JP2013243063A - Method of manufacturing electrode using porous metal collector - Google Patents

Abstract

An object of the present invention is to provide a method for producing an electrode using a porous metal current collector, which can be filled with a high density of an electrode mixture containing an active material in the pores of the current collector made of a porous metal.
A method for manufacturing an electrode containing an electrode mixture containing an active material, the method comprising a hole defined by a metal wall, wherein the holes communicate with each other through a small hole formed in the metal wall. Impregnating a current collector made of porous metal with a slurry in which the electrode mixture is dispersed in a solvent; drying the porous metal impregnated with the slurry to scatter and evaporate the solvent; Filling a hole with the electrode mixture; and a particle size of the electrode mixture is ¼ or less of a circle-equivalent diameter of the small hole. The manufacturing method of the electrode used.
[Selection] Figure 1

Description

  The present invention relates to a method for producing an electrode using a porous metal current collector, which can be filled with an electrode mixture containing an active material in pores of the porous metal at a high packing density.

  A metal foil such as an aluminum foil or a copper foil is generally used as an electrode current collector (support) that carries the positive electrode material or the negative electrode material. As such a metal foil, a porous aluminum current collector has been proposed (Patent Documents 1 and 2).

Patent Document 1 describes a high energy density electrode in which porous aluminum having a characteristic metal skeleton cross-sectional shape is filled with an active material. This porous aluminum forms a metal film that forms a low-melting eutectic alloy with aluminum on the skeleton of foamed resin, and after depositing aluminum powder on it, the foamed resin is burned off and the metals are sintered together To obtain.
Patent Document 2 describes a high energy density current collector in which titanium is used as a sintering aid and porous aluminum produced by a slurry foaming method is filled with an active material.

  However, the conventional electrode using the porous aluminum current collector has a problem that the amount of the active material filled in the pores of the porous aluminum is not sufficient, and a desired electrode capacity cannot be obtained.

JP-A-8-170126 JP 2010-236082 A

  An object of the present invention is to provide a method for producing an electrode using a porous metal current collector that can be filled with an electrode mixture containing an active material at high density in the pores of the current collector made of the porous metal. That is.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have determined that the particle size of the electrode mixture containing the active material is smaller than the small holes opened in the metal wall constituting the porous metal current collector to be filled. By setting it to a predetermined ratio or less with respect to the dimensions, the electrode mixture can smoothly pass through the small holes communicating with each other, and as a result, the filling amount of the electrode mixture into the holes is increased. I found out that I can do it.

  That is, the present invention provides a method for producing an electrode containing an electrode mixture containing an active material according to claim 1, having pores defined by a metal wall, and a small hole formed in the metal wall. Impregnating a current collector made of a porous metal in which pores communicate with each other by a slurry impregnated with the electrode mixture in a solvent; drying the porous metal impregnated with the slurry into a solvent And a step of filling the pores with the electrode mixture into the pores, the particle diameter of the electrode mixture being ¼ or less of the circle equivalent diameter of the small holes An electrode manufacturing method using a porous metal current collector was adopted.

  According to a second aspect of the present invention, in the first aspect, after the filling step of the electrode mixture, the method further includes a step of pressing a porous metal in which pores are filled with the electrode mixture.

  By the electrode manufacturing method using the porous metal current collector according to the present invention, an electrode in which the electrode mixture containing the active material is filled in the pores of the porous metal current collector with high density is obtained. High energy density lithium ion secondary batteries and capacitors can be manufactured.

It is a scanning electron micrograph which shows the cross section of the porous aluminum electrical power collector used for this invention.

  In the method of manufacturing an electrode using a porous metal current collector, which includes an electrode mixture containing an active material according to the present invention, the electrode has pores defined by a metal wall, and is formed on the metal wall. A porous metal in which pores communicate with each other through small holes is used as a current collector. First, the porous metal is impregnated with a slurry in which an electrode mixture is dispersed in a solvent. Next, the porous metal impregnated with the slurry is dried to scatter and evaporate the solvent, whereby the electrode mixture is filled into the pores. The particle size of a component such as an active material in the electrode mixture is regulated to ¼ or less of the equivalent circle diameter of the small hole. In addition, it is preferable to further press the porous metal in which the electrode mixture is filled in the pores.

