Electrolytes, electrolyte compositions, and electrochemical elements

Abstract

Provided is an electrolytic solution, an electrolyte composition, and an electrochemical element, whereby the transport number of ions contributing to energy conversion can be increased. The electrolytic solution contains a nonaqueous solvent, and in the color coordinates of the CIE 1976 L*a*b* color space, b* ≥ 2. The electrolytic solution preferably satisfies 1 ≤ L* ≤ 3, and the chroma expressed by c* = {(a*)2 + (b*)2}1 / 2 is preferably 2 ≤ c* ≤ 8. The electrolyte composition comprises the electrolytic solution and particles of an oxide solid electrolyte. The electrochemical element is provided with an electrode containing the electrolytic solution.

Description

[Technical Field]

[0001] This invention relates to an electrolyte, electrolyte composition, and electrochemical element containing a non-aqueous solvent. [Background technology]

[0002] Electrochemical elements, such as lithium-ion secondary batteries, convert chemical energy into electrical energy. Prior art in which an electrolyte containing a non-aqueous solvent is included in an electrochemical element is disclosed in Patent Document 1. The electrolyte plays the role of a medium for ion movement. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2011-44252 [Overview of the project] [Problems that the invention aims to solve]

[0004] Because not only ions that contribute to the energy conversion of electrochemical elements but also ions that do not contribute to energy conversion move through the electrolyte, prior art suffers from the problem of a low transport rate of ions that contribute to energy conversion.

[0005] This invention was made to solve this problem and aims to provide an electrolyte, electrolyte composition, and electrochemical element that can increase the transport rate of ions that contribute to energy conversion. [Means for solving the problem]

[0006] A first embodiment for achieving this objective is an electrolyte containing a non-aqueous solvent, CIE 1976L * a * b * In the color coordinates of the color space, b * It is ≥ 2.

[0007] The second aspect is that in the first aspect, 1 ≦ L * ≦ 3

[0008] The third aspect is that in the first or second aspect, c * = {(a * ) 2 + (b * ) 2} 1 / 2 where the chroma represented by 2 ≦ c * ≦ 8

[0009] The fourth aspect is that in any one of the first to third aspects, a lithium salt is dissolved in a non-aqueous solvent

[0010] The fifth aspect is that in any one of the first to fourth aspects, it consists of a compound other than an aromatic compound (non-aromatic compound), and the signal of the proton nuclear magnetic resonance spectrum exists in the range of chemical shift 6 ppm to 8 ppm

[0011] The sixth aspect is that in the fifth aspect, the absorption spectrum by Fourier transform infrared spectroscopy exists in the range of wavenumber 1100 cm -1 to 1120 cm -1

[0012] The seventh aspect is an electrolyte composition, which includes an electrolytic solution according to any one of the first to sixth aspects and particles of an oxide solid electrolyte

[0013] The eighth aspect is that in the seventh aspect, the oxide solid electrolyte has a garnet-type crystal structure containing Li, La, and Zr

[0014] The ninth aspect is an electrochemical element including an electrode, and the electrode includes an electrolytic solution according to any one of the first to sixth aspects

[0015] The tenth aspect is that in the ninth aspect, the electrode is a positive electrode

Advantages of the Invention

[0016] ​The present invention relates to an electrolyte, an electrolyte composition containing the electrolyte, and an electrochemical element, wherein the electrolyte is CIE 1976L * a * b * In the color coordinates of the color space, b * Since it is ≥ 2, the mobility of ions contributing to energy conversion increases, and the transport rate can be increased. [Brief explanation of the drawing]

[0017] [Figure 1] This is a cross-sectional view of the electrochemical element in the first embodiment. [Figure 2] This is a schematic diagram showing the crystal structure of a garnet-type crystal. [Figure 3] This is a cross-sectional view of the electrochemical element in the second embodiment. [Modes for carrying out the invention]

[0018] Preferred embodiments of the present invention will be described below with reference to the accompanying drawings. Figure 1 is a schematic cross-sectional view of the electrochemical element 10 in the first embodiment. The electrochemical element 10 is an element that directly converts chemical energy and electrical energy. The ions that contribute to the energy conversion of the electrochemical element 10 (hereinafter referred to as "charge carriers") are Li + kaNa + , K + Mg 2+ Cu + Ag + Examples of cations include the following.

[0019] An example of an electrochemical element 10 is described as an energy storage device. Examples of energy storage devices include ion batteries such as lithium-ion batteries, redox reactions of electrodes and ions in the electrolyte, and electrochemical capacitors that utilize an electric double layer. The electrochemical element 10 includes, in order, a positive electrode 11, a separator 14, and a negative electrode 15.

[0020] The separator 14 is made of a porous material that is durable against the active materials 19 and 20 contained in the positive electrode 11 and negative electrode 15, as well as the electrolyte, and allows the charge carrier to pass through but does not conduct electrons. Examples of separators 14 include nonwoven fabrics and porous membranes made of cellulose, polypropylene, polyethylene, polyimide, alumina, etc.

[0021] The positive electrode 11 consists of a current collector 12 and an active material layer 13 superimposed on each other. The current collector 12 is a conductive material. Examples of materials for the current collector 12 include metals selected from Ni, Ti, Fe, and Al, alloys containing two or more of these elements, stainless steel, and carbon materials.

[0022] The active material layer 13 contains an active material 19. The active material 19 is appropriately selected depending on the type of charge carrier or energy storage device. When the energy storage device is an electrochemical capacitor, the active material 19 is a material that can reversibly support anions, and examples of carbon-based materials include porous carbon, natural graphite, artificial graphite, easily graphitizable carbon (hard carbon), difficult-to-graphitize carbon (soft carbon), and carbon fiber.

