Secondary battery

Abstract

The purpose of the present invention is to achieve both voltage resistance and ion conductivity of an electrolyte layer in a secondary battery having an electrolyte layer containing a sulfide solid electrolyte. This secondary battery has a positive electrode, an electrolyte layer, and a negative electrode. The electrolyte layer contains a sulfide solid electrolyte and a perfluoropolyether represented by formula (1). E1-Rf1-RF-O-Rf2-E2 (1) [In formula (1), Rf1 and Rf2 each independently represent a C1-16 divalent alkylene group which may be substituted by one or more fluorine atoms; e1 and E2 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, and RF is a divalent fluoropolyether group].

Description

Technical Field

[0001] The present application discloses a secondary battery. Background Art

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

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Publication No. 2012-094437

[0006] Patent Document 2: Japanese Patent Application Publication No. 2018-200866

[0007] Patent Document 3: Japanese Patent Application No. 2019-524977 Summary of the invention

[0008] Problems to be solved by the invention

[0009] The electrolyte layer of the secondary battery requires high insulation (voltage resistance). On the other hand, when the electrolyte layer contains an insulating material in order to improve the voltage resistance of the electrolyte layer, the ion conductivity of the electrolyte layer decreases, and there is a case where the resistance of the battery increases. According to the new insights of the inventors, such a problem is likely to occur when the electrolyte layer contains a sulfide solid electrolyte. That is, the electrolyte layer containing a sulfide solid electrolyte has room for improvement in terms of both voltage resistance and ion conductivity.

[0010] Methods used to solve problems

[0011] The present application discloses the following multiple aspects as means for solving the above-mentioned problems.

[0012] <Method 1>

[0013] A secondary battery comprising a positive electrode, an electrolyte layer and a negative electrode,

[0014] The electrolyte layer contains a sulfide solid electrolyte and a perfluoropolyether represented by the following formula (1).

[0015] E1-Rf1-R F -O-Rf2-E2 (1)

[0016] [In formula (1), Rf1 and Rf2 are each independently a C1-16 divalent alkylene group which may be substituted with one or more fluorine atoms,

[0017] E1 and E2 are each independently a monovalent group selected from the group consisting of a fluoro 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,

[0018] R F is a divalent fluoropolyether group.]

[0019] <Method 2>

[0020] The secondary battery according to embodiment 1, wherein the R F It is a group represented by formula (2).

[0021] -(OC6F 12 ) a -(OC5F 10 ) b -(OC4F8) c -(OC3R Fa 6) d -(OC2F4) e -(OCF2) f - (2)

[0022] [In formula (2), each occurrence of R Fa are each independently a hydrogen atom, a fluorine atom or a chlorine atom,

[0023] a, b, c, d, e and f are each independently an integer of 0 to 200,

[0024] The sum of a, b, c, d, e and f is greater than 1,

[0025] The order of the repeating units indicated by a, b, c, d, e or f and enclosed in parentheses is arbitrary in the formula.

[0026] Among them, in all R Fa When it is a hydrogen atom or a chlorine atom, at least one of a, b, c, e and f is 1 or more.]

[0027] <Method 3>

[0028] The secondary battery according to embodiment 2, wherein the R Fa A fluorine atom.

[0029] <Method 4>

[0030] The secondary battery according to Embodiment 3, wherein each of the above-mentioned R FEach independently represents a group represented by the following formula (2-1), (2-2), (2-3), (2-4) or (2-5).

[0031] -(OC3F6) d -(OC2F4) e - (2-1)

[0032] [In formula (2-1), d is an integer of 1 to 200, and e is 0 or 1.]

[0033] -(OC4F8) c -(OC3F6) d -(OC2F4) e -(OCF2) f - (2-2)

[0034] [In formula (2-2), c and d are each independently an integer of 0 to 30,

[0035] e and f are each independently an integer of 1 to 200,

[0036] The sum of c, d, e and f is an integer from 10 to 200,

[0037] The order of presence of the repeating units marked with the subscript c, d, e or f and enclosed in parentheses is arbitrary in the formula.]

[0038] -(R 6 -R 7 ) g - (2-3)

[0039] [In formula (2-3), R 6 For OCF2 or OC2F4,

[0040] R 7 is selected from OC2F4, OC3F6, OC4F8, OC5F 10 and OC6F 12 or a combination of two or three groups selected from these groups,

[0041] g is an integer from 2 to 100.]

[0042] -(OC6F 12 ) a -(OC5F 10 ) b -(OC4F8) c -(OC3F6) d -(OC2F4) e -(OCF2) f - (2-4)

[0043] [In formula (2-4), e is an integer of 1 to 200,

[0044] a, b, c, d and f are each independently an integer of 0 to 200,

[0045] The order of presence of the repeating units indicated by a, b, c, d, e or f and enclosed in parentheses is arbitrary in the formula.]

[0046] -(OC6F 12 ) a -(OC5F 10 ) b -(OC4F8) c -(OC3F6) d -(OC2F4) e -(OCF2) f - (2-5)

[0047] [In formula (2-5), f is an integer of 1 to 200,

[0048] a, b, c, d and e are each independently an integer of 0 to 200,

[0049] The order of presence of the repeating units indicated by a, b, c, d, e or f and enclosed in parentheses is arbitrary in the formula.]

[0050] <Method 5>

[0051] The secondary battery according to embodiment 4, wherein the R F It is a group represented by the following formula (2-6).

[0052] -(OCF2CF2CF2) a -(OCF(CF3)CF2) b -(OCF2CF(CF3)) c -(OCF2CF2) d -(OCF(CF3)) e -(OCF2) f - (2-6)

[0053] [In formula (2-6), a, b, c, d, e and f are each independently an integer of 0 to 200,

[0054] The sum of a, b, c, d, e and f is greater than 1,

[0055] The order of presence of the repeating units indicated by a, b, c, d, e or f and enclosed in parentheses is arbitrary in the formula.]

[0056] <Method 6>

[0057] The secondary battery according to embodiment 4, wherein the R F It is a group represented by the following formula (2-7).

