Powder, sheet and secondary battery

Abstract

Provided are a powder, a sheet, and a secondary battery that can reduce peeling at the interface of the sheet. [Solution] The powder contains particles of a solid electrolyte, and the particles have a cross-sectional contour angularity of 300 or more and 1600 or less. The sheet contains the powder. The secondary battery contains, in order, a positive electrode, an electrolyte layer, and a negative electrode, the negative electrode containing an active material layer made of lithium metal, and the electrolyte layer containing the sheet.

Description

[Technical Field]

[0001] This invention relates to a solid electrolyte powder, a sheet containing the powder, and a secondary battery. [Background technology]

[0002] Prior art relating to a secondary battery comprising, in order, a positive electrode, an electrolyte layer (sheet) containing solid electrolyte powder, and a negative electrode is disclosed in Patent Document 1. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2022-108509 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] This type of secondary battery has a problem in that the negative electrode repeatedly expands and contracts during charging and discharging, which can easily cause delamination at the interface between the sheet and the negative electrode due to changes in the thickness of the negative electrode.

[0005] This invention was made to solve this problem and aims to provide a powder, a sheet, and a secondary battery that can reduce peeling at the sheet interface. [Means for solving the problem]

[0006] A first embodiment for achieving this objective is a powder containing solid electrolyte particles, wherein the particles have a cross-sectional contour with a degree of angularity of 300 to 1600.

[0007] In the second embodiment, the particles have a Vickers hardness of 80 HV or higher, as in the first embodiment.

[0008] The third embodiment is a sheet containing the powder of the first or second embodiment.

[0009] The fourth embodiment is a secondary battery, comprising, in order, a positive electrode, an electrolyte layer, and a negative electrode, wherein the negative electrode comprises an active material layer made of lithium metal, and the electrolyte layer comprises the sheet of the third embodiment. [Effects of the Invention]

[0010] According to the present invention, in a powder containing solid electrolyte particles, the angularity of the cross-sectional contour of the particles is 300 to 1600. In a secondary battery comprising, in order, a positive electrode, an electrolyte layer consisting of a sheet, and a negative electrode, when the sheet contains powder, the corners of the particles easily penetrate the negative electrode, increasing the peeling force between the sheet and the negative electrode, thereby reducing interfacial peeling of the sheet. [Brief explanation of the drawing]

[0011] [Figure 1] This is a cross-sectional view of a secondary battery in one embodiment. [Figure 2] This is a schematic diagram showing the crystal structure of a garnet-type crystal. [Figure 3] This is a cross-section of a particle. [Modes for carrying out the invention]

[0012] Preferred embodiments of the present invention will be described below with reference to the accompanying drawings. Figure 1 is a schematic cross-sectional view of a secondary battery 10 containing powder in 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). Examples of 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. Alkali metal ions are preferred, and lithium ions are particularly preferred.

[0013] The positive electrode 11 consists of a current collector layer 12 and an active material layer 13 superimposed on each other. The current collector layer 12 is a conductive material. Examples of materials for the current collector layer 12 include metals selected from Ni, Ti, Fe, and Al, alloys containing two or more of these elements, stainless steel, and carbon materials.

[0014] The active material layer 13 contains an active material. To lower the resistance of the active material layer 13, a conductive additive may be included in the active material layer 13. Examples of conductive additives include carbon black, acetylene black, Ketjenblack, carbon fiber, Ni, Pt, and Ag. One or more of the following solid electrolytes (powder, binder, and electrolyte solution) may also be included in the active material layer 13.

[0015] Examples of active materials included in the active material layer 13 are metal oxides containing transition metals, sulfur-based active materials, and organic active materials. When the charge carrier is lithium ions, examples of metal oxides containing transition metals include metal oxides containing one or more elements selected from Mn, Co, Ni, Fe, Cr, and V, along with Li. Examples of metal oxides containing transition metals include LiCoO2 and LiNi 0.8 Co 0.15 Al 0.05 O2, LiMn2O4, LiNiVO4, LiNi 0.5 Mn 1.5 O4, LiSa 1 / 3 Mn 1 / 3 Co 1 / 3 O2 and LiFePO4 are examples.

