WO2020110994A1

WO2020110994A1 - Composite solid electrolyte, and composite solid electrolyte secondary battery

Info

Publication number: WO2020110994A1
Application number: PCT/JP2019/045953
Authority: WO
Inventors: 克人三浦; 琢寛幸; 康雄菊園; 託也三輪; 雅人田渕
Original assignee: 株式会社大阪ソーダ; 技術研究組合リチウムイオン電池材料評価研究センター
Priority date: 2018-11-26
Filing date: 2019-11-25
Publication date: 2020-06-04
Also published as: CN113273010A; JPWO2020110994A1

Abstract

Provided is a novel composite solid electrolyte that causes a solid electrolyte secondary battery to exhibit excellent charging/discharging properties. This composite solid electrolyte contains an inorganic solid electrolyte and a polymer solid electrolyte including a branched-type polyether.

Description

Composite solid electrolyte and composite solid electrolyte secondary battery

The present invention relates to a composite solid electrolyte and a composite solid electrolyte secondary battery.

In the past, non-aqueous electrolyte secondary batteries, typified by lithium-ion batteries, have been used as electrolytes in the form of solutions or pastes because of their ionic conductivity. However, since there is a risk of equipment damage due to liquid leakage, various safety measures are required, which is a barrier to the development of large batteries.

On the other hand, solid electrolytes in which solid electrolytes such as polymer solid electrolytes and inorganic solid electrolytes are solidified have been proposed. Polymer solid electrolytes are generally superior in flexibility, bending workability, and moldability, and have the advantage of increasing the degree of freedom in the design of the device to which they are applied, but due to poor load characteristics and low-temperature characteristics, high temperature It has the drawback of being limited to operating battery applications. On the other hand, the inorganic solid electrolyte is higher in ion conductivity than the polymer solid electrolyte, but the electrolyte is crystalline or amorphous, and it is difficult to alleviate the volume change due to the positive and negative electrode active materials during charge and discharge, and However, since the interface resistance between the electrode and the electrolyte is high, there is a problem that the charge/discharge characteristics are insufficient.

As a method of lowering the interfacial resistance between the electrode and the electrolyte, it is known to improve the binding property between the electrolyte and the electrode interface by mixing a polymer with the inorganic solid electrolyte. For example, in Patent Document 1, a hydrogenated polymer such as hydrogenated styrene-butadiene rubber as a branched polymer is used as a binder in a sulfide-based solid electrolyte, but such a polymer suppresses a decrease in ion conductivity. I can't do it. Further, in Patent Documents 2 and 3, polyethylene oxide (polyethylene glycol) having relatively high ionic conductivity is used, but polyethylene oxide has high crystallinity, and the melting point of the polymer is around 60° C. Low ionic conductivity. In addition, there is a problem that when heated above the melting point, it softens, the strength cannot be maintained, and a short circuit due to breakage easily occurs.

International Publication No. 2013-1623 JP-A-3-129603 JP, 2010-33918, A

The main object of the present invention is to provide a novel composite solid electrolyte that allows a solid electrolyte secondary battery to exhibit excellent charge/discharge characteristics. A further object of the present invention is to provide a composite solid electrolyte secondary battery containing the composite solid electrolyte.

The present inventor has diligently studied to solve the above problems. As a result, they have found that a composite solid electrolyte containing an inorganic solid electrolyte and a polymer solid electrolyte containing a branched polyether exhibits excellent charge/discharge characteristics for a solid electrolyte secondary battery. The present invention has been completed by further studies based on such findings.

That is, the present invention provides the inventions of the following modes.
Item 1. A composite solid electrolyte containing an inorganic solid electrolyte and a polymer solid electrolyte containing a branched polyether.
Item 2. Item 2. The composite solid electrolyte according to Item 1, wherein the branched polyether includes a constituent unit formed of an ether compound having an ethylene oxide unit in a side chain.
Item 3. Item 3. The composite solid electrolyte according to Item 1 or 2, wherein the branched polyether includes a constituent unit formed of at least one selected from the group consisting of allyl glycidyl ether, acrylic acid glycidyl ether, and methacrylic acid glycidyl ether. ..
Item 4. Item 4. The composite solid electrolyte according to any one of Items 1 to 3, wherein the branched polyether is crosslinked.
Item 5. Item 5. The composite solid electrolyte according to any one of Items 1 to 4, wherein the inorganic solid electrolyte is an oxide solid electrolyte or a sulfide solid electrolyte.
Item 6. Item 7. A composite solid electrolyte secondary battery containing the composite solid electrolyte according to any one of items 1 to 5.

According to the present invention, it is possible to provide a novel composite solid electrolyte that allows a solid electrolyte secondary battery to exhibit excellent charge/discharge characteristics. Furthermore, according to the present invention, it is also possible to provide a composite solid electrolyte secondary battery containing the composite solid electrolyte.

The composite solid electrolyte of the present invention is characterized by containing an inorganic solid electrolyte and a polymer solid electrolyte containing a branched polyether. Since the composite solid electrolyte of the present invention has such a configuration, when applied as a solid electrolyte of a solid electrolyte secondary battery, the solid electrolyte secondary battery can exhibit excellent charge/discharge characteristics. .. More specifically, the composite solid electrolyte of the present invention, in addition to the inorganic solid electrolyte, contains a polymer solid electrolyte containing a branched polyether, the solid electrolyte is formed only by the inorganic solid electrolyte. It is considered that the contact area at the interface between the electrode material layer and the solid electrolyte layer is larger than that in the case where the electrode material layer and the solid electrolyte layer are large, and as a result, the interface resistance between the electrode and the electrolyte is reduced and excellent charge/discharge characteristics are exhibited. .. Further, even in the composite solid electrolyte, it is considered that the polymer solid electrolyte is brought into close contact with the inorganic solid electrolyte to reduce the resistance inside the composite solid electrolyte. Further, the solid electrolyte secondary battery may be used in a high temperature environment (for example, a high temperature environment of 100° C. or higher), but by using the composite solid electrolyte of the present invention, excellent charge/discharge characteristics are exhibited in the high temperature environment. To be done. Hereinafter, the composite solid electrolyte of the present invention and the solid electrolyte secondary battery using the same will be described in detail.

Note that, in the present specification, the numerical value connected by “to” means a numerical value range including the numerical values before and after “to” as the lower limit value and the upper limit value. When a plurality of lower limit values and a plurality of upper limit values are described separately, any lower limit value and upper limit value can be selected and connected by "...".

