JP2014139903A - Method for manufacturing laminate for storage element and lithium ion battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To manufacture a laminate for a storage element in which a thin separator formed of a cellulose fiber is laminated with an electrode and which is capable of suppressing the separator from being broken or damaged even if the laminate is wound.SOLUTION: A method for manufacturing a laminate for a storage element includes the steps of: forming a coating layer for a separator on an electrode for a storage element by coating a dispersion liquid containing a minute cellulose fiber and an organic solvent (coating step); drying the coating layer for the separator (drying step); and forming a laminate in which the separator is integrated with the electrode by pressurizing the dried coating layer for the separator and the electrode (pressurizing step). An average thickness of the separator may be 10 μm or less. An average fiber diameter of the minute cellulose fiber may be 1 μm or less (especially, 50 to 500 nm). The ratio of an average fiber length to the average fiber diameter may be approx. 3,000 to 20,000. The electrode may be a negative electrode of a lithium ion battery.

Description

  The present invention relates to a method for producing a laminate for a storage element in which a separator containing fine cellulose fibers and an electrode are integrated, and a lithium ion battery including the laminate obtained by this method.

  Battery separators such as batteries, capacitors, and capacitors require characteristics such as electrolyte permeability (high porosity). However, in recent years, due to downsizing and longer life of electric and electronic devices, etc. Even higher performance is required for battery and capacitor separators. In particular, lithium ion batteries (lithium ion secondary batteries) are widely used as driving sources for electronic devices and electric vehicles, but a thin separator is effective to increase the capacity per unit volume of the battery. Therefore, there is a need for a separator that can maintain the strength even when the thickness is reduced or the internal resistance is reduced.

  A lithium ion battery is interposed between both positive and negative electrodes, an electrolyte, and a negative electrode, and a separator for preventing the active material of the electrode from contacting and holding the electrolyte in the pores It is formed with. Such a lithium ion battery is usually manufactured by sandwiching a separator between a positive electrode and a negative electrode, winding the obtained laminate into a case, injecting an electrolyte, and sealing. For this reason, the separator is required to have a certain level of strength in order to prevent problems such as breakage and damage in the winding process, and thus it has been difficult to reduce the thickness.

  As the separator, an olefin-based microporous membrane having a function (shutdown) that melts at a high temperature to close the fine pores and shuts off the ionic conductivity is widely used. On the other hand, in recent years, due to global environmental demands, rapid spread is expected as a driving source for electric vehicles such as hybrid vehicles (HEV) and electric vehicles (EV), and these are installed in these electric vehicles. Lithium ion batteries must be safer than consumer products. However, olefinic microporous membranes have low heat resistance and are high risk materials for mounting on electric vehicles. Therefore, as a separator capable of improving heat resistance, use of cellulose fibers having excellent heat resistance and electrochemical stability is being studied.

  In Japanese Patent No. 4628764 (Patent Document 1), the film thickness is 5 to 50 μm, the porosity is 60 to 90%, and the maximum pore diameter obtained by the bubble point method is 0.03 to 0.25 μm. As a method for producing a separator for an electricity storage device comprising a cellulose fiber having a maximum fiber thickness of 1000 nm or less, a dispersion obtained by highly dispersing fine cellulose fibers in a dispersion medium such as water is formed by a papermaking method or a coating method. And a method of drying a bacterial cellulose gel obtained by stationary culture, in the case of drying, water or a dispersion medium mainly composed of water is substituted with a more hydrophobic organic solvent and then dried. A separator obtained by the method is disclosed. In the examples of this document, the separator is manufactured by a method in which a homogenized cellulose is formed into a film by a papermaking method and then peeled off from a filter cloth, or a method in which a bacterial cellulose gel film is attached to a metal vat and dried. A separator having a thickness of 11 to 31 μm is manufactured.

  However, in order to secure voids when making cellulose nanofiber into a sheet, it is necessary to perform paper substitution with solvent substitution, but the solvent system lacks absolute sheet strength compared to aqueous papermaking. . For this reason, it breaks during the manufacture of the separator, or causes wrinkles and breakage during winding, resulting in a significant decrease in usage rate. Furthermore, the greatest advantage of nanofibers is that they can be reduced in thickness by reducing the basis weight, but the strength decreases as the thickness is reduced.

Japanese Patent No. 4628764 (Claim 1, paragraph [0046], Example)

  Accordingly, an object of the present invention is obtained by a method for producing a laminated body for a storage element, which is formed of cellulose fibers and can suppress the breakage and damage of the separator even when the thin separator is laminated with the electrode and wound. Another object of the present invention is to provide a lithium ion battery including the laminated body.

  Another object of the present invention is to provide a method for producing a laminated body for a storage element capable of realizing rapid discharge and high capacity of a battery (particularly a lithium ion battery) and a lithium ion battery provided with the laminated body obtained by this method. There is to do.

  Still another object of the present invention is to produce a laminated body for an electricity storage element in which a separator that is thin and has no pinholes is integrated with an electrode even though it is thin.

  Another object of the present invention is to produce a laminate for an electricity storage device in which electrodes and a thin separator are easily laminated with high productivity.

