JPWO2019188693A1 - Electrolyte sheet and secondary battery - Google Patents

Abstract

One aspect of the present invention is an electrolyte sheet containing one or more polymers, inorganic oxide particles, and an electrolyte salt, and the total surface area of the inorganic oxide particles per 1 cm3 of the electrolyte sheet is from 1000 to It is the electrolyte sheet which is 12000 cm-1.

Description

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

  In recent years, with the spread of portable electronic devices, electric vehicles, and the like, high-performance secondary batteries are required. Among them, the lithium secondary battery has a high energy density, and thus has attracted attention as a power source for electric vehicle batteries, power storage batteries, and the like. Specifically, lithium secondary batteries as batteries for electric vehicles include zero-emission electric vehicles that do not have an engine, hybrid electric vehicles that have both an engine and a secondary battery, and plug-in hybrids that are directly charged from a power system. It is used in electric vehicles such as electric vehicles. Further, a lithium secondary battery as a power storage battery is used in a stationary power storage system or the like that supplies electric power stored in advance in an emergency when the power system is cut off.

  Among such secondary batteries, in particular, a lithium secondary battery for an electric vehicle is required to have high safety in addition to high input / output characteristics and high energy density. More advanced technology is required. As a battery with higher safety, for example, Patent Document 1 describes a lithium secondary battery including a sheet-shaped electrolyte (electrolyte sheet) by applying a slurry containing inorganic oxide particles onto an electrode and drying the slurry. Has been done.

JP, 2005-191710, A

  The electrolyte sheet is required to have high electrical conductivity and mechanical strength such as tensile strength in order to improve the characteristics of the secondary battery.

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

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

  A first structural unit selected from the group consisting of ethylene tetrafluoride and vinylidene fluoride among the structural units constituting one or more polymers, and hexafluoropropylene, acrylic acid, maleic acid, ethyl methacrylate , And a second structural unit selected from the group consisting of methyl methacrylate.

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

The inorganic oxide particles are at least one kind of particles 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. You can

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

Each of the pair of electrodes includes a current collector and an electrode mixture layer containing an electrode active material, which is provided on the current collector, and has a total surface area of the inorganic oxide particles in 1 cm ³ of the electrolyte sheet, The sum of 1 cm ³ of each electrode mixture layer and the total surface area of each electrode active material may be 8000 cm ⁻¹ or more. In this case, a secondary battery having excellent discharge characteristics can be obtained.

The total surface area of the inorganic oxide particles occupying the electrolyte sheet 1 cm ³ is at 5000 cm ^-1 or more, and the total surface area of each electrode active material occupying in the electrode mixture layer 1 cm ³ may be at 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 having excellent conductivity and tensile strength, and a secondary battery using the same.

It is a perspective view showing the secondary battery concerning a 1st embodiment. FIG. 2 is an exploded perspective view showing an embodiment of an electrode group in the secondary battery shown in FIG. 1. It is a schematic cross section which shows one Embodiment of the electrode group in the secondary battery shown in FIG. (A) is a schematic sectional view showing an electrolyte sheet according to one embodiment, and (b) is a schematic sectional view showing an electrolyte sheet according to another embodiment. It is a schematic cross section which shows one Embodiment of the electrode group in the secondary battery which concerns on 2nd Embodiment.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings as appropriate. However, the present invention is not limited to the following embodiments. In the following embodiments, the constituent elements (including steps and the like) are not essential unless otherwise specified. The sizes of the constituent elements in each figure are conceptual, and the relative size relationships between the constituent elements are not limited to those shown in each figure.

  Numerical values and ranges thereof in the present specification do not limit the present invention. In the present specification, the numerical range indicated by using “to” indicates a range including the numerical values before and after “to” as the minimum value and the maximum value, respectively. In the numerical ranges described stepwise in the present specification, the upper limit or the lower limit described in one numerical range may be replaced with the upper limit or the lower limit described in another step. Further, in the numerical range described in the present specification, the upper limit value or the lower limit value of the numerical range may be replaced with the value shown in the examples.

[First Embodiment]
FIG. 1 is a perspective view showing a secondary battery according to the first embodiment. As shown in FIG. 1, the secondary battery 1 includes an electrode group 2 including a positive electrode, a negative electrode, and an electrolyte sheet, and a bag-shaped battery exterior body 3 that houses the electrode group 2. A positive electrode current collecting tab 4 and a negative electrode current collecting tab 5 are provided on the positive electrode and the negative electrode, respectively. The positive electrode current collecting tab 4 and the negative electrode current collecting tab 5 project from the inside of the battery case 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 case 3 may be formed of, for example, a laminated film. The laminated film may be, for example, a laminated 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 the electrode group 2 in the secondary battery 1 shown in FIG. FIG. 3 is a schematic cross-sectional view showing an embodiment of the electrode group 2 in the secondary battery 1 shown in FIG. As shown in FIGS. 2 and 3, the electrode group 2A according to the present embodiment includes a positive electrode 6, an electrolyte sheet (electrolyte layer) 7, and a negative electrode 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 the 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 made 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 hole with a hole 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 made of any material as long as it does not cause changes such as dissolution and oxidation during use of the battery, and its shape, manufacturing method, and the like. Not limited.

  The thickness of the positive electrode current collector 9 may be 10 μm or more, and may be 100 μm or less. From the viewpoint of reducing the volume of the entire positive electrode, it is preferably 10 to 50 μm, which is small when forming a battery. From the viewpoint that the positive electrode can be wound with a curvature, the thickness is more preferably 10 to 20 μm.

