TW201941475A - Electrolyte composition, electrolyte sheet, and secondary battery - Google Patents

Abstract

In one aspect, the present invention provides an electrolyte composition comprising a matrix polymer, at least one electrolyte salt selected from the group consisting of a lithium salt, a sodium salt, a calcium salt and a magnesium salt, oxide particles and fibers, wherein the average length of the fibers is equal to or larger than the average particle diameter of the oxide particles.

Description

Electrolyte composition, electrolyte sheet and secondary battery

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

In recent years, high-performance secondary batteries have been required due to the spread of portable electronic devices and electric vehicles. Among them, lithium secondary batteries have attracted attention as power sources such as batteries for electric vehicles and batteries for power storage due to their high energy density. Specifically, lithium secondary batteries, which are batteries for electric vehicles, have been used in the following electric vehicles: zero-emission electric vehicles without engines; hybrid electric vehicles with both engines and secondary batteries; directly from the power system Charging plug-in hybrid electric vehicles and the like. In addition, a lithium secondary battery as a battery for power storage has been used in a stationary power storage system that supplies pre-stored power in an emergency situation where the power system is interrupted.

In order to be used for such a wide range of applications, lithium secondary batteries with higher energy density are being sought and are being developed. In particular, since lithium secondary batteries for electric vehicles require high safety in addition to high input-output characteristics and high energy density, a higher level of technology is required to ensure safety.

Conventionally, as a method for improving the safety of a lithium secondary battery, a method is known in which a flame retardant is added to flame retard an electrolyte, and the electrolyte is changed to a polymer electrolyte or a gel electrolyte. Method, etc. In particular, a gel electrolyte has an ionic conductivity equivalent to that of an electrolytic solution used in a conventional lithium secondary battery. Therefore, by changing the electrolytic solution to a gel electrolyte, it is possible to prevent the deterioration of battery characteristics. In some cases, the amount of free electrolyte is reduced to suppress the electrolyte from burning.

Patent Document 1 discloses a solid electrolyte sheet including a sheet-like porous substrate and an inorganic solid electrolyte material, and an inorganic solid electrolyte material is filled in the voids of the porous substrate. Patent Document 2 discloses an invention related to a lithium secondary battery, which is composed of a positive electrode, a negative electrode, a separator, and a gel electrolyte; the gel electrolyte includes: particles of a filler, and a matrix polymer compound for holding an electrolyte Composition of resin and electrolyte. Patent Document 2 discloses a technology that can improve the transparency of a gel electrolyte and ensure safety without sacrificing capacity by setting the shape of particles and the refractive index of particles to predetermined conditions. Patent Document 3 also discloses an invention related to a gel electrolyte, and also discloses an electrolyte obtained by setting the following conditions: a particle diameter of a particle, a refractive index of a particle, and a mass ratio of a particle to a matrix polymer compound ( Particles / matrix polymer compound), and the mass ratio of particles to electrolyte salt (particle / electrolyte salt).
[Prior technical literature]
(Patent Literature)

Patent Document 1: Japanese Patent Laid-Open Publication No. 2015-153460 Patent Document 2: International Publication No. 2015/068324 Patent Document 3: International Publication No. 2015/097952

[Problems to be solved by the invention]
However, the conventional gel electrolytes as described above have room for improvement in terms of safety. According to research by the present inventors, the gel electrolytes of Patent Documents 1 to 3 may cause thermal contraction of the gel electrolyte at a high temperature and cause a short circuit in the secondary battery, which may cause a problem in terms of safety. In addition, as a test for evaluating the safety of a lithium secondary battery, tests under severe conditions such as a nail penetration test and a crush test are known, but in lithium ion secondary batteries using a gel electrolyte, also It is expected that excellent evaluation results will be obtained in such tests.

Therefore, an object of the present invention is to provide an electrolyte composition and an electrolyte sheet in several aspects, which can suppress a short circuit even at a high temperature. Another object of the present invention is to provide a secondary battery in another aspect, which can suppress short-circuits at high temperatures and improve safety.
[Technical means to solve the problem]

A first aspect of the present invention provides an electrolyte composition including: a matrix polymer; at least one electrolyte salt selected from the group consisting of a lithium salt, a sodium salt, a calcium salt, and a magnesium salt; and an oxide particle Fibers; and ionic liquids; and the average length of the fibers is equal to or larger than the average particle diameter of the oxide particles.

The fiber is preferably at least one selected from the group consisting of cellulose fibers, resin fibers, and glass fibers.

The matrix polymer preferably has a first structural unit, and the first structural unit is selected from the group consisting of tetrafluoroethylene and vinylidene fluoride.

The structural unit constituting the matrix polymer preferably contains: a first structural unit; and a second structural unit, the second structural unit is composed of hexafluoropropylene, acrylic acid, maleic acid, ethyl methacrylate, and Selected from the group consisting of methyl methacrylate.

The electrolyte salt preferably contains a lithium imine-based lithium salt.

The ionic liquid preferably contains at least one kind of an anionic component represented by the following formula (1) as an anionic component:

m and n each independently represent an integer of 0 to 5.

The ionic liquid preferably contains at least one selected from the group consisting of a chain quaternary onium salt cation, a piperidinium salt cation, a pyrrolidinium salt cation, a pyridinium salt cation, and an imidazolium salt cation. As a cationic component.

According to a second aspect of the present invention, there is provided an electrolyte sheet including: a base material; and an electrolyte layer provided on the base material and formed of the electrolyte composition.

A third aspect of the present invention provides a secondary battery including: a positive electrode; a negative electrode; and an electrolyte layer provided between the positive electrode and the negative electrode and formed of the electrolyte composition.

In the second aspect and the third aspect, the average fiber diameter of the fibers is preferably equal to or less than the thickness of the electrolyte layer.
[efficacy]

According to several aspects of the present invention, it is possible to provide an electrolyte composition and an electrolyte sheet that can suppress short circuits at high temperatures. According to another aspect of the present invention, it is possible to provide a secondary battery that can suppress short-circuits at high temperatures and improve safety.

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, etc.) are not necessary except for the cases specified otherwise. The sizes of the constituent elements in each figure are only concepts, and the relative relationship between the sizes of the constituent elements is not limited to the relationships shown in the figures.

The numerical values and ranges in this specification are not intended to limit the present invention. In the present specification, a numerical range expressed using "~" means a range including numerical values described before and after "~" as the minimum and maximum values, respectively. In the numerical ranges described in stages in this specification, an upper limit value or a lower limit value described in one numerical range may be replaced with an upper limit value or a lower limit value in another numerical range described in stages. In addition, in the numerical range described in the specification, an upper limit value or a lower limit value of the numerical range may be replaced with a value disclosed in the embodiment.

[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 composed of a positive electrode, a negative electrode, and an electrolyte layer, and a pouch-shaped battery case 3 for accommodating the electrode group 2. A positive electrode current collector terminal (tab) 4 and a negative electrode current collector terminal 5 are provided on the positive electrode and the negative electrode, respectively. The positive electrode current collecting terminal 4 and the negative electrode current collecting terminal 5 respectively protrude 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.

The battery case 3 may be formed of, for example, a laminated film. The laminated film may be, for example, a laminated film which is sequentially laminated as follows: a resin film such as a polyethylene terephthalate (PET) film; a metal foil such as aluminum, copper, and stainless steel; and polypropylene, etc. Sealant layer.

Fig. 2 is an exploded perspective view showing an embodiment of the electrode group 2 in the secondary battery 1 shown in Fig. 1. FIG. 3 is a schematic perspective view showing an embodiment of the electrode group 2 in the secondary battery 1 shown in FIG. 1. As shown in FIGS. 2 and 3, the electrode group 2A of the present embodiment includes a positive electrode 6, an 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, and the positive electrode mixture layer 10 is provided on the positive electrode current collector 9. The positive electrode current collector 9 is provided with a positive electrode current collecting terminal 4. The negative electrode 8 includes a negative electrode current collector 11 and a negative electrode mixture layer 12, and the negative electrode mixture layer 12 is provided on the negative electrode current collector 11. The negative electrode current collector 11 is provided with a negative electrode current collecting terminal 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 holes having a pore diameter of 0.1 to 10 mm, an expanded metal, a foamed 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 undergo changes such as dissolution or oxidation during use of the battery, and its shape, manufacturing method, and the like are not limited.

