negative electrode active material such as a carbon material, a positive electrode using a positive electrode active material such as a lithium transition metal oxide such as lithium cobaltate, and ethylene carbonate or diethyl carbonate. organic solvents and lithium hexafluorophosphate lithium salt (LiPF ₆₎ or the like having a used electrolyte are known. In addition, as a non-aqueous electric double layer capacitor, one having a polarizable electrode in which activated carbon is used as an active material is known to increase the capacitance.

  In general, the electrode of the above-described electricity storage device is manufactured by pasting an electrode forming composition prepared by mixing an active material, a solvent, and a binder onto a current collector, and drying the paste. . Specifically, for example, a negative electrode of a lithium ion battery is prepared by mixing a composition for forming an electrode prepared by mixing a carbon material powder (negative electrode active material), a solvent, and a binder with a current collector (copper foil or the like). ) And then dried.

  Lithium ion batteries and non-aqueous electric double layer capacitors use a non-aqueous electrolyte solution, so a high voltage exceeding the electrolysis voltage of the aqueous electrolyte solution is obtained, and the energy density is high. However, since the energy density is high, there is a high risk of overheating when the short circuit occurs. Furthermore, the electrolyte solution, which is an organic solvent, volatilizes, which may cause a fire accident. In addition, a short circuit may occur inside a battery or a capacitor when an external force is applied to a lithium ion battery or a non-aqueous electric double layer capacitor, and protection against an impact is also required. For this reason, in manufacture of the electrode in the above-mentioned electrical storage device, it was necessary to make it not have the fault which leads to these problems.

  Conventionally, as the electrode forming composition, an “organic solvent-based composition” using an organic solvent as a solvent or a dispersion medium (hereinafter sometimes collectively referred to as “solvent” in the present specification) and water as a solvent. "Aqueous composition" is known. Typical organic solvent-based compositions are those using fluorine-containing polymers such as NMP (N-methylpyrrolidone) as a solvent and PVDF (polyvinylidene fluoride) or PTFE (polytetrafluoroethylene) as a binder. Typical examples of the aqueous composition include water as a solvent and a rubber polymer such as SBR (styrene-butadiene rubber) as a binder (see, for example, Patent Documents 1 and 2).

JP-A-5-074741 JP 2008-181870 A

  An organic solvent-based electrode forming composition in which a binder such as PVDF or PTFE is dissolved in NMP is easy to obtain a good slurry by a simple process. On the other hand, NMP as a solvent absorbs moisture and PVDF or It should be noted that the solubility of binders such as PTFE decreases and the slurry properties change. In addition, since the conventional organic solvent-based electrode forming composition is applied to the current collector and then dried at a high temperature, PVDF crystal melting occurs. Therefore, the adhesion of the electrode active material layer to the current collector and the active materials There is a problem that the binding property (hereinafter, sometimes referred to as “binding property” in this specification) is lowered, and the charge / discharge characteristics of the electricity storage device are lowered. For this reason, in the manufacture of an electrode using a conventional organic solvent-based electrode forming composition, it has been difficult to increase the drying temperature of the solvent, shorten the drying time, and further improve the productivity.

  On the other hand, the water-based electrode forming composition using SBR described above is a state in which polymer particles of SBR are dispersed in water, and unlike an organic solvent-based composition, SBR as a binder is a composition (slurry). ) Does not have an effect of imparting an appropriate viscosity, it is difficult to produce an electrode-forming composition using only SBR. Therefore, in order to impart appropriate rheological properties to the aqueous electrode-forming composition, it is essential to use a water-soluble thickener such as CMC (carboxymethylcellulose). It is most important to note that such an aqueous electrode-forming composition must be prepared by adding water to the CMC aqueous solution to dilute it to a desired viscosity and then adding a binder thereto. Should. This is because, as described above, the state in which the polymer particles of SBR are uniformly dispersed in water is sensitive to mechanical impact such as shearing force, and the viscosity of the electrode forming composition is increased by adopting an incorrect process. This is because problems such as SBR aggregation and SBR may occur. Therefore, in the production of a negative electrode using a conventional aqueous electrode-forming composition, it has been difficult to simplify the preparation process of the electrode-forming composition and further improve productivity.

  In addition, since the battery voltage of the lithium ion battery is higher than the electrolysis voltage of the aqueous electrolyte, if water is present in the battery, the electrolyte salt is hydrolyzed to produce hydrofluoric acid, and this phenomenon is caused by the elution of the active material. One cause is the deterioration of the charge / discharge characteristics of the electricity storage device. For this reason, it is preferable to sufficiently remove moisture in the step of manufacturing the electrode.

Accordingly, an object of the present invention is to provide charge / discharge characteristics and productivity without causing deterioration of charge / discharge characteristics (characteristics in which performance deterioration is small even if charge / discharge is repeated and charge / discharge cycle life is long) due to the manufacturing process. It is an object of the present invention to provide an electrode for an electricity storage device (for example, a lithium ion battery, a non-aqueous electric double layer capacitor, etc.) excellent in both, and an electricity storage device having the electrode.
Another object of the present invention is a method for producing an electrode using an organic solvent (a method for producing an organic solvent system), and shortening a process for removing the organic solvent without deteriorating charge / discharge characteristics. An object of the present invention is to provide a method for manufacturing an electrode for an electricity storage device with high productivity.
Furthermore, another object of the present invention is a method for producing an electrode using water (aqueous production method), which does not require the use of styrene-butadiene rubber as a binder, and does not involve deterioration in charge / discharge characteristics. It is an object of the present invention to provide a method for manufacturing an electrode for an electricity storage device with high productivity that can simplify the manufacturing process.

  As a result of intensive studies to achieve the above object, the present inventors have a current collector and an electrode active material layer on the current collector, and the electrode active material layer includes an electrode active material and a specific cellulose acetate. The present inventors completed the present invention by finding that an electrode for an electricity storage device containing an essential component is excellent in both charge / discharge characteristics and productivity without causing deterioration in charge / discharge characteristics due to the production process.

  That is, the present invention is an electrode having a current collector and an electrode active material layer on the current collector, wherein the electrode active material layer has an electrode active material (A) and a total acetyl group substitution degree of 0. It provides the electrode for electrical storage devices characterized by including the cellulose acetate (B) which is 4-1.2.

ＤＳ：アセチル基総置換度
ＤＰｗ：重量平均重合度（酢酸セルロース（試料）の残存水酸基をすべてプロピオニル化して得られるセルロースアセテートプロピオネートを用いてＧＰＣ−光散乱法により求めた値） Furthermore, the above-mentioned electrode for an electricity storage device, wherein the composition distribution index (CDI) defined below of cellulose acetate (B) is 1.0 to 2.0, is provided.
CDI = (actual value of composition distribution half width) / (theoretical value of composition distribution half width)
Measured value of half width of composition distribution: half width of composition distribution obtained by HPLC analysis of cellulose acetate propionate obtained by propionylating all remaining hydroxyl groups of cellulose acetate (sample)

DS: Degree of total substitution of acetyl groups DPw: Weight average degree of polymerization (value determined by GPC-light scattering method using cellulose acetate propionate obtained by propionylating all remaining hydroxyl groups of cellulose acetate (sample))

  Furthermore, the said electrode for electrical storage devices which is an electrode for lithium ion batteries is provided.

  Furthermore, the electrode for an electricity storage device is provided in which the electrode active material layer does not contain styrene-butadiene rubber.

  Furthermore, the said electrode for electrical storage devices which is an electrode for non-aqueous electric double layer capacitors is provided.

  Moreover, this invention provides the lithium ion battery which has the said electrode for electrical storage devices.

  The present invention also provides a non-aqueous electric double layer capacitor having the above-described electrode for an electricity storage device.

The present invention also includes a step of preparing an electrode-forming composition containing an electrode active material (A), cellulose acetate (B), and an organic solvent;
Applying the electrode-forming composition obtained in the step onto a current collector and drying to form an electrode active material layer on the current collector. A manufacturing method is provided.

The present invention also includes a step of preparing an electrode-forming composition comprising an electrode active material (A), cellulose acetate (B) having a total acetyl group substitution degree of 0.5 to 1.1, and water;
Applying the electrode-forming composition obtained in the step onto a current collector and drying to form an electrode active material layer on the current collector. A manufacturing method is provided.

  Since the electrode for an electricity storage device of the present invention and the electricity storage device having the electrode have the above-described configuration, both the charge / discharge characteristics and the productivity are excellent without causing deterioration of the charge / discharge characteristics due to the manufacturing process. Further, in the method for producing an electrode for an electricity storage device of the present invention, the organic solvent-based production method is not accompanied by a decrease in charge / discharge characteristics even if the heating temperature for removing the organic solvent and drying is increased, The drying time can be greatly shortened and productivity can be improved. On the other hand, the method for producing an electrode for an electricity storage device of the present invention, wherein the aqueous production method does not require the use of styrene-butadiene rubber as a binder, and simplifies the electrode production process without deteriorating charge / discharge characteristics. The manufacturing time can be greatly shortened and the productivity can be improved. Thus, the method for producing an electrode for an electricity storage device of the present invention is a method that is excellent in productivity for both organic solvent systems and aqueous systems.

<Electrode for power storage device>
The electrode for an electricity storage device of the present invention is an electrode used in an electricity storage device having at least a current collector and an electrode active material layer on the current collector. Examples of the electricity storage device include a lithium ion battery and a non-aqueous electric double layer capacitor as described later. That is, examples of the electrode for an electricity storage device of the present invention include a lithium ion battery electrode (positive electrode, negative electrode), a non-aqueous electric double layer capacitor electrode (positive electrode, negative electrode), and the like.

[Current collector]
As the current collector in the electrode for an electricity storage device of the present invention, a known or commonly used current collector in an electricity storage device such as a lithium ion battery or a non-aqueous electric double layer capacitor can be used, and is not particularly limited. , Stainless steel, nickel, nickel alloy, copper, copper alloy, aluminum or the like formed into a foil, film, film, sheet or the like. Note that the current collector may have a surface subjected to adhesion treatment of carbon, nickel, titanium, copper, or the like. Further, the current collector may be subjected to a surface roughening process such as etching. The thickness of the said electrical power collector is not specifically limited, According to the capacity | capacitance, size, etc. of an electrical storage device, it can select suitably from the range of 1-500 micrometers, for example. Especially, as a collector in the electrode for lithium ion batteries, copper is preferably used in the case of a negative electrode, and aluminum is preferably used in the case of a positive electrode. On the other hand, as the current collector in the electrode for the non-aqueous electric double layer capacitor, aluminum is preferably used, and an aluminum foil having a roughened surface is particularly preferably used.

[Electrode active material layer]
The electrode active material layer in the electrode for an electricity storage device of the present invention is an electrode active material layer formed on the current collector and containing the electrode active material (A) and cellulose acetate (B) as essential components. . Among these, an electrode active material layer containing, as essential components, an electrode active material (A) and cellulose acetate (B) having an acetyl group total substitution degree of 0.4 to 1.2 from the viewpoint of charge / discharge characteristics of the electricity storage device. preferable. Since the electrode active material layer generally has a layered shape such as a plate shape or a film shape, it is referred to as a “layer” for convenience. However, other shapes (for example, a layered shape) may be used as long as the shape is similar to this. Similar irregular shapes and the like) are also included. When the electricity storage device is a non-aqueous electric double layer capacitor, the electrode active material layer may be referred to as a “polarizable electrode” or a “charged layer”.

  The electrode active material layer may be formed only on one surface of the current collector, or may be formed on both surfaces. Moreover, the thickness of the said electrode active material layer is not specifically limited, For example, it can select suitably from 1-1000 micrometers in thickness.

1. Electrode active material (A)
As the electrode active material (A) in the electrode for the electricity storage device of the present invention, a well-known and commonly used material such as a positive electrode active material or negative electrode active material in a lithium ion battery, an active material (polarizable electrode material) in a non-aqueous electric double layer capacitor, etc. Can be used.

