JP2016111245A - Electrode for power storage device and power storage device using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrode for a power storage device of a large capacity and small internal resistance.SOLUTION: By using a porous metal having high porosity and a large specific surface area for a current collector, much amount of polarizable electrode materials are filled in the porous metal to increase a capacity. A porous current collector having a high specific surface area, it is possible to have a large contact area between the polarizable electrode and the porous metal and, as a result, internal resistance is reduced.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an electrode for a power storage device having a large capacity and having a good electrical conductivity between a current collector and an active material, and a power storage device using the same.

  In recent years, power storage systems related to power generation using natural energy such as solar power generation and wind power generation, power supplies for memory backup such as computers, power supplies for instantaneous voltage drop, power supplies for regeneration such as trains, power supplies for automobiles and construction machinery, etc. Various electric storage devices have been actively developed. In particular, electric double layer capacitors and lithium ion capacitors are attracting attention from the viewpoint of excellent input / output characteristics and reliability.

  The electric double layer capacitor is placed so that a pair of electrodes with a polarizable electrode material capable of electrostatically adsorbing and desorbing ions such as activated carbon on a current collector of a metal plate or a metal foil is placed across the separator. And an electricity storage device enclosed in an airtight container together with an electrolytic solution.

  A lithium ion capacitor is an asymmetrical electricity storage device that uses a polarizable electrode capable of electrostatically absorbing and desorbing ions such as activated carbon as a positive electrode and an electrode capable of occluding and releasing lithium ions such as hard carbon as a negative electrode.

  Currently, these electricity storage devices mainly use perforated or non-porous metal foils or expanded metals as current collectors, but in addition to this, they form holes that communicate with each other for the purpose of increasing the capacity. An electrode to which a porous metal composed of a metal skeleton is applied has been proposed.

  As such a porous metal, Patent Document 1 discloses porous aluminum having a porosity of 80 to 99.5%, an average number of pores crossed by a straight line having a length of 1 cm, and a thickness of 0.3 to 5 mm. The electrode is characterized in that it is applied to or poured into a sheet-shaped current collector to be dried and then compacted by a press to have a thickness of 0.2 to 2 mm and a porosity of 5 to 35%.

  Patent Document 2 discloses that a porous body mainly composed of aluminum used for a current collector has an aluminum content of 95 wt% or more, an average pore diameter of 200 μm or more and 800 μm or less, and a thickness of 0.2 mm or more and 3 mm or less. It is described that it is characterized.

  However, the porous metal used only paying attention to the porosity, constituent components, pore diameter, and thickness is formed from a thin rod-shaped metal skeleton as expressed in a network shape, and has few irregularities on the surface of the metal skeleton. For this reason, the contact area between the polarizable electrode filled in the porous metal and the porous metal is small, and a sufficient internal resistance reduction effect has not been obtained.

Japanese Patent No. 3591055 JP2011-254030

  In view of the above problems, an object of the present invention is to provide an electrode for an electricity storage device having a high capacity and a small internal resistance.

  As a result of repeated studies to solve the above problems, the present inventors have found that the use of a porous metal having a high specific surface area for the current collector is effective in reducing the internal resistance of the electrode.

The present invention has the following configuration.
(1) An electrode in which a polarizable electrode material is filled in the pores of a current collector made of a porous metal, wherein the porous metal has an average pore diameter of 50 μm or more and 1000 μm or less, and a specific surface area of 0.1 m ² / g. It is the above, The electrode for electrical storage devices characterized by the above-mentioned.
(2) The electrode for an electricity storage device, wherein the porous metal is made of aluminum or an aluminum alloy.
(3) An electricity storage device comprising the electrode according to any one of claims 1 and 2 as at least one electrode.

  The electrode for an electricity storage device according to the present invention uses a porous metal having a high porosity and a large specific surface area as a current collector, thereby filling the porous metal with a large amount of polarizable electrode material to achieve a high capacity. it can. Further, since the porous current collector has a high specific surface area, a large contact area between the polarizable electrode and the porous metal can be obtained, and as a result, the internal resistance of the electricity storage device using the electricity storage device electrode is reduced. Reduced.

  Hereinafter, the electrode for an electricity storage device according to the present invention will be specifically described.

(A) Electrode for electricity storage device The electrode for electricity storage device of the present invention is an electrode in which a polarizable electrode material is filled in the pores of a current collector made of a porous metal, the positive electrode and the negative electrode of an electric double layer capacitor, Or it is an electrode applicable to the positive electrode of a lithium ion capacitor. The pores of the porous metal may be filled together with additives such as a conductive additive and a binder in addition to the polarizable electrode material.

