Electrolyte solution, electrolyte composition, and electrochemical element

Abstract

Provided are an electrolyte solution, an electrolyte composition, and an electrochemical element with which it is possible to increase the transference number of ions contributing to energy conversion. The electrolyte solution contains a non-aqueous solvent, and the difference between the loss modulus at 25 DEG C and the storage modulus at 25 DEG C is 2440 Pa or more and 6720 Pa or less. The electrolyte solution preferably has a loss modulus of 5400 Pa or more and a storage modulus of 0.34 Pa or less. The electrolyte composition includes an electrolyte solution and particles of an oxide solid electrolyte. The electrochemical element is provided with an electrode containing an electrolyte solution.

Description

Technical Field

[0001] This invention relates to electrolytes containing non-aqueous solvents, electrolyte compositions, and electrochemical elements. Background Technology

[0002] Electrochemical devices such as lithium-ion secondary batteries convert chemical energy into electrical energy. Patent Document 1 discloses prior art in which an electrolyte containing a non-aqueous solvent is included in the electrochemical device. The electrolyte acts as a medium for ion movement.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2011-44252 Summary of the Invention

[0006] The problem that the invention aims to solve

[0007] Because not only ions that contribute to energy conversion in electrochemical elements move in the electrolyte, but also ions that do not contribute to energy conversion, the prior art suffers from a low transport number of ions that contribute to energy conversion.

[0008] The present invention was made to solve this problem, and aims to provide electrolytes, electrolyte compositions and electrochemical elements that can increase the transport number of ions that contribute to energy conversion.

[0009] Methods for solving problems

[0010] The first method for achieving this purpose is an electrolyte containing a non-aqueous solvent, wherein the difference between the loss modulus and the storage modulus at 25°C is greater than 2440 Pa and less than 6720 Pa.

[0011] The second method is as follows: In the first method, the loss modulus is above 5400 Pa.

[0012] The third method is as follows: In the first or second method, the energy storage modulus is below 0.34 Pa.

[0013] The fourth method is as follows: In any of methods 1 to 3, the concentration of the supporting electrolyte added to the non-aqueous solvent is 1 mol / dm³. 3 Above and 2mol / dm 3 the following.

[0014] The fifth method is as follows: In any of the methods 1 to 4, the supporting electrolyte added to the non-aqueous solvent is a lithium salt.

[0015] The sixth method is an electrolyte composition comprising an electrolyte of any one of methods 1 to 5 and particles of an oxide solid electrolyte.

[0016] The seventh method is as follows: In the sixth method, the oxide solid electrolyte has a garnet-type crystal structure containing Li, La and Zr.

[0017] The eighth method is an electrochemical element that includes electrodes, wherein the electrodes contain an electrolyte of any one of the methods 1 to 5.

[0018] The ninth method is as follows: In the eighth method, the electrode is the positive electrode.

[0019] Invention Effects

[0020] Regarding the electrolyte, electrolyte composition containing the electrolyte, and electrochemical element of the present invention, the difference between the loss modulus and the storage modulus of the electrolyte at 25°C is 2440 Pa or more and 6720 Pa or less, thus increasing the mobility of ions that contribute to energy conversion and improving the transport number. Attached Figure Description

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

[0022] Figure 2 This is a schematic diagram illustrating the crystal structure of garnet.

[0023] Figure 3 This is a cross-sectional view of the electrochemical element according to the second embodiment. Detailed Implementation

[0024] Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. Figure 1 This is a schematic cross-sectional view of the electrochemical element 10 according to the first embodiment. The electrochemical element 10 is a device that directly converts chemical energy into electrical energy. Ions (hereinafter referred to as "charge carriers") that facilitate energy conversion in the electrochemical element 10 can be exemplified by Li. + Na + K + Mg 2+ Cu + Ag + Isocations.

[0025] As an example of electrochemical element 10, an energy storage device will be described. Examples of energy storage devices include lithium-ion batteries, plasma batteries, redox reactions utilizing electrodes, redox reactions of ions in an electrolyte, and electrochemical capacitors with double layers. Electrochemical element 10 sequentially includes a positive electrode 11, a separator 14, and a negative electrode 15.

[0026] The diaphragm 14 is composed of a porous body that is durable for the active materials 19 and 20 contained in the positive electrode 11 and the negative electrode 15, as well as for the electrolyte, and through which charge carriers pass but which are not electronically conductive. Examples of diaphragm 14 include nonwoven fabrics and porous membranes made of cellulose, polypropylene, polyethylene, polyimide, alumina, etc.

[0027] The positive electrode 11 has a current collector 12 and an active material layer 13 superimposed on it. The current collector 12 is a conductive component. Examples of materials for the current collector 12 include metals selected from Ni, Ti, Fe and Al, alloys containing two or more of these elements, stainless steel, and carbon materials.

