Mixture, sheet, electrochemical element and electricity storage device

Abstract

Provided are a mixture, a sheet, an electrochemical element and a power storage device that can improve the dispersibility of a substance at the boundary between an oxide and an electrolytic solution. A mixture (10) includes an oxide (19) and an electrolytic solution. The electrolytic solution comprises a sulfone compound represented by chemical formula (1) with an electrolytic salt dissolved therein. In chemical formula (1), R1 and R2 are each independently: an alkyl group, an alkenyl group, or a halogenated alkyl group with not more than four carbons; or a ring structure formed by mutually bonding an alkyl group, an alkenyl group, or a halogenated alkyl group. The self-diffusion coefficient which is of one or more components included in the electrolytic solution that is in contact with the oxide and which is measured by a pulsed field gradient nuclear magnetic resonance spectroscopy is at least six times greater than the self-diffusion coefficient of a component included in the electrolytic solution that is not in contact with the oxide.

Description

[Technical Field]

[0001] The present invention relates to a mixture containing an oxide and an electrolyte, a sheet, an electrochemical element, and an electricity storage device. [Background technology]

[0002] A technique for providing an electrochemical element with a mixture containing an oxide and an electrolyte solution to reduce leakage and improve safety of the electrochemical element containing an electrolyte solution is known. In the prior art disclosed in Patent Document 1, an electrolyte sheet is formed from a mixture containing an oxide made of silicon dioxide and an electrolyte solution containing tetraglyme. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2020-113527 Summary of the Invention [Problem to be solved by the invention]

[0004] To improve the ionic conductivity of a mixture containing an oxide and an electrolyte, it is important to improve the diffusion rate of electrolyte components near the interface, including desolvation of cations at the interface between the oxide and the electrolyte. In the prior art, there is room for improvement in the diffusivity of materials at the oxide interface.

[0005] The present invention has been made to solve this problem, and has an object to provide a mixture, a sheet, an electrochemical element, and an electricity storage device that can improve the diffusibility of substances at an interface. [Means for solving the problem]

[0006] A first aspect to achieve this object is a mixture containing an oxide and an electrolyte, wherein the electrolyte is a sulfone compound represented by chemical formula (1) having an electrolyte salt dissolved therein. In chemical formula (1), R1 and R2 are each independently an alkyl group, an alkenyl group, or a halogenated alkyl group having four or fewer carbon atoms, or the alkyl groups, alkenyl groups, or halogenated alkyl groups 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, measured by pulsed field gradient nuclear magnetic resonance spectroscopy, is at least six times the self-diffusion coefficient of the same component contained in the electrolyte not in contact with the oxide, measured at the same temperature as the measurement.

[0007] [ka]

[0008] In a second embodiment, in the first embodiment, the oxide is alumina.

[0009] In a third embodiment, in the first or second embodiment, the electrolyte salt is a lithium salt.

[0010] A fourth embodiment is a sheet comprising a mixture of any of the first to third embodiments.

[0011] A fifth embodiment is an electrochemical device comprising a mixture of any of the first to third embodiments.

[0012] A sixth aspect is an electricity storage device comprising a positive electrode layer, a negative electrode layer, and a separator separating the positive electrode layer and the negative electrode layer, the electricity storage device comprising the mixture of any one of the first to third aspects.

[0013] In a seventh embodiment, in the sixth embodiment, at least one of the positive electrode layer, the negative electrode layer, and the separator includes a mixture.

[0014] In an eighth embodiment, in the sixth embodiment, at least one of the positive electrode layer and the negative electrode layer includes a current collecting layer, and a protective layer is provided in contact with at least one of the separator and the current collecting layer, and the protective layer includes the mixture. [Effects of the Invention]

[0015] The mixture, sheet, electrochemical element, and electricity storage device of the present invention can improve the diffusibility of substances at the interface between the oxide and the electrolyte. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 2 is a cross-sectional view of an electrochemical device containing a mixture according to the first embodiment. [Figure 2] FIG. 2 is an enlarged cross-sectional view of the electrochemical device showing a portion indicated by II in FIG. [Figure 3] FIG. 1 is a diagram schematically illustrating a garnet-type crystal structure. [Figure 4] FIG. 4 is a cross-sectional view of an electrochemical device according to a second embodiment. [Figure 5] FIG. 10 is a cross-sectional view of an electrochemical device according to a third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0017] Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. Fig. 1 is a schematic cross-sectional view of an electrochemical element 11 containing a mixture 10 according to one embodiment. The electrochemical element 11 in this embodiment is a lithium ion solid-state battery (electricity storage device) in which the power generating element is made of a solid. "The power generating element is made of a solid" means that the skeleton of the power generating element is made of a solid, and includes a form in which the skeleton is impregnated with a liquid.

[0018] The electrochemical device 11 includes, in order, 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 case (not shown).

[0019] The positive electrode layer 12 is formed by stacking a current collecting layer 13 and an active material layer 14. The current collecting layer 13 is a conductive member. Examples of materials for the current collecting layer 13 include metals selected from Ni, Ti, Fe, and Al, alloys containing two or more of these elements, stainless steel, and carbon materials.

[0020] 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, the active material layer 14 may contain a conductive additive. Examples of the conductive additive include carbon black, acetylene black, ketjen black, carbon fiber, Ni, Pt, and Ag.

[0021] The active material 20 is exemplified by a metal oxide containing a transition metal, a sulfur-based active material, and an organic active material. The metal oxide containing a transition metal is exemplified by a metal oxide containing Li and one or more elements selected from Mn, Co, Ni, Fe, Cr, and V. The metal oxide containing a transition metal is exemplified by 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 Examples include O2 and LiFePO4.

