Composite electrolyte and power storage device

Abstract

This composite electrolyte contains an inorganic solid electrolyte and an organic solid electrolyte, the organic solid electrolyte containing a molecular crystal and having a porosity of 15% or less.

Description

Composite electrolyte and energy storage device

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to Japanese Patent Application No. 2023-108816, filed on June 30, 2023, the entire contents of which are incorporated herein by reference. The present disclosure relates to a composite electrolyte 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. Organic electrolyte solutions have traditionally been used as the electrolyte. In recent years, solid or gel electrolytes using inorganic or organic materials have been proposed as a way to eliminate concerns about electrolyte leakage and short circuits within batteries due to overcharge and overdischarge.

[0004] Among these, inorganic solid electrolytes have excellent ionic conductivity, but because they are in the form of powder, their formability during the production of electrolyte layers is not particularly good. Furthermore, when attempting to obtain an electrolyte layer with excellent ionic conductivity using inorganic solid electrolytes, there are disadvantages, such as the need for sintering at high temperatures (e.g., temperatures exceeding 1,000°C) in the case of oxide-based solid electrolytes, and the need for high-pressure pressing at high pressures (e.g., pressures exceeding 10 MPa) in the case of sulfide-based solid electrolytes, which impose significant process constraints. While organic solid electrolytes have moderate flexibility and high formability, they tend to have lower ionic conductivity than inorganic solid electrolytes.

[0005] Therefore, in recent years, in order to develop a new solid electrolyte with excellent performance, a composite electrolyte formed by an inorganic solid electrolyte and an organic solid electrolyte has been investigated (see, for example, Patent Document 1). Patent Document 1 discloses a composite electrolyte using lithium lanthanum zirconium oxide as the inorganic solid electrolyte and polyethylene oxide containing a lithium salt as the organic solid electrolyte.

[0006] Japanese Patent Application Laid-Open No. 2022-160569

[0007] According to the investigations of the present inventors, conventional composite electrolytes formed using an inorganic solid electrolyte and an organic solid electrolyte have low ionic conductivity and are inferior in performance. From the viewpoint of further improving the quality of electricity storage devices, it is necessary to develop a composite electrolyte with further improved ionic conductivity.

[0008] The present disclosure has been made in view of the above circumstances, and one object of the present disclosure is to provide a composite electrolyte of an inorganic solid electrolyte and an organic solid electrolyte that exhibits high ionic conductivity.

[0009] As a result of intensive research to solve the above problems, the present inventors have found that in a composite electrolyte of an inorganic solid electrolyte and an organic solid electrolyte, a solid electrolyte exhibiting high ionic conductivity can be obtained by using a specific substance as the organic solid electrolyte and focusing on porosity. According to the present disclosure, the following composite electrolyte and electricity storage device are provided.

[0010] [1] A composite electrolyte comprising an inorganic solid electrolyte and an organic solid electrolyte, wherein the organic solid electrolyte contains molecular crystals and has a porosity of 15% or less. [2] The composite electrolyte according to [1], wherein the inorganic solid electrolyte contains an oxide having a NASICON-type crystal structure. [3] 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[4] The composite electrolyte according to [2], wherein the oxide having a NASICON-type crystal structure is represented by the general formula: Na ３＋２ｘ＋ｙ＋α M4 ｘ M5 ｙ M6 ｚ Zr ２－ｘ－ｙ－ｚ Si ２＋α P １－α O １２ (wherein M4 contains an element that forms a divalent cation, M5 contains Al and may contain an element that forms a trivalent cation other than Al, and M6 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). [5] The composite electrolyte according to any of [1] to [4], wherein the molecular crystal contains an organic molecule and an alkali metal salt as constituent units. [6] The composite electrolyte according to [5], wherein the number of carbon atoms per molecule of the organic molecule is 6 or less. [7] The composite electrolyte according to [5] or [6], wherein the alkali metal salt contains an imide-based alkali metal salt. [8] The composite electrolyte according to any of [5] to [7], wherein the organic molecule has at least one atom selected from the group consisting of a sulfur atom, an oxygen atom, a nitrogen atom, and a phosphorus atom. [9] The composite electrolyte according to any one of [5] to [8], wherein the organic molecule is at least one selected from the group consisting of sulfones and nitriles.

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

[0011] According to the present disclosure, a composite electrolyte of an inorganic solid electrolyte and an organic solid electrolyte can be obtained that exhibits high ionic conductivity. Furthermore, by using the composite electrolyte in the electrolyte layer of an electricity storage device such as a secondary battery or a capacitor, it is possible to obtain an electricity storage device that combines ionic conductivity with the safety ensured by the solidification of the electrolyte layer in a good balance.

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

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

[0014] <<Composite Electrolyte>> The composite electrolyte of the present disclosure contains an inorganic solid electrolyte (hereinafter also referred to as “component (X)”) and a molecular crystal (hereinafter also referred to as “component (Y)”) as an organic solid electrolyte. The composite electrolyte of the present disclosure has a porosity of 15% or less.

[0015] If the porosity of the composite electrolyte exceeds 15%, the ionic conductivity of the composite electrolyte is low and the practicality is poor. From the viewpoint of obtaining a composite electrolyte with excellent ionic conductivity, the porosity of the composite electrolyte is preferably 12% or less, more preferably 10% or less, and even more preferably 8% or less. There is no particular restriction on the lower limit of the porosity of the composite electrolyte, as long as it is 0% or more.

[0016] In this specification, the porosity of the composite electrolyte is expressed as φ (unit: %) and the density of the composite electrolyte is expressed as D (unit: g cm －３ ), and the theoretical density of the composite electrolyte is D' (unit: g cm －３ ), it can be expressed by the following formula: φ=(1−D / D′)×100

[0017] The density (D) of the composite electrolyte used to calculate the porosity is calculated using the mass (M, unit: g) of the composite electrolyte and the contact area (S, unit: cm ２ The theoretical density (D') can be expressed by the following formula using the thickness (L, unit: cm) of the composite electrolyte (S), and the density (D) of the composite electrolyte: D = M / (S x L). The theoretical density (D') is a value calculated by the sum of the values ​​obtained by multiplying the densities of the (X) component and the (Y) component contained in the composite electrolyte by the mass ratio of each component. Details of the method for calculating the porosity and density (D) follow the method described in the Examples below. The porosity of the composite electrolyte can be adjusted, for example, by the temperature of the heat treatment after mixing the (X) component and the (Y) component.

[0018] Next, each component constituting the composite electrolyte of the present disclosure will be described in detail.

[0019] <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) because of their high ion conductivity, and oxide-based solid electrolytes are more preferred because of their high safety in the atmosphere.

[0020] The crystal structure of the component (X) is not particularly limited, and examples of the crystal structure that the component (X) may have include a NASICON structure, a LISICON structure, a perovskite structure, and a garnet structure.

[0021] 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.).

[0022] As a solid electrolyte having a LISICON structure, Li １４ ZnGe ４ O １６Examples of the solid electrolyte having a perovskite structure include oxides in which some of the elements constituting the compound are substituted with the above-mentioned various elements. 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 compound are substituted with the above-mentioned various elements. ７ La ３ Zr ２ O １２ and Li ５ La ３ Nb ２ O １２ and oxides in which some of the elements constituting these compounds are substituted with the above-mentioned various elements.

