JP2013232295A - Positive electrode for nonaqueous electrolyte secondary battery, manufacturing method therefor, and nonaqueous electrolyte secondary battery using positive electrode for nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a positive electrode for nonaqueous electrolyte secondary battery in which lowering of electrode capacity is prevented by suppressing exfoliation of an active material when repeating charge/discharge cycle, and to provide a manufacturing method of a positive electrode for nonaqueous electrolyte secondary battery, and a nonaqueous electrolyte secondary battery using the positive electrode for nonaqueous electrolyte secondary battery.SOLUTION: In the positive electrode for nonaqueous electrolyte secondary battery having an electrode mixture containing a positive electrode active material capable of absorbing and desorbing lithium, a collector of three-dimensional porous aluminum has holes defined by a metal wall, and the holes are filled with the electrode mixture, and the metal wall is in contact with the electrode mixture via a coating film formed of a conductive additive and a polymeric binder. A manufacturing method of a positive electrode for nonaqueous electrolyte secondary battery, and a nonaqueous electrolyte secondary battery using the positive electrode for nonaqueous electrolyte secondary battery are also provided.

Description

  The present invention relates to a positive electrode for a nonaqueous electrolyte secondary battery using a three-dimensional porous aluminum current collector suitable for a lithium ion battery or a lithium ion polymer secondary battery, a method for producing the positive electrode for the nonaqueous electrolyte secondary battery, In addition, the present invention relates to a non-aqueous electrolyte secondary battery using the positive electrode for a non-aqueous electrolyte secondary battery.

  In recent years, non-aqueous electrolyte secondary batteries, in particular lithium ion secondary batteries and lithium ion polymer secondary batteries, have become widespread for reasons such as having high energy density, and have come to be used in hybrid vehicles and electric vehicles. Further, higher output and higher energy density are required. Such a non-aqueous electrolyte secondary battery is generally constituted by a non-aqueous electrolyte solution containing a positive and negative electrodes capable of inserting and removing lithium, a microporous separator, and a lithium salt.

  A metal foil such as an aluminum foil or a copper foil is generally used as a current collector (support) that supports the positive electrode material or the negative electrode material. As such a metal foil, a porous aluminum current collector has been proposed for the purpose of increasing the electrode capacity (Patent Documents 1 to 3).

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 non-woven nickel-chrome porous current collector having a chromium content of 25% by mass or more by chromizing non-woven nickel as an electrode for increasing output and capacity. ing.
Patent Document 3 describes a high energy density current collector in which fine carbon fibers are attached to porous aluminum produced by slurry foaming using titanium as a sintering aid.

  However, the conventional electrode using porous aluminum has a problem that the active material falls off when the charge / discharge cycle accompanied by the volume change of the active material is repeated, and the electrode capacity decreases.

JP-A-8-170126 JP 2009-176517 A JP 2010-272427 A

  The present invention suppresses falling off of the positive electrode active material when the charge / discharge cycle is repeated, and prevents a decrease in electrode capacity, a positive electrode for a nonaqueous electrolyte secondary battery, a method for producing the positive electrode for the nonaqueous electrolyte secondary battery, Another object is to provide a non-aqueous electrolyte secondary battery using the positive electrode for a non-aqueous electrolyte secondary battery.

  As a result of intensive studies, the present inventors have found that the above problem is caused by the adhesion between the current collector and the active material. Therefore, the present inventors have further studied, and a mixture of a conductive additive and a polymer binder on the surface of the metal wall defining the pores of the three-dimensional porous aluminum containing the electrode mixture containing the positive electrode active material. The electrode active material containing the positive electrode active material is disposed in the pores through the coating film, so that the positive electrode active material does not fall off even after repeated charge / discharge cycles, and has a high electrode capacity. It has been found that an electrode capable of maintaining the above can be obtained.

  That is, the present invention is the positive electrode for a non-aqueous electrolyte secondary battery containing an electrode mixture containing a positive electrode active material capable of occluding and releasing lithium, and having a void defined by a metal wall. The electrode mixture is filled in the pores of a three-dimensional porous aluminum current collector, and the metal wall and the electrode mixture are formed of a conductive additive and a polymer binder. It was set as the positive electrode for nonaqueous electrolyte secondary batteries characterized by contacting through.

According to a second aspect of the present invention, in the first aspect, the mass of the coating film per unit volume of the three-dimensional porous aluminum is 0.001 to 0.07 g / cm ³ . In the third aspect of the present invention, in the first or second aspect, the mass ratio of the conductive additive to the solid content of the polymer binder in the coating film is 20 to 80%.

