Powder, ion conductor, sheet and electricity storage device

Abstract

Provided are a powder (19), an ion conductor (10), a sheet (12), and an electricity storage device (11) that can reduce changes in crystal structure. The powder is an oxide-based solid electrolyte having a garnet-type crystal structure, and has a specific surface area (m 2 The inequality y≦0.04x+0.05 is satisfied when x is the mass (mass / g) of the ionic conductor. The ionic conductor includes a powder and an electrolyte solution (23) in which a lithium salt is dissolved in a solvent. The sheet includes the ionic conductor and a binder that binds the solid electrolyte. The electricity storage device includes the powder.

Description

[Technical Field]

[0001] The present invention relates to a powder, an ion conductor, a sheet, and an electricity storage device of a garnet-type oxide solid electrolyte. [Background technology]

[0002] Among oxide-based solid electrolytes, oxide-based solid electrolytes having a garnet-type crystal structure have excellent ionic conductivity, and therefore, prior art in which solid electrolyte powder is used in an electricity storage device is disclosed in Patent Document 1. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6797619 Summary of the Invention [Problem to be solved by the invention]

[0004] However, the crystal structure of the powder can change depending on the surrounding atmosphere, and this change in the powder's crystal structure can lead to a deterioration in electrical properties.

[0005] The present invention has been made to solve this problem, and has an object to provide a powder, an ion conductor, a sheet, and an electricity storage device that can reduce changes in the crystal structure. [Means for solving the problem]

[0006] The first aspect to achieve this object is a powder of an oxide-based solid electrolyte having a garnet-type crystal structure, in which the half-width (°) of the peak of the plane index (042) in the powder X-ray diffraction pattern is defined as y, and the specific surface area (m 2 / g) satisfies the inequality y≦0.04x+0.05 where x is the sum of the two.

[0007] In a second embodiment, in the first embodiment, the lattice constant is 1.30 nm or more.

[0008] In a third aspect, in the first or second aspect, the solid electrolyte contains Li, La, Zr, Mg, and Sr as components.

[0009] A fourth embodiment is an ion conductor, which includes the powder of any one of the first to third embodiments and an electrolyte solution in which a lithium salt is dissolved in a solvent.

[0010] A fifth embodiment is a sheet comprising the powder of any one of the first to third embodiments, or the ion conductor of the fourth embodiment.

[0011] A sixth embodiment is an electrode comprising the powder of any one of the first to third embodiments, or comprising the ion conductor of the fourth embodiment.

[0012] The seventh embodiment is an electrode that is in contact with a protective layer containing the powder of any one of the first to third embodiments, or in contact with a protective layer containing the ion conductor of the fourth embodiment.

[0013] An eighth embodiment is a separator, which comprises the powder of any one of the first to third embodiments, or the ion conductor of the fourth embodiment.

[0014] A ninth embodiment is a separator that is in contact with a protective layer containing the powder of any one of the first to third embodiments, or in contact with a protective layer containing the ion conductor of the fourth embodiment.

[0015] A tenth aspect is an electricity storage device, which includes the electrode according to the sixth or seventh aspect, or the separator according to the eighth or ninth aspect. [Effects of the Invention]

[0016] According to the powder of the present invention, the smaller the half-width of the peak in the powder X-ray diffraction pattern, the fewer the defects that cause changes in the crystal structure. Therefore, the half-width (°) of the peak with the plane index (042) is defined as y, and the specific surface area (m 2When x is the inequality y≦0.04x+0.05 (where x is the total mass of the polymer) and x is the total mass of the polymer, the change in the crystal structure can be reduced by satisfying the inequality y≦0.04x+0.05 (where x is the total mass of the polymer). [Brief explanation of the drawings]

[0017] [Figure 1] 1 is a cross-sectional view of an electricity accumulation device according to a first embodiment. [Figure 2] FIG. 1 is a diagram schematically illustrating a garnet-type crystal structure. [Figure 3] FIG. 2 is a cross-sectional view of a separator. [Figure 4] FIG. 10 is a cross-sectional view of an electricity accumulation device according to a second embodiment. [Figure 5] FIG. 10 is a cross-sectional view of an electricity accumulation device according to a third embodiment. [Figure 6] 10(a) is a cross-sectional view of an insulator in the fourth embodiment, (b) is a cross-sectional view of an electrode in the fifth embodiment, and (c) is a cross-sectional view of an electrode in the sixth embodiment. [Figure 7] This is a correlation diagram in which the half-width (°) of the peak with plane index (042) in the powder X-ray diffraction pattern is defined as y and the specific surface area (m2 / g) is defined as x. DETAILED DESCRIPTION OF THE INVENTION

[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 electricity storage device 11 including an ion conductor 10 according to a first embodiment. The electricity storage device 11 in this embodiment is a secondary battery that uses lithium ions as charge carriers. The electricity storage device 11 includes, in order, a positive electrode layer 12, a separator 15, and a negative electrode layer 16. The positive electrode layer 12, the separator 15, and the negative electrode layer 16 are housed in a case (not shown).

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

[0020] The active material layer 14 includes an ion conductor 10 and an active material 20. The ion conductor 10 includes an oxide-based solid electrolyte powder 19. To reduce the resistance of the active material layer 14, the active material layer 14 may contain a conductive additive. Examples of the conductive additive include carbon black, acetylene black, ketjen black, carbon fiber, Ni, Pt, and Ag.

