JP5961067B2 - Non-aqueous electrolyte secondary battery and method for producing non-aqueous electrolyte secondary battery - Google Patents

Description

  The present invention relates to a non-aqueous electrolyte secondary battery, and more particularly to a lithium secondary battery including porous aluminum having a three-dimensional porosity as a current collector for a positive electrode and a negative electrode used in a lithium secondary battery.

The positive electrode of the non-aqueous electrolyte secondary battery includes lithium cobalt oxide (LiCoO ₂ ), lithium manganate (LiMn ₂ O ₄ ), lithium nickelate (LiNiO ₂ ), and lithium iron phosphate as positive electrode active materials. (LiFePO ₄₎ or the like which was applied to a current collector made of aluminum foil is developed advanced aiming been put to practical use, or commercialization. As the negative electrode, a material mainly composed of carbon, particularly graphite, as a negative electrode active material, or a material in which a part of metallic lithium, a lithium-containing alloy, a metal oxide, or the like is applied to a current collector made of copper foil is used. As the separator, a microporous thin film is generally used. Further, as the electrolyte, a nonaqueous electrolytic solution in which a lithium salt is dissolved in an organic solvent is generally used, and in addition, a gel electrolyte solution or a solid electrolyte system has attracted attention as an electrolyte.

  In recent years, non-aqueous electrolyte secondary batteries have become widespread for reasons such as high energy density, and have been put into practical use as power sources for portable small electronic devices such as mobile phones, digital cameras, and notebook computers. And from the viewpoint of recent energy resource depletion problems and global warming problems, non-aqueous electrolyte secondary batteries are used in large-scale industrial applications such as hybrid vehicles, electric vehicles, and power storage applications using natural energy generation such as solar and wind power. Development is underway, and there is a need for higher capacity and longer life.

  Therefore, in order to improve the capacity and suppress the decrease in capacity when the cycle of charging and discharging is repeated, it is used as a positive electrode current collector of a nonaqueous secondary battery having a thickness in the range of 10 μm to 40 μm. A fine hole having a non-uniform pore diameter of 30 nm to 50 μm is formed on the entire surface of aluminum, and a porosity representing a ratio in a volume occupied by a void including the fine hole is 15% or more and 40% or less, and a gas density is 0.2. A porous current collector for a non-aqueous secondary battery with a second / 100 cc to 100 seconds / 100 cc has been proposed (see, for example, Patent Document 1).

JP 2000-231923 A

In Patent Document 1, a metal foil made of aluminum or copper is provided with micropores to form a porous current collector, and an active material is applied or immersed in the porous current collector to form a positive electrode and / or a negative electrode. And by adopting the said method, it is possible to hold | maintain much active material compared with what applied the active material to metal foil.
However, in Patent Document 1, the increase in the amount of active material retained by using a porous current collector is small, and it is difficult to increase the thickness of the coating layer of the positive electrode and / or the negative electrode. It is not possible to achieve a high capacity that satisfies the market.
In addition, the positive and negative electrode active materials may fall off from the current collector in the drying process or pressing process of the positive electrode and / or negative electrode, and it is not possible to achieve a long life that satisfies the current market. .
Furthermore, since fibrous, spherical, and polygonal graphite is used as the negative electrode active material, the nonaqueous electrolyte that is in physical contact with the positive electrode is oxidized and decomposed particularly in a high temperature region, gas is generated, and the battery swells and bursts. Not only does it cause defects such as leakage, but the transition metal contained in the active material elutes into the non-aqueous electrolyte and deposits on the negative electrode, leading to a minute internal short circuit (short circuit), which may significantly impair safety. .