  According to the present invention, in claim 4, a suspension containing a conductive additive, a polymer binder, and a dispersion medium is impregnated inside a three-dimensional porous aluminum current collector having pores defined by metal walls. Drying the three-dimensional porous aluminum impregnated with the suspension to disperse and evaporate the dispersion medium, and forming a coating film containing the conductive additive and the polymer binder on the metal wall. A step of impregnating a slurry in which an electrode mixture containing a positive electrode active material capable of occluding and releasing lithium in a solvent is impregnated in a three-dimensional porous aluminum in which the coating film is formed on a metal wall; Drying the three-dimensional porous aluminum impregnated with the slurry to disperse and evaporate the solvent, and filling the pores with the electrode mixture so as to contact the metal wall through the coating film; ; Tertiary filled with electrode mixture in pores And a positive electrode manufacturing method for a non-aqueous electrolyte secondary battery which comprises a; and a step of pressing the current collector of the porous aluminum.

  According to a fifth aspect of the present invention, in the fourth aspect of the present invention, in the suspension, the ratio of the solid content of the conductive assistant to the solid content of 100 mass parts of the polymer binder is 20 to 80 mass parts.

  An invention according to claim 6 of the present invention is arranged between the positive electrode for a nonaqueous electrolyte secondary battery according to any one of claims 1 to 3, a negative electrode capable of occluding and releasing lithium, and the positive and negative electrodes. A non-aqueous electrolyte secondary battery comprising a separator and a non-aqueous electrolyte was obtained.

  In the positive electrode for a nonaqueous electrolyte secondary battery according to the present invention, the electrode mixture containing the positive electrode active material is filled in the pores defined by the metal wall of the three-dimensional porous aluminum current collector. The electrode mixture is held so as to be encased in the metal wall while in contact with the metal wall via a coating film formed from the conductive additive and the binder. Thereby, conductivity between the three-dimensional porous aluminum current collector and the electrode mixture is ensured, and a high electrode capacity is achieved. In addition, since the holding power of the positive electrode active material by the current collector is reinforced, dropping of the positive electrode active material is suppressed, and good charge / discharge cycle characteristics are achieved. Furthermore, a high energy density nonaqueous electrolyte secondary battery can be obtained by using the positive electrode for a nonaqueous electrolyte secondary battery.

It is a scanning electron micrograph which shows the cross section of the three-dimensional porous aluminum used for this invention.

A. Positive electrode for non-aqueous electrolyte secondary battery The positive electrode for a non-aqueous electrolyte secondary battery according to the present invention uses, as a current collector, three-dimensional porous aluminum having pores defined by metal walls. An electrode mixture containing a positive electrode active material capable of occluding and releasing lithium is filled in the pores of the three-dimensional porous aluminum, and the metal wall and the electrode mixture are composed of a conductive additive and a polymer binder. It is characterized by contacting through the coating film to be formed.

1. Three-dimensional porous aluminum As shown in FIG. 1, the three-dimensional porous aluminum used in the present invention is a porous sintered body having a wall made by sintering metal powder around the pores 1 as a skeleton. . The holes 1 are separated from each other by a metal wall 2 (bubble film surface) made of aluminum, and the holes 1 communicate with each other by a small hole 3 opened in the metal wall 2. The electrode mixture containing the positive electrode active material filled in the holes 1 is held so as to be wrapped by the metal wall 2. A coating film made of a conductive additive and a polymer binder is formed on the surface of the metal wall 2, and the metal wall 2 and the electrode mixture are in contact with each other through this coating film. The electrode mixture containing the positive electrode active material is more firmly held on the three-dimensional porous aluminum by the adhesion of the coating film. Moreover, the electrical conductivity based on the electronic conduction of the three-dimensional porous aluminum and electrode mixture through a coating film is ensured because the metal wall 2 and electrode mixture contact through a coating film.

1-1. Shape The shape of the three-dimensional porous aluminum 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 2 mm, and the pore diameter is preferably about 10 μm to 1 mm. Here, the pore diameter refers to the maximum diameter of pores appearing in the cross section when the cross section of the three-dimensional porous aluminum is observed.

1-2. Porosity The porosity of the three-dimensional porous aluminum is preferably 80 to 95%. Here, the porosity p (%) of the three-dimensional porous aluminum is calculated by the following formula (1).
p = [{hv− (hw / 2.7)} / hv] × 100 (1)
Where hv: total volume of three-dimensional porous aluminum (cm ³ )
hw: Mass of three-dimensional porous aluminum (g)
2.7: Density of aluminum material (g / cm ³ ).

2. The coating film provided on the surface of the metal wall of the three-dimensional porous aluminum has a conductive auxiliary agent for imparting conductivity between the three-dimensional porous aluminum and the electrode mixture, and the holding power of the electrode mixture. Formed from a mixture of polymeric binders for application.