  The filling of the polarizable electrode material into the porous metal hole as a current collector is, for example, a method of reducing the pressure in a state where the porous metal is immersed in a suspension in which the polarizable electrode material is suspended in a solvent. The suspension is placed on one side of the porous metal and pressurized from the suspension side, or the side opposite to the side on which the suspension is placed is decompressed and the suspension is placed in the porous metal hole. Known methods can be used such as a method of passing through and a method in which a suspension is placed on a porous metal and pressed with a spatula or the like to be introduced into the hole. A conductive additive or a binder can be added to the suspension composed of the polarizable electrode material and the solvent. In addition, a thickener for viscosity adjustment may be added, and a dispersant may be added to obtain a good dispersion state. The viscosity of the suspension is preferably adjusted to be 0.5 to 10 Pa · s. The suspension is prepared using a device such as a planetary mixer, a ball mill, a Henschel mixer, or the like.

  The porous metal in which the polarizable electrode material is filled in the pores provides an electrode for an electricity storage device by removing the solvent by drying at 50 to 200 ° C. After drying, pressurize with a roll press or flat plate press as necessary to increase the density of the polarizable electrode material filled in the porous metal or adjust the thickness of the electrode for the electricity storage device. Can do.

(B) Porous metal The porous metal of the present invention is classified as an open cell type, has pores defined by a metal skeleton, and the pores communicate with each other to form a porous metal surface. Holes that are not located in the space are also connected to the outside. The average pore diameter of the porous metal is preferably 50 μm or more and 1000 μm or less, and more preferably 100 μm or more and 500 μm or less. Here, the pore diameter refers to the longest part of the pores defined by the metal skeleton when the cross section of the porous metal is observed with a scanning electron microscope or the like. Then, the average pore diameter is determined by taking the arithmetic average of 10 or more locations. When the pore diameter is too small, it becomes difficult to fill the polarizable electrode material. On the other hand, if the pore diameter is too large, the retainability of the polarizable electrode material is lowered, and the capacity is reduced when charging and discharging are repeated. Moreover, the thickness of a porous metal is 0.2-3 mm from a viewpoint of the function as an electrode.

The porous metal preferably has a large specific surface area in order to increase the contact area with the polarizable electrode material and the conductive additive, and the specific surface area of the porous metal is 0.1 m ² / g or more. Although it is not a problem that the specific surface area is too large, since the effect of reducing the internal resistance reaches its peak, it is sufficient if it is about 1 m ² / g. In order to realize a large specific surface area, irregularities are formed on the surface of the metal skeleton constituting the porous metal. This unevenness is, for example, a method using a metal powder shape used as a raw material for porous metal, a chemical method using a treatment liquid such as acid or alkali, and an electrochemical method such as an electrolytic surface roughening method. Etc. can be used.

  The porosity of the porous metal is preferably 80% or more and 95% or less in order to ensure a sufficient filling amount of the polarizable electrode material. Here, the porosity is determined from the size and mass of the porous metal before filling with the polarizable electrode material, and the density of the metal skeleton constituting the porous metal. If the porosity is less than 80%, a sufficient filling amount cannot be ensured. On the other hand, if the porosity exceeds 95%, the strength necessary for the electrode cannot be maintained.

  As the material of the porous metal, aluminum, titanium, nickel, copper, platinum, gold and alloys thereof, stainless steel, and the like can be used from the viewpoint of the anti-electrolytic property, but the anti-electrolytic property, conductivity, cost, Aluminum and aluminum alloys are most preferable from the viewpoint of density and the like.

(C) Polarizable electrode material Examples of the polarizable electrode material according to the present invention include activated carbon, carbon nanotube, graphite, graphene, and carbon nanohorn. The activated carbon can use what is marketed for electric double layer capacitors. Examples of the activated carbon material include wood, coconut shell, pulp waste liquid, coal, heavy petroleum oil, coal / petroleum pitch, and resins such as phenol resins. Generally, it is preferable to use a polarizable electrode material having a large specific surface area because the electrode capacity of the electrode for an electricity storage device is increased when a polarizable electrode material having a large surface area is used. The specific surface area of the polarizable electrode material is preferably 300 to 4000 m ² / g. The particle size of the polarizable electrode material is preferably 20 μm or less.

(D) Solvent An organic solvent or water can be used as a solvent for obtaining a paste in which a polarizable electrode material is dispersed. When a binder is added to the paste, a solvent is selected in consideration of the solubility or dispersibility of the binder. As the organic solvent, acetone, acetonitrile, dimethyl carbonate, ethyl acetate, butyl acetate, tetrahydrofuran, methyl ethyl ketone, toluene, xylene, N-methylpyrrolidone and the like can be used.