[0028] The active material layer 13 includes an active material 19. The active material 19 can be appropriately selected according to the type of charge carrier and energy storage device. When the energy storage device is an electrochemical capacitor, the active material 19 is made of a material that can reversibly load anions, such as porous carbon, natural graphite, artificial graphite, easily graphitized carbon (hard carbon), difficult-to-graphitize carbon (soft carbon), carbon fiber, and other carbon-based materials.

[0029] When the energy storage device is an ion battery, the active material 19 can be exemplified by metal oxides containing transition metals, sulfide-based active materials, or organic active materials. When the charge carrier is Li... + In this case, metal oxides containing transition metals can be exemplified by metal oxides comprising one or more elements selected from Mn, Co, Ni, Fe, Cr, and V, as well as Li. Examples of metal oxides containing transition metals include LiCoO2 and LiNi. 0.8 Co 0.15 Al 0.05 O2, LiMn2O4, LiNiVO4, LiNi 0.5 Mn 1.5 O2, LiNi 1 / 3 Mn 1 / 3 Co 1 / 3 O2 and LiFePO4.

[0030] Examples of sulfur-based active substances include S, TiS2, NiS, FeS2, Li2S, MoS3, and sulfur-carbon composites. Examples of organic active substances include free radical compounds such as 2,2,6,6-tetramethylpiperidinoxy-4-yl methacrylate and polytetramethylpiperidinoxy vinyl ether, quinone compounds, axialene compounds, tetracyanobenzoquinone dimethane, and phenazine oxides.

[0031] To reduce the resistance of the active material layer 13, a conductive additive may be included in the active material layer 13. Examples of conductive additives include carbon black, acetylene black, Ketjen black, carbon fiber, Ni, Pt, and Ag.

[0032] In this embodiment, the active material layer 13 comprises an electrolyte composition. The electrolyte composition comprises oxide solid electrolyte particles 18 and an electrolyte solution. Particles 18 may exemplify oxides having a NASICON (sodium superionic conductor) type structure, oxides having a perovskite structure, and oxides having a garnet type structure. Oxides having a NASICON type structure may include oxides containing at least Li, M (M being one or more elements selected from Ti, Zr, and Ge), and P, such as Li(Al, Ti)₂(PO₄)₃ and Li(Al, Ge)₂(PO₄)₃. Oxides having a perovskite structure may include oxides containing at least Li, Ti, and La, such as La. 2 / 3-X Li 3X TiO3.

[0033] Particle 18 is preferably a composite oxide having a garnet-type crystal structure containing Li, La, and Zr. This is because it has a 10 -3 It exhibits ionic conductivity on the order of S / cm and is resistant to reduction by metallic lithium. The garnet-type crystal structure is based on the general formula C3A2B3O. 12 express.

[0034] Figure 2 This diagram schematically illustrates a garnet-type crystal structure. In this structure, the C site Sc is dodecahedral coordinated with the oxygen atom Oa, the A site Sa is octahedral coordinated with Oa, and the B site Sb is tetrahedral coordinated with Oa. In a typical garnet-type crystal structure, oxide solid electrolytes can contain Li at sites octahedral coordinated with Oa, forming vacancies V. Vacancy V is, for example, a site sandwiched between B sites Sb1 and Sb2. The Li present in vacancy V is octahedral coordinated with the oxygen atom Oa forming the octahedron containing the tetrahedron face Fb1 forming B site Sb1 and the tetrahedron face Fb2 forming B site Sb2. For example, Li7La3Zr2O has a garnet-type crystal structure. 12 In this context, La can occupy site C (Sc), Zr can occupy site A (Sa), and Li can occupy site B (Sb) and the void (V).

[0035] Garnet-type crystal structures can be identified using X-ray diffraction. The garnet-type crystal structure corresponds to X-ray diffraction file No. 422259 (Li7La3Zr2O) in the CSD (Cambridge Structural Database). 12Similar XRD patterns. Solid electrolytes sometimes differ from No. 422259 in the types of constituent elements, Li concentration, etc., thus resulting in different diffraction angles and intensity ratios. This representative crystal structure is cubic (space group Ia-3d (- indicates an overline signifying rotation-inversion operation), JCPDS: 84-1753).

[0036] Solid electrolytes with garnet-type crystal structures can typically be exemplified by Li7La3Zr2O. 12 In solid electrolytes, Li7La3Zr2O 12 A portion of the constituent elements may be replaced by other elements, or trace amounts of other elements may be added without replacing the constituent elements. Other elements may be exemplified by 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 the lanthanides (excluding La).

