Non-aqueous electrolyte and electrochemical element

Abstract

To provide a non-aqueous electrolyte and an electrochemical element capable of reducing desolvation resistance.MEANS FOR SOLVING THE PROBLEM: The non-aqueous electrolyte contains zirconium in an amount of 200 wtppb or more and / or lanthanum in an amount of 30 wtppb or more. The non-aqueous electrolyte may further contain strontium at 10 wtppb or more. The non-aqueous electrolyte contains zirconium and lanthanum, in which the ratio of lanthanum concentration to zirconium concentration may be 0.2 or more and 0.5 or less. The electrochemical device contains the non-aqueous electrolyte.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a non-aqueous electrolyte and an electrochemical device. [Background technology]

[0002] In a non-aqueous electrolyte solution in which an electrolyte is dissolved in a non-aqueous solvent, charge carriers (ions) exist in a state coordinated with the solvent molecules. In the prior art disclosed in Patent Document 1, the non-aqueous electrolyte solution contains a solvated ionic liquid, a low-viscosity organic solvent, and a negative electrode interface stabilizer in order to improve the input / output characteristics of an electrochemical device containing the non-aqueous electrolyte solution. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2020-145054 Summary of the Invention [Problem to be solved by the invention]

[0004] In non-aqueous electrolytes, charge carriers coordinated to solvent molecules desolvate at the electrode interface and move through the electrode. Therefore, there is a need for technology to reduce the desolvation resistance, which affects the input / output characteristics of electrochemical devices.

[0005] The present invention has been made to meet this demand, and an object of the present invention is to provide a nonaqueous electrolyte and an electrochemical element that can reduce desolvation resistance. [Means for solving the problem]

[0006] A first aspect for achieving this object is a non-aqueous electrolyte containing at least one of 200 wtppb or more of zirconium and 30 wtppb or more of lanthanum.

[0007] In a second embodiment, the composition of the first embodiment further contains 10 wt ppb or more of strontium.

[0008] In a third aspect, in the first or second aspect, the ratio of the concentration of lanthanum to the concentration of zirconium is 0.2 or more and 0.5 or less.

[0009] A fourth aspect is an electrochemical device, which contains the nonaqueous electrolyte solution of any one of the first to third aspects. [Effects of the Invention]

[0010] The nonaqueous electrolyte of the present invention contains at least one of 200 wtppb or more of zirconium and 30 wtppb or more of lanthanum, and therefore can reduce desolvation resistance. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a cross-sectional view of an electrochemical device according to a first embodiment. [Figure 2] FIG. 1 is a diagram schematically illustrating a garnet-type crystal structure. [Figure 3] FIG. 4 is a cross-sectional view of an electrochemical device according to a second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0012] 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 converts chemical energy into electrical energy and vice versa. 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+ , Ca 2+ , Cu + , Ag + Examples of cations include:

[0013] Examples of the electrochemical device 10 include secondary batteries such as lithium ion batteries, sodium ion batteries, potassium ion batteries, magnesium ion batteries, and calcium ion batteries, electrochemical capacitors, and metal-air batteries that use metals such as lithium, zinc, aluminum, magnesium, and iron as the negative electrode active material. Examples of the electrochemical capacitor include electric double layer capacitors, redox capacitors that utilize redox reactions of electrodes or redox reactions of ions in a non-aqueous electrolyte, and hybrid capacitors that combine electric double layers and redox reactions, or that combine them with secondary battery materials.

[0014] The electrochemical device 10 includes, in order, a positive electrode 11, a separator 14, and a negative electrode 15. The separator 14 is made of a porous material that is durable against the active materials 19, 20 and non-aqueous 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.

[0015] 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.