The present invention has been made in view of the above-described circumstances, and an object thereof is to provide a non-aqueous electrolyte secondary battery having high capacity, excellent charge / discharge cycle characteristics, and excellent safety , and a method for producing the same. To

In order to achieve the above object, the present invention comprises a positive electrode in which a three-dimensional porous aluminum current collector is filled with a positive electrode active material, and a negative electrode in which a three-dimensional porous aluminum current collector is filled with a negative electrode active material, In the inert atmosphere, the three-dimensional porous aluminum current collector used for the positive electrode and the negative electrode is formed by press-molding a mixed powder of an aluminum powder and a support powder mixed at a predetermined volume ratio. causing aluminum powder or et liquid phase by heat treatment to bond the aluminum powder same, and the support powder is a three-dimensional porous aluminum current collector manufactured by removing the supporting powder is removed And a bonded metal powder wall of bonded aluminum powder that forms the periphery of the void, and the bonded metal powder wall has many fine holes formed between them. A structure of an open-cell joined by micropores, the negative active material provides a non-aqueous electrolyte secondary battery with a lithium der Rukoto metal acid.
The particle size of the aluminum powder may be 1 to 50 μm.
The porosity of the three-dimensional porous aluminum current collector may be 80% or more and 95% or less.
The present invention gives rise to aluminum Powder or et liquid phase by heat treating the molded body formed by pressure-molding a mixed powder of aluminum powder and support powder mixed in a predetermined volume ratio in an inert atmosphere, aluminum powder joining the same, and the support powder was removed and the the support powder was removed void, is constituted by a coupling metal powder walls of the joined aluminum powder to form the periphery of the air gap, the coupling metal powder the walls are formed a number of fine pores, a step of voids each other to produce a three dimensional porous aluminum current collector structure of open cell type linked by these micropores, said three-dimensional porous aluminum current a positive electrode filled with the positive electrode active material in the collector, in that it comprises the step of producing a negative electrode filled with a negative active material for a lithium metal oxide on the three-dimensional porous aluminum collector To provide a method of manufacturing a nonaqueous electrolyte secondary battery according to symptoms.

According to the present invention, the positive electrode and negative electrode current collectors are made of porous aluminum current collectors, so that high capacity and charge / discharge cycle characteristics are excellent, and graphite and the like are not used for the negative electrode active material. An excellent nonaqueous electrolyte secondary battery can be obtained.
Furthermore, the nonaqueous electrolyte secondary battery excellent in discharge capacity can be obtained by using a positive electrode and a negative electrode current collector as a porous aluminum current collector.

Hereinafter, embodiments of the present invention will be described.
The nonaqueous electrolyte secondary battery according to the present embodiment is a porous aluminum current collector for both the positive electrode and the negative electrode, and is filled with a slurry in which a positive electrode that absorbs and releases lithium ions and a negative electrode active material are dispersed in a solvent, respectively. It is comprised by. In addition to the positive electrode active material and the negative electrode active material, a conductive additive, a binder, and a thickener may be further added to this solvent.

  According to the nonaqueous electrolyte secondary battery of the present embodiment, since a porous aluminum current collector is used for the positive electrode and negative electrode current collectors, a high capacity, long life nonaqueous electrolyte secondary battery can be obtained. . In the case of a coated electrode using a metal foil, if a large amount of an active material layer is applied to increase the capacity, the active material falls off from the current collector in the electrode drying process or pressing process. By using a porous aluminum current collector as described above, this can be suppressed, and a high-capacity, long-life nonaqueous electrolyte secondary battery can be obtained.

<Porous aluminum current collector>
The porous aluminum current collector of the present embodiment is prepared by press-molding a mixed powder of an aluminum powder and a support powder mixed at a predetermined volume ratio, and then heat-treating the molded body in an inert atmosphere to obtain an aluminum powder or an aluminum It is obtained by producing a liquid phase from the plates, joining the aluminum powders together, the aluminum powder and the aluminum plate, and finally removing the supporting powder. Further, the mixed powder may be combined with a metal plate. The porous aluminum current collector is composed of a void from which the support powder has been removed and a bonded metal powder wall of the joined aluminum powder that forms the periphery of the void. Many fine holes are formed in the bonded metal powder wall, and an open cell structure is formed in which voids are connected by these fine holes.
Further, the porosity of the porous aluminum current collector is 80% or more and 95% or less, preferably 85% or more. By making it within this range, it is possible to fill the pores of the current collector with a desired amount of active material slurry while maintaining the strength as an electrode, and it is possible to increase the output and capacity of the battery. .
In addition, the porous aluminum electrical power collector used for the nonaqueous electrolyte secondary battery which concerns on this invention can be manufactured as follows.

