JP2015191871A - Membrane electrode composite and method for manufacturing the same, and electrochemical element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a membrane electrode composite including a fine porous membrane that can be reduced in thickness and has a high porosity.SOLUTION: A membrane electrode composite includes an electrode and a fine porous membrane including fibers, at least a part of the fine porous membrane adhering to the electrode. A method for manufacturing a membrane electrode composite includes: a dispersion step of dispersing fibers on an electrode; a membrane formation step of binding the fibers to one another to form a fine porous membrane; and an integration step of integrating the fine porous membrane and the electrode.

Description

  The present invention particularly relates to a membrane electrode composite suitable for a secondary battery or a capacitor, a method for producing the same, and an electrochemical device.

In recent years, the use of electricity as an energy source is increasing in order to cope with environmental problems such as depletion of fossil resources and CO ₂ reduction. Therefore, the development of electric vehicles using secondary batteries is actively performed in the automobile industry. Secondary batteries are also attracting attention from the viewpoint of effective use of natural energy such as sunlight and wind power.

  As a secondary battery for driving an electric vehicle, in general, a lithium ion secondary battery is currently employed from the relationship between output and energy density. On the other hand, each company is devoted to the development of next-generation batteries from the viewpoint of higher energy density, power output, safety, etc., and this is a field where a large market is expected.

  On the other hand, not only lithium ion secondary batteries, but separators such as paper, non-woven fabric, and microporous film are used for primary batteries and capacitors. In general, the performance required for the separator is prevention of short circuit between the positive and negative electrodes, chemical stability against the electrolyte, low internal resistance, and the like. Although these required performances vary depending on the degree required between devices, they are characteristics commonly required for separators regardless of the type.

And the separator of most lithium ion secondary batteries employs a microporous membrane made of polyolefin such as polypropylene or polyethylene. These microporous membranes have several characteristics suitable for lithium ion secondary batteries. For example,
1) It is chemically stable to the electrolyte and does not cause a fatal defect due to the separator.
2) Since the thickness of the separator can be designed freely, it is possible to provide a separator that meets various requirements.
3) Since the pore size can be designed to be small, the lithium barrier property is excellent, and a short circuit due to lithium dendrite hardly occurs.
4) When a lithium ion secondary battery undergoes thermal runaway, the polyolefin melts and closes, and initial thermal runaway can be suppressed.
It is such a point.

  As described above, the separator made of polyolefin has a mechanism that melts and closes when the battery becomes high temperature, stops the reaction in the battery, and suppresses further increase in the battery temperature. However, the battery temperature may rise even after the separator has melted and closed. In this case, the separator is further melted to cause a meltdown in which a large hole is opened, and the electrodes may be short-circuited. The occurrence of such meltdown is considered to be a cause of battery thermal runaway.

  As a technique for preventing meltdown, a technique (Patent Document 1) is known in which a heat resistant layer made of a mixture of fine particles of inorganic oxide and a binder is provided on the surface of a microporous membrane made of polyolefin. However, when using a separator having such a laminated structure, the thickness of the separator increases, the number of unit battery layers that can be accommodated in a battery of the same volume decreases, and the electrical resistance value of the separator increases. There is a possibility that it is difficult to reduce the size and performance of the battery.

  On the other hand, it has been proposed to provide a single-layer microporous film made of a mixture of inorganic oxide fine particles and a binder between electrodes as a separator (Patent Documents 2 and 3). In this case, since the polyolefin microporous film is not required, the microporous film can be thinned.

JP 2006-318892 A JP-A-10-241656 JP-A-2005-294216

  However, it is difficult to increase the porosity in a microporous film formed by an accumulation of fine particles. Therefore, a separator made of such a microporous membrane is difficult to hold an electrolyte solution, and it may be difficult to ensure ion conductivity between electrodes.

  The present invention has been made in view of the above situation, and an object thereof is to provide a membrane electrode assembly including a microporous membrane that can be thinned and has a high porosity.

  As a result of intensive studies, the present inventor has found that the use of a microporous membrane made of fiber as a separator makes it possible to reduce the thickness and achieve a high porosity, thereby completing the present invention. I let you.

  That is, the present invention relates to a membrane electrode assembly including a microporous membrane including an electrode and a fiber, and at least a part of the microporous membrane is fixed to the electrode.

  The microporous membrane is preferably in the form of a fiber assembly.

  The average fiber diameter of the fibers is preferably 0.5 μm or less.

  The thickness of the microporous membrane is preferably 30 μm or less.

  The fibers are preferably cellulose fibers.

  The microporous film may contain a binder.

  The binder preferably has at least a carboxy group and / or a hydroxyl group.

  The porosity of the microporous membrane is preferably 30% or more.

The present invention
A dispersion step of dispersing the fiber on the electrode;
A film forming step of bonding the fibers to form a microporous film; and
The present invention also relates to a method for producing a membrane electrode assembly including an integration step of integrating the microporous membrane and the electrode.

  The film formation step and the integration step are preferably performed in one step, and all of the dispersion step, the film formation step and the integration step are preferably performed in one step.

  The present invention also relates to an electrochemical device comprising a membrane electrode assembly.

  The electrochemical element is preferably a battery or a capacitor. The battery is preferably a secondary battery, and more preferably a lithium ion secondary battery.

  The microporous membrane in the membrane electrode assembly of the present invention can be thinned and can have a high porosity.

  Since the membrane electrode assembly of the present invention can suppress the overall thickness by thinning the microporous membrane as a separator, the number of unit battery layers that can be accommodated in a battery of the same volume is increased, and the battery capacity is increased. improves. Further, the electrical resistance value can be reduced by reducing the thickness of the microporous film, and the cost can be further reduced.

  In the membrane electrode assembly of the present invention, since the microporous membrane as the separator has a high porosity, it is possible to easily hold the electrolytic solution in the pores. Therefore, the membrane electrode assembly of the present invention can ensure good ion conductivity between the electrodes.

  Thereby, an electrochemical element provided with the membrane electrode assembly of the present invention can be easily reduced in size and performance.

  Since the microporous membrane in the membrane electrode assembly of the present invention is made of fiber, high strength can be exhibited by the entanglement of the fibers. Therefore, superior strength can be exhibited as compared with a microporous film formed by an accumulation of fine particles.

  In particular, when cellulose fibers are used as the fibers constituting the microporous membrane, since the cellulose has higher heat resistance than polyolefin, the microporous membrane is excellent in heat resistance. The membrane electrode assembly of the present invention comprising can also have excellent heat resistance.

  Moreover, in the manufacturing method of the membrane electrode composite of this invention, it is easy to adhere a microporous film to an electrode, and the membrane electrode composite of this invention can be manufactured easily.

  The membrane electrode assembly of the present invention includes a microporous membrane containing electrodes and fibers, and at least a part of the microporous membrane is fixed to the electrode. It is preferable that 50% or more, preferably 70% or more, more preferably 90% or more, and still more preferably all of the surface of the microporous membrane is fixed to the electrode.

