separators for electrochemical elements and electrochemical elements

Abstract

This invention provides a separator for electrochemical components made of pulped regenerated cellulose fibers, which balances density and low impedance characteristics and can withstand the typical component winding process of aluminum electrolytic capacitors. The separator, sandwiched between a pair of electrodes and composed of pulped regenerated cellulose fibers, is capable of retaining an electrolyte-containing solution and has the following technical characteristics: it is a single-layer separator with a thickness of 10–35 μm and a density of 0.35–0.80 g / cm³. 3 When the tensile strength is ≥9.8N / 15mm, the average pore size is 0.05~1.00μm, the tensile strength measured by setting the clamp spacing of the tensile strength testing machine to 0.1mm and the elongation speed of the test piece to 200mm / min, and the value of the tensile strength is taken as the variable tensile strength, the variable tensile strength is ≥5.9N / 15mm.

Description

Technical Field

[0001] This invention relates to a separator for electrochemical elements and an electrochemical element using the separator for electrochemical elements. Background Technology

[0002] Electrochemical components include aluminum electrolytic capacitors, double-layer capacitors, lithium-ion capacitors, lithium-ion secondary batteries, and lithium primary batteries.

[0003] The main function of the separator in an electrochemical element is to isolate the two electrodes and retain the electrolyte. To isolate the two electrode foils, the separator requires both low resistance and high shielding properties. Furthermore, the raw materials for the separator must be electrically insulating, and to retain various electrolytes, they must be hydrophilic and oleophilic.

[0004] Cellulose is a raw material that combines these characteristics, and cellulose paper has been used as a separator for electrochemical components since ancient times. Among cellulose fibers, pulpable regenerated cellulose fibers have the characteristic of producing fibrils with high rigidity and small fiber diameter when highly pulped. It is known that microporous and highly dense separators can be manufactured by using pulped regenerated cellulose fibers. Therefore, many separators using pulpable regenerated cellulose fibers have been proposed in recent years. (See, for example, Patent Documents 1 to 8)

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent Application Publication No. 5-267103

[0008] Patent Document 2: Japanese Patent Application Publication No. 9-45586

[0009] Patent Document 3: International Patent Publication No. 2017 / 047699

[0010] Patent Document 4: Japanese Patent Application Publication No. 2012-221566

[0011] Patent Document 5: Japanese Patent Application Publication No. 2018-073856

[0012] Patent Document 6: Japanese Patent Application Publication No. 2006-253728

[0013] Patent Document 7: Japanese Patent Application Publication No. 2016-134425

[0014] Patent Document 8: Japanese Patent Application Publication No. 2017-69229 Summary of the Invention

[0015] The problem the invention aims to solve

[0016] In Patent Document 1, a method using pulpable regenerated cellulose fibers was proposed to improve the density of the separator and enhance its impedance characteristics. The separator, made from pulped regenerated cellulose fibers, forms a highly dense, microporous paper. Aluminum electrolytic capacitors manufactured using this separator exhibit reduced short-circuit failure rates and improved impedance characteristics.

[0017] Regenerated cellulose fibers capable of beating can be further refined to obtain fine fibrils with a diameter of less than 3 μm. These fibrils are highly rigid and resistant to flattening, thus preventing them from forming a thin film-like bond when used in papermaking, unlike the fibrils of natural cellulose fibers. Therefore, by using beated regenerated cellulose fibers as separators, highly dense separators can be obtained, formed by numerous point bonds between independent fibrils using hydrogen bonds. Despite their high density, these separators exhibit a microporous paper-like structure. Furthermore, the unrefined main fibers and the fibrils with a diameter of less than 3 μm each have nearly circular cross-sections, thus avoiding obstruction of ion flow in the electrolyte, unlike the relatively flattened natural cellulose fibers.

[0018] For the reasons mentioned above, spacers made of regenerated cellulose fibers exhibit excellent short-circuit withstand and impedance characteristics, leading to a surge in their use, particularly in automotive applications where both compactness and low impedance are highly desirable. Furthermore, to achieve miniaturization or high capacitance, there is an increasing trend towards using thin spacers with a thickness of 35 μm or less. Additionally, when spacers made of regenerated cellulose fibers are used as spacers for aluminum electrolytic capacitors, they are often cut into pieces of approximately 2 mm for finer applications.

[0019] In the manufacturing process of aluminum electrolytic capacitors, electrode foils and separators are alternately stacked, cut to a specified length, and wound up. The element is then manufactured using a belt brake. The following operation is repeated: the cutting of the separators and the belt brake temporarily stop the winding machine, and then the winding machine is restarted to wind up the next element.

[0020] Therefore, when rewinding the next element for another operation, the separators mounted on the winding machine are subjected to rapid tension. Because separators made of regenerated cellulose fibers have low tensile strength, especially when the thickness is less than 35 μm, there is a problem that separator breakage is likely to occur during the manufacturing process of aluminum electrolytic capacitors. Therefore, when using separators made of regenerated cellulose fibers, sometimes element winding machines with measures implemented to reduce the load applied to the separators are used, and the winding speed is also reduced, to produce aluminum electrolytic capacitor elements.

[0021] Furthermore, the separator is temporarily pressed near the end furthest from the core using a jig and then cut to the desired length. During winding, it is pulled out by the temporary pressing part. However, even if the pressure of the temporary pressing is set to the minimum required for winding, the separator may still break during pulling. Moreover, due to its weak strength, it has low resistance to stress-prone areas such as the tabs of aluminum electrolytic capacitors and foil burrs, and the separator may break, causing a short circuit.

[0022] In the case of separators made of natural cellulose fibers, the cross-sections of the main fibers and the original fibers are relatively flat and have low rigidity, resulting in a wide contact area and strong bonding strength between the fibers. Therefore, the tensile strength is usually above 9.8 N / 15 mm. Thus, even without modifying the winding machine of the aluminum electrolytic capacitor to reduce the load on the separator, the separator will hardly break.

[0023] However, separators composed of regenerated cellulose fibers have narrow contact areas and weak inter-fiber bonding strength because the cross-sections of the main fibers (with a diameter of 3 μm or more) and the protofibrils (with a diameter of less than 3 μm) are nearly circular and highly rigid. Therefore, even with a tensile strength of 9.8 N / 15 mm or higher, they cannot withstand rapid changes in tension, and the separators may break.

[0024] Patent document 1 also proposes blending Manila hemp pulp, sisal pulp, etc. into regenerated cellulose fibers that can be pulped.

