Powder, ion conductor, sheet, electrode, separator, and power storage device

Abstract

Provided are: a powder (19) in which growth of dendrites is reduced; an ion conductor (10); a sheet (12); an electrode (12); a separator (15); and a power storage device (11). This powder is a solid electrolyte having a garnet-type crystal structure including Li, La, Zr, and O. When a molded article (23) is obtained by press-molding the powder by applying, in a mold (40) including a pressure application surface (44) having an arithmetic mean roughness not more than 5.0 µm, a pressure of 90 MPa on the pressure application surface, and droplets of a liquid obtained by dissolving lithium bis(fluorosulfonyl)imide in a solvent which is 1-methyl-1-propylpyrrolidinium bis(fluorosulfonyl)imide so as to achieve a salt concentration of 1 mol / L were dropped on a flat surface (23a) made by the pressure application surface, the contact angle θ therebetween is not more than 40°. This ion conductor contains the powder and an electrolytic solution (22). A sheet, an electrode, a separator, and a power storage device according to the present invention include said ion conductor.

Description

Powder, ion conductor, sheet, electrode, separator and electricity storage device

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

[0002] A solid electrolyte having a garnet-type crystal structure containing Li, La, Zr, and O has excellent ionic conductivity, and therefore, Patent Document 1 discloses a prior art technique in which a powder of the solid electrolyte is used in an electricity storage device.

[0003] Patent No. 6797619

[0004] In this type of energy storage device, needle-like dendrites appear due to the deposition of metallic lithium. Because the current density is high in the voids of solid electrolyte powder, dendrites tend to grow in the voids. The growth of dendrites can cause problems, such as short circuits between the electrodes of the energy storage device and a significant decrease in capacity.

[0005] The present invention has been made to solve this problem, and has an object to provide a powder, an ion conductor, a sheet, an electrode, a separator, and an electricity storage device that can reduce dendrite growth.

[0006] A first aspect for achieving this object is a powder of a solid electrolyte having a garnet-type crystal structure containing Li, La, Zr, and O, wherein the powder is press-molded using a mold including a pressure surface having an arithmetic mean roughness of 5.0 μm or less, by applying a pressure of 90 MPa to the pressure surface, and the contact angle when a liquid obtained by dissolving lithium bis(fluorosulfonyl)imide (LiFSI) in 1-methyl-1-propylpyrrolidinium bis(fluorosulfonyl)imide (P13FSI) to a salt concentration of 1 mol / L is dropped onto the flat surface formed by the pressure surface.

[0007] In a second aspect, in the first aspect, the median diameter of the particle size distribution of the powder is 0.1 μm or more and 5.0 μm or less.

[0008] A third aspect is an ion conductor, which includes the powder of the first or second aspect and an electrolyte solution having a lithium salt concentration of 0.01 mol / L or more and 3.0 mol / L or less.

[0009] A fourth embodiment is a sheet comprising the ion conductor of the third embodiment.

[0010] A fifth aspect is an electrode, which includes the ion conductor of the third aspect or is in contact with a protective layer which includes the ion conductor of the third aspect.

[0011] A sixth embodiment is a separator, which includes the ion conductor of the third embodiment or is in contact with a protective layer which includes the ion conductor of the third embodiment.

[0012] A seventh aspect is an electricity storage device, which includes the electrode according to the fifth aspect or the separator according to the sixth aspect.

[0013] The powder of the present invention has good wettability and can reduce non-uniformity of the current density in the powder, thereby reducing dendrite growth.

[0014] FIG. 1 is a cross-sectional view of an electricity storage device according to a first embodiment; FIG. 2 is a diagram schematically showing a garnet-type crystal structure; FIG. 3 is a cross-sectional view of a separator; (a) is a cross-sectional view of a mold for forming a compact, and (b) is a side view of the compact; (a) is a cross-sectional view of an electricity storage device according to a second embodiment; (b) is a cross-sectional view of an electrode according to a fifth embodiment, and (c) is a cross-sectional view of an electrode according to a sixth embodiment.

[0015] 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).

[0016] 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 a metal selected from Ni, Ti, Fe, and Al, an alloy containing two or more of these elements, stainless steel, and a carbon material.