[0023] One embodiment of the composite electrolyte of the present disclosure is an organic-inorganic hybrid solid electrolyte comprising an inorganic solid electrolyte having a NASICON-type crystal structure and a molecular crystal as an organic solid electrolyte. 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 with 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 (XRD).

[0024] When an oxide having a NASICON-type crystal structure is used as the component (X), preferred examples of the oxide include the oxide (y1) and oxide (y2) shown below. Oxide (y1): General formula Li １＋ｘ＋ｙ－ｚ M1 ｘ Zr ２－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 (y2): General formula: Na３＋２ｘ＋ｙ＋α M4 ｘ M5 ｙ M6 ｚ Zr ２－ｘ－ｙ－ｚ Si ２＋α P １－α O １２ (wherein M4 contains an element that forms a divalent cation, M5 contains Al and may contain an element that forms a trivalent cation other than Al, M6 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.)

[0025] ・About oxide (y1) Oxide (y1) is LiZr ２ (P.O. ４ ) ３ In an oxide having a basic skeleton, a portion of Zr is substituted with M1 (containing Fe, In, or Al), and a portion of P is substituted with M2 (containing Si) and / or M3 (containing W).

[0026] In the oxide (y1), M1 may contain Fe or In. That is, M1 may be Fe, In, or Al, or 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 a trivalent cation other than Fe, In, or Al include Group 13 elements, transition elements (Groups 3 to 11 elements) that form trivalent cations, Sb, Bi, etc.

[0027] 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.

[0028] 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.

[0029] In the general formula of the oxide (y1), 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 (y1) 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 (y1) 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 (y1) 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:

[0030] More specifically, x, y, and z in the general formula of the oxide (y1) preferably satisfy x≦0.3, and more preferably satisfy x≦0.25, in that an impurity phase is unlikely to be formed, thereby enabling a solid electrolyte exhibiting high ionic conductivity to be obtained. The lower limit of x preferably satisfies x≧0.01, more preferably satisfies x≧0.05, and even more preferably satisfies x≧0.10.

[0031] Regarding y, since it has a dominant effect on the formation of the α phase, thereby enabling a solid electrolyte with higher ion conductivity to be obtained, it is preferable that y≦0.2, more preferably y≦0.15, and even more preferably y≦0.10. Furthermore, when y>0, the lower limit of y is preferably y≧0.01, and more preferably y≧0.03. 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 because its crystal structure is isotropic.

[0032] 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≦0.2, 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.

[0033] ・About oxide (y2) Oxide (y2) is Na ３ Zr ２ Si ２ P.O. １２ In an oxide having a basic skeleton, a portion of Zr is substituted with at least one of M4 (containing an element that becomes a divalent cation), M5 (containing Al), and M6 (containing Ti), and the amount of Si in the composition is higher than that of the basic skeleton.

[0034] In the oxide (y2), examples of M4 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.

[0035] M5 may contain Al. That is, M5 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).

[0036] M6 may contain Ti. That is, M6 may be Ti, or may further contain an element other than Ti, Zr, and Si that forms a tetravalent cation. Examples of elements other than Ti, Zr, and Si that form a tetravalent cation include Group 14 elements other than Si, and transition elements (Groups 3 to 11 elements) other than Ti and Zr that form a tetravalent cation (Te, Ce, Th).

[0037] In the general formula of the oxide (y2), 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 (y2) is "Na ３＋ｙ＋α M5 ｙ M6 ｚ Zr ２－ｙ－ｚ Si ２＋α P １－α O １２ When y=0, x>0 and z>0, the oxide (y2) is represented by "Na ３＋２ｘ＋α M4 ｘ M6 ｚ Zr ２－ｘ－ｚ Si ２＋α P １－α O １２ When z=0, x>0 and y>0, the oxide (y2) is represented by "Na ３＋２ｘ＋ｙ＋α M4 ｘ M5 ｙ Zr ２－ｘ－ｙ Si ２＋α P １－α O １２ When x=0, y=0 and z>0, the oxide (y2) is represented by "Na ３＋α M6 ｚ Zr ２－ｚ Si ２＋α P １－α O １２ " is expressed as:

[0038] More specifically, x, y, z, and α in the general formula of the oxide (y2) 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.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] In the above general formulas representing the oxide (y1) and the oxide (y2), the stoichiometric ratio of O is written as 12, but as long as the charge neutrality of the oxide as a whole can be maintained, the stoichiometric ratio of O does not have to be strictly 12. In other words, the O content in the oxide (y1) may be less than 12 or more than 12, as long as the charge neutrality of the oxide (y1) 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 general formula of oxide (y1) above) are also included in oxide (y1) as long as the charge neutrality of oxide (y1) as a whole is maintained. Similarly, O in oxide (y2) may be a value less than 12 or a value greater than 12, as long as the charge neutrality of oxide (y2) as a whole can be maintained. For example, Na ３＋２ｘ＋ｙ＋α M4 ｘ M5 ｙ M6 ｚ Zr ２－ｘ－ｙ－ｚ Si ２＋α P １－α O １２＋γ (where 0≦γ≦1 is satisfied, and M4, M5, M6, x, y, z, and α are the same as M4, M5, M6, x, y, z, and α in the above formula shown as the general formula of oxide (y2)) is also included in oxide (y2) as long as the charge neutrality of oxide (y2) as a whole is maintained.

[0043] The method for producing the oxide (y1) and the oxide (y2) is not particularly limited. The oxide (y1) and the oxide (y2) 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).

[0044] As the raw material of oxide (y1), a supply component corresponding to an element for obtaining the target oxide (y1) 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 (y1) 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.

[0045] Examples of the Li supply component, M1 supply component (Fe supply component, In supply component, or Al supply component), M2 supply component, M3 supply component, Zr supply component, and P supply component for obtaining oxide (y1) include carbonates, hydrogencarbonates, sulfates, sulfites, nitrates, nitrites, phosphates, acetates, citrates, ammonium salts, oxides, hydroxides, chlorides, and sulfides of these metal elements. Note that one type of these supply components may be a compound containing two or more elements selected from Li, M1, M2, M3, Zr, and P.

[0046] 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.

[0047] As the raw material for oxide (y2), a supply component corresponding to the element for obtaining the target oxide (y2) can be used from among a Na supply component, an M4 supply component, an M5 supply component, an M6 supply component, a Zr supply component, a Si supply component, and a P supply component. For example, when obtaining an oxide (y2) where x = 0 and y = 0, a Na supply component, an M6 supply component, a Zr supply component, a Si supply component, and a 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, M4, M5, M6, Zr, Si, and P.

[0048] As the Na supply component, M4 supply component, M5 supply component, M6 supply component, Zr supply component, Si supply component, and P supply component, which are raw materials for oxide (y2), 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, M4, M5, M6, 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.

[0049] When producing the oxide (y1) and the oxide (y2), 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.

[0050] 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.

[0051] 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.

[0052] The oxide (y1) exhibits high Li ion conductivity, and the oxide (y2) exhibits high Na ion conductivity. Therefore, the oxide (y1) is suitable as a material for a composite electrolyte for an electricity storage device in which the ion-conducting carrier is a lithium ion. The oxide (y2) is suitable as a material for a composite electrolyte for an electricity storage device in which the ion-conducting carrier is a sodium ion.

[0053] 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.

[0054] The average particle size of the inorganic solid electrolyte used to produce 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 preferable that a composite electrolyte exhibiting high ionic conductivity can be obtained while improving handleability. From the viewpoint of handleability, 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 ionic conductivity, 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.

