KR20200135489A - Electrolyte sheet and secondary battery - Google Patents

Abstract

One aspect of the present invention is an electrolyte sheet containing one or two or more polymers, inorganic oxide particles, and electrolyte salt, wherein the total surface area of the inorganic oxide particles occupied by 1 cm ³ of the electrolyte sheet is 1000 to 12000 cm ^-1 , It is an electrolyte sheet.

Description

Electrolyte sheet and secondary battery

The present invention relates to an electrolyte sheet and a secondary battery.

BACKGROUND ART In recent years, with the spread of portable electronic devices and electric vehicles, high-performance secondary batteries are required. Among them, lithium secondary batteries are attracting attention as power sources for electric vehicle batteries and power storage batteries because they have a high energy density. Specifically, a lithium secondary battery as a battery for an electric vehicle is a zero emission electric vehicle without an engine, a hybrid electric vehicle equipped with both an engine and a secondary battery, and a plug-in that directly charges from the power system. · It is used in electric vehicles such as hybrid electric vehicles. Further, a lithium secondary battery as a battery for power storage is used in a stationary power storage system or the like that supplies pre-stored power in an emergency when the power system is cut off.

Among such secondary batteries, especially lithium secondary batteries for electric vehicles, since high safety is required in addition to high input/output characteristics and high energy density, a more advanced technology for securing safety is required. As a battery with higher safety, for example, Patent Document 1 discloses a lithium secondary battery including a sheet-like electrolyte (electrolyte sheet) by applying a slurry containing inorganic oxide particles onto an electrode and drying it.

Patent Document 1: Japanese Laid-Open Patent Publication No. 2015-191710

The electrolyte sheet is required not only to have high electrical conductivity, but also to mechanical strength such as tensile strength in order to improve the characteristics of the secondary battery.

Accordingly, an object of the present invention is to provide an electrolyte sheet excellent in electrical conductivity and tensile strength, and a secondary battery using the same.

One aspect of the present invention is an electrolyte sheet containing one or two or more polymers, inorganic oxide particles, and electrolyte salt, wherein the total surface area of the inorganic oxide particles occupied by 1 cm ³ of the electrolyte sheet is 1000 to 12000 cm ^-1 , It is an electrolyte sheet.

Among the structural units constituting one or two or more polymers, a first structural unit selected from the group consisting of ethylene tetrafluoride and vinylidene fluoride, hexafluoropropylene, acrylic acid, maleic acid, ethyl methacrylate, and The second structural unit selected from the group consisting of methyl methacrylate may be contained.

The polymer content may be 10 to 40% by mass based on the total amount of the electrolyte sheet.

The inorganic oxide particles may be at least one particle selected from the group consisting of SiO ₂ , Al ₂ O ₃ , AlOOH, MgO, CaO, ZrO ₂ , TiO ₂ , Li ₇ La ₃ Zr ₂ O ₁₂ , and BaTiO ₃ .

Another aspect of the present invention is a secondary battery provided with a pair of electrodes and the electrolyte sheet according to any one of claims 1 to 4 provided between the pair of electrodes.

One each of the electrodes of the pair, collector and house provided on the entire image, comprising an electrode material mixture layer containing an electrode active material, the electrolyte sheet the total surface area of the inorganic oxide particles and the electrode material mixture layer occupied in 1cm ³ 1cm ³ The sum of the total surface area of each electrode active material occupied by may be 8000 cm ^-1 or more. In this case, a secondary battery having excellent discharge characteristics is obtained.

The total surface area of the inorganic oxide particles occupied by 1 cm ³ of the electrolyte sheet may be 5000 cm ^-1 or more, and the total surface area of each electrode active material occupied by 1 cm ³ of each electrode mixture layer may be 3000 cm ^-1 or more.

The electrode mixture layer may further contain a binder.

According to the present invention, it is possible to provide an electrolyte sheet excellent in electrical conductivity and tensile strength, and a secondary battery using the same.

1 is a perspective view showing a secondary battery according to a first embodiment.
FIG. 2 is an exploded perspective view illustrating an embodiment of an electrode group in the secondary battery shown in FIG. 1.
3 is a schematic cross-sectional view illustrating an embodiment of an electrode group in the secondary battery shown in FIG. 1.
4A is a schematic cross-sectional view showing an electrolyte sheet according to one embodiment, and (b) is a schematic cross-sectional view showing an electrolyte sheet according to another embodiment.
5 is a schematic cross-sectional view showing an embodiment of an electrode group in a secondary battery according to a second embodiment.

Hereinafter, embodiments of the present invention will be described with appropriate reference to the drawings. However, this invention is not limited to the following embodiment. In the following embodiments, the constituent elements (steps, etc. are also included) are not essential except when specifically indicated. The sizes of constituent elements in each drawing are conceptual, and the relative relationship between the sizes of constituent elements is not limited to those shown in each drawing.

The numerical values and ranges in this specification do not limit the present invention. In the present specification, the numerical range indicated by using "~" represents a range including the numerical values described before and after "~" as a minimum value and a maximum value, respectively. In the numerical range described stepwise in the present specification, the upper limit value or the lower limit value described in one numerical range may be substituted with the upper limit value or the lower limit value of another stepwise description. In addition, in the numerical range described in this specification, the upper limit value or the lower limit value of the numerical range may be substituted with a value shown in Examples.

[First embodiment]

1 is a perspective view showing a secondary battery according to a first embodiment. As shown in FIG. 1, the secondary battery 1 includes an electrode group 2 composed of a positive electrode, a negative electrode, and an electrolyte sheet, and a bag-shaped battery exterior body 3 accommodating the electrode group 2, have. The positive electrode and the negative electrode are provided with a positive electrode current collecting tab 4 and a negative electrode current collecting tab 5, respectively. The positive electrode current collecting tab 4 and the negative electrode current collecting tab 5 protrude from the inside of the battery exterior body 3 to the outside so that the positive electrode and the negative electrode can be electrically connected to the outside of the secondary battery 1, respectively.

The battery exterior body 3 may be formed of a laminate film, for example. The laminate film may be a laminate film in which a resin film such as a polyethylene terephthalate (PET) film, a metal foil such as aluminum, copper, and stainless steel, and a sealant layer such as polypropylene are laminated in this order.

FIG. 2 is an exploded perspective view showing an embodiment of an electrode group 2 in the secondary battery 1 shown in FIG. 1. 3 is a schematic cross-sectional view illustrating an embodiment of an electrode group 2 in the secondary battery 1 shown in FIG. 1. 2 and 3, the electrode group 2A according to the present embodiment includes an anode 6, an electrolyte sheet (electrolyte layer) 7 and a cathode 8 in this order. . The positive electrode 6 includes a positive electrode current collector 9 and a positive electrode mixture layer 10 provided on the positive electrode current collector 9. The positive electrode current collector 9 is provided with a positive electrode current collector tab 4. The negative electrode 8 includes a negative electrode current collector 11 and a negative electrode mixture layer 12 provided on the negative electrode current collector 11. The negative electrode current collector 11 is provided with a negative electrode current collector tab 5.

The positive electrode current collector 9 may be formed of aluminum, stainless steel, titanium, or the like. Specifically, the positive electrode current collector 9 may be, for example, an aluminum perforated foil having a pore diameter of 0.1 to 10 mm, an expanded metal, a foam metal plate, or the like. In addition to the above, the positive electrode current collector 9 may be formed of any material, as long as it does not cause changes such as dissolution or oxidation during use of the battery, and the shape and manufacturing method thereof are not limited.

The thickness of the positive electrode current collector 9 may be 10 μm or more, 100 μm or less, and from the viewpoint of reducing the overall volume of the positive electrode, it is preferably 10 to 50 μm, and the positive electrode is wound with a small curvature when forming a battery ( From the viewpoint of being able to recover, it is more preferably 10 to 20 μm.

The positive electrode material mixture layer 10 contains a positive electrode active material, a conductive material, and a binder in one embodiment.

The positive electrode active material is LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , LiMnO ₃ , LiMn ₂ O ₃ , LiMnO ₂ , Li ₄ Mn ₅ O ₁₂ , LiMn _2-a M ¹ _a O ₂ (however, M ¹ =Co, It is one selected from the group consisting of Ni, Fe, Cr, Zn, and Ta, and a=0.01 to 0.2), Li ₂ Mn ₃ M ² O ₈ (however, M ² =Fe, Co, Ni, Cu, And Zn), Li _1-b M ³ _b Mn ₂ O ₄ (however, M ³ =Mg, B, Al, Fe, Co, Ni, Cr, Zn, and Ca It is one type selected from, b=0.01~0.1), LiFeO ₂ , Fe ₂ (SO ₄ ) ₃ , LiCo _1-d M ⁵ _d O ₂ (However, M ⁵ =Ni, Fe, and the group consisting of Mn Is one selected from, and d=0.01~0.2), LiNi _1-e M ⁶ _e O ₂ (however, M ⁶ =Mn, Fe, Co, Al, Ga, Ca, and Mg selected from the group consisting of It is 1 type, and e=0.01~0.2), Fe(MoO ₄ ) ₃ , FeF ₃ , LiFePO ₄ , LiMnPO _4, etc. may be used. The positive electrode active material may be primary particles that are not granulated, or may be secondary particles that are granulated.