  Here, “adhesion” means that the microporous membrane is (1) directly in contact with and fixed to the surface of the electrode, and (2) is indirectly fixed via an intermediate layer. Mean any embodiment. Therefore, in the membrane electrode assembly of the present invention, the electrode and the microporous membrane are integrated. The number of microporous membranes included in the membrane electrode assembly of the present invention is not limited, but it is preferable to include one microporous membrane per membrane electrode assembly for miniaturization. From the viewpoint of reducing the thickness of the microporous film, the mode (1) in which the microporous film is in direct contact with the surface of the electrode is preferable. The intermediate layer of (2) is not particularly limited. For example, when the electrode to which the microporous film is fixed is a positive electrode, it is acid resistant for the purpose of preventing the surface of the microporous film on the positive electrode side from being deteriorated by oxidation. It is preferable to provide a chemical layer as an intermediate layer. As another example of the intermediate layer, a heat-resistant layer containing inorganic particles such as alumina, silica, and ceramic and a binder may be provided for the purpose of improving heat resistance.

[Microporous membrane]
The microporous membrane in the membrane electrode assembly of the present invention may be self-standing capable of maintaining its shape as a membrane itself, or non-self-supporting as it cannot maintain its shape as a membrane by itself. Although it may be non-self-standing, it is preferably non-self-standing from the viewpoint of thinning. When the microporous film is self-supporting, it is possible to peel the microporous film from the electrode.

  The microporous membrane in the membrane electrode assembly of the present invention contains at least one type of fiber. Compared to a microporous membrane composed of an aggregate of fine particles of inorganic oxide or the like, in the present invention, the microporous membrane is composed of an aggregate of fibers, so that the porosity of the microporous membrane can be increased. it can.

  Here, the “fiber” is generally thin and flexible having a sufficient length (for example, an aspect ratio of 300 or more, 500 or more, 800 or more, or 1000 or more) as compared with the thickness. Typically, long continuous fibers are long fibers (filaments), and short fibers are short fibers (staples). The “fiber” in the present invention does not include particles having a relatively small aspect ratio, for example, particles having an aspect ratio of less than 100, less than 50, less than 30, or less than 10.

  In the microporous membrane of the present invention, it is preferable that the fibers are uniformly distributed in the membrane from the viewpoint of thinning. When non-uniform portions occur, not only thinning is difficult, but even if the thickness of the microporous film is relatively large, there is an increased possibility that the insulation cannot be maintained and a short circuit between the electrodes is caused, and the mechanical strength is increased. There is a risk of going down extremely. Therefore, in order to uniformly distribute the fibers, it is preferable to adjust the size and shape of the fibers within a certain range as much as possible, and appropriately adjust the dispersibility of the fibers when dispersed on the electrode.

  The fibers used in the present invention are preferably fine fibers, and more preferably ultrafine fibers. Specifically, the average fiber diameter of the fibers is preferably 0.5 μm or less, and more preferably 0.3 μm or less. An average fiber diameter refers to the value which converted the area of the fiber cross section into the diameter of the same area of a perfect circle. When the average fiber diameter is larger than 0.5 μm, it may be difficult to reduce the thickness of the microporous film. Further, as described above, it is preferable to suppress variation in fiber diameter as much as possible from the viewpoint of uniformly distributing the fibers in the microporous membrane.

  The average fiber length of the fibers is preferably a number average fiber length of 0.2 to 2.0 mm, more preferably 0.2 to 1.7 mm, and even more preferably 0.5 to 1.5 mm. If the fiber length is less than 0.2 mm, the strength of the microporous membrane may be insufficient. If the length is longer than 2.0 mm, the fibers may be twisted to cause defects, or the fibers in the microporous membrane may be uniform. Distribution may not be realized. Further, from the viewpoint of uniformly distributing the fibers in the microporous membrane, it is preferable to suppress variations in fiber length as much as possible.

  In the present invention, 1% by weight (mass)% or more of fibers having an average fiber diameter of 1 μm or more, preferably 2 μm or more, and more preferably 3 μm or more with respect to the total weight (mass) of the fibers constituting the microporous membrane. It is preferable that it is contained in an amount of 3% by weight or more, more preferably 5% by weight or more. Strength such as tear strength of the microporous membrane obtained by the presence of 1% by weight or more of fibers having an average fiber diameter of 1 μm or more can be improved. For fibers other than fibers having an average fiber diameter of 1 μm or more, it is possible to use very thin nanofibers of about several to several tens of nanometers. In addition, when adopting the cast method described later, it is difficult to prepare and use a slurry using only thin fibers having a fiber diameter of less than 1 μm so that the viscosity of the slurry becomes extremely high. In order to make this possible, it is necessary to reduce the concentration of the slurry, and the drying cost for forming the microporous membrane increases, which is not economical.

  The upper limit of the amount of fibers having an average fiber diameter of 1 μm or more in the fibers constituting the microporous membrane is not particularly limited, but can be, for example, 40% by weight or less, preferably 30% by weight or less, 20% by weight or less is more preferable.

  The material of the fiber is not particularly limited, and natural fiber, regenerated fiber, synthetic fiber, inorganic fiber, and the like can be used. Examples of natural fibers include cellulose fibers derived from wood, cellulose fibers derived from non-wood such as hemp, cotton, and sugarcane, biocellulose fibers, wool, and silk. Examples of regenerated fibers include solvent-spun cellulose fibers and cupra fibers. Synthetic fibers include polypropylene, polyethylene, polymethylpentene, polyester, polyester derivatives, acrylic polymers, polyvinyl acetate, ethylene-vinyl acetate copolymers, polyvinyl chloride, polyvinylidene chloride, polyvinyl ether, polyvinyl ketone, poly Ether, polyvinyl alcohol, aliphatic polyamide, aromatic polyamide, wholly aromatic polyamide, wholly aromatic polyester, polyamideimide, polyimide, polyetheretherketone, polyphenylene sulfide, polybenzimidazole, poly-p-phenylenebenzobisthiazole, poly -P-phenylene benzobisoxazole, polytetrafluoroethylene, single fiber consisting of these derivatives, or composite fiber formed by combining two or more of these resins. Examples of the inorganic fibers include silica / alumina fibers, alumina fibers, glass fibers, micro glass fibers, zirconia fibers, silicon nitride fibers, silicon carbide fibers, and the like. Examples of the composite fiber include a core-sheath type, an eccentric type, a sea-island type, and a split type. Examples of the split type composite fibers include fibers in which resins composed of different components are adjacent to each other.

  The fibers contained in the microporous membrane are preferably cellulose fibers. Since cellulose has higher heat resistance than polyolefin, the use of cellulose fibers improves the heat resistance of the microporous membrane.

  Cellulose fibers usable in the present invention are not particularly limited to cellulose types such as cellulose type I and cellulose type II, but cellulose type I natural fibers such as cotton, cotton linter and wood pulp are preferred. . Cellulose II type fibers typified by regenerated cellulose are not preferred because they have a lower crystallinity than cellulose I type fibers and tend to be shortened during fibrillation treatment.