[0055] The content of the inorganic solid electrolyte in the composite electrolyte is preferably 1% by volume or more, more preferably 2% by volume or more, even more preferably 5% by volume or more, and even more preferably 10% by volume or more, based on the total amount of the composite electrolyte, from the viewpoint of obtaining a composite electrolyte with high ionic conductivity by utilizing the characteristics of the inorganic solid electrolyte. Furthermore, the upper limit of the content of the inorganic solid electrolyte is preferably 99% by volume or less, more preferably 95% by volume or less, even more preferably 85% by volume or less, even more preferably 75% by volume or less, even more preferably 70% by volume or less, and even more preferably 65% ​​by volume or less, based on the total amount of the composite electrolyte, in order to sufficiently reduce the resistance at the particle interface of the inorganic solid electrolyte, thereby increasing ionic conductivity. One type of inorganic solid electrolyte may be used alone, or two or more types may be used in combination.

[0056] <Component (Y): Molecular Crystal> In the composite electrolyte of the present disclosure, the molecular crystal contained as the component (Y) is a solid in which structural units are regularly arranged in a crystal lattice. An organic solid electrolyte containing an organic molecule and an alkali metal salt as structural units can be preferably used as the component (Y). In particular, an organic solid electrolyte containing an organic molecule having at least one atom selected from the group consisting of sulfur, oxygen, nitrogen, and phosphorus atoms (hereinafter also referred to as "organic molecule (A)") and an alkali metal salt as structural units can be preferably used as the component (Y). The molecular crystal containing the organic molecule (A) and the alkali metal salt has an ion conduction path due to the regular arrangement of the structural units, the organic molecule (A) and the alkali metal salt, and is therefore suitable in that it exhibits excellent ion conductivity.

[0057] (A) Organic Molecule The number of atoms of at least one kind selected from the group consisting of sulfur atoms, oxygen atoms, nitrogen atoms, and phosphorus atoms contained in the (A) organic molecule is not particularly limited. In the (A) organic molecule, the number of atoms of at least one kind selected from the group consisting of sulfur atoms, oxygen atoms, nitrogen atoms, and phosphorus atoms is preferably 1 to 8, and more preferably 2 to 6, per molecule. Of these, the (A) organic molecule preferably contains two or more, and more preferably 2 to 6, atoms of at least one kind selected from sulfur atoms, oxygen atoms, and nitrogen atoms per molecule.

[0058] The molecular weight of the (A) organic molecule 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 (A) organic molecule is, for example, 20 or more, preferably 40 or more, and more preferably 50 or more. From the viewpoint of promoting crystallization of the mixture of the (A) organic molecule and the alkali metal salt, the total number of carbon atoms per molecule of the (A) organic molecule is preferably 10 or less, more preferably 8 or less, and even more preferably 6 or less. The total number of carbon atoms per molecule of the (A) organic molecule is preferably 2 or more.

[0059] Specific examples of (A) organic molecules include organic molecules having a sulfur atom, such as sulfone, sulfide, thiol, thioester, thiocarbonate, sulfoxide, and sulfamide. Examples of organic molecules having a nitrogen atom include nitrile, amine, and amide. Examples of organic molecules having a phosphorus atom include phosphine, phosphine oxide, and phosphinimine. Examples of 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 ethers, esters, ketones, and carbonates. The (A) organic molecule constituting the molecular crystal may be one type alone or two or more types.

[0060] In terms of being able to further increase the ionic conductivity of the molecular crystal, it is preferable that the (A) organic molecule be at least one selected from the group consisting of organic molecules having a sulfur atom and an oxygen atom, organic molecules having a nitrogen atom, and organic molecules having a phosphorus atom.

[0061] (Organic molecule having sulfur atom and oxygen atom) As the organic molecule having sulfur atom and oxygen atom, sulfone can be preferably used. Preferred examples of sulfone include those 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 16.

[0062] The molecule represented by the above formula (1) (hereinafter also referred to as "molecule (A-1)") has a sulfonyl group (-SO ２ -) in the above formula (1). １ and R ２When 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 on the number of carbon atoms, as long as the total number of carbon atoms is 2 to 16. From the viewpoint of inducing crystallization in the mixture of the supply component of the (A-1) molecule and the alkali metal salt during the production of molecular crystals, R １ and R ２ Each of the groups preferably has 1 to 3 carbon atoms, more preferably 1 or 2.

[0063] 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 ２ The 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.

[0064] R in the above formula (1) is preferred because it can improve the ionic conductivity of the molecular crystal. １ and R ２ is R １ and R ２ and more preferably, the cyclic structure has a saturated ring skeleton.

[0065] The total number of carbon atoms in the above formula (1) is 2 to 16. From the viewpoint of promoting crystallization of a mixture of the supply component of the (A-1) molecule and the alkali metal salt during the production of molecular crystals, the total number of carbon atoms in the above formula (1) is preferably 2 to 8, more preferably 2 to 6, and even more preferably 2 to 5.

[0066] Specific examples of the (A-1) molecule 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 (A-1) molecule that represents a cyclic 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. The (A-1) molecule that constitutes the molecular crystal may be one type alone or a combination of two or more types.

[0067] (Nitrogen Atom-Containing Organic Molecule) As the nitrogen atom-containing organic molecule, a nitrile can be preferably used. A preferred example of the nitrile is a compound 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 16 or less.

[0068] The molecule represented by the above formula (2) (hereinafter also referred to as "(A-2) molecule") is a molecule having two or more cyano groups (-CN). ３ R may be a saturated hydrocarbon chain or may have an unsaturated bond. R is a group that can be used to obtain molecular crystals with excellent ionic conductivity. ３ Preferably, R represents a saturated hydrocarbon chain. ３ has, for example, 1 to 10 carbon atoms, preferably 1 to 6 carbon atoms, and more preferably 2 to 4 carbon atoms.

[0069] R ４ or R ５When 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 group is preferably 0 to 3, more preferably 0 or 1, from the viewpoint of causing crystallization by mixing the supply component of the (A-2) molecule with an alkali metal salt during production of the molecular crystal.

[0070] From the viewpoint of promoting crystallization of the mixture of the supply component of the (A-2) molecule and the alkali metal salt during the production of molecular crystals, the total number of carbon atoms in the above formula (2) is preferably 8 or less, more preferably 6 or less.

[0071] Specific examples of the (A-2) molecule include succinonitrile, adiponitrile, 3-hexenedinitrile, 1,3,5-pentanetricarbonitrile, tert-butylmalononitrile, 1,2,2,3-propanetetracarbonitrile, etc. The (A-2) molecule constituting the molecular crystal may be one type alone or a combination of two or more types.

[0072] (Organic Molecule 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, and triphenylphosphine imine.

[0073] From the viewpoint of ease of production of the molecular crystal, the organic molecule (A) is preferably at least one selected from the group consisting of sulfones and nitriles. Furthermore, the (A-1) molecule is more preferable in terms of superior ionic conductivity of the molecular crystal, and R １ and R ２ More preferably, the cyclic structure has a saturated ring skeleton.

[0074] Alkali Metal Salt The alkali metal salt is not particularly limited as long as it generates alkali metal ions. Examples of the alkali metal salt include lithium salt, sodium salt, and potassium salt.

[0075] Specific examples of alkali metal salts include Li ２ CO 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 lithium salts such as lithium(fluorosulfonyl)(trifluoromethanesulfonyl)imide; 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 provide molecular crystals with higher ionic conductivity.