2-1. The amount of coating film About the coating amount, the value obtained by dividing the total coating amount by the total volume of the three-dimensional porous aluminum, that is, 0.001 to 0.07 g as the coating amount per unit volume of the three-dimensional porous aluminum. / Cm ³ is preferred. The amount of the coating film can improve the conductivity between the three-dimensional porous aluminum current collector and the electrode mixture through the coating film, and the holding power of the electrode mixture containing the positive electrode active material. When the coating amount is less than 0.001 g / cm ³ , the holding power of the electrode mixture becomes insufficient, and when the charge / discharge cycle is repeated in the battery, the electrode mixture may drop out and the electrode capacity may decrease. . On the other hand, if the coating amount exceeds 0.07 g / cm ³ , there is a high possibility that the small holes in the metal wall of the three-dimensional porous aluminum are blocked by the coating film, and the electrodes are formed in the pores of the three-dimensional porous aluminum. It may be difficult to fill the mixture, and the battery capacity may decrease.

2-2. Conductive aid As the conductive aid used in the present invention, carbon powder, metal powder and the like are used, and among these, carbon powder is suitably 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 which has a high structure and can improve the conductivity even when added in a small amount. The mixing ratio of the conductive additive to the polymer binder is preferably 20 to 80 parts by mass with respect to 100 parts by mass of the solid content of the polymer binder. If the amount is less than 20 parts by mass, the electrical resistance of the coating film increases, and if it exceeds 80 parts by mass, the adhesion of the coating film to the electrode mixture decreases, and the holding power to the electrode mixture containing the active material decreases.

2-3. Polymer binder The polymer binder used in the present invention does not react with an active material, an electrolyte, an electrolytic solution, or the like when used for an electrode, and is electrochemical in a state where a potential is applied during battery operation. It is preferable that the material is not easily oxidized. Specifically, acrylic resins mainly composed of acrylic acid or methacrylic acid or derivatives thereof; high-molecular polysaccharides such as cellulose, nitrified cotton, and chitosan; and the like can be preferably used.

  In the acrylic resin, the ratio of the acrylic component in the monomer is, for example, 50% by mass or more, and preferably 80% by mass or more, but the upper limit is not particularly limited, and the monomer is substantially only the acrylic component. It may be comprised. Moreover, the monomer of acrylic resin may contain the acrylic component individually by 1 type, or 2 or more types. Among acrylic resins, an acrylic copolymer comprising methacrylic acid or a derivative thereof; and one or more monomers of a polar group-containing acrylic compound is preferable. By using such an acrylic copolymer, the high rate characteristics can be further improved.

  Examples of methacrylic acid or derivatives thereof include methacrylic acid, methyl methacrylate, ethyl methacrylate, isopropyl methacrylate and the like. Examples of the polar group-containing acrylic compound include acrylonitrile, methacrylonitrile, acrylamide, and methacrylamide. Among the polar group-containing acrylic compounds, an acrylic compound having an amide group is preferable. As the acrylic compound having an amide group, acrylamide, N-methylolacrylamide, diacetoneacrylamide and the like are preferably used.

  The weight average molecular weight of the acrylic resin is not particularly limited, but is preferably 30000 or more and 200000 or less. When the weight average molecular weight is less than 30000, the flexibility of the coating film is insufficient, and the electrode capacity may decrease due to the occurrence of cracks. On the other hand, when the weight average molecular weight exceeds 200,000, the adhesion between the coating film and the electrode mixture is lowered, the holding power of the coating film with respect to the electrode mixture is lowered, and the electrode mixture may be easily dropped. Such a weight average molecular weight can be measured by dispersing an acrylic resin in a suitable solvent and using GPC.

  About polymeric polysaccharide, although the same kind or a mixture of different types may be used, it can also be used together with another polymeric component. For example, the conductivity can be further improved by adding a melamine resin to nitrified cotton as a polymer polysaccharide.

3. Electrode Mixture The positive electrode for a non-aqueous electrolyte secondary battery according to the present invention contains an electrode mixture containing an active material capable of occluding and releasing lithium. The electrode mixture is supported in a state of being filled in the pores of the three-dimensional porous aluminum while being in contact with the metal wall through the coating film. The electrode mixture may contain a conductive additive and a binder in addition to the active material.

3-1. Positive electrode active material The positive electrode active material is not particularly limited as long as it can be used for a nonaqueous electrolyte secondary battery. For example, lithium cobaltate, lithium manganate, lithium nickelate, lithium iron phosphate, etc. A lithium metal oxide can be mentioned.

3-2. Conductive aid By adding a conductive aid to the electrode mixture, the conductivity of the electrode mixture is also improved. As a conductive support agent, the same thing as that used for the said coating film can be used.

