Mixture, sheet, electrochemical element, and electricity storage device

Abstract

Provided are a mixture, a sheet, an electrochemical element, and an electricity storage device with which it is possible to improve the diffusivity of a substance at the interface between an oxide and an electrolyte solution. The mixture (10) contains an oxide (19) and an electrolyte solution, and the electrolyte solution is obtained by dissolving an electrolyte salt in a sulfone compound represented by chemical formula (1). In chemical formula (1), R1 and R2 are each independently an alkyl group, an alkenyl group, or a haloalkyl group having 4 or less carbon atoms, or an alkyl group, an alkenyl group, or a haloalkyl group are bonded to each other to form a ring structure. The self-diffusion coefficient of one or more components contained in the electrolyte in contact with the oxide as measured by pulsed field gradient nuclear magnetic resonance is at least 6 times the self-diffusion coefficient of components contained in the electrolyte not in contact with the oxide as measured at the same temperature as the measurement. # imgabs0 #

Description

Technical Field

[0001] The present invention relates to a mixture, a sheet, an electrochemical element, and a storage device, which contain an oxide and an electrolyte solution. Background Art

[0002] In order to reduce the leakage of an electrolyte solution in an electrochemical element and improve safety, a technique of providing a mixture containing an oxide and an electrolyte solution in the electrochemical element is known. In the prior art disclosed in Patent Document 1, an electrolyte sheet is formed from a mixture containing an oxide composed of silicon dioxide and an electrolyte solution containing tetraglyme (Tetraglyme).

[0003] Prior Art Documents

[0004] Patent Documents

[0005] Patent Document 1: Japanese Patent Application Laid-Open No. 2020-113527 Summary of the Invention

[0006] Problems to be Solved by the Invention

[0007] In order to increase the ionic conductivity of a mixture containing an oxide and an electrolyte solution, it is important to increase the diffusion rate of the electrolyte component near the interface where the desolvation of cations occurs at the interface between the oxide and the electrolyte solution. In the prior art, there is room for improvement in the diffusivity of substances at the interface of the oxide.

[0008] The present invention has been completed to solve this problem, and an object thereof is to provide a mixture, a sheet, an electrochemical element, and a storage device capable of increasing the diffusivity of substances at the interface.

[0009] Means for Solving the Problems

[0010] A first aspect for achieving this object is a mixture containing an oxide and an electrolyte solution, where the electrolyte solution is obtained by dissolving an electrolyte salt in a sulfone compound represented by Chemical Formula (1). In Chemical Formula (1), R1 and R2 are each independently an alkyl group, an alkenyl group, or a haloalkyl group having 4 or fewer carbon atoms, or the alkyl group, the alkenyl group, or the haloalkyl group combine with each other to form a ring structure. The self-diffusion coefficient of one or more components contained in the electrolyte solution in contact with the oxide, measured by pulsed-field gradient nuclear magnetic resonance method, is 6 times or more the self-diffusion coefficient of the same component contained in the electrolyte solution not in contact with the oxide measured at the same temperature as the measurement.

[0011]

[0012] A second aspect is that, in the first aspect, the oxide is aluminum oxide.

[0013] A third aspect is that, in the first or second aspect, the electrolyte salt is a lithium salt.

[0014] The fourth mode is a sheet, which contains a mixture of any one of the first to third modes.

[0015] The fifth mode is an electrochemical element, which contains a mixture of any one of the first to third modes.

[0016] The sixth mode is an electrical storage device having a positive electrode layer, a negative electrode layer, and a separator that separates the positive electrode layer from the negative electrode layer, and it contains a mixture of any one of the first to third modes.

[0017] The seventh mode is that, in the sixth mode, at least one of the positive electrode layer, the negative electrode layer, and the separator contains a mixture.

[0018] The eighth mode is that, in the sixth mode, at least one of the positive electrode layer and the negative electrode layer contains a current collector layer, and there is a protective layer in contact with at least one of the separator and the current collector layer, and the protective layer contains a mixture.

[0019] Advantages of the Invention

[0020] According to the mixture, sheet, electrochemical element, and electrical storage device of the present invention, the diffusivity of substances at the interface between the oxide and the electrolyte can be improved. Description of the Drawings

[0021] Figure 1 is a cross-sectional view of an electrochemical element containing a mixture according to the first embodiment.

[0022] Figure 2 is to Figure 1 the cross-sectional view of the electrochemical element with the part shown in II enlarged.

[0023] Figure 3 is a diagram schematically showing the crystal structure of the garnet type.

[0024] Figure 4 is a cross-sectional view of the electrochemical element according to the second embodiment.

[0025] Figure 5 is a cross-sectional view of the electrochemical element according to the third embodiment. Detailed Embodiments

[0026] Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. Figure 1 is a schematic cross-sectional view of an electrochemical element 11 containing a mixture 10 according to an embodiment. The electrochemical element 11 of the present embodiment is a lithium-ion solid battery (electrical storage device) in which the power generation element is composed of a solid. That the power generation element is composed of a solid means that the framework of the power generation element is composed of a solid, including a form in which the framework is impregnated with a liquid.

[0027] The electrochemical element 11 successively includes a positive electrode layer 12, an electrolyte layer 15, and a negative electrode layer 16. The positive electrode layer 12, the electrolyte layer 15, and the negative electrode layer 16 are housed in a housing (not shown).

[0028] In the positive electrode layer 12, a current collector layer 13 overlaps with an active material layer 14. The current collector layer 13 is a conductive member. Examples of the material of the current collector layer 13 include metals selected from Ni, Ti, Fe, and Al, alloys containing two or more of these elements, stainless steel, and carbon materials.

[0029] The active material layer 14 contains a mixture 10 and an active material 20. The mixture 10 contains an oxide 19. In order to reduce the resistance of the active material layer 14, a conductive additive may also be included in the active material layer 14. Examples of the conductive additive include carbon black, acetylene black, Ketjen black, carbon fiber, Ni, Pt, and Ag.