[0016] 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.

[0017] The electrolyte layer 14 isolates the positive electrode 11 and the negative electrode 15, electrically insulating them from each other. The electrolyte layer 14 contains solid electrolyte powder. A binder or electrolyte solution that binds the powder together may also be included in the electrolyte layer 14.

[0018] Examples of binders contained in the electrolyte layer 14 include rubbery polymers such as fluorinated resins, polyolefins, polyimides, polyvinylpyrrolidone, polyvinyl alcohol, cellulose ethers, and 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.

[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-containing 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 ethers. Examples of non-halogen-containing copolymerizable monomers include olefins such as ethylene and propylene; acrylic monomers such as acrylic acid, methacrylic acid, their esters or salts; and vinyl monomers such as acrylonitrile, vinyl acetate, and styrene. One or more copolymerizable monomers polymerize with vinylidene fluoride to form a copolymer.

[0020] The solvent of the electrolyte contained in the electrolyte layer 14 can be an aqueous solvent or a non-aqueous solvent. Non-aqueous solvents are broadly classified into molecular solvents, which consist mostly of molecules, and ionic liquids, which consist of cations and anions. Among molecular solvents, aprotic solvents are preferred in order to widen 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, fluorescein solvents, and sulfone solvents. Mixtures of these may also be used.

[0021] Examples of cyclic esters include carbonate esters such as propylene carbonate, ethylene carbonate, butylene carbonate, vinylene carbonate, vinylethylene carbonate, and fluoroethylene carbonate, as well as 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 monoglycerides. Examples of nitro compounds include nitromethane and nitrobenzene. Fluorine solvents are compounds in which hydrogen atoms of hydrocarbons are replaced with fluorine atoms, and their derivatives.

[0023] Examples of sulfone-based solvents include trimethylene sulfone, sulfolane, difluorosulfolane, dimethyl sulfolane, monofluorosulfolane, 3-methylsulfolane, ethylmethylsulfone, and ethyl isopropylsulfone. Sulfone-based solvents are preferred because of their high thermal stability.

[0024] Ionic liquids are compounds composed of cations and anions, and are liquids at room temperature and pressure. If the solvent of a non-aqueous electrolyte is an ionic liquid, the flame retardancy of the non-aqueous electrolyte can be improved. Preferably, the ionic liquid 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. The anion component is BF4 - , N(SO2F)2 - and other inorganic anions, B(C6H5)4 - , CH3SO3 - , CF3SO3 - , N(SO2CF3)2 - , N(SO2C4F9)2 - and other organic anions are exemplified.

[0026] The ionic liquid may be a solvated ionic liquid. Examples of the solvated ionic liquid include those obtained by dissolving an electrolyte in a sulfone solvent such as sulfolane or a sulfolane derivative, or a glyme solvent such as tetraglyme.

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

[0028] The active material layer 17 contains an active material. The active material is made of lithium metal. The lithium metal includes a single lithium, a lithium alloy composed of metallic lithium and a non-metallic element or a metal element other than lithium. Examples of the lithium alloy include Li-Al alloy, Li-Sn alloy, Li-Si alloy, Li-Mg alloy, and an alloy of metallic lithium and a lithium transition metal oxide such as Li4Ti5O 12 and other lithium transition metal nitrides.

[0029] The powder of the solid electrolyte contained in the electrolyte layer 14 is an inorganic substance, and examples thereof include one or more selected from sulfide-based, oxide-based, hydride-based, and halide-based. The solid electrolyte may be crystalline or amorphous. The sulfide-based solid electrolyte includes a crystalline thiolicon type, Li 10 GeP2S 12 type, argyrodite type, Li7P3S 11Examples of solid electrolytes include glass and glass-ceramic systems, such as Li2S-P2S5. Examples of hydride-based solid electrolytes include solid solutions of LiBH4 with lithium halide compounds (LiI, LiBr, LiCl) and lithium amide (LiNH2). An example of a halide-based solid electrolyte is Li3YCl6.