[0022] In order to suppress the reaction between the active material 20 and the oxide 19, a coating layer can be provided on the surface of the active material 20. The coating layer can be made of Al2O3, ZrO2, LiNbO3, Li4Ti5O 12 , LiTaO3, LiNbO3, LiAlO2, Li2ZrO3, Li2WO4, Li2TiO3, Li2B4O7, Li3PO4 and Li2MoO4 are examples.

[0023] Examples of sulfur-based active materials include S, TiS2, NiS, FeS2, Li2S, MoS3, and sulfur-carbon composites. Examples of organic-based active materials include radical compounds typified by 2,2,6,6-tetramethylpiperidinoxyl-4-yl methacrylate and polytetramethylpiperidinoxyl vinyl ether, quinone compounds, radicalene compounds, tetracyanoquinodimethane, and phenazine oxide.

[0024] The electrolyte layer 15 consists of the mixture 10. The mixture 10 contains the oxide 19 and the electrolyte solution 22 (see Figure 2). The mixture 10 may further contain a binder. The electrolyte layer 15 corresponds to a separator that separates the positive electrode layer 12 and the negative electrode layer 16.

[0025] In the negative electrode layer 16, the current collector layer 17 and the active material layer 18 are overlapped. 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.

[0026] The active material layer 18 contains the mixture 10 and the active material 21. In order to lower the resistance of the active material layer 18, a conductive aid may be contained in the active material layer 18. Examples of the conductive aid include carbon black, acetylene black, ketjen black, carbon fiber, Ni, Pt, and Ag. The active material 21 includes 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, a binder may be contained in the active material layers 14 and 18.

[0027] FIG. 2 is an enlarged cross-sectional view of the electrochemical element 11 showing a portion II in FIG. 1. The mixture 10 contained in the electrochemical element 11 contains an oxide 19 and an electrolyte solution 22. The oxide 19 is preferably insoluble in the electrolyte solution 22 and does not have electronic conductivity. The shape of the oxide 19 may be granular, spherical, rod-like, needle-like, polygonal, fibrous, or scaly. The oxide 19 is appropriately selected from inorganic compounds such as alumina, silica, ceria, zirconia, and oxide-based solid electrolytes.

[0028] Examples of oxide-based solid electrolytes include those having a crystal structure of perovskite type, NASICON type, LISICON type, and garnet type containing Li, La, and Zr. Perovskite-type oxides include oxides containing at least Li, Ti, and La, such as La 2 / 3-X Li 3X Examples of NASICON-type oxides include oxides containing at least Li, M (where 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 LISICON-type oxides include oxides containing Li 14 An example is Zn(GeO4)4.

[0029] Figure 3 is a diagram showing a typical garnet-type crystal structure. The garnet-type crystal structure is represented by the general formula C3A2B3O 12 In a garnet-type crystal structure, Sc at the C-site is dodecahedrally coordinated with an oxygen atom Oa, Sa at the A-site is octahedrally coordinated with an oxygen atom Oa, and Sb at the B-site is tetrahedrally coordinated with an oxygen atom Oa. In an ordinary garnet-type crystal structure, oxide 19 is a position where oxygen atoms Oa are octahedrally coordinated, and Li can exist in a position that becomes a vacancy V. The vacancy V is, for example, a position sandwiched between B-site Sb1 and B-site Sb2. The Li present in the vacancy V is octahedrally coordinated with an oxygen atom Oa that forms an octahedron including the tetrahedral face Fb1 that forms the B-site Sb1 and the tetrahedral face Fb2 that forms the B-site Sb2. For example, in Li7La3Zr2O having a garnet-type crystal structure, 12In the formula, La can occupy the C-site Sc, Zr can occupy the A-site Sa, and Li can occupy the B-site Sb and the vacant V.

[0030] The oxides containing Li, La, and Zr with a garnet-type crystal structure are listed in the X-ray diffraction file No. 422259 (Li7La3Zr2O) of the Cambridge Structural Database (CSD). 12 The XRD pattern of this oxide is similar to that of No. 422259. The type of constituent elements and the Li concentration of this oxide may differ from those of No. 422259, and therefore the diffraction angle and intensity ratio may differ. Li7La3Zr2O 12 Either a tetragonal crystal having low ionic conductivity or a cubic crystal having high ionic conductivity can be used.

[0031] Oxides containing Li, La, and Zr and having a garnet-type or garnet-like crystal structure may have some of their constituent elements substituted with other elements, or may have trace amounts of other elements added without substituting the constituent elements. Examples of 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 lanthanides (excluding La).

[0032] Returning to FIG. 2, the oxide 19 is, for example, Li6La3Zr 1.5 W 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 ,Li 6.25 La3Zr2Ga 0.25 O 12 ,Li 6.4 La3Zr 1.4 Ta 0.6 O 12 ,Li 6.5 La3Zr 1.75 Te0.25 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 ZrO 12 Examples include:

[0033] The oxide having a garnet-type or garnet-like crystal structure preferably contains, in addition to Li, La, and Zr, at least one of Mg and element A (A is at least one element selected from the group consisting of Ca, Sr, and Ba), with the molar ratio of each element satisfying all of the following (1) to (3), or contains both Mg and element A, with the molar ratio of each element satisfying all of the following (4) to (6). Element A is preferably Sr, as it increases the ionic conductivity of oxide 19. (1) 1.33≦Li / (La+A)≦3 (2) 0≦Mg / (La+A)≦0.5 (3) 0≦A / (La+A)≦0.67 (4) 2.0≦Li / (La+A)≦2.5 (5) 0.01≦Mg / (La+A)≦0.14 (6) 0.04≦A / (La+A)≦0.17

[0034] The median diameter of the circle-equivalent diameter of the oxide 19 appearing on the cross section of the electrolyte layer 15 is preferably 0.2 to 10 μm, more preferably 0.2 to 6 μm, in order to make the surface area of ​​the oxide 19 appropriately large and to enhance the diffusibility of the components of the electrolyte solution 22 present on the surface of the oxide 19.