[0030] Examples of the active material 20 include metal oxides having transition metals, chalcogen-based active materials, and organic-based active materials. Examples of the metal oxides having transition metals include metal oxides containing one or more elements selected from Mn, Co, Ni, Fe, Cr, and V and Li. Examples of the metal oxides having transition metals include LiCoO2, LiNi 0.8 Co 0.15 Al 0.05 O4, LiMn2O4, LiNiVO4, LiNi 0.5 Mn 1.5 O4, LiNi 1 / 3 Mn 1 / 3 Co 1 / 3 O2, and LiFePO4.

[0031] In order to suppress the reaction between the active material 20 and the oxide 19, a coating layer may be provided on the surface of the active material 20. Examples of the coating layer include Al2O3, ZrO2, LiNbO3, Li4Ti5O 12 , LiTaO3, LiNbO3, LiAlO2, Li2ZrO3, Li2WO4, Li2TiO3, Li2B4O7, Li3PO4, and Li2MoO4.

[0032] Examples of the chalcogen-based active materials include S, TiS2, NiS, FeS2, Li2S, MoS3, and sulfur-carbon composite materials. Examples of the organic-based active materials include radical compounds represented by 2,2,6,6-tetramethylpiperidine-4-yl methacrylate and poly(tetramethylpiperidineoxy) vinyl ether, quinone compounds, axleene compounds, tetracyanoquinodimethane, and phenazine oxide.

[0033] The electrolyte layer 15 is composed of a mixture 10. The mixture 10 contains an oxide 19 and an electrolytic solution 22 (seeFigure 2 )。The mixture 10 may further contain a binder. The electrolyte layer 15 serves as a separator that isolates the positive electrode layer 12 from the negative electrode layer 16.

[0034] In the negative electrode layer 16, the current collector layer 17 overlaps with the active material layer 18. The current collector layer 17 is a conductive member. Examples of the material of the current collector layer 17 include metals selected from Ni, Ti, Fe, Cu, and Si, alloys containing two or more of these elements, stainless steel, and carbon materials.

[0035] The active material layer 18 contains the mixture 10 and the active material 21. In order to reduce the resistance of the active material layer 18, a conductive additive may also be included in the active material layer 18. Examples of the conductive additive include carbon black, acetylene black, Ketjen black, carbon fiber, Ni, Pt, and Ag. Examples of the active material 21 include Li, Li - Al alloy, Li4Ti5O 12 , graphite, In, Si, Si - Li alloy, and SiOx (for example, 0.5 < X < 1.5). Similar to the electrolyte layer 15, the active material layers 14 and 18 may also contain a binder.

[0036] Figure 2 is a Figure 1 cross - sectional view of the electrochemical element 11 that magnifies the part shown in II. The mixture 10 contained in the electrochemical element 11 contains the oxide 19 and the electrolyte 22. The oxide 19 is preferably a substance that is insoluble in the electrolyte 22 and does not have electronic conductivity. Examples of the shape of the oxide 19 include granular, spherical, rod - shaped, needle - shaped, polygonal, fibrous, and flaky. The oxide 19 can be appropriately selected and used from inorganic compounds such as alumina, silica, cerium oxide, zirconium oxide, and oxide - based solid electrolytes.

[0037] Examples of the oxide - based solid electrolyte include substances having a crystal structure of perovskite type, NASICON type, LISICON type, and garnet type containing Li, La, and Zr. Examples of the perovskite - type oxide include oxides containing at least Li, Ti, and La, such as La 2 / 3-X Li 3X TiO3. Examples of the NASICON - type oxide include oxides containing at least Li, M (M is one or more elements selected from Ti, Zr, and Ge), and P, such as Li(Al,Ti)2(PO4)3 and Li(Al,Ge)2(PO4)3. Examples of the LISICON - type oxide include Li 14 Zn(GeO4)4.

[0038] Figure 3 is a diagram schematically showing the crystal structure of the garnet type. The crystal structure of the garnet type can be represented by the general formula C3A2B3O 12representation. In the garnet-type crystal structure, Sc at the C site forms a dodecahedral coordination with oxygen atoms Oa, Sa at the A site forms an octahedral coordination with oxygen atoms Oa, and Sb at the B site forms a tetrahedral coordination with oxygen atoms Oa. In the normal garnet-type crystal structure, oxide 19 may form an octahedral coordination with oxygen atoms Oa and Li may be present at the site that becomes the void V. The void V is, for example, a site sandwiched between Sb1 at the B site and Sb2 at the B site. Li present in the void V forms an octahedral coordination with oxygen atoms Oa that constitute an octahedron including the face Fb1 of the tetrahedron forming Sb1 at the B site and the face Fb2 of the tetrahedron forming Sb2 at the B site. For example, in Li7La3Zr2O having a garnet-type crystal structure 12 La can occupy the Sc site at the C site, Zr can occupy the Sa site at the A site, and Li can occupy the Sb site at the B site and the void V.

[0039] The oxide having a garnet-type crystal structure containing Li, La, and Zr has an XRD pattern similar to the X-ray diffraction file No. 422259 of the CSD (Cambridge Structural Database). Compared with No. 422259, this oxide sometimes has different types of constituent elements, Li concentration, etc., and thus sometimes has different diffraction angles and intensity ratios. Li7La3Zr2O 12 can be either tetragonal crystal with low ionic conductivity or cubic crystal with high ionic conductivity. 12 For the oxide having a garnet-type or garnet-like crystal structure containing Li, La, and Zr, a part of the constituent elements can be replaced by other elements, or other elements can be added in trace amounts without replacing the constituent elements. Examples of the other elements include at least one element selected from the group consisting of Mg, Al, Si, Ca, Ti, V, Ga, Sr, Y, Nb, Sn, Sb, Ba, Hf, Ta, W, Bi, Rb, and lanthanide elements (excluding La).

