JP2012150896A - Resin current collector and secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a resin current collector for a bipolar lithium secondary battery, which can be manufactured by a simple manufacturing process, has excellent charging and discharging characteristics, and has reduced conductivity in an in-plane direction, and to provide a laminated electrode for a bipolar lithium secondary battery including the current collector.SOLUTION: In a resin current collector used for a bipolar lithium secondary battery, a resin current collector for a bipolar lithium secondary battery contains a conductive agent containing conductive particles, and a resin binder. A particle diameter of the conductive particles is 0.5 to 2 times the thickness of a resin current collector layer, and the resin current collector has the thickness of 1 to 500 μm. There is also provided a bipolar lithium secondary battery using the resin current collector.

Description

  The present invention relates to a resin current collector for a bipolar lithium secondary battery. More specifically, a resin current collector for a bipolar lithium secondary battery that can be suitably used as a conductor for an anode and a cathode of a lithium secondary battery, and a laminated electrode for a bipolar lithium secondary battery having the current collector About.

  In recent years, hybrid vehicles, electric vehicles, and fuel cell vehicles have been manufactured and sold from the viewpoints of environment and fuel efficiency, and new developments are continuing. In these so-called electric vehicles, it is indispensable to use a power supply device capable of discharging and charging. As the power supply device, a secondary battery such as a lithium battery or a nickel metal hydride battery, an electric double layer capacitor, or the like is used. In particular, lithium secondary batteries are considered suitable for electric vehicles because of their high energy density and high durability against repeated charge and discharge, and various developments have been intensively advanced. However, in order to apply to the power sources for driving motors of various automobiles as described above, it is necessary to use a plurality of secondary batteries connected in series in order to ensure a large output.

  However, when a battery is connected via the connection portion, the output is reduced due to the electrical resistance of the connection portion. Further, the battery having the connection portion has a disadvantage in terms of space. That is, the connection portion causes a reduction in the output density and energy density of the battery.

  As a solution to this problem, bipolar lithium secondary batteries (bipolar batteries) have been developed (see, for example, Patent Document 1). The bipolar battery has a configuration in which a plurality of bipolar electrodes each having a positive electrode active material layer formed on one surface and a negative electrode active material layer formed on the other surface are stacked via an electrolyte layer. As the current collector, a metal foil or the like is usually used, and the positive electrode active material layer or the negative electrode active material layer generally includes a positive electrode active material or a negative electrode active material, a conductive material, and a binder.

  Since the bipolar battery as described in the above-mentioned Patent Document 1 is connected in series in the stacking direction in the battery, the voltage of the battery can be increased, and since there is no contact resistance value, the resistance can be reduced. it can. Furthermore, since there is no connection part at the time of series, the packaging of a battery can be made compact and the output density of a battery can be increased. Patent Document 2 proposes a resin current collector in which a conductive agent is added to a resin instead of a metal foil as a technique for increasing the strength of the current collector, and Patent Document 3 reduces the weight by using a resin current collector. A technique is disclosed that makes it possible to do this.

  As an effort to impart further functions to this resin current collector, Patent Documents 4, 5, and 6 propose to lower the resistance value in the film thickness direction while maintaining the in-plane resistance value of the resin current collector as high as possible. ing. As a result, when a micro short circuit occurs inside the battery, it is possible to effectively suppress a large amount of current from concentrating the current collector surface locally and causing further heat generation.

In Patent Document 4, anisotropy is imparted to the conductivity by controlling the aggregation state of the conductive agent and between the aggregates, but it is difficult to control the aggregation during actual production, and stable quality cannot be obtained. . Patent Document 5 proposes to solve the above-mentioned problem by impregnating a film containing a hole in the film thickness direction with a paste containing a conductive agent, but impregnating a fine hole with a paste containing a filler. It is difficult and there is a problem in productivity. In Patent Document 6, the resin layer separated from the micro layer is decomposed and washed with a xenon lamp, electroless plating is performed, and plasma etching is performed to provide conductivity only in the film thickness direction. Due to the complexity of multiple stages, there was a problem of high costs.

JP-A-11-204136 JP-A 61-285664 JP 2006-190649 A JP 2010-67580 A JP 2010-73500 A JP 2010-257712 A

  The present invention has been made in view of the above prior art, and can be prepared by a simple process, and the resin current collector for a bipolar lithium secondary battery that maintains high charge / discharge characteristics and in-plane resistance. And a laminated electrode for a bipolar lithium secondary battery having the current collector.

The present invention
(1) A resin current collector used in a lithium secondary battery, comprising a conductive agent containing conductive particles and a resin binder, wherein the particle diameter of the conductive particles is the thickness of the resin current collector layer. A resin current collector for a bipolar lithium secondary battery, wherein the resin current collector is 0.5 to 2 times and the thickness of the resin current collector is 1 to 500 μm;
(2) The bipolar lithium secondary battery resin current collector according to (1), wherein the conductive particles are spherical conductive particles having a major axis / minor axis ratio (major axis / minor axis) value of 1-2. 3) The resin current collector for a bipolar lithium secondary battery according to (1) to (2), wherein the conductive agent further contains carbon black,
(4) The resin current collector for bipolar lithium secondary batteries according to (3), wherein the mass ratio of the conductive particles to carbon black (conductive particles / carbon black) is 80/20 to 95/5,
(5) A laminated electrode for a bipolar lithium secondary battery in which a resin current collector and an active material layer are sequentially laminated, and the resin current collector is any one of (1) to (4) The present invention relates to a laminated electrode for a bipolar lithium secondary battery, characterized in that a resin current collector is used.

  According to the present invention, a resin current collector for a bipolar lithium secondary battery that is simple to produce, has excellent charge / discharge characteristics, and maintains a high in-plane resistance value, and a bipolar lithium secondary battery having the current collector are provided. A laminated electrode for a secondary battery is provided.

1 is a schematic cross-sectional view schematically showing an outline of a bipolar lithium secondary battery which is a typical embodiment of a bipolar secondary battery according to the present invention. Schematic cross-sectional view of membrane pressure direction resistance

FIG. 1 is a schematic cross-sectional view schematically showing the entire structure of a bipolar lithium secondary battery according to the first embodiment of the present invention.

Referring to FIG. 1, the bipolar lithium secondary battery can be summarized as follows. A positive electrode active material layer 4 is formed on one surface of a resin current collector 3, and a negative electrode active material layer 2 is formed on the other surface. This is a bipolar lithium secondary battery in which a plurality of bipolar electrodes 10 are stacked in series with a separator 1 containing an electrolyte in between. The bipolar lithium secondary battery has a seal portion 6 in contact with the outer peripheral edge of the resin current collector 3. The seal portion 6 is formed of an insulating seal material. The seal portion 6 fixes an end portion that is an outer peripheral portion of the resin current collector 3. The seal portion 6 is disposed between the outer peripheral portions of the two separators 1. In the illustrated example, the two separators 1 are adjacent separators. Details will be described below.
FIG. 1 shows a bipolar lithium secondary battery to which the present invention is applied. In the bipolar lithium secondary battery, a plurality of bipolar electrodes 10 are stacked in series with the separator 1 interposed therebetween. The separator 1 contains an electrolyte and forms an electrolyte layer. In the bipolar electrode 10, the positive electrode active material layer 4 and the negative electrode active material layer 2 of the adjacent bipolar electrode 10 face each other with the separator 1 interposed therebetween. The adjacent positive electrode active material layer 4, separator 1 and negative electrode active material layer 2 constitute one single battery layer (single cell). The basic configuration of the bipolar lithium secondary battery is a configuration in which a plurality of stacked unit cell layers are connected in series. The outermost layer electrode 5 located in the outermost layer of the battery element has a structure in which the positive electrode active material layer 4 or the negative electrode active material layer 2 is disposed on one side, and is formed as a battery tab and is led out of the battery.