[0037] Solid electrolytes, for example, include Li6La3Zr. 1.5 W 0.5 O 12 Li 6.15 La3Zr 1.75 Ta 0.25 Al 0.2 O 12 Li 6.15 La3Zr 1.75 Ta 0.25 Ga 0.2 O 12 Li 6.25 La3Zr2Ga 0.25 O 12 Li 6.4 La3Zr 1.4 Ta 0.6 O 12 Li 6.5 La3Zr 1.75 Te 0.25 O 12 Li 6.75 La3Zr 1.75 Nb 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 6.8La 2.95 Ca 0.05 Zr 1.75 Nb 0.25 O 12 Li 7.05 La 3.00 Zr 1.95 Gd 0.05 O 12 Li 6.20 Ba 0.30 La 2.95 Rb 0.05 Zr2O 12 .

[0038] The solid electrolyte is particularly preferred to be a solid electrolyte containing at least one of Mg and element A (A being at least one element selected from the group consisting of Ca, Sr, and Ba) and the molar ratio of each element satisfies all of the following (1) to (3); or, a solid electrolyte containing both Mg and element A and the molar ratio of each element satisfies all of the following (4) to (6). To improve the ionic conductivity of the solid electrolyte, element A is preferably Sr.

[0039] (1) 1.33≤Li / (La+A)≤3

[0040] (2) 0 ≤ Mg / (La+A) ≤ 0.5

[0041] (3) 0 ≤ A / (La+A) ≤ 0.67

[0042] (4) 2.0 ≤ Li / (La+A) ≤ 2.5

[0043] (5) 0.01 ≤ Mg / (La+A) ≤ 0.14

[0044] (6) 0.04 ≤ A / (La+A) ≤ 0.17

[0045] The electrolyte contained in the active material layer 13 is a medium for charge carrier movement and is a solution in which the supporting electrolyte is dissolved in a non-aqueous solvent. Non-aqueous solvents are broadly classified into molecular solvents, which are mostly composed of molecules, and ionic liquids, which are composed of cations and anions. One reason for using a non-aqueous solvent in the electrolyte is that it widens the potential window compared to electrolytes using water as a solvent. Ionic liquids are preferred because they can widen the potential window compared to electrolytes using water as a solvent.

[0046] When using molecular solvents as non-aqueous solvents, aprotic solvents are preferred to broaden 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 fluorinated solvents. Mixtures of these may also be used.

[0047] Examples of cyclic esters include propylene carbonate, ethylene carbonate, butyl carbonate, vinylene carbonate, vinyl ethylene carbonate, fluoroethylene carbonate, and other cyclic carbonates; β-propiolactone, γ-butyrolactone, δ-valerolactone, α-pyranone, coumarin, and other lactones. Examples of chain esters include dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, and other chain carbonates. 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.

[0048] Amides can be exemplified as formamide, N-methylformamide, dimethylformamide, N-methylacetamide, dimethylacetamide, N-methylpropionamide, hexamethylphosphoramide, and N-methylpyrrolidone. Sulfur compounds can be exemplified as dimethyl sulfoxide, sulfolane, dimethylthioformamide, and N-methylthiopyrrolidone. Ketones can be exemplified as acetone, 4-methyl-2-pentanone, and acetylacetone. Ethers can be exemplified as tetrahydrofuran and ethylene glycol dimethyl ether. Nitro compounds can be exemplified as nitromethane and nitrobenzene. Fluorinated solvents are compounds and their derivatives in which hydrogen atoms of hydrocarbons are replaced with fluorine atoms.

[0049] The higher the relative permittivity of the solvent and the easier it is for ions to solvate, the easier it is for the reaction that supports the dissolution of the electrolyte into free ions in the molecular solvent to proceed. Therefore, solvents with a relatively high permittivity εr (εr > 20) are preferred. Examples of molecular solvents with a relative permittivity greater than 20 include cyclic esters, nitriles, amides, sulfur compounds, acetone, acetylacetone, and nitro compounds. It is also possible to mix solvents with a relative permittivity greater than 20 with solvents with a relative permittivity less than 20 to adjust the viscosity, etc.

[0050] Ionic liquids are compounds composed of cations and anions, and are liquids at room temperature and pressure. Using an ionic liquid as the solvent in an electrolyte can improve its flame retardancy. Preferred ionic liquids are those made from ammonium or imidazole. pyrrolidine and piperidine One or more species in the group are classified as cationic species.

[0051] There are no particular limitations on the anionic composition of ionic liquids. An example of anionic composition is BF4. - N(SO2F)2 - Inorganic anions, B(C6H5)4 - CH3SO3 - CF3SO3 - N(SO2CF3)2 - N(SO2C4F9)2 - Organic anions, etc.

[0052] Ionic liquids can also be solvated ionic liquids. Examples of solvated ionic liquids include substances formed by dissolving a supporting electrolyte in sulfone solvents such as sulfolane or sulfolane derivatives, or in ethylene glycol dimethyl ether solvents such as tetraethylene glycol dimethyl ether.