The thickness of the positive electrode current collector 9 may be 10 μm or more and 100 μm or less. From the viewpoint of reducing the overall volume of the positive electrode, 10 to 50 μm is preferable. From the viewpoint of reducing the curvature of the battery when forming it, From the viewpoint of positive electrode winding, it is preferably 10 to 20 μm.

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

The positive electrode active material may be: 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 (where M ¹ = One selected from the group consisting of Co, Ni, Fe, Cr, Zn, and Ta, a = 0.01 to 0.2), Li ₂ Mn ₃ M ² O ₈ (where M ² = from Fe, Co 1 selected from the group consisting of Ni, Cu, Zn), Li _1-b M ³ _b Mn ₂ O ₄ (where M ³ = from Mg, B, Al, Fe, Co, Ni, Cr One selected from the group consisting of Zn, Ca and Zn, b = 0.01 to 0.1), LiFeO ₂ , Fe ₂ (SO ₄ ) ₃ , LiCo _{1 - d} M ⁵ _d O ₂ (where M ⁵ = free from One selected from the group consisting of Ni, Fe, and Mn, d = 0.01 to 0.2), LiNi _{1 - e} M ⁶ _e O ₂ (where M ⁶ = from Mn, Fe, Co, Al, Ga, One selected from the group consisting of Ca and Mg, e = 0.01 to 0.2), Fe (MoO ₄ ) ₃ , FeF ₃ , LiFePO ₄ , LiMnPO ₄ and the like.

The positive electrode active material may be primary particles that are not granulated, or secondary particles that are granulated.

The particle diameter of the positive electrode active material is adjusted so as to be equal to or smaller than the thickness of the positive electrode material mixture layer 10. When the positive electrode active material includes coarse particles having a particle diameter larger than the thickness of the positive electrode mixture layer 10, the coarse particles are removed in advance by screening classification, air flow classification, and the like, and a particle diameter having a thickness less than the thickness of the positive electrode mixture layer 10 is selected. Positive active material.

From the viewpoint of suppressing the filling property of the positive electrode active material from deteriorating as the particle size decreases and improving the retention ability of the electrolyte, the average particle size of the positive electrode active material is preferably 0.1 μm or more, more preferably 1 μm or more, and It is more preferably 2 μm or more, more preferably 20 μm or less, more preferably 10 μm or less, and even more preferably 8 μm or less. The average particle diameter of the positive electrode active material is a particle diameter (D ₅₀ ) when the ratio (volume fraction) to the volume of the entire positive electrode active material is 50%. The average particle diameter (D ₅₀ ) of the positive electrode active material is obtained by measuring a suspension by a laser scattering method using a laser scattering type particle size measuring device (for example, Microtrac). The suspension is obtained by suspending the positive electrode active material in water. Made.

Based on the total amount of the positive electrode mixture layer, the content of the positive electrode active material may be 70% by mass or more, 80% by mass or more, or 85% by mass or more. Based on the total amount of the positive electrode mixture layer, the content of the positive electrode active material may be 95% by mass or less, 92% by mass or less, or 90% by mass or less.

The conductive agent may be carbon black, acetylene black, graphite, carbon fiber, carbon nanotube, or the like.

Based on the total amount of the positive electrode mixture layer, the content of the conductive agent may be 0.1% by mass or more, 1% by mass or more, or 3% by mass or more. From the viewpoint of suppressing the increase in the volume of the positive electrode 6 and the decrease in the energy density of the secondary battery 1 as the volume increases, based on the total amount of the positive electrode mixture layer, the content of the conductive agent is preferably 15% by mass or less. It is preferably 10% by mass or less, and more preferably 8% by mass or less.

The binder is not particularly limited as long as it does not decompose on the surface of the positive electrode 6, and is, for example, a polymer. Binders can be: celluloses such as carboxymethyl cellulose, ethyl cellulose, ethyl cellulose; copolymers of polyvinylidene fluoride, vinylidene fluoride, and hexafluoropropylene; styrene-butadiene rubber , Fluorine rubber, ethylene-propylene rubber, polyacrylic acid, polyimide, polyimide, etc.

Based on the total amount of the positive electrode mixture layer, the content of the binder may be 0.5% by mass or more, 1% by mass or more, or 3% by mass or more. The content of the binder may be 15% by mass or less, 10% by mass or less, or 7% by mass based on the total amount of the positive electrode mixture layer.

The positive electrode material mixture layer 10 may further contain an ionic liquid described later. When the positive electrode mixture layer 10 contains an ionic liquid, based on the total amount of the positive electrode mixture layer, the content of the ionic liquid is preferably 3% by mass or more, more preferably 5% by mass or more, more preferably 10% by mass or more, and It is preferably 30% by mass or less, more preferably 25% by mass or less, and even more preferably 20% by mass or less.

From the viewpoint of further improving the conductivity, the thickness of the positive electrode mixture layer 10 may be a thickness equal to or greater than the average particle diameter of the positive electrode active material, preferably 5 μm or more, more preferably 10 μm or more, and even 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 even more preferably 50 μm or less. By setting the thickness of the positive electrode mixture layer 10 to 100 μm or less, it is possible to suppress the charging and discharging bias caused by the vicinity of the surface of the positive electrode mixture layer 10 and the vicinity of the surface of the positive electrode current collector 9. The charge level of the positive electrode active material is uneven.

From the viewpoint of reducing the electrical resistance of the positive electrode mixture layer 10 by bringing the conductive agent and the positive electrode active material into close contact with each other, the mixture density of the positive electrode mixture layer 10 is preferably 2 g / cm ³ or more.

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 hole having a diameter of 0.1 to 10 mm, a rolled 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 and 100 μm or less. From the viewpoint of reducing the overall volume of the negative electrode, 10 to 50 μm is preferable. From the battery, the negative electrode is wound with a small curvature. From the viewpoint of winding, it is preferably 10 to 20 μm.

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

As the negative electrode active material, one commonly used in the field of energy devices can be used. Specific examples of the negative electrode active material include metal lithium, lithium alloys, metal compounds, carbon materials, metal complexes, and organic polymer compounds. The negative electrode active material may be used singly or in combination of two or more kinds.

The negative electrode active material is preferably a carbon material. As the carbon material, natural graphite (e.g., flaky graphite), artificial graphite, and the like; amorphous carbon; carbon fiber; and carbons such as acetylene black, ketjen black, groove black, furnace black, lamp black, and thermal black Black and so on. The negative electrode active material may be natural graphite covered 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), it may include silicon , Tin or compounds of these elements (oxides, nitrides, alloys with other metals). When 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 accommodated in the secondary battery 1 can be increased. As a result, the resistance of the secondary battery 1 can be reduced to achieve a high output, and at the same time, the capacity of the secondary battery 1 can be increased more than when the graphite negative electrode is used.

From the viewpoint of obtaining a negative electrode 8 which can suppress the increase of the irreversible capacity as the particle size decreases and improves the electrolyte retention ability, the negative electrode active material has an average particle diameter (D ₅₀ ) of 1 μm or more. 5 μm or more is preferable, 10 μm or more is more preferable, and 50 μm or less is preferable, 30 μm or less is preferable, and 20 μm or less is more preferable. Negative electrode active material average particle diameter (D ₅₀₎ is by the average particle diameter (D ₅₀₎ of the positive electrode active material was measured by the same method.

Based on the total amount of the negative electrode mixture layer, the content of the negative electrode active material may be 60% by mass or more, 65% by mass or more, or 70% by mass or more. Based on the total amount of the negative electrode mixture layer, the content of the negative electrode active material may be 99% by mass or less, 95% by mass or less, or 90% by mass or less.

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

From the viewpoint of further reducing the resistance of the negative electrode 8, the negative electrode mixture layer 12 may further contain a conductive agent and an ionic liquid. The types and contents of the conductive agent and the ionic liquid are the same as those of the conductive agent and the ionic liquid 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 equal to or larger than the average particle diameter of the negative electrode active material, specifically, preferably 10 μm or more, more preferably 15 μm or more, and more preferably 20 μm or more. . The thickness of the negative electrode mixture layer 12 is preferably 50 μm or less, more preferably 40 μm or less, and even more preferably 30 μm or less. By setting the thickness of the negative electrode mixture layer 12 to 50 μm or less, it is possible to suppress the charging and discharging bias caused by the vicinity of the surface of the negative electrode mixture layer 12 and the vicinity of the surface of the negative electrode current collector 11. The charge level of the positive electrode active material is uneven.