The particle diameter of the positive electrode active material is adjusted so as to be less than or equal to the thickness of the positive electrode mixture layer 10. If there is a coarse particle having a particle diameter equal to or greater than the thickness of the positive electrode mixture layer 10 in the positive electrode active material, the coarse particles are removed in advance by sieve classification, wind-flow classification, etc. Select the active material.

The average particle diameter Dp ₅₀ of the positive electrode active material is preferably 0.1 μm or more from the viewpoint of suppressing the deterioration of the chargeability of the positive electrode active material due to a decrease in particle diameter and increasing the holding capacity of the electrolyte, because the positive electrode active material can be suitably prepared. , More preferably 1 μm or more, and still more preferably 2 μm or more. The average particle diameter of the positive electrode active material is, from the viewpoint of increasing the reaction surface area of the positive electrode active material and improving the input/output characteristics of the secondary battery, preferably 20 μm or less, more preferably 10 μm or less, further preferably 8 μm or less. The average particle diameter Dp ₅₀ of the positive electrode active material is a particle diameter when the ratio (volume fraction) to the volume of the entire positive electrode active material is 50%. The average particle diameter Dp ₅₀ of the positive electrode active material is obtained by measuring a suspension in which the positive electrode active material is suspended in water by a laser scattering method using a laser scattering type particle diameter measuring device (for example, microtrack).

The charging rate fp of the positive electrode active material is based on the total volume of the positive electrode active material, the conductive material, and the binder, from the viewpoint of suppressing a decrease in the energy density of the secondary battery, preferably 30% by volume or more, more preferably 40% by volume. % Or more, more preferably 50% by volume or more. The charging rate fp of the positive electrode active material is preferably 90% by volume or less, more preferably 85% by volume, based on the total volume of the positive electrode active material, the conductive material, and the binder from the viewpoint of suppressing the reduction in the life of the secondary battery. Below, it is more preferably 80% by volume or less.

The filling rate fp of the positive electrode active material is an area (occupied area) of the positive electrode active material occupied in a unit area of the surface or cross section by observing an arbitrary surface or cross section of the positive electrode mixture layer 10 with a scanning electron microscope. Area %), measured by image processing (binary processing). In addition, since the area occupied by the positive electrode active material in an arbitrary surface or cross section of the positive electrode mixture layer 10 is considered to be substantially constant, the occupied area can be regarded as the filling rate fp.

The total surface area Sp of the positive electrode active material occupied (per unit volume) in a unit volume of 1 cm ³ of the positive electrode mixture layer 10 (hereinafter, simply referred to as “total surface area Sp of the positive electrode active material”) is, for example, 1000 cm ^-1 or more or 2000 cm ^It may be ^-1 or more, and from the viewpoint of excellent conductivity, it is 3000 cm ^-1 or more, preferably 5000 cm ^-1 or more, more preferably 6000 cm ^-1 or more, and still more preferably 7000 cm ^-1 or more. The total surface area Sp of the positive electrode active material is, for example, or may be less than 10000cm ^-1, 9000cm ^-1 or less, or less than 8000cm ^-1.

The total surface area Sp of the positive electrode active material is defined by the following formula (1).

Sp=6×10 ⁴ ×fp/Dp ₅₀ (1)

In the formula, fp represents the filling rate (volume %) of the above-described positive electrode active material, and Dp ₅₀ represents the average particle diameter (μm) of the above-described positive electrode active material.

In addition, the physical meaning of the constant term "6" on the right side of Formula (1) is as follows. First, assuming that the charging rate fp is 1 (100% by volume), that is, the positive electrode active material is a rigid sphere, a case where it is charged in a cube of the minimum size is considered. These cubes are arranged vertically and horizontally without gaps, and one positive electrode active material is present in each cube. Here, the radius of the active material is set to R (cm). Since the positive electrode active materials are of the same size and the state in which each active material is present is the same, the total surface area Sp of the positive electrode active material pays attention to the active material present in one cube, and becomes equal to the ratio of the surface area and the volume. That is, Sp is represented by the following equation.

Sp = surface area of positive electrode active material/volume of positive electrode active material

=4πR ² /(4πR ³ /3)

=3/R (2)

Here, from the relationship of R(cm) = Db ₅₀ (μm) x 10 ^-4 /2, equation (2) is converted to equation (3).

Sp=3/(Db ₅₀ ×10 ^-4 /2)

=6×10 ⁴ /Dp ₅₀ (3)

And, when fp is less than 1, since it is sufficient to multiply the right side of Formula (3) by fp, the general formula when the charging rate of the positive electrode active material is fp becomes the above-mentioned Formula (1).

As represented by Equation (1), the total surface area Sp of the positive electrode active material is expressed as a function of the charge rate fp of the positive electrode active material and the average particle diameter Dp ₅₀ , and increases as the charging rate fp increases or the average particle diameter Dp ₅₀ decreases. It shows the behavior of saying that. The filling rate fp is in a monotonically proportional relationship to the number of positive electrode active materials in the unit volume of the positive electrode material mixture layer 10, and as the Dp ₅₀ decreases, the surface area increases, so that the behavior of equation (1) can be understood. .

The conductive material may be a conductive carbon material such as carbon black, graphite, carbon fiber, or carbon nanotube.

The content of the conductive material is preferably 0.1% by mass or more, more preferably 0.5% by mass, based on the total amount of the positive electrode mixture layer, from the viewpoint of improving the input/output characteristics of the secondary battery because the positive electrode 6 has excellent conductivity. % Or more, more preferably 1 mass% or more, particularly preferably 3 mass% or more. The content of the conductive material is, based on the total amount of the positive electrode mixture layer, preferably 20% by mass or less, more preferably, from the viewpoint of suppressing the increase in the volume of the positive electrode and the decrease in the energy density of the secondary battery 1 accompanying it. Is 15% by mass or less, more preferably 10% by mass or less, and particularly preferably 8% by mass or less.

The binder is not limited as long as it does not decompose on the surface of the anode 6, but is, for example, a polymer. The binder may be a cellulose compound such as carboxylmethylcellulose, cellulose acetate, or ethylcellulose, polyvinylidene fluoride, styrene butadiene rubber, fluorine rubber, ethylene propylene rubber, polyacrylic acid, polyimide, polyamide, or the like. .

The content of the binder is preferably 0.5% by mass or more, more preferably 1% by mass or more, and still more preferably 3 based on the total amount of the positive electrode mixture layer, from the viewpoint of excellent durability and lifespan characteristics of the secondary battery. It is not less than mass%. The content of the binder is preferably 20% by mass or less, more preferably 15% by mass or less, and still more preferably 10% by mass or less based on the total amount of the positive electrode material mixture layer from the viewpoint of excellent energy density of the secondary battery. , Particularly preferably 7% by mass or less.

The thickness of the positive electrode material mixture layer 10 is a thickness equal to or greater than the average particle diameter of the positive electrode active material from the viewpoint of further improving the conductivity, specifically preferably 5 μm or more, more preferably 10 μm or more, and even more preferably 20 μm That's it. The thickness of the positive electrode mixture layer 10 is preferably 100 μm or less, more preferably 80 μm or less, and still more preferably 50 μm or less. By making the thickness of the positive electrode mixture layer 80 μm or less, it is possible to suppress deflection in charge and discharge due to variations in the charge level of the positive electrode active material in the vicinity of the surface of the positive electrode mixture layer 10 and in the vicinity of the surface of the positive electrode current collector 9. .

The mixture density of the positive electrode material mixture layer 10 is preferably 2 g/cm ³ or more from the viewpoint of bringing the conductive material and the positive electrode active material into close contact with each other to reduce the electronic resistance of the positive electrode material mixture layer 10, for example 3.5 It may be less than or equal to g/cm ³ .

The negative electrode current collector 11 may be formed of copper, stainless steel, titanium, nickel, or the like. Specifically, the negative electrode current collector 11 may be a rolled copper foil, for example, a copper perforated foil having a pore diameter of 0.1 to 10 mm, an expanded metal, a foamed metal plate, or the like. The negative electrode current collector 11 may be formed of any material other than the above, and its shape, manufacturing method, and the like are not limited.