[0021] The active material 20 is exemplified by a metal oxide containing a transition metal, a sulfur-based active material, and an organic active material. The metal oxide containing a transition metal is exemplified by a metal oxide containing Li and one or more elements selected from Mn, Co, Ni, Fe, Cr, and V. The metal oxide containing a transition metal is exemplified by LiCoO2, LiNi 0.8 Co 0.15 Al 0.05 O2, LiMn2O4, LiNiVO4, LiNi 0.5 Mn 1.5 O4,LiNi 1 / 3 Mn 1 / 3 Co 1 / 3 Examples include O2 and LiFePO4.

[0022] 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.

[0023] The separator 15 separates the positive electrode layer 12 and the negative electrode layer 16, electrically insulating them from each other. The separator 15 is made of an ion conductor 10. The ion conductor 10 includes a powder 19 and an electrolyte (described below). The ion conductor 10 may further include a binder.

[0024] The negative electrode layer 16 is formed by stacking a current collecting layer 17 and an active material layer 18. The current collecting layer 17 is a conductive member. Examples of materials for the current collecting layer 17 include metals selected from Ni, Ti, Fe, Cu, and Si, alloys containing two or more of these elements, stainless steel, and carbon materials.

[0025] The active material layer 18 includes an ion conductor 10 and an active material 21. To reduce the resistance of the active material layer 18, the active material layer 18 may contain a conductive additive. Examples of the conductive additive include carbon black, acetylene black, ketjen black, carbon fiber, Ni, Pt, and Ag. The active material 21 may be Li, a Li-Al alloy, Li4Ti5O 12 Examples of the binder include graphite, In, Si, a Si—Li alloy, and SiO. As with the separator 15, the active material layers 14 and 18 may contain a binder.

[0026] The electricity storage device 11 is manufactured, for example, as follows: A solution in which a binder is dissolved in a solvent is mixed with a mixture of an electrolyte solution in which a lithium salt is dissolved in a solvent and powder 19 to form a slurry. The slurry is formed into a sheet and then dried to obtain a green sheet (electrolyte sheet) for the separator 15.

[0027] An electrolyte solution in which a lithium salt is dissolved in a solvent is mixed with powder 19, and then an active material 20 is mixed with this, followed by a solution in which a binder is dissolved in a solvent to form a slurry. The slurry is applied onto current collecting layer 13 and then dried to obtain a green sheet (positive electrode sheet) for positive electrode layer 12.

[0028] An electrolyte solution in which a lithium salt is dissolved in a solvent is mixed with powder 19, and then an active material 21 is mixed with this, followed by a solution in which a binder is dissolved in a solvent to form a slurry. The slurry is applied onto current collecting layer 17 and then dried to obtain a green sheet (negative electrode sheet) for negative electrode layer 16.

[0029] The electrolyte sheet, positive electrode sheet, and negative electrode sheet are each cut to a predetermined shape, and then stacked in this order: positive electrode sheet, electrolyte sheet, negative electrode sheet, and then pressed together to form a single sheet. Terminals (not shown) are connected to the current collecting layers 13 and 17, respectively, and the device is sealed in a case (not shown), resulting in an electricity storage device 11 including a positive electrode layer 12, a separator 15, and a negative electrode layer 16. The sheet containing the powder 19 in this manner can become an electrolyte sheet, a positive electrode sheet, and a negative electrode sheet by the ion conductor 10.

[0030] Powder 19 is an oxide-based solid electrolyte having a garnet-type crystal structure. Garnet has the general formula C3A2B3O 12 It is expressed as:

[0031] FIG. 2 is a diagram showing a schematic diagram of a garnet-type crystal structure. In the garnet-type crystal structure, Sc in the C-site is dodecahedrally coordinated with an oxygen atom Oa, Sa in the A-site is octahedrally coordinated with an oxygen atom Oa, and Sb in the B-site is tetrahedrally coordinated with an oxygen atom Oa. In the garnet-type crystal structure, Li can exist in a vacancy V, which is a position where the oxygen atom Oa is octahedrally coordinated. 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 12 In the garnet-type solid electrolyte having the composition above, 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.

[0032] The garnet-type solid electrolyte is X-ray diffraction file No. 422259 (Li7La3Zr2O) in the CSD (Cambridge Structural Database). 12) has an XRD pattern similar to that of No. 422259. Various elements are substituted in garnet-type solid electrolytes. For example, Ca, Sr, Ba, etc. are substituted at the C site, Nb, Ta, Sn, Hf, etc. are substituted at the A site, and Al, Ga, etc. are substituted at the B site. The amount of lithium changes with the substitution of elements, and the arrangement, occupancy rate, and occupied sites of lithium ions within the crystal structure change, which in turn changes the ionic conductivity. The diffraction angle and intensity ratio may differ compared to No. 422259 due to the substitution of elements.

[0033] Returning to FIG. 1, powder 19 is typically Li7La3Zr2O 12 Powder 19 may have some of its constituent elements substituted with other elements, or may have a small amount of other elements added without substituting the constituent elements. Examples of other elements include at least one element selected from the group consisting of Mg, Al, Si, Ca, Ti, V, Ga, Sr, Y, Nb, Sn, Sb, Ba, Hf, Ta, W, Bi, Rb, and lanthanides (excluding La).

