Powder, sheet, and secondary battery

Abstract

Provided are: a powder with which it is possible to reduce peeling at the interface of a sheet (14), and a corresponding sheet and secondary battery (10) The powder contains solid electrolyte particles (18), and the angularity of a cross-sectional contour (19) of the particles is 300-1600. The particles more preferably have a Vickers hardness of 80 HV or more. This sheet contains said powder. This secondary battery includes, in order, a positive electrode (11), an electrolyte layer (14), and a negative electrode (15). The negative electrode includes an active material layer (17) comprising lithium metal. The electrolyte layer includes said sheet.

Description

Powder, sheet and secondary battery

[0001] The present invention relates to a solid electrolyte powder, a sheet containing the powder, and a secondary battery.

[0002] Patent Document 1 discloses a prior art related to a secondary battery including, in order, a positive electrode, an electrolyte layer (sheet) containing a powder of a solid electrolyte, and a negative electrode.

[0003] Japanese Patent Application Laid-Open No. 2022-108509

[0004] In this type of secondary battery, the negative electrode repeatedly expands and contracts during charging and discharging, which causes a problem in that peeling easily occurs at the interface between the sheet and the negative electrode due to changes in the thickness of the negative electrode.

[0005] The present invention has been made to solve this problem, and has an object to provide a powder, a sheet, and a secondary battery that can reduce peeling at the interface of the sheet.

[0006] A first aspect for achieving this object is a powder containing particles of a solid electrolyte, the particles having a cross-sectional contour angularity of 300 or more and 1600 or less.

[0007] In a second aspect, in the first aspect, the particles have a Vickers hardness of 80 HV or more.

[0008] A third embodiment is a sheet comprising the powder of the first or second embodiment.

[0009] A fourth aspect is a secondary battery comprising, in order, a positive electrode, an electrolyte layer, and a negative electrode, the negative electrode comprising an active material layer made of lithium metal, and the electrolyte layer comprising the sheet of the third aspect.

[0010] According to the present invention, in a powder containing solid electrolyte particles, the particles have a cross-sectional contour angularity of 300 to 1600. In a secondary battery including, in order, a positive electrode, an electrolyte layer made of a sheet, and a negative electrode, when the sheet contains the powder, the corners of the particles tend to penetrate into the negative electrode, increasing the peeling force between the sheet and the negative electrode, thereby reducing interfacial peeling of the sheet.

[0011] It is a cross-sectional view of a secondary battery according to an embodiment. It is a diagram showing a garnet-type crystal structure. It is a cross-sectional view of a particle.

[0012] Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. FIG. 1 is a schematic cross-sectional view of a secondary battery 10 containing a powder according to one embodiment. The secondary battery 10 includes, in order, a positive electrode 11, an electrolyte layer 14, and a negative electrode 15. The positive electrode 11, the electrolyte layer 14, and the negative electrode 15 are housed in a case (not shown). Charge carriers in the secondary battery 10 that carry charge between the positive electrode 11 and the negative electrode 15 include metal ions such as lithium ions, sodium ions, potassium ions, and calcium ions. The metal ions are preferably ions of alkali metals, with lithium ions being particularly preferred.

[0013] The positive electrode 11 has a current collecting layer 12 and an active material layer 13 stacked on top of each other. The current collecting layer 12 is a conductive member. Examples of materials for the current collecting layer 12 include a metal selected from Ni, Ti, Fe, and Al, an alloy containing two or more of these elements, stainless steel, and a carbon material.

[0014] The active material layer 13 contains an active material. To reduce the resistance of the active material layer 13, the active material layer 13 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 layer 13 may contain one or more of a solid electrolyte powder, a binder, and an electrolytic solution (all of which will be described later).

[0015] Examples of the active material contained in the active material layer 13 include a metal oxide containing a transition metal, a sulfur-based active material, and an organic active material. When the charge carrier is lithium ions, 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 O２ and LiFePO ４ is exemplified.

[0016] 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.

[0017] The electrolyte layer 14 separates the positive electrode 11 and the negative electrode 15, electrically insulating them from each other. The electrolyte layer 14 contains a powder of a solid electrolyte. The electrolyte layer 14 may also contain a binder that binds the powder and an electrolytic solution.