The thickness of the negative electrode current collector 11 may be 10 μm or more, 100 μm or less, and from the viewpoint of reducing the overall volume of the negative electrode, it is preferably 10 to 50 μm, and the negative electrode can be wound with a small curvature when forming a battery. From a possible viewpoint, it is more preferably 10 to 20 μm.

The negative electrode mixture layer 12 contains a negative electrode active material and a binder in one embodiment.

As the negative electrode active material, those commonly used in the field of energy devices can be used. Specific examples of the negative electrode active material include metal lithium, lithium alloy, metal compound, carbon material, metal complex, and organic polymer compound. As for the negative electrode active material, one of the above may be used alone, or two or more may be used in combination. The negative electrode active material is preferably a carbon material. Carbon materials include natural graphite (scale graphite, etc.), graphite such as artificial graphite, amorphous carbon, carbon fiber, and carbon such as acetylene black, Ketchen black, channel black, furnace black, lamp black, and thermal black. And black. The negative electrode active material may be natural graphite coated with amorphous carbon (theoretical capacity: 372 Ah/kg), and from the viewpoint of obtaining a larger theoretical capacity (for example, 500 to 1500 Ah/kg), silicon, tin, or containing these elements It may be a compound (oxide, nitride, alloy with another metal). When a material having a large capacity is used, the thickness of the negative electrode mixture layer 12 can be made thin, and the area of the electrode that can be accommodated in the secondary battery 1 can be increased. As a result, the resistance of the secondary battery 1 is lowered to enable high output, and at the same time, the capacity of the secondary battery 1 can be increased compared to when a graphite negative electrode is used.

The average particle diameter Dn ₅₀ of the negative electrode active material is from the viewpoint of obtaining a negative electrode 8 having a good balance in which the negative electrode active material can be suitably prepared, suppresses an increase in irreversible capacity due to a decrease in particle size, and increases the holding capacity of the electrolyte. It is preferably 0.1 μm or more, more preferably 1 μm or more, more preferably 5 μm or more, and particularly preferably 10 μm or more. The average particle diameter (Dn ₅₀ ) of the negative electrode active material is preferably 50 μm or less, more preferably 30 μm or less, and more preferably, from the viewpoint of increasing the reaction surface area of the negative electrode active material and improving the input/output characteristics of the secondary battery. It is 20 μm or less, and particularly preferably 15 μm or less. The average particle diameter Dn ₅₀ of the negative electrode active material is a particle diameter when the ratio (volume fraction) to the volume of the entire negative electrode active material is 50%, and can be measured in the same manner as the average particle diameter Dp ₅₀ of the positive electrode active material.

The charging rate fn of the negative electrode active material is based on the total volume of the negative electrode active material, the conductive material, and the binder, from the viewpoint of suppressing a decrease in the energy density of the secondary battery, preferably 30% by volume or more, more preferably 40% by volume. % Or more, more preferably 50% by volume or more. The charging rate fn of the negative electrode active material is preferably 90% by volume or less, more preferably 80% by volume, based on the total volume of the negative electrode active material, the conductive material, and the binder from the viewpoint of suppressing the reduction in the life of the secondary battery. Below, it is more preferably 70% by volume or less. The charging rate fn of the negative electrode active material can be measured in the same manner as the charging rate fp of the positive electrode active material.

The total surface area Sn of the negative electrode active material occupied (per unit volume) in a unit volume of 1 cm ³ of the negative electrode mixture layer 12 (hereinafter, also simply referred to as "total surface area of the negative electrode active material Sn") is, for example, 1000 cm ^-1 or more or 2000 cm ^It may be ^-1 or more, and from the viewpoint of excellent conductivity, it is 3000 cm ^-1 or more, preferably 4000 cm ^-1 or more, more preferably 5000 cm ^-1 or more, and still more preferably 7000 cm ^-1 or more. The total surface area of the negative electrode active material is Sn, for example, or may be less than 10000cm ^-1, 9000cm ^-1 or less, or less than 8000cm ^-1.

The total surface area Sn of the negative electrode active material is defined by the following formula (4).

Sn=6×10⁴×fn/Dn₅₀ (4)

In the formula, fn represents the charging rate (volume %) of the negative active material described above, and Dn ₅₀ represents the average particle diameter (μm) of the negative active material described above. In addition, the physical meaning of the constant term "6" on the right side of the equation (4) is the same as in the equation (1). In addition, as in equation (1), the total surface area Sn of the negative electrode active material is expressed as a function of the charging rate fn and the average particle diameter Dn ₅₀ of the negative electrode active material, and as the charging rate fn increases or the average particle diameter Dn ₅₀ decreases, It exhibits a behavior of increasing. The charging rate fn is in a monotonically proportional relationship to the number of negative electrode active materials in the unit volume of the negative electrode mixture layer 12, and as Dn ₅₀ decreases, the surface area increases, so that the behavior of equation (4) can be understood. .

The binder and its content may be the same as the binder and its content in the positive electrode mixture layer 10 described above.

The negative electrode mixture layer 12 may further contain a conductive material from the viewpoint of lowering the resistance of the negative electrode 8. The conductive material and its content may be the same as the conductive material and its content in the positive electrode mixture layer 10 described above.

The thickness of the negative electrode mixture layer 12 is not less than the average particle diameter of the negative electrode active material, specifically preferably 10 μm or more, more preferably 15 μm or more, and still more preferably 20 μm or more, from the viewpoint of further improving the conductivity. to be. The thickness of the negative electrode mixture layer 12 is preferably 70 μm or less, more preferably 50 μm or less, still more preferably 40 μm or less, and particularly preferably 30 μm or less. By setting the thickness of the negative electrode mixture layer 12 to 70 μm or less, deflection in charge and discharge caused by variations in the charge level of the positive electrode active material in the vicinity of the surface of the negative electrode mixture layer 12 and in the vicinity of the surface of the negative electrode current collector 11 is suppressed. can do.

The mixture density of the negative electrode mixture layer 12 is preferably 1 g/cm ³ or more from the viewpoint of reducing the electronic resistance of the negative electrode mixture layer 12 by bringing the conductive material and the negative electrode active material into close contact with each other.

The electrolyte sheet 7 contains one or more polymers, inorganic oxide particles, and electrolyte salts.

Among the structural units (monomer units) constituting one or two or more polymers, a first structural unit (monomer unit) selected from the group consisting of ethylene tetrafluoride and vinylidene fluoride, and hexafluoropropylene, acrylic acid, male A second structural unit (monomer unit) selected from the group consisting of acid, ethyl methacrylate, and methyl methacrylate may be contained.

The first structural unit and the second structural unit may be contained in one type of polymer to constitute a copolymer. That is, in one embodiment, the electrolyte sheet 7 contains at least one type of copolymer containing both the first structural unit and the second structural unit. The copolymer may be a copolymer of vinylidene fluoride and hexafluoropropylene, a copolymer of vinylidene fluoride and maleic acid, a copolymer of vinylidene fluoride and methyl methacrylate, or the like. When the electrolyte sheet 7 contains a copolymer, it may further contain other polymers.

The first structural unit and the second structural unit may be contained in different polymers, respectively, and may constitute at least two polymers of a first polymer having a first structural unit and a second polymer having a second structural unit. That is, in one embodiment, the electrolyte sheet 7 contains, as a polymer, at least two or more of a first polymer including a first structural unit and a second polymer including a second structural unit. When the electrolyte sheet 7 contains the first polymer and the second polymer, it may further contain other polymers.

The first polymer may be a polymer comprising only the first structural unit, or may be a polymer further having other structural units in addition to the first structural unit. Other structural units may be oxygen-containing hydrocarbon structures such as ethylene oxide (-CH ₂ CH ₂ O-) and carboxylic acid ester (-CH ₂ COO-). The first polymer may be polyethylene tetrafluoride, polyvinylidene fluoride, polyvinylidene fluoride, and a polymer in which the oxygen-containing hydrocarbon structure is introduced into the molecular structure.

The second polymer may be a polymer comprising only the second structural unit, or may be a polymer further having other structural units in addition to the second structural unit. Other structural units may be oxygen-containing hydrocarbon structures such as ethylene oxide (-CH ₂ CH ₂ O-) and carboxylic acid ester (-CH ₂ COO-).

Examples of the combination of the first polymer and the second polymer include polyvinylidene fluoride and polyacrylic acid, poly ethylene tetrafluoride and polymethyl methacrylate, polyvinylidene fluoride and polymethyl methacrylate, and the like.