  Still another object of the present invention is to provide a laminate for a storage element having high heat resistance and electrochemical stability, a method for producing the laminate, and a lithium ion battery including the laminate obtained by this method. is there.

  As a result of intensive studies to achieve the above-mentioned problems, the present inventors have coated a dispersion containing fine cellulose fibers and an organic solvent on an electrode for a storage element, and then dried and pressurized cellulose fibers. The present invention has been completed by finding that even when a thin separator formed by 1 is laminated with an electrode and wound, the separator can be prevented from being broken or damaged.

That is, the method for producing a laminated body for a storage element according to the present invention comprises a coating step of coating a dispersion containing fine cellulose fibers and an organic solvent on a storage element electrode to form a separator coating layer. A drying step of drying the coating layer and a pressing step of pressing the separator coating layer after drying and the electrode to form a laminate in which the separator and the electrode are integrated are included. The average thickness of the separator may be 10 μm or less. The average fiber diameter of the fine cellulose fibers may be 1 μm or less (particularly 50 to 500 nm), and the ratio of the average fiber length to the average fiber diameter may be about 3000 to 20000. You may heat the manufacturing method of this invention at a pressurization process. The dispersion includes a dispersion preparation step of preparing a dispersion by dispersing plant-derived raw material cellulose fibers in water, a microfibrillation step of microfibrillation of the dispersion, and water of microfibrillated microcellulose fibers. It may be a dispersion obtained through a substitution step of substituting the dispersion with an organic solvent. The organic solvent may be a C _1-4 alkanol. The concentration of the fine cellulose fiber in the dispersion may be 0.01 to 10% by weight. The electrode may be a negative electrode of a lithium ion battery.

  The present invention also includes a lithium ion battery provided with the laminate for a storage element obtained by the above manufacturing method.

  In the present invention, on the electrode for the electricity storage element, after coating a dispersion containing fine cellulose fibers and an organic solvent, drying and pressurizing are performed, and a thin separator formed of cellulose fibers is laminated with the electrode, Even when wound, the separator can be prevented from being broken or damaged. Since the obtained separator is thin and has no damage such as pinholes, it can increase the amount of active agent packed per unit volume, and can contribute to rapid charge / discharge and high capacity of a battery (particularly a lithium ion battery).

  Moreover, although it is thin, the laminated body for electrical storage elements in which the separator which is uniform and does not have a pinhole was integrated with the electrode is obtained. Therefore, it is possible to manufacture a stacked body for a storage element in which an electrode and a thin separator are easily stacked with a high yield and high productivity.

  Furthermore, since the separator is formed of cellulose fibers, a laminate for a storage element that has high heat resistance and is electrochemically stable can be manufactured.

[Method for producing laminated body for power storage element]
The method for producing a laminate for an electricity storage device of the present invention comprises a coating step of coating a dispersion containing fine cellulose fibers and an organic solvent on an electrode for an electricity storage device to form a separator application layer, the separator application layer A drying step of drying the separator, and a pressing step of pressurizing the separator coating layer after drying and the electrode to form a laminate in which the separator and the electrode are integrated.

(Dispersion)
The dispersion liquid used for the coating process contains fine cellulose fibers and an organic solvent.

(A) Fine cellulose fiber The fine cellulose fiber is not particularly limited as long as it is a polysaccharide having a β-1,4-glucan structure. Cellulose fibers derived from higher plants [for example, wood fibers (coniferous trees, hardwood trees, etc. Wood pulp, etc.), bamboo fiber, sugarcane fiber, seed hair fiber (cotton linter, Bombax cotton, Kapok, etc.), gin leather fiber (eg, hemp, Kozo, Mitsumata, etc.), leaf fiber (eg, Manila hemp, New Zealand hemp, etc.) ) Natural cellulose fibers (pulp fibers, etc.), animal-derived cellulose fibers (squirt cellulose, etc.), bacteria-derived cellulose fibers, chemically synthesized cellulose fibers [cellulose acetate (cellulose acetate), cellulose propionate , Cellulose butyrate, cellulose acetate propione Organic acid esters such as cellulose acetate butyrate; inorganic acid esters such as cellulose nitrate, cellulose sulfate and cellulose phosphate; mixed acid esters such as cellulose nitrate acetate; hydroxyalkyl cellulose (eg, hydroxyethyl cellulose (HEC), hydroxypropyl cellulose Carboxyalkyl cellulose (carboxymethyl cellulose (CMC), carboxyethyl cellulose, etc.); alkyl cellulose (methyl cellulose, ethyl cellulose, etc.); cellulose derivatives such as regenerated cellulose (rayon, cellophane, etc.)] and the like. Since natural plant-derived cellulose fibers are on the order of microns, they are usually obtained by microfibrillation of raw material cellulose fibers. These fine cellulose fibers may be used alone or in combination of two or more.

  The fine cellulose fiber is a high-purity cellulose having a high α-cellulose content, for example, an α-cellulose content of 70 to 100% by weight (for example, 95 to 100% by weight), preferably 98 to 90%. It may be about 100% by weight. Furthermore, in the present invention, by using high-purity cellulose with a low content of lignin and hemicellulose, even if wood fibers or seed hair fibers are used, fine cellulose fibers having nanometer size and uniform fiber diameter can be prepared. . Cellulose having a low lignin or hemicellulose content is particularly a cellulose having a kappa number (κ value) of 30 or less (eg, 0 to 30), preferably 0 to 20, more preferably 0 to 10 (particularly 0 to 5). There may be. The kappa number can be measured by a method based on “Pulp-Kappa number test method” of JIS P8211.