  In the present invention, cellulose fibers may be microfibrillated. The apparatus for microfibrillation treatment of cellulose fibers is not particularly limited. For example, high-pressure homogenizer treatment (high-pressure dispersion treatment using a Manton-Gorin type disperser), Lanier-type pressure homogenizer, ultra-high pressure homogenizer treatment (artemizer) TM (manufactured by Sugino Machine Co., Ltd.)), dispersing devices such as bead mills and meteor mills, and abrasive plate rubbing devices (mass colloider, MASUKO SANGYO) that rubbed and arranged a plurality of abrasive plates equipped with abrasive grains of size 16 to 120 And the like. It is also possible to use a beating machine used for papermaking such as a double disc refiner and a beater before the microfibrillation treatment. Moreover, although the addition amount is limited, it is also possible to use cellulose nanofibers that have been made into nanofibers with a TEMPO oxidation catalyst. In particular, when cellulose fibers are used in the present invention, the cellulose fibers are beaten in advance to the rubbing portion of an abrasive plate rubbing apparatus in which a plurality of abrasive plates having abrasive grains with a particle size of 16 to 120 are disposed. It is preferable that the refined process which passes the processed pulp slurry or the refined process which carries out the high pressure homogenizer process for the pulp slurry which carried out the beating process previously is preferable.

  The microporous membrane in the present invention may further contain a binder as an adhesive for connecting the fibers. By using a binder, the strength of the microporous membrane can be increased. For example, the microporous membrane can be made self-supporting.

  The material of the binder is not particularly limited, and for example, various kinds of natural or synthetic polymers can be used alone or in combination of two or more. Examples of the polymer binder include polyvinylidene fluoride-hexafluoropropylene copolymer, polyvinylidene fluoride-trichloroethylene copolymer, polymethyl methacrylate, polyacrylonitrile, polyvinyl pyrrolidone, polyvinyl acetate, ethylene vinyl acetate copolymer, Examples include polyethylene oxide, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethyl pullulan, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, cyanoethyl sucrose, pullulan, carboxymethyl cellulose, acrylonitrile styrene butadiene copolymer, polyimide or a mixture thereof. It is done.

  In particular, when the fiber used in the present invention is a cellulose fiber, a hydrophilic binder is preferable as the binder. And it is preferable that a hydrophilic binder has a carboxy group and / or a hydroxyl group. The hydrophilic binder, preferably a hydrophilic binder containing a carboxy group and / or a hydroxyl group, more preferably a hydrophilic polymer binder containing a carboxy group and / or a hydroxyl group is in the form of an emulsion, even in the form of a resin. There may be. Specifically, cellulose derivatives such as carboxymethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, hydroxypropylmethylcellulose, hydroxyalkylcellulose, alginic acid, amphoteric starch, carboxyl modified starch, phosphate esterified starch, corn starch and other polysaccharide derivatives, Polyacrylic acid, polyvinyl alcohol, carboxy group-modified polyvinyl alcohol, and the like can be used, but are not limited thereto. Of these, carboxymethylcellulose is preferably used. This is thought to be because carboxymethylcellulose has a skeleton in which glucose residues are linked by β-1,4 glycosidic bonds, as in cellulose, and therefore, when both are mixed, the affinity between the two is high. .

  The binder may be cross-linked. The crosslinking may be formed by self-crosslinking of the binder, or may be formed by adding a crosslinking agent separately. By forming a crosslink in the microporous membrane, the movement of molecules by heat is limited, so that the stability to heat can be increased.

  Moreover, it becomes possible to block the active functional group which exists in a binder by bridge | crosslinking by bridge | crosslinking of a binder by bridge | crosslinking. Examples of the functional group include a hydroxyl group, a carboxy group, and an amino group. It is said that the thermal decomposition reaction of a polymer is an oxidation reaction by generation of a radical and a chain. By blocking active functional groups in the polymer by cross-linking, it is possible to suppress the generation of radicals due to heat, and it is difficult to be attacked by the generated radicals, thus suppressing the thermal decomposition of molecules. As a result, the heat stability of the entire microporous membrane can be enhanced.

  The cross-linking may be formed only between the binder molecules or between the binder and the molecules constituting the fiber. In particular, when the fiber used in the present invention is a cellulose fiber, if a crosslinked structure is formed between the binder and the cellulose, the interaction between the celluloses is strengthened, and the strength of the microporous membrane made of cellulose is raised. It is preferable because of its effect. However, only the binder may be crosslinked as necessary.

  The type of the crosslinking agent that crosslinks between binders and, in some cases, between the molecules constituting the binder and the fiber is not particularly limited, but urea formaldehyde resin, melamine formaldehyde resin, carbodiimide group-containing compound, oxazoline group-containing compound Glyoxal group-containing compounds, isocyanate group-containing compounds, and the like can be used as the crosslinking agent. Among these, it is preferable that the cross-linking agent is a polymer compound having a plurality of cross-linking points because a cross-linked structure including more molecules and fibers can be formed.

  By the crosslinking of the binder, the heat resistance of the microporous membrane in the present invention can be further improved. Specifically, the heat shrinkage rate in the longitudinal direction and the width direction at 170 ° C. of the microporous film can be less than 2%, respectively. When the heat shrinkage rate at 170 ° C. is 2% or more, there is a risk that the battery may be short-circuited or ignited due to deformation or damage of the microporous film when the temperature rises due to battery abnormality. The heat shrinkage in the longitudinal direction and the width direction at 170 ° C. is preferably less than 1.8%, more preferably less than 1.5%, and even more preferably less than 1.2%.

  The amount of the binder used is not particularly limited, but is preferably 3 to 80 parts by weight, more preferably 5 to 50 parts by weight, and more preferably 10 to 40 parts by weight with respect to 100 parts by weight of the fiber. Part is even more preferred. When the added amount of the binder is less than 3 parts by weight, the strength of the microporous membrane may be lowered, and the dispersibility of the fibers in the slurry deteriorates in the production method by the casting method described later, so that uniform pores May be difficult to obtain. On the other hand, when the amount is more than 80 parts by weight, it is not preferable because the binder fills the pores and the volume resistivity of the microporous film is increased.

  On the other hand, a binder may not be used depending on the type of fiber. For example, when the microporous membrane in the present invention is non-self-supporting, it is not necessary to use a binder.

  The microporous membrane in the present invention is preferably a fiber assembly. The “fiber assembly” in the present invention means a sheet-like composition obtained by fixing, entanglement, fusion, lamination, braiding and the like of fibers by mechanical, chemical and / or thermal treatment, It may be self-supporting or non-self-supporting. The fiber aggregate is not particularly limited according to this definition. For example, the fiber aggregate may be in the form of a woven fabric or a nonwoven fabric, but is preferably in the form of a nonwoven fabric. In the case of a non-woven fabric, the porosity of the microporous membrane can be further increased as compared to the woven fabric, and the electrical resistance of the microporous membrane can be further reduced.

  The thickness of the microporous membrane in the present invention is preferably 30 μm or less, more preferably 25 μm or less, and more preferably 20 μm or less. On the other hand, the thickness of the microporous membrane in the present invention is preferably 2 μm or more, and more preferably 3 μm or more. Therefore, the thickness of the microporous membrane in the present invention can be, for example, 2 to 30 μm, more preferably 2 to 25 μm, and still more preferably 3 to 20 μm. In addition, since the shape of the microporous film depends on the shape of the electrode surface, fine irregularities may be formed on the surface. In this case, the thickness of the microporous film refers to the thinnest part. Point to. If the microporous membrane is too thick, not only will it be difficult to reduce the size of the membrane electrode assembly, but the number of unit battery layers that can be accommodated in the same volume of battery will decrease, and the electrical resistance value of the separator will increase. There is a risk that it will be difficult to reduce the size and performance of the battery. On the other hand, if the microporous membrane is too thin, the risk of a short circuit between the electrodes increases.