[0034] Powder 19 is, for example, Li6La3Zr 1.5 W 0.5 O 12 ,Li 6.15 La3Zr 1.75 Ta 0.25 Al 0.2 O 12 ,Li 6.15 La3Zr 1.75 Ta 0.25 Ga 0.2 O 12 ,Li 6.25 La3Zr2Ga 0.25 O 12 ,Li 6.4 La3Zr 1.4 Ta 0.6 O 12 ,Li 6.5 La3Zr 1.75 Te 0.25 O 12 ,Li 6.75 La3Zr 1.75 Nb 0.25 O 12 ,Li 6.9 La3Zr 1.675 Ta0.289 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:

[0035] Powder 19 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) in which the molar ratios of the respective elements satisfy all of the following (1) to (3), or contains both Mg and element A in which the molar ratios of the respective elements satisfy all of the following (4) to (6). Element A is preferably Sr, as this increases the ionic conductivity of powder 19. (1) 1.33≦Li / (La+A)≦3 (2) 0≦Mg / (La+A)≦0.5 (3) 0≦A / (La+A)≦0.67 (4) 2.0≦Li / (La+A)≦2.6 (5) 0.01≦Mg / (La+A)≦0.14 (6) 0.04≦A / (La+A)≦0.17

[0036] The powder 19 made of solid electrolyte may contain, as components, Li, La, Zr, Mg, and Sr. The components contained in the solid electrolyte can be analyzed by an inductively coupled plasma mass spectrometer (ICP-MS).

[0037] When it is difficult to extract only the powder 19 from the positive electrode layer 12 or the negative electrode layer 16, the active material layers 14, 18 can be removed from the electricity storage device 11, and the powder 19 can be analyzed by powder X-ray diffraction of the materials contained in the active material layers 14, 18. The elemental species contained in the powder 19 can be confirmed by elemental mapping of the cross section of the active material layers 14, 18 using time-of-flight secondary ion mass spectrometry (TOF-SIMS), electron probe microanalyzer (EPMA), Auger electron spectroscopy (AES), or the like, or by point analysis of the portion corresponding to the powder 19 (for example, the portion where La or Zr is present).

[0038] The median diameter of the circle-equivalent diameter of the powder 19 appearing on the cross section of the separator 15 is preferably 0.1 to 10 μm, and more preferably 0.1 to 6 μm, in order to ensure that the surface area of ​​the powder 19 is of an appropriate size and to ensure the amount of Li ions that can move between the powder 19 and the electrolyte present on the surface of the powder 19.

[0039] To determine the median diameter of the powder 19, first, a scanning electron microscope (SEM) image of the powder 19 appearing on the cross section of the separator 15 (a polished surface, a surface obtained by irradiating with a focused ion beam (FIB), or a surface obtained by ion milling) is analyzed, and the circle-equivalent diameter is calculated from the area of ​​each particle of the powder 19, and the volume-based particle size distribution is determined. The median diameter is the circle-equivalent diameter at which the cumulative frequency in the particle size distribution is 50%. To ensure accuracy, the image for determining the particle size distribution is taken from a 400 μm area of ​​the separator 15. 2 The area shall be equal to or greater than this.

[0040] The ionic conductor 10 may contain one or more other solid electrolytes in addition to the powder 19 having a garnet-type crystal structure containing Li, La, Zr, and O. Examples of other solid electrolytes include crystalline or amorphous oxide-based solid electrolytes such as perovskite-type, NASICON-type, and LISICON-type, and hydride-based solid electrolytes.

[0041] FIG. 3 is a cross-sectional view of the separator 15 (see FIG. 1). The ionic conductor 10 contains an electrolyte solution 23 in which a lithium salt is dissolved in a solvent. The lithium salt is a compound used for the exchange of cations between the positive electrode layer 12 and the negative electrode layer 16. The anion of the lithium salt is a halide ion (I - ,Cl - ,Br - etc.),SCN - ,BF4 - ,BF3(CF3) - ,BF3(C2F5) - ,PF6 - ,ClO4 - ,SbF6 - ,N(SO2F)2 - ,N(SO2CF3)2 - ,N(SO2C2F5)2 - ,B(C6H5)4 - ,B(O2C2H4)2 - ,C(SO2F)3 - ,C(SO2CF3)3 - ,CF3COO - ,CF3SO2O - ,C6F5SO2O - ,B(O2C2O2)2 - ,RCOO - (R is an alkyl group having 1 to 4 carbon atoms, a phenyl group, or a naphthyl group).

[0042] The anion of the lithium salt is N(SO2F)2, which has a sulfonyl group -S(=O)2-. - ,N(SO2CF3)2 - ,N(SO2C2F5)2 - Sulfonylimides such as PF6 - The halophosphate ions, such as sulfonylimide anions, are preferably used. This is because sulfonylimide anions are less susceptible to increases in electrolyte viscosity and decreases in ionic conductivity even when the salt concentration is high, while halophosphate ions have a high degree of dissociation. Both are preferred because they can form a highly stable and low-resistance coating (SEI), which reduces the reductive decomposition of the non-aqueous solvent and widens the reduction-side potential window.

[0043] Examples of the solvent include aqueous solvents and non-aqueous solvents. 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. As molecular solvents, aprotic solvents are preferred because they broaden the potential window of the non-aqueous 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 sulfone-based solvents. Mixtures of these solvents are also acceptable.

[0044] 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, methyl acetate, and ethyl propionate. Examples of phosphate esters include trimethyl phosphate. Examples of nitriles include acetonitrile, propionitrile, butyronitrile, and benzonitrile.

[0045] 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 their derivatives.

[0046] Examples of sulfone solvents include trimethylene sulfone, sulfolane, difluorosulfolane, dimethyl sulfolane, monofluorosulfolane, 3-methyl sulfolane, ethyl methyl sulfone, and ethyl isopropyl sulfone. Sulfone solvents are preferred because of their high thermal stability.