[0017] 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. The active material layer 14 may contain a conductive additive to reduce the resistance of the active material layer 14. Examples of the conductive additive include carbon black, acetylene black, ketjen black, carbon fiber, Ni, Pt, and Ag.

[0018] Examples of the active material 20 include a metal oxide containing a transition metal, a sulfur-based active material, and an organic active material. Examples of the metal oxide containing a transition metal include a metal oxide containing Li and one or more elements selected from Mn, Co, Ni, Fe, Cr, and V. Examples of the metal oxide containing a transition metal include LiCoO ２ , LiNi ０．８ Co ０．１５ Al ０．０５ O ２ , LiMn ２ O ４ , LiNiVO ４ , LiNi ０．５ Mn １．５ O ４ , LiNi １／３ Mn １／３ Co １／３ O ２ and LiFePO ４ is exemplified.

[0019] The sulfur-based active material is S, TiS ２ , NiS, FeS ２ , Li ２ S, MoS ３ Examples of organic active materials include radical compounds such as 2,2,6,6-tetramethylpiperidinoxyl-4-yl methacrylate and polytetramethylpiperidinoxyl vinyl ether, quinone compounds, radialene compounds, tetraciaquinodimethane, and phenazine oxide.

[0020] 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 later). The ion conductor 10 may further include a binder.

[0021] 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 a metal selected from Ni, Ti, Fe, Cu, and Si, an alloy containing two or more of these elements, stainless steel, and a carbon material.

[0022] 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, Li, ４ Ti ５ O １２ , 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.

[0023] The electricity storage device 11 is manufactured, for example, as follows: A slurry is prepared by mixing an electrolyte solution, in which a lithium salt is dissolved in a solvent, with the powder 19, and then mixing the mixture with a solution in which a binder is dissolved in a solvent. The slurry is formed into a sheet and then dried to obtain a green sheet (electrolyte sheet) for the separator 15.

[0024] 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.

[0025] 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.

[0026] 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, and negative electrode sheet, and then pressed together to form an integrated unit. 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 depending on the ion conductor 10.

[0027] Powder 19 is an oxide-based solid electrolyte having a garnet-type crystal structure. Garnet is represented by the general formula C ３ A ２ B ３ O １２ It is expressed as:

[0028] FIG. 2 is a diagram schematically showing a garnet-type crystal structure. In the garnet-type crystal structure, the C site Sc is dodecahedrally coordinated with an oxygen atom Oa, the A site Sa is octahedrally coordinated with an oxygen atom Oa, and the B site Sb is tetrahedrally coordinated with an oxygen atom Oa. In the garnet-type crystal structure, Li can exist in a location that is octahedrally coordinated with an oxygen atom Oa and that becomes a void V. The void V is, for example, a location sandwiched between the B site Sb1 and the B site Sb2. The Li present in the void V is octahedrally coordinated with an oxygen atom Oa that constitutes an octahedron including the tetrahedral face Fb1 that forms the B site Sb1 and the tetrahedral face Fb2 that forms the B site Sb2. For example, Li ７ La ３ Zr ２ O 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 voids V.

[0029] The garnet-type solid electrolyte is X-ray diffraction file No. 422259 (Li) in the Cambridge Structural Database (CSD). ７ La ３ Zr ２ O １２) has an XRD pattern similar to that of No. 422259. 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 due to the substitution of elements, and the arrangement, occupancy, 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.

[0030] Returning to FIG. 1, powder 19 is typically Li ７ La ３ Zr ２ O １２ In the powder 19, some of the constituent elements may be substituted with other elements, or a small amount of other elements may be added without substituting the constituent elements. Examples of the other elements include at least one element selected from the group consisting of Mg, Al, Si, Ca, Ti, V, Ga, Sr, Y, Nb, Sn, Sb, Ba, Hf, Ta, W, Bi, Rb, and lanthanides (excluding La).