[0025] In addition, Patent Document 2 proposes a separator for a double-layer capacitor composed of solvent-spun rayon, which is a regenerated cellulose fiber capable of being pulped, and sisal pulp.

[0026] While blending Manila hemp pulp and sisal pulp into beating regenerated cellulose fibers improves tensile and tear strength, the resulting Manila hemp and sisal pulps with low CSF values ​​(which are rarely beating) suffer from poor separator quality due to their long fibers. This is because longer fibers are more difficult to disperse evenly in water, making it harder to form a uniform paper layer during papermaking. To improve quality, beating Manila hemp pulp is necessary. While beating sisal pulp shortens fiber length, beating Manila hemp and sisal pulp significantly worsens impedance characteristics.

[0027] Patent document 3 proposes a separator for electrochemical elements composed of natural cellulose fiber A, natural cellulose fiber B, and regenerated cellulose fiber, which improves tensile strength and short-circuit withstand capability while maintaining the density and impedance characteristics of the separator composed of highly pulped regenerated cellulose fiber. However, compared with the original fibers of regenerated cellulose fiber, the fiber diameter of natural cellulose fiber is larger, thus inevitably leading to a deterioration in density and impedance characteristics. In particular, it is difficult to use natural cellulose fiber in cases where both density and low impedance characteristics are strongly required, such as aluminum electrolytic capacitors with a thickness of less than 35 μm for automotive applications.

[0028] Patent document 4 proposes a separator for an electrochemical element composed of cellulose fibers, which has excellent strength when attached to electrolyte, obtained by specifying the water filtration degree, length-weighted average fiber length, and fiber length distribution bar chart pattern of solvent-spun cellulose fibers.

[0029] In addition, Patent Document 5 proposes a separator for an aluminum electrolytic capacitor made of regenerated cellulose fibers using a cylinder multilayer paper machine.

[0030] The separators in Patent Documents 4 and 5 are manufactured using a cylinder paper machine. While separators made using a cylinder paper machine exhibit excellent strength properties, thinner separators are more prone to pinholes caused by the linear patterns of the cylinder wire during papermaking. Furthermore, cylinder paper machines require structurally sound, short-time dehydration to form the paper layer, thus limiting the use of highly beaten raw materials. Therefore, cylinder paper machines are unsuitable for manufacturing highly dense separators in the thinner range (below 35 μm).

[0031] Patent document 6 proposes a separator with low impedance and improved tensile strength by using pulped regenerated cellulose fibers as raw materials for papermaking and impregnating them with a paper strength enhancer.

[0032] However, Patent Document 6 relates to a technique for making low-density paper with almost no pulping using a cylinder paper machine, which is not suitable for producing separators with a thickness of less than 35 μm and high density.

[0033] Patent Document 7 proposes a separator composed of pulped regenerated cellulose fibers, with controlled CSF value and tear index. Compared with the separators in Patent Documents 1 and 2, the separator in Patent Document 7 has stronger tear strength. Therefore, in the manufacturing process of aluminum electrolytic capacitors, when tension is applied to the separator, even if the separator is torsioned, breakage can be expected to be suppressed.

[0034] However, in terms of tensile strength and resistance to rapid changes in tension, the separator in Patent Document 7 is almost unchanged compared to the separators in Patent Documents 1 and 2. Therefore, the separator in Patent Document 7 does not eliminate the need for measures to reduce the load on the separator in the component winding machine of the aluminum electrolytic capacitor. Furthermore, during the production of aluminum electrolytic capacitor components, the breakage of the separator when it is pulled out from the jig that temporarily presses the separator cannot be completely resolved.

[0035] Patent document 8 proposes a separator for electrochemical elements that is thin, has excellent strength and shielding properties, and is composed of regenerated cellulose fibers with an average fiber length of 0.25 to 0.80 mm, an average fiber width of 3 to 35 μm, and a value of 15 to 70 calculated by dividing the average fiber length by the average fiber width.

[0036] However, even if the fine fibrils generated on the fiber surface and the fiber length are within the range of Patent Document 8, it is possible to achieve both density and low impedance characteristics, but it is still not possible to achieve the strength required to withstand the rapid tension changes in the element winding process of aluminum electrolytic capacitors, and further resistance to breakage is required.

[0037] As mentioned above, even with a tensile strength of 9.8 N / 15 mm or higher, spacers made of regenerated cellulose fibers with a thickness of 35 μm or less are prone to breakage during the manufacturing process of aluminum electrolytic capacitor components. Blending in natural cellulose fibers degrades density and impedance characteristics. Furthermore, while spacers produced using a cylinder paper machine exhibit excellent strength characteristics, their density is reduced. Therefore, there is a need for spacers made of regenerated cellulose fibers with a thickness of 35 μm or less, possessing both density and low impedance characteristics, and having the strength to withstand the winding process of aluminum electrolytic capacitor components.

[0038] The present invention was made in view of the above-mentioned problems, and its object is to provide a separator for electrochemical elements composed of pulped regenerated cellulose fibers, which has a thickness of less than 35 μm, and takes into account both density and low impedance characteristics, and can withstand the conventional element winding process of aluminum electrolytic capacitors.

[0039] Furthermore, the object of the present invention is to provide an electrochemical element that improves productivity and reduces short-circuit failure rate by using the separator of the electrochemical element.

[0040] Solution for solving the problem

[0041] The separator for electrochemical elements of the present invention is a separator for electrochemical elements sandwiched between a pair of electrodes, composed of pulped regenerated cellulose fibers, and capable of maintaining an electrolyte containing electrolytes.

[0042] Furthermore, the separator for the electrochemical element of the present invention is characterized in that it is a single-layer separator with a thickness of 10 to 35 μm and a density of 0.35 to 0.80 g / cm³. 3 When the tensile strength is ≥9.8N / 15mm, the average pore size is 0.05~1.00μm, the tensile strength measured by setting the clamp spacing of the tensile strength testing machine to 0.1mm and the elongation speed of the test piece to 200mm / min, and the value of the tensile strength is taken as the variable tensile strength, the variable tensile strength is ≥5.9N / 15mm.

[0043] In the separator for electrochemical elements of the present invention described above, the pulped regenerated cellulose fiber preferably consists of a protofibril portion with a fiber diameter of less than 3 μm and a main fiber with a fiber diameter of more than 3 μm, and the average fiber diameter of the main fiber is 3 to 12 μm.

[0044] The electrochemical element of the present invention is characterized in that it uses the separator for electrochemical elements described above.