3-3. Binder By adding a binder to the electrode mixture, binding of components via the binder, that is, positive electrode active materials, conductive assistants, and positive active material and conductive assistants are strongly bonded. Thus, the active material is less likely 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.

  Usually, a conductive additive and a binder are added to the electrode mixture. In this case, the ratio of the positive electrode active material to the total electrode mixture (positive electrode active material + conductive auxiliary agent + binder) is 85 to 95% by weight is preferable. If this ratio is less than 85% by weight, the positive electrode active material may be insufficient and high electrode capacity may not be achieved. On the other hand, if this ratio exceeds 95% by weight, the conductivity of the positive electrode as a whole is lowered, and sufficient bonding between the components and between components cannot be obtained, and a high electrode capacity cannot be achieved.

B. Manufacturing method of positive electrode for nonaqueous electrolyte secondary battery The positive electrode for a nonaqueous electrolyte secondary battery according to the present invention first produces three-dimensional porous aluminum using a mixed powder of an aluminum powder and a support powder. Next, a suspension containing a conductive additive, a polymer binder, and a dispersion medium is impregnated inside the current collector of the three-dimensional porous aluminum, and this is dried to disperse and evaporate the dispersion medium. A coating film containing an agent and a polymer binder is formed on the metal wall. Furthermore, the slurry in which the electrode mixture is dispersed in the solvent is impregnated into the interior of the three-dimensional porous aluminum on which the coating film is formed, and this is dried to scatter and evaporate the solvent. The electrode mixture is filled into the holes so as to come into contact with each other. Finally, the three-dimensional porous aluminum filled with the electrode mixture is pressed.

1. Method for producing three-dimensional porous aluminum Three-dimensional porous aluminum is formed by pressing a mixed powder of an aluminum powder and a supporting powder at a predetermined pressure, and then pressing the pressure-molded body in an inert atmosphere to a temperature equal to or higher than the melting point of the aluminum powder. And it sinters by the heat processing in the temperature range below melting | fusing point of the support powder mentioned later, and removes support powder after that and manufactures.

1-1. Aluminum powder Pure aluminum powder, aluminum alloy powder, or a mixture thereof is used for the aluminum powder used in the present invention. In the case where the alloy components cause corrosion resistance deterioration under the usage environment, it is preferable to use pure aluminum powder. 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.

  The particle size of the aluminum powder is preferably 1 to 50 μm. In order to uniformly cover the surface of the support powder with the aluminum powder in the production of the porous aluminum current collector, the particle size of the aluminum powder is preferably smaller and more preferably 1 to 10 μm. The particle size of the aluminum powder is defined by the median diameter measured by the laser diffraction scattering method (microtrack method).

1-2. Additive Element Powder 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 additive element powder is preferably 1 to 50 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 (microtrack method) in the same manner as the aluminum powder.

1-3. Supporting powder In the present invention, a supporting powder 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, 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. Accordingly, porous aluminum having a uniform pore diameter can be obtained by making the particle diameter of the support powder uniform by classification.

1-4. Metal Plate In the present invention, the mixed powder may be used in a state where it is combined 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, expanded metal, or punching 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.

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 porous aluminum 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 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.

1-5. Mixing method 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 5 to 10%. It is. Here, the volumes Val and Vs are values obtained from the respective mass and specific gravity. When the volume ratio of the aluminum 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 porous aluminum. On the other hand, when the volume ratio of the aluminum powder is less than 5%, the wall constituting the porous aluminum becomes too thin, so that the strength of the porous aluminum becomes insufficient, and handling and shape maintenance become difficult.
In order to achieve a state where the support powder is sufficiently covered with the aluminum powder, the particle size (dal) of the aluminum powder is sufficiently smaller than the particle size (ds) of the support powder, for example, dal / ds. Is preferably 0.1 or less.

  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.

1-6. Compounding Method When the mixed powder is filled in a molding die, the mixed powder and the metal plate may be combined. 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.

1-7. Pressure molding method The pressure during 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. When an electrode is produced in the presence of an aluminum lump, this ball-shaped aluminum lump breaks through the separator, causing a short circuit. The three-dimensional porous aluminum wall on which the molding pressure is as large as the apparatus and mold used allow 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.

1-8. Heat treatment method The heat treatment is carried out at a temperature not lower than the melting point of the aluminum powder used and lower than the melting point of the supporting powder. When the mixed powder is combined with the metal plate, the heat treatment is performed at a temperature not lower than the melting point of the aluminum powder and lower than the melting point of the supporting 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 metal plate, and the aluminum phases and the aluminum powder and the metal plate are metallicly bonded 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 a sintered body having a surface with a large aperture ratio 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 equal to or higher than the melting point of the support powder, the support powder is melted. 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. When heated at a temperature equal to or higher than the melting point of the support powder, the shape of the porous body cannot be maintained as the support powder melts. 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. When an electrode is produced in the presence of an aluminum lump, 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 for performing the heat treatment is an atmosphere for suppressing oxidation of aluminum, 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 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 200 ppm or less and the dew point is −35 ° C. or less.