[0035] To determine the median diameter of the oxides 19, first, a scanning electron microscope (SEM) image of the oxides 19 appearing on the cross section of the electrolyte layer 15 (a polished surface, a surface obtained by irradiating with a focused ion beam (FIB), or a surface obtained by ion milling) is analyzed, and the equivalent circle diameter (the diameter of a circle with the same area as the area of ​​the oxides 19 appearing on the cross section) is calculated from the area of ​​each oxide 19, and a volume-based particle size distribution is determined. The median diameter is the equivalent circle diameter at which the cumulative frequency in the particle size distribution is 50%. To ensure accuracy, the image for determining the particle size distribution is taken from 400 μm of the electrolyte layer 15. 2 The area shall be equal to or greater than this.

[0036] The electrolyte solution 22 is an organic solvent in which an electrolyte salt is dissolved. The electrolyte salt is a compound used for transferring cations between the positive electrode layer 12 and the negative electrode layer 16. When the electrolyte salt is a lithium salt, the anion of the lithium salt is a halide ion (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 - (R is an alkyl group having 4 or less carbon atoms, a phenyl group, or a naphthyl group).

[0037] The anion of the lithium salt is N(SO2F)2, which has a sulfonyl group -S(=O)2-. - ,N(SO2CF3)2 - ,N(SO2C2F5)2 - Sulfonylimides such as the above are preferred. This is because the sulfonylimide anion is less susceptible to increases in the viscosity of the electrolyte and decreases in ionic conductivity even when the salt concentration is high, and furthermore, it forms a highly stable and low-resistance coating (SEI), which reduces the reductive decomposition of the electrolyte and widens the reduction-side potential window.

[0038] N(SO2F)2 - is abbreviated as [FSI] - : It is called bis(fluorosulfonyl)imide anion, N(SO2CF3)2 - abbreviated as [TFSI] - : It is sometimes called bis(trifluoromethanesulfonyl)imide anion. The lithium salt is particularly preferably lithium bis(fluorosulfonyl)imide (LiFSI), because LiFSI has little effect on increasing the viscosity of the electrolyte and is effective in forming a good passive oxide film (SEI).

[0039] The organic solvent of the electrolytic solution 22 contains a sulfone compound represented by chemical formula (1). The organic solvent of the electrolytic solution 22 can be one or more types appropriately selected from the group of materials shown below.

[0040] [ka]

[0041] In chemical formula (1), R1 and R2 are each independently an alkyl group, alkenyl group, or halogenated alkyl group having 4 or less carbon atoms, or the alkyl groups, alkenyl groups, or halogenated alkyl groups are bonded to each other to form a ring structure. R1 and R2 may be a linear hydrocarbon group, or a hydrocarbon group having a branched or cyclic structure.

[0042] Examples of alkyl groups having 4 or less carbon atoms include methyl, ethyl, n-propyl, isopropyl, 1-ethylpropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, 2-methylbutyl, and 3,3-dimethylbutyl. Examples of alkenyl groups having 4 or less carbon atoms include vinyl, 1-propenyl, allyl, 1-butenyl, 2-butenyl, and 3-butenyl.

[0043] Halogenated alkyl groups having 4 or less 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, and perchloroethyl. Examples of such groups include a 2,2,3,3-tetrachloropropyl group, a perchloropropyl group, a perchloroisopropyl group, a perchlorobutyl group, a perchloroisobutyl group, a bromomethyl group, a dibromomethyl group, a tribromomethyl group, a 2,2,2-tribromoethyl group, a 1,1,2,2-tetrabromoethyl group, a 2,2,3,3-tetrabromopropyl group, an iodomethyl group, a diiodomethyl group, a triiodomethyl group, a 2,2,2-triiodoethyl group, a 1,1,2,2-tetraiodoethyl group, and a 2,2,3,3-tetraiodopropyl group.

[0044] Examples of cyclic compounds in which alkyl groups, alkenyl groups, or halogenated alkyl groups are bonded to each other to form a ring structure in chemical formula (1) include trimethylene sulfone, sulfolane, fluorosulfolane, difluorosulfolane, methylsulfolane, and dimethylsulfolane. The sulfone compounds represented by chemical formula (1) have high oxidation resistance, and are therefore advantageous for increasing the voltage of the electrochemical device 11.

[0045] Although there is no limitation on the salt concentration of the electrolyte solution 22, the salt concentration (molar concentration) of the electrolyte solution 22 is preferably 1.4 mol / kg or more, and more preferably 1.6 mol / kg or more. This is because, compared to a general electrolyte solution with a salt concentration of around 1 mol / kg, the number of solvent molecules coordinated to cations is increased and the amount of uncoordinated solvent is reduced, thereby making it possible to increase the transference number of the cations of the electrolyte salt.

[0046] The electrolyte solution 22 can contain a solvated ionic liquid. The solvated ionic liquid is composed of a cation solvated in a sulfone compound represented by chemical formula (1) and its counterion. The electrolyte solution 22 can be in a state where all solvent molecules are coordinated to the cations and there is no uncoordinated solvent, or in a state where all solvent molecules are coordinated to the cations and there is no uncoordinated solvent, and there is an excess of cations that are not coordinated to the solvent molecules. It is known that electrolyte solution 22, which has a high salt concentration in which cations are solvated in a sulfone compound, takes on a unique coordination structure when it becomes a solvated ionic liquid, and the transport rate of lithium ions increases.