[0040] Return

[0041] is described. Examples of oxide 19 include, for example, Li6La3Zr Figure 2 W 1.5 O 0.5 O 12 , Li 6.15 La3Zr 1.75 Ta 0.25 Al 0.2 O 12 , Li 6.15 La3Zr 1.75 Ta 0.25 Ga 0.2 O 12 , Li6.25 La3Zr2Ga 0.25 O 12 、Li 6.4 La3Zr 1.4 Ta 0.6 O 12 、Li 6.5 La3Zr 1.75 Te 0.25 O 12 、Li 6.75 La3Zr 1.75 Nb 0.25 O 12 、Li 6.9 La3Zr 1.675 Ta 0.289 Bi 0.036 O 12 、Li 6.46 Ga 0.23 La3Zr 1.85 Y 0.15 O 12 、Li 6.8 La 2.95 Ca 0.05 Zr 1.75 Nb 0.25 O 12 、Li 7.05 La 3.00 Zr 1.95 Gd 0.05 O 12 、Li 6.20 Ba 0.30 La 2.95 Rb 0.05 Zr2O 12 。

[0042] Oxides having a garnet-type or garnet-like crystal structure preferably contain at least one of Mg and element A (where A is at least one element selected from the group consisting of Ca, Sr, and Ba) in addition to Li, La, and Zr, and the molar ratios of the respective elements satisfy all of the following (1) to (3), or contain both Mg and element A, and the molar ratios of the respective elements satisfy all of the following (4) to (6). To increase the ionic conductivity of oxide 19, element A is preferably Sr.

[0043] (1) 1.33 ≤ Li / (La + A) ≤ 3

[0044] (2) 0 ≤ Mg / (La + A) ≤ 0.5

[0045] (3) 0 ≤ A / (La + A) ≤ 0.67

[0046] (4) 2.0 ≤ Li / (La + A) ≤ 2.5

[0047] (5) 0.01 ≤ Mg / (La + A) ≤ 0.14

[0048] (6) 0.04 ≤ A / (La + A) ≤ 0.17

[0049] The median particle size of the equivalent circle diameter of the oxide 19 exposed in the cross-section of the electrolyte layer 15 is preferably 0.2 to 10 μm, more preferably 0.2 to 6 μm. This is to make the surface area of the oxide 19 of a moderate size and improve the diffusibility of the components of the electrolyte 22 present on the surface of the oxide 19.

[0050] To determine the median particle size of the oxide 19, first, an image of the oxide 19 exposed on the cross-section of the electrolyte layer 15 (ground surface, surface obtained by irradiating a focused ion beam (FIB), surface obtained by ion milling) based on a scanning electron microscope (SEM) is analyzed. The equivalent circle diameter (the diameter of a circle having the same area as the area of the oxide 19 exposed in the cross-section) is calculated from the area of each oxide 19, and the volume-based particle size distribution is obtained. The median particle size is the equivalent circle diameter at which the cumulative value of the frequency in the particle size distribution is 50%. To ensure accuracy, the image for obtaining the particle size distribution is an area of 400 μm 2 or more in the electrolyte layer 15.

[0051] The electrolyte 22 is obtained by dissolving an electrolyte salt in an organic solvent. The electrolyte salt is a compound for the transfer of cations between the positive electrode layer 12 and the negative electrode layer 16. In the case where a lithium salt is the electrolyte salt, examples of the anion of the lithium salt include halide ions (I - , Cl - , Br - , etc.), SCN - , BF4 - , BF3(CF3) - , BF3(C2F5) - , PF6 - , ClO4 - , SbF6 - , N(SO2F)2 - , N(SO2CF3)2 - , N(SO2C2F5)2 - , B(C6H5)4 - , B(O2C2H4)2 - , C(SO2F)3 - , C(SO2CF3)3 - , CF3COO - , CF3SO2O - , C6F5SO2O- , B(O2C2O2)2 - , RCOO - (where R is an alkyl group having 4 or less carbon atoms, a phenyl group or a naphthyl group), etc.

[0052] The anion of the lithium salt preferably has N(SO2F)2 having a sulfonyl group -S(=O)2- - , N(SO2CF3)2 - , N(SO2C2F5)2 - and other sulfonimides. This is because even when the salt concentration increases, the sulfonimide anion has little effect on the increase in the viscosity of the electrolyte and the decrease in the ionic conductivity. Furthermore, by forming a highly stable and low-resistance film (SEI), the reduction decomposition of the electrolyte can be reduced and the reduction-side potential window can be expanded.

[0053] Sometimes N(SO2F)2 - is abbreviated as [FSI] - : bis(fluorosulfonyl)imide anion, and N(SO2CF3)2 - is abbreviated as [TFSI] - : bis(trifluoromethanesulfonyl)imide anion. Lithium salt is particularly preferably lithium bis(fluorosulfonyl)imide (LiFSI). This is because LiFSI has little effect on the increase in the viscosity of the electrolyte and is effective for the formation of a good passive film (SEI).

[0054] The organic solvent of the electrolyte 22 contains a sulfone compound represented by the chemical formula (1). The organic solvent of the electrolyte 22 can be appropriately selected from one or more of the following material groups for use.

[0055]

[0056] In the chemical formula (1), R1 and R2 are each independently an alkyl group having 4 or less carbon atoms, an alkenyl group or a haloalkyl group, or the alkyl group, alkenyl group or haloalkyl group combine with each other to form a ring structure. R1 and R2 can be straight-chain hydrocarbon groups or hydrocarbon groups having a branched chain or a ring structure.

[0057] Examples of the alkyl group having 4 or less carbon atoms include: methyl, ethyl, n-propyl, isopropyl, 1-ethylpropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, 2-methylbutyl, 3,3-dimethylbutyl. Examples of the alkenyl group having 4 or less carbon atoms include: vinyl, 1-propenyl, allyl, 1-butenyl, 2-butenyl, 3-butenyl.

[0058] Examples of haloalkyl groups having 4 or fewer carbon atoms include fluoromethyl, difluoromethyl, trifluoromethyl, 2,2,2-trifluoroethyl, 1,1,2,2-tetrafluoroethyl, perfluoroethyl, 2,2,3,3-tetrafluoropropyl, perfluoropropyl, perfluoroisopropyl, perfluorobutyl, perfluoroisobutyl, chloromethyl, dichloromethyl, trichloromethyl, 2,2,2-trichloroethyl, 1,1,2,2-tetrachloroethyl, perchloroethyl, 2,2,3,3-tetrachloropropyl, perchloropropyl, perchloroisopropyl, perchlorobutyl, perchloroisobutyl, bromomethyl, dibromomethyl, tribromomethyl, 2,2,2-tribromoethyl, 1,1,2,2-tetrabromoethyl, 2,2,3,3-tetrabromopropyl, iodomethyl, diiodomethyl, triiodomethyl, 2,2,2-triiodoethyl, 1,1,2,2-tetraiodoethyl, 2,2,3,3-tetraiodopropyl.