  The porosity of the microporous membrane in the present invention is preferably 30% or more, more preferably 40% or more, and even more preferably 50% or more. When the porosity is less than 30%, the resistance value is high, so the output is lowered and the performance as an electrochemical device may not be sufficient. The upper limit of the porosity is preferably 70% or less. When the porosity exceeds 70%, the risk of occurrence of a short circuit increases, which is not preferable for safety. The porosity in the present invention can be calculated by analyzing the image of a cross section of the microporous film taken with an electron micrograph.

  The microporous membrane in the present invention can have excellent strength characteristics. Specifically, the microporous membrane in the present invention can have a tensile strength per basis weight of 50 N · m / g or more and / or a tear strength of 0.40 kN / m or more. The tensile strength can be measured according to JIS C2151. On the other hand, the tear strength can be measured by the trouser tear method according to JIS K7128-1. The tensile strength per basis weight is preferably 55 N · m / g or more, and more preferably 60 N · m / g or more. The tear strength is preferably 0.5 kN / m or more, more preferably 0.55 kN / g or more, and even more preferably 0.6 kN / m or more. Normally, it is difficult to make both the tensile strength and the tear strength excellent. However, in the present invention, fibers having an average fiber diameter of 1 μm or more are based on the total weight of the fibers in the fibers constituting the microporous membrane. Therefore, both the tensile strength and tear strength can be improved.

  The microporous membrane in the present invention can maintain excellent strength characteristics even under high temperature conditions. Specifically, the microporous membrane according to the present invention has a tensile strength reduction rate of 20% or less, preferably 15% or less after drying under reduced pressure at 150 ° C. for 10 hours and a gauge pressure of −0.08 Mpa or less. More preferably, it can be 10% or less. When the reduction rate of the tensile strength is 20% or more, the sheet easily breaks due to the stress applied to the sheet when assembling an electricity storage device such as a battery or a capacitor, and this is not preferable.

  The microporous membrane in the present invention has a puncture strength reduction rate of 30% or less, preferably 25% or less after drying at 150 ° C. for 10 hours under a condition where the gauge pressure is −0.08 Mpa or less. May be 20% or less. When the reduction rate of the puncture strength is 30% or more, there is an increased possibility that the sheet breaks and short-circuits when lithium dendrite is generated, which is not preferable.

  Furthermore, the microporous membrane in the present invention can maintain excellent flexibility even under high temperature conditions. Specifically, the microporous membrane in the present invention has a tensile elongation of 0.5% or more, preferably 0.7% after being dried under reduced pressure at 150 ° C. for 10 hours under a condition where the gauge pressure is −0.08 Mpa or less. As mentioned above, it is still more preferably 0.9% or more. A sheet having a tensile elongation of 0.5% or less is not preferable because it is vulnerable to deformation due to abrupt stress, and is easily broken when an electric storage device such as a battery or a capacitor is assembled.

  In the microporous membrane of the present invention, the air resistance per 10 μm thickness is preferably 20 to 600 seconds (/ 100 cc), more preferably 20 to 450 seconds, and even more preferably 30 to 250 seconds. The air resistance can be measured based on JIS P8117. When the air resistance is less than 20 seconds, the lithium barrier property is lowered in lithium ion secondary battery applications, and the risk of short-circuiting due to lithium dendrite increases, which is not preferable for safety. If it exceeds 600 seconds, the volume resistivity is particularly large, and the output characteristics of the electrochemical device are deteriorated.

  The microporous membrane in the present invention has a pore distribution mode diameter (maximum frequency) measured by mercury porosimetry of less than 0.3 μm, preferably 0.25 μm or less, and more preferably 0.2 μm or less. When the mode diameter is 0.3 μm or more, in lithium ion secondary battery applications, the lithium barrier property is lowered, and the risk of short circuiting due to lithium dendrite is increased, which is not preferable for safety.

  As for the pore diameter of the microporous membrane in the present invention, the maximum value of the pore diameter measured by mercury porosimetry is preferably 1.5 μm or less. Since the particle diameter of the electrode active material used in an electrochemical element such as a lithium ion battery has various sizes, the pore diameter does not necessarily have to be small. As a rough standard, a short circuit does not occur if the pore diameter is 1/4 of the particle diameter of the active material used. On the other hand, when used for an electrochemical device using an active material having a small particle size, the maximum value may need to be smaller than 1.5 μm.

The microporous membrane in the present invention preferably has a volume resistivity measured by using an alternating current of 20 kHz in a state impregnated with a propylene carbonate solution of LiPF _{6 having} a concentration of 1 mol / L is 1500 Ω · cm or less. Volume resistivity correlates with the above-mentioned air permeability resistance and porosity. Basically, the air resistance is low, and the volume resistivity tends to decrease as the porosity increases. The rate is also affected by the size of the pores and the distribution of the pores in the membrane, so that a low air permeability resistance and a high porosity do not necessarily indicate a low volume resistivity. Here, the purpose of using an alternating current with a frequency of 20 kHz is to remove electrochemical elements such as reaction at the electrode interface from the measured value of volume resistivity. Thereby, since only the sum of the resistance of the measuring device and the ionic conductivity of the cellulose microporous membrane contributes to the measured value, the measured value can reflect the pore distribution and pore diameter of the cellulose microporous membrane. The volume resistivity of the microporous membrane in the present invention is preferably 1500 Ω · cm or less, and more preferably 1000 Ω · cm or less. If it exceeds 1500 Ω · cm, the cycle characteristics may be deteriorated. When it is 1500 Ω · cm or less, good cycle characteristics are exhibited and it can be suitably used as a separator for electrochemical devices.

The volume resistivity measurement using an alternating current of 20 kHz in the present invention can be performed by the following procedure. First, a microporous membrane punched out to a size of 20 mm in diameter is dried at 150 ° C. for 24 hours or more. Next, for example, five dried microporous membranes are put on a sample holder for SH2-Z type solid (manufactured by Toyo Technica Co., Ltd.) and sufficiently immersed in an electrolyte solution of LiPF ₆ / propylene carbonate having a concentration of 1 mol / L. . Preferably, after reducing the pressure to 0.8 MPa and degassing the air remaining between the microporous membranes, it is sandwiched between two opposing gold electrodes, and a frequency response analyzer VSP (Bio AC impedance value (Ω) is measured under the conditions of a sweep frequency of 100 m to 1 MHz and an amplitude of 10 mV. This value and the thickness of the microporous membrane are converted into a resistivity per unit volume (volume resistivity). Note that it is desirable to measure only the resistance component of the measuring device or cancel it so that it is not reflected in the measurement result.