[0016] The active material layer 13 includes an active material 19. The active material 19 is selected appropriately depending on the type of charge carrier and electrochemical device. When the electrochemical device is an electrochemical capacitor, a material capable of reversibly supporting anions is used as the active material 19, and examples of such material include carbon-based materials such as porous carbon, natural graphite, artificial graphite, graphitizable carbon (hard carbon), non-graphitizable carbon (soft carbon), and carbon fiber. When the electrochemical device is a metal-air battery, oxygen in the atmosphere is used as the positive electrode active material, and therefore the active material layer 13 includes a gas diffusion layer through which air (oxygen) diffuses and a catalyst layer in which an oxygen reduction reaction occurs.

[0017] When the electrochemical 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 LiCoO2, 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 Examples include O2 and LiFePO4.

[0018] 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.

[0019] 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.

[0020] In this embodiment, the active material layer 13 includes an oxide-based solid electrolyte 18 and a non-aqueous electrolyte solution. The solid electrolyte 18 has ion conductivity. Examples of the solid electrolyte 18 include oxides having a NASICON structure, oxides having a perovskite structure, and oxides having a garnet structure. Examples of oxides having a NASICON structure include oxides containing at least Li, M (M is one or more elements selected from Ti, Zr, and Ge), and P, such as Li(Al,Ti)2(PO4)3 and Li(Al,Ge)2(PO4)3. Examples of oxides having a perovskite structure include oxides containing at least Li, Ti, and La, such as La 2 / 3-X Li 3X Examples include TiO3.

[0021] The solid electrolyte 18 is preferably a composite oxide containing Li, La, and Zr and having a garnet-type crystal structure. -3 This is because it has an ionic conductivity of the order of 500 S / cm and is resistant to reduction by metallic lithium. The garnet-type crystal structure has the general formula C3A2B3O 12 It is expressed as:

[0022] FIG. 2 is a diagram showing a schematic diagram of a garnet-type crystal structure. In a garnet-type crystal structure, Sc at the C site is dodecahedrally coordinated with an oxygen atom Oa, Sa at the A site is octahedrally coordinated with an oxygen atom Oa, and Sb at the B site is tetrahedrally coordinated with an oxygen atom Oa. In an oxide solid electrolyte, Li can exist in a vacancy V, which is a position where Li is octahedrally coordinated with an oxygen atom Oa in a normal garnet-type crystal structure. The vacancy V is, for example, a position sandwiched between the B site Sb1 and the B site Sb2. The Li present in the vacancy 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, in Li7La3Zr2O having a garnet-type crystal structure, 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 vacant V.

[0023] The garnet-type crystal structure can be identified by X-ray diffraction. The garnet-type crystal structure is identified in X-ray diffraction file No. 422259 (Li7La3Zr2O) of the CSD (Cambridge Structural Database). 12 ) has an XRD pattern similar to that of No. 422259. Compared to No. 422259, the solid electrolyte may have different constituent elements and Li concentrations, resulting in different diffraction angles and intensity ratios. 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).

[0024] Solid electrolytes with a garnet-type crystal structure are typically Li7La3Zr2O 12 The solid electrolyte is Li7La3Zr2O 12 Some of the constituent elements may be substituted with other elements, or a small amount of other elements may be added without substituting the constituent elements. Examples of other elements include at least one element selected from the group consisting of Mg, Al, Si, Ca, Ti, V, Ga, Sr, Y, Nb, Sn, Sb, Ba, Hf, Ta, W, Bi, Rb, and lanthanides (excluding La).

[0025] The solid electrolyte is, for example, Li6La3Zr 1.5 W 0.5 O 12 , Li 6.15 La3Zr 1.75 Ta 0.25 Al 0.2 O 12 , Li 6.15 La3Zr 1.75 Ta 0.25 Ga 0.2 O 12 , Li 6.25 La3Zr2Ga 0.25 O 12 , Li 6.4 La3Zr 1.4 Ta 0.6 O 12 , Li 6.5 La3Zr 1.75 Te 0.25 O 12 , Li 6.75 La3Zr1.75 Nb 0.25 O 12 , Li 6.9 La3Zr 1.675 Ta 0.289 Bi 0.036 O 12 , Li 6.46 Ga 0.23 La3Zr 1.85 Y 0.15 O 12 , Li 6.8 La 2.95 Ca 0.05 Zr 1.75 Nb 0.25 O 12 , Li 7.05 La 3.00 Zr 1.95 Gd 0.05 O 12 , Li 6.20 Ba 0.30 La 2.95 Rb 0.05 ZrO 12 Examples include:

[0026] 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, as it increases 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)≦2.6 (5) 0.01≦Mg / (La+A)≦0.14 (6) 0.04≦A / (La+A)≦0.17

[0027] Returning to FIG. 1, the explanation will be made. The nonaqueous electrolyte contained in the active material layer 13 is a medium through which charge carriers move, and is a solution in which an electrolyte is dissolved in a nonaqueous solvent. Examples of electrolytes include compounds composed of charge carriers (anions) and cations. Nonaqueous solvents are broadly classified into molecular solvents, which are mostly composed of molecules, and ionic liquids, which are composed of cations and anions. Nonaqueous electrolytes containing nonaqueous solvents can have a wider potential window than aqueous electrolytes, which use water as the solvent.

[0028] The molecular solvent is preferably an aprotic solvent to widen the potential window of the nonaqueous electrolyte. Examples of aprotic solvents include cyclic esters, chain esters, aliphatic carboxylic acid esters, phosphate esters, nitriles, amides, sulfur compounds, ketones, ethers, nitro compounds, fluorous solvents, and sulfones. Mixtures of these solvents are also acceptable.

[0029] Examples of cyclic esters include carbonate esters 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 carbonate esters such as dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. Examples of aliphatic carboxylic acid esters include methyl formate, ethyl formate, methyl acetate, ethyl acetate, and ethyl propionate. Examples of phosphate esters include trimethyl phosphate. Examples of nitriles include acetonitrile, propionitrile, butyronitrile, and benzonitrile.

[0030] Examples of amides include formamide, N-methylformamide, dimethylformamide, N-methylacetamide, dimethylacetamide, N-methylpropionamide, 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.

[0031] Examples of ethers include tetrahydrofuran, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, monoglyme, diglyme, triglyme, and tetraglyme. 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. Examples of sulfones include trimethylene sulfone, tetramethylene sulfone (sulfolane), dimethyl sulfone, ethyl methyl sulfone, and ethyl isopropyl sulfone.

[0032] The reaction in which an electrolyte dissolves in a molecular solvent and dissociates into free ions proceeds more easily as the relative dielectric constant of the solvent increases and as the solvation of ions becomes more likely. Therefore, the relative dielectric constant ε r The solvent with a relatively large r >20) is preferred. Examples of molecular solvents with a relative dielectric constant of greater than 20 include cyclic esters, nitriles, amides, sulfur compounds, acetone, acetylacetone, nitro compounds, and sulfones. It is of course possible to mix a solvent with a relative dielectric constant of 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.

[0033] Ionic liquids are compounds consisting of cations and anions, and are liquid at room temperature and normal pressure. If the solvent of a non-aqueous electrolyte is an ionic liquid, the flame retardancy of the non-aqueous 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.

[0034] The anion component of the ionic liquid is not particularly limited. The anion component is BF4 - ,N(SO2F)2 - Inorganic anions such as B(C6H5)4 - ,CH3SO3 - ,CF3SO3 - ,N(SO2CF3)2 - ,N(SO2C4F9)2 - Examples of organic anions include:

[0035] 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 an electrolyte is dissolved.

[0036] 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 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.

[0037] The active material layer 17 contains an active material 20. To reduce the resistance of the active material layer 17, the active material layer 17 may contain 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 contains a solid electrolyte 18.

[0038] 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 can be a carbon-based material such as porous carbon, natural graphite, artificial graphite, graphitizable carbon, non-graphitizable carbon, or carbon fiber, or Li4Ti5O 12 , Si, Si-Li alloys, and compounds containing Si and O as constituent elements (hereinafter referred to as "SiO x (where 0.5≦x≦1.5), examples include metallic lithium, lithium alloys such as Li-Al alloy, Li-Sn alloy, Li-Si alloy, Li-Mg alloy, and Li-Si alloy, In-Sb alloy, and Si-Li alloy. SiO x Examples of the material include oxides of Si and those having a structure in which microcrystalline or amorphous Si is dispersed in an amorphous SiO2 matrix.