[0047] The reaction in which an 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 easier it is for ions to solvate, 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. Of course, it is 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 to adjust the viscosity of the solvent, etc.

[0048] 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.

[0049] 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:

[0050] 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 lithium salt is dissolved.

[0051] The ionic conductor 10 may contain a binder that binds the powder 19. Examples of binders include fluorinated resins, polyolefins, polyimides, polyvinylpyrrolidone, polyvinyl alcohol, cellulose ethers, and rubber-like polymers such as styrene-butadiene rubber. Examples of fluorinated resins include vinylidene fluoride polymers, polychlorotrifluoroethylene, polyvinyl fluoride, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymers, tetrafluoroethylene-hexafluoropropylene copolymers, ethylene-tetrafluoroethylene copolymers, and ethylene-chlorotrifluoroethylene copolymers.

[0052] Examples of vinylidene fluoride polymers include homopolymers of vinylidene fluoride and copolymers of vinylidene fluoride and copolymerizable monomers. Examples of copolymerizable monomers include halogen-containing monomers (excluding vinylidene fluoride) and non-halogen copolymerizable monomers. Examples of halogen-containing monomers include chlorine-containing monomers such as vinyl chloride; and fluorine-containing monomers such as trifluoroethylene, tetrafluoroethylene, chlorotrifluoroethylene, hexafluoropropylene, and perfluoroalkyl vinyl ether. Examples of non-halogen copolymerizable monomers include olefins such as ethylene and propylene; acrylic monomers such as acrylic acid, methacrylic acid, and esters or salts thereof; and vinyl monomers such as acrylonitrile, vinyl acetate, and styrene. One or more copolymerizable monomers are polymerized with vinylidene fluoride to form the copolymer.

[0053] Even when handled in an inert gas atmosphere, Powder 19 reacts with traces of moisture and carbon dioxide present in the inert gas, causing changes in its crystal structure, resulting in a decrease in its electrical properties. The causes of changes in the crystal structure of Powder 19 include the atmosphere surrounding Powder 19, defects present in the crystals of Powder 19, disturbances in the crystal structure on the surface of Powder 19, and instability due to the mixing of multiple crystal systems. It is believed that defects and disturbances in the crystal structure of Powder 19 are likely to be the starting points for reactions with moisture and carbon dioxide. Therefore, Powder 19 with fewer defects and disturbances in the crystal structure is less likely to react with moisture and carbon dioxide, and is less likely to undergo changes in its crystal structure.

[0054] Defects and crystal structure disturbances in Powder 19 are easily introduced during the process of crushing a lump of solid electrolyte to produce Powder 19. On the other hand, the finer the powder 19 is crushed by crushing a lump of solid electrolyte, the larger the specific surface area of ​​Powder 19. Therefore, it is estimated that the larger the specific surface area of ​​the crushed Powder 19, the larger the defects and crystal structure disturbances in Powder 19 tend to be.

[0055] The use of high-energy X-rays with short wavelengths from synchrotron radiation allows for accurate measurement of the reciprocal lattice space, so the half-width of the peak measured using the powder X-ray diffraction pattern using synchrotron X-rays (the full width at the scattering angle (2θ) at which the intensity is half the peak value) is used as an index of defects and disturbances in the crystalline structure of powder 19. The half-width of the peak is inversely proportional to the size of the smallest crystallites that make up the crystal, and therefore can be used to accurately determine the quality of the crystallinity.

[0056] The acquired powder X-ray diffraction pattern is corrected by subtracting the peak broadening of the powder X-ray diffraction pattern of the standard sample (NIST-Si) as broadening due to the optical system of the instrument. Because the lowest-angle peak in the powder X-ray diffraction pattern of the standard sample is located at 15.5°, peaks that appear in the powder X-ray diffraction pattern at scattering angles smaller than 15.5° are unreliable. Therefore, the half-width of the strongest peak that appears in the scattering angle range larger than 15.5°, which can be corrected, is used to evaluate the powder 19.

[0057] The positions of peaks that appear in powder X-ray diffraction patterns follow the Bragg equation, which is the physical law of X-ray diffraction and reflection. The Bragg equation is 4 sin 2 θ / λ 2 =1 / d 2 =(h 2 +k 2 +l 2 ) / a 2 (hkl) is the plane index that specifies the type of crystal plane. The left side of the equation can be calculated from the scattering angle 2θ of each peak and the wavelength λ of the incident X-ray. The value of the left side is the sum of the squares of the plane indexes h 2 +k 2 +l 2 This is equal to the ratio of the square of the lattice constant a to the value on the left side of the equation. Divide the value on the left side by a constant to find a number that gives a series of small integer values. Using these integer values, the plane index (hkl) of each peak can be determined. In the powder X-ray diffraction pattern of a garnet-type solid electrolyte, the strongest peak that appears in the range of scattering angles 2θ greater than 15.5°, which can be corrected, has a plane index of (042).

[0058] Powder 19 has a half-width (°) of the peak with a plane index of (042) as y, and a specific surface area (m 2 When x is the inequality y≦0.04x+0.05, where x is the mass of the powder 19 (g / g), the powder 19 satisfies the inequality y≦0.04x+0.05. The powder 19 preferably satisfies the inequality y≦0.04x+0.025, and more preferably satisfies the inequality y≦0.04x+0.005. The powder 19 that satisfies these inequalities is presumed to have few defects in the crystal, little disturbance in the crystal structure on the surface, and a crystal system close to a single phase. The high crystal stability of the powder 19 reduces changes in the crystal structure.