The surface roughness of the microporous membrane in the present invention is preferably an Ra value of 1.5 or less on both the front and back sides. It is known that the surface roughness affects the AC impedance as the contact resistance between the positive electrode and the separator when the electrochemical device is manufactured. This contact resistance can be calculated from the difference between a value of 0.1 Hz and an AC impedance value of 20000 Hz measured with an electrochemical element such as a laminate cell or coin battery. As the surface roughness Ra value increases, the difference between the value of 0.1 Hz and the value of 20000 Hz increases. The value of AC impedance is inversely proportional to the facing area according to Ohm's law. However, if the facing area is increased, the measured value itself becomes smaller, so it is more susceptible to measurement errors, and as the frequency decreases, the resistance components of the positive and negative electrodes Is also included in the value of AC impedance, it is not possible to specify a value only by the difference in separators. However, if the batteries have the same electrode, the same electrolyte, and the same size, the difference in the surface property of the separator can be seen. For example, this value of a laminated cell having a facing area of 15 cm ² made of a material used in a general lithium ion secondary battery such as LiPF ₆ as a electrolyte using a CoLiO ₂ positive electrode and a graphite negative electrode has an Ra value of 1.5. Is about 1Ω. Since the contact resistance of the battery is preferably as low as possible, the condition where Ra is as small as possible is preferable. When measuring the AC impedance by assembling the batteries, it is desirable to charge and discharge at a low rate of about 3 to 5 cycles in advance and then measure the impedance after charging to a certain voltage.

[electrode]
The membrane electrode assembly of the present invention includes an electrode. As long as at least a part of the electrode included in the membrane electrode composite of the present invention is fixed to the microporous membrane, the number, shape and the like are not limited, but one or two is preferable, and in the case of two, two A form in which a microporous membrane is sandwiched between electrodes is preferable.

  The electrode is preferably a positive electrode or a negative electrode. In particular, when a microporous membrane is sandwiched between two electrodes, each electrode is preferably a positive electrode and a negative electrode, respectively.

The positive electrode and the negative electrode preferably contain an electrode active material. As the positive electrode active material, conventionally known materials can be used, and examples thereof include lithium transition metal oxides such as LiCoO ₂ , LiNiO ₂ , and LiMn ₂ O ₄ , lithium metal phosphates such as LiFePO _{4, and the} like. A conventionally well-known thing can be used as a negative electrode active material, For example, carbon materials, such as a graphite, lithium alloys, etc. are mentioned. Moreover, a conventionally well-known conductive support material and a binder are added to an electrode as needed.

  For each of the positive electrode and the negative electrode, for example, an electrode mixture containing activated carbon powder and a conventionally known conductive additive, binder, etc. is applied to a conventionally known current collector, dried, and pressure molded. Can be obtained. As the current collector, for example, aluminum or the like can be used for the positive electrode, and copper or nickel can be used for the negative electrode. In addition, although the said pressure forming is a process for raising the density of an electrode active material, you may perform this process, after adhering a microporous film to an electrode. It is preferable to perform pressure molding after fixing the microporous film to the electrode, because it is possible to reduce the number of manufacturing steps and to further increase the adhesion between the electrode and the microporous film. When the pressure molding is performed after the microporous membrane is fixed, it is preferable to use a fiber having a large fiber diameter for the microporous membrane. For example, fibers having a fiber diameter of 1 μm or more are based on the weight of the whole fiber. It may be contained in an amount of 1% by weight or more, more preferably 3% by weight or more.

[Production method]
The membrane electrode assembly of the present invention can be produced by fixing at least a part of the microporous membrane to the electrode.

  In one embodiment, the microporous membrane manufactured separately is bonded to one electrode or sandwiched between two electrodes, for example, so that the microporous membrane and the electrode are integrated to form the membrane electrode composite of the present invention. Can be manufactured. When the microporous membrane is self-supporting, it is preferable to produce the membrane electrode assembly of the present invention according to this embodiment.

  The microporous membrane in this embodiment is preferably in the form of a nonwoven fabric. The manufacturing method of a nonwoven fabric is not specifically limited, According to the material of a fiber, it can select suitably. For example, when the fibers are made of a thermoplastic material, a nonwoven fabric can be obtained by forming a sheet made of the fibers by a wet method or a dry method, and heating the sheet to partially fuse the fibers. Specific examples include a method of using a thermoplastic resin fiber as a fiber, forming the fiber into a sheet by an airlaid method or the like, and partially fusing the fibers together by a thermal bond method to form a nonwoven fabric. On the other hand, when the fiber is made of a non-thermoplastic material, a sheet made of the fiber is formed by a wet method or a dry method, and the fibers in the sheet are entangled with each other by a mechanical force such as a needle punch or a high-pressure water stream. A nonwoven fabric can be comprised.

  In this embodiment, the microporous membrane may be adhered to the electrode using an adhesive, but the physical properties of the microporous membrane are changed by the adhesive, or the pores of the microporous membrane are blocked with the adhesive. Therefore, it is preferable to fix the microporous film to the electrode by the adhesiveness of the fiber itself without using a separate adhesive. For example, a non-woven fabric made of thermoplastic resin fibers is placed on an electrode, and a part of the fiber is heated and melted to adhere to the electrode, thereby fixing the microporous film to the electrode without using an adhesive. can do.

  On the other hand, instead of integrating the separately manufactured microporous membrane with the electrode, it is also possible to directly form the microporous membrane on the electrode and integrate the two. For example, when the microporous membrane is not self-supporting, it is preferable to produce the membrane electrode assembly of the present invention according to this embodiment. In the case of this embodiment, it is possible to accumulate fibers along the surface shape of the electrode, and it is preferable because there is no gap between the microporous film and the electrode due to the surface shape.

In this embodiment, which is the production method of the present invention, for example,
A dispersion step of dispersing the fiber on the electrode;
A film forming step of bonding the fibers to form a microporous film; and
The membrane electrode assembly of the present invention can be manufactured through an integration step of integrating the microporous membrane and the electrode.

  In the dispersing step, the dispersing means is not limited as long as the fibers can be dispersed on the electrode surface. For example, the thin sheet | seat which consists of a fiber can be formed on an electrode by spraying a fiber on an electrode at random using an air flow.

  The means for forming the membrane is not limited as long as the microporous membrane can be formed by bonding fibers on the electrode. For example, when the fiber is heat-meltable, high-temperature air is blown onto the surface of the thin fiber sheet obtained as described above for a short time to melt part of the fiber and bond the fibers together to form a microporous membrane. Can be formed.

  In the integration step, the means is not limited as long as the microporous membrane can be integrated with the electrode. For example, when the fiber is heat-meltable, heating the electrode melts a part of the fiber in the microporous membrane, adheres the microporous membrane to the electrode, and fixes the microporous membrane to the electrode Can do.

  In the above example, the film formation step and the integration step can be performed in one step by heating the electrode simultaneously with the blowing of high-temperature air onto the fiber sheet surface. As a result, the entire manufacturing process can be simplified and the manufacturing time can be shortened.

  Another example of directly forming a microporous membrane on an electrode is a casting method using a fiber slurry. The casting method is suitable when non-heat-meltable fibers such as cellulose fibers are used.

In the casting method, for example,
An application step of applying a slurry containing at least cellulose fiber to the electrode; and
A membrane electrode assembly can be obtained by a production method including at least a drying step of drying the slurry to form a microporous film on the electrode.