[0076] The alkali metal salt constituting the molecular crystal preferably includes an imide-based alkali metal salt, in order to increase the ionic conductivity of the molecular crystal. Among these, an imide-based lithium salt or an imide-based sodium salt is preferred, in terms of high ionic dissociation.

[0077] Among the imide-based lithium salts, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, or lithium (fluorosulfonyl)(trifluoromethanesulfonyl)imide is particularly preferred, lithium bis(fluorosulfonyl)imide or lithium bis(trifluoromethanesulfonyl)imide is more preferred, and lithium bis(fluorosulfonyl)imide is even more preferred.

[0078] 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.

[0079] 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. The alkali metal salt constituting the molecular crystal may be one type alone or two or more types.

[0080] The melting point of the alkali metal salt is, for example, 60° C. or higher, preferably 70° C. or higher, and more preferably 80° C. or higher. There is no particular upper limit to the melting point of the alkali metal salt, but it may be, for example, 300° C. or lower, or 250° C. or lower.

[0081] <Production of Molecular Crystal> The method for producing the molecular crystal that is the component (Y) constituting the composite electrolyte of the present disclosure is not particularly limited. For example, when an organic solid electrolyte containing an organic molecule (A) and an alkali metal salt as constituent units is used as the component (Y), the molecular crystal can be produced using a supply component for the organic molecule (A) (hereinafter also referred to as "organic substance (A)") and an alkali metal salt.

[0082] A molecular crystal containing (A) an organic molecule and an alkali metal salt as structural units is preferably obtained by a method of mixing (A) an organic substance and an alkali metal salt and then heating. Specifically, it is preferably produced by a method including the following mechanical mixing step and heating step. Mechanical mixing step: A step of mixing (A) an organic substance and an alkali metal salt while applying mechanical energy to obtain a mixture. Heating step: A step of heating the mixture obtained by the mechanical mixing step. Each step will be described in detail below.

[0083] <Mechanical Mixing Step> In the mechanical mixing step, (A) the organic substance and the alkali metal salt are mixed while applying mechanical energy to a substance containing the organic substance and the alkali metal salt by means of impact, shear, compression, friction, or the like. This preferably causes changes in the physicochemical properties of the organic substance, the alkali metal salt, or both. In this specification, the process of mixing substances while applying mechanical energy is also referred to as "mechanical mixing."

[0084] The blending ratio of the (A) organic substance and the alkali metal salt when mixing them is not particularly limited and may be set depending on the types of the (A) organic substance and the alkali metal salt, etc. The blending ratio of the (A) organic substance and the alkali metal salt may be, for example, 0.1 to 10 moles of the (A) organic substance per mole of the alkali metal salt. The blending ratio of the (A) organic substance and the alkali metal salt is preferably 0.2 to 5 moles, more preferably 0.25 to 4 moles, and even more preferably 0.5 to 2 moles, of the (A) organic substance per mole of the alkali metal salt.

[0085] In addition, when producing a molecular crystal, a substance other than the (A) organic substance and alkali metal salt (for example, a sulfur-containing organic molecule other than the (A) organic substance) may be further used as a constituent unit of the crystal lattice, as long as the effects of the present disclosure are not impaired. However, in consideration of the ionic conductivity and ease of production of the molecular crystal, it is preferable to minimize the amount of the substance other than the (A) organic substance and alkali metal salt used. Specifically, the amount of the substance other than the (A) organic substance and alkali metal salt used is preferably 0.1 mol or less, more preferably 0.05 mol or less, per 1 mol of the total amount of the (A) organic substance and alkali metal salt.

[0086] The method for mixing the (A) organic substance and the alkali metal salt while applying mechanical energy is not particularly limited. In the mechanical mixing step, the (A) organic substance and the alkali metal salt can be mixed using various devices, such as a ball mill, a bead mill, a blender, a homogenizer, a stamp mill, a homomixer, or a disperser-type mixer. Furthermore, when producing molecular crystals on a small scale, the (A) organic substance and the alkali metal salt can also be mechanically mixed using a mortar and pestle. The (A) organic substance and the alkali metal salt can be mechanically mixed in a dry or wet manner. Furthermore, the (A) organic substance and the alkali metal salt can be mechanically mixed at room temperature or at a low temperature. For example, when the melting point of the (A) organic substance is lower than room temperature, the (A) organic substance in a liquid state can be mechanically mixed with the alkali metal salt. Alternatively, the (A) organic substance in a solid state can be mechanically mixed with the alkali metal salt at a temperature lower than the melting point of the (A) organic substance.

[0087] The mechanical mixing of the (A) organic substance and the alkali metal salt may be performed while heating. However, in order to suppress volatilization or sublimation of the (A) organic substance, the mechanical mixing step is preferably performed at a temperature lower than the heating temperature in the subsequent heating step. Specifically, the mechanical mixing step is performed, for example, at 50°C or lower, preferably 40°C or lower, and more preferably 35°C or lower. The time for mechanical mixing varies depending on the amount and type of the (A) organic substance and alkali metal salt used, but may be, for example, 1 to 60 minutes, or 1 to 30 minutes.

[0088] The mixture of (A) organic substance and alkali metal salt obtained by mechanical mixing (hereinafter also simply referred to as "mixture") preferably has a melting point of 40°C or higher, more preferably 50°C or higher, and even more preferably 55°C or higher. In addition, the melting point of the mixture is preferably 110°C or lower, more preferably 100°C or lower, and even more preferably 95°C or lower, in order to suppress decomposition of molecular crystals accompanying volatilization or sublimation of the (A) organic substance or (A) organic molecules in the heating step after the mechanical mixing step. In this specification, the melting point of the mixture of (A) organic substance and alkali metal salt is a value obtained by differential scanning calorimetry (DSC). Details of the measurement method follow the method described in the Examples below.

[0089] <Heating Step> In the heating step, after the mechanical mixing step is performed, the mixture obtained by the mechanical mixing step is heated. The method for heating the mixture is not particularly limited. The heating temperature of the mixture can be appropriately set depending on the types of (A) organic substance and alkali metal salt used as raw materials. From the viewpoint of making the (A) organic substance and alkali metal salt in the mixture more uniform, it is preferable to heat the mixture in this heating step at a temperature equal to or higher than the melting point of the mixture of the (A) organic substance and alkali metal salt obtained by mechanical mixing. Setting the heating temperature equal to or higher than the melting point of the mixture melts the mixture, thereby promoting uniform mixing of the (A) organic substance and alkali metal salt.

[0090] The temperature at which the mixture is heated is preferably higher than the melting point of the mixture, from the viewpoint of homogenizing the organic substance (A) and the alkali metal salt in the mixture by melting the mixture. Furthermore, from the viewpoint of promoting homogenization of the organic substance (A) and the alkali metal salt in the mixture, the heating temperature of the mixture is more preferably 5°C or higher, and even more preferably 7°C or higher, than the melting point of the mixture (unit: °C). Regarding the upper limit of the heating temperature of the mixture, from the viewpoint of suppressing volatilization or sublimation of the components contained in the mixture, when the melting point of the mixture is expressed as Mp (unit: °C), it is preferably (Mp + 20)°C or lower, and more preferably (Mp + 15)°C or lower. The heating time is not particularly limited as long as it homogenizes the organic substance (A) and the alkali metal salt in the mixture. The heating time is, for example, 1 minute to 3 hours, preferably 15 minutes to 2 hours, and more preferably 30 minutes to 2 hours. Furthermore, the heat treatment is usually carried out under normal pressure, but may also be carried out under pressure or reduced pressure.