(E) Conductive aid By adding the polarizable electrode material to the porous metal, the resistance of the electricity storage device can be reduced. As the conductive assistant, carbon black such as acetylene black and ketjen black, graphite such as natural graphite and artificial graphite, carbon fiber, ruthenium oxide and the like can be used. The conductive additive is preferably added at 0 to 20 parts by mass with respect to 100 parts by mass of the polarizable electrode material.

(F) Binder By adding a binder to the electrode mixture, binding of the components via the binder, that is, bonding between the positive electrode active materials, between the conductive assistants, and between the positive electrode active material and the conductive auxiliary agent. Becomes stronger, and the falling off of the active material from the current collector is less likely to occur. The binder is not particularly limited, and a known or commercially available binder can be used. For example, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinylpyrrolidone (PVP), polyvinyl chloride (PVC), polyethylene (PE), polypropylene (PP), ethylene-propylene copolymer, styrene butadiene rubber (SBR), polyvinyl alcohol (PVA), carboxymethyl cellulose (CMC) and the like. The binder is preferably added at 0 to 20 parts by mass with respect to 100 parts by mass of the polarizable electrode material.

(Method for producing porous metal)
Below, the manufacturing method of the porous aluminum by the space holder method is demonstrated as an example of the manufacturing method of a porous metal.

  In the space holder method, after the mixed powder of aluminum powder and support powder is pressure-molded, the compact is heat-treated in an inert atmosphere and sintered, and finally the support powder is removed to obtain porous aluminum. can get. The porous aluminum may be integrated by pressing the mixed powder together with the metal plate. As shown in FIG. 1, the porous aluminum current collector is composed of a hole (space) 1 from which the supporting powder has been removed, and a sintered metal skeleton 2 that forms the periphery of the space 1. Many fine holes 3 are formed in the metal skeleton, and the space 1 has an open cell structure in which the fine holes 3 are connected to each other.

  Aluminum or aluminum alloy powder can be used as the aluminum powder, and these are used alone or in combination. In the case where the alloy components cause corrosion resistance deterioration under the usage environment, it is preferable to use aluminum powder. On the other hand, when it is desired to obtain higher strength, it is preferable to use aluminum alloy powder. Examples of the elements contained in the aluminum alloy powder include magnesium, silicon, titanium, manganese, iron, nickel, copper, and zinc.

  The particle size of the aluminum powder is preferably 1 to 20 μm. In order to increase the specific surface area of the porous aluminum, the particle size of the aluminum powder is preferably smaller, and more preferably 1 to 7 μm. The particle diameter of the aluminum powder is defined by the median diameter measured by the laser diffraction scattering method.

  As the aluminum powder, a powder containing the elements listed as elements contained in the aluminum alloy powder can be mixed and used. As such an additive element, a plurality of elements consisting of a single element selected from magnesium, silicon, titanium, iron, nickel, copper, zinc and the like or any combination of two or more are preferably used. Such a mixture forms an alloy of aluminum and an additive element by heat treatment. Depending on the type of additive element, an intermetallic compound of aluminum and the additive element is further formed. Various effects can be obtained by including such an aluminum alloy or an intermetallic compound. For example, in an aluminum alloy of aluminum and an additive element such as silicon or copper, the melting point of the aluminum powder is lowered and the temperature required for the heat treatment can be lowered, so that the energy required for production can be reduced and the strength by alloying can be reduced. Will improve. Further, when an intermetallic compound of aluminum and an additive element such as nickel is formed, heat is generated and sintering is promoted, and a structure in which the intermetallic compound is dispersed is formed, so that high strength can be achieved.

The addition amount of the additive element powder or additive element alloy powder to the aluminum powder is appropriately determined based on the chemical formula amount of the alloy or intermetallic compound to be formed.
The particle size of the additive element powder is preferably 1 to 20 μm. In order to achieve sufficient mixing with the pure aluminum powder, the aluminum alloy powder, and the support powder, it is preferably finer, and at least finer than the support powder is used. The particle diameter of the additive element powder is defined by the median diameter measured by the laser diffraction scattering method as in the case of the aluminum powder.

  As the support powder, one having a melting point higher than that of the aluminum powder is used. When the mixed powder is combined with a metal plate, a powder having a melting point higher than the lower melting point of the aluminum powder and the metal plate is used. As such a supporting powder, a water-soluble salt is preferable, and sodium chloride and potassium chloride are preferably used from the viewpoint of availability. Since the space formed by removing the support powder becomes pores of porous aluminum, the particle size of the support powder is reflected in the pore diameter. Therefore, for the production of the porous metal of the present invention, the particle size of the support powder is preferably 50 to 1000 μm. The particle size of the support powder is defined by the opening of the sieve.

