Composite electrolyte, method for producing same, and power storage device

Abstract

Provided is a composite electrolyte containing an inorganic solid electrolyte and a non-aqueous electrolyte. The non-aqueous electrolyte contains: organic molecules having at least one atom selected from the group consisting of sulfur atoms, oxygen atoms (excluding oxygen atoms in carbonate groups), nitrogen atoms, and phosphorus atoms; and an alkali metal salt.

Description

Composite electrolyte, method for producing the same, and electricity storage device

[0001] [CROSS-REFERENCE TO RELATED APPLICATIONS] This application claims priority to Japanese Patent Application No. 2023-208613, filed on December 11, 2023, the entire contents of which are incorporated herein by reference. The present disclosure relates to a composite electrolyte and a method for producing the same, and an electricity storage device.

[0002] Various types of energy storage devices have been put to practical use, including various secondary batteries such as nickel-metal hydride secondary batteries and lithium-ion secondary batteries, as well as electric double-layer capacitors. Among these, lithium-ion secondary batteries are used in a wide range of applications due to their high energy density and battery capacity. In recent years, sodium-ion secondary batteries, potassium-ion secondary batteries, and magnesium-ion secondary batteries have been attracting attention as post-lithium-ion secondary batteries that use elements that replace the rare metal lithium.

[0003] Lithium-ion secondary batteries, which are widely used as energy storage devices, have a negative electrode, a positive electrode, and an electrolyte, and are charged and discharged by transferring lithium ions between the electrodes via the electrolyte. Conventionally, nonaqueous electrolytes have primarily been used as the electrolyte. However, because nonaqueous electrolytes contain flammable organic solvents, there are concerns about electrolyte leakage and short-circuiting within the battery due to overcharging and overdischarging.

[0004] In response to this, non-flammable solid electrolytes using inorganic materials have been proposed as an alternative to non-aqueous electrolyte solutions. However, while inorganic solid electrolytes are safe, they have the disadvantage that, because they are manufactured by molding powder, gaps are likely to form at the interfaces with the positive and negative electrodes, resulting in high interfacial resistance.

[0005] Therefore, in recent years, in order to achieve both improved safety and reduced interface resistance, it has been proposed to use a composite electrolyte formed from an inorganic solid electrolyte and a non-aqueous electrolyte solution as the electrolyte used in lithium ion secondary batteries (see, for example, Patent Document 1). Patent Document 1 discloses a method in which an inorganic oxide is sintered as the inorganic solid electrolyte to produce a sintered body having a dense portion and a porous portion, and the sintered body is immersed in an electrolyte solution such as an organic electrolyte solution or an ionic liquid and then evacuated, thereby filling the porous portion of the sintered body with the electrolyte solution to obtain a composite electrolyte.

[0006] JP 2017-111890 A

[0007] The inventors have found that the composite electrolyte of Patent Document 1 is hard and has poor flexibility. Therefore, it easily breaks when an external force is applied, making it difficult to handle. Furthermore, the composite electrolyte of Patent Document 1 easily allows the nonaqueous electrolyte to escape from the sintered body, and the ionic conductivity of the composite electrolyte decreases rapidly over time after production. From the perspective of further improving the quality of electricity storage devices, a composite electrolyte that is flexible and can stably maintain ionic conductivity is required.

[0008] The present disclosure has been made in view of the above circumstances, and has as one object to provide a composite electrolyte that is flexible and exhibits little change in ionic conductivity over time, and another object to provide an electricity storage device including the composite electrolyte.

[0009] As a result of intensive research into solving the above-mentioned problems, the present inventors have found that the above-mentioned problems can be solved by using a specific liquid as the non-aqueous electrolyte in a composite electrolyte containing an inorganic solid electrolyte and a non-aqueous electrolyte.

[0010] [1] A composite electrolyte comprising an inorganic solid electrolyte and a non-aqueous electrolyte solution, the non-aqueous electrolyte solution containing an organic molecule having at least one atom selected from the group consisting of a sulfur atom, an oxygen atom (excluding oxygen atoms in a carbonate group), a nitrogen atom, and a phosphorus atom, and an alkali metal salt. [2] The composite electrolyte of [1], wherein the ratio of the alkali metal salt to the organic molecule is 0.5 to 15 moles of the organic molecule per mole of the alkali metal salt. [3] The composite electrolyte of [1] or [2], wherein the organic molecule is at least one selected from the group consisting of a sulfone compound, a nitrile compound, and an amide compound. [4] The composite electrolyte of any of [1] to [3], wherein the inorganic solid electrolyte contains an oxide having a NASICON-type crystal structure. [5] The oxide having a NASICON-type crystal structure is represented by the general formula: Li １＋ｘ＋ｙ－ｚ M1 ｘ Zr ２－ｘ M2 ｙ M3 ｚ P ３－ｙ－ｚ O １２ [6] The composite electrolyte according to [4], wherein the oxide having a NASICON-type crystal structure is represented by the general formula Li １＋ｘ M4 ｘ Ge ｙ Zr ２－ｘ－ｙ P ３ O １２ [7] The composite electrolyte according to [4] or [5], wherein the oxide having a NASICON-type crystal structure is a solid electrolyte represented by the general formula: Na ３＋２ｘ＋ｙ＋α M5 ｘ M6 ｙ M7 ｚ Zr ２－ｘ－ｙ－ｚ Si ２＋α P １－α O １２(wherein M5 contains an element that forms a divalent cation, M6 contains Al and may contain an element that forms a trivalent cation other than Al, and M7 contains Ti and may contain an element that forms a tetravalent cation other than Ti, Zr, and Si, and x≧0, y≧0, z≧0, x+y+z>0, and α>0 are satisfied). [8] The composite electrolyte of any of [1] to [7], wherein the alkali metal salt contains an imide alkali metal salt. [9] The composite electrolyte of any of [1] to [8], wherein the content of the inorganic solid electrolyte is 50% by mass or more and 90% by mass or less.

[10] A method for producing the composite electrolyte of any of [1] to [9], comprising a step of mixing the inorganic solid electrolyte in powder form with the non-aqueous electrolytic solution.

[11] An electricity storage device comprising the composite electrolyte of any of [1] to [9].

[0011] According to the present disclosure, a composite electrolyte having flexibility and exhibiting little change in ionic conductivity over time can be obtained. Furthermore, by using the composite electrolyte of the present disclosure as an electrolyte for an electricity storage device such as a secondary battery or a capacitor, it is possible to obtain an electricity storage device that combines the safety ensured by the solidification of the electrolyte with stable ionic conductivity over time.

[0012] FIG. 1 is a schematic diagram of a press die used to prepare the sample pellets.

[0013] The solid electrolyte and the electricity storage device of the present disclosure will be described in detail below.

[0014] <<Composite Electrolyte>> The composite electrolyte of the present disclosure contains the following component (X) and component (Y): Component (X): inorganic solid electrolyte Component (Y): non-aqueous electrolyte Each component contained in the composite electrolyte of the present disclosure will be described in detail below.

[0015] <Component (X): Inorganic Solid Electrolyte> In the composite electrolyte of the present disclosure, the inorganic solid electrolyte contained as component (X) is not particularly limited as long as it is an inorganic solid exhibiting ion conductivity. For example, oxide-based solid electrolytes, sulfide-based solid electrolytes, chloride-based solid electrolytes, etc. can be used as component (X). Of these, oxide-based solid electrolytes and sulfide-based solid electrolytes are preferred as component (X) in terms of high ion conductivity, and oxide-based solid electrolytes are more preferred in terms of high safety in the atmosphere.

[0016] The crystal structure of component (X) is not particularly limited, and examples of the crystal structure that component (X) may have include a NASICON structure, a LISICON structure, a perovskite structure, and a garnet structure.

[0017] Specific examples of the component (X) include solid electrolytes having a NASICON structure, such as Li １＋ｘ Al ｘ Ti ２－ｘ (P.O. ４ ) ３ (x≧0, also referred to as “LTP” or “LATP”), Li １＋ｘ Al ｘ Ge ２－ｘ (P.O. ４ ) ３ (x≧0, also referred to as “LGP” or “LAGP”), LiZr ２ (P.O. ４ ) ３ (also known as "LZP") and NASICON, Na ３ Zr ２ Si ２ P.O. １２ (also referred to as "NZSP"), and oxides in which some of the elements constituting these compounds are substituted with various elements (for example, B, Na, Al, Si, Ca, Ga, Ge, Sc, Fe, Sr, In, Ti, Hf, Sn, V, Nb, Ta, Sb, Bi, W, lanthanoid elements, etc.).