[0018] Examples of the binder contained in the electrolyte layer 14 include fluorinated resins, polyolefins, polyimides, polyvinylpyrrolidone, polyvinyl alcohol, cellulose ethers, styrene-butadiene rubber, and other rubber-like polymers. Examples of the fluorinated resins include vinylidene fluoride polymers, polychlorotrifluoroethylene, polyvinyl fluoride, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymers, tetrafluoroethylene-hexafluoropropylene copolymers, ethylene-tetrafluoroethylene copolymers, and ethylene-chlorotrifluoroethylene copolymers.

[0019] 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.

[0020] Examples of the solvent for the electrolyte solution contained in the electrolyte layer 14 include aqueous solvents and nonaqueous solvents. Nonaqueous solvents are broadly classified into molecular solvents, which are mostly composed of molecules, and ionic liquids, which are composed of cations and anions. Among molecular solvents, aprotic solvents are preferred because they broaden the potential window of the nonaqueous electrolyte solution. 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.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] 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 C４ F ９ ) ２ － Examples of organic anions include:

[0026] The ionic liquid may be a solvated ionic liquid, such as a sulfone-based solvent such as sulfolane or a sulfolane derivative, or a glyme-based solvent such as tetraglyme, in which an electrolyte is dissolved.

[0027] The negative electrode 15 has a current collecting layer 16 and an active material layer 17 superposed thereon. The current collecting layer 16 is a conductive member. Examples of the material for the current collecting layer 16 include a metal selected from Ni, Ti, Fe, and Cu, an alloy containing two or more of these elements, stainless steel, and a carbon material.

[0028] The active material layer 17 contains an active material. The active material is made of lithium metal. Examples of lithium metal include simple lithium, lithium alloys made of metallic lithium and a non-metallic element or a metallic element other than lithium, and lithium alloys such as Li-Al alloys, Li-Sn alloys, Li-Si alloys, Li-Mg alloys, and alloys of metallic lithium and Li. ４ Ti ５ O １２ Examples include alloys with lithium transition metal oxides or lithium transition metal nitrides such as those mentioned above.

[0029] The solid electrolyte powder contained in the electrolyte layer 14 is an inorganic material, and examples thereof include one or more types selected from sulfides, oxides, hydrides, and halides. The solid electrolyte may be crystalline or amorphous. Sulfide-based solid electrolytes include crystalline thiolisicone-type, Li １０ GeP ２ S １２ type, argyrodite type, Li ７ P ３ S １１ Type, Li ２ S-P ２ S ５ Examples of hydride-based solid electrolytes include glass and glass ceramics, such as LiBH ４ and lithium halide compounds (LiI, LiBr, LiCl) and lithium amide (LiNH ２) is an example of a solid solution. ３ YCl ６ is exemplified.

[0030] Examples of oxide-based solid electrolytes include crystalline and amorphous materials such as NASICON-based materials, LISICON-based materials, oxides having a perovskite structure, and oxides having a garnet structure. NASICON-based materials are represented by the general formula A ｘ M ２ (TO ４ ) ３ Examples of A include Na and Li, examples of M include Zr, Ti, V, Mn, Cr, Fe, Ni, Al, and Ge, and examples of T include P, Si, and As. For example, Na ３ V ２ (P.O. ４ ) ３ , Li １＋ｘ Al ｘ Ti ２－ｘ (P.O. ４ ) ３ , Li １＋ｘ Ge ｘ Ti ２－ｘ (P.O. ４ ) ３ Examples include:

[0031] LISICON-based materials are Li ４－２ｘ Zn ｘ GeO ４ (0≦x≦1). Oxides having a perovskite structure include Li ｘ La （１－ｘ）／３ NbO ３ , La ２／３－Ｘ Li ３Ｘ TiO ３ (0≦x≦1). The crystal structure of a garnet-type oxide is represented by the general formula C ３ A ２ B ３ O １２ Oxides having a garnet structure are preferred because they have excellent resistance to reduction by lithium metal.

[0032] 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.

[0033] 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.

[0034] Garnet-type solid electrolytes are typically Li ７ La ３ Zr ２ O １２The solid electrolyte 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 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).