  The outer peripheral portion of the separator 1 extends outward with respect to the bipolar electrode 10. Here, “extends outward with respect to the bipolar electrode 14” means a surface of the members (resin current collector 3, positive electrode active material layer 4, and negative electrode active material layer 2) constituting the bipolar electrode 10. The term “extends outward in the plane direction from the end of the smallest member in the direction” and extends beyond the end of the largest member in the plane direction among the members constituting the bipolar electrode 10. A seal portion 6 formed of an insulating sealing material is disposed in contact with the outer peripheral edge of the resin current collector between the outer peripheral portions of the adjacent separators 1. The sealing portion 6 is filled with a sealing material between each of the adjacent separators 1 and the exposed portion, and encloses the entire outer peripheral portion of the bipolar electrode 10. As a result, the end part which is the outer peripheral part of the resin current collector 3 is fixed between the adjacent separators 1 by the seal part 6. For this reason, even if stress due to external force is applied to the resin current collector 3, the resin current collector 3 can be prevented from penetrating the separator 1. Thereby, an internal short circuit between the resin current collectors 3 can be prevented by an external force.

  Furthermore, by providing the seal portion 6 between the outer peripheral portions of the separator 1, the rigidity against the external force in the stacking direction can be increased while ensuring the sealing effect of the outer peripheral portion of the single cell layer. For this reason, it is not necessary to provide the battery element with a reinforcing frame that increases the rigidity against external force in the stacking direction.

  The insulating sealing material is effective in fixing the end of the resin current collector to prevent an internal short circuit between the resin current collectors 3 and is capable of leaking electrolyte and sealing against moisture from the outside (sealing Any known insulating sealing material can be used as long as the material exhibits high performance). Specifically, examples of the insulating sealing material include silicon resin, epoxy resin, urethane resin, polybutadiene resin, polypropylene resin, polyethylene resin, paraffin wax, poly (meth) acrylic resin, and the like. Of these, urethane resins, epoxy resins, and poly (meth) acrylic resins are preferable from the viewpoints of corrosion resistance, chemical resistance, film-forming properties, economy, and the like.

  The electrolyte layer of this embodiment uses a separator 1 containing an electrolyte. As the electrolyte material, a polymer gel electrolyte (gel polymer electrolyte), an all solid electrolyte (polymer solid electrolyte, inorganic solid electrolyte), or a liquid electrolyte (electrolytic solution) can be used.

The specific form of the separator 1 is not particularly limited, and a microporous membrane separator and a non-woven fabric (non-woven fabric) separator can be used.
Examples of the material of the microporous membrane separator include polyolefins such as polyethylene (PE) and polypropylene (PP), laminates having a three-layer structure of PP / PE / PP, and polyimide.

  The thickness of the microporous membrane separator is preferably 1 to 60 μm for a single layer or multiple layers from the viewpoint of thinning the battery. The fine pore diameter of the microporous membrane separator is 1 μm or less (usually a pore diameter of about several tens of nanometers), and the porosity is preferably 20 to 80%. The nonwoven fabric separator is not particularly limited as long as it has a separator function and can hold the polymer gel electrolyte, and conventionally known nonwoven fabric separators can be used. Further, the fiber used is not particularly limited, and conventionally known fibers such as cotton, rayon, acetate, nylon, polyester, polypropylene, polyethylene and other polyolefins, polyimide, and aramid can be used. These may be used alone or in combination depending on the purpose of use (such as mechanical strength required for the electrolyte layer).

  The porosity of the nonwoven fabric separator is preferably 30 to 70%. If the porosity is less than 30%, the electrolyte retention may be deteriorated, and if it exceeds 70%, the strength may be insufficient. Furthermore, the thickness of the nonwoven fabric separator is preferably 5 to 40 μm, particularly preferably 5 to 30 μm. If the thickness is less than 5 μm, short-circuit defects will increase, and the retention of the electrolyte will deteriorate. If it exceeds 40 μm, the resistance will increase.

  As described above, the resin current collector for a bipolar lithium secondary battery of the present invention is a resin current collector used for a lithium secondary battery, and contains a conductive agent containing conductive particles and a resin binder. The particle diameter of the conductive particles is 0.5 to 2 times the thickness of the resin current collector layer, and the thickness of the resin current collector is 1 to 500 μm. In the laminated electrode for a lithium secondary battery of the present invention, a resin current collector and an active material layer are sequentially laminated, and the resin current collector is used as the conductive layer.

  Generally, when the diameter of the conductive particles contained in the resin current collector composed of the bipolar lithium secondary battery is 0.5 to 2 times the thickness of the resin current collector, for example, the conductive particles and the resin Since the interface of the binder extends in the film thickness direction, there is a concern that a liquid junction of the electrolytic solution may occur through the resin collector and through the interface.

  Therefore, conventionally, using conductive particles having a diameter 0.5 to 2 times as large as the thickness of the resin current collector is not appropriate for producing a resin current collector for a bipolar lithium secondary battery. It is believed that.

  However, when the present inventor conducted extensive research focusing on the resin current collector used in the bipolar lithium secondary battery, the diameter of the conductive particles is 0.5 to 0.5 times the thickness of the resin current collector. When the resin current collector is doubled and the thickness of the resin current collector is 1 to 500 μm, it is surprising that the laminated electrode for a lithium secondary battery has excellent conductivity in the film thickness direction and excellent charge / discharge characteristics. Was found to be obtained. The present invention has been completed based on such findings.

  The thickness of the resin current collector is preferably 1 to 500 μm, more preferably 3 to 300 μm, and still more preferably 5 to 200 μm because the use is a laminated electrode for a bipolar lithium secondary battery. In addition, the size of the resin current collector is normally selected as a size suitable for a laminated electrode for a lithium secondary battery, and the shape of the resin current collector is not limited to such illustration.

  The value of the ratio of the major axis to the minor axis (major axis / minor axis) of the spherical conductive particles selectively improves the film-direction conductivity of the resin current collector and improves the charge / discharge characteristics of the laminated electrode. From the viewpoint, it is 1 to 2, preferably 1 to 1.9, more preferably 1 to 1.8.

  The ratio of the major axis to the minor axis (major axis / minor axis) of the conductive carbon particles is determined by measuring the conductive particles with an ultrahigh resolution field emission scanning electron microscope [manufactured by Hitachi High-Technologies Corporation, product number: S- 4800], the major axis and minor axis of 50 particles arbitrarily selected from the conductive particles included in the photographed image obtained when observing at a magnification of 1000 times are measured. The ratio of the major axis to the minor axis (major axis / minor axis) is obtained by dividing the major axis by the minor axis, and the ratio of the major axis to the minor axis (major axis / minor axis) is obtained for 50 particles. Mean value of

The particle size of the conductive particles is 0.5 times or more, preferably 0.7 times or more the thickness of the resin current collector, from the viewpoint of improving the charge / discharge characteristics of the laminated electrode. From the viewpoint of improving the adhesion to the material layer, it is not more than twice the thickness of the conductive layer, preferably not more than 1.5 times.

  The particle diameter of the conductive particles is determined when the conductive particles are observed at a magnification of 1000 times using an ultra-high resolution field emission scanning electron microscope (manufactured by Hitachi High-Technologies Corporation, product number: S-4800). From the conductive particles contained in the obtained photographed image, 50 conductive carbon particles are selected in order from the longest diameter, and the long and short diameters of these particles are measured. An intermediate value is obtained by dividing the sum of the major axis and minor axis by 2 and means the average value of the intermediate values obtained for 50 selected particles.

As the conductive agent, for example, metal particles such as aluminum particles, SUS particles, silver particles, gold particles, copper particles, and titanium particles, and carbon particles are preferable, and carbon particles are particularly preferable. Carbon particles such as carbon black and graphite have a very wide potential window, are stable in a wide range with respect to both the positive electrode potential and the negative electrode potential, and are excellent in conductivity. Also, since the carbon particles are very light, the increase in mass is minimized. Furthermore, since carbon particles are often used as a conductive aid for electrodes, even if they come into contact with these conductive aids, the contact resistance is very low because of the same material. In addition, when carbon particles are used as conductive particles, it is possible to reduce the compatibility of the electrolyte by applying hydrophobic treatment to the surface of the carbon, making it possible for the electrolyte to hardly penetrate into the pores of the resin current collector. It is.
Examples of the spherical conductive agent having a ratio of the major axis to the minor axis (major axis / minor axis) of the conductive particles of 1 to 2 include spheroidized natural graphite and spherical amorphous carbon particles. Examples of the amorphous carbon particles include a carbide of a resin such as polyacrylonitrile, but the present invention is not limited to such examples.