[0031] The powder 19 is, for example, Li ６ La ３ Zr １．５ W ０．５ O １２ , Li ６．１５ La ３ Zr １．７５ Ta ０．２５ Al ０．２ O １２ , Li ６．１５ La ３ Zr １．７５ Ta ０．２５ Ga ０．２ O １２ , Li ６．２５ La ３ Zr ２ Ga ０．２５ O １２ , Li ６．４ La ３ Zr １．４ Ta ０．６ O １２ , Li ６．５ La ３ Zr １．７５ Te ０．２５ O１２ , Li ６．７５ La ３ Zr １．７５ Nb ０．２５ O １２ , Li ６．９ La ３ Zr １．６７５ Ta ０．２８９ Bi ０．０３６ O １２ , Li ６．４６ Ga ０．２３ La ３ Zr １．８５ Y ０．１５ O １２ , Li ６．８ La ２．９５ Ca ０．０５ Zr １．７５ Nb ０．２５ O １２ , Li ７．０５ La ３．００ Zr １．９５ Gd ０．０５ O １２ , Li ６．２０ Ba ０．３０ La ２．９５ Rb ０．０５ Zr ２ O １２ Examples include:

[0032] 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) and the molar ratio of each element satisfies all of the following (1) to (3), or contains both Mg and element A and the molar ratio of each element satisfies all of the following (4) to (6). Element A is preferably Sr in order to increase 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

[0033] The median diameter of the particle size distribution of powder 19 is preferably 0.1 to 5.0 μm. This is to ensure that the surface area of ​​powder 19 is of an appropriate size and to ensure the amount of Li ions moving between powder 19 and the electrolyte present on the surface of powder 19. The median diameter of the particle size distribution of powder 19 is determined by a laser diffraction / scattering method.

[0034] 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 the 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.

[0035] FIG. 3 is a cross-sectional view of the separator 15 (see FIG. 1). The ionic conductor 10 contains an electrolyte solution 22 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 － , BF ４ － , BF ３ (CF ３ ) － , BF ３ (C ２ F ５ ) － , P.F. ６ － , ClO ４ － , SbF ６ － , N(SO ２ F) ２ － , N(SO ２ CF ３ ) ２ － , N(SO ２ C ２ F ５ ) ２ － , B(C ６ H ５ ) ４ － , B(O ２C ２ H ４ ) ２ － , C(SO ２ F) ３ － , C(SO ２ CF ３ ) ３ － , C.F. ３ COO － , C.F. ３ SO ２ O － , C ６ F ５ SO ２ O － , B(O ２ C ２ O ２ ) ２ － , RCOO － (R is an alkyl group having 1 to 4 carbon atoms, a phenyl group, or a naphthyl group).

[0036] The anion of the lithium salt is a sulfonyl group -S(=O) ２ - N(SO ２ F) ２ － , N(SO ２ CF ３ ) ２ － , N(SO ２ C ２ F ５ ) ２ － Sulfonylimides such as PF ６ － The sulfonylimide anion is less susceptible to an increase in the viscosity of the electrolyte solution 22 and a decrease in the ionic conductivity even when the salt concentration is high, while the halophosphate ion has a high degree of dissociation. Both are preferred because they can form a highly stable and low-resistance coating (SEI) that reduces the reductive decomposition of the non-aqueous solvent and widens the reduction-side potential window.

[0037] 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.

[0038] 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.

[0039] Examples of amides include formamide, N-methylformamide, dimethylformamide, N-methylacetamide, dimethylacetamide, N-methylpropioamide, hexamethylphosphoramide, and N-methylpyrrolidone. Examples of sulfur compounds include dimethyl sulfoxide, sulfolane, dimethylthioformamide, and N-methylthiopyrrolidone. Examples of ketones include acetone, 4-methyl-2-pentanone, and acetylacetone. Examples of ethers include tetrahydrofuran and monoglyme. Examples of nitro compounds include nitromethane and nitrobenzene. Fluorous solvents are compounds in which the hydrogen atoms of hydrocarbons are replaced with fluorine atoms, and derivatives thereof.

[0040] 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.

[0041] 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 more easily ions are solvated, so a solvent with a relatively high relative dielectric constant εr (εr>20) is preferred. Examples of molecular solvents with a relative dielectric constant greater than 20 include cyclic esters, nitriles, amides, sulfur compounds, acetone, acetylacetone, and nitro compounds. It is of course possible to mix a solvent with a relative dielectric constant greater than 20 with a solvent with a relative dielectric constant of 20 or less in order to adjust the viscosity of the solvent, etc.

[0042] 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 preferably contains one or more cation species selected from the group consisting of ammonium, imidazolium, pyrrolidinium, and piperidinium.