[0053] With Li as the charge carrier + In this case, the supporting electrolyte is a lithium salt. An example of a supporting electrolyte anion is OH-. - , halide ions (I - Cl - ,Br - etc.), SCN - BF4 - BF3 (CF3) - BF3 (C2F5) - PF6 - ClO4 - SbF6 - N(SO2F)2 - N(SO2CF3)2 - N(SO2C2F5)2 - B(C6H5)4 - B(O2C2H4)2 - C(SO2F)3 - C(SO2CF3)3 - CF3COO - CF3SO2O - C6F5SO2O - B(O2C2O2)2 - RCOO - (R is an alkyl, phenyl, or naphthyl group with 1-4 carbon atoms, etc.) The supporting electrolyte can also be a mixture of them.

[0054] The supporting electrolyte concentration of the electrolyte solution is 0.2 mol / dm³. 3 The above is preferably 0.5 mol / dm 3 The above, more preferably 1.0 mol / dm 3 The above describes the process. 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 dominance of coordination based on counter anions (so-called ion association). Consequently, reductive decomposition of the electrolyte is suppressed, while the oxidation potential increases and the potential window widens. The preferred concentration of the supporting electrolyte is 4.0 mol / dm³. 3 The following is more preferably 2.0 mol / dm 3 The following is true. This is because the concentration of the supporting electrolyte exceeds 4.0 mol / dm³.3 At that time, the ionic conductivity tends to decrease significantly due to the increase in electrolyte viscosity.

[0055] The electrical conduction of an electrolyte is primarily ionic. The ionic conductivity of an electrolyte is proportional to the product of the concentration and mobility of charge carriers. The concentration of charge carriers is equal to the concentration of the supporting electrolyte. The mobility of charge carriers depends on the ease of molecular movement and is therefore closely related to the viscosity of the solvent. In an electrolyte, solvation occurs when solvent molecules combine with ions dissociated from the supporting electrolyte in the solvent; the ions constituting the supporting electrolyte also interact with each other; and the viscosity of the electrolyte is related to the strength of the intermolecular forces between solvent molecules.

[0056] The viscosity of the electrolyte can be measured using a dynamic viscoelasticity measuring device (rheometer) of parallel circular plates. The rheometer periodically applies shear strain to the electrolyte added between two parallel circular plates by the vibration of the plates, and determines the storage modulus and loss modulus based on the waveform of the shear stress in response and their phase difference.

[0057] The difference between the loss modulus and storage modulus of the electrolyte at 25°C is greater than 2440 Pa and less than 6720 Pa. Although many aspects remain unclear, it is believed that when the difference between the loss modulus and storage modulus is greater than 2440 Pa and less than 6720 Pa, the mobility of anions decreases, while the mobility of cations (charge carriers) relatively increases. This, in turn, can increase the transport number of charge carriers that facilitate energy conversion.

[0058] The loss modulus of the electrolyte at 25°C is preferably 5400 Pa or higher, and more preferably 6800 Pa or lower. The storage modulus of the electrolyte at 25°C is preferably 0.12 Pa or higher, and more preferably 0.34 Pa or lower. These are all for the purpose of further increasing the transport number of the charge carriers.

[0059] Adjusting the viscosity of the electrolyte can be exemplified by modifying the surface of particle 18 before contacting it with the electrolyte. This reduces the storage modulus and increases the loss modulus of the electrolyte. Methods for surface modification of particle 18 include chemical treatment. Chemical treatment can make the surface of particle 18 acidic or alkaline. Examples of chemical treatment include adsorbing a modifier onto the surface of particle 18 in a liquid phase such as a non-aqueous solvent, or reacting the modifier with particle 18 in a gas phase. As a pretreatment for surface modification, it is preferable to apply compressive or shear forces to particle 18 using a rotating container or rotating blades, either individually or in combination, or to disperse particle 18 in a high-speed gas flow to apply an impact force, thereby increasing the surface activity of particle 18.

[0060] When the composite oxide with a garnet-type crystal structure containing Li, La, and Zr is particle 18, lithium hydroxide and lithium carbonate are generated on the surface of particle 18 through a gas-phase reaction between carbon dioxide, water, and particle 18, thus modifying the surface of particle 18 to be alkaline. Since the surface modification of particle 18 is simple, an electrolyte can be easily prepared by contacting particle 18.

[0061] The particles 18 can be placed together with the electrolyte in the active material layer 13 after contacting the particles 18, or the particles 18 can be separated from the electrolyte after contacting the particles 18, and only the electrolyte can be supplied to the active material layer 13. Examples of methods for separating the particles 18 from the electrolyte include filtration, sedimentation, and centrifugation.

[0062] The proportion of impurities such as water, alcohols, epoxides, alkyl lithium carbonates, and products obtained from their further reaction with the electrolyte in the electrolyte is preferably 200 ppm or less, more preferably 100 ppm or less, and particularly preferably 10 ppm or less. This is to reduce the degradation of the electrolyte over time caused by the presence of impurities.