[0018] As a solid electrolyte having a LISICON structure, Li １４ ZnGe ４ O １６ Ya, Li １４ ZnGe４ O １６ Examples of the solid electrolyte having a perovskite structure include oxides in which some of the elements constituting the solid electrolyte are substituted with the above-mentioned various elements. ０．３５ La ０．５５ TiO ３ Ya, Li ０．３５ La ０．５５ TiO ３ Examples of the solid electrolyte having a garnet structure include oxides in which some of the elements constituting the solid electrolyte are substituted with the above-mentioned various elements. ７ La ３ Zr ２ O １２ and Li ５ La ３ Nb ２ O １２ Ya, Li ７ La ３ Zr ２ O １２ or Li ５ La ３ Nb ２ O １２ and oxides in which some of the elements constituting the above-mentioned compound are substituted with the above-mentioned various elements.

[0019] One aspect of the composite electrolyte of the present disclosure is a hybrid semi-solid electrolyte comprising an inorganic solid electrolyte having a NASICON-type crystal structure and a non-aqueous electrolyte solution. Unlike layered structures, the NASICON-type crystal structure provides three-dimensional mobility for alkali metal ions, and zirconium (Zr) is stable even under high voltages, making it useful as a solid electrolyte for high operating voltages. In the composite electrolyte of the present disclosure, an oxide having a NASICON-type crystal structure can be preferably used as the inorganic solid electrolyte (component (X)). The crystal structure of the solid electrolyte can be determined from the diffraction profile obtained by powder X-ray diffraction measurement.

[0020] When an oxide having a NASICON-type crystal structure is used as component (X), preferred examples of the oxide include oxide (x1), oxide (x2), and oxide (x3) shown below. Oxide (x1): Oxide represented by the general formula Li １＋ｘ＋ｙ－ｚ M1 ｘ Zr２－ｘ M2 ｙ M3 ｚ P ３－ｙ－ｚ O １２ (wherein M1 contains Fe, In or Al, M2 contains Si, M3 contains W, and x>0, y≧0, z≧0, and y+z>0 are satisfied) Oxide (x2): represented by the general formula Li １＋ｘ M4 ｘ Ge ｙ Zr ２－ｘ－ｙ P ３ O １２ (wherein M4 contains Al and satisfies 0≦x≦2, 0≦y≦2, and 0≦x+y≦2) Oxide (x3): General formula: Na ３＋２ｘ＋ｙ＋α M5 ｘ M6 ｙ M7 ｚ Zr ２－ｘ－ｙ－ｚ Si ２＋α P １－α O １２ (wherein M5 contains an element that forms a divalent cation, M6 contains Al and may contain an element that forms a trivalent cation other than Al, M7 contains Ti and may contain an element that forms a tetravalent cation other than Ti, Zr, and Si, and x≧0, y≧0, z≧0, x+y+z>0, and α>0 are satisfied.)

[0021] ・About oxide (x1) Oxide (x1) is LiZr ２ (P.O. ４ ) ３ In an oxide having a basic skeleton, a portion of Zr is substituted with M1 (containing Fe or In), and a portion of P is substituted with M2 (containing Si) and / or M3 (containing W).

[0022] In the oxide (x1), M1 may contain Fe, In, or Al, and M2 may contain Si. That is, M1 may be Fe, In, or Al, and may further contain, together with Fe, In, or Al, an element other than Fe, In, or Al that forms a trivalent cation. Examples of elements that form trivalent cations other than Fe or In include Group 13 elements, transition elements (Groups 3 to 11 elements) that form trivalent cations, Sb, Bi, etc.

[0023] M2 may contain Si. That is, M2 may be Si, or may further contain an element other than Si that forms a tetravalent cation. Examples of elements other than Si that form a tetravalent cation include Group 14 elements other than Si, transition elements (Groups 3 to 11 elements) that form a tetravalent cation, and Te.

[0024] M3 may contain W. That is, M3 may be W, or may further contain an element other than W that becomes a hexavalent cation. Examples of elements other than W that become a hexavalent cation include transition elements (elements of Groups 3 to 11) other than W that become a hexavalent cation, and Group 16 elements.

[0025] In the general formula of the oxide (x1), x, y, and z are not particularly limited as long as x > 0, y ≥ 0, z ≥ 0, and y + z > 0 are satisfied. For example, when x > 0, y > 0, and z = 0, the oxide (x1) is "Li １＋ｘ＋ｙ M1 ｘ Zr ２－ｘ M2 ｙ P ３－ｙ O １２ When x>0, y=0 and z>0, the oxide (x1) is represented by "Li １＋ｘ－ｚ M1 ｘ Zr ２－ｘ M3 ｚ P ３－ｚ O １２ " When x>0, y>0 and z>0, the oxide (x1) is represented by "Li １＋ｘ＋ｙ－ｚ M1 ｘ Zr ２－ｘ M2 ｙ M3 ｚ P ３－ｙ－ｚ O １２ " is expressed as:

[0026] More specifically, x, y, and z in the general formula of the oxide (x1) are, for example, 0.55 or less, and may be 0.5 or less. Since an impurity phase is unlikely to be formed and an inorganic solid electrolyte exhibiting high ionic conductivity can be obtained, it is preferable that x≦0.3, and more preferably that x≦0.25. The lower limit of x is preferably x≧0.01, more preferably x≧0.05, and even more preferably x≧0.10.

[0027] For example, y is 1.5 or less, and may be 1.0 or less. Since y has a dominant effect on α-phase formation, thereby enabling a solid electrolyte with higher ion conductivity to be obtained, it is preferable that y≦0.2 be satisfied, more preferably that y≦0.15 be satisfied, and even more preferably that y≦0.10 be satisfied. Furthermore, when y>0, the lower limit of y is preferably y≧0.01, and more preferably that y≧0.03 be satisfied. Note that zirconium phosphate-based oxides having a NASICON-type crystal structure can have four phase structures: α-phase, α'-phase, β-phase, and β'-phase. Of these, the α-phase has the highest Li-ion conductivity due to its isotropic crystal structure.

[0028] For example, z is 0.3 or less, and may be 0.25 or less. In terms of suppressing the formation of impurity phases and obtaining a solid electrolyte exhibiting higher ionic conductivity, it is preferable that z≦0.2, more preferably z≦0.15, and even more preferably z≦0.10. When z>0, the lower limit of z is preferably z≧0.01, and more preferably z≧0.03.

[0029] ・About oxide (x2) Oxide (x2) is LiZr ２ (P.O. ４ ) ３ In an oxide having the basic skeleton, a part or all of Zr is substituted with M4 (containing Al) and Ge.

[0030] In the oxide (x2), M4 may contain Al. That is, M4 may be Al, or may further contain, together with Al, an element other than Al that forms a trivalent cation. Examples of elements that form trivalent cations other than Al include Group 13 elements, transition elements (Groups 3 to 11 elements) that form trivalent cations, Sb, Bi, etc.

[0031] In the general formula of the oxide (x2), x and y are not particularly limited as long as they satisfy the following conditions: 0≦x≦2, 0≦y≦2, and 0≦x+y≦2. For example, when x=0, the oxide (x2) is "LiGe ｙ Zr ２－ｙ P ３ O １２ When y=0, the oxide (x2) is represented by "Li １＋ｘ M4 ｘ Zr ２－ｘ P ３ O １２ " is expressed as:

[0032] More specifically, x and y in the general formula of the oxide (x2) are 2.0 or less, and may be 1.0 or less. Since an impurity phase is unlikely to be formed and an inorganic solid electrolyte exhibiting high ionic conductivity can be obtained, it is preferable that x≦0.6, and more preferably that x≦0.55. The lower limit of x is preferably x≧0.01, more preferably x≧0.05, and even more preferably x≧0.10.

[0033] y is 2.0 or less, and may be 1.8 or less. In terms of suppressing the formation of impurity phases and obtaining a solid electrolyte exhibiting higher ionic conductivity, it is preferable that y≦1.7, and more preferably that y≦1.6. The lower limit of y is preferably y≧0.1, and more preferably y≧0.3.

[0034] ・About oxide (x3) Oxide (x3) is Na ３ Zr ２ Si ２ P.O. １２In an oxide having a basic skeleton, a portion of Zr is substituted with at least one of M5 (containing an element that becomes a divalent cation), M6 (containing Al), and M7 (containing Ti), and the amount of Si in the composition is higher than that of the basic skeleton.

[0035] In the oxide (x3), examples of M5 include elements that form divalent cations among Group 2 elements, Group 12 elements, and transition elements (Groups 3 to 11 elements), as well as Sn and Pd.

[0036] M6 may contain Al. That is, M6 may be Al, or may further contain an element other than Al that becomes a trivalent cation. Examples of elements that become trivalent cations other than Al include Group 3 elements, Group 13 elements other than Al, transition elements (Groups 3 to 11 elements) that become trivalent cations, Sb, Bi, etc. The Group 13 element other than Al is preferably B (boron).

[0037] M7 may contain Ti. That is, M7 may be Ti, or may further contain an element other than Ti, Zr, and Si that forms tetravalent cations. Examples of elements other than Ti, Zr, and Si that form tetravalent cations include Group 14 elements other than Si, and transition elements (Groups 3 to 11 elements) other than Ti and Zr that form tetravalent cations (Te, Ce, Th).