The composite solid electrolyte of the present invention contains at least an inorganic solid electrolyte and a polymer solid electrolyte containing a branched polyether. Specifically, the composite solid electrolyte of the present invention is a mixture of at least an inorganic solid electrolyte and a polymer solid electrolyte containing a branched polyether.

The branched polyether may include a crosslinked product.

The branched polyether preferably contains a constitutional unit formed from an epoxy compound having an ethylene oxide unit in its side chain. That is, the branched polyether is preferably a polymer having at least a monomer of an epoxy compound having an ethylene oxide unit in its side chain.

Examples of the epoxy compound having an ethylene oxide unit in the side chain include a monomer represented by the following formula (2), which is represented by the following formula (2) and, if necessary, the following formula (1) and the following formula (3). The branched polyether using the represented monomer is the polyether (i) having an ethylene oxide unit in the side chain. The monomers represented by the formulas (1) to (3) may be used alone or in combination of two or more.

[In the formula (2), R is —CH ₂ O(CH ₂ CH ₂ O) _n R ⁴ , R ⁴ is an alkyl group having 1 to 6 carbon atoms, and n is a number of 0 to 12]. ]

[In the formula (3), R ⁵ represents a group containing an ethylenically unsaturated group. ]

Examples of the monomer of the formula (3) include allyl glycidyl ether, 4-vinylcyclohexyl glycidyl ether, α-terpinyl glycidyl ether, cyclohexenyl methyl glycidyl ether, p-vinyl benzyl glycidyl ether, allyl phenyl glycidyl ether, vinyl glycidyl. Ether, 3,4-epoxy-1-butene, 3,4-epoxy-1-pentene, 4,5-epoxy-2-pentene, 1,2-epoxy-5,9-cyclododecanediene, 3,4- Epoxy-1-vinylcyclohexene, 1,2-epoxy-5-cyclooctene, glycidyl acrylate, glycidyl methacrylate, glycidyl sorbate, glycidyl cinnamate, glycidyl crotonic acid, and glycidyl-4-hexenoate are used. Preferred are allyl glycidyl ether, acrylic acid glycidyl ether, and methacrylic acid glycidyl ether.

The polyether (i) having an ethylene oxide unit in its side chain can be synthesized, for example, as follows. Coordination anion initiators such as organoaluminum-based catalyst systems, organozinc-based catalyst systems, and organotin-phosphate ester condensate catalyst systems as ring-opening polymerization catalysts, or potassium containing K ⁺ in the counterion Anionic initiators such as alkoxides, potassium diphenylmethyl, and potassium hydroxide are used to react each monomer in the presence or absence of a solvent at a reaction temperature of 10 to 120° C. under stirring to obtain a polyether (i. ) Is obtained. From the viewpoint of the degree of polymerization or the properties of the resulting copolymer, a coordinating anion initiator is preferable, and an organotin-phosphate ester condensate catalyst system is particularly preferable because it is easy to handle.

In the polyether (i) having an ethylene oxide unit in its side chain, a repeating unit (A) derived from the monomer of formula (1), a repeating unit (B) derived from the monomer of formula (2), The molar ratio of the repeating unit (C) derived from the monomer of the formula (3) is 95 to 5 mol% of (A), 5 to 95 mol% of (B), and 0 to 20 mol% of (C). Suitable, preferably (A) 92 to 9 mol %, (B) 7 to 90 mol %, and (C) 1 to 15 mol %, more preferably (A) 88 to 18 mol %, (B) 10 ˜80 mol %, and (C) 2 to 15 mol %. When the content of the repeating unit (A) is 95 mol% or less, the glass transition temperature is not increased and the oxyethylene chain is not crystallized, and as a result, it is preferable in terms of ion conductivity.

Specific examples of the polyether (i) having an ethylene oxide unit in the side chain include ethylene oxide/diethylene glycol methyl glycidyl ether/allyl glycidyl ether terpolymer, ethylene oxide/diethylene glycol methyl glycidyl ether/glycidyl methacrylate terpolymer, Examples thereof include ethylene oxide/diethylene glycol methyl glycidyl ether/glycidyl acrylate terpolymer.

The weight average molecular weight of the polyether (i) having an ethylene oxide unit in the side chain is not particularly limited, but may be 10,000 to 3,000,000, more preferably 50,000 to 2,500,000, and preferably 100,000 to 2,000,000. It is particularly preferable that The weight average molecular weight is calculated by gel permeation chromatography (GPC) using dimethylformamide (DMF) as a solvent, and is calculated in terms of standard polystyrene.

The polymer solid electrolyte of the branched polyether preferably contains a lithium salt compound. As the lithium salt compound, a lithium salt compound having a wide potential window, which is generally used for lithium ion batteries, is suitable. Examples of the lithium salt compound include LiBF ₄ , LiPF ₆ , LiClO ₄ , LiCF ₃ SO ₃ , LiN(CF ₃ SO ₂ ) ₂ (LiTFSI), LiN(SFO ₂ ) ₂ (LiFSI), LiN(C ₂ F _{5 ).} SO ₂ ) ₂ , LiN[CF ₃ SC(C ₂ F ₅ SO ₂ ) ₃ ] _{2 and the} like can be mentioned, but the invention is not limited thereto. These may be used alone or in combination of two or more.

When the solid polymer electrolyte contains lithium chloride, the content thereof is preferably such that the value of the number of moles of the lithium salt compound/the total number of moles of ether oxygen atoms of the branched polyether is 0.0001 to 5, and The range of 0.001 to 0.5 is preferable.

The branched polyether polymer solid electrolyte may contain a room temperature molten salt. The room-temperature molten salt is a salt that is at least partially in a liquid state at room temperature, and the room temperature refers to a temperature range in which the power supply is supposed to normally operate. The temperature range in which the power supply is supposed to normally operate has an upper limit of about 120° C., in some cases about 60° C., and a lower limit of about −40° C., in some cases about −20° C.

Normal temperature molten salt is also called ionic liquid, and quaternary ammonium organic cations of pyridine type, aliphatic amine type, and alicyclic amine type are known. Examples of the quaternary ammonium organic cation include imidazolium ions such as dialkylimidazolium and trialkylimidazolium, tetraalkylammonium ions, alkylpyridinium ions, pyrazolium ions, pyrrolidinium ions, piperidinium ions and the like. Particularly, an imidazolium cation is preferable.