[0039] The concentration of the electrolyte in the non-aqueous electrolyte is 0.2 mol / dm 3 or more, preferably 0.5 mol / dm 3 More preferably, 1.0 mol / dm 3As the electrolyte concentration increases, the number of solvent molecules coordinated to the charge carriers increases, leaving less uncoordinated solvent, and coordination with counter anions (so-called ionic association) predominates. This suppresses the reductive decomposition of the nonaqueous electrolyte, while increasing the oxidation potential and widening the potential window. The electrolyte concentration is 4.0 mol / dm 3 Preferably, it is less than 2.0 mol / dm 3 The electrolyte concentration is 4.0 mol / dm or less. 3 If the temperature exceeds this range, the ionic conductivity tends to decrease significantly due to an increase in the viscosity of the non-aqueous electrolyte.

[0040] In some electrochemical devices 10, during charging, charge carriers in the non-aqueous electrolyte are desolvated at the interface between the negative electrode 15 and the non-aqueous electrolyte, causing an intercalation reaction, electrodeposition, or alloying reaction depending on the type of active material 20. In other devices, during discharging, charge carriers in the non-aqueous electrolyte are desolvated at the interface between the positive electrode 11 and the non-aqueous electrolyte, causing an intercalation reaction, conversion reaction, or the like depending on the type of active material 19.

[0041] The nonaqueous electrolyte contained in the electrochemical device 10 contains at least one of 200 wtppb or more of zirconium and 30 wtppb or more of lanthanum. Zirconium and lanthanum are present in the nonaqueous electrolyte in one or more forms of ions, fine particles containing these ions, and oxide particles containing zirconium or lanthanum (hereinafter referred to as "fine particles, etc."). This reduces the desolvation resistance of charge carriers. Since the internal resistance of the electrochemical device 10 during charging and discharging, which is associated with the desolvation resistance of charge carriers, can be reduced, the input / output characteristics of the electrochemical device 10 can be improved.

[0042] The mechanism by which the fine particles present in the non-aqueous electrolyte reduce the desolvation resistance is presumed to be as follows: The fine particles present in the non-aqueous electrolyte are adsorbed to the positive electrode 11 and the negative electrode 15. Because oxides containing the fine particles have relatively strong ionic bonding properties, some of the solvent molecules coordinated to the charge carriers preferentially coordinate to the fine particles in the microscopic regions near the fine particles adsorbed to the positive electrode 11 and the negative electrode 15. This facilitates desolvation of the charge carriers coordinated to some of the solvent molecules, reducing the solvation resistance.

[0043] Furthermore, when the charge carriers are alkali metal ions and the negative electrode 15 is an alkali metal, zirconium or lanthanum, which precipitates at a potential more noble than the charge carrier ions, serves as an active site for crystalline nucleation, facilitating the deposition of the charge carriers as metals, thereby reducing overvoltage during deposition of the alkali metal on the negative electrode 15. Furthermore, the product generated by the reaction of the fine particles and the like with the negative electrode 15 acts as a protective film for the negative electrode 15, thereby reducing decomposition of the nonaqueous electrolyte at the negative electrode 15.

[0044] The amount of zirconium and lanthanum present in the non-aqueous electrolyte is preferably 10 wt % or less, respectively, in order to reduce side reactions caused by zirconium and lanthanum.

[0045] The non-aqueous electrolyte may further contain strontium at 10 wtppb or more, since strontium acts similarly to zirconium and lanthanum. The concentrations of zirconium, lanthanum, and strontium can be measured, for example, by inductively coupled plasma mass spectrometry (ICP-MS).