[0091] When the mixture is heated, it is preferable to heat the mixture while stirring it to further homogenize the organic substance (A) and the alkali metal salt. The stirring method is not particularly limited, and examples thereof include a magnetic stirrer, a stirring rod, a stirrer with stirring blades, and external circulation stirring. Stirring may also be performed by a mechanical mixing operation that can generate a greater shear force, such as a homomixer, a disperser-type mixer, or a homogenizer.

[0092] After heating a mixture containing (A) an organic substance and an alkali metal salt, the heated mixture can be crystallized by lowering the temperature of the heated mixture, thereby obtaining the desired molecular crystal. The temperature of the heated mixture can be lowered by gradually cooling the mixture (e.g., slowly lowering the temperature at room temperature over 1 to 48 hours). Alternatively, the heated mixture can be rapidly cooled (e.g., placing the heated mixture in a thermostatic bath at a temperature lower than room temperature (e.g., 15°C or lower) for a short period of time). From the viewpoint of favorable crystallization of the heated mixture, it is preferable to cool the heated mixture by gradually lowering the temperature of the mixture. The fact that the product obtained by this production method is a molecular crystal containing (A) an organic molecule and an alkali metal salt can be detected by powder X-ray diffraction measurement of the product. Details of the measurement method follow those described in the Examples below.

[0093] In addition, according to a manufacturing method including a mechanical mixing step and a heating step, it is believed that in the production of molecular crystals, the mechanical mixing performed before the heat treatment generates an intermolecular interaction between the alkali metal ions derived from the alkali metal salt and the organic substance (A). Therefore, in a manufacturing method in which the heat treatment is performed after the mechanical mixing, it is believed that sublimation or volatilization of the organic substance (A) is suppressed during the heat treatment, thereby suppressing the variation in the composition of the molecular crystal. Furthermore, it is believed that suppressing the variation in the composition of the molecular crystal forms a uniform ion conduction path, making it possible to produce molecular crystals that exhibit excellent ion conductivity.

[0094] In the composite electrolyte, the content of the molecular crystal as the (Y) component is preferably 1% by volume or more, more preferably 5% by volume or more, even more preferably 15% by volume or more, even more preferably 25% by volume or more, still more preferably 30% by volume or more, and even more preferably 35% by volume or more, based on the viewpoint of sufficiently reducing the resistance at the particle interface of the inorganic solid electrolyte, thereby increasing ionic conductivity, and improving the formability of the composite electrolyte. Furthermore, from the viewpoint of obtaining a composite electrolyte with high ionic conductivity by utilizing the properties of the inorganic solid electrolyte, the upper limit of the content of the molecular crystal is preferably 99% by volume or less, more preferably 98% by volume or less, even more preferably 95% by volume or less, and even more preferably 90% by volume or less, based on the total amount of the composite electrolyte.

[0095] The composite electrolyte of the present disclosure may further contain other components in addition to the inorganic solid electrolyte and the molecular crystals, as long as the effects of the present disclosure are not impaired. Examples of other components include molecular crystals other than the molecular crystals of the present disclosure (i.e., component (Y)), polymer solid electrolytes, polymer gel electrolytes, binders, etc. However, considering the ionic conductivity and ease of production of the composite electrolyte, it is preferable to use as few other components as possible. Specifically, the content of the other components is preferably 1% by volume or less, and more preferably 0.5% by volume or less, of the total amount of the inorganic solid electrolyte and the molecular crystals.

[0096] <Method for producing composite electrolyte> The composite electrolyte of the present disclosure can be produced by mixing an inorganic solid electrolyte as component (X) with a molecular crystal as component (Y). Specifically, the composite electrolyte of the present disclosure is preferably produced by a method including the following mixing step and heating step. Mixing step: A step of mixing an inorganic solid electrolyte with a molecular crystal to obtain a mixture. Heating step: A step of heating the mixture of the inorganic solid electrolyte and the molecular crystal.

[0097] <Mixing Step> In the mixing step when producing a composite electrolyte, the inorganic solid electrolyte and the molecular crystals may be mixed uniformly, and the method is not particularly limited. The inorganic solid electrolyte and the molecular crystals may be mixed dry or wet. Dry mixing is preferred. The mechanical mixing step is advantageous in that the molecular crystals as raw materials can be melted by the heat of mechanical mixing and mixed uniformly with the inorganic solid electrolyte, and that a composite electrolyte with a sufficiently small porosity can be obtained because no solvent is required during mixing. As a specific embodiment of mechanical mixing, the description of the mechanical mixing step in the method for producing molecular crystals can be applied.

[0098] The compounding ratio when mixing the inorganic solid electrolyte and the molecular crystal is not particularly limited and may be set depending on the types of inorganic solid electrolyte and molecular crystal, etc. From the viewpoint of improving ionic conductivity and formability in a well-balanced manner, the compounding ratio of the inorganic solid electrolyte and the molecular crystal is preferably inorganic solid electrolyte:molecular crystal = 1:99 to 99:1 by volume, more preferably 5:95 to 95:2, even more preferably 15:85 to 90:10, even more preferably 25:75 to 90:10, even more preferably 30:70 to 90:10, and even more preferably 35:65 to 90:10.

[0099] <Heating Step> In the heating step, after the above-mentioned mixing step, the mixture of inorganic solid electrolyte and molecular crystals obtained in the mixing step is heated. This heating step is thought to reduce the porosity by filling the gaps in the inorganic solid electrolyte with molecular crystals, thereby reducing the interfacial resistance and obtaining a composite electrolyte with excellent ionic conductivity.

[0100] In the heating step, the mixture (typically in particulate form) obtained in the mixing step may be used as is and heated. Alternatively, a mixture of the inorganic solid electrolyte and molecular crystals may be molded, and the resulting molded body may be heated. When the molded body is heated, the molding method is not particularly limited, and known methods such as extrusion molding, injection molding, pressure molding, slip casting, mold cast molding, and tape molding can be used. Among these, it is preferable to obtain a molded body by pressure molding, since this can minimize the porosity of the composite electrolyte and facilitate 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 electricity storage device. The shape of the molded body is, for example, rectangular or circular.

[0101] The heating temperature when heating the mixture of the inorganic solid electrolyte and the molecular crystals can be appropriately set depending on the types of inorganic solid electrolyte and molecular crystals used as raw materials, etc. From the viewpoint of filling the gaps in the inorganic solid electrolyte with the molecular crystals and obtaining a composite electrolyte (i.e., a solid electrolyte) with a small porosity, it is preferable to heat the mixture at a temperature at which the molecular crystals do not ooze out of the mixture during heating.

[0102] Specifically, in the heating step during the production of the composite electrolyte, it is preferable to heat the mixture of the inorganic solid electrolyte and the molecular crystal at or near the melting point of the molecular crystal (for example, in the case of a molecular crystal containing (A) an organic molecule and an alkali metal salt as constituent units, the melting point of the mixture of the raw material (A) organic substance and the alkali metal salt). From the viewpoint of maintaining a state in which the gaps in the inorganic solid electrolyte are filled with the molecular crystal in the mixture of the inorganic solid electrolyte and the molecular crystal, when the melting point of the molecular crystal is represented by Mr (unit: °C), the heating temperature of the mixture of the inorganic solid electrolyte and the molecular crystal is preferably in the range of (Mr±15)°C, and more preferably in the range of (Mr±10)°C.