[0038] In the general formula of the oxide (x3), x, y, and z satisfy x≧0, y≧0, z≧0, and x+y+z>0, and α is not particularly limited as long as it satisfies α>0. For example, when x=0, y>0, and z>0, the oxide (x3) is "Na ３＋ｙ＋α M6 ｙ M7 ｚ Zr ２－ｙ－ｚ Si ２＋α P １－α O １２ When y=0, x>0 and z>0, the oxide (x3) is represented by "Na ３＋２ｘ＋α M5 ｘ M7 ｚ Zr ２－ｘ－ｚ Si ２＋α P １－α O １２When z=0, x>0 and y>0, the oxide (x3) is represented by "Na ３＋２ｘ＋ｙ＋α M5 ｘ M6 ｙ Zr ２－ｘ－ｙ Si ２＋α P １－α O １２ When x=0, y=0 and z>0, the oxide (x3) is represented by "Na ３＋α M7 ｚ Zr ２－ｚ Si ２＋α P １－α O １２ " is expressed as:

[0039] More specifically, x, y, z, and α in the general formula of the oxide (x3) preferably satisfy x≦0.3, more preferably satisfy x≦0.2, and even more preferably satisfy x≦0.1, in that an impurity phase is unlikely to be formed and thus a solid electrolyte exhibiting high ionic conductivity can be obtained. When x>0, the lower limit of x preferably satisfies x≧0.01, more preferably satisfy x≧0.03, and even more preferably satisfy x≧0.05.

[0040] Regarding y, in order to suppress the formation of an impurity phase and thereby obtain a solid electrolyte having higher ion conductivity, it is preferable that y≦0.3, more preferably y≦0.2, and even more preferably y≦0.1. Furthermore, when y>0, the lower limit of y is preferably y≧0.01, more preferably y≧0.03, and even more preferably y≧0.05.

[0041] Regarding z, in order to suppress the formation of an impurity phase and obtain a solid electrolyte exhibiting higher ionic conductivity, it is preferable that z≦0.3, more preferably z≦0.2, and even more preferably z≦0.1. When z>0, the lower limit of z is preferably z≧0.01, more preferably z≧0.03, and even more preferably z≧0.05.

[0042] With regard to α, since a large amount of Si substitution is thought to result in a decrease in ionic conductivity, it is preferable that α≦1.0 be satisfied, more preferably α≦0.9 be satisfied, even more preferably α≦0.8 be satisfied, still more preferably α≦0.7 be satisfied, even more preferably α≦0.6 be satisfied, and even more preferably α≦0.5 be satisfied. Furthermore, with regard to the lower limit of α, it is preferable that α≧0.15 be satisfied, more preferably α≧0.25 be satisfied, and even more preferably α≧0.3 be satisfied.

[0043] In the above general formulas representing the oxide (x1), oxide (x2), and oxide (x3), the stoichiometric ratio of O is written as 12, but the stoichiometric ratio of O does not have to be strictly 12 as long as the charge neutrality of the oxide as a whole can be maintained. In other words, the O content in the oxide (x1) may be less than 12 or more than 12, as long as the charge neutrality of the oxide (x1) as a whole can be maintained. For example, Li １＋ｘ＋ｙ－ｚ M1 ｘ Zr ２－ｘ M2 ｙ M3 ｚ P ３－ｙ－ｚ O １２±β (where 0≦β≦1 is satisfied, and M1, M2, M3, x, y, and z are the same as M1, M2, M3, x, y, and z in the above formula shown as the general formula of oxide (x1)) is also included in oxide (x1) as long as the charge neutrality of the oxide (x1) as a whole is maintained.

[0044] Similarly, the O content in the oxide (x2) may be less than 12 or more than 12, as long as the oxide (x2) as a whole can be kept neutral. For example, Li １＋ｘ M4 ｘ Ge ｙ Zr ２－ｘ－ｙ P ３ O １２±γ(where 0≦γ≦1 is satisfied, and M4 and x are the same as M4 and x in the general formula of oxide (x2) above) are also included in oxide (x2) as long as the charge neutrality of oxide (x2) as a whole is maintained. Similarly, O in oxide (x3) may have a value of less than 12 or a value of more than 12 as long as the charge neutrality of oxide (x3) as a whole can be maintained. For example, Na ３＋２ｘ＋ｙ＋α M5 ｘ M6 ｙ M7 ｚ Zr ２－ｘ－ｙ－ｚ Si ２＋α P １－α O １２±δ (where 0≦δ≦1 is satisfied, and M5, M6, M7, x, y, z, and α are the same as M5, M6, M7, x, y, z, and α in the above general formula of oxide (x3)) is also included in oxide (x3) as long as the charge neutrality of the oxide (x3) as a whole is maintained.

[0045] The method for producing the oxide (x1), the oxide (x2), and the oxide (x3) is not particularly limited. The oxide (x1), the oxide (x2), and the oxide (x3) can be produced, for example, by weighing and mixing raw materials so as to satisfy the stoichiometric ratio of the composition represented by each of the general formulas above (mixing step), and then firing the resulting mixture (firing step).

[0046] As the raw material of oxide (x1), a supply component corresponding to an element for obtaining the target oxide (x1) can be used from among a Li supply component, an M1 supply component (Fe supply component, In supply component, or Al supply component), an M2 supply component (Si supply component), an M3 supply component (W supply component), a Zr supply component, and a P supply component. For example, when obtaining an oxide (x1) where y > 0 and z = 0, a Li supply component, an M1 supply component, an M2 supply component, a Zr supply component, and a P supply component are used as raw materials.

[0047] Examples of the Li supply component, M1 supply component, M2 supply component, M3 supply component, Zr supply component, and P supply component for obtaining oxide (x1) include carbonates, hydrogen carbonates, sulfates, sulfites, nitrates, nitrites, phosphates, acetates, citrates, ammonium salts, oxides, hydroxides, chlorides, sulfides, etc. of these metal elements. Note that these supply components may be compounds in which one type of supply component contains two or more elements selected from Li, M1, M2, M3, Zr, and P.

[0048] As the P supply component, it is preferable to use a compound containing one or more elements selected from Li, M1, M2, M3, and Zr. Among these, it is preferable to use a zirconium phosphate compound as the supply component (Zr and P supply component). As the zirconium phosphate compound, Zr(HPO ４ ) ２ , Zr(HPO ４ ) ２ ・nH ２ Zirconium hydrogen phosphate such as O; Zr ３ (P.O. ４ ) ４ Zirconium phosphate such as Zr(PO ４ ) (H ２ P.O. ４ ), Zr(PO ４ ) (H ２ P.O. ４ ) ２ ・nH ２ Zirconium hydrogen phosphate (n is 0≦n≦2) such as HZr ２ (P.O. ４ ) ３ , ZrP ２ O ７ , (ZrO) ２ P ２ O ７ Among these, Zr(HPO), which is called layered zirconium phosphate, is preferred because it has good handling properties as an inorganic solid electrolyte during production. ４ ) ２ ・nH ２ O can be preferably used.

[0049] As the raw material of oxide (x2), a supply component corresponding to an element for obtaining the target oxide (x2) can be used from among a Li supply component, an M4 supply component (Al supply component), a Ge supply component, a Zr supply component, and a P supply component. For example, when obtaining an oxide (x2) where y = 0, a Li supply component, an M4 supply component, a Zr supply component, and a P supply component are used as raw materials.

[0050] As the Li supply component, M4 supply component, Ge supply component, and P supply component for obtaining the oxide (x2), for example, carbonates, hydrogen carbonates, sulfates, sulfites, nitrates, nitrites, phosphates, acetates, citrates, ammonium salts, oxides, hydroxides, chlorides, sulfides, etc. of these metal elements can be used. Note that these supply components may be compounds in which one type of supply component contains two or more elements selected from Li, M4, Ge, and P. As the P supply component, zirconium phosphate-based compounds can be preferably used, and among these, layered zirconium phosphate is preferred.

[0051] As the raw material for oxide (x3), a supply component corresponding to the element for obtaining the target oxide (x3) can be used from among the Na supply component, M5 supply component, M6 supply component, M7 supply component, Zr supply component, Si supply component, and P supply component. For example, when obtaining oxide (x3) where x = 0 and y = 0, the Na supply component, M7 supply component, Zr supply component, Si supply component, and P supply component are used as raw materials. Note that these supply components may be compounds in which one type of supply component contains two or more elements selected from Na, M5, M6, M7, Zr, Si, and P.

[0052] As the raw materials for oxide (x3), namely, the Na supply component, M5 supply component, M6 supply component, M7 supply component, Zr supply component, Si supply component, and P supply component, carbonates, hydrogen carbonates, sulfates, sulfites, nitrates, nitrites, phosphates, acetates, citrates, ammonium salts, oxides, hydroxides, chlorides, sulfides, etc. of these metal elements can be used. Note that these supply components may be compounds in which one type of supply component contains two or more elements selected from Na, M5, M6, M7, Zr, Si, and P. As the P supply component, zirconium phosphate-based compounds can be preferably used, and among these, layered zirconium phosphate is preferred.