[0046] The non-aqueous electrolyte preferably contains zirconium and lanthanum, and the ratio of the lanthanum concentration to the zirconium concentration is preferably 0.2 to 0.5, because the non-aqueous electrolyte can be easily produced by contacting the oxide particles containing zirconium and lanthanum with the non-aqueous electrolyte.

[0047] The method for producing a nonaqueous electrolyte solution includes a preparation step of preparing a nonaqueous electrolyte solution and a contact step of contacting the nonaqueous electrolyte solution with a solid electrolyte 18. It is known that residual moisture in a nonaqueous electrolyte solution can generate impurities through hydrolysis of anions and subsequent decomposition reactions. Impurities in a nonaqueous electrolyte solution can have positive or negative effects on the ionic conductivity of the nonaqueous electrolyte solution, the interfacial resistance of electrodes, and low-temperature characteristics. Therefore, it is necessary to control the amount of impurities in the nonaqueous electrolyte solution.

[0048] When the solid electrolyte 18 comes into contact with the non-aqueous electrolyte solution in the contacting step, the amount of water and impurities in the non-aqueous electrolyte solution is reduced. The mechanisms by which the water content in the non-aqueous electrolyte solution is reduced are believed to be that lithium ions in the solid electrolyte 18 are exchanged with hydrogen ions, changing the crystal structure of the solid electrolyte 18, or that the solid electrolyte 18 reacts with hydroxide ions to produce lithium carbonate. The mechanisms by which the amount of impurities in the non-aqueous electrolyte solution is reduced are believed to be that impurities contained in the non-aqueous electrolyte solution are decomposed by the basic solid electrolyte 18 and adsorbed onto the solid electrolyte 18 as insoluble or poorly soluble compounds. The amount of water and impurities in the non-aqueous electrolyte solution can be controlled by the simple process of contacting the solid electrolyte 18 with the non-aqueous electrolyte solution, without requiring special procedures such as precision distillation of the non-aqueous solvent.

[0049] An example of the contact step is a process in which the nonaqueous electrolyte solution and the solid electrolyte 18 (particles) are placed in a container and stirred. After this process, the solid electrolyte 18 and the nonaqueous electrolyte solution may be placed together in the electrochemical device 10, or a nonaqueous electrolyte solution in which the solid electrolyte 18 is suspended in the nonaqueous electrolyte solution may be placed in the electrochemical device 10. Alternatively, after this process, the solid electrolyte 18 and the nonaqueous electrolyte solution may be separated, and only the nonaqueous electrolyte solution may be supplied to the electrochemical device 10. The nonaqueous electrolyte solution may also be used when manufacturing an electrochemical device other than the electrochemical device 10. Examples of means for separating the solid electrolyte 18 and the nonaqueous electrolyte solution include filtration, sedimentation, and centrifugation. The nonaqueous electrolyte solution may be passed through a column in which the solid electrolyte 18 is placed or a filter holding the solid electrolyte 18, thereby allowing contact and separation of the nonaqueous electrolyte solution and the solid electrolyte 18 to occur simultaneously.

[0050] The electrochemical device 10 is manufactured, for example, as follows: A solid electrolyte 18, an active material 19, and a 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.

[0051] The solid electrolyte 18, active material 20, and conductive additive are mixed, 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.

[0052] A 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 using a winding machine to produce a cylindrical or rectangular cell. Terminals (not shown) are connected to the current collectors 12 and 16, respectively, and a nonaqueous electrolyte is filled into a container (not shown) containing the cell. The container is then sealed to produce an electrochemical device 10 including a positive electrode 11, a separator 14, and a negative electrode 15.

[0053] There are no particular limitations on the binder as long as it binds together the solid electrolyte 18 and the active materials 19, 20. Examples of binders include fluorinated resins, polyolefins, polyimides, polyvinylpyrrolidone, polyvinyl alcohol, cellulose ethers, and rubber-like polymers such as styrene-butadiene rubber. Examples of fluorinated resins include vinylidene fluoride polymers, polychlorotrifluoroethylene, polyvinyl fluoride, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymers, tetrafluoroethylene-hexafluoropropylene copolymers, ethylene-tetrafluoroethylene copolymers, and ethylene-chlorotrifluoroethylene copolymers.