[0059] Examples of cyclic compounds in which the alkyl, alkenyl or haloalkyl groups in formula (1) are bonded to each other to form a ring structure include trimethylene sulfone, sulfolane, fluorosulfolane, difluorosulfolane, methylsulfolane, dimethylsulfolane. Since the sulfone compound represented by formula (1) has high antioxidant properties, it is advantageous for increasing the voltage of the electrochemical element 11.

[0060] The salt concentration of the electrolyte 22 is not limited, but the salt concentration (molality) of the electrolyte 22 is preferably 1.4 mol / kg or more, more preferably 1.6 mol / kg or more. This is because, compared with a general electrolyte having a salt concentration of around 1 mol / kg, the number of solvent molecules coordinated with the cation increases and the number of uncoordinated solvents decreases, so that the transference number of the cation of the electrolyte salt can be increased.

[0061] The electrolyte 22 may contain a solvated ionic liquid. The solvated ionic liquid is composed of a cation solvated with the sulfone compound represented by formula (1) and its counter ion. The electrolyte 22 may be in a state where all solvent molecules are coordinated with the cation and there is no uncoordinated solvent, or a state where all solvent molecules are coordinated with the cation and there is no uncoordinated solvent, and furthermore, a state where cations not coordinated with the solvent molecules exist in excess. It is known that in the electrolyte 22 having a high salt concentration in which the cation is solvated with the sulfone compound, an inherent coordination structure is obtained in the state of becoming a solvated ionic liquid, and the transport rate of lithium ions becomes faster.

[0062] In mixture 10, in addition to the sulfone compound represented by chemical formula (1), other organic solvents may also be contained. Other organic solvents, for example, help to reduce the viscosity of electrolyte 22 and increase the ionic conductivity of electrolyte 22. Examples of other organic solvents include propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, trimethyl phosphate, triethyl phosphate, γ-butyrolactone, dimethyl methylphosphonate, acetonitrile, isobutyl methyl ketone, nitromethane, methyl ethyl ketone, tetramethylsilane, siloxane compounds, and organosilicate compounds. One or more organic solvents that are not likely to affect the coordination state of cations and solvent molecules can be appropriately selected as other organic solvents.

[0063] Mixture 10 may contain various additives used in lithium-ion batteries. Examples of additives include carbonate compounds containing unsaturated bonds and halogens such as vinylene carbonate and fluoroethylene carbonate, flame retardant compounds such as ionic liquids, acid anhydrides, nitrile compounds, redox shuttle compounds such as anisole derivatives, and overcharge preventives such as aromatic compounds.

[0064] The proportion (by weight) of the sulfone compound contained in mixture 10 relative to the total of the sulfone compound and other organic solvents is preferably 75% or more. This is to ensure the transference number of cations.

[0065] The salt concentration of electrolyte 22 is preferably 4.0 mol / kg or less. This is because when the salt concentration of electrolyte 22 exceeds 4.0 mol / kg, the ionic conductivity tends to decrease significantly due to the increase in the viscosity of electrolyte 22.

[0066] Mixture 10 sets the combination of oxide 19 and electrolyte 22 in such a way that the self-diffusion coefficient of one or more components contained in electrolyte 22 in contact with oxide 19, measured by pulsed field gradient nuclear magnetic resonance (PFG-NMR), is 6 times or more the self-diffusion coefficient of the same component contained in electrolyte 22 not in contact with oxide 19, measured at the same temperature.

[0067] The self-diffusion coefficient D of the components of electrolyte 22 in contact with oxide 19 M represents the diffusion rate of the components of electrolyte 22 in a sample formed by mixing oxide 19 and electrolyte 22. The self-diffusion coefficient D of the components of electrolyte 22 not in contact with oxide 19 L represents the diffusion rate of the components of electrolyte 22. The self-diffusion coefficient D M 、D L is measured at the same temperature. If the temperature difference when measuring both is within 1 °C, it can be tolerated as the same temperature. Comparing the self-diffusion coefficients D M 、D L of the same component, the self-diffusion coefficient D of the components of electrolyte 22 in contact with oxide 19M The self-diffusion coefficient D of the components of the electrolyte 22 that do not come into contact with the oxide 19 L being more than six times that indicates that the diffusivity of substances at the interface of the oxide 19 in contact with the electrolyte 22 is more than six times greater than the case where the electrolyte exists alone.

[0068] Sometimes, it is difficult to determine the accuracy of the value of the apparent self-diffusion coefficient obtained by measurement based on PFG-NMR with respect to the value of the actual self-diffusion coefficient. In cases where it is difficult to perform measurements other than PFG-NMR for comparative verification (such as alternating current impedance measurement, evaluation of diffusion coefficient using radioactive isotopes), of course, the apparent self-diffusion coefficient obtained by PFG-NMR is used. However, in cases where measurements other than PFG-NMR can be performed, in order to unify the measurement method, the apparent self-diffusion coefficient based on PFG-NMR is also used.

[0069] When cations move from the electrolyte 22 to the oxide 19, at the interface of the oxide 19, the desolvation of cations from solvent molecules or the dissociation of ion pairs formed by the complexation of ions with counterions occurs. Therefore, it is presumed that these become the rate-limiting steps of ion conduction.

[0070] If the diffusivity of substances at the interface of the oxide 19 is large, when an electric current flows through the mixture 10 and desolvation of cations and dissociation of ion pairs occur at the interface between the oxide 19 and the electrolyte 22, the concentration gradients of the desolvated solvent molecules and anions are easily alleviated. As a result, it is speculated that desolvation at the interface between the oxide 19 and the electrolyte 22 becomes easier and the interfacial resistance of the oxide 19 becomes smaller. In addition, the concentration gradient of the ions of the electrolyte 22 generated during charge and discharge is also easily alleviated in the same way. Therefore, the rate characteristics of the electrochemical element 11 are improved, and an improvement in fast charging performance and power density can be expected. Furthermore, when the diffusion rate of the decomposition products accompanying the charge and discharge of the electrochemical element 11 also increases, an improvement in cycle life can be expected by reducing the accumulation of decomposition products.