As the positive electrode active material in the lithium ion battery described above, a material capable of reversibly occluding and releasing lithium can be used, and is not particularly limited. For example, manganese dioxide (MnO ₂ ); lithium-manganese composite oxide (for example, LiMn ₂ O ₄ , LiMnO ₂ etc.); lithium-nickel composite oxide (eg LiNiO ₂ etc.); lithium-cobalt composite oxide (eg LiCoO ₂ etc.); lithium-nickel-cobalt composite oxide (eg LiNi _{1) -x} Co _x O _2, etc.); lithium - manganese - cobalt composite oxide _{(e.g., LiMn x Co 1-x O} 2 , etc.); lithium - nickel - cobalt - manganese composite oxide (e.g., LiNi _x Mn _y Co _{1 -xy} O _2); polyanionic lithium compounds _{(e.g., LiFePO 4, LiCoPO 4 F,} Li 2 Mn iO _4, etc.); vanadium oxide (e.g., V ₂ O _5, etc.); conductive polymers; disulfide-based polymer; sulfur compounds (for example, lithium sulfide, etc.) and the like. The shape and size of the positive electrode active material are not particularly limited, and can be appropriately selected from shapes and sizes known as positive electrode active materials in lithium ion batteries.

As the negative electrode active material in the above-described lithium ion battery, those capable of reversibly occluding and releasing lithium can be used, and are not particularly limited. For example, natural graphite, artificial graphite, coke, carbon fiber, amorphous carbon (soft Carbon-based materials such as carbon and hard carbon); lithium-transition metal complex oxides such as lithium-titanate complex oxides (for example, Li ₄ Ti ₅ O ₁₂ ); silicon, germanium, tin, lead, aluminum, Indium, magnesium, zinc, hydrogen, calcium, strontium, barium, ruthenium, rhodium, iridium, palladium, platinum, silver, gold, cadmium, mercury, gallium, titanium, carbon, nitrogen, antimony, bismuth, oxygen, sulfur, selenium, Elements that can be alloyed with lithium, such as tellurium and chlorine, and this Compounds containing Luo element; said element or composite compound of the compound and the carbon-based material containing these elements; nitrides containing lithium and the like. The shape and size of the negative electrode active material are not particularly limited, and can be appropriately selected from shapes and sizes known as negative electrode active materials in lithium ion batteries.

  Examples of the active material (polarizable electrode material) in the non-aqueous electric double layer capacitor described above include activated carbon [for example, sawdust activated carbon, ashigara activated carbon, pitch coke activated carbon, phenol resin activated carbon, polyacrylonitrile activated carbon, Cellulose-based activated carbon, etc.], carbon-based materials such as carbon black and carbon nanotubes; metal oxide materials such as ruthenium oxide, manganese oxide, and cobalt oxide; polyaniline, polypyrrole, polythiophene, poly (3,4-ethylenedioxythiophene), etc. And the like. The shape and size of the active material are not particularly limited, and can be appropriately selected from shapes and sizes known as active materials in non-aqueous electric double layer capacitors.

  In the electrode active material layer of the electrode for an electricity storage device of the present invention, the electrode active material (A) can be used alone or in combination of two or more. Moreover, a commercial item can also be used as an electrode active material (A).

  The content of the electrode active material (A) in the electrode active material layer (100% by weight) can be appropriately selected from known contents and is not particularly limited, but is preferably 50 to 99.5% by weight, more Preferably it is 80-99 weight%. By making content of an electrode active material (A) into the said range, there exists a tendency which can obtain the electrical storage device (battery, a capacitor, etc.) which has the more superior charging / discharging characteristic.

2. Cellulose acetate (B)
Cellulose acetate (B) in the electrode active material layer is cellulose acetate (cellulose acetate). Cellulose acetate (B) functions as a binder for the electrode active material (A) in the electrode active material layer. Cellulose acetate (B) in the composition for forming the electrode active material layer (electrode forming composition) when the electrode for an electricity storage device of the present invention is produced by an aqueous production method described later. It functions also as a thickener and improves the dispersibility of the electrode active material (A) in the composition.

(Total substitution degree of acetyl group)
The total acetyl group substitution degree (average substitution degree; sometimes simply referred to as “substitution degree”) of cellulose acetate (B) is not particularly limited, and cellulose acetate having various acetyl group total substitution degrees is selected from acetic acid according to the present invention. It can be used as cellulose (B). Examples of cellulose acetate (B) include triacetyl cellulose (for example, cellulose acetate having a total acetyl group substitution degree of 2.6 or more); diacetyl cellulose (for example, a total acetyl group substitution degree of 2.0 to less than 2.6). Low-substituted cellulose acetate (for example, a total acetyl group substitution degree of more than 0 and less than 2.0; in particular, a cellulose acetate having a total acetyl group substitution degree of 0.5 to 1.1) and the like. .

  In particular, as the cellulose acetate (B) in the electrode for an electricity storage device of the present invention, cellulose acetate (B) having a total acetyl group substitution degree of 0.4 to 1.2 is preferable from the viewpoint of charge / discharge characteristics of the electricity storage device.

  Especially, when manufacturing an electrode (electrode active material layer) with the below-mentioned aqueous manufacturing method, 0.5-1.1 are preferable, and, as for the acetyl group total substitution degree of a cellulose acetate (B), 0.55 is more preferable. It is -1.0, More preferably, it is 0.6-0.95. When the total acetyl group substitution degree of cellulose acetate (B) is in the above range, the water solubility tends to be excellent. On the other hand, if it is out of the above range, the solubility in water tends to decrease. When manufacturing an electrode with an aqueous manufacturing method, the solubility of cellulose acetate (B) in the composition for electrode formation is high as the acetyl group total substitution degree of cellulose acetate (B) is 0.5 to 1.1. This is presumably because, however, an electrical storage device with improved binding properties and excellent charge / discharge characteristics can be obtained.

  On the other hand, when an electrode (electrode active material layer) is manufactured by an organic solvent-based manufacturing method described later, the total acetyl group substitution degree of cellulose acetate (B) is preferably 0.4 to 2.8, more preferably 0.8. 6 to 1.4. From the viewpoint of solubility in organic solvents, a certain degree of acetyl group total substitution is desirable, but if the degree of total acetyl group substitution is too high, the degree of swelling in electrolyte solvents such as propylene carbonate tends to increase and the binding property tends to be impaired. .

  The total acetyl group substitution degree of cellulose acetate (B) can be measured by a known titration method in which cellulose acetate is dissolved in water and the substitution degree of cellulose acetate is determined. The total degree of acetyl group substitution can also be measured by NMR after propionylating the hydroxyl group of cellulose acetate (see the method described later) and dissolving in deuterated chloroform.

The total acetyl group substitution degree of cellulose acetate (B) is calculated by converting the acetylation degree obtained according to the measurement method of the acetylation degree in ASTM: D-817-96 (test method for cellulose acetate, etc.) by the following formula. It is calculated by. This is the most common method for determining the degree of substitution of cellulose acetate.
DS = 162.14 × AV × 0.01 / (60.052-42.037 × AV × 0.01)
DS: Degree of total acetyl group substitution AV: Degree of acetylation (%)
First, 500 mg of dried cellulose acetate (sample) was precisely weighed and dissolved in 50 ml of a mixed solvent of ultrapure water and acetone (volume ratio 4: 1), and then 50 ml of 0.2N sodium hydroxide aqueous solution was added. Saponify at 25 ° C. for 2 hours. Next, 50 ml of 0.2N hydrochloric acid is added, and the amount of acetic acid released is titrated with a 0.2N sodium hydroxide aqueous solution (0.2N sodium hydroxide normal solution) using phenolphthalein as an indicator. In addition, a blank test (a test without using a sample) is performed by the same method. Then, AV (degree of acetylation) (%) is calculated according to the following formula.
AV (%) = (A−B) × F × 1.201 / sample weight (g)
A: Titration amount of 0.2N sodium hydroxide normal solution (ml)
B: Titration of 0.2N sodium hydroxide normal solution in blank test (ml)
F: Factor of 0.2N sodium hydroxide normal solution

(Composition distribution index: CDI)
For example, the composition distribution index (CDI) of cellulose acetate (B) is preferably 1.0 to 2.0, more preferably 1.0 to 2.0. 1.8, more preferably 1.0 to 1.6, particularly preferably 1.0 to 1.5. As the composition distribution index (CDI) of cellulose acetate (B) is smaller (closer to 1.0), the composition distribution (intermolecular acetyl group substitution degree distribution) becomes more uniform, and even if the substitution degree is low, the electrode active material layer Tend to be very strong. Moreover, even if there is much content of an electrode active material (A), generation | occurrence | production of the crack to an electrode active material layer can be prevented, and there exists a tendency for the charging / discharging characteristic of an electrical storage device to improve. This is because defects in the electrode active material layer are reduced due to the uniform composition distribution. In the case of low-substituted cellulose acetate, if the composition distribution is uniform, the water-solubility tends to be ensured in a range where the total degree of acetyl group substitution is wider than usual.

  Here, the compositional distribution index (CDI) is the ratio of the measured value to the theoretical value of the composition distribution half width [(actual value of the composition distribution half width) / (theoretical value of the composition distribution half width)]. Defined. The half width of the composition distribution is also referred to as “intermolecular acetyl group substitution degree half width” or simply “substitution degree distribution half width”.

  In order to evaluate the intermolecular uniformity of the degree of acetyl group substitution of cellulose acetate (B) (the degree of fluctuation of the degree of substitution between molecules), the full width at half maximum of the intermolecular acetyl group substitution degree distribution curve of cellulose acetate The size (also referred to as “half width”) can be used as an index. Note that the half-value width is that of the chart at half the height of the peak of the chart, where the acetyl group substitution degree is on the horizontal axis (x axis) and the abundance at this substitution degree is on the vertical axis (y axis). It is a width and is an index representing a standard of variation in distribution. The half value width of the substitution degree distribution can be determined by high performance liquid chromatography (HPLC) analysis. In addition, the method of converting the horizontal axis (elution time) of the cellulose ester elution curve in HPLC into the substitution degree (0 to 3) is described in JP-A No. 2003-201301 (paragraphs 0037 to 0040).

ｍ：酢酸セルロース１分子中の水酸基とアセチル基の全数
ｐ：酢酸セルロース１分子中の水酸基がアセチル置換されている確率
ｑ＝１−ｐ
ＤＰｗ：重量平均重合度（ＧＰＣ−光散乱法による）
重量平均重合度（ＤＰｗ）の測定法は後述する。 (Theoretical value of the half width of composition distribution)
The theoretical distribution of the half value width of composition distribution (substitution degree distribution half width) can be calculated stochastically. That is, the theoretical value of the composition distribution half width is obtained by the following equation (1).

m: Total number of hydroxyl groups and acetyl groups in one molecule of cellulose acetate p: Probability of hydroxyl groups in one molecule of cellulose acetate being acetyl substituted q = 1-p
DPw: weight average polymerization degree (by GPC-light scattering method)
A method for measuring the weight average degree of polymerization (DPw) will be described later.

ＤＳ：アセチル基総置換度
ＤＰｗ：重量平均重合度（ＧＰＣ−光散乱法による）
重量平均重合度（ＤＰｗ）の測定法は後述する。 Furthermore, when the theoretical value of the composition distribution half width is represented by the substitution degree and the polymerization degree, it is expressed as follows. The following formula (2) is a defining formula for obtaining the theoretical value of the composition distribution half width.

DS: Total substitution degree of acetyl group DPw: Weight average polymerization degree (by GPC-light scattering method)
A method for measuring the weight average degree of polymerization (DPw) will be described later.

(Measured value of composition distribution half width)
The above-mentioned measured value of the half width of the composition distribution is all the half width of the composition distribution obtained by HPLC analysis of cellulose acetate (sample) without pretreatment, or all remaining hydroxyl groups (unsubstituted hydroxyl groups) of cellulose acetate (sample) It is a half width of composition distribution obtained by HPLC analysis of cellulose acetate propionate obtained by propionylation.

  In general, for cellulose acetate having an acetyl group total substitution degree of 2.0 to 3.0, high performance liquid chromatography (HPLC) analysis can be performed without pretreatment, thereby obtaining the half width of the composition distribution. Can do. For example, JP 2011-158664 A describes a composition distribution analysis method for cellulose acetate having an acetyl group total substitution degree of 2.27 to 2.56.