[0054] The ratio (vol %) of the volume of the nonaqueous electrolyte to the combined volume of the nonaqueous electrolyte 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 interfacial resistance of active material 19, which is the reaction field for charge and discharge reactions.

[0055] When the active material layer 13 contains the solid electrolyte 18, the ratio (vol %) of the volume of the solid electrolyte 18 to the combined volume of the solid electrolyte 18 and the active material 19 is preferably 15% or more and 20% or less. This is to ensure the equilibrium potential of the positive electrode 11 and the contact interface between the solid electrolyte 18 and the active material 19.

[0056] The proportions (vol%) of the solid electrolyte 18, active material 19, and non-aqueous electrolyte solution can be determined by analyzing a randomly selected cross-section of the 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 backscattered electron images to determine the area of ​​the solid electrolyte 18, the area of ​​the active material 19, and the area of ​​the non-aqueous electrolyte solution. The proportion (vol%) of the solid electrolyte 18 is determined by considering the proportion of the area of ​​the solid electrolyte 18 to the total area of ​​the solid electrolyte 18 and the active material 19 as the volume proportion. The proportion (vol%) of the non-aqueous electrolyte solution is also determined by considering the proportion of the area of ​​the non-aqueous electrolyte solution to the total area of ​​the active material 19 and the non-aqueous electrolyte solution as the volume proportion.

[0057] 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.

[0058] 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 denoted by the same reference numerals, and the following description will be omitted.

[0059] 3 is a cross-sectional view of an electrochemical element 21 according to the second embodiment. The electrochemical element 21 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 composition in which the electrolyte 23 and a non-aqueous electrolyte solution are mixed may be disposed in the separator 22.

[0060] The electrolyte 23 includes at least one selected from sulfide-based, oxide-based, hydride-based, halide-based, and organic-based electrolytes. The sulfide-based electrolytes include crystalline thiolithium-based, Li 10 GeP2S 12 type, argyrodite type, Li7P3S 11 Examples of oxide electrolytes include oxides with a NASICON structure, oxides with a perovskite structure, and oxides with a garnet structure.

[0061] Examples of hydride electrolytes include solid solutions of LiBH4 with lithium halide compounds (LiI, LiBr, LiCl) and lithium amide (LiNH2). Examples of halide solid electrolytes include Li3YCl6. Examples of organic solid electrolytes include polyethylene oxide, polypropylene oxide, and polyacrylonitrile.

[0062] The electrochemical element 21 is manufactured, for example, as follows: A mixture of a nonaqueous electrolyte and a solid electrolyte 18 is mixed with an active material 19, and then a solvent in which a binder is dissolved is mixed to form a slurry. The slurry is applied onto a current collector 12 and then dried to obtain an active material layer 13.

[0063] A solvent in which a binder is dissolved is mixed with a mixture of a non-aqueous electrolytic solution and an electrolyte 23 to prepare a separator slurry. The separator slurry is applied onto the active material layer 13 and then dried to obtain a positive electrode sheet.

[0064] A mixture of a nonaqueous electrolyte solution and a solid electrolyte 18 is mixed with an active material 20, and then a solvent in which a binder is dissolved is mixed to form a slurry. The slurry is applied onto a current collector 16 and then dried to obtain an active material layer 17. A separator slurry is applied onto the active material layer 17 and then dried to obtain a negative electrode sheet.

[0065] 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.

[0066] In the electrochemical device 21 of the second embodiment, a nonaqueous electrolyte solution with a controlled amount of water and impurities is contained in the positive electrode 11, the negative electrode 15, and the separator 22, and therefore, similar to the electrochemical device 10 of the first embodiment, it is expected to have advantageous effects on ionic conductivity, electrode interface resistance, low-temperature characteristics, and the like. [Example]

[0067] The present invention will be explained in more detail with reference to examples, but the present invention is not limited to these examples.