Examples of the tetraalkylammonium ion include, but are not limited to, trimethylethylammonium ion, trimethylethylammonium ion, trimethylpropylammonium ion, trimethylhexylammonium ion, tetrapentylammonium ion, and triethylmethylammonium ion. is not.

The alkylpyridinium ion includes N-methylpyridinium ion, N-ethylpyridinium ion, N-propylpyridinium ion, N-butylpyridinium ion, 1-ethyl-2methylpyridinium ion, 1-butyl-4-methyl. Examples thereof include, but are not limited to, pyridinium ion and 1-butyl-2,4 dimethylpyridinium ion.

Examples of the imidazolium cation include 1,3-dimethylimidazolium ion, 1-ethyl-3-methylimidazolium ion, 1-methyl-3-ethylimidazolium ion, 1-methyl-3-butylimidazolium ion, 1- Butyl-3-methylimidazolium ion, 1,2,3-trimethylimidazolium ion, 1,2-dimethyl-3-ethylimidazolium ion, 1,2-dimethyl-3-propylimidazolium ion, 1-butyl- 2,3-Dimethylimidazolium ion and the like can be mentioned, but the present invention is not limited thereto.

The room temperature molten salt having these cations may be used alone or in combination of two or more kinds.

When the polymer solid electrolyte contains a room temperature molten salt, the content thereof is preferably 10 to 1000 parts by mass, more preferably 20 to 500 parts by mass with respect to 100 parts by mass of the branched polyether.

The solid polymer electrolyte may include a plasticizer in addition to the branched polyether. The plasticizer is not particularly limited, but dicyano compounds and branched ether compounds are preferable. When a plasticizer is added, it is preferable to crosslink the branched polyether. This cross-linking is a chemical cross-linking and can suppress the outflow of the plasticizer from the inside of the electrode.

Examples of dicyano compounds include succinonitrile, glutaronitrile, adiponitrile, 1,5-dicyanopentane, 1,6-dicyanohexane, 1,7-dicyanoheptane, and 1,8-dicyanooctane. Examples of branched ether compounds include the following multi-branched ether compounds.

When the solid polymer electrolyte contains a plasticizer, the content of the plasticizer is preferably 10 to 1000 parts by mass, more preferably 20 to 500 parts by mass with respect to 100 parts by mass of the branched polyether.

Further, examples of the inorganic solid electrolyte include oxide-based solid electrolytes and sulfide-based solid electrolytes. In the composite solid electrolyte of the present invention, the inorganic solid electrolyte is contained, for example, in the form of particles, and has a structure in which the particles of the inorganic solid electrolyte are adhered to each other by the polymer solid electrolyte.

The oxide solid electrolyte is particularly limited as long as it contains oxygen, has ion conductivity of a metal belonging to Group 1 or 2 of the periodic table, and has electronic insulation. Not a thing.

Specific examples of the compound forming the oxide-based solid electrolyte include Li _x La _y TiO ₃ [x=0.3 to 0.7, y=0.3 to 0.7] (LLT), Li _x La _y Zr _z M _m O _n (M is at least one element of Al, Mg, Ca, Sr, V, Nb, Ta, Ti, Ge, In, Sn, and x satisfies 5≦x≦10, and y satisfies 1 ≦ y ≦ 4, z satisfies 1 ≦ z ≦ 4, m satisfies 0 ≦ m ≦ 2, n satisfies 5 ≦ n ≦ 20.) Li x B y M z O n ( wherein Medium M is at least one element of C, S, Al, Si, Ga, Ge, In, Sn, x satisfies 0≦x≦5, y satisfies 0≦y≦1, and z is 0. meet ≦ z ≦ 1, n satisfies 0 ≦ n ≦ 6.), Li x (Al, Ga) y (Ti, Ge) z Si a P m O n ( however, 1 ≦ x ≦ 3,0 ≦ y≦1, 0≦z≦2, 0≦a≦1, 1≦m≦7, 3≦n≦13), Li _(3-2x) M _x DO (x is a number from 0 to 0.1 _). , M represents a divalent metal atom, D represents a halogen atom or a combination of two or more kinds of halogen atoms), Li _x Si _y O _z (1≦x≦5, 0<y≦3, 1) ≦z≦10), Li _x S _y O _z (1≦x≦3, 0<y≦2, 1≦z≦10), Li ₃ BO ₃ —Li ₂ SO ₄ , Li ₂ O—B ₂ O ₃ -P ₂ O ₅ , Li ₂ O-SiO ₂ , Li ₆ BaLa ₂ Ta ₂ O ₁₂ , Li ₃ PO _(4-3/2w) N _w (w is w<1), LISON (Lithium superionic conductor) type Li _3.5 Zn _0.25 GeO ₄ having a crystal structure, La _0.55 Li _0.35 TiO ₃ having a perovskite type crystal structure, LiTi ₂ P ₃ O ₁₂ having a NASICON (Naturium super ionic conductor) type crystal structure, Li _{(1+x+y) )} (Al, Ga) _x (Ti, Ge) _(2-x) Si _y P _(3-y) O ₁₂ (where 0≦x≦1, 0≦y≦1), Li having a garnet-type crystal structure ₇ La ₃ Zr _₂ O1 _2, and the like. A phosphorus compound containing Li, P and O is also desirable. For example, lithium phosphate (Li ₃ PO ₄ ), LiPON and LiPOD (D is Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zr, Nb) in which a part of oxygen of lithium phosphate is replaced with nitrogen. , Mo, Ru, Ag, Ta, W, Pt, Au and the like) and the like. LiAON (A is at least one selected from Si, B, Ge, Al, C, Ga, etc.) and the like can also be preferably used.

Among them, Li _x La _y TiO ₃ [x=0.3 to 0.7, y=0.3 to 0.7] (LLT), Li _x La _y Zr _z M _m O _n (M is Al, Mg , Ca, Sr, V, Nb, Ta, Ti, Ge, In, Sn, and at least one element, x satisfies 5≦x≦10, y satisfies 1≦y≦4, and z is 1 ≦z≦4, m satisfies 0≦m≦2, and n satisfies 5≦n≦20), Li ₇ La ₃ Zr ₂ O ₁₂ (LLZ), Li ₃ BO ₃ , Li ₃ BO ₃ _{_{_{-Li 2 SO 4, Li 3 BO}}} 3 -Li 2 CO 3, Li x (Al, Ga) y (Ti, Ge) z Si a P m O n ( however, 1 ≦ x ≦ 3,0 ≦ y ≦ 1 , 0≦z≦2, 0≦a≦1, 1≦m≦7, 3≦n≦13) are preferable. These may be used alone or in combination of two or more.

