Electrolytic solution, electrolyte composition, and electrochemical element

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

Electrolyte solution, electrolyte composition and electrochemical element

[0001] The present invention relates to an electrolyte solution containing a non-aqueous solvent, an electrolyte composition, and an electrochemical device.

[0002] Electrochemical devices such as lithium ion secondary batteries convert chemical energy into electrical energy. Prior art in which an electrochemical device contains an electrolyte solution containing a non-aqueous solvent is disclosed in Patent Document 1. The electrolyte solution serves as a medium for transferring ions.

[0003] JP 2011-44252 A

[0004] Not only ions that contribute to the energy conversion of an electrochemical element but also ions that do not contribute to the energy conversion move in the electrolyte, so the prior art has a problem in that the transport number of ions that contribute to the energy conversion is low.

[0005] The present invention has been made to solve this problem, and an object of the present invention is to provide an electrolyte, an electrolyte composition and an electrochemical element that can increase the transport number of ions that contribute to energy conversion.

[0006] A first aspect of the present invention to achieve this object is an electrolyte solution containing a non-aqueous solvent, which meets the CIE 1976L ＊ a ＊ b ＊ In the color coordinates of the color space, b ＊ ≧2.

[0007] The second aspect is the same as the first aspect except that 1≦L ＊ ≦3.

[0008] The third aspect is the same as the first or second aspect c ＊ = {(a ＊ ) ２ +(b ＊ ) ２} １／２ The saturation expressed by 2≦c ＊ ≦8.

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

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

[0011] In a sixth aspect, in the fifth aspect, an absorption spectrum by Fourier transform infrared spectroscopy is －１ From 1120cm －１ It exists in the range.

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

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

[0014] A ninth aspect is an electrochemical device including an electrode, the electrode including the electrolyte solution of any one of the first to sixth aspects.

[0015] A tenth aspect is the ninth aspect, wherein the electrode is a positive electrode.

[0016] The electrolyte solution, the electrolyte composition containing the electrolyte solution, and the electrochemical element of the present invention are characterized in that the electrolyte solution meets CIE 1976L ＊ a ＊ b ＊ In the color coordinates of the color space, b ＊ Since the ratio is ≧2, the mobility of ions that contribute to energy conversion increases, and the transport number can be increased.

[0017] It is a cross-sectional view of the electrochemical element in the first embodiment. It is a diagram showing a garnet-type crystal structure. It is a cross-sectional view of the electrochemical element in the second embodiment.

[0018] 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 device 10 according to a first embodiment. The electrochemical device 10 is a device that directly converts chemical energy to electrical energy. The ions (hereinafter referred to as "charge carriers") that contribute to the energy conversion of the electrochemical device 10 are Li. ＋ , Na ＋ , K.＋ , Mg ２＋ , Cu ＋ , Ag ＋ Examples of cations include:

[0019] An electricity storage device will be described as an example of the electrochemical element 10. Examples of electricity storage devices include an ion battery such as a lithium ion battery, an electrochemical capacitor that utilizes a redox reaction of an electrode or an ion in an electrolyte, or 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, 20 and the electrolyte solution contained in the positive electrode 11 and the negative electrode 15, and that allows charge carriers to pass through but does not have electronic conductivity. Examples of the separator 14 include nonwoven fabrics and porous films made of cellulose, polypropylene, polyethylene, polyimide, alumina, etc.

[0021] The positive electrode 11 is formed by stacking a current collector 12 and an active material layer 13. The current collector 12 is a conductive member. Examples of materials for the current collector 12 include a metal selected from Ni, Ti, Fe, and Al, an alloy containing two or more of these elements, stainless steel, and a carbon material.

[0022] The active material layer 13 includes an active material 19. The active material 19 is appropriately selected depending on the type of charge carrier and the electricity storage device. When the electricity storage device is an electrochemical capacitor, a material capable of reversibly supporting anions is used as the active material 19, and examples of such carbon-based materials include porous carbon, natural graphite, artificial graphite, graphitizable carbon (hard carbon), non-graphitizable carbon (soft carbon), and carbon fiber.

[0023] When the power storage device is an ion battery, examples of the active material 19 include metal oxides containing transition metals, sulfur-based active materials, and organic active materials. ＋ In this case, 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 LiCoO ２ , LiNi ０．８ Co ０．１５ Al ０．０５ O２ , LiMn ２ O ４ , LiNiVO ４ , LiNi ０．５ Mn １．５ O ２ , LiNi １／３ Mn １／３ Co １／３ O ２ and LiFePO ４ is exemplified.