[0023] Examples of active materials 19 when the energy storage device is an ion battery include metal oxides containing transition metals, sulfur-based active materials, and organic active materials. + In this case, examples of metal oxides containing transition metals include metal oxides containing one or more elements selected from Mn, Co, Ni, Fe, Cr, and V, and Li. Examples of metal oxides containing transition metals include LiCoO2 and LiNi 0.8 Co 0.15 Al 0.05 O2, LiMn2O4, LiNiVO4, LiNi 0.5 Mn 1.5 O2, LiNi 1 / 3 Mn 1 / 3 Co 1 / 3 O2 and LiFePO4 are examples.

[0024] Examples of sulfur-based active materials include S,TiS2,NiS,FeS2,Li2S,MoS3, and sulfur-carbon composites. Examples of organic active materials include radical compounds such as 2,2,6,6-tetramethylpiperidinoxyl-4-yl methacrylate and polytetramethylpiperidinoxyl vinyl ether, quinone compounds, radialene compounds, tetraciaquinodimethane, and phenazine oxide.

[0025] To lower the resistance of the active material layer 13, the active material layer 13 may contain a conductive additive. Examples of conductive additives include carbon black, acetylene black, Ketjenblack, carbon fiber, Ni, Pt, and Ag.

[0026] In this embodiment, the active material layer 13 includes an electrolyte composition. The electrolyte composition includes oxide solid electrolyte particles 18 and an electrolyte solution. Examples of the particles 18 include oxides having a NASICON-type structure, oxides having a perovskite structure, and oxides having a garnet-type structure. Oxides having a NASICON-type structure 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. Oxides having a perovskite structure include oxides containing at least Li, Ti, and La, such as La 2 / 3-X Li 3X TiO3 is one example.

[0027] Particle 18 is preferably a composite oxide having a garnet-type crystalline structure containing Li, La, and Zr. -3 This is because it has an ionic conductivity in the S / cm range and is resistant to reduction by metallic lithium. The garnet-type crystal structure is general formula C3A2B3O 12 It is represented as follows.

[0028] Figure 2 schematically shows a garnet-type crystal structure. In a garnet-type crystal structure, the C site Sc coordinates dodecahedrally with the oxygen atom Oa, the A site Sa coordinates octahedrally with the oxygen atom Oa, and the B site Sb coordinates tetrahedrally with the oxygen atom Oa. In oxide solid electrolytes, Li can be present in the void V, which is the site where the oxygen atom Oa would normally coordinate octahedrally in a typical garnet-type crystal structure. The void V is, for example, the area between B site Sb1 and B site Sb2. The Li present in void V is octahedrally coordinated with the oxygen atom Oa that constitutes an octahedron including the tetrahedral face Fb1 forming B site Sb1 and the tetrahedral face Fb2 forming B site Sb2. For example, Li7La3Zr2O has a garnet-type crystal structure. 12 In this case, La may occupy site C (Sc), Zr may occupy site A (Sa), and Li may occupy site B (Sb) and the void V.

[0029] Garnet-type crystal structures can be identified by X-ray diffraction. The garnet-type crystal structure is found in the Cambridge Structural Database (CSD) X-ray diffraction file No. 422259 (Li7La3Zr2O 12 It has an XRD pattern similar to ). The solid electrolyte may differ from No. 422259 in terms of the types of constituent elements and Li concentration, so the diffraction angle and intensity ratio may differ. A typical crystal structure of this type is cubic (space group Ia-3d (- indicates an overline meaning reversal operation), JCPDS:84-1753).

[0030] Solid electrolytes with a garnet-type crystal structure are typically Li7La3Zr2O 12 Examples include: The solid electrolyte is Li7La3Zr2O 12 Some of the constituent elements may be substituted with other elements, or trace amounts of other elements may be added without substituting any 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).

[0031] Solid electrolytes include, 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 Te 0.25 O 12 、Li 6.75 La3Zr 1.75 Nb<9<000006< 0.25 O 12 、Li 6.9 La3Zr C 1.675 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 [ 6.20 Ba 0.30 La P 2.95 2.95 Rb 0.05 Zr2O 12 and the like.

[0032] The solid electrolyte is preferably one that contains Mg and at least one of element A (where A is at least one element selected from the group consisting of Ca, Sr, and Ba), and the molar ratio of each element satisfies all of (1) to (3) below, or one that contains both Mg and element A, and the molar ratio of each element satisfies all of (4) to (6) below. Element A is preferably Sr in order to increase the ionic conductivity of the solid electrolyte. (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

[0033] The electrolyte contained in the active material layer 13 is the medium through which the charge carrier moves, and is a solution in which the supporting electrolyte is dissolved in a non-aqueous solvent. Non-aqueous solvents are broadly classified into molecular solvents, which consist mostly of molecules, and ionic liquids, which consist of cations and anions. One reason for using a non-aqueous solvent as the electrolyte is to widen the potential window compared to an electrolyte using water as the solvent. Ionic liquids are preferred because they can widen the potential window compared to an electrolyte using water as the solvent.

[0034] When using a molecular solvent as a non-aqueous solvent, an aprotic solvent is preferred to broaden the potential window of the electrolyte. Examples of aprotic solvents include cyclic esters, linear esters, aliphatic carboxylic acid esters, phosphate esters, nitriles, amides, sulfur compounds, ketones, ethers, nitro compounds, and fluorescein solvents. Mixtures of these are also acceptable.