The sulfide-based solid electrolyte is not particularly limited as long as it contains sulfur, has ionic conductivity of a metal belonging to Group 1 or 2 of the periodic table, and has electronic insulation. Not a thing. For example, a lithium ion conductive inorganic solid electrolyte satisfying the composition represented by the following formula can be given.

Li _a M _b P _c S _d A _e

In the formula, M represents an element selected from B, Zn, Sn, Si, Cu, Ga, Sb, Al and Ge. Among them, B, Sn, Si, Al and Ge are preferable, and Sn, Al and Ge are more preferable. A represents I, Br, Cl or F, preferably I or Br, and particularly preferably I. a to e indicate composition ratios of respective elements, and a:b:c:d:e satisfies 1 to 12:0 to 1:1:2 to 12:0 to 5. Further, a is preferably 1 to 9, more preferably 1.5 to 4. b is preferably 0 to 0.5. Further, d is preferably 3 to 7, and more preferably 3.25 to 4.5. Further, e is preferably 0 to 3, and more preferably 0 to 2.

In the formula, the composition ratio of Li, M, P, S and A is preferably b and e being 0, more preferably b=0, e=0 and the ratio of a, c and d (a:c). :D) is a:c:d=1 to 9:1:3 to 7, more preferably b=0, e=0 and a:c:d=1.5 to 4:1:3. It is 25 to 4.5.

When the inorganic solid electrolyte is in the form of particles, its particle size is, for example, 0.01 to 100 μm, preferably 0.1 to 20 μm.

In the composite solid electrolyte of the present invention, the mass ratio of the inorganic solid electrolyte and the polymer solid electrolyte is not particularly limited, from the viewpoint of more suitably exhibiting excellent charge and discharge characteristics in the solid electrolyte secondary battery, the inorganic solid The amount is preferably 0.1 to 1000 parts by mass, more preferably 0.5 to 500 parts by mass, and further preferably 1 to 400 parts by mass with respect to 100 parts by mass of the electrolyte.

Since the composite solid electrolyte of the present invention contains a polymer solid electrolyte in addition to the inorganic solid electrolyte, it can be suitably formed into a sheet, unlike the case where only the inorganic solid electrolyte is used. The thickness when the composite solid electrolyte of the present invention is applied to a solid electrolyte secondary battery is not particularly limited, but is, for example, about 0.01 to 1 mm, preferably about 0.05 to 0.3 mm.

Method for producing composite solid electrolyte The composite solid electrolyte of the present invention can be prepared by utilizing a conventionally known method. For example, a method of obtaining a composite solid electrolyte by dispersing an inorganic solid electrolyte in a solvent containing a branched polyether and a lithium salt compound to prepare a composite solid electrolyte slurry, spraying and drying the slurry in hot air, It can be produced by a method of heating and evaporating the solvent of the dispersion slurry under atmospheric pressure or a reduced pressure to dryness, or a method of applying the dispersion slurry to a current collector sheet or the like and drying it.

As the dispersion solvent, water, an organic solvent, or a mixture of these in any ratio can be used. Even if the obtained dispersion slurry is a uniform solution, even if the solute that does not dissolve in the dispersion solvent is an inorganic solid electrolyte and/or a polymer solid electrolyte of branched polyether, the above general preparation method is used. Can be prepared by In the composite solid electrolyte obtained by removing the dispersion solvent, it is desirable to remove the remaining solvent and water as much as possible. For example, it can be realized by evacuation under heating at 30° C. to 200° C. for 1 hour to 48 hours. Since the dried composite solid electrolyte of the present invention has ionic conductivity and binding property, the electrolyte powder itself can be pressure-molded and used as a solid electrolyte material. Furthermore, by performing the heat treatment under pressure, the porosity can be reduced and the particle interface adhesion can be increased. The organic solvent is preferably a polar solvent. Specifically, acetonitrile, ethyl alcohol, methyl alcohol, tetrahydrofuran, dimethylformamide, dimethylsulfoxide, dioxane, methyl ethyl ketone, methyl isobutyl ketone and the like are used alone or in combination. When the inorganic solid electrolyte alone is pressure-molded, it has almost no binding property, so that it becomes a thick-film electrolyte, but in the composite solid electrolyte, it is possible to manufacture a thinner solid electrolyte due to the binding property of the polymer solid electrolyte. is there.

Crosslinking of composite solid electrolyte The composite solid electrolyte can be crosslinked to increase the binding strength between the inorganic solid electrolyte and the polymer solid electrolyte in the composite solid electrolyte, and also the binding pressure and the deposition of dendride of the battery It is also possible to prevent a short circuit. As a cross-linking method, the cross-linking can be carried out by applying heat or irradiating active energy rays such as ultraviolet rays.

In the case of crosslinking by heat, a radical initiator selected from organic peroxides, azo compounds, etc. is used. As the organic peroxide, ketone peroxides, peroxyketals, hydroperoxides, dialkyl peroxides, diacyl peroxides, peroxyesters and the like which are commonly used for crosslinking are used, and azo compounds are azonitriles. Compounds, azoamide compounds, azoamidine compounds and the like which are usually used for crosslinking are used. Although the amount of the radical initiator added varies depending on the type, it is usually within the range of 0.1 to 10 parts by mass with 100 parts by mass of the branched polyether (ion conductive polymer).

As a radical initiator in the case of cross-linking irradiated with active energy rays, alkylphenone-based, benzophenone-based, acylphosphine oxide-based, titanocenes, triazines, bisimidazoles, oxime esters and the like are used. The addition amount of these radical polymerization initiators varies depending on the type, but is usually in the range of 0.01 to 5.0 parts by mass with 100 parts by mass of the branched polyether (ion conductive polymer).

In the present invention, a crosslinking aid may be used when the composite solid electrolyte is crosslinked. As a cross-linking aid, ethylene glycol diacrylate, ethylene glycol dimethacrylate, oligoethylene glycol diacrylate, oligoethylene glycol dimethacrylate, trimethylolpropane triacrylate, allyl methacrylate, allyl acrylate, diallyl malate, triallyl isocyanurate, maleimide, phenyl Maleimide, maleic anhydride and the like can be optionally used.

