Secondary battery

Abstract

The present invention enables a secondary battery, which comprises an electrolyte layer that contains a sulfide solid electrolyte, to achieve a good balance between the withstand voltage properties and the ion conductivity of the electrolyte layer. A secondary battery according to the present disclosure comprises a positive electrode, an electrolyte layer and a negative electrode; and the electrolyte layer contains a sulfide solid electrolyte and a perfluoropolyether which is represented by formula (1). (1): E1-Rf1-RF-O-Rf2-E2 (In formula (1), each of Rf1 and Rf2 independently represents a C1-16 divalent alkylene group which may be substituted by one or more fluorine atoms; each of E1 and E2 independently represents a monovalent group that is selected from the group consisting of a fluorine group, a hydrogen group, a hydroxyl group, an aldehyde group, a carboxylic acid group, a C1-10 alkyl ester group, an amide group which may have one or more substituents, and an amino group which may have one or more substituents; and RF represents a divalent fluoropolyether group.)

Description

secondary battery

[0001] The present application discloses a secondary battery.

[0002] Patent Document 1 discloses a secondary battery having an electrolyte layer, the electrolyte layer including a solid electrolyte material and an insulating material. Patent Document 2 discloses a perfluoropolyether as an additive component of a non-aqueous electrolyte solution. Patent Document 3 discloses a perfluoropolyether as an ion-conductive polymer.

[0003] JP 2012-094437 A JP 2018-200866 A JP 2019-524977 A

[0004] High insulation properties (voltage resistance) are required for the electrolyte layer of a secondary battery. On the other hand, if an insulating material is added to the electrolyte layer to increase the voltage resistance of the electrolyte layer, the ionic conductivity of the electrolyte layer may decrease, resulting in an increase in the resistance of the battery. According to the inventor's new findings, such a problem is likely to occur when the electrolyte layer contains a sulfide solid electrolyte. In other words, electrolyte layers containing a sulfide solid electrolyte have room for improvement in terms of achieving both voltage resistance and ionic conductivity.

[0005] The present application discloses the following multiple aspects as means for solving the above problems. <Aspect 1> A secondary battery having a positive electrode, an electrolyte layer, and a negative electrode, wherein the electrolyte layer contains a sulfide solid electrolyte and a perfluoropolyether represented by the following formula (1): E １ -Rf １ -R Ｆ -O-Rf ２ -E ２ (1) [In formula (1), Rf １ and Rf ２ each independently represents a C1-16 divalent alkylene group optionally substituted by one or more fluorine atoms, １ and E ２are each independently a monovalent group selected from the group consisting of a fluorine group, a hydrogen group, a hydroxyl group, an aldehyde group, a carboxylic acid group, a C1-10 alkyl ester group, an amide group which may have one or more substituents, and an amino group which may have one or more substituents; R Ｆ is a divalent fluoropolyether group.] <Aspect 2> The R Ｆ is expressed by the formula (2): -(OC ６ F １２ ) ａ - (OC ５ F １０ ) ｂ - (OC ４ F ８ ) ｃ - (OC ３ R Ｆａ ６ ) ｄ - (OC ２ F ４ ) ｅ -(OCF ２ ) ｆ - (2) [In formula (2), R Ｆａ are each independently a hydrogen atom, a fluorine atom, or a chlorine atom in each occurrence; a, b, c, d, e, and f are each independently an integer of 0 to 200; the sum of a, b, c, d, e, and f is 1 or more; the order of occurrence of each repeating unit enclosed in parentheses with a, b, c, d, e, or f is arbitrary in the formula; provided that all R Ｆａ is a hydrogen atom or a chlorine atom, at least one of a, b, c, e, and f is 1 or more. Ｆａ The secondary battery of Aspect 2, wherein R is a fluorine atom. Ｆ each occurrence independently represents the following formula (2-1), (2-2), (2-3), (2-4) or (2-5): -(OC ３ F ６ ) ｄ - (OC ２ F ４ ) ｅ - (2-1) [In formula (2-1), d is an integer of 1 to 200, and e is 0 or 1.], -(OC４ F ８ ) ｃ - (OC ３ F ６ ) ｄ - (OC ２ F ４ ) ｅ -(OCF ２ ) ｆ - (2-2) [In formula (2-2), c and d each independently represent an integer of 0 to 30, e and f each independently represent an integer of 1 to 200, the sum of c, d, e and f is an integer of 10 to 200, and the order of occurrence of each repeating unit enclosed in parentheses with the subscript c, d, e or f is arbitrary in the formula.], - (R ６ -R ７ ) ｇ - (2-3) [In formula (2-3), R ６ is OCF ２ or O.C. ２ F ４ and R ７ is O.C. ２ F ４ , O.C. ３ F ６ , O.C. ４ F ８ , O.C. ５ F １０ and O.C. ６ F １２ or a combination of two or three groups selected from these groups, and g is an integer of 2 to 100. ６ F １２ ) ａ - (OC ５ F １０ ) ｂ - (OC ４ F ８ ) ｃ - (OC ３ F ６ ) ｄ - (OC ２ F ４ ) ｅ -(OCF ２ ) ｆ- (2-4) [In formula (2-4), e represents an integer of 1 or more and 200 or less, a, b, c, d, and f each independently represent an integer of 0 or more and 200 or less, and the order of occurrence of each repeating unit enclosed in parentheses with a, b, c, d, e, or f is arbitrary in the formula.] - (OC ６ F １２ ) ａ - (OC ５ F １０ ) ｂ - (OC ４ F ８ ) ｃ - (OC ３ F ６ ) ｄ - (OC ２ F ４ ) ｅ -(OCF ２ ) ｆ - (2-5) [in formula (2-5), f is an integer of 1 or more and 200 or less, a, b, c, d, and e are each independently an integer of 0 or more and 200 or less, and the order of the repeating units enclosed in parentheses with a, b, c, d, e, or f is arbitrary in the formula]. Ｆ is represented by the following formula (2-6): -(OCF ２ CF ２ CF ２ ) ａ -(OCF(CF ３ )CF ２ ) ｂ -(OCF ２ CF (CF ３ )) ｃ -(OCF ２ CF ２ ) ｄ -(OCF(CF ３ )) ｅ -(OCF ２ ) ｆ- (2-6) [in formula (2-6), a, b, c, d, e, and f each independently represent an integer of 0 to 200, the sum of a, b, c, d, e, and f is 1 or more, and the order of the repeating units enclosed in parentheses with a, b, c, d, e, or f is arbitrary in the formula]. Ｆ is represented by the following formula (2-7): -(OCF ２ CF ２ ) ｄ -(OCF(CF ３ )) ｅ -(OCF ２ ) ｆ - (2-7) [in formula (2-7), d, e, and f each independently represent an integer of 0 to 200, the sum of d, e, and f is 1 or more, and the order of the repeating units enclosed in parentheses with d, e, or f is arbitrary in the formula]. １ -Rf １ and the above E ２ -Rf ２ are each independently -CF ３ , -CF ２ CF ３ , and -CF ２ CF ２ CF ３ The secondary battery of any one of Aspects 1 to 6, wherein the perfluoropolyether is a group selected from the group consisting of: Aspect 8 The secondary battery of any one of Aspects 1 to 7, wherein the electrolyte layer contains 1% by volume or more and 25% by volume or less of the perfluoropolyether.