[0030] Examples of oxide-based solid electrolytes include crystalline and amorphous materials such as NASICON-based materials, LISICON-based materials, oxides with perovskite structures, and oxides with garnet-type structures. NASICON-based materials are represented by general formula A x This material is represented as M2(TO4)3. A is exemplified by Na and Li, M is exemplified by Zr, Ti, V, Mn, Cr, Fe, Ni, Al, and Ge, and T is exemplified by P, Si, and As. For example, Na3V2(PO4)3, Li 1+x Al x Ti 2-x (PO4)3, Li 1+x Ge x Ti 2-x (PO4)3 is one example.

[0031] LISICON-based materials are Li 4-2x Zn x GeO4 (0 ≤ x ≤ 1) is an example. Oxides having a perovskite structure include Li x La (1-x) / 3 NbO3, La 2 / 3-X Li 3X One example is TiO3 (0 ≤ x ≤ 1). The crystal structure of garnet-type oxides is given by the general formula C3A2B3O 12 It is represented as follows. Oxides having a garnet-type structure are preferred because they have excellent reduction resistance to lithium metal.

[0032] Figure 2 schematically shows a garnet-type crystal structure. In the garnet-type crystal structure, the C site Sc is dodecahedral in coordination with the oxygen atom Oa, the A site Sa is octahedral in coordination with the oxygen atom Oa, and the B site Sb is tetrahedral in coordination with the oxygen atom Oa. In the garnet-type crystal structure, Li can be present in the void V, which is the site where the oxygen atom Oa is octahedral in coordination. The void V is, for example, the area between B site Sb1 and B site Sb2. The Li present in void V is octahedral in coordination with the oxygen atom Oa that constitutes an octahedron including the tetrahedral face Fb1 forming B site Sb1 and the tetrahedral face Fb2 forming B site Sb2. For example, Li7La3Zr2O 12 In a garnet-type solid electrolyte with this composition, La may occupy the C site Sc, Zr may occupy the A site Sa, and Li may occupy the B site Sb and the void V.

[0033] Garnet-type solid electrolytes are found in the CSD (Cambridge Structural Database) X-ray diffraction file No. 422259 (Li7La3Zr2O 12 It has an XRD pattern similar to ). In garnet-type solid electrolytes, various elements are substituted. 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 elemental substitution, and the ionic conductivity changes as the arrangement, occupancy rate, and occupancy sites of lithium ions in the crystal structure change. The diffraction angle and intensity ratio may differ compared to No. 422259 due to elemental substitution.

[0034] Garnet-type solid electrolytes are typically Li7La3Zr2O 12 Examples include: The solid electrolyte may have some of its constituent elements substituted with other elements, or it may have trace amounts of other elements added without substituting any 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).

[0035] The solid electrolyte is, for example, Li6La3Zr 1.5 W 0.5 O 12 ,Li 6.15 La3Zr 1.75 Ta 0.25 Al 0.2 O 12 ,Li 6.15 La3Zr 1.75 Ta 0.25 Ga 0.2 O 12 ,Li 6.25 La3Zr2Ga 0.25 O 12 ,Li 6.4 La3Zr 1.4 Ta 0.6 O 12 ,Li 6.5 La3Zr 1.75 Te 0.25 O 12 ,Li 6.75 La3Zr 1.75 Nb 0.25 O 12 ,Li 6.9 La3Zr 1.675 Ta 0.289 Bi 0.036 O 12 ,Li 6.46 Ga 0.23 La3Zr 1.85 Y 0.15 O 12 ,Li 6.8 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 Zr2O 12 are exemplified.

[0036] The solid electrolyte is preferably one that contains Mg and at least one of element A (where 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 (1) to (3) below, or one that contains both Mg and element A, and the molar ratio of each element satisfies all of (4) to (6) below. 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 slurry for the electrolyte layer 14 is made by mixing an electrolyte solution, which is an electrolyte dissolved in a solvent, with a solid electrolyte powder, and then mixing this with a binder solution, which is a binder dissolved in a solvent. The slurry is applied onto the active material layer 17 of a negative electrode sheet, which has lithium metal (active material layer 17) laminated on a current collector layer 16, and then dried to obtain the first sheet.

