Composite for secondary batteries, composite sheet for secondary batteries, method for manufacturing the same, and solid secondary battery

Abstract

The present disclosure provides a secondary battery binder that contains an oxide-based electrolyte and exhibits favorable properties, a secondary battery binder sheet containing the binder, and a solid-state secondary battery using the secondary battery binder sheet. The present disclosure also provides a method for producing a secondary battery binder sheet containing a binding agent having a fine fiber structure. Specifically provided is a secondary battery binder containing an oxide-based solid electrolyte and a binding agent, said secondary battery binder being characterized in that the binding agent is a fibrillary resin. The fibrillary resin ideally has a fibrous structure with a fibril diameter (median value) of 100 nm or less.

Description

[Technical Field]

[0001] This disclosure relates to a secondary battery mixture, a secondary battery mixture sheet, a method for manufacturing the same, and a solid-state secondary battery. [Background technology]

[0002] In lithium-ion secondary batteries, it is common practice to prepare a sheet for solid-state secondary batteries by coating an electrode active material and a conductive additive with a slurry obtained by mixing a binder and a solvent, and then drying the mixture.

[0003] On the other hand, fibrillating resins such as polytetrafluoroethylene resins are also used as binders by fibrillating them.

[0004] Patent Document 1 discloses a method for producing an electrode in which polytetrafluoroethylene is fibrillated by subjecting a mixture containing an active material and a polytetrafluoroethylene mixed binder material to high shear treatment using a jet mill.

[0005] Patent Document 2 discloses obtaining an all-solid-state lithium-ion secondary battery by using a specific oxide-based solid electrolyte and fabricating the electrolyte layer and electrode layer from a slurry. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Special Publication No. 2017-517862 [Patent Document 2] Special Publication No. 2015-153588 [Overview of the project] [Problems that the invention aims to solve]

[0007] This disclosure aims to provide a secondary battery mixture containing an oxide-based solid electrolyte having good properties, a secondary battery mixture sheet containing the mixture, and a solid secondary battery using the secondary battery mixture sheet. Furthermore, this disclosure aims to provide a method for manufacturing a composite sheet for secondary batteries containing a binder having a fine fibrous structure. [Means for solving the problem]

[0008] This disclosure relates to a composite material for secondary batteries containing an oxide-based solid electrolyte and a binder, The aforementioned binder is a composite material for secondary batteries, characterized in that it is a fibrillary resin.

[0009] The fibrillated resin preferably has a fibrous structure with a median fibril diameter of 100 nm or less. The fibrillary resin is preferably a polytetrafluoroethylene resin.

[0010] The aforementioned secondary battery mixture is a secondary battery mixture obtained using a raw material composition containing an oxide-based solid electrolyte and a binder, It is preferable that the binder in the raw material composition is a powdered fibrillary resin. Preferably, the raw material composition contains substantially no liquid medium. The aforementioned powdered fibrillary resin preferably has a moisture content of 500 ppm or less.

[0011] Preferably, the powdered fibrillary resin is a powdered polytetrafluoroethylene resin. The powdered polytetrafluoroethylene resin preferably has a standard specific gravity of 2.12 to 2.20. The aforementioned powdered polytetrafluoroethylene resin preferably contains 50% by mass or more of polytetrafluoroethylene resin with a secondary particle size of 450 μm or more. The aforementioned powdered polytetrafluoroethylene resin preferably contains 80% by mass or more of polytetrafluoroethylene resin with a secondary particle diameter of 450 μm or more.

[0012] The oxide-based solid electrolyte is preferably a solid electrolyte that contains four or more elements (excluding carbon atoms and hydrogen atoms) in addition to oxygen atoms. It is preferable that at least one of the four or more elements mentioned above is selected from the group consisting of Mg, Al, Si, Ca, Ti, Ga, Sr, Nb, Sn, Ba, and W.

[0013] The aforementioned secondary battery mixture preferably further contains a nickel-containing positive electrode active material. This disclosure also includes a secondary battery mixture sheet containing the aforementioned secondary battery mixture. This disclosure also relates to an electrode including a secondary battery mixture sheet containing the nickel-containing positive electrode active material.