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

The electrolyte layer 7 is formed of an electrolyte composition. The electrolyte layer 7 (electrolyte composition) contains: a matrix polymer; at least one electrolyte salt selected from the group consisting of a lithium salt, a sodium salt, a calcium salt, and a magnesium salt; an oxide particle; a fiber; and, an ion liquid.

The matrix polymer is a polymer (binder polymer) serving as a matrix (forming a continuous phase) for holding other materials contained in the electrolyte composition. The matrix polymer preferably has a first structural unit, and the first structural unit is selected from the group consisting of tetrafluoroethylene and vinylidene fluoride.

The matrix polymer is preferably one or two or more polymers. Among the structural units (monomer units) constituting one or two or more polymers, the first polymer (monomer unit) is preferably contained. The first structural unit is selected from the group consisting of tetrafluoroethylene and vinylidene fluoride; and the second structural unit (monomer unit), the second structural unit is selected from hexafluoropropylene, acrylic acid , Maleic acid, ethyl methacrylate, and methyl methacrylate.

The first structural unit and the second structural unit may be contained in one polymer to constitute a copolymer. In other words, in one embodiment, the electrolyte composition contains at least one copolymer, and the copolymer includes 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 composition contains a copolymer, it may further contain other polymers.

The first structural unit and the second structural unit may be respectively contained in different polymers to constitute at least two types of polymers: a first polymer having a first structural unit, and a second polymer having a second structural unit. polymer. In other words, in one embodiment, the electrolyte composition contains, as a matrix polymer, at least two types of polymers including a first polymer including a first structural unit and a second polymer including a second structural unit. When the electrolyte composition 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 a polymer having other structural units in addition to the first structural unit. The other structural units may be oxygen-containing hydrocarbon structures such as ethylene oxide (-CH ₂ CH ₂ O-) and carboxylic acid esters (-CH ₂ COO-). The first polymer may be polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride, or a polymer obtained by introducing the aforementioned oxygen-containing hydrocarbon structure into the molecular structure.

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

From the viewpoint of further improving the strength when the electrolyte composition is formed into a sheet shape (electrolyte layer 7), based on the total amount of the structural units constituting the matrix polymer, the content of the first structural unit is 5% by mass or more. Preferably, it is more preferably 10% by mass or more, and more preferably 20% by mass or more. From the viewpoint of further improving the affinity with the ionic liquid contained in the electrolyte composition, based on the total amount of the structural units constituting the matrix polymer, the content of the first structural unit is preferably 60% by mass or less. It is preferably 40% by mass or less, and more preferably 30% by mass or less.

From the viewpoint of further improving the strength when the electrolyte composition is formed into a sheet shape (electrolyte layer 7), the total content of the first structural unit and the second structural unit is used as a reference, and the content of the first structural unit is better. It is 50% by mass or more, 70% by mass or more, 80% by mass or more, 90% by mass or more, or 95% by mass or more. From the viewpoint of further improving the affinity with the ionic liquid (the details will be described later) contained in the electrolyte composition, the total content of the first structural unit and the second structural unit is used as a reference. The content of 1 structural unit is preferably 99% by mass or less, 98% by mass or less, 97% by mass or less, or 96% by mass or less.

From the viewpoint of further improving the affinity with the ionic liquid contained in the electrolyte composition, based on the total amount of the structural units constituting the matrix polymer, the content of the second structural unit is preferably 1% by mass or more. It is preferably 3% by mass or more, and more preferably 5% by mass or more. From the viewpoint of further improving the strength when the electrolyte composition is formed into a sheet shape (electrolyte layer 7), based on the total amount of the structural units constituting the matrix polymer, the content of the second structural unit is 50% by mass or less. Preferably, it is preferably 20% by mass or less, and more preferably 10% by mass or less.

From the viewpoint of further improving the affinity with the ionic liquid contained in the electrolyte composition, the total content of the first structural unit and the second structural unit is used as a reference, and the content of the second structural unit is preferably 1 Mass% or more, 3 mass% or more, or 4 mass% or more. From the viewpoint of further improving the strength when the electrolyte composition is formed into a sheet (electrolyte layer 7), the content of the second structural unit is preferably based on the total content of the first structural unit and the second structural unit as a reference. It is 50% by mass or less, 40% by mass or less, 30% by mass or less, 20% by mass or less, 10% by mass or less, or 5% by mass or less.

From the viewpoint of further improving the strength when the electrolyte composition is formed into a sheet shape (electrolyte layer 7), the total amount of the electrolyte composition (except the dispersion medium described later, in other words, the total amount of the electrolyte layer, the same applies hereinafter) is used as The content of the matrix polymer is preferably 10% by mass or more, more preferably 15% by mass or more, more preferably 20% by mass or more, and particularly preferably 25% by mass or more. From the viewpoint of further improving the conductivity, based on the total amount of the electrolyte composition, the content of the matrix polymer is preferably 40% by mass or less, more preferably 35% by mass or less, and more preferably 30% by mass or less. 28% by mass or less is particularly preferred.

Since the matrix polymer has excellent affinity with the ionic liquid contained in the electrolyte composition, it can retain the electrolyte salt in the ionic liquid, and can suppress the occurrence of the ionic liquid when a load is applied to the electrolyte composition (electrolyte layer 7). Leaking.

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 for receiving a cation between the positive electrode 6 and the negative electrode 8. The above electrolyte salt has a low degree of dissociation at a low temperature and easily diffuses in an ionic liquid, and does not thermally decompose due to a high temperature. Therefore, it is preferable from the viewpoint of a wide range of ambient temperatures in which secondary batteries can be used. The electrolyte salt may be an electrolyte salt used in a fluoride ion battery.

Electrolyte salt anion may be: a halide ion ^{(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 ^- etc. The anions are 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 ^－ .

In addition, the following abbreviations may be used hereinafter.
^{[FSI] -: N (SO} 2 F) 2 -, bis (fluoromethyl sulfonylurea) imide anion
^{[TFSI] -: N (SO} 2 CF 3) 2 -, bis (trifluoromethanesulfonyl XI) imide anion
^{[BOB] -: B (O} 2 C 2 O 2) 2 -, bis (oxalato) borate (bisoxalatoborate) anion
[f3C] ^－ : C (SO ₂ F) ₃ ^－ , ginseng (fluorosulfonium) carbon anion

The lithium salt can be selected from 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 , Phenyl, or naphthyl), at least one selected from the group consisting of:

The sodium salt can be selected from 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 , Phenyl, or naphthyl), at least one selected from the group consisting of:

The calcium salt may be from 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, benzene Group, or naphthyl group).

The magnesium salt may be from Mg (PF ₆ ) ₂ , Mg (BF ₄ ) ₂ , Mg [FSI] ₂ , Mg [TFSI] ₂ , Mg [f3C] ₂ , Mg [BOB] ₂ , Mg (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, phenyl group , Or at least one selected from the group consisting of naphthyl).

The electrolyte salt is preferably one selected from the group consisting of a sulfonium-based lithium salt, a sulfonium-based sodium salt, a sulfonium-based calcium salt, and a sulfonium-based magnesium salt, and more preferably a fluorene Amine lithium salt.

The fluorene imide-based lithium salt may be Li [TFSI], Li [FSI], or the like. The ammonium-based sodium salt may be Na [TFSI], Na [FSI], and the like. The ammonium-based calcium salt may be Ca [TFSI] ₂ , Ca [FSI] _2, or the like. The sulfonium-imide-based magnesium salt may be Mg [TFSI] ₂ , Mg [FSI] _2, or the like.

In order to make the electrolyte layer 7 suitable, based on the total amount of the electrolyte composition, the content of the electrolyte salt may be 10% by mass or more and 60% by mass or less. From the viewpoint of further improving the conductivity of the electrolyte layer, the content of the electrolyte salt is preferably 20% by mass or more. From the viewpoint of being able to charge and discharge the lithium secondary battery with a high load factor, the content is more than 30% by mass. good.