[0035] Examples of cyclic esters include cyclic carbonate esters such as propylene carbonate, ethylene carbonate, butylene carbonate, vinylene carbonate, vinylethylene carbonate, and fluoroethylene carbonate, as well as lactones such as β-propiolactone, γ-butyrolactone, δ-valerolactone, α-pyrone, and coumarin. Examples of linear esters include linear carbonate esters such as dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. Examples of aliphatic carboxylic acid esters include methyl formate, methyl acetate, and ethyl propionate. Examples of phosphate esters include trimethyl phosphate. Examples of nitriles include acetonitrile, propionitrile, butyronitrile, and benzonitrile.

[0036] Examples of amides include formamide, N-methylformamide, dimethylformamide, N-methylacetamide, dimethylacetamide, N-methylpropioamide, hexamethylphosphoramide, and N-methylpyrrolidone. Examples of sulfur compounds include dimethyl sulfoxide, sulfolane, dimethylthioformamide, and N-methylthiopyrrolidone. Examples of ketones include acetone, 4-methyl-2-pentanone, and acetylacetone. Examples of ethers include tetrahydrofuran and monoglycerides. Examples of nitro compounds include nitromethane and nitrobenzene. Fluorine solvents are compounds in which hydrogen atoms of hydrocarbons are replaced with fluorine atoms, and their derivatives.

[0037] The reaction in which a supporting electrolyte dissolves in a molecular solvent and dissociates into free ions proceeds more readily when the relative permittivity of the solvent is high and when solvation of ions is easy. Therefore, solvents with a relatively high relative permittivity εr (εr > 20) are preferred. Examples of molecular solvents with a relative permittivity greater than 20 include cyclic esters, nitriles, amides, sulfur compounds, acetone, acetylacetone, and nitro compounds. It is naturally possible to mix solvents with a relative permittivity greater than 20 with solvents with a relative permittivity of 20 or less in order to adjust the viscosity of the solvent, etc.

[0038] An ionic liquid is a compound composed of a cation and an anion and is a liquid at normal temperature and pressure. If the solvent of the electrolyte is an ionic liquid, the flame retardancy of the electrolyte can be improved. The ionic liquid is preferably one having one or more selected from the group consisting of ammonium, imidazolium, pyrrolidinium and piperidinium as cation species.

[0039] The anion component of the ionic liquid is not particularly limited. The anion component is BF4 - , N(SO2F)2 - and other inorganic anions, B(C6H5)4 - , CH3SO3 - , CF3SO3 - , N(SO2CF3)2 - , N(SO2C4F9)2 - and other organic anions are exemplified.

[0040] The ionic liquid may be a solvated ionic liquid. Examples of the solvated ionic liquid include those obtained by dissolving a supporting electrolyte in a sulfone-based solvent such as sulfolane or a sulfolane derivative, or a glyme-based solvent such as tetraglyme.

[0041] When the charge carrier is Li + , the supporting electrolyte is a lithium salt. The anion of the supporting electrolyte is OH - , 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 - Examples include (where R is an alkyl group having 1-4 carbon atoms, a phenyl group, or a naphthyl group). The supporting electrolyte may be a mixture of these.

[0042] The concentration of the supporting electrolyte in the electrolyte solution is 0.2 mol / dm³ 3 The above is preferable, and preferably 0.5 mol / dm 3 The above is a comfortable 1.0 mol / dm³ 3 That concludes the explanation. As the concentration of the supporting electrolyte increases, the number of solvent molecules coordinating to the charge carrier increases, reducing the amount of uncoordinated solvent, and counter-anion coordination (so-called ion association) becomes dominant. This suppresses the reductive decomposition of the electrolyte, while increasing the oxidation potential and widening the potential window. The concentration of the supporting electrolyte is 4.0 mol / dm³. 3 The following are preferred, and more preferably, 2.0 mol / dm³ 3 The following applies: The concentration of the supporting electrolyte is 4.0 mol / dm³. 3 This is because beyond a certain point, the ionic conductivity tends to decrease significantly due to the increased viscosity of the electrolyte.

[0043] The electrical conductivity of an electrolyte is predominantly due to ionic conduction. The ionic conductivity of an electrolyte is proportional to the product of the concentration and mobility of the charge carriers contained in the electrolyte. The mobility of charge carriers in the electrolyte is thought to be related to solvation, where solvent molecules bind to ions dissociated from the supporting electrolyte in the solvent, and to the interactions between the ions constituting the supporting electrolyte. This includes quantities related to the lightness, saturation, and hue of the electrolyte, respectively (CIE 1976L). * a * b * Color coordinates in a color space are one indicator of solvation.

[0044] CIE 1976L * a * b * The color space is based on the L color space recommended by the CIE (International Commission on Illumination) in 1976. * ,a * ,b *This is a nearly uniform three-dimensional color space obtained by plotting it on a Cartesian coordinate system. CIE 1976L * a * b * The color space is defined in JIS Z8781-4:2013. CIE 1976L * a * b * In the color space, brightness is L * It is expressed as a, and the chromaticity, which shows the hue and saturation, is a * ,b * Represented by a. * ,b * The symbol indicates the direction of the color, and a * The red direction, -a * The direction is green, b * Yellow direction, -b * This indicates the blue direction. A higher value results in more vibrant colors, while values ​​closer to the origin result in duller colors. Saturation c * is {(a * ) 2 +(b * ) 2} 1 / 2 (a * and b * It is expressed as L (the square root of the sum of the squares of). * ,a * ,b * This can be measured using the CM-5 spectrophotometer (Konica Minolta, Inc.).