[0068] (Preparation of solid electrolyte) Li 6.95 Mg 0.15 La 2.75 Sr 0.25 Zr 2.0 O 12Li2CO3, MgO, La(OH)3, SrCO3, and ZrO2 were weighed out so that the total weight of the raw materials was 100g. An excess amount of Li2CO3 was used to account for the volatilization of Li during firing. The weighed raw materials and ethanol were placed in a nylon pot along with zirconia balls and milled 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 sagger, and further fired at 1100°C for 4 hours. The fired powder was crushed in an argon-atmosphere glove box to obtain an oxide-based solid electrolyte (hereinafter referred to as "LLZ"). The garnet-type crystal structure of LLZ was confirmed by powder X-ray diffraction.

[0069] Using a dry jet mill (Aisin Nano Technologies Co., Ltd., Nano Jetmizer (registered trademark) NJ-50 model), the LLZ was milled by passing it through the jet mill twice in a nitrogen atmosphere until the particle size distribution of the LLZ had a median diameter (D50) of 0.8 μm as measured by laser diffraction / scattering. After milling, the LLZ was stored in an argon atmosphere with a dew point of -80°C for at least 7 days. The LLZ after milling and storage is hereinafter referred to as "LLZ powder."

[0070] (Example) A non-aqueous solvent was prepared by mixing lithium battery grade ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate in a 1:1:1 (volume ratio) ratio, and further mixing 1 wt% vinylene carbonate. The electrolyte LiPF6 was added at 1 mol / dm 3 The nonaqueous electrolyte solution (before treatment) and the LLZ powder were placed in a sealed container under an argon atmosphere in a ratio of 5:1 (mass ratio), and the mixture was stirred intermittently for 1 hour, then allowed to stand for 24 hours, and the supernatant was removed to prepare the nonaqueous electrolyte solution in this example.

[0071] (Comparative Example) The nonaqueous electrolyte (before treatment) was used as the nonaqueous electrolyte in the comparative example.

[0072] (Concentration measurement) The non-aqueous electrolyte solutions in the examples were diluted 10 times with pure water, and the concentrations of zirconium, lanthanum, and strontium in the non-aqueous electrolyte solutions before dilution were measured using an inductively coupled plasma mass spectrometer (iCAP·Q, manufactured by Thermo Fisher Scientific Co., Ltd.). The concentrations of zirconium, lanthanum, and strontium in the non-aqueous electrolyte solutions in the comparative examples were also measured in the same manner.

[0073] (Measurement of electrodeposition resistance) A SUS316 case and cap, an 18 mm diameter synthetic resin separator, a 15 mm diameter lithium metal foil, a gasket, and a 16 mm diameter SUS316 spacer and washer for a CR2032 coin cell were prepared, and the case, gasket, lithium metal foil, separator, spacer, washer, and cap were stacked in this order under an argon atmosphere while the nonaqueous electrolyte solution of the example was poured in to prepare a cell of the example. Similarly, a comparative example cell was also prepared by pouring in the nonaqueous electrolyte solution of the comparative example.

[0074] A constant current of a predetermined volume was applied to the cell to charge it. The average voltage when metallic lithium was deposited in an amount of 1 mAh in the range of potentials less noble than the equilibrium potential was divided by the current value during charging to calculate the value (electrodeposition resistance). When the current density, calculated by dividing the current value by the area of ​​the spacer, was 0.25 mA / cm 2 , 1.0mA / cm 2 , 2.5mA / cm 2 The electrodeposition resistance at each time point was calculated, and the average electrodeposition resistance (n = 3) for the cells in the examples was calculated relative to the average electrodeposition resistance (n = 4) for the cells in the comparative examples, which was set to 100. The concentrations of zirconium, lanthanum, and strontium and the electrodeposition resistance (relative values) are shown in Table 1.