[0103] The heating time is, for example, 1 to 72 hours, preferably 2 to 48 hours, and more preferably 5 to 36 hours. The heating process may be carried out under normal pressure, or under increased or reduced pressure. To lower the temperature of the mixture after heating, the mixture may be gradually cooled (e.g., air-cooled) or rapidly cooled using a cooler or the like. When the mixture after heating is a compact, the compact may be used as is as the solid electrolyte layer of the electricity storage device. Alternatively, a plurality of compacts may be stacked to form the solid electrolyte layer of the electricity storage device. When the composite electrolyte of the present disclosure is obtained as a compact, the thickness of the compact is, for example, 5 to 5,000 μm, preferably 5 to 3,500 μm, and more preferably 10 to 3,000 μm.

[0104] The composite electrolyte obtained as described above exhibits high ionic conductivity. Therefore, by using the composite electrolyte of the present disclosure as an electrolyte material for an electricity storage device, an electricity storage device with high ionic conductivity can be obtained. Specifically, for a molded body made of the composite electrolyte of the present disclosure and 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 1×10 －６ From the viewpoint of obtaining an electricity storage device with excellent performance, the ionic conductivity under the same conditions is preferably 2×10 S / cm or more. －６ S / cm or more is more preferable, and 5×10 －６ The ionic conductivity is more preferably 100 S / cm or more. The ionic conductivity can be measured by AC impedance measurement. Details of the measurement method follow the method described in the Examples below.

[0105] <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. Examples of the device include a secondary battery, a capacitor, and the like. When the device is a secondary battery, one embodiment thereof is an all-solid-state battery, and a lithium-ion secondary battery or a sodium-ion secondary battery is preferred in terms of excellent ionic conductivity.

[0106] An all-solid-state secondary battery, which is one embodiment of the device, will now be described. The all-solid-state 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 secondary batteries. For example, in the case of a lithium-ion secondary battery, 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.

[0107] In the all-solid-state secondary battery, the solid electrolyte layer is formed from the composite electrolyte of the present disclosure (i.e., a composite electrolyte containing an inorganic solid electrolyte and a molecular crystal). The thickness of the solid electrolyte layer is not particularly limited and can be set appropriately depending on the application of the secondary battery, etc. The thickness of the solid electrolyte layer is, for example, 5 to 5,000 μm, preferably 5 to 3,500 μm, and more preferably 10 to 3,000 μm.

[0108] The method for producing an all-solid-state 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, preferably by 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 particulate composite electrolyte between a positive electrode and a negative electrode and placing it in a container, and then subjecting the container to a heat treatment to obtain the above-mentioned composite electrolyte, preferably by applying a pressure treatment for bonding. 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.

[0109] The ion-conducting carrier in the device is not particularly limited. The device may also be a capacitor. One embodiment of the capacitor includes an anode body, a cathode body, and a solid electrolyte layer, with the solid electrolyte layer disposed between the anode body and the cathode body so that the solid electrolyte layer contacts the electrode.

[0110] An electricity storage device including a solid electrolyte layer formed using the composite electrolyte of the present disclosure can be used in a variety of applications, 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.

[0111] 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 "volume parts" and "volume %", respectively, unless otherwise specified.

[0112] <<Production of Inorganic Solid Electrolyte and Physical Properties>> [Production Example 1] 1. Production of Inorganic Solid Electrolyte ISE-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 Production Example 1 in Table 1. ４ ) ２ ・nH ２ 4.000 g of Zr(HPO), 0.432 g of zirconium hydroxide, 0.415 g of lithium carbonate (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, and 25 g of pure water was 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 (capacity 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 an inorganic solid electrolyte ISE-1. In each production example, Zr(HPO ４ ) ２ ・nH ２ The value of n in O was set to 1.0.

[0113] 2. Confirmation of Crystallinity by Powder X-ray Diffraction Measurement The obtained inorganic solid electrolyte ISE-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 ISE-1 was monoclinic or rhombohedral LiZr ２ P ３ O １２ It was confirmed that the inorganic solid electrolyte ISE-1 has a NASICON-type crystal structure.

[0114] 3. Measurement of Volumetric Median Diameter Inorganic solid electrolyte ISE-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 volumetric median diameter (D50) of inorganic solid electrolyte ISE-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 used as the volumetric median diameter of inorganic solid electrolyte ISE-1. The volumetric median diameter of inorganic solid electrolyte ISE-1 was 1.4 μm.

[0115] 4. Measurement of Ionic Conductivity Using a press die consisting of a die set 11, an upper punch 12, and a lower punch 13 (see Figure 1), sample pellets were prepared in a dry room with a dew point of -40°C or below. First, the die set 11 containing 0.150 g of inorganic solid electrolyte ISE-1 was placed on the lower punch 13, and the upper punch 12 was placed on the die set 11. The inorganic solid electrolyte ISE-1 was compressed using a hydraulic press at a pressure of 10 MPa for 1 minute to obtain a circular sample pellet with a diameter of 1 cm and a thickness of 1000 μm. Next, the sample pellet was encapsulated in an all-solid-state battery evaluation cell (KP-SolidCell, manufactured by Hosen Co., Ltd.) in a dry room with a dew point of -40°C or below. The resistance value at 25°C was measured by AC impedance measurement using the all-solid-state battery evaluation cell encapsulating the sample pellet. The ionic conductivity (σ) was calculated using the obtained resistance value according to the following formula (1): σ = L / (R × S) (1) (In formula (1), 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 ), and L represents the distance between the electrodes (unit: cm). The ionic conductivity (σ ＩＳＥ ) is 2.0 x 10 －7 The viscosity was S / cm.

[0116] 5. Measurement of Porosity After measuring the ionic conductivity, the all-solid-state battery evaluation cell was disassembled to take out the inorganic solid electrolyte ISE-1 obtained in Production Example 1. The thickness (L) of the inorganic solid electrolyte ISE-1 was measured using a film thickness meter (manufactured by Mitutoyo Corporation) and found to be 928 μm. In addition, the density (D ＩＳＥ ) was obtained. ＩＳＥ =M ＩＳＥ / (S ＩＳＥ ×L ＩＳＥ ) ... (2) (In formula (2), D ＩＳＥ is the density of the inorganic solid electrolyte (unit: g cm －３ ), M ＩＳＥ is the mass of the inorganic solid electrolyte (unit: g), S ＩＳＥ is the contact area between the electrode and the inorganic solid electrolyte (unit: cm ２ ), L ＩＳＥrepresents the thickness of the inorganic solid electrolyte (unit: cm). The solid electrolyte ISE-1 is M ＩＳＥ = 0.015, S ＩＳＥ = 0.785, and the density (D ＩＳＥ ) is 2.06 (g cm －３ The density (D ＩＳＥ ) and the porosity (φ ＩＳＥ The result was 35%. ＩＳＥ = (1-D ＩＳＥ / D' ＩＳＥ )×100...(3) (In formula (3), φ ＩＳＥ is the porosity (unit: %), D ＩＳＥ is the density of the inorganic solid electrolyte (unit: g cm －３ ), D' ＩＳＥ is the theoretical density of the inorganic solid electrolyte (the theoretical density of the inorganic solid electrolyte ISE-1 is 3.17, unit: g cm －３ ) where D' is the theoretical density. ＩＳＥ was calculated from the information of the crystalline phase identified by the XRD measurement using the following formula (4): ＩＳＥ = N / V (4) (In formula (4), N is the atomic mass (unit: g) in the unit lattice of the inorganic solid electrolyte, and V is the volume (unit: cm ３ ) The inorganic solid electrolyte ISE-1 has a value of N=4.79×10 －２１ , V = 1.51 × 10 －２１ It was.