[0045] L * ,a * ,b * Each of these values ​​is not something that can be controlled independently and completely, and there are many unknown aspects, but the chromaticity b of the electrolyte * When the value is ≥ 2, the mobility of anions decreases, and the mobility of cations (charge carriers) increases. This allows for a higher transport rate of charge carriers, which contribute to energy conversion.

[0046] The mobility of the charge carrier contained in the electrolyte and b * The reason for the relationship between the two is unknown, but as the supporting electrolyte dissolves in the solvent, the number of solvent molecules coordinating to the cations decreases, while the number of solvent molecules coordinating to the anions increases, causing the chromaticity of the electrolyte to change, b * It is estimated that it will become larger.

[0047] Discoloration of the solvent due to the presence of impurities such as water, alcohols, epoxides, lithium alkyl carbonates, and products resulting from further reactions of these with the electrolyte. * To distinguish it from the increase of b, * The maximum value of is preferably 30. The amount of impurities in the electrolyte is preferably 200 ppm or less, more preferably 100 ppm or less, and particularly preferably 10 ppm or less. This is to reduce the deterioration of the electrolyte over time due to the presence of impurities.

[0048] Brightness L of the electrolyte * is 1 ≤ L * ≤3 is preferred, and the saturation c of the electrolyte * is 2≦c * A value of ≤8 is preferable. This is to further increase the transport rate of the charge carrier.

[0049] L of electrolyte * ,a * ,b * ,c * One example of this adjustment is to modify the surface of the particle 18 and then bring the particle 18 into contact with the electrolyte. This results in the b of the electrolyte. * ya c * The size increases. A method for surface modification of particle 18 is chemical treatment. Chemical treatment can make the surface of particle 18 acidic or basic. Examples of chemical treatment include a method of adsorbing a modifier onto the surface of particle 18 in a liquid phase such as a non-aqueous solvent, and a method of reacting a modifier with particle 18 in a gas phase. As a pretreatment for surface modification, it is preferable to increase the surface activity of particle 18 by applying compressive or shear force to particle 18 using a rotating container or rotor blade alone or in combination, or by dispersing particle 18 in a high-speed airflow and applying impact force.

[0050] When particle 18 is a composite oxide having a garnet-type crystalline structure containing Li, La, and Zr, lithium hydroxide and lithium carbonate are generated on the surface of particle 18 by a gas-phase reaction between carbon dioxide or moisture and particle 18, thereby modifying the surface of particle 18 to a basic state. Because the surface modification of particle 18 is simple, an electrolyte can be easily prepared by contacting particle 18.

[0051] After bringing the particles 18 into contact with the electrolyte, the particles 18 and the electrolyte may be placed together in the active material layer 13, or after bringing the particles 18 into contact with the electrolyte, the particles 18 and the electrolyte may be separated and only the electrolyte may be supplied to the active material layer 13. Examples of means for separating the particles 18 and the electrolyte include filtration, sedimentation separation, and centrifugation. Alternatively, the electrolyte may be poured into the active material layer 13 in which the particles 18 are placed, bringing the particles 18 and the electrolyte into contact, and preparing the electrolyte within the active material layer 13.

[0052] The electrolyte consists of compounds other than aromatic compounds (non-aromatic compounds) (including mixtures of non-aromatic compounds), and proton nuclear magnetic resonance spectroscopy is performed by combining the pulse method and the Fourier transform method. 1 (H-NMR) of the electrolyte 1 When measuring the H-NMR spectrum 1 It is preferable that the H-NMR spectrum signal lies in the chemical shift range of 6 ppm to 8 ppm. The chemical shift is the value obtained by dividing the difference in resonance frequency from the signal by the measurement frequency, with the resonance frequency of the methyl group of tetramethylsilane being set to 0.

[0053] The electrolyte's absorption spectrum, obtained by Fourier transform infrared spectroscopy (FT-IR), shows that at wavenumber 1100 cm⁻¹... -1 From 1120cm -1 It is preferable that the material is within the specified range. The absorption spectrum is preferably measured using the attenuated total reflection (ATR) method via FT-IR.

[0054] The active material layer 13 may contain a binder that binds the active material 19. The binder is not particularly limited as long as it binds the active material 19. Examples of binders include rubbery polymers such as fluorinated resins, polyolefins, polyimides, polyvinylpyrrolidone, polyvinyl alcohol, cellulose ethers, and 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.

[0055] The ratio (vol%) of the volume of the electrolyte to the combined volume of the electrolyte and active material 19 in the active material layer 13 is preferably 10% to 20%. This is to reduce the interfacial resistance of the active material 19, which is the reaction field for the charge-discharge reaction, while ensuring the equilibrium potential of the positive electrode 11.

[0056] When the active material layer 13 contains particles 18, it is preferable that the ratio (vol%) of the volume of particles 18 to the combined volume of particles 18 and active material 19 is 15% or more and 20% or less. This is to ensure the equilibrium potential of the positive electrode 11 and to ensure the contact interface between particles 18 and active material 19.

[0057] The content (vol%) of particles 18, active material 19, and electrolyte can be determined by analyzing a 5000x magnification field of view randomly selected from the cross-section of the active material layer 13 using a scanning electron microscope (SEM) equipped with an energy-dispersive X-ray spectrometer (EDS). The analysis identifies the area of ​​particles 18, the area of ​​active material 19, and the area of ​​electrolyte by identifying elemental distributions and performing image analysis of the contrast of backscattered electron images. The content (vol%) of particles 18 is obtained by considering the ratio of the area of ​​particles 18 to the total area of ​​particles 18 and active material 19 as a volume ratio. Similarly, the content (vol%) of electrolyte is obtained by considering the ratio of the area of ​​electrolyte to the total area of ​​active material 19 and electrolyte as a volume ratio.