[0038] A slurry for the active material layer 13 is prepared by mixing an electrolyte solution (an electrolyte dissolved in a solvent) with a solid electrolyte powder, then mixing in a binder solution (a binder dissolved in a solvent). After applying the slurry onto the current collector layer 12, it is dried to obtain a sheet for the positive electrode 11 (positive electrode sheet). After applying the slurry for the electrolyte layer 14 onto the active material layer 13 of the positive electrode sheet, it is dried to obtain a second sheet.

[0039] After cutting the first and second sheets into predetermined shapes, the electrolyte layer 14 is placed facing each other, the first and second sheets are stacked on top of each other, and then pressed together to form a single unit. Terminals (not shown) are connected to the current collector layers 12 and 16, respectively, and the unit is sealed in a case (not shown) to obtain 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 prepared separately. After cutting the positive electrode sheet, electrolyte sheet, and negative electrode sheet into predetermined shapes, the positive electrode sheet, electrolyte sheet, and negative electrode sheet are stacked in order and pressed together to form a single unit. Terminals (not shown) are connected to the current collector layers 12 and 16, respectively, and the unit is sealed in a case (not shown) to obtain a secondary battery 10 including a positive electrode 11, an electrolyte layer 14, and a negative electrode 15.

[0041] Various methods can be used to press the sheets together, such as a roll press, a uniaxial press, or a hydrostatic press. Heating the sheets when pressing them together is preferable because it softens the binder and active material layer 17 contained in the sheets.

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

[0043]

number

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

[0045] The angularity of the cross-sectional contour 19 of the particle 18 is between 300 and 1600. The angularity of the particle 18 being between 300 and 1600 indicates that the convex parts of the particle 18 are sharp. When the angularity of the particle 18 is between 300 and 1600, the sharp convex parts (corners) of the particle 18 can easily penetrate the active material layer 17 of the negative electrode 15 when the electrolyte layer 14 is pressed against it during the manufacturing process of the secondary battery 10. This increases the peeling force between the electrolyte layer 14 and the negative electrode 15, thereby reducing interfacial peeling of the electrolyte layer 14.

[0046] When the angularity of the particles 18 decreases, the particles 18 become closer to a spherical shape, and when the angularity of the particles 18 increases, the particles 18 become elongated. In both cases, it becomes more difficult for the particles 18 to penetrate the active material layer 17, and as a result, 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 in conjunction with the charging and discharging of the secondary battery 10. When delamination occurs at the interface between the electrolyte layer 14 and the active material layer 17 due to changes in the thickness of the active material layer 17, the variation in the supply of lithium ions in the in-plane direction of the active material layer 17 increases, making it easier for needle-shaped dendritic crystals (dendrites) to appear due to the deposition of metallic lithium. When dendrites grow, they can short-circuit the positive electrode 11 and the negative electrode 15 or significantly reduce the capacity.

[0048] In contrast, the electrolyte layer 14 contains particles 18 whose cross-sectional contour 19 has an angularity of 300 to 1600. As a result, the particles 18 penetrate the active material layer 17, reducing the peeling of the electrolyte layer 14 from the negative electrode 15. This reduces variations in the supply of lithium ions in the in-plane direction of the active material layer 17 and reduces the generation of dendrites, thereby reducing the occurrence of short circuits between the positive electrode 11 and the negative electrode 15. Furthermore, it improves the capacity retention rate of the secondary battery 10.

[0049] To calculate the angularity of the solid electrolyte particles 18, first, an electrolyte layer 14 is embedded in a tetrafunctional epoxy resin or the like, or a thermosetting resin is mixed with the particles 18 and solidified. Then, a scanning electron microscope (SEM) image of the particles 18 appearing in the cross-section (polished surface, surface obtained by irradiation with a focused ion beam (FIB), or surface obtained by ion milling) is acquired. The image acquisition magnification can be, for example, 5000-10000x. To improve the accuracy of discriminating the contours 19 of the particles 18, an image resolution of 220 dpi or higher is preferable.