  Among these fine cellulose fibers, from the point of high productivity and having an appropriate fiber diameter and fiber length, plant-derived cellulose fibers such as wood fibers (wood pulp of conifers, hardwoods, etc.), seed hair fibers ( Fine cellulose fibers derived from pulp such as cotton linter pulp) and gin leather fibers (hemp etc.) are preferred. The pulp is a pulp obtained by a mechanical method (eg, groundwood pulp, refiner ground pulp, thermomechanical pulp, semi-chemical pulp, chemiground pulp), or a pulp obtained by a chemical method (craft pulp, sulfite). Pulp or the like), or beating fibers (beating pulp or the like) that have been subjected to beating (preliminary beating) as described below, if necessary. The fine cellulose fiber may be a fiber subjected to a conventional refining treatment such as degreasing (for example, absorbent cotton). In the present invention, from the viewpoint of suppressing the entanglement of raw material fibers, realizing efficient microfibril formation by homogenization treatment, and obtaining uniform nanometer-sized microfibers, never dry pulp, that is, pulp having no drying history (dried) Pulp that retains its wet state without being) is particularly preferred. The never dry pulp is a pulp composed of wood fibers and / or seed hair fibers, and may be a pulp having a copper number of 30 or less (particularly about 0 to 10). Such pulp may be prepared by bleaching wood fibers and / or seed hair fibers with chlorine.

  The fiber diameter of the fine cellulose fibers may be an average fiber diameter of 1 μm or less, and can be selected, for example, from a range of about 4 to 1000 nm (for example, 5 to 900 nm). From the standpoint of compatibility, the average fiber diameter may be about 10 to 800 nm, for example, about 30 to 700 nm, preferably about 50 to 500 nm, and more preferably about 100 to 300 nm (particularly about 120 to 200 nm).

  In the present invention, the average fiber diameter, the standard deviation of the fiber diameter distribution, and the maximum fiber diameter are values calculated from a fiber diameter (about n = 20) measured based on an electron micrograph.

  The average fiber length of the fine cellulose fibers can be selected from a range of about 10 to 5000 μm. From the viewpoint that the mechanical properties of the nonwoven fabric can be improved, for example, 100 to 3000 μm, preferably 200 to 2500 μm, and more preferably 300 to 2000 μm (particularly 500 to 1500 μm). Furthermore, the ratio of the average fiber length to the average fiber diameter (average fiber length / average fiber diameter) (average aspect ratio) may be 300 or more, for example, 500 or more (for example, 500 to 50000), preferably 1000 to It is about 30000, more preferably about 3000-20000 (particularly 5000-10000). In the present invention, as described above, by using micro cellulose fibers having a nano-sized average diameter and a large aspect ratio, the fibers are sufficiently entangled with each other, or even if they are thin, the strength is large. A separator that can suppress the breakage and damage of the separator even when wound is obtained. On the other hand, micro cellulose fibers having a large aspect ratio have a high degree of entanglement, and it is difficult to form a uniform and thin separator. However, by coating under the conditions described later, a uniform and thin wall is obtained. Can be formed.

  The cross-sectional shape of the fine cellulose fiber (cross-sectional shape perpendicular to the longitudinal direction of the fiber) may be an anisotropic shape (flat shape) such as bacterial cellulose, but is substantially isotropic in the case of plant-derived cellulose fiber. Shape is preferred. Examples of the substantially isotropic shape include a perfect circle shape and a regular polygon shape. In the case of a substantially circular shape, the ratio of the major axis to the minor axis of the cross section (average aspect ratio) is, for example, 1 to 2, preferably 1. It is about -1.5, More preferably, it is about 1-1.3 (especially 1-1.2) grade.

  The dehydration time of the fine cellulose fibers can be selected from a range of about 100 to 5000 seconds, for example, when measured using a 0.5% by weight concentration fiber slurry in accordance with the test method for dewatering amount of API standard. For example, it is about 100 to 3000 seconds, preferably 150 to 1000 seconds, more preferably about 200 to 500 seconds (especially 250 to 400 seconds). The longer the dehydration time, the higher the average fiber length / average fiber diameter ratio, and the higher the water retention, the better the mechanical properties with a small amount. However, if too large, the air permeability tends to decrease and is too small. And there exists a tendency for intensity | strength to fall and for thickness reduction to become difficult.

  The method for producing the fine cellulose fiber is not particularly limited, and a conventional method, for example, a method for microfibrillating the raw fiber, a method using bacteria, or the like can be used. Among these methods, a method of microfibrating the raw fiber is preferable. The microfibrillation method may be a method of microfibrillation in the course of the dispersion preparation method, as will be described later.