[0035] The solid electrolyte is, for example, Li ６ La ３ Zr １．５ W ０．５ O １２ , Li ６．１５ La ３ Zr １．７５ Ta ０．２５ Al ０．２ O １２ , Li ６．１５ La ３ Zr １．７５ Ta ０．２５ Ga ０．２ O １２ , Li ６．２５ La ３ Zr ２ Ga ０．２５ O １２ , Li ６．４ La ３ Zr １．４ Ta ０．６ O １２ , Li ６．５ La ３ Zr １．７５ Te ０．２５ O １２ , Li ６．７５ La ３ Zr １．７５ Nb ０．２５ O １２ , Li ６．９ La ３ Zr １．６７５ Ta ０．２８９ Bi ０．０３６ 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 １．７５Nb 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:

[0036] The solid electrolyte preferably contains at least one of Mg and element A (A is at least one element selected from the group consisting of Ca, Sr, and Ba), with the molar ratio of each element satisfying all of the following (1) to (3), or contains both Mg and element A, with the molar ratio of each element satisfying all of the following (4) to (6). Element A is preferably Sr, in order to increase the ionic conductivity of the solid electrolyte. (1) 1.33≦Li / (La+A)≦3 (2) 0≦Mg / (La+A)≦0.5 (3) 0≦A / (La+A)≦0.67 (4) 2.0≦Li / (La+A)≦2.6 (5) 0.01≦Mg / (La+A)≦0.14 (6) 0.04≦A / (La+A)≦0.17

[0037] The secondary battery 10 is manufactured, for example, as follows: A mixture of an electrolyte solution in which an electrolyte is dissolved in a solvent and a powder of a solid electrolyte is mixed with a solution in which a binder is dissolved in a solvent to produce a slurry for the electrolyte layer 14. The slurry is then applied onto the active material layer 17 of the negative electrode sheet, which is made by laminating lithium metal (active material layer 17) on the current collecting layer 16, and then dried to obtain a first sheet.

[0038] An active material is mixed with an electrolytic solution in which an electrolyte is dissolved in a solvent and a powder of a solid electrolyte, and then a solution in which a binder is dissolved in a solvent is mixed to prepare a slurry for the active material layer 13. The slurry is applied onto the current collecting layer 12 and then dried to obtain a sheet for the positive electrode 11 (positive electrode sheet). A slurry for the electrolyte layer 14 is applied onto the active material layer 13 of the positive electrode sheet and then dried to obtain a second sheet.

[0039] After the first sheet and the second sheet are cut into a predetermined shape, the first sheet and the second sheet are stacked with the electrolyte layers 14 facing each other and then compressed together to form an integrated unit. Terminals (not shown) are connected to the current collecting layers 12 and 16, respectively, and the resulting product is sealed in a case (not shown), thereby obtaining a secondary battery 10 including a positive electrode 11, an electrolyte layer 14, and a negative electrode 15.

[0040] The secondary battery 10 can also be manufactured as follows: A negative electrode sheet, a positive electrode sheet, and an electrolyte sheet formed from a slurry for the electrolyte layer 14 are each prepared, and the positive electrode sheet, electrolyte sheet, and negative electrode sheet are each cut to a predetermined shape. The positive electrode sheet, electrolyte sheet, and negative electrode sheet are then stacked in this order and compressed together. Terminals (not shown) are connected to the current collecting layers 12 and 16, respectively, and the battery is sealed in a case (not shown), thereby obtaining the secondary battery 10 including the positive electrode 11, electrolyte layer 14, and negative electrode 15.

[0041] The sheet may be pressed by various means such as a roll press, a uniaxial press, a hydrostatic press, etc. Heating the sheet when pressing the sheet is preferred because the binder and active material layer 17 contained in the sheet are softened.

[0042] 3 is a cross-sectional view of a particle 18 constituting the solid electrolyte powder contained in the electrolyte layer 14. The solid electrolyte powder is an aggregate of particles 18. The angularity of the particle 18 is calculated according to formula (1) when the largest circle 20 inscribed in the outline 19 of the cross section of the particle 18 is drawn.

[0043]

[0044] In formula (1), x ｉ is the distance between the vertices of all the convex portions (number n, n=7 in this embodiment) of the contour 19 and the center 21 of the circle 20, and a ｉ is the angle formed by the two half lines (two tangents to the convex portion) that make up the convex portion, and r is the radius of the circle 20.