[0058] -(OCF2CF2) d -(OCF(CF3)) e -(OCF2) f - (2-7)

[0059] [In formula (2-7), d, e and f are each independently an integer of 0 to 200,

[0060] The sum of d, e and f is greater than 1,

[0061] The order of presence of the repeating units marked with d, e or f and enclosed in parentheses is arbitrary in the formula.]

[0062] <Method 7>

[0063] The secondary battery according to any one of aspects 1 to 6, wherein the E1-Rf1 and the E2-Rf2 are each independently a group selected from the group consisting of -CF3, -CF2CF3, and -CF2CF2CF3.

[0064] <Method 8>

[0065] The secondary battery according to 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.

[0066] Effects of the Invention

[0067] The electrolyte layer of the present invention can easily achieve both high withstand voltage and high ion conductivity. A secondary battery having such an electrolyte layer can easily become a secondary battery having low resistance, for example. BRIEF DESCRIPTION OF THE DRAWINGS

[0068] Figure 1 An example of the configuration of a secondary battery is schematically shown.

[0069] Figure 2 An example of the evaluation results of the voltage resistance of the electrolyte layer is shown. DETAILED DESCRIPTION

[0070] 1. Secondary battery

[0071] Hereinafter, the embodiments of the technology of the present invention will be described, but the technology of the present invention is not limited to the following embodiments. Figure 1As shown, a secondary battery 100 according to one embodiment includes 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).

[0072] 1.1 Positive electrode

[0073] The structure of the positive electrode 10 is not particularly limited as long as it can properly function as the positive electrode of the secondary battery. Figure 1 As shown, the positive electrode 10 may include a positive electrode active material layer 11 and a positive electrode collector 12 .

[0074] 1.1.1 Positive electrode active material layer

[0075] The positive electrode active material layer 11 contains at least a positive electrode active material, and may optionally contain an electrolyte, a conductive aid, a binder, and the like. The positive electrode active material layer 11 may contain various additives in addition to this. For example, it may contain a dispersant, a perfluoropolyether described later, and the like. The content of each component in the positive electrode active material layer 11 can be appropriately determined according to the target battery performance. For example, the entire positive electrode active material layer 11 (the entire solid component) is set to 100 mass%, and the content of the positive electrode active material may be 40 mass% or more, 50 mass% or more, 60 mass% or more, or 70 mass% or more, or 100 mass% or less or 90 mass% or less. The shape of the positive electrode active material layer 11 is not particularly limited, for example, it may be a sheet-shaped positive electrode active material layer having a substantially flat surface. The thickness of the positive electrode active material layer 11 is not particularly limited, for example, it may be 0.1 μm or more, 1 μm or more, or 10 μm or more, or it may be 2 mm or less, 1 mm or less, or 500 μm or less.

[0076] As the positive electrode active material, an active material known as a positive electrode active material for a secondary battery can be used. Among the known active materials, a material with a relatively high potential (charge and discharge potential) for absorbing and releasing specified carrier ions (for example, lithium ions) can be used as the positive electrode active material, and a material with a relatively low potential can be used as the negative electrode active material described later. The positive electrode active material can be, for example, at least one selected from various lithium-containing compounds, elemental sulfur, and sulfur compounds. The lithium-containing compound used as the positive electrode active material can be lithium cobalt oxide, lithium nickel oxide, Li 1±α Ni 1 / 3 Co 1 / 3 Mn 1 / 3 O 2±δ , lithium manganate, spinel lithium compounds (composed of Li 1+x Mn 2-x-y M yO4 (M is one or more selected from Al, Mg, Co, Fe, Ni and Zn) represented by heterogeneous element substitution Li-Mn spinel, etc.), lithium titanate, lithium metal phosphate (LiMPO4, etc., M is one or more selected from Fe, Mn, Co and Ni). In particular, in the case where the positive electrode active material includes a lithium-containing oxide containing at least one of Ni, Co and Mn, Li and O as constituent elements, a higher effect can be expected. The positive electrode active material can be used alone or in combination of two or more.

[0077] The shape of the positive electrode active material can be any shape generally used as a positive electrode active material for a battery. The positive electrode active material can be, for example, in a particle shape. The positive electrode active material can be hollow, can have voids, or can be porous. The positive electrode active material can be a primary particle, or a secondary particle obtained by agglomerating multiple primary particles. The average particle size D50 of the positive electrode active material can be, for example, greater than 1 nm, greater than 5 nm, or greater than 10 nm, and can also be less than 500 μm, less than 100 μm, less than 50 μm, or less than 30 μm. It should be noted that the average particle size D50 described in this application refers to the particle size (median particle size) when the cumulative value in the volume-based particle size distribution obtained by the laser diffraction / scattering method is 50%.

[0078] A protective layer containing an ion-conductive oxide may be formed on the surface of the positive electrode active material. This makes it easy to suppress the reaction between the positive electrode active material and the sulfide (for example, the sulfide solid electrolyte described later). Examples of ion-conductive oxides include: Li3BO3, LiBO2, Li2CO3, LiAlO2, Li4SiO4, Li2SiO3, Li3PO4, Li2SO4, Li2TiO3, Li4Ti5O 12 , Li2Ti2O5, Li2ZrO3, LiNbO3, Li2MoO4, Li2WO4, etc. The ion conductive oxide may also be a substance in which a part of the elements are replaced by doping elements such as P and B. The coverage rate (area rate) of the protective layer on 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 less, or 100 nm or less or 20 nm or less.

[0079] The electrolyte contained in the positive electrode active material layer 11 may be a solid electrolyte, a liquid electrolyte (electrolyte), or a combination thereof. In particular, when the positive electrode active material layer 11 contains at least a solid electrolyte as an electrolyte, a high effect is easily obtained.