[0006] The electrolyte layer of the present disclosure is likely to have both high voltage resistance and high ionic conductivity, and a secondary battery including such an electrolyte layer is likely to have low resistance, for example.

[0007] 1 shows an example of the structure of a secondary battery, and an example of the evaluation result of the voltage resistance of an electrolyte layer.

[0008] 1. Secondary Battery Hereinafter, embodiments of the technology of the present disclosure will be described, but the technology of the present disclosure is not limited to the following embodiments. As shown in Figure 1, a secondary battery 100 according to one embodiment has a positive electrode 10, an electrolyte layer 20, and a negative electrode 30. Here, the electrolyte layer 20 contains a sulfide solid electrolyte and a perfluoropolyether represented by the following formula (1):

[0009] 1.1 Positive Electrode The positive electrode 10 may be any electrode capable of functioning appropriately as a positive electrode for a secondary battery, and its configuration is not particularly limited. As shown in FIG. 1 , the positive electrode 10 may include a positive electrode active material layer 11 and a positive electrode current collector 12.

[0010] 1.1.1 Positive Electrode Active Material Layer The positive electrode active material layer 11 contains at least a positive electrode active material and may further contain, optionally, an electrolyte, a conductive additive, a binder, and the like. The positive electrode active material layer 11 may also contain various other additives. For example, it may contain a dispersant or a perfluoropolyether, as described below. The content of each component in the positive electrode active material layer 11 may be appropriately determined depending on the desired battery performance. For example, the content of the positive electrode active material may be 40% by mass or more, 50% by mass or more, 60% by mass or more, or 70% by mass or more, or 100% by mass or less, or 90% by mass or less, where the total weight of the positive electrode active material layer 11 (total solid content) is taken as 100% by mass. The shape of the positive electrode active material layer 11 is not particularly limited, and may be, for example, a sheet-like positive electrode active material layer having a substantially flat surface. The thickness of the positive electrode active material layer 11 is not particularly limited, and may be, for example, 0.1 μm or more, 1 μm or more, or 10 μm or more, and may be 2 mm or less, 1 mm or less, or 500 μm or less.

[0011] As the positive electrode active material, any known positive electrode active material for secondary batteries may be used. Among known active materials, a material having a relatively noble potential (charge / discharge potential) for absorbing and releasing a predetermined carrier ion (e.g., lithium ion) can be used as the positive electrode active material, and a relatively base material can be used as the negative electrode active material described below. The positive electrode active material may be, for example, at least one selected from various lithium-containing compounds, elemental sulfur, sulfur compounds, etc. Examples of lithium-containing compounds as the positive electrode active material include lithium cobalt oxide, lithium nickel oxide, Li １±α Ni １／３ Co １／３ Mn １／３ O ２±δ , lithium manganate, spinel-based lithium compounds (Li １＋ｘ Mn ２－ｘ－ｙ M ｙ O ４ (wherein M is one or more selected from Al, Mg, Co, Fe, Ni, and Zn)), lithium titanate, lithium metal phosphate (LiMPO ４ and the like, where M is one or more selected from Fe, Mn, Co, and Ni). In particular, when the positive electrode active material contains a lithium-containing oxide containing at least Li, at least one of Ni, Co, and Mn, and O as constituent elements, a higher effect can be expected. Only one type of positive electrode active material may be used alone, or two or more types may be used in combination.

[0012] The shape of the positive electrode active material may be any shape commonly used for positive electrode active materials in batteries. The positive electrode active material may be, for example, particulate. The positive electrode active material may be hollow, voided, or porous. The positive electrode active material may be primary particles or secondary particles formed by aggregation of multiple primary particles. The average particle diameter D50 of the positive electrode active material may be, for example, 1 nm or more, 5 nm or more, or 10 nm or more, or 500 μm or less, 100 μm or less, 50 μm or less, or 30 μm or less. The average particle diameter D50 referred to in this application is the particle diameter (median diameter) at 50% of the integrated value in a volume-based particle size distribution determined by a laser diffraction / scattering method.

[0013] A protective layer containing an ion-conductive oxide may be formed on the surface of the positive electrode active material. This makes it easier to suppress the reaction between the positive electrode active material and a sulfide (for example, a sulfide solid electrolyte, which will be described later). Examples of the ion-conductive oxide include Li ３ BO ３ , LiBO ２ , Li ２ CO ３ , LiAlO ２ , Li ４ SiO ４ , Li ２ SiO ３ , Li ３ P.O. ４ , Li ２ SO ４ , Li ２ TiO ３ , Li ４ Ti ５ O １２ , Li ２ Ti ２ O ５ , Li ２ ZrO ３ , LiNbO ３ , Li ２ MoO ４ , Li ２ WO ４ Examples of the ion-conductive oxide include oxides in which some elements are substituted with doping elements such as P or B. The coverage (area ratio) of the protective layer with respect to the surface of the positive electrode active material may be, for example, 70% or more, 80% or more, or 90% or more. The thickness of the protective layer may be, for example, 0.1 nm or more or 1 nm or more, and may be 100 nm or less or 20 nm or less.

[0014] The electrolyte that can be contained in the positive electrode active material layer 11 may be a solid electrolyte, a liquid electrolyte (electrolytic solution), or a combination thereof. In particular, when the positive electrode active material layer 11 contains at least a solid electrolyte as the electrolyte, a higher effect is likely to be obtained.

[0015] The solid electrolyte may be any known solid electrolyte for secondary batteries. The solid electrolyte may be an inorganic solid electrolyte or an organic polymer electrolyte. In particular, inorganic solid electrolytes have higher ionic conductivity than organic polymer electrolytes. Furthermore, inorganic solid electrolytes have superior heat resistance than organic polymer electrolytes. Examples of inorganic solid electrolytes include lithium lanthanum zirconate, LiPON, and Li １＋Ｘ Al Ｘ Ge ２－Ｘ (P.O. ４ ) ３ oxide solid electrolytes such as Li—SiO-based glass and Li—Al—S—O-based glass; Li ２ S-P ２ S ５ , Li ２ S-SiS ２ , LiI-Li ２ S-SiS ２ , LiI-Si ２ S-P ２ S ５ , Li ２ S-P ２ S ５ -LiI-LiBr, LiI-Li ２ S-P ２ S ５ , LiI-Li ２ S-P ２ O ５ , LiI-Li ３ P.O. ４ -P ２ S ５ , Li ２ S-P ２ S ５ -GeS ２ Examples of sulfide solid electrolytes include sulfide solid electrolytes such as those described above. In particular, sulfide solid electrolytes, especially sulfide solid electrolytes containing at least Li, S, and P as constituent elements, have high performance. The solid electrolyte may be amorphous or crystalline. The solid electrolyte may be, for example, particulate. Only one type of solid electrolyte may be used alone, or two or more types may be used in combination.