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

The positive electrode active _{material, 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 , Ni, Fe, Cr, Zn, and Ta, which are one kind selected from the group consisting of a, and a = 0.01 to 0.2.), Li ₂ Mn ₃ M ² O ₈ (provided that M ² = It is one kind selected from the group consisting of Fe, Co, Ni, Cu, and Zn.), Li _1-b M ³ _b Mn ₂ O ₄ (where M ³ = Mg, B, Al, Fe, Co, It is one kind selected from the group consisting of Ni, Cr, Zn, and Ca, and b = 0.01 to 0.1.), LiFeO ₂ , Fe ₂ (SO ₄ ) ₃ , LiCo _1-d M ⁵ _d O ₂ ^(where, M 5 = ^{Ni, Fe,} Fine Mn is one selected from the group consisting of a _{d = 0.01~0.2.), LiNi 1} -e M 6 e O 2 ( ^{however, M 6 = Mn, Fe,} Co, Al, It is one kind selected from the group consisting of Ga, Ca, and Mg, and e = 0.01 to 0.2.), Fe (MoO ₄ ) ₃ , FeF ₃ , LiFePO ₄ , LiMnPO _{4, and the} like. Good. The positive electrode active material may be ungranulated primary particles or granulated secondary particles.

  The particle size of the positive electrode active material is adjusted to be equal to or less than the thickness of the positive electrode mixture layer 10. When the positive electrode active material contains coarse particles having a particle size equal to or larger than the thickness of the positive electrode mixture layer 10, the coarse particles are removed in advance by sieving, airflow classification, etc. A positive electrode active material having a diameter is selected.

The average particle size Dp ₅₀ of the positive electrode active material is preferably from the viewpoint that the positive electrode active material can be preferably produced and the deterioration of the filling property of the positive electrode active material due to the particle size reduction is suppressed, and at the same time, the electrolyte retention capacity is increased. Is 0.1 μm or more, more preferably 1 μm or more, still more preferably 2 μm or more. The average particle size of the positive electrode active material is preferably 20 μm or less, more preferably 10 μm or less, and further preferably 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. It is 8 μm or less. The average particle size Dp ₅₀ of the positive electrode active material is the particle size when the ratio (volume fraction) to the volume of the entire positive electrode active material is 50%. The average particle size Dp ₅₀ of the positive electrode active material is measured by a laser scattering method using a laser scattering particle size measuring device (for example, Microtrac) to measure a suspension of the positive electrode active material in water. can get.

  The filling rate fp of the positive electrode active material is preferably 30% by volume or more, and more preferably 40% 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 decrease in energy density of the secondary battery. It is at least volume%, more preferably at least 50 volume%. The filling rate fp of the positive electrode active material is preferably 90% by volume or less, more preferably 85 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. % Or less, more preferably 80% by volume or less.

  The filling factor fp of the positive electrode active material is the area (occupied area; area%) of the positive electrode active material occupying the unit area of the surface or the cross section of the positive electrode mixture layer 10 observed by a scanning electron microscope. Is measured by image processing (binarization processing). Since the area occupied by the positive electrode active material on any surface or cross section of the positive electrode mixture layer 10 is considered to be almost constant, the occupied area can be regarded as the filling rate fp.

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

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-mentioned positive electrode active material, and Dp ₅₀ represents the average particle diameter (μm) of the above-mentioned positive electrode active material.

The physical meaning of the constant term “6” on the right side of the equation (1) is as follows. First, assume that the filling rate fp is 1 (100% by volume), that is, the positive electrode active material is a rigid sphere, and that it is filled in a cube of the minimum size. The cubes are aligned vertically and horizontally without a gap, 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 have the same size and the respective active materials are in the same state, the total surface area Sp of the positive electrode active material is the active material present in one cube, and the total surface area Sp is calculated as the ratio of the surface area to the volume. Will be equal. That is, Sp is represented by the following formula.
Sp = positive electrode active volume area / positive active material of the material ^{= 4πR 2 / (4πR 3/} 3)
= 3 / R (2)
Here, from the relationship of R (cm) = Db ₅₀ (μm) × 10 ⁻⁴ / 2, Expression (2) is converted into Expression (3).
Sp = 3 / (Db ₅₀ × 10 ⁻⁴ / 2)
= 6 × 10 ⁴ / Dp ₅₀ (3)
When fp is less than 1, the right side of the formula (3) may be multiplied by fp, so that the general formula when the filling rate of the positive electrode active material is fp is the above formula (1).

As shown by the formula (1), the total surface area Sp of the positive electrode active material is expressed by a function of the filling rate fp of the positive electrode active material and the average particle diameter Dp ₅₀ , and the larger the filling rate fp is, or the average particle diameter Dp _50. The smaller the value, the larger the value. The filling rate fp has a relationship that is monotonically proportional to the number of positive electrode active materials in the unit volume of the positive electrode mixture layer 10, and the smaller the Dp ₅₀ , the larger the surface area. Therefore, the behavior of equation (1) is understood. can do.

  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, and more preferably 0% based on the total amount of the positive electrode mixture layer, from the viewpoint of excellent conductivity of the positive electrode 6 and improving the input / output characteristics of the secondary battery. It is 0.5% by mass or more, more preferably 1% by mass or more, and particularly preferably 3% by mass or more. The content of the conductive material is preferably 20% by mass or less, and more preferably 15% by mass or less, based on the total amount of the positive electrode mixture layer, from the viewpoint of suppressing the increase in the volume of the positive electrode and the accompanying decrease in the energy density of the secondary battery 1. It is not more than 10% by mass, preferably not more than 10% by mass, particularly preferably not more than 8% by mass.

  The binder is not limited as long as it does not decompose on the surface of the positive electrode 6, but is, for example, a polymer. The binder may be a cellulose compound such as carboxymethyl cellulose, cellulose acetate or ethyl cellulose, polyvinylidene fluoride, styrene / butadiene rubber, fluororubber, ethylene / propylene rubber, polyacrylic acid, polyimide or polyamide.