[0080] The solid electrolyte can be a solid electrolyte known as a solid electrolyte for a secondary battery. The solid electrolyte can be an inorganic solid electrolyte or an organic polymer electrolyte. In particular, the ion conductivity of an inorganic solid electrolyte is higher than that of an organic polymer electrolyte. In addition, the heat resistance of an inorganic solid electrolyte is excellent compared to that of an organic polymer electrolyte. Examples of the inorganic solid electrolyte include lithium lanthanum zirconate, LiPON, Li 1+X Al X Ge 2-X (PO4)3, Li-SiO glass, Li-Al-SO glass and other oxide solid electrolytes; Li2S-P2S5, Li2S-SiS2, LiI-Li2S-SiS2, LiI-Si2S-P2S5, Li2S-P2S5-LiI-LiBr, LiI-Li2S-P2S5, LiI-Li2S-P2O5, LiI-Li3PO4-P2S5, Li2S-P2S5-GeS2 and other sulfide solid electrolytes. 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, in a particle form. The solid electrolyte may be used alone or in combination of two or more.

[0081] The electrolyte may contain specified carrier ions (e.g., lithium ions). The electrolyte may be, for example, a non-aqueous electrolyte. The composition of the electrolyte may be the same as the composition known as the composition of the electrolyte of a secondary battery. For example, as the electrolyte, an electrolyte in which a lithium salt is dissolved in a carbonate solvent at a specified concentration may be used. Examples of carbonate solvents include: fluoroethylene carbonate (FEC), ethylene carbonate (EC), dimethyl carbonate (DMC), and the like. Examples of lithium salts include LiPF6, and the like.

[0082] As the conductive aid that can be included in the positive electrode active material layer 11, for example, carbon materials such as vapor grown carbon fiber (VGCF), acetylene black (AB), Ketjen black (KB), carbon nanotubes (CNT), and carbon nanofibers (CNF); metal materials such as nickel, aluminum, and stainless steel. The conductive aid can be, for example, in the form of particles or fibers, and its size is not particularly limited. The conductive aid can be used alone or in combination of two or more.

[0083] As the binder that can be included in the positive electrode active material layer 11, for example, there can be listed: butadiene rubber (BR) type binder, butylene rubber (IIR) type binder, acrylate butadiene rubber (ABR) type binder, styrene butadiene rubber (SBR) type binder, polyvinylidene fluoride (PVdF) type binder, polytetrafluoroethylene (PTFE) type binder, polyimide (PI) type binder, etc. The binder can be used alone or in combination of two or more.

[0084] 1.1.2 Positive electrode collector

[0085] like Figure 1 As shown, the positive electrode 10 may have a positive electrode collector 12 in contact with the above-mentioned positive electrode active material layer 11. The positive electrode collector 12 may be any of the collectors generally used as positive electrode collectors of batteries. In addition, the positive electrode collector 12 may be in the form of foil, plate, mesh, punched metal, foam, etc. The positive electrode collector 12 may be composed of a metal foil or a metal mesh. In particular, the metal foil has excellent operability. The positive electrode collector 12 may be composed of a plurality of foils. As metals constituting the positive electrode collector 12, there may be listed: Cu, Ni, Cr, Au, Pt, Ag, Al, Fe, Ti, Zn, Co, stainless steel, etc. In particular, from the viewpoint of ensuring oxidation resistance, etc., the positive electrode collector 12 may contain Al. The positive electrode collector 12 may have a coating on its surface for the purpose of adjusting resistance, etc. In addition, the positive electrode collector 12 may be plated or vapor-deposited with the above-mentioned metal on the metal foil or substrate. When the positive electrode current collector 12 is composed of a plurality of metal foils, some layers may be provided between the plurality of metal foils. 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 less, or 1 mm or less or 100 μm or less.

[0086] 1.2 Electrolyte layer

[0087] The electrolyte layer 20 is arranged 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 specified perfluoropolyether, and may optionally contain a binder, etc. The electrolyte layer 20 may also contain other components such as a dispersant. The content of each component in the electrolyte layer 20 is not particularly limited, and can be appropriately determined according to the target battery performance. For example, the electrolyte layer 20 as a whole is set to 100 volume%, and a total of 85 volume %, 90 volume % or more, or 95 volume % or more of a sulfide solid electrolyte, a specified perfluoropolyether and an optional binder may be included, and the remaining part may be a void or other components. The thickness of the electrolyte layer 20 is not particularly limited, for example, it may be 0.1 μm or more or 1 μm or less, or it may be 2 mm or less or 1 mm or less.

[0088] 1.2.1 Sulfide solid electrolyte

[0089] As the sulfide solid electrolyte contained in the electrolyte layer 20, it can be appropriately selected from the sulfide solid electrolytes exemplified as the sulfide solid electrolytes that can be contained in the above-mentioned positive electrode active material layer 11. In particular, the performance of the sulfide solid electrolyte containing at least Li, S and P as constituent elements is high. The sulfide solid electrolyte can be amorphous or crystalline. The sulfide solid electrolyte can be, for example, in the form of particles. Only one sulfide solid electrolyte can be used alone, or two or more sulfide solid electrolytes can be used in combination. The electrolyte layer 20 can contain other electrolytes together with the sulfide solid electrolyte.

[0090] 1.2.2 Perfluoropolyether (PFPE)

[0091] The electrolyte layer 20 contains a perfluoropolyether (PFPE) represented by the following formula (1). According to the new findings of the present inventors, the sulfide solid electrolyte contained in the electrolyte layer has high chemical reactivity, and therefore sometimes reacts with other materials to deteriorate and deteriorate. In this case, the ion conductivity of the electrolyte layer is easily reduced. For example, in order to improve the insulation of the electrolyte layer, when an insulating material is contained in the electrolyte layer, the sulfide solid electrolyte sometimes reacts with the insulating material, thereby reducing the ion conductivity of the electrolyte layer. In contrast, the PFPE contained in the electrolyte layer 20 has high insulation and low reactivity with the sulfide solid electrolyte. That is, when a predetermined PFPE is contained in the electrolyte layer 20 together with the sulfide solid electrolyte, the degradation of the sulfide solid electrolyte can be suppressed, and the voltage resistance of the electrolyte layer can be improved. As a result, it is easy to achieve both voltage resistance and ion conductivity in the electrolyte layer 20.