1-9. Support Powder Removal Method A method of removing the support powder in the sintered body by eluting the support powder into 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.

2. Method for forming coating film 2-1. Preparation of Suspension for Coating Film A coating film composed of a conductive additive and a polymer binder is formed on the surface of the metal wall of the three-dimensional porous aluminum produced as described above. First, a suspension composed of a conductive aid, a polymer binder, and a dispersion medium is prepared. The above-mentioned conductive assistant and polymer binder are used. By adding a conductive additive to a dispersion medium in which a high molecular binder is dispersed or dissolved, a suspension composed of the conductive auxiliary, the high molecular binder, and the dispersion medium is prepared. It is preferable to add the conductive additive at a ratio of 20 to 80 parts by mass with respect to 100 parts by mass of the solid content of the polymer binder. As a dispersion medium, an organic solvent such as NMP can be used in addition to water and alcohol. Further, for the purpose of adjusting the viscosity of the suspension, a thickener such as CMC may be added as long as the performance of the coating film is not impaired. In addition, the content (concentration) of the conductive additive and the polymer binder in the suspension is appropriately determined in consideration of the viscosity of the suspension. The dispersion method is not particularly limited, and a known dispersion method such as a ball mill or a homogenizer can be applied.

2-2. Coating formation The above-mentioned suspension is brought into contact with and impregnated into the entire interior including the pore inner surface of the three-dimensional porous aluminum. Next, the excess suspension that cannot be completely impregnated is removed, and the dispersion medium is scattered and evaporated by drying. The method for bringing the suspension into contact with the three-dimensional porous aluminum is not particularly limited. For example, a method of immersing three-dimensional porous aluminum in the suspension, a method of allowing the suspension to permeate through the fixed three-dimensional porous aluminum, and the like are used. Three-dimensional porosity that prevents contact with the suspension by holding the three-dimensional porous aluminum under reduced pressure immediately before or during contact with the suspension in contact with the three-dimensional porous aluminum Air in the quality aluminum may be removed. Furthermore, in order to increase the wettability of the suspension with respect to the three-dimensional porous aluminum, the three-dimensional porous with a suspension medium and an affinity solvent immediately before the suspension is brought into contact with the three-dimensional porous aluminum. The entire aluminum may be processed.

  The method for removing the excess suspension from the three-dimensional porous aluminum is not particularly limited. For example, a method in which three-dimensional porous aluminum is suspended along the vertical direction, and the excess suspension is allowed to fall spontaneously by gravity; three-dimensional porous aluminum is contacted with a material that is easily infiltrated by the dispersion medium, and the excess suspension And a method of expelling excess suspension from the inside by allowing gas to permeate through the three-dimensional porous aluminum, or a combination of two or more of these methods. The drying conditions after removing the excess suspension are not particularly limited, but it is preferable to hold at a temperature of 50 to 250 ° C. for 1 to 60 minutes.

3. 3. Method for filling electrode mixture 3-1. Preparation of slurry for filling The electrode mixture is filled into the pores of the three-dimensional porous aluminum having the coating film formed as described above so as to come into contact with the metal wall through the coating film.
The electrode mixture preferably contains a positive electrode active material and further contains a conductive additive and a binder. The concentration of the positive electrode 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 and the like. 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.

3-2. Filling of electrode mixture A slurry in which components of a positive electrode active material, a conductive additive and a binder (thickener and / or dispersant as required) are dispersed in a solvent is, for example, a known method such as a press-fitting method. To fill the porous aluminum. As a press-fitting method, a slurry is disposed on one side with porous aluminum as a diaphragm, and the other side is a slurry permeation side. And the said each component is filled in the void | hole of porous aluminum by making the permeation | transmission side of the other side pressure-reduced, and making a slurry permeate | transmit. Alternatively, the above-mentioned components may be filled in the pores of the porous aluminum by pressurizing the slurry disposed on one side.
In place of the press-fitting method, porous aluminum 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 aluminum (hereinafter referred to as “immersion method”). ) May be adopted.
As described above, the positive electrode filled with each of the above components is dried by scattering and evaporating the solvent. The drying condition is preferably maintained at 50 to 200 ° C. for 1 to 60 minutes.