[0058] The cross-sections of the active material layer 13 used for analysis are polished surfaces, surfaces obtained by irradiation with a focused ion beam (FIB), and surfaces obtained by ion milling. Polished surfaces are, for example, surfaces obtained by freezing the active material layer 13 or by embedding and solidifying the active material layer 13 in a tetrafunctional epoxy resin or the like, and then polishing it.

[0059] The negative electrode 15 consists of a current collector 16 and an active material layer 17 superimposed on each other. The current collector 16 is a conductive material. Examples of materials for the current collector 16 include metals selected from Ni, Ti, Fe, Cu, and Si, alloys containing two or more of these elements, stainless steel, and carbon materials.

[0060] The active material layer 17 contains the active material 20. To lower the resistance of the active material layer 17, the active material layer 17 may contain a conductive additive. Examples of conductive additives include carbon black, acetylene black, Ketjen black, carbon fiber, Ni, Pt, and Ag. In this embodiment, the active material layer 17 contains particles 18.

[0061] The active material 20 is not limited to any material as long as it can absorb and release charge carriers. The active material 20 is appropriately selected depending on the type of charge carrier. The active material 20 can be porous carbon, natural graphite, artificial graphite, easily graphitizable carbon, difficult-to-graphitize carbon, carbon fibers, and other carbon-based materials, as well as Li4Ti5O 12 Examples include Si, Si-Li alloys, compounds containing Si and O as constituent elements (hereinafter referred to as "SiOx," where 0.5 ≤ X ≤ 1.5), metallic lithium, lithium alloys such as Li-Al alloys, Li-Sn alloys, Li-Si alloys, Li-Mg alloys, and Li-Si alloys, In-Sb alloys, and Si-Li alloys. Examples of SiOx include those having a structure in which microcrystalline or amorphous Si is dispersed in an amorphous SiO2 matrix, such as Si oxides.

[0062] The electrochemical element 10 is manufactured, for example, as follows: Particles 18, active material 19, and conductive additive are mixed, and a solution of binder dissolved in a solvent is further mixed to make a slurry. After coating the current collector 12 with the slurry, it is dried to obtain a positive electrode sheet.

[0063] Particles 18, active material 20, and conductive additive are mixed, and then a solution of binder dissolved in a solvent is added to make a slurry. The slurry is applied to the current collector 16 and then dried to obtain a negative electrode sheet.

[0064] A separator 14 separates the positive electrode sheet and the negative electrode sheet. The positive electrode sheet and the negative electrode sheet are wound together on a winding machine to create a cylindrical or rectangular cell. Terminals (not shown) are connected to the current collectors 12 and 16, respectively, and the cell is placed in a container (not shown) with chromaticity b * After filling the container with an electrolyte solution of ≥2, the container is sealed to obtain an electrochemical element 10 including a positive electrode 11, a separator 14, and a negative electrode 15.

[0065] According to the electrochemical element 10, high chromaticity b of the charge carrier * Since the electrolyte with a coefficient of ≥2 is filled into the active material layer 13 of the positive electrode 11, even if the thickness of the active material layer 13 is increased and the distance the charge carrier moves within the active material layer 13 during charging and discharging increases, the resistance to the movement of the charge carrier does not increase. Because the thickness of the active material layer 13 can be increased, an electrochemical element 10 with a large capacity and capable of high-speed charging can be obtained.

[0066] chromaticity b * Electrolytes with a charge transport rate of ≥2 can achieve a higher transport rate for charge carriers compared to conventional electrolytes, thereby reducing concentration polarization that tends to occur during high-speed charging and discharging. This prevents the operating voltage (terminal voltage) of the electrochemical element 10 from dropping rapidly, which is advantageous for extending the lifespan of the electrochemical element 10.

[0067] Since the electrolyte with high charge carrier mobility is filled into the active material layer 13 of the positive electrode 11, not only is the mobility of the charge carrier at the position in contact with the particle 18 within the active material layer 13 ensured, but the mobility of the charge carrier at positions away from the particle 18 can also be ensured. The migration speed (diffusion speed) of the charge carrier is highly temperature-dependent and decreases as the temperature decreases, but since the mobility of the charge carrier can be ensured, the operation of the electrochemical element 10 can be ensured even when the ambient temperature around the electrochemical element 10 is low.

[0068] A second embodiment will be described with reference to Figure 3. In the first embodiment, the separator 14 separating the positive electrode 11 and the negative electrode 15 was described as a nonwoven fabric or porous membrane made of cellulose, polypropylene, or the like. In contrast, in the second embodiment, an electrochemical element 21 containing an electrolyte 23 will be described as a separator 22 separating the positive electrode 11 and the negative electrode 15. In the second embodiment, the same parts as in the first embodiment are denoted by the same reference numerals and their descriptions will be omitted below.

[0069] Figure 3 is a cross-sectional view of the electrochemical element 21 in the second embodiment. The electrochemical element 21 (energy storage device) includes, in order, a positive electrode 11, a separator 22, and a negative electrode 15. The separator 22 contains an electrolyte 23. The electrolyte 23 is exemplified by an ionic conductive solid or gel-like electrolyte. A mixture of the electrolyte 23 and an electrolyte solution may be placed in the separator 22.

[0070] Electrolyte 23 includes one or more selected from sulfide-based, oxide-based, hydride-based, halide-based, and organic-based electrolytes. Sulfide-based electrolytes include crystalline thiolysicone-type, Li 10 GeP2S 12 Type, argyrodite type, Li7P3S 11 Examples of oxide-based electrolytes include glass and glass-ceramic systems, such as Li2S-P2S5. Examples of oxide-based electrolytes include oxides with a NASICON-type structure, oxides with a perovskite structure, and oxides with a garnet-type structure.