  The coating process in the manufacturing method by the casting method corresponds to the dispersion process, and the drying process corresponds to the film forming process and the integration process. Thus, since the film forming step and the integration step can be performed in one step even by the casting method, the entire manufacturing process can be simplified and the manufacturing time can be shortened.

  As the cellulose fibers, those described above can be used, but when a slurry is prepared using only thin cellulose fibers having an average fiber diameter of less than 1 μm, the viscosity of the slurry increases, so a solvent or the like is added to the slurry. However, it is necessary to lower the viscosity, but this is not preferable because the subsequent drying cost of the solvent and the like increases. In addition, when cellulose fibers having a small fiber diameter are produced by applying shearing force to cellulose fibers by a general method, the fiber length tends to be shortened, and the strength such as tear strength of the prepared sheet tends to decrease. Therefore, the strength of the obtained sheet can be improved by the presence of fibers having an average fiber diameter of 1 μm or more in an amount of 1% by weight or more, preferably 5% by weight or more, more preferably 10% by weight or more. However, if fibers having an average fiber diameter of 1 μm or more are present in excess of a predetermined amount, the number of contacts at which the cellulose fibers are brought into contact with each other by hydrogen bonding decreases, so that the strength of the obtained sheet may be reduced.

  Cellulose fibers can be uniformly dispersed in water due to the hydroxyl groups of cellulose molecules, but the viscosity of the slurry depends on the fiber length and surface area of the cellulose fibers. As the cellulose fibers become thinner, the surface area of the cellulose increases accordingly, and the viscosity of the slurry inevitably increases. Further, as the fiber length becomes longer, the interaction between fibers increases, which is also considered as a factor that leads to an increase in viscosity. The increase in viscosity due to these interactions is a factor that hinders the formation of a sheet at a high concentration, and means for decreasing the concentration is generally taken to handle nanocellulose.

  Furthermore, the cellulose fiber has a property of hydrogen bonding between the fibers in the dehydration process due to its hydroxyl group, and there is a characteristic not found in nonwoven fabrics made of synthetic fibers other than regenerated cellulose. While the strength is developed in the hydrogen bond formation process, the shrinkage in the drying process is larger than that of the nonwoven fabric using synthetic fibers due to the interaction between the fibers. In particular, as the fiber diameter becomes thinner, the stiffness of the fiber decreases, and this contraction is noticeable. In addition, it is known that a sheet prepared using extremely fibrillated fibers is transparent because the fibers are completely in close contact with each other. That is, it is difficult to make a porous sheet rather than controlling the pore diameter only by reducing the fiber diameter. For this reason, in order to produce a porous sheet, it is necessary to suppress shrinkage during drying and inhibit hydrogen bonding between fibers. The specific method that has been proposed so far is that the raw material sheeted by the papermaking or casting method is replaced with a hydrophilic solvent such as acetone, and then a more hydrophobic solvent such as a mixed solvent of toluene and acetone. It is a method such as substitution with a solvent and drying. However, this method has two problems. The first is the operation of replacing the dispersion solvent water with acetone. Cellulose fibers have a higher water retention capacity as the fiber diameter becomes smaller, so replacement of water with a solvent is a very time-consuming operation, which is a factor of reducing productivity in terms of actual production. Furthermore, since the pore diameter depends on the fiber thickness, the pore diameter is only controlled by the fiber thickness. If a uniform fiber is not used, the target pore diameter can be obtained. In addition, time and cost are required for the cellulose fiber treatment process.

  In the production method of the present invention by a cast method using a slurry of cellulose fibers, a pore-opening agent is preferably used for the slurry, and a hydrophilic pore-opening agent having a boiling point of 180 ° C. or higher is more preferable. Production efficiency can be greatly improved by applying a slurry containing a hydrophilic pore-opening agent having a boiling point of 180 ° C. or higher on a release substrate and drying as a means for making a sheet of cellulose fiber porous. Furthermore, in the present invention, the pore size of the sheet can be controlled by adjusting the solubility of the hydrophilic pore-opening agent in water. In the present invention, the porosity can be freely controlled by adjusting the amount of the hydrophilic pore-opening agent added. For example, in the present invention, the hydrophilic pore-opening agent is preferably 50 to 600 parts by weight, more preferably 80 to 400 parts by weight, and still more preferably 100 to 300 parts by weight with respect to 100 parts by weight (mass) of cellulose fibers. Can be used in proportions.

  The hydrophilic pore-opening agent is not particularly limited as long as it is a hydrophilic substance capable of forming fine pores in a sheet made of cellulose fibers, but the boiling point of the hydrophilic pore-opening agent is 180 ° C. or higher. Is preferred. It is known that hydrogen bonds between fibers are formed when the sheet moisture during drying is between 10 and 20% by weight. When this hydrogen bond is formed, a pore-opening agent is present in the sheet, and pore formation is possible by inhibiting the hydrogen bond between the fibers. When a pore-opening agent having a boiling point of less than 180 ° C. is used, the pore-opening agent volatilizes in the drying step even if the amount added is increased, and there is a possibility that the pores cannot be made sufficiently porous. Therefore, a pore opening agent having a boiling point of 180 ° C. or higher is preferable, but 200 ° C. or higher is more preferable. For example, a primary alcohol having a molecular weight lower than that of hexanol is a material having both water-solubility and hydrophobicity. However, in the present invention, hydrogen bonds cannot be sufficiently inhibited because it is more volatile than water in the drying process. Cannot be used. However, when using a drying method that is different from normal drying conditions, such as drying with air filled with a pore-forming agent, or using multistage drying with a solvent having a lower vapor pressure than water. The boiling point is not necessarily 180 ° C or higher.

  The hydrophilic pore-opening agent preferably has a water solubility of 10% by weight or more, more preferably 20% by weight or more, and still more preferably 30% by weight or more. When a pore-opening agent having a solubility in water of less than 10% by weight is used, the amount of pore-opening agent added is limited, so that the target porosity can be controlled only by the amount of pore-opening agent added. It can be difficult. Moreover, since the pore-opening agent which cannot be melt | dissolved isolate | separates because the amount of solvent decreases as drying progresses, it may become difficult to make it porous uniformly in the surface direction and thickness direction of the sheet. Such a hydrophobic pore-opening agent can be made evenly porous to some extent by emulsifying with an emulsifier or the like, but it is difficult to control the pore size. On the other hand, when a pore-opening agent having a solubility in water of 10% by weight or more is used, it can be uniformly dispersed in the slurry, and since it is highly soluble in water, it does not separate in the drying step. In this case, the pores can be made uniform by uniformly inhibiting hydrogen bonding.

  The hydrophilic pore opening agent preferably has a vapor pressure at 25 ° C. of less than 0.1 kPa, more preferably less than 0.09 kPa, and even more preferably less than 0.08 kPa. Since the hydrophilic pore-opening agent having a vapor pressure of 0.1 kPa or more has high volatility, it tends to volatilize before contributing to the porosity of the cellulose membrane, and as a result, it is difficult to obtain a microporous cellulose membrane. There is a risk.