  The content of the binder is preferably 0.5% by mass or more, more preferably 1% by mass or more, and further preferably, based on the total amount of the positive electrode mixture layer, from the viewpoint of excellent durability and life characteristics of the secondary battery. It is 3% by mass or more. The content of the binder is preferably 20% by mass or less, more preferably 15% by mass or less, further preferably 10% by mass or less, particularly preferably 10% by mass or less, based on the total amount of the positive electrode mixture layer, from the viewpoint of excellent energy density of the secondary battery. It is preferably 7% by mass or less.

  From the viewpoint of further improving the conductivity, the thickness of the positive electrode mixture layer 10 is not less than the average particle diameter of the positive electrode active material, specifically, preferably 5 μm or more, more preferably 10 μm or more. And more preferably 20 μm or more. The thickness of the positive electrode mixture layer 10 is preferably 100 μm or less, more preferably 80 μm or less, and further preferably 50 μm or less. By setting the thickness of the positive electrode mixture layer to 80 μm or less, uneven charging / discharging due to variations in the charge level of the positive electrode active material near the surface of the positive electrode mixture layer 10 and near the surface of the positive electrode current collector 9 is suppressed. it can.

The mixture density of the positive electrode 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 and reducing the electronic resistance of the positive electrode mixture layer 10, and for example, 3. It may be 5 g / cm ³ or less.

  The negative electrode current collector 11 may be made 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 holes with a hole diameter of 0.1 to 10 mm, an expanded metal, a foam metal plate, or the like. The negative electrode current collector 11 may be formed of any material other than the above, and the shape, manufacturing method, and the like are not limited.

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

  In one embodiment, the negative electrode mixture layer 12 contains a negative electrode active material and a binder.

  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 metallic lithium, lithium alloys, metallic compounds, carbon materials, metallic complexes, and organic polymer compounds. As the negative electrode active material, one of the above materials may be used alone, or two or more thereof may be used in combination. The negative electrode active material is preferably a carbon material. Examples of the carbon material include natural graphite (scaly graphite, etc.), graphite such as artificial graphite, amorphous carbon, carbon fiber, and carbon such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black. Examples include black. The negative electrode active material may be natural graphite coated with amorphous carbon (theoretical capacity: 372 Ah / kg). From the viewpoint of obtaining a larger theoretical capacity (for example, 500 to 1500 Ah / kg), silicon, tin, or these It may be a compound (oxide, nitride, alloy with another metal) containing the element. If a material having a large capacity is used, the thickness of the negative electrode mixture layer 12 can be reduced, and the electrode area that can be stored in the secondary battery 1 can be increased. As a result, the resistance of the secondary battery 1 can be reduced and a high output can be achieved, and at the same time, the capacity of the secondary battery 1 can be increased more than when the graphite negative electrode is used.

The average particle size Dn ₅₀ of the negative electrode active material is such that the negative electrode active material can be suitably manufactured, and the well-balanced negative electrode 8 having an improved electrolyte retention ability while suppressing an increase in irreversible capacity due to a decrease in particle size is obtained. From the viewpoint, it is preferably 0.1 μm or more, more preferably 1 μm or more, further preferably 5 μm or more, and particularly preferably 10 μm or more. The average particle size (Dn ₅₀ ) of the negative electrode active material is preferably 50 μm or less, more preferably 30 μm or less 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. , More preferably 20 μm or less, 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 filling rate fn of the negative electrode active material is preferably 30% by volume or more, more preferably 40% or more, based on the total volume of the negative electrode active material, the conductive material and the binder, from the viewpoint of suppressing the decrease in energy density of the secondary battery. It is at least volume%, more preferably at least 50 volume%. The filling rate fn of the negative electrode active material is preferably 90% by volume or less, more preferably 80 volume% based on the total volume of the negative electrode active material, the conductive material and the binder, from the viewpoint of suppressing the decrease in the life of the secondary battery. % Or less, more preferably 70% by volume or less. The filling rate fn of the negative electrode active material can be measured in the same manner as the filling rate fp of the positive electrode active material.

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

The total surface area Sn of the negative electrode active material is defined by the following formula (4).
Sn = 6 × 10 ⁴ × fn / Dn ₅₀ (4)
In the formula, fn represents the filling rate (volume%) of the negative electrode active material described above, and Dn ₅₀ represents the average particle size (μm) of the negative electrode active material described above. The physical term of the constant term “6” on the right side of the equation (4) is the same as that of the equation (1). Further, like the formula (1), the total surface area Sn of the negative electrode active material is expressed by a function of the filling rate fn of the negative electrode active material and the average particle size Dn _{50. As} the filling rate fn becomes larger, or the average particle size Dn becomes larger. _The smaller ₅₀ is, the larger the behavior is. The filling rate fn is in a relationship that is monotonically proportional to the number of negative electrode active materials in the unit volume of the negative electrode mixture layer 12, and the surface area increases as Dn ₅₀ decreases, so the behavior of equation (4) is understood. can do.

  The binder and the content thereof may be the same as the binder and the content thereof 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 further lowering the resistance of the negative electrode 8. The conductive material and the content thereof may be the same as the conductive material and the content thereof in the positive electrode mixture layer 10 described above.

  From the viewpoint of further improving the conductivity, 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, More preferably, it is 20 μm or more. 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, uneven charging and discharging due to variations in the charge level of the positive electrode active material near the surface of the negative electrode mixture layer 12 and near the surface of the negative electrode current collector 11 can be prevented. Can be suppressed.

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

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

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

  The first structural unit and the second structural unit may be included in one type of polymer to form 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, and 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 are contained in different polymers, respectively, and at least two of the first polymer having the first structural unit and the second polymer having the second structural unit are included. It may also constitute the polymer of the seed. That is, in one embodiment, the electrolyte sheet 7 contains, as a polymer, at least two or more polymers of a first polymer containing the first structural unit and a second polymer containing the 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 composed of only the first structural unit, or may be a polymer further having another structural unit in addition to the first structural unit. Other structural units are ethylene oxide _{(-CH 2} CH 2 O-), may be oxygenated hydrocarbon structure, such as a carboxylic acid ester _(-CH 2 COO-). The first polymer may be polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride, or a polymer in which the oxygen-containing hydrocarbon structure is introduced inside the molecular structure thereof.