The content of the first structural unit is preferably 5% by mass or more, more preferably 10% by mass, based on the total amount of structural units constituting the polymer, from the viewpoint of further improving the strength of the electrolyte sheet 7 % Or more, more preferably 20% by mass or more. The content of the first structural unit is preferably 60% by mass or less, more preferably 40% by mass or less, and still more preferably 30% by mass or less, based on the total amount of structural units constituting the polymer.

The content of the second structural unit is preferably 1% by mass or more, more preferably 3% by mass or more, and still more preferably 5% by mass or more, based on the total amount of the structural units constituting the polymer. The content of the second structural unit is preferably 50% by mass or less, more preferably 20% by mass, based on the total amount of structural units constituting the polymer from the viewpoint of further improving the strength of the electrolyte sheet 7 % Or less, more preferably 10% by mass or less.

The content of the polymer is preferably 10% by mass or more, more preferably 15% by mass or more, further preferably based on the total amount of the electrolyte sheet, from the viewpoint of further improving the strength of the electrolyte sheet 7 Is 20% by mass or more, particularly preferably 25% by mass or more. The content of the polymer is preferably 40% by mass or less, more preferably 35% by mass or less, and still more preferably 30% by mass or less based on the total amount of the electrolyte sheet from the viewpoint of further improving the conductivity. , Particularly preferably 28% by mass or less. The content of the polymer is 10 to 40% by mass, 10 to 35% by mass, 10 to 30% by mass, 10 to 38% by mass, 15 to 40% by mass, 15 to 35% by mass, 15 to 30% by mass, 15 to 38 Mass %, 20 to 40 mass %, 20 to 35 mass %, 20 to 30 mass %, 20 to 38 mass %, 25 to 40 mass %, 25 to 35 mass %, 25 to 30 mass %, or 25 to 38 mass %.

The inorganic oxide particles may contain, for example, Li, Mg, Al, Si, Ca, Ti, Zr, La, Na, K, Ba, Sr, V, Nb, B, Ge, etc. as constituent elements. The inorganic oxide particles are preferably at least one selected from the group consisting of SiO ₂ , Al ₂ O ₃ , AlOOH, MgO, CaO, ZrO ₂ , TiO ₂ , Li ₇ La ₃ Zr ₂ O ₁₂ , and BaTiO ₃ It is a particle. Since the inorganic oxide particles have polarity, the dissociation of the electrolyte in the electrolyte sheet 7 is promoted, and amorphization of the polymer is promoted to increase the diffusion rate of the cation component of the electrolyte.

The average particle diameter (Di ₅₀ ) of the inorganic oxide particles is preferably 0.005 μm or more, more preferably 0.01 μm or more, from the viewpoint of further improving the electrical conductivity by increasing the cross-sectional area through which the cation component of the electrolyte diffuses. Preferably it is 0.03 μm or more. The average particle diameter (Di ₅₀ ) of the inorganic oxide particles is preferably 5 μm or less, more preferably 3 μm or less, and still more preferably 1 μm or less from the viewpoint of making the electrolyte sheet 7 more suitably thinner. . The average particle diameter (Di ₅₀ ) of the inorganic oxide particles is a particle diameter when the ratio (volume fraction) to the volume of the entire inorganic oxide particles is 50%. The average particle diameter (Di ₅₀ ) of the inorganic oxide particles is obtained by measuring a suspension in which the inorganic oxide particles are suspended in water by means of a laser scattering method using a laser scattering type particle size measuring device (for example, microtrack).

The shape of the inorganic oxide particles may be, for example, a mass or a substantially spherical shape. The aspect ratio of the inorganic oxide particles is preferably 10 or less, more preferably 5 or less, and still more preferably 2 or less from the viewpoint of facilitating thinning of the electrolyte sheet 7. The aspect ratio is defined as a ratio of the length in the major axis direction of the particles (maximum length of the particles) and the length in the minor axis direction of the particles (minimum length of the particles) in the scanning electron micrograph of the inorganic oxide particles. The length of the particles can be calculated statistically using commercially available image processing software (for example, Asahi Kasei Engineering Co., Ltd. image analysis software, Azokun (registered trademark)).

The filling rate fi of the inorganic oxide particles may be 5% by volume or more, 7% by volume or more, or 10% by volume or more, 50% by volume or less, 40% by volume or less, or 20% by volume or less based on the total volume of the electrolyte sheet. You can open it. The filling rate fi of the inorganic oxide particles is the area (occupied area; area%) of the inorganic oxide particles occupied by a unit area of the surface or cross section by observing an arbitrary surface or cross section of the electrolyte sheet 7 with a scanning electron microscope. As, it is measured by image processing (binary processing). In addition, since the area occupied by the inorganic oxide particles in an arbitrary surface or cross section of the electrolyte sheet 7 is considered to be substantially constant, the occupied area can be regarded as the filling factor fi.

The total surface area Si of inorganic oxide particles occupied (per unit volume) in a unit volume of 1 cm ³ of the electrolyte sheet 7 (hereinafter, simply referred to as “total surface area Si of inorganic oxide particles”) is 1000 cm ^{− It is 1} or more, preferably 2000 cm ^-1 or more, more preferably 3000 cm ^-1 or more, and still more preferably 5000 cm ^-1 or more. The total surface area Si of the inorganic oxide particles, from the viewpoint that excellent tensile strength, and 12000cm ^-1 or less, and preferably from 10000cm ^-1, more preferably at most 9000cm ^-1 or less, more preferably less than 8000cm ^-1. The total surface area Si of the inorganic oxide particles is from the viewpoint of excellent conductivity and tensile strength, preferably 1000 to 12000 cm ^-1 , 1000 to 10000 cm ^-1 , 1000 to 9000 cm ^-1 , 1000 to 8000 cm ^-1 , 2000 to 12000 cm ^-1 , 2000~10000cm ^-1 , 2000~9000cm ^-1 , 2000~8000cm ^-1 , 3000~12000cm ^-1 , 3000~10000cm ^-1 , 3000~9000cm ^-1 , 3000~8000cm ^-1 , 5000~12000cm ^-1 , 5000 It is ~10000cm ^-1 , 5000~9000cm ^-1 , or 5000~8000cm ^-1 .

The total surface area Si of the inorganic oxide particles is defined by the following formula (5).

Si=6×10 ⁴ ×fi/Di ₅₀ (5)

In the formula, fi represents the filling rate (volume %) of the inorganic oxide particles described above, and Di ₅₀ represents the average particle diameter (μm) of the inorganic oxide particles described above. In addition, the physical meaning of the constant term "6" on the right side of the equation (5) is the same as in the equation (1).

In the electrolyte sheet 7, from the viewpoint of further improving the conductivity, the total surface area Si of the inorganic oxide particles is in the above range, and the mass ratio of the content of the inorganic oxide particles to the content of the polymer (content of inorganic oxide particles/ The polymer content) is preferably 0.5/2 or more, more preferably 0.7/2 or more, more preferably 0.8/2 or more, preferably 1.8/2 or less, more preferably 1.4/2 or less, More preferably, it is 1.2/2 or less.

The electrolyte salt is at least one selected from the group consisting of a lithium salt, a sodium salt, a calcium salt, and a magnesium salt. The electrolyte salt is a compound used to transfer cations between the positive electrode 6 and the negative electrode 8. The above-described electrolyte salt has a low degree of dissociation at a low temperature, is easily diffused in a solvent, and does not thermally decompose at a high temperature, so it is preferable that the environmental temperature at which a secondary battery can be used becomes wider. The electrolyte salt may be an electrolyte salt used in a fluorine ion battery.

Electrolyte salt anion is a halide ion to ^{(I -, Cl -, Br} - , _{^{etc.), SCN -, BF 4 -}} , BF 3 (CF 3) -, BF 3 (C 2 F 5) -, PF 6 -, _{^{ClO 4 -, SbF 6 -,}} N (SO 2 F) 2 -, N (SO 2 CF 3) 2 -, N (SO 2 C 2 F 5) 2 -, B (C 6 H 5) 4 -, B _{(O 2 C 2 H 4)} 2 -, C (SO 2 F) 3 -, C (SO 2 CF 3) 3 -, CF 3 COO -, CF 3 SO 2 O -, C 6 F 5 SO 2 O - , B(O ₂ C ₂ O ₂ ) ₂ ^- and the like may be used. Anion, preferably _{^{PF 6 -, BF 4 -,}} N (SO 2 F) 2 -, N (SO 2 CF 3) 2 -, B (O 2 C 2 O 2) 2 -, or ClO ₄ ^- is .

In addition, below, the following abbreviation may be used.