4). Press treatment In the positive electrode for a non-aqueous secondary battery produced in this manner, the electrode density of the electrode mixture containing an active material is adjusted by press treatment using a roll press or a flat plate press. In particular, it is desirable to perform press processing using a flat plate press. It is preferable that the electrode density improvement rate of the electrode mixture is set to 110 to 500% by such press treatment. If the electrode density improvement rate is less than 110%, the press treatment is insufficient, and there may be a case where the electrode mixture and the metal wall of the three-dimensional porous aluminum cannot be sufficiently contacted through the coating film, resulting in an increase in electrical resistance. is there. On the other hand, when the electrode density improvement rate exceeds 500%, it becomes difficult for the electrolytic solution to permeate into the electrode due to excessive press treatment, and the diffusion of lithium ions may be hindered to deteriorate the battery characteristics.

Here, the electrode density of the electrode mixture is W / V when the volume occupied by the electrode mixture containing the active material in the electrode is V (cm ³ ) and the mass of the electrode mixture is W (g). It shall be represented by (g / cm ³ ). The electrode density improvement rate is the ratio of the electrode density (W / V) af after being densified by press treatment or the like to the electrode density (W / V) be immediately after the electrode mixture is filled in%. What is represented, ie, {(W / V) af / (W / V) be} × 100 (%).

C. Nonaqueous electrolyte secondary battery The nonaqueous electrolyte secondary battery according to the present invention includes the above positive electrode for nonaqueous electrolyte, a negative electrode capable of occluding and releasing lithium, a separator disposed between positive and negative electrodes, and a nonaqueous electrolyte. It is assembled using.

1. Negative electrode The same porous aluminum current collector as the positive electrode may be used for the negative electrode, and the electrode mixture containing the negative electrode active material may be filled in the pores. An agent and a binder may be used. Instead, a negative electrode may be used from a negative electrode current collector and an electrode mixture layer formed by applying a slurry in which an electrode mixture containing a negative electrode active material is dispersed in a solvent on the negative electrode current collector. . Also in this case, the electrode mixture may contain a conductive additive and a binder.

The negative electrode active material is not particularly limited as long as it can be used for a non-aqueous electrolyte secondary battery. For example, natural graphite, artificial graphite, mesocarbon microbeads (MCMB), carbon such as hard carbon and soft carbon Materials: Metal materials and alloy materials that can be combined with lithium such as Al, Si, and Sn; oxide materials such as lithium titanate (Li ₄ Ti ₅ O ₁₂ ) can be used.

2. Separator and Nonaqueous Electrolyte As the separator for the positive electrode and the negative electrode, 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 1-7 and Comparative Examples 1-5
(Production of three-dimensional porous aluminum)
Pure aluminum powder (melting point: 660 ° C.) having an aluminum purity of 99.9% and a particle diameter of 3 μm was used as the aluminum powder, and sodium chloride powder (melting point: 800 ° C.) having a sieve opening of 300 to 500 μm was used as the supporting powder. These aluminum powder and support powder were mixed at a volume ratio of aluminum powder: support powder = 1: 9 to prepare a mixed powder.

The mixed powder was filled in a mold having a hole with a diameter of 13 mm and pressure-molded at 400 MPa. The filling amount of the mixture was set to a weight at which the thickness of the pressure-molded body was 1 mm. The pressure-formed body was subjected to heat treatment for 5 minutes in an atmosphere at a maximum ultimate pressure of 1 × 10 ⁻² Pa or less and 670 ° C. to produce a sintered body. After cooling the obtained current collector, it was immersed in flowing water (tap water) at 20 ° C. for 6 hours to elute the supporting powder, thereby preparing a three-dimensional porous aluminum sample (diameter 13 mm × thickness 1 mm). About the produced three-dimensional porous aluminum sample, the porosity was calculated | required from said Formula (1).

(Formation of coating film)
A coating film containing a conductive additive and a polymer binder was formed on the metal wall of the three-dimensional porous aluminum produced as described above. In Comparative Example 1, no coating film was formed.

  As a polymer binder monomer, ethyl methacrylate, butyl acrylate, and methyl methacrylate are used, and these monomers are blended in this order at a mass ratio of 10:70:20, and an acrylic copolymer having a weight average molecular weight in the range of 90000 to 120,000. The polymer was polymerized to obtain a polymer binder. Next, the above polymer binder was dispersed in water as a dispersion medium using a surfactant to prepare a dispersion. To this dispersion, acetylene black was added as a conductive aid in a mass part shown in Table 1 with respect to 100 parts by mass of the solid content of the polymer binder, and dispersed for 8 hours in a ball mill to form a suspension for coating film formation. Was prepared.