[0071] Examples of hydride-based electrolytes include solid solutions of LiBH4 with lithium halide compounds (LiI, LiBr, LiCl) and lithium amide (LiNH2). An example of a halide solid electrolyte is Li3YCl6. Examples of organic solid electrolytes include polyethylene oxide, polypropylene oxide, and polyacrylonitrile.

[0072] The electrochemical element 21 is manufactured, for example, as follows: A mixture of a non-aqueous solvent containing a dissolved lithium salt and particles 18 is mixed with an active material 19, and then a solvent containing a dissolved binder is added to create a slurry. The slurry is then applied to the current collector 12 and dried to obtain an active material layer 13.

[0073] A separator slurry is prepared by mixing a non-aqueous solvent containing a dissolved lithium salt with particles 18, and then mixing it with a solvent containing a dissolved binder. After coating the separator slurry onto the active material layer 13, it is dried to obtain a positive electrode sheet.

[0074] A slurry is made by mixing a non-aqueous solvent containing a dissolved lithium salt with particles 18, adding the active material 20, and then adding a solvent containing a dissolved binder. The slurry is applied to the current collector 16 and then dried to obtain the active material layer 17. A separator slurry is applied to the active material layer 17 and then dried to obtain the negative electrode sheet.

[0075] After cutting the positive electrode sheet and the negative electrode sheet into predetermined shapes, the positive electrode sheet and the negative electrode sheet are stacked and pressed together so that a separator 22 is formed between the positive electrode 11 and the negative electrode 15, and a cell is manufactured. Terminals (not shown) are connected to the current collectors 12 and 16 respectively, and the cell is sealed in a container (not shown) to obtain an electrochemical element 21 including the positive electrode 11, the separator 22, and the negative electrode 15.

[0076] In the second embodiment, the electrochemical element 21 contains an electrolyte in the positive electrode 11, the negative electrode 15, and the separator 22, and therefore, like the electrochemical element 10 in the first embodiment, it is advantageous for increasing capacity and speeding up charging. [Examples]

[0077] The present invention will be described in more detail by reference to examples, but the present invention is not limited to these examples.

[0078] (Example 1) Li 6.95 Mg 0.15 La 2.75 Sr 0.25 Zr2.0 O 12 Li2CO3, MgO, La(OH)3, SrCO3, and ZrO2 were weighed accordingly. Li2CO3 was kept in excess by approximately 15 mol% elementally, considering the volatilization of Li during calcination. The weighed raw materials and ethanol were placed in a nylon pot along with zirconia balls and ground and mixed in a ball mill for 15 hours. After drying the slurry removed from the pot, it was calcined at 1100°C for 15 hours on an MgO plate. The resulting powder was ground, placed in an MgO pod, and further calcined at 1100°C for 4 hours. The resulting powder was ground in a glove box under an argon atmosphere to obtain an oxide solid electrolyte (hereinafter referred to as "LLZ").

[0079] The garnet-type crystal structure of LLZ was confirmed by powder X-ray diffraction. The median diameter (D50) of the LLZ particle size distribution, measured by laser diffraction and scattering, was 74 μm.

[0080] Using a dry jet mill (Aisin Nanotechnologies Corporation, NanoJetmizer® NJ-50 model), the LLZ was pulverized by passing it through the jet mill three times under conditions of a nitrogen atmosphere with a nozzle pressure of 2.0 MPa and a processing rate of 480 g / hr. The pulverized LLZ was stored for 24 hours in an argon atmosphere with a dew point of -70°C to obtain the particles used in Example 1.

[0081] (Example 2) The particles in Example 2 were obtained in the same manner as in Example 1, except that the LLZ was pulverized by passing it through a jet mill twice.

[0082] (Example 3) The particles for Example 3 were obtained in the same manner as in Example 1, except that the processing volume for one grinding pass was set to 960 g / hr and the LLZ was ground by passing it through the jet mill a total of one time.

[0083] (Example 4) The particles in Example 4 were obtained in the same manner as in Example 1, except that the LLZ was pulverized by passing it through a jet mill 10 times.

[0084] (Measurement of particle size distribution and specific surface area) The median diameter (D50) of the particle size distribution in Examples 1-4 was measured by laser diffraction and scattering. The specific surface area of ​​the particles in Examples 1-4 was also measured in accordance with JIS R1626:1996.

[0085] (Preparation of electrolyte solution and measurement of color) A non-aqueous solvent prepared by mixing ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate in a 1:1:1 (volume ratio) ratio, with a supporting electrolyte of LiPF6 at a concentration of 1 mol / dm³. 3 The mixture was prepared by adding 1 wt% vinylene carbonate to the mixture. The particles and electrolyte from Examples 1-4 were placed in separate test tubes in a ratio of 16.5:83.5 (mass ratio) and mixed for 30 minutes. The test tubes were then covered and allowed to stand for 24 hours to allow the particles to settle and separate. The supernatant liquid was collected to obtain the electrolyte from Examples 1-4. The electrolyte before mixing with the particles was designated as the electrolyte from Comparative Example 1.

[0086] A non-aqueous solvent prepared by mixing ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate in a 1:1:1 (volume ratio) ratio, with a supporting electrolyte of LiPF6 at a concentration of 1 mol / dm³. 3 The mixture was prepared in this manner to form the electrolyte in Comparative Example 2. The electrolyte in Comparative Example 1 contained vinylene carbonate, while the electrolyte in Comparative Example 2 did not contain vinylene carbonate.