In the composite solid electrolyte secondary battery of the present invention, at least one of the positive electrode and the composite solid electrolyte, and between the negative electrode and the composite solid electrolyte, ionic conduction having an ethylene oxide unit in the side chain containing a lithium salt compound. A cross-linked film of a polymeric material may be placed. A crosslinked film of an ion conductive polymer material is a crosslinked film of a composition containing a lithium salt compound and an ion conductive polymer. By disposing the crosslinked film, the interfacial resistance of the electrode and the composite solid electrolyte can be further reduced.

The crosslinked film is formed by crosslinking at least a composition containing a lithium salt compound and an ion conductive polymer having an ethylene oxide unit in a side chain. That is, the crosslinked film is a crosslinked film of a composition containing a lithium salt compound and an ion conductive polymer. The lithium salt compound and the ion conductive polymer are as described above.

The content of the ion conductive polymer contained in the crosslinked film is 100 parts by mass of the entire crosslinked film, preferably 10 to 90 parts by mass, more preferably 20 to 80 parts by mass.

Content of lithium chloride contained in cross-linked film The number of moles of lithium salt compound/the total number of moles of ether oxygen atoms of the ion conductive polymer is preferably 0.0001 to 5, and more preferably 0.001 to 0. A range of 5 is good.

Further, the crosslinked film may contain a room temperature molten salt. The room temperature molten salt is as described above.

When the cross-linked film contains a room temperature molten salt, the content thereof is preferably 10 to 1000 parts by mass, more preferably 20 to 500 parts by mass with respect to 100 parts by mass of the ion conductive polymer.

The crosslinked film may contain a plasticizer and the like. The plasticizer is as described above.

When the cross-linked film contains a plasticizer, the content of the plasticizer is preferably 10 to 1000 parts by mass, more preferably 20 to 500 parts by mass with respect to 100 parts by mass of the ion conductive polymer.

A crosslinked film may be formed by adding a reaction initiator or a crosslinking aid to a composition containing a lithium salt compound and an ion conductive polymer. Examples of the reaction initiator include a thermal reaction initiator and a photoreaction initiator.

A radical initiator selected from organic peroxides, azo compounds, etc. is used as the thermal reaction initiator. As the organic peroxide, ketone peroxides, peroxyketals, hydroperoxides, dialkyl peroxides, diacyl peroxides, peroxyesters and the like which are commonly used for crosslinking are used, and azo compounds are azonitriles. Compounds, azoamide compounds, azoamidine compounds and the like which are usually used for crosslinking are used. Although the amount of the radical initiator added varies depending on the type, it is usually within the range of 0.1 to 10 parts by mass with 100 parts by mass of the ion conductive polymer.

Radical initiators such as alkylphenones, benzophenones, acylphosphine oxides, titanocenes, triazines, bisimidazoles, and oxime esters are used as photoreaction initiators. The addition amount of these radical polymerization initiators varies depending on the type, but is usually within the range of 0.01 to 5.0 parts by mass with 100 parts by mass of the ion conductive polymer.

As the cross-linking aid, ethylene glycol diacrylate, ethylene glycol dimethacrylate, oligoethylene glycol diacrylate, oligoethylene glycol dimethacrylate, trimethylolpropane triacrylate, allyl methacrylate, allyl acrylate, diallyl malate, triallyl isocyanurate, maleimide , Phenylmaleimide, maleic anhydride, etc. can be optionally used.

An organic solvent may be added to the composition containing the lithium salt compound and the ion conductive polymer, and as the organic solvent, toluene, xylene, benzene, acetonitrile, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, THF ( Tetrahydrofuran).

The crosslinked film is produced by, for example, mixing an ion conductive polymer, a reaction initiator if necessary, and a lithium salt compound in an organic solvent and dissolving them to form a composition, and then forming a composition on a substrate (for example, PET film or Teflon). (Registered trademark) plate, etc., the composition is cast, the solvent is removed, and then a crosslinked film is produced by heating or irradiation with active energy rays such as ultraviolet rays. Alternatively, the composition may be directly cast on the surface of the composite solid electrolyte to produce a crosslinked film.

The thickness of the crosslinked film is preferably in the range of 0.1 μm to 200 μm, more preferably 0.5 μm to 100 μm.

Examples of the laminated constitution of the composite solid electrolyte secondary battery of the present invention include the following constitutions.
A laminated structure in which a positive electrode, an inorganic composite solid electrolyte, and a negative electrode are sequentially laminated;
A laminated structure in which a positive electrode, a crosslinked film, a composite solid electrolyte, a crosslinked film, and a negative electrode are laminated in order;
A laminated structure in which a positive electrode, a crosslinked film, a composite solid electrolyte, and a negative electrode are laminated in this order;
A laminated structure in which a positive electrode, a composite solid electrolyte, a crosslinked film, and a negative electrode are sequentially laminated.

In the composite solid electrolyte secondary battery of the present invention, it is preferable that the composite solid electrolyte and the aforementioned crosslinked film are in contact with each other. Since the crosslinked film is a crosslinked product of a composition containing an ion conductive polymer containing a lithium salt compound, it has ion conductivity and has high flexibility as compared with an inorganic material. .. Therefore, the crosslinked film has a large contact area with the composite solid electrolyte, and as a result, the interfacial resistance of the composite solid electrolyte is effectively reduced, and the composite solid electrolyte secondary battery of the present invention has excellent charge/discharge characteristics. It is considered to be effective. In the composite solid electrolyte secondary battery of the present invention, it is also preferable that the crosslinked film is in contact with the electrode material layer of the electrode, and the crosslinked film is in contact with both the electrode material layer and the composite solid electrolyte. Is also preferable.