[0047] In addition to the sulfone compound represented by chemical formula (1), mixture 10 may contain other organic solvents. The other organic solvents contribute to, for example, reducing the viscosity of electrolyte solution 22 and increasing the ionic conductivity of electrolyte solution 22. Examples of other organic solvents include propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, trimethyl phosphate, triethyl phosphate, γ-butyrolactone, dimethyl methylphosphonate, acetonitrile, isobutyl methyl ketone, nitromethane, methyl ethyl ketone, tetramethylsilane, siloxane compounds, and organic silicate compounds. One or more other organic solvents are appropriately selected from those that do not easily affect the coordination state of cations and solvent molecules.

[0048] The mixture 10 may contain various additives used in lithium-ion batteries. Examples of additives include carbonate compounds containing unsaturated bonds or halogens, such as vinylene carbonate and fluoroethylene carbonate, flame-retardant compounds such as ionic liquids, redox shuttle compounds such as acid anhydrides, nitrile compounds, and anisole derivatives, and overcharge inhibitors such as aromatic compounds.

[0049] The ratio (wt%) of the sulfone compound to the total of the sulfone compound and other organic solvents contained in the mixture 10 is preferably 75% or more in order to ensure the transference number of the cation.

[0050] The salt concentration of the electrolyte solution 22 is preferably 4.0 mol / kg or less. If the salt concentration of the electrolyte solution 22 exceeds 4.0 mol / kg, the viscosity of the electrolyte solution 22 increases, which significantly reduces the ionic conductivity.

[0051] The mixture 10 is a combination of the oxide 19 and the electrolyte 22 such that the self-diffusion coefficient of one or more components contained in the electrolyte 22 in contact with the oxide 19, as measured by pulsed field gradient nuclear magnetic resonance spectroscopy (PFG-NMR), is at least six times the self-diffusion coefficient of the component contained in the electrolyte 22 not in contact with the oxide 19, as measured at the same temperature.

[0052] The self-diffusion coefficient D of the component of the electrolyte 22 in contact with the oxide 19 M represents the diffusion rate of the components of the electrolyte 22 in a sample in which the oxide 19 and the electrolyte 22 are mixed. The self-diffusion coefficient D of the components of the electrolyte 22 that are not in contact with the oxide 19 L indicates the diffusion rate of the components of the electrolyte solution 22. M ,D L are measured at the same temperature. If the temperature difference between the two measurements is within 1°C, they can be considered to be the same temperature. The self-diffusion coefficient D of the same component M ,D L By comparing the self-diffusion coefficient D of the components of the electrolyte 22 in contact with the oxide 19, M is the self-diffusion coefficient D of the component of the electrolyte 22 that is not in contact with the oxide 19. L This indicates that the diffusivity of the substance at the interface of the oxide 19 in contact with the electrolyte 22 is six times or more greater than when the electrolyte is present alone.

[0053] It may be difficult to judge the accuracy of the apparent self-diffusion coefficient obtained by PFG-NMR measurement relative to the actual self-diffusion coefficient. When it is difficult to perform measurements other than PFG-NMR for comparison verification (e.g., AC impedance measurements, evaluation of the diffusion coefficient using radioisotopes), the apparent self-diffusion coefficient obtained by PFG-NMR is of course used. However, even when measurements other than PFG-NMR can be performed, the apparent self-diffusion coefficient obtained by PFG-NMR is used for the sake of uniformity of measurement methods.

[0054] When cations move from the electrolyte 22 to the oxide 19, desolvation of the cations from the solvent molecules or desorption of ions from ion pairs formed by complexation of counterions and cations occurs at the interface of the oxide 19, and it is presumed that these are the rate-limiting steps for ionic conduction.

[0055] High diffusivity of materials at the interface of oxide 19 facilitates the alleviation of the concentration gradient of desorbed solvent molecules and anions when current is passed through mixture 10, resulting in desolvation of cations and dissociation of ion pairs at the interface between oxide 19 and electrolyte solution 22. As a result, desolvation at the interface between oxide 19 and electrolyte solution 22 is facilitated, presumably reducing the interfacial resistance of oxide 19. Furthermore, the concentration gradient of ions in electrolyte solution 22 that occurs during charge and discharge is also likely to be alleviated, improving the rate characteristics of electrochemical device 11 and contributing to improved rapid charging performance and power density. Furthermore, if the diffusion rate of decomposition products associated with the charge and discharge of electrochemical device 11 is also increased, the accumulation of decomposition products is reduced, thereby improving cycle life.

[0056] The nuclide for which the NMR signal is observed depends on the type of organic solvent contained in the electrolyte solution 22 and the type of electrolyte salt dissolved in the organic solvent. 1 H, 13 C, 19 F, 6 Li, 7 Li, 11 B, 23 Na, 31 P is an example. Within the same molecule, for example, PF6 - of 19 F nucleus and 31 Even when observed with the P nucleus, two types of signals are observed: CH3 and CH2 of the ethyl group. 1 Even when observing H nuclei, the same self-diffusion coefficient is obtained. Therefore, even in an electrolyte solution that is a mixture of multiple solvents or components, if there is even one signal that does not overlap with other components, the self-diffusion coefficient can be obtained for each component.

[0057] The self-diffusion coefficient D of the components of the electrolyte 22 not in contact with the oxide 19 L In order to measure this, information such as the concentration of the electrolyte in electrolyte solution 22 and the mixing ratio of the solvent is required. The concentration of the electrolyte in electrolyte solution 22 contained in mixture 10 is determined, for example, as follows. Here, the case of determining the concentration of the lithium salt in mixture 10 constituting electrolyte layer 15 will be described, but the concentrations of mixture 10 and electrolyte salts other than lithium salt constituting active material layers 14 and 18 can also be determined in a similar manner.