  In the production of porous aluminum by the space holder method, the mixed powder may be used in a state of being integrated with a metal plate. The metal plate is a non-porous plate or foil, and a net-like body such as a perforated wire mesh or expanded metal. The metal plate serves as a support, and the strength of the porous aluminum current collector is improved and the conductivity is further improved. As the metal plate, a material that does not evaporate or decompose during heat treatment, specifically, a metal such as aluminum, titanium, iron, nickel, copper, or an alloy thereof can be suitably used.

When the mixed powder and the metal plate are integrated, for example, when a metal mesh is used for the metal plate, the mixed powder is filled in the mesh and the entire mesh is covered with the mixed powder. When filling the polarizable electrode material with porous aluminum provided with a metal skeleton on both sides of the metal plate, even if the metal plate is a perforated network, it can be filled from one side of the region divided by the metal plate, Since the other region can be filled, the metal plate is preferably a net-like body. Here, the perforated means a mesh part of a metal mesh, a punch part of a punching metal, a mesh part of an expanded metal, and a gap part between fibers of metal fibers.
The pore diameter of the pores of the network may be larger or smaller than the diameter of the holes obtained by removing the support powder from the joined mixed powder.
It is preferable that the aperture ratio of the perforated hole in the network is large so as not to impair the porosity of the porous aluminum current collector.

  The mixing ratio of the aluminum powder and the support powder is preferably such that Val / (Val + Vs), which is the volume ratio of the aluminum powder, is 5 to 20%, more preferably 7 to 15%, with the respective volumes being Val and Vs. . Here, the volumes Val and Vs are values obtained from the respective masses and densities. When the volume fraction of the aluminum powder exceeds 20%, the porous aluminum thus produced has a too low porosity, so that a sufficient amount of polarizable electrode material cannot be filled. On the other hand, when the volume ratio of the aluminum powder is less than 5%, the strength required for the electrode cannot be maintained.

  The mixing means for mixing aluminum with the support powder may be a vibration stirrer or a container rotating mixer, but is not particularly limited as long as a sufficient mixing state can be obtained.

  Further, the mixed powder and the metal plate may be combined when the mixed powder is filled in the molding die. As a composite form, a metal plate may be sandwiched between mixed powders, or a mixed powder may be sandwiched between metal plates. Further, the composite of the mixed powder and the metal plate can be repeated to make multiple stages. In the case of compounding, mixed powders having different particle sizes and mixing ratios of aluminum powder and support powder, and a plurality of different types of metal plates can be combined.

  The pressure during the pressure molding is preferably 200 MPa or more. By forming by applying sufficient pressure, the aluminum powders rub against each other, and the strong oxide film on the surface of the aluminum powder that inhibits the sintering of the aluminum powders is destroyed. This oxide film confines molten aluminum and prevents it from coming into contact with each other, and is inferior in wettability with molten aluminum and has the effect of rejecting liquid aluminum. Therefore, when the pressure of pressure molding is less than 200 MPa, the destruction of the oxide film on the surface of the aluminum powder is insufficient, and the aluminum melted during heating oozes out of the molded body to form a ball-shaped aluminum lump. There is a case. The porosity of porous aluminum becomes higher than the target by forming the aluminum lump. Therefore, the formation of such an aluminum lump is detrimental in that the porosity of the porous aluminum cannot be controlled. In addition, there is a problem in that the shape collapses due to the formation of an aluminum lump and must be removed. The porous aluminum wall on which the molding pressure is as large as the apparatus and mold used allow is strong, which is preferable. However, if it exceeds 400 MPa, the effect tends to be saturated. For the purpose of enhancing the releasability of the pressure-molded body, it is preferable to use a lubricant such as a fatty acid such as stearic acid, a metal soap such as zinc stearate, various waxes, synthetic resins, and olefinic synthetic hydrocarbons.

  The heat treatment is performed at a temperature not lower than the melting point of the aluminum powder to be used and lower than the melting point of the supporting powder. When the aluminum powder is integrated with the metal plate, heat treatment is performed at a temperature that is equal to or higher than the lower melting point of the aluminum powder and the metal plate and lower than the melting point of the support powder. The melting point of the aluminum powder is a temperature at which a liquid phase of pure aluminum or an aluminum alloy is generated, and the melting point of the metal plate is a temperature at which a liquid phase is similarly generated. By heating to a temperature at which a liquid phase is generated, the liquid phase oozes out from the aluminum powder, and the aluminum powders are bonded metallically by contacting the liquid phases. When the heat treatment temperature is lower than the melting point, aluminum is not melted, so that bonding between the aluminum powders and between the aluminum powder and the metal plate becomes insufficient. Moreover, when heated above the melting point, the aluminum covering the surface of the support powder located on the outermost surface of the sintered body is removed, and porous aluminum having a surface with a large aperture ratio is formed. A large aperture ratio of the sintered body is advantageous for filling the polarizable electrode material.