Composite solid electrolyte secondary battery The composite solid electrolyte secondary battery of the present invention includes at least a positive electrode, a negative electrode, and the composite solid electrolyte of the present invention. The composite solid electrolyte of the present invention is as described above. The composite solid electrolyte of the present invention is arranged between the positive electrode and the negative electrode. In particular, the composite solid electrolyte used in the composite solid electrolyte secondary battery of the present invention, as described above, in addition to the inorganic solid electrolyte, since it contains a polymer solid electrolyte containing a branched polyether, the inorganic solid electrolyte It is considered that the contact area of the interface between the electrode material layer and the composite solid electrolyte layer is larger than that in the case where the solid electrolyte is formed only by itself, and as a result, the interface resistance between the electrode and the electrolyte decreases, which is excellent. It is considered that the excellent charge/discharge characteristics are exhibited. Further, even in the composite solid electrolyte, it is considered that the polymer solid electrolyte reduces the resistance inside the composite solid electrolyte by bringing the particles of the inorganic solid electrolyte into close contact with each other.

Known electrodes can be used for both the positive electrode and the negative electrode, and an electrode including a current collector with an electrode material layer, that is, a positive electrode material layer or a negative electrode material layer can be exemplified.

A known current collector can be used for the positive electrode and the negative electrode. Specifically, for the positive electrode, a metal such as aluminum, nickel, stainless steel, gold, platinum, or titanium is used as a current collector. For the negative electrode, a metal such as copper, nickel, stainless steel, gold, platinum or titanium is used as a current collector.

Further, the positive electrode material layer and the negative electrode material layer each contain at least a positive electrode active material and a negative electrode active material, and may further contain a conductive auxiliary agent, a binder, and a thickener, if necessary, the above-mentioned inorganic material. A solid electrolyte may be included.

The positive electrode active material used in the present invention is a lithium metal-containing composite oxide powder having a composition of any one of LiMO ₂ , LiM ₂ O ₄ , Li ₂ MO ₃ and LiMEO ₄ . Here, M in the formula is mainly composed of a transition metal and contains at least one of Co, Mn, Ni, Cr, Fe, and Ti. Although M is a transition metal, Al, Ga, Ge, Sn, Pb, Sb, Bi, Si, P, B and the like may be added in addition to the transition metal. E contains at least one of P and Si. The particle size of the positive electrode active material is preferably 50 μm or less, more preferably 20 μm or less. These active materials have an electromotive force of 3 V (vs. Li/Li+) or more.

Specific examples of the positive electrode active material include lithium cobalt oxide, lithium nickel oxide, nickel/cobalt/lithium manganate (ternary system), spinel type lithium manganate, and lithium iron phosphate.

The negative electrode active material used in the present invention is a carbon material (natural graphite, artificial graphite, amorphous carbon, etc.) having a structure (intercalation compound) capable of occluding and releasing alkali metal ions such as lithium ions, or lithium ions. Metals such as lithium, aluminum-based compounds, tin-based compounds, silicon-based compounds, and titanium-based compounds that can store and release alkali metal ions such as. In the case of powder, the particle size is preferably 10 nm or more and 100 μm or less, and more preferably 20 nm or more and 20 μm or less. Moreover, you may use as a mixed active material of a metal and a carbon material.

When using a conductive auxiliary agent, a known conductive auxiliary agent can be used, such as graphite, furnace black, acetylene black, conductive carbon black such as Ketjen black, carbon fiber such as carbon nanotubes, or metal powder. Can be mentioned. These conductive aids may be used alone or in combination of two or more.

As the binder, for example, one or more selected from fluororesins such as PVdF, fluororubber, acrylic rubber, modified acrylic rubber, styrene-butadiene rubber, acrylic polymers, vinyl polymers, and branched polyethers described above. Compounds can be used. The amount of the active material added to these binders is 100 parts by mass, preferably 5 parts by mass or less, more preferably 3 parts by mass or less, for example 0.01 to 2 parts by mass.

Specific examples of the thickener include carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose and salts thereof (alkali metal salts such as sodium salt, ammonium salt), polyvinyl alcohol, polyacrylic acid salt, polyethylene oxide and the like. You may use these thickeners 1 type(s) or 2 or more types. The thickener is added in an amount of preferably 5 parts by mass or less, more preferably 3 parts by mass or less, for example, 0.01 to 2 parts by mass, based on 100 parts by mass of the active material. Further, when the viscosity of the coating liquid is low, a thickener can be used together.

The method for producing the positive electrode and the negative electrode including the current collector, the positive electrode material layer, and the negative electrode material layer is not particularly limited, and a general method is used. For example, a positive electrode active material or a negative electrode active material, a conductive auxiliary agent, a binder, a solvent such as water or N-methyl-2-pyrrolidone (NMP), and a positive electrode material and a negative electrode material paste (thickener, if necessary) ( The coating solution) is uniformly applied to the surface of the current collector by a doctor blade method or a silk screen method so as to have an appropriate thickness.

For example, in the doctor blade method, a negative electrode active material powder, a positive electrode active material powder, a conductive auxiliary agent, a binder and the like are dispersed in water to form a slurry, which is applied to a metal electrode substrate, and then a blade having a predetermined slit width is used. Make it uniform in thickness. After applying the active material, the electrode is dried, for example, in hot air at 100° C. or under reduced pressure at 80° C. to remove excess organic solvent. The dried electrode is press-molded by a press machine to manufacture the electrode.

When the positive electrode material layer and the negative electrode material layer are formed on the current collector, voids are generated between the positive electrode material layer and the negative electrode material electrode material, for example, between the active materials, between the active material and another electrode material, and the like. It will be. In the composite solid electrolyte secondary battery of the present invention, such a void may contain the above-mentioned branched polyether which is an ion conductive polymer.

Manufacturing method of composite solid electrolyte secondary battery The manufacturing method of the composite solid electrolyte secondary battery of the present invention is not particularly limited, and is composed of at least a positive electrode, a negative electrode, and the composite solid electrolyte of the present invention, and manufactured by a known method. To be done. For example, in the case of a coin type lithium ion battery, the positive electrode, the composite solid electrolyte, and the negative electrode are inserted in an outer can. After that, the storage body is obtained by joining the sealing body with tab welding or the like, enclosing the sealing body, and caulking. The shape of the battery is not limited, but examples thereof include a coin type, a cylinder type, and a sheet type, and a structure in which two or more batteries are laminated may be used.

The present invention will be described more specifically in the following examples, but the present invention is not limited to these.

In this example, a coin battery was produced using the composite solid electrolyte, and the performance of the charge/discharge characteristics of the coin battery was evaluated in the following experiment.

[Evaluation of fabricated battery]
For the evaluation of the manufactured battery, a charge/discharge test was performed using a charge/discharge device, and the charge capacity and the discharge capacity were obtained.