1. Porous metal 1-1. Structure and Shape As shown in FIG. 1, the porous metal used in the present invention is a porous sintered body having a metal wall 2 formed by sintering metal powder as a skeleton. A number of pores 1 are formed in the porous metal, and the pores 1 are defined by metal walls 2. A small hole 3 is opened in the metal wall 2, and the holes 1 communicate with each other through the small hole 3. The electrode mixture containing the active material filled in the holes 1 is held so as to be enclosed by the metal wall 2 surrounding the holes 1.

  The shape of the porous metal can be an arbitrary shape such as a sheet shape or a cylindrical shape depending on the electrode shape. The thickness is preferably about 200 μm to 1 mm, and the pore diameter is preferably about 10 to 1000 μm. Here, the pore diameter refers to the maximum length of pores appearing in the cross section when the cross section of the porous metal is observed. The small holes 3 formed in the metal wall 2 have various shapes such as a circle, an ellipse, and a rectangle. As will be described later, the particle diameter of the component having the largest average particle diameter among the electrode mixture components such as the active material is defined to be ¼ or less of the equivalent circle diameter of the small holes 3. By doing so, the electrode mixture component contained in the slurry can smoothly pass through the small holes 3, and a large amount of the electrode mixture component can be filled in the pores 1.

1-2. Porosity The porosity of a porous metal is defined by the porosity. The porosity of the porous metal used in the present invention is preferably 80 to 95%. If it is less than 80%, the pores 1 may not be filled with a large amount of the electrode mixture component. On the other hand, if it exceeds 95%, the strength of the porous metal itself may be insufficient and the function as a current collector may not be achieved.

The porosity p (%) of the porous metal is calculated by the following formula (1).
p = [{hv− (hw / d)} / hv] × 100 (1)
Here, hv: the total volume of the porous metal (cm ³ )
hw: Mass of porous metal (g)
d: Density (g / cm ³ ) of the metal material.

2. Electrode mixture The electrode mixture to be used is supported in a state filled in the pores of the porous metal. The electrode mixture may contain a conductive additive and a binder in addition to the active material.

2-1. Active material The active material used is suitable for the battery in which the electrode is used. When the electrode according to the present invention is used, for example, as a positive electrode for a nonaqueous electrolyte secondary battery, the positive electrode active material may be a lithium metal oxide such as lithium cobaltate, lithium manganate, lithium nickelate, or lithium iron phosphate. Etc. can be used. When used for a negative electrode for non-aqueous electrolyte secondary batteries, the negative electrode active material includes natural graphite, artificial graphite, mesocarbon microbeads (MCMB), carbon materials such as hard carbon and soft carbon; Al, Si, Sn, etc. Metal materials and alloy materials that can be combined with lithium; oxide materials such as lithium titanate (Li ₄ Ti ₅ O ₁₂ ) can be used.

2-2. Conductive aid By adding a conductive aid to the electrode mixture, the conductivity of the electrode mixture is improved. As the conductive aid used, carbon powder, metal powder, and the like are used, and among these, carbon powder is preferably used. Examples of the carbon powder include acetylene black, ketjen black, furnace black, and carbon nanotube. Among these, it is preferable to use acetylene black that has a relatively long length as an aggregate and can improve conductivity even when the addition amount is small.

2-3. Binder By adding a binder to the electrode mixture, the binding of components via the binder, that is, the bonding between the active materials, the conductive assistants, and the active material and the conductive assistant is strengthened. This makes it difficult for the active material to fall off the current collector. It does not specifically limit as a binder to be used, A well-known or commercially available thing 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.

  When a conductive additive and a binder are added to the electrode mixture, the ratio of the active material to the total electrode mixture (active material + conductive additive + binder) is 85 to 95% by mass. preferable. If this ratio is less than 85% by mass, the active material may be insufficient and high electrode capacity may not be achieved. On the other hand, if this ratio exceeds 95% by mass, the conductivity of the entire electrode is reduced, and sufficient coupling between components and between components cannot be obtained, and this also makes it impossible to achieve high electrode capacity.