[0087] The particles from Example 1 and the electrolyte from Comparative Example 2 were placed in a test tube in a ratio of 16.5:83.5 (mass ratio) and mixed for 30 minutes. The test tube was then covered and allowed to stand for 24 hours to allow the particles to settle and separate. The supernatant was collected to obtain the electrolyte from Comparative Example 3. The electrolytes in Examples 1-4 and Comparative Examples 1-3 were made from non-aromatic compounds.

[0088] The color of the electrolytes in Examples 1-4 and Comparative Examples 1-3 was measured at 25°C using a spectrophotometer CM-5 (Konica Minolta, Inc.), and the CIE 1976L* a * b * L in color space * ,a * ,b * We sought the saturation c. * ={(a * ) 2 +(b * ) 2} 1 / 2 a in the equation * ,b * Substituting this value, we obtain the saturation c of the electrolyte in Examples 1-4 and Comparative Examples 1-3. * They sought it.

[0089] ( 1 (Measurement of H-NMR spectrum) The electrolytes from Examples 1-4 and Comparative Examples 1-3 were placed in 5 mm outer diameter sample tubes under an argon atmosphere, and the NMR spectra of proton nuclei were measured using pulsed wave Fourier chromatography with a nuclear magnetic resonance spectrometer (JEOL ECZ700R). The observation frequency was 700 MHz, the magnetic field strength was 16.45 T, and the measurement temperature was 25 °C. The chemical shift (ppm) of signals with a chemical shift in the range of 6 ppm to 8 ppm was measured, with the resonance position of tetramethylsilane as the reference.

[0090] (Measurement of infrared absorption spectrum by FT-IR) The electrolytes in Examples 1-4 and Comparative Examples 1-3 were brought into contact with crystals under an argon atmosphere, and infrared light was shone onto the electrolytes from the back of the crystals. The infrared absorption spectra were measured using the ATR method. The number of integrations was 32, and the resolution was 4 cm. -1 The aperture was 80 μm, and the measurement temperature was 25°C. The wavenumber was 1100 cm⁻¹. -1 From 1120cm -1 The wavenumber (cm) of the infrared absorption spectrum that exists in the range -1 ) was measured.

[0091] (Measurement of export rate) Two stainless steel plates with a diameter of 20 mm were each fitted with metallic lithium foil, and 38 layers of 15 μm thick polypropylene separators were sandwiched between the metallic lithium foils. The electrolytes for Example 1-4 and Comparative Example 1-3 were injected into the separators, and then fixed with polyimide adhesive tape to obtain the symmetrical cells for Example 1-4 and Comparative Example 1-3. The preparation of the symmetrical cells and the following measurements were performed in a glove box filled with argon gas at a dew point of -60°C.

[0092] The transport factor of lithium ions was determined by combining AC impedance measurement and chronoamperometry. Specifically, after measuring the AC impedance of a symmetric cell, a DC polarization voltage ΔV was applied to the cell, and the change in current flowing through the cell over time was measured. After reaching a steady state, the AC impedance was measured again. The transport factor of lithium ions t was determined from the following formula.

[0093] t={I S (ΔV-I0R0)} / {I0(ΔV-I S R S )} However, I S R0 and R are the current values ​​in the steady state, I0 is the current value at the beginning of voltage application, and R0 and R are the current values ​​in the steady state. S These values ​​represent the resistance at the interface between the separator and the electrode before and after chronoamperometry measurement. The applied voltage ΔV for chronoamperometry measurement was set to 3mV.

[0094] Median diameter D50 and specific surface area of ​​particles in Examples 1-4 and Comparative Example 3, and L of the electrolyte in Examples 1-4 and Comparative Example 1-3. * ,a * ,b * ,c * , chemical shift (ppm), wavenumber (cm) -1 Table 1 shows the percentage change (%) between the lithium ion transport fraction and the interfacial resistance R0. The percentage change of R0 for Examples 1-4 is the percentage change relative to the electrolyte R0 in Comparative Example 1, and the percentage change of R0 for Comparative Example 3 is the percentage change relative to the electrolyte R0 in Comparative Example 2.

[0095] [Table 1]

[0096] As shown in Table 1, the electrolytes in Examples 1-4 and Comparative Example 1, which contain vinylene carbonate, have a chemical shift in the range of 6 ppm to 8 ppm. 1 A signal (7.15 ppm) was present in the H-NMR spectrum, but the electrolytes in Comparative Examples 2 and 3 showed chemical shifts in the range of 6 ppm to 8 ppm. 1 No signal was observed in the H-NMR spectrum. The electrolyte in Examples 1-4 had a wavenumber of 1100 cm⁻¹. -1 From 1120cm -1 Infrared absorption spectrum in the range (1105-1118 cm) -1 ) existed, but the electrolyte in Comparative Examples 1-3 had a wavenumber of 1100 cm. -1 From 1120cm -1 No infrared absorption spectra were found in that range.

[0097] The transport fraction of the electrolyte in Examples 1-4 was higher than that of Comparative Example 1 (0.125). Electrolyte chromaticity b * Examples 1-4 had a value of 2.00 or higher, while Comparative Example 1 had a value of -0.95. The electrolyte that came into contact with the particles that had undergone the predetermined treatment had a color b * It was found that the chromaticity b of the electrolyte increased. According to Examples 1-4 and Comparative Example 1, the chromaticity b of the electrolyte * It was found that when the value is 2.00 or higher, the lithium ion transport rate can be increased compared to the electrolyte before contact with the particles (Comparative Example 1).