[0045] The angularity of the cross-sectional outline 19 of the particles 18 is 300 or more and 1600 or less. The angularity of the particles 18 being 300 or more and 1600 or less means that the convex portions of the particles 18 are sharp. If the angularity of the particles 18 is 300 or more and 1600 or less, when the electrolyte layer 14 is pressed against the active material layer 17 of the negative electrode 15 during the manufacturing process of the secondary battery 10, the sharp convex portions (corners) of the particles 18 are likely to penetrate into the active material layer 17. Since the peeling force between the electrolyte layer 14 and the negative electrode 15 is increased, interfacial peeling of the electrolyte layer 14 can be reduced.

[0046] If the angularity of the particles 18 decreases, the particles 18 become closer to a sphere, and if the angularity of the particles 18 increases, the particles 18 become elongated. In either case, the particles 18 become less likely to penetrate into the active material layer 17, and the peeling force between the electrolyte layer 14 and the negative electrode 15 tends to decrease.

[0047] The active material layer 17 of the negative electrode 15 repeatedly expands and contracts as the secondary battery 10 is charged and discharged. If peeling occurs at the interface between the electrolyte layer 14 and the active material layer 17 due to a change in the thickness of the active material layer 17, the amount of lithium ions supplied in the in-plane direction of the active material layer 17 will vary greatly, making it more likely that needle-shaped dendrites will appear due to the precipitation of metallic lithium. When dendrites grow, they can cause a short circuit between the positive electrode 11 and the negative electrode 15 or significantly reduce capacity.

[0048] In contrast, since the electrolyte layer 14 contains particles 18 whose cross-sectional outline 19 has a degree of angularity of 300 or more and 1600 or less, the particles 18 penetrate into the active material layer 17, reducing peeling of the electrolyte layer 14 from the negative electrode 15. This reduces the variation in the amount of lithium ions supplied in the in-plane direction of the active material layer 17 and reduces the occurrence of dendrites, thereby reducing the occurrence of short circuits between the positive electrode 11 and the negative electrode 15. Furthermore, the capacity retention rate of the secondary battery 10 can be improved.

[0049] To calculate the angularity of the solid electrolyte particles 18, the electrolyte layer 14 is first embedded in a tetrafunctional epoxy resin or the like, or the particles 18 are mixed with a thermosetting resin and solidified, and then an image of the particles 18 appearing on a cross section (a polished surface, a surface obtained by irradiating with a focused ion beam (FIB), or a surface obtained by ion milling) is obtained using a scanning electron microscope (SEM). The image magnification can be, for example, 5,000 to 10,000 times. To increase the accuracy of identifying the outlines 19 of the particles 18, the image resolution is preferably 220 dpi or higher.

[0050] Since the shape of the outline 19 cannot be determined for particles with broken outlines 19, and it is difficult to determine the shape of the outline 19 for small particles, 20 or more particles 18 whose entire outline 19 is included in the image are selected, and the angularity is calculated for each particle 18, since large particles 18 penetrate deeper into the active material layer 17 than small particles 18. Therefore, it is preferable to select particles 18 whose diameter of the circle 20 is 0.2 μm or more to calculate the angularity.

[0051] The angularity of all of 20 or more particles 18 selected from the image is 300 or more and 1600 or less. That is, the minimum angularity of the selected particles 18 is 300 or more, and the maximum angularity of the selected particles 18 is 1600 or less. The mode of angularity of the particles 18 is preferably between 400 and 1000, and more preferably between 500 and 800. This is to ensure a proportion of sharp particles 18 that can easily penetrate into the active material layer 17.

[0052] The particles 18 preferably have a Vickers hardness of 80 HV or more. This is to allow the particles 18 contained in the electrolyte layer 14 to penetrate more deeply into the active material layer 17 when the electrolyte layer 14 is pressed against the active material layer 17 of the negative electrode 15 during the manufacturing process of the secondary battery 10. The Vickers hardness of the particles 18 is measured by pressing an indenter into multiple locations on the flat surface of the sintered body in accordance with JIS Z2244:2009, and then averaging the measured values. The average Vickers hardness is rounded to one decimal place.