  On the other hand, the measured value of the composition distribution half-width (substitution degree distribution half-width) of cellulose acetate (low-substituted cellulose acetate) having an acetyl group total substitution degree of less than 2.0 (particularly 0.5 to 1.4) is HPLC Before analysis, as a pretreatment, derivatization of the residual hydroxyl group in the cellulose acetate molecule is performed, and then HPLC analysis is performed. The purpose of this pretreatment is to convert the low-substituted cellulose acetate into a derivative that is easily dissolved in an organic solvent to enable HPLC analysis. That is, the residual hydroxyl group in the molecule is completely propionylated, and the fully derivatized cellulose acetate propionate (CAP) is subjected to HPLC analysis to determine the composition distribution half width (actual value). Here, the derivatization is completely carried out, there should be no residual hydroxyl groups in the molecule, and only acetyl and propionyl groups must be present. That is, the sum of the acetyl group total substitution degree (DSac) and the propionyl group total substitution degree (DSpr) is 3. This is because the relational expression: DSac + DSpr = 3 is used to create a calibration curve for converting the horizontal axis (elution time) of the HPLC elution curve of CAP to the total degree of acetyl group substitution (0 to 3). . Hereinafter, a method for measuring an actual measurement value of the composition distribution half-value width of low-substituted cellulose acetate will be described.

  Complete derivatization of cellulose acetate can be performed by reacting propionic anhydride with N, N-dimethylaminopyridine as a catalyst in a pyridine / N, N-dimethylacetamide mixed solvent. More specifically, a mixed solvent [pyridine / N, N-dimethylacetamide = 1/1 (v / v)] as a solvent is 20 parts by weight with respect to cellulose acetate (sample), and propionic anhydride as a propionylating agent. 6.0 to 7.5 equivalents based on the hydroxyl group of the cellulose acetate, and N, N-dimethylaminopyridine as a catalyst is used at 6.5 to 8.0 mol% with respect to the hydroxyl group of the cellulose acetate. Propionylation is carried out under conditions of reaction time of 1.5 to 3.0 hours. And after reaction, fully derivatized cellulose acetate propionate is obtained by making it precipitate using methanol as a precipitation solvent. More specifically, for example, at room temperature, 1 part by weight of the reaction mixture is added to 10 parts by weight of methanol to precipitate, and the resulting precipitate is washed 5 times with methanol and vacuum dried at 60 ° C. for 3 hours. Thus, fully derivatized cellulose acetate propionate (CAP) can be obtained. The polydispersity (Mw / Mn) and the weight average polymerization degree (DPw) described later were also measured using cellulose acetate (sample) as a fully derivatized cellulose acetate propionate (CAP) by this method.

  In the above HPLC analysis, a plurality of cellulose acetate propionates having different degrees of total acetyl group substitution are used as standard samples, HPLC analysis is performed with a predetermined measuring device and measurement conditions, and the analysis values of these standard samples are used. From the calibration curve [the curve showing the relationship between the elution time of cellulose acetate propionate and the total degree of acetyl group substitution (0 to 3), usually a cubic curve], the composition distribution half-width (measured value) of cellulose acetate (sample) ). What is required by HPLC analysis is the relationship between the elution time and the distribution of acetyl group substitution degree of cellulose acetate propionate. This is the relationship between the elution time of the substance in which all of the remaining hydroxy groups in the sample molecule have been converted to propionyloxy groups and the acetyl group substitution degree distribution. It is essentially the same as what you want.

The conditions for the above HPLC analysis are as follows.
Equipment: Agilent 1100 Series
Column: Waters Nova-Pak phenyl 60Å 4 μm (150 mm × 3.9 mmΦ) + guard column Column temperature: 30 ° C.
Detection: Varian 380-LC
Injection volume: 5.0 μL (sample concentration: 0.1% (wt / vol))
Eluent: Liquid A: MeOH / H ₂ O = 8/1 (v / v), Liquid B: CHCl ₃ / MeOH = 8/1 (v / v)
Gradient: A / B = 80/20 → 0/100 (28 min); Flow rate: 0.7 mL / min

  Substitution degree distribution curve obtained from the calibration curve [Substitution degree distribution curve of cellulose acetate propionate with the abscissa representing the amount of cellulose acetate propionate and the abscissa representing the degree of acetyl group substitution] ("Intermolecular substitution degree distribution For the maximum peak [E] corresponding to the total degree of acetyl group substitution, the half-value width of substitution degree distribution is determined as follows. The base [A] on the low substitution degree side of the peak [E] and the base line [AB] in contact with the base [B] on the high substitution degree side are drawn, and from this peak, the maximum peak [E] is drawn. Take a vertical line on the horizontal axis. An intersection point [C] between the perpendicular line and the baseline [AB] is determined, and an intermediate point [D] between the maximum peak [E] and the intersection point [C] is obtained. A straight line parallel to the base line [AB] is drawn through the intermediate point [D], and two intersection points [A ′, B ′] with the intermolecular substitution degree distribution curve are obtained. A perpendicular line is drawn from the two intersections [A ′, B ′] to the horizontal axis, and the width between the two intersections on the horizontal axis is defined as the half-value width of the maximum peak (ie, the substitution value distribution half-value width).

The half-value width of the substitution degree distribution depends on the degree of acetylation of the hydroxyl chain of each glucose chain constituting the molecular chain of cellulose acetate propionate in the sample. (Retention time) is different. Therefore, ideally, the holding time width indicates the width of the composition distribution (in units of substitution degree). However, there are tubes (such as a guide column for protecting the column) that do not contribute to the distribution in HPLC. Therefore, depending on the configuration of the measurement apparatus, the width of the holding time that is not caused by the width of the composition distribution is often included as an error. As described above, this error is affected by the length and inner diameter of the column, the length from the column to the detector, the handling, and the like, and varies depending on the apparatus configuration. For this reason, the half value width of the substitution degree distribution of cellulose acetate propionate can be usually obtained as the correction value Z based on the correction formula represented by the following formula. By using such a correction formula, even if the measurement apparatus (and measurement conditions) are different, a more accurate substitution degree distribution half-value width (actual measurement value) can be obtained as the same (substantially the same) value.
Z = (X ² −Y ² ) ^1/2
[In the formula, X is the half-value width (uncorrected value) of the substitution degree distribution obtained with a predetermined measuring apparatus and measurement conditions. Y = (a−b) x / 3 + b (0 ≦ x ≦ 3). Here, a is the half-value width of the substitution degree distribution of cellulose acetate having a total substitution degree of 3 determined using the same measuring apparatus and measurement conditions as X, and b is the total substitution degree of 3 determined using the same measuring apparatus and measurement conditions as X above. It is a half value width of substitution degree distribution of cellulose propionate. x is the total acetyl group substitution degree of the measurement sample (0 ≦ x ≦ 3)]

  The cellulose acetate (or cellulose propionate) having a total substitution degree of 3 refers to a cellulose ester in which all of the hydroxy groups (hydroxyl groups) of cellulose are esterified, and actually (ideally) the substitution degree. It is a cellulose ester having no distribution half width (that is, a substitution degree distribution half width of 0).

  In the present invention, the actually measured value of the composition distribution half width (substitution degree distribution half width) of cellulose acetate (B) is not particularly limited, but is preferably 0.12 to 0.34, more preferably 0.13 to 0.3. 25.

  The substitution degree distribution theoretical formula (formula for obtaining a theoretical value of the composition distribution half width) described above is a stochastic calculation value that assumes that all acetylation and deacetylation proceed independently and equally. That is, the calculated value according to the binomial distribution. Such an ideal situation is not realistic. Unless special measures are taken for the hydrolysis reaction of cellulose acetate or the post-treatment after the reaction, the substitution degree distribution of the cellulose ester is much wider than that stochastically determined by the binomial distribution. In particular, low-substituted cellulose acetate tends to have a particularly wide substitution degree distribution because the number of partial deacetylation reactions is large in the production process.

  In producing low-substituted cellulose acetate, as one of the special measures for the reaction, for example, it is conceivable to maintain the system under the condition where deacetylation and acetylation are balanced. However, in this case, the decomposition of cellulose proceeds with an acid catalyst, which is not preferable. Another special contrivance for the reaction is to employ reaction conditions in which the deacetylation rate is slow for low substitution products. However, conventionally, such a specific method is not known. In other words, no special device for the reaction is known that controls the substitution degree distribution of the cellulose ester to follow the binomial distribution according to the reaction probability theory. Furthermore, various circumstances such as non-uniformity in the acetylation process (cellulose acetylation process) and partial or temporary precipitation due to water added stepwise in the maturation process (cellulose hydrolysis process) It works in the direction to make the substitution degree distribution wider than the binomial distribution, avoiding all of these, and realizing the ideal condition is impossible in practice. This is similar to the fact that an ideal gas is an ideal product, and the behavior of an actual gas is more or less different.

  In the synthesis and post-treatment of conventional low-substituted cellulose acetate, little attention has been paid to the problem of such substitution degree distribution, and substitution degree distribution has not been measured, verified, or considered. For example, according to the literature (Journal of the Textile Society of Japan, 42, p25 (1986)), it is argued that the solubility of low-substituted cellulose acetate is determined by the distribution of acetyl groups to the glucose residues 2, 3, and 6. The composition distribution is not considered at all.

  According to the study by the present inventors, as described later, the substitution degree distribution of cellulose acetate can be surprisingly controlled by devising the post-treatment conditions after the cellulose acetate hydrolysis step. Literature (CiBment, L., and Rivibre, C., Bull. SOC. Chim., (5) 1, 1075 (1934), Sookne, AM, Rutherford, HA, Mark, H., and Harris, M. J. Research Natl. Bur. Standards, 29, 123 (1942), AJ Rosenthal, BB White Ind. Eng. Chem., 1952, 44 (11), pp 2693-2696.) In the precipitation fractionation of cellulose acetate No. 3, fractionation depending on the molecular weight and slight fractionation accompanying the substitution degree (chemical composition) occur, and the substitution degree (chemical composition) as found by the present inventors. There is no report that a remarkable fraction can be produced. Furthermore, it has not been verified that the substitution degree distribution (chemical composition) can be controlled by dissolution fractionation or precipitation fractionation for low-substituted cellulose acetate.

  Another device for narrowing the substitution degree distribution found by the present inventors is a hydrolysis reaction (aging reaction) of cellulose acetate at a high temperature of 90 ° C. or higher (or higher than 90 ° C.). Conventionally, although detailed analysis and consideration have not been made on the degree of polymerization of a product obtained by a high-temperature reaction, it has been considered that decomposition of cellulose is preferred in a high-temperature reaction at 90 ° C. or higher. This idea can be said to be a belief (stereotype) based solely on the consideration of viscosity. When the present inventors hydrolyze cellulose acetate to obtain low-substituted cellulose acetate, it is in a large amount of acetic acid at a high temperature of 90 ° C. or higher (or higher than 90 ° C.), preferably in the presence of a strong acid such as sulfuric acid. It was found that when the reaction was carried out with the above, the degree of polymerization was not lowered, but the viscosity was lowered with a decrease in CDI. That is, it has been clarified that the viscosity decrease due to the high temperature reaction is not due to a decrease in the degree of polymerization but is based on a decrease in structural viscosity due to a narrow substitution degree distribution. When cellulose acetate is hydrolyzed under the above conditions, not only forward reaction but also reverse reaction occurs, so the product (low-substituted cellulose acetate) has a very small CDI, and the solubility in water is significantly improved. On the other hand, when cellulose acetate is hydrolyzed under conditions where reverse reaction is unlikely to occur, the substitution degree distribution becomes wide due to various factors, and cellulose acetate and acetyl groups having a total degree of substitution of less than 0.4 acetyl groups that are difficult to dissolve in water. The content of cellulose acetate exceeding the total substitution degree 1.1 increases, and the solubility in water as a whole decreases.