  100 ml of the suspension and the three-dimensional porous aluminum sample were put in a sealed container, and the container was decompressed with a rotary pump for 5 minutes. A three-dimensional porous aluminum sample was immersed in the suspension under reduced pressure, and the three-dimensional porous aluminum was pulled up from the suspension when the inside of the container was returned to atmospheric pressure. Each three-dimensional porous aluminum sample pulled up from the suspension was placed on a buch funnel covered with filter paper, and excess suspension adhering to each three-dimensional porous aluminum was removed by suction filtration. Subsequently, each three-dimensional porous aluminum filtered by suction was dried for 10 minutes in a drying apparatus at 150 ° C., and a coating film was formed on the metal wall of each three-dimensional porous aluminum.

Table 1 shows the coating mass (g / cm ³ ) per unit volume of each three-dimensional porous aluminum sample. The coating mass is the total coating mass (g) obtained by subtracting the mass before coating formation from the mass of the three-dimensional porous aluminum sample after coating formation. Divided by volume.

(Filling electrode mixture)
Using 100 parts by weight of lithium iron phosphate as the positive electrode active material, 5.0 parts by weight of acetylene black as the conductive auxiliary agent, and 5.5 parts by weight of PVDF as the binder, these were dispersed in 200 parts by weight of NMP and electrode mixture A slurry was prepared.

  Using the dipping method, each three-dimensional porous aluminum provided with a coating film in a slurry in which a positive electrode active material, a conductive additive, and a binder are dispersed in a solvent is placed in a sealed container, and is rotated with a rotary pump for 5 minutes. After decompression, the three-dimensional porous aluminum was immersed in the slurry. After immersion, the inside of the container was returned to atmospheric pressure, and excess slurry adhering to the front and back surfaces of the porous aluminum pulled up from the slurry was scraped off using a spatula.

Next, each three-dimensional porous aluminum sample filled with the slurry was dried in a drying apparatus at 120 ° C. for 60 minutes to prepare each three-dimensional porous aluminum sample filled with the positive electrode mixture. Finally, these samples were pressed by a flat plate press at a pressure of 0.50 ton / cm ² to obtain positive electrode samples for each non-aqueous electrolyte secondary battery.

(Production of evaluation cell)
The positive electrode sample subjected to the above press treatment was used as a working electrode, lithium metal was used for the counter electrode and the reference electrode, and a polypropylene microporous separator was sandwiched between these electrodes and housed in a battery case to produce a coin-type battery. As the electrolytic solution, a nonaqueous electrolytic solution in which 1 mol / L of LiPF ₆ was dissolved in a mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) (volume ratio EC: EMC = 3: 7) was used.

(Discharge rate characteristics)
Using the battery prepared as described above, an evaluation test of charge / discharge characteristics was performed. In the charge / discharge test, the battery was charged to 4.0 V with a current of 0.2 C and discharged with a current of 0.2 C and 5 C, and the difference in initial discharge voltage between 0.2 C discharge and 5 C discharge was measured. Here, 1C is a current value (A) when the current capacity (Ah) of the battery is taken out in one hour (h). The difference between the initial discharge voltages is 0.65V or less, ◯, the one that is higher than 0.65V and 0.70V or less is △, the one that exceeds 0.70V is ×, ○ and △ are acceptable, and x is unacceptable. It was. The results are shown in Table 1.

(0.2C discharge capacity)
Moreover, the 0.2C discharge capacity which calculated | required the capacity | capacitance when discharged at 0.2 C by the mass of the active material in an electrode was calculated | required. When this was 120 mAh / g or more, it was evaluated as “◯”, and those less than that as “×”, “◯” as acceptable, and “x” as unacceptable. The results are shown in Table 1.

(Drop off of positive electrode active material after 500 cycle test)
A charge / discharge test in which the battery is charged to 4 V at a current of 0.2 C and discharged to 2.0 V at 0.2 C is taken as one cycle, and whether or not the positive electrode active material has dropped from the positive electrode sample after 500 cycles of the charge / discharge test. Evaluation was made by visual observation. The case where the positive electrode active material did not fall off was marked as ◯, the case where the positive electrode active material was slightly removed as △, the case where the positive electrode active material was markedly dropped as x, and ○ and △ passed, x It was rejected. The results are shown in Table 1.

(Comprehensive evaluation)
In the evaluation of the discharge rate characteristics, 0.2C discharge capacity, and the presence or absence of the positive electrode active material after the 500 cycle test, the overall evaluation is a case where the overall evaluation is composed of ○, ○ and Δ. A case where the evaluation was Δ and one or more xs were included was an overall evaluation, and ○ and Δ were a pass for the overall evaluation, and × was a pass for the overall evaluation. The results are shown in Table 1.

  In Invention Examples 1 to 7, the coating mass per unit volume of the three-dimensional porous aluminum sample and the mass of the positive electrode active material were within the ranges specified in the present invention. As a result, the discharge rate characteristics, 0.2C discharge capacity, and evaluation of the presence or absence of the positive electrode active material after the 500 cycle test were all passed, and the overall evaluation was also passed.