[0059] The specific surface area of ​​Powder 19 is measured in accordance with JIS R1626:1996. The specific surface area of ​​Powder 19 is 10 m 2 / g or more 50m 2 / g or less is preferable because a conductive path on the surface of the powder 19 is appropriately provided.

[0060] The median diameter in the cumulative particle size distribution of the powder 19 measured by a laser diffraction particle size distribution analyzer is preferably 0.1 μm or more and 10 μm or less, and more preferably 0.1 μm or more and 6 μm or less, in order to make the specific surface area of ​​the powder 19 an appropriate size.

[0061] The lattice constant a of powder 19 is preferably 1.30 nm or more. This is because the larger the lattice constant a of powder 19, the more suitable it is for the diffusion of ions that contribute to electrical conductivity. The lattice constant a can be determined from a powder X-ray diffraction pattern. The lattice constant a of powder 19 is preferably 1.32 nm or less to ensure the crystal structure of a garnet-type solid electrolyte. In order to improve the ionic conductivity of powder 19, it is more preferable that the crystal system of powder 19 be a cubic system.

[0062] The lithium salt concentration of the electrolyte solution is preferably 4.0 mol / kg or less. This is because if the salt concentration of the electrolyte solution exceeds 4.0 mol / kg, the viscosity of the electrolyte solution increases, which significantly reduces the ionic conductivity. The salt concentration of the electrolyte solution is determined, for example, as follows. Here, the ionic conductor 10 constituting the separator 15 will be described, but the ionic conductor 10 constituting the active material layers 14 and 18 can also be determined in the same way.

[0063] First, the separator 15 is crushed and immersed in a solvent, and the electrolyte contained in the separator 15 is dissolved in the solvent, and then the solid and liquid components are separated using a centrifuge. The Li content of the separated liquid component is determined using high-frequency inductively coupled plasma spectroscopy (ICP).

[0064] The type of nonaqueous solvent contained in separator 15 is identified by, for example, gas chromatography-mass spectrometry (GC-MS). The identified solvent (hereinafter referred to as a "standard substance") and separator 15 are analyzed by thermogravimetric-differential thermal analysis (TG-DTA), and the analysis results of the standard substance and separator 15 are compared to identify the content of the solvent contained in separator 15. The molar concentration (mol / kg) of the lithium salt in the electrolyte is calculated based on the content of Li in the liquid component and the content of the solvent in separator 15.

[0065] In the ionic conductor 10, the ratio of the volume of the powder 19 to the total volume of the powder 19 and the electrolyte is preferably 52% or more and less than 100%, and more preferably 61% or more and less than 100%. The combination of the powder 19 and the electrolyte can reduce the interface resistance of the powder 19, thereby increasing the operational stability of the electricity storage device 11 in which the ionic conductor 10 is disposed.

[0066] The contents (volume %) of powder 19 and electrolyte are determined by freezing separator 15 or embedding separator 15 in a tetrafunctional epoxy resin or the like and then analyzing a randomly selected area of ​​the cross section of separator 15 at a magnification of 5000 times using an SEM equipped with an energy dispersive X-ray spectrometer (EDS). The analysis involves identifying the distribution of La, Zr, and S and performing image analysis of the contrast of the backscattered electron image to identify the area of ​​powder 19 and the area of ​​electrolyte, and the proportion of this area in the cross section of separator 15 is considered to be the volume proportion of ion conductor 10 in separator 15 to obtain the contents (volume %) of powder 19 and electrolyte.

[0067] The Li ion conductivity of the ionic conductor 10 is determined by the type of powder 19 and the electrolyte, the salt concentration, etc. The lithium ion conductivity of the ionic conductor 10 at 25°C is 1.0 × 10 -5 The ionic conductivity is preferably S / cm or more in order to ensure the output density of the electricity storage device 11 including the ionic conductor 10.

[0068] A second embodiment will be described with reference to Fig. 4. In the first embodiment, an electricity storage device 11 using a powder 19 and an electrolytic solution as the electrolyte was described. In the second embodiment, a case where an ion conductor 10 is used in a liquid-based lithium ion battery using an electrolytic solution as the electrolyte will be described. The same parts as those described in the first embodiment are given the same reference numerals, and the following description will be omitted. Fig. 4 is a cross-sectional view of an electricity storage device 24 in the second embodiment.

[0069] The electricity storage device 24 includes, in this order, a positive electrode layer 12, a separator 25, and a negative electrode layer 16. These are housed in a case (not shown). The separator 25 is made of a porous material that is durable against the active materials 20, 21 and the electrolyte solution contained in the positive electrode layer 12 and the negative electrode layer 16, and that allows lithium ions to pass through but does not have electronic conductivity. Examples of the separator 25 include nonwoven fabrics and porous membranes made of cellulose, polypropylene, polyethylene, polyimide, alumina, etc. The nonaqueous electrolyte solution is the same as that described in the first embodiment, so its description will be omitted.

[0070] In the electricity storage device 24 of the second embodiment, the positive electrode layer 12 and the negative electrode layer 16 contain the ion conductor 10, and therefore, like the electricity storage device 11 of the first embodiment, the stability of operation is increased.

[0071] A third embodiment will be described with reference to Fig. 5. In the first and second embodiments, the positive electrode layer 12, separator 15, and negative electrode layer 16 contain the ion conductor 10. In the third embodiment, the protective layers 29 and 32 contain the ion conductor 10. The same parts as those described in the first and second embodiments are designated by the same reference numerals, and the following description will be omitted. Fig. 5 is a cross-sectional view of an electricity storage device 26 in the third embodiment.