[0024] The sulfur-based active material is S, TiS ２ , NiS, FeS ２ , Li ２ S, MoS ３ 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] The active material layer 13 may contain a conductive additive to reduce the resistance of the active material layer 13. Examples of the conductive additive include carbon black, acetylene black, ketjen black, carbon fiber, Ni, Pt, and Ag.

[0026] In this embodiment, the active material layer 13 contains an electrolyte composition. The electrolyte composition includes particles 18 of an oxide solid electrolyte and an electrolyte solution. Examples of the particles 18 include oxides having a NASICON structure, oxides having a perovskite structure, and oxides having a garnet structure. The oxides having a NASICON 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 (P.O. ４ ) ３ and Li(Al,Ge) ２ (P.O. ４ ) ３ The oxide having a perovskite structure is an oxide containing at least Li, Ti, and La, for example, La ２／３－Ｘ Li ３Ｘ TiO ３ Examples include:

[0027] The particles 18 are preferably made of a composite oxide containing Li, La, and Zr and having a garnet-type crystal structure. －３ This is because the garnet-type crystal structure has an ionic conductivity of the order of 50 S / cm and is resistant to reduction by metallic lithium. ３ A ２ B ３ O １２ It is expressed as:

[0028] FIG. 2 is a diagram schematically showing a garnet-type crystal structure. In the garnet-type crystal structure, the C site Sc is dodecahedrally coordinated with an oxygen atom Oa, the A site Sa is octahedrally coordinated with an oxygen atom Oa, and the B site Sb is tetrahedrally coordinated with an oxygen atom Oa. In an oxide solid electrolyte, Li can exist in a position that is octahedrally coordinated with an oxygen atom Oa in a normal garnet-type crystal structure, but becomes a void V. The void V is, for example, a position sandwiched between the B site Sb1 and the B site Sb2. The Li present in the void V is octahedrally coordinated with an oxygen atom Oa that constitutes 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, Li having a garnet-type crystal structure ７ La ３ Zr ２ O １２ In 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 void V.

[0029] The garnet-type crystal structure can be identified by X-ray diffraction. The garnet-type crystal structure is identified by X-ray diffraction file No. 422259 (Li) in the Cambridge Structural Database (CSD). ７ La ３ Zr ２ O １２ ) has an XRD pattern similar to that of No. 422259. Compared to No. 422259, the solid electrolyte may differ in the type of constituent elements, Li concentration, etc., and therefore the diffraction angle and intensity ratio may differ. A typical crystal structure of this type is a cubic system (space group Ia-3d (- indicates an overline indicating a reversal operation), JCPDS: 84-1753).

[0030] Solid electrolytes with a garnet-type crystal structure are typically Li ７ La ３ Zr ２ O １２ The solid electrolyte is Li ７ La ３ Zr ２ O １２ A part of the constituent elements may be substituted with another element, or a small amount of another element may be added without substituting the constituent elements. Examples of the other element 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] The solid electrolyte is, for example, Li ６ La ３ Zr １．５ W ０．５ O １２ , Li ６．１５ La ３ Zr １．７５ Ta ０．２５ Al ０．２ O １２ , Li ６．１５ La ３ Zr １．７５ Ta ０．２５ Ga ０．２ O １２ , Li ６．２５ La ３ Zr ２ Ga ０．２５ O １２ , Li ６．４ La ３ Zr １．４ Ta ０．６ O １２ , Li ６．５ La ３ Zr １．７５ Te ０．２５ O １２ , Li ６．７５ La ３ Zr １．７５ Nb ０．２５ O １２ , Li ６．９ La ３ Zr １．６７５ Ta ０．２８９ Bi ０．０３６ O１２ , Li ６．４６ Ga ０．２３ La ３ Zr 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 Zr ２ O １２ Examples include:

[0032] The solid electrolyte preferably contains 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, 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 solution contained in the active material layer 13 is a medium through which charge carriers move, and is a solution in which a supporting electrolyte is dissolved in a non-aqueous solvent. Non-aqueous solvents are broadly classified into molecular solvents, which are mostly composed of molecules, and ionic liquids, which are composed of cations and anions. One of the reasons for using a non-aqueous solvent in the electrolyte solution is to widen the potential window compared to electrolyte solutions that use water as the solvent. Ionic liquids are preferred because they can widen the potential window compared to electrolyte solutions that use water as the solvent.

[0034] When a molecular solvent is used as the nonaqueous solvent, an aprotic solvent is preferred to widen the potential window of the electrolyte. Examples of aprotic solvents include cyclic esters, chain esters, aliphatic carboxylic acid esters, phosphate esters, nitriles, amides, sulfur compounds, ketones, ethers, nitro compounds, and fluorous solvents. Mixtures of these solvents are also acceptable.