The oxide particles are, for example, particles of an inorganic oxide. The inorganic oxide may be, for example, an inorganic oxide including the following as constituent elements: Li, Mg, Al, Si, Ca, Ti, Zr, La, Na, K, Ba, Sr, V, Nb, B, Ge, etc. . The 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 particle. Since the oxide particles have polarity, they promote the dissociation of the electrolyte in the electrolyte layer 7 and promote the amorphization of the matrix polymer to increase the diffusion rate of the cationic component of the electrolyte.

From the viewpoint of further improving the conductivity, the average primary particle diameter (average particle diameter of the primary particles) of the oxide particles is preferably 0.005 μm (5 nm) or more, more preferably 0.01 μm (10 nm) or more, and 0.015 μm (15 nm) or more is preferred. From the viewpoint of thinning the electrolyte layer 7, the average primary particle diameter of the oxide particles is preferably 1 μm (1000 nm) or less, more preferably 0.1 μm (100 nm) or less, and 0.05 μm (50 nm) or less. Better. From the viewpoint of thinning the electrolyte layer 7 while increasing the conductivity, and from suppressing the oxide particles from protruding from the surface of the electrolyte composition (electrolyte layer 7), the average primary particle diameter of the oxide particles is 0.005 to 1 μm, 0.01 to 0.1 μm, or 0.015 to 0.05 μm is preferred. The average primary particle diameter of the oxide particles can be measured by observing the oxide particles using a transmission electron microscope or the like.

The average particle diameter of the oxide particles is preferably 0.005 μm or more, more preferably 0.01 μm or more, and even more preferably 0.03 μm or more. The average particle diameter of the oxide particles is preferably 5 μm or less, more preferably 3 μm or less, and even more preferably 1 μm or less. The average particle diameter of the oxide particles is measured by a laser diffraction method. When a volume cumulative particle size distribution curve is drawn from the small particle diameter side, it corresponds to a particle diameter where the volume accumulation becomes 50%.

The shape of the oxide particles may be, for example, massive or approximately spherical. From the viewpoint of making the electrolyte layer 7 thin easily, the aspect ratio of the oxide particles is preferably 10 or less, more preferably 5 or less, and even more preferably 2 or less. The aspect ratio is defined as the ratio of the length in the major axis direction of the particles (the maximum length of the particles) to the length in the minor axis direction of the particles (the minimum length of the particles) in the scanning electron microscope photograph of the oxide particles. The particle length can be determined by statistically calculating the aforementioned photos using commercially available image processing software (for example, image analysis software manufactured by Asahi Kasei Engineering Co., Ltd .: A Xiangjun (registered trademark)).

From the viewpoint of promoting the dissociation of the electrolyte, based on the total amount of the electrolyte composition, the content of the oxide particles is preferably 5% by mass or more, more preferably 7% by mass or more, and even more preferably 10% by mass or more. From the viewpoint of further improving the conductivity, the content of the oxide particles is preferably 50% by mass or less, more preferably 40% by mass or less, and even more preferably 20% by mass or less.

The fiber may be an organic fiber or an inorganic fiber, or may be an organic-inorganic mixed fiber obtained by mixing an organic fiber and an inorganic fiber. Examples of the organic fibers include cellulose fibers, resin fibers, and carbon fibers. Examples of the inorganic fibers include glass fibers and ceramic fibers. The fiber is preferably at least one selected from the group consisting of cellulose fibers, resin fibers, and glass fibers. From the viewpoint of improving the smoothness of the electrolyte layer, cellulose fibers are preferred.

Cellulose fibers may be, for example, natural cellulose fibers such as coniferous wood pulp, broadleaf wood pulp, esparto pulp, manila hemp pulp, sisal pulp, cotton pulp, or organic solvent spinning of these natural cellulose fibers Regenerated cellulose fibers such as soluble fibers (Lyocell) obtained from the yarn.

The resin fiber may be a natural resin fiber or a synthetic resin fiber. The natural resin constituting the natural resin fiber may be, for example, latex, natural rubber, or the like. The synthetic resin constituting the synthetic resin fiber may be, for example, polyetheretherketone, polyimide, polyester, polyacrylonitrile, or the like. In one embodiment, the resin fibers are fibers of a resin (polymer) different from the matrix polymer.

From a viewpoint of being able to suppress a short circuit more, the fiber is preferably a fiber having heat resistance. The heat resistance refers to a property that the fiber does not melt or decompose at a high temperature and maintains the original state (solid state). The fiber may be a fiber that does not melt or decompose in an environment of preferably 150 ° C or higher, more preferably 200 ° C or higher, and even more preferably 300 ° C or higher. The state in which the fiber is melted or decomposed is equivalent to using Thermal Gravimetry (TG; Thermal Gravimetry, DTA; Differential Thermal Analysis). Under atmospheric conditions, the fiber is heated at a certain rate of temperature to reduce the weight. Or exothermic / endothermic reactions. As an example of a method for determining the melting or decomposition of a fiber (there is a case of weight reduction), when the weight reduction of the sample reaches 1% and the weight reduction continues, it can be determined that the fiber is thermally decomposed. The starting temperature of melting or decomposition is a temperature at which the tangent of the aforementioned weight reduction curve is extended to the baseline before the weight reduction starts, and the temperature is in contact with the intersection of the tangent and the baseline. In addition, when the fiber is left in the above-mentioned temperature environment in the atmosphere, it can be confirmed with the naked eye that the fiber disappears and the fiber is deformed or discolored due to melting.

The shape of the fiber may be an elongated shape having a certain length of length. From the viewpoint of easily suppressing the thermal shrinkage of the electrolyte composition, the aspect ratio of the fiber may be 10 or more, preferably more than 10, more preferably 20 or more, more preferably 50 or more, and particularly preferably 100 or more. The aspect ratio of the fiber can be obtained by the same method as the method for calculating the aspect ratio of the oxide particles. In other words, the fiber length and fiber diameter can be obtained from the scanning electron microscope photograph of the fiber and statistical calculation can be performed.

In this embodiment, from the viewpoint of easily suppressing thermal contraction of the electrolyte composition, the average length of the fibers is equal to or larger than the average particle diameter of the oxide particles, and is preferably 2 or more and 5 times or more the average particle diameter of the oxide particles. 10 times or more, 20 times or more, 50 times or more, or 100 times or more. The average length of the fibers is preferably 1 μm or more, 5 μm or more, 10 μm or more, 30 μm or more, and 40 μm or more. From the viewpoint of suppressing fibers from protruding from the electrolyte layer when the secondary battery is formed and smoothing the electrolyte layer 7, the average length of the fibers is preferably 10,000 μm or less, 5000 μm or less, 3000 μm or less, 2000 μm or less, 1500 μm or less, 1000 μm or less, 500 μm or less, 100 μm or less, or 50 μm or less. In this manual, the average length of the fiber is selected from the scanning electron microscope photographs. Three photographs are selected to avoid the repeated measurement. The entire fiber is taken into the photographs. The cumulative value of the fiber length is divided by the fibers for each photograph. The average of the values.

Generally, as long as the matrix polymer, oxide particles, and electrolyte salt are used, an electrolyte composition can be produced. However, in an environment of 150 ° C or higher or 200 ° C or higher, the matrix polymer softens or melts, and the electrolyte composition Things slowly shrink. At this time, since the oxide particles contained in the electrolyte composition move with shrinkage, the electrical insulation properties of the electrolyte composition may deteriorate. For example, if a metal such as a nail penetrates into a secondary battery for any reason and a short circuit caused by the metal occurs locally between the positive electrode and the negative electrode, a sudden exotherm will occur here, and it will be composed of an electrolyte The electrolyte layer formed by the object will shrink due to heat. In this case, there is a possibility that the short-circuit area between the positive electrode and the negative electrode is further enlarged, the short-circuit current is also increased, and the heat generation is continued or expanded. As a result, the secondary battery may catch fire, smoke, or rupture, which may cause problems in terms of safety.

The present inventors considered that the movement of oxide particles has become a major cause of short circuit (short circuit area expansion) as the electrolyte composition thermally contracts, and after exploring the composition of the electrolyte composition where the oxide particles still do not move at high temperatures, As a result, the electrolyte composition of this embodiment was found. It is presumed that the electrolyte composition of this embodiment contains fibers having an average length equal to or larger than the average particle diameter of the oxide particles. Therefore, the fibers exert the effect of inhibiting the movement of the oxide particles, thereby suppressing the heat of the electrolyte composition. As a result, it is possible to suppress short circuits at high temperatures.