[0072] The power storage device 26 includes, in order, a positive electrode layer 27, a separator 25, and a negative electrode layer 30. These are housed in a case (not shown). The power storage device 26 is a liquid-based lithium-ion battery that uses a non-aqueous electrolyte solution as the electrolyte.

[0073] The positive electrode layer 27 is formed by stacking the current collecting layer 13 and an active material layer 28. The active material layer 28 contains an active material 20. In order to reduce the resistance of the active material layer 28, the active material layer 28 may contain a conductive additive such as carbon black, acetylene black, ketjen black, carbon fiber, Ni, Pt, or Ag.

[0074] A protective layer 29 is disposed between the separator 25 and the negative electrode layer 30. The protective layer 29 includes an ion conductor 10.

[0075] The negative electrode layer 30 is formed by stacking an active material layer 31, a protective layer 32, and a current collecting layer 17 in this order. The active material layer 31 is made of, for example, Li, a Li-Al alloy, a Li-Sn alloy, a Li-Si alloy, a Li-Mg alloy, a Li-Si alloy, or a Si-Li alloy. The protective layer 32 contains an ion conductor 10. The protective layers 29 and 32 are arranged by stacking sheet-like compacts made of a slurry containing the ion conductor 10, or by applying a slurry containing the ion conductor 10 to the separator 25 or the current collecting layer 17, or the like.

[0076] Powder 19, which has a garnet-type crystal structure containing Li, La, Zr, and O and is contained in ionic conductor 10, is resistant to reduction by the metallic lithium of active material layer 31, and therefore protective layer 29 increases the operational stability of electricity storage device 26. Furthermore, protective layer 29 suppresses short circuits caused by dendrite growth of metallic lithium. Protective layer 32, which is interposed between active material layer 31 and current collecting layer 17, suppresses deterioration of current collecting layer 17.

[0077] Fourth to sixth embodiments will be described with reference to Fig. 6. Note that the same parts as those described in the first to third embodiments are given the same reference numerals and the description thereof will be omitted. Fig. 6(a) is a cross-sectional view of an insulator 33 in the fourth embodiment.

[0078] The insulator 33 includes a separator 25 and a protective layer 29 in contact with the separator 25. The separator 25 includes a first interface 34 and a second interface 35 opposite the first interface 34, and the protective layer 29 is disposed at the first interface 34 and the second interface 35. The protective layer 29 disposed on the separator 25 can reduce short circuits caused by dendritic growth of metallic lithium contained in the electricity storage device. Even if a short circuit occurs in the electricity storage device and the separator 25 attempts to thermally deform, the presence of the protective layer 29 allows the shape of the separator 25 to be maintained, thereby suppressing the occurrence of thermal runaway in the electricity storage device.

[0079] 6(b) is a cross-sectional view of an electrode 36 according to a fifth embodiment. The electrode 36 includes a positive electrode layer 12 and a protective layer 29 in contact with the active material layer 14 of the positive electrode layer 12. The electrode 36 has the protective layer 29 disposed at an interface 37 of the active material layer 14 opposite the surface on which the current collecting layer 13 is disposed. The protective layer 29 disposed at the interface 37 of the active material layer 14 can reduce dendrite growth from the negative electrode layer 16 of the electricity storage device.

[0080] 6(c) is a cross-sectional view of an electrode 38 according to a sixth embodiment. The electrode 38 includes a negative electrode layer 16 and a protective layer 29 in contact with the active material layer 18 of the negative electrode layer 16. The electrode 38 has the protective layer 29 disposed at an interface 39 opposite the surface of the active material layer 18 on which the current collecting layer 17 is disposed. The protective layer 29 disposed at the interface 39 of the active material layer 18 can reduce dendrite growth from the negative electrode layer 16 of the electricity storage device.

[0081] The insulator 33 is disposed in the electricity storage device in place of the separator 25 of the electricity storage device 24 of the second embodiment or the electricity storage device 26 of the third embodiment. The insulator 33 may omit one of the two protective layers 29 disposed at the interfaces 34, 35 of the separator 25.

[0082] The electrode 36 is disposed in the electricity storage device in place of the positive electrode layers 12, 27 of the electricity storage device 24 of the second embodiment or the electricity storage device 26 of the third embodiment. The electrode 38 is disposed in the electricity storage device in place of the negative electrode layers 16, 30 of the electricity storage device 24 of the second embodiment or the electricity storage device 26 of the third embodiment. [Example]

[0083] The present invention will be explained in more detail with reference to examples, but the present invention is not limited to these examples.

[0084] Example 1 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 composition satisfies the above formula. Li2CO3 was used in excess of approximately 15 mol% in elemental terms, taking into account the volatilization of Li during firing. The weighed raw materials and ethanol were placed in a nylon pot along with zirconia balls and ground and mixed in a ball mill for 15 hours. The slurry removed from the pot was dried, then placed on an MgO plate and fired at 900°C for 1 hour, and then further fired at 1200°C for 10 hours.

[0085] 35 g of the calcined powder was milled for 168 hours in a ball mill at 400 rpm in the presence of 210 mL of methanol with a viscosity of 0.54 cP at 25°C. The viscosity was measured using a vibration viscometer (VM-ICA-M) (the same device was used to measure viscosity in Examples 2-4 and Comparative Examples 1-3). The milled powder was dried to obtain the powder in Example 1.