[0053] When producing oxide (x1), oxide (x2), and oxide (x3), the raw materials may be mixed by dry mixing, but it is preferable to mix them by wet mixing using a liquid. By adopting wet mixing, the density of the sintered product obtained by the firing step can be increased compared to the case of dry mixing, and the ionic conductivity of the resulting solid electrolyte can also be relatively improved. As the liquid used for wet mixing, water, various organic solvents, and mixtures thereof can be appropriately used.

[0054] In the firing step, the mixture obtained in the mixing step may be fired without molding, or may be molded and then fired. The firing temperature is not limited, but can be, for example, 900°C or higher, preferably 1,000°C or higher, more preferably 1,150°C or higher, and even more preferably 1,200°C or higher. The upper limit of the firing temperature can be, for example, 1,500°C or lower, preferably 1,400°C or lower, and more preferably 1,350°C or lower. During firing, the temperature may be increased stepwise from a temperature lower than the firing temperature (pre-firing), and the temperature required for firing may finally be maintained.

[0055] When pre-firing is performed, the obtained pre-firing product may be pulverized before the next firing process. When firing is performed at multiple temperature ranges, firing may be performed in three stages, for example, by performing a first pre-firing in a temperature range of 100°C or higher and lower than 800°C, a second pre-firing in a temperature range of 800°C or higher and lower than 1,200°C, and a main firing in a temperature range of 1,200°C or higher, and the pre-firing product may be pulverized each time the firing temperature range is changed. The firing time is not limited, but for example, the pre-firing may be performed for 1 hour to 40 hours and the main firing may be performed for 1 hour to 40 hours.

[0056] The oxides (x1) and (x2) exhibit high Li ion conductivity, and the oxide (x3) exhibits high Na ion conductivity. Therefore, the oxides (x1) and (x2) are suitable as materials for composite electrolytes for electricity storage devices in which the ion-conducting carrier is a lithium ion. The oxide (x3) is also suitable as a material for composite electrolytes for electricity storage devices in which the ion-conducting carrier is a sodium ion.

[0057] The inorganic solid electrolyte obtained by the firing step is preferably pulverized by any method to prepare a powder for use in the production of a composite electrolyte. The pulverization treatment of the inorganic solid electrolyte may be carried out using a pulverizer such as a ball mill, a bead mill, or a blender.

[0058] The average particle size of the inorganic solid electrolyte used in producing the composite electrolyte is preferably 0.1 μm or more and 20 μm or less in volume-based median particle size measured in an aqueous medium. When the average particle size of the inorganic solid electrolyte is within the above range, it is advantageous in that a composite electrolyte exhibiting high ionic conductivity can be obtained while improving the handleability of the inorganic solid electrolyte raw material. From the viewpoint of improving the handleability of the raw materials in producing the composite electrolyte, the average particle size of the inorganic solid electrolyte is more preferably 0.2 μm or more, and even more preferably 0.3 μm or more, in volume-based median diameter. Furthermore, from the viewpoint of further increasing the ionic conductivity of the composite electrolyte, the average particle size of the inorganic solid electrolyte is more preferably 15 μm or less, and even more preferably 10 μm or less, in volume-based median diameter. The average particle size of the inorganic solid electrolyte is a value measured by laser diffraction / scattering particle size measurement. Details of the measurement method follow the method described in the Examples below.

[0059] The content of the inorganic solid electrolyte in the composite electrolyte is preferably 50% by mass or more, more preferably 55% by mass or more, even more preferably 60% by mass or more, even more preferably 70% by mass or more, and even more preferably 75% by mass or more, based on the total amount of the composite electrolyte, from the viewpoint of ensuring formability. Furthermore, the upper limit of the content of the inorganic solid electrolyte is preferably 90% by mass or less, more preferably 85% by mass or less, based on the total amount of the composite electrolyte, from the viewpoint of ensuring flexibility of the composite electrolyte. One type of inorganic solid electrolyte may be used alone, or two or more types may be used in combination.

[0060] <Component (Y): Nonaqueous Electrolyte> The nonaqueous electrolyte contained in the composite electrolyte of the present disclosure is a liquid mixture containing an organic molecule (hereinafter also referred to as "organic molecule (M)") having at least one atom selected from the group consisting of a sulfur atom, an oxygen atom (excluding the oxygen atom in the carbonate group), a nitrogen atom, and a phosphorus atom, and an alkali metal salt. Note that, hereinafter, the "oxygen atoms excluding the oxygen atom in the carbonate group" will also be referred to as "specific oxygen atoms."

[0061] The ratio of the organic molecule (M) to the alkali metal salt contained in the non-aqueous electrolyte is preferably such that the mixture of the organic molecule (M) and the alkali metal salt is liquid at room temperature (e.g., 15 to 30 ° C.) and atmospheric pressure. The ratio of the organic molecule (M) to the alkali metal salt contained in the non-aqueous electrolyte is preferably 0.5 to 15 moles of organic molecule (M) per mole of alkali metal salt, in order to achieve excellent ionic conductivity at room temperature while suppressing a decrease in ionic conductivity over time. From this perspective, the ratio of the organic molecule (M) to the alkali metal salt contained in the non-aqueous electrolyte is more preferably 0.7 to 12 moles of organic molecule (M) per mole of alkali metal salt, more preferably 0.8 to 10 moles, even more preferably 0.9 to 7.0 moles, and even more preferably 1.0 mole to 5.0 moles. By setting the ratio of the organic molecule (M) to the alkali metal salt contained in the nonaqueous electrolyte within the above range, the viscosity of the nonaqueous electrolyte can be appropriately increased, and the gaps formed between the particles of the inorganic solid electrolyte can be sufficiently filled with the nonaqueous electrolyte, which is thought to result in the minimization of interfacial resistance and the production of a composite electrolyte exhibiting high ionic conductivity.

[0062] (Organic Molecule (M)) The number of at least one atom selected from the group consisting of sulfur atoms, specific oxygen atoms, nitrogen atoms, and phosphorus atoms contained in the organic molecule (M) is not particularly limited. In the organic molecule (M), the number of at least one atom selected from the group consisting of sulfur atoms, specific oxygen atoms, nitrogen atoms, and phosphorus atoms is preferably 1 to 8, and more preferably 2 to 6, per molecule. Of these, the organic molecule (M) preferably contains a total of two or more, and more preferably two to six, of at least one atom selected from sulfur atoms, specific oxygen atoms, and nitrogen atoms per molecule.

[0063] The molecular weight of the organic molecule (M) is, for example, 300 or less, preferably 250 or less, and more preferably 200 or less. The lower limit of the molecular weight of the organic molecule (M) is, for example, 20 or more, preferably 40 or more, and more preferably 50 or more. The total number of carbon atoms per molecule of the organic molecule (M) is preferably 8 or less, and more preferably 7 or less.

[0064] Specific examples of the organic molecule (M) include organic molecules having a sulfur atom, such as sulfone compounds, sulfide compounds, thiol compounds, thioester compounds, thiocarbonate compounds, sulfoxide compounds, and sulfamide compounds. Organic molecules having a nitrogen atom include nitrile compounds, amine compounds, and amide compounds. Organic molecules having a phosphorus atom include phosphine compounds, phosphine oxide compounds, and phosphinimine compounds. Organic molecules having an oxygen atom include organic molecules having an oxygen atom among the examples of organic molecules having a sulfur atom, organic molecules having an oxygen atom among the examples of organic molecules having a nitrogen atom, and organic molecules having an oxygen atom among the examples of organic molecules having a phosphorus atom, as well as ether compounds, ester compounds, and ketone compounds. However, carbonate compounds are not included in the organic molecule (M). When the organic molecule (M) is a compound having a specific oxygen atom, it is preferable that the organic molecule (M) have a sulfur atom, nitrogen atom, or phosphorus atom in addition to the specific oxygen atom, from the viewpoint of improving ion conductivity and its retention characteristics.

[0065] From the viewpoint of further increasing the ionic conductivity of the nonaqueous electrolyte solution, the organic molecule (M) is preferably at least one selected from the group consisting of an organic molecule having a sulfur atom and a specific oxygen atom, an organic molecule having a nitrogen atom, and an organic molecule having a phosphorus atom.

[0066] Organic molecule having a sulfur atom and a specific oxygen atom As the organic molecule having a sulfur atom and a specific oxygen atom, a compound having a functional group containing a sulfur atom and a specific oxygen atom can be preferably used, and among them, a sulfone compound can be preferably used. A preferred example of the sulfone compound is a compound represented by the following formula (1): (In formula (1), R １ and R ２ are each independently an alkyl group or an alkoxy group, or R １ and R ２ and represents a cyclic structure formed by bonding together, and the total number of carbon atoms in formula (1) is 2 to 8.