  When the heating temperature is equal to or higher than the melting point of the support powder, the support powder melts and the shape may be lost. Therefore, heating is performed at a temperature lower than the melting point of the support powder. When a water-soluble salt such as sodium chloride or potassium chloride is used as the support powder, the heat treatment is preferably performed at a temperature lower than 700 ° C., more preferably lower than 680 ° C. In addition, the higher the temperature, the lower the viscosity of the molten aluminum, and the molten aluminum oozes out to the outside of the pressure-molded body, forming a convex aluminum lump. By forming an aluminum lump, the porosity of porous aluminum becomes higher than intended. The formation of such an aluminum lump is detrimental in that the porosity of porous aluminum cannot be controlled. In addition, there is a problem in that the shape collapses due to the formation of an aluminum lump and must be removed. The heat holding time in the heat treatment is preferably about 1 to 60 minutes. In addition, a load may be applied to the pressure-formed body during heat treatment to compress the pressure-formed body, or heating and cooling may be repeated a plurality of times.

The inert atmosphere in which the heat treatment is performed is an atmosphere that suppresses oxidation of aluminum, and an atmosphere of vacuum; nitrogen, argon, hydrogen, decomposed ammonia, and a mixed gas thereof is preferably used, but a vacuum atmosphere is particularly preferable. The vacuum atmosphere is preferably 2 × 10 ⁻² Pa or less, more preferably 1 × 10 ⁻² Pa or less. When it exceeds 2 × 10 ⁻² Pa, removal of moisture adsorbed on the surface of the aluminum powder becomes insufficient, and oxidation of the aluminum surface proceeds during heat treatment. As described above, the oxide film on the aluminum surface is inferior in wettability with liquid aluminum, and as a result, molten aluminum oozes out to form a ball-like lump. In the case of an inert gas atmosphere such as nitrogen, it is preferable that the oxygen concentration is 1000 ppm or less and the dew point is −30 ° C. or less.

  A method of removing the supporting powder in the sintered body by eluting the supporting powder in water is suitably used. The supporting powder can be easily eluted by a method such as immersing the sintered body in a sufficient amount of water bath or flowing water bath. When a water-soluble salt is used as the support powder, the water for eluting it is preferably free from impurities such as ion exchange water or distilled water, but tap water is not particularly problematic. The immersion time is usually appropriately selected within the range of several hours to 24 hours. Elution can be promoted by applying vibration by ultrasonic waves or the like during the immersion. After removing the supporting powder, the porous aluminum is obtained by drying. For drying, a known method can be used, and natural drying may be used.

  When using the porous metal as a current collector, a lead portion can be provided in the porous metal for the purpose of facilitating the movement of electrons between the current collector and the outside of the electricity storage device. The lead portion can be formed, for example, by bonding a metal lead to a part of the porous metal. For the joining, a known method such as spot welding, ultrasonic welding, or adhesion using a conductive adhesive can be used. The lead portion may be formed before or after filling with the polarizable electrode material.

  Hereinafter, an electricity storage device according to the present invention will be described. The electric storage device targeted by the present invention is specifically an electric double layer capacitor or a lithium ion capacitor, and the electrode for the electric storage device of the present invention is used for both positive and negative electrodes in an electric double layer capacitor, and in the positive electrode in a lithium ion capacitor. .

(F) Electric Double Layer Capacitor In the electric double layer capacitor of the present invention, the electrodes for the electricity storage device are arranged with the surfaces facing each other with the separator interposed therebetween. The electricity storage device electrode is divided into a positive electrode and a negative electrode in constituting the electric double layer capacitor, but there is no particular difference between the positive electrode and the negative electrode in the electricity storage device electrode. The positive and negative electrodes for the electricity storage device are sealed in the case while being immersed in the electrolyte together with the separator.

(G) Separator A known or commercially available separator can be used. For example, an insulating microporous film made of polyolefin, polyethylene terephthalate, polyamide, polyimide, cellulose, glass fiber or the like. The separator preferably has a pore diameter of 0.01 to 5 μm and a thickness of 10 to 100 μm.