[0058] First, the crushed electrolyte layer 15 is immersed in a solvent to dissolve the electrolyte solution 22 contained in the electrolyte layer 15 in the solvent, and then the solid and liquid components are separated by centrifugation or filtration. The Li content of the separated liquid component is determined by high-frequency inductively coupled plasma spectroscopy (ICP).

[0059] The type of organic solvent contained in the electrolyte layer 15 is identified, for example, by gas chromatography-mass spectrometry (GC-MS). A calibration curve is created using the identified type of organic solvent (hereinafter referred to as the "standard substance"), and the content of the organic solvent contained in the electrolyte layer 15 is identified based on the area of ​​the chromatogram. Alternatively, the standard substance and the electrolyte layer 15 are analyzed by thermogravimetric differential thermal analysis (TG-DTA), and the analysis results of the standard substance and the electrolyte layer 15 are compared to identify the content of the organic solvent contained in the electrolyte layer 15. The molar concentration (mol / kg) of the lithium salt in the electrolyte solution 22 is calculated based on the content of Li in the liquid components and the content of the organic solvent in the electrolyte layer 15.

[0060] Based on the components of the electrolyte solution 22 thus identified, an electrolyte solution having 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 similarly measured to obtain the self-diffusion coefficient D L The self-diffusion coefficient D of each component of the electrolyte 22 is obtained from the literature. L If known, these values ​​can also be used.

[0061] In the mixture 10, the ratio of the volume of the oxide 19 to the total volume of the oxide 19 and the electrolyte solution 22 is preferably 52% or more and less than 100%, and more preferably 61% or more and less than 100%. The ratio of the volume of the oxide 19 to the total volume of the oxide 19 and the electrolyte solution 22 is particularly preferably 93% or less. By combining the oxide 19 and the electrolyte solution 22, the transport number of the Li ions in the mixture 10 can be made larger than that of a typical electrolyte solution 22. As a result, the operational stability of the electrochemical device 11 in which the mixture 10 is disposed is increased.

[0062] The contents (volume %) of oxide 19 and electrolyte solution 22 are determined by freezing electrolyte layer 15 or embedding electrolyte layer 15 in a tetrafunctional epoxy resin or the like and then analyzing a randomly selected cross section of electrolyte layer 15 at a magnification of 5000 times using an SEM equipped with an energy dispersive X-ray spectrometer (EDS). The analysis involves identifying the distribution of La, Zr, and S and analyzing the contrast of the backscattered electron image to identify the areas of oxide 19 and electrolyte solution 22, and the proportions of these areas in the cross section of electrolyte layer 15 are considered to be the volume proportions of electrolyte layer 15 in mixture 10 to obtain the contents (volume %) of oxide 19 and electrolyte solution 22.

[0063] The mixture 10 may contain a binder that binds the oxide 19. Examples of binders include fluorinated resins, polyolefins, polyimides, polyvinylpyrrolidone, polyvinyl alcohol, cellulose ethers, and rubber-like polymers such as styrene-butadiene rubber. Examples of fluorinated resins include vinylidene fluoride polymers, polychlorotrifluoroethylene, polyvinyl fluoride, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymers, tetrafluoroethylene-hexafluoropropylene copolymers, ethylene-tetrafluoroethylene copolymers, and ethylene-chlorotrifluoroethylene copolymers.

[0064] Examples of vinylidene fluoride polymers include homopolymers of vinylidene fluoride and copolymers of vinylidene fluoride and copolymerizable monomers. Examples of copolymerizable monomers include halogen-containing monomers (excluding vinylidene fluoride) and non-halogen copolymerizable monomers. Examples of halogen-containing monomers include chlorine-containing monomers such as vinyl chloride; and fluorine-containing monomers such as trifluoroethylene, tetrafluoroethylene, chlorotrifluoroethylene, hexafluoropropylene, and perfluoroalkyl vinyl ether. Examples of non-halogen copolymerizable monomers include olefins such as ethylene and propylene; acrylic monomers such as acrylic acid, methacrylic acid, and esters or salts thereof; and vinyl monomers such as acrylonitrile, vinyl acetate, and styrene. One or more copolymerizable monomers are polymerized with vinylidene fluoride to form the copolymer.

[0065] The electrochemical device 11 is manufactured, for example, as follows: A mixture 10, which is a mixture of an electrolyte solution 22 in which a lithium salt is dissolved in an organic solvent and an oxide 19, is mixed with a solution in which a binder is dissolved in a solvent to form a slurry. After tape casting, the mixture is dried to obtain a green sheet (electrolyte sheet) for the electrolyte layer 15.

[0066] An active material 20 is mixed with a mixture 10, which is a mixture of an electrolyte solution 22 in which a lithium salt is dissolved in an organic solvent and an oxide 19, and then a solution in which a binder is dissolved in a solvent is mixed to form a slurry. After tape casting on a current collecting layer 13, the mixture is dried to obtain a green sheet (positive electrode sheet) for the positive electrode layer 12.

[0067] An active material 21 is mixed with a mixture 10, which is a mixture of an electrolyte solution 22 in which a lithium salt is dissolved in an organic solvent and an oxide 19, and then a solution in which a binder is dissolved in a solvent is mixed to form a slurry. After tape casting on a current collecting layer 17, the mixture is dried to obtain a green sheet (negative electrode sheet) for the negative electrode layer 16.

[0068] The electrolyte sheet, positive electrode sheet, and negative electrode sheet are cut into predetermined shapes, and then stacked in this order, positive electrode sheet, electrolyte sheet, and negative electrode sheet, and then pressed together to form a single sheet. Terminals (not shown) are connected to the current collecting layers 13 and 17, respectively, and the sheet is sealed in a case (not shown), to obtain an electrochemical device 11 including a positive electrode layer 12, an electrolyte layer 15, and a negative electrode layer 16.