[0045] The electrochemical element of the present invention described above is preferably any one of aluminum electrolytic capacitor, double-layer capacitor, lithium-ion capacitor, lithium-ion secondary battery, and lithium primary battery.

[0046] The effects of the invention

[0047] According to the present invention, a separator for electrochemical components, composed of pulped regenerated cellulose fibers, can be provided. This separator has a thickness of less than 35 μm, combines both density and low impedance characteristics, and can withstand the conventional component winding process of aluminum electrolytic capacitors. Furthermore, an electrochemical component can be provided that improves productivity and reduces short-circuit failure rate by using this separator. Detailed Implementation

[0048] The following provides a detailed description of embodiments of the present invention.

[0049] The separator for electrochemical elements of the present invention is a separator for electrochemical elements sandwiched between a pair of electrodes, composed of pulped regenerated cellulose fibers, and capable of maintaining an electrolyte containing electrolytes.

[0050] Furthermore, the separator for the electrochemical element of the present invention is a single-layer separator with a thickness of 10–35 μm and a density of 0.35–0.80 g / cm³. 3 It has a tensile strength of ≥9.8N / 15mm and an average pore size of 0.05~1.00μm.

[0051] Furthermore, for the separator for the electrochemical element of the present invention, when the spacing of the clamps of the tensile strength testing machine is set to 0.1 mm and the elongation speed of the test piece is set to 200 mm / min, and the measured tensile strength value is taken as the variable tensile strength, the variable tensile strength is 5.9 N / 15 mm or more.

[0052] In addition to the examples shown in the embodiments and examples described below, the inventors of this invention have also conducted experimental research on various materials and manufacturing methods.

[0053] The result is a single-layer separator composed of pulped regenerated cellulose fibers, with a thickness of 10–35 μm and a density of 0.35–0.80 g / cm³. 3 In electrochemical element separators with a tensile strength of 9.8 N / 15 mm or higher and an average pore size of 0.05 to 1.00 μm, a variable tensile strength of 5.9 N / 15 mm or higher is achieved.

[0054] Furthermore, it was determined that if the tensile strength of the variable method is 5.9 N / 15 mm or higher, it can provide an electrochemical element separator that balances both density and low impedance characteristics and can withstand the element winding process of aluminum electrolytic capacitors.

[0055] In this invention, "variable tensile strength" refers to the tensile strength value measured when the clamp spacing of the tensile strength testing machine is set to 0.1 mm and the elongation speed of the test piece is set to 200 mm / min.

[0056] It should be noted that if the clamp spacing of the tensile strength testing machine is 0mm, the clamps will be in contact with each other, and the load at the zero point of the tensile testing machine will become unstable, making it difficult to obtain accurate measurement values. Therefore, as the setting for the tensile testing machine with the narrowest clamp spacing that can be measured, the clamp spacing is set to 0.1mm.

[0057] For spacers used in aluminum electrolytic capacitors, a tensile strength of 9.8 N / 15 mm or higher is typically required to withstand the element winding process. If the tensile strength is less than 9.8 N / 15 mm, spacers, whether made of natural cellulose or regenerated cellulose fibers, are prone to breakage during the element winding process. However, even with a tensile strength of 9.8 N / 15 mm or higher, natural cellulose-based spacers will not break during the element winding process, while spacers made of regenerated cellulose fibers may break. This difference represents a variation in resistance to rapid changes in tension. In this invention, a variable tensile strength value is used as an indicator of this resistance.

[0058] The separator made of regenerated cellulose fibers is prone to breakage during the element winding process of aluminum electrolytic capacitors, even if the tensile strength is above 9.8 N / 15 mm, when the variable tensile strength is less than 5.9 N / 15 mm.

[0059] The tensile strength is usually measured with a clamp spacing of 180 mm and an elongation rate of 20 mm / min for the test piece. However, since the spacers elongate during the measurement and absorb some of the load applied to them, no sharp tension is applied to the spacers, and they can withstand relatively strong loads.

[0060] In contrast, variable tensile strength, due to the almost non-existent clamping gaps, prevents the spacer from elongating and is subjected to rapid tension, resulting in fracture under relatively weak loads. Therefore, variable tensile strength is a suitable indicator for evaluating tolerance to rapid changes in tension.

[0061] Examples of regenerated cellulose fibers that can be used in the separators for electrochemical elements of the present invention include solvent-spun rayon, such as Lyocell rayon, and Polynosic rayon. However, these examples are not limited to, and any regenerated cellulose fiber that can be pulped can be used.

[0062] Regenerated cellulose fibers of any diameter can be used as the pre-beating regenerated cellulose fibers. However, if the fiber diameter is too coarse, poor flowability and clogging during beating will occur. If the fiber diameter is too fine, the amount of fibrils produced through beating will be less, making it difficult to ensure density. Therefore, the preferred fiber diameter before beating is 4–18 μm.

[0063] The pulped regenerated cellulose fibers preferably consist of protofibrils with a diameter of less than 3 μm and main fibers with a diameter of more than 3 μm, and the average fiber diameter of the main fibers is 3 to 12 μm. The average fiber diameter of the main fibers can be controlled by pulping the regenerated cellulose fibers with a diameter of 4 to 18 μm before pulping. By making them as fine as possible within the range of 3 to 12 μm, the surface area of ​​the fibers constituting the separators can be increased, thus widening the bonding area between the fibers and improving the variable tensile strength of the separators.

[0064] However, if the difference between the fiber diameter of the regenerated cellulose fiber before pulping and the average fiber diameter of the main fibers in the separator (which is 3 μm or larger) is small, even if the average fiber diameter of the main fibers is in the range of 3–12 μm, the generation of fibrils through pulping will be insufficient, resulting in inadequate compactness of the separator and an average pore size greater than 1.00 μm. By pulping the regenerated cellulose fiber until the average pore size of the separator is less than 1.00 μm, the variable tensile strength of the separator can be increased to 5.9 N / 15 mm or more.

[0065] It should be noted that if the regenerated cellulose fibers are pulped until the main fibers with a diameter of 3μm or more disappear, and the regenerated cellulose fibers only form fibrils with a diameter of less than 3μm, the strength of the fibers themselves will be significantly reduced, thus weakening the tensile strength. Furthermore, if only fibrils are formed, the fibers will be too fine, resulting in more fibers flowing out of the system along with water through the papermaking wire, making it unsuitable even as a raw material for papermaking.

[0066] On the other hand, since the larger the average fiber diameter, the fewer the number of overlapping fibers between the main fibers and the separator, when the average fiber diameter is larger than 12μm, in addition to the weakening of the tensile strength, it is also difficult to manufacture a dense separator with a thickness of less than 35μm.