^{[FSI] -: N (SO} 2 F) 2 -, bis (sulfonyl fluorophenyl) imide anion

^{[TFSI] -: N (SO} 2 CF 3) 2 -, bis (trifluoromethanesulfonyl) imide anion

^{[BOB] -: B (O} 2 C 2 O 2) 2 -, bis oxalate anion

^{[f3C] -: C (SO} 2 F) 3 -, ( sulfonyl fluorophenyl) carbonyl tris anion

Lithium salts are LiPF ₆ , LiBF ₄ , Li[FSI], Li[TFSI], Li[f3C], Li[BOB], LiClO ₄ , LiBF ₃ (CF ₃ ), LiBF ₃ (C ₂ F ₅ ), LiBF ₃ (C ₃ F ₇ ), LiBF ₃ (C ₄ F ₉ ), LiC(SO ₂ CF ₃ ) ₃ , LiCF ₃ SO ₂ O, LiCF ₃ COO, and LiRCOO (R is an alkyl group having 1 to 4 carbon atoms, a phenyl group , Or a naphthyl group) at least one selected from the group consisting of.

Sodium salt, NaPF ₆ , NaBF ₄ , Na[FSI], Na[TFSI], Na[f3C], Na[BOB], NaClO ₄ , NaBF ₃ (CF ₃ ), NaBF ₃ (C ₂ F ₅ ), NaBF ₃ (C ₃ F ₇ ), NaBF ₃ (C ₄ F ₉ ), NaC(SO ₂ CF ₃ ) ₃ , NaCF ₃ SO ₂ O, NaCF ₃ COO, and NaRCOO (R is an alkyl group having 1 to 4 carbon atoms, a phenyl group , Or a naphthyl group) at least one selected from the group consisting of.

Calcium salts are Ca(PF ₆ ) ₂ , Ca(BF ₄ ) ₂ , Ca[FSI] ₂ , Ca[TFSI] ₂ , Ca[f3C] ₂ , Ca[BOB] ₂ , Ca(ClO ₄ ) ₂ , Ca [BF ₃ (CF ₃ )] ₂ , Ca[BF ₃ (C ₂ F ₅ )] ₂ , Ca[BF ₃ (C ₃ F ₇ )] ₂ , Ca[BF ₃ (C ₄ F ₉ )] ₂ , Ca [C(SO ₂ CF ₃ ) ₃ ] ₂ , Ca(CF ₃ SO ₂ O) ₂ , Ca(CF ₃ COO) ₂ , and Ca(RCOO) ₂ (R is an alkyl group having 1 to 4 carbon atoms, a phenyl group, or Naphthyl group) may be at least one selected from the group consisting of.

Magnesium salts are Mg(PF ₆ ) ₂ , Mg(BF ₄ ) ₂ , Mg[FSI] ₂ , Mg[TFSI] ₂ , Mg[f3C] ₂ , Mg[BOB] ₂ , Na(ClO ₄ ) ₂ , Mg [BF ₃ (CF ₃ )] ₂ , Mg[BF ₃ (C ₂ F ₅ )] ₂ , Mg[BF ₃ (C ₃ F ₇ )] ₂ , Mg[BF ₃ (C ₄ F ₉ )] ₂ , Mg [C(SO ₂ CF ₃ ) ₃ ] ₂ , Mg(CF ₃ SO ₃ ) ₂ , Mg(CF ₃ COO) ₂ , and Mg(RCOO) ₂ (R is an alkyl group having 1 to 4 carbon atoms, a phenyl group, or a naphe It may be at least 1 type selected from the group consisting of butyl group).

Among these, from the viewpoint of dissociation and electrochemical stability, the electrolyte salt is preferably LiPF ₆ , LiBF ₄ , Li[FSI], Li[TFSI], Li[f3C], Li[BOB], LiClO ₄ , LiBF ₃ (CF ₃ ), LiBF ₃ (C ₂ F ₅ ), LiBF ₃ (C ₃ F ₇ ), LiBF ₃ (C ₄ F ₉ ), LiC(SO ₂ CF ₃ ) ₃ , LiCF ₃ SO ₂ O, LiCF ₃ COO, and at least one selected from the group consisting of LiRCOO (R is an alkyl group having 1 to 4 carbon atoms, a phenyl group, or a naphthyl group), more preferably Li[TFSI], Li[FSI], LiPF ₆ , It is at least one selected from the group consisting of LiBF ₄ , Li[BOB], and LiClO ₄ , and more preferably one selected from the group consisting of Li[TFSI] and Li[FSI].

The content of the electrolyte salt may be 10% by mass or more, or 60% by mass or less, based on the total amount of the electrolyte sheet, in order to suitably manufacture the electrolyte sheet 7. The content of the electrolyte salt, based on the total amount of the electrolyte sheet, is preferably 20% by mass or more from the viewpoint of further increasing the conductivity of the electrolyte sheet 7, which makes it possible to charge and discharge the lithium secondary battery at a high load factor. From a viewpoint, it is more preferably 30% by mass or more.

The electrolyte sheet 7 may further contain a solvent capable of dissolving an electrolyte salt. The solvent preferably has a low vapor pressure and is difficult to burn.

The solvent may be a glyme represented by the following formula (6).

R ¹ O-(CH ₂ CH ₂ O) _n -R ² (6)

In formula (6), R ¹ and R ² each independently represent an alkyl group having 4 or less carbon atoms or a fluoroalkyl group having 4 or less carbon atoms, and n represents an integer of 1 to 6. Each of R ¹ and R ² is independently a methyl group or an ethyl group.

Specifically, glyme is monoglyme (n = 1), diglyme (n = 2), triglyme (n = 3), tetraglyme (n = 4), pentaglyme (n = 5 ), hexaglyme (n=6) may be used.

When the electrolyte sheet 7 contains glyme as a solvent, some or all of the glyme may form a complex with an electrolyte salt.

The electrolyte sheet 7 is a solvent, for the purpose of further improving the conductivity, for example, propylene carbonate, butylene carbonate, vinylene carbonate, γ-butyrolactone, diethyl carbonate, methyl ethyl carbonate, 1, 2-dimethoxyethane, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, methyl propionate, ethyl propionate, phosphate tryester, trimethoxymethane , Dioxolein, diethyl ether, sulfolane, 3-methyl-2-oxazolidinone, tetrahydrofuran, 1,2-diethoxyethane, chloroethylene carbonate, chloropropylene carbonate, etc. You may contain it. From the viewpoint of improving safety, the electrolyte sheet 7 preferably contains only at least one selected from the above-described glyme as a solvent.

The content of the solvent may be 10% by mass or more, or 60% by mass or less based on the total amount of the electrolyte sheet from the viewpoint of suitably producing the electrolyte sheet 7. The content of the solvent is based on the total amount of the electrolyte sheet, from the viewpoint of further increasing the conductivity of the electrolyte sheet 7 by increasing the content of the electrolyte salt, thereby enabling charging and discharging of the lithium secondary battery at a high load factor, It is preferably 40% by mass or less, and more preferably 30% by mass or less.

The total content of the electrolyte salt and the solvent is preferably 10% by mass or more, more preferably 25% by mass, based on the total amount of the electrolyte sheet, from the viewpoint of further improving the conductivity and suppressing the capacity decrease of the secondary battery. It is mass% or more, More preferably, it is 40 mass% or more. The total content of the electrolyte salt and the solvent is preferably 80% by mass or less, and more preferably 70% by mass or less, based on the total amount of the electrolyte sheet, from the viewpoint of suppressing a decrease in strength of the electrolyte sheet.

The thickness of the electrolyte sheet 7 is preferably 5 µm or more, and more preferably 10 µm or more, from the viewpoint of further increasing the conductivity and further improving the strength. From the viewpoint of suppressing the resistance of the electrolyte sheet 7, the thickness of the electrolyte sheet 7 is preferably 100 μm or less, more preferably 50 μm or less, and still more preferably 30 μm or less.

In the secondary battery 1 described above, from the viewpoint of improving the discharge characteristics, the sum of the total surface area Si of the inorganic oxide particles and the total surface areas Sp and Si of each electrode active material is preferably 8000 cm ^-1 or more. That is, the sum of the total surface area Si of the inorganic oxide particles and the total surface area Sp of the positive electrode active material (Si+Sp), and the sum of the total surface area Si of the inorganic oxide particles and the total surface area Sn of the negative electrode active material (Si+Sn) are respectively preferable. Hagi is 8000cm ^-1 or more.

The sum of the total surface area Si of the inorganic oxide particles and the total surface area Sp and Si of each electrode active material (each of Si+Sp and Si+Sn) is more preferably 9000cm ^-1 or more from the viewpoint of further improving the discharge characteristics. , More preferably 10000 cm ^-1 or more, particularly preferably 14000 cm ^-1 or more. Sum the art (each of Si + Sp and Sn + Si), for example, or may be 20000cm ^-1 or less, 18000cm ^-1 or less, or less than 16000cm ^-1.