(Standard deviation of substitution degree at 2, 3, 6 position)
The degree of substitution of each acetyl group at the 2, 3, and 6 positions of the glucose ring of cellulose acetate (B) can be measured by the NMR method according to the method of Tezuka (Carbonydr. Res. 273, 83 (1995)). That is, a free hydroxyl group of a cellulose acetate sample is propionylated with propionic anhydride in pyridine. The obtained sample is dissolved in deuterated chloroform, and a ¹³ C-NMR spectrum is measured. The carbon signal of the acetyl group appears in the order of 2, 3, 6 from the high magnetic field in the region of 169 ppm to 171 ppm, and the signal of the carbonyl carbon of the propionyl group appears in the same order in the region of 172 ppm to 174 ppm. From the abundance ratio of the acetyl group and propionyl group at the corresponding positions, the degree of substitution of each acetyl group at the 2, 3, 6 positions of the glucose ring in the original cellulose acetate (B) can be determined. In addition, the sum of the substitution degree of each acetyl group at the 2, 3, and 6 positions thus obtained is the total substitution degree of acetyl group, and the total substitution degree of acetyl group can be obtained by this method. The total substitution degree of acetyl group can be analyzed by ¹ H-NMR in addition to ¹³ C-NMR.

The standard deviation σ of the substitution degree of acetyl groups at the 2, 3, 6 positions is defined by the following formula.

  Although the standard deviation of the acetyl group substitution degree at the 2, 3 and 6 positions of the glucose ring of cellulose acetate (B) is not particularly limited, it is preferably 0.08 or less (0 to 0.08). In the cellulose acetate (B) having a standard deviation of 0.08 or less, the 2, 3, and 6 positions of the glucose ring are evenly substituted, and particularly in the case of a low-substituted cellulose acetate, it has excellent solubility in water. Tend. In addition, the strength of the electrode active material layer tends to be improved.

(Polydispersity (Mw / Mn))
In the present invention, the polydispersity (dispersity; Mw / Mn) of cellulose acetate (B) is a value obtained by GPC-light scattering method using cellulose acetate (sample) without pretreatment (for example, total acetyl group In the case of cellulose acetate having a degree of substitution of 2.0 to 3.0), or cellulose acetate propionate obtained by propionylating all remaining hydroxyl groups of cellulose acetate (sample), it was determined by GPC-light scattering method. Value (for example, in the case of low-substituted cellulose acetate having a total degree of acetyl group substitution of less than 2.0 (particularly 0.5 to 1.1)).

  The polydispersity (dispersion degree; Mw / Mn) of cellulose acetate (B) is not particularly limited, but is in the range of 1.2 to 2.5, particularly when cellulose acetate (B) is a low-substituted cellulose acetate. It is preferable that Cellulose acetate (B) having polydispersity Mw / Mn in the above range has a uniform molecular size, and is excellent in solubility in water and tends to improve the strength of the electrode active material layer. In particular, when the cellulose acetate (B) is diacetyl cellulose or triacetyl cellulose, the polydispersity is preferably more than 2.0 and not more than 7.5. There exists a tendency for the electrode active material layer excellent in intensity | strength to be obtained by using the cellulose acetate (B) which has polydispersity Mw / Mn in said range.

The number average molecular weight (Mn), weight average molecular weight (Mw) and polydispersity (Mw / Mn) of cellulose acetate (B) can be determined by a known method using HPLC. In the present invention, polydispersity (Mw / Mn) of cellulose acetate (B) is determined by cellulose acetate without any pretreatment (sample; for example, cellulose acetate having an acetyl group total substitution degree of 2.0 to 3.0) or acetic acid. It can be determined by a GPC-light scattering method using cellulose acetate propionate obtained by propionylating all remaining hydroxyl groups of cellulose (sample; for example, low-substituted cellulose acetate). In particular, the polydispersity (Mw / Mn) of cellulose acetate having an acetyl group total substitution degree of less than 2.0 is used to obtain a measured value of the above-described half-width of the composition distribution in order to make the measurement sample soluble in an organic solvent. In the same manner as above, the cellulose acetate (sample) is converted into a fully derivatized cellulose acetate propionate (CAP) and then subjected to size exclusion chromatography analysis under the following conditions (GPC-light scattering method) .
Equipment: GPC “SYSTEM-21H” manufactured by Shodex
Solvent: Acetone Column: 2 GMHxl (Tosoh), same guard column Flow rate: 0.8 ml / min
Temperature: 29 ° C
Sample concentration: 0.25% (wt / vol)
Injection volume: 100 μl
Detection: MALLS (multi-angle light scattering detector) (manufactured by Wyatt, “DAWN-EOS”)
MALLS correction standard substance: PMMA (molecular weight 27600)

(Weight average degree of polymerization (DPw))
In the present invention, the weight average polymerization degree (DPw) of cellulose acetate (B) is a value obtained by GPC-light scattering method using cellulose acetate (sample) without pretreatment (for example, the total substitution degree of acetyl group is 2). (In the case of cellulose acetate of 0.0 to 3.0), or a value obtained by GPC-light scattering method using cellulose acetate propionate obtained by propionylating all remaining hydroxyl groups of cellulose acetate (sample) (for example, The total degree of acetyl group substitution is less than 2.0 (particularly in the case of low-substituted cellulose acetate having 0.5 to 1.1).

  The weight average polymerization degree (DPw) of cellulose acetate (B) in the present invention is preferably in the range of 50 to 800. When the weight average degree of polymerization (DPw) is too low, the strength of the electrode active material layer tends to be low. On the other hand, if the weight average degree of polymerization (DPw) is too high, filterability tends to deteriorate. The weight average polymerization degree (DPw) is preferably 55 to 700, and more preferably 60 to 600.

  The weight average degree of polymerization (DPw) is the same as in the case of obtaining the measured value of the half width of the composition distribution as in the case of the polydispersity (Mw / Mn). After cellulose acetate (sample; for example, low-substituted cellulose acetate) is completely derivatized cellulose acetate propionate (CAP) Determined by performing size exclusion chromatography analysis (GPC-light scattering method).

  As described above, the molecular weight (degree of polymerization) of water-soluble cellulose acetate (B) (particularly, low-substituted cellulose acetate having a total substitution degree of acetyl group of 0.5 to 1.1), polydispersity (Mw / Mn ) Is measured by GPC-light scattering method (GPC-MALLS, GPC-LALLS, etc.). Note that detection of light scattering is generally difficult with an aqueous solvent. This is because aqueous solvents generally have a large amount of foreign matter and are easily contaminated by secondary contamination once purified. In addition, in the case of aqueous solvents, the spread of molecular chains may not be stable due to the influence of ionic dissociation groups present in a trace amount, and if water-soluble inorganic salt (for example, sodium chloride) is added to suppress this, it will dissolve. The state may become unstable, and an aggregate may be formed in an aqueous solution. One effective method for avoiding this problem is to derivatize low-substituted cellulose acetate so that it is dissolved in an organic solvent that is less contaminated and less susceptible to secondary contamination. Is to do. Propionylation is effective as the derivatization of low-substituted cellulose acetate for this purpose, and the specific reaction conditions and post-treatment are as described in the explanation of the measured value of the half width of the composition distribution.

(6% viscosity)
Although 6% viscosity of a cellulose acetate (B) is not specifically limited, 5-500 mPa * s is preferable, More preferably, it is 6-300 mPa * s. If the 6% viscosity is too high, filterability may deteriorate. On the other hand, if the 6% viscosity is too low, the strength of the electrode active material layer tends to decrease.

The 6% viscosity of cellulose acetate (B) can be measured by the following method.
Add 3.00 g of dry sample to a 50 ml volumetric flask and add distilled water to dissolve. The obtained 6 wt / vol% solution is transferred to a predetermined Ostwald viscometer mark and temperature-controlled at 25 ± 1 ° C. for about 15 minutes. Measure the flow-down time between the time marks and calculate the 6% viscosity by the following formula.
6% viscosity (mPa · s) = C × P × t
C: Sample solution constant P: Sample solution density (0.997 g / cm ³ )
t: The number of seconds that the sample solution flows down The sample solution constant is the same as described above using a standard solution for viscometer calibration [manufactured by Showa Oil Co., Ltd., trade name “JS-200” (based on JIS Z 8809)]. Measure the flow-down time and obtain it from the following formula.
Sample solution constant = {Standard solution absolute viscosity (mPa · s)} / {Standard solution density (g / cm ³ ) × Standard solution flow down seconds}

  Cellulose acetate (B) can be produced by a known or conventional method. For example, cellulose diacetate can be produced by the methods described in JP2009-155555A, JP2011-158664A, and the like. Moreover, as a cellulose acetate (B), a commercial item can also be used. Below, among cellulose acetate (B), the manufacturing method of low substituted cellulose acetate (especially cellulose acetate (B) whose acetyl group total substitution degree is 0.5-1.1) is demonstrated in detail.

(Production of low-substituted cellulose acetate)
Among the cellulose acetates (B), the low-substituted cellulose acetate is, for example, (a) a medium to high-substituted cellulose acetate hydrolysis step (aging step), (b) a precipitation step, and as necessary (c) ) It can be produced by a method including washing and neutralization steps.

[(A) Hydrolysis step (aging step)]
In this step, medium to high-substituted cellulose acetate (hereinafter sometimes referred to as “raw cellulose acetate”) is hydrolyzed. The total acetyl group substitution degree of the medium to high substitution cellulose acetate used as the raw material is preferably 1.5 to 3, more preferably 2 to 3. Examples of the raw material cellulose acetate include commercially available cellulose diacetate (for example, cellulose acetate having a total acetyl group substitution degree of 2.0 to less than 2.6) and cellulose triacetate (for example, acetic acid having a total substitution degree of acetyl group of 2.6 or more). Cellulose).

  The hydrolysis reaction can be performed by reacting raw material cellulose acetate and water in an organic solvent in the presence of a catalyst (aging catalyst). Examples of the organic solvent include acetic acid, acetone, alcohol (such as methanol), and mixed solvents thereof. Among these, a solvent containing at least acetic acid is preferable. As the catalyst, a catalyst generally used as a deacetylation catalyst can be used. As the catalyst, sulfuric acid is particularly preferable.

  Although the usage-amount of an organic solvent (for example, acetic acid) is not specifically limited, 0.5-50 weight part is preferable with respect to 1 weight part of raw material cellulose acetate, More preferably, it is 1-20 weight part, More preferably, it is 3 -10 parts by weight.

  The amount of catalyst (for example, sulfuric acid) used is preferably 0.005 to 1 part by weight, more preferably 0.01 to 0.5 part by weight, and still more preferably 0.02 with respect to 1 part by weight of raw material cellulose acetate. -0.3 parts by weight. If the amount of the catalyst is too small, the hydrolysis time becomes too long, which may cause a decrease in the molecular weight of cellulose acetate. On the other hand, if the amount of the catalyst is too large, the degree of change in the depolymerization rate with respect to the hydrolysis temperature increases, and even if the hydrolysis temperature is low to some extent, the depolymerization rate increases and it is difficult to obtain cellulose acetate having a somewhat high molecular weight. Become.

  The amount of water in the hydrolysis step is not particularly limited, but is preferably 0.5 to 20 parts by weight, more preferably 1 to 10 parts by weight, and even more preferably 2 to 7 parts by weight with respect to 1 part by weight of raw material cellulose acetate. Part. The amount of the water is preferably 0.1 to 5 parts by weight, more preferably 0.3 to 2 parts by weight, and still more preferably 0.5 to 5 parts by weight with respect to 1 part by weight of the organic solvent (eg, acetic acid). 1.5 parts by weight. Although all amounts of water may be present in the system at the start of the reaction, in order to prevent precipitation of cellulose acetate, a part of the water to be used is present in the system at the start of the reaction, and the remaining water is removed. It may be added to the system in 1 to several times.

  Although the reaction temperature in a hydrolysis process is not specifically limited, 40-130 degreeC is preferable, More preferably, it is 50-120 degreeC, More preferably, it is 60-110 degreeC. In particular, when the reaction temperature is 90 ° C. or higher (or a temperature exceeding 90 ° C.), preferably when a strong acid such as sulfuric acid is used as a catalyst and acetic acid is used excessively as a reaction solvent, a positive reaction (hydrolysis reaction). In addition to this, a reverse reaction (acetylation reaction) occurs, and as a result, the substitution degree distribution becomes narrow, and it is possible to obtain a low substituted cellulose acetate having a very small composition distribution index CDI without any particular ingenuity in the post-treatment conditions. . Even when the reaction temperature is 90 ° C. or lower, as described later, in the precipitation step, precipitation is performed using a mixed solvent containing two or more solvents as the precipitation solvent, precipitation separation and / or dissolution. By performing the fractionation, a low-substituted cellulose acetate having a very small composition distribution index CDI can be obtained.