<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).

<Additive element powder>
You may use the mixture which added the additive element powder to the pure aluminum powder. As such an additive element, a plurality of elements selected from magnesium, silicon, titanium, iron, nickel, copper, zinc, etc., or a combination of two or more arbitrary elements are suitably 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.

<Supporting powder>
In the present invention, as the support powder, one having a melting point higher than that of the aluminum powder is used. When the mixed powder is combined with a metal plate, a powder having a melting point higher than the lower melting point of the aluminum powder and the metal plate is used. As such a supporting powder, a water-soluble salt is preferable, and sodium chloride and potassium chloride are preferably used from the viewpoint of availability. Since the space formed by removing the support powder becomes pores of porous aluminum, the particle size of the support powder is reflected in the pore diameter. Therefore, 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.

<Metal plate>
In the present invention, the mixed powder may be used in a composite state 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, which improves the strength of the porous aluminum urine current collector and further improves the conductivity. 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.

<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 10 to 15%, where the respective volumes are Val and Vs. . 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.

<Composite method>
When the mixed powder is filled in the 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.

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

<Heat treatment method>
The heat treatment is performed at a temperature not lower than the melting point of the aluminum powder to be used and lower than the melting point of the supporting powder. When the mixed powder is combined with the metal plate, heat treatment is performed at a temperature that is equal to or higher than the lower melting point of the aluminum powder and the metal plate and lower than the melting point of the support powder. The melting point of the aluminum powder is a temperature at which a liquid phase of pure aluminum or an aluminum alloy is generated, and the melting point of the metal plate is a temperature at which a liquid phase is similarly generated. By heating to a temperature at which a liquid phase is generated, the liquid phase oozes out from the aluminum powder, and the aluminum powders are bonded metallically by contacting the liquid phases.

  When the heat treatment temperature is lower than the melting point, aluminum is not melted, so that bonding between the aluminum powders and between the aluminum powder and the metal plate becomes insufficient. Moreover, when heated above the melting point, the aluminum covering the surface of the support powder located on the outermost surface of the sintered body is removed, and 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. Therefore, heating is performed at a temperature lower than the melting point of the support powder. When a water-soluble salt such as sodium chloride or potassium chloride is used as the support powder, the heat treatment is preferably performed at a temperature lower than 700 ° C., more preferably lower than 680 ° C. 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. By forming an aluminum lump, the porosity of porous aluminum becomes higher than intended. The formation of such an aluminum lump is detrimental in that the porosity of porous aluminum cannot be controlled. In addition, there is a problem in that the shape collapses due to the formation of an aluminum lump and must be removed. The heat holding time in the heat treatment is preferably about 1 to 60 minutes. 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 1000 ppm or less and the dew point is −30 ° C. or less.

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

<Negative electrode>
Examples of lithium metal oxide that occludes and releases lithium ions include lithium titanium composite oxide, lithium tungsten composite oxide, lithium niobium composite oxide, and lithium molybdenum composite oxide. Among these lithium metal oxides, it is preferable to use a lithium titanium composite oxide from the viewpoints of increasing the capacity, extending the life and safety of the nonaqueous electrolyte secondary battery.

Specific examples of the lithium titanium composite oxide include, for example, Li _4-x Ti ₅ O ₁₂ (0 ≦ x ≦ 3), Li _{2 + y} Ti ₃ O ₇ (0 ≦ y ≦ 3) and the like, and constituent elements of these oxides And lithium-titanium composite oxide in which a part of is substituted with a different element. A lithium containing complex oxide can be used individually by 1 type or in combination of 2 or more types.

<Conductive aid>
The conductive auxiliary agent used in the present embodiment is not particularly limited, and a known or commercially available one can be used. Examples thereof include carbon black such as acetylene black and ketjen black, activated carbon, graphite and the like. Furthermore, as the thickener, an aqueous solution of carboxymethyl cellulose (CMC) or the like can be used.

<Binder>
The binder used in the present embodiment is not particularly limited, and a known or commercially available one can be used. For example, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), fluorine-based rubber, styrene-butadiene rubber, core-shell binder, imide-based resin such as polyimide and polyamideimide, and the like are used.