Subsequently, a method of manufacturing the secondary battery 1 described above will be described. The manufacturing method of the secondary battery 1 according to the present embodiment includes a first step of forming the positive electrode mixture layer 10 on the positive electrode current collector 9 to obtain the positive electrode 6, and the negative electrode current collector 11 A second step of forming the negative electrode mixture layer 12 to obtain the negative electrode 8 and a third step of providing the electrolyte sheet 7 between the positive electrode 6 and the negative electrode 8 are provided.

In the first step, the positive electrode 6, for example, disperses the material used for the positive electrode mixture layer in a dispersion medium using a kneader, a disperser, etc. to obtain a slurry-like positive electrode mixture, and then the positive electrode mixture is used in a doctor blade method or It is obtained by coating on the positive electrode current collector 9 by a ping method, a spray method, or the like, and then volatilizing a dispersion medium. After volatilizing the dispersion medium, a compression molding step by a roll press may be provided if necessary. The positive electrode mixture layer 10 may be formed as a multi-layered positive electrode mixture layer by performing a plurality of steps from application of the positive electrode mixture to volatilization of the dispersion medium described above.

The dispersion medium used in the first step may be water, 1-methyl-2-pyrrolidone (hereinafter, also referred to as NMP), or the like.

In the second step, the method of forming the negative electrode mixture layer 12 on the negative electrode current collector 11 may be the same as that of the first step described above.

In the third step, in one embodiment, the electrolyte sheet 7 is applied to at least one of the positive electrode mixture layer 10 side of the positive electrode 6 and the negative electrode mixture layer 12 side of the negative electrode 8. It is formed by, and is preferably formed by coating on both sides of the anode mixture layer 10 of the anode 6 and the cathode mixture layer 12 of the cathode 8. In this case, for example, by laminating the positive electrode 6 provided with the electrolyte sheet 7 and the negative electrode 8 provided with the electrolyte sheet 7 in contact with each other, for example, by lamination. , A secondary battery 1 is obtained.

The method of forming the electrolyte sheet 7 on the positive electrode mixture layer 10 by coating is, for example, dispersing the material used for the electrolyte sheet 7 in a dispersion medium to obtain a slurry, and then adding the electrolyte composition to the positive electrode mixture layer. This is a method of applying on (10) using an applicator. The dispersion medium is preferably water or NMP. When the electrolyte sheet 7 contains a solvent, the electrolyte can be dissolved in the solvent and then dispersed in a dispersion medium together with other materials.

The method of forming the electrolyte sheet 7 on the negative electrode mixture layer 12 by coating may be the same method as the method of forming the electrolyte sheet 7 on the positive electrode mixture layer 10 by coating.

In the third step, in another embodiment, the electrolyte sheet 7 is formed, for example, by producing a laminated sheet provided with an electrolyte sheet on a substrate. 4A is a schematic cross-sectional view showing a laminated sheet according to an embodiment. As shown in FIG. 4A, the laminated sheet 13A includes a substrate 14 and an electrolyte sheet 7 provided on the substrate 14.

The laminated sheet 13A is produced, for example, by dispersing a material used for the electrolyte sheet 7 in a dispersion medium to obtain a slurry, and then coating this on the substrate 14 and then volatilizing the dispersion medium. The dispersion medium is preferably water, NMP, toluene, or the like.

The substrate 14 is not limited as long as it has heat resistance that can withstand heating when the dispersion medium is volatilized, does not react with the electrolyte composition, and does not swell by the electrolyte composition. For example, a film-like resin It is composed of (polymer). Specifically, the substrate 14 may be a film made of a resin (general purpose engineered plastic) such as polyethylene terephthalate, polytetrafluoride ethylene, polyimide, polyethersulfone, and polyetherketone.

The substrate 14 is a substrate that is likely to withstand a treatment temperature for volatilizing a dispersion medium in the process of manufacturing the electrolyte sheet 7. If the lower temperature of the softening point (the temperature at which plastic deformation starts) or the melting point of the substrate 14 is set as the heat resistance temperature, the heat resistance temperature is preferably from the viewpoint of adaptability with the solvent used for the electrolyte sheet 7 It is 50 degreeC or more, More preferably, it is 100 degreeC or more, More preferably, it is 150 degreeC or more, and, for example, it may be 400 degreeC or less. When a substrate having the above heat-resistant temperature is used, a dispersion medium (NMP, toluene, etc.) as described above can be suitably used.

It is preferable that the thickness of the substrate 14 is as thin as possible while maintaining the strength that can withstand the tensile force in the application device. The thickness of the substrate 14 is preferably 5 μm or more, more preferably 10 μm from the viewpoint of securing strength when applying the electrolyte composition to the substrate 14 while reducing the overall volume of the laminated sheet 13A. Or more, more preferably 25 μm or more, more preferably 100 μm or less, more preferably 50 μm or less, and still more preferably 40 μm or less.

The laminated sheet can also be continuously manufactured while winding up in a roll shape. In that case, the electrolyte sheet 7 may be damaged when the surface of the electrolyte sheet 7 comes into contact with the back surface of the base material 14 and a part of the electrolyte sheet 7 is affixed to the base material 14. In order to prevent such a situation, as another embodiment, the electrolyte sheet may have a protective material provided on the side opposite to the base 14 of the electrolyte sheet 7. 4B is a schematic cross-sectional view showing an electrolyte sheet according to another embodiment. As shown in FIG. 4B, the laminated sheet 13B further includes a protective material 15 on the side opposite to the base 14 of the electrolyte sheet 7.

The protective material 15 can be easily peeled from the electrolyte sheet 7 and is preferably a non-polar resin (polymer) film such as polyethylene, polypropylene, or polyethylene tetrafluoride. When a non-polar resin film is used, the electrolyte sheet 7 and the protective material 15 are not adhered to each other, and the protective material 15 can be easily peeled off.

The thickness of the protective material 15 is preferably 5 μm or more, more preferably 10 μm, and preferably 100 μm or less, from the viewpoint of securing strength while reducing the overall volume of the laminated sheet 13B. It is preferably 50 μm or less, and more preferably 30 μm or less.

The heat-resistant temperature of the protective material 15 is, from the viewpoint of suppressing deterioration in a low-temperature environment and suppressing softening in a high-temperature environment, preferably -30°C or higher, more preferably 0°C or higher, and more preferably It is preferably 100°C or less, more preferably 50°C or less. In the case of providing the protective material 15, since the step of volatilizing the dispersion medium described above is not essential, there is no need to increase the heat resistance temperature.

The method of providing the electrolyte sheet 7 between the positive electrode 6 and the negative electrode 8 using the laminated sheet 13A is, for example, by peeling the substrate 14 from the laminated sheet 13A, 6) The secondary battery 1 is obtained by laminating the electrolyte sheet 7 and the negative electrode 8 by, for example, lamination. At this time, the electrolyte sheet 7 is positioned on the positive electrode mixture layer 10 side of the positive electrode 6 and the negative electrode mixture layer 12 side of the negative electrode 8, that is, the positive electrode current collector 9 and the positive electrode mixture layer ( 10), the electrolyte sheet 7, the negative electrode mixture layer 12, and the negative electrode current collector 11 are stacked so that they are arranged in this order. In the case of continuous production while winding the laminated sheet in a roll shape, the rolled laminated sheet may be unwound and cut after providing the electrolyte sheet 7 between the positive electrode 6 and the negative electrode 8, or After cutting the upper laminated sheet, the electrolyte sheet 7 may be provided between the positive electrode 6 and the negative electrode 8.

In the third process, for the purpose of suitably laminating the electrolyte sheet 7 and the positive electrode 6 or the negative electrode 8, an adhesive layer (not shown) may be further provided on the electrolyte sheet 7. The pressure-sensitive adhesive layer is a film-like pressure-sensitive adhesive, or a pressure-sensitive adhesive layer prepared on a release film is compressed to the electrolyte sheet 7 to peel the release film to transfer the pressure-sensitive adhesive layer, or a liquid pressure-sensitive adhesive is applied to an electrolyte sheet ( It can be provided by applying to 7). In the case of using the laminated sheet 13A, it may be an electrolyte sheet in which a pressure-sensitive adhesive layer is previously formed at the time of manufacture of the laminated sheet 13A.

The pressure-sensitive adhesive layer may contain at least one selected from the group consisting of acrylic resin, methacrylic resin, silicone resin, urethane resin, polyvinyl ether, and styrene-butadiene rubber.