[0053] The median diameter of the equivalent circle diameters of the solid electrolyte particles 18 appearing in the cross section of the electrolyte layer 14 is preferably 0.1 to 5.0 μm, in order to ensure that the surface area of ​​the solid electrolyte powder is of an appropriate size and the amount of lithium ion movement is secured.

[0054] To determine the median diameter of the particles 18, first, an SEM image of the particles 18 appearing on the cross section of the electrolyte layer 14 (a polished surface, a surface obtained by irradiating with an FIB, or a surface obtained by ion milling) is analyzed, and the circle-equivalent diameter is calculated from the area of ​​each particle 18, and a 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 400 μm of the electrolyte layer 14. ２ The area shall be equal to or greater than this.

[0055] When the electrolyte layer 14 contains an electrolytic solution, the ratio of the volume of the powder to the total volume of the solid electrolyte powder and the electrolytic solution 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 solid electrolyte powder and the electrolytic solution can reduce the interfacial resistance of the powder, thereby increasing the operational stability of the secondary battery 10. It is of course possible to omit the electrolytic solution from the electrolyte layer 14.

[0056] The contents (volume %) of the solid electrolyte powder and the electrolyte solution are determined by freezing the electrolyte layer 14 or embedding the electrolyte layer 14 in a tetrafunctional epoxy resin or the like and then analyzing a randomly selected cross section of the electrolyte layer 14 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 elements constituting the powder and performing image analysis of the contrast of the backscattered electron image to identify the areas of the powder and the electrolyte solution, and the proportions of these areas in the cross section of the electrolyte layer 14 are regarded as the proportions of the volume of the electrolyte layer 14 to obtain the contents (volume %) of the powder and the electrolyte solution.

[0057] The present invention will be explained in more detail with reference to examples, but the present invention is not limited to these examples.

[0058] (Preparation of solid electrolyte) Li ６．９５ Mg ０．１５ La ２．７５ Sr ０．２５Zr 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 approximately 15 mol% in excess in elemental terms, 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, then placed on an MgO plate and pre-fired at 900°C for 1 hour and at 1200°C for 10 hours. The resulting pre-fired product was placed on an MgO plate and fired at 1100°C for 4 hours in an inert gas atmosphere to obtain a fired LLZ product.

[0059] (Preparation of Powder for Sample No. 1) Using a dry jet mill (Nano Jetmizer (registered trademark) NJ-80 model, manufactured by Aisin Nano Technologies Co., Ltd.), the fired material was dry-pulverized by passing it through the jet mill twice under conditions of a pulverization pressure of 1.1 MPa, an indentation pressure of 1.5 MPa, and a throughput of 120 g / Hr in a nitrogen atmosphere. This yielded a powder of the solid electrolyte (LLZ) for Sample No. 1.

[0060] (Preparation of Powder for Sample No. 2) Powder for Sample No. 2 was obtained in the same manner as for Sample No. 1, except that the fired product was pulverized by passing it through a jet mill four times.

[0061] (Preparation of Powder for Sample No. 3) The fired product, non-aqueous solvent, and zirconia balls with a diameter of 5 mm were placed in a 45 cc zirconia pot in an argon atmosphere, and pulverized for 100 hours at 650 rpm using a planetary ball mill (Fritsch P-6). The slurry removed from the pot was dried and then pulverized using a mortar and pestle in a glove box in an argon atmosphere to obtain powder for Sample No. 3.

[0062] (Preparation of Powder for Sample No. 4) Zr(OC ３ H ７ ) ４1-Butanol was added to the solution, and the mixture was refluxed at 118°C for 3 hours. After refluxing, acetic acid was added to the solution, and the mixture was stirred at room temperature for 2 hours. Water was then added, and the mixture was stirred at 5°C for 2 hours to obtain a precursor containing Zr. La(NO ３ ) ３ ・6H ２ After drying O at 150°C for 2 hours, 1-butanol was added and stirred at room temperature for 2 hours to obtain a precursor containing La. The precursor containing Zr and the precursor containing La were mixed and stirred at 60°C for 2 hours to obtain a precursor containing Zr and La.