(B) Organic solvent The organic solvent is not particularly limited as long as it does not cause chemical or physical damage to the raw fiber. For example, alcohols (C _1-4 alkanols such as methanol, ethanol, 1-propanol, isopropanol, etc.) , Ethers (diC _1-4 alkyl ethers such as diethyl ether and diisopropyl ether, cyclic ethers such as tetrahydrofuran (cyclic C _4-6 ether etc.)), esters (alkanoic acid esters such as ethyl acetate), ketones (acetone , Di- _C1-5 alkyl ketones such as methyl ethyl ketone and methyl butyl ketone, C _4-10 cycloalkanones such as cyclohexanone), aromatic hydrocarbons (toluene, xylene, etc.), halogenated hydrocarbons (methyl chloride, trichloroethylene) Etc.) It is. These organic solvents may be used alone or in combination of two or more.

Of these organic solvents, hydrophilic organic solvents (C _1-4 alkanols such as ethanol and isopropanol, di-C _1-4 alkyl ketones such as acetone and methyl ethyl ketone, etc.) are preferable from the viewpoint of productivity and cost, and water. C _1-4 alkanols such as isopropanol are particularly preferred from the standpoint of excellent solvent substitution efficiency with respect to the dispersion liquid containing. As the organic solvent, a hydrophobic organic solvent may be used in combination with these hydrophilic organic solvents. However, in view of compatibility (mixability) with water and environmental and hygienic aspects, the organic solvent is substantially hydrophobic. It is preferred not to use a solvent.

  The concentration of the fine cellulose fibers in the dispersion is, for example, 0.01 to 10% by weight, preferably 0.05 to 5% by weight, more preferably 0.1 to 3% by weight (particularly 0.5 to 1% by weight). %) Degree. If the concentration of the fine cellulose fibers is too thin, it is difficult to form a separator having high strength, and if it is too thick, it is difficult to form a thin separator.

(C) Dispersion Preparation Method The dispersion is not particularly limited as long as fine cellulose fibers are dispersed in an organic solvent, and the fiber diameter and fiber length of the cellulose fibers can be easily controlled and uniformly dispersed. In view of the above, it is prepared by a production method including a dispersion preparation step of preparing a dispersion by dispersing raw material cellulose fibers (especially plant-derived cellulose fibers) in a solvent, and a microfibrillation step of microfibrillation of the dispersion. Is preferred.

(C1) Dispersion Preparation Step In the dispersion preparation step, the average fiber length of the raw material fibers is, for example, 0.01 to 5 mm, preferably 0.03 to 4 mm, more preferably 0.06 to 3 mm (especially 0.00. 1 to 2 mm), usually about 0.1 to 5 mm. Moreover, the average fiber diameter of raw material fibers is 0.01-500 micrometers, Preferably it is 0.05-400 micrometers, More preferably, it is about 0.1-300 micrometers (especially 0.2-250 micrometers).

The solvent may be the organic solvent, but water is preferable from the viewpoint of productivity and cost. If necessary, a mixed solvent of water and a hydrophilic organic solvent (C _1-4 alkanol, acetone, etc.). May be used.

  The raw material fiber used for the microfibrillation step may be in a state of coexisting at least in the solvent, and the raw fiber may be dispersed (or suspended) in the solvent prior to microfibrillation. Dispersion may be performed using, for example, a conventional disperser (such as an ultrasonic disperser, a homodisper, or a three-one motor). The disperser may include mechanical stirring means (such as a stirring bar and a stirring bar).

  The concentration of the raw fiber in the solvent is, for example, 0.01 to 20% by weight, preferably 0.05 to 10% by weight, more preferably 0.1 to 5% by weight (particularly 0.5 to 3% by weight). It may be.

(C2) Microfibrillation step In the microfibrillation step, the dispersion can be microfibrillated by conventional methods such as beating and homogenization.

  In the beating process, for example, a conventional beating machine such as a beater, a Jordan, a conical refiner, a single disc refiner, a double disc refiner, or the like can be used.

  Of these, refiner treatment is preferred, and the disk clearance may be, for example, about 0.1 to 0.3 mm, preferably about 0.12 to 0.28 mm, and more preferably about 0.13 to 0.25 mm. The number of revolutions of the disk may be, for example, about 1,000 to 8,000 rpm, preferably 1,300 to 6,000 rpm, and more preferably about 1,600 to 4,000 rpm. The number of treatments (passes) may be 1 to 50 times, preferably 5 to 40 times, and more preferably about 10 to 30 times.

  In the homogenization treatment, a conventional homogenizer such as a homogenizer (particularly, a high-pressure homogenizer) can be used. If necessary, the dispersion may be subjected to beating treatment (preliminary beating treatment) by the above method and then homogenized.

  The high-pressure homogenizer has a narrowed flow path (for example, a small-diameter orifice) inside, and by passing the dispersion through the narrowed flow path, pressure is applied and by colliding with the wall surface such as the inner wall of the container, It may be a device of the type that imparts shear stress or cutting action. In such a high-pressure homogenizer, the pressure for passing through the flow path (or the pressure for pumping the dispersion to the high-pressure homogenizer) is, for example, about 30 to 100 MPa, preferably about 35 to 80 MPa, and more preferably about 40 to 70 MPa. May be. For example, the number of passes may be 1 to 30 times, preferably 2 to 20 times, and more preferably about 3 to 10 times.