[0098] Electrolyte solution saturation c * While the values ​​for Examples 1-4 were between 2.00 and 8.00, the value for Comparative Example 1 was 1.01. The electrolyte solution that came into contact with the particles that had undergone the predetermined treatment had a chrominance of c * It was found that the saturation c of the electrolyte solution becomes larger. * It was found that when the value is between 2.00 and 8.00, the lithium ion transport rate can be increased.

[0099] Brightness L of the electrolyte* While the values ​​for Examples 1-3 were between 1.00 and 3.00, Comparative Example 1 was 3.76. (Electrolyte lightness L) * It was found that when the value is between 1.00 and 3.00, the lithium ion transport rate can be increased.

[0100] Chemical shifts range from 6 ppm to 8 ppm. 1 In Examples 1-4, where an electrolyte containing a signal in the H-NMR spectrum was used, the rate of change of the interface resistance R0 of the symmetric cell was 70-88% compared to the interface resistance R0 of Comparative Example 1, where the signal was in the chemical shift range of 6 ppm to 8 ppm. On the other hand, when the chemical shift was in the range of 6 ppm to 8 ppm... 1 In Comparative Example 3, which used an electrolyte with no H-NMR spectrum signals, the rate of change of the resistance R0 at the interface of the symmetric cell was only 54% compared to the resistance R0 at the interface of the symmetric cell in Comparative Example 2, where no signals were present in the chemical shift range of 6 ppm to 8 ppm. 1 By using an electrolyte containing a signal in the H-NMR spectrum, the chemical shift range from 6 ppm to 8 ppm can be measured. 1 It was found that the resistance at the electrode interface can be reduced compared to using an electrolyte that does not produce any signal in the H-NMR spectrum.

[0101] Although the present invention has been described above based on embodiments, it can be easily inferred that the present invention is not limited in any way to the above embodiments, and that various improvements and modifications are possible without departing from the spirit of the present invention.

[0102] In the embodiment, the electrochemical element 10 was described as comprising a positive electrode 11 with an active material layer 13 provided on one side of a current collector 12, and a negative electrode 15 with an active material layer 17 provided on one side of a current collector 16, but it is not necessarily limited to this. For example, it is certainly possible to apply each element in the embodiment to an electrochemical element comprising electrode layers (so-called bipolar electrodes) with an active material layer 13 and an active material layer 17 provided on both sides of the current collector 12. By alternately stacking bipolar electrodes and separators 14 and housing them in a case (not shown), a so-called bipolar structure electrochemical element can be obtained.

[0103] In the embodiment, the case in which the active material layers 13 and 17 include particles 18 has been described, but it is not necessarily limited to this. It is certainly possible to omit at least one of the particles 18 in the active material layers 13 and 17.

[0104] Although not described in the embodiments, it is of course possible to place a protective layer between the active material layer 17 and the separators 14 and 22, or between the current collector 16 and the active material layer 17. The protective layer contains a composite oxide having a garnet-type crystal structure containing Li, La, and Zr. Placing a protective layer between the active material layer 17 and the separators 14 and 22 can reduce short circuits caused by dendrites. Placing a protective layer between the current collector 16 and the active material layer 17 can reduce deterioration of the current collector 16.

[0105] In the embodiments, electrochemical elements 10 and 21 were described using ion batteries such as lithium-ion batteries and electrochemical capacitors as examples, but are not necessarily limited to these. Other examples of electrochemical elements include metal-air batteries and electrolytic capacitors, which use oxygen from the air as the positive electrode active material and metals such as Li, Zn, Al, Mg, and Fe as the negative electrode active material. [Explanation of Symbols]

[0106] 10,21 Electrochemical elements 11 Positive electrode 15. Negative electrode 18 particles

Claims

1. An electrolyte containing a non-aqueous solvent, CIE 1976L ＊ a ＊ b ＊ In the color coordinates of the color space, b ＊ ≥ 2, An electrolyte where 1 ≤ L * ≤ 3 in the aforementioned color coordinate system.

2. An electrolyte containing a non-aqueous solvent, CIE 1976L ＊ a ＊ b ＊ In the color coordinates of the color space, b ＊ ≥ 2, An electrolyte in which the saturation represented by the color coordinate c* = {(a*)² + (b*)²} 1 / 2 is 2 ≤ c* ≤ 8.

3. An electrolyte containing a non-aqueous solvent, CIE 1976 L ＊ a ＊ b ＊ in the color coordinates of the color space, b ＊ ≧ 2, and An electrolyte consisting of non-aromatic compounds, in which the proton nuclear magnetic resonance spectrum signal is in the chemical shift range of 6 ppm to 8 ppm.

4. The absorption spectrum obtained by Fourier transform infrared spectroscopy is at wavenumber 1100 cm⁻¹. －１ From 1120cm －１ The electrolyte according to claim 3, which is present within the range.

5. The electrolyte according to any one of claims 1 to 4, wherein a lithium salt is dissolved in the non-aqueous solvent.

6. An electrolyte composition comprising an electrolyte solution and particles of an oxide solid electrolyte, The electrolyte is an electrolyte composition comprising a non-aqueous solvent, wherein b* ≥ 2 in the color coordinates of the CIE 1976 L * a * b * color space.

7. The electrolyte composition according to claim 6, wherein the oxide solid electrolyte has a garnet-type crystalline structure containing Li, La, and Zr.

8. An electrochemical element including electrodes, The electrode is an electrochemical element containing the electrolyte according to any one of claims 1 to 4.

9. An electrochemical element including electrodes, The electrode is a positive electrode and contains an electrolyte, The electrolyte comprises a non-aqueous solvent and is an electrochemical element in which b* ≥ 2 in the color coordinates of the CIE 1976 L * a * b * color space.

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