[0035] Examples of cyclic esters include cyclic carbonates such as propylene carbonate, ethylene carbonate, butylene carbonate, vinylene carbonate, vinylethylene carbonate, and fluoroethylene carbonate, and lactones such as β-propiolactone, γ-butyrolactone, δ-valerolactone, α-pyrone, and coumarin. Examples of chain esters include chain carbonates 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 monoglyme. Examples of nitro compounds include nitromethane and nitrobenzene. Fluorous solvents are compounds in which the hydrogen atoms of hydrocarbons are replaced with fluorine atoms, and derivatives thereof.

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

[0038] Ionic liquids are compounds consisting of cations and anions, and are liquid at room temperature and pressure. If the solvent of an electrolyte is an ionic liquid, the flame retardancy of the electrolyte can be improved. The ionic liquid is preferably one having one or more cation species selected from the group consisting of ammonium, imidazolium, pyrrolidinium, and piperidinium.

[0039] The anion component of the ionic liquid is not particularly limited. ４ － , N(SO ２ F) ２ － inorganic anions such as B(C ６ H ５ ) ４ － , CH ３ SO ３ － , C.F. ３ SO ３ － , N(SO ２ CF ３ ) ２ － , N(SO ２ C ４ F ９ ) ２ － Examples of organic anions include:

[0040] The ionic liquid may be a solvated ionic liquid, such as a sulfone-based solvent such as sulfolane or a sulfolane derivative, or a glyme-based solvent such as tetraglyme, in which a supporting electrolyte is dissolved.

[0041] The charge carrier is Li ＋In this case, the supporting electrolyte is a lithium salt. The anion of the supporting electrolyte is OH. － , halide ions (I － , Cl － ,Br － etc.), SCN － , BF ４ － , BF ３ (CF ３ ) － , BF ３ (C ２ F ５ ) － , P.F. ６ － , ClO ４ － , SbF ６ － , N(SO ２ F) ２ － , N(SO ２ CF ３ ) ２ － , N(SO ２ C ２ F ５ ) ２ － , B(C ６ H ５ ) ４ － , B(O ２ C ２ H ４ ) ２ － , C(SO ２ F) ３ － , C(SO ２ CF ３ ) ３ － , C.F. ３ COO － , C.F. ３ SO ２ O － , C ６ F ５ SO ２ O － , B(O ２ C ２ O ２ ) ２ － , RCOO －(R is an alkyl group having 1 to 4 carbon atoms, a phenyl group, or a naphthyl group), etc. The supporting electrolyte may be a mixture of these.

[0042] The concentration of the supporting electrolyte in the electrolyte solution is 0.2 mol / dm ３ or more, preferably 0.5 mol / dm ３ More preferably, 1.0 mol / dm ３ As the concentration of the supporting electrolyte increases, the number of solvent molecules coordinated to the charge carrier increases, resulting in less uncoordinated solvent and the predominant coordination with counter anions (so-called ionic association). 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 / dm ３ Preferably, it is 2.0 mol / dm or less, more preferably 2.0 mol / dm ３ The concentration of the supporting electrolyte is 4.0 mol / dm or less. ３ This is because, when the temperature exceeds this value, the ionic conductivity tends to decrease significantly due to an increase in the viscosity of the electrolyte.

[0043] Ionic conduction is dominant in the electrical conduction of an electrolyte. 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 an electrolyte is thought to be related to the solvation in which solvent molecules bind to ions dissociated from the supporting electrolyte in the solvent, and the interaction between the ions that make up the supporting electrolyte. The CIE 1976L standard, which includes quantities related to the lightness, chroma, and hue of the electrolyte, is ＊ a ＊ b ＊ The color coordinates of the color space are one of the indicators of solvation.

[0044] CIE 1976L ＊ a ＊ b ＊ The color space is L, which was recommended by the CIE (International Commission on Illumination) in 1976. ＊ , a ＊ , b ＊ It is a nearly uniform three-dimensional color space obtained by plotting the above on Cartesian coordinates. ＊ a ＊ b ＊ The color space is specified in JIS Z8781-4:2013. CIE 1976L＊ a ＊ b ＊ In color space, lightness is L ＊ and chromaticity, which indicates hue and saturation, is expressed as a ＊ , b ＊ It is expressed as: ＊ , b ＊ indicates the color direction, and a ＊ is the red direction, -a ＊ is the green direction, b ＊ is yellow direction, -b ＊ indicates the blue direction. The larger the value, the more vivid the color, and the closer to the origin, the duller the color. ＊ is {(a ＊ ) ２ +(b ＊ ) ２} １／２ (a ＊ and b ＊ It is expressed as the square root of the sum of the squares of L ＊ , a ＊ , b ＊ can be measured using a spectrophotometer CM-5 (Konica Minolta, Inc.).