The second polymer may be a polymer composed of only the second structural unit, or may be a polymer further having another structural unit in addition to the second structural unit. Other structural units are ethylene oxide _{(-CH 2} CH 2 O-), may be oxygenated hydrocarbon structure, such as a carboxylic acid ester _(-CH 2 COO-).

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

  From the viewpoint of further improving the strength of the electrolyte sheet 7, the content of the first structural unit is preferably 5% by mass or more, more preferably 10% by mass or more, based on the total amount of structural units constituting the polymer. Yes, and 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 further 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 further preferably 5% by mass or more, based on the total amount of structural units constituting the polymer. From the viewpoint of further improving the strength of the electrolyte sheet 7, the content of the second structural unit is preferably 50% by mass or less, more preferably 20% by mass or less, based on the total amount of structural units constituting the polymer. Yes, and more preferably 10% by mass or less.

  From the viewpoint of further improving the strength of the electrolyte sheet 7, the content of the polymer is preferably 10% by mass or more, more preferably 15% by mass or more, and further preferably 20% by mass, based on the total amount of the electrolyte sheet. It is above, and particularly preferably 25% by mass or more. From the viewpoint of further improving the conductivity, the content of the polymer is preferably 40% by mass or less, more preferably 35% by mass or less, and further preferably 30% by mass or less, based on the total amount of the electrolyte sheet. And 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 15% by mass. 38 mass%, 20-40 mass%, 20-35 mass%, 20-30 mass%, 20-38 mass%, 25-40 mass%, 25-35 mass%, 25-30 mass%, or 25-38. It may be% by mass.

The inorganic oxide particles may include, for example, Li, Mg, Al, Si, Ca, Ti, Zr, La, Na, K, Ba, Sr, V, Nb, B, Ge 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. Particles. Since the inorganic oxide particles have polarity, they accelerate the dissociation of the electrolyte in the electrolyte sheet 7 and promote the amorphization of the polymer 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, and more preferably 0.005 μm or more, from the viewpoint of increasing the cross-sectional area in which the cation component of the electrolyte diffuses and further improving the conductivity. It is at least 01 μm, more preferably at least 0.03 μm. The average particle diameter (Di ₅₀ ) of the inorganic oxide particles is preferably 5 μm or less, more preferably 3 μm or less, and further preferably 1 μm or less, from the viewpoint that the electrolyte sheet 7 can be made thinner more suitably. is there. 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 size (Di ₅₀ ) of the inorganic oxide particles is measured by a laser scattering method using a laser scattering particle size measuring device (for example, Microtrac) to suspend a suspension of the inorganic oxide particles in water. Obtained by measuring.

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

  The filling factor fi of the inorganic oxide particles may be 5% by volume or more, 7% by volume or more, or 10% by volume or more, and 50% by volume or less, 40% by volume or less, or 20 based on the total volume of the electrolyte sheet. It may be less than or equal to volume%. The filling rate fi of the inorganic oxide particles is the area (occupied area; area%) of the inorganic oxide particles occupying the unit area of the surface or the cross section by observing an arbitrary surface or the cross section of the electrolyte sheet 7 with a scanning electron microscope. Is measured by image processing (binarization processing). Since the occupied area of the inorganic oxide particles on any surface or cross section of the electrolyte sheet 7 is considered to be substantially constant, the occupied area can be regarded as the filling rate fi.

The total surface area Si (per unit volume) of the inorganic oxide particles occupying a unit volume of 1 cm ³ of the electrolyte sheet 7 (hereinafter, also simply referred to as “total surface area Si of the inorganic oxide particles”) is excellent in conductivity. and at 1000 cm ^-1 or more, preferably 2000 cm ^-1 or more, more preferably 3000 cm ^-1 or more, more preferably 5000 cm ^-1 or more. The total surface area Si of the inorganic oxide particles, from the viewpoint of excellent tensile strength is at 12000 ^-1 or less, preferably 10000 cm ^-1 or less, more preferably 9000 cm ^-1 or less, more preferably 8000 cm ^-1 or less. The total surface area Si of the inorganic oxide particles, from the viewpoint of excellent conductivity and tensile strength, ^{preferably, 1000~12000cm -1, 1000~10000cm -1, 1000~9000cm} -1, 1000~8000cm -1, 2000~12000cm ^{-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 , 5000~10000cm ^-1, a 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 above-mentioned inorganic oxide particles, and Di ₅₀ represents the average particle diameter (μm) of the above-mentioned inorganic oxide particles. The physical term of the constant term “6” on the right side of the equation (5) is the same as that of 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 (inorganic oxide particles Content / polymer content) is preferably 0.5 / 2 or more, more preferably 0.7 / 2 or more, still more preferably 0.8 / 2 or more, and preferably 1.8 / 2 or less. , More preferably 1.4 / 2 or less, still more preferably 1.2 / 2 or less.

  The electrolyte salt is at least one selected from the group consisting of lithium salt, sodium salt, calcium salt and magnesium salt. The electrolyte salt is a compound used for exchanging cations between the positive electrode 6 and the negative electrode 8. The above electrolyte salt is preferable in that it has a low degree of dissociation at low temperatures, is easily diffused in a solvent, and does not undergo thermal decomposition at high temperatures, so that the environmental temperature in which the secondary battery can be used is wide. The electrolyte salt may be an electrolyte salt used in a fluorine ion battery.

Anions of the electrolyte salt include halide ions (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. The anion is 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 there.

The following abbreviations may be used below.
[FSI] ⁻ : N (SO ₂ F) ₂ ⁻ , bis (fluorosulfonyl) imide anion [TFSI] ⁻ : N (SO ₂ CF ₃ ) ₂ ⁻ , bis (trifluoromethanesulfonyl) imide anion [BOB] ⁻ : B _{(O 2 C 2 O 2)} 2 -, bis oxalate borate anion _{^{[f3C] -: C (SO}} 2 F) 3 -, tris (fluorosulfonyl) carbanions

Lithium salts include 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.).