[0075] [Table 1]

[0076] According to Table 1, the concentrations of zirconium, lanthanum, and strontium in the nonaqueous electrolytes in the Examples were higher than those in the nonaqueous electrolytes in the Comparative Examples. The nonaqueous electrolytes in the Examples had zirconium concentrations of 200 wtppb or more, lanthanum concentrations of 30 wtppb or more, and strontium concentrations of 10 wtppb or more. It was estimated that fine particles of LLZ powder may be present in the nonaqueous electrolytes in the Examples.

[0077] According to Table 1, the electrodeposition resistance of the cell in the example was smaller than that of the cell in the comparative example, and the current density was 0.25 mA / cm 2 When the current density was 1.0 mA / cm, the electrodeposition resistance was 80.3% of that of the comparative cell. 2 When the current density was 2.5 mA / cm, the electrodeposition resistance was 91.4% of that of the comparative cell. 2 The electrodeposition resistance was 90.3% of the electrodeposition resistance of the cell in the comparative example. The electrodeposition resistance is the resistance when lithium ions coordinated to the solvent molecules of the nonaqueous electrolyte desolvate and deposit on the lithium metal foil during charging, and therefore corresponds to the desolvation resistance of lithium ions. Therefore, it was revealed that the desolvation resistance of the nonaqueous electrolyte in the example was smaller than the desolvation resistance of the nonaqueous electrolyte in the comparative example. The input / output characteristics, such as charge / discharge rate characteristics, of the cell in the example are expected to be improved compared to the cell in the comparative example.

[0078] 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.

[0079] In the embodiment, the case where the desolvation resistance of the non-aqueous electrolyte is reduced by bringing the non-aqueous electrolyte into contact with an oxide-based solid electrolyte 18 having a garnet-type crystal structure containing Li, La, and Zr has been described, but the present invention is not necessarily limited to this. It is, of course, possible to reduce the desolvation resistance of the non-aqueous electrolyte by bringing the non-aqueous electrolyte into contact with a basic oxide containing La or a basic oxide containing Zr instead of the solid electrolyte 18. An electrolyte (fluoride) such as LiPF6 may react with residual moisture in the non-aqueous electrolyte to produce hydrofluoric acid (acidic impurity). However, by bringing the non-aqueous electrolyte into contact with a basic oxide, the basic oxide reacts with the acidic impurity, thereby reducing the acidic impurity contained in the non-aqueous electrolyte.

[0080] The basic oxides containing La have a perovskite structure. 2 / 3-X Li 3X Examples of basic oxides containing Zr include HZr2(PO4)3, NaZr2(PO4)3, which have a NASICON structure, and Zr(HPO4)2·nH2O, which has a two-dimensional layer structure.

[0081] In the embodiments, electrochemical elements 10 and 21 have 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 embodiments 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.

[0082] In the embodiment, the active material layers 13, 17 each contain the solid electrolyte 18, but this is not necessarily limited to this. It is of course possible to omit the solid electrolyte 18 from at least one of the active material layers 13, 17.

[0083] Although not described in the embodiment, it is of course possible to dispose a protective layer containing solid electrolyte 18 between active material layer 17 and separator 14, 22, or between current collector 16 and active material layer 17. Disposing a protective layer between active material layer 17 and separator 14, 22 can reduce short circuits caused by dendrites. Disposing a protective layer between current collector 16 and active material layer 17 can reduce deterioration of current collector 16. [Explanation of symbols]

[0084] 10,21 Electrochemical elements

Claims

1. A non-aqueous electrolyte solution containing at least one of 200 wtppb or more of zirconium and 30 wtppb or more of lanthanum.

2. 2. The nonaqueous electrolyte according to claim 1, further comprising strontium in an amount of 10 wtppb or more.

3. 2. The nonaqueous electrolyte according to claim 1, comprising zirconium and lanthanum, wherein the ratio of the concentration of lanthanum to the concentration of zirconium is 0.2 or more and 0.5 or less.

4. An electrochemical device comprising the nonaqueous electrolyte solution according to any one of claims 1 to 3.

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