[0045] L ＊ , a ＊ , b ＊ The values ​​of b and c cannot be controlled independently and there are many unknowns. ＊ When the ratio is ≧2, it is believed that the mobility of anions decreases and the mobility of cations (charge carriers) increases, thereby increasing the transport number of charge carriers that contribute to energy conversion.

[0046] The mobility of charge carriers in the electrolyte and b ＊ The reason for the relationship between b and c is unclear, but the color of the electrolyte solution changes because the number of solvent molecules coordinating with the cations produced when the supporting electrolyte is dissolved in the solvent decreases, while the number of solvent molecules coordinating with the anions increases. ＊ is estimated to be large.

[0047] Discoloration of the solvent caused by impurities such as water, alcohols, epoxides, lithium alkyl carbonates, and their reaction products with the electrolyte. ＊ To distinguish it from the increase in b ＊The maximum value is preferably 30. The impurities contained in the electrolyte are preferably 200 ppm or less, more preferably 100 ppm or less, and particularly preferably 10 ppm or less, in order to reduce deterioration of the electrolyte over time due to the presence of impurities.

[0048] Electrolyte lightness L ＊ is 1≦L ＊ ≦3, and the saturation c of the electrolyte ＊ is 2≦c ＊ Preferably, it is ≦8. In either case, this is to further increase the transport number of the charge carriers.

[0049] Electrolyte L ＊ , a ＊ , b ＊ , c ＊ The adjustment of b is exemplified by modifying the surface of the particles 18 and then contacting the particles 18 with an electrolyte solution. ＊ and ＊ becomes larger. Methods for modifying the surface of the particles 18 include chemical treatment. The surface of the particles 18 can be made acidic or basic by chemical treatment. Examples of chemical treatment include a method in which a modifier is adsorbed onto the surface of the particles 18 in a liquid phase such as a non-aqueous solvent, and a method in which a modifier is reacted with the particles 18 in a gas phase. As a pretreatment for surface modification, it is preferable to increase the activity of the surface of the particles 18 by applying a compressive force or shear force to the particles 18 using a rotating container or a rotating blade alone or in combination, or by dispersing the particles 18 in a high-speed airflow and applying an impact force.

[0050] When the particles 18 are a composite oxide having a garnet-type crystal structure containing Li, La, and Zr, a gas phase reaction between carbon dioxide or water and the particles 18 generates lithium hydroxide or lithium carbonate on the surface of the particles 18, thereby modifying the surface of the particles 18 to be basic. Since the surface modification of the particles 18 is easy, an electrolyte solution can be easily prepared by contacting the particles 18.

[0051] After contacting the particles 18 with the electrolyte solution, both the particles 18 and the electrolyte solution may be placed in the active material layer 13, or after contacting the particles 18 with the electrolyte solution, the particles 18 and the electrolyte solution may be separated and only the electrolyte solution may be supplied to the active material layer 13. Examples of means for separating the particles 18 from the electrolyte solution include filtration, sedimentation, and centrifugation. The electrolyte solution may be poured into the active material layer 13 in which the particles 18 are placed, causing the particles 18 and the electrolyte solution to come into contact with each other, and preparing the electrolyte solution in 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 the proton nuclear magnetic resonance spectroscopy ( １ H-NMR) １ When the H-NMR spectrum was measured １ Preferably, the H-NMR spectrum signal is in the chemical shift range of 6 ppm to 8 ppm. The chemical shift is calculated by dividing the resonance frequency of the methyl group of tetramethylsilane, which is set to 0, by the measurement frequency.

[0053] The absorption spectrum of the electrolyte by Fourier transform infrared spectroscopy (FT-IR) was －１ From 1120cm －１ The absorption spectrum by FT-IR is preferably measured by the attenuated total reflection method (ATR method).

[0054] The active material layer 13 may contain a binder that binds the active material 19. There are no particular limitations on the binder as long as it binds the active material 19. Examples of the binder 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.

[0055] The ratio (vol %) of the volume of the electrolyte solution to the combined volume of the electrolyte solution and active material 19 contained in active material layer 13 is preferably 10% or more and 20% or less. This is to ensure the equilibrium potential of positive electrode 11 while reducing the interface resistance of active material 19, which is the reaction field for charge / discharge reactions.