[0016] The electrolyte may contain a predetermined carrier ion (e.g., lithium ion). The electrolyte may be, for example, a non-aqueous electrolyte. The composition of the electrolyte may be the same as that of a known electrolyte for a secondary battery. For example, the electrolyte may be a solution in which a lithium salt is dissolved in a carbonate-based solvent at a predetermined concentration. Examples of carbonate-based solvents include fluoroethylene carbonate (FEC), ethylene carbonate (EC), and dimethyl carbonate (DMC). Examples of lithium salts include LiPF ６ etc.

[0017] Examples of conductive additives that can be contained in the positive electrode active material layer 11 include carbon materials such as vapor grown carbon fiber (VGCF), acetylene black (AB), ketjen black (KB), carbon nanotubes (CNT), and carbon nanofibers (CNF); and metal materials such as nickel, aluminum, and stainless steel. The conductive additive may be, for example, particulate or fibrous, and its size is not particularly limited. Only one type of conductive additive may be used alone, or two or more types may be used in combination.

[0018] Examples of binders that can be contained in the positive electrode active material layer 11 include butadiene rubber (BR)-based binders, butylene rubber (IIR)-based binders, acrylate butadiene rubber (ABR)-based binders, styrene butadiene rubber (SBR)-based binders, polyvinylidene fluoride (PVdF)-based binders, polytetrafluoroethylene (PTFE)-based binders, polyimide (PI)-based binders, etc. Only one type of binder may be used alone, or two or more types may be used in combination.

[0019] 1.1.2 Positive Electrode Current Collector As shown in FIG. 1 , the positive electrode 10 may include a positive electrode current collector 12 in contact with the positive electrode active material layer 11. Any common positive electrode current collector for batteries can be used as the positive electrode current collector 12. The positive electrode current collector 12 may be in the form of a foil, plate, mesh, punched metal, foam, or the like. The positive electrode current collector 12 may be composed of a metal foil or metal mesh. Metal foil is particularly advantageous in terms of ease of handling. The positive electrode current collector 12 may be composed of multiple foils. Examples of metals that may constitute the positive electrode current collector 12 include Cu, Ni, Cr, Au, Pt, Ag, Al, Fe, Ti, Zn, Co, stainless steel, and the like. In particular, the positive electrode current collector 12 may contain Al from the viewpoint of ensuring oxidation resistance. The positive electrode current collector 12 may have some kind of coating layer on its surface for the purpose of adjusting the resistance, etc. Furthermore, the positive electrode current collector 12 may be a metal foil or a substrate on which the above-mentioned metal is plated or vapor-deposited. Furthermore, when the positive electrode current collector 12 is made of multiple sheets of metal foil, some kind of layer may be present between the multiple sheets of metal foil. The thickness of the positive electrode current collector 12 is not particularly limited. For example, it may be 0.1 μm or more or 1 μm or more, or may be 1 mm or less or 100 μm or less.

[0020] 1.2 Electrolyte Layer The electrolyte layer 20 is disposed between the positive electrode 10 and the negative electrode 30 and can function as a separator. The electrolyte layer 20 contains at least a sulfide solid electrolyte and a predetermined perfluoropolyether, and may further contain, optionally, a binder. The electrolyte layer 20 may further contain other components such as a dispersant. The content of each component in the electrolyte layer 20 is not particularly limited and may be determined appropriately depending on the desired battery performance. For example, the sulfide solid electrolyte, the predetermined perfluoropolyether, and the optional binder may total 85% by volume or more, 90% by volume or more, or 95% by volume or more, assuming the entire electrolyte layer 20 to be 100% by volume, with the remainder being voids or other components. The thickness of the electrolyte layer 20 is not particularly limited and may be, for example, 0.1 μm or more or 1 μm or more, and 2 mm or less or 1 mm or less.

[0021] 1.2.1 Sulfide Solid Electrolyte The sulfide solid electrolyte contained in the electrolyte layer 20 may be appropriately selected from the sulfide solid electrolytes exemplified above as those that can be contained in the positive electrode active material layer 11. Among them, sulfide solid electrolytes containing at least Li, S, and P as constituent elements have high performance. The sulfide solid electrolyte may be amorphous or crystalline. The sulfide solid electrolyte may be, for example, particulate. Only one type of sulfide solid electrolyte may be used alone, or two or more types may be used in combination. The electrolyte layer 20 may contain other electrolytes in addition to the sulfide solid electrolyte.

[0022] 1.2.2 Perfluoropolyether (PFPE) The electrolyte layer 20 contains perfluoropolyether (PFPE) represented by the following formula (1). According to the inventors' new findings, the sulfide solid electrolyte contained in the electrolyte layer has high chemical reactivity and may react with other materials to alter or deteriorate. In this case, the ionic conductivity of the electrolyte layer is likely to decrease. For example, if an insulating material is contained in the electrolyte layer to improve the insulation of the electrolyte layer, the sulfide solid electrolyte may react with the insulating material, resulting in a decrease in the ionic conductivity of the electrolyte layer. In contrast, the PFPE contained in the electrolyte layer 20 has high insulation properties and low reactivity with the sulfide solid electrolyte. In other words, when a specific PFPE is contained in the electrolyte layer 20 together with the sulfide solid electrolyte, the voltage resistance of the electrolyte layer can be improved while suppressing deterioration of the sulfide solid electrolyte. As a result, the electrolyte layer 20 is likely to achieve both voltage resistance and ionic conductivity.

[0023] Furthermore, according to the inventors' new findings, PFPE, having an ether bond, is believed to have a high affinity for the surfaces of various battery materials such as sulfide solid electrolytes, and is believed to be able to appropriately exist, for example, in the voids between sulfide solid electrolyte materials, which further increases the voltage resistance of the electrolyte layer.

[0024] The perfluoropolyether is represented by the following formula (1).

[0025] E １ -Rf １ -RＦ -O-Rf ２ -E ２ (1) [In formula (1), Rf １ and Rf ２ each independently represents a C1-16 divalent alkylene group optionally substituted by one or more fluorine atoms, １ and E ２ are each independently a monovalent group selected from the group consisting of a fluorine group, a hydrogen group, a hydroxyl group, an aldehyde group, a carboxylic acid group, a C1-10 alkyl ester group, an amide group which may have one or more substituents, and an amino group which may have one or more substituents; R Ｆ is a divalent fluoropolyether group.