[0043] The anion component of the ionic liquid is not particularly limited. ４ － , N(SO ２ F) ２ － inorganic anions such as B(C ６ H ５ ) ４ － , CH ３ SO ３ － , C.F. ３ SO ３ － , N(SO ２ CF ３ ) ２ － , N(SO ２ C ４ F ９ ) ２ － Examples of organic anions include:

[0044] 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.

[0045] 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.

[0046] 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 a copolymer.

[0047] The concentration of the lithium salt in the electrolyte solution 22 is preferably 0.01 mol / L or more and 3.0 mol / L or less. This is because if the salt concentration of the electrolyte solution 22 is less than 0.01 mol / L, the ionic conductivity tends to decrease significantly, and if the salt concentration of the electrolyte solution 22 exceeds 3.0 mol / L, the ionic conductivity tends to decrease significantly due to an increase in the viscosity of the electrolyte solution 22. The salt concentration of the electrolyte solution 22 is specified, for example, as follows. Here, the ionic conductor 10 constituting the separator 15 will be described, but the ionic conductors 10 constituting the active material layers 14, 18 can also be specified in the same manner.

[0048] First, the separator 15 is crushed and immersed in a solvent to dissolve the electrolyte 22 contained in the separator 15 in the solvent, and then the separator 15 is separated into a solid component and a liquid component using a centrifuge. The Li content of the separated liquid component is determined by inductively coupled plasma spectroscopy (ICP-MS).

[0049] The type of 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 of the lithium salt in electrolyte solution 22 is calculated based on the Li content in the liquid components and the content of the solvent in separator 15.

[0050] 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 solution 22 is preferably 52% or more and less than 100%, and more preferably 61% or more and less than 100%. This is because the combination of the powder 19 and the electrolyte solution 22 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.

[0051] The contents (volume %) of the powder 19 and the electrolyte solution 22 are determined by freezing the separator 15 or embedding the separator 15 in a tetrafunctional epoxy resin or the like and then analyzing a randomly selected area of ​​the cross section of the 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 a backscattered electron image to identify the areas of the powder 19 and the electrolyte solution 22, and the proportions of these areas in the cross section of the separator 15 are regarded as the proportions of the volume of the ionic conductor 10 in the separator 15 to obtain the contents (volume %) of the powder 19 and the electrolyte solution 22.

[0052] The lithium ion conductivity of the ionic conductor 10 is determined by the type and salt concentration of the powder 19 and the electrolyte solution 22. The lithium ion conductivity of the ionic conductor 10 at 25° C. is 1.0×10 －５ The ionic conductivity is preferably 25 S / cm or more in order to ensure the output density of the electricity storage device 11 including the ionic conductor 10.

[0053] The properties of powder 19 will be explained with reference to Figure 4. Figure 4(a) is a cross-sectional view of a mold 40 used to form compact 23 for investigating the properties of powder 19. Figure 4(b) is a side view of compact 23 formed by compressing powder 19. Powder 19 used to make compact 23 has a median diameter of 0.1-5.0 µm in the particle size distribution determined by laser diffraction / scattering method.

[0054] The mold 40 shown in Figure 4(a) includes a die 41 having a cylindrical cross section into which the powder 19 is filled, a lower punch 42 that presses the powder 19 from below, and an upper punch 43 that presses the powder 19 from above. The mold 40 can be made of stainless steel. The pressing surface 44 of the upper punch 43 that comes into contact with the powder 19 is a flat surface set to a surface roughness of 5.0 µm or less, preferably 3.0 µm or less, in arithmetic mean roughness Ra (JIS B0031:2003). The compact 23 is produced by applying a pressure of 90 MPa to the pressing surface 44 without mixing a binder with the powder 19 to increase the mechanical strength of the compact 23.

[0055] As shown in FIG. 4( b), a liquid containing P13FSI dissolved in LiFSI at a salt concentration of 1 mol / L is dropped onto the flat surface 23a of the compact 23 of the powder 19, and the contact angle θ of the droplet 45 formed is measured. The flat surface 23a of the compact 23 is formed by the pressure surface 44 of the upper punch 43. The surface roughness of the flat surface 23a is, for example, an arithmetic mean roughness Ra (JIS B0031:2003) of 1.0 μm or less, more preferably 0.5 μm or less. The contact angle θ is determined by measuring the radius r and height h of the droplet 45 that remains stationary one second after the liquid is dropped onto the flat surface 23a and substituting the results into the equation θ = 2 arctan(h / r) (θ / 2 method). The θ / 2 method assumes that the droplet 45 is a portion of a sphere, and therefore, an amount of liquid is dropped that will produce a droplet 45 that can be made without regard to the effects of gravity.