[0117] [Production Examples 2 to 4] Inorganic solid electrolytes (referred to as "Inorganic Solid Electrolyte ISE-2," "Inorganic Solid Electrolyte ISE-3," and "Inorganic Solid Electrolyte ISE-4," 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. In addition, the volume-based median diameter and ionic conductivity (σ ＩＳＥThe results are shown in Table 1. Furthermore, powder X-ray diffraction measurements were carried out on the inorganic solid electrolytes ISE-2, ISE-3, and ISE-4 in the same manner as in Production Example 1. As a result, it was found that the main crystalline phase of the inorganic solid electrolytes ISE-2 and ISE-3 was monoclinic or rhombohedral Na ３ Zr ２ Si ２ P.O. １２ The main crystalline phase of the inorganic solid electrolyte ISE-4 is monoclinic or rhombohedral LiZr ２ P ３ O １２ These results confirmed that the inorganic solid electrolytes ISE-2, ISE-3, and ISE-4 have a NASICON-type crystal structure.

[0118]

[0119] <<Production and physical properties of organic solid electrolyte>> [Production Example 5] 1. Production of molecular crystal (organic solid electrolyte OSE-1) In a dry room with a dew point of -40 ° C. or less, 0.1616 g of succinonitrile (manufactured by Tokyo Chemical Industry Co., Ltd.) as an organic molecule and 0.1384 g of lithium bis(fluorosulfonyl)imide (manufactured by Kanto Chemical Co., Ltd.) as an alkali metal salt were weighed out to the molar ratio (organic molecule: alkali metal salt = 2: 1) shown in Production Example 5 in Table 2, and mechanically mixed using a mortar at room temperature (25 ° C.) for 5 minutes to obtain a mixture (mechanical mixing step). The melting point of the mixture was measured using a differential scanning calorimeter (TA Instruments, DSC250, measurement atmosphere: nitrogen atmosphere) at a heating rate of 10 ° C. per minute, and a large endothermic peak (melting point) was observed at 60 ° C. The mixture was transferred to a vial and stirred with a magnetic stirrer at a set temperature of 80°C for 1 hour, and it was confirmed that the mixture was dissolved uniformly (heating step). Thereafter, the resulting melt was allowed to cool to room temperature, and a white solid was obtained.

[0120] 2. Confirmation of Crystallinity by Powder X-ray Diffraction Measurement The obtained white solid 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, with an applied voltage of 40 kV and a current of 40 mA. The measurement range was 2θ = 5-60 deg, the scanning speed was 2.3 deg / min, and the step angle was 0.02 deg. When an X-ray diffraction spectrum having a sharp peak within the angle range of measurement was observed, it indicated that the measured sample (white solid) was crystalline. Therefore, when an X-ray diffraction spectrum having a sharp peak within the angle range of measurement and different from that of the organic molecule and alkali metal salt used as raw materials was obtained, it was determined that a molecular crystal composed of an organic molecule and an alkali metal salt had been formed. When the organic molecule used as raw material was liquid at room temperature, it was determined that a molecular crystal composed of a lithium salt and an organic molecule had been formed when an X-ray diffraction spectrum different from that of a lithium salt was observed. The white solid obtained as described above was subjected to powder X-ray diffraction measurement, and an X-ray diffraction spectrum having a sharp peak in the angle range of measurement and different from that of the raw material was observed. From this, it was confirmed that the obtained white solid was crystalline, that is, a molecular crystal composed of organic molecules and alkali metal salts (this will be referred to as "organic solid electrolyte OSE-1").

[0121] 3. Measurement of Ionic Conductivity Using the press die 10 shown in Figure 1, sample pellets were prepared in a dry room with a dew point of -40°C or below. First, a die set 11 containing 0.0200 g of white solid (organic solid electrolyte OSE-1) was placed on the lower punch, and an upper punch 13 was placed on the die set 11. The white solid was compressed for 1 minute at a pressure of 10 MPa using a hydraulic press, yielding a circular sample pellet with a diameter of 1 cm and a thickness of 200 μm. Next, the sample pellet was encapsulated in an all-solid-state battery evaluation cell (KP-SolidCell, manufactured by Hosen Co., Ltd.) in a dry room with a dew point of -40°C or below. Ionic conductivity was measured using the all-solid-state battery evaluation cell encapsulating the sample pellet. To measure ionic conductivity, the sealed cell encapsulating the sample pellet was first heat-treated in a thermostatic chamber at 40°C (corresponding to the heat treatment temperature in Table 2), while the resistance value was measured by AC impedance measurement. The heat treatment was terminated when the resistance value became constant. Next, the resistance value at 25°C was measured by AC impedance measurement. Using the obtained resistance value, the ionic conductivity (σ) was calculated by the above formula (3). The AC impedance measurement for calculating the ionic conductivity was carried out after the cell was kept at the measurement temperature in a thermostatic bath for 2 hours. The ionic conductivity (σ) of the organic solid electrolyte OSE-1 at 25°C was ＯＳＥ ) is 3.9 x 10 －５ The viscosity was S / cm.

[0122] 4. Measurement of Porosity After measuring the ionic conductivity, the all-solid-state battery evaluation cell was disassembled to take out the organic solid electrolyte OSE-1 obtained in Production Example 5. The thickness (L ОＳＥ The density (D) of the organic solid electrolyte was calculated by the following formula (5). ОＳＥ ) was obtained. ОＳＥ =M ОＳＥ / (S ОＳＥ ×L ОＳＥ ) ... (5) (In formula (5), D ОＳＥ is the density of the organic solid electrolyte (unit: g cm －３ ), M ОＳＥ is the mass of the organic solid electrolyte (unit: g), S is the contact area between the electrode and the organic solid electrolyte (unit: cm ２ ), LОＳＥ represents the thickness of the organic solid electrolyte (unit: cm). The organic solid electrolyte OSE-1 is M ОＳＥ = 0.002, S ОＳＥ = 0.785, and the density (D ОＳＥ ) is 1.49 (g cm －３ The density (D ОＳＥ ) and the porosity (φ ОＳＥ The result of the calculation was 0%. ОＳＥ = (1-D ОＳＥ / D' ОＳＥ )×100...(6) (In formula (6), φ ОＳＥ is the porosity (unit: %), D ОＳＥ is the density of the organic solid electrolyte (unit: g cm －３ ), D' ОＳＥ represents the theoretical density of the organic solid electrolyte.) The theoretical density D' ОＳＥ was calculated from the information of the crystalline phase identified by the XRD measurement using the following formula (7): ＯＳＥ = N / V (7) (In formula (7), N is the atomic mass (unit: g) in the unit lattice of the organic solid electrolyte, and V is the volume (unit: cm ３ ) The organic solid electrolyte OSE-1 has a value of N = 1.15 × 10 －２１ , V = 7.71 × 10 －２２ The theoretical density of the organic solid electrolyte OSE-1 is 1.49 (unit: g cm －３ ) was.