(H) Electrolytic Solution Although there are aqueous and non-aqueous electrolytic solutions, it is preferable to use a non-aqueous electrolytic solution because the operating voltage can be set high. As the non-aqueous electrolytic solution, an electrolyte prepared by dissolving an electrolyte in an aprotic organic solvent or an ionic liquid can be used. Examples of the aprotic organic solvent include cyclic carbonates such as ethylene carbonate, propylene carbonate, and butylene carbonate, chain carbonates such as dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, and ethyl methyl carbonate, tetrahydrofuran, 2-methyltetrahydrofuran, Ethers such as 1,4-dioxane, 1,2-dimethoxyethane, 1,2-dibutoxyethane, cyclic esters such as γ-butyrolactone, nitriles such as acetonitrile, esters such as methyl propionate, amides such as dimethylformamide , Methyl acetate, methyl formate and the like, and these can be used alone or in combination. Examples of the electrolyte include lithium salts such as lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium bis [trifluoromethanesulfonyl] imide, tetraethylammonium tetrafluoroborate, triethylmethylammonium tetrafluoroborate, and the like. These can be used alone or in combination. An ionic liquid is a salt that exists in a liquid at 100 ° C. or lower. Examples of ionic liquids include 1-ethyl-3-methylimidazolium tetrafluoroborate, 1-ethyl-3-methylimidazolium-bis (fluorosulfonyl) imide, 1-ethyl-3-methylimidazolium-bis (trifluoromethanesulfonyl). ) Imido, 1-butyl-3-methylimidazolium-bis (trifluoromethanesulfonyl) imide, 1-hexyl-3-methylimidazolium tetrafluoroborate, 1-hexyl-3-methylimidazolium-bis (trifluoromethanesulfonyl) Imido, 1-ethyl-3-methylimidazolium-fluorohydrogenate, N, N-diethyl-N-methyl-N- (2-methoxyethyl) -tetrafluoroborate, N, N-diethyl-N-methyl- N- (2-methoxyethyl) -bis (Trifluoromethanesulfonyl) imide, N-methyl-N-propylpiperidinium-bis (trifluoromethanesulfonyl) imide, triethylsulfonium-bis (trifluoromethanesulfonyl) imide, N-methyl-Npropylpyrrolidinium-bis (trifluoro) (Romethanesulfonyl) imide, triethyloctylphosphonium-bis (trifluoromethanesulfonyl) imide, N-methyl-methoxymethylpyrrolidinium-tetrafluoroborate and the like, and these can be used alone or in combination. Further, the electrolyte may be dissolved in an ionic liquid. The concentration of the electrolyte is preferably 0.1 to 5 mol / L.

(G) Lithium Ion Capacitor In the lithium ion capacitor of the present invention, the electrode for the electricity storage device is disposed with the separator sandwiched therebetween, the negative electrode and the surface facing each other, and sealed in a case in a state immersed in an electrolytic solution. For the negative electrode, a capacitor having a larger capacity than the electrode for the electricity storage device facing is used, and a metal lithium foil is pressure-bonded to the surface of the negative electrode facing the electrode for the energy storage device. Although the same thing as an electrical double layer capacitor can be used for a separator and electrolyte solution, the electrolyte containing said lithium salt can be used for electrolyte solution.

(H) Negative electrode The negative electrode, which is one of the constituent elements of the lithium ion capacitor, is integrated with the negative electrode current collector by a method such as coating or filling of a negative electrode mixture containing a negative electrode active material capable of occluding and releasing lithium ions. It has been made. The coating and filling can be generally carried out by a known method in a state where the negative electrode active material is suspended in a solvent, similarly to the production of the electrode for an electricity storage device of the present invention. In addition to the negative electrode active material, a conductive additive, a binder, a thickener, a dispersant, and the like can be added to the negative electrode mixture, and the power storage device of the present invention includes a solvent that dissolves and suspends these. The materials used in the production of the electrodes for the use can be used. Although there is no restriction | limiting in particular in the dimension of a negative electrode, It is preferable to enlarge a capacity | capacitance compared with a positive electrode.

(I) Negative electrode active material The negative electrode active material is a material that can reversibly absorb and release lithium ions. Specifically, natural graphite, artificial graphite, mesocarbon microbeads (MCMB), carbon materials such as hard carbon and soft carbon, metal materials and alloy materials that can be combined with lithium such as Al, Si, and Sn, titanium An oxide material such as lithium acid (Li ₄ Ti ₅ O ₁₂ ) can be used.

(J) Negative electrode current collector As the negative electrode current collector, a porous or non-porous metal foil, an expanded metal, a porous metal, or the like can be used. Examples of the material include aluminum, titanium, nickel, copper, platinum, gold and alloys thereof, and stainless steel.

  The present invention will be specifically described below with reference to invention examples and comparative examples. The present invention is not limited to the following invention examples and comparative examples.