  Furthermore, the conditions for the homogenization treatment are described in JP-B-60-19921, JP-A-2011-26760, JP-A-2012-25833, JP-A-2012-36517, and JP-A-2012-36518. In particular, when producing nanofibers having a fiber diameter of about 100 nm or less, JP2011-26760A, JP2012-25833A, JP2012-36517A, and JP2012-36518A. Among the methods described in Japanese Patent Publication No. Gazette, a homogenization process using a homogenizer equipped with a crushing type homovalve seat may be used.

(C3) Substitution Step When water is used as a solvent in the dispersion preparation step, the dispersion is further prepared through a substitution step. In the replacement step, the aqueous dispersion of microfibrillated microcellulose fibers is replaced with the organic solvent described above. That is, by adding an organic solvent to the aqueous dispersion of fine cellulose fibers, the dispersion medium of the fibrillated cellulose fibers is replaced with water from the organic solvent.

  In order to replace the dispersion medium contained in the aqueous dispersion from water to a hydrophilic organic solvent, it is preferable to add a hydrophilic organic solvent in an amount equal to or greater than that of water. The ratio of the hydrophilic organic solvent is, for example, water The amount is about 100 to 3000 parts by weight, preferably 200 to 2000 parts by weight, more preferably about 300 to 1000 parts by weight (particularly 400 to 800 parts by weight) with respect to 100 parts by weight of water contained in the dispersion. The ratio of the hydrophilic organic solvent to the fiber aggregate is, for example, 500 to 10,000 parts by weight, preferably 1000 to 10,000 parts by weight, and more preferably 2000 to 8000 parts by weight with respect to 100 parts by weight of the fiber aggregate (solid content). Degree.

  In the present invention, in order to improve the degree of substitution with an organic solvent, substitution with an organic solvent may be repeated a plurality of times. The number of repetitions is usually about 1 to 5 times, preferably 2 to 4 times, more preferably about 2 to 3 times, from the balance between substitution efficiency and simplicity.

  In the case of repeating replacement with an organic solvent, in order to easily improve the replacement efficiency, the dispersion of the organic solvent containing water may be removed by a conventional liquid removal method, for example, filtration, pressing, centrifugation, or the like. preferable. Usually, after concentrating to about 2 to 20 times, preferably about 5 to 15 times by liquid removal, an organic solvent is further added. The ratio of the organic solvent after the second time in the case of repeating is, for example, 100 to 5000 parts by weight, preferably 300 to 3000 parts by weight, with respect to 100 parts by weight of the solvent (total of water and organic solvent) contained in the dispersion. More preferably, it is about 400 to 2000 parts by weight. The ratio of the organic solvent to the fine cellulose fibers is, for example, 500 to 10,000 parts by weight, preferably 1000 to 10,000 parts by weight, and more preferably about 2000 to 8000 parts by weight with respect to 100 parts by weight of the fine cellulose fibers (solid content). is there.

  In the present invention, in order to further increase the degree of substitution with an organic solvent and suppress aggregation due to excessive entanglement of the fine cellulose fibers, it is preferable to add the organic solvent and stir the dispersion with mechanical shearing force. As means for applying the mechanical shearing force, conventional means such as mechanical stirring means (stirring bar, stirring bar, etc.), ultrasonic disperser and the like can be used.

  Among these stirring means, a stirrer having a rotating blade as a stirrer is preferable because stirring can be easily performed with a high shearing force. Examples of the stirrer include conventional stirrers such as a homomixer, a homodisper, a Henschel mixer, a Banbury mixer, a ribbon mixer, and a V-type mixer. The shape of the rotary blade is not particularly limited, and for example, a paddle shape, a turbine shape, a propeller shape, or the like can be used. In the present invention, by using such a stirring condition, the solvent can be replaced while the fiber assembly is defibrated. Therefore, even when the cellulose fiber is highly microfibrillated with a high-pressure homogenizer, the solvent is sufficiently replaced. Is possible.

  In the dispersion, depending on the application, conventional additives such as other fibers, sizing agents, waxes, inorganic fillers, colorants, stabilizers (antioxidants, heat stabilizers, UV absorbers) Etc.), plasticizers, antistatic agents, flame retardants and the like. In particular, as another fiber, a synthetic fiber formed of a thermoplastic resin such as polyethylene fiber may be blended to give a shutdown function.

(Electrode for storage element)
The electrode for a storage element is not particularly limited as long as it contains an active material that forms a positive electrode or a negative electrode, but an electrode of a lithium ion battery (lithium ion secondary battery) that has a high demand for thinning is preferable.

A conventional electrode material can be used as an electrode of the lithium ion battery. Examples of the positive electrode material include a current collector made of a metal foil such as aluminum, copper, gold, silver, and a lithium composite oxide (LiCoO ₂ , LiMn ₂ O ₄ , LiNiO ₂ , LiFePO _4, etc.). Or a positive electrode active material. Examples of the negative electrode material include a current collector made of a metal foil such as aluminum, copper, gold, and silver, and a carbon material (expandable graphite, graphitizable carbon, non-graphitizable carbon, coke powder, conductive material) May be formed with a negative electrode active material composed of carbon black or the like.