[0071] The nuclides for observing the NMR signal depend on the types of organic solvents contained in the electrolyte 22 and the materials of the electrolyte salts dissolved in the organic solvents, and examples include 1 H, 13 C, 19 F, 6 Li, 7 Li, 11 B, 23 Na, 31 P. If within the same molecule, for example, observing PF6 with 19 F nuclei and 31 P nuclei, or observing CH3 and CH2 of ethyl that are observed as two signals - ​1 For all H nuclei, the same self-diffusion coefficient can be obtained. Therefore, even for an electrolyte solution composed of a mixture of multiple solvents and components, as long as there is a signal that does not overlap with other components, the self-diffusion coefficient can be obtained for each component.

[0072] To measure the self-diffusion coefficient D of the components of the electrolyte solution 22 that is not in contact with the oxide 19 L , information such as the concentration of the electrolyte and the mixing ratio of the solvents in the electrolyte solution 22 is required. The concentration of the electrolyte of the electrolyte solution 22 contained in the mixture 10 is determined as follows, for example. Here, the case of determining the concentration of the lithium salt for the mixture 10 constituting the electrolyte layer 15 is described, but the concentration of the electrolyte salt other than the lithium salt in the mixtures 10 and the active material layers 14 and 18 can be determined in the same way.

[0073] First, the electrolyte layer 15 is broken and immersed in a solvent. After the electrolyte solution 22 contained in the electrolyte layer 15 is dissolved in the solvent, it is separated into a solid component and a liquid component by centrifugation or filtration. Taking the separated liquid component as the object, the content of Li is determined by high-frequency inductively coupled plasma analysis (ICP).

[0074] In addition, the types of organic solvents contained in the electrolyte layer 15 are determined by, for example, gas chromatography-mass spectrometry (GC-MS). By preparing a standard curve using the identified organic solvents (hereinafter referred to as "standard substances"), the content of the organic solvents contained in the electrolyte layer 15 is determined based on the area of the chromatogram. Or the standard substances and the electrolyte layer 15 are analyzed by thermogravimetric differential thermal analysis (TG-DTA), and the analysis results of the standard substances are compared with the analysis results of the electrolyte layer 15 to determine the content of the organic solvents contained in the electrolyte layer 15. Based on the content of Li in the liquid component and the content of the organic solvents in the electrolyte layer 15, the molality (mol / kg) of the lithium salt in the electrolyte solution 22 is calculated.

[0075] Based on the components of the electrolyte solution 22 determined as such, an electrolyte solution with the same composition as the electrolyte solution 22 contained in the electrolyte layer 15 is prepared, and the self-diffusion coefficient of the electrolyte solution is measured in the same way, thereby obtaining the self-diffusion coefficient D L . If the self-diffusion coefficients D of the components of the electrolyte solution 22 are known from the literature or the like L , these values can also be used.

[0076] In the mixture 10, the volume ratio of the oxide 19 to the total volume of the oxide 19 and the electrolyte 22 is preferably 52% or more and less than 100%, more preferably 61% or more and less than 100%. The volume ratio of the oxide 19 to the total volume of the oxide 19 and the electrolyte 22 is particularly preferably 93% or less. By combining the oxide 19 and the electrolyte 22, the transference number of Li ions in the mixture 10 can be made larger than that of general electrolyte 22. As a result, the working stability of the electrochemical element 11 equipped with the mixture 10 is increased.

[0077] Regarding the contents (volume %) of the oxide 19 and the electrolyte 22, after freezing the electrolyte layer 15 or embedding and curing the electrolyte layer 15 in a tetrafunctional epoxy resin or the like, analysis is performed using SEM equipped with an energy dispersive X-ray spectrometer (EDS) with a field of view 5000 times randomly selected from the cross-section of the electrolyte layer 15 to obtain the results. The distribution of La, Zr, and S is analyzed or image analysis is performed on the contrast of the backscattered electron image to determine the area of the oxide 19 and the area of the electrolyte 22, and the ratio of the areas in the cross-section of the electrolyte layer 15 is regarded as the volume ratio in the mixture 10 of the electrolyte layer 15, thereby obtaining the contents (volume %) of the oxide 19 and the electrolyte 22.

[0078] The mixture 10 may also contain a binder for bonding the oxide 19. Examples of the binder include rubber-like polymers such as fluororesins, polyolefins, polyimides, polyvinylpyrrolidone, polyvinyl alcohol, cellulose ethers, and styrene-butadiene rubber. Examples of the fluororesin include vinylidene fluoride-based polymers, polychlorotrifluoroethylene, polyvinyl fluoride, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymers, tetrafluoroethylene-hexafluoropropylene copolymers, ethylene-tetrafluoroethylene copolymers, and ethylene-chlorotrifluoroethylene copolymers.

[0079] Examples of the vinylidene fluoride-based polymer include homopolymers of vinylidene fluoride and copolymers of vinylidene fluoride and copolymerizable monomers. Examples of the copolymerizable monomers include halogen-containing monomers (excluding vinylidene fluoride) and non-halogen-based copolymerizable monomers. Examples of the halogen-containing monomers include chlorine-containing monomers such as vinyl chloride; fluorine-containing monomers such as trifluoroethylene, tetrafluoroethylene, chlorotrifluoroethylene, hexafluoropropylene, and perfluoroalkyl vinyl ether. Examples of the non-halogen-based copolymerizable monomers include olefins such as ethylene and propylene; acrylic monomers such as acrylic acid, methacrylic acid, their esters or salts; and vinyl monomers such as acrylonitrile, vinyl acetate, and styrene. One or two or more copolymerizable monomers are polymerized with vinylidene fluoride to form a copolymer.

[0080] The electrochemical element 11 is manufactured as follows. In a mixture 10 formed by mixing an electrolytic solution 22 in which a lithium salt is dissolved in an organic solvent and an oxide 19, a solution in which a binder is dissolved in a solvent is mixed to prepare a slurry. After tape casting, drying is performed to obtain a green sheet (electrolyte sheet) for the electrolyte layer 15.