[0067] The molecule represented by the above formula (1) (hereinafter also referred to as "molecule (M-1)") has a sulfonyl group (-SO ２ -) in the above formula (1). １ and R ２ When R is an alkyl group or an alkoxy group, the alkyl group and the alkoxy group may be linear or branched. １ and R ２ The number of carbon atoms in each group of R １ and R ２ There are no particular limitations as long as the total number of carbon atoms in R is 2 to 8. １ and R ２ Each of the groups preferably has 1 to 3 carbon atoms, more preferably 1 or 2.

[0068] R in the above formula (1) １ and R ２ But, R １ and R ２ When R represents a cyclic structure formed by bonding R to R, the cyclic structure may have a saturated ring skeleton or an unsaturated bond in the ring skeleton. １ and R ２ The cyclic structure formed by bonding R may be a structure in which an alkyl group (e.g., a methyl group or an ethyl group) is bonded to the ring skeleton. １ and R ２The number of carbon atoms in the cyclic structure formed by bonding of is preferably 2 to 8, more preferably 2 to 6, and even more preferably 3 to 5.

[0069] In order to improve the ionic conductivity of the composite electrolyte, R １ and R ２ is R １ and R ２ and more preferably, the cyclic structure has a saturated ring skeleton.

[0070] The total number of carbon atoms in the above formula (1) is 2 to 8. The total number of carbon atoms in the above formula (1) is preferably 2 to 6, and more preferably 2 to 5.

[0071] Specific examples of the molecule (M-1) include R １ and R ２ are each an alkyl group or an alkoxy group, examples of which include dimethyl sulfone, ethyl methyl sulfone, diethyl sulfone, dioctyl sulfone, dimethyl sulfate, and diethyl sulfate. １ and R ２ But, R １ and R ２ Examples of the ring structure formed by bonding include tetrahydrothiophene 1,1-dioxide, 3-methylsulfolane, 3-sulfolene, 1,3-propane sultone, 1,4-butane sultone, 1,3,2-dioxathiolane 2,2-dioxide, etc. As the molecule (M-1), one type may be used alone, or two or more types may be used in combination.

[0072] Nitrogen-containing organic molecule As the nitrogen-containing organic molecule, a nitrile compound or an amide compound can be preferably used. Preferred examples of the nitrile compound include those represented by the following formula (2): (In formula (2), R ３ represents a hydrocarbon chain, R ４ and R ５ each independently represents a hydrogen atom, an alkyl group, or a cyano group, and the total number of carbon atoms in formula (2) is 8 or less.

[0073] The molecule represented by the above formula (2) (hereinafter also referred to as "molecule (M-2)") is a molecule having two or more cyano groups (-CN). ３ R may be a saturated hydrocarbon chain or may have an unsaturated bond. ３ Preferably, R represents a saturated hydrocarbon chain. ３ has, for example, 1 to 6 carbon atoms, preferably 1 to 4 carbon atoms, and more preferably 2 to 4 carbon atoms.

[0074] R ４ or R ５ When R is an alkyl group, the alkyl group may be linear or branched. It is preferably linear. ４ and R ５ The number of carbon atoms in each of the groups is preferably 0 to 2, and more preferably 0 or 1.

[0075] The total number of carbon atoms in the formula (2) may be 8 or less. The total number of carbon atoms in the formula (2) is preferably 6 or less, and more preferably 4 or less.

[0076] Specific examples of the molecule (M-2) include succinonitrile, adiponitrile, 3-hexenedinitrile, 1,3,5-pentanetricarbonitrile, tert-butylmalononitrile, etc. As the molecule (M-2), one type may be used alone, or two or more types may be used in combination.

[0077] The amide compound includes an amide group (—CO—NR ６ R ７ or -NR ６ -COR ８ , where R ６ and R ７ are each independently a hydrogen atom or an alkyl group, and R ８ A compound (diamide) having two N,N,N',N'-tetramethylmalonamide, N,N,N',N'-tetraethylmalonamide, N,N'-diacetylethylenediamine, etc. can be preferably used.

[0078] Organic Molecules Having a Phosphorus Atom Examples of organic molecules having a phosphorus atom include ethylenebis(dimethylphosphine), ethylenebis(diphenylphosphine), methyl(diphenyl)phosphine oxide, triphenylphosphine oxide, methyl(diphenyl)phosphine imine, triphenylphosphine imine, and trimethyl phosphate.

[0079] From the viewpoint of availability of raw materials, the organic molecule (M) is preferably at least one selected from the group consisting of sulfone compounds, nitrile compounds, and amide compounds. Furthermore, from the viewpoint of providing more excellent ionic conductivity to the non-aqueous electrolyte, at least one selected from the group consisting of molecules (M-1), (M-2), and diamides is more preferable, and R １ and R ２ a molecule representing a cyclic structure formed by bonding of R ３ represents a saturated hydrocarbon chain and N,N,N',N'-tetraalkylmalonamide. As the organic molecule (M), one type may be used alone, or two or more types may be used in combination.

[0080] (Alkali Metal Salt) The alkali metal salt is not particularly limited as long as it is a salt that generates alkali metal ions. Examples of the alkali metal salt include lithium salt, sodium salt, and potassium salt.

[0081] Specific examples of alkali metal salts include LiCO ３ , LiBr, LiCl, LiI, LiSCN, LiBF ４ , LiAsF ６ , LiClO ４ , C.H. ３ COOLi, CF ３ COOLi, LiCF ３ SO ３ , LiPF ６ , LiC(CF ３ SO ２ ) ３ , lithium bis(fluorosulfonyl)imide (Li ＋ (FSO ２) ２ N － ), lithium bis(trifluoromethanesulfonyl)imide (Li ＋ (CF ３ SO ２ ) ２ N － and salts of the anions of these lithium salts with alkali metals other than lithium (for example, sodium, potassium, etc.). Of these, lithium salts and sodium salts are preferred because they have high ionic dissociation properties and can further increase the ionic conductivity of the non-aqueous electrolyte solution.

[0082] The alkali metal salt contained in the non-aqueous electrolyte preferably contains an imide-based alkali metal salt, which can increase the ionic conductivity of the non-aqueous electrolyte. Among the imide-based alkali metal salts, imide-based lithium salts and imide-based sodium salts are preferred, which have high ionic dissociation properties.

[0083] As the imide-based lithium salt, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, or lithium (fluorosulfonyl)(trifluoromethanesulfonyl)imide is preferred, lithium bis(fluorosulfonyl)imide or lithium bis(trifluoromethanesulfonyl)imide is more preferred, and lithium bis(fluorosulfonyl)imide is even more preferred.

[0084] As the imide-based sodium salt, sodium bis(fluorosulfonyl)imide, sodium bis(trifluoromethanesulfonyl)imide, or sodium trifluoromethanesulfonimide is preferred, sodium bis(fluorosulfonyl)imide or sodium bis(trifluoromethanesulfonyl)imide is more preferred, and sodium bis(fluorosulfonyl)imide is even more preferred.

[0085] The molecular weight of the alkali metal salt is, for example, 500 or less, preferably 400 or less, more preferably 350 or less, and even more preferably 300 or less. The lower limit of the molecular weight of the alkali metal salt is, for example, 20 or more, preferably 50 or more, more preferably 100 or more, and even more preferably 150 or more. One type of alkali metal salt may be used alone, or two or more types may be used in combination.

[0086] The melting point of the alkali metal salt under atmospheric pressure is, for example, 60° C. or higher, preferably 70° C. or higher, and more preferably 80° C. or higher. There are no particular limitations on the upper limit of the melting point of the alkali metal salt, but it may be, for example, 300° C. or lower, or 250° C. or lower.

[0087] The concentration of the alkali metal salt in the non-aqueous electrolyte is preferably 0.1 to 10 mol / L, more preferably 0.2 to 8 mol / L, and even more preferably 0.5 to 5 mol / L.

[0088] The nonaqueous electrolyte may further contain components other than the organic molecule (M) and the alkali metal salt, provided that the effects of the present disclosure are not impaired. However, in consideration of the ionic conductivity and ease of manufacture of the nonaqueous electrolyte, the nonaqueous electrolyte is preferably a liquid mixture comprising the organic molecule (M) and the alkali metal salt.

[0089] In the composite electrolyte of the present disclosure, the content of the nonaqueous electrolyte is preferably 10% by mass or more, more preferably 15% by mass or more, based on the total amount of the composite electrolyte, from the viewpoint of ensuring flexibility of the composite electrolyte. The upper limit of the content of the nonaqueous electrolyte is preferably 50% by mass or less, more preferably 40% by mass or less, even more preferably 30% by mass or less, and even more preferably 25% by mass or less, based on the total amount of the composite electrolyte, from the viewpoint of obtaining a composite electrolyte that exhibits good ionic conductivity.