[0067] The equipment used in beating the regenerated cellulose fibers used in this invention can be any equipment commonly used in the manufacture of papermaking raw materials. Examples of such equipment include pulpers, conical refiners, disc refiners, and high-pressure homogenizers.

[0068] The separator for the electrochemical element of the present invention is preferably formed as a separator having only one layer of wire formed by papermaking using a wire papermaking machine.

[0069] If a paper machine, such as a cylinder paper machine, short-wire paper machine, or forming machine, is used, which performs water filtration and paper layer formation in a short time, fibers will accumulate at the openings of the paper wire, while it will be difficult for fibers to accumulate in the wire section. Areas where fibers do not accumulate are called pinholes, which can easily become a cause of short circuits in electrochemical components.

[0070] On the other hand, when using a long wire paper machine, due to the use of a long wire for slow dewatering, fibers also accumulate in the wire section of the wire, thus forming a dense paper layer without pinholes.

[0071] The separator for the electrochemical element of the present invention is preferably prepared by adding a drying paper strength enhancer to the papermaking raw material during papermaking, or by coating the separator with a drying paper strength enhancer after papermaking. Alternatively, additives commonly used in the papermaking process, such as dispersants and defoamers, may be used as needed. The drying paper strength enhancer strengthens the bonding at the fiber junctions by increasing the number of hydrogen bonds between cellulose fibers, thus enhancing the paper strength during drying. Therefore, by using a drying paper strength enhancer, the variable tensile strength can be improved.

[0072] The separator for the electrochemical element of the present invention is composed of regenerated cellulose fibers, which are produced by pulping to generate many fibrils with a fiber diameter of less than 3 μm. It has a large surface area and is particularly good at exhibiting the paper strength enhancement effect of the drying paper strength enhancer.

[0073] Dry paper strength enhancers can be used appropriately as long as the content of ionic impurities is below a level that will not corrode the electrode foil of aluminum electrolytic capacitors.

[0074] As paper drying force enhancers, synthetic polymer compounds such as polyacrylamide resins and polyvinyl alcohol resins, as well as natural polymer compounds such as cationic starch, amphoteric starch, plant gums, and carboxymethyl cellulose, are commonly known. From the viewpoint of ease of reducing ionic impurities and ease of processing, polyacrylamide resins are preferred.

[0075] The separator for the electrochemical element of the present invention has a thickness of 10–35 μm and a density of 0.35–0.80 g / cm³. 3 To control thickness and density, calendering can be performed as needed.

[0076] If the thickness is less than 10 μm, the mechanical strength weakens, making the separator prone to breakage during the manufacturing processes of the separator and electrochemical element. Furthermore, the closer distance between the electrodes compromises short-circuit withstand capability. The separator of this invention forms a dense paper layer through fiber miniaturization, thus ensuring a density that is unlikely to fall below 0.35 g / cm³. 3 .

[0077] On the other hand, if the density is higher than 0.80 g / cm³ 3 The gaps in the separator are reduced, and the permeability of ions is hindered, resulting in a sharp deterioration in impedance characteristics.

[0078] The average pore size of the separator for the electrochemical element of the present invention is 0.05 to 1.00 μm.

[0079] 0.05 μm is the lower limit of measurement for the apparatus used in the assay. However, the average pore size cannot be measured, meaning that separators below the lower limit of measurement have poor ion permeability and impedance characteristics. In addition, if the average pore size is greater than 1.00 μm, the density of the separator is insufficient, which can easily lead to short circuits in the electrochemical elements.

[0080] The electrochemical element of the present invention can be fabricated using the separator of the electrochemical element of the present invention. The electrochemical element of the present invention is preferably any one of an aluminum electrolytic capacitor, an electric double-layer capacitor, a lithium-ion capacitor, a lithium-ion secondary battery, and a lithium primary battery.

[0081] Example

[0082] The following describes specific embodiments, comparative examples, and existing examples of the present invention.

[0083] (Evaluation Method)

[0084] In the examples, comparative examples, and existing examples, the specific determination of each characteristic of the papermaking raw material and separator, aluminum electrolytic capacitor, and wound double-layer capacitor was carried out under the following conditions and methods.

[0085] [thickness]

[0086] Using the micrometer specified in "JIS C 2300-2 Electrochemical Cellulose Paper - Part 2: Test Methods (Electrical Cellulose Paper - Part 2: Test Methods) 5.1 Thickness" under "5.1.1 Measuring Instrument and Method: a. External Micrometer", the thickness of the separator was measured using the method of folding the paper into 10 sheets as described in "5.1.3 Folding the Paper and Measuring the Thickness".

[0087] [density]

[0088] The density of the separator in an oven-dry state was determined using the method specified in Method B of "JIS C 2300-2 Electro-cellulose Paper - Part 2: Test Methods (Electro-cellulose Paper - Part 2: Test Methods) 7.0A Density".

[0089] Tensile strength

[0090] The longitudinal tensile strength of the separator was determined using the method specified in "JIS C 2300-2 Electro-cellulose Paper - Part 2: Test Methods (Electro-cellulose Paper - Part 2: Test Methods) 8. Tensile Strength and Elongation".

[0091] [Modified Tensile Strength]

[0092] The clamping interval of the tensile strength testing machine was set to 0.1 mm, and the elongation speed of the test piece was set to 200 mm / min. In addition, the longitudinal tensile strength of the separator was determined using the method specified in "JIS C 2300-2 Electro-cellulose Paper - Part 2: Test Methods (Electro-cellulose Paper - Part 2: Test Methods) 8. Tensile Strength and Elongation".

[0093] [Average Aperture]

[0094] In the determination of average pore size, a Parm-Porometer manufactured by PMI was used. The pore size distribution was determined using the bubble point method (ASTM F316-86, JIS K3832), and the average pore size (μm) was calculated from this distribution. GALWICK (manufactured by Porous Materials, Inc.) was used as the test solution for the average pore size determination. It should be noted that the lower limit for determining the average pore size using the Parm-Porometer is 0.05 μm.

[0095] [Average fiber diameter of main fibers with a diameter of 3μm or more]

[0096] The surface of the separator was observed using a scanning electron microscope at 1000x magnification. For the main fibers with different fiber diameters of 3μm or more, the width of 200 fibers was measured and the average value was calculated.