[0063] An adhesive for binding the active material 19 may also be included in the active material layer 13. There are no particular limitations on the adhesive as long as it binds the active material 19. Examples of adhesives include fluorinated resins, polyolefins, polyimides, polyvinylpyrrolidone, polyvinyl alcohol, cellulose ethers, styrene-butadiene rubber, and other rubber-like polymers. Examples of fluorinated resins include vinylidene fluoride polymers, polychlorotrifluoroethylene, polyvinyl fluoride, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymers, tetrafluoroethylene-hexafluoropropylene copolymers, ethylene-tetrafluoroethylene copolymers, and ethylene-chlorotrifluoroethylene copolymers.

[0064] The volume ratio (volume %) of the electrolyte relative to the total volume of the electrolyte and active material 19 contained in the active material layer 13 is preferably 10% or more and 20% or less. This is to reduce the interfacial resistance of the active material 19, which serves as the reaction field for the charge and discharge reaction, while ensuring the equilibrium potential of the positive electrode 11.

[0065] When the active material layer 13 includes particles 18, the volume ratio (volume %) of particles 18 to the total 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 the positive electrode 11 and to ensure the contact interface between particles 18 and active material 19.

[0066] The contents (volume %) of particles 18, active material 19, and electrolyte can be determined by analysis using a scanning electron microscope (SEM) equipped with an energy-dispersive X-ray spectrometer (EDS), with a randomly selected 5000x field of view from the cross-section of the active material layer 13 as the object. In the analysis, the area of ​​particles 18, the area of ​​active material 19, and the area of ​​electrolyte are determined by determining the elemental distribution or by image analysis of the contrast of the reflected electron image. The content (volume %) of particles 18 is obtained by considering the proportion of the area of ​​particles 18 to the total area of ​​active material 19 as the volume proportion. Similarly, the content (volume %) of electrolyte is obtained by considering the proportion of the area of ​​electrolyte to the total area of ​​active material 19 to the total volume proportion.

[0067] The cross-section of the active material layer 13 used in the analysis is a polished surface, a surface obtained by irradiation 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 the active material layer 13 in a tetrafunctional epoxy resin and then polishing it.

[0068] The negative electrode 15 has a current collector 16 and an active material layer 17 superimposed on it. The current collector 16 is a conductive component. 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.

[0069] The active material layer 17 contains active material 20. To reduce the resistance of the active material layer 17, a conductive additive may be included in the active material layer 17. Examples of conductive additives include carbon black, acetylene black, Ketjen black, carbon fiber, Ni, Pt, and Ag. In this embodiment, particles 18 are included in the active material layer 17.

[0070] The active material 20 only needs to be capable of adsorption / release of charge carriers; there are no restrictions on the material. The active material 20 can be appropriately selected according to the type of charge carrier. Examples of active materials 20 include porous carbon, natural graphite, artificial graphite, easily graphitized carbon, difficult-to-graphitize carbon, carbon fibers, and other carbon-based materials, as well as Li4Ti5O. 12 Lithium oxides, Si, Si-Li alloys, compounds whose constituent elements include Si and O (hereinafter referred to as "SiOx", where 0.5 ≤ X ≤ 1.5), metallic lithium, Li-Al alloys, Li-Sn alloys, Li-Si alloys, Li-Mg alloys, Li-Si alloys and other lithium alloys, In-Sb alloys, and Si-Li alloys. SiOx can refer to oxides of Si and substances having a structure in which microcrystalline or amorphous Si is dispersed in an amorphous SiO2 matrix.

[0071] Electrochemical element 10 is manufactured, for example, as follows: A slurry is prepared by mixing particles 18, active material 19, and conductive additive, and further mixing the resulting solution obtained by dissolving a binder in a solvent. After coating the slurry onto current collector 12, it is dried to obtain a positive electrode.

[0072] Particles 18, active material 20, and conductive additives are mixed, and the resulting solution, obtained by dissolving the binder in a solvent, is further mixed to prepare a slurry. After coating the slurry onto the current collector 16, it is dried to obtain the negative electrode sheet.

[0073] A cylindrical or square battery is fabricated by winding the separator 14 (which separates the positive and negative electrodes), the positive electrode, and the negative electrode simultaneously using a winding machine. Terminals (not shown) are connected to the current collectors 12 and 16, respectively. After filling an electrolyte (not shown) containing the battery with a loss modulus of 2440 Pa or more and a storage modulus of 6720 Pa or less, the container is sealed to obtain an electrochemical element 10 containing a positive electrode 11, a separator 14, and a negative electrode 15.