  Among these, a positive electrode and a negative electrode containing an active material formed of a carbon material from the viewpoint that the separator can be brought into intimate contact without deteriorating the performance of the active material of the electrode by the moisture (a trace amount of moisture) contained in the separator coating layer. A positive electrode including a positive electrode active material composed of lithium iron phosphate is preferable. A negative electrode of a lithium ion battery, for example, a negative electrode active material composed of natural or artificial graphite (especially artificial graphite) and a binder component (carboxymethylcellulose) (CMC) etc.) is particularly preferable.

(Coating process)
In the coating process, the dispersion can be coated by a conventional coating method such as roll coater, air knife coater, blade coater, rod coater, reverse coater, bar coater, comma coater, dip squeeze coater, die coater, gravure coater. , Micro gravure coater, silk screen coater method, dip method, spray method, spinner method and the like. Of these methods, a blade coater, a bar coater method, a comma coater method, and the like are widely used.

  In the present invention, by adjusting the coating conditions in the coating step, a thin and uniform separator coating layer can be formed even for fine cellulose fibers having a large aspect ratio.

  Specifically, the concentration of the dispersion (ratio of fine cellulose fibers) is preferably adjusted to a range of about 0.3 to 3% by weight, for example, 0.35 to 2.5% by weight, preferably 0.00. It is about 4 to 2% by weight, more preferably about 0.5 to 1.5% by weight (particularly 0.6 to 1% by weight). If the concentration of the dispersion is too small, pinholes are likely to be generated, and if it is too large, it is difficult to make uniform and thin.

  The viscosity of the dispersion is preferably adjusted to a range of about 500 to 10000 mPa · s, for example, 600 to 8000 mPa · s, preferably 800 to 5000 mPa · s (for example, 1000 to 3000), and more preferably 1200 to 2000 mPa · s. s (particularly 1300 to 1800 mPa · s). If the viscosity is too small, pinholes are likely to occur, and if it is too large, it is difficult to make uniform and thin. The viscosity was measured using a B-type viscometer using a rotor No. 4 is a value measured as an apparent viscosity at 25 ° C. at a rotation speed of 60 rpm.

  In coating, it is preferable to coat while applying a predetermined shearing force to the dispersion. For example, when coating with a clearance of 500 μm using a doctor blade, it is preferable to coat at a coating speed of 0.15 m / second or more. Preferably, the coating speed is, for example, 0.18 m / second or more (for example, about 0.18 to 10 m / second), preferably 0.2 m / second or more (for example, about 0.2 to 5 m / second), and more preferably. May be 0.25 m / sec or more (for example, about 0.25 to 1 m / sec). If the coating speed is too low, the entangled state of the fine cellulose fibers having a large aspect ratio cannot be solved, and it is difficult to form a thin and uniform separator coating layer.

  Furthermore, in order to improve the uniformity of the thickness of the separator coating layer, a coating method described in Japanese Patent Application Laid-Open No. 2010-240513 or a coating apparatus described in Japanese Patent No. 4080261 may be used.

(Drying process)
The coated separator coating layer is further subjected to a drying step. In the drying step, the organic solvent is removed from the dispersion liquid constituting the separator coating layer.

  The organic solvent is volatilized by drying, and the drying method may be natural drying, but may be a method of heating and drying from the viewpoint of productivity and the like. The heating temperature for drying may be, for example, about 50 to 150 ° C, preferably 60 to 140 ° C, more preferably about 80 to 135 ° C (particularly 100 to 130 ° C). The heating temperature is preferably higher from the viewpoint of removing the solvent, but if it is too high, the microfibers are likely to aggregate due to rapid volatilization of the solvent, and heat degradation is likely to occur.

  The heating time may be, for example, 1 to 30 minutes, preferably 2 to 20 minutes, and more preferably about 3 to 10 minutes.

  As a drier, a conventional drier, for example, a Nauter drier, a shelf drier, a rotary mixer with a heating jacket, or the like can be used as necessary.

(Pressure process)
The dried separator coating layer is further subjected to a pressing step. In the pressurizing step, the separator is thinned, the adhesion with the electrode is improved, and both are integrated.

  In the pressurizing step, for example, press working may be performed at a pressure of about 0.1 to 100 MPa, preferably 1 to 80 MPa, more preferably about 10 to 50 MPa (particularly 20 to 40 MPa). If the pressure is too low, it will be difficult to reduce the thickness, and the uniformity of thickness and density will be reduced. If the pressure is too high, the density will be too high and the air permeability will tend to decrease.

  The pressurizing step may be press-worked under heating, and the heating temperature in the press-working is not particularly limited, and can be selected, for example, from the range of about 60 to 250 ° C., for example, 80 to 200 ° C., preferably 90 -180 degreeC, More preferably, about 100-150 degreeC (especially 110-140 degreeC) may be sufficient. If the temperature is too low, the uniformity of thickness and density is lowered, and if the temperature is too high, the microcellulose fibers are likely to be thermally deteriorated.