  In Comparative Example 1, since the coating film composed of the mixture of the conductive auxiliary agent and the polymer binder was not formed, the holding power of the positive electrode active material in the three-dimensional porous aluminum was insufficient, and the positive electrode active material after the 500 cycle test was Material dropout was significant. Moreover, the discharge rate characteristic was disqualified because the part which electrical contact with an electrode compound material and a three-dimensional porous aluminum electrical power collector becomes inadequate arises. As a result, the overall evaluation also failed.

  In Comparative Example 2, since the coating film mass formed on the three-dimensional porous aluminum was too small, the holding power of the positive electrode active material in the three-dimensional porous aluminum became insufficient, and the positive electrode active material dropped after the 500 cycle test. Was noticeable. As a result, the overall evaluation also failed.

  In Comparative Example 3, since the coating film mass formed on the three-dimensional porous aluminum was too much, the small holes of the three-dimensional porous aluminum were partially blocked by the coating film, and the pores were sufficient. The positive electrode active material could not be filled. Moreover, ion conductivity fell because the small hole was partially plugged, and the 0.2 C discharge capacity was rejected, and the overall evaluation was also rejected.

  In Comparative Example 4, since the coating film mass formed on the three-dimensional porous aluminum was too much, the small holes of the three-dimensional porous aluminum were partially blocked by the coating film, and the pores were sufficient. The positive electrode active material could not be filled. Moreover, the ionic conductivity was lowered by partially closing the small holes, and the 0.2C discharge capacity was rejected. In addition, since the proportion of the conductive additive in the coating film formed on the three-dimensional porous aluminum is too small, the electrical continuity between the three-dimensional porous aluminum and the active material is insufficient, and the discharge rate characteristics are not acceptable. there were. As a result, the overall evaluation also failed.

  In Comparative Example 5, since the coating film mass formed on the three-dimensional porous aluminum is too small and the ratio of the polymer binder in the coating film is too small, the positive electrode active material is retained in the three-dimensional porous aluminum. The force was insufficient, and the active material dropped out after the 500 cycle test. As a result, the overall evaluation also failed.

  In the positive electrode for a non-aqueous electrolyte secondary battery according to the present invention, the active material is prevented from dropping when the charge / discharge cycle is repeated, and the electrode capacity is also prevented from decreasing. Furthermore, a high energy density is achieved as battery performance by the non-aqueous electrolyte secondary battery using the positive electrode for non-aqueous electrolyte secondary batteries.

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

Claims (6)

  A positive electrode for a non-aqueous electrolyte secondary battery containing an electrode mixture containing a positive electrode active material capable of occluding and releasing lithium, and using a three-dimensional porous aluminum having pores defined by metal walls as a current collector The electrode mixture is filled in the pores, and the metal wall and the electrode mixture are in contact with each other through a coating film formed from a conductive additive and a polymer binder. A positive electrode for a non-aqueous electrolyte secondary battery. The positive electrode for a nonaqueous electrolyte secondary battery according to claim 1, wherein a mass of the coating film per unit volume of the three-dimensional porous aluminum is 0.001 to 0.07 g / cm ³ .   The positive electrode for a non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein a mass ratio as a solid content of the conductive additive to the polymer binder in the coating film is 20 to 80%.   Impregnating a suspension containing a conductive aid, a polymer binder, and a dispersion medium into a three-dimensional porous aluminum current collector having pores defined by metal walls; Drying the three-dimensional porous aluminum impregnated inside to disperse and evaporate the dispersion medium to form a coating film containing the conductive auxiliary agent and the polymer binder on the metal wall; Impregnating a slurry in which an electrode mixture containing a releasable positive electrode active material is dispersed in a solvent into a three-dimensional porous aluminum in which the coating film is formed on a metal wall; impregnating the slurry in the interior; Drying the three-dimensional porous aluminum to disperse and evaporate the solvent, and filling the electrode mixture into the pores so as to contact the metal wall through the coating film; and the electrode mixture into the pores; Of Three-dimensional Porous Aluminum Filled with Metal Process and pressing process; the positive electrode manufacturing method for a non-aqueous electrolyte secondary battery, which comprises a.   The positive electrode for a non-aqueous electrolyte secondary battery according to claim 4, wherein in the suspension, the ratio of the solid content of the conductive additive to the solid content of 100 parts by mass of the polymer binder is 20 to 80 parts by mass. Method.   A positive electrode for a nonaqueous electrolyte secondary battery according to any one of claims 1 to 3, a negative electrode capable of occluding and releasing lithium, a separator disposed between the positive and negative electrodes, and a nonaqueous electrolyte. A non-aqueous electrolyte secondary battery.

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