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

[0057] The contents (vol%) of particles 18, active material 19, and electrolyte solution can be determined by analyzing a randomly selected cross-section of active material layer 13 at a magnification of 5000x using a scanning electron microscope (SEM) equipped with an energy dispersive X-ray spectrometer (EDS). The analysis involves identifying element distribution and performing image analysis of the contrast of a backscattered electron image to determine the areas of particles 18, active material 19, and electrolyte solution. The content (vol%) of particles 18 is obtained by regarding the ratio of the area of ​​particles 18 to the total area of ​​particles 18 and active material 19 as the volume ratio. The content (vol%) of electrolyte solution is also obtained by regarding the ratio of the area of ​​electrolyte solution to the total area of ​​active material 19 and electrolyte solution as the volume ratio.

[0058] The cross section of the active material layer 13 used for analysis is a polished surface, a surface obtained by irradiating with a focused ion beam (FIB), or a surface obtained by ion milling. The polished surface is, for example, a surface 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 is formed by stacking a current collector 16 and an active material layer 17. The current collector 16 is a conductive member. Examples of the material for the current collector 16 include a metal selected from Ni, Ti, Fe, Cu, and Si, an alloy containing two or more of these elements, stainless steel, and a carbon material.

[0060] The active material layer 17 includes an active material 20. To reduce the resistance of the active material layer 17, the active material layer 17 may include a conductive additive. Examples of the conductive additive include carbon black, acetylene black, ketjen black, carbon fiber, Ni, Pt, and Ag. In this embodiment, the active material layer 17 includes particles 18.

[0061] There is no limitation on the material of the active material 20 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 may be a carbon-based material such as porous carbon, natural graphite, artificial graphite, graphitizable carbon, non-graphitizable carbon, or carbon fiber; Li ４ Ti ５ O １２ Examples of the oxides 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. SiOx includes oxides of Si, amorphous SiO ２ Examples include those having a structure in which microcrystalline or amorphous Si is dispersed in a matrix.

[0062] The electrochemical element 10 is manufactured, for example, as follows: The particles 18, the active material 19, and the conductive additive are mixed together, and then a solution in which a binder is dissolved in a solvent is mixed to form a slurry. The slurry is then applied onto the current collector 12 and dried to obtain a positive electrode sheet.

[0063] The particles 18, the active material 20, and the conductive additive are mixed together, and then mixed with a solution in which a binder is dissolved in a solvent to form a slurry. The slurry is applied onto the current collector 16 and then dried to obtain a negative electrode sheet.

[0064] The separator 14 separating the positive electrode sheet from the negative electrode sheet, the positive electrode sheet, and the negative electrode sheet are stacked and wound up by a winding machine to prepare a cylindrical or rectangular cell. Terminals (not shown) are connected to the current collectors 12 and 16, respectively, and a container (not shown) containing the cell is filled with a material having a chromaticity of b ＊ After filling with the electrolyte ≧2, the container is sealed to obtain an electrochemical device 10 including a positive electrode 11, a separator 14, and a negative electrode 15.

[0065] According to the electrochemical device 10, the chromaticity b ＊ Since the active material layer 13 of the positive electrode 11 is filled with an electrolyte solution of ≥ 2, it is possible to prevent the resistance to charge carrier movement from increasing even if the thickness of the active material layer 13 is increased and the distance that charge carriers move within the active material layer 13 during charging or discharging is lengthened. Because the thickness of the active material layer 13 can be increased, an electrochemical device 10 having a large capacity and capable of high-speed charging can be obtained.

[0066] chromaticity b ＊ The electrolyte solution having a conductivity of 2 or more can increase the transport number of charge carriers compared to conventional electrolyte solutions, thereby reducing the concentration polarization that tends to occur during high-speed charging and discharging. This is advantageous for extending the life of the electrochemical device 10 because it can prevent the operating voltage (terminal voltage) of the electrochemical device 10 from decreasing in a short period of time.

[0067] Because the active material layer 13 of the positive electrode 11 is filled with an electrolyte solution having high charge carrier mobility, it is possible to ensure the mobility of charge carriers not only at positions in the active material layer 13 that are in contact with the particles 18, but also at positions away from the particles 18. The migration speed (diffusion speed) of charge carriers is highly temperature-dependent and therefore decreases as the temperature decreases; however, because the mobility of charge carriers can be ensured, the operation of the electrochemical device 10 can be ensured even when the ambient temperature of the electrochemical device 10 is low.

[0068] A second embodiment will be described with reference to Fig. 3. In the first embodiment, the separator 14 separating the positive electrode 11 and the negative electrode 15 is a nonwoven fabric or porous film made of cellulose, polypropylene, or the like. In contrast, in the second embodiment, an electrochemical element 21 will be described in which the separator 22 separating the positive electrode 11 and the negative electrode 15 contains an electrolyte 23. In the second embodiment, the same parts as in the first embodiment are designated by the same reference numerals, and the following description will be omitted.