  The hydrophilic pore-opening agent preferably has a water / octanol distribution coefficient (Log Pow) in the range of -1.2 to 0.8, more preferably in the range of -1.1 to 0.8,- Even more preferred is a range of 0.7 to 0.4. As the octanol, n-octanol is preferable. If a hydrophilic pore-opening agent having a partition coefficient of less than -1.2 is used, the impedance value of the resulting cellulose microporous membrane may be increased.

  Specific examples of the hydrophilic pore-opening agent include the following. For example, higher alcohols such as 1,5-pentanediol, 1-methylamino-2,3-propanediol, lactones such as iprosin caprolactone, α-acetyl-γ-butyllactone, diethylene glycol, 1,3-butylene glycol , Glycols such as propylene glycol, triethylene glycol dimethyl ether, tripropylene glycol dimethyl ether, diethylene glycol monobutyl ether, triethylene glycol monomethyl ether, triethylene glycol butyl methyl ether, tetraethylene glycol dimethyl ether, diethylene glycol monoethyl ether acetate, diethylene glycol monoethyl ether , Triethylene glycol monobutyl ether, tetraethylene glycol monobutyl Ether, dipropylene glycol monomethyl ether, diethylene glycol monomethyl ether, diethylene glycol monoisopropyl ether, ethylene glycol monoisobutyl ether, glycol ethers such as tripropylene glycol monomethyl ether, diethylene glycol methyl ethyl ether, diethylene glycol diethyl ether, and others, glycerin, propylene carbonate N-methylpyrrolidone and the like are not limited thereto. Among these, glycol ethers have a low vapor pressure and are most suitable for the production method of the present invention.

  The slurry preferably contains a binder as an adhesive for connecting the fibers in addition to the cellulose fibers and the hydrophilic pore-opening agent. As described above, the binder is preferably a polymer binder, and more preferably a hydrophilic polymer binder. The binder can exhibit a function of improving the dispersibility of cellulose in addition to the function as an adhesive. In order to obtain a uniform pore distribution, the fibers need to be uniformly dispersed in the slurry, but the binder, preferably a polymer binder, more preferably a hydrophilic polymer binder, should be fixed on the surface of the cellulose fiber. Dispersibility is improved because it plays a role similar to protective colloid. The blending amount of the binder is preferably 3 to 80 parts by weight and more preferably 5 to 50 parts by weight with respect to 100 parts by weight of the cellulose fiber. If the added amount of the binder is less than 3 parts by weight, the strength of the finished sheet may be reduced, and the dispersibility of the cellulose fibers is deteriorated, so that it is difficult to obtain uniform pores. On the other hand, when the amount is more than 80 parts by weight, it is not preferable because the binder fills the pores and the volume resistivity of the cellulose microporous film is increased.

  As the binder to be added to the slurry, those already described can be used, but it is preferable to include carboxymethyl cellulose. As described above, carboxymethylcellulose has high affinity with cellulose and high hydrophilicity due to the action of the carboxy group, and therefore has good performance for dispersing cellulose fibers. Moreover, since it has both the carboxy group and hydroxyl group which are common with the functional group which exists in the cellulose surface, since it is easy to form the bridge | crosslinking between a binder and a cellulose, it is preferable.

  As other polymer binders, as described above, cellulose derivatives such as methylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, hydroxypropylmethylcellulose, hydroxyalkylcellulose, phosphate esterified starch, corn starch, alginic acid or a salt thereof, etc. Polysaccharide derivatives, styrene butadiene copolymer emulsions known as binders for electrodes, and binders such as polyvinylidene fluoride can be used alone or in combination.

  The slurry preferably further contains a crosslinking agent. As the crosslinking agent, those described above can be used. By adding the crosslinking agent at the slurry stage, the crosslinking agent can be uniformly mixed with the cellulose fibers or the cellulose fibers and the binder, and a more uniform crosslinked structure can be formed in the microporous film. Further, since the production can be performed in one step as compared with the method of applying the cross-linking agent in the subsequent step, the production cost can be suppressed. Although the compounding quantity of a crosslinking agent is not specifically limited, 1-30 weight part is preferable with respect to 100 weight part of cellulose fibers, 2-20 weight part is more preferable, 3-10 weight part is still more preferable. .

  In the above application step, the method of applying a slurry containing cellulose fibers and a hydrophilic pore-opening agent (further, a polymer binder and a cross-linking agent as necessary) on the electrode, the film thickness of the application layer is within a certain range. Any coating method can be used as long as it can be uniformly applied. For example, coating can be performed by a pre-weighing type coater such as a slot die coater or a curtain coater, or a post-weighing type such as an MB coater, MB reverse coater, comma coater, dipping device, or spray coater. Various impregnation apparatuses may be used.

  In the application step, it is preferable that the fibers in the slurry are applied uniformly on the electrode. In particular, from the viewpoint of reducing the thickness of the microporous membrane, not only is it difficult to reduce the thickness of the fiber after the formation of the membrane, but also insulation is maintained even if the thickness of the microporous membrane is relatively large. This may increase the possibility of causing a short circuit between the electrodes or extremely reduce the mechanical strength. In order to uniformly distribute the fibers, it is preferable to adjust the size and shape of the fibers within a certain range as much as possible and appropriately adjust the dispersibility of the fibers when dispersed on the electrode. Therefore, a dispersant that improves the dispersibility of the slurry can be used as long as it does not affect the performance of the electrochemical device.

  In the present invention, if necessary, a surfactant can be added to the slurry as an additive. A nonionic surfactant represented by acetylene glycol or the like as an antifoaming agent or a leveling agent can be used as long as it does not affect the performance of the electrochemical device. It is preferable not to use an ionic surfactant because it may affect electrochemical device performance.

  In addition, the slurry can include a filler. As the filler, for example, inorganic fillers such as silica particles and alumina particles, organic fillers such as silicone powder, and the like can be used. These particles can be added to the extent that they do not affect the pores of the separator, but it is preferable to use particles having an average particle size of less than 2 μm as much as possible. An average particle size of 2 μm or more is not preferable because a pore having a large pore size is opened by a gap between particles. Since these fillers have the effect of lowering the viscosity of the slurry, it is possible to increase the paint concentration and is suitable for increasing the production efficiency. On the other hand, since an intensity | strength will fall when there is too much addition amount, the addition amount larger than 100 weight part with respect to 100 weight part of cellulose fibers is unpreferable.

  The solvent of the slurry basically needs to use water, but for the purpose of improving the drying efficiency, alcohols such as methanol, ethanol and t-butyl alcohol, ketones such as acetone and methyl ethyl ketone, diethyl ether, It is possible to add a solvent having a higher vapor pressure than water such as ethers such as ethyl methyl ether to 50% by weight of the total amount of the solvent. When these solvents are added in an amount of 50% by weight or more, the dispersibility of the cellulose fibers is deteriorated and the uniformity of the pore distribution is deteriorated, which is not preferable.

  The drying means in the drying step is not particularly limited. Specifically, it may be carried out using a commonly used drying method such as hot air drying and far infrared drying alone or in combination. For example, the hot air temperature can be 30 to 150 ° C., preferably 60 to 120 ° C., but the hot air temperature so that the structure in the thickness direction of the sheet (microporous film) can be dried as uniformly as possible, It is necessary to adjust the hot air volume, far-infrared irradiation conditions, and the like. Microwave heating can also be used to improve drying efficiency.