Charge/discharge measurement After CCCV charging (0.01C cut) up to 4.2V with a current equivalent to 0.1C (10 hour rate), CCCV discharge (0.01C cut) up to 2.5V with a current corresponding to 0.1C. ) Was done. The test temperature was 100° C. environment.

[Example of producing positive electrode]
(1) To 100 parts by mass of NCM (nickel/cobalt/lithium manganate=5/2/3) as a positive electrode active material, 3 parts by mass of acetylene black as a conduction aid, 3 parts by mass of graphite, and 3 parts by mass of PVdF as a binder were added. Further, the slurry was added to the NMP solution so that the solid content concentration of the slurry was 35% by mass, and sufficiently mixed to obtain a positive electrode slurry. The obtained positive electrode slurry was applied onto a 20 μm thick aluminum current collector using a die coater, dried and dried at 100° C. for 12 hours or more, and then pressed by a roll press machine to prepare a 20 μm thick positive electrode precursor. A body was produced (Basis weight: 6.6 mg/cm ² , positive electrode density: 3.1 g/cm ³ , porosity: 26%).

(2) 100 parts by mass of ethylene oxide/diethylene glycol methyl glycidyl ether/allyl glycidyl ether=80/17/3 mol% terpolymer (weight average molecular weight 1.5 million) as a branched polyether, and lithium borofluoride 12 as a lithium salt compound. By mass, 10 parts by mass of trimethylolpropane triacrylate as a crosslinking aid and 0.3 parts by mass of benzoyl peroxide (Nyper BMT, NOF CORPORATION) as a radical initiator were completely dissolved in 900 parts by mass of acetonitrile. A coating solution for impregnating the positive electrode was prepared.

(3) The positive electrode impregnating coating solution of (2) was applied onto the positive electrode precursor of (1). Then, by leaving it to stand for 2 hours, the branched polyether and the electrolyte lithium compound were impregnated into the voids in the positive electrode while removing the solvent. The impregnated branched polyether was crosslinked under reduced pressure at 100° C. for 2 hours to prepare a positive electrode.

[Production Example of Negative Electrode]
(1) 100 parts by mass of artificial graphite (particle size: 10 μm) as a negative electrode active material, 2 parts by mass of vapor grown carbon fiber (VGCF) as a conduction aid, 3 parts by mass of SBR as a binder, and sodium carboxymethyl cellulose as a thickener. 2 parts by mass of salt was added, water was further added so that the solid content concentration of the slurry was 35% by mass, and they were sufficiently mixed to obtain a slurry for negative electrode. The obtained negative electrode slurry was applied onto a copper current collector having a thickness of 16.5 μm using a die coater, dried and dried at 100° C. for 12 hours or more, and then pressed with a roll press machine to obtain a negative electrode having a thickness of 22 μm. Was prepared (a basis weight of 3.1 mg/cm ² , a negative electrode density of 1.2 g/cm ³ , and a porosity of 23%).

(2) 100 parts by mass of ethylene oxide/diethylene glycol methyl glycidyl ether/allyl glycidyl ether=80/17/3 mol% terpolymer (weight average molecular weight 1.5 million) as a branched polyether, and 38 parts by mass of LiTFSI as a lithium salt compound. As a crosslinking aid, 10 parts by mass of trimethylolpropane triacrylate, and 0.3 parts by mass of benzoyl peroxide (Nyper BMT, manufactured by NOF CORPORATION) as a radical initiator were completely dissolved in 900 parts by mass of acetonitrile. A coating solution for impregnation was prepared.

(3) The electrode impregnating coating solution of (2) was applied onto the negative electrode precursor of (1). Then, by leaving it to stand for 2 hours, the branched polyether and the electrolyte lithium compound were impregnated into the voids in the negative electrode while removing the solvent. The impregnated branched polyether was crosslinked under reduced pressure at 100° C. for 2 hours to prepare a negative electrode.

[Exemplary production example of composite solid electrolyte]
(1) Preparation of Inorganic Solid Electrolyte 0.5 parts by mass of lithium borate was dissolved in 99.5 parts by mass of ion-exchanged water to prepare a 0.5% by mass aqueous solution of lithium borate. Separately, 0.5 parts by mass of lithium sulfate monohydrate was dissolved in 99.5 parts by mass of ion-exchanged water, 13 parts by mass of a 0.5% by mass aqueous solution of lithium sulfate was added, and further, oxide solid electrolyte LATP (Toyoshima). (Manufactured by Seisakusho) (composition: Li _1.3 Al _0.3 Ti _1.7 P ₃ O ₁₂ , average particle size: 1 μm) (10.5 parts by mass) was added, and the mixture was stirred at room temperature. This slurry was transferred to a rotary evaporator equipped with a 60° C. water bath, and the solvent was distilled off and dried under heating, stirring, and reduced pressure to obtain a white dry product. This was vacuum dried at 150° C. for 1 hour to obtain a dry product of LATP (inorganic solid electrolyte) coated with 5% by mass of lithium borate-lithium sulfate. 84 mg of the dried product (powder) was put into a tablet forming die having a diameter of 10 mmφ and pressed at 20 kN for 5 minutes to obtain a molded product having a thickness of 500 μm. In addition, when the powder was 50 mg or less, the molded product was damaged when taken out, and the molded product could not be obtained.

(2) Preparation of Polymer Solid Electrolyte of Branched Polyether Ethylene oxide/diethylene glycol methyl glycidyl ether/allyl glycidyl ether=80/17/3 mol% terpolymer (weight average molecular weight 1.5 million) as branched polyether 100 12 parts by mass of lithium borofluoride as a lithium salt compound, 10 parts by mass of trimethylolpropane triacrylate as a crosslinking aid, 0.3 parts by mass of Niper BMT (manufactured by NOF CORPORATION) as a radical initiator in acetonitrile, The mixture was stirred at room temperature for 10 hours and completely dissolved to prepare an acetonitrile solution containing 0.5% by mass of a branched polyether polymer solid electrolyte.

(3) Preparation of Composite Solid Electrolyte of Inorganic Solid Electrolyte and Polymer Solid Electrolyte 100 parts by mass of an acetonitrile solution containing the polymer solid electrolyte of 0.5% by mass branched polyether of (2) above is added to the above (1). 8.7 parts by mass of a dried inorganic solid electrolyte was added, and the solvent was distilled off under heating, stirring and reduced pressure with a rotary evaporator equipped with a hot water bath at 60°C. The dried product was vacuum dried at 110° C. for 2 hours to obtain a white dried product. 39 mg of the dried powder was put into a tablet forming die having a diameter of 10 mmφ and pressurized at 20 kN for 5 minutes. Under these pressure molding conditions, the molded product could be smoothly taken out, and a molded product having a thickness of 230 μm could be obtained.