[0074] According to the electrochemical element 10, the active material layer 13 of the positive electrode 11 is filled with an electrolyte whose loss modulus and storage modulus difference is more than 2440 Pa and less than 6720 Pa. This increases the mobility of the charge carriers. Therefore, even if the thickness of the active material layer 13 is increased, thus lengthening the movement distance of the charge carriers during charging and discharging, the moving resistance of the charge carriers remains constant. Because the thickness of the active material layer 13 can be increased, an electrochemical element 10 with large capacity and high-speed charging capability can be obtained.

[0075] Electrolytes with a loss modulus to storage modulus difference of 2440 Pa or more and 6720 Pa or less can increase the transference number of charge carriers compared to conventional electrolytes, thus reducing concentration polarization that is prone to occur during high-speed charging and discharging. Since the operating voltage (terminal voltage) of the electrochemical element 10 can be kept from decreasing for a short period of time, it is beneficial to extend the lifespan of the electrochemical element 10.

[0076] Because the active material layer 13 of the positive electrode 11 is filled with an electrolyte with high charge carrier mobility, the mobility of charge carriers in the active material layer 13 at locations in contact with the particles 18 is ensured, as well as the mobility of charge carriers at locations away from the particles 18. The migration speed (diffusion speed) of the charge carriers is highly temperature-dependent and decreases at lower temperatures; however, because the mobility of the charge carriers is ensured, the operation of the electrochemical element 10 is guaranteed even at low temperatures around it.

[0077] Reference Figure 3The second embodiment will be described. In the first embodiment, the separator 14 separating the positive electrode 11 and the negative electrode 15 was described as a nonwoven fabric or porous membrane made of cellulose, polypropylene, or the like. In contrast, in the second embodiment, the separator 22 separating the positive electrode 11 and the negative electrode 15 includes an electrochemical element 21 containing an electrolyte 23. In the second embodiment, the same reference numerals are used for parts that are the same as in the first embodiment, and the following description is omitted.

[0078] Figure 3 This is a cross-sectional view of the electrochemical element 21 in the second embodiment. The electrochemical element 21 (energy storage device) sequentially includes a positive electrode 11, a separator 22, and a negative electrode 15. The separator 22 contains an electrolyte 23. The electrolyte 23 can be exemplified as a solid or gel-like electrolyte with ion conductivity. Alternatively, a mixture of the electrolyte 23 and an electrolyte solution can be disposed in the separator 22.

[0079] Electrolyte 23 comprises one or more selected from sulfide, oxide, hydride, halide, and organic systems. Examples of sulfide-based electrolytes include crystalline Thio-LISICON (thio-lithium superionic conductor) type, Li... 10 GeP2S 12 Type, sulfide-germanium ore type, Li7P3S 11 Electrolytes of the oxide type, represented by Li₂S-P₂S₅, are glass and glass-ceramic systems. Examples of oxide-based electrolytes include oxides with NASICON-type structures, oxides with perovskite structures, and oxides with garnet-type structures.

[0080] Examples of hydride-based electrolytes include solid solutions of LiBH4 with lithium halides (LiI, LiBr, LiCl) and lithium amides (LiNH2). Examples of halide-based solid electrolytes include Li3YCl6. Examples of organic-based solid electrolytes include polyethylene oxide, polypropylene oxide, and polyacrylonitrile.

[0081] Electrochemical element 21 is manufactured, for example, as follows: Active material 19 is mixed with a mixture of a non-aqueous solvent containing dissolved lithium salt and particles 18, and a solvent containing dissolved binder is further mixed to prepare a slurry. After coating the slurry onto the current collector 12, it is dried to obtain an active material layer 13.

[0082] A slurry for preparing a separator is prepared by mixing a non-aqueous solvent containing dissolved lithium salt with a solvent containing dissolved binder in a mixture of particles 18. After coating the separator slurry onto the active material layer 13, the mixture is dried to obtain a positive electrode sheet.

[0083] Active material 20 is mixed into a mixture of a non-aqueous solvent containing dissolved lithium salt and particles 18, and a solvent containing dissolved binder is further mixed in to prepare a slurry. After coating the slurry onto the current collector 16, it is dried to obtain an active material layer 17. After coating the active material layer 17 with a separator slurry, it is dried to obtain a negative electrode sheet.

[0084] After cutting the positive and negative electrode sheets into specified shapes, they are overlapped and pressed together to form a separator 22 between the positive electrode 11 and the negative electrode 15 to fabricate a battery. Terminals (not shown) are connected to the current collectors 12 and 16 respectively, and the battery is sealed in a container (not shown) to obtain an electrochemical element 21 containing the positive electrode 11, the separator 22, and the negative electrode 15.

[0085] Since the electrochemical element 21 in the second embodiment contains an electrolyte in the positive electrode 11, the negative electrode 15, and the separator 22, it is similar to the electrochemical element 10 in the first embodiment in terms of large capacity and high-speed charging.