2-4. Packing density of electrode mixture The packing density of an electrode mixture containing an active material is defined as the mass of the electrode mixture filled per unit volume of pores in the porous metal. Specifically, it calculates | requires as follows. First, the volume of pores (cm ³ ) in the electrode is obtained by subtracting the volume of the metal material obtained by dividing the mass of the porous metal by the density of the metal material constituting the porous metal from the total volume of the electrode. Next, the mass (g) of the electrode mixture is obtained by subtracting the mass of the porous metal before filling the electrode mixture from the total mass of the porous metal after filling. Finally, the mass (g) of the electrode mixture is divided by the pore volume (cm ³ ), and the amount of electrode mixture (g / cm ³ ) filled in the pores per unit volume is obtained to determine the packing density and To do.

Such a packing density is preferably 50% or more of the composite density. Here, the composite material density refers to the density of the composite material layer obtained by applying the composite material slurry to the aluminum foil in the manner of providing the composite material layer and drying it. The composite density is the value obtained by subtracting the mass (g) of the aluminum foil from the total mass (g) of the aluminum foil coated with the composite slurry, and the aluminum foil from the total volume (cm ³ ) of the aluminum foil coated with the composite slurry. Divided by the value obtained by subtracting the volume (cm ³ ). When the packing density is less than 50% of the composite material density, the amount of active material contained in the electrode is small and sufficient electrode capacity cannot be obtained. On the other hand, the upper limit of the packing density is not particularly limited. However, when the packing density after the press treatment exceeds 250% of the composite material density, it becomes difficult for the electrolyte solution to penetrate into the electrode, and the charged component such as lithium ion does not reach In some cases, diffusion is hindered and battery characteristics are deteriorated.

3. Manufacturing method of electrode 3-1. Method for producing porous metal After pressure-molding a mixed powder of metal powder and support powder at a predetermined pressure, the pressure-molded body in an inert atmosphere at a temperature not less than 0.5 times the melting point of the metal powder, And it sinters by the heat processing in the range which does not exceed 1.05 times the melting | fusing point of metal powder, and a porous metal is manufactured by removing a support powder after that.

(A) Metal powder The metal powder used in the present invention includes pure aluminum powder, aluminum alloy powder or an aluminum powder which is a mixture thereof; and metal powder such as titanium powder, copper powder, nickel powder and SUS powder, and alloy powder. And mixed powders thereof are used. From the viewpoints of lightness and corrosion resistance, it is preferable to use aluminum powder.

  When aluminum powder is used, it is preferable to use pure aluminum powder if the alloy components cause corrosion resistance deterioration under the usage environment. Pure aluminum is aluminum having a purity of 99.0 mass% or more. On the other hand, when it is desired to obtain higher strength, it is preferable to use aluminum alloy powder or a mixture of this and pure aluminum powder. As the aluminum alloy, 1000 series, 2000 series, 3000 series, 4000 series, 5000 series, 6000 series, and 7000 series aluminum alloys are used.

  When aluminum powder is used, a mixture obtained by adding additive element powder to pure aluminum powder may be 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 additive element powder may be added to the aluminum alloy powder, or the additive element powder may be added to a mixture of the aluminum alloy powder and the pure aluminum powder. In these cases, new alloy systems and intermetallic compounds are formed. Furthermore, an additive element alloy powder obtained by alloying a plurality of additive element powders may be used as the additive element powder. The addition amount of the additive element powder or additive element alloy powder to the aluminum alloy powder or pure 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 metal powder is preferably 1 to 50 μm. In order to uniformly cover the surface of the support powder with the metal powder in the production of the porous metal current collector, the metal powder preferably has a smaller particle size, more preferably 1 to 10 μm. The particle size of the metal powder is defined by the median diameter measured by the laser diffraction scattering method (microtrack method). Even when aluminum powder is used as the metal powder, the particle diameters of pure aluminum powder, aluminum alloy powder, additive element powder and additive element alloy powder are preferably 1 to 50 μm, and more preferably 1 to 10 μm, as described above.