[0092] In addition, according to the new findings of the present inventors, it is believed that PFPE has a high affinity for the surface of various battery materials such as sulfide solid electrolytes due to its ether bond, and it is believed that, for example, it can be appropriately present in the gaps between sulfide solid electrolyte materials. As a result, the voltage resistance of the electrolyte layer is likely to be further improved.

[0093] The perfluoropolyether is represented by the following formula (1).

[0094] E1-Rf1-R F -O-Rf2-E2 (1)

[0095] [In formula (1), Rf1 and Rf2 are each independently a C1-16 divalent alkylene group which may be substituted with one or more fluorine atoms,

[0096] E1 and E2 are each independently a monovalent group selected from the group consisting of a fluoro 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,

[0097] R F is a divalent fluoropolyether group.]

[0098] In the above formula (1), Rf1 and Rf2 are each independently a C1-16 divalent alkylene group which may be substituted with one or more fluorine atoms.

[0099] In one embodiment, the "C1-16 divalent alkylene" in the above-mentioned C1-16 divalent alkylene which may be substituted with one or more fluorine atoms may be a linear or branched chain, preferably a linear or branched C1-6 alkyl alkylene, particularly a C1-3 alkylene, more preferably a linear C1-6 alkylene, particularly a C1-3 alkylene.

[0100] In one embodiment, the "C1-16 divalent alkylene group" in the above-mentioned C1-16 divalent alkylene group which may be substituted with one or more fluorine atoms may be a linear or branched group, and is preferably a linear or branched C1-6 fluoroalkylene group, in particular a C1-3 fluoroalkylene group, and specifically -CF2CH2- and -CF2CF2CH2-. In addition, a linear C1-6 perfluoroalkylene group, in particular a C1-3 perfluoroalkylene group, and specifically a group selected from the group consisting of -CF2-, -CF2CF2- and -CF2CF2CF2- is more preferred.

[0101] In the above formula (1), E1 and E2 are each independently a monovalent group selected from the group consisting of a fluoro 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.

[0102] The above-mentioned PFPE has low reactivity to sulfide solid electrolytes. Therefore, even when PFPE is in contact with a sulfide solid electrolyte, it is not easy to cause a decrease in ionic conductivity caused by the deterioration and degradation of the sulfide solid electrolyte. In particular, when the electrolyte layer contains PFPE having a non-polar group as an end group, the reaction of PFPE with the sulfide solid electrolyte is further suppressed, and a higher effect can be expected. In this regard, the above-mentioned E1 and E2 are each independently preferably a fluorine group. In one embodiment, E1-Rf1 and E2-Rf2 can each independently be a group selected from the group consisting of -CF3, -CF2CF3 and -CF2CF2CF3.

[0103] In the above formula (1), each occurrence of R F Each is independently a divalent fluoropolyether group.

[0104] R F Preferred is a group represented by formula (2).

[0105] -(OC6F 12 ) a -(OC5F 10 ) b -(OC4F8) c -(OC3R Fa 6) d -(OC2F4) e -(OCF2) f - (2)

[0106] [In formula (2): Each occurrence of R Fa are each independently a hydrogen atom, a fluorine atom or a chlorine atom,

[0107] a, b, c, d, e and f are each independently an integer of 0 to 200,

[0108] The sum of a, b, c, d, e and f is greater than 1,

[0109] The order of the repeating units indicated by a, b, c, d, e or f and enclosed in parentheses is arbitrary in the formula.

[0110] Among them, in all R Fa When it is a hydrogen atom or a chlorine atom, at least one of a, b, c, e and f is 1 or more.]

[0111] R Fa It is preferably a hydrogen atom or a fluorine atom, and more preferably a fluorine atom.

[0112] Preferably, a, b, c, d, e and f are each independently an integer of 0 to 100.

[0113] The sum of a, b, c, d, e and f is preferably 5 or more, more preferably 10 or more, 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, further preferably 60 or less, for example, 50 or less or 30 or less.

[0114] These repeating units can be linear or branched. For example,

[0115] -(OC6F 12)- can be any of -(OCF2CF2CF2CF2CF2CF2)-, -(OCF(CF3)CF2CF2CF2CF2)-, -(OCF2CF(CF3)CF2CF2CF2)-, -(OCF2CF2CF(CF3)CF2CF2CF2)-, -(OCF2CF2CF(CF3)CF2CF2)-, -(OCF2CF2CF2CF(CF3)CF2)-, -(OCF2CF2CF2CF(CF3)CF2)- and -(OCF2CF2CF2CF2CF(CF3))-.

[0116] -(OC5F 10 )- can be any of -(OCF2CF2CF2CF2CF2)-, -(OCF(CF3)CF2CF2CF2)-, -(OCF2CF(CF3)CF2CF2)-, -(OCF2CF2CF(CF3)CF2)-, -(OCF2CF2CF(CF3)CF2)- and -(OCF2CF2CF2CF(CF3))-.

[0117] -(OC4F8)- can be any one of -(OCF2CF2CF2CF2)-, -(OCF(CF3)CF2CF2)-, -(OCF2CF(CF3)CF2)-, -(OCF2CF2CF(CF3))-, -(OC(CF3)2CF2)-, -(OCF2C(CF3)2)-, -(OCF(CF3)CF(CF3))-, -(OCF(C2F5)CF2)- and -(OCF2CF(C2F5))-.

[0118] -(OC3F6)- (i.e., R Fa In the case of a fluorine atom), it may be any of -(OCF2CF2CF2)-, -(OCF(CF3)CF2)- and -(OCF2CF(CF3))-.

[0119] -(OC2F4)- can be any of -(OCF2CF2)- and -(OCF(CF3))-.

[0120] In one approach, each occurrence of R F Each independently may be a group represented by any one of the following formulae (2-1) to (2-5).

[0121] -(OC3F6) d -(OC2F4) e - (2-1)

[0122] [In formula (2-1), d is an integer of 1 to 200, and e is 0 or 1.]