[0090] In the composite electrolyte of the present disclosure, the mass ratio of the inorganic solid electrolyte to the non-aqueous electrolyte solution, expressed as "inorganic solid electrolyte / non-aqueous electrolyte solution," is preferably 90 / 10 to 50 / 50. When the mass ratio of the inorganic solid electrolyte to the non-aqueous electrolyte solution is within the above range, a composite electrolyte can be obtained that exhibits a well-balanced improvement in ionic conductivity (particularly, ionic conductivity retention characteristics) and flexibility. In terms of achieving both ionic conductivity and flexibility of the composite electrolyte, the mass ratio of the inorganic solid electrolyte to the non-aqueous electrolyte solution is more preferably 90 / 10 to 55 / 45, even more preferably 90 / 10 to 60 / 40, even more preferably 85 / 15 to 70 / 30, and even more preferably 80 / 20 to 75 / 25. The mass ratio expressed as "inorganic solid electrolyte / non-aqueous electrolyte solution" is the ratio of each component when the total amount of the inorganic solid electrolyte and the non-aqueous electrolyte solution is taken as 100.

[0091] <Other Components> The composite electrolyte of the present disclosure may further contain components (hereinafter also referred to as "other components") different from the inorganic solid electrolyte and non-aqueous electrolyte solution described above. Examples of other components include polymer solid electrolytes, polymer gel electrolytes, inorganic fillers, binders, conductive additives, plasticizers, positive electrode active materials, and negative electrode active materials. However, in consideration of the ionic conductivity and ease of manufacture of the composite electrolyte, it is preferable that the content of other components be as small as possible. Specifically, the content of other components is preferably 1% by mass or less, and more preferably 0.5% by mass or less, of the total amount of the composite electrolyte.

[0092] <Method for producing composite electrolyte> The composite electrolyte of the present disclosure can be produced by mixing an inorganic solid electrolyte with the non-aqueous electrolyte solution described above. One preferred embodiment of the method for producing the composite electrolyte of the present disclosure includes a step of mixing a powdered inorganic solid electrolyte with a non-aqueous electrolyte solution (hereinafter also referred to as a "mixing step"). According to this method, a composite electrolyte that is flexible and has excellent ionic conductivity can be obtained by the simple method of mixing a powdered inorganic solid electrolyte with a non-aqueous electrolyte solution.

[0093] Mixing Step In the mixing step for producing a composite electrolyte, the powdered inorganic solid electrolyte and the non-aqueous electrolyte solution may be mixed uniformly, and the method is not particularly limited. When mixing the inorganic solid electrolyte and the non-aqueous electrolyte solution, it is preferable to mix the inorganic solid electrolyte and the non-aqueous electrolyte solution while applying mechanical energy to a substance containing the inorganic solid electrolyte and the non-aqueous electrolyte solution by means of impact, shear, compression, friction, or the like (hereinafter also referred to as "mechanical mixing"). Mixing the inorganic solid electrolyte and the non-aqueous electrolyte solution by mechanical mixing is thought to cause changes in the physicochemical properties of the inorganic solid electrolyte and / or the non-aqueous electrolyte solution, thereby increasing the ionic conductivity of the mixture.

[0094] The method for mixing the inorganic solid electrolyte and the non-aqueous electrolyte while applying mechanical energy is not particularly limited. Mechanical mixing of the inorganic solid electrolyte and the non-aqueous electrolyte can be performed using various devices such as a ball mill, a bead mill, a blender, a homogenizer, a stamp mill, a homomixer, and a disperser mixer. Furthermore, when producing a composite electrolyte on a small scale, mechanical mixing of the inorganic solid electrolyte and the non-aqueous electrolyte can also be performed using a mortar and pestle. Mixing the inorganic solid electrolyte and the non-aqueous electrolyte may be performed at room temperature or at a low temperature. Furthermore, the inorganic solid electrolyte and the non-aqueous electrolyte may be mixed while heating. When mixing the inorganic solid electrolyte and the non-aqueous electrolyte while heating, the heating temperature is preferably set to a temperature that allows the inorganic solid electrolyte to remain solid (i.e., below the melting point of the inorganic solid electrolyte) and the non-aqueous electrolyte to remain liquid (i.e., below the boiling point of the non-aqueous electrolyte). The preferred range of the average particle size of the inorganic solid electrolyte used to produce the composite electrolyte is as described above.

[0095] The blending ratio of the inorganic solid electrolyte to the non-aqueous electrolyte solution, expressed as "inorganic solid electrolyte / non-aqueous electrolyte solution," is preferably 90 / 10 to 50 / 50 by mass. In order to achieve both ionic conductivity and flexibility of the composite electrolyte, the blending ratio of the inorganic solid electrolyte to the non-aqueous electrolyte solution is more preferably 90 / 10 to 55 / 45, even more preferably 90 / 10 to 60 / 40, even more preferably 85 / 15 to 70 / 30, and even more preferably 80 / 20 to 75 / 25.

[0096] The composite electrolyte obtained as described above exhibits high ionic conductivity at room temperature (25°C) and can stably maintain high ionic conductivity over time. Therefore, by using the composite electrolyte of the present disclosure as an electrolyte material for an electricity storage device, an electricity storage device with excellent ionic conductivity can be obtained. Specifically, for a solid electrolyte having a thickness of about 1,000 µm (specifically, 1,000 ± 50 µm), the ionic conductivity measured at 25°C using an AC impedance method is 1.0 × 10 －６ From the viewpoint of obtaining an electricity storage device with excellent performance, the ionic conductivity under the same conditions is preferably 5.0 × 10 S / cm or more. －６ S / cm or more, and more preferably 1.0×10 －５ The ionic conductivity is more preferably 25 S / cm or more. Details of the method for measuring the ionic conductivity follow the method described in the examples below.

[0097] Furthermore, the composite electrolyte of the present disclosure can stably maintain its initial ionic conductivity regardless of the passage of time. Specifically, the ionic conductivity at room temperature (25° C.) immediately after production is defined as the initial ionic conductivity σ ＨＥ１ After the production, the ionic conductivity after being left in an environment of room temperature (25°C) and a dew point of -40°C or less for 20 hours is determined as ionic conductivity after 20 hours σ ＨＥ２ When the initial ionic conductivity σ ＨＥ１ Ionic conductivity after 20 hours σ ＨＥ２ The ratio (= σ ＨＥ２ / σ ＨＥ１×100 (unit: %) is preferably 50% or more, more preferably 60% or more, even more preferably 70% or more, and even more preferably 80% or more.

[0098] <Electricity Storage Device> The electricity storage device of the present disclosure (hereinafter also referred to as "the device") includes the composite electrolyte of the present disclosure. Specific embodiments of the device include a secondary battery, a capacitor, and the like. When the device is a secondary battery, one embodiment is an all-solid-state or semi-solid-state battery, and a lithium-ion secondary battery is preferred in terms of excellent ionic conductivity.

[0099] An all-solid-state or semi-solid lithium-ion secondary battery, which is one embodiment of the device, will now be described. A lithium-ion secondary battery is a laminate comprising electrodes consisting of a positive electrode and a negative electrode, and a solid electrolyte layer, with the solid electrolyte layer disposed between the positive electrode and the negative electrode so that the solid electrolyte layer is in contact with the electrode. The materials constituting the positive electrode and the negative electrode are not particularly limited, and can be appropriately selected from materials known as electrode materials for lithium-ion secondary batteries. For example, a metal foil such as aluminum or stainless steel can be used as the positive electrode current collector. A metal foil such as copper foil or lithium foil can be used as the negative electrode current collector.

[0100] In the lithium ion secondary battery of the present disclosure, the solid electrolyte layer is formed using the composite electrolyte of the present disclosure, which contains an inorganic solid electrolyte and a nonaqueous electrolyte solution. The solid electrolyte layer can be obtained by molding the composite electrolyte of the present disclosure into a desired shape. The molding method is not particularly limited, and known methods such as extrusion molding, injection molding, pressure molding, slip casting, mold casting, and tape casting can be used. Among these, obtaining a molded body by pressure molding is preferred, as it minimizes the porosity of the resulting solid electrolyte layer and facilitates the formation of ion conduction paths. The shape of the molded body is not particularly limited and can be appropriately set depending on the shape of the applied power storage device. The shape of the molded body is, for example, rectangular or circular. The thickness of the solid electrolyte layer is not particularly limited and can be appropriately set depending on the application of the secondary battery. The thickness of the solid electrolyte layer is, for example, 5 to 500 μm.

[0101] When the composite electrolyte finally obtained is a molded body, the molded body may be used as it is as the solid electrolyte layer of the electricity storage device, or a plurality of molded bodies may be stacked to form the solid electrolyte layer of the electricity storage device.