[Comparative Preparation Example of Composite Solid Electrolyte]
(1) Preparation of Polymer Solid Electrolyte of Polyethylene Oxide 100 parts by mass of polyethylene oxide (weight average molecular weight of 1.1 million) and 12 parts by mass of lithium borofluoride as a lithium salt compound are stirred in acetonitrile at room temperature for 10 hours to be completely stirred. The solution was dissolved to prepare an acetonitrile solution containing 0.5% by mass of polyethylene oxide as a solid polymer electrolyte.

(2) Preparation of composite solid electrolyte In 100 parts by mass of an acetonitrile solution containing a polymer solid electrolyte of 0.5% by mass of polyethylene oxide, a dried product of the inorganic solid electrolyte obtained in (1) Preparation of inorganic solid electrolyte 8.7. A mass part was added, and the solvent was distilled off under heating, stirring and reduced pressure with a rotary evaporator equipped with a hot water bath at 60° C. to dryness. The dried product was vacuum dried at 110° C. for 2 hours to obtain a white dried product. 45 mg of the dried powder was put into a tablet forming die having a diameter of 10 mmφ and pressurized at 20 kN for 5 minutes. Under these pressure molding conditions, the molded product could be smoothly taken out, and a molded product having a thickness of 350 μm could be obtained.

[Preparation of cross-linked film of ion conductive polymer material]
100 parts by mass of ethylene oxide/diethylene glycol methyl glycidyl ether/allyl glycidyl ether=80/17/3 mol% terpolymer as an ion conductive polymer having an ethylene oxide unit in a side chain, and 38 parts by mass of LiTFSI as a lithium salt compound are crosslinked. A solution was prepared by dissolving 10 parts by mass of trimethylolpropane triacrylate as an auxiliary agent and 0.3 parts by mass of Niper BMT (manufactured by NOF CORPORATION) as a radical initiator in 900 parts by mass of acetonitrile. This solution was cast on a polytetrafluoroethylene mold, dried at room temperature, and then thermally crosslinked at 100° C. for 2 hours to prepare a crosslinked film of an ion conductive polymer material having a thickness of 20 μm.

Battery Manufacturing Example [Coin Battery Working Manufacturing Example 1]
In the dry room, the positive electrode obtained in the practical production example of the positive electrode, the molded product of the composite solid electrolyte (thickness: 230 μm), the crosslinked film of the ion conductive polymer material of the production example, and the metallic lithium foil as the negative electrode were laminated in that order, and Therefore, a test 2032 type coin battery was manufactured.
<Charging/discharging conditions>
Lower limit voltage 2.5V-Upper limit voltage 4.2V, 100°C
CC-CV/CC-CV 0.1C-0.01C charge, 0.1C-0.01C discharge <charge/discharge test result>
Charge capacity 165mAh/g, discharge capacity 150mAh/g

[Coin Battery Implementation Manufacturing Example 2]
In a dry room, the positive electrode obtained in the practical production example of the positive electrode, the molded product of the composite solid electrolyte obtained in the practical production example of the composite solid electrolyte, and the negative electrode obtained in the practical production example of the negative electrode were laminated, crimped, and tested. A 2032 type coin battery was manufactured.
<Charging/discharging conditions>
Lower limit voltage 2.5V-Upper limit voltage 4.2V, 100°C
CC(0.1C)-CV(0.01C) charge CC(0.1C)-CV(0.01C) discharge <Charge/discharge test result>
Charge capacity 151mAh/g Discharge capacity 130mAh/g

[Comparative Production Example 1 of Coin Battery]
In a dry room, the positive electrode obtained in the positive production example of the positive electrode, a composite solid electrolyte molded article obtained in a comparative production example of a composite solid electrolyte using polyethylene oxide, a cross-linked film of the ion conductive polymer material of the production example, a negative electrode After laminating the metallic lithium foil as described above in order, caulking was performed to manufacture a test 2032 type coin battery.
<Charging/discharging conditions>
Lower limit voltage 2.5V-Upper limit voltage 4.2V, 100°C
CC(0.1C)-CV(0.01C) charge CC(0.1C)-CV(0.01C) discharge <Charge/discharge test result>
Charge capacity 110mAh/g, discharge capacity 90mAh/g

From the production example and the comparative production example, the composite solid electrolyte consisting of the inorganic solid electrolyte and the polymer solid electrolyte containing the branched polyether, compared with the solid electrolyte not containing the polymer solid electrolyte, apparently solid electrolyte It can be seen that the secondary battery exhibits high charge and discharge capacities. In addition, when pressure molding is performed using the inorganic solid electrolyte alone, it has almost no flexibility and binding property, so that it becomes a thick film electrolyte, but in the composite solid electrolyte, due to the flexibility and binding property of the polymer solid electrolyte, A thin solid electrolyte is obtained.

The composite solid electrolyte of the present invention, and a solid electrolyte secondary battery produced using the composite solid electrolyte, are excellent in charge/discharge characteristics, and are storage batteries for in-vehicle applications such as electric vehicles and hybrid electric vehicles and household power storage. Can be suitably used for large-sized battery applications such as.

Claims

A composite solid electrolyte containing an inorganic solid electrolyte and a polymer solid electrolyte containing a branched polyether.
The composite solid electrolyte according to claim 1, wherein the branched polyether includes a constituent unit formed of an ether compound having an ethylene oxide unit in a side chain.
The composite solid according to claim 1 or 2, wherein the branched polyether includes a constituent unit formed of at least one selected from the group consisting of allyl glycidyl ether, acrylic acid glycidyl ether, and methacrylic acid glycidyl ether. Electrolytes.
The composite solid electrolyte according to any one of claims 1 to 3, wherein the branched polyether is crosslinked.
The composite solid electrolyte according to any one of claims 1 to 4, wherein the inorganic solid electrolyte is an oxide solid electrolyte or a sulfide solid electrolyte.
A composite solid electrolyte secondary battery containing the composite solid electrolyte according to any one of claims 1 to 5.