[0086] Example

[0087] The invention will be described in more detail through embodiments, but the invention is not limited to these embodiments.

[0088] (Example 1)

[0089] To become Li 6.95 Mg 0.15 La 2.75 Sr 0.25 Zr 2.0 O 12 The following method was used: Li₂CO₃, MgO, La(OH)₃, SrCO₃, and ZrO₂ were weighed. Considering the volatilization of Li during calcination, Li₂CO₃ was added in excess by approximately 15 mol%. The weighed raw materials and ethanol were added together with zirconium oxide pellets into a nylon can and pulverized and mixed using a ball mill for 15 hours. The slurry removed from the can was dried and calcined at 1100°C on an MgO plate for 15 hours. The calcined powder was pulverized and placed in an MgO crucible for further calcination at 1100°C for 4 hours. The calcined powder was then pulverized in an argon-atmospheric glove box to obtain the oxide solid electrolyte (hereinafter referred to as "LLZ").

[0090] The crystal structure of LLZ was confirmed to be garnet-type by powder X-ray diffraction. The median diameter (D50) of the LLZ particle size distribution, determined by laser diffraction / scattering, was 74 μm.

[0091] The LLZ was pulverized using a dry jet mill (Aishin Nano Technologies, Inc., Nano Jetmizer (registered trademark) NJ-50 model) with an initial nozzle pressure of 2.0 MPa, passing through the mill three times under a nitrogen atmosphere at a throughput of 480 g / Hr. The pulverized LLZ was then stored for 24 hours under an argon atmosphere with a dew point of -70°C to obtain the particles of Example 1.

[0092] (Example 2)

[0093] The LLZ was pulverized twice in a jet mill, otherwise the operation was the same as in Example 1, to obtain the particles of Example 2.

[0094] (Example 3)

[0095] The LLZ particles were pulverized in a jet mill once by setting the processing rate to 960 g / Hr, and otherwise operated in the same manner as in Example 1 to obtain the particles of Example 3.

[0096] (Example 4)

[0097] The LLZ was pulverized by passing it through a jet mill 10 times, otherwise the operation was the same as in Example 1, to obtain the particles of Example 4.

[0098] (Determination of particle size distribution and specific surface area)

[0099] The median diameter (D50) of the particle size distribution of Examples 1-4 was determined by laser diffraction / scattering. Additionally, the specific surface area of ​​the particles in Examples 1-4 was determined according to JIS R1626:1996.

[0100] (Preparation and determination of electrolyte)

[0101] In a non-aqueous solvent prepared by mixing ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate in a 1:1:1 (volume ratio), the supporting electrolyte LiPF6 is mixed to achieve a concentration of 1 mol / dm³. 3 Electrolytes were prepared. The particles from Examples 1-4 and the electrolytes were added to test tubes at a ratio of 16.5:83.5 (mass ratio) and mixed for 30 minutes. The test tubes were then capped and allowed to stand for 24 hours to allow the particles to settle and separate. The supernatant was collected to obtain the electrolytes from Examples 1-4. The electrolyte before mixing with the particles was used as the electrolyte for the comparative example.

[0102] The storage modulus and loss modulus of the electrolytes of Examples 1-4 and the Comparative Example were determined using a parallel circular plate type dynamic viscoelasticity measuring device (rheometer). The two parallel circular plates were spaced 0.3 mm apart, with a diameter of 25 mm. The temperature around the electrolyte and the plates was 25°C, the vibration frequency of the plates was 100 Hz, and the strain applied to the electrolyte was 1%.

[0103] (Determination of migration numbers)

[0104] Lithium foil was adhered to two stainless steel plates with a diameter of 20 mm. Thirty-eight polypropylene separators, each 15 μm thick, were overlapped and clamped between the lithium foils. The electrolytes from Examples 1-4 and the Comparative Example were injected into the separators and then fixed with polyimide adhesive tape to obtain the symmetrical cells of Examples 1-4 and the Comparative Example. The fabrication of the symmetrical cells and the following measurements were performed in a glove box filled with argon gas at a dew point of -60°C.

[0105] The lithium-ion transport number is determined by combining AC impedance measurement and chronoamperometry. Specifically, after performing AC impedance measurement on a symmetrical battery, a DC polarization voltage ΔV is applied to the battery, and the change in current flowing through the battery over time is measured. After reaching steady state, AC impedance measurement is performed again. The lithium-ion transport number t is calculated using the following formula.

[0106] t={I S (ΔV-I0R0)} / {I0(ΔV-I S R S )}

[0107] Among them, I S I0 is the steady-state current value, I0 is the current value at the initial stage of voltage application, and R0 ... are the current values. S These are the resistances of the diaphragm-electrode interface before and after chronoamperometry measurement. The applied voltage ΔV measured by chronoamperometry is 3mV.