  On the other hand, it is possible to carry out all of the above-described dispersion process, film formation process and integration process in one process. In this case, the manufacturing process can be further simplified and the manufacturing time can be further shortened.

  For example, if the material of the fiber is a meltable material such as a thermoplastic resin, the melted fiber can be sprayed onto the electrode surface by a general spunbond method, preferably a melt blow method. In this case, at the same time as the molten fibers are dispersed on the electrode surface, the fibers are bonded to each other to form a microporous film, and a part of the fibers is fixed to the electrode. Thereby, a microporous film and an electrode can be integrated.

  On the other hand, if the fiber material is not meltable, the fiber component solution can be sprayed onto the electrode surface connected to the ground by, for example, electrostatic spinning. In this case, at the same time as the solution is sprayed on the electrode surface, the solvent in the solution is volatilized, fibers appear and are dispersed on the electrode surface, and bonded to each other to form a microporous film, and A part of the fiber adheres to the electrode. Thereby, a microporous film and an electrode can be integrated.

  In the manufacturing method of the present invention, since the microporous membrane is manufactured directly on the electrode without being integrated with the electrode after being manufactured alone, the microporous membrane can be made considerably thin. Further, since the microporous membrane is manufactured in a state of being fixed on the electrode, it is easy to manufacture an integrated membrane electrode assembly.

  Therefore, in the production method of the present invention, a membrane electrode assembly including a thin microporous membrane can be easily produced.

[Electrochemical element]
The membrane electrode assembly of the present invention can be used as a component of an electrochemical device.

  The membrane electrode assembly of the present invention can be used for batteries or capacitors such as lithium ion secondary batteries, polymer lithium batteries, aluminum electrolytic capacitors (capacitors), electric double layer capacitors, and lithium ion capacitors.

  The membrane electrode assembly of the present invention is preferably used for a secondary battery, and more preferably used for a lithium ion secondary battery.

  The structure of the battery as the electrochemical element of the present invention can be the same as that of a conventional battery except that the membrane electrode assembly of the present invention is used as a unit battery layer. The structure of the electrochemical element is not particularly limited, and examples thereof include a laminated type, a cylindrical type, a square type, and a coin type.

  For example, the lithium ion secondary battery as the electrochemical element of the present invention can include a unit battery layer in which a microporous film of the membrane electrode assembly of the present invention is impregnated with an electrolyte.

  Further, a capacitor as an electrochemical element of the present invention, for example, an electric double layer capacitor, can also include a unit cell in which a microporous film of the membrane electrode assembly of the present invention is impregnated with an electrolytic solution.

  A lithium ion secondary battery or an electric double layer capacitor is, for example, configured by stacking or winding a plurality of unit battery layers to form an element, and then storing the element in an exterior material and connecting a current collector to an external electrode And after impregnating conventionally well-known electrolyte solution, it can manufacture by sealing an exterior material.

  EXAMPLES Hereinafter, although this invention is demonstrated more concretely using an Example and a comparative example, the scope of the present invention is not limited to an Example.

(Example 1)
NBKP was dispersed in ion-exchanged water so as to have a concentration of 2.5% by weight, and beaten by cycling to a condition where the number average fiber length was 0.4 mm or less using a double disc refiner. Cellulose fine fibers 1 having a number average fiber length of 0.3 mm or less are obtained by treating the cellulose fiber dispersion having a number average fiber length of 0.4 mm or less with a mass colloider (manufactured by Masuko Sangyo Co., Ltd.) twice. It was.

  Cellulose fine fiber 1 has a solid content of 100 parts by weight, and glycol ether type pore-opening agent (trade name: manufactured by Hisolv MTEM Toho Chemical Co.) is 220 parts by weight. Add 10 parts by weight of carboxymethylcellulose (trade name: Sunrose F1400MG, manufactured by Nippon Paper Chemicals) dissolved in exchanged water, and add a paint to which water is added so that the final solid content concentration is 1.5% by weight. Dispersion was carried out until the mixture was evenly mixed (manufactured by ASONE Corporation).

A kneading machine containing 95% by mass of artificial graphite (average particle size: 20 μm) as a negative electrode active material, 2% by weight of acetylene black as a conductive additive, 2% by mass of SBR as an aqueous binder, and 1% by mass of CMC (carboxymethylcellulose) as a thickener. A slurry was prepared using Next, the obtained slurry was applied onto a copper foil using an applicator so that the active material density was 5 mg / cm ² , dried and rolled to obtain a negative electrode.

  The prepared paint was applied on the negative electrode prepared in 3 above using an applicator so that the WET film thickness was 100 μm, and dried for 12 minutes using hot air at 120 ° C. and an infrared heater. Thus, a membrane electrode assembly having a cellulose layer thickness of 3 μm and a porosity of 40% was obtained.

(Comparative Example 1)
94 parts by mass of high-purity alumina (trade name: AKP-50 manufactured by Sumitomo Chemical Co., Ltd.), 6 parts by mass of acrylonitrile butadiene rubber (trade name: Nipol-1561 manufactured by Nippon Zeon Co., Ltd.) as a binder were stirred in a bead mill using NMP as a solvent, Created. This paste was formed on one side of the negative electrode prepared in Example 1 using a comma coater so as to form a film having a thickness of 3 μm to obtain a membrane electrode composite. The porosity of this film was 3.5%.

As described above, the results of Example 1 and Comparative Example 1 showed that the microporous membrane of the present invention can realize a microporous membrane having a high porosity even though it is a membrane electrode composite.

Claims (14)

Electrodes, and
A membrane electrode assembly comprising a microporous membrane containing fibers, wherein at least a part of the microporous membrane is fixed to the electrode.   The membrane electrode assembly according to claim 1, wherein the microporous membrane is in the form of a fiber assembly.   The membrane electrode assembly according to claim 1 or 2, wherein an average fiber diameter of the fibers is 0.5 µm or less.   The membrane electrode assembly according to any one of claims 1 to 3, wherein the microporous membrane has a thickness of 30 µm or less.   The membrane electrode assembly according to any one of claims 1 to 4, wherein the fibers are cellulose fibers.   The membrane electrode assembly according to any one of claims 1 to 5, wherein the microporous membrane contains a binder.   The membrane electrode assembly according to claim 6, wherein the binder has at least a carboxy group and / or a hydroxyl group.   The membrane electrode assembly according to any one of claims 1 to 7, wherein a porosity of the microporous membrane is 30% or more. A dispersion step of dispersing the fiber on the electrode;
A film forming step of bonding the fibers to form a microporous film; and
A method for producing a membrane electrode assembly, comprising an integration step of integrating the microporous membrane and the electrode.   The method for producing a membrane electrode assembly according to claim 9, wherein the film formation step and the integration step, or the dispersion step, the film formation step, and the integration step are all performed in one step.   An electrochemical device comprising the membrane electrode assembly according to claim 1.   The electrochemical device according to claim 11, which is a battery or a capacitor.   The electrochemical device according to claim 12, which is a secondary battery.   The electrochemical device according to claim 13, which is a lithium ion secondary battery.