[0026] In the above formula (1), Rf １ and Rf ２ are each independently a C1-16 divalent alkylene group optionally substituted with one or more fluorine atoms.

[0027] In one aspect, the "C1-16 divalent alkylene group" in the above-mentioned C1-16 divalent alkylene group optionally substituted by one or more fluorine atoms may be straight-chain or branched-chain, and may preferably be a straight-chain or branched-chain C1-6 alkylalkylene group, particularly a C1-3 alkylene group, and more preferably a straight-chain C1-6 alkylene group, particularly a C1-3 alkylene group.

[0028] In one embodiment, the "C1-16 divalent alkylene" in the C1-16 divalent alkylene group optionally substituted by one or more fluorine atoms may be a straight chain or a branched chain, and is preferably a straight chain or branched chain C1-6 fluoroalkylene group, particularly a C1-3 fluoroalkylene group, and specifically, -CF ２ CH ２ - and -CF ２ CF ２ CH ２ -, and more preferably a linear C1-6 perfluoroalkylene group, particularly a C1-3 perfluoroalkylene group, specifically -CF２ -, -CF ２ CF ２ - and -CF ２ CF ２ CF ２ - may be a group selected from the group consisting of

[0029] In the above formula (1), E １ and E ２ are each independently a monovalent group selected from the group consisting of a fluorine group, a hydrogen group, a hydroxyl group, an aldehyde group, a carboxylic acid group, a C1-10 alkyl ester group, an amide group which may have one or more substituents, and an amino group which may have one or more substituents.

[0030] The above-mentioned PFPE has low reactivity with the sulfide solid electrolyte. Therefore, even when the PFPE comes into contact with the sulfide solid electrolyte, the ion conductivity is unlikely to decrease due to the alteration or deterioration of the sulfide solid electrolyte. In particular, when the electrolyte layer contains PFPE having a non-polar group as a terminal group, the reaction between the PFPE and the sulfide solid electrolyte is further suppressed, and even higher effects can be expected. In this regard, the above-mentioned E １ and E ２ are each independently preferably a fluorine group. １ -Rf １ and E ２ -Rf ２ are each independently -CF ３ , -CF ２ CF ３ , and -CF ２ CF ２ CF ３ It may be a group selected from the group consisting of:

[0031] In the above formula (1), R Ｆ is independently at each occurrence a divalent fluoropolyether group.

[0032] R Ｆ is preferably represented by the formula (2): -(OC ６ F １２ ) ａ - (OC ５ F １０ ) ｂ - (OC４ F ８ ) ｃ - (OC ３ R Ｆａ ６ ) ｄ - (OC ２ F ４ ) ｅ -(OCF ２ ) ｆ - (2) [In formula (2): R Ｆａ are each independently a hydrogen atom, a fluorine atom, or a chlorine atom in each occurrence; a, b, c, d, e, and f are each independently an integer of 0 to 200; the sum of a, b, c, d, e, and f is 1 or more; the order of occurrence of each repeating unit enclosed in parentheses with a, b, c, d, e, or f is arbitrary in the formula; provided that all R Ｆａ is a hydrogen atom or a chlorine atom, then at least one of a, b, c, e and f is 1 or greater.]

[0033] R Ｆａ is preferably a hydrogen atom or a fluorine atom, and more preferably a fluorine atom.

[0034] a, b, c, d, e and f may preferably each independently be an integer of 0 to 100.

[0035] The sum of a, b, c, d, e, and f is preferably 5 or more, more preferably 10 or more, and may be, for example, 15 or more or 20 or more. The sum of a, b, c, d, e, and f is preferably 200 or less, more preferably 100 or less, and even more preferably 60 or less, and may be, for example, 50 or less or 30 or less.

[0036] These repeating units may be linear or branched. For example, -(OC ６ F １２ )- is -(OCF ２ CF ２ CF ２ CF ２ CF ２ CF ２ )-,-(OCF(CF ３ )CF ２ CF２ CF ２ CF ２ ) -, -(OCF ２ CF (CF ３ )CF ２ CF ２ CF ２ ) -, -(OCF ２ CF ２ CF (CF ３ )CF ２ CF ２ ) -, -(OCF ２ CF ２ CF ２ CF (CF ３ )CF ２ )-, and -(OCF ２ CF ２ CF ２ CF ２ CF (CF ３ ))-. ５ F １０ )- is -(OCF ２ CF ２ CF ２ CF ２ CF ２ )-,-(OCF(CF ３ )CF ２ CF ２ CF ２ ) -, -(OCF ２ CF (CF ３ )CF ２ CF ２ ) -, -(OCF ２ CF ２ CF (CF ３ )CF ２ )-, and -(OCF ２ CF ２ CF ２ CF (CF ３ ))-. ４ F ８ )- is -(OCF ２ CF ２ CF ２ CF ２ )-,-(OCF(CF ３ )CF ２ CF ２ ) -, -(OCF ２ CF (CF３ )CF ２ ) -, -(OCF ２ CF ２ CF (CF ３ )) -, -(OC(CF ３ ) ２ CF ２ ) -, -(OCF ２ C (CF ３ ) ２ )-,-(OCF(CF ３ )CF(CF ３ ))-,-(OCF(C ２ F ５ )CF ２ )-, and -(OCF ２ CF (C ２ F ５ ))-. ３ F ６ ) - (i.e., in the above formula (2), R Ｆａ is a fluorine atom), -(OCF ２ CF ２ CF ２ )-,-(OCF(CF ３ )CF ２ )-, and -(OCF ２ CF (CF ３ ))-. ２ F ４ )- is -(OCF ２ CF ２ )-, and -(OCF(CF ３ ))-.

[0037] In one embodiment, R Ｆ may be, independently in each occurrence, a group represented by any one of the following formulas (2-1) to (2-5):

[0038] - (OC ３ F ６ ) ｄ - (OC ２ F ４ ) ｅ - (2-1) [In formula (2-1), d is an integer of 1 to 200, and e is 0 or 1.]

[0039] - (OC ４ F８ ) ｃ - (OC ３ F ６ ) ｄ - (OC ２ F ４ ) ｅ -(OCF ２ ) ｆ - (2-2) [In formula (2-2), c and d each independently represent an integer of 0 or more and 30 or less, e and f each independently represent an integer of 1 or more and 200 or less, the sum of c, d, e, and f is 2 or more, and the order of occurrence of each repeating unit enclosed in parentheses with the subscript c, d, e, or f is arbitrary in the formula.],

[0040] - (R ６ -R ７ ) ｇ - (2-3) [In formula (2-3), R ６ is OCF ２ or O.C. ２ F ４ and R ７ is O.C. ２ F ４ , O.C. ３ F ６ , O.C. ４ F ８ , O.C. ５ F １０ and O.C. ６ F １２ or a combination of two or three groups selected from these groups, and g is an integer from 2 to 100;

[0041] - (OC ６ F １２ ) ａ - (OC ５ F １０ ) ｂ - (OC ４ F ８ ) ｃ - (OC ３ F ６ ) ｄ - (OC ２ F ４ ) ｅ -(OCF ２ ) ｆ- (2-4) [In formula (2-4), e represents an integer of 1 or more and 200 or less, a, b, c, d, and f each independently represent an integer of 0 or more and 200 or less, and the order of the repeating units enclosed in parentheses with a, b, c, d, e, or f is arbitrary in the formula.]