[0108] The median diameter and specific surface area of ​​the particles in Examples 1-4, the loss modulus, storage modulus, the difference between loss modulus and storage modulus of the electrolytes in Examples 1-4 and the comparative examples, and the transport number of lithium ions are recorded in Table 1.

[0109]

[0110] As shown in Table 1, the transport number of the electrolytes in Examples 1-4 was 0.125 greater than that of the comparative example. Regarding the difference between the loss modulus and storage modulus of the electrolytes, the difference was 2440 Pa or more and 6720 Pa or less in Examples 1-4, compared to 1760 Pa in the comparative example. It can be seen that the difference between the loss modulus and storage modulus of the electrolyte that came into contact with the particles subjected to the prescribed treatment increased. It is clear that when the difference between the loss modulus and storage modulus of the electrolyte is 2440 Pa or more and 6720 Pa or less, the transport number of lithium ions can be increased compared to the electrolyte before contact with the particles (comparative example).

[0111] Regarding the loss modulus of the electrolyte, Examples 1 and 4 had a loss modulus of 5400 Pa or higher, while the Comparative Example had a loss modulus of 2980 Pa. It is evident that the loss modulus of the electrolyte increases when it comes into contact with particles that have undergone the prescribed treatment. It is clear that when the loss modulus of the electrolyte is 5400 Pa or higher, the transport number of lithium ions can be increased.

[0112] Regarding the storage modulus of the electrolyte, Examples 1-4 had a modulus of 0.34 Pa or less, while the Comparative Example had a modulus of 1220 Pa. This demonstrates that an electrolyte with a storage modulus of 0.34 Pa or less can increase the transport number of lithium ions.

[0113] The present invention has been described above based on the embodiments, but the present invention is not limited to any of the above embodiments, and it is easy to deduce that various modifications and variations can be made without departing from the spirit of the present invention.

[0114] In this embodiment, the electrochemical element 10 is described as an electrochemical element having a positive electrode 11 with an active material layer 13 disposed on one side of the current collector 12 and a negative electrode 15 with an active material layer 17 disposed on one side of the current collector 16, but it is not necessarily limited to this. For example, it is certainly possible to apply the elements in this embodiment to an electrochemical element having an electrode layer (so-called bipolar electrode) with an active material layer 13 and an active material layer 17 disposed on both sides of the current collector 12, respectively. If the bipolar electrode and the separator 14 are alternately stacked and housed in a housing (not shown), a so-called bipolar structure electrochemical element can be obtained.

[0115] In this embodiment, the active material layers 13 and 17 are described as containing particles 18, but this is not a limitation. It is also possible to omit particles 18 from at least one of the active material layers 13 and 17.

[0116] Although the description is omitted in the embodiments, it is of course possible to provide a protective layer between the active material layer 17 and the separators 14, 22, or between the current collector 16 and the active material layer 17. The protective layer comprises a composite oxide having a garnet-type crystal structure containing Li, La, and Zr. When a protective layer is provided between the active material layer 17 and the separators 14, 22, short circuits caused by dendrites can be reduced. When a protective layer is provided between the current collector 16 and the active material layer 17, the deterioration of the current collector 16 can be reduced.

[0117] In this embodiment, lithium-ion batteries, plasma batteries, and electrochemical capacitors are used as examples to describe electrochemical elements 10 and 21, but this is not a limitation. Other electrochemical elements may include metal-air batteries and electrolytic capacitors, where the positive electrode active material uses oxygen from the air and the negative electrode active material uses metals such as Li, Zn, Al, Mg, and Fe.

[0118] Symbol Explanation

[0119] 10, 21 Electrochemical Components

[0120] 11 Positive electrode

[0121] 15. Negative electrode (electrode)

[0122] 18 particles

Claims

1. An electrolyte comprising a non-aqueous solvent, wherein the difference between its loss modulus at 25°C and its storage modulus at 25°C is greater than 2440 Pa and less than 6720 Pa.

2. The electrolyte according to claim 1, wherein, The loss modulus is above 5400 Pa.

3. The electrolyte according to claim 1 or 2, wherein, The energy storage modulus is below 0.34 Pa.

4. The electrolyte according to claim 1 or 2, wherein, The concentration of the supporting electrolyte added to the non-aqueous solvent is 1 mol / dm³. 3 Above and 2mol / dm 3 the following.

5. The electrolyte according to claim 1 or 2, wherein, The supporting electrolyte added to the non-aqueous solvent is a lithium salt.

6. An electrolyte composition comprising particles of the electrolyte and oxide solid electrolyte as described in claim 1 or 2.

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

8. An electrochemical element comprising electrodes, wherein, The electrode comprises the electrolyte as described in claim 1 or 2.

9. The electrochemical element according to claim 8, wherein, The electrode is a positive electrode.

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