[0123] -(OC4F8) c -(OC3F6) d-(OC2F4) e -(OCF2) f - (2-2)

[0124] [In formula (2-2), c and d are each independently an integer of 0 to 30,

[0125] e and f are each independently an integer of 1 to 200,

[0126] The sum of c, d, e and f is greater than 2,

[0127] The order of presence of the repeating units marked with the subscript c, d, e or f and enclosed in parentheses is arbitrary in the formula.]

[0128] -(R 6 -R 7 ) g - (2-3)

[0129] [In formula (2-3), R 6 For OCF2 or OC2F4,

[0130] R 7 is selected from OC2F4, OC3F6, OC4F8, OC5F 10 and OC6F 12 or a combination of two or three groups selected from these groups,

[0131] g is an integer from 2 to 100.]

[0132] -(OC6F 12 ) a -(OC5F 10 ) b -(OC4F8) c -(OC3F6) d -(OC2F4) e -(OCF2) f - (2-4)

[0133] [In formula (2-4), e is an integer of 1 to 200,

[0134] a, b, c, d and f are each independently an integer of 0 to 200,

[0135] The order of presence of the repeating units indicated by a, b, c, d, e or f and enclosed in parentheses is arbitrary in the formula.]

[0136] -(OC6F 12 ) a -(OC5F 10 ) b-(OC4F8) c -(OC3F6) d -(OC2F4) e -(OCF2) f - (2-5)

[0137] [In formula (2-5), f is an integer of 1 to 200,

[0138] a, b, c, d and e are each independently an integer of 0 to 200,

[0139] The order of presence of the repeating units indicated by a, b, c, d, e or f and enclosed in parentheses is arbitrary in the formula.]

[0140] In the above formula (2-1), d is preferably 5 to 200, more preferably 10 to 100, further preferably 15 to 50, for example, an integer of 25 to 35. The above formula (2-1) is preferably -(OCF2CF2CF2) d -or-(OCF(CF3)CF2) d -, more preferably -(OCF2CF2CF2) d In one embodiment, e is 0. In another embodiment, e is 1.

[0141] In the above formula (2-2), e and f are each independently preferably an integer of 5 to 200, more preferably an integer of 10 to 200. In addition, the sum of c, d, e and f is preferably 5 or more, more preferably 10 or more, for example, 15 or more or 20 or more. In one embodiment, the above formula (2-2) is preferably -(OCF2CF2CF2CF2) c -(OCF2CF2CF2) d -(OCF2CF2) e -(OCF2) f In another embodiment, formula (2-2) may be -(OC2F4) e -(OCF2) f -represented group.

[0142] In the above formula (2-3), R 6 Preferably, it is OC2F4. In the above (2-3), R 7It is preferably a group selected from OC2F4, OC3F6 and OC4F8 or a combination of two or three groups selected from these groups, and more preferably a group selected from OC3F6 and OC4F8. There is no particular limitation on the combination of two or three groups selected from OC2F4, OC3F6 and OC4F8, and examples thereof include: -OC2F4OC3F6-, -OC2F4OC4F8-, -OC3F6OC2F4-, -OC3F6OC3F6-, -OC3F6OC4F8-, -OC4F8OC4F8-, -OC4F8OC3F6-, -OC4F8OC2F4-, -OC2F4 OC2F4OC3F6-, -OC2F4OC2F4OC4F8-, -OC2F4OC3F6OC2F4-, -OC2F4OC3F6OC3F6-, -OC2F4OC4F8OC2F4-, -OC3F6OC2F4OC2F4-, -OC3F6OC2F4OC3F6-, -OC3F6OC3F6OC2F4-, and, -OC4F8OC2F4OC2F4-. In the above formula (2-3), g is preferably an integer greater than or equal to 3, and more preferably an integer greater than or equal to 5. The above g is preferably an integer less than or equal to 50. In the above formula (2-3), OC2F4, OC3F6, OC4F8, OC5F 10 and OC6F 12 It may be either a straight chain or a branched chain, preferably a straight chain. In this embodiment, the above formula (2-3) is preferably -(OC2F4-OC3F6) g -or-(OC2F4-OC4F8) g -.

[0143] In the above formula (2-4), e is preferably an integer of 1 to 100, more preferably an integer of 5 to 100. 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.

[0144] In the above formula (2-5), f is preferably an integer of 1 to 100, more preferably an integer of 5 to 100. 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.

[0145] In one embodiment, the above R F It is a group represented by the above formula (2-1).

[0146] In one embodiment, the above R F It is a group represented by the above formula (2-2).

[0147] In one embodiment, the above R FIt is a group represented by the above formula (2-3).

[0148] In one embodiment, the above R F It is a group represented by the above formula (2-4).

[0149] In one embodiment, the above R F It is a group represented by the above formula (2-5).

[0150] In R F In the embodiment of the present invention, the ratio of e to f (hereinafter referred to as "e / f ratio") can 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, lubricity and chemical stability are further improved. The smaller the e / f ratio, the further 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 improved. The larger the e / f ratio, the further the stability of the fluoropolyether structure is improved. In this case, the value of f is preferably 0.8 or more.

[0151] In one embodiment, the above R F It may be a group represented by the following formula (2-6).

[0152] -(OCF2CF2CF2) a -(OCF(CF3)CF2) b -(OCF2CF(CF3)) c -(OCF2CF2) d -(OCF(CF3)) e -(OCF2) f - (2-6)

[0153] [In formula (2-6), a, b, c, d, e and f are each independently an integer of 0 to 200,

[0154] The sum of a, b, c, d, e and f is greater than 1,

[0155] The order of presence of the repeating units indicated by a, b, c, d, e or f and enclosed in parentheses is arbitrary in the formula.]

[0156] In one embodiment, the above R F It may be a group represented by the following formula (2-7).

[0157] -(OCF2CF2) d -(OCF(CF3)) e -(OCF2) f - (2-7)

[0158] [In formula (2-7), d, e and f are each independently an integer of 0 to 200,

[0159] The sum of d, e and f is greater than 1,

[0160] The order of presence of the repeating units marked with d, e or f and enclosed in parentheses is arbitrary in the formula.]