When providing the pressure-sensitive adhesive layer on the electrolyte sheet 7, the pressure-sensitive adhesive layer may be provided on at least a part of the main surface of the electrolyte sheet 7 or may be provided at one end of the electrolyte sheet 7. Thus, when stacking the electrolyte sheet 7 and the positive electrode 6 or the negative electrode 8, or when stacking the electrolyte sheets 7 formed on the positive electrode mixture layer 10 and the negative electrode mixture layer 12, the adhesive Since it is laminated through layers, it becomes difficult to generate wrinkles or flapping during lamination, and a secondary battery in which the electrodes (positive electrode 6 and negative electrode 8) and the electrolyte sheet 7 are suitably laminated can be manufactured. have.

[Second Embodiment]

Next, a secondary battery according to a second embodiment will be described. 5 is a schematic cross-sectional view showing an embodiment of an electrode group in a secondary battery according to a second embodiment. As shown in FIG. 5, the difference between the secondary battery in the second embodiment and the secondary battery in the first embodiment is that the electrode group 2B includes a bipolar electrode 16. That is, the electrode group 2B includes an anode 6, a first electrolyte sheet 7, a bipolar electrode 16, a second electrolyte sheet 7 and a cathode 8 in this order. have.

The bipolar electrode 16 includes a bipolar electrode current collector 17, a positive electrode mixture layer 10 provided on a surface (anode surface) of the bipolar electrode current collector 17 on the negative electrode 8 side, and a bipolar electrode current collector ( It has a negative electrode mixture layer 12 provided on the surface (cathode surface) of 17) on the anode 6 side.

In the bipolar electrode current collector 17, the anode surface may preferably be formed of a material excellent in oxidation resistance, or may be formed of aluminum, stainless steel, titanium, or the like. The negative electrode surface of the bipolar electrode current collector 17 using graphite or an alloy as the negative electrode active material in the negative electrode mixture layer 12 may be formed of a material that does not form an alloy with lithium, specifically stainless steel or nickel. , Iron, titanium, etc. may be formed. When different types of metals are used for the positive electrode surface and the negative electrode surface, the bipolar electrode current collector 17 may be a cladding material in which different types of metal foils are laminated. However, in the case of using the negative electrode 8 operating at a potential that does not form an alloy with lithium, such as lithium titanate, the above limitation is eliminated, and the negative electrode surface may be made of the same material as the positive electrode current collector 9. In that case, the bipolar electrode current collector 17 may be a single metal foil. The bipolar electrode current collector 17 as a single metal foil may be an aluminum perforated foil, expanded metal, foamed metal plate, or the like having pores having a pore diameter of 0.1 to 10 mm. In addition to the above, the bipolar electrode current collector 17 may be formed of an arbitrary material as long as it does not cause changes such as dissolution or oxidation during use of the battery, and its shape and manufacturing method are not limited.

The thickness of the bipolar electrode current collector 17 may be 10 μm or more, or 100 μm or less, and from the viewpoint of reducing the volume of the entire bipolar electrode, it is preferably 10 to 50 μm, and the bipolar electrode with a small curvature when forming a battery From the viewpoint that can be wound, it is more preferably 10 to 20 μm.

In this secondary battery, from the viewpoint of improving the discharge characteristics, the sum of the total surface area Si of the inorganic oxide particles and the total surface area Sp of the positive electrode active material in the adjacent electrolyte sheet 7 and the positive electrode mixture layer 10 is preferable. it is more than ^8000cm-1, more preferably from 9000cm ^-1 or more, more preferably 10000cm ^-1 or more, and particularly preferably not less than 14000cm ^-1, for example 20000cm ^-1 or less, 18000cm ^-1 or less, or It may be 16000cm ^-1 or less.

Similarly, from the viewpoint of improving the discharge characteristics, in the adjacent electrolyte sheet 7 and the negative electrode mixture layer 12, the sum of the total surface area Si of the inorganic oxide particles and the total surface area Sn of the negative electrode active material is preferably 8000 cm ^-1, more preferably at least 9000cm ^-1, more preferably from 10000cm ^-1 or more, and particularly preferably not less than ^14000cm-1, for example 20000cm ^-1 or less, 18000cm ^-1 or less, or less than 16000cm ^-1 You can open it.

Subsequently, a method of manufacturing a secondary battery according to the second embodiment will be described. The manufacturing method of the secondary battery according to the present embodiment includes a first step of forming a positive electrode mixture layer 10 on the positive electrode current collector 9 to obtain a positive electrode 6, and a negative electrode mixture on the negative electrode current collector 11. A second step of forming a layer 12 to obtain a negative electrode 8, forming a positive electrode mixture layer 10 on one surface of the bipolar electrode current collector 17, and forming a negative electrode mixture layer 12 on the other surface. The third step of forming the bipolar electrode 16 and preparing the electrolyte sheet 7 between the anode 6 and the bipolar electrode 16 and between the cathode 8 and the bipolar electrode 16 It has 4 processes.

The 1st process and the 2nd process may be the same method as the 1st process and 2nd process in 1st Embodiment.

In the third step, the method of forming the positive electrode material mixture layer 10 on one surface of the bipolar electrode current collector 17 may be the same method as in the first step in the first embodiment. The method of forming the negative electrode material mixture layer 12 on the other surface of the bipolar electrode current collector 17 may be the same method as in the second step in the first embodiment.

As a method of providing the electrolyte sheet 7 between the positive electrode 6 and the bipolar electrode 16 during the fourth step, in one embodiment, the electrolyte sheet 7 comprises a positive electrode mixture layer ( 10) and formed by coating on at least one of the anode mixture layer 12 side of the bipolar electrode 16 and preferably the anode mixture layer 10 side of the anode 6 and the bipolar electrode 16 It is formed by coating on both sides of the negative electrode mixture layer 12 side. In this case, for example, the positive electrode 6 provided with the electrolyte sheet 7 and the bipolar electrode 16 provided with the electrolyte sheet 7 were laminated by, for example, lamination so that the electrolyte sheets 7 were in contact with each other. do.

The method of forming the electrolyte sheet 7 by coating on the positive electrode mixture layer 10 of the positive electrode 6 and the negative electrode mixture layer 12 of the bipolar electrode 16 by coating is described in the third embodiment. According to an embodiment of the process, a method of forming an electrolyte sheet 7 on the positive electrode mixture layer 10 by coating and a method of forming the electrolyte sheet 7 on the negative electrode mixture layer 12 by coating, and The same method may be used.

As a method of providing the electrolyte sheet 7 between the positive electrode 6 and the bipolar electrode 16 during the fourth step, in another embodiment, the electrolyte sheet 7 includes, for example, an electrolyte composition on a substrate. It is formed by manufacturing the provided electrolyte sheet. The manufacturing method of the electrolyte sheet may be the same method as the manufacturing method of the laminated sheets 13A and 13B in the first embodiment.

In the fourth step, the method of providing the electrolyte sheet 7 between the cathode 8 and the bipolar electrode 16 is an electrolyte sheet 7 between the anode 6 and the bipolar electrode 16 described above. It may be the same method as the method of providing.

As described above, in the electrolyte sheet 7, excellent electrical conductivity and tensile strength are obtained by having the total surface area of the inorganic oxide particles occupied by 1 cm ³ of the electrolyte sheet of 1000 to 12000 cm ^-1 . Accordingly, the secondary battery 1 using the electrolyte sheet 7, that is, a secondary battery comprising a pair of electrodes 6 and 8 and an electrolyte sheet 7 provided between the pair of electrodes 6 and 8 ( Also in 1), suitable properties are obtained. In addition, a pair of electrodes means two electrodes facing each other with the electrolyte sheet 7 interposed therebetween and having different polarities. For example, in the electrode group 2A shown in FIG. 3, the anode 6 and the cathode 8 constitute a pair of electrodes. In the electrode group 2B shown in Fig. 5, the anode 6 and the bipolar electrode 16 (the cathode mixture layer 12 side) constitute a pair of electrodes, and the cathode 8 and the bipolar electrode 16 (Anode mixture layer 10 side) also constitutes a pair of electrodes.

In addition, in the secondary battery 1, when the sum of the total surface area of the inorganic oxide particles occupied by 1 cm ³ of the electrolyte sheet and the total surface area of each electrode active material occupied by 1 cm ³ of each electrode mixture layer is 8000 cm ^-1 or more, especially discharge characteristics This excellent secondary battery is obtained.

Example

Hereinafter, the present invention will be described in more detail by examples, but the present invention is not limited to these examples.