(B) Support powder In this invention, what has melting | fusing point higher than melting | fusing point of metal powder is used as support powder. 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 supporting powder becomes pores of the porous metal, the particle size of the supporting powder is reflected in the pore diameter. Therefore, the particle size of the support powder used in the present invention is preferably 10 to 1000 μm. The particle size of the support powder is defined by the opening of the sieve. Therefore, a porous metal having a uniform pore diameter can be obtained by aligning the particle diameter of the support powder by classification.

(C) Metal plate In this invention, you may use the mixed powder of a metal powder and support powder in the state compounded with the metal plate. The metal plate is a non-porous plate or foil, and a net-like body such as a perforated wire mesh, expanded metal, or punching metal. The metal plate serves as a support, and the strength of the porous metal 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.

The composite of the mixed powder and the metal plate refers to an integrated state in which, for example, when a metal mesh is used for the metal plate, the entire net is covered with the mixed powder while filling the mixed powder in the mesh. When, for example, a catalyst or an active material is filled in a porous metal provided with bonded metal powder walls on both sides of the metal plate, if the metal plate is a perforated network, the filling is from one side of the region divided by the metal plate. However, 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 perforated body of the network may be larger or smaller than the diameter of the pores obtained by removing the supporting powder from the joined mixed powder.
The aperture ratio of the perforated holes in the network is preferably large so as not to impair the porosity of the porous metal current collector.

(D) Mixing method The mixing ratio of the metal powder and the support powder is preferably such that Val / (Val + Vs), which is the volume ratio of the metal powder, is 5 to 20%, more preferably 5 with the respective volumes being Val and Vs. -10%. Here, the volumes Val and Vs are values obtained from the respective mass and specific gravity. When the volume ratio of the metal powder exceeds 20%, the support powder content is too small and the support powders exist independently without contacting each other, and the support powder cannot be removed sufficiently. . Support powder that cannot be removed causes corrosion of the porous metal. On the other hand, when the volume ratio of the metal powder is less than 5%, the metal wall constituting the porous metal becomes too thin, the strength of the porous metal becomes insufficient, and handling and shape maintenance become difficult.
Also, in order to achieve a state where the support powder is sufficiently covered with the metal powder, the particle size (dal) of the metal powder is sufficiently smaller than the particle size (ds) of the support powder, for example, dal / ds. Is preferably 0.1 or less.

  In addition, as a mixing means for mixing the metal powder with the support powder, a vibration agitator, a container rotation mixer, or the like is used, but there is no particular limitation as long as a sufficient mixed state can be obtained.

(E) Pressure molding method The pressure during pressure molding is preferably 200 MPa or more. By forming by applying sufficient pressure, the metal powders rub against each other, and the strong oxide film on the surface of the metal powder that inhibits the sintering of the metal powders is destroyed. This oxide film confines molten metal, prevents contact with each other, and is inferior in wettability with molten metal, and has the effect of rejecting liquid metal. Therefore, when the pressure of pressure molding is less than 200 MPa, the destruction of the oxide film on the surface of the metal powder is insufficient, and the metal melted during heating oozes out of the molded body to form a ball-shaped metal lump. There is a case. When an electrode is produced in the presence of a metal lump, this ball-shaped metal lump breaks through the separator, causing a short circuit. It is preferable that the molding pressure is as large as the apparatus and mold used allow the porous metal wall to be formed to be strong. 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.

(F) Compounding method When the mixed powder is pressure-molded, the mixed powder filled in the molding die and the metal plate may be compounded. 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. At the time of compounding, mixed powders having different particle sizes and mixing ratios of metal powder and support powder, and a plurality of different types of metal plates can be combined.