[0050] Since the shape of the contour 19 cannot be determined for particles whose contour 19 is broken, and the shape of the contour 19 is difficult to determine for small particles, 20 or more particles 18 in which the entire contour 19 is included in the image are selected, and the diameter of the circle 20 is 1 / 50 or more of the length of the shorter side of the image, and the angularity is calculated for each particle 18. Since larger particles 18 penetrate to a greater depth in the active material layer 17 than smaller particles 18, it is preferable to select particles 18 in which the diameter of the circle 20 is 0.2 μm or more and calculate the angularity.

[0051] The angularity of all 20 or more particles 18 selected from the image is between 300 and 1600. 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. Preferably, the mode of the angularity of the particles 18 is 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 the active material layer 17.

[0052] The particles 18 preferably have a Vickers hardness of 80 HV or higher. This is to allow the particles 18 contained in the electrolyte layer 14 to penetrate deeper 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 after firing a molded body made by pressing the particles 18 into a disc shape, in accordance with JIS Z2244:2009, and calculating the average. The average Vickers hardness is rounded to the nearest tenth.

[0053] The median diameter of the equivalent circular diameter of the solid electrolyte particles 18 appearing in the cross-section of the electrolyte layer 14 is preferably 0.1-5.0 μm. This is to ensure an appropriate surface area for the solid electrolyte powder and to secure the amount of lithium ion movement.

[0054] To determine the median diameter of particle 18, first, SEM images of the particles 18 appearing on the cross-section of the electrolyte layer 14 (polished surface, surface obtained by FIB irradiation, surface obtained by ion milling) are analyzed, and the equivalent circular diameter is calculated from the area of ​​each particle 18 to determine the volume-based particle size distribution. The median diameter is the equivalent circular diameter at which the cumulative frequency in the particle size distribution reaches 50%. To ensure accuracy, the image used to determine the particle size distribution is 400 μm of the electrolyte layer 14. 2 The area shall be as stated above.

[0055] When the electrolyte layer 14 contains an electrolyte solution, the ratio of the volume of the powder to the sum of the volume of the solid electrolyte powder and the volume of the electrolyte solution is preferably 52% or more and less than 100%, and more preferably 61% or more and less than 100%. This is because the interfacial resistance of the powder can be reduced by the combination of the solid electrolyte powder and the electrolyte solution, thereby increasing the operational stability of the secondary battery 10. It is, of course, possible to omit the electrolyte solution from the electrolyte layer 14.

[0056] The volume %) content of the solid electrolyte powder and electrolyte solution is determined by freezing the electrolyte layer 14 or embedding and solidifying the electrolyte layer 14 in a tetrafunctional epoxy resin, and then analyzing a randomly selected 5000x magnification field of view from the cross-section of the electrolyte layer 14 using a scanning electron microscope (SEM) equipped with an energy-dispersive X-ray spectrometer (EDS). The analysis identifies the distribution of elements constituting the powder and the contrast of the backscattered electron image to determine the area of ​​the powder and the area of ​​the electrolyte solution. The area ratio in the cross-section of the electrolyte layer 14 is then considered as the volume ratio in the electrolyte layer 14 to obtain the volume %) content of the powder and electrolyte solution. [Examples]

[0057] The present invention will be described 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 0.25 Zr 2.0 O 12 Li2CO3, MgO, La(OH)3, SrCO3, and ZrO2 were weighed so as to obtain the above composition. Considering the volatilization of Li during firing, Li2CO3 was made about 15 mol% excessive in terms of elements. The weighed raw materials and ethanol were put into a nylon pot together with zirconia balls and pulverized and mixed with a ball mill for 15 hours. The slurry taken out from the pot was dried and then placed on a MgO plate and calcined at 900 °C for 1 hour and at 1200 °C for 10 hours. The obtained calcined product was placed on a MgO plate and fired at 1100 °C for 4 hours in an inert gas atmosphere to obtain a fired product of LLZ.