  The negative electrode active material, the conductive additive, and the binder are filled in the porous aluminum current collector as a slurry dispersed in a solvent. The blending ratio of the negative electrode active material, the conductive additive and the binder is appropriately selected so as to obtain a desired effect. Further, the concentration of these components in the slurry is not limited. Although the solvent of the slurry is not particularly limited, 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, or the like as a binder, water is used. It is preferable to use it as a solvent.

  A slurry in which a negative electrode active material, a conductive additive and a binder are dispersed in a solvent is filled in a porous aluminum current collector by a known method such as a press-fitting method. In the press-fitting method, a slurry is disposed on one side using a porous aluminum current collector as a diaphragm, and the other side is a slurry permeation side. And the negative electrode active material, the conductive support agent, and the binder are filled in the pores of the porous aluminum current collector by reducing the pressure on the other permeate side and allowing the slurry to permeate. Alternatively, the negative electrode active material, the conductive aid, and the binder may be filled in the pores of the porous aluminum current collector by pressurizing the slurry disposed on one side. In place of the press-fitting method, the porous aluminum current collector is immersed in a slurry in which a negative electrode active material, a conductive auxiliary agent, and a binder are dispersed in a solvent, and the negative electrode active material, the conductive auxiliary agent, and the binder are made porous. A method of diffusing into the pores of the porous aluminum current collector (hereinafter referred to as an immersion method) may be employed.

The negative electrode for a non-aqueous electrolyte secondary battery filled with the negative electrode active material, the conductive additive and the binder as described above is dried by scattering the solvent at 50 to 200 ° C.
The negative electrode for a non-aqueous electrolyte secondary battery thus obtained is preferably improved in the electrode density of the active material by press treatment using a roll press machine or a flat plate press machine. In particular, press processing using a flat plate press is desirable. This is because, in the press treatment using a roll press, the porous aluminum current collector may be distorted and the electrode may collapse.
In addition, it is preferable that the press process by a flat plate press presses with the pressure of 10-100 Mpa.

<Positive electrode>
The positive electrode is obtained by filling a porous aluminum current collector with a slurry in which an active material capable of occluding and releasing lithium ions is dispersed in a solvent. In addition to the positive electrode active material, a conductive additive, a binder and a thickener may be further added to this solvent.
The positive electrode active material is not particularly limited as long as it can be used for a non-aqueous electrolyte secondary battery. For example, lithium metal oxides such as lithium cobaltate, lithium manganate, lithium nickelate, and lithium iron phosphate Can be mentioned.

A binder is not specifically limited, 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.
Examples of the conductive auxiliary agent are the same as those used for the negative electrode, for example, carbon black such as acetylene black and ketjen black, activated carbon, graphite and the like. Further, an aqueous solution of carboxymethyl cellulose (CMC) or the like can be used as the thickener.

<Separator>
For the separator between the negative electrode and the positive 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. be able to.

  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.

(Preparation of porous aluminum current collector)
First, a porous aluminum current collector used for the electrode for a nonaqueous electrolyte secondary battery according to the present invention was produced as follows.
Pure aluminum powder (median diameter 3 μm, melting point 660 ° C.) was used as the aluminum powder, and sodium chloride powder (particle size 400 μm (median sieve opening, melting point 800 ° C.)) was used as the supporting powder. Powder 8 vol%: Sodium chloride powder 92 vol% was mixed at a volume ratio to prepare a mixed powder.
This mixed powder was filled in a mold having a hole with a diameter of 20 mm and pressure-molded at a pressure of 400 MPa. The filling amount of the mixture was set to a mass at which the thickness of the pressure molded body was 1 mm. The sintered compact is produced by heat-treating this pressure-molded body in an atmosphere having a maximum ultimate pressure of 1 × 10 ⁻² Pa or less at 670 ° C. for 5 minutes, and the resulting sintered body is washed with running water (tap water). ) For 6 hours to elute the supporting powder to prepare a porous aluminum current collector (diameter 20 mm × thickness 1 mm).
(Preparation of negative electrode for non-aqueous electrolyte secondary battery)
90 parts by weight of lithium titanate as a negative electrode active material, 5 parts by weight of acetylene black as a conductive auxiliary agent, and 5 parts by weight of polyvinylidene fluoride as a binder are dispersed in an appropriate amount of N-methyl-2-pyrrolidone as a solvent and stirred. Mix to prepare a slurry.
Porous aluminum current collector (φ20, porosity 93%, pore diameter 300 μm) prepared by the above method in a slurry in which a negative electrode active material, a conductive additive and a binder are dispersed in a solvent using the above-described immersion method Was immersed and depressurized (−0.1 MPa). After soaking, excess slurry adhered to the front and back surfaces of the porous aluminum current collector was scraped off using a spatula. Next, the porous aluminum current collector filled with the slurry is placed in a drying apparatus, dried at 80 ° C. for 2 hours, pressed (60 MPa) until the density reaches 2.0 g / cc, and the non-aqueous electrolyte secondary A negative electrode sample for a battery (hereinafter referred to as a negative electrode sample) was prepared.