[(B) Precipitation step]
In this step, after completion of the hydrolysis reaction, the temperature of the reaction system is cooled to room temperature, and a precipitation solvent is added to precipitate low-substituted cellulose acetate. As the precipitation solvent, an organic solvent miscible with water or an organic solvent having high solubility in water can be used. Examples include ketones such as acetone and methyl ethyl ketone; alcohols such as methanol, ethanol and isopropyl alcohol; esters such as ethyl acetate; nitrogen-containing compounds such as acetonitrile; ethers such as tetrahydrofuran; and mixed solvents thereof.

  When a mixed solvent containing two or more kinds of solvents is used as the precipitation solvent, the same effect as the precipitation fractionation described later can be obtained, the composition distribution (intermolecular substitution degree distribution) is narrow, and the low substitution with a small composition distribution index (CDI). Degree cellulose acetate can be obtained. Preferred examples of the mixed solvent include a mixed solvent of acetone and methanol, a mixed solvent of isopropyl alcohol and methanol, and the like.

  Further, by performing precipitation fractionation (fractional precipitation) and / or dissolution fractionation (fractional dissolution) on the low-substituted cellulose acetate obtained by precipitation, the composition distribution (intermolecular substitution degree distribution) is narrow, Low substituted cellulose acetate having a very small composition distribution index (CDI) can be obtained.

  For precipitation fractionation, for example, low-substituted cellulose acetate (solid matter) obtained by precipitation is dissolved in water to obtain an aqueous solution having an appropriate concentration (for example, 2 to 10% by weight, preferably 3 to 8% by weight). Then, a poor solvent is added to this aqueous solution (or the above aqueous solution is added to the poor solvent), and kept at an appropriate temperature (for example, 30 ° C. or lower, preferably 20 ° C. or lower) to precipitate low-substituted cellulose acetate, This can be done by collecting the precipitate. Examples of the poor solvent include alcohols such as methanol and ketones such as acetone. The amount of the poor solvent used is preferably, for example, 1 to 10 parts by weight, and more preferably 2 to 7 parts by weight with respect to 1 part by weight of the aqueous solution.

  For the dissolution fractionation, for example, the low-substituted cellulose acetate (solid matter) obtained by the precipitation or the low-substituted cellulose acetate (solid matter) obtained by the precipitation fractionation is mixed with water and an organic solvent (for example, acetone or the like). A mixed solvent of ketone, alcohol such as ethanol) and stirring at an appropriate temperature (for example, 20 to 80 ° C., preferably 25 to 60 ° C.), and then separated into a concentrated phase and a diluted phase by centrifugation, A precipitation solvent (for example, a ketone such as acetone or an alcohol such as methanol) is added to the diluted phase, and the precipitate (solid matter) is recovered. The concentration of the organic solvent in the mixed solvent of water and organic solvent is preferably, for example, 5 to 50% by weight, and more preferably 10 to 40% by weight.

[(C) Washing and neutralization step]
The precipitate (solid matter) obtained in the above-described (b) precipitation step is preferably washed with an organic solvent (poor solvent) such as alcohol such as methanol or ketone such as acetone. Moreover, it is also preferable to wash and neutralize with an organic solvent containing a basic substance (for example, alcohol such as methanol, ketone such as acetone).

  Examples of the basic substance include alkali metal compounds (for example, alkali metal hydroxides such as sodium hydroxide and potassium hydroxide; alkali metal carbonates such as sodium carbonate and potassium carbonate; alkali metal carbonates such as sodium hydrogen carbonate) Hydrogen salts; alkali metal carboxylates such as sodium acetate and potassium acetate; sodium alkoxides such as sodium methoxide and sodium ethoxide), alkaline earth metal compounds (for example, alkaline earth such as magnesium hydroxide and calcium hydroxide) Metal hydroxides; alkaline earth metal carbonates such as magnesium carbonate and calcium carbonate; alkaline earth metal carboxylates such as magnesium acetate and calcium acetate; alkaline earth metal alkoxides such as magnesium ethoxide, etc.) can be used. . Among these, alkali metal compounds such as potassium acetate are particularly preferable.

  By washing and neutralization, impurities such as a catalyst (such as sulfuric acid) used in the hydrolysis step can be efficiently removed.

  In the electrode active material layer of the electrode for an electricity storage device of the present invention, cellulose acetate (B) can be used alone or in combination of two or more.

  Although content of the cellulose acetate (B) in the said electrode active material layer is not specifically limited, 0.1-50 weight% is preferable with respect to an electrode active material layer (100 weight%), More preferably, it is 1-30. % By weight, more preferably 2 to 20% by weight, particularly preferably 5 to 15% by weight. There exists a tendency which can obtain the electrical storage device (a battery, a capacitor, etc.) which has the outstanding charging / discharging characteristic by controlling content of a cellulose acetate (B) to the above-mentioned range.

3. Other Components The electrode active material layer may contain components other than the electrode active material (A) and cellulose acetate (B) (sometimes referred to as “other components”). As other components, known or commonly used additives used for electrodes in lithium ion batteries and non-aqueous electric double layer capacitors can be used, and are not particularly limited. For example, a conductive additive (for example, acetylene black, Graphite, metal powder, etc.), surfactants, resins other than cellulose acetate (B), fillers (excluding the negative electrode active material (A)), light stabilizers, colorants, flow modifiers, antistatic agents, antibacterial agents Agents, ultraviolet absorbers, antioxidants, lubricants, plasticizers, mold release agents, flame retardants and the like. The amount of other components used is not particularly limited, but the content in the electrode active material layer (100% by weight) is preferably 30% by weight or less, more preferably 15% by weight or less, and still more preferably 5% by weight. % Or less. The total addition amount of these additives is preferably 30% by weight or less, more preferably 20% by weight or less, and still more preferably 10% by weight or less as the content in the electrode active material layer (100% by weight).

  The electrode active material layer (particularly, the negative electrode active material layer in a lithium ion battery) may not contain styrene-butadiene rubber. When the above-described negative electrode active material layer is formed by an aqueous manufacturing method, the stability of the electrode-forming composition (aqueous) is improved and the productivity of the negative electrode tends to be improved by not including styrene-butadiene rubber. is there.

  The electrode for an electricity storage device of the present invention may have a member (component) other than the above-described current collector and electrode active material layer.

<Method for producing electrode for power storage device>
The electrode for an electricity storage device of the present invention can be produced by a known or conventional method for producing an electrode of an electricity storage device, and is not particularly limited. For example, the electrode active material layer in the electrode is a dry method (a method that does not use a solvent), It can be produced by any of wet methods (method using a solvent). Among these, a wet method is preferable in that an electrode excellent in adhesion between the current collector and the electrode active material layer can be easily obtained. The electrode for an electricity storage device of the present invention includes, among wet methods, a method using an organic solvent as a solvent (sometimes referred to as “organic solvent-based production method”) and a method using water as a solvent (“water-based method”). It may also be produced by any of the methods described in the above. For example, it may be preferable to adopt a water-based manufacturing method from the viewpoint of environmental protection or improvement in safety of the working environment.

  Among the methods for producing an electrode for an electricity storage device of the present invention, as an organic solvent-based production method, specifically, electrode formation comprising an electrode active material (A), cellulose acetate (B), and an organic solvent as essential components A step of preparing a composition for an electrode (sometimes referred to as “step 1”), and the electrode-forming composition obtained in step 1 is applied on a current collector and dried, and then on the current collector. And a step of forming an electrode active material layer (sometimes referred to as “step 2”) as an essential step.

[Step 1]
In step 1 of the organic solvent-based production method described above, an electrode-forming composition ("electrode-forming composition (") containing the electrode active material (A), cellulose acetate (B), and an organic solvent as essential components. Organic solvent system)) ") may be prepared. As the organic solvent, known or commonly used organic solvents can be used, and preferred organic solvents vary depending on the total degree of acetyl group substitution of cellulose acetate (B) and are not particularly limited. For example, acetone, Ketones such as methyl ethyl ketone, isobutyl ketone, methyl t-butyl ketone and cyclohexanone; alcohols such as methanol, ethanol, isopropanol and butanol; linear or cyclic ethers such as tetrahydrofuran (THF) and dioxane; N, N-dimethylformamide (DMF), Examples include aprotic polar solvents such as dimethylacetamide, dimethylsulfoxide and N-methylpyrrolidone (NMP); halogen solvents such as methylene chloride and chloroform; and mixtures thereof. For example, among cellulose acetate (B), low-substituted cellulose acetate (for example, cellulose acetate having an acetyl group total substitution degree of 0.5 to 1.1) has particularly high solubility in water, NMP, and the like. Cellulose diacetate (for example, cellulose acetate having an acetyl group total substitution degree of 2 or more and less than 2.6) is particularly highly soluble in acetone, THF, DMF, etc .; cellulose triacetate (for example, acetyl group total substitution degree is Since 2.6 or more cellulose acetate is particularly highly soluble in chloroform, methylene chloride, and the like, it is preferable to select an appropriate solvent according to the total degree of acetyl group substitution of cellulose acetate (B) to be used.

  The amount of the organic solvent used can be appropriately selected according to the type and amount of use of the electrode active material (A), such as the total acetyl group substitution degree and amount of use of cellulose acetate (B), and is not particularly limited. B) 100 to 3000 parts by weight is preferable with respect to 100 parts by weight, more preferably 200 to 2000 parts by weight, and still more preferably 300 to 1000 parts by weight.

The method for preparing the electrode-forming composition (organic solvent system) in Step 1 is not particularly limited. For example, the electrode active material (A), cellulose acetate (B), an organic solvent, and further, if necessary. Examples include a method in which other additives and the like are supplied to a general-purpose mixer and mixed uniformly. Although it does not specifically limit as a mixer, For example, a container with a stirrer, a Henschel mixer, a bead mill, a plast mill, a Banbury mixer, a planetary mixer, an extruder etc. are mentioned. The electrode-forming composition (organic solvent system) can be prepared by, for example, a one-stage mixing operation in which the components are mixed at one time, or in two steps in which the components are mixed stepwise (sequentially). It can also be performed by the above multistage mixing operation. Among these, from the viewpoint of dispersibility of the electrode active material (A), the preparation of the electrode forming composition (organic solvent system) is preferably performed by a mixing operation including the following two steps (stages).
(I) Step of preparing cellulose acetate (B) solution by dissolving cellulose acetate (B) in an organic solvent (ii) Step of blending and dispersing electrode active material (A) in cellulose acetate (B) solution

  By the process 1, the composition for electrode formation (organic solvent type | system | group) which contains an electrode active material (A), a cellulose acetate (B), and an organic solvent as an essential component is obtained.

[Step 2]
In step 2 of the organic solvent-based manufacturing method described above, the electrode-forming composition (organic solvent-based) obtained in step 1 is applied onto a current collector and dried to provide an electrode on the current collector. An active material layer is formed. As a method for applying the electrode forming composition (organic solvent system) onto the current collector, a known or conventional method can be applied, and is not particularly limited. For example, a reverse roll method, a direct roll method, a gravure method, an extensible method. Examples include a rouge method, a brush coating method, and a doctor blade method. The thickness of the electrode-forming composition (organic solvent system) applied on the current collector can be appropriately set according to the thickness of the electrode active material layer formed by drying, and is not particularly limited. , 1 to 1000 μm can be selected.

  In Step 2, a known or conventional method can be applied as a method for drying the electrode-forming composition (organic solvent) applied on the current collector, and is not particularly limited. Among these, from the viewpoint of productivity, a drying method by heating is preferable. In addition, drying by heating can be performed under normal pressure, or can be performed under reduced pressure or under pressure. Although the heating temperature in the said drying is not specifically limited, 80-200 degreeC is preferable, More preferably, it is 110-190 degreeC, More preferably, it is 140-180 degreeC. By setting the heating temperature to 80 ° C. or higher, the drying time can be shortened and the productivity tends to be further improved. On the other hand, when the heating temperature is set to 200 ° C. or lower, a decrease in charge / discharge characteristics of the electricity storage device tends to be suppressed. The heating temperature can be controlled to be constant during drying, or can be controlled to vary stepwise or continuously. Further, the heating time (total time) is not particularly limited, but can be appropriately selected from 0.1 to 60 minutes, for example.