[0069] Instead of obtaining the positive electrode layer 12, the electrolyte layer 15, and the negative electrode layer 16 by tape casting of a slurry containing the mixture 10, it is of course possible to obtain the electrolyte layer 15 by press molding the mixture 10, or to obtain the positive electrode layer 12 and the negative electrode layer 16 by press molding the mixture 10 containing the active material 20 or the active material 21.

[0070] The second embodiment will be described with reference to Fig. 4. In the first embodiment, the mixture 10 is used in an electricity storage device in which the power generating element is made of a solid. In the second embodiment, the mixture 10 is used in a liquid-based lithium-ion battery that uses an organic solvent as the electrolyte. The same parts as those described in the first embodiment are given the same reference numerals, and the following description will be omitted. Fig. 4 is a cross-sectional view of an electrochemical element 24 (electricity storage device) in the second embodiment.

[0071] The electrochemical device 24 includes, in this order, a positive electrode layer 12, a separator 25, and a negative electrode layer 16. These are housed in a case (not shown). The separator 25 is made of a porous material that is durable against the active materials 20, 21 and the electrolyte solution contained in the positive electrode layer 12 and the negative electrode layer 16, and that allows lithium ions to pass through but does not have electronic conductivity. Examples of the separator 25 include a nonwoven fabric or porous film made of cellulose, polypropylene, polyethylene, or the like. The electrolyte solution is the same as that described in the first embodiment, so its description will be omitted.

[0072] In the electrochemical element 24 of the second embodiment, the mixture 10 is contained in the positive electrode layer 12 and the negative electrode layer 16, and thus, similar to the electrochemical element 11 of the first embodiment, the diffusibility of substances between the oxide 19 in the positive electrode layer 12 and the negative electrode layer 16 and the electrolyte solution 22 can be improved.

[0073] A third embodiment will be described with reference to Fig. 5. In the first and second embodiments, the positive electrode layer 12, the electrolyte layer 15, and the negative electrode layer 16 contain the mixture 10. In the third embodiment, the protective layers 29 and 32 contain the mixture 10. The same parts as those described in the first and second embodiments are designated by the same reference numerals, and the following description will be omitted. Fig. 5 is a cross-sectional view of an electrochemical element 26 (electricity storage device) in the third embodiment.

[0074] The electrochemical device 26 includes, in order, a positive electrode layer 27, a separator 25, and a negative electrode layer 30. These are housed in a case (not shown). The electrochemical device 26 is a liquid-based lithium-ion battery that uses an organic solvent as the electrolyte.

[0075] The positive electrode layer 27 is formed by stacking the current collecting layer 13 and an active material layer 28. The active material layer 28 contains an active material 20. In order to reduce the resistance of the active material layer 28, the active material layer 28 may contain a conductive additive such as carbon black, acetylene black, ketjen black, carbon fiber, Ni, Pt, or Ag.

[0076] A protective layer 29 is disposed between the separator 25 and the negative electrode layer 30. The protective layer 29 contains the mixture 10.

[0077] The negative electrode layer 30 is formed by stacking an active material layer 31, a protective layer 32, and a current collecting layer 17 in this order. The active material layer 31 is made of, for example, Li, a Li-Al alloy, a Li-Sn alloy, a Li-Si alloy, a Li-Mg alloy, a Li-Si alloy, or a Si-Li alloy. The protective layer 32 contains the mixture 10. The protective layers 29 and 32 are arranged by sheet lamination, coating on the separator 25 or the current collecting layer 17, or the like. Because the protective layers 29 and 32 contain the mixture 10, the diffusibility of substances between the oxide 19 in the protective layers 29 and 32 and the electrolyte solution 22 can be improved.

[0078] When the oxide 19 contained in the protective layers 29, 32 has a garnet-type crystal structure containing Li, La, Zr, and O, it is resistant to reduction by the metallic lithium of the active material layer 31, thereby increasing the stability of the operation of the electrochemical device 26. Furthermore, since the protective layer 29 is interposed between the active material layer 31 and the separator 25, it suppresses short circuits caused by dendrite growth of metallic lithium. The protective layer 32 interposed between the active material layer 31 and the current collecting layer 17 suppresses deterioration of the current collecting layer 17. [Example]

[0079] The present invention will be explained in more detail with reference to examples, but the present invention is not limited to these examples.

[0080] Example 1 Alpha-alumina oxide and an electrolyte solution prepared by mixing sulfolane and lithium bis(fluorosulfonyl)imide (LiFSI) in a molar ratio of 3:1 were placed in a mortar in a volume ratio of 61:39 and mixed using a pestle to obtain the mixture in Example 1. The median diameter of the volume-based particle size distribution of the alpha-alumina measured by laser diffraction / scattering was 0.9 μm.

[0081] Example 2 Instead of α-alumina, tetragonal Li7La3Zr2O 12 The mixture in Example 2 was obtained in the same manner as in Example 1, except that Li7La3Zr2O was mixed into the electrolyte. 12 The median diameter of the particle size distribution on a volume basis measured by the laser diffraction / scattering method was 0.8 μm.

[0082] (Comparative Example 1) The mixture in Comparative Example 1 was obtained in the same manner as in Example 1, except that an electrolyte solution prepared by mixing N-methyl-N-propylpyrrolidinium bis(fluorosulfonyl)imide (MPPy-FSI) and LiFSI in a molar ratio of 1.46:1 was mixed with α-alumina instead of the electrolyte solution prepared by mixing sulfolane and LiFSI.