[0042] - (OC ６ F １２ ) ａ - (OC ５ F １０ ) ｂ - (OC ４ F ８ ) ｃ - (OC ３ F ６ ) ｄ - (OC ２ F ４ ) ｅ -(OCF ２ ) ｆ - (2-5) [In formula (2-5), f represents an integer of 1 or more and 200 or less, a, b, c, d, and e each independently represent an integer of 0 or more and 200 or less, and the order of the repeating units enclosed in parentheses with a, b, c, d, e, or f is arbitrary in the formula.]

[0043] In the above formula (2-1), d is preferably an integer of 5 to 200, more preferably 10 to 100, and even more preferably 15 to 50, for example, an integer of 25 to 35. The above formula (2-1) is preferably -(OCF ２ CF ２ CF ２ ) ｄ -, or -(OCF(CF ３ )CF ２ ) ｄ -, and more preferably -(OCF ２ CF ２ CF ２ ) ｄ In one embodiment, e is 0. In another embodiment, e is 1.

[0044] In the formula (2-2), e and f are each independently an integer of preferably 5 to 200, more preferably 10 to 200. The sum of c, d, e, and f is preferably 5 or more, more preferably 10 or more, and may be, for example, 15 or more or 20 or more. In one aspect, the formula (2-2) is preferably -(OCF ２ CF ２ CF ２ CF ２ ) ｃ -(OCF ２ CF ２ CF ２ ) ｄ -(OCF ２ CF ２ ) ｅ -(OCF ２ ) ｆ In another embodiment, formula (2-2) is a group represented by -(OC ２ F ４ ) ｅ -(OCF ２ ) ｆ It may be a group represented by -.

[0045] In the above formula (2-3), R ６ is preferably OC ２ F ４ In the above (2-3), R ７ is preferably OC ２ F ４ , O.C. ３ F ６ and O.C. ４ F ８ or a combination of two or three groups selected from these groups, more preferably OC ３ F ６ and O.C. ４ F ８ is a group selected from ２ F ４ , O.C. ３ F ６ and O.C. ４ F ８ The combination of two or three groups selected from the above is not particularly limited, but examples thereof include —OC ２ F ４ O.C.３ F ６ -、-OC ２ F ４ OC ４ F ８ -、-OC ３ F ６ OC ２ F ４ -、-OC ３ F ６ OC ３ F ６ -、-OC ３ F ６ OC ４ F ８ -、-OC ４ F ８ OC ４ F ８ -、-OC ４ F ８ OC ３ F ６ -、-OC ４ F ８ OC ２ F ４ -、-OC ２ F ４ OC ２ F ４ OC ３ F ６ -、-OC ２ F ４ OC ２ F ４ OC ４ F ８ -、-OC ２ F ４ OC ３ F ６ OC ２ F ４ -、-OC ２ F ４ OC ３ F ６ OC ３ F ６ -、-OC ２ F ４ OC ４ F ８ OC ２ F ４ -、-OC ３ F ６ OC ２ F ４ OC ２ F ４ -、-OC３ F ６ O.C. ２ F ４ O.C. ３ F ６ -, -OC ３ F ６ O.C. ３ F ６ O.C. ２ F ４ - and -OC ４ F ８ O.C. ２ F ４ O.C. ２ F ４ In the above formula (2-3), g is preferably an integer of 3 or more, more preferably an integer of 5 or more. The above g is preferably an integer of 50 or less. In the above formula (2-3), OC ２ F ４ , O.C. ３ F ６ , O.C. ４ F ８ , O.C. ５ F １０、 and O.C. ６ F １２ may be either a straight chain or a branched chain, and is preferably a straight chain. In this embodiment, the above formula (2-3) is preferably -(OC ２ F ４ -OC ３ F ６ ) ｇ -, or - (OC ２ F ４ -OC ４ F ８ ) ｇ - is.

[0046] In the above formula (2-4), e is preferably an integer of 1 or more and 100 or less, more preferably an integer of 5 or more and 100 or less. The sum of a, b, c, d, e, and f is preferably 5 or more, more preferably 10 or more, for example, 10 or more and 100 or less.

[0047] In the above formula (2-5), f is preferably an integer of 1 or more and 100 or less, more preferably an integer of 5 or more and 100 or less. The sum of a, b, c, d, e, and f is preferably 5 or more, more preferably 10 or more, for example, 10 or more and 100 or less.

[0048] In one embodiment, the R Ｆ is a group represented by the above formula (2-1).

[0049] In one embodiment, the R Ｆ is a group represented by the above formula (2-2).

[0050] In one embodiment, the R Ｆ is a group represented by the above formula (2-3).

[0051] In one embodiment, the R Ｆ is a group represented by the above formula (2-4).

[0052] In one embodiment, the R Ｆ is a group represented by the above formula (2-5).

[0053] R Ｆ In the formula, the ratio of e to f (hereinafter referred to as the "e / f ratio") may be 0.5 to 4, preferably 0.6 to 3, more preferably 0.7 to 2, and even more preferably 0.8 to 1.4. By setting the e / f ratio to 4 or less, the lubricity and chemical stability are further improved. The smaller the e / f ratio, the more the lubricity is improved. On the other hand, by setting the e / f ratio to 0.5 or more, the stability of the compound can be further increased. The larger the e / f ratio, the more the stability of the fluoropolyether structure is improved. In this case, the value of f is preferably 0.8 or more.

[0054] In one embodiment, the R Ｆ is represented by the following formula (2-6): -(OCF ２ CF ２ CF ２ ) ａ -(OCF(CF ３ )CF ２ ) ｂ -(OCF ２ CF (CF ３ )) ｃ -(OCF ２ CF ２ ) ｄ -(OCF(CF ３ )) ｅ -(OCF ２ )ｆ - (2-6) [In formula (2-6), a, b, c, d, e, and f each independently represent an integer of 0 to 200, the sum of a, b, c, d, e, and f is 1 or more, and the order of the repeating units enclosed in parentheses after a, b, c, d, e, or f is arbitrary in the formula.]