The average fiber diameter of the fibers is preferably less than or equal to the thickness of the electrolyte layer 7 and more preferably less than 1/3 of the thickness of the electrolyte layer 7. The average fiber diameter of the fibers is preferably 10 μm or less, more preferably 5 μm or less, and even more preferably 1 μm or less. By setting the average fiber diameter to be equal to or less than the thickness of the electrolyte layer 7, a thin electrolyte layer 7 can be produced, and even with a small amount of fiber added, the movement of the oxide particles can be suppressed. The average fiber diameter of the fibers may be, for example, 0.01 μm or more. In this manual, the average fiber diameter of a fiber is selected from the scanning electron microscope photographs. Three photographs are selected to avoid the repeated measurement of the entire fiber in the photographs, and the cumulative value of the fiber diameter is divided for each photograph. The average of the values obtained by the total number of fibers.

Based on the total amount of the electrolyte composition, the fiber content is preferably 0.05% by mass or more, more preferably 0.1% by mass or more, and even more preferably 0.3% by mass or more. Accordingly, the fibers are uniformly blended in the electrolyte composition, and the movement of the oxide particles can be effectively suppressed. Based on the total amount of the electrolyte composition, the content of the fiber is preferably 10% by mass or less, more preferably 8% by mass or less, and even more preferably 5% by mass or less. Thereby, more oxide particles having high heat resistance can be blended in the electrolyte composition, and when a slurry containing the electrolyte composition is blended to form the electrolyte layer 7 in the secondary battery 1, the slurry has good fluidity , And a thin electrolyte layer 7 can be formed.

The ionic liquid contains the following anionic and cationic components. In the present embodiment, the ionic liquid is a substance that is liquid at a temperature of -20 ° C or higher.

Anionic component of the ionic liquid is not particularly limited, and may be Cl ^-, Br ^-, I ^- anions, such as ^{_{halogen; BF 4 -, N (SO}} 2 F) 2 - and the like inorganic _{anion; B (C 6 H 5)} 4 -, CH ₃ SO ₂ O ^－ , CF ₃ SO ₂ O ^－ , N (SO ₂ C ₄ F ₉ ) ₂ ^－ , N (SO ₂ CF ₃ ) ₂ ^－ , N (SO ₂ C ₂ F ₅ ) ₂ ^－ and other organic anions Wait. The anionic component of the ionic liquid preferably contains at least one type of an anionic component represented by the following formula (1).

In Formula (1), m and n each independently represent an integer of 0 to 5. m and n may be the same or different from each other, and preferably are the same as each other.

The cationic component of the ionic liquid is preferably at least 1 selected from the group consisting of a chain quaternary onium salt cation, a piperidinium salt cation, a pyrrolidinium salt cation, a pyridinium salt cation, and an imidazolium salt cation. Species.

The chain quaternary onium salt cation is, for example, a compound represented by the following formula (2).

In formula (2), R ¹ to R ⁴ each independently represent a chain alkyl group having 1 to 20 carbon atoms, or a chain alkoxyalkyl group represented by R—O— (CH ₂ ) _n —, and R Represents a methyl group or an ethyl group, n represents an integer of 1 to 4, X represents a nitrogen atom or a phosphorus atom; the number of carbon atoms of the alkyl group represented by R ¹ to R ⁴ is preferably 1 to 20, and 1 to 10 is more preferred. It is more preferably 1 to 5.

The piperidinium salt cation is, for example, a nitrogen-containing six-membered ring cyclic compound represented by the following formula (3).

In formula (3), R ⁵ and R ⁶ each independently represent an alkyl group having 1 to 20 carbon atoms, or an alkoxyalkyl group represented by R—O— (CH ₂ ) _n —, and R represents a methyl group or Ethyl, n represents an integer of 1 to 4; the carbon number of the alkyl group represented by R ⁵ and R ⁶ is preferably 1 to 20, more preferably 1 to 10, and even more preferably 1 to 5.

The pyrrolidinium salt cation is, for example, a five-membered ring cyclic compound represented by the following formula (4).

In formula (4), R ⁷ and R ⁸ each independently represent an alkyl group having 1 to 20 carbon atoms, or an alkoxyalkyl group represented by R—O— (CH ₂ ) _n —, and R represents a methyl group or Ethyl, n represents an integer of 1 to 4; the carbon number of the alkyl group represented by R ⁷ and R ⁸ is preferably 1 to 20, more preferably 1 to 10, and even more preferably 1 to 5.

The pyridinium salt cation is, for example, a compound represented by the following formula (5).

In the formula (5), R ⁹ to R ¹³ each independently represent an alkyl group having 1 to 20 carbon atoms, an alkoxyalkyl group represented by R—O— (CH ₂ ) _n —, or a hydrogen atom, and R represents Methyl or ethyl, n represents an integer of 1 to 4; the carbon number of the alkyl group represented by R ⁹ to R ¹³ is preferably 1 to 20, more preferably 1 to 10, and even more preferably 1 to 5.

The imidazolium cation is, for example, a compound represented by the following formula (6).

In formula (6), R ¹⁴ to R ¹⁸ each independently represent an alkyl group having 1 to 20 carbon atoms, an alkoxyalkyl group represented by R—O— (CH ₂ ) _n —, or a hydrogen atom, and R represents Methyl or ethyl, n represents an integer of 1 to 4; the carbon number of the alkyl group represented by R ¹⁴ to R ¹⁸ is preferably 1 to 20, more preferably 1 to 10, and even more preferably 1 to 5.

From the viewpoint of making the electrolyte layer 7 suitable, based on the total amount of the electrolyte composition, the content of the ionic liquid may be 10% by mass or more and 60% by mass or less. From the viewpoint that the lithium secondary battery can be charged and discharged at a high load rate by increasing the conductivity of the electrolyte layer 7 by increasing the content of the electrolyte salt, the content of the ionic liquid is based on the total amount of the electrolyte composition as a reference. 55 mass% or less is preferable, and 50 mass% or less is more preferable.

From the viewpoint of further increasing the conductivity and suppressing the decrease in the capacity of the secondary battery, based on the total amount of the electrolyte composition, the total content of the electrolyte salt and the ionic liquid is preferably 10% by mass or more and 25% by mass or more. Preferably, it is more preferably 40% by mass or more. From the viewpoint of suppressing the decrease in the strength of the electrolyte composition, the total content of the electrolyte salt and the ionic liquid is preferably 80% by mass or less, and more preferably 70% by mass or less based on the total amount of the electrolyte composition.

From the viewpoint of further improving the charge and discharge characteristics, the concentration of the electrolyte salt per unit volume of the ionic liquid is preferably 0.5 mol / L or more, more preferably 0.7 mol / L or more, and more preferably 1.0 mol / L or more, and It is preferably 2.0 mol / L or less, more preferably 1.8 mol / L or less, and even more preferably 1.6 mol / L or less.

The electrolyte composition may further contain, for example, the following non-aqueous solvents for the purpose of further improving conductivity: propylene carbonate, butyl carbonate, vinylene carbonate, γ-butyrolactone, diethyl carbonate, and methyl carbonate Ethyl ester, 1,2-dimethoxyethane, 2-methyltetrahydrofuran, dimethylsulfene, 1,3-dioxolane, formamidine, dimethyl Methylformamide, methyl propionate, ethyl propionate, phosphate triesters, trimethoxymethane, dioxolane, diethyl ether, cyclobutane, 3-methyl-2-oxazolidinone ( 3-methyl-2-oxazolidinone), tetrahydrofuran, 1,2-diethoxyethane, chloroethylene carbonate, chloroethylene carbonate and the like.

From the viewpoint of improving the conductivity and improving the strength, the thickness of the electrolyte layer 7 is preferably 5 μm or more, and more preferably 10 μm or more. From the viewpoint of suppressing the resistance of the electrolyte layer 7, the thickness of the electrolyte layer 7 is preferably 100 μm or less, more preferably 50 μm or less, and even more preferably 30 μm or less.