[0083] (Comparative Example 2) The mixture in Comparative Example 2 was obtained in the same manner as in Example 1, except that sulfolane (in which no lithium salt was dissolved) was mixed with α-alumina at 40°C instead of the electrolyte solution prepared by mixing sulfolane and LiFSI.

[0084] (Measurement of self-diffusion coefficient) The self-diffusion coefficient D of each component of the electrolyte in the mixture at 25°C M was measured using a nuclear magnetic resonance spectrometer (JNM-ECA600II, manufactured by JEOL RESONANCE Co., Ltd.) using a pulsed magnetic field gradient. The mixture (sample) was placed in a symmetrical micro-sample tube with an outer diameter of 5 mm at a height of 5 mm from the bottom of the outer tube, and then sealed with the inner tube. A diffusion measurement probe was used, the sample was not rotated, and the magnetic field gradient was appropriately set within the range of 0.1-13.5 T / m. A stimulated echo pulse sequence was used. 1 The self-diffusion coefficient of the component containing H nuclei (sulfolane) was measured at 600 MHz. 19 The self-diffusion coefficient of the component containing the F nucleus (bis(fluorosulfonyl)imide anion) was measured at 564.73 MHz. 7 The self-diffusion coefficient of the component containing Li nuclei (lithium ions) was measured at 233.25 MHz. The magnetic field gradient pulse width, diffusion time, recovery time after the magnetic field gradient pulse, and number of integrations were adjusted for each sample depending on the observed signal conditions.

[0085] The mixture in Comparative Example 2 is 1 Only H nuclei were used. 1 Self-diffusion coefficient D of component containing H nucleus (sulfolane) M was measured at 40°C because the melting point of sulfolane is 29°C.

[0086] Self-diffusion coefficient D M In the same manner as in the measurement of the oxides in the mixtures of Examples 1 and 2 and Comparative Example 1, the electrolytes were measured using sulfolane, [FSI], - and Li + The self-diffusion coefficient D L was measured at 25°C. The sulfolane obtained by removing the oxide from the mixture in Comparative Example 2 was 19F nuclei and 7 Since it does not contain Li nuclei, the self-diffusion coefficient D L The measurement target of 1 Since only H nuclei are used and the melting point of sulfolane is 29°C, the self-diffusion coefficient D L The self-diffusion coefficient was measured at 40°C. The main measurement conditions for the self-diffusion coefficient are shown in Table 1.

[0087] [Table 1]

[0088] In Examples 1 and 2 and Comparative Example 1, the mixture, i.e., sulfolane in the electrolyte in contact with the oxide, [FSI] - and Li + The self-diffusion coefficient D M The electrolyte, sulfolane, which does not contact the oxide, [FSI] - and Li + The self-diffusion coefficient D L The values ​​divided by (D M / D L ) are shown in Table 2. In Comparative Example 2, the self-diffusion coefficient D of sulfolane in contact with the mixture, i.e., the oxide, M is the self-diffusion coefficient D of sulfolane not in contact with the oxide. L Divided by (D M / D L ) are listed in Table 2.

[0089] [Table 2]

[0090] As shown in Table 2, the D M / D L is sulfolane 10 and [FSI] - is 42, and Li + The D of the mixture in Example 2 was 1. M / D L [FSI] - is 15, and sulfolane and Li + The D of the mixture in Comparative Example 1 was 1. M / D Lis sulfolane 3 and [FSI] - is 5 and Li + The D of the mixture in Comparative Example 2 was 1. M / D L For sulfolane, the ratio was 0.6.

[0091] Comparing the mixture in Example 1 with the mixture in Comparative Example 2, the oxide (α-alumina) and solvent (sulfolane) contained in the mixture are the same. However, Example 1 differs in that the electrolyte solution contains an electrolyte salt (LiFSI) dissolved in the solvent, while Comparative Example 1 does not contain an electrolyte salt dissolved in the solvent. This difference leads to the difference in D of Example 1. M / D L The sulfolane content was 10, but the D M / D L The diffusivity of the oxide at the interface was 0.6 for sulfolane. This result revealed that the electrolyte in sulfolane, in addition to the oxide and sulfolane, improves the diffusivity of the substance at the oxide interface.

[0092] Comparing the mixture in Example 1 with the mixture in Comparative Example 1, the oxide (α-alumina) and electrolyte salt (LiFSI) contained in the mixture are the same. However, the two are different in that the solvent of the electrolyte is sulfolane in Example 1, while it is MPPy-FSI in Comparative Example 1. This difference leads to the D M / D L is sulfolane 10, [FSI] - was 42, but the D M / D L is sulfolane 3 and [FSI] - The result was 5. This result revealed that when sulfolane is contained in the electrolyte in addition to the oxide and electrolyte salt, the diffusibility of materials at the oxide interface is significantly improved.

[0093] Although the mechanism by which the diffusibility of substances at the oxide interface is improved is unclear, it is presumed that when components of the electrolyte solution are adsorbed onto the oxide surface, the coordination sites of the adsorbed molecules or ions are occupied, weakening the electrostatic interaction with the surrounding ions in the electrolyte solution, and creating a layer near the oxide interface through which substances diffuse more rapidly.

[0094] Comparing the mixture in Example 1 and the mixture in Example 2, the electrolyte contained in the mixture is the same. However, the oxide contained in the mixture in both cases is α-alumina in Example 1, while it is tetragonal Li7La3Zr2O in Example 2. 12 This difference makes it possible to obtain the D M / D L is sulfolane 10, [FSI] - was 42, but D in Example 2 M / D L is sulfolane 1 and [FSI] - was 15.