[0069] 3 is a cross-sectional view of an electrochemical element 21 according to the second embodiment. The electrochemical element 21 (electricity storage device) includes, in order, a positive electrode 11, a separator 22, and a negative electrode 15. The separator 22 includes an electrolyte 23. The electrolyte 23 may be, for example, a solid or gel electrolyte having ion conductivity. A mixture of the electrolyte 23 and an electrolytic solution may be disposed in the separator 22.

[0070] The electrolyte 23 includes at least one selected from sulfide-based, oxide-based, hydride-based, halide-based, and organic-based electrolytes. The sulfide-based electrolyte includes crystalline thiolithium-based, Li １０ GeP ２ S １２ type, argyrodite type, Li ７ P ３ S １１ Type, Li ２ S-P ２ S ５ Examples of oxide electrolytes include glass and glass ceramics, such as those listed below. Examples of oxide electrolytes include oxides having a NASICON structure, oxides having a perovskite structure, and oxides having a garnet structure.

[0071] The hydride electrolyte is LiBH ４ and lithium halide compounds (LiI, LiBr, LiCl) and lithium amide (LiNH ２ ) is an example of a solid solution. ３ YCl ６ Examples of organic solid electrolytes include polyethylene oxide, polypropylene oxide, and polyacrylonitrile.

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

[0073] A separator slurry is prepared by mixing a solvent in which a binder is dissolved with a mixture of a nonaqueous solvent in which a lithium salt is dissolved and particles 18. The separator slurry is applied onto active material layer 13 and then dried to obtain a positive electrode sheet.

[0074] A mixture of particles 18 and a nonaqueous solvent in which a lithium salt is dissolved is mixed with active material 20, and then a solvent in which a binder is dissolved is mixed to form a slurry. The slurry is applied onto current collector 16 and then dried to obtain active material layer 17. A separator slurry is applied onto active material layer 17 and then dried to obtain a negative electrode sheet.

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

[0076] The electrochemical device 21 of the second embodiment contains an electrolyte in the positive electrode 11, the negative electrode 15, and the separator 22, and is therefore advantageous for increasing the capacity and speeding up charging, similar to the electrochemical device 10 of the first embodiment.

[0077] The present invention will be explained in more detail with 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 Zr ２．０ O １２ So that Li ２ CO ３ , MgO, La(OH) ３ , SrCO ３, ZrO ２ was weighed. ２ CO ３ Considering the volatilization of Li during firing, the amount of Li was in excess of approximately 15 mol% in elemental terms. The weighed raw materials and ethanol were placed in a nylon pot together with zirconia balls and ground and mixed in a ball mill for 15 hours. The slurry removed from the pot was dried and then fired on an MgO plate at 1100°C for 15 hours. The fired powder was crushed, placed in an MgO sheath, and further fired at 1100°C for 4 hours. The fired powder was crushed in a glove box under an argon atmosphere to obtain an oxide solid electrolyte (hereinafter referred to as "LLZ").

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

[0080] Using a dry jet mill (Nano Jetmizer (registered trademark) NJ-50 model, manufactured by Aisin Nano Technologies Co., Ltd.), the LLZ was pulverized by passing it through the jet mill three times under conditions of a nozzle source pressure of 2.0 MPa, a nitrogen atmosphere, and a throughput of 480 g / Hr. The pulverized LLZ was stored in an argon atmosphere with a dew point of -70°C for 24 hours to obtain the particles in Example 1.

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

[0082] Example 3 Particles in Example 3 were obtained in the same manner as in Example 1, except that the throughput of each grinding was set to 960 g / Hr and the LLZ was ground by passing it through the jet mill once in total.

[0083] Example 4 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 of the particles in Examples 1 to 4 was measured by a laser diffraction / scattering method. The specific surface area of ​​the particles in Examples 1 to 4 was also measured in accordance with JIS R1626:1996.

[0085] (Preparation of Electrolyte Solution and Measurement of Color) A non-aqueous solvent was prepared by mixing ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate in a ratio of 1:1:1 (volume ratio). ６ is 1 mol / dm ３ The electrolyte solution was prepared by mixing the particles and the electrolyte solution in Example 1-4 in a ratio of 16.5:83.5 (mass ratio) in a test tube and mixing for 30 minutes. The test tube was then capped and left to stand for 24 hours to allow the particles to settle and separate, and the supernatant was collected to obtain the electrolyte solution in Example 1-4. The electrolyte solution before mixing with the particles was used as the electrolyte solution in Comparative Example 1.