As described above, in the electrolyte composition of the present embodiment, the following effects are obtained: it is not easy to cause thermal contraction and suppress short circuits (the short-circuit area is enlarged). This effect can be confirmed, for example, by supplying the electrolyte composition to the nail penetration simulation test. The nail penetration simulation test is a test that assumes that a metal such as a nail penetrates into a secondary battery, and is a test to evaluate the safety of the secondary battery. In the nail penetration simulation test, a soldering iron or the like heated to a certain temperature above 100 ° C may be used. The temperature can be arbitrarily set, and can be, for example, 150 ° C or higher. A sample is prepared by sandwiching an electrolyte composition between metal foils such as a copper foil assumed as an electrode, and a voltage is applied to the sample. Instead of the metal foil, a positive electrode and a negative electrode actually used in a battery may be used, and an electrolyte composition may be interposed therebetween. If a certain voltage is maintained between the positive electrode and the negative electrode, the current will slowly decay. However, since the electrolyte composition has ionic conductivity, a current will flow due to ion movement for a short period of time after applying a certain voltage. After the current reaches the bottom value, pierce the heated tip of the soldering iron towards the sample. Then, the tip of the soldering iron was pulled out from the sample, and the insulation resistance between the copper foils after the tip of the soldering iron was pierced was confirmed. Then, for example, if a resistance value of 1 kΩ or more is obtained, it can be determined that a short circuit due to thermal contraction of the electrolyte composition has been sufficiently suppressed. In addition, the voltage that can be applied in the nail penetration simulation test is only required to be more than 10 mV and less than 1 V. In order to shorten the test time, the voltage is preferably small, and to improve the measurement accuracy of the resistance, the voltage is preferably high. As a condition satisfying both, it is preferable that the applied voltage be 0.1 V or more and 0.5 V or less.

Next, a method for manufacturing the secondary battery 1 will be described. The manufacturing method of the secondary battery 1 according to this 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 second step of forming the negative electrode current collector 11 The negative electrode mixture layer 12 obtains the negative electrode 8; and, in the third step, an electrolyte layer 7 is provided between the positive electrode 6 and the negative electrode 8.

In the first step, the positive electrode 6 is obtained, for example, by using a kneader, a disperser, or the like to disperse the materials used in the positive electrode mixture layer in a dispersion medium to obtain a slurry positive electrode mixture, and then This positive electrode mixture is applied to the positive electrode current collector 9 by a doctor blade coating method, a dip coating method, a spray method, or the like, and then the dispersion medium is volatilized. After the dispersion medium is volatilized, a compression molding step can be set by rolling as needed. The positive electrode mixture layer 10 can be formed into a multi-layered positive electrode mixture layer by performing a plurality of steps from the application of the positive electrode mixture to the evaporation of the dispersion medium.

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

The method of forming the negative electrode mixture layer 12 on the negative electrode current collector 11 in the second step may be the same method as in the first step.

In the third step, in one embodiment, the electrolyte layer 7 is formed on 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 by coating, and is preferably formed by coating. It is applied and formed on both 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. At this time, for example, the positive electrode 6 provided with the electrolyte layer 7 and the negative electrode 8 provided with the electrolyte layer 7 are laminated so that the electrolyte layers 7 are in contact with each other, for example, to obtain a secondary battery 1.

The method of forming the electrolyte layer 7 on the positive electrode mixture layer 10 by coating is, for example, a method in which a material used in the electrolyte layer 7 is dispersed in a dispersion medium to obtain a slurry, and then an applicator is used to This electrolyte composition is applied to the positive electrode material mixture layer 10. The dispersion medium is preferably water or NMP. The electrolyte salt can be dissolved in the ionic liquid and then dispersed in the dispersion medium together with other materials.

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

In the third step, in another embodiment, the electrolyte layer 7 is formed, for example, by preparing an electrolyte sheet having an electrolyte composition on a substrate. Fig. 4 (a) is a schematic cross-sectional view showing an electrolyte sheet according to an embodiment. As shown in FIG. 4 (a), the electrolyte sheet 13A includes a base material 14 and an electrolyte layer 7 provided on the base material 14.

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

The base material 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 due to the electrolyte composition, and is, for example, a film-like resin. The substrate 14 may be a thin film composed of resins such as polyethylene terephthalate, polytetrafluoroethylene, polyimide, polyether fluorene, and polyether ketone. Engineering Plastics).

The condition of the substrate 14 is that it can withstand the processing temperature at which the dispersion medium is vaporized during the process of producing the electrolyte layer. When the lower temperature of the softening point (temperature at which the plastic starts to deform) or the melting point of the base material 14 is set to a heat-resistant temperature, this temperature is from the viewpoint of adaptability to the ionic liquid used in the electrolyte layer 7. It is preferably 50 ° C or higher, more preferably 100 ° C or higher, more preferably 150 ° C or higher, and may be, for example, 400 ° C or lower. When a substrate having the above-mentioned heat-resistant temperature is used, a dispersion medium (NMP, toluene, etc.) such as the above 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 generated by the coating device. From the viewpoint of reducing the overall volume of the electrolyte sheet 13A while ensuring the strength when the electrolyte composition is applied to the substrate 14, the thickness of the substrate 14 is preferably 5 μm or more, more preferably 10 μm or more, and 25 μm or more is more preferable, and 100 μm or less is preferable, 50 μm or less is preferable, and 40 μm or less is more preferable.

The electrolyte sheet can be continuously produced while being wound into a roll shape. At this time, a part of the electrolyte layer 7 may be adhered to the substrate 14 due to the contact between the surface of the electrolyte layer 7 and the back surface of the substrate 14, and the electrolyte layer 7 may be damaged. In order to prevent such a situation, the electrolyte sheet may be provided with a protective material on the opposite side of the electrolyte layer 7 from the substrate 14 as another embodiment. Fig. 4 (b) is a schematic cross-sectional view showing an electrolyte sheet according to another embodiment. As shown in FIG. 4 (b), the electrolyte sheet 13B is further provided with a protective material 15 on the side of the electrolyte layer 7 opposite to the substrate 14.

The protective material 15 may be easily peeled from the electrolyte layer 7, and is preferably a non-polar resin film such as polyethylene, polypropylene, or polytetrafluoroethylene. When a non-polar resin film is used, the electrolyte layer 7 and the protective material 15 do not stick to each other, and the protective material 15 can be easily peeled off.

From the viewpoint of reducing the overall volume of the electrolyte sheet 13B while ensuring strength, the thickness of the protective material 15 is preferably 5 μm or more, more preferably 10 μm or more, and more preferably 100 μm or less, and 50 μm or less. It is better to be less than 30 μm.

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 preferably 100 ° C or lower. It is preferably below 50 ° C. When the protective material 15 is provided, since the volatilization step of the above-mentioned dispersion medium is not required, it is not necessary to increase the heat-resistant temperature.

As a method of using the electrolyte sheet 13A to provide the electrolyte layer 7 between the positive electrode 6 and the negative electrode 8, for example, the substrate 14 is peeled from the electrolyte sheet 13A, and the positive electrode 6, the electrolyte layer 7, and the negative electrode 8 are separated by layers, for example. The layers are laminated together to obtain a secondary battery 1. At this time, the electrolyte layer 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, the positive electrode mixture layer 10, the electrolyte layer 7, and The negative electrode mixture layer 12 and the negative electrode current collector 11 are laminated. When the electrolyte sheet has been continuously manufactured while being wound into a roll shape, the roll-shaped electrolyte sheet may be unwound (unrolled), and the electrolyte layer 7 may be disposed between the positive electrode 6 and the negative electrode 8 before cutting. Alternatively, the roll-shaped electrolyte sheet may be cut, and then the electrolyte layer 7 may be disposed between the positive electrode 6 and the negative electrode 8.

In the third step, an adhesive layer (not shown) is further provided on the electrolyte layer 7 for the purpose of making the electrolyte layer 7 and the positive electrode 6 or the negative electrode 8 suitable for lamination. The adhesive layer can be provided by laminating a film-shaped adhesive, or laminating an adhesive produced on a release film to the electrolyte layer 7, peeling the release film, and then adhering the adhesive layer. The electrolyte layer 7 is transferred or applied with a liquid adhesive. When the electrolyte sheet 13A is used, when the electrolyte sheet 13A is manufactured, an electrolyte sheet having an adhesive layer formed thereon can be prepared in advance.