The sodium salt includes 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.).

The calcium salt is 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, phenyl Group or a naphthyl group).

The magnesium salt includes 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 naphthyl group).

Of 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, At least one selected from the group consisting of LiCF ₃ COO and LiRCOO (R is an alkyl group having 1 to 4 carbon atoms, a phenyl group, or a naphthyl group.), And more preferably Li [TFSI] or Li. _{[FSI], LiPF 6, LiBF} 4, Li [BOB], and at least one selected from the group consisting of LiClO _4, more preferably Li [TF I], and is one selected from the group consisting of Li [FSI].

  The content of the electrolyte salt may be 10% by mass or more and 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 is preferably 20% by mass or more from the viewpoint of further increasing the conductivity of the electrolyte sheet 7 based on the total amount of the electrolyte sheet, and the lithium secondary battery can be charged and discharged at a high load factor. From the viewpoint of, it is more preferably 30 mass% or more.

  The electrolyte sheet 7 can 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 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. R ¹ and R ² are each independently preferably a methyl group or an ethyl group.

  Specifically, the grime includes monoglyme (n = 1), diglyme (n = 2), triglyme (n = 3), tetraglyme (n = 4), pentaglyme (n = 5), and hexaglyme (n =). 6).

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

  As a solvent, the electrolyte sheet 7 is, for example, propylene carbonate, butylene carbonate, vinylene carbonate, γ-butyrolactone, diethyl carbonate, methyl ethyl carbonate, 1,2-dimethoxyethane, 2-, as a solvent for the purpose of further improving the conductivity. Methyltetrahydrofuran, dimethylsulfoxide, 1,3-dioxolane, formamide, dimethylformamide, methyl propionate, ethyl propionate, phosphoric acid triester, trimethoxymethane, dioxolane, diethyl ether, sulfolane, 3-methyl-2-oxazolidinone , Tetrahydrofuran, 1,2-diethoxyethane, chloroethylene carbonate, chloropropylene carbonate and the like may be further contained. From the viewpoint of improving safety, the electrolyte sheet 7 preferably contains only at least one selected from the above-mentioned grime as a solvent.

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

  The total content of the electrolyte salt and the solvent is preferably 10% by mass or more, and more preferably, 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 25 mass% or more, more preferably 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 the strength reduction 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 further preferably 30 μm or less.

In the secondary battery 1 described above, the sum of the total surface area Si of the inorganic oxide particles and the total surface area Sp, Si of each electrode active material is preferably 8000 cm ⁻¹ or more from the viewpoint of improving discharge characteristics. is there. 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 , And preferably at least 8000 cm ⁻¹ .

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

  Subsequently, a method for manufacturing the above-described secondary battery 1 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 a negative electrode mixture on the negative electrode current collector 11. The method includes a second step of forming the 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.

  In the first step, for the positive electrode 6, for example, the material used for the positive electrode mixture layer is dispersed in a dispersion medium using a kneader, a disperser or the like to obtain a slurry positive electrode mixture, and then this positive electrode mixture is obtained. Is applied onto the positive electrode current collector 9 by a doctor blade method, a dipping method, a spray method or the like, and then the dispersion medium is volatilized. After volatilizing the dispersion medium, a compression molding step using a roll press may be provided, if necessary. The positive electrode mixture layer 10 may be formed as a positive electrode mixture layer having a multi-layer structure by performing the above-described steps from coating the positive electrode mixture to volatilizing the dispersion medium a plurality of times.

  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 method as the above-described first step.

  In the third step, in one embodiment, the electrolyte sheet 7 is formed by coating on at least one of the positive electrode mixture layer 10 side of the positive electrode 6 and the negative electrode 8 side of the negative electrode mixture layer 12, and preferably the positive electrode 6 It is formed by coating on both the positive electrode mixture layer 10 side and the negative electrode 8 side of the negative electrode mixture layer 12. In this case, for example, the positive electrode 6 provided with the electrolyte sheet 7 and the negative electrode 8 provided with the electrolyte sheet 7 are laminated by, for example, lamination so that the electrolyte sheets 7 are in contact with each other to obtain the secondary battery 1. To be

  The method of forming the electrolyte sheet 7 on the positive electrode mixture layer 10 by coating is, for example, by dispersing the material used for the electrolyte sheet 7 in a dispersion medium to obtain a slurry, and then applying this electrolyte composition on the positive electrode mixture layer 10. It is a method of applying using an applicator. The dispersion medium is preferably water, NMP or the like. 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 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 by, for example, producing a laminated sheet having an electrolyte sheet on a base material. FIG. 4A is a schematic cross-sectional view showing a laminated sheet according to one embodiment. As shown in FIG. 4A, the laminated sheet 13A has a base material 14 and an electrolyte sheet 7 provided on the base material 14.

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

  The base material 14 has heat resistance that can withstand heating when volatilizing the dispersion medium, and is not limited as long as it does not react with the electrolyte composition and does not swell with the electrolyte composition, for example, a film shape. It is composed of a resin. Specifically, the base material 14 may be a film made of a resin (general-purpose engineering plastic) such as polyethylene terephthalate, polytetrafluoroethylene, polyimide, polyether sulfone, and polyether ketone.

  The base material 14 is a base material that can withstand the processing temperature for volatilizing the dispersion medium in the process of manufacturing the electrolyte sheet 7. Of the softening point (the temperature at which plastic deformation begins) or the melting point of the base material 14, when the lower temperature is the heat resistant temperature, the heat resistant temperature is preferably 50 ° C. from the viewpoint of compatibility with the solvent used for the electrolyte sheet 7. Or higher, more preferably 100 ° C. or higher, even more preferably 150 ° C. or higher, and, for example, 400 ° C. or lower. If the base material having the above heat resistant temperature is used, the above-mentioned dispersion medium (NMP, toluene, etc.) can be preferably used.