[0097] [Manufacturing Method of Aluminum Electrolytic Capacitors]

[0098] Anode and cathode aluminum foils, which have undergone etching and oxide coating processes, are wound together in a non-contact manner using separators to fabricate a capacitor element. This element is then impregnated with a specified electrolyte, installed into a housing, and sealed, thereby producing an aluminum electrolytic capacitor with a diameter of 10 mm, a height of 10 mm, and a rated voltage of 35V or 160V. It should be noted that the length of the anode aluminum foil remains constant during the fabrication of the capacitor element.

[0099] [Workability during the fabrication of aluminum electrolytic capacitor components]

[0100] When manufacturing 100 of each capacitor element, the number of times the separator breaks is measured under the same manufacturing conditions. Cases with fewer than 1 breakage are marked as ○, cases with fewer than 9 breakages are marked as △, and cases with more than 10 breakages are marked as ×.

[0101] [Defect rate of aluminum electrolytic capacitors after aging]

[0102] For each capacitor sample of 100, the voltage is slowly increased to approximately 110% of the rated voltage for aging. The number of defective capacitors, including those with aging short circuits, malfunctioning explosion-proof valves, leakage, and bulging of the seal, is divided by 100, and the percentage is used as the defect rate.

[0103] [Impedance of aluminum electrolytic capacitors]

[0104] The impedance of aluminum electrolytic capacitors was measured using an LCR meter at 20°C and 100kHz.

[0105] [Method for fabricating a wound double-layer capacitor]

[0106] Activated carbon electrodes and separators are wound to obtain a double-layer capacitor element. This element is housed in a bottomed cylindrical aluminum shell, and an electrolyte solution made by dissolving tetraethylammonium tetrafluoroborate as the electrolyte in propylene carbonate solvent is injected. After vacuum impregnation, the shell is sealed with sealing rubber to produce a double-layer capacitor (10mmφ×35mmL) with a rated voltage of 2.5V and a rated capacitance of 10F.

[0107] [Workability of fabricating wound double-layer capacitors]

[0108] When manufacturing 100 wound double-layer capacitor elements, the number of times the separator breaks is measured under the same manufacturing conditions. Cases with less than 1 breakage are marked as ○, cases with less than 9 breakages are marked as △, and cases with more than 10 breakages are marked as ×.

[0109] Internal resistance of a wound double-layer capacitor

[0110] The internal resistance of the wound double-layer capacitor is determined by the AC resistance method as specified in "4.6 Internal Resistance" of "JIS C 5160-1 Fixed Double-Layer Capacitor for Electronic Instruments".

[0111] Leakage current of wound double-layer capacitors

[0112] The leakage current of the wound double-layer capacitor was measured according to "4.7 Leakage Current" in "JIS C 5160-1 Fixed Double-Layer Capacitor for Electronic Instruments" under a voltage application time of 30 minutes.

[0113] [Short-circuit failure rate of wound double-layer capacitors]

[0114] For each type of wound double-layer capacitor sample of 100, if the charging voltage does not rise to the rated voltage, it is considered a short circuit failure. The number of failures is divided by 100 to obtain the percentage as the failure rate.

[0115] [Example 1]

[0116] Leocell fibers with a diameter of 14 μm, used as regenerated cellulose fibers, were pulped and processed using a single-layer, long-wire paper machine to obtain a thickness of 25 μm and a basis weight of 10.5 g / m². 2 Density 0.42 g / cm³ 3 The separator has a tensile strength of 9.8 N / 15 mm, a variable tensile strength of 5.9 N / 15 mm, an average pore size of 0.50 μm, and an average fiber diameter of 8.5 μm for the main fibers with a fiber diameter of 3 μm or more.

[0117] Capacitor elements were fabricated using separators cut to a width of 6mm. After being impregnated with GBL-based electrolyte, the separators were inserted into the casing and sealed to form an aluminum electrolytic capacitor with a rated voltage of 35V, a capacitance of 330μF, and a diameter of 10mm × a length of 10mm. The workability during capacitor element fabrication was 0%, the defect rate after aging was 0%, and the impedance was 0.113Ω.

[0118] [Example 2]

[0119] Lyocell fibers with a diameter of 18 μm, used as regenerated cellulose fibers, were pulped and used as a dry paper strength enhancer. Polyacrylamide resin was added at 3% of the solids content relative to the Lyocell fibers. Using a single-layer, four-wire paper machine, a paper with a thickness of 10 μm and a basis weight of 5.0 g / m² was obtained. 2 Density 0.50 g / cm³ 3 The separator has a tensile strength of 10.0 N / 15 mm, a variable tensile strength of 7.2 N / 15 mm, an average pore size of 0.55 μm, and an average fiber diameter of 3.2 μm for the main fibers with a fiber diameter of 3 μm or more.

[0120] Capacitor elements are fabricated using separators cut to a width of 6mm. After being impregnated with GBL-based electrolyte, they are inserted into a casing and sealed to form an aluminum electrolytic capacitor with a rated voltage of 35V, a capacitance of 330μF, and a diameter of 10mm × length of 10mm. The workability during capacitor element fabrication is 0, the defect rate after aging is 2%, and the impedance is 0.096Ω.

[0121] [Example 3]

[0122] Lyocell fibers with a diameter of 4 μm, used as regenerated cellulose fibers, were pulped, formed using a single-layer wire paper machine, and dried. After coating with an aqueous solution of polyacrylamide resin diluted to a solids concentration of 1% as a drying force enhancer, the paper was dried again to obtain a thickness of 35 μm and a basis weight of 12.3 g / m². 2 Density 0.35 g / cm³ 3The separator has a tensile strength of 12.7 N / 15 mm, a variable tensile strength of 9.9 N / 15 mm, an average pore size of 0.96 μm, and an average fiber diameter of 3.1 μm for the main fibers with a fiber diameter of 3 μm or more.

[0123] Capacitor elements are fabricated using separators cut to a width of 6mm. After being impregnated with GBL-based electrolyte, they are inserted into a casing and sealed to form an aluminum electrolytic capacitor with a rated voltage of 35V, a capacitance of 330μF, a diameter of 10mm, and a length of 10mm. The workability during capacitor element fabrication is 0, the defect rate after aging is 3%, and the impedance is 0.120Ω.