[0063] Li (metal), Mg (metal), and Sr (metal) were added to 2-methoxyethanol and refluxed at 125°C for 5 hours to obtain a precursor containing Li, Mg, and Sr. Note that Li was added in 20% excess relative to the composition ratio of LLZ. A precursor containing Zr and La and a precursor containing Li, Mg, and Sr were mixed and stirred at 5°C for 12 hours to obtain a precursor of LLZ.

[0064] A LLZ precursor was placed in a syringe with a 0.4 mm inner diameter stainless steel nozzle, and the syringe was extruded at an injection rate of 1 cc / Hr while applying a voltage of 15 kV to the nozzle. This produced a fibrous, sheet-like structure on the surface of an electrode (aluminum foil coated with a silicone-based release agent) placed 10 cm from the tip of the nozzle. After peeling the structure from the electrode, it was heat-treated in air at 650-850°C for 2-4 hours. The heat-treated structure was pulverized in a dry ball mill to obtain powder, designated Sample No. 4.

[0065] (Preparation of Electrolyte) The ionic liquid N-methyl-N-propylpyrrolidinium bis(fluorosulfonyl)imide (P13FSI) was dissolved in lithium salt LiN(SO ２ F) ２ (LiFSI) was dissolved, and the salt concentration was 2.1 mol / dm ３ The electrolyte solution was obtained.

[0066] (Preparation of Electrolyte Layer) After mixing each powder and electrolyte solution of Sample No. 1-4 in a mortar at a ratio of 61:39 (volume ratio), a binder solution in which poly(vinylidene fluoride-hexafluoropropylene) (PVdF-HFP) was dissolved in carbonate ester was added so that the binder was 4 wt% relative to the combined mass of the powder, electrolyte solution, and binder, and the mixture was mixed with a planetary stirrer to obtain a slurry for the electrolyte layer. The slurry for the electrolyte layer that had passed through a filter with a pore size of 25 μm was degassed, then coated on a polyethylene terephthalate film and dried to obtain an electrolyte sheet (thickness: approximately 50 μm) for Sample No. 1-4.

[0067] (Preparation of Positive Electrode Sheet) Active Material LiNi ０．８ Co ０．１５ Al ０．０５ O ２ The LLZ, electrolyte, and conductive additive (carbon fiber) were weighed and mixed in a mortar, followed by the addition of a binder solution to form a slurry. The slurry was then applied to an aluminum foil (current collecting layer) and dried to form a positive electrode sheet (approximately 50 μm thick).

[0068] (Preparation of Evaluation Cells) The positive electrode sheet, each electrolyte sheet of Samples 1-4, and a negative electrode sheet having a 10 μm-thick lithium metal foil laminated on a copper foil (current collecting layer) were each cut to a predetermined size, and then stacked in order and pressure-bonded by a roll press. After connecting a terminal to each current collecting layer, the cells were sealed in a vacuum to obtain evaluation cells for Samples 1-4.

[0069] For comparison, an evaluation cell was also prepared for Sample No. 5 in which an electrolyte gel (50 μm thick) was placed between the positive and negative electrodes instead of the electrolyte sheet. The electrolyte gel was formed into a sheet using a slurry prepared by mixing a binder solution and an electrolyte solution in a mass ratio of 54:46 and mixing the mixture using a planetary centrifugal mixer.

[0070] (Measurement of Capacity Retention Rate) The evaluation cell of Sample No. 1-5 was charged at a constant current of 0.1 C rate until the battery voltage reached 4.2 V, and then discharged at a constant current of 0.1 C rate until the battery voltage reached 3.0 V, which constituted one cycle, and this cycle was repeated at room temperature to measure the ratio (capacity retention rate) of the discharge capacity at the 50th cycle to the initial discharge capacity.

[0071] (Measurement of Particle Angularity) The evaluation cells of Samples No. 1-4 for which the capacity retention rate was measured were disassembled to remove the electrolyte layer. The electrolyte layer was then embedded in a tetrafunctional epoxy resin and solidified. The cross section of the electrolyte layer was polished, and an SEM image (magnification 10,000x) of the cross section of the electrolyte layer was obtained. From the SEM image, 20 particles with a diameter of a circle inscribed in the particle outline of 0.2 μm or more were randomly selected, and the angularity of each particle was calculated according to formula (1). The minimum (min.) and maximum (max.) angularity values ​​of the 20 particles, as well as the capacity retention rate (%), are shown in Table 1.