The mass ratio of the conductive particles to the resin binder [conductive carbon particles / resin binder (nonvolatile content)] is preferably 10/90 or more, more preferably 30/70, from the viewpoint of improving the charge / discharge characteristics of the laminated electrode. From the viewpoint of firmly bonding the current collector and the active material layer through the conductive layer, it is preferably 80/20 or less, more preferably 70/30 or less.

  The conductive agent contains conductive particles, may be composed only of conductive particles, and includes particles having conductivity other than the conductive particles as long as the object of the present invention is not impaired. It may be.

The conductive agent preferably contains carbon black from the viewpoint of improving charge / discharge characteristics. Examples of carbon black include acetylene black, ketjen black, furnace black, channel black, and thermal lamp black. However, the present invention is not limited to such examples. These carbon blacks may be used alone or in combination of two or more.

Carbon black usually has a particle size of 1 μm or less. The average particle size of carbon black is preferably 0.05 μm or more, more preferably 0.07 μm or more, and further preferably 0.08 μm or more from the viewpoint of improving dispersion stability in the conductive layer. From the viewpoint of improving the charge / discharge characteristics of the laminated electrode by increasing the rate, it is preferably 0.8 μm or less, more preferably 0.6 μm or less. The average particle size of the carbon black is determined by a laser diffraction / scattering particle size distribution measuring device [manufactured by Horiba, Ltd., product number: LA.
-910] is used to mean the average particle size of D50.

  From the viewpoint of improving the charge / discharge characteristics of the laminated electrode and the adhesion between the conductive layer, the current collector and the active material layer, the mass ratio of conductive particles to carbon black (conductive particles / carbon black) , Preferably 85/15 to 95/5.

  In the present invention, the resin current collector may contain carbon fibers, carbon whiskers and the like within the range in which the object of the present invention is not impaired, in addition to the conductive particles and carbon black.

  The resin binder is a component for adhering the active material layers formed on both surfaces of the resin current collector. Examples of the resin binder include olefin resins such as polyethylene and polypropylene, acrylic resins, diene resins, fluororesins, polyamides, polyimides, polyurethanes, and the like, but the present invention is limited only to such examples. is not. Among these resin binders, an acrylic resin, an olefin resin, and a diene resin are preferable, and an acrylic resin is more preferable from the viewpoint of firmly bonding the resin current collector and the active material layer.

  Among acrylic resins, (meth) acrylic acid having an cycloalkyl group which may have a substituent in the ester portion from the viewpoint of firmly bonding the current collector and the active material layer through the conductive layer Monomer mainly composed of (meth) acrylic acid (cyclo) alkyl ester containing at least one of cycloalkyl ester and (meth) acrylic acid alkyl ester having an alkyl group having 4 to 8 carbon atoms in the ester moiety An acrylic resin obtained by polymerizing the body component is preferred. In the present specification, “(meth) acrylic acid” means “acrylic acid” and / or “methacrylic acid”. “(Cyclo) alkyl ester” means “alkyl ester” and / or “cycloalkyl ester”. “(Meth) acrylate” means “acrylate” and / or “methacrylate”.

    The (meth) acrylic acid cycloalkyl ester having an cycloalkyl group which may have a substituent in the ester part and the (meth) acrylic acid alkyl ester having an alkyl group having 4 to 8 carbon atoms in the ester part are each independent. It may be used in a mixture of two or more.

  The cycloalkyl group of the (meth) acrylic acid cycloalkyl ester having an cycloalkyl group that may have a substituent in the ester portion is the number of carbon atoms from the viewpoint of firmly bonding the resin current collector and the active material layer. Is preferably a cycloalkyl group having 4 to 20 carbon atoms, and more preferably a cycloalkyl group having 4 to 10 carbon atoms.

  The (meth) acrylic acid cycloalkyl ester having an cycloalkyl group which may have a substituent in the ester portion may have a substituent within a range in which the object of the present invention is not inhibited. Examples of the substituent that the (meth) acrylic acid cycloalkyl ester may have include, for example, an alkyl group such as a methyl group and a tert-butyl group, a nitro group, a nitrile group, an alkoxyl group, an acyl group, a sulfone group, Although a hydroxyl group, a halogen atom, etc. are mentioned, this invention is not limited only to this illustration.

  Examples of the (meth) acrylic acid cycloalkyl ester having an optionally substituted cycloalkyl group in the ester portion include cycloalkyl (meth) acrylate, cycloalkylalkyl (meth) acrylate, and the like. These monomers may be used alone or in combination of two or more.

  As the cycloalkyl (meth) acrylate, for example, a cycloalkyl group such as isobornyl (meth) acrylate, cyclohexyl (meth) acrylate and the like preferably has 4 to 20 carbon atoms, more preferably 4 to 10 cycloalkyl (meth) acrylates. These cycloalkyl (meth) acrylates may be used alone or in combination of two or more.

  Examples of the cycloalkylalkyl (meth) acrylate include carbon numbers of cycloalkyl groups such as cyclohexylmethyl (meth) acrylate, cyclohexylethyl (meth) acrylate, cyclohexylpropyl (meth) acrylate, and 4-methylcyclohexylmethyl (meth) acrylate. Is preferably 4 to 20, more preferably 4 to 10, and examples thereof include cycloalkylalkyl (meth) acrylates in which the number of carbon atoms of the alkyl group bonded to the cycloalkyl group is preferably 1 to 4, and these These cycloalkylalkyl (meth) acrylates may be used alone or in combination of two or more.

  Among the (meth) acrylic acid cycloalkyl ester having an cycloalkyl group which may have a substituent in the ester portion, cycloalkyl (meth) acrylate having a cycloalkyl group having 4 to 20 carbon atoms is preferable, A cycloalkyl (meth) acrylate having a cycloalkyl group having 4 to 10 carbon atoms is more preferred, isobornyl (meth) acrylate and cyclohexyl (meth) acrylate are more preferred, and cyclohexyl (meth) acrylate is particularly preferred.

  Examples of the (meth) acrylic acid alkyl ester having an alkyl group having 4 to 8 carbon atoms in the ester portion include n-butyl (meth) acrylate, isobutyl (meth) acrylate, sec-butyl (meth) acrylate, and tert-butyl. (Meth) acrylate, n-pentyl (meth) acrylate, isopentyl (meth) acrylate, n-hexyl (meth) acrylate, isohexyl (meth) acrylate, n-heptyl (meth) acrylate, isoheptyl (meth) acrylate, n- Although octyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, etc. are mentioned, this invention is not limited only to this illustration. These monomers may be used alone or in combination of two or more.

Among (meth) acrylic acid (cyclo) alkyl esters, butyl acrylate, butyl methacrylate, 2-ethylhexyl acrylate, methacrylic acid are used from the viewpoint of firmly bonding the current collector and the active material layer through the conductive layer. 2-ethylhexyl acid, cyclohexyl acrylate and cyclohexyl methacrylate are preferred, 2-ethylhexyl acrylate and cyclohexyl methacrylate are more preferred, and the combined use of 2-ethylhexyl acrylate and cyclohexyl methacrylate is further preferable.
The content of the (meth) acrylic acid (cyclo) alkyl ester in the monomer component is preferably 5% by mass or more, more preferably 10% from the viewpoint of firmly bonding the resin current collector and the active material layer. % Or more, more preferably 15% by mass or more, and preferably 99% by mass or less, more preferably 90% by mass or less, and still more preferably 80% by mass or less from the viewpoint of improving the charge / discharge characteristics of the laminated electrode.

  The monomer component may contain a carboxyl group-containing monomer. Examples of the carboxyl group-containing monomer include (meth) acrylic acid, maleic acid, fumaric acid, crotonic acid, itaconic acid, citraconic acid, maleic anhydride, maleic acid monomethyl ester, maleic acid monobutyl ester, and itaconic acid monomethyl. Examples thereof include carboxyl group-containing aliphatic monomers such as esters, itaconic acid monobutyl ester, and vinyl benzoic acid, but the present invention is not limited to such examples. These carboxyl group-containing monomers may be used alone or in combination of two or more. Among these carboxyl group-containing monomers, acrylic acid and methacrylic acid are preferable from the viewpoint of copolymerizability.