[0161] In R F In the formula (hereinafter referred to as "d / f ratio"), the ratio of d to f can 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, lubricity and chemical stability are further improved. The smaller the d / f ratio, the further 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 improved. The larger the d / f ratio, the further the stability of the fluoropolyether structure is improved. In this case, the value of f is preferably 0.8 or more.

[0162] In the above-mentioned fluoropolyether group-containing compounds, R F The number average molecular weight of the part is not particularly limited, and 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 is 19 The value measured by F-NMR.

[0163] The content of PFPE in the electrolyte layer 20 is not particularly limited and can be appropriately selected according to the target withstand voltage and ion conductivity. In particular, when the electrolyte layer 20 contains the above-mentioned PFPE at 1 volume % or more and 25 volume % or less, a higher effect is easily obtained. For example, the electrolyte layer 20 may contain the above-mentioned PFPE at 1 volume %, 3 volume %, 5 volume %, 7 volume % or more, or 8 volume % or more and 25 volume %, 24 volume %, 22 volume %, 20 volume %, 18 volume %, 16 volume %, 14 volume % or less, or 12 volume % or less.

[0164] It should be noted that the volume ratio of PFPE in the electrolyte layer 20 is determined as follows. That is, the volume of the electrolyte layer 20 is measured in advance using an optical microscope or SEM. Regarding the volume of PFPE contained, the electrolyte layer 20 can be cleaned with a solvent (a solvent that can dissolve PFPE and does not dissolve other electrode materials), and the filtrate in which PFPE is dissolved can be recovered by suction filtration, and the recovered solvent can be analyzed by GC-MS to determine that in the case of a solvent with a boiling point significantly different from that of PFPE, the volume of PFPE can be directly measured by extraction by distillation. Thus, the volume ratio of PFPE in the volume of the electrolyte layer 20 measured in advance is calculated.

[0165] 1.2.3 Binder

[0166] The binder that can be contained in the electrolyte layer 20 can be appropriately selected from the binders exemplified as the binders that can be contained in the positive electrode active material layer 11 .

[0167] 1.3 Negative electrode

[0168] The negative electrode 30 has no particular limitation on its structure as long as it can properly function as the negative electrode of the secondary battery. Figure 1 As shown, the negative electrode 30 may include a negative electrode active material layer 31 and a negative electrode collector 32 .

[0169] 1.3.1 Negative electrode active material layer

[0170] The negative electrode active material layer 31 contains at least a negative electrode active material, and may optionally contain an electrolyte, a conductive aid, a binder, and the like. The negative electrode active material layer 31 may contain various additives in addition to this. For example, it may contain a dispersant, the above-mentioned perfluoropolyether, and the like. The content of each component in the negative electrode active material layer 31 can be appropriately determined according to the target battery performance. For example, the entire negative electrode active material layer 31 (the entire solid component) is set to 100 mass%, and the content of the negative electrode active material may be 40 mass% or more, 50 mass% or more, 60 mass% or more, or 70 mass% or more, or 100 mass% or less or 90 mass% or less. The shape of the negative electrode active material layer 31 is not particularly limited, for example, it may be a sheet-shaped negative electrode active material layer having a substantially flat surface. The thickness of the negative electrode active material layer 31 is not particularly limited, for example, it may be 0.1 μm or more, 1 μm or more, or 10 μm or more, or it may be 2 mm or less, 1 mm or less, or 500 μm or less.

[0171] As the negative electrode active material, various materials can be used whose potential (charge and discharge potential) of absorbing and releasing specified carrier ions (for example, lithium ions) is lower than that of the above-mentioned positive electrode active material. For example, the negative electrode active material can 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, etc. The negative electrode active material can be used alone or in combination of two or more.

[0172] The shape of the negative electrode active material can be any shape that is generally used as a negative electrode active material for a battery. The negative electrode active material can be, for example, in a particle shape. The negative electrode active material can be hollow, have voids, or be porous. The negative electrode active material can be a primary particle, or a secondary particle obtained by agglomerating multiple primary particles. The average particle size D50 of the negative electrode active material can be, for example, greater than 1 nm, greater than 5 nm, or greater than 10 nm, and can also be less than 500 μm, less than 100 μm, less than 50 μm, or less than 30 μm. Alternatively, the negative electrode active material can be in the form of a sheet (foil, film) such as lithium foil. That is, the negative electrode active material layer 31 can be composed of sheets of negative electrode active material.

[0173] The electrolyte that may be included in the negative electrode active material layer 31 may be a solid electrolyte, a liquid electrolyte (electrolyte), or a combination thereof. In particular, when the negative electrode active material layer 31 contains at least a solid electrolyte as an electrolyte, a higher effect is easily obtained. The negative electrode active material layer 31 may contain a solid electrolyte, especially a sulfide solid electrolyte, and further especially a sulfide solid electrolyte containing Li2S-P2S5. As conductive aids that may be included in the negative electrode active material layer 31, the above-mentioned carbon materials, the above-mentioned metal materials, etc. may be listed. The binder that may be included in the negative electrode active material layer 31 may be appropriately selected, for example, from the binders exemplified as the binders that may be included in the above-mentioned positive electrode active material layer 11.

[0174] 1.3.2 Negative electrode collector

[0175] like Figure 1As shown, the negative electrode 30 may have a negative electrode collector 32 in contact with the above-mentioned negative electrode active material layer 31. The negative electrode collector 32 may be any of the collectors generally used as negative electrode collectors of batteries. In addition, the negative electrode collector 32 may be in the form of foil, plate, mesh, punched metal, foam, etc. The negative electrode collector 32 may be a metal foil or a metal mesh, or may be a carbon sheet. In particular, the metal foil has excellent operability. The negative electrode collector 32 may be composed of a plurality of foils and sheets. As metals constituting the negative electrode collector 32, there may be listed: Cu, Ni, Cr, Au, Pt, Ag, Al, Fe, Ti, Zn, Co, stainless steel, etc. In particular, from the viewpoint of ensuring reduction resistance and the viewpoint of not being easily alloyed with lithium, the negative electrode collector 32 may contain at least one metal selected from Cu, Ni and stainless steel. The negative electrode collector 32 may have a coating on its surface for the purpose of adjusting resistance, etc. In addition, the negative electrode current collector 32 may be formed by plating or vapor-depositing the above metal on a metal foil or a substrate. In addition, when the negative electrode current collector 32 is composed of a plurality of metal foils, a certain layer may be provided between the plurality of metal foils. 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 less, or 1 mm or less or 100 μm or less.