(Preparation of positive electrode for nonaqueous electrolyte secondary battery)
100 parts by weight of carbon-coated lithium iron phosphate as a positive electrode active material, 6.8 parts by weight of acetylene black as a conductive additive, and 3 parts by weight of an acrylic copolymer having a solid content concentration of 40% by mass as a water-dispersing binder A slurry was prepared by dispersing 2 parts by weight (as a solid content) of carboxymethyl cellulose (as a solid content) and 2 parts by weight of a carboxymethyl cellulose having a solid content concentration of 2% by mass (as a solid content) in an aqueous solution as a dispersant.
A porous aluminum current collector (φ20, porosity 93%, pore diameter 300 μm) prepared by the above method in a slurry in which a positive electrode active material, a conductive additive and a binder were dispersed in a solvent using the above-described immersion method. ) Was immersed and depressurized (−0.1 MPa). After immersion, surplus slurry adhered to the front and back surfaces of the porous aluminum current collector was scraped off using a spatula. Next, the porous aluminum current collector filled with the slurry is placed in a drying apparatus, dried at 80 ° C. for 2 hours, pressed (60 MPa) until the density becomes 1.8 g / cc, and the non-aqueous electrolyte secondary A battery positive electrode sample (hereinafter referred to as a positive electrode sample) was prepared.
That is, in this example, the current collector is a porous aluminum current collector for both the positive electrode and the negative electrode.

(Production of evaluation cell)
An evaluation cell was prepared using the negative electrode sample and the positive electrode sample subjected to the press treatment. As the electrolytic solution, a non-aqueous electrolytic solution in which 1.3 mol / L of LiPF ₆ was dissolved in a mixed solvent of ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate (volume ratio 2: 5: 3) was used, and the separator was microporous. A quality polyethylene film was used. A resin container in which a polypropylene block was processed was used as the outer package, and the electrode group was housed and sealed so that the negative electrode sample and the open end of each terminal provided on the positive electrode sample were exposed to the outside.

  In the negative electrode for a non-aqueous electrolyte secondary battery, 98 parts by weight of lithium titanate as a negative electrode active material, 1 part by weight of an SBR aqueous binder having a solid content concentration of 40% by weight as a binder (as solid content), In addition, a slurry was prepared by dispersing 1 part by weight (as solid content) of carboxymethylcellulose having a solid content concentration of 1% by mass in an aqueous solution as a dispersant in an appropriate amount of ion-exchanged water as a solvent. A slurry was filled in the porous aluminum current collector by the same dipping method as in Example 1 to prepare a negative electrode sample. Thereafter, an evaluation cell was prepared in the same manner as in Example 1, and a battery test was performed.

<Comparative Example 1>
In Comparative Example 1, a metal foil is used for the current collector of the negative electrode in Example 1.
That is, in Comparative Example 1, the negative electrode was replaced with a porous aluminum current collector, an aluminum foil having a thickness of 20 μm was used as the current collector, and the slurry prepared in Example 1 was applied onto the current collector. And dried to prepare a negative electrode sample. Thereafter, an evaluation cell was prepared in the same manner as in Example 1, and a battery test was performed.