[0124] [Example 4]

[0125] Lyocell fibers with a diameter of 16 μm, used as regenerated cellulose fibers, were pulped and used as a dry paper strength enhancer. Polyacrylamide resin was added at 0.5% of the solids content relative to the Lyocell fibers. After papermaking on a single-layer, four-wire paper machine, calendering was performed to obtain a paper with a thickness of 12 μm and a basis weight of 9.0 g / m². 2 Density 0.75 g / cm³ 3 The separator has a tensile strength of 13.7 N / 15 mm, a variable tensile strength of 11.0 N / 15 mm, an average pore size of 0.72 μm, and an average fiber diameter of 12.0 μm for the main fibers with a fiber diameter of 3 μm or more.

[0126] Capacitor elements are fabricated using separators cut to a width of 6mm. After being impregnated with GBL-based electrolyte, they are inserted into a casing and sealed to form an aluminum electrolytic capacitor with a rated voltage of 35V, a capacitance of 330μF, and a diameter of 10mm × length of 10mm. The workability during capacitor element fabrication is 0, the defect rate after aging is 1%, and the impedance is 0.109Ω.

[0127] [Example 5]

[0128] Lyocell fibers with a diameter of 8 μm, used as regenerated cellulose fibers, were pulped and used as a dry paper strength enhancer. Polyacrylamide resin was added at 2% of the solids content relative to the Lyocell fibers. Using a single-layer, four-wire paper machine, a paper with a thickness of 30 μm and a basis weight of 13.5 g / m² was obtained. 2 Density 0.45 g / cm³ 3 The separator has a tensile strength of 19.3 N / 15 mm, a variable tensile strength of 15.4 N / 15 mm, an average pore size of 0.37 μm, and an average fiber diameter of 6.1 μm for the main fibers with a fiber diameter of 3 μm or more.

[0129] Capacitor elements were fabricated using a separator cut to a width of 6 mm. After impregnation with GBL-based electrolyte, the elements were inserted into a housing and sealed to form an aluminum electrolytic capacitor with a rated voltage of 35 V, a capacitance of 330 μF, and a diameter of 10 mm × a length of 10 mm. The workability during capacitor element fabrication was 0%, the defect rate after aging was 0%, and the impedance was 0.124 Ω. ​​Furthermore, when using the separator obtained in Example 5, the linear velocity could be increased by 40% compared to using the separator of the conventional Example 1 described later.

[0130] [Comparative Example 1]

[0131] Leocell fibers with a diameter of 20 μm, used as regenerated cellulose fibers, were pulped and processed using a single-layer, long-wire paper machine to obtain a thickness of 25 μm and a basis weight of 10.5 g / m². 2 Density 0.42 g / cm³ 3 The separator has a tensile strength of 10.8 N / 15 mm, a variable tensile strength of 5.4 N / 15 mm, an average pore size of 0.77 μm, and an average fiber diameter of 12.5 μm for the main fibers with a fiber diameter of 3 μm or more.

[0132] Capacitor elements are fabricated using separators cut to a width of 6mm. After being impregnated with GBL-based electrolyte, they are inserted into a casing and sealed to form an aluminum electrolytic capacitor with a rated voltage of 35V, a capacitance of 330μF, and a diameter of 10mm × length of 10mm. The workability during capacitor element fabrication is Δ, the defect rate after aging is 4%, and the impedance is 0.118Ω.

[0133] [Reference Example 1]

[0134] Lyocell fibers with a diameter of 10 μm, used as regenerated cellulose fibers, were pulped and processed using a single-layer, long-wire paper machine to obtain a thickness of 30 μm and a basis weight of 10.5 g / m². 2 Density 0.35 g / cm³ 3 The separator has a tensile strength of 9.5 N / 15 mm, a variable tensile strength of 5.2 N / 15 mm, an average pore size of 0.77 μm, and an average fiber diameter of 9.2 μm for the main fibers with a fiber diameter of 3 μm or more.

[0135] Capacitor elements are fabricated using separators cut to a width of 6mm. After being impregnated with GBL-based electrolyte, they are inserted into a casing and sealed to form an aluminum electrolytic capacitor with a rated voltage of 35V, a capacitance of 330μF, and a diameter of 10mm × length of 10mm. The workability during capacitor element fabrication is Δ, the defect rate after aging is 11%, and the impedance is 0.117Ω.

[0136] [Existing Example 1]

[0137] Lyocell fibers with a diameter of 10 μm, used as regenerated cellulose fibers, were pulped and processed using a single-layer, long-wire paper machine to obtain a thickness of 20 μm and a basis weight of 9.0 g / m². 2 Density 0.45 g / cm³ 3 The separator has a tensile strength of 9.8 N / 15 mm, a variable tensile strength of 5.0 N / 15 mm, an average pore size of 0.59 μm, and an average fiber diameter of 7.3 μm for the main fibers with a fiber diameter of 3 μm or more.

[0138] Capacitor elements are fabricated using separators cut to a width of 6mm. After being impregnated with GBL-based electrolyte, they are inserted into a casing and sealed to form an aluminum electrolytic capacitor with a rated voltage of 35V, a capacitance of 330μF, a diameter of 10mm, and a length of 10mm. The workability during capacitor element fabrication is ×, the defect rate after aging is 5%, and the impedance is 0.109Ω.

[0139] [Existing Example 2]

[0140] Lyocell fibers with a diameter of 14 μm, used as regenerated cellulose fibers, were pulped and processed using a three-layer cylinder paper machine to obtain a thickness of 35 μm and a basis weight of 14.0 g / m². 2 Density 0.40 g / cm³ 3 The separator has a tensile strength of 9.8 N / 15 mm, a variable tensile strength of 6.9 N / 15 mm, an average pore size of 1.13 μm, and an average fiber diameter of 11.1 μm for the main fibers with a fiber diameter of 3 μm or more.

[0141] Capacitor elements were fabricated using separators cut to a width of 6mm. After being impregnated with GBL-based electrolyte, the separators were inserted into the casing and sealed to form an aluminum electrolytic capacitor with a rated voltage of 35V, a capacitance of 330μF, a diameter of 10mm, and a length of 10mm. The workability during capacitor element fabrication was 0, the defect rate after aging was 22%, and the impedance was 0.127Ω.

[0142] [Existing Example 3]

[0143] A raw material obtained by mixing 40% by mass of hardwood kraft pulp, 10% by mass of sisal pulp, and 50% by mass of leocel fiber with a fiber diameter of 14 μm was used to make paper using a single-layer, four-wire paper machine, yielding a paper with a thickness of 30 μm and a basis weight of 15.0 g / m². 2 Density 0.50 g / cm³ 3 The separator has a tensile strength of 11.8 N / 15 mm, a variable tensile strength of 7.6 N / 15 mm, an average pore size of 0.81 μm, and an average fiber diameter of 15.6 μm for the main fibers with a fiber diameter of 3 μm or more.