[Laminated body for power storage element]
In the laminated body for a storage element of the present invention, the separator and the storage electrode for the storage element are integrated, and the separator can be formed thin. The average thickness of the separator may be 10 μm or less, for example, 1 to 10 μm, preferably 1.5 to 8 μm, and more preferably about 2 to 5 μm (particularly 2.5 to 4 μm). When the thickness is too thin, the strength is lowered and the separator characteristics are also lowered. If the thickness is too thick, it will be difficult to cope with downsizing of the electricity storage element.

  The average pore diameter of the separator is, for example, about 0.001 to 0.1 μm, preferably about 0.005 to 0.08 μm, and more preferably about 0.01 to 0.06 μm. The maximum pore diameter of the separator is, for example, about 0.2 μm or less, preferably about 0.15 μm or less. If the hole diameter is too large, short-circuiting easily occurs.

The basis weight of the separator is, for example, about 0.1 to 30 g / m ² , preferably 1 to 10 g / m ² , and more preferably 1.5 to 5 g / m ² (particularly ^{2 to 4} g / m ² ). Also good.

  The laminate for an electricity storage device of the present invention is suitable for a lithium ion battery in which the separator is required to be thin, and is combined with an electrolytic solution (ethylene carbonate, propylene carbonate, butyrolactone, dimethyl carbonate, etc.) to form a lithium ion battery. May be.

  Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited to these examples. Evaluation of the fine cellulose fiber and the nonwoven fabric (separator) obtained in Examples and Comparative Examples was measured by the following method.

[Fiber diameter]
Take a 50000x scanning electron microscope (SEM) photo of microfibrillated microfiber and regenerated cellulose fiber, draw two lines at any position across the photo, and cross the line. The average fiber diameter (n = 20 or more) was calculated by counting all the fiber diameters. The method of drawing a line is not particularly limited as long as the number of fibers crossing the line is 20 or more.

[Fiber length]
The fiber length was measured using a fiber length measuring device (“FS-200” manufactured by Kajaani).

[Average thickness of separator]
In accordance with JIS L1085, using a thickness measuring instrument (“FFA-12” manufactured by Ozaki Mfg. Co., Ltd., measuring element 16 mmφ), 10 arbitrary points on the sheet were measured, and the average value was obtained. Since the thickness of the separator alone cannot be measured, the average thickness of the electrode was measured in advance, and the value obtained by subtracting the thickness of the electrode from the total thickness was taken as the thickness of the separator.

[Dehydration time]
The slurry prepared in Examples and Comparative Examples was measured for dehydration time in accordance with a test method for dewatering amount of API standard. That is, 400 g of a 0.5 wt% slurry was prepared by setting the fine fibers to 4 g in solid content. This slurry was put into a metal container having a diameter of 76.2 mm and a height of 127.0 mm, a pressure of 0.7 MPa was applied, and the time until 200 ml of the retained water in the slurry was drained was measured.

[Air permeability]
Using a Gurley type densometer (“Model G-B2C” manufactured by Toyo Seiki Co., Ltd.), the permeation time (unit: second / 100 ml) of 100 ml of air was measured at room temperature in accordance with JIS P8117. The air permeability was an average value obtained by measuring five points at various positions of the membrane.

[Tensile strength]
According to JIS P8113, the separators obtained in the examples and comparative examples were cut into strips having a width of 15 mm and a length of 250 mm to obtain samples, which were then chucked by a variable speed tensile tester (manufactured by Toyo Seiki Seisakusho Co., Ltd.). The tensile strength was measured at an interval of 100 mm and a tensile speed of 20 mm / min. The tensile strength was measured in the length direction (or longitudinal direction).

(Creation of negative electrode)
As a negative electrode active agent, carbon particles (manufactured by Hitachi Chemical Co., Ltd., “MAG-D”, average particle diameter D50 approximately 21.3 μm) 98 parts by weight, binder [400 cm pass product of “CMC1190” manufactured by Daicel Corporation ( 1 part by weight, 1 part by weight of SBR latex (“TRD-2001” manufactured by JSR Corporation, solid content 48.5%), and 100 parts by weight of water are homodispers (special machine industry Co., Ltd.) Using “Model L”) for 5 minutes at 3000 rpm, and then kneading and defoaming for 10 minutes using a mixer [Shinky Corporation “Awatori Netaro (vacuum type, ARV-310)”] A negative electrode paste was obtained. The obtained negative electrode paste was applied to a 10 μm thick copper foil with an applicator at 10 mil and dried to obtain a negative electrode.

Example 1
A 100% 2% slurry of Philippine hemp pulp (manufactured by Alindeco, S2 grade) was prepared, and a double disk refiner (manufactured by Hasegawa Tekko Co., Ltd., SUPERFIBRATER400-TFS) was used with a clearance of 0.15 mm and a disk rotation speed of 1750 rpm. Rough cracking was performed 20 times. Subsequently, the treatment was performed 3 times at 50 MPa using a homogenizer (manufactured by Gorin, 15M8AT). The obtained fine cellulose fibers had an average fiber length of 1.1 mm, an average fiber diameter of 0.15 μm, and an aspect ratio of 7333.