<Comparative example 2>
This comparative example 2 uses a metal foil for the current collector of the negative electrode in the example 2.
That is, in Comparative Example 2, the negative electrode was replaced with a porous aluminum current collector, an aluminum foil having a thickness of 20 μm was used as the current collector, and the slurry prepared in Example 2 was applied onto the current collector. And dried to prepare a negative electrode sample. Thereafter, an evaluation cell was prepared in the same manner as in Example 1, and a battery test was performed.

<Comparative Example 3>
This Comparative Example 3 uses a metal foil as the positive electrode current collector in Example 1.
That is, in Comparative Example 3, the positive electrode was replaced with a porous aluminum current collector, an aluminum foil with a thickness of 20 μm was used as the current collector, and the slurry prepared in Example 1 was applied onto this current collector. And dried to prepare a positive electrode sample. Thereafter, an evaluation cell was prepared in the same manner as in Example 1, and a battery test was performed.

<Comparative example 4>
In Comparative Example 4, the metal foil is used for the positive and negative electrode current collectors in Example 1.
That is, in Comparative Example 4, the negative electrode was replaced with a porous aluminum current collector, an aluminum foil having a thickness of 20 μm was used as the current collector, and the slurry prepared in Example 1 was applied onto this current collector. And dried to prepare a negative electrode sample. Further, the positive electrode was replaced with a porous aluminum current collector, and an aluminum foil having a thickness of 20 μm was used as the current collector. The slurry produced in Example 1 was applied onto the current collector and dried, and the positive electrode A sample was prepared. Thereafter, an evaluation cell was prepared in the same manner as in Example 1, and a battery test was performed.

Table 1 shows the electrode capacities of the negative electrode samples and the positive electrode samples prepared in Example 1, Example 2, and Comparative Examples 1 to 4.
The electrode capacity was determined from electrode capacity (mAh) = theoretical capacity of active material (mAh / g) × active material weight (g) of each prepared electrode. The thicknesses of the negative electrode and positive electrode samples were measured using a film thickness meter.

  As shown in Table 1, Examples 1 and 2 in which the positive electrode and negative electrode current collectors were porous aluminum were used in Comparative Examples 1 to 4 (in which positive electrode and / or negative electrode current collectors were metal foils). It can be seen that the electrode capacity reaches 4 times or more (about 6 to 7 times) as compared with the negative electrodes of Comparative Examples 1, 2, and 4 and the positive electrodes of Comparative Examples 3 and 4. That is, from this result, it was difficult to increase the capacity by increasing the thickness of the electrode coating layer using the conventional metal foil current collector and electrode active material, but by using a porous aluminum current collector, It has been clarified that the capacity can be increased even though the electrode has the same area as the electrode using the metal foil current collector.

  Furthermore, the capacity of the battery is determined by the electrode capacity, and is regulated by an electrode having a lower capacity of the positive electrode and the negative electrode. Therefore, the batteries of Example 1 and Example 2 have a capacity of about 6 to 7 times that of the batteries of Comparative Examples 1 to 4. Therefore, a battery composed of electrodes using a porous aluminum current collector for the positive electrode and the negative electrode has the same electrode area and number of electrodes as a battery composed of an electrode using a metal foil current collector. It is clear that the capacity can be increased.

(Battery test)
Using the batteries obtained in Example 1, Example 2, and Comparative Examples 1 to 4, an evaluation test of charge / discharge characteristics was performed.
In the first charge / discharge test, the battery was charged to 2.2 V with a current of 0.5 mA and discharged to 1.5 V with a current of 0.5 mA. Table 2 shows the initial discharge capacity per area.
In the cycle test, a cycle in which charging was performed at a current of 0.5 mA up to 2.2 V and discharging was performed at a current of 0.5 mA up to 1.2 V was performed for 100 cycles. Table 3 shows the capacity retention rate after 100 cycles of this cycle test.
The capacity maintenance rate after 100 cycles is a ratio of the capacity after 100 cycles when the initial capacity is 100%.