[0081] An active material 20 is mixed in the mixture 10 formed by mixing the electrolytic solution 22 in which the lithium salt is dissolved in the organic solvent and the oxide 19. Further, a solution in which a binder is dissolved in a solvent is mixed to prepare a slurry. After tape casting on the current collector layer 13, drying is performed to obtain a green sheet (positive electrode sheet) for the positive electrode layer 12.

[0082] An active material 21 is mixed in the mixture 10 formed by mixing the electrolytic solution 22 in which the lithium salt is dissolved in the organic solvent and the oxide 19. Further, a solution in which a binder is dissolved in a solvent is mixed to prepare a slurry. After tape casting on the current collector layer 17, drying is performed to obtain a green sheet (negative electrode sheet) for the negative electrode layer 16.

[0083] After the electrolyte sheet, the positive electrode sheet, and the negative electrode sheet are respectively cut into a prescribed shape, they are overlapped in the order of the positive electrode sheet, the electrolyte sheet, and the negative electrode sheet, and are integrally pressed and joined. Terminals (not shown) are respectively connected to the current collector layers 13 and 17, and are sealed in a case (not shown) to obtain the electrochemical element 11 including the positive electrode layer 12, the electrolyte layer 15, and the negative electrode layer 16.

[0084] Of course, instead of obtaining the positive electrode layer 12, the electrolyte layer 15, and the negative electrode layer 16 by tape casting of the slurry containing the mixture 10, the electrolyte layer 15 can be obtained by press molding of the mixture 10, and the positive electrode layer 12 and the negative electrode layer 16 can be obtained by press molding of the mixture 10 containing the active material 20 and the active material 21.

[0085] Refer to Figure 4 A description will be given of a second embodiment. In the first embodiment, the case where the mixture 10 is used in a storage device in which a power generation element is solid is described. In the second embodiment, the case where the mixture 10 is used in a liquid lithium ion battery using an organic solvent in the electrolyte is described. Parts that are the same as those described in the first embodiment are denoted by the same reference numerals, and the following description is omitted. Figure 4 FIG. is a cross-sectional view of an electrochemical element 24 (storage device) according to the second embodiment.

[0086] The electrochemical element 24 successively includes a positive electrode layer 12, a separator 25, and a negative electrode layer 16. They are housed in a case (not shown). The separator 25 is made of a porous body which is durable against the active materials 20 and 21 and the electrolytic solution contained in the positive electrode layer 12 and the negative electrode layer 16, allows lithium ions to pass through but does not have electron conductivity. Examples of the separator 25 include non-woven fabrics and porous membranes made of cellulose, polypropylene, polyethylene, etc. The electrolytic solution is the same as the electrolytic solution described in the first embodiment, and thus the description thereof is omitted.

[0087] Since the electrochemical element 24 of the second embodiment contains the mixture 10 in the positive electrode layer 12 and the negative electrode layer 16, the diffusibility of substances between the oxide 19 and the electrolytic solution 22 in the positive electrode layer 12 and the negative electrode layer 16 can be improved in the same manner as the electrochemical element 11 of the first embodiment.

[0088] Refer to Figure 5 A description will be given of the third embodiment. In the first embodiment and the second embodiment, the case where the mixture 10 is contained in the positive electrode layer 12, the electrolyte layer 15, and the negative electrode layer 16 has been described. In the third embodiment, the case where the mixture 10 is contained in the protective layers 29 and 32 will be described. Parts that are the same as those described in the first embodiment and the second embodiment are denoted by the same reference numerals, and the following description thereof is omitted. Figure 5 is a cross-sectional view of the electrochemical element 26 (electric storage device) of the third embodiment.

[0089] The electrochemical element 26 successively includes a positive electrode layer 27, a separator 25, and a negative electrode layer 30. They are housed in a case (not shown). The electrochemical element 26 is a liquid lithium ion battery using an organic solvent in the electrolyte.

[0090] In the positive electrode layer 27, the current collector layer 13 overlaps with the active material layer 28. The active material layer 28 contains the active material 20. In order to reduce the resistance of the active material layer 28, conductive assistants such as carbon black, acetylene black, Ketjen black, carbon fiber, Ni, Pt, and Ag may be contained in the active material layer 28.

[0091] A protective layer 29 is disposed between the separator 25 and the negative electrode layer 30. The protective layer 29 contains the mixture 10.

[0092] The negative electrode layer 30 is sequentially overlapped with an active material layer 31, a protective layer 32, and a current collector layer 17. The active material layer 31 is composed of, for example, Li, Li-Al alloy, Li-Sn alloy, Li-Si alloy, Li-Mg alloy, Li-Si alloy, or Si-Li alloy. The protective layer 32 contains the mixture 10. The protective layers 29 and 32 are arranged by means of sheet lamination, coating on the separator 25, the current collector layer 17, etc. Since the protective layers 29 and 32 contain the mixture 10, the diffusivity of substances between the oxide 19 and the electrolyte 22 in the protective layers 29 and 32 can be improved.

[0093] When the oxide 19 contained in the protective layers 29 and 32 has a garnet-type crystal structure containing Li, La, Zr, and O, it has reducibility resistance to metallic lithium in the active material layer 31, so the working stability of the electrochemical element 26 increases. Furthermore, since the protective layer 29 is interposed between the active material layer 31 and the separator 25, a short circuit caused by the dendritic growth of metallic lithium is suppressed. The protective layer 32 interposed between the active material layer 31 and the current collector layer 17 suppresses the deterioration of the current collector layer 17.

[0094] Examples

[0095] The present invention will be described in more detail by way of examples, but the present invention is not limited to these examples.

[0096] (Example 1)

[0097] α-aluminum oxide as an oxide and an electrolyte prepared by mixing sulfolane and lithium bis(fluorosulfonyl)imide (LiFSI) in a molar ratio of 3:1 were placed in a mortar in a ratio of 61:39 (volume ratio) and mixed using a pestle to obtain the mixture of Example 1. The median particle size of the volume-based particle size distribution of α-aluminum oxide measured by laser diffraction / scattering method was 0.9 μm.

[0098] (Example 2)

[0099] Instead of α-aluminum oxide, cubic Li7La3Zr2O 12 was mixed into the electrolyte, and the same operations as in Example 1 were performed otherwise to obtain the mixture of Example 2. The median particle size of the volume-based particle size distribution of Li7La3Zr2O 12 measured by laser diffraction / scattering method was 0.8 μm.