  If the content of the carboxyl group-containing monomer in the monomer component is increased, the charge / discharge capacity is reduced because the lithium salt that is the electrolyte is neutralized. More preferably, it is 10 mass% or less, More preferably, it is 5 mass% or less.

  The monomer component may contain other monomers as long as the object of the present invention is not inhibited. As another monomer, for example, (meth) acrylic acid alkyl ester having an alkyl group having 1 to 3 carbon atoms such as methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate and the like in the ester portion; Styrene monomers such as styrene, α-methylstyrene, p-methylstyrene, tert-methylstyrene, chlorostyrene, vinyltoluene; benzyl (meth) acrylate, phenylethyl (meth) acrylate, methylbenzyl (meth) acrylate, Aralkyl (meth) acrylates such as naphthylmethyl (meth) acrylate; 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate Hydroxy group-containing (meth) acrylic acid esters such as 4-hydroxybutyl (meth) acrylate; ethylene glycol (meth) acrylate, ethylene glycol methoxy (meth) acrylate, diethylene glycol (meth) acrylate, diethylene glycol methoxy (meth) acrylate, etc. Oxo group-containing monomers; fluorine atom-containing monomers such as trifluoroethyl (meth) acrylate, tetrafluoropropyl (meth) acrylate, octafluoropentyl (meth) acrylate; glycidyl (meth) acrylate, α-methylglycidyl Epoxy group-containing monomers such as (meth) acrylate and glycidyl allyl ether; methoxyethyl (meth) acrylate, methoxybutyl (meth) acrylate, ethoxybutyl (meta Acrylates, alkoxyalkyl (meth) acrylates such as trimethylolpropane tripropoxy (meth) acrylate; vinyltrimethoxysilane, vinyltriethoxysilane, vinyltri (methoxyethoxy) silane, γ- (meth) acryloyloxypropyltrimethoxysilane, 2 Silane group-containing monomers such as styrylethyltrimethoxysilane, vinyltrichlorosilane, γ- (meth) acryloyloxypropylhydroxysilane, γ- (meth) acryloyloxypropylmethylhydroxysilane; (meth) acryloylaziridine, (meta ) Examples include aziridinyl group-containing monomers such as 2-aziridinylethyl acrylate, but the present invention is not limited to such examples. These monomers may be used alone or in combination of two or more.

  Examples of the diene resin include conjugated diene homopolymers and copolymers of conjugated dienes and other monomers, but the present invention is not limited to such examples. Specific examples of diene polymers include conjugated diene homopolymers such as polybutadiene and polyisoprene; aromatic vinyl-conjugated diene copolymers such as styrene-butadiene copolymers; Copolymers, terpolymers composed of aromatic vinyl-conjugated diene-carboxylic acid group-containing monomers such as terpolymers composed of styrene-butadiene-itaconic acid; cyanides such as acrylonitrile-butadiene copolymer Examples thereof include vinyl fluoride-conjugated diene copolymers, but the present invention is not limited to such examples.

  The resin binder exemplifies that it can be prepared, for example, as follows, but it can also be adjusted by other methods. For example, the monomer component can be prepared by various polymerization methods such as solvent-based homogeneous polymerization, precipitation polymerization, dispersion polymerization, and emulsion polymerization. Examples of the method for emulsion polymerization of the monomer component include, for example, an aqueous medium containing a water-soluble organic solvent such as lower alcohol such as methanol and water, an emulsifier dissolved in a medium such as water, and the monomer under stirring. Examples of the method include dropping a component and a polymerization initiator, and a method of dropping a monomer component that has been pre-emulsified with an emulsifier and water into water or an aqueous medium. It is not limited. In addition, what is necessary is just to set the quantity of a medium suitably in consideration of the non volatile matter amount contained in the resin emulsion obtained. The medium may be charged in the reaction vessel in advance or used as a pre-emulsion. The medium may be used when a resin emulsion is produced by emulsion polymerization of monomer components as required.

  When the monomer component is emulsion-polymerized, the monomer component, the emulsifier and the medium may be mixed and then emulsion polymerization may be performed. The emulsion polymerization may be carried out after preparing the emulsion, or the emulsion polymerization may be carried out by mixing at least one of the monomer component, the emulsifier and the medium and the remaining pre-emulsion. The monomer component, the emulsifier, and the medium may be added all at once, dividedly, or continuously dropped.

  Examples of the emulsifier include an anionic emulsifier, a nonionic emulsifier, a cationic emulsifier, an amphoteric emulsifier, and a polymer emulsifier. These emulsifiers may be used alone or in combination of two or more.

  Examples of the anionic emulsifier include alkyl sulfate salts such as ammonium dodecyl sulfate and sodium dodecyl sulfate; alkyl sulfonate salts such as ammonium dodecyl sulfonate and sodium dodecyl sulfonate; alkyl aryl sulfonate salts such as ammonium dodecyl benzene sulfonate and sodium dodecyl naphthalene sulfonate; Examples include polyoxyethylene alkyl sulfate salts; polyoxyethylene alkyl aryl sulfate salts; dialkyl sulfosuccinates; aryl sulfonic acid-formalin condensates; fatty acid salts such as ammonium laurate and sodium stearate. It is not limited to illustration only.

  Nonionic emulsifiers include, for example, polyoxyethylene alkyl ether, polyoxyethylene alkyl aryl ether, condensate of polyethylene glycol and polypropylene glycol, sorbitan fatty acid ester, polyoxyethylene sorbitan fatty acid ester, fatty acid monoglyceride, ethylene oxide and aliphatic Although the condensation product with an amine etc. are mentioned, this invention is not limited only to this illustration.

Examples of the cationic emulsifier include alkylammonium salts such as dodecylammonium chloride, but the present invention is not limited to such examples.

Examples of amphoteric emulsifiers include betaine ester type emulsifiers, but the present invention is not limited to such examples.

Examples of the polymer emulsifier include poly (meth) acrylates such as sodium polyacrylate; polyvinyl alcohol; polyvinyl pyrrolidone; polyhydroxyalkyl (meth) acrylates such as polyhydroxyethyl acrylate; single polymers constituting these polymers. Although the copolymer etc. which use 1 or more types of a monomer as a copolymerization component are mentioned, this invention is not limited only to this illustration.

Further, as the emulsifier, an emulsifier having a polymerizable group, that is, a so-called reactive emulsifier is preferable from the viewpoint of improving water resistance, and a non-nonylphenyl emulsifier is preferable from the viewpoint of environmental protection.

  As the reactive emulsifier, for example, propenyl-alkylsulfosuccinic acid ester salt, (meth) acrylic acid polyoxyethylene sulfonate salt, (meth) acrylic acid polyoxyethylene phosphonate salt [for example, manufactured by Sanyo Chemical Industries, Ltd., Product name: Eleminol RS-30, etc.], polyoxyethylene alkylpropenyl phenyl ether sulfonate salt [for example, product name: Aqualon HS-10, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.], allyloxymethylalkyloxypolyoxyethylene Sulfonate salt [for example, product name: Aqualon KH-10 manufactured by Daiichi Kogyo Seiyaku Co., Ltd.], sulfonate salt of allyloxymethylnonylphenoxyethylhydroxypolyoxyethylene [for example, product name: ADEKA manufactured by ADEKA Corporation Rear soap SE-10 etc.), Ryloxymethylalkoxyethylhydroxypolyoxyethylene sulfate ester salt (for example, manufactured by ADEKA, trade name: Adekaria soap SR-10, SR-30, etc.), bis (polyoxyethylene polycyclic phenyl ether) methacrylated sulfonate Salts (for example, Nippon Emulsifier Co., Ltd., trade name: Antox MS-60, etc.), allyloxymethylalkoxyethylhydroxypolyoxyethylene [eg, ADEKA Corporation, trade name: Adeka Soap ER-20, etc. ], Polyoxyethylene alkylpropenyl phenyl ether [for example, manufactured by Daiichi Kogyo Seiyaku Co., Ltd., trade name: Aqualon RN-20, etc.], allyloxymethylnonylphenoxyethyl hydroxypolyoxyethylene [for example, manufactured by ADEKA Corporation, Product Name: Adekaria Soap E-10, etc.) and the like, the present invention is not limited only to those exemplified.