[0056] The contact angle θ is measured using, for example, a portable contact angle meter PCA-1 (Kyowa Interface Science Co., Ltd.). The molding of the compact 23 and the measurement of the contact angle θ are performed in an inert gas atmosphere (20°C) with a dew point of -80°C dp or lower. Examples of the inert gas include rare gases such as helium and argon, and nitrogen gas. The electrolyte 22 may be the same type as the liquid that forms the droplets 45 for measuring the contact angle θ, or it may be a different type. This is because the liquid is a reagent for identifying the wettability of the powder 19.

[0057] The contact angle θ is an index of the wettability of the powder 19. Powder 19 with a contact angle θ of 40° or less is used. Powder 19 with a contact angle θ of 40° or less has good wettability, and therefore liquid (e.g., electrolyte 22) more easily penetrates between particles (voids) of the powder 19 than powder with a contact angle θ of more than 40°. When the electrolyte 22 sufficiently penetrates between the particles of the powder 19, the electrolyte 22 is widely distributed at the grain boundaries of the powder 19, and lithium ions diffuse widely throughout the powder 19 and the electrolyte 22. Non-uniform ionic conduction promotes the growth of needle-like dendrites due to the precipitation of metallic lithium, but powder 19 with good wettability can reduce non-uniform ionic conduction and therefore reduce dendrite growth.

[0058] Powder 19 having a small particle size is preferable, but compact 23 made from powder 19 having a large particle size has large voids between the particles, so that droplets 45 dropped onto flat surface 23a of compact 23 of powder 19 tend to be absorbed into the voids, resulting in a small contact angle θ. In order to exclude compacts 23 in which droplets 45 have been absorbed into the voids and the contact angle θ has become small, the contact angle θ of droplets 45 may be, for example, 17° or more.

[0059] A second embodiment will be described with reference to Fig. 5. In the first embodiment, an electricity storage device 11 using a powder 19 and an electrolytic solution 22 as the electrolyte was described. In the second embodiment, a case where an ionic conductor 10 is used in a liquid-based lithium ion battery using an electrolytic solution 22 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. 5 is a cross-sectional view of an electricity storage device 24 in the second embodiment.

[0060] The power storage device 24 includes, in 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 electrolyte 22 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 is the same as that described in the first embodiment, so its description will be omitted.

[0061] In the electricity storage device 24 of the second embodiment, the ion conductor 10 is contained in the positive electrode layer 12 and the negative electrode layer 16, and therefore, the stability of operation is increased, similar to the electricity storage device 11 of the first embodiment.

[0062] A third embodiment will be described with reference to Fig. 6. In the first and second embodiments, the positive electrode layer 12, the separator 15, and the 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. 6 is a cross-sectional view of an electricity storage device 26 in the third embodiment.

[0063] 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.

[0064] 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.

[0065] 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.

[0066] 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, 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 the slurry containing the ion conductor 10 to the separator 25 or the current collecting layer 17, or the like.

[0067] 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 the growth of metallic lithium dendrites. Protective layer 32, which is interposed between active material layer 31 and current collecting layer 17, suppresses deterioration of current collecting layer 17.

[0068] Fourth to sixth embodiments will be described with reference to Fig. 7. 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. 7(a) is a cross-sectional view of an insulator 33 in the fourth embodiment.

[0069] 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, with the protective layer 29 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 the growth of dendrites 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.

[0070] 7(b) is a cross-sectional view of an electrode 36 according to the 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 the growth of dendrites from the negative electrode layer 16 of the electricity storage device.

[0071] 7( c) is a cross-sectional view of an electrode 38 according to the 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 the growth of dendrites from the negative electrode layer 16 of the electricity storage device.

[0072] The insulator 33 is disposed in the electric storage device in place of the separator 25 of the electric storage device 24 of the second embodiment or the electric 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.