The adhesive layer may include at least 1 selected from the group consisting of acrylic resin, methacrylic resin, silicone resin, urethane resin, polyvinyl ether, and styrene-butadiene rubber. Species.

When the adhesive layer is provided on the electrolyte layer 7, the adhesive layer may be provided on at least a part of the electrolyte layer 7, and may be provided on one end portion of the electrolyte layer 7. Therefore, when the electrolyte layer 7 and the positive electrode 6 or the negative electrode 8 are laminated, or when the electrolyte layer 7 formed on the positive electrode mixture layer 10 and the negative electrode mixture layer 12 are laminated on each other, the adhesive layer is laminated to laminate, Therefore, wrinkles and corrugations are not easily generated during lamination, and a secondary battery in which the electrodes (positive electrode 6 and negative electrode 8) and the electrolyte layer 7 are appropriately laminated can be produced.

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

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

In the bipolar electrode current collector 17, the positive electrode surface is preferably formed of a material having excellent oxidation resistance, and may be formed of aluminum, stainless steel, titanium, or the like. In the bipolar electrode current collector 17 using graphite or an alloy as a negative electrode active material, the negative electrode surface may be formed of a material that does not form an alloy with lithium, and specifically, may be formed of stainless steel, nickel, iron, titanium, or the like. When different metals are used for the positive electrode surface and the negative electrode surface, the bipolar electrode current collector 17 may be a coating material obtained by laminating different types of metal foils. However, when a negative electrode 8 such as lithium titanate, which operates at a potential that does not form an alloy with lithium, is used, there is no such limitation, and the negative electrode surface may be the same material as the positive electrode current collector 9. In this 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 having a hole with a diameter of 0.1 to 10 mm, a developed metal, a foamed metal plate, or the like. In addition to the above, the bipolar electrode current collector 17 can be formed of any material as long as it does not undergo changes such as dissolution or oxidation during battery use, and its shape, manufacturing method, and the like are not limited.

The thickness of the bipolar electrode current collector 17 may be 10 μm or more and 100 μm or less. From the viewpoint of reducing the overall volume of the positive electrode, 10 to 50 μm is preferable, and the battery is formed with a small curvature. From the viewpoint of winding the bipolar electrode, it is preferably 10 to 20 μm.

Next, a method for manufacturing a secondary battery according to the second embodiment will be described. The method for manufacturing a secondary battery in this 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 second step of forming a negative electrode on the negative electrode current collector 11 The negative electrode 8 is obtained by the mixture layer 12; the third step is to form the positive electrode mixture layer 10 on one side of the bipolar electrode current collector 17 and the negative electrode mixture layer 12 on the other side to obtain the bipolar electrode 16; and, the fourth step A step in which an electrolyte layer 7 is provided 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 as the first step and the second step of the first embodiment.

In the third step, the method of forming the positive electrode mixture layer 10 on one side 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 method as the second step in the first embodiment.

In the fourth step, as a method of providing an electrolyte layer 7 between the positive electrode 6 and the bipolar electrode 16, in one embodiment, the electrolyte layer 7 is formed on the positive electrode mixture layer 10 side of the positive electrode 6 and the bipolar electrode by coating. At least one of the negative electrode mixture layer 12 side of the electrode 16 is preferably formed 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 by coating. At this time, for example, the positive electrode 6 provided with the electrolyte layer 7 and the bipolar electrode 16 provided with the electrolyte layer 7 are laminated such that the electrolyte layers 7 are in contact with each other, for example, by lamination.

The method of forming the electrolyte layer 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 can be the same method as the following method. In a three-step embodiment, a method of forming the electrolyte layer 7 on the positive electrode mixture layer 10 by coating, and a method of forming the electrolyte layer 7 on the negative electrode mixture layer 12 by coating.

In the fourth step, as a method of providing an electrolyte layer 7 between the positive electrode 6 and the bipolar electrode 16, in other embodiments, the electrolyte layer 7 is formed by, for example, manufacturing a substrate having an electrolyte composition. Of electrolyte sheet. The manufacturing method of the electrolyte sheet may be the same method as the manufacturing method of the electrolyte sheets 13A and 13B in the first embodiment.

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

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

[Manufacture of electrolyte sheet]
> Example 1>
30 mass parts of a matrix polymer, that is, a copolymer of vinylidene fluoride and hexafluorofluorene (PVDF-HFP), and 20 masses of oxide particles that are SiO ₂ particles (product name: AEROSIL OX50, manufactured by Japan AEROSIL Co., Ltd.) Bis (fluorosulfofluorene) imide N-methyl-N-propyl, which is obtained by dissolving lithium bis (fluorosulfohydrazone) imine (Li [FSI]) at a concentration of 1.5 mol / L Pyrrolidinium (Py13-FSI) (hereinafter, when the composition of an ionic liquid obtained by dissolving an electrolyte salt is shown, it may be indicated as "the concentration of lithium salt / type of lithium salt / type of ionic liquid") 50 Parts by mass and 0.4 parts by mass of cellulose fibers (average length 50 μm, average fiber diameter 0.1 μm) are dispersed in a dispersion medium, namely 1-methyl-2-pyrrolidone (NMP), to prepare an electrolyte composition containing Slurry. This slurry was applied to a substrate made of polyethylene terephthalate (product name: Teonex R-Q51, manufactured by Dupont Teijin Films Co., Ltd., thickness: 38 μm) using an applicator. The coated slurry was heated and dried at 80 ° C. for 1 hour to volatilize the dispersion medium to obtain an electrolyte sheet. In the obtained electrolyte sheet, the thickness of the electrolyte layer was 25 ± 5 μm.

> Example 2>
An electrolyte sheet was produced in the same manner as in Example 1 except that the content of cellulose fibers was changed to 1.0 part by mass in the electrolyte sheet of Example 1.

[3 layer sample making]
Two pieces of copper foils, which are assumed to be a positive electrode and a negative electrode, were prepared. The substrate was peeled from the electrolyte sheets of Examples 1 and 2 above, and the electrolyte layer was sandwiched between two copper foils to prepare three layers of samples. In the three-layer sample, each layer was arranged such that the electrolyte layer insulated two copper foils (so that the copper foils did not contact each other).

[Evaluation of safety 1 (nail simulation test)]
For the obtained three-layer sample, a nail penetration simulation test was performed using a nail penetration simulation test device. The nail penetration simulation test device uses a bracket having a movable portion capable of being raised and lowered so that a tip of a soldering iron (FX-600, manufactured by Baiguang Co., Ltd.) is oriented substantially vertically downward with respect to the ground. Stationary. Before the test, a voltage of 0.1 V was applied to the three-layer sample, and after about 10 seconds, it was confirmed that the current almost reached the bottom value. Then, as shown in FIG. 6, a three-layer sample 19 in which the electrolyte layer 7 is sandwiched between two copper foils 18 and 18 is placed below the front end of the soldering iron 20, and the three-layer sample 19 is heated. After the tip of the soldering iron 20 after reaching 200 ° C was inserted in the stacking direction of the three-layer sample 19, it was held for about 3 seconds. At this time, the insertion depth D of the tip of the soldering iron 20 was set to 0.5 mm so that the through-hole of the copper foil was 3 mm. Then, with the tip of the soldering iron 20 inserted, the current between the two copper foils 18 and 18 was recorded. Then, the tip of the soldering iron 20 is drawn out above the three-layer sample 19. The insulation resistance of the three-layer sample 19 was calculated from the maximum value of the current during the three-second period inserted into the tip of the soldering iron 20 by the following formula (7). Furthermore, if the insulation resistance is 1 kΩ or more, it can be said that short-circuiting is sufficiently suppressed.
Insulation resistance (Ω) = voltage (V) ÷ maximum current during 3 seconds (A) (7)

As a result, the insulation resistance of Example 1 was 1.7 kΩ, and the insulation resistance of Example 2 was 1.1 kΩ. It can be seen that in all the examples, there is sufficient insulation after the nail penetration simulation test.