[0102] The method for producing a lithium ion secondary battery is not particularly limited, and known methods can be appropriately adopted depending on the battery structure, etc. For example, a laminate including a positive electrode, a solid electrolyte layer, and a negative electrode may be produced by sandwiching a solid electrolyte layer formed from the composite electrolyte of the present disclosure between a positive electrode and a negative electrode, and preferably applying a pressure treatment for bonding. Alternatively, a laminate including a positive electrode, a solid electrolyte layer, and a negative electrode may be produced by sandwiching an electrolyte material including a granular composite electrolyte between a positive electrode and a negative electrode and placing it in a container, and preferably applying a pressure treatment for bonding to the container. A laminate including a positive electrode, a solid electrolyte layer, and a negative electrode is usually housed in a case and used as a secondary battery.

[0103] The device is not limited to the above-described configuration in which the carrier for ion conduction is lithium ions, but may also be a secondary battery in which other ions, such as sodium ions, are used as carriers. The device may also be a capacitor. One form of the capacitor includes a positive electrode layer, a negative electrode layer, and a solid electrolyte layer, with the solid electrolyte layer disposed between the positive electrode layer and the negative electrode layer so that the solid electrolyte layer is in contact with each electrode layer.

[0104] The power storage device including the composite electrolyte of the present disclosure can be used for various purposes, specifically, as a power source for various mobile devices such as mobile phones, personal computers, smartphones, game consoles, and wearable devices; various moving objects such as electric vehicles, hybrid vehicles, robots, and drones; and various electric and electronic devices such as digital cameras, video cameras, music players, power tools, and home appliances.

[0105] The present disclosure will be specifically described below based on examples. However, the present disclosure is not limited to these examples. In the following, "parts" and "%" mean "parts by mass" and "% by mass", respectively, unless otherwise specified.

[0106] <<Production of Inorganic Solid Electrolyte and Physical Properties>> [Production Example 1] 1. Production of Inorganic Solid Electrolyte SE-1 Layered zirconium phosphate (Zr(HPO)) was used as a feed component so as to achieve the molar ratio (Li:In:Zr:Si:P=1.25:0.20:1.80:0.05:2.95) shown in Table 1. ４ ) ２ ・nH ２ 0), 4.000 g of zirconium hydroxide, 0.432 g of lithium carbonate (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.), 0.415 g of silicon dioxide (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.), 0.027 g of silicon dioxide (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.), and 0.25 g of indium oxide (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.) were weighed and placed in a mortar. 25 g of pure water was further added and wet-mixed to obtain a mixture (mixing step). The obtained mixture was dried at 100 ° C. for 2 hours, then transferred to an alumina crucible (volume 30 mL), heated to 1,250 ° C. over 5.5 hours, and held for 5 hours to perform firing (firing step). Thereafter, the mixture was allowed to cool to room temperature (25 ° C.) to obtain a fired product. The obtained fired product was pulverized in a mortar to obtain inorganic solid electrolyte SE-1. In addition, in each production example, Zr(HPO ４ ) ２ ・nH ２ The value of n in O was set to 1.0.

[0107] 2. Confirmation of Crystallinity by Powder X-ray Diffraction Measurement The obtained inorganic solid electrolyte SE-1 was subjected to powder X-ray diffraction measurement using an X-ray diffractometer (D8 ADVANCE, manufactured by Bruker AXS). CuKα was used as the X-ray source, and the applied voltage was 40 kV and the current was 40 mA. The measurement conditions were a measurement range of 2θ = 10-80 deg, a scanning rate of 2.5 deg / min, and a step angle of 0.01 deg. As a result, it was found that the main crystalline phase of the inorganic solid electrolyte SE-1 was monoclinic or rhombohedral LiZr ２ P ３ O １２ It was confirmed that the inorganic solid electrolyte SE-1 has a NASICON-type crystal structure.

[0108] 3. Measurement of particle size (volume-based median diameter) Inorganic solid electrolyte SE-1 was diluted with pure water in a 30 mL sample bottle to give a 1% by mass dispersion. The diluted dispersion was irradiated with 1 kHz ultrasound for 10 minutes. Using the dispersion immediately after ultrasound irradiation as a measurement sample, the volume-based median diameter (D50) of inorganic solid electrolyte SE-1 was measured at room temperature (25 ° C.) using a laser diffraction / scattering particle size measuring device MT-3000 (manufactured by Microtrac). Particle size measurements were performed twice, and the average value was adopted as the volume-based median diameter of inorganic solid electrolyte SE-1. The volume-based median diameter of inorganic solid electrolyte SE-1 was 1.4 μm.

[0109] [Production Examples 2 to 4] Inorganic solid electrolytes (referred to as "Inorganic Solid Electrolyte SE-2," "Inorganic Solid Electrolyte SE-3," and "Inorganic Solid Electrolyte SE-5," respectively) were obtained by the same operation as in Production Example 1, except that the types and amounts of raw materials were changed as shown in Table 1. For the inorganic solid electrolytes obtained in each Production Example, powder X-ray diffraction measurements were performed in the same manner as in Production Example 1. As a result, it was found that the main crystalline phase of inorganic solid electrolytes SE-2 and SE-3 was monoclinic or rhombohedral Na ３ Zr ２ Si ２ P.O. １２ The main crystalline phase of the inorganic solid electrolyte SE-5 is monoclinic or rhombohedral LiZr ２ P ３ O １２ These results confirmed that the inorganic solid electrolytes SE-2, SE-3, and SE-5 had a NASICON-type crystal structure. Furthermore, the volume-based median diameters of the inorganic solid electrolytes SE-2, SE-3, and SE-5 were measured in the same manner as in Production Example 1. The results are shown in Table 1.

[0110]

[0111] <<Production of Nonaqueous Electrolyte>> [Production Example 5] 1. Production of Non-Aqueous Electrolyte LE-1 In a dry room with a dew point of -40°C or less, 0.2159 g of succinonitrile (manufactured by Tokyo Chemical Industry Co., Ltd.) as an organic molecule and 0.0841 g of lithium bis(fluorosulfonyl)imide (manufactured by Kanto Chemical Co., Ltd.) as an alkali metal salt were weighed out and placed in a vial so as to achieve the molar concentrations shown in Table 2. The vial was stirred for 30 minutes using a magnetic stirrer set at 25°C to obtain non-aqueous electrolyte LE-1 (liquid at 25°C). The molar concentration M (unit: moles / liter) of the non-aqueous electrolyte was calculated using the following formula (1), where m is the amount of substance of the alkali metal salt (unit: moles) and V is the volume of the non-aqueous electrolyte (unit: liters). M = m / V (1)

[0112] [Production Examples 6 to 11, 13] Non-aqueous electrolyte solutions LE-2 to LE-7 and LE-13 (all of which were liquid at 25°C) were obtained in the same manner as in Production Example 5, except that the types and amounts of raw materials were changed as shown in Table 2.

[0113] [Production Example 12] In a dry room with a dew point of -40°C or lower, 0.1306 g of N,N'-diacetylethylenediamine (manufactured by Tokyo Chemical Industry Co., Ltd.) as an organic molecule and 0.1694 g of lithium bis(fluorosulfonyl)imide (manufactured by Kanto Chemical Co., Inc.) as an alkali metal salt were weighed out so as to have the molar concentrations shown in Production Example 12 in Table 2, and mechanically mixed using a mortar at room temperature (25°C) to obtain nonaqueous electrolyte solution LE-8 (liquid at 25°C).

[0114] Comparative Production Examples 1 to 3 The same operation as in Production Example 5 was carried out except that the types and amounts of raw materials were changed as shown in Table 2, to obtain nonaqueous electrolyte solutions LE-9 to LE-11 (all of which were liquid at 25°C).

[0115] Comparative Production Example 4 Vinylene carbonate (VC) and fluoroethylene carbonate (FEC) were added to a mixed solvent of ethylene carbonate and dimethyl carbonate (EC:DMC=3:7 by mass) so that the concentrations were 1% by mass and 2% by mass, respectively, to obtain LiPF ６ was dissolved to a concentration of 1.2 mol / L to obtain a non-aqueous electrolyte LE-12 (liquid at 25° C.).

[0116]

[0117] Details of the compounds used in Table 2 are shown below. SN: succinonitrile (manufactured by Tokyo Chemical Industry Co., Ltd.) SL: sulfolane (manufactured by Tokyo Chemical Industry Co., Ltd.) AdN: adiponitrile (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) TMMA: N,N,N',N'-tetramethylmalonamide (manufactured by Tokyo Chemical Industry Co., Ltd.) TMP: trimethyl phosphate (manufactured by Tokyo Chemical Industry Co., Ltd.) DAEDA: N,N'-diacetylethylenediamine (manufactured by Tokyo Chemical Industry Co., Ltd.) PC: propylene carbonate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) EC: ethylene carbonate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) DMC: dimethyl carbonate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) VC: vinylene carbonate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) FEC: fluoroethylene carbonate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) LiFSI: Lithium bis(fluorosulfonyl)imide (manufactured by Kanto Chemical Co., Ltd.) LiPF ６ : Lithium hexafluorophosphate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) NaFSI: Sodium bis(fluorosulfonyl)imide (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.)