[0144] Capacitor elements were fabricated using separators cut to a width of 6mm. After being impregnated with GBL-based electrolyte, the separators were inserted into the casing and sealed to form an aluminum electrolytic capacitor with a rated voltage of 35V, a capacitance of 330μF, a diameter of 10mm, and a length of 10mm. The workability during capacitor element fabrication was 0%, the defect rate after aging was 0%, and the impedance was 0.137Ω.

[0145] [Existing Example 4]

[0146] 50% by mass of raw material made from pulped Leocel fibers with a fiber diameter of 14 μm and 50% by mass of raw material made from highly pulped Leocel fibers with a fiber diameter of 14 μm were mixed and paper was made using a single-layer, four-wire paper machine to obtain a paper with a thickness of 20 μm and a basis weight of 9.0 g / m². 2 Density 0.45 g / cm³ 3 The separator has a tensile strength of 9.8 N / 15 mm, a variable tensile strength of 4.9 N / 15 mm, an average pore size of 0.48 μm, and an average fiber diameter of 5.3 μm for the main fibers with a fiber diameter of 3 μm or more.

[0147] Capacitor elements are fabricated using separators cut to a width of 6mm. After being impregnated with GBL-based electrolyte, they are inserted into a casing and sealed to form an aluminum electrolytic capacitor with a rated voltage of 35V, a capacitance of 330μF, a diameter of 10mm, and a length of 10mm. The workability during capacitor element fabrication is ×, the defect rate after aging is 7%, and the impedance is 0.107Ω.

[0148] The evaluation results of each separator of Examples 1 to 5, Comparative Example 1, Reference Example 1, and Existing Examples 1 to 4 described above, as well as the evaluation results of an aluminum electrolytic capacitor with a rated voltage of 35V, are shown in Table 1.

[0149] [Table 1]

[0150]

[0151] The separators in Examples 1 to 5 have a thickness of 10–35 μm and a density of 0.35–0.80 g / cm³. 3 The tensile strength is 9.8 N / 15 mm or more, the average pore size is 0.05 to 1.00 μm, and the variable tensile strength is 5.9 N / 15 mm or more. Therefore, the separators in Examples 1 to 5 combine both compactness and low impedance characteristics, and exhibit high resistance to rapid tension changes. This results in good workability during the fabrication of aluminum electrolytic capacitor components and a low defect rate after aging.

[0152] The aluminum electrolytic capacitors made using the separators from Examples 1 to 5 operate without problems.

[0153] In Comparative Example 1, the average fiber diameter of the main fibers with a fiber diameter of 3 μm or more in the separator is coarse, at 12.5 μm. The thickness and density of the separator in Comparative Example 1 are the same as those in Example 1, but the average fiber diameter of the main fibers is coarser, and the number of overlapping main fibers in the separator is less. Therefore, the tensile strength is weaker, and the workability during capacitor element manufacturing is worse. Furthermore, because the average fiber diameter of the main fibers in Comparative Example 1 is coarser, the density is lower than that of the separator in Example 1, the average pore size is larger, and the defect rate of the aluminum electrolytic capacitor after aging is also worse.

[0154] In Reference Example 1, the regenerated cellulose fibers of the separator before pulping have a fiber diameter of 10 μm, the average fiber diameter of the main fibers of the separator with a fiber diameter of 3 μm or more is 9.2 μm, the difference is 0.8 μm, and the reduction rate shown by [(fiber diameter of regenerated cellulose fibers before pulping - average fiber diameter of main fibers of the separator with a fiber diameter of 3 μm or more) / fiber diameter of regenerated cellulose fibers before pulping] is small, at 8.0%. Therefore, the regenerated cellulose fibers of the separator in Reference Example 1 are not sufficiently fibrillated, resulting in low variable tensile strength and increased average pore size.

[0155] The separator in Existing Example 1 is manufactured using the technology disclosed in Patent Document 8. Although the separator in Existing Example 1 is composed of pulped regenerated cellulose fibers, has a thickness of 10–35 μm, and a density of 0.35–0.80 g / cm³, it is not identical to the separator in Existing Example 1. 3 The tensile strength is 9.8 N / 15 mm or higher, and the average pore size is 0.05 to 1.00 μm. However, the variable tensile strength is only 5.0 N / 15 mm. Therefore, in addition to being unable to withstand the rapid tension changes during component winding, the separator sometimes breaks. Furthermore, when the separator is pulled out from the jig that temporarily presses it during component manufacturing, the separator also breaks. In addition, because the variable tensile strength of the separator in Example 1 is weak, it has lower resistance to stress points compared to the separators in Examples 1 to 5. At the capacitor's tab, the separator breaks, causing a short circuit.

[0156] The separator in Existing Example 2 is manufactured using the technology disclosed in Patent Document 5. Because the tensile strength of the separator in Existing Example 2 is 6.9 N / 15 mm, its workability during capacitor element manufacturing is not a problem. However, since it is manufactured using a cylinder paper machine, even with three layers of paper and a thickness of 35 μm or less, pinholes cannot be avoided. The density of the separator in Existing Example 2 is reduced, resulting in an increased average pore size of 1.13 μm. Compared to the separators in Examples 1 to 5, the defect rate after aging is higher.

[0157] The separator in Example 3 is manufactured using the technology disclosed in Patent Document 3. Natural cellulose fibers have a larger fiber diameter than regenerated cellulose fibers; therefore, mixing natural cellulose fibers with regenerated cellulose fibers again confirms the unavoidable deterioration in density and impedance characteristics. In particular, it is difficult to use natural cellulose fibers in applications such as aluminum electrolytic capacitors with a thickness of 35 μm or less for automotive use, where both density and low impedance characteristics are critically demanding.

[0158] The separator in Existing Example 4 is manufactured using the technology disclosed in Patent Document 7. Because the separator in Existing Example 4 has high tear strength, it does not break during capacitor element manufacturing processes involving torsion or similar actions. However, because the separator in Existing Example 4 has low variable tensile strength, it sometimes breaks due to its inability to withstand rapid tension changes during element winding, and it also breaks when the separator is pulled from a jig that temporarily presses it during element manufacturing.

[0159] [Example 6]

[0160] Lyocell fibers with a diameter of 10 μm, used as regenerated cellulose fibers, were pulped, formed using a single-layer fourdrinier paper machine, and then calendered to obtain a paper with a thickness of 30 μm and a basis weight of 19.5 g / m². 2 Density 0.65 g / cm³ 3 The separator has a tensile strength of 16.7 N / 15 mm, a variable tensile strength of 10.0 N / 15 mm, an average pore size of 0.12 μm, and an average fiber diameter of 4.5 μm for the main fibers with a fiber diameter of 3 μm or more.