(Invention Examples 1 to 10 and Comparative Examples 11 to 14)
First, as a porous metal used for the positive electrode for a nonaqueous electrolyte secondary battery according to the present invention, porous aluminum was produced as follows.
The following pure aluminum powders (A1 to A3) having different particle diameters were used as the aluminum powder. In addition, sodium chloride powders (B1 to B6) having different particle diameters and potassium chloride (C1) on a sieve having a sieve opening of 300 μm and a sieve of 212 μm were used as the support powder. As shown in Table 1, each powder was mixed at a predetermined volume ratio to prepare a mixed powder.

A mold having a hole with a diameter of 20 mm was filled with the above-mentioned mixed powder with a predetermined mass, and pressure-molded at 400 MPa. A sintered body is produced by heat-treating the pressure-formed body at 670 ° C. in an atmosphere having a maximum ultimate pressure of 1 × 10 ⁻² Pa or less, and the obtained sintered body is subjected to running water (tap water) at 20 ° C. The support powder was eluted by immersing in it for 6 hours. As a result, porous aluminum samples (φ20 mm) having a thickness of 1 mm with different porosities were prepared (samples 1 to 13).

<Pure aluminum powder, (aluminum purity 99.7 mass% or more, melting point 660 ° C.)>
A1: Median diameter 3μm
A2: Median diameter 7 μm
A3: Median diameter 17 μm

<Sodium chloride powder (melting point: 800 ° C.)>
B1: sieve opening 53-106 μm
B2: Sieve opening 106-212 μm
B3: Sieve opening 212-300 μm
B4: Sieve opening 300 to 425 μm
B5: sieve opening 425-500 μm
B6: Sieve opening 500 to 710 μm
<Potassium chloride powder (melting point: 776 ° C.)>
C1: Sieve opening particle diameter of 212 to 300 μm

  Next, using the porous aluminum current collector sample, an electrode for an electricity storage device according to the present invention was produced as follows.

(Production of electrodes for power storage devices)
Activated carbon derived from coconut shell as a polarizable electrode material (specific surface area 1000 m ² / g); acetylene black as a conductive aid; SBR as a binder; CMC as a thickener; distilled water as a solvent; As mass parts, 11.8 parts by mass of acetylene black, 3.5 parts by mass of SBR, 3.5 parts by mass of CMC, and 270 parts by mass of distilled water were mixed to prepare a suspension.

A porous aluminum sample (samples 1 to 13) punched in a circle with an area of 2 cm ² was placed on a filter paper having a pore diameter of 1 μm, and the side opposite to the porous aluminum sample was decompressed with a rotary pump through the filter paper. The suspension was supplied to the porous aluminum sample side which is the high pressure side through the filter paper, and the suspension was filtered through the filter paper while allowing the suspension to penetrate into the porous aluminum sample. Filtration of the suspension was continued until the surface of the porous aluminum sample was completely covered by the suspension filtrate. Thereafter, the filtrate not filled in the pores around the porous aluminum sample was removed by removing with a spatula. After removing the filtrate, the porous aluminum sample was dried at 80 ° C. for 1 hour. After drying, the porous aluminum sample was pressed at a pressure of 100 MPa using a flat plate press to obtain an electrode for an electricity storage device. The porous aluminum current collector sample 12 was not used for producing an electrode for an electricity storage device because the porosity was too high to keep the shape. As a comparison, the above suspension was applied to an A1085 aluminum foil to prepare a coated electrode (Comparative Example 10). The gap during coating was 400 μm, and drying was performed under the same conditions as the porous aluminum sample.

  Table 1 shows the porosity, specific surface area, and amount of activated carbon per unit area of the porous aluminum sample. The specific surface area was calculated | required by BET method from the adsorption isotherm by the constant capacity type gas adsorption method using BELSORP-mini2 by Nippon Bell Co., Ltd. Moreover, the amount of activated carbon per unit area is a value obtained by dividing the difference between the mass before filling the porous aluminum sample and the mass when the suspension is filled and dried, by the electrode area. Here, the electrode area is an area filled with activated carbon. In comparison with the amount of activated carbon of the coated electrode of Comparative Example 10, more than this was passed and less was rejected. In addition, when the gap at the time of coating was made larger than 400 μm, the strain generated at the time of drying was large, and the composite layer was cracked and could not be used as an electrode. Is considered the upper limit of the coated electrode.