  The amount of the emulsifier is preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, further preferably 1 part by mass or more, from the viewpoint of improving the polymerization stability per 100 parts by mass of the monomer component. Particularly preferably, it is 2 parts by mass or more, and preferably 20 parts by mass or less, more preferably 10 parts by mass or less, and further preferably 8 from the viewpoint of firmly bonding the current collector and the active material layer through the conductive layer. It is at most 6 parts by mass, particularly preferably at most 6 parts by mass.

  Examples of the polymerization initiator include azobisisobutyronitrile, 2,2-azobis (2-methylbutyronitrile), 2,2-azobis (2,4-dimethylvaleronitrile), 2,2-azobis ( Azo compounds such as 2-diaminopropane) hydrochloride, 4,4-azobis (4-cyanovaleric acid), 2,2-azobis (2-methylpropionamidine); persulfates such as potassium persulfate; hydrogen peroxide , Benzoyl peroxide, parachlorobenzoyl peroxide, lauroyl peroxide, peroxides such as ammonium peroxide, and the like, but the present invention is not limited to such examples. These polymerization initiators may be used alone or in combination of two or more.

  The amount of the polymerization initiator is preferably 0.05 parts by mass or more, more preferably 0 from the viewpoint of increasing the polymerization rate and reducing the residual amount of the unreacted monomer component per 100 parts by mass of the monomer component. From the viewpoint of improving water resistance, it is preferably 3 parts by mass or less, more preferably 1 part by mass or less.

  The method for adding the polymerization initiator is not particularly limited. Examples of the addition method include batch charging, divided charging, and continuous dripping. From the viewpoint of advancing the completion time of the polymerization reaction, a part of the polymerization initiator may be added before or after the monomer component is added to the reaction system.

  In order to accelerate the decomposition of the polymerization initiator, for example, a reducing agent such as sodium bisulfite and a polymerization initiator decomposition agent such as transition metal salt such as ferrous sulfate are added in an appropriate amount to the reaction system. Also good.

  Further, if necessary, additives such as chain transfer agents such as compounds having a thiol group such as tert-dodecyl mercaptan, pH buffering agents, chelating agents, and film-forming aids may be added to the reaction system. Good. Since the amount of the additive varies depending on the type, it cannot be determined unconditionally. Usually, it is preferably about 0 to 5 parts by mass, more preferably about 0 to 3 parts by mass per 100 parts by mass of the monomer component. It is.

  The atmosphere for emulsion polymerization of the monomer component is not particularly limited, but is preferably an inert gas such as nitrogen gas from the viewpoint of improving the efficiency of the polymerization initiator.

  Although the polymerization temperature at the time of carrying out emulsion polymerization of a monomer component does not have limitation, Usually, Preferably it is 50-100 degreeC, More preferably, it is 60-95 degreeC. The polymerization temperature may be constant or may be changed during the polymerization reaction.

  The glass transition temperature of the polymer constituting the emulsion particles is preferably −70 ° C. or higher, more preferably −65 ° C. or higher, more preferably −60 ° C. or higher, from the viewpoint of improving the charge / discharge characteristics of the laminated electrode. From the viewpoint of firmly bonding the current collector and the active material layer through the conductive layer, the temperature is preferably 80 ° C. or lower, more preferably 50 ° C. or lower, and further preferably 30 ° C. or lower. The glass transition temperature of the polymer can be easily adjusted by adjusting the composition of the monomer used for the monomer component.

In the present specification, the glass transition temperature of the polymer is expressed by the following formula: the glass transition temperature of the homopolymer of the monomer used in the monomer component constituting the polymer.
1 / Tg = Σ (Wm / Tgm) / 100
[Wherein Wm represents the content (% by mass) of the monomer m in the monomer component constituting the polymer, and Tgm represents the glass transition temperature (absolute temperature: K) of the homopolymer of the monomer m. ] The temperature calculated | required based on the formula of Fox (Fox) represented by this.

  The glass transition temperature of the polymer is, for example, 83 ° C. for a cyclohexyl methacrylate homopolymer, 16 ° C. for a cyclohexyl acrylate homopolymer, 95 ° C. for a homopolymer of acrylic acid, and −− for a homopolymer of 2-ethylhexyl acrylate. 70 ° C., −56 ° C. for n-butyl acrylate homopolymer, 20 ° C. for n-butyl methacrylate homopolymer, and 130 ° C. for methacrylic acid homopolymer.

  The glass transition temperature of the polymer is a value obtained based on the Fox equation, but the measured value of the glass transition temperature of the polymer was obtained based on the Fox equation. The value is preferably the same. The actual measured value of the glass transition temperature of the polymer can be obtained, for example, by measuring the differential scanning calorimetry.

  Examples of the differential scanning calorimeter measuring device include Seiko Instruments Inc., product number: DSC220C. Further, when measuring the differential scanning calorific value, a method of drawing a differential scanning calorific value (DSC) curve, a method of obtaining a first derivative curve from the differential scanning calorific value (DSC) curve, a method of performing a smoothing process, and a method of obtaining a target peak temperature There is no limitation in particular. For example, when the measuring device is used, the drawing may be performed from data obtained by using the measuring device. At that time, analysis software capable of performing mathematical processing can be used. Examples of the analysis software include analysis software [manufactured by Seiko Instruments Inc., product number: EXSTAR6000], but the present invention is not limited to such examples. In addition, the peak temperature obtained in this way may include an error due to plotting of about 5 ° C. up and down.

  Since the average particle diameter of the emulsion particles varies depending on the thickness of the conductive layer, it cannot be determined unconditionally. Therefore, it is preferable to appropriately determine the thickness depending on the thickness of the conductive layer. Is preferably 0.03 μm or more, more preferably 0.05 μm or more, and even more preferably 0.07 μm or more, and a viewpoint of firmly bonding the current collector and the active material layer through the conductive layer Therefore, it is preferably 1 μm or less, more preferably 0.7 μm or less, and still more preferably 0.5 μm or less.

  In the present specification, the average particle size of the emulsion particles is measured using a particle size distribution measuring instrument (manufactured by Particle Sizing Systems, trade name: NICOMP Model 380) by a dynamic light scattering method. It means the volume average particle diameter.

  The resin current collector preferably contains a dispersant in order to uniformly disperse the conductive agent in the resin binder.

  Examples of the dispersant include a carboxymethyl cellulose compound and a surfactant in an aqueous formulation, but the present invention is not limited to such examples. These components may be used alone or in combination. Among the dispersants, a carboxymethyl cellulose compound is preferable from the viewpoint of uniformly dispersing the conductive agent in the resin binder.

  Examples of the carboxymethylcellulose-based compound include carboxymethylcellulose, carboxymethylcellulose ammonium salt, carboxymethylcellulose alkali metal salt, carboxymethylcellulose alkaline earth metal salt, and the like, but the present invention is not limited to such examples. . These carboxymethyl cellulose compounds may be used alone or in combination of two or more. Among these carboxymethyl cellulose compounds, carboxymethyl cellulose alkali metal salts are preferable.

  Examples of the surfactant include anionic surfactants such as alkyl sulfate ester salts, alkylbenzene sulfonates, fatty acid salts, and naphthalene sulfonic acid formalin condensates, and nonionic surfactants such as polyoxyethylene aralkyl ethers and glycerin fatty acid esters. Examples include surfactants, cationic surfactants such as alkylamine salts and quaternary ammonium salts, and amphoteric surfactants such as alkylamine oxides and alkylbetaines, but the present invention is limited to such examples only. It is not something. Among the surfactants, anionic surfactants and nonionic surfactants are preferred, and anionic surfactants are more preferred from the viewpoint of improving the durability of the laminated electrode of the present invention.

  The amount of the dispersant is preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, and further preferably 1 from the viewpoint of uniformly dispersing the conductive agent in the resin binder per 100 parts by mass of the conductive agent. From the viewpoint of firmly bonding the resin current collector and the active material layer, it is preferably 20 parts by mass or less, more preferably 15 parts by mass or less, and further preferably 10 parts by mass or less.

  The resin current collector is, for example, mixed with a conductive agent, a resin binder, and, if necessary, a dispersant and a solvent, and the obtained resin current collector composition was applied to a substrate having good releasability and dried. It can be obtained by peeling later. It can also be formed by kneading the dried binder and conductive agent into pellets and extrusion forming.