  The thickness of the base material 14 is preferably as thin as possible while maintaining the strength capable of withstanding the tensile force of the coating device. The thickness of the base material 14 is preferably 5 μm or more, and more preferably 10 μm or more, from the viewpoint of ensuring strength when applying the electrolyte composition to the base material 14 while reducing the volume of the entire laminated sheet 13A. And more preferably 25 μm or more, preferably 100 μm or less, more preferably 50 μm or less, still more preferably 40 μm or less.

  The laminated sheet can be continuously manufactured while being wound into a roll. In that case, the surface of the electrolyte sheet 7 contacts the back surface of the base material 14 and a part of the electrolyte sheet 7 sticks to the base material 14, whereby the electrolyte sheet 7 may be damaged. In order to prevent such a situation, the electrolyte sheet may be provided with a protective material on the side opposite to the base material 14 of the electrolyte sheet 7 as another embodiment. FIG. 4B is a schematic 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 opposite side of the electrolyte sheet 7 from the base material 14.

  The protective material 15 may be any material that can be easily peeled from the electrolyte sheet 7, and is preferably a non-polar resin (polymer) film such as polyethylene, polypropylene, or polytetrafluoroethylene. When a non-polar resin film is used, the electrolyte sheet 7 and the protective material 15 do not stick 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 ensuring strength while reducing the volume of the entire laminated sheet 13B, and The thickness is preferably 50 μm or less, more preferably 30 μm or less.

  From the viewpoint of suppressing deterioration in a low temperature environment and suppressing softening in a high temperature environment, the heat resistant temperature of the protective material 15 is preferably −30 ° C. or higher, more preferably 0 ° C. or higher, and The temperature is preferably 100 ° C or lower, and more preferably 50 ° C or lower. When the protective material 15 is provided, the step of volatilizing the dispersion medium described above is not essential, and therefore it is not necessary to raise the heat resistant 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 base material 14 from the laminated sheet 13A, and laminating the positive electrode 6, the electrolyte sheet 7 and the negative electrode 8 by, for example, laminating. The secondary battery 1 is obtained by stacking. At this time, the electrolyte sheet 7 is located on the positive electrode mixture layer 10 side of the positive electrode 6 and on the negative electrode mixture layer 12 side of the negative electrode 8, that is, the positive electrode current collector 9, the positive electrode mixture layer 10, and the electrolyte sheet 7. The negative electrode mixture layer 12 and the negative electrode current collector 11 are laminated in this order. When the laminated sheet is continuously manufactured while being wound into a roll, the rolled sheet may be unwound and the electrolyte sheet 7 may be provided between the positive electrode 6 and the negative electrode 8 and then cut. The electrolyte sheet 7 may be provided between the positive electrode 6 and the negative electrode 8 after cutting the sheet.

  In the third step, a pressure-sensitive adhesive layer (not shown) may be further provided on the electrolyte sheet 7 for the purpose of suitably stacking the electrolyte sheet 7 and the positive electrode 6 or the negative electrode 8. The pressure-sensitive adhesive layer is formed by pressure-bonding a film-shaped pressure-sensitive adhesive, pressure-bonding the pressure-sensitive adhesive layer formed on the release film to the electrolyte sheet 7 and peeling the release film to transfer the pressure-sensitive adhesive layer, It can be provided by applying an adhesive to the electrolyte sheet 7. When the laminated sheet 13A is used, it may be an electrolyte sheet on which a pressure-sensitive adhesive layer is formed in advance when the laminated sheet 13A is manufactured.

  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 the pressure-sensitive adhesive layer is provided 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, and may be provided on one end of the electrolyte sheet 7. Thereby, when the electrolyte sheet 7 and the positive electrode 6 or the negative electrode 8 are laminated, or when the electrolyte sheets 7 formed on the positive electrode mixture layer 10 and the negative electrode mixture layer 12 are laminated, an adhesive layer is interposed. Since they are laminated, wrinkles or waviness are less likely to occur during lamination, and a secondary battery in which the electrodes (the positive electrode 6 and the negative electrode 8) and the electrolyte sheet 7 are suitably laminated can be manufactured.

[Second Embodiment]
Next, the secondary battery according to the second embodiment will be described. FIG. 5 is a schematic cross-sectional view showing an embodiment of an electrode group in the secondary battery according to the second embodiment. As shown in FIG. 5, the secondary battery according to the second embodiment is different from the secondary battery according to the first embodiment in that the electrode group 2B includes the bipolar electrode 16. That is, the electrode group 2B includes the positive electrode 6, the first electrolyte sheet 7, the bipolar electrode 16, the second electrolyte sheet 7, and the negative electrode 8 in this order.

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

  In the bipolar electrode current collector 17, the positive electrode surface may be preferably formed of a material having excellent oxidation resistance, and 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, It may be formed of nickel, iron, titanium, or the like. When different kinds of metals are used for the positive electrode surface and the negative electrode surface, the bipolar electrode current collector 17 may be a clad material in which different kinds of metal foils are laminated. However, when the negative electrode 8 that operates at a potential that does not form an alloy with lithium, such as lithium titanate, is used, 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 a perforated foil made of aluminum having a hole having a hole diameter of 0.1 to 10 mm, an expanded metal, a foam metal plate, or the like. In addition to the above, the bipolar electrode current collector 17 may be made of any material as long as it does not cause changes such as dissolution and oxidation during use of the battery, and its shape, manufacturing method, etc. Is not limited.