[0095] Because the self-diffusion coefficient of the electrolyte in contact with α-alumina (oxide) is large, it was found that the ionic conductivity of the oxide itself may not necessarily be necessary to improve the diffusivity of the material at the interface between the oxide and the electrolyte. From this, it is presumed that some kind of ionic conduction path is formed in the liquid at or near the oxide interface as a result of the interaction between the oxide and the electrolyte.

[0096] In the mixtures of the present invention, including the mixtures in Examples 1 and 2, the self-diffusion coefficient D M The ionic conductivity of the mixture can be estimated to some extent by calculating the ionic conductivity of each ion using the Nernst-Einstein equation from the values ​​of , and then summing the ionic conductivities of all ionic components contained in the electrolyte. However, the ionic conductivity value of the mixture estimated by this method is inaccurate due to the self-diffusion coefficient D MThe value of the ionic conductivity measured at the same temperature as the temperature at which the self-diffusion coefficient D is measured does not necessarily coincide with the value of the ionic conductivity obtained by, for example, electrochemical impedance measurement. Similarly, the diffusion coefficient of an electrolyte contained in an electrolyte solution measured by other methods, including electrochemical methods based on the change in the concentration of the electrolyte, is not necessarily consistent with the value of the self-diffusion coefficient D M does not necessarily have to match the value of

[0097] The reasons for this are: (1) the diffusivity of ions does not directly contribute to ionic conductivity; (2) signals are not necessarily observed for all constituent ions in a mixture when measuring the self-diffusion coefficient using the pulsed magnetic field gradient method; and (3) D M / D L This is because there are isolated areas in the sample where the value of D is large, and therefore the entire sample may not form a continuous ion conduction path. M / D L In regions where the value of is large, the diffusivity of the substance is high, so it is thought that the effect of mitigating the concentration gradient can be obtained locally.

[0098] The present invention has been described above based on the embodiments, but the present invention is not limited to the above embodiments, and it can be easily inferred that various improvements and modifications are possible within the scope of the present invention.

[0099] In the embodiment, the electrochemical element 11 has been described as including a positive electrode layer 12 in which an active material layer 14 is provided on one side of a current collecting layer 13, and a negative electrode layer 16 in which an active material layer 18 is provided on one side of a current collecting layer 17, but the present invention is not necessarily limited to this. For example, it is of course possible to apply each element in the embodiment to an electrochemical element including electrode layers (so-called bipolar electrodes) in which an active material layer 14 and an active material layer 18 are provided on both sides of a current collecting layer 13. If bipolar electrodes and electrolyte layers 15 are alternately stacked and housed in a case (not shown), an electrochemical element with a so-called bipolar structure can be obtained.

[0100] In the embodiments, the electrochemical element 11 in which the active material layers 14, 18 and the electrolyte layer 15 all contain the mixture 10 and the electrochemical element 24 in which both the active material layers 14, 18 contain the mixture 10 have been described, but the present invention is not necessarily limited to this. The electrochemical element may contain the mixture 10 in any case as long as at least one of the active material layers 14, 18 and the electrolyte layer 15 contains the mixture 10.

[0101] In the embodiment, the electrochemical element 26 has been described in which the protective layer 29 is disposed between the separator 25 and the negative electrode layer 30, and the protective layer 32 is disposed on the current collecting layer 17, but the present invention is not necessarily limited to this. Of course, it is possible to omit one of the protective layers 29, 32.

[0102] In the embodiments, the mixture 10 has been described using electrochemical elements 11, 24, and 26 made of lithium ion batteries (power storage devices) as examples, but is not necessarily limited to these. Examples of other electrochemical elements that can include the mixture 10 include metal ion batteries other than lithium ion batteries, such as sodium ion batteries and magnesium batteries, electrochemical capacitors that utilize redox reactions of electrodes or redox reactions of ions in an electrolyte, or electric double layers, metal-air batteries that use oxygen in the air as the positive electrode active material, fuel cells, and electrolyzers that chemically decompose compounds or generate substances through chemical decomposition. [Explanation of symbols]

[0103] 10 mixture 11, 24, 26 Electrochemical elements (electricity storage devices) 12,27 Positive electrode layer 15 Electrolyte layer (sheet, separator) 16,30 Negative electrode layer 17 Current collecting layer 19 Oxides 22 Electrolyte 25 Separator 29,32 Protective layer

Claims

1. A mixture comprising an oxide and an electrolyte, a ratio of the volume of the oxide to the total volume of the oxide and the electrolyte is 61% or more and less than 100%; The electrolyte solution is prepared by dissolving an electrolyte salt in a sulfone compound represented by chemical formula (1), In the chemical formula (1), R １ , R ２ each independently represents an alkyl group, an alkenyl group, or a halogenated alkyl group having 4 or less carbon atoms, or the alkyl groups, alkenyl groups, or halogenated alkyl groups are bonded to each other to form a ring structure, A mixture in which 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 spectroscopy, is at least six times the self-diffusion coefficient of the component contained in the electrolyte not in contact with the oxide, as measured by pulsed field gradient nuclear magnetic resonance spectroscopy, at the same temperature as that at which the self-diffusion coefficient is measured. 【Chemistry 1】

2. 2. The mixture of claim 1, wherein said oxide is alumina.

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

4. A sheet comprising the mixture according to claim 1 or 2.

5. Electrochemical device comprising the mixture according to claim 1 or 2.

6. a positive electrode layer, a negative electrode layer, and a separator separating the positive electrode layer and the negative electrode layer; An electricity storage device comprising the mixture according to claim 1 or 2.

7. The electricity 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. At least one of the positive electrode layer and the negative electrode layer includes a current collecting layer; a protective layer in contact with at least one of the separator and the current collecting layer; The electricity storage device according to claim 6 , wherein the protective layer contains the mixture.

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