[0100] (Comparative Example 1)

[0101] N-methyl-N-propylpyrrolidine was mixed in a molar ratio of 1.46:1 A mixture of Comparative Example 1 was obtained in the same manner as in Example 1, except that an electrolyte solution prepared by mixing bis(fluorosulfonyl)imide (MPPy-FSI) and LiFSI was mixed with α-alumina instead of an electrolyte solution prepared by mixing sulfolane and LiFSI.

[0102] (Comparative Example 2)

[0103] A mixture of Comparative Example 2 was obtained in the same manner as in Example 1 except that sulfolane (in which lithium salt was not dissolved) was mixed with α-alumina at 40° C. instead of the electrolyte solution prepared by mixing sulfolane and LiFSI.

[0104] (Determination of self-diffusion coefficient)

[0105] The self-diffusion coefficient D of each component of the electrolyte solution contained in the mixture at 25° C. was measured by a nuclear magnetic resonance apparatus (JNM-ECA600II manufactured by JEOL Resonance Co., Ltd.) using a pulsed field gradient. M The mixture (sample) was placed from the bottom of the outer tube of a symmetrical micro-sample tube with an outer diameter of 5 mm to a height of 5 mm, and then sealed with an inner tube. A diffusion measurement probe was used, and the sample was not rotated. The magnetic field gradient was appropriately set within the range of 0.1 to 13.5 T / m, and the stimulated echo pulse sequence was used to measure the content of the mixture at 600 MHz. 1 The self-diffusion coefficient of the H-nuclear component (sulfolane) was measured at 564.73 MHz. 19 The self-diffusion coefficient of the F core component (bis(fluorosulfonyl)imide anion) was measured at 233.25 MHz. 7 The self-diffusion coefficient of the component of the Li core (lithium ions), the field gradient pulse width, the diffusion time, the recovery time after the field gradient pulse, and the number of integrations were adjusted for each sample according to the observed signal conditions.

[0106] The mixture of Comparative Example 2 was measured only as 1 H nucleus. Since the melting point of sulfolane is 29°C, it contains 1 The self-diffusion coefficient D of the H core component (sulfolane) M Measured at 40°C.

[0107] and the self-diffusion coefficient D M The electrolyte after removing the oxide from the mixture of Examples 1, 2 and Comparative Example 1 was measured in the same manner as in Example 1, 2 and Comparative Example 1, and the concentrations of sulfolane, [FSI] and [FSI] were measured at 25°C. - and Li + The self-diffusion coefficient D L The sulfolane after removing the oxide from the mixture of Comparative Example 2 does not contain 19 F nucleus and 7 Li nuclei, therefore, will have a self-diffusion coefficient DL The measurement object is only set as 1 the H nucleus. The melting point of sulfolane is 29 °C, so the self-diffusion coefficient D is measured at 40 °C. L The main measurement conditions of the self-diffusion coefficient are listed in Table 1.

[0108]

[0109] In Examples 1 and 2 and Comparative Example 1, the self-diffusion coefficients D of the mixture, that is, the sulfolane, [FSI] - and Li + in the electrolyte in contact with the oxide are respectively divided by the self-diffusion coefficients D of the sulfolane, [FSI] M and Li - in the electrolyte not in contact with the oxide. + The obtained values (D L / D M ) are shown in Table 2. In Comparative Example 2, the self-diffusion coefficient D of the mixture, that is, the sulfolane in contact with the oxide, is L divided by the self-diffusion coefficient D of the sulfolane not in contact with the oxide. M The obtained value (D L / D M ) is shown in Table 2. L

[0110]

[0111] As shown in Table 2, for the D M / D L of the mixture in Example 1, the value for sulfolane is 10, for [FSI] - is 42, and for Li + is 1. For the D M / D L of the mixture in Example 2, the value for [FSI] - is 15, and the values for sulfolane and Li + are 1. For the D M / D L of the mixture in Comparative Example 1, the value for sulfolane is 3, for [FSI] - is 5, and for Li + is 1. For the D M / D L of the mixture in Comparative Example 2, the value for sulfolane is 0.6.

[0112] ​When comparing the mixture of Example 1 with the mixture of Comparative Example 2, the oxides (α-aluminum oxide) and the solvent (sulfolane) contained in the mixtures are the same. However, Example 1 contains an electrolyte solution in which an electrolyte salt (LiFSI) is dissolved in the solvent, while Comparative Example 1 is different in that no electrolyte salt is dissolved in the solvent. Due to this difference, the D in Example 1 M / D L has 10 of sulfolane, but the D in Comparative Example 2 M / D L has 0.6 of sulfolane. From this result, it is clear that in addition to the oxide and sulfolane, the diffusivity of substances at the interface of the oxide is improved by the electrolyte in the sulfolane.

[0113] When comparing the mixture of Example 1 with the mixture of Comparative Example 1, the oxides (α-aluminum oxide) and the electrolyte salts (LiFSI) contained in the mixtures are the same. However, the difference between the two is that the solvent of the electrolyte solution is sulfolane in Example 1, while it is MPPy-FSI in Comparative Example 1. Due to this difference, the D in Example 1 M / D L has 10 of sulfolane and [[FSI]] - is 42, while the D in Comparative Example 1 M / D L has 3 of sulfolane and [[FSI]] - is 5. From this result, it is clear that in addition to the oxide and the electrolyte salt, when the electrolyte solution contains sulfolane, the diffusivity of substances at the interface of the oxide is significantly improved.

[0114] The mechanism by which the diffusivity of substances at the interface of the oxide is improved is not yet clear, but it is presumed that by adsorbing the components of the electrolyte solution on the surface of the oxide, the ligand sites of the adsorbed molecules or ions are occupied, the electrostatic interaction with the ions in the surrounding electrolyte solution is weakened, and a layer with a fast diffusion rate of substances is formed near the interface of the oxide.

[0115] When comparing the mixture of Example 1 with the mixture of Example 2, the electrolyte solutions contained in the mixtures are the same. However, the difference between the two is that the oxide contained in the mixture is α-aluminum oxide in Example 1, while it is tetragonal Li7La3Zr2O 12 in Example 2. Due to this difference, the D in Example 1 M / D L has 10 of sulfolane and [[FSI]] - is 42, but the D in Example 2 M / D L has 1 of sulfolane and [[FSI]] - is 15.