[0073] 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 in the second embodiment or the electricity storage device 26 in 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 in the second embodiment or the electricity storage device 26 in the third embodiment.

[0074] The present invention will be explained in more detail with reference to examples, but the present invention is not limited to these examples.

[0075] (Preparation of solid electrolyte) Li ６．９５ Mg ０．１５ La ２．７５ Sr ０．２５ Zr ２．０ O １２ So that Li ２ CO ３ , MgO, La(OH) ３ , SrCO ３ , ZrO ２ was weighed. ２ CO ３ The amount of Li was set to about 15 mol% excess in terms of element, taking into account the volatilization of Li during firing. The weighed raw materials and ethanol were placed in a nylon pot together with zirconia balls and ground and mixed in a ball mill for 15 hours. The slurry removed from the pot was dried, placed on an MgO plate, and fired at 900°C for 1 hour, and then further fired at 1200°C for 10 hours to obtain a solid electrolyte.

[0076] (Powder Preparation) (Sample No. 1) Using a dry jet mill (Aisin Nano Technologies Co., Ltd., Nano Jetmizer (registered trademark) NJ-50 type), the solid electrolyte was dry-pulverized by passing it through the jet mill once in an argon atmosphere with a dew point of -80°C dp. This yielded powder in Sample No. 1. The median diameter of the particle size distribution of the powder in Sample No. 1 measured by laser diffraction / scattering method was 0.8 µm.

[0077] (Sample No. 2) Powder in Sample No. 2 was obtained in the same manner as Sample No. 1, except that dry pulverization was performed in an air atmosphere with a dew point of −40° C. dp. The median diameter of the particle size distribution of the powder in Sample No. 2 measured by the laser diffraction / scattering method was 0.8 μm.

[0078] (Sample No. 3) Powder in Sample No. 3 was obtained in the same manner as Sample No. 1, except that dry pulverization was performed in an air atmosphere with a dew point of −10° C. dp. The median diameter of the particle size distribution of the powder in Sample No. 3 measured by a laser diffraction / scattering method was 0.8 μm.

[0079] (Sample No. 4) Powder for Sample No. 4 was obtained in the same manner as Sample No. 1, except that the supply rate of the solid electrolyte to the jet mill was slowed. The median diameter of the particle size distribution of the powder for Sample No. 4 measured by the laser diffraction / scattering method was 0.1 μm.

[0080] (Sample No. 5) Powder for Sample No. 5 was obtained in the same manner as Sample No. 1, except that the supply rate of the solid electrolyte to the jet mill was increased. The median diameter of the particle size distribution of the powder for Sample No. 5 measured by the laser diffraction / scattering method was 3.5 μm.

[0081] (Sample No. 6) Powder for Sample No. 6 was obtained in the same manner as Sample No. 1, except that dry pulverization was performed in an air atmosphere with a dew point of 10°C dp. The median diameter of the particle size distribution of the powder for Sample No. 6 measured by a laser diffraction / scattering method was 0.8 µm.

[0082] (Measurement of Contact Angle) In a glove box (20°C) containing an inert gas atmosphere with a dew point of -80°C dp, the powder was placed in a mold including a circular pressure surface set to a surface roughness of 1.0 µm (arithmetic mean roughness Ra (JIS B0031:2003)), and a pressure of 90 MPa was applied to the pressure surface to produce a disk-shaped molded body in Sample No. 1-6. The arithmetic mean roughness Ra (JIS B0031:2003) of the plane of the molded body formed by the pressure surface was 0.3 µm.

[0083] The contact angle was measured by the θ / 2 method using a portable contact angle meter PCA-1 (Kyowa Interface Science Co., Ltd.). After stopping the flow in the glove box, 1 μL of a liquid prepared by dissolving LiFSI in P13FSI to a salt concentration of 1 mol / L was dropped onto the flat surface of the compact formed on the pressurized surface to create a droplet, and the contact angle of the droplet was measured after 1.0 ± 0.1 seconds. The contact angle was measured three times and the average was calculated.

[0084] (Preparation of Ionic Conductor) The powder in Sample No. 1-6 and lithium hexafluorophosphate (LiPF) were mixed in a solvent of ethylene carbonate and dimethyl carbonate in a volume ratio of 1:1 to give a salt concentration of 1 mol / L. ６ ) was dissolved in an electrolyte solution, and the mixture was mixed in a mortar at a volume ratio of 61:39 to obtain an ionic conductor in Sample No. 1-6.