  As shown in Table 2, it can be seen that the batteries of Example 1 and Example 2 have a larger discharge capacity than the batteries of Comparative Examples 1 to 4. The capacity of the battery is determined by the electrode capacity, and is regulated by an electrode having a lower capacity of the positive electrode and the negative electrode. Therefore, the batteries of Example 1 and Example 2 had a capacity about 5 to 7 times that of the batteries of Comparative Examples 1 to 4. Therefore, a battery composed of electrodes using a porous aluminum current collector for the positive electrode and the negative electrode has the same electrode area and number of electrodes as a battery composed of an electrode using a metal foil current collector. It can be seen that the capacity can be increased.

  As shown in Table 3, it can be seen that Example 1 and Example 2 are superior in capacity retention rate as compared with Comparative Examples 1 to 4. This is probably because the active material is held by the porous structure of the current collector, so that the deterioration behavior such as dropping of the active material with the number of cycles is suppressed.

As described above, according to the present invention, since the non-aqueous electrolyte secondary battery is configured using the porous aluminum current collector as the current collector for both the positive electrode and the negative electrode, it is generally used as the current collector. A positive electrode for a non-aqueous electrolyte secondary battery having a high capacity and a long life can be obtained as compared with a coated electrode formed by applying an electrode material to a metal foil.
In addition, according to the present invention, since the positive and negative electrode active materials are held by the porous structure of the current collector, deterioration behavior such as positive and negative electrode active materials falling off due to repeated charge and discharge is suppressed. . In particular, when a large amount of positive and negative electrode active material layers are applied to a metal foil current collector to increase the capacity, the positive and negative electrode active materials may fall off from the current collector in the electrode drying process or pressing process. This can be suppressed by using a porous current collector.
Furthermore, by using a porous aluminum current collector as the current collector for the negative electrode, the cost can be reduced compared to the case where copper is used as the current collector.
Therefore, according to the present invention, by using a porous aluminum current collector for both the positive electrode and the negative electrode, it is possible to obtain a non-aqueous electrolyte secondary battery that suppresses deterioration of battery characteristics and has high capacity and excellent charge / discharge cycle characteristics.

Claims (4)

A positive electrode in which a three-dimensional porous aluminum current collector is filled with a positive electrode active material, and a negative electrode in which a three-dimensional porous aluminum current collector is filled with a negative electrode active material,
In the inert atmosphere, the three-dimensional porous aluminum current collector used for the positive electrode and the negative electrode is formed by press-molding a mixed powder of an aluminum powder and a support powder mixed at a predetermined volume ratio. causing aluminum powder or et liquid phase by heat treatment to bond the aluminum powder same, and the support powder is a three-dimensional porous aluminum current collector manufactured by removing the supporting powder is removed And the bonded metal powder wall of the joined aluminum powder that forms the periphery of the void. The bonded metal powder wall has many fine holes, and the voids are formed by these fine holes. It is a connected open cell type structure,
The negative active material of the nonaqueous electrolyte secondary battery comprising lithium der Rukoto metal acid.   The nonaqueous electrolyte secondary battery according to claim 1, wherein a particle diameter of the aluminum powder is 1 to 50 μm.   3. The nonaqueous electrolyte secondary battery according to claim 1, wherein the three-dimensional porous aluminum current collector has a porosity of 80% or more and 95% or less. Given mixed with aluminum powder in a volume ratio of the molded body of the mixed powder formed by pressure-molding of the support powder was heat-treated in an inert atmosphere to cause the aluminum Powder or al-liquid phase, joining the aluminum powder What happened and removal of the support powder, and the support powder is removed void, it is constituted by a coupling metal powder walls of the joined aluminum powder to form the periphery of the void, many of the bound metal powder walls A step of producing a three-dimensional porous aluminum current collector having an open cell structure in which fine pores are formed and voids are connected by these fine pores ;
Producing a positive electrode in which the three-dimensional porous aluminum current collector is filled with a positive electrode active material , and a negative electrode in which the three-dimensional porous aluminum current collector is filled with a negative electrode active material of lithium metalate. A method for producing a non-aqueous electrolyte secondary battery.