[0086] Example 2 The powder of Example 2 was obtained in the same manner as in Example 1, except that 35 g of the calcined powder was ground for 24 hours in a ball mill at 400 rpm in the presence of 210 mL of ethanol having a viscosity of 1.1 cP at 25°C.

[0087] Example 3 The powder of Example 3 was obtained in the same manner as in Example 1, except that 35 g of the calcined powder was ground for 72 hours in a ball mill at 400 rpm in the presence of 210 mL of ethanol having a viscosity of 1.1 cP at 25°C.

[0088] Example 4 The powder of Example 4 was obtained in the same manner as in Example 1, except that 35 g of the calcined powder was ground for 48 hours in the presence of 210 mL of methanol having a viscosity of 0.54 cP at 25°C in a ball mill at 400 rpm.

[0089] (Comparative Example 1) The powder of Comparative Example 1 was obtained in the same manner as in Example 1, except that 35 g of the calcined powder was ground for 168 hours in a ball mill at 400 rpm in the presence of 210 mL of butyl carbitol having a viscosity of 6.6 cP at 25°C.

[0090] (Comparative Example 2) The powder in Comparative Example 2 was obtained in the same manner as in Example 1, except that 35 g of the fired powder was ground for 24 hours in the presence of 210 mL of ethanol having a viscosity of 1.1 cP at 25°C in a ball mill at 105 rpm.

[0091] (Comparative Example 3) The powder of Comparative Example 3 was obtained in the same manner as in Example 1, except that 35 g of the fired powder was pulverized for 168 hours in the presence of 210 mL of ethylene glycol having a viscosity of 16.5 cP at 25°C in a ball mill at 400 rpm.

[0092] (Measurement of specific surface area of ​​powder) The specific surface areas of the powders in Examples 1-4 and Comparative Examples 1-3 were measured in accordance with JIS R1626:1996. Prior to measuring the specific surface area, the powders were degassed in an inert gas (He) atmosphere (at 200°C for 60 minutes) to remove any substances physically adsorbed to the powder surface. The adsorption gas used to measure the specific surface area was a mixed gas (He:N2 = 7:3), and the amount of adsorbed gas was measured by the flow method. Parameters were calculated using the single-point method.

[0093] (Powder X-ray diffraction) Powder X-ray diffraction patterns of the powders in Examples 1-4 and Comparative Examples 1-3 were obtained by powder X-ray diffraction using synchrotron radiation. Powder X-ray diffraction was performed at the Aichi Synchrotron Light Center BL5S2 under the following conditions: camera length: 340 mm, beam size: 0.5 mm x 0.5 mm, incident X-ray wavelength: 0.07 nm, capillary: Lindemann glass 0.3 mm Φ, detector: PILATUS100K. The obtained powder X-ray diffraction patterns were corrected using the powder X-ray diffraction pattern of a standard sample (NIST-Si).

[0094] Based on the powder X-ray diffraction patterns of the powders in Examples 1-4 and Comparative Examples 1-3, the peak with plane index (042) located between 2θ of 16.0° and 17.5° was identified, and the half-width (°) of the peak with plane index (042) was calculated. Furthermore, the lattice constants were calculated from the powder X-ray diffraction patterns.

[0095] (Powder exposure test) The powders for which the half-width of the peak with plane index (042) was measured were exposed to an argon atmosphere with a dew point of -40°C for 168 hours, after which powder X-ray diffraction was performed under the same conditions as for the powder X-ray diffraction before exposure. The half-width (°) of the peak with plane index (042) in each powder X-ray diffraction pattern was measured, and the rate of change in the half-width of the powder after exposure relative to the half-width of the powder before exposure was calculated.

[0096] Table 1 shows the specific surface area, half-width of the peak with plane index (042), and lattice constant of the powders in Examples 1-4 and Comparative Examples 1-3 before exposure, as well as the rate of change in half-width of the peak of the powders after exposure relative to the half-width of the peak of the powders before exposure.

[0097] [Table 1]

[0098] According to Table 1, the powders in Examples 1-4 and Comparative Examples 1-3 had a positive rate of change, and therefore the half width of the peak after exposure was larger than the half width of the peak before exposure. The increase in the half width of the peak due to the exposure test indicates that the crystallite size was reduced by the exposure test, and that the powder reacted with moisture, carbon dioxide, etc. in the atmosphere to which the powder was exposed, resulting in a decrease in the crystallinity of the powder.

[0099] Table 1 reveals that the rate of change in half-width before and after exposure for the powders in Examples 1-4 is smaller than that for the powders in Comparative Examples 1-3. The powders in Examples 1-4 are less susceptible to deterioration in crystallinity than the powders in Comparative Examples 1-3, and are presumed to have fewer disturbances and defects in the crystal structure that cause deterioration in crystallinity. Because the powders in Examples 1-4 are less susceptible to environmental influences, there is a wide range of atmospheres to choose from for storing the powder (acceptable dew point range), and the occurrence of cracks due to changes in the crystal structure of the powder (changes in volume) when used in an electricity storage device and changes in the characteristics of the electricity storage device due to changes in the volume ratio of the powder to the electrolyte can be reduced.

[0100] The viscosity of the solvent used when wet-milling the powder in a ball mill for Example 1-4 was lower than that for Comparative Example 1-3, at 5 cP or less. This is thought to have reduced the adhesion and aggregation of the powder during milling, making it easier for the force of the milling media to be applied uniformly to the powder, resulting in fewer defects being introduced into the crystals and less disruption of the crystal structure on the surface of the powder.