[0161] Capacitor elements were fabricated using the separator cut to a width of 6 mm. After impregnation with GBL-based electrolyte, the elements were inserted into a housing and sealed to form an aluminum electrolytic capacitor with a rated voltage of 160 V, a capacitance of 47 μF, and a diameter of 10 mm × a length of 10 mm. The workability during capacitor element fabrication was 0%, and the defect rate after aging was 0%. It was confirmed that the separator of Example 6 can be used at a rated voltage of 160 V in the medium voltage region.

[0162] Next, 100 wound double-layer capacitors were fabricated using the separators obtained in Example 5 and Existing Example 1, and their internal resistance, leakage current, and short-circuit failure rate were measured.

[0163] For the wound double-layer capacitor that uses the separator of Existing Example 1, the workability during manufacturing is ×, the internal resistance is 80mΩ, the leakage current is 380μA, and the defect rate is 3%.

[0164] On the other hand, for the wound double-layer capacitor using the separator obtained in Example 5, the workability during manufacturing is 0, the internal resistance is 92mΩ, the leakage current is 343μA, and the defect rate is 0%, confirming the effect of increased productivity and reduced leakage current achieved through improved workability. Furthermore, when using the separator obtained in Example 5, the winding speed can be increased by 20% compared to using the separator of the existing Example 1.

[0165] Next, a stacked double-layer capacitor was fabricated using the separator from Example 5.

[0166] By alternately folding activated carbon electrodes and separators, a double-layer capacitor element is obtained. This element is housed in an aluminum shell, injected with an electrolyte solution made by dissolving triethylmethyl hexafluorophosphate in acetonitrile, vacuum impregnated, and then sealed, thereby fabricating a double-layer capacitor.

[0167] The fabricated multilayer double-layer capacitor works without any problems.

[0168] Next, the separator from Example 5 was used to fabricate a lithium-ion capacitor.

[0169] Activated carbon electrodes, typically used in lithium-ion capacitors, are used as the positive electrode material, and graphite electrodes are used as the negative electrode material. The separator and electrode materials are alternately folded to obtain a lithium-ion capacitor element. This element, along with a lithium pre-doped foil, is placed in a multilayer laminated film, injected with electrolyte, vacuum impregnated, and then sealed to fabricate a lithium-ion capacitor. The electrolyte used is lithium hexafluorophosphate dissolved in propylene carbonate solvent.

[0170] The lithium-ion capacitors that were made work without any problems.

[0171] Next, the separator from Example 5 was used to fabricate a lithium-ion secondary battery.

[0172] A lithium cobalt oxide electrode, used in lithium-ion secondary batteries, is used as the positive electrode material, and a graphite electrode is used as the negative electrode material. These are wound together with a separator to obtain a lithium-ion secondary battery element. This element is then housed in a bottomed cylindrical casing, and an electrolyte solution, prepared by dissolving tetraethylammonium tetrafluoroborate in propylene carbonate solvent, is injected. The casing is then sealed using a pressurizer, thus fabricating a lithium-ion secondary battery.

[0173] The manufactured lithium-ion secondary batteries work without any problems.

[0174] Next, a primary lithium battery was fabricated using the separator from Example 5.

[0175] A conductive agent such as carbon powder and a binder such as fluororesin are mixed with heat-treated manganese dioxide to obtain an alloy. This alloy is then pressurized into a hollow cylindrical shape to obtain a positive electrode alloy. This positive electrode alloy is then tightly packed onto the inner circumferential surface of a battery can. A cylindrical separator is then tightly packed onto the hollow inner surface of the positive electrode alloy. An electrolyte solution, prepared by dissolving LiClO4 in a 1:1 (weight ratio) mixture of propylene carbonate and 1,2-dimethoxyethane, is used to permeate the separator until it is fully wetted. A negative electrode agent, made by cutting sheet-like lithium metal into specified dimensions, is then wound and tightly packed onto the inner circumferential surface of the separator. Finally, the can is sealed by riveting with gaskets to produce a cylindrical lithium primary battery.

[0176] The manufactured lithium primary batteries work without any problems.

[0177] As can be seen from the above results, according to the various embodiments of the present invention, the separator for an electrochemical element is composed of pulped regenerated cellulose fibers, is a single layer, has a thickness of 10–35 μm, and a density of 0.35–0.80 g / cm³. 3 The separator possesses a tensile strength of 9.8 N / 15 mm or higher, an average pore size of 0.05–1.00 μm, and a variable tensile strength of 5.9 N / 15 mm or higher. These technical characteristics allow for the provision of electrochemical element separators composed of pulped regenerated cellulose fibers, which balance density and low impedance characteristics and can withstand the typical element winding process of aluminum electrolytic capacitors. Furthermore, the use of this separator enables electrochemical elements with improved productivity and reduced short-circuit failure rates.

[0178] The separator for electrochemical elements of the present invention can be applied to various electrochemical elements such as aluminum electrolytic capacitors, double-layer capacitors, lithium-ion capacitors, lithium-ion secondary batteries, and lithium primary batteries.

Claims

1. A separator for an electrochemical element, characterized in that, It is a separator for electrochemical elements, sandwiched between a pair of electrodes, composed of pulped regenerated cellulose fibers, and capable of retaining the electrolyte solution. It is a partition for one layer. Thickness ranges from 10 to 35 μm, and density ranges from 0.35 to 0.80 g / cm³. 3 The tensile strength is above 9.8 N / 15 mm, and the average pore size is 0.05–1.00 μm. When the clamp spacing of the tensile strength testing machine is set to 0.1 mm and the elongation speed of the test piece is set to 200 mm / min, and the measured tensile strength value is taken as the variable tensile strength, The modified tensile strength is above 5.9 N / 15 mm. The regenerated cellulose fiber is composed of protofibrils with a diameter of less than 3 μm and main fibers with a diameter of more than 3 μm, and the average fiber diameter of the main fibers is 3 to 12 μm.

2. An electrochemical element, characterized in that, It uses the separator for the electrochemical element as described in claim 1.

3. The electrochemical element according to claim 2, characterized in that, It can be any one of aluminum electrolytic capacitors, double-layer capacitors, lithium-ion capacitors, lithium-ion secondary batteries, and lithium primary batteries.

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