[0176] 1.4 Other components

[0177] In the secondary battery 100, each of the above-mentioned structures can be housed inside the outer casing. The outer casing can be any of the outer casings known as the outer casing of the battery. In addition, a plurality of secondary batteries 100 can be electrically connected arbitrarily, and can be arbitrarily overlapped to form a battery pack. In this case, the battery pack can be housed inside a known battery casing. The secondary battery 100 can have obvious structures such as necessary terminals in addition. As the shape of the secondary battery 100, for example, coin-shaped, laminated, cylindrical, and square shapes can be listed.

[0178] 2. Method for manufacturing secondary battery

[0179] 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 following method, and each layer can be formed by dry molding or the like, for example.

[0180] (1) The negative electrode active material constituting the negative electrode active material layer is dispersed in a solvent to obtain a negative electrode slurry. The solvent used in this case is not particularly limited, and water, various organic solvents, or N-methylpyrrolidone (NMP) can be used. Then, the negative electrode slurry is coated on the surface of the negative electrode collector or the electrolyte layer described later using a doctor blade, and then dried to form a negative electrode active material layer on the surface of the negative electrode collector or the electrolyte layer to prepare a negative electrode. Here, the negative electrode active material layer can be pressed into shape.

[0181] (2) The positive electrode active material constituting the positive electrode active material layer is dispersed in a solvent to obtain a positive electrode slurry. The solvent used in this case is not particularly limited, and water, various organic solvents, or N-methylpyrrolidone (NMP) can be used. Then, the positive electrode slurry is coated on the surface of the positive electrode collector or the electrolyte layer described later using a doctor blade, and then dried to form a positive electrode active material layer on the surface of the positive electrode collector or the electrolyte layer to prepare a positive electrode. Here, the positive electrode active material layer can be pressed into shape.

[0182] (3) The layers are stacked in such a manner that the electrolyte layer is sandwiched between the negative electrode and the positive electrode to obtain a laminate having a negative electrode collector, a negative electrode active material layer, an electrolyte layer, a positive electrode active material layer and a positive electrode collector in sequence. The electrolyte layer may be, for example, an electrolyte layer formed by molding an electrolyte mixture containing a sulfide solid electrolyte, PFPE and a binder, or an electrolyte layer obtained by press molding. Here, the laminate may be further press molded. Other components such as terminals may be installed on the laminate as needed.

[0183] (4) The stacked body is housed in a battery case and sealed to obtain a secondary battery.

[0184] 3. Supplement

[0185] The technology of the present invention can be applied not only to lithium ion secondary batteries but also to secondary batteries other than lithium ion secondary batteries (for example, sodium ion secondary batteries), etc. However, when the technology of the present invention is applied to lithium ion secondary batteries, a higher effect is likely to be exerted.

[0186] [Example]

[0187] Hereinafter, the technology of the present invention will be described in further detail while showing examples, but the technology of the present invention is not limited to the following examples.

[0188] 1. Fabrication of electrolyte layer (diaphragm layer)

[0189] A sulfide solid electrolyte (LiI-LiBr-Li2S-P2S5), a binder (PVdF) and an additive (styrene-butadiene rubber (SBR), polyethylene oxide (PEO) or PFPE) are added to an organic solvent, and they are kneaded using an ultrasonic homogenizer to obtain an electrolyte slurry. The obtained electrolyte slurry is coated on an Al foil and dried to form an electrolyte layer on the Al foil. The volume ratio (volume %) of the sulfide solid electrolyte, binder and additive contained in the electrolyte layer is shown in Table 1 below. In addition, PFPE is a liquid compound having a chemical structure represented by the following formula (I) (m / n is 1.2, the number average molecular weight is 5120, and the terminal R exists in an average ratio of 1:0.17, CF3 and CF2CF3).

[0190]

[0191] 2. Determination of electrolyte layer thickness

[0192] The obtained electrolyte layer and Al foil were punched out to φ11.28 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.

[0193] 3. Evaluation of voltage resistance

[0194] The Al foil was removed from the above-mentioned measurement sample punched out with a diameter of 11.28 mm to obtain an electrolyte layer, and then the electrolyte layer was sandwiched between SUS electrodes. In this state, the voltage was swept from 0 V to 110 V. At this time, if Figure 2 As shown in the figure, the voltage at which the current rises and short-circuits is measured as the "withstand voltage (V)".

[0195] 4. Evaluation of ionic conductivity

[0196] Prepare two samples punched out with a diameter of 11.28 mm, attach the electrolyte layers to each other, remove the two Al foils, and then sandwich them with carbon-coated Al foils, so that the SUS electrodes can collect current on both sides, and then perform resistance measurement using the AC impedance method. Read the resistance value of the real axis intercept at 300 kHz from the obtained Nyquist plot, and calculate the ion conductivity based on the resistance value and the thickness of the electrolyte layer.

[0197] 5. Evaluation results

[0198] The evaluation results are shown in the following Table 1. In Table 1, the evaluation results of ion conductivity are shown relative to the ion conductivity of Comparative Example 1 being 100.

[0199] [Table 1]

[0200]

[0201] From the results shown in Table 1, we can see the following.

[0202] (1) In Comparative Example 1, the electrolyte layer does not contain any additive component, and sufficient withstand voltage cannot be obtained.

[0203] (2) For Comparative Examples 2 to 4, the electrolyte layer contains a large amount of PVdF and SBR, so although the voltage resistance of the electrolyte layer is improved, the ion conductivity of the electrolyte layer is reduced. It can be seen that PVdF and SBR both function as binders, but even if the binder is added to the electrolyte layer, it is difficult to achieve both voltage resistance and ion conductivity.