[0059] (Preparation of Powder for Sample No. 1) Using a dry jet mill (Aisin Nanotechnology Co., Ltd., Nano Jet Mizer (registered trademark) NJ-80 type), the fired product was dry-pulverized by passing it through the jet mill twice under the conditions of a pulverization pressure of 1.1 MPa, a pushing pressure of 1.5 MPa, and a throughput of 120 g / Hr in a nitrogen atmosphere. Thereby, a powder of the solid electrolyte (LLZ) for Sample No. 1 was obtained.

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

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

[0062] (Preparation of powder in Sample No. 4) 1-butanol was added to Zr(OC3H7)4 and refluxed at 118°C for 3 hours. Acetic acid was added to the refluxed solution and stirred at room temperature for 2 hours, then water was added and stirred at 5°C for 2 hours to obtain a precursor containing Zr. La(NO3)3·6H2O was dried at 150°C for 2 hours, then 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 both 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. Li was added in an excess of 20% relative to the composition ratio of LLZ. The precursor containing Zr and La was mixed with the precursor containing Li, Mg, and Sr, and stirred at 5°C for 12 hours to obtain the precursor of LLZ.

[0064] An LLZ precursor was placed in a syringe with a stainless steel nozzle having an inner diameter of 0.4 mm. By applying a voltage of 15 kV to the nozzle and pushing the syringe out at an injection speed of 1 cc / hr, a fibrous and sheet-like structure was fabricated on the surface of an electrode (aluminum foil coated with a silicon-based release agent) placed 10 cm from the nozzle tip. After peeling the structure from the electrode, it was heat-treated in an air atmosphere at 650-850°C for 2-4 hours. The heat-treated structure was pulverized in a dry ball mill to obtain the powder for sample No. 4.

[0065] (Preparation of electrolyte solution) The lithium salt LiN(SO2F)2(LiFSI) was dissolved in the ionic liquid N-methyl-N-propylpyrrolidinium bis(fluorosulfonyl)imide (P13FSI) to a salt concentration of 2.1 mol / dm³. 3 We obtained the electrolyte.

[0066] (Preparation of the electrolyte layer) Each powder and electrolyte of Samples No. 1-4 were mixed in a mortar in a ratio of 61:39 (by volume). Then, a binder solution of poly(vinylidene fluoride-hexafluoropropylene) (PVdF-HFP) dissolved in carbonate ester was added so that the binder amounted to 4 wt% of the combined mass of the powders, electrolyte, and binder. The mixture was then mixed using a rotary-orbiting agitator to obtain an electrolyte layer slurry. The slurry that passed through a filter with a pore size of 25 μm was degassed, and then applied to a polyethylene terephthalate film and dried to obtain the electrolyte sheet (approximately 50 μm thick) for Samples No. 1-4.

[0067] (Fabrication of the positive electrode sheet) Active material LiNi 0.8 Co 0.15 Al 0.05 O2, LLZ, electrolyte, and conductive additive (carbon fiber) were weighed and mixed in a mortar, then mixed with a binder solution to obtain a slurry. The slurry was applied to aluminum foil (current collector layer) and dried to obtain a positive electrode sheet (approximately 50 μm thick).

[0068] (Creation of evaluation cells) The positive electrode sheet, the electrolyte sheets for each of samples No. 1-4, and the negative electrode sheet (a 10 μm thick lithium metal foil laminated on a copper foil current collector layer) were each cut to the predetermined size, stacked in order, and pressed together using a roll press. After connecting terminals to each current collector layer, the cells were sealed under vacuum to obtain the evaluation cells for samples No. 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 an electrolyte sheet. The electrolyte gel was prepared by mixing a binder solution and electrolyte in a ratio of 54:46 (by mass) and then forming a sheet using a slurry prepared by mixing with a rotating agitator.

[0070] (Measurement of capacity retention rate) For the evaluation cells in samples No. 1-5, constant current charging at a 0.1C rate was performed until the battery voltage reached 4.2V, followed by constant current discharge at a 0.1C rate until the battery voltage reached 3.0V. This cycle was repeated at room temperature, and the ratio of the discharge capacity after 50 cycles to the initial discharge capacity (capacity retention rate) was measured.