  When mixing the conductive agent, the resin binder, and if necessary, the dispersant and the solvent, for example, the components are uniformly distributed using a dispersing machine such as a ball mill, a sand mill, a crusher, an ultrasonic dispersing machine, a homogenizer, or a mixer. It is preferable to be dispersed.

  In addition, when using a solvent, it is preferable that a solvent is water from a viewpoint of environmental protection. Moreover, when using a resin emulsion as a resin binder, there exists an advantage that it is not necessary to use a solvent.

  The solid content in the resin current collector composition is preferably 10 to 70% by mass, more preferably 15 to 60% by mass, and still more preferably 20 to 55% by mass, from the viewpoint of improving coatability and productivity. is there.

  The viscosity of the resin current collector composition (measured at a rotation speed of 30 r / m at 25 ° C. using a BM viscometer) is preferably from the viewpoint of improving the coating property and the uniformity of the conductive layer to be formed. Is 5 to 5000 mPa · s, more preferably 10 to 3000 mPa · s, and still more preferably 15 to 2000 mPa · s.

Examples of the method for applying the resin current collector composition include a dipping method, a roll coater method, a doctor blade method, a brush coating method, a reverse roll method, a direct roll method, and a gravure method. However, the present invention is not limited to such examples.
Examples of the method for drying the resin current collector composition applied to the substrate include a warm air or hot air drying method, a vacuum drying method, a drying method by infrared irradiation, and the like. It is not limited to only. Although the drying temperature at the time of drying the composition for resin collectors apply | coated to the base material is not specifically limited, It is preferable that it is normal temperature-about 200 degreeC. Moreover, since the drying time required for drying the composition for resin collectors apply | coated on the base material changes with drying methods, it cannot be determined unconditionally. The drying time is usually preferably dried until the content of the solvent in the resin current collector composition is 0.1% by mass or less.

  The thickness of the resin current collector layer formed as described above is preferably 1 μm or more, more preferably 3 μm or more, and even more preferably 5 μm or more in order to ensure the strength of the current collector and prevent liquid junction. From the viewpoint of improving the charge / discharge characteristics of the laminated electrode, it is preferably 500 μm or less, more preferably 300 μm or less, and even more preferably 200 μm or less.

  A positive electrode active material layer is laminated on one surface of the resin current collector, and a negative electrode active material layer is laminated on the other surface. The active material layer contains an active material, a conductive agent for active material, and a resin binder for active material layer.

  The type of the active material is different between the positive electrode and the negative electrode of the lithium secondary battery. In the present invention, any of the positive electrode active material and the negative electrode active material can be used as the active material. As the positive electrode active material and the negative electrode active material, those commonly used can be used, and the present invention is not limited by the types of the positive electrode active material and the negative electrode active material. Examples of the positive electrode active material include lithium cobaltate and lithium manganate, but the present invention is not limited to such examples. Examples of the negative electrode active material include metallic lithium, graphite, amorphous carbon, and lithium titanate. However, the present invention is not limited to such examples.

  Examples of the conductive material for the active material include carbon black such as acetylene black, ketjen black, furnace black, channel black, and thermal lamp black. However, the present invention is not limited to such examples. . Moreover, you may use the graphite used as an active material for negative electrodes as a electrically conductive agent for active materials. These conductive materials for active materials may be used alone or in combination of two or more. The average particle diameter of the conductive agent for the active material is preferably 0.05 μm or more, more preferably 0.07 μm or more, and further preferably 0.08 μm or more from the viewpoint of improving dispersion stability. From the viewpoint of improving the charge / discharge characteristics of the laminated electrode by increasing the rate, it is preferably 30 μm or less, more preferably 20 μm or less, and even more preferably 15 μm or less. The average particle diameter of carbon black means the average particle diameter of D50 measured using a laser diffraction / scattering particle size distribution measuring apparatus [manufactured by Horiba, Ltd., product number: LA-910].

  The amount of the conductive material for the active material is preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, and further preferably 100 parts by mass of the active material from the viewpoint of improving the conductivity of the active material layer. From the viewpoint of increasing the charge capacity per unit volume of the laminated electrode, it is preferably 50 parts by mass or less, more preferably 20 parts by mass or less, and even more preferably 15 parts by mass or less.

  In the present invention, the conductive material for active material may contain carbon fiber, carbon whisker, and the like as long as the object of the present invention is not impaired.

  The active material layer resin binder is used to bind the active material and the active material conductive agent. Examples of the resin binder for the active material layer include acrylic resins, SBR resins, diene resins, fluororesins, polyamides, polyimides, polyurethanes, etc., but the present invention is not limited to such examples. Absent. Among these resin binders, a fluororesin and an SBR resin are preferable, and polyvinylidene fluoride is more preferable from the viewpoint of firmly bonding the active material and the conductive material for the active material.

  The amount of the resin binder for the active material layer is preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass from the viewpoint of firmly bonding the active material and the conductive material for the active material per 100 parts by mass of the active material. Part or more, more preferably 1 part by weight or more, and from the viewpoint of improving the conductivity of the active material layer, it is preferably 50 parts by weight or less, more preferably 30 parts by weight or less, and even more preferably 10 parts by weight or less.

  In addition, the active material dispersant may be used for the active material layer from the viewpoint of improving the dispersibility of the active material and the conductive material for the active material, if necessary. Examples of the active material dispersant include celluloses such as carboxymethyl cellulose, methyl cellulose, ethyl cellulose, and hydroxypropyl cellulose, ammonium salts or alkali metal salts thereof; poly (meth) acrylates such as sodium poly (meth) acrylate; Examples include polyvinyl alcohol, modified polyvinyl alcohol, polyethylene oxide; polyvinyl pyrrolidone, polycarboxylic acid, oxidized starch, phosphate starch, casein, various modified starches, chitin, chitosan derivatives, etc., but the present invention is limited to such examples only. It is not something. These active material dispersants may be used alone or in combination of two or more.

  The amount of the active material dispersant is preferably 0.1 parts by mass or more, more preferably 0.3 parts by mass, from the viewpoint of improving the dispersibility of the active material and the conductive material for active material per 100 parts by mass of the active material. From the viewpoint of improving the mechanical strength of the active material layer, it is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, and further preferably 3 parts by mass or less. is there.

  In addition, you may make the composition for active materials contain water or an organic solvent from a viewpoint of improving applicability | paintability as needed. Examples of the organic solvent include ethylene glycol dimethyl ether, ethylene glycol diethyl ether, triethylene glycol dimethyl ether, triethylene glycol diethyl ether, tetraethylene glycol dimethyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, 2,6-dimethyltetrahydrofuran, tetrahydro Ethers such as pyran, 1,4-dioxane, 1,3-dioxolane; carbonates such as ethylene carbonate, propylene carbonate, diethyl carbonate, methyl ethyl carbonate; dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, diphenyl carbonate, methyl carbonate Carbonates such as phenyl, ethylene carbonate, propylene carbonate; methyl formate, methyl acetate, propionic acid Aliphatic carboxylic acid esters such as til, ethyl acetate, propyl acetate, butyl acetate, amyl acetate; aromatic carboxylic acid esters such as methyl benzoate and ethyl benzoate; γ-butyrolactone, γ-valerolactone, δ-valero Cyclic esters such as lactone; phosphate esters such as trimethyl phosphate, ethyl dimethyl phosphate, diethyl methyl phosphate, triethyl phosphate; acetonitrile, propionitrile, methoxypropionitrile, glutaronitrile, adiponitrile, 2- Nitriles such as methylglutaronitrile; amides such as N-methylformamide, N-ethylformamide, N, N-dimethylformamide, N, N-dimethylacetamide, N-methylpyrrolidinone, N-methylpyrrolidone, N-vinylpyrrolidone Kind; Eth Alcohols such as ethylene glycol, propylene glycol, ethylene glycol monomethyl ether, and ethylene glycol monoethyl ether; and sulfoxides such as dimethyl sulfoxide, methyl ethyl sulfoxide, and diethyl sulfoxide. However, the present invention is limited to such examples. It is not something. These solvents may be used alone or in combination of two or more. Among these organic solvents, amides are preferable, and N-methylformamide, N-ethylformamide, N, N-dimethylformamide, N, N-dimethylacetamide, N-methylpyrrolidinone, N-methylpyrrolidone and N-vinyl are preferred. Pyrrolidone is more preferable, and N-methylpyrrolidone is more preferable. The amount of the organic solvent is not particularly limited, but is usually adjusted so that the nonvolatile content (nonvolatile content) in the composition for active material is about 5 to 50% by mass from the viewpoint of improving the coatability. It is preferable.