[0116] It is known that since the self-diffusion coefficient of the electrolyte in contact with α-aluminum oxide (oxide) is large, in order to improve the diffusivity of substances at the interface between the oxide and the electrolyte, it may not necessarily be required to have the ionic conductivity of the oxide itself. Thus, it is presumed that as a result of the interaction between the oxide and the electrolyte, some kind of ionic conduction pathway is formed at the interface of the oxide or in the liquid near the interface.

[0117] It should be noted that, taking the mixtures of Examples 1 and 2 as representatives, in the mixtures of the present invention, the self-diffusion coefficient D of each ion contained in the electrolyte M The value of is used to calculate the ionic conductivity of the ion through the Nernst-Einstein equation. For all ionic components contained in the electrolyte, by summing up this ionic conductivity, the ionic conductivity of the mixture can be estimated to a certain extent. However, the value of the ionic conductivity of the mixture estimated by this method may not necessarily be consistent with the value of the ionic conductivity obtained by, for example, electrochemical impedance measurement at the same temperature as the temperature at which the self-diffusion coefficient D M is measured. Similarly, in the electrolytes contained in the electrolyte, the diffusion coefficients measured by other methods including electrochemical methods based on the change in the concentration of the electrolyte may not necessarily be consistent with the value of the self-diffusion coefficient D M either.

[0118] The reason is that (1) the diffusivity of ions does not directly contribute to ionic conductivity, so for (2) all constituent ions in the mixture, signals may not necessarily be observable in the measurement of the self-diffusion coefficient based on the pulsed field gradient method. Therefore, (3) the region where the value of D M / D L is large exists locally isolated in the sample, and thus it is possible that a continuous ionic conduction pathway is not formed in the whole sample. However, it is considered that the diffusivity of substances is high in the region where the value of D M / D L is large, so the effect of relaxing the concentration gradient is locally obtained.

[0119] As described above, the present invention has been described based on the embodiments, but the present invention is not limited by any of the above embodiments, and it can be easily inferred that various modifications and variations can be made without departing from the gist of the present invention.

[0120] In an embodiment, as the electrochemical element 11, an electrochemical element having a positive electrode layer 12 with an active material layer 14 provided on one side of a current collector layer 13 and a negative electrode layer 16 with an active material layer 18 provided on one side of a current collector layer 17 was described, but it is not necessarily limited thereto. For example, of course, each element in the embodiment can be applied to an electrochemical element having an electrode layer (so-called bipolar electrode) with an active material layer 14 and an active material layer 18 provided on both sides of a current collector layer 13. If the bipolar electrode and the electrolyte layer 15 are alternately laminated and housed in a case (not shown), an electrochemical element having a so-called bipolar structure can be obtained.

[0121] In the embodiment, an electrochemical element 11 in which the active material layers 14 and 18 and the electrolyte layer 15 all contain the mixture 10 and an electrochemical element 24 in which both the active material layers 14 and 18 contain the mixture 10 were described, but it is not necessarily limited thereto. For an electrochemical element, it is sufficient that at least one of the active material layers 14 and 18 and the electrolyte layer 15 contains the mixture 10.

[0122] In the embodiment, an electrochemical element 26 in which a protective layer 29 is disposed between the separator 25 and the negative electrode layer 30 and a protective layer 32 is disposed on the current collector layer 17 was described, but it is not necessarily limited thereto. Of course, one of the protective layers 29 and 32 can be omitted.

[0123] In the embodiment, the mixture 10 was described by exemplifying electrochemical elements 11, 24, and 26 composed of lithium ion batteries (electrical storage devices), but it is not necessarily limited thereto. As other electrochemical elements containing the mixture 10, metal ion batteries such as sodium ion batteries and magnesium batteries other than lithium ion batteries, electrochemical capacitors using redox reactions of electrodes, redox reactions of ions in electrolytes, double layer electrochemical capacitors, metal air batteries using oxygen in the air as a positive electrode active material, fuel cells, and electrolysis devices that chemically decompose compounds or generate substances through chemical decomposition can be exemplified.

[0124] Symbol Explanation

[0125] 10 Mixture

[0126] 11, 24, 26 Electrochemical element (electrical storage device)

[0127] 12, 27 Positive electrode layer

[0128] 15 Electrolyte layer (sheet, separator)

[0129] 16, 30 Negative electrode layer

[0130] 17 Current collector layer

[0131] 19 Oxide

[0132] 22 Electrolyte

[0133] 25 Separator

[0134] 29, 32 Protective layer

Claims

1. A mixture, which is a mixture containing an oxide and an electrolyte, wherein, the electrolyte is obtained by dissolving an electrolyte salt in a sulfone compound represented by Chemical Formula (1), in Chemical Formula (1), R1 and R2 are each independently an alkyl group, alkenyl group or haloalkyl group having 4 or less carbon atoms, or the alkyl group, alkenyl group or haloalkyl group combine with each other to form a ring structure, the self-diffusion coefficient of one or more components contained in the electrolyte in contact with the oxide, measured by pulsed field gradient nuclear magnetic resonance method, is 6 times or more of the self-diffusion coefficient of the same component contained in the electrolyte not in contact with the oxide at the same temperature as the measurement of the self-diffusion coefficient.

2. The mixture according to claim 1, wherein The oxide is alumina.

3. The mixture according to claim 1 or 2, wherein, The electrolyte salt is a lithium salt.

4. A sheet, which contains the mixture according to Claim 1 or 2.

5. An electrochemical element, which contains the mixture according to Claim 1 or 2.

6. A storage device, which includes a positive electrode layer, a negative electrode layer and a separator that separates the positive electrode layer from the negative electrode layer, and contains the mixture according to Claim 1 or 2.

7. The electrical storage device according to claim 6, wherein, At least one of the positive electrode layer, the negative electrode layer and the separator contains the mixture.

8. According to the storage device of Claim 6, wherein, at least one of the positive electrode layer and the negative electrode layer contains a current collector layer, it has a protective layer in contact with at least one of the separator and the current collector layer, the protective layer contains the mixture.

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