[0085] (Preparation of Symmetric Cells) In an argon atmosphere, the same amount of ionic conductor was placed in a cylindrical insulating member with an inner diameter of 10 mm, and a compact was obtained by uniaxial pressing (pressure 360 ​​MPa). Li metal foil with a diameter of 10 mm was attached to both sides of the compact, and a symmetric cell for Sample No. 1-6 was obtained.

[0086] (Test Method) A test was conducted in which a constant DC current was passed between the metal foils on both sides of a symmetrical cell for 500 seconds. If no short circuit occurred during that time, the current density was increased slightly and a constant DC current was passed. This was repeated until a short circuit occurred, and the current density when the short circuit occurred was measured. The current density was determined by dividing the average value of the current that flowed when the short circuit occurred by the area of ​​the metal foil. When the current density was 0.4 mA / cm ２ The above samples were judged as A, and the current density was 0.4 mA / cm ２ Samples with less than this were rated B.

[0087] (Results) Table 1 lists the contact angle of the droplet, the median diameter of the powder, and the current density.

[0088]

[0089] According to Table 1, Sample No. 1-5, which had a contact angle of 40° or less, was evaluated as an A, while Sample No. 6, which had a contact angle of more than 40°, was evaluated as a B. Sample No. 1-6 revealed that powders with a contact angle of 40° or less can reduce dendrite growth of metallic lithium.

[0090] Three types of electrolyte solutions were prepared by dissolving lithium bis(fluorosulfonyl)imide (LiFSI) in N-methyl-N-propylpyrrolidinium bis(fluorosulfonyl)imide (P13FSI) to salt concentrations of 0.01 mol / L, 1.0 mol / L, and 3.0 mol / L, respectively. The powder in Sample No. 1 and the electrolyte solution were mixed in a mortar at a volume ratio of 61:39 to obtain three types of ionic conductors. Symmetric cells were prepared using these ionic conductors, and the current density when the symmetric cells were short-circuited was measured. All were rated A. Therefore, it can be said that the ability of the powder to reduce dendrite growth of metallic lithium does not depend on the type or concentration of the electrolyte solution contained in the ionic conductor.

[0091] 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.

[0092] 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 this 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.

[0093] 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. It is sufficient for the power storage device that at least one of the active material layers 14, 18 and the separator 15 contains the ion conductor 10.

[0094] 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.

[0095] 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 separator 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 separator 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.

[0096] REFERENCE SIGNS LIST 10 ion conductor 11, 24, 26 electricity storage device 12 positive electrode layer (sheet, electrode) 15 separator (sheet) 16 negative electrode layer (sheet, electrode) 19 powder 22 electrolyte solution 23 compact 23a plane 25 separator 29, 32 protective layer 40 mold 44 pressing surface

Claims

1. A powder of a solid electrolyte having a garnet-type crystal structure containing Li, La, Zr, and O, wherein the powder is press-molded by applying a pressure of 90 MPa to a pressure surface of a mold having an arithmetic mean roughness of 5.0 μm or less. When a liquid prepared by dissolving lithium bis(fluorosulfonyl)imide in 1-methyl-1-propylpyrrolidinium bis(fluorosulfonyl)imide to a salt concentration of 1 mol / L is dropped onto the flat surface of the pressure surface, the contact angle is 40° or less.

2. The powder according to claim 1, wherein the median diameter of the particle size distribution of said powder is 0.1 μm or more and 5.0 μm or less.

3. An ionic conductor comprising the powder according to claim 1 or 2 and an electrolyte solution having a lithium salt concentration of 0.01 mol / L or more and 3.0 mol / L or less.

4. A sheet comprising the ionic conductor according to claim 3.

5. An electrode comprising the ionic conductor of claim 3.

6. An electrode in contact with a protective layer containing the ionic conductor according to claim 3.

7. An electricity storage device comprising the electrode according to claim 5 or 6.

8. A separator comprising the ionic conductor according to claim 3.

9. A separator in contact with a protective layer containing the ionic conductor according to claim 3.

10. An electricity storage device comprising the separator according to claim 8 or 9.

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