[0086] A non-aqueous solvent was prepared by mixing ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate in a ratio of 1:1:1 (volume ratio), and the supporting electrolyte LiPF ６ is 1 mol / dm ３ The mixture was used as the electrolyte solution in Comparative Example 2. The electrolyte solution in Comparative Example 1 contained vinylene carbonate, but the electrolyte solution in Comparative Example 2 was different in that it did not contain vinylene carbonate.

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

[0088] The color of the electrolyte solutions in Examples 1-4 and Comparative Examples 1-3 was measured at 25°C using a spectrophotometer CM-5 (Konica Minolta, Inc.), and the color was measured according to CIE 1976L. ＊ a ＊ b ＊ L in color space ＊ , a ＊ , b ＊ Furthermore, the saturation c ＊ = {(a ＊ ) ２ +(b ＊ ) ２} １／２ In the formula ＊ , b ＊ Substituting the above, the saturation c of the electrolyte in Examples 1-4 and Comparative Examples 1-3 is ＊ asked for.

[0089] ( １ Measurement of H-NMR spectrum) The electrolyte solutions in Examples 1-4 and Comparative Examples 1-3 were placed in solution sample tubes with an outer diameter of 5 mm under an argon atmosphere, and the NMR spectrum of the proton nuclei was measured by the pulsed wave Fourier method using a nuclear magnetic resonance apparatus (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 present in the chemical shift range of 6 ppm to 8 ppm was measured based on the resonance position of tetramethylsilane.

[0090] (Measurement of infrared absorption spectrum by FT-IR) The electrolyte solutions in Examples 1-4 and Comparative Examples 1-3 were brought into contact with crystals in an argon atmosphere, and infrared light was irradiated onto the electrolyte solution from the backside of the crystal, and the infrared absorption spectrum was measured by 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 wave number was 1100 cm －１ From 1120cm －１ The wavenumber (cm) of the infrared absorption spectrum that exists in the range －１ ) was measured.

[0091] (Transportance Number Measurement) Metallic lithium foil was attached to each of two 20 mm diameter stainless steel plates, and 38 15 μm thick polypropylene separators were sandwiched between the metallic lithium foils. The electrolyte solutions in Examples 1-4 and Comparative Examples 1-3 were injected into the separators, and then the separators were secured with polyimide adhesive tape to obtain symmetric cells in Examples 1-4 and Comparative Examples 1-3. The preparation of the symmetric cells and the following measurements were carried out in a glove box filled with argon gas at a dew point of −60°C.

[0092] The lithium ion transport number was determined by a combination of AC impedance measurement and chronoamperometry measurement. Specifically, after AC impedance measurement 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 the cell reached a steady state, AC impedance measurement was performed again. The lithium ion transport number t was calculated using the following formula:

[0093] t = {I Ｓ (ΔV-I ０ R ０ ) / {I ０ (ΔV-I Ｓ R Ｓ ) However, I Ｓ is the steady-state current value, I ０ is the current value at the beginning of voltage application, R ０ and R Ｓ are the resistances at the interface between the separator and the electrode before and after the chronoamperometry measurement. The applied voltage ΔV in the chronoamperometry measurement was 3 mV.

[0094] The median diameter D50 and specific surface area of ​​the particles in Examples 1-4 and Comparative Example 3, and the L of the electrolyte in Examples 1-4 and Comparative Example 1-3 ＊ , a ＊ , b ＊ , c ＊ , chemical shift (ppm), wave number (cm －１ ), the transference number of lithium ions and the interfacial resistance R ０ The change rate (%) of R in Examples 1-4 is shown in Table 1. ０ The rate of change of R ０ The rate of change relative to R ０ The rate of change of R ０ The rate of change is shown.

[0095]

[0096] As shown in Table 1, the electrolyte solutions in Examples 1-4 and Comparative Example 1 containing vinylene carbonate had chemical shifts in the range of 6 ppm to 8 ppm. １ The H-NMR spectrum signal (7.15 ppm) was present, but the electrolyte solutions in Comparative Examples 2 and 3 had chemical shifts in the range of 6 ppm to 8 ppm.１ The electrolyte solution in Example 1-4 had no signal in the H-NMR spectrum at a wave number of 1100 cm －１ From 1120cm －１ Infrared absorption spectrum (1105-1118 cm －１ ) was present, but the electrolyte solution in Comparative Example 1-3 had a wave number of 1100 cm －１ From 1120cm －１ There was no infrared absorption spectrum in the range of

[0097] The transference number of the electrolyte in Example 1-4 was larger than the transference number of 0.125 in Comparative Example 1. Chromaticity b of the electrolyte ＊ The chromaticity b of Examples 1-4 was 2.00 or more, whereas that of Comparative Example 1 was -0.95. ＊ According to Examples 1-4 and Comparative Example 1, the chromaticity b ＊ It was revealed that when the transference number is 2.00 or more, the transference number of lithium ions can be increased compared to the electrolyte solution before contact with the particles (Comparative Example 1).