  In the electrode for an electricity storage device of the present invention, since cellulose acetate (B) functions as a binder in the electrode active material layer, an electrode obtained by using a conventional organic solvent-based composition, specifically, for example, lithium Compared to the electrode (especially the negative electrode) using polyvinylidene fluoride as a binder in ion batteries, the above heating temperature can be set higher (for example, it can be set to a temperature exceeding 110 ° C.), and the time required for drying is greatly reduced. Is possible. Therefore, the electrode for an electricity storage device of the present invention can significantly improve productivity by shortening the step 2. In addition, even when an organic solvent that easily absorbs moisture (such as NMP) is used, moisture can be removed to a high degree by increasing the heating temperature, and the deterioration of battery characteristics or capacitor characteristics due to moisture can be suppressed. it can. On the other hand, an electrode (especially a negative electrode) using polyvinylidene fluoride as a binder in a conventional lithium ion battery has a high heating temperature during drying (for example, a temperature exceeding 110 ° C.). The crystal melting of vinylidene chloride occurs, the binding property is lowered, and the battery characteristics are significantly lowered. For this reason, it has been difficult to shorten the time required for drying by increasing the heating temperature during drying. Further, it is difficult to remove moisture at a high level, and there is a possibility that battery characteristics may be deteriorated due to moisture. Therefore, especially when the electrode for an electricity storage device of the present invention is an electrode for a lithium ion battery (particularly, a negative electrode), the above-mentioned merit can be enjoyed effectively.

  Through Steps 1 and 2, an electricity storage having at least a current collector and an electrode active material layer [electrode active material layer containing electrode active material (A) and cellulose acetate (B) as essential components] on the current collector A device electrode is obtained. In addition, the above-described organic solvent-based manufacturing method is used to improve the adhesion between the current collector and the electrode active material layer using steps other than steps 1 and 2 (for example, using a die press or a roll press). A step of applying a pressure treatment; a step of performing a cutting process; a step of laminating electrodes and other members, and the like].

  On the other hand, among the method for producing an electrode for an electricity storage device of the present invention, as an aqueous production method, specifically, an electrode active material (A), cellulose acetate having an acetyl group total substitution degree of 0.5 to 1.1 (B) (sometimes referred to as “cellulose acetate (B ′)”), a step of preparing an electrode-forming composition containing water as an essential component (sometimes referred to as “step 3”), and step 3 Applying the electrode-forming composition obtained in (1) above onto a current collector and drying to form an electrode active material layer on the current collector (sometimes referred to as “step 4”). The method of including as an essential process is mentioned.

[Step 3]
In step 3 of the above-described aqueous production method, an electrode-forming composition (“electrode-forming composition (aqueous)) containing electrode active material (A), cellulose acetate (B ′), and water as essential components. Is prepared).

  The method for preparing the electrode-forming composition (aqueous) in Step 3 is not particularly limited, and for example, the electrode active material (A), cellulose acetate (B ′), water, and, if necessary, other Examples thereof include a method in which additives and the like are supplied to a general-purpose mixer and mixed uniformly. It does not specifically limit as a mixer, The mixer etc. which were illustrated in the process 1 are mentioned. The electrode-forming composition (aqueous system) can be prepared by, for example, a one-step mixing operation in which the components are mixed together, or in two or more steps in which the components are mixed stepwise (sequentially). It can also be performed by a multistage mixing operation. Among these, from the viewpoint of productivity, the preparation of the electrode forming composition (aqueous) is preferably performed by a one-step mixing operation.

  The amount of water used can be appropriately selected depending on the amount of cellulose acetate (B ′) used, the type of electrode active material (A) and the amount used, and is not particularly limited, but is 100 parts by weight of cellulose acetate (B). On the other hand, 100-10000 weight part is preferable, More preferably, it is 200-8000 weight part, More preferably, it is 300-6000 weight part.

  Among the methods for producing an electrode for an electricity storage device of the present invention, an aqueous production method is more useful than conventional methods in that an electrode-forming composition (aqueous) can be produced by a one-step mixing operation. In an electrode obtained by using a conventional aqueous composition, specifically, for example, an aqueous composition for forming an electrode for lithium ion batteries (particularly, a negative electrode), a binder such as styrene-butadiene rubber is used. In addition, it is necessary to use a thickener such as carboxymethylcellulose together, and in order to prepare a composition in which rheological properties such as viscosity are appropriately controlled, the above-mentioned binder and thickener are added to water. It had to be done sequentially and carefully. If a composition is prepared by a one-step mixing operation and an electrode is produced from the composition, it is assumed that the binding property of the electrode becomes poor, but the charge / discharge characteristics of the electricity storage device are significantly reduced. Was produced. On the other hand, in the present invention, cellulose acetate (B ′) has both a function as a binder and a function as a thickener, and is also excellent in water solubility. Careful mixing operation is unnecessary, and even if the electrode-forming composition is prepared by one-step mixing operation, the charge / discharge characteristics of the electricity storage device do not deteriorate. For this reason, according to the method for producing an electrode for an electricity storage device of the present invention, according to the aqueous production method, the production process of the electrode forming composition can be simplified, and the productivity of the electrode and the electricity storage device including the electrode is improved. . In addition, the water-based manufacturing method can contribute to environmental protection and safety improvement of the working environment.

[Step 4]
In step 4 of the above-described aqueous manufacturing method, the electrode-forming composition (aqueous) obtained in step 3 is applied onto a current collector and dried to form an electrode active material layer on the current collector. Form. Examples of the method of applying the electrode forming composition (aqueous) on the current collector include the same methods as those exemplified in Step 2. In addition, the thickness of the electrode forming composition (aqueous) applied on the current collector can be appropriately set according to the thickness of the electrode active material layer formed by drying, and is not particularly limited. It can select suitably from -1000 micrometers.

  In Step 4, a known or conventional method can be applied as a method for drying the electrode-forming composition (aqueous system) applied on the current collector, and is not particularly limited. Among these, from the viewpoint of productivity, a drying method by heating is preferable. In addition, drying by heating can be performed under normal pressure, or can be performed under reduced pressure or under pressure. Although the heating temperature in the said drying is not specifically limited, 50-180 degreeC is preferable, More preferably, it is 55-160 degreeC, More preferably, it is 60-140 degreeC. By setting the heating temperature to 50 ° C. or higher, the heating time required for drying can be shortened, and the productivity tends to be improved. On the other hand, by setting the heating temperature to 180 ° C. or lower, there is a tendency that a decrease in charge / discharge characteristics of the electricity storage device is suppressed. The drying temperature can be controlled to be constant during drying, or can be controlled to vary stepwise or continuously. Moreover, although heating time (total time) is not specifically limited, For example, it can select suitably from 0.1 to 60 minutes.

  Through Steps 3 and 4, an electricity storage having at least a current collector and an electrode active material layer on the current collector [an electrode active material layer containing negative electrode active material (A) and cellulose acetate (B) as essential components] A device electrode is obtained. The water-based manufacturing method described above is a process other than steps 3 and 4 (for example, using a die press, a roll press, etc., for increasing the adhesion between the current collector and the electrode active material layer) A step of performing a treatment; a step of performing a cutting process; a step of laminating electrodes and other members, and the like].

  The electrode for an electricity storage device of the present invention can be obtained by the above-described organic solvent-based or aqueous-based manufacturing method. The electrode for an electricity storage device of the present invention is excellent in both charge / discharge characteristics and productivity without causing deterioration in charge / discharge characteristics resulting from the production process.

<Power storage device>
By using the electrode for an electricity storage device of the present invention as an electrode, an electricity storage device excellent in both productivity and charge / discharge characteristics (sometimes referred to as “the electricity storage device of the present invention”) is obtained. Examples of the electricity storage device of the present invention include a lithium ion battery, a non-aqueous electric double layer capacitor, and a hybrid capacitor. Hereinafter, a lithium ion battery and a non-aqueous electric double layer capacitor as typical examples of the electricity storage device of the present invention will be specifically described, but the electricity storage device of the present invention is not limited thereto.

[Lithium ion battery]
Among the electricity storage devices of the present invention, a lithium ion battery is a lithium ion battery having the electrode for an electricity storage device (electrode for lithium ion battery) of the present invention as a positive electrode and / or a negative electrode (either one or both of a positive electrode and a negative electrode). It may be referred to as a “lithium ion battery of the present invention”. The lithium ion battery of the present invention has the electrode for an electricity storage device of the present invention as a positive electrode and / or a negative electrode, and further includes a separator, a non-aqueous electrolyte, and the like, and the electrode for an electricity storage device of the present invention as necessary. Electrode (when either one of the positive electrode and the negative electrode is the electrode for an electricity storage device of the present invention). The electrode other than the electrode for the electricity storage device of the present invention, the separator, the non-aqueous electrolyte and the like are not particularly limited, and well-known members can be used in the lithium ion battery.

  The lithium ion battery of the present invention can be produced by a known or conventional method, and is not particularly limited. For example, the positive electrode and the negative electrode are overlapped via a separator, and this is wound as necessary according to the shape of the battery. After being folded, it is put into a battery container, and a nonaqueous electrolytic solution is injected into the battery container, and then it is sealed (sealed). The lithium ion battery of this invention may have other members, such as an overcurrent prevention apparatus, such as a fuse and a PTC element, an expanded metal, and a lead board, for example. The shape of the lithium ion battery of the present invention is not particularly limited, and may be any of a coin type, a button type, a sheet type, a cylindrical type, a square type, a flat type, and the like. The lithium ion battery of the present invention can be used as a lithium ion battery in various applications such as portable electronic devices, electric vehicles, electric devices, and stationary devices. The lithium ion battery of the present invention has both the charge / discharge characteristics and productivity without causing deterioration of the charge / discharge characteristics (battery characteristics) due to the manufacturing process by having the electrode for the electricity storage device of the present invention as an electrode. Excellent.

[Non-aqueous electric double layer capacitor]
Among the electricity storage devices of the present invention, the non-aqueous electrical double layer capacitor is a non-aqueous electrical double layer capacitor (“non-aqueous electrical double layer capacitor of the present invention”) having the electrode for electrical storage devices (non-aqueous electrical double layer capacitor) of the present invention as a positive electrode and / or a negative electrode. It may be referred to as a “water-based electric double layer capacitor”. The non-aqueous electric double layer capacitor of the present invention includes the electrode for an electricity storage device of the present invention as a positive electrode and / or a negative electrode, and further includes a separator, a non-aqueous electrolyte, and the like. An electrode other than the device electrode (when either one of the positive electrode and the negative electrode is the electrode for an electricity storage device of the present invention) is included. The electrode other than the electrode for the electricity storage device of the present invention, the separator, the non-aqueous electrolyte and the like are not particularly limited, and well-known members can be used in the non-aqueous electric double layer capacitor. Specifically, for example, propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate or the like is used as the solvent in the non-aqueous electrolyte solution. As the cation (cation) constituting the electrolyte in the nonaqueous electrolyte solution, for example, tetraethylammonium salt or the like is used. As the anion (anion), for example, tetrafluoroborate ion (BF ₄ ⁻ ), bistri Fluoromethylsulfonylimide ((CF ₃ SO ₂ ) ₂ N ⁻ ) or the like is used.

  The non-aqueous electric double layer capacitor of the present invention can be produced by a known or conventional method, and is not particularly limited. For example, the positive electrode and the negative electrode are overlapped via a separator, and this is made according to the shape of the container as necessary. After being rolled or folded, it is put into a container, a non-aqueous electrolyte is injected into the container, and then sealed (sealed). The non-aqueous electric double layer capacitor of the present invention may have other members such as an overcurrent prevention device such as a fuse and a PTC element, an expanded metal, and a lead plate. The shape of the non-aqueous electric double layer capacitor of the present invention is not particularly limited, and may be any of a coin type, a button type, a sheet type, a cylindrical type, a square type, a flat type, and the like. The non-aqueous electric double layer capacitor of the present invention can be used as a non-aqueous electric double layer capacitor in various applications such as portable electronic devices, electric vehicles, electric devices, and stationary devices. The non-aqueous electric double layer capacitor of the present invention has the electrode for the electricity storage device of the present invention as an electrode, so that charge / discharge characteristics and productivity are not deteriorated without causing deterioration of charge / discharge characteristics (capacitor characteristics) due to the manufacturing process. Both are excellent.

  Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited to these examples.

(Synthesis Example 1)
5.1 parts by weight of acetic acid and 2.0 parts by weight with respect to 1 part by weight of cellulose acetate (manufactured by Daicel, trade name “L-50”, acetyl group total substitution degree 2.43, 6% viscosity: 110 mPa · s) A part by weight of water was added and stirred at 40 ° C. for 5 hours to obtain a solution having a uniform appearance. 0.13 parts by weight of sulfuric acid was added to this solution, and the resulting solution was kept at 70 ° C. to carry out hydrolysis (partial deacetylation reaction; aging). In this aging process, water was added to the system twice in the middle. That is, 0.67 parts by weight of water was added 1 hour after the reaction was started, and 1.67 parts by weight of water was added after another 2 hours, and the reaction was further continued for 3 hours. The total hydrolysis time is 6 hours. The first aging from the start of the reaction to the first water addition, the second aging from the first water addition to the second water addition, the reaction from the second water addition to the end of the reaction (ripening completed) This is called the third aging.
After carrying out the hydrolysis, the temperature of the system is cooled to room temperature (about 25 ° C.), and 15 parts by weight of acetone / methanol = 1/2 (weight ratio) mixed solvent (precipitating agent) is added to the reaction mixture to cause precipitation. Was generated.
The precipitate was recovered as a wet cake having a solid content of 15% by weight, and washed by adding 8 parts by weight of methanol and draining to a solid content of 15% by weight. This was repeated three times. The washed precipitate was further washed twice with 8 parts by weight of methanol containing 0.004% by weight of potassium acetate, neutralized and dried to obtain cellulose acetate (low-substituted cellulose acetate).

(Synthesis Examples 2 to 12)
Cellulose acetate (low-substituted cellulose acetate) in the same manner as in Synthesis Example 1 except that the reaction temperature, first aging time, second aging time, third aging time, and precipitating agent were changed as shown in Table 1. Got.

  Acetyl group total substitution degree (DS), weight average polymerization degree (DPw), polydispersity (dispersion degree) (Mw / Mn), and composition distribution index (CDI) of low substituted cellulose acetate obtained in each synthesis example Was measured by the following method. Table 1 shows production conditions and measurement results (analytical values) of physical properties of the obtained low-substituted cellulose acetate. The “sample number” in Table 1 means the sample number of the obtained low-substituted cellulose acetate.

(Measurement of substitution degree (DS))
According to the method of Tezuka (Carbohydr. Res. 273, 83 (1995)), the unsubstituted hydroxyl group of the low-substituted cellulose acetate sample was propionylated. The total substitution degree of acetyl group of propionylated cellulose acetate was determined from 169 to 171 ppm acetylcarbonyl signal and 172 to 174 ppm propionylcarbonyl signal in ¹³ C-NMR according to the method of Tezuka (same).

(Measurement of weight average degree of polymerization (DPw), degree of dispersion (Mw / Mn))
The weight average polymerization degree and dispersion degree of low substituted cellulose acetate were determined by conducting GPC-light scattering measurement under the following conditions after being led to propionylated low substituted cellulose acetate.
Equipment: GPC “SYSTEM-21H” manufactured by Shodex
Solvent: Acetone Column: 2 GMHxl (Tosoh), same guard column Flow rate: 0.8 ml / min
Temperature: 29 ° C
Sample concentration: 0.25% (wt / vol)
Injection volume: 100 μl
Detection: MALLS (multi-angle light scattering detector) (manufactured by Wyatt, “DAWN-EOS”)
MALLS correction standard substance: PMMA (molecular weight 27600)

ＤＰｗ：重量平均重合度
ｐ：（未知試料のアセチルＤＳ）／３
ｑ：１−ｐ (Measurement of composition distribution index (CDI))
The CDI of low substituted cellulose acetate was determined by conducting HPLC analysis under the following conditions after leading to propionylated low substituted cellulose acetate.
Equipment: Agilent 1100 Series
Column: Waters Nova-Pak phenyl 60Å 4 μm (150 mm × 3.9 mmΦ) + guard column Column temperature: 30 ° C.
Detection: Varian 380-LC
Injection volume: 5.0 μL (sample concentration: 0.1% (wt / vol))
Eluent: Liquid A: MeOH / H ₂ O = 8/1 (v / v), Liquid B: CHCl ₃ / MeOH = 8/1 (v / v)
Gradient: A / B = 80/20 → 0/100 (28 min); Flow rate: 0.7 mL / min
First, a calibration curve of elution time versus DS was created by HPLC analysis of a sample with known DS in the range of 0 to 3 acetyl DS (acetyl group total substitution degree). Based on the calibration curve, the elution curve (time vs. detected intensity curve) of the unknown sample is converted to the DS vs. detected intensity curve (composition distribution curve), and the uncorrected half-value width X of this composition distribution curve is determined. The corrected half width Z of the distribution was determined.
Z = (X ² −Y ² ) ^1/2
Y is a device constant defined by the following equation.
Y = (a−b) x / 3 + b
a: X value of a sample with acetyl DS = 3 b: X value of a sample with acetyl DS = 0 x: Acetyl DS of unknown sample
From the corrected half width Z, the composition distribution index (CDI) was determined by the following formula.
CDI = Z / Z ₀
Here, Z ₀ is the composition distribution generated when acetylation and partial deacetylation in the preparation of all partially substituted cellulose acetates occur with equal probability for all hydroxyl groups (or acetyl groups) of all molecules. Yes, defined by

DPw: weight average polymerization degree p: (acetyl DS of unknown sample) / 3
q: 1-p

Synthesis Example 13 Production of Modified Polyvinylidene Fluoride Polyvinylidene fluoride homopolymer (KF1000; manufactured by Kureha Chemical Co., Ltd., molecular weight 150,000, average particle size 180 μm, obtained by suspension polymerization) 10 g of powder The mixture was dispersed in 50 g and swollen, and 0.5 g of γ-aminopropyltriethoxysilane was added and mixed therein to form a slurry. The slurry was allowed to stand at room temperature (about 25 ° C.) for 24 hours, and then the acetone solution layer was analyzed by gas chromatography. As a result, γ-aminopropyltriethoxysilane was not detected. The solid content obtained by filtering the slurry was vacuum-dried to obtain powdered modified polyvinylidene fluoride.

Example 1
[Manufacture of negative electrode]
After uniformly dissolving 5.26 parts by weight of cellulose acetate (WSCA-70-0.9) obtained in Synthesis Example 4 in 47.37 parts by weight of N-methyl-2-pyrrolidone (NMP), room temperature (about (25 ° C.) for 24 hours to prepare a binder composition. Next, 47.37 parts by weight of coke powder (pitch coke baked at 100 ° C. for 1 hour in nitrogen gas and pulverized to an average particle size of 10 μm) was added to the binder composition, and the mixture was stirred and mixed. A forming composition (a composition for forming a negative electrode, slurry) was prepared.
The electrode-forming composition obtained above was uniformly applied on a rolled copper foil (area: 100 mm × 200 mm) having a thickness of 10 μm so that the film thickness after drying would be 80 μm. It dried for minutes and the electrode (negative electrode) which has a negative electrode active material layer on a collector (rolled copper foil) was manufactured.

[Manufacture of lithium-ion batteries]
90 parts by weight of lithium cobalt oxide (LiCoO ₂ ) having an average particle size of 30 μm, 5 parts by weight of graphite as a conductive material, 5 parts by weight of polyvinylidene fluoride homopolymer (KF1000), and 100 parts by weight of NMP are mixed and dispersed by a ball mill. Kneaded. The obtained paste was applied to a 20 μm aluminum foil and dried to obtain a thin film electrode having a one-side film thickness of 80 μm (the thickness of the positive electrode active material layer). This was pressed with a 200 degreeC hot roll, and the positive electrode of the lithium ion battery was manufactured.
Also, 1 of propylene carbonate and 1,2-dimethoxyethane: 1 mixed solution (volume ratio), what was the LiPF ₄ dissolved at a concentration of 1 mol / L, was used as an electrolyte for lithium-ion batteries.
Furthermore, a porous polypropylene film having a thickness of 25 μm was used as a separator for a lithium ion battery.
The positive electrode obtained above was processed into a circle having a diameter of 15 mm. Further, a separator (circular with a diameter of 18 mm), a negative electrode (circular with a diameter of 18 mm), and an expanded metal (circular with a diameter of 18 mm) are laminated in this order on the positive electrode active material layer surface side of the positive electrode, and the obtained laminate is made of polypropylene. It was stored in a stainless steel coin-type outer container (diameter 20 mm, height 1.8 mm, stainless steel thickness 0.25 mm) provided with a packing made of steel. The electrolyte is poured into the container so that no air remains, and the outer container is fixed with a 0.2 mm-thick stainless steel cap through a polypropylene packing, and thus obtained. The battery can was sealed to produce a battery (lithium ion battery) having a diameter of 20 mm and a thickness of about 2 mm.

(Comparative Example 1)
Using the modified polyvinylidene fluoride (modified PVDF) obtained in Synthesis Example 13 instead of cellulose acetate, the temperature for drying the electrode-forming composition coated on the rolled copper foil was changed to 110 ° C., and the drying time An electrode (negative electrode) and a lithium ion battery were produced in the same manner as in Example 1 except that was changed to 10 minutes.

(Examples 2 to 5, Comparative Example 2)
An electrode (negative electrode) and a lithium ion battery were produced in the same manner as in Example 1 except that the composition of the electrode forming composition and the drying conditions were changed as shown in Table 2.

(Example 6)
5 parts by weight of cellulose acetate (WSCA-70-1.1) obtained in Synthesis Example 2, 50 parts by weight of water, artificial graphite (average particle diameter 24.5 μm, distance between graphite layers (plane spacing of 002 planes) 0 .354 nm) and 100 parts by weight were stirred and mixed with a planetary mixer for 30 minutes to prepare a composition for electrode formation.
The electrode-forming composition obtained above was uniformly applied on a rolled copper foil (area: 100 mm × 200 mm) having a thickness of 10 μm so that the film thickness after drying was 80 μm, and then at 60 ° C. for 2 minutes. Subsequently, drying was performed at 120 ° C. for 2 minutes to produce an electrode (negative electrode).
Moreover, the lithium ion battery was manufactured like Example 1 except having used the negative electrode obtained above.

(Comparative Example 3)
25 parts by weight of a 2% aqueous solution of carboxymethyl cellulose (Serogen BSH-12, manufactured by Daiichi Kogyo Seiyaku) and artificial graphite (average particle size 24.5 μm, distance between graphite layers (plane spacing of 002 plane) 0.354 nm) 100 weights The mixture was stirred and mixed with a planetary mixer for 60 minutes to obtain a mixture (sometimes referred to as “mixture 1”).
Next, 25 parts by weight of a 2% aqueous solution of carboxymethylcellulose (Serogen BSH-12, manufactured by Daiichi Kogyo Seiyaku) is added to the mixture 1 obtained above, and the mixture is stirred and mixed with a planetary mixer for 10 minutes. In some cases).
Further, 3.75 parts by weight of a 40% suspension of styrene-butadiene rubber (BM-400B, manufactured by Nippon Zeon Co., Ltd.) was added to the mixture 2 obtained above, and the mixture was stirred for 10 minutes with a planetary mixer to form an electrode. A composition was prepared. Table 2 shows the composition (final composition) of the electrode forming composition thus obtained.
An electrode (negative electrode) and a lithium ion battery were produced in the same manner as in Example 6 except that the electrode forming composition obtained above was used.