[0204] (3) In Comparative Example 5, since the electrolyte layer contained PEO as an additive component, the withstand voltage of the electrolyte layer was reduced and the ion conductivity was also reduced.

[0205] (4) In contrast, in Examples 1 to 5, the electrolyte layer contains PFPE as an additive, which can improve the voltage resistance of the electrolyte layer and maintain sufficient ion conductivity. It is believed that PFPE has excellent insulation and low reactivity with sulfide solid electrolytes. It can be said that a secondary battery having an electrolyte layer with high voltage resistance and ion conductivity as in Examples 1 to 5 is likely to have low resistance and battery performance is likely to be improved.

[0206] It should be noted that, in the above-mentioned embodiments, PFPE having a specific chemical structure is exemplified, but the chemical structure of PFPE is not limited thereto. In addition, in the above-mentioned embodiments, a sulfide solid electrolyte having a specific chemical composition is exemplified as the sulfide solid electrolyte, but the chemical composition of the sulfide solid electrolyte is not limited thereto. In addition, in the above-mentioned embodiments, PVdF is exemplified as the binder, but the binder that can be included in the electrolyte layer is not limited to PVdF, and various binders other than PVdF may be used, or no binder may be used.

[0207] As described above, it is considered that a secondary battery having the following configuration can easily achieve both the voltage resistance and ion conductivity of the electrolyte layer and can exhibit excellent performance.

[0208] (1) It has a positive electrode, an electrolyte layer and a negative electrode.

[0209] (2) The electrolyte layer contains a sulfide solid electrolyte and a predetermined perfluoropolyether.

[0210] Explanation of symbols

[0211] 10 Positive electrode

[0212] 11Positive electrode active material layer

[0213] 12Positive electrode collector

[0214] 20 electrolyte layer

[0215] 30 negative electrode

[0216] 31 Negative electrode active material layer

[0217] 32 Negative electrode collector

[0218] 100 Secondary Batteries

Claims

1. A secondary battery comprising a positive electrode, an electrolyte layer and a negative electrode, The electrolyte layer comprises a sulfide solid electrolyte and a perfluoropolyether represented by the following formula (1): E1-Rf1-R F -O-Rf2-E2 (1) In formula (1), Rf1 and Rf2 are each independently a C1-16 divalent alkylene group which may be substituted with one or more fluorine atoms, E1 and E2 are each independently a monovalent group selected from the group consisting of a fluoro 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 It is a divalent fluoropolyether group.

2. The secondary battery according to claim 1, wherein The R F is a group represented by formula (2), -(OC6F 12 ) a -(OC5F 10 ) b -(OC4F8) c -(OC3R Fa 6) d -(OC2F4) e -(OCF2) f - (2) In formula (2), each occurrence of R Fa are each independently a hydrogen atom, a fluorine atom or a chlorine atom, 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 greater than 1, The order of the repeating units indicated by a, b, c, d, e or f and enclosed in parentheses is arbitrary in the formula. Among them, in all R Fa When it is a hydrogen atom or a chlorine atom, at least one of a, b, c, e and f is 1 or more.

3. The secondary battery according to claim 2, wherein: The R Fa A fluorine atom.

4. The secondary battery according to claim 3, wherein Each occurrence of R F are each independently a group represented by the following formula (2-1), (2-2), (2-3), (2-4) or (2-5), -(OC3F6) d -(OC2F4) e - (2-1) In formula (2-1), d is an integer of 1 to 200, e is 0 or 1, -(OC4F8) c -(OC3F6) d -(OC2F4) e -(OCF2) f - (2-2) In formula (2-2), c and d are each independently an integer of 0 to 30, e and f are each independently an integer of 1 to 200, The sum of c, d, e and f is an integer from 10 to 200, The order of the repeating units marked with the subscript c, d, e or f and enclosed in parentheses is arbitrary in the formula. -(R 6 -R 7 ) g - (2-3) In formula (2-3), R 6 For OCF2 or OC2F4, R 7 is selected from OC2F4, OC3F6, OC4F8, OC5F 10 and OC6F 12 or a combination of two or three groups selected from these groups, g is an integer from 2 to 100, -(OC6F 12 ) a -(OC5F 10 ) b -(OC4F8) c -(OC3F6) d -(OC2F4) e -(OCF2) f - (2-4) In formula (2-4), e is an integer of 1 to 200, a, b, c, d and f are each independently an integer of 0 to 200, The order of the repeating units indicated by a, b, c, d, e or f and enclosed in parentheses is arbitrary in the formula. -(OC6F 12 ) a -(OC5F 10 ) b -(OC4F8) c -(OC3F6) d -(OC2F4) e -(OCF2) f - (2-5) In formula (2-5), f is an integer greater than or equal to 1 and less than or equal to 200, a, b, c, d and e are each independently an integer of 0 to 200, The order of presence of the repeating units indicated by a, b, c, d, e or f and enclosed in parentheses in the formula is arbitrary.

5. The secondary battery according to claim 4, wherein The R F is a group represented by the following formula (2-6), -(OCF2CF2CF2) a -(OCF(CF3)CF2) b -(OCF2CF(CF3)) c -(OCF2CF2) d -(OCF(CF3)) e -(OCF2) f - (2-6) In formula (2-6), 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 greater than 1, The order of presence of the repeating units indicated by a, b, c, d, e or f and enclosed in parentheses in the formula is arbitrary.

6. The secondary battery according to claim 4, wherein The R F is a group represented by the following formula (2-7), -(OCF2CF2) d -(OCF(CF3)) e -(OCF2) f - (2-7) In formula (2-7), d, e and f are each independently an integer of 0 to 200, The sum of d, e and f is greater than 1, The order of presence of the repeating units indicated by d, e or f and enclosed in parentheses is arbitrary in the formula.

7. The secondary battery according to any one of claims 1 to 6, wherein The E1-Rf1 and the E2-Rf2 are each independently a group selected from the group consisting of -CF3, -CF2CF3 and -CF2CF2CF3.

8. The secondary battery according to any one of claims 1 to 7, wherein The electrolyte layer contains 1 volume % or more and 25 volume % or less of the perfluoropolyether.

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