[0118] <<Production and Evaluation of Composite Electrolytes>> [Example 1] 1. Production of Composite Electrolyte HE-1 In a dry room with a dew point of −40° C. or less, Li, １．２５ In ０．２ Zr １．８ Si ０．０５ P ２．９５ O １２ 0.100 g of (the inorganic solid electrolyte SE-1 obtained in Production Example 1) and 0.025 g of Li(FSI)(SN) (the nonaqueous electrolyte LE-1 obtained in Production Example 5) were weighed and mechanically mixed in a mortar at room temperature (25° C.) to obtain a composite electrolyte HE-1.

[0119] 2. Evaluation (1) Flexibility Test Using a press mold consisting of a die set 11, an upper punch 12, and a lower punch 13 (see FIG. 1), a sample pellet was prepared in a dry room with a dew point of −40° C. or less. First, the die set 11 containing 0.100 g of composite electrolyte HE-1 was placed on the lower punch 13, and the upper punch 12 was placed on the die set 11. The composite electrolyte HE-1 was compressed for 10 seconds at a pressure of 10 MPa using a hydraulic press to obtain a circular sample pellet with a diameter of 1 cm and a thickness of 1,000 μm. The end of the sample pellet placed on the lower punch 13 was pinched with tweezers and bent, and the flexibility was evaluated based on the angle at which the sample pellet broke when bent. The evaluation was performed based on the following criteria. As a result, the flexibility of the composite electrolyte HE-1 was evaluated as △. ○: No break even when bent by 90° or more △: Bendable, but breaks when bent by 90° ×: Cannot be bent, breaks when force is applied

[0120] (2) Measurement of Ionic Conductivity A sample pellet of composite electrolyte HE-1 was placed on a 10 mm square stainless steel plate, and then another 10 mm square stainless steel plate was placed on top of it to obtain an evaluation cell. The resistance value at room temperature (25°C) was measured by AC impedance measurement. The obtained resistance value was used to calculate the ionic conductivity (σ) according to the following formula (2), and this was referred to as the initial ionic conductivity σ ＨＥ１ σ = L / (R × S) (2) (In formula (2), σ is the ionic conductivity (unit: S / cm), R is the resistance (unit: Ω), and S is the cross-sectional area of ​​the sample pellet (unit: cm ２ ), L represents the distance between the electrodes (unit: cm). As a result, the initial ionic conductivity σ ＨＥ１ is 5.0 x 10 －５ The initial ionic conductivity was σ ＨＥ１ After the measurement, the sample pellet of composite electrolyte HE-1 was removed from the composite electrolyte evaluation cell and left to stand in a dry room at room temperature (25°C) and a dew point of -40°C or less for 20 hours. ＨＥ１ The resistance value at 25°C was measured by AC impedance measurement in the same manner as in the measurement procedure in 1., and the ionic conductivity (σ) was calculated by the above formula (2). ＨＥ２As a result, the ionic conductivity σ ＨＥ２ is 4.0 x 10 －５ The viscosity was S / cm.

[0121] (3) Retention of ionic conductivity The initial ionic conductivity σ of the composite electrolyte HE-1 obtained above ＨＥ１ and ionic conductivity σ after 20 hours ＨＥ２ Using the above, the retention rate of ionic conductivity (γ ＨＥ ) was calculated. ＨＥ = σ ＨＥ２ / σ ＨＥ１ ×100...(3) (In formula (3), γ ＨＥ represents the retention rate of the ionic conductivity of the composite electrolyte.) As a result, γ of the composite electrolyte HE-1 ＨＥ was 80%.

[0122] [Examples 2 to 14, Comparative Examples 1 to 4] Composite electrolytes HE-2 to HE-18 were obtained by the same procedure as in Example 1, except that the types and amounts of raw materials were changed as shown in Table 3. The obtained composite electrolytes HE-2 to HE-18 were subjected to a flexibility test and an ionic conductivity (σ ＨＥ１ , σ ＨＥ２ ) was measured, and the retention rate of ionic conductivity was calculated. The results are shown in Table 3. In Comparative Example 4, the sample pellet was brittle after being left to stand for 20 hours in a dry room at room temperature (25°C) with a dew point of -40°C or less, and therefore the ionic conductivity could not be measured. Therefore, in Table 3, σ ＨＥ２ and γ ＨＥ In the production of the composite electrolyte HSE-12, Li was used as the inorganic solid electrolyte SE-4. １．５ Al ０．５ Ge １．５ P ３ O １２ (manufactured by Toshima Manufacturing Co., Ltd.) was used.

[0123]

[0124] <Evaluation Results> As is clear from the results in Table 3, all of the composite electrolytes of Examples 1 to 14, which were prepared using a liquid composition containing an organic molecule (M) and an alkali metal salt as a non-aqueous electrolyte together with an inorganic solid electrolyte, had flexibility and a high ionic conductivity retention rate γ ＨＥ The reason why the composite electrolytes of Examples 1 to 14 exhibited such excellent properties is presumably due to the high affinity between the inorganic solid electrolyte and the non-aqueous electrolyte and the low volatility of the non-aqueous electrolyte.

[0125] In contrast, the composite electrolytes of Comparative Examples 1 to 4, which used a carbonate-based solvent as the nonaqueous electrolyte, were inflexible and brittle. In particular, the composite electrolyte of Comparative Example 4 was so brittle that the ionic conductivity could not be measured. Furthermore, the composite electrolytes of Comparative Examples 1 and 3 had a low ionic conductivity retention rate γ ＨＥ was significantly lower than in Examples 1 to 14.

[0126] From the above results, it has become clear that a composite electrolyte produced using an inorganic solid electrolyte and a liquid composition containing an organic molecule (M) and an alkali metal salt as a non-aqueous electrolyte solution exhibits high ionic conductivity at room temperature, has flexibility, and exhibits little change in ionic conductivity over time.

[0127] The present invention is not limited to the above-described embodiments, and encompasses various modifications and equivalent modifications within the scope of the spirit of the present invention. Therefore, in light of the above teachings, various combinations and forms, as well as other combinations and forms including only one element, more than one element, or less than one element, are to be understood as falling within the scope and spirit of the present invention.

[0128] 10... Press mold

Claims

1. A composite electrolyte comprising an inorganic solid electrolyte and a non-aqueous electrolyte solution, the non-aqueous electrolyte solution containing an organic molecule having at least one atom selected from the group consisting of a sulfur atom, an oxygen atom (excluding oxygen atoms in a carbonate group), a nitrogen atom, and a phosphorus atom, and an alkali metal salt.

2. The composite electrolyte according to claim 1, wherein the ratio of said alkali metal salt to said organic molecule is 0.5 to 15 moles of said organic molecule per mole of said alkali metal salt.

3. The composite electrolyte according to claim 1, wherein the organic molecule is at least one selected from the group consisting of a sulfone compound, a nitrile compound, and an amide compound.

4. The composite electrolyte according to claim 1, wherein the inorganic solid electrolyte comprises an oxide having a NASICON type crystal structure.

5. The oxide having a NASICON type crystal structure is represented by the general formula: Li １＋ｘ＋ｙ－ｚ M1 ｘ Zr ２－ｘ M2 ｙ M3 ｚ P ３－ｙ－ｚ O １２ wherein M1 comprises Fe, In or Al, M2 comprises Si, M3 comprises W, and x > 0, y > 0, z > 0, and y + z > 0 are satisfied.

6. The oxide having a NASICON type crystal structure is represented by the general formula: Li １＋ｘ M4 ｘ Ge ｙ Zr ２－ｘ－ｙ P ３ O １２ 5. The composite electrolyte according to claim 4, comprising a solid electrolyte represented by the formula (wherein M4 contains Al and satisfies 0≦x≦2, 0≦y≦2, and 0≦x+y≦2).

7. The oxide having a NASICON type crystal structure is represented by the general formula: Na ３＋２ｘ＋ｙ＋α M5 ｘ M6 ｙ M7 ｚ Zr ２－ｘ－ｙ－ｚ S ２＋α P １－α O １２ (wherein M5 contains an element that can be a divalent cation, M6 contains Al and may contain an element that can be a trivalent cation other than Al, M7 contains Ti and may contain an element that can be a tetravalent cation other than Ti, Zr, and Si, and x≧0, y≧0, z≧0, x+y+z>0, and α>0 are satisfied).

8. The composite electrolyte of claim 1, wherein said alkali metal salt comprises an imide-based alkali metal salt.

9. The composite electrolyte according to claim 1, wherein the content of the inorganic solid electrolyte is 50% by mass or more and 90% by mass or less.

10. A method for producing a composite electrolyte according to any one of claims 1 to 9, comprising the step of mixing the powdered inorganic solid electrolyte with the non-aqueous electrolyte.

11. An electricity storage device comprising the composite electrolyte according to any one of claims 1 to 9.

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