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

In this secondary battery, 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 positive electrode mixture layer 10 is preferably from the viewpoint of improving discharge characteristics. Is 8000 cm ⁻¹ or more, more preferably 9000 cm ⁻¹ or more, further preferably 10000 cm ⁻¹ or more, particularly preferably 14000 cm ⁻¹ or more, for example, 20000 cm ⁻¹ or less, 18000 cm ⁻¹ or less, or 16000 cm ^−1. May be:

Similarly, from the viewpoint of improving discharge characteristics, in the adjacent electrolyte sheet 7 and 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. or more, more preferably 9000 cm ^-1 or more, more preferably 10000 cm ^-1 or more, particularly preferably 14000 cm ^-1 or more, for example, 20000 cm ^-1 or less, 18000Cm ^-1 or less, or 16000Cm ^-1 may be less.

  Subsequently, a method of manufacturing the secondary battery according to the second embodiment will be described. The method for manufacturing a secondary battery according to the present embodiment includes a first step of forming a positive electrode mixture layer 10 on a positive electrode current collector 9 to obtain a positive electrode 6, and a negative electrode mixture layer on a negative electrode current collector 11. The second step of forming the negative electrode 8 by forming 12 and the positive electrode mixture layer 10 is formed on one surface of the bipolar electrode current collector 17 and the negative electrode mixture layer 12 is formed on the other surface of the bipolar electrode current collector 17. 16 is provided, and the fourth step is to provide the electrolyte sheet 7 between the positive electrode 6 and the bipolar electrode 16 and between the negative electrode 8 and the bipolar electrode 16.

  The first step and the second step may be the same methods as the first step and the second step in the first embodiment.

  In the third step, the method of forming the positive electrode mixture layer 10 on the one surface of the bipolar electrode current collector 17 may be the same method as the first step in the first embodiment. The method of forming the negative electrode mixture layer 12 on the other surface of the bipolar electrode current collector 17 may be the same as the method of 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 in the fourth step, in one embodiment, the electrolyte sheet 7 includes the positive electrode mixture layer 10 side of the positive electrode 6 and the negative electrode of the bipolar electrode 16. It is formed by coating on at least one of the mixture layer 12 sides, and is preferably formed by coating on both the positive electrode mixture layer 10 side of the positive electrode 6 and the negative electrode mixture layer 12 side of the bipolar electrode 16. 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 are laminated by, for example, lamination so that the electrolyte sheets 7 are in contact with each other.

  The method of forming the electrolyte sheet 7 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 a positive electrode mixture according to one embodiment of the third step in the first embodiment. The method may be the same as the method for forming the electrolyte sheet 7 on the layer 10 by coating and the method for forming the electrolyte sheet 7 on the negative electrode mixture layer 12 by coating.

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

  In the fourth step, the method of providing the electrolyte sheet 7 between the negative electrode 8 and the bipolar electrode 16 may be the same as the method of providing the electrolyte sheet 7 between the positive electrode 6 and the bipolar electrode 16 described above. .

As described above, in the electrolyte sheet 7, excellent conductivity and tensile strength are obtained because the total surface area of the inorganic oxide particles occupying 1 cm ³ of the electrolyte sheet is 1000 to 12000 cm ⁻¹ . Therefore, the secondary battery 1 using the electrolyte sheet 7, that is, the secondary battery 1 including the pair of electrodes 6 and 8 and the electrolyte sheet 7 provided between the pair of electrodes 6 and 8 also has favorable characteristics. Is obtained. The pair of electrodes means two electrodes facing each other across the electrolyte sheet 7 and having different polarities. For example, in the electrode group 2A shown in FIG. 3, the positive electrode 6 and the negative electrode 8 form a pair of electrodes. In the electrode group 2B shown in FIG. 5, the positive electrode 6 and the bipolar electrode 16 (on the negative electrode mixture layer 12 side) form a pair of electrodes, and the negative electrode 8 and the bipolar electrode 16 (on the positive electrode mixture layer 10 side) also form a pair. Configure electrodes.

In the secondary battery 1, when the sum of the total surface area of the inorganic oxide particles occupying 1 cm ³ of the electrolyte sheet and the total surface area of each electrode active material occupying 1 cm ³ of each electrode mixture layer is 8000 cm ⁻¹ or more. In particular, a secondary battery having excellent discharge characteristics can be obtained.

  Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples.

<Example 1>
[Preparation of electrolyte sheet]
A copolymer of vinylidene fluoride and hexafluoropyrene (PVDF-HFP, vinylidene fluoride: hexafluoropyrene = 95% by mass: 5% by mass) as a polymer, and SiO ₂ particles (average particle size Di ₅₀ : 1 as an inorganic oxide particle). 0.0 μm), and lithium bis (fluorosulfonyl) imide (LiFSI) as an electrolyte salt and tetraglyme as a solvent in equimolar amounts were mixed at the compounding amounts shown in Table 1 to form a dispersion medium 1- An electrolyte slurry was prepared by dispersing in methyl-2-pyrrolidone (NMP). The obtained slurry was applied once to a substrate made of polyethylene terephthalate by the doctor blade method and heated to volatilize the dispersion medium to form an electrolyte sheet. The thickness of the obtained electrolyte sheet was 25 ± 2 μm.

[Measurement of filling rate fi and total surface area Si]
The surface of the obtained electrolyte sheet is observed by a scanning electron microscope to calculate the area (occupied area; area%) of the SiO ₂ particles occupying the unit area of the surface, and the occupied area is the filling rate of the SiO ₂ particles. and fi. Further, the total surface area Si of the SiO ₂ particles was calculated from the average particle diameter Di ₅₀ of the SiO ₂ particles and the filling rate fi according to the above formula (1). The results are shown in Table 1.

[Measurement of conductivity]
The electrical conductivity was obtained by sandwiching an electrolyte sheet between two lithium metal foils and measuring the resistance between the lithium metal foils. The results are shown in Table 1. 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 × 5 cm, both ends were attached to a fixture of a tensile test device (manufactured by Shimadzu Corporation, Autograph) and pulled, and the strength at the time of breaking was defined as the tensile strength. The results are shown in Table 1. If 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>
An electrolyte sheet was prepared and measured in the same manner as in Example 1 except that the blending amount of each component in the electrolyte sheet was changed as shown in Table 1. The results are shown in Table 1.