(G) Heat treatment method The heat treatment is performed in the vicinity of the melting point of the metal powder to be used, at a temperature of at least 0.5 times the melting point and not exceeding 1.05 times the melting point of the metal powder. Even when the mixed powder is combined with a metal plate, heat treatment is performed at a temperature near the melting point of the metal powder, at least 0.5 times the melting point. Here, the melting point of the metal powder is a temperature at which a liquid phase is generated in the case of a single substance, and a temperature at which a liquid phase of a single component having the highest proportion is generated in the case of an alloy. Similarly, the melting point of the metal plate is a temperature at which a liquid phase is generated. In particular, when aluminum powder is used as the metal powder, heat treatment is performed at a temperature equal to or higher than its melting point. Even when the mixed powder of the aluminum powder and the supporting powder is combined with the metal plate, heat treatment is performed at a temperature equal to or higher than the melting point of the aluminum powder. Since a strong oxide film exists on the surface of the aluminum powder, the liquid phase oozes out of the aluminum powder or this and the metal plate by heating to a temperature at which the liquid phase is generated above the melting point of the aluminum powder. By contacting each other, the aluminum powders, and the aluminum powder and the metal plate are firmly bonded metallically.

  When the heat treatment temperature is less than 0.5 times the melting point of the metal powder, the sintering between the metal powders and between the metal powder and the metal plate becomes insufficient. In the case of aluminum powder, a liquid phase is not generated from the aluminum powder unless its melting point is exceeded, so that the bonding between the aluminum powder and the aluminum powder and the metal plate becomes insufficient. By heating the metal powder to a melting point of 0.5 times or more of the melting point of the metal powder, the metal powder covering the surface of the support powder located on the outermost surface of the sintered body is removed, and a sintered body having a surface with a large aperture ratio is obtained. It is formed. A large aperture ratio of the sintered body is advantageous for filling the active material when applied to the current collector.

  When the heating temperature is heated to a temperature exceeding 1.05 times the melting point of the metal powder, the viscosity of the molten metal decreases, and the molten metal oozes out to the outside of the press-molded body, resulting in a convex shape. A metal mass is formed. When an electrode is produced in the presence of a metal block, this convex portion breaks the separator and causes a short circuit, which is a harmful effect. The heat holding time in the heat treatment is preferably about 1 to 60 minutes. Further, a load may be applied to the pressure-formed body during the 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 metal oxidation, and an atmosphere of vacuum; nitrogen, argon, hydrogen, decomposed ammonia, and a mixed gas thereof is preferably used, and a vacuum atmosphere is 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 metal powder becomes insufficient, and oxidation of the metal surface proceeds during heat treatment. As described above, the oxide film on the metal surface is inferior in wettability with the liquid metal, and as a result, the molten metal exudes and a ball-like lump is formed. In the case of an inert gas atmosphere such as nitrogen, it is preferable that the oxygen concentration is 200 ppm or less and the dew point is −35 ° C. or less.

(H) Support powder removal method The support powder in the sintered body is preferably removed by eluting the support powder into water. 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.

3-2. Method for filling electrode mixture (a) Preparation of filling slurry The electrode mixture is filled into the pores of the porous metal produced as described above. The electrode mixture preferably contains an active material, and further contains a conductive additive and a binder. Here, what is important is that the particle size of the active material constituting the electrode mixture is made equal to or less than ¼ of the circle-equivalent diameter of the small holes communicating with the pores of the porous metal. When a conductive additive and / or binder is added to the electrode mixture in addition to the active material, all the electrode mixture components need to pass through the small holes smoothly. It is necessary that the particle diameter is ¼ or less of the circle equivalent diameter of the small hole. When this ratio exceeds 1/4, an electrode mixture component such as an active material is easily caught in the small holes, and the small holes cannot be smoothly passed. As a result, a sufficient amount of the electrode mixture cannot be filled in the pores, and the electrode density is decreased due to the decrease in the packing density. Note that the smaller the particle size of each electrode mixture including the active material, the more smoothly the electrode mixture can pass through the small holes.