[0055] In one embodiment, the R Ｆ is represented by the following formula (2-7): -(OCF ２ CF ２ ) ｄ -(OCF(CF ３ )) ｅ -(OCF ２ ) ｆ - (2-7) [In formula (2-7), d, e, and f each independently represent an integer of 0 to 200, the sum of d, e, and f is 1 or more, and the order of the repeating units enclosed in parentheses with d, e, or f is arbitrary in the formula.]

[0056] R Ｆ In the formula, the ratio of d to f (hereinafter referred to as the "d / f ratio") may be 0.5 to 4, preferably 0.6 to 3, more preferably 0.7 to 2, and even more preferably 0.8 to 1.4. By setting the d / f ratio to 4 or less, the lubricity and chemical stability are further improved. The smaller the d / f ratio, the more the lubricity is improved. On the other hand, by setting the d / f ratio to 0.5 or more, the stability of the compound can be further increased. The larger the d / f ratio, the more the stability of the fluoropolyether structure is improved. In this case, the value of f is preferably 0.8 or more.

[0057] In the above fluoropolyether group-containing compound, R Ｆ The number average molecular weight of the portion is not particularly limited, but is, for example, 500 to 30,000, preferably 1,500 to 30,000, and more preferably 2,000 to 10,000. Ｆ The number average molecular weight of １９ The value is measured by F-NMR.

[0058] The content of PFPE in the electrolyte layer 20 is not particularly limited and can be appropriately selected depending on the desired voltage resistance and ionic conductivity. In particular, when the electrolyte layer 20 contains the PFPE in an amount of 1 vol% or more and 25 vol% or less, a higher effect is likely to be obtained. The electrolyte layer 20 may contain the PFPE in an amount of, for example, 1 vol% or more, 3 vol% or more, 5 vol% or more, 7 vol% or more, or 8 vol% or more, and 25 vol% or less, 24 vol% or less, 22 vol% or less, 20 vol% or less, 18 vol% or less, 16 vol% or less, 14 vol% or less, or 12 vol% or less.

[0059] The volume fraction of PFPE in the electrolyte layer 20 is measured as follows. That is, the volume of the electrolyte layer 20 is measured in advance using an optical microscope or SEM. The PFPE content volume may be determined by washing the electrolyte layer 20 with a solvent (one that can dissolve PFPE but does not dissolve other electrode materials), recovering the filtrate in which PFPE has been dissolved by suction filtration or the like, and analyzing the recovered solvent by GC-MS. Alternatively, if the solvent has a boiling point significantly different from that of PFPE, the PFPE may be extracted by distillation, and the volume of the PFPE may be measured directly. This allows the volume fraction of PFPE in the volume of the electrolyte layer 20 measured in advance to be calculated.

[0060] 1.2.3 Binder The binder that can be contained in the electrolyte layer 20 may be appropriately selected from, for example, the binders that can be contained in the positive electrode active material layer 11 described above.

[0061] 1.3 Negative Electrode The negative electrode 30 may be any electrode capable of functioning appropriately as a negative electrode for a secondary battery, and its configuration is not particularly limited. As shown in FIG. 1 , the negative electrode 30 may include a negative electrode active material layer 31 and a negative electrode current collector 32.

[0062] 1.3.1 Negative Electrode Active Material Layer The negative electrode active material layer 31 contains at least a negative electrode active material and may further contain, optionally, an electrolyte, a conductive additive, a binder, and the like. The negative electrode active material layer 31 may also contain various other additives. For example, it may contain a dispersant or the above-mentioned perfluoropolyether. The content of each component in the negative electrode active material layer 31 may be appropriately determined depending on the desired battery performance. For example, the content of the negative electrode active material may be 40% by mass or more, 50% by mass or more, 60% by mass or more, or 70% by mass or more, or 100% by mass or less, or 90% by mass or less, where the total weight of the negative electrode active material layer 31 (total solid content) is taken as 100% by mass. The shape of the negative electrode active material layer 31 is not particularly limited, and may be, for example, a sheet-like negative electrode active material layer having a substantially flat surface. The thickness of the negative electrode active material layer 31 is not particularly limited, and may be, for example, 0.1 μm or more, 1 μm or more, or 10 μm or more, and may be 2 mm or less, 1 mm or less, or 500 μm or less.

[0063] As the negative electrode active material, various substances can be used that have a potential (charge / discharge potential) at which a predetermined carrier ion (e.g., lithium ion) is absorbed and released that is lower in potential than the above-mentioned positive electrode active material. For example, the negative electrode active material may be at least one selected from silicon-based active materials such as Si, Si alloys, and silicon oxide; carbon-based active materials such as graphite and hard carbon; various oxide-based active materials such as lithium titanate; metallic lithium, lithium alloys, and the like. Only one type of negative electrode active material may be used alone, or two or more types may be used in combination.

[0064] The shape of the negative electrode active material may be any shape commonly used for negative electrode active materials in batteries. The negative electrode active material may be, for example, particulate. The negative electrode active material may be hollow, void-containing, or porous. The negative electrode active material may be primary particles or secondary particles formed by aggregation of multiple primary particles. The average particle diameter D50 of the negative electrode active material may be, for example, 1 nm or more, 5 nm or more, or 10 nm or more, and may be 500 μm or less, 100 μm or less, 50 μm or less, or 30 μm or less. Alternatively, the negative electrode active material may be in the form of a sheet (foil or film) such as lithium foil. That is, the negative electrode active material layer 31 may be made of a sheet of negative electrode active material.

[0065] The electrolyte that can be contained in the negative electrode active material layer 31 may be a solid electrolyte, a liquid electrolyte (electrolytic solution), or a combination thereof. In particular, when the negative electrode active material layer 31 contains at least a solid electrolyte as the electrolyte, a higher effect is likely to be obtained. The negative electrode active material layer 31 is preferably a solid electrolyte, particularly a sulfide solid electrolyte, and particularly a Li ２ S-P ２ S ５ The negative electrode active material layer 31 may contain a sulfide solid electrolyte containing the above-mentioned carbon material or the above-mentioned metal material. The binder that can be contained in the negative electrode active material layer 31 may be appropriately selected from, for example, the binders that can be contained in the above-mentioned positive electrode active material layer 11.

[0066] 1.3.2 Negative Electrode Current Collector As shown in FIG. 1 , the negative electrode 30 may include a negative electrode current collector 32 in contact with the negative electrode active material layer 31. Any of the negative electrode current collectors commonly used in batteries can be used as the negative electrode current collector 32. The negative electrode current collector 32 may be in the form of a foil, plate, mesh, punched metal, foam, or the like. The negative electrode current collector 32 may be a metal foil or metal mesh, or a carbon sheet. Metal foil is particularly advantageous in terms of ease of handling. The negative electrode current collector 32 may be composed of multiple foils or sheets. Examples of metals that may constitute the negative electrode current collector 32 include Cu, Ni, Cr, Au, Pt, Ag, Al, Fe, Ti, Zn, Co, and stainless steel. In particular, from the viewpoint of ensuring reduction resistance and being less likely to alloy with lithium, the negative electrode current collector 32 may contain at least one metal selected from Cu, Ni, and stainless steel. The negative electrode current collector 32 may have a coating layer on its surface for purposes such as adjusting resistance. The negative electrode current collector 32 may also be a metal foil or a substrate plated or vapor-deposited with the above metal. When the negative electrode current collector 32 is made of multiple sheets of metal foil, some layer may be present between the multiple sheets of metal foil. The thickness of the negative electrode current collector 32 is not particularly limited. For example, it may be 0.1 μm or more or 1 μm or more, or may be 1 mm or less or 100 μm or less.