<Test Example 1>
[Production of positive electrode]
LiNi _0.6 Co _0.2 Mn _0.2 O ₂ (positive electrode active material, average particle size Dp ₅₀ : 5.0 μm) 96 parts by mass, carbon black (conductive material, product name: HS-100, average particle size 48 nm) , Denka Co., Ltd.) 1.75 parts by mass and 2.5 parts by mass of a copolymer (binder) of polyvinylidene fluoride and hexafluoropropylene are mixed with 1-methyl-2-pyrrolidone to prepare a positive electrode mixture slurry. Prepared. This positive electrode material mixture slurry was applied onto an aluminum foil (positive electrode current collector) having a thickness of 15 μm, and heated at 80 ° C. to dry it to form a positive electrode material mixture layer having a thickness of 45 μm.

[Preparation of negative electrode]
Natural graphite (negative electrode active material, manufactured by Hitachi Chemical Co., Ltd., average particle diameter Dn ₅₀ : 12 μm) 94 parts by mass, carbon black (conductive material, product name: HS-100, average particle diameter 48 nm, manufactured by DENKA CORPORATION) 1 mass Parts and 5 parts by mass of polyvinylidene fluoride (binder) were mixed with 1-methyl-2-pyrrolidone to prepare a negative electrode mixture slurry. The negative electrode mixture slurry was applied onto a rolled copper foil (negative electrode current collector) having a thickness of 10 μm, and heated at 80 ° C. to dry it, thereby forming a negative electrode mixture layer having a thickness of 40 μm.

[Measurement of filling rate fp, fn and total surface area Sp, Sn]
For the obtained positive electrode and negative electrode, binarization processing was performed on a photograph of the positive electrode mixture layer and the negative electrode mixture layer observed by a scanning electron microscope, and the occupied areas of the positive electrode active material and the negative electrode active material were calculated, respectively. . The ratios of the occupied areas of the positive electrode active material and the negative electrode active material to the areas of the positive electrode mixture layer and the negative electrode mixture layer in the micrograph were taken as the filling rate fp of the positive electrode active material and the filling rate fn of the negative electrode active material, respectively. The average particle diameters Dp ₅₀ and Dn ₅₀ of each active material were measured using a laser scattering particle size measuring device (Microtrac). By substituting these values into the above formula (4) or (5), 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. The results are shown in Table 2.

[Assembly of secondary battery]
As shown in FIG. 2, strip-shaped positive electrodes, negative electrodes, and electrolyte sheets were prepared. The positive electrode active material or the negative electrode active material and the mixture layer containing a binder or the like were formed into a quadrangle and had substantially the same size. The exposed current collector was extended above the mixture layer, and the electrode and the tab were welded. The electrolyte sheet was made larger than the mixture layer and sandwiched between the positive electrode and the negative electrode so that both electrodes were not electrically short-circuited. After stacking the positive electrode, the electrolyte sheet, the negative electrode, and the electrolyte sheet, the positive electrode was stacked again, and then the same arrangement was performed. Then, tabs of the same pole were welded together and sealed in an aluminum laminate bag to manufacture a lithium secondary battery as shown in FIG. 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 with a constant current at 0.05 CA (0.15 A), and after the voltage reached 4.2 V, it was charged until the current value of constant voltage charging was 0.005 CA, and then, A constant current discharge was performed at 0.05 CA to 2.7 V. Then, after charging in the same manner as above, constant current discharge was performed at 1.0 CA (3.0 A) to 2.7 V, 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 negative electrode active material in the negative electrode. A secondary battery was prepared and evaluated in the same manner as in Test Example 1 except that the average particle size Dn ₅₀ , the filling rate fn, and the total surface area Sn were changed as shown in Table 2. The results are shown in Table 2.

  DESCRIPTION OF SYMBOLS 1 ... Secondary battery, 6 ... Positive electrode, 7 ... Electrolyte sheet, 8 ... Negative electrode, 9 ... Positive electrode collector, 10 ... Positive electrode mixture layer, 11 ... Negative electrode collector, 12 ... Negative electrode mixture layer.

Claims (8)

An electrolyte sheet containing one or more polymers, inorganic oxide particles, and an electrolyte salt,
An electrolyte sheet in which the total surface area of the inorganic oxide particles in 1 cm ³ of the electrolyte sheet is 1000 to 12000 cm ⁻¹ .   The first structural unit selected from the group consisting of ethylene tetrafluoride and vinylidene fluoride among the structural units constituting the one or more polymers, and hexafluoropropylene, acrylic acid, maleic acid, ethyl The electrolyte sheet according to claim 1, comprising a second structural unit selected from the group consisting of methacrylate and methyl methacrylate.   The electrolyte sheet according to claim 1 or 2, wherein the content of the polymer is 10 to 40 mass% based on the total amount of the electrolyte sheet. The inorganic oxide particles are at least one kind of particles 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. The electrolyte sheet according to any one of claims 1 to 3. A pair of electrodes,
An electrolyte sheet according to any one of claims 1 to 4, which is provided between the pair of electrodes,
A secondary battery including. Each of the pair of electrodes comprises a current collector, and an electrode mixture layer provided on the current collector and containing an electrode active material,
6. The sum of the total surface area of the inorganic oxide particles occupying 1 cm ³ of the electrolyte sheet and the total surface area of each electrode active material occupying 1 cm ³ of each electrode mixture layer is 8000 cm ⁻¹ or more. The secondary battery according to. The total surface area of the inorganic oxide particles occupying the electrolyte sheet 1 cm ³ is at 5000 cm ^-1 or more, and the total surface area of each electrode active material occupying in the electrode mixture layer 1 cm ³ is 3000 cm ^-1 or more, The secondary battery according to claim 6.   The secondary battery according to claim 6, wherein the electrode mixture layer further contains a binder.

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