  The concentration of the active material, the conductive additive, and the binder in the slurry is not limited, and may be appropriately selected from the viewpoint of slurry viscosity. Further, a thickener may be added to adjust the viscosity, and a dispersant may be added to obtain a good dispersion state. The solvent for the slurry is not particularly limited, and for example, N-methyl-2-pyrrolidone, water and the like are preferably used. When using polyvinylidene fluoride as a binder, it is preferable to use N-methyl-2-pyrrolidone as a solvent. When using polytetrafluoroethylene, polyvinyl alcohol, carboxymethyl cellulose (CMC), etc. as a binder, Preferably, water is used as a solvent.

(B) Slurry impregnation A slurry in which an electrode mixture component such as an active material, a conductive additive, and a binder (thickener and / or dispersant as required) is dispersed in a solvent is, for example, a press-fitting method. The porous metal is impregnated by a known method. As a press-fitting method, a slurry is disposed on one side with a porous metal as a diaphragm, and the other side is a slurry permeation side. The pores of the porous metal are filled with the above components by reducing the pressure on the other permeate side and allowing the slurry to permeate. Alternatively, the above-described components may be filled in the pores of the porous metal by pressurizing the slurry disposed on one side.
In place of the press-fitting method, the porous metal is immersed in a slurry in which the above components are dispersed in a solvent, and the above components are diffused into the pores of the porous metal (hereinafter referred to as “immersion method”). ) May be adopted.

(C) Solvent scattering / evaporation The porous metal filled with the electrode mixture as described above is dried by scattering / evaporating the solvent. If it is, it will not specifically limit. As specific drying conditions, it is preferable to hold at 50 to 200 ° C. for 1 to 60 minutes.

3-3. Press treatment In the porous metal current collector thus produced, the filling density of the electrode mixture containing the active material is adjusted by press treatment using a roll press machine, a flat plate press machine or the like. preferable. In particular, it is desirable to use a flat plate press as the pressing method. What is necessary is just to select the pressure of a press process suitably so that a filling density may be 50% or more of a compound material density, Preferably it is 70% or more, More preferably, it is 80 to 250%.

4). Battery The electrode according to the present invention is, for example, a positive electrode and a negative electrode for a non-aqueous electrolyte secondary battery as described above, and these electrodes are combined using a separator disposed between the positive and negative electrodes and a non-aqueous electrolyte. A non-aqueous electrolyte secondary battery is obtained. As the separator, generally used polymer films such as polyethylene (PE) and polypropylene (PP) are used. As the non-aqueous electrolyte, lithium hexafluorophosphate (LiPF ₆ ) or lithium perchlorate (LiClO ₄ ) dissolved in an organic solvent such as ethylene carbonate (EC) or diethyl carbonate (DEC) is used. it can.

  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 examples.

Invention Examples 1 to 6 and Comparative Example 1
(Preparation of porous aluminum)
First, porous aluminum was produced as follows as a porous metal current collector according to the present invention.
The following pure aluminum powders (A1 to A3) having different particle diameters were used as the aluminum powder. As support powders, sodium chloride powders (B1 to B2) having different particle diameters and potassium chloride (C1) having a particle diameter of 605 μm were used. As shown in Table 1, each powder was mixed at a predetermined volume ratio to prepare a mixed powder.

The mixed powder was filled in a mold having a hole with a diameter of 13 mm, and press-molded with the pressure shown in Table 1. The filling amount of the mixed powder was set to a mass at which the thickness of the pressure molded body was 1 mm. A sintered body was produced by heat-treating the pressure-formed body at a temperature and time shown in Table 1 in an atmosphere having a maximum ultimate pressure of 1 × 10 ⁻² Pa or less, and the obtained sintered body was heated to 20 ° C. The supporting powder was eluted by immersing in running water (tap water, ion exchange water) for 6 hours. Next, the sintered body was dried at 105 ° C. for 1 hour. In this way, a porous aluminum sample (φ13 mm × thickness 1 mm) was produced.

<Pure aluminum powder, (Aluminum purity 99.7 mass% or more)>
A1: Median diameter 3 μm (melting point: 660 ° C.)
A2: Median diameter 17 μm (melting point: 660 ° C.)
<Aluminum alloy powder (Al-7.5 mass% Si-1.0 mass% Mg)>
A3: Median diameter 27 μm (melting point: 555 ° C.)