[0067] 1.4 Other Configurations The secondary battery 100 may have the above-described configurations housed inside an exterior body. Any known exterior body for a battery can be used as the exterior body. Furthermore, a plurality of secondary batteries 100 may be electrically connected and stacked in any manner to form an assembled battery. In this case, the assembled battery may be housed inside a known battery case. The secondary battery 100 may also have other obvious configurations such as necessary terminals. Examples of shapes of the secondary battery 100 include coin type, laminate type, cylindrical type, and square type.

[0068] 2. Method for Manufacturing Secondary Battery The secondary battery 100 can be manufactured by applying a known method. For example, it can be manufactured as follows. However, the manufacturing method of the secondary battery 100 is not limited to the method described below, and each layer may be formed by, for example, dry molding. (1) A negative electrode active material and the like that constitute the negative electrode active material layer are dispersed in a solvent to obtain a negative electrode slurry. The solvent used in this case is not particularly limited, and water or various organic solvents can be used, and N-methylpyrrolidone (NMP) can also be used. Thereafter, the negative electrode slurry is applied to the surface of the negative electrode current collector or the electrolyte layer described below using a doctor blade or the like, and then dried to form a negative electrode active material layer on the surface of the negative electrode current collector or the electrolyte layer, thereby forming a negative electrode. Here, the negative electrode active material layer may be press-molded. (2) A positive electrode slurry is obtained by dispersing a positive electrode active material and the like that constitute the positive electrode active material layer in a solvent. The solvent used in this case is not particularly limited, and water or various organic solvents can be used, and N-methylpyrrolidone (NMP) can also be used. Thereafter, the positive electrode slurry is applied to the surface of a positive electrode current collector or an electrolyte layer (described later) using a doctor blade or the like, and then dried to form a positive electrode active material layer on the surface of the positive electrode current collector or the electrolyte layer, thereby forming a positive electrode. Here, the positive electrode active material layer may be press-molded. (3) The layers are stacked so that the electrolyte layer is sandwiched between the negative electrode and the positive electrode, thereby obtaining a laminate having the negative electrode current collector, the negative electrode active material layer, the electrolyte layer, the positive electrode active material layer, and the positive electrode current collector in this order. The electrolyte layer may be obtained, for example, by molding an electrolyte mixture containing a sulfide solid electrolyte, PFPE, and a binder, or may be obtained by press-molding. Here, the laminate may be further press-molded. Other components such as terminals may be attached to the laminate as needed. (4) The laminate is housed in a battery case and sealed to obtain a secondary battery.

[0069] 3. Supplementary Note: The technology of the present disclosure can be applied not only to lithium-ion secondary batteries, but also to secondary batteries other than lithium-ion secondary batteries (e.g., sodium-ion secondary batteries), etc. However, when the technology of the present disclosure is applied to lithium-ion secondary batteries, it is likely to exhibit even greater effects.

[0070] The technology of the present disclosure will be described in more detail below with reference to examples, but the technology of the present disclosure is not limited to the following examples.

[0071] 1. Preparation of electrolyte layer (separator layer) A sulfide solid electrolyte (LiI-LiBr-Li ２ S-P ２ S ５ ), a binder (PVdF), and an additive component (styrene butadiene rubber (SBR), polyethylene oxide (PEO), or PFPE) were added, and these were kneaded using an ultrasonic homogenizer to obtain an electrolyte slurry. The obtained electrolyte slurry was applied to an Al foil and dried to form an electrolyte layer on the Al foil. The volume ratios (volume %) of the sulfide solid electrolyte, binder, and additive component contained in the electrolyte layer are as shown in Table 1 below. PFPE is a sulfide solid electrolyte represented by the following formula (I) (m / n is 1.2, number average molecular weight is 5120, terminal R is CF ３ and CF ２ CF ３ and are present in an average ratio of 1:0.17)

[0072]

[0073] 2. Measurement of Electrolyte Layer Thickness The obtained electrolyte layer was punched together with an Al foil to a diameter of 11.28 mm to obtain a measurement sample. The thickness of the obtained measurement sample was measured using a micrometer. The thickness of the electrolyte layer was determined by subtracting the thickness of the Al foil from the measured thickness.

[0074] 3. Evaluation of voltage resistance The Al foil was removed from the above-mentioned measurement sample punched out to a diameter of 11.28 mm to obtain an electrolyte layer, which was then sandwiched between SUS electrodes. In this state, the voltage was swept from 0 V to 110 V. At this time, the voltage at which the current rose and short-circuited, as shown in Figure 2, was measured as the "voltage resistance (V)."

[0075] Two of the above-mentioned measurement samples were prepared by punching out a diameter of 11.28 mm, and the electrolyte layers were bonded together. After removing the two Al foils, the sample was sandwiched between carbon-coated Al foils. Furthermore, SUS electrodes were used to collect current from both sides, and resistance was measured using the AC impedance method. The resistance value at the real axis intercept at 300 kHz was read from the obtained Nyquist plot, and the ionic conductivity was calculated from this value and the thickness of the electrolyte layer.

[0076] 5. Evaluation Results The evaluation results are shown in the following Table 1. In Table 1, the evaluation results of ionic conductivity are shown relative to the ionic conductivity of Comparative Example 1, which is set to 100.

[0077]

[0078] The results shown in Table 1 reveal the following: (1) In Comparative Example 1, the electrolyte layer did not contain any additive components, and therefore sufficient voltage resistance was not achieved. (2) In Comparative Examples 2 to 4, the electrolyte layer contained large amounts of PVdF and SBR, which improved the voltage resistance of the electrolyte layer but reduced the ionic conductivity of the electrolyte layer. Both PVdF and SBR function as binders, but it is clear that even if the binder content in the electrolyte layer is increased, it is difficult to achieve both voltage resistance and ionic conductivity. (3) In Comparative Example 5, the electrolyte layer contained PEO as an additive component, which actually reduced the voltage resistance of the electrolyte layer and also reduced the ionic conductivity. (4) In contrast, in Examples 1 to 5, the electrolyte layer contained PFPE as an additive component, which improved the voltage resistance of the electrolyte layer while maintaining sufficient ionic conductivity. PFPE is thought to have excellent insulating properties and low reactivity with sulfide solid electrolytes. It can be said that secondary batteries provided with electrolyte layers having high voltage resistance and ionic conductivity as in Examples 1 to 5 tend to have low resistance and tend to have improved battery performance.