[0098] Electrolyte saturation c ＊ The chroma c of Examples 1-4 was 2.00 or more and 8.00 or less, while that of Comparative Example 1 was 1.01. ＊ It was found that the saturation of the electrolyte c ＊ It was revealed that when the transference number of lithium ions is 2.00 or more and 8.00 or less, the transference number of lithium ions can be increased.

[0099] Electrolyte lightness L ＊ The lightness L of the electrolyte solution was 1.00 or more and 3.00 or less in Examples 1-3, while it was 3.76 in Comparative Example 1. ＊ It has been revealed that when the transference number of lithium ions is 1.00 or more and 3.00 or less, the transference number of lithium ions can be increased.

[0100] Chemical shifts in the range of 6 ppm to 8 ppm １ The interface resistance R of the symmetric cell in Example 1-4 using the electrolyte solution in which a signal in the H-NMR spectrum exists ０The change rate of the resistance R of the interface of Comparative Example 1, in which a signal exists in the chemical shift range of 6 ppm to 8 ppm, is ０ On the other hand, the chemical shifts were in the range of 6 ppm to 8 ppm. １ The interface resistance R of the symmetric cell in Comparative Example 3 using an electrolyte solution with no H-NMR spectrum signal ０ The rate of change of the interfacial resistance R of the symmetric cell in Comparative Example 2, where no signal exists in the chemical shift range of 6 ppm to 8 ppm, is ０ The chemical shift range of 6 ppm to 8 ppm was only 54%. １ By using an electrolyte in which a signal exists in the H-NMR spectrum, the chemical shift range is 6 ppm to 8 ppm. １ It was revealed that the resistance at the electrode interface can be reduced compared to when an electrolyte solution that does not exhibit a signal in the H-NMR spectrum is used.

[0101] 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.

[0102] In the embodiment, the electrochemical element 10 has been described as including a positive electrode 11 having an active material layer 13 provided on one side of a current collector 12, and a negative electrode 15 having an active material layer 17 provided on one side of a current collector 16, 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 13 and an active material layer 17 are provided on both sides of a current collector 12. If bipolar electrodes and separators 14 are alternately stacked and housed in a case (not shown), an electrochemical element with a so-called bipolar structure can be obtained.

[0103] In the embodiment, the active material layers 13 and 17 include the particles 18, but this is not necessarily limited to this. It is of course possible to omit the particles 18 from at least one of the active material layers 13 and 17.

[0104] Although not described in the embodiments, it is of course possible to dispose a protective layer between the active material layer 17 and the separator 14, 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. Disposing a protective layer between the active material layer 17 and the separator 14, 22 can reduce short circuits caused by dendrites. Disposing 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, the electrochemical elements 10 and 21 have been 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 that use oxygen in the air as the positive electrode active material and a metal such as Li, Zn, Al, Mg, or Fe as the negative electrode active material.

[0106] 10, 21 Electrochemical element 11 Positive electrode (electrode) 15 Negative electrode (electrode) 18 Particles

Claims

1. An electrolyte containing a non-aqueous solvent, which meets CIE 1976L ＊ a ＊ b ＊ In the color coordinates of the color space, ＊ ≧2.

2. In the above color coordinates, 1≦L ＊ 2. The electrolyte of claim 1, wherein the pH is ≦3.

3. In the above color coordinates, ＊ = {(a ＊ ) ２ + (b ＊ ) ２ } １／２ The saturation represented by 2≦c ＊ 3. The electrolyte according to claim 1, wherein the pH is ≦8.

4. The electrolyte according to claim 1 or 2, wherein a lithium salt is dissolved in the non-aqueous solvent.

5. The electrolyte according to claim 1 or 2, which is composed of a non-aromatic compound and has a proton nuclear magnetic resonance spectrum signal in the chemical shift range of 6 ppm to 8 ppm.

6. The absorption spectrum by Fourier transform infrared spectroscopy is at a wave number of 1100 cm －１ From 1120cm －１ The electrolyte according to claim 5, wherein the content of 7. An electrolyte composition comprising the electrolyte solution according to claim 1 or 2 and particles of an oxide solid electrolyte.

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

9. An electrochemical element comprising an electrode, the electrode comprising the electrolyte solution according to claim 1 or 2.

10. The electrochemical element according to claim 9, wherein said electrode is a positive electrode.

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