[0014] This disclosure relates to a step (1) of applying shear force while mixing a raw material composition containing an oxide-based solid electrolyte and a binder. Step (2) involves forming the secondary battery mixture obtained in step (1) into a bulk form, and Step (3) involves rolling the bulk secondary battery mixture obtained in step (2) into a sheet. The present invention relates to a method for manufacturing a composite sheet for secondary batteries, wherein the binder is a powdered fibrillary resin. This disclosure also relates to a solid-state secondary battery having the aforementioned secondary battery compound sheet. [Effects of the Invention]

[0015] In this disclosure, by not using a solvent when forming a composite sheet for secondary batteries containing an oxide-based solid electrolyte and by using a low-moisture powder binder, it is possible to manufacture batteries with less degradation of the oxide-based solid electrolyte. Furthermore, in the manufacturing method of this disclosure, it is possible to manufacture a composite sheet for secondary batteries containing a binder having a fine fibrous structure, and since a slurry is not prepared, the burden on the manufacturing process can be reduced. [Brief explanation of the drawing]

[0016] [Figure 1] This is an explanatory diagram showing a schematic cross-section of the pressure cell used in the example. [Modes for carrying out the invention]

[0017] The details of this disclosure are described below. This disclosure provides a secondary battery mixture and a mixture sheet containing the same, which can be suitably used in oxide-based solid secondary batteries. In the secondary battery mixture and mixture sheet containing the same disclosed herein, a fibrillary resin such as polytetrafluoroethylene resin (PTFE) is used as a binder. In conventional solid secondary battery mixtures, a solvent-soluble resin such as a copolymer of vinylidene fluoride and hexafluoropropylene was used as a binder, and the mixture was generally prepared by coating and drying a slurry containing the same. However, conventional solvents that can dissolve binder resins react with oxide-based solid electrolytes, degrading their performance and thus reducing battery performance. For this reason, solvents are limited to specific low-polarity solvents such as butyl butyrate. However, low-polarity solvents have low boiling points and high volatility, posing challenges in controlling slurry preparation and storage. In addition, alkaline components originating from the active material and solid electrolyte promote gelation of the slurry, leading to processing defects and reducing battery performance.

[0018] On the other hand, it is known that PTFE in particulate form readily fibrillates when shear stress is applied. This fibrillating property can be utilized to use PTFE as a binder. That is, the fibrillated PTFE can entangle with other powder components, binding them together and thus acting as a binder when molding the powder components.

[0019] This disclosure is completed by discovering that, in obtaining a secondary battery mixture containing an oxide-based solid electrolyte, a secondary battery mixture with good properties and a mixture sheet containing the same can be obtained without using a solvent by using a fibrilous resin as a binder.

[0020] The secondary battery mixture described herein is obtained using a raw material composition containing an oxide-based solid electrolyte and a binder, wherein the binder is preferably a powdered fibrillary resin. Since a powdered binder is used as a raw material instead of a binder-containing dispersion, the problem of solvent selectivity is eliminated. Furthermore, because no dispersion is used, there is less moisture derived from the raw materials in the secondary battery mixture, and problems caused by moisture contamination do not occur. This has the advantage of making it possible to produce a battery with excellent ion conductivity and improve battery performance.

[0021] Furthermore, it is preferable that the above raw material composition substantially does not contain a liquid medium. Thus, the secondary battery mixture of this disclosure has the advantage of not using a solvent in its manufacture. That is, conventional methods for forming secondary battery mixtures generally involve preparing a slurry in which powder components of the secondary battery mixture are dispersed using a solvent in which a binder is dissolved, and then preparing a secondary battery mixture sheet by coating and drying the slurry. In this case, a solvent that dissolves the binder is used. However, certain solvents such as butyl butyrate that have been commonly used in the past and can dissolve binder resins degrade oxide-based solid electrolytes, as described above, and cause a decrease in battery performance. In addition, with low-polarity solvents such as heptane, the binder resins that can be dissolved are very limited, and they have a low flash point and are difficult to handle.