[0101] The lattice constant of the powder in Example 1-4 was 1.30 nm or more. This is presumably because the powder in Example 1-4 has little disorder in the crystal structure. The powder in Example 1-4 has a larger lattice constant than the powder in Comparative Example 1-3, and therefore is presumed to have excellent lithium ion diffusibility.

[0102] Figure 7 shows the relationship between the full width at half maximum (°) of the peak with plane index (042) in the powder X-ray diffraction pattern of the powder before exposure and the specific surface area (m 2 This is a correlation diagram where x is the ratio of the specific surface area of ​​the powder to the specific surface area of ​​the powder. It was revealed that the powder in Example 1-4 satisfies the inequality y≦0.04x+0.05. The powder in Comparative Example 1-3 is in the range of inequality y>0.04x+0.05, so the half-width is large relative to the specific surface area of ​​the powder, and there are many defects and disturbances in the crystal structure. It is therefore presumed that the crystallinity of the powder was reduced by the exposure test.

[0103] The powders in Examples 1-4 satisfy the inequality y≦0.04x+0.025, thereby reducing defects and disturbances in the crystal structure, and are therefore presumed to be able to further reduce the deterioration of the powder's crystallinity due to the exposure test.The powders in Examples 1-4 satisfy the inequality y≦0.04x+0.005, thereby reducing defects and disturbances in the crystal structure, and are therefore presumed to be able to further reduce the deterioration of the powder's crystallinity due to the exposure test.

[0104] Oxide-based solid electrolytes with a garnet-type crystal structure containing Li, La, and Zr have the excellent characteristics of bulk conductivity comparable to nonaqueous electrolytes and electrochemical stability against metallic lithium. However, oxide-based solid electrolytes are highly reactive, reacting with moisture, carbon dioxide, etc. to form a resistive layer, resulting in high interfacial resistance. Therefore, energy storage devices employing compacts of solid electrolyte powders compacted by pressure molding have difficulty achieving practical battery performance. In contrast, the examples demonstrate that solid electrolytes that are less susceptible to reactions with moisture, carbon dioxide, etc. can be obtained. Therefore, energy storage devices with practical battery performance can be expected to be developed by using compacts of powders compacted by pressure molding, or by using compacts in which powders and electrolyte solutions coexist, without forming and sintering solid electrolyte powders to form high-density sintered bodies.

[0105] 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.

[0106] In the embodiment, the electricity storage device 11 has been described as including a positive electrode layer 12 in which an active material layer 14 is provided on one side of a current collecting layer 13, and an negative electrode layer 16 in which an active material layer 18 is provided on one side of a current collecting layer 17, but the present invention is not necessarily limited to this. For example, it is of course possible to apply each element in the embodiment to an electricity storage device including electrode layers in which an active material layer 14 and an active material layer 18 are provided on both sides of a current collecting layer 13 (so-called bipolar electrodes). If bipolar electrodes and separators 15 are alternately stacked and housed in a case (not shown), an electricity storage device with a so-called bipolar structure can be obtained.

[0107] In the embodiment, the active material layers 14, 18 and the separator 15 all contain the ion conductor 10, but this is not necessarily limited to this. The power storage device may be configured such that at least one of the active material layers 14, 18 and the separator 15 contains the ion conductor 10.

[0108] In the embodiments, the power storage devices 11, 24, and 26 are described as being composed of lithium-ion batteries, but the present invention is not necessarily limited to this. It is clear that other power storage devices may include the powder 19. Examples of other power storage devices include electrochemical capacitors. Examples of electrochemical capacitors include redox capacitors that utilize redox reactions and hybrid capacitors that are asymmetric cells that combine an electric double layer capacitor with the powder 19.

[0109] Although not described in the embodiment, it is of course possible to dispose a protective layer 29 between the active material layer 18 and the separators 15, 25, or between the current collecting layer 17 and the active material layer 18. Disposing a protective layer 29 between the active material layer 18 and the separators 15, 25 can reduce short circuits caused by dendrites. Disposing a protective layer 29 between the current collecting layer 17 and the active material layer 18 can reduce deterioration of the current collecting layer 17. [Explanation of symbols]

[0110] 10 Ionic conductors 11,24,26 Energy storage devices 12 Positive electrode layer (sheet, electrode) 15 Separator (sheet) 16 Negative electrode layer (sheet, electrode) 19 powder 23 Electrolyte 25 Separator 29,32 Protective layer

Claims

1. A powder of an oxide-based solid electrolyte having a garnet-type crystal structure, The half-width (°) of the peak with plane index (042) in the powder X-ray diffraction pattern is defined as y, and the specific surface area (m ２ / g) is defined as x, the powder satisfies the inequality y≦0.04x+0.

05.

2. 2. The powder according to claim 1, wherein the lattice constant is 1.30 nm or more.

3. 2. The powder according to claim 1, wherein the solid electrolyte contains Li, La, Zr, Mg, and Sr as components.

4. The powder according to any one of claims 1 to 3, an electrolyte solution in which a lithium salt is dissolved in a solvent; and

5. A sheet comprising the powder according to any one of claims 1 to 3.

6. An electrode comprising the powder according to any one of claims 1 to 3.

7. An electrode in contact with a protective layer comprising the powder according to any one of claims 1 to 3.

8. An electricity storage device comprising the electrode according to claim 6.

9. An electricity storage device comprising the electrode according to claim 7.

10. A separator comprising the powder according to any one of claims 1 to 3.

11. A separator in contact with a protective layer containing the powder according to any one of claims 1 to 3.

12. An electricity storage device comprising the separator according to claim 10.

13. An electricity storage device comprising the separator according to claim 11.

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