(Production of electric double layer capacitor)
Each of the two pressed electrodes for the electricity storage device was opposed to each other with a separator interposed therebetween, and an electrolytic solution was injected, and then housed in an R2032-type coin cell case to produce an electric double layer capacitor. A separator made of cellulose fiber (“TF4035” manufactured by Nippon Kogyo Paper Industries Co., Ltd.) was used as the separator, and propylene carbonate in which triethylmethylammonium tetrafluoroborate was dissolved at 1.0 mol / L was used as the electrolyte.

(Evaluation)
The electric resistance when an alternating voltage of 1 kHz was applied to the electric double layer capacitor produced as described above was measured, and the internal resistance was calculated. The amplitude of the voltage was 10 mV. When the internal resistance of the coated electrode of Comparative Example 11 was 1.82Ω or less, it was passed, and when it was larger than that, it was rejected.

  In Invention Examples 1 to 10, the thickness of the positive electrode and the active material filling ratio were within the range defined by the present invention, and the amount of activated carbon per unit area and the internal resistance were acceptable.

  In the coated electrode of Comparative Example 11, the amount of activated carbon as in the invention example could not be achieved, and the internal resistance was high because the area of the current collector in contact with the composite material was small.

  In Comparative Example 12, since the porosity of the porous aluminum current collector was too low, a sufficient amount of activated carbon could not be achieved.

  In Comparative Example 13, since the porosity of the porous aluminum current collector was too high, the porous aluminum could not keep its shape, and the electrode for the electricity storage device in which the electrode mixture was filled in the pores of the porous aluminum current collector was I couldn't make it. Therefore, the amount of activated carbon could not be measured, and the battery performance could not be evaluated.

  In Comparative Example 14, since the specific surface area was too small, the contact area with the composite was insufficient and the internal resistance was high.

(Production of lithium ion capacitor)
Each one of the pressed electrodes for each electric storage device was opposed to the negative electrode with a separator interposed therebetween, and an electrolyte was injected, and then housed in an R2032-type coin cell case to produce an electric double layer capacitor. As the negative electrode, an electrode obtained by coating natural spherical graphite on copper foil at 5.3 mg / cm 2 was used. This negative electrode was immersed together with a metallic lithium foil in a mixed solution of ethylene carbonate and ethyl methyl carbonate (volume ratio of 3: 7) in which 1.0 mol / L LiPF ₆ was dissolved. After short-circuiting for 2 hours and pre-doping, the cell was prepared. The separator is a cellulose fiber separator (“TF4035” manufactured by Nippon Kogyo Paper Industry Co., Ltd.), and the electrolyte is a mixed solution of ethylene carbonate and ethyl methyl carbonate (volume ratio) in which 1.0 mol / L LiPF ₆ is dissolved. 3: 7) was used.

(Evaluation)
With respect to the lithium ion capacitor produced as described above, the current when an AC voltage of 10 Hz was applied was measured, and the internal resistance was calculated. The amplitude of the voltage was 10 mV. When the internal resistance of the coated electrode of Comparative Example 24 was 6.79Ω or less, it was accepted, and when it was larger than that, it was rejected.

  In Invention Examples 15 to 24, the thickness of the positive electrode and the active material filling ratio were within the range defined by the present invention, and the amount of activated carbon per unit area and the internal resistance were acceptable.

  In the coated electrode of Comparative Example 25, the amount of activated carbon as in the inventive example could not be achieved, and the internal resistance was high because the area of the current collector in contact with the composite material was small.

  In Comparative Example 26, since the porosity of the porous aluminum current collector was too low, a sufficient amount of activated carbon could not be achieved.

  In Comparative Example 27, since the specific surface area was too small, the contact area with the composite was insufficient and the internal resistance was high.

  The electrode for an electricity storage device according to the present invention uses a porous metal having a high porosity and a large specific surface area as a current collector, thereby filling the porous metal with a large amount of polarizable electrode material to achieve a high capacity. In addition, since the porous current collector has a high specific surface area, a large contact area between the polarizable electrode and the porous metal can be obtained, and as a result, the internal resistance of the electricity storage device can be reduced.

It is explanatory drawing of porous aluminum. DESCRIPTION OF SYMBOLS 1 ... The hole (space) of a porous aluminum electrical power collector 2 ... The joint metal powder wall of a porous aluminum electrical power collector 3 ... The micropore formed in the joint metal powder wall

Claims (3)

An electrode in which a polarizable electrode material is filled in pores of a current collector made of a porous metal, wherein the porosity of the porous metal is 80% or more and 95% or less, and a specific surface area is 0.1 m ² / g or more. The electrode for electrical storage devices characterized by the above-mentioned.   The electrode for an electricity storage device, wherein the porous metal is made of aluminum or an aluminum alloy.   An electricity storage device, wherein the electrode according to claim 1 or 2 is used for at least one of the electrodes.

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