  The active material layer may be, for example, an active material, a conductive material for active material, a resin binder for active material layer, and if necessary, a dispersant for active material and a solvent, and the resulting active material composition may be used as a resin current collector layer. It can be laminated by forming it on top.

  As a method for forming the active material composition on the resin current collector, for example, the active material composition is formed into a sheet shape, and the obtained sheet-shaped active material layer composition is formed on the resin current collector. Examples thereof include a dry method of laminating and a wet method of applying a composition for an active material on a resin current collector and then drying, but the present invention is not limited to such examples. Among these methods, the wet method is preferable from the viewpoint of improving productivity. When the wet method is adopted, the active material, the conductive material for the active material, the resin binder for the active material layer, the organic solvent and, if necessary, the dispersant for the active material are mixed, and each component is dispersed using a disper, etc. The active material layer can be laminated on the resin current collector layer by forming the active material composition on the resin current collector by a coating means such as a doctor blade, an applicator or a bar coater. After the formation of the active material layer, the organic solvent contained in the active material layer may be removed by heating and drying, if necessary.

  The thickness of the active material layer is not particularly limited, but is usually preferably 5 to 1000 μm, more preferably 20 to 500 μm, and still more preferably 30 to 300 μm.

  The resin current collector for a bipolar lithium secondary battery of the present invention obtained as described above is excellent in charge / discharge characteristics and conductivity in the film thickness direction. In addition, since the resin current collector is used for the laminated electrode for the bipolar lithium secondary battery of the present invention, it has excellent charge / discharge characteristics and excellent adhesion between the active material layer and the resin current collector. Therefore, it can be suitably used as a current collector for forming an anode and a cathode of a bipolar lithium secondary battery.

  The resin current collector for a bipolar lithium secondary battery of the present invention is formed by forming an active material layer on the surface of a substrate, bonding the formed active material layer and the resin current collector, It can also be produced by separating the substrate from the material layer. In this case, the surface of the base material is preferably subjected to a release treatment from the viewpoint of easily peeling the base material and the active material layer. Examples of the substrate include a metal substrate such as an aluminum foil, and a film made of a thermoplastic resin such as polyethylene, polypropylene, and polyester. However, the present invention is not limited to such examples.

The method for producing a lithium secondary battery using the laminated electrode for a bipolar lithium secondary battery of the present invention is not particularly limited, and a normal production method can be adopted. For example, a positive electrode and a negative electrode formed on the metal foil current collector of the laminated electrode for a lithium secondary battery of the present invention are arranged on the counter electrode via a separator. In the case of producing a laminated cell type lithium secondary battery, a bipolar lithium secondary battery can be assembled using the laminated electrode for a lithium secondary battery, the negative electrode, the electrolyte (electrolyte) and the separator of the present invention.

EXAMPLES Next, although this invention is demonstrated further in detail based on an Example, this invention is not limited only to this Example. In the following Examples, “part” means “part by mass” and “%” means “mass%” unless otherwise specified.
Production Example 1
In a flask equipped with a dropping funnel, a stirrer, a nitrogen introducing tube, a thermometer and a reflux condenser, 101.0 parts of deionized water was charged.

  On the other hand, in a dropping funnel, 4.0 parts of 25% aqueous solution of polyoxyethylene alkylpropenyl phenyl ether sulfonate salt [Daiichi Kogyo Seiyaku Co., Ltd., trade name: Aqualon HS-10], polyoxyethylene alkyl propenyl phenyl ether [No. 4 parts of 25% aqueous solution of Ichi Kogyo Seiyaku Co., Ltd., trade name: Aqualon RN-20], 5.8 parts of deionized water, 34 parts of 2-ethylhexyl acrylate and 66 parts of cyclohexyl methacrylate as monomer components were added. A pre-emulsion composed of these components was prepared.

  Of the obtained pre-emulsion, 5.7 parts corresponding to 5% of the total amount of the monomer components were added to the flask, and the temperature was raised to 80 ° C. with stirring while gently blowing nitrogen gas. After raising the temperature, 6 parts of 5% aqueous potassium persulfate solution was added to the flask to initiate polymerization, and maintained at a reaction temperature of 80 ° C. for 10 minutes to complete the initial reaction.

  After completion of the initial reaction, the remaining pre-emulsion was uniformly dropped into the flask over 120 minutes while maintaining the reaction system at 80 ° C. After completion of the dropping, the dropping funnel was washed with 5 g of deionized water, and the resulting cleaning solution was added to the flask. Thereafter, the internal temperature in the flask was maintained at 80 ° C. for 30 minutes and stirred.

  The obtained reaction mixture was cooled to room temperature, adjusted to pH 8 with 10% aqueous sodium hydroxide solution and filtered through a 100 mesh (JIS mesh) wire mesh. As a result, the nonvolatile content was 45.0%, 25 An acrylic resin emulsion having a viscosity at 50 ° C. of 50 mPa · s was obtained. The glass transition temperature of the resin constituting the emulsion particles contained in the obtained acrylic resin emulsion was 10 ° C.

In the present specification, the nonvolatile content, viscosity and pH of the acrylic resin emulsion were measured based on the following methods.
(1) Nonvolatile content of acrylic resin emulsion The mass (1 g) of the acrylic resin emulsion was weighed, and the nonvolatile content of the acrylic resin emulsion obtained by drying at 105 ° C. for 1 hour with a hot air drier was measured. Measure and formula:
[Non-volatile content of acrylic resin emulsion (%)] = [Mass of non-volatile content of acrylic resin emulsion] / [Mass of acrylic resin emulsion (1 g)] × 100
Based on.
(2) Viscosity of acrylic resin emulsion The viscosity of the acrylic resin emulsion was measured at a rotational speed of 30 r / m and 25 ° C using a BM viscometer [manufactured by Tokyo Keiki Co., Ltd.]. When measuring the viscosity, a rotor corresponding to the measured viscosity was selected.
(3) pH of acrylic resin emulsion
The pH of the acrylic resin emulsion was measured at a temperature of 25 ° C. using a pH meter [manufactured by Horiba, Ltd., product number: F-23].

Example 1
100 parts of the acrylic resin emulsion obtained in Production Example 1, spherical graphite particles [manufactured by Ito Graphite Industry Co., Ltd., product number: SG-BL40, the ratio of the major axis to the minor axis (major axis / minor axis) of the graphite particles Value: 1.6, graphite particle size: 40 μm] 36 parts, carbon black [manufactured by Lion Corporation, product number: W-310A] 20 parts, carboxymethylcellulose sodium salt as a dispersant [Daiichi Kogyo Seiyaku Co., Ltd.] Manufactured, trade name: Serogen F-BSH4] and 56 parts of purified water were mixed, and the resulting mixture was dispersed with a disper and then filtered through a 100 mesh (JIS mesh) wire mesh to obtain a resin. A current collector composition (solid content: 40%) was prepared. In the obtained resin current collector composition, the mass ratio of graphite particles to resin binder [graphite particles / resin binder (nonvolatile content)] was 44/56.

The ratio of the major axis to the minor axis of the graphite particles (major axis / minor axis) and the particle diameter of the graphite particles were determined based on the following method.
[Ratio of major axis / minor axis (major axis / minor axis) of graphite particles]
Conductivity contained in a photographed image obtained when a graphite particle is observed at a magnification of 200 times using an ultra high resolution field emission scanning electron microscope (manufactured by Hitachi High-Technologies Corporation, product number: S-4800). The major axis and minor axis of 50 graphite particles arbitrarily selected from the carbon particles are measured, and the ratio of the major axis to the minor axis of the graphite particle (major axis) is obtained by dividing the major axis by the minor axis for each graphite particle. / Minor axis) value, the average value of the ratio of the major axis to the minor axis (major axis / minor axis) obtained for 50 graphite particles was determined, and the value was calculated as the major axis and minor axis of the graphite particle. The ratio (major axis / minor axis) was used.
[Particle diameter of graphite particles]
The particle size of the graphite particles is a photographed image obtained when the graphite particles are observed at a magnification of 1000 times using an ultra-high resolution field emission scanning electron microscope (manufactured by Hitachi High-Technologies Corporation, product number: S-4800). Among the graphite particles contained in the above, 50 graphite particles are selected in order from the longest longest diameter, and the longest and shortest diameters of these particles are measured. An intermediate value was obtained by dividing the sum by 2 and an average value of the intermediate values obtained for 50 selected particles was adopted.