  The dispersion containing fine cellulose fibers was drained and the solid content was adjusted to 10% by weight. 990 parts by weight of isopropanol is added to 100 parts by weight of the dispersion having a solid content of 10% by weight (the solid content is adjusted to 1% by weight), and homodisper (manufactured by Tokushu Kika Kogyo Co., Ltd., Model L) ) At 4000 rpm for 20 minutes and dispersed. Further, the same amount of isopropanol was added and stirred in the same manner to obtain a 0.7% slurry of fine cellulose fibers. The viscosity was 1530 mPa · s.

Using a doctor blade, the obtained slurry was coated on the negative electrode with a clearance of 500 μm and a coating speed of 0.3 m / second with a wet thickness of 500 μm (corresponding to a basis weight of 2.8 g / m ² ), and at 120 ° C. for 4 minutes. Dried.

  A uniform film having a thickness of 5 μm was formed on the negative electrode. Further, pressing was performed at 100 ° C. × 30 MPa × 3 minutes. The average thickness of the separator was 3 μm. The appearance of the separator was visually confirmed, but no pinholes or fiber lump was found, and the separator was uniformly uniform.

A positive electrode (manufactured by Piotrec Co., Ltd., a positive electrode material having a layer formed of a positive electrode active material containing lithium cobaltate on an aluminum foil, a capacity of 1.5 mAh / cm ² ) is stacked on the negative electrode coated with the separator. Then, a length of 10 cm was applied manually with a 5N tension. I was able to wind without any problems.

Example 2
In the step of coating the slurry of fine cellulose fibers, a uniform film having a thickness of 5 μm was formed in the same manner as in Example 1 except that the coating speed was 1 m / second. The average thickness of the separator after pressing was 3 μm. The appearance of the separator was visually confirmed, but no pinholes or fiber lump was found, and the separator was uniformly uniform.

Example 3
Instead of Philippine hemp pulp, fine cellulose fibers (cellulose nanofibers) were produced by using the dissolving pulp by the method described in Example 3 of JP 2011-26760 A. The obtained fine cellulose fibers had an average fiber length of 231 μm, an average fiber diameter of 93 nm, and an aspect ratio of 2473.

  Using this fine cellulose fiber, after removing the liquid and replacing the solvent in the same manner as in Example 1, the obtained / rally was coated to form a film having a uniform thickness of 4 μm. The average thickness of the separator after pressing was 2 μm. The appearance of the separator was visually confirmed, but no pinholes or fiber lump was found, and the separator was uniformly uniform.

Comparative Example 1
A square paper machine (Toyo Seiki Seisakusho Co., Ltd.) was used with a filter paper (No. 5C) so that the 0.7% slurry containing the fine cellulose fibers and isopropanol of Example 1 corresponded to a basis weight of 2.8 g / m ^{2 in} terms of solid content. The paper was made with “Standard Square Machine” manufactured by Co., Ltd., and after removing the liquid, sandwiched with filter paper (No. 5C) and dried at 120 ° C. for 30 minutes. Papermaking unevenness occurred due to the low basis weight. The tensile strength of the portion that was barely made was measured and found to be 2.3 N / 15 mm. When the positive electrode, the separator, and the negative electrode were applied with a tension of 5 N and a length of 10 cm was manually handed, the separator broke. When the appearance of the separator was visually confirmed, there were many aggregates in which the fibers were aggregated.

  The laminated body for an electricity storage device of the present invention is an electricity storage device such as a battery (a lithium battery, a lithium secondary battery, a fuel battery, an alkaline secondary battery, a nickel hydride secondary battery, a nickel-cadmium battery, a lead storage battery, etc.), a capacitor, a capacitor, etc. It is useful for a laminate in which an element separator and an electrode are integrated, particularly for a laminate of a lithium ion battery (lithium ion secondary battery) used for a drive source of an electric vehicle (EV), a stationary power storage system, or the like.

Claims (9)

  A coating process for forming a separator coating layer by coating a dispersion containing fine cellulose fibers and an organic solvent on an electrode for a storage element, a drying process for drying the separator coating layer, and a separator coating layer after drying And the electrode are pressed to form a laminated body in which the separator and the electrode are integrated, and a method for manufacturing a laminated body for a storage element including a pressing step.   The manufacturing method according to claim 1, wherein the separator has an average thickness of 10 μm or less.   The production method according to claim 1 or 2, wherein the average fiber diameter of the fine cellulose fibers is 1 µm or less.   The production method according to any one of claims 1 to 3, wherein the average fiber diameter of the fine cellulose fibers is 50 to 500 nm, and the ratio of the average fiber length to the average fiber diameter is 3000 to 20000.   The manufacturing method in any one of Claims 1-4 heated by a pressurization process.   The dispersion is a dispersion preparation step for preparing a dispersion by dispersing plant-derived raw material cellulose fibers in water, a microfibrillation step for microfibrillation of the dispersion, and water dispersion of microfibrillated microcellulose fibers. The manufacturing method in any one of Claims 1-5 obtained through the substitution process which substitutes a liquid with an organic solvent. The production method according to any one of claims 1 to 6, wherein the organic solvent is _C1-4 alkanol, and the concentration of the fine cellulose fibers in the dispersion is 0.01 to 10% by weight.   The production method according to claim 1, wherein the electrode is a negative electrode of a lithium ion battery.   The lithium ion battery provided with the laminated body for electrical storage elements obtained with the manufacturing method in any one of Claims 1-8.