[0079] In the above examples, PFPE having a specific chemical structure is exemplified, but the chemical structure of the PFPE is not limited to this. Furthermore, in the above examples, a sulfide solid electrolyte having a specific chemical composition is exemplified, but the chemical composition of the sulfide solid electrolyte is not limited to this. Furthermore, in the above examples, PVdF is exemplified as the binder, but the binder that can be contained in the electrolyte layer is not limited to PVdF, and various other binders may be used, or no binder may be used.

[0080] As described above, a secondary battery having the following configuration is likely to achieve both voltage resistance and ionic conductivity in the electrolyte layer and exhibit excellent performance: (1) Having a positive electrode, an electrolyte layer, and a negative electrode, and (2) The electrolyte layer contains a sulfide solid electrolyte and a specified perfluoropolyether.

[0081] 10 Positive electrode 11 Positive electrode active material layer 12 Positive electrode current collector 20 Electrolyte layer 30 Negative electrode 31 Negative electrode active material layer 32 Negative electrode current collector 100 Secondary battery

Claims

1. A secondary battery having a positive electrode, an electrolyte layer, and a negative electrode, The electrolyte layer contains a sulfide solid electrolyte and a perfluoropolyether represented by the following formula (1): Secondary battery. E １ -Rf １ -R Ｆ -O-Rf ２ -E ２ (1) [In formula (1), Rf １ and Rf ２ each independently represents a C1-16 divalent alkylene group optionally substituted by one or more fluorine atoms, E １ and E ２ each independently represents a monovalent group selected from the group consisting of a fluorine group, a hydrogen group, an aldehyde group, a C1-10 alkyl ester group, an amide group which may have one or more substituents, and an amino group which may have one or more substituents; R Ｆ is a divalent fluoropolyether group.

2. The R Ｆ is expressed by the formula (2): -(OC ６ F １２ ) ａ -(OC ５ F １０ ) ｂ -(OC ４ F ８ ) ｃ -(OC ３ R Ｆａ ６ ) ｄ -(OC ２ F ４ ) ｅ -(OCF ２ ) ｆ - (2) [In formula (2), R Ｆａ is independently at each occurrence a hydrogen atom, a fluorine atom, or a chlorine atom; a, b, c, d, e, and f each independently represent an integer from 0 to 200; the sum of a, b, c, d, e, and f is greater than or equal to 1; The order of occurrence of each repeating unit enclosed in parentheses with a, b, c, d, e, or f in the formula is arbitrary. However, all R Ｆａ is a hydrogen atom or a chlorine atom, at least one of a, b, c, e and f is 1 or more. is a group represented by The secondary battery according to claim 1 .

3. The R Ｆａ is a fluorine atom, The secondary battery according to claim 2 .

4. The R Ｆ each occurrence independently represents the following formula (2-1), (2-2), (2-3), (2-4) or (2-5): -(OC ３ F ６ ) ｄ -(OC ２ F ４ ) ｅ - (2-1) [In formula (2-1), d is an integer of 1 to 200, and e is 0 or 1.] -(OC ４ F ８ ) ｃ -(OC ３ F ６ ) ｄ -(OC ２ F ４ ) ｅ -(OCF ２ ) ｆ - (2-2) [In formula (2-2), c and d each independently represent an integer of 0 to 30, e and f each independently represent an integer from 1 to 200; The sum of c, d, e, and f is an integer from 10 to 200, The order of occurrence of each repeat unit enclosed in parentheses with the subscript c, d, e, or f is arbitrary in the formula. -(R ６ -R ７ ) ｇ - (2-3) [In formula (2-3), R ６ is O.C.F. ２ Or O.C. ２ F ４ and R ７ , O.C. ２ F ４ , O.C. ３ F ６ , O.C. ４ F ８ , O.C. ５ F １０ and O.C. ６ F １２ or a combination of two or three groups selected from these groups, g is an integer from 2 to 100. -(OC ６ F １２ ) ａ -(OC ５ F １０ ) ｂ -(OC ４ F ８ ) ｃ -(OC ３ F ６ ) ｄ -(OC ２ F ４ ) ｅ -(OCF ２ ) ｆ - (2-4) [In formula (2-4), e represents an integer of 1 or more and 200 or less, a, b, c, d, and f each independently represent an integer of 0 to 200; The order of occurrence of each repeating unit enclosed in parentheses with a, b, c, d, e, or f is arbitrary in the formula. -(OC ６ F １２ ) ａ -(OC ５ F １０ ) ｂ -(OC ４ F ８ ) ｃ -(OC ３ F ６ ) ｄ -(OC ２ F ４ ) ｅ -(OCF ２ ) ｆ - (2-5) [In formula (2-5), f represents an integer of 1 or more and 200 or less, a, b, c, d, and e each independently represent an integer of 0 to 200; The order of occurrence of each repeating unit enclosed in parentheses with a, b, c, d, e, or f is arbitrary in the formula. is a group represented by The secondary battery according to claim 3 .

5. The R Ｆ is expressed by the following formula (2-6): -(OCF ２ CF ２ CF ２ ) ａ -(OCF(CF ３ )CF ２ ) ｂ -(OCF ２ CF(CF ３ )) ｃ -(OCF ２ CF ２ ) ｄ -(OCF(CF ３ )) ｅ -(OCF ２ ) ｆ - (2-6) [In formula (2-6), a, b, c, d, e and f each independently represent an integer of 0 to 200, the sum of a, b, c, d, e, and f is greater than or equal to 1; The order of occurrence of each repeating unit enclosed in parentheses with a, b, c, d, e, or f is arbitrary in the formula. is a group represented by The secondary battery according to claim 4 .

6. The R Ｆ is expressed by the following formula (2-7): -(OCF ２ CF ２ ) ｄ -(OCF(CF ３ )) ｅ -(OCF ２ ) ｆ - (2-7) [In formula (2-7), d, e and f each independently represent an integer of 0 to 200, the sum of d, e, and f is 1 or more; The order of occurrence of each repeating unit enclosed in parentheses with d, e, or f is arbitrary in the formula. is a group represented by The secondary battery according to claim 4 .

7. The above E １ -Rf １ and the above E ２ -Rf ２ are each independently -CF ３ , -CF ２ CF ３ , and -CF ２ CF ２ CF ３ is a group selected from the group consisting of The secondary battery according to any one of claims 1 to 6.

8. The electrolyte layer contains the perfluoropolyether in an amount of 1% by volume or more and 25% by volume or less. The secondary battery according to any one of claims 1 to 6.