[0072] (Measurement of Vickers Hardness) The powders in Samples No. 1-4 were placed in a mold, and uniaxially molded using a hand press under a pressure of 36 MPa. A pressure of 147 MPa was then applied by cold isostatic pressing (CIP) to obtain a disk-shaped molded body with a diameter of 5 mm. The molded body was placed on a MgO plate and fired at 1100°C for 4 hours in a reducing atmosphere to obtain a sintered body. In accordance with JIS Z2244:2009, an indenter was pressed into five locations on the flat surface of the sintered body, and the Vickers hardness was measured and averaged. The Vickers hardness of the sintered body of the powder in Samples No. 1-4 was 80 HV or higher.

[0073]

[0074] For Sample No. 1, the grinding pressure and powder compression pressure of the dry jet mill were appropriately controlled, allowing the preparation of a powder with a suitable degree of angularity. For Sample No. 2, the number of passes through the dry jet mill was increased compared to Sample No. 1, which led to increased particle wear and rounding of the particle corners, resulting in a lower degree of angularity compared to Sample No. 1. For Sample No. 3, the strong grinding force of the planetary ball mill was applied to the powder for a long period of time, which led to increased particle grinding and wear, rounding of the particle corners, and an even lower degree of angularity.

[0075] As shown in Table 1, it was revealed that the evaluation cells of Samples 1 and 2, in which the particle angularity was 300 or more and 1600 or less, were able to increase the capacity retention rate compared to Sample No. 3, in which the particle angularity was less than 300, Sample No. 4, in which the particle angularity was greater than 1600, and Sample No. 5, which contained no particles. In other words, the evaluation cells of Samples 1 and 2 had improved cycle characteristics compared to the evaluation cells of Samples 3 to 5.

[0076] In the evaluation cells of Samples 1 and 2, when the evaluation cells were fabricated by pressing the electrolyte layer against the active material layer of the negative electrode, the sharp protrusions of the particles contained in the electrolyte layer penetrated into the active material layer, increasing the peeling force between the electrolyte layer and the negative electrode and reducing interfacial peeling of the electrolyte layer. The variation in the amount of lithium ions supplied in the in-plane direction of the active material layer was reduced, reducing the occurrence of dendrites, which is presumably why the capacity retention rate of the evaluation cells was improved.

[0077] 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.

[0078] In the embodiment, the secondary battery 10 has been described as including a positive electrode 11 in which an active material layer 13 is provided on one side of a current collecting layer 12, and an negative electrode 15 in which an active material layer 17 is provided on one side of a current collecting layer 16, but the present invention is not necessarily limited to this. For example, it is of course possible to apply each element in the embodiment to a secondary battery including an electrode in which an active material layer 13 and an active material layer 17 are provided on both sides of a current collecting layer 12 (a so-called bipolar electrode). If bipolar electrodes and electrolyte layers 14 are alternately stacked and housed in a case (not shown), a so-called bipolar structure secondary battery can be obtained.

[0079] In the embodiment, the case where the particles 18 are included in the secondary battery 10 made of a lithium ion battery has been described, but this is not necessarily limited to this. It is clear that other power storage devices may also include the particles 18. An example of the other power storage device is an electrochemical capacitor. Examples of electrochemical capacitors include a redox capacitor that utilizes a redox reaction and a hybrid capacitor that is an asymmetric cell that combines an electric double layer capacitor with the particles 18.

[0080] 10 Secondary battery 11 Positive electrode 14 Electrolyte layer (sheet) 15 Negative electrode 17 Active material layer 18 Particles 19 Contour

Claims

1. A powder containing particles of a solid electrolyte, wherein the particles have a cross-sectional contour angularity of 300 or more and 1600 or less.

2. The powder according to claim 1, wherein the particles have a Vickers hardness of 80 HV or more.

3. A sheet containing the powder according to claim 1 or 2.

4. A secondary battery comprising, in order, a positive electrode, an electrolyte layer, and a negative electrode, the negative electrode including an active material layer made of lithium metal, and the electrolyte layer including the sheet according to claim 3.

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