(Comparative Example 4)
50 parts by weight of a 2% aqueous solution of carboxymethylcellulose (Serogen BSH-12, manufactured by Daiichi Kogyo Seiyaku) and artificial graphite (average particle size 24.5 μm, distance between graphite layers (plane spacing of 002 plane: 0.354 nm) 100 weights Part and 3.75 parts by weight of a 40% suspension of styrene-butadiene rubber (BM-400B, manufactured by Nippon Zeon) were stirred and mixed with a planetary mixer for 80 minutes to prepare an electrode forming composition.
An electrode (negative electrode) and a lithium ion battery were produced in the same manner as in Example 6 except that the electrode forming composition obtained above was used.

(Examples 7 to 15)
An electrode (negative electrode) and a lithium ion battery were produced in the same manner as in Example 6 except that the composition of the electrode forming composition and the drying conditions were changed as shown in Table 2.

  The binding properties of the negative electrodes obtained in Examples and Comparative Examples were evaluated by the following procedure. Moreover, the battery characteristic (cycle property) of the battery (lithium ion battery) obtained by the Example and the comparative example was evaluated in the following procedure.

(Evaluation of binding properties)
1. Evaluation by peel strength About the obtained electrode (negative electrode), peel strength by 180 ° peel test in accordance with JIS K6854-2 [Adhesion strength (adhesive strength of negative electrode active material layer to current collector), unit g / mm] The results are shown in the column “Binding” in Table 2.

2. Evaluation by Cross Cut Test According to the cross cut test method of JIS K5400: 1990, the binding property of the negative electrode active material layer to the current collector in the obtained electrode (negative electrode) was evaluated in 10 stages. The results are shown in the “Binding” column of Table 2. It should be noted that the higher the result obtained in the above test, the better the binding property.

(Evaluation of battery characteristics)
The operation of charging the obtained battery to 4.3 V at 20 ° C. with a constant current of 0.1 C and discharging to 3.0 V with a constant current of 0.1 C was repeated.
Based on the second discharge capacity, the number of repetitions of the above operation when the discharge capacity reached 90% of the second discharge capacity was determined as “cycle number”. In addition, it shows that it is excellent in the characteristic as a battery, so that cycle number is large.

  As shown in Table 2, the negative electrodes obtained by the organic solvent-based production methods of Examples 1 to 5 are excellent in the binding property of the negative electrode active material layer to the current collector, and the battery having the negative electrode is It was excellent in cycle performance (battery characteristics). In addition, high productivity and high quality are compatible with each other without deteriorating battery characteristics even when drying during the production of the negative electrode is carried out at a high temperature and in a short time. On the other hand, the negative electrode obtained in Comparative Example 1 and the battery having the negative electrode were excellent in binding properties and battery characteristics, but it was necessary to take a longer drying time during the production of the negative electrode. It was inferior. On the other hand, in Comparative Example 1, when the drying temperature during the production of the negative electrode was increased and the drying time was shortened (Comparative Example 2), the binding property and the battery characteristics were remarkably lowered.

  Further, as shown in Table 2, the negative electrodes obtained by the aqueous production methods of Examples 6 to 15 are excellent in the binding property of the negative electrode active material layer to the current collector, and the battery having the negative electrode is It was excellent in cycle performance (battery characteristics). Moreover, even when the electrode-forming composition was prepared by a one-step mixing operation, high productivity and high quality were compatible with each other without causing deterioration in battery characteristics. In contrast, the negative electrode obtained in Comparative Example 3 and the battery having the negative electrode were excellent in binding properties and battery characteristics, but it was necessary to prepare the electrode forming composition by a three-stage mixing operation. Yes, productivity was inferior. On the other hand, when the electrode-forming composition was prepared by a one-step mixing operation in Comparative Example 3 (Comparative Example 4), the binding properties and battery characteristics were significantly reduced.

(Example 16)
[Production of positive electrode]
As shown in Table 3, 3 parts by weight of cellulose acetate (WSCA-70-1.1) obtained in Synthesis Example 2 and lithium cobaltate (trade name “Cellseed C-10N”, manufactured by Nippon Chemical Industry Co., Ltd.) 94 parts by weight, 3 parts by weight of carbon black (trade name “Ketjen Black EC300J”, manufactured by Ketjen Black International, 200 mesh, 75 μm pass 98% or more), NMP (solid content of electrode forming composition is 67 %) Is placed in a kneader (trade name “AR-250”, manufactured by Shinky Co., Ltd.) and mixed for 5 minutes to form an electrode forming composition (positive electrode forming composition, positive electrode mixture paste). ) Was prepared.
The electrode-forming composition (paste) obtained above was spread on an aluminum foil having a thickness of 10 μm, the thickness of the paste was adjusted with a bar coater, and then dried under the conditions shown in Table 3 (drying temperature and drying time). . Thereafter, pressing was performed at 40 MPa to produce an electrode (positive electrode) having a positive electrode active material layer (positive electrode mixture) having a thickness of 80 μm on a current collector (aluminum foil).

(Example 17, comparative example 5)
An electrode (positive electrode) was produced in the same manner as in Example 16 except that the composition of the electrode forming composition and the drying conditions were changed as shown in Table 3.
In addition, PVDF used as a binder in the comparative example 5 is a brand name "KF polymer L # 1120" (made by Kureha Co., Ltd.).

(Evaluation of 90 ° peel strength)
The 90 ° peel strength of the positive electrode active material layer in the positive electrode obtained in Examples and Comparative Examples was measured according to JIS K6854. The results are shown in Table 3.
In addition, it shows that it is excellent in the binding property of the positive electrode active material layer with respect to a collector, so that the peeling strength measured above is high.

  As shown in Table 3, the positive electrodes obtained in Examples 16 and 17 had high peel strength of the positive electrode active material layer with respect to the current collector. On the other hand, the positive electrode obtained in Comparative Example 5 that does not satisfy the provisions of the present invention was inferior in the peel strength of the positive electrode active material layer with respect to the current collector.

(Example 18)
[Manufacture of capacitor electrodes]
As shown in Table 4, 5 parts by weight of cellulose acetate (WSCA-70-0.7) obtained in Synthesis Example 6 and activated carbon (trade name “Max Soap”, manufactured by MC Evatech, specific surface area of 1,800 m ² / g , 90 parts by weight of an average particle diameter of 3 μm) and 5 parts by weight of acetylene black (trade name “Denka Black”, manufactured by Denki Kagaku Kogyo Co., Ltd.) are weighed and mixed, and pure water is added to make the total solid concentration 30 Adjusted to wt%. The mixture thus obtained was mixed with a planetary mixer for 30 minutes to prepare an electrode-forming composition (electrode paste).
The composition for electrode formation (electrode paste) obtained above was applied to both surfaces of an aluminum foil having a thickness of 20 μm using a comma coater. Next, the electrode-forming composition on the aluminum foil was dried at 90 ° C. Thereafter, the electrode layer on the obtained aluminum foil was pressed using a roll press machine to reduce the electrode layer thickness by 10%, and the electrodes having the thicknesses shown in Table 4 on both sides of the current collector (aluminum foil). A capacitor electrode having a layer was produced. In addition, in application | coating of the composition for electrode formation by a comma coater, the application quantity was adjusted so that the electrode layer after press work might become predetermined thickness.

[Manufacture of non-aqueous electric double layer capacitors]
Using the capacitor electrode obtained above, a non-aqueous electric double layer capacitor was produced by the following procedure according to the method described in JP-A-2009-278135.
The capacitor electrode obtained above was cut to the size shown in Table 4. Next, an aluminum lead wire was attached to the aluminum foil in the capacitor electrode after cutting. In this way, two electrodes to which the lead wires were attached were produced.
Next, a paper separator was sandwiched between the two electrodes and wound. The wound electrode and separator were impregnated with 1.0 M tetraethylammonium tetrafluoroborate / propylene carbonate solution as an electrolyte.
Finally, a wound body of an electrode impregnated with an electrolytic solution and a separator was inserted into a bottomed cylindrical case and sealed to obtain a capacitor (non-aqueous electric double layer capacitor).

(Example 19, Comparative Examples 6 and 7)
A capacitor electrode and a capacitor were produced in the same manner as in Example 18 except that the composition of the electrode forming composition and the electrode specifications (electrode layer thickness, electrode layer size) were changed as shown in Table 4.
In addition, the carboxymethylcellulose ammonium salt used as a binder in Comparative Examples 6 and 7 is a trade name “DN-800H” (manufactured by Daicel Finechem Co., Ltd.). Moreover, the butadiene copolymer used as a binder in Comparative Examples 6 and 7 is a trade name “Nipol LX432M” (manufactured by Nippon Zeon Co., Ltd., modified styrene-butadiene latex, solid content 41% as an emulsion product). . Moreover, the amount of the butadiene copolymer in Table 4 is shown by the solid content conversion amount of “Nipol LX432X”.

(Evaluation of charge / discharge characteristics)
A voltage was applied to the capacitors obtained in Examples and Comparative Examples at a constant voltage of 2.0 V for 12 hours in a constant temperature bath at 60 ° C. Thereafter, the capacitor was discharged.
Next, the capacitor was placed in a laboratory atmosphere conditioned at 25 ° C., charged with a constant voltage of 2.0 V for 5 minutes, and then discharged with 1 A current.
The capacity in this discharge (discharge at 25 ° C.) and the resistance (DC resistance) obtained from the initial voltage drop of 0.5 seconds were measured. The results are shown in Table 4.
Moreover, the capacity | capacitance in the discharge in -30 degreeC and the resistance (DC resistance) calculated | required from the voltage drop of the initial 0.5 second were measured like the above except having changed 25 degreeC into -30 degreeC. did. The results are shown in Table 4.

  As shown in Table 4, the capacitors obtained in Examples 18 and 19 were excellent in that the DC resistance was low, and this was particularly remarkable at a low temperature (−30 ° C.). This is probably because the electrode layer of the capacitor electrode of the present invention is excellent in the dispersibility of the carbon material and the binding property of the carbon material and aluminum, and such characteristics are not impaired even at low temperatures. Is done. The capacitors obtained in Comparative Examples 6 and 7 had higher DC resistance than the capacitors obtained in Examples 18 and 19.

  Since the electrode for an electricity storage device of the present invention is excellent in both charge / discharge characteristics and productivity without causing deterioration in charge / discharge characteristics due to the manufacturing process, for example, a portable electronic device, an electric vehicle, an electric device, It is useful as an electrode for power storage devices (lithium ion batteries, non-aqueous electric double layer capacitors, etc.) used for various applications such as stationary equipment.

Claims (9)

An electrode having a current collector and an electrode active material layer on the current collector,
The electrode active material layer includes an electrode active material (A) and cellulose acetate (B) having an acetyl group total substitution degree of 0.4 to 1.2. The electrode for an electrical storage device according to claim 1, wherein the composition distribution index (CDI) defined below of cellulose acetate (B) is 1.0 to 2.0.
CDI = (actual value of composition distribution half width) / (theoretical value of composition distribution half width)
Measured value of half width of composition distribution: half width of composition distribution obtained by HPLC analysis of cellulose acetate propionate obtained by propionylating all remaining hydroxyl groups of cellulose acetate (sample)

DS: Degree of total substitution of acetyl groups DPw: Weight average degree of polymerization (value determined by GPC-light scattering method using cellulose acetate propionate obtained by propionylating all remaining hydroxyl groups of cellulose acetate (sample))   The electrode for an electricity storage device according to claim 1, which is an electrode for a lithium ion battery.   The electrode for an electricity storage device according to claim 3, wherein the electrode active material layer does not contain styrene-butadiene rubber.   The electrode for an electricity storage device according to claim 1, which is an electrode for a non-aqueous electric double layer capacitor.   The lithium ion battery which has an electrode for electrical storage devices of Claim 3 or 4.   A non-aqueous electric double layer capacitor having the electrode for an electricity storage device according to claim 5. Preparing an electrode-forming composition comprising an electrode active material (A), cellulose acetate (B), and an organic solvent;
Applying the electrode-forming composition obtained in the step onto a current collector and drying to form an electrode active material layer on the current collector. Manufacturing method. Preparing an electrode-forming composition comprising an electrode active material (A), cellulose acetate (B) having a total substitution degree of acetyl groups of 0.5 to 1.1, and water;
Applying the electrode-forming composition obtained in the step onto a current collector and drying to form an electrode active material layer on the current collector. Manufacturing method.