  Next, an aluminum foil was used as a base material, and the resin current collector composition obtained above was applied on one surface of the aluminum foil with an applicator according to the design film thickness, and then heated with a hot air dryer. The resin current collector coating film was obtained by drying at 40 ° C. for 10 minutes and further drying at 40 ° C. for 5 hours with a vacuum dryer.

  By cutting the obtained resin current collector coating film into a size of 5 cm in length and 5 cm in width, weighing the cut resin current collector, and subtracting the mass of the aluminum foil from the mass of the resin current collector The mass of the resin current collector layer was determined. When the specific gravity of the resin current collector was calculated from the composition of the resin current collector, the specific gravity was 1.5. When the thickness of the resin current collector was calculated from the mass of the resin current collector and its specific gravity, the thickness of the conductive layer was 40 μm.

  On the other hand, lithium cobaltate [manufactured by Nippon Chemical Industry Co., Ltd., trade name: Cellseed C] 87 parts, polyvinylidene fluoride [manufactured by Arkema Co., Ltd., trade name: Kyner HSV-900], Ketjen Black [Lion ( 8 parts, palm oil fatty acid diethanolamide [Daiichi Kogyo Seiyaku Co., Ltd., trade name: Dianol 300] as a dispersant and N-methylpyrrolidone [Wako Pure Chemical Industries, Ltd.] Co., Ltd., special grade] is blended in an appropriate amount so that the nonvolatile content is 35%, and the resulting mixture is dispersed with a disper to obtain a composition for the positive electrode active material layer (solid content: 35%). Obtained.

  The obtained composition for positive electrode active material layer was applied on the conductive layer of the current collector obtained above with an applicator so that the thickness when applied was about 500 μm, and dried in an atmosphere at 100 ° C. for 15 minutes. Then, after vacuum drying at a temperature of 100 ° C. for 1 hour to form a positive electrode active material layer, the aluminum foil as a base material was peeled off to obtain a resin current collector having a positive electrode layer formed on one side It was.

  Also, 93 parts of natural graphite [manufactured by Nippon Graphite Industry Co., Ltd., trade name: CGB-20], 7 parts of polyvinylidene fluoride [manufactured by Arkema Co., Ltd., trade name: Kyner HSV-900], and N-methylpyrrolidone [ Wako Pure Chemical Industries, Ltd., special grade] is blended in an appropriate amount such that the nonvolatile content is 40%, and the resulting mixture is dispersed with a disper to obtain a composition for the negative electrode active material layer (solid content: 40%).

  The obtained negative electrode active material layer composition was applied to the substrate release surface of the resin current collector obtained above using an applicator so that the thickness at the time of application was about 150 μm, and the atmosphere at 100 ° C. After being dried for 15 minutes, it was further vacuum dried at a temperature of 100 ° C. for 24 hours to obtain a laminated electrode in which a positive electrode active material layer and a negative electrode active material layer were formed on a resin current collector.

In the obtained resin collector of the laminated electrode, the particle diameter of the graphite particles is 1.0 times the thickness of the resin current collector layer, and the mass ratio of graphite particles to carbon black (graphite particles / carbon black) Was 93/7. Moreover, in the obtained composition for conductive layers (solid content: 40%), the mass ratio of graphite particles to resin binder [graphite particles / resin binder (nonvolatile content)] was 44/56.

Comparative Example 1
In Example 1, flake graphite particles [manufactured by SEC Carbon Co., product number: SGP-10, graphite particle aspect ratio: 3, graphite particle diameter: 10 μm] were used as the graphite particles. Obtained a laminated electrode of Comparative Example 1 in the same manner as in Example 1. In the obtained laminated electrode, the particle diameter of the graphite particles was 0.25 times the thickness of the conductive layer, and the mass ratio of graphite particles to carbon black (graphite particles / carbon black) was 93/7. Moreover, in the obtained composition for conductive layers (solid content: 40%), the mass ratio of graphite particles to resin binder [graphite particles / resin binder (nonvolatile content)] was 44/56.

Comparative Example 2
In Example 1, 15 parts of flake-like graphite particles [manufactured by SEC Carbon Co., product number: SGP-10, aspect ratio of graphite particles: 3, particle diameter of graphite particles: 10 μm] were purified as graphite particles. A laminated electrode of Comparative Example 2 was obtained in the same manner as in Example 1 except that water was changed to 26 parts. In the obtained laminated electrode, the particle diameter of the graphite particles is 0.25 times the thickness of the resin current collector layer, and the mass ratio of graphite particles to carbon black (graphite particles / carbon black) is 85/15. there were. Further, in the obtained resin current collector composition (solid content: 40%), the mass ratio of graphite particles to resin binder [graphite particles / resin binder (nonvolatile content)] was 25/75.

In-plane direction resistance values and film thickness direction resistance values were evaluated based on the following methods as the physical properties of the resin current collector obtained above and the laminated electrode. The results are shown in Table 1.
(In-plane resistance measurement)
The resin current collector composition is applied to a pet film with an applicator so that the dry film thickness is 40 μm, dried at 100 ° C. for 15 minutes, and then vacuum dried at 100 ° C. for 24 hours. A surface resistance measurement specimen formed on the film was obtained. The surface resistance value of this specimen for measuring surface resistance was measured using a 4-terminal 4-probe resistivity meter Loresta GP (manufactured by Mitsubishi Chemical Analytech Co., Ltd.).
(Evaluation criteria)
○: 10 ³ Ω / □ or more ×: Less than 10 ³ Ω / □ [Measurement of film thickness resistance]
The laminated electrode prepared in Example 1 was cut into 5 × 5 cm. In order to measure the resistance value, aluminum foils with aluminum tabs attached by ultrasonic welding are overlapped as shown in Fig. 2, and a 5 x 5 cm acrylic plate is stacked from above for pressing, and a load of 0.5 MPa is applied. While being applied, the resistance value between the aluminum tabs was measured so that the aluminum foils were not short-circuited.
(Evaluation criteria)
○: Less than 10 ⁰ Ω ×: 10 ⁰ Ω or more

From the results shown in Table 1, each of the laminated electrodes using the conductive layer obtained in each example is excellent in charge / discharge characteristics and also in the adhesion between the current collector and the conductive layer. It turns out that it is excellent. Especially, since the conductive electrode obtained in Examples 1-5 used the electroconductive carbon particle and carbon black together, it turns out that the charge / discharge characteristic is further excellent.

DESCRIPTION OF SYMBOLS 1 Separator 2 Negative electrode active material layer 3 Resin current collector 4 Positive electrode active material layer 5 Outermost layer current collector 6 Seal portion 7 Acrylic plate 10 Bipolar electrode

Claims (5)

  A resin current collector used for a lithium secondary battery, comprising a conductive agent containing conductive particles and a resin binder, wherein the particle diameter of the conductive particles is 0.5 of the thickness of the resin current collector layer. Resin current collector for bipolar lithium secondary battery, characterized in that the thickness of the resin current collector is 1 to 500 μm.   2. The resin current collector for a bipolar lithium secondary battery according to claim 1, wherein the resin current collector is a spherical conductive particle having a major axis / minor axis ratio (major axis / minor axis) value of 1 to 2.   The resin current collector for a bipolar lithium secondary battery according to claim 1, wherein the conductive agent further contains carbon black.   The resin current collector for a bipolar lithium secondary battery according to claim 3, wherein the mass ratio of the conductive particles to carbon black (conductive particles / carbon black) is 80/20 to 95/5.   A laminated electrode for a bipolar lithium secondary battery in which a resin current collector and an active material layer are sequentially laminated, wherein the resin current collector according to any one of claims 1 to 4 is used as the resin current collector. Laminated electrode for bipolar lithium secondary battery characterized by being used

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