[0123] [Production Examples 6 to 7] White solids were obtained by the same procedure as in Production Example 5, except that the types and amounts of raw materials and the heating temperature of the mixture in the heating step were changed as shown in Table 2. Powder X-ray diffraction measurements were performed on the white solids obtained in each Production Example in the same manner as in Production Example 5. As a result, X-ray diffraction spectra having sharp peaks in the angle range measured and different from those of the raw materials were observed. It was therefore confirmed that all of the white solids were molecular crystals composed of organic molecules and alkali metal salts (referred to as "organic solid electrolyte OSE-2," "organic solid electrolyte OSE-3," and "organic solid electrolyte OSE-4," respectively). Furthermore, the ionic conductivity (σ) at 25°C was measured using the white solids of each Production Example (organic solid electrolyte OSE-2, organic solid electrolyte OSE-3, and organic solid electrolyte OSE-4) at the heat treatment temperatures shown in Table 2. ОＳＥ The melting point of the mixture of organic molecules and alkali metal salts obtained by the mechanical mixing step was measured, along with the ionic conductivity (σ ОＳＥ The measurement results of ion conductivity are shown in Table 2. After measuring the ionic conductivity, the porosity of the organic solid electrolyte was measured in the same manner as in Production Example 5. As a result, the porosity (φ ОＳＥ ) were all 0%.

[0124]

[0125] Details of the compounds used in Table 2 are as follows: 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.) LiFSI: lithium bis(fluorosulfonyl)imide (manufactured by Kanto Chemical Co., Ltd.) NaFSI: sodium bis(fluorosulfonyl)imide (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.)

[0126] <<Production and Evaluation of Composite Electrolyte>> [Example 1] 1. Production of Composite Electrolyte HSE-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 ２．９５O １２ 0.200 g of the inorganic solid electrolyte ISE-1 obtained in Production Example 1 and Li(FSI)(SN) ２ 0.0938 g of each of the organic solid electrolytes OSE-1 obtained in Production Example 5 was weighed and mechanically mixed in a mortar at room temperature (25°C) to obtain a mixture (mixing step). Using the press mold 10 shown in FIG. 1 , a sample pellet consisting of a mixture of an inorganic solid electrolyte and an organic solid electrolyte was prepared in a dry room with a dew point of -40°C or less by the following procedure. First, a die set 11 containing 0.150 g of the mixture was placed on a lower punch 13, and an upper punch 12 was placed on the die set 11. The mixture was compressed for 1 minute 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. Next, the sample pellet was sealed in an all-solid-state battery evaluation cell (KP-SolidCell, manufactured by Hosen Co., Ltd.) in a dry room with a dew point of -40°C or less. The all-solid-state battery evaluation cell containing the sample pellets was heat-treated in a thermostatic chamber at 55°C (corresponding to the temperature in the heating step in Table 3) (heating step), and the resistance value was measured by AC impedance measurement during the heat treatment. When the resistance value became constant, the heat treatment was terminated, and the cell was air-cooled to 25°C to obtain a composite electrolyte (referred to as composite electrolyte HSE-1).

[0127] 2. Evaluation (1) Measurement of Ionic Conductivity The ionic conductivity (σ) of the composite electrolyte HSE-1 at 25°C was measured in the same manner as in Production Example 1. ＳＥ The result was 1.9 × 10 －4 The viscosity was S / cm.

[0128] (2) Measurement of porosity After measuring the ionic conductivity, the all-solid-state battery evaluation cell was disassembled to take out the composite electrolyte HSE-1 obtained in Example 1. The thickness (L ＳＥ The density (D ＳＥ ) was obtained. ＳＥ =M ＳＥ / (S ＳＥ ×L ＳＥ ) ... (8) (In formula (8), D ＳＥis the density of the composite electrolyte (unit: g cm －３ ), M ＳＥ is the mass of the composite electrolyte (unit: g), S ＳＥ is the contact area between the electrode and the composite electrolyte (unit: cm ２ ), L ＳＥ represents the thickness of the composite electrolyte (unit: cm). The composite electrolyte HSE-1 obtained in Example 1 had a thickness of M ＳＥ = 0.015, S ＳＥ = 0.785, and the density (D ＳＥ ) is 2.33 (g cm －３ The density of the composite electrolyte obtained above (D ＳＥ ) and the porosity (φ ＳＥ The result of the calculation was 0%. ＳＥ = (1-D ＳＥ / D' ＳＥ )×100...(9) (In formula (9), φ ＳＥ is the porosity (unit: %), D ＳＥ is the density of the composite electrolyte (unit: g cm －３ ), D' ＳＥ represents the theoretical density of the composite electrolyte.) The theoretical density D' in the porosity measurement ＳＥ The theoretical density D' of the composite electrolyte HSE-1 obtained in Example 1 was the sum of the values ​​obtained by multiplying the theoretical density of each solid electrolyte (inorganic solid electrolyte and organic solid electrolyte) by the mass ratio of each component. ＳＥ is 2.33 (unit: g cm －３ ) was.

[0129] [Examples 2 to 7, Comparative Examples 1 to 3] Composite electrolytes HSE-1 to HSE-10 were obtained by the same procedure as in Example 1, except that the types and amounts of raw materials and the temperature in the heating step were changed as shown in Table 3. In addition, the ionic conductivity (σ ＳＥ ) and porosity (φ ＳＥ The results are shown in Table 3.

[0130]

[0131] <Evaluation Results> As is clear from the results in Table 3, the composite electrolytes of Examples 1 to 7, which were produced using molecular crystals as the organic solid electrolyte and had a porosity of 15% or less, all had high and favorable ionic conductivity compared to the composite electrolytes of Comparative Examples 1 to 3, which had a porosity of more than 15%. The reason why the composite electrolytes of Examples 1 to 7 exhibited such excellent ionic conductivity is thought to be that the molecular crystals, which are the organic solid electrolyte, filled the gaps between the particles of the inorganic solid electrolyte, forming ion conduction paths.

[0132] From the above results, it is clear that a composite electrolyte containing an inorganic solid electrolyte and a molecular crystal (organic solid electrolyte) and having a porosity of a predetermined value or less exhibits high ionic conductivity.

[0133] 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.

[0134] 10... Press mold

Claims

1. A composite electrolyte comprising an inorganic solid electrolyte and an organic solid electrolyte, the organic solid electrolyte comprising molecular crystals, and having a porosity of 15% or less.

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

3. 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 3. The composite electrolyte according to claim 2, comprising a solid electrolyte represented by the formula (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.

4. The oxide having a NASICON type crystal structure is represented by the general formula: Na ３＋２ｘ＋ｙ＋α M4 ｘ M5 ｙ M6 ｚ Zr ２－ｘ－ｙ－ｚ S ２＋α P １－α O １２ (wherein M4 contains an element that can be a divalent cation, M5 contains Al and may contain an element that can be a trivalent cation other than Al, M6 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).

5. The composite electrolyte according to claim 1, wherein the molecular crystal comprises an organic molecule and an alkali metal salt as building blocks.

6. The composite electrolyte according to claim 5, wherein the number of carbon atoms per molecule of said organic molecule is 6 or less.

7. The composite electrolyte of claim 5, wherein said alkali metal salt comprises an imide-based alkali metal salt.

8. The composite electrolyte according to claim 5, wherein said organic molecule has at least one atom selected from the group consisting of a sulfur atom, an oxygen atom, a nitrogen atom, and a phosphorus atom.

9. The composite electrolyte according to claim 5, wherein the organic molecule is at least one selected from the group consisting of sulfones and nitriles.

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

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