<Sodium chloride powder>
B1: Particle size 400 μm (median sieve opening) (melting point: 800 ° C.)
B2: Particle size 605 μm (medium value of sieve opening) (melting point: 800 ° C.)
<Potassium chloride powder>
C1: Particle size 605 μm (medium value of sieve opening) (melting point: 776 ° C.)

(Measurement of small pore size in porous aluminum sample)
As shown in FIG. 1, the cross section of the porous aluminum sample was observed with a scanning electron microscope to measure the size of the small holes. Ten small holes were arbitrarily selected in each sample, and the area of each small hole was measured. The equivalent circle diameter at each location was calculated from the measurement results, and the arithmetic average value thereof was defined as the equivalent circle diameter <dp (μm)> of the small holes in each sample. The results are shown in Table 1.

(Filling electrode mixture)
Lithium iron phosphate (LiFePO ₄ , particle size 3 μm) 89.5 parts by weight as a positive electrode active material, acetylene black (particle size 48 nm) 5.0 parts by weight as a conductive assistant, PVDF (mesh opening 355 μm below sieve) ) Using 5.5 parts by weight, these were dispersed in 125 parts by weight of NMP to prepare an electrode mixture slurry. In addition, when filling a slurry to porous aluminum, since PVDF exists in the state melt | dissolved in NMP, the particle size as a powder does not become a problem when passing a small hole. As described above, as a result of comparing the particle size of the positive electrode active material used for the electrode mixture and the conductive additive, the lithium iron phosphate used as the positive electrode active material was larger, so the particle size of the electrode mixture component As <da (μm)>, 3 μm, which is the particle diameter of lithium iron phosphate, which is most difficult to pass through the small holes, was employed. Table 1 shows da / dp. Moreover, the density (mixed material density) of the composite material layer obtained by coating the slurry on an aluminum foil and drying was 1.50 g / cm ³ .

  Using the dipping method, a slurry in which a positive electrode active material, a conductive additive and a binder were dispersed in a solvent and the porous aluminum sample were placed in a sealed container and decompressed for 5 minutes. Three-dimensional porous aluminum was immersed in the slurry under reduced pressure, and the inside of the container was returned to atmospheric pressure. Then, excess slurry adhered to the front and back surfaces of the porous aluminum was scraped off using a spatula.

Next, the porous aluminum sample filled with the slurry was dried in a drying apparatus at 120 ° C. for 60 minutes to prepare a porous aluminum sample filled with the positive electrode mixture. Table 1 shows the packing density of the positive electrode sample for the non-aqueous electrolyte secondary battery. A packing density of 50% or more of the composite material density using the slurry, that is, 0.75 g / cm ³ or more was regarded as acceptable (◯), and less than that was regarded as unacceptable (x). The results are shown in Table 1.

  In all of Invention Examples 1 to 6, the particle size of the positive electrode active material was ¼ or less of the circle-equivalent diameter of the small holes, and the packing density was 50% or more of the composite material density, which was acceptable. On the other hand, in Comparative Example 1, the particle size of the positive electrode active material exceeded ¼ of the circle equivalent diameter of the small holes, so the packing density was unacceptable.

  By the electrode manufacturing method according to the present invention, an electrode capable of being filled with an electrode mixture containing an active material at high density in the pores of a current collector made of a porous metal is obtained.

1 .... Hole 2 .... Metal wall 3 .... Small hole

Claims (2)

  A method for producing an electrode containing an electrode mixture containing an active material, comprising a pore defined by a metal wall, wherein the pores communicate with each other through a small hole formed in the metal wall A step of impregnating a slurry in which the electrode mixture is dispersed in a solvent into a current collector comprising: drying a porous metal impregnated with the slurry to disperse and evaporate the solvent; And filling the pores with a particle diameter of the electrode mixture is equal to or less than ¼ of the equivalent circle diameter of the small holes. Production method.   The electrode using the porous metal current collector according to claim 1, further comprising a step of pressing the porous metal in which the pores are filled with the electrode mixture after the electrode mixture filling step. Production method.

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