[0071] (Measurement of particle angularity) The evaluation cells in samples No. 1-4, for which the volume retention rate was measured, were disassembled, and the electrolyte layer was extracted. The electrolyte layer was embedded and solidified in a tetrafunctional epoxy resin, and then the cross-section of the electrolyte layer was polished. 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's contour of 0.2 μm or more were arbitrarily selected, and the angularity was calculated for each particle according to equation (1). The minimum (min.) and maximum (max.) angularity values ​​and volume retention rate (%) for the 20 particles are shown in Table 1.

[0072] (Measurement of Vickers hardness) The powders from samples No. 1-4 were placed in a mold and uniaxially molded by hand press under a pressure of 36 MPa. Then, a pressure of 147 MPa was applied by cold isostatic pressing (CIP) to obtain a disc-shaped molded body with a diameter of 5 mm. The molded body was placed on an 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 the average was calculated. The Vickers hardness of the sintered bodies of the powders from samples No. 1-4 was 80 HV or higher.

[0073] [Table 1]

[0074] Sample No. 1 was prepared by appropriately controlling the grinding pressure and powder compression pressure of the dry jet mill, resulting in a powder with a suitable degree of angularity. Sample No. 2 had more passes through the dry jet mill compared to Sample No. 1, which led to increased particle wear and rounded edges, resulting in a lower degree of angularity compared to Sample No. 1. Sample No. 3 had a strong grinding force applied to the powder for a long period of time by a planetary ball mill, which led to increased particle grinding and wear, further rounding the edges and reducing the degree of angularity.

[0075] As shown in Table 1, the evaluation cells in samples No. 1 and 2, where the particle angularity was between 300 and 1600, demonstrated higher volume retention rates compared to sample No. 3 (particle angularity less than 300), sample No. 4 (particle angularity greater than 1600), and sample No. 5 (no particles). In other words, the evaluation cells in samples No. 1 and 2 showed improved cycle characteristics compared to the evaluation cells in samples No. 3-5.

[0076] In the evaluation cells of samples No. 1 and 2, it is presumed that 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 the active material layer, increasing the peeling force between the electrolyte layer and the negative electrode, and reducing interfacial delamination of the electrolyte layer. It is presumed that the variation in the supply amount of lithium ions in the in-plane direction of the active material layer was reduced, and the generation of dendrites was reduced, thus improving the capacity retention rate of the evaluation cells.

[0077] Although the present invention has been described above based on embodiments, it can be easily inferred that the present invention is not limited in any way to the above embodiments, and that various improvements and modifications are possible without departing from the spirit of the present invention.

[0078] In the embodiment, a secondary battery 10 was described that comprises a positive electrode 11 with an active material layer 13 on one side of a current collector layer 12, and a negative electrode 15 with an active material layer 17 on one side of a current collector layer 16, but it is not necessarily limited to this. For example, it is certainly possible to apply each element of the embodiment to a secondary battery that has electrodes (so-called bipolar electrodes) with an active material layer 13 and an active material layer 17 on both sides of the current collector layer 12, respectively. By alternately stacking bipolar electrodes and electrolyte layers 14 and housing them in a case (not shown), a secondary battery with a so-called bipolar structure can be obtained.

[0079] In the embodiment, the case in which the particles 18 are included in a secondary battery 10 consisting of a lithium-ion battery was described, but it is not necessarily limited to this. It is clear that other energy storage devices may also include the particles 18. Examples of other energy storage devices include electrochemical capacitors. Examples of electrochemical capacitors include redox capacitors that utilize redox reactions and hybrid capacitors, which are asymmetric cells that combine an electric double-layer capacitor with the particles 18. [Explanation of Symbols]

[0080] 10 Secondary battery 11 Positive electrode 14. Electrolyte layer (sheet) 15 negative electrode 17 Active material layer 18 particles 19 Outline

Claims

1. A powder containing particles of a solid electrolyte, The particles are powders having a cross-sectional contour angularity of 300 or more and 1600 or less.

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

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

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

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