> Example 3>
(Production of positive electrode)
78.5 parts by mass of layered lithium-nickel-manganese-cobalt composite oxide (positive electrode active material), 5 parts by mass of acetylene black (conductive agent, product name: HS-100, manufactured by DENKA Co., Ltd.), and vinylidene fluoride It was mixed with 2.5 parts by mass of a hexafluoropropylene copolymer solution (solid content: 12% by mass) and 14 parts by mass of an ionic liquid (1.5 mol / L / Li [FSI] / Py13-FSI) to prepare a positive electrode mixture slurry. This positive electrode mixture slurry was applied to both sides of a positive electrode current collector (aluminum foil having a thickness of 15 μm) at a coating amount of 125 g / m ² , and dried by heating. By pressing this electrode, the mixture density was adjusted to 2.7 g / cm ³ . The mixture layer was punched so that the size of the mixture layer was 82 mm × 112 mm, and a positive electrode was produced.

(Production of negative electrode)
80.4 parts by mass of graphite (negative electrode active material, manufactured by Hitachi Chemical Co., Ltd.), 0.6 parts by mass of carbon fiber (conducting agent, product name: VGCF-H, manufactured by Showa Denko Corporation), of vinylidene fluoride and hexafluoropropylene 5 parts by mass of a copolymer solution (12% by mass of solid content) and 14 parts by mass of an ionic liquid (1.5 mol / L / Li [FSI] / Py13-FSI) were mixed to prepare a negative electrode mixture slurry. This negative electrode mixture slurry was applied to both sides of a current collector (a copper foil having a thickness of 10 μm) at a coating amount of 60 g / m ² , and dried by heating. By pressing this electrode, the mixture density was adjusted to 1.8 g / cm ³ . The mixture layer was punched so that the size of the mixture layer became 86 mm × 116 mm to produce a negative electrode.

(Production of evaluation batteries)
A positive electrode, a negative electrode, and an electrolyte layer obtained from the electrolyte sheet prepared in Example 1 were used to prepare an evaluation battery. The negative electrode, the electrolyte layer, and the positive electrode were stacked in this order to laminate 9 negative electrodes, 16 electrolyte layers, and 8 positive electrodes to form an electrode group. An Al terminal was welded to the positive electrode of the electrode group by ultrasonic waves, a Ni terminal was connected to the negative electrode, and this electrode group was sealed by laminating aluminum to prepare an evaluation battery.

> Example 4>
A battery for evaluation was produced in the same manner as in Example 3 except that the electrolyte layer obtained from the electrolyte sheet of Example 2 was used.

[Evaluation of safety 2 (nail penetration test)]
The prepared evaluation battery was subjected to a nail penetration test. Prior to the nail penetration test, a battery for evaluation was charged using a charge-discharge device (manufactured by Toyo System Co., Ltd.) under the following charge-discharge conditions.
(1) Initialize the cycle three times: charge at a constant current of 0.1 C until the cut-off voltage is 4.2 V, and charge at a constant voltage of 4.2 V until the total charge time becomes 15 hours or the charge current becomes 0.02 C After charging with constant current and constant voltage (CCCV), discharge at 0.1 C constant current (CC) until the cut-off voltage is 2.7 V. The term "C" means "current value (A) / battery capacity (Ah)".
(2) Then, charge at a constant current of 0.1 C until the cut-off voltage is 4.2 V, and charge at a constant voltage at the cut-off voltage of 4.2 V until the total charging time becomes 15 hours or the charging current becomes 0.02 C, and then CCCV charging is performed.

After the aforementioned unit for evaluating the state of charge was fixed to a fixture for a nail penetration test, a nail penetration test was performed. In the nail penetration test, a SUS nail (φ3 mm) with a thermocouple was used, the nail penetration speed was set to 40 mm / s, and the nail penetration depth was set to the penetration unit. The evaluation results of the nail penetration test are shown in Table 1. The rate of decrease in voltage caused by the nail penetration test is determined by the following formula.
Voltage decrease rate (%) = (voltage after test (after 5 seconds)-voltage after test (after 600 seconds)) / voltage after test (after 5 seconds) × 100

[Table 1]

After the nailing test, the results of the evaluation batteries of Examples 3 and 4 showed that the voltage drop was small immediately after the nailing was completed (after 1 second) and after a predetermined time elapsed, and short circuits were suppressed. In addition, if the reduction rate of the voltage is less than 10%, it can be said that the short circuit is sufficiently suppressed. At this time, when the battery was evaluated, smoke, fire, and battery rupture could not be confirmed, and it showed high safety. In addition, the maximum battery surface temperature was as low as 39 ° C in Example 3 and 50 ° C in Example 4. In addition, if the maximum battery surface temperature is 150 ° C or lower, it can be said that safety is sufficient. From the above results, it was found that the batteries for evaluation of Examples 3 and 4 had sufficient insulation and safety.

1‧‧‧ secondary battery

2, 2A, 2B‧‧‧ electrode group

3‧‧‧ Battery case

4‧‧‧Positive collector terminal

5‧‧‧ negative collector terminal

6‧‧‧Positive

7‧‧‧ electrolyte layer

8‧‧‧ negative

9‧‧‧Positive collector

10‧‧‧ Positive electrode mixture layer

11‧‧‧ negative current collector

12‧‧‧ Negative electrode mixture layer

13A, 13B‧‧‧electrolyte sheet

14‧‧‧ substrate

15‧‧‧protective material

16‧‧‧Bipolar electrode

17‧‧‧bipolar electrode current collector

18‧‧‧ copper foil

19‧‧‧3 layer sample

20‧‧‧Soldering iron

D‧‧‧Insertion depth

FIG. 1 is a perspective view showing a secondary battery according to the first embodiment.

Fig. 2 is an exploded perspective view showing an embodiment of an electrode group in the secondary battery shown in Fig. 1.

Fig. 3 is a schematic perspective view showing an embodiment of an electrode group in the secondary battery shown in Fig. 1.

FIG. 4 (a) is a schematic cross-sectional view showing an electrolyte sheet according to one embodiment, and FIG. 4 (b) is a schematic cross-sectional view showing an electrolyte sheet according to another embodiment.

FIG. 5 is a schematic cross-sectional view showing an embodiment of an electrode group in a secondary battery according to a second embodiment.

Fig. 6 is a schematic cross-sectional view showing a situation of a nail penetration simulation test.

Domestic storage information (please note in order of storage organization, date, and number)
no

Information on foreign deposits (please note according to the order of the country, institution, date, and number)
no

Claims (11)

An electrolyte composition containing: Matrix polymer At least one electrolyte salt selected from the group consisting of lithium, sodium, calcium and magnesium salts; Oxide particles Fiber; and, Ionic liquid The average length of the fibers is equal to or greater than the average particle diameter of the oxide particles. The electrolyte composition according to claim 1, wherein the fibers are at least one selected from the group consisting of cellulose fibers, resin fibers, and glass fibers. The electrolyte composition according to claim 1 or 2, wherein the matrix polymer has a first structural unit, and the first structural unit is selected from the group consisting of tetrafluoroethylene and vinylidene fluoride. The electrolyte composition according to claim 3, wherein the structural unit constituting the matrix polymer includes: the first structural unit; and a second structural unit, the second structural unit is made of hexafluoropropylene , Acrylic acid, maleic acid, ethyl methacrylate, and methyl methacrylate. The electrolyte composition according to any one of claims 1 to 4, wherein the electrolyte salt includes a sulfonium-imide-based lithium salt. The electrolyte composition according to any one of claims 1 to 5, wherein the ionic liquid contains at least one of an anionic component represented by the following formula (1) as an anionic component: m and n each independently represent an integer of 0 to 5. The electrolyte composition according to any one of claims 1 to 6, wherein the ionic liquid contains a chain quaternary onium salt cation, a piperidinium salt cation, a pyrrolidinium salt cation, a pyridinium salt cation and At least one selected from the group consisting of imidazolium cations is used as a cationic component. An electrolyte sheet comprising: Substrate; and, The electrolyte layer is provided on the aforementioned substrate and is formed of the electrolyte composition according to any one of claims 1 to 7. The electrolyte sheet according to claim 8, wherein the average fiber diameter of the fibers is equal to or less than the thickness of the electrolyte layer. A secondary battery having: positive electrode; Negative electrode; and, The electrolyte layer is provided between the positive electrode and the negative electrode, and is formed of the electrolyte composition according to any one of claims 1 to 7. The secondary battery according to claim 10, wherein an average fiber diameter of the fibers is equal to or less than a thickness of the electrolyte layer.