<Example 1>

[Production of Electrolyte Sheet]

As a polymer, a copolymer of vinylidene fluoride and hexafluoropropylene (PVDF-HFP, vinylidene fluoride: hexafluoropropylene = 95% by mass: 5% by mass), SiO ₂ particles as inorganic oxide particles (average particle diameter Di ₅₀ : 1.0 μm), and an electrolyte solution in which lithium bis(fluorosulfonyl)imide (LiFSI) as an electrolyte salt and tetraglyme as a solvent are mixed in equimolar amounts in the amount shown in Table 1, and the dispersion medium 1- It was dispersed in methyl-2-pyrrolidone (NMP) to prepare an electrolyte slurry. The resulting slurry was coated once on a polyethylene terephthalate substrate by a doctor blade method, and heated to volatilize a dispersion medium to form an electrolyte sheet. The thickness of the obtained electrolyte sheet was 25±2 μm.

[Measurement of filling factor fi and total surface area Si]

The surface of the obtained electrolyte sheet was observed with a scanning electron microscope, the area (occupied area; area%) of SiO ₂ particles occupied by the unit area of the surface was calculated, and the occupied area was taken as the filling rate fi of the SiO ₂ particles. . Further, from the average particle diameter Di ₅₀ of the SiO ₂ particles and the filling rate fi, the total surface area Si of the SiO ₂ particles was calculated according to the above formula (1). Table 1 shows the results.

[Measurement of conductivity]

The conductivity was determined by holding the electrolyte sheet between two lithium metal foils and measuring the resistance between the lithium metal foils. Table 1 shows the results. If the conductivity is 0.10 mS/cm or more, it can be said that the conductivity is excellent.

[Measurement of tensile strength]

The electrolyte sheet was cut into a size of 1 cm x 5 cm, and both ends were attached to a fixture of a tensile testing apparatus (manufactured by Shimadzu Corporation, Autograph) and stretched, and the strength at break was taken as tensile strength. Table 1 shows the results. When the conductivity is 0.20 N/cm or more, it can be said that the tensile strength is excellent.

<Examples 2 to 8 and Comparative Examples 1 and 2>

Preparation and measurement of an electrolyte sheet were performed in the same manner as in Example 1, except that the compounding amount of each component in the electrolyte sheet was changed as shown in Table 1. Table 1 shows the results.

[Table 1]

<Test Example 1>

[Production of the anode]

LiNi _0.6 Co _0.2 Mn _0.2 O ₂ (anode active material, average particle diameter Dp ₅₀ : 5.0 μm) 96 parts by mass, carbon black (conductive material, product name: HS-100, average particle diameter 48 nm, manufactured by Denka Corporation) 1.75 parts by mass, and poly 2.5 parts by mass of a copolymer (binder) of vinylidene fluoride and hexafluoropropylene was mixed together with 1-methyl-2-pyrrolidone to prepare a positive electrode mixture slurry. This positive electrode mixture slurry was coated on an aluminum foil (positive electrode current collector) having a thickness of 15 μm, heated at 80° C. and dried to form a positive electrode mixture layer having a thickness of 45 μm.

[Production of the cathode]

Natural graphite (cathode active material, Hitachi Kasei Co., Ltd. product, average particle diameter Dn ₅₀ : 12 μm) 94 parts by mass, carbon black (conductive material, product name: HS-100, average particle diameter 48 nm, Denka Corporation product) 1 part by mass, and polyfluoride bis 5 parts by mass of nilidene (binder) was mixed together with 1-methyl-2-pyrrolidone to prepare a negative electrode mixture slurry. This negative electrode mixture slurry was coated on a rolled copper foil (cathode current collector) having a thickness of 10 μm, heated at 80° C. and dried to form a negative electrode mixture layer having a thickness of 40 μm.

[Measurement of filling factor fp, fn and total surface area Sp, Sn]

For the obtained positive electrode and negative electrode, a binarization treatment was performed on a photograph of the positive electrode mixture layer and the negative electrode mixture layer observed with a scanning electron microscope, and the occupied areas of the positive electrode active material and the negative electrode active material were calculated, respectively. The ratio of the area occupied by the positive electrode active material and the negative electrode active material to the area of the positive electrode mixture layer and the negative electrode mixture layer in the micrograph was taken as the charge rate fp of the positive electrode active material and the charge rate fn of the negative electrode active material, respectively. Moreover, the average particle diameters Dp ₅₀ and Dn ₅₀ of each active material were measured using a laser scattering type particle diameter measuring device (micro track). These values were substituted for the above formula (4) or (5), and the total surface area Sp of the positive electrode active material and the total surface area Sn of the negative electrode active material were calculated, respectively. The results are shown in Table 2.

[Assembly of secondary battery]

As shown in Fig. 2, a positive electrode, a negative electrode, and an electrolyte sheet cut into strips were prepared. A positive electrode active material or a mixture layer containing a negative electrode active material and a binder, etc. was made into a square, and the dimensions were substantially the same. The exposed current collector was extended on the upper part of the mixture layer, and the electrode and the tab were welded. The electrolyte sheet was made larger than the mixture layer, and was sandwiched between the positive electrode and the negative electrode, so that the positive electrode was not electrically shorted. After stacking the positive electrode, the electrolyte sheet, the negative electrode, and the electrolyte sheet, the positive electrode was laminated again, and then laminated in the same arrangement. Subsequently, the tabs of the same pole were welded and sealed with an aluminum laminated bag to produce a lithium secondary battery as shown in FIG. 1. The rated capacity (calculated value) of the obtained secondary battery was 3 Ah.

[Evaluation of discharge characteristics of secondary battery]

The obtained secondary battery was charged at a constant current with 0.05CA (0.15A), after the voltage reached 4.2V, charged until the current value of constant voltage charging became 0.005CA, and then discharged constant current with 0.05CA to 2.7V. did. Then, after charging in the same manner as above, constant current discharge was performed to 2.7 V at 1.0 CA (3.0 A), and the discharge capacity (Ah) at that time was measured. The results are shown in Table 2.

<Test Examples 2 to 13>

The average particle diameter Di ₅₀ of the inorganic oxide particles in the electrolyte sheet, the filling rate fi and the total surface area Si, the average particle diameter Dp ₅₀ of the positive electrode active material in the positive electrode, the filling rate fp and the total surface area Sp, and the average particle diameter of the negative electrode active material in the negative electrode Except having changed Dn ₅₀ , charge rate fn and total surface area Sn as shown in Table 2, it carried out similarly to Test Example 1, and fabrication and evaluation of a secondary battery were performed. The results are shown in Table 2.

[Table 2]

One… Secondary battery
6... anode
7... Electrolyte sheet
8… cathode
9... Positive electrode current collector
10… Anode mixture layer
11... Negative electrode current collector
12... Negative electrode mixture layer

Claims (8)

As an electrolyte sheet containing one or two or more polymers, inorganic oxide particles, and electrolyte salt,
The electrolyte sheet, wherein the total surface area of the inorganic oxide particles occupied by 1 cm ³ of the electrolyte sheet is 1000 to 12000 cm ^-1 . The method according to claim 1,
Among the structural units constituting the one or two or more polymers, a first structural unit selected from the group consisting of ethylene tetrafluoride and vinylidene fluoride, hexafluoropropylene, acrylic acid, maleic acid, ethyl methacrylate, And a second structural unit selected from the group consisting of methyl methacrylate. The method according to claim 1 or 2,
The electrolyte sheet, wherein the polymer content is 10 to 40 mass% based on the total amount of the electrolyte sheet. The method according to any one of claims 1 to 3,
The inorganic oxide particles are at least one particle selected from the group consisting of SiO ₂ , Al ₂ O ₃ , AlOOH, MgO, CaO, ZrO ₂ , TiO ₂ , Li ₇ La ₃ Zr ₂ O ₁₂ , and BaTiO ₃ , Electrolyte sheet. A pair of electrodes,
A secondary battery comprising the electrolyte sheet according to any one of claims 1 to 4 provided between the pair of electrodes. The method of claim 5,
Each of the pair of electrodes includes a current collector and an electrode mixture layer containing an electrode active material provided on the current collector,
The secondary battery, wherein the sum of the total surface area of the inorganic oxide particles occupied by 1 cm ³ of the electrolyte sheet and the total surface area of each electrode active material occupied by 1 cm ³ of each electrode mixture layer is 8000 cm ^-1 or more. The method of claim 6,
The electrolyte sheet 1cm and a total surface area of the inorganic oxide particles occupy at least ³ 5000cm ^-1, and the total surface area of each of the electrode active material occupying in the above-mentioned electrode material mixture layer 1cm ³ 3000cm ^-1 or more, a secondary battery. The method according to claim 6 or 7,
The secondary battery, wherein the electrode mixture layer further contains a binder.

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