[0022] From the above viewpoint, it is preferable that the secondary battery mixture of this disclosure has a liquid medium content of 1% by mass or less. Furthermore, it is also preferable that the raw material composition has a liquid medium content of 1% by mass or less.

[0023] The secondary battery mixture of this disclosure contains an oxide-based electrolyte and includes a binder having a fibrous structure as a component. In this disclosure, it is important that the binder exists in a fibrillated state. The fibrillated binder is present in the secondary battery mixture and acts to bind the powders of the components constituting the secondary battery mixture, thereby achieving the objective of the present invention. In other words, this disclosure has found that by using a fibrilous resin as a binder and making the binder in the secondary battery mixture have a fibrous structure, it is possible to obtain a secondary battery mixture with good properties and a mixture sheet containing the same, and thus this disclosure is completed.

[0024] Furthermore, the binder in the secondary battery mixture is preferably a fibrilous resin having a fibrous structure with a median fibril diameter of 100 nm or less. The presence of a binder with a fine fibril diameter in the secondary battery mixture provides a stronger binding effect on the powder components that make up the secondary battery mixture.

[0025] In this disclosure, by performing fine fibrillation processing on the binder so that it has a fibrous structure with a median fibril diameter of 100 nm or less, the fibrillated binder can reduce the degradation of the oxide-based solid electrolyte when used as a binder in a secondary battery mixture, and can exhibit good performance.

[0026] The above fibril diameter (median) was measured using the following method. (1) Using a scanning electron microscope (S-4800 model, manufactured by Hitachi, Ltd.), a magnified photograph (7000x) of the composite sheet for secondary batteries is taken and an image is obtained. (2) Draw two lines horizontally at equal intervals on this image to divide the image into three equal parts. (3) For all fibrillated binders on the upper straight line, measure the diameter at three points for each fibrillated binder and take the average value as the diameter of that fibrillated binder. The three points to be measured are selected as the intersection of the fibrillated binder and the straight line, and points shifted 0.5 μm above and below the intersection (excluding unfibrillated primary binder particles). (4) Perform the procedure in (3) above on all fibrillated binders that lie in the straight line below. (5) Starting from the first image, move 1 mm to the right of the screen and take another picture, then measure the diameter of the fibrillated binder according to (3) and (4) above. Repeat this process until the number of measured particles exceeds 80, at which point the process is complete. (6) The median of the diameters of all the fibrillated binders measured above was defined as the fibril diameter.

[0027] The median fibril diameter is preferably 100 nm or less, more preferably 85 nm or less, and even more preferably 70 nm or less. Note that excessive fibrilization tends to result in a loss of flexibility. While there is no particular lower limit, from the viewpoint of strength, for example, it is preferably 15 nm or more, more preferably 20 nm or more, and particularly preferably 31 nm or more.

[0028] The method for obtaining a binder having the above fibril diameter (median) is not particularly limited, but for example, (1) A step in which shear force is applied while mixing a raw material composition containing an oxide-based solid electrolyte and a binder powder. Step (2) involves forming the secondary battery mixture obtained in step (1) into a bulk form, and One possible method is to carry out the process by rolling the bulk secondary battery mixture obtained in step (2) into a sheet in step (3).

[0029] In this method, for example, in step (1), by setting the mixing conditions of the raw material composition to 1000 rpm or less, the fibrillation of the binder can be promoted while maintaining flexibility, and by controlling the applied shear stress, the fibril diameter (median) of the binder can be set to 100 nm or less.

[0030] Furthermore, it is preferable to have a step (4) after step (3) in which a larger load is applied to the obtained rolled sheet and it is further rolled into a thinner sheet. It is also preferable to repeat step (4). Furthermore, the fibril diameter can also be adjusted by having a step (5) after step (3) or step (4) in which the obtained rolled sheet is roughly crushed, then reshaped into a bulk form, and rolled into a sheet form again. It is preferable that step (5) be repeated, for example, one to twelve times.

[0031] In other words, by applying shear force, the binder powder is fibrillated, and this fibrillation then intertwines with powder components such as oxide-based solid electrolytes, thereby enabling the production of a composite material for secondary batteries. The manufacturing method will be described later.

[0032] Furthermore, the term "binding agent powder" above refers to a solid state as a powder, not a dispersed state mixed with a liquid medium. By utilizing such a state and manufacturing a composite material for secondary batteries using a binding agent in the absence of a liquid medium, the objectives of this disclosure can be suitably achieved.

[0033] The fibrillary resin in powder form used as a raw material when preparing the composite material for secondary batteries according to this disclosure preferably has a moisture content of 500 ppm or less. Having a moisture content of 500 ppm or less is preferable because it reduces the degradation of the oxide-based solid electrolyte. The above moisture content is more preferably 300 ppm or less.

[0034] In this disclosure, a fibrillating resin refers to a resin that readily fibrillates when subjected to shear stress. By using such a fibrillating resin as a binder, the fibrillated resin entangles with other powder components, thereby binding the powder components together and acting as a binder when the powder components are molded. Examples of fibrillating resins include liquid crystal polymers (LCP), cellulose, acrylic resins, ultra-high molecular weight polyethylene, and PTFE, among which PTFE is preferred in terms of chemical stability, thermal stability, and processability.

[0035] In this disclosure, the PTFE is not particularly limited and may be a homopolymer or a copolymer that can be fibrillated. In the case of copolymers, examples of fluorine atom-containing monomers that act as comonomers include chlorotrifluoroethylene, hexafluoropropylene, fluoroalkylethylene, perfluoroalkylethylene, and fluoroalkyl fluorovinyl ether.

[0036] The powdered PTFE preferably has a standard specific gravity of 2.12 to 2.20. Having a standard specific gravity within this range has the advantage of enabling the production of electrode mixture sheets with high strength. The lower limit of the standard specific gravity is more preferably 2.13 or higher. The upper limit of the standard specific gravity is more preferably 2.19 or lower, and even more preferably 2.18 or lower.

[0037] The standard specific gravity (SSG) is determined by preparing a sample in accordance with ASTM D-4895-89, and measuring the specific gravity of the obtained sample by the water displacement method.

[0038] The above-mentioned powdered PTFE preferably contains 50% by mass or more of polytetrafluoroethylene resin with a secondary particle size of 450 μm or larger, and more preferably 80% by mass or more. Having PTFE with a secondary particle size of 450 μm or larger within this range has the advantage of enabling the production of a highly strong composite sheet. By using PTFE with a secondary particle size of 450 μm or larger, a composite sheet with lower resistance and greater toughness can be obtained.

[0039] The lower limit of the average secondary particle diameter of the above-mentioned powdered PTFE is more preferably 450 μm, and even more preferably 500 μm. The upper limit of the above-mentioned secondary particle diameter is more preferably 700 μm or less, and even more preferably 600 μm or less. The secondary particle diameter can be determined, for example, by sieving.

[0040] The above-mentioned powdered PTFE is preferably such that it has an average primary particle diameter of 150 nm or more, in order to obtain an electrode mixture sheet with higher strength and superior homogeneity. More preferably, it is 180 nm or more, even more preferably 210 nm or more, and particularly preferably 220 nm or more. The larger the average primary particle size of PTFE, the lower the increase in extrusion pressure when using the powder for extrusion molding, resulting in superior moldability. There is no particular upper limit, but it may be 500 nm. From the viewpoint of productivity in the polymerization process, an upper limit of 350 nm is preferable.

[0041] The above average primary particle diameter can be determined by creating a calibration curve using an aqueous dispersion of PTFE obtained by polymerization, adjusting the polymer concentration to 0.22% by mass, and comparing the transmittance of 550 nm projected light per unit length of the aqueous dispersion with the average primary particle diameter determined by measuring the directional diameter in transmission electron microscope images. The transmittance of the aqueous dispersion to be measured is then measured, and the average primary particle diameter can be determined based on the above calibration curve.

[0042] The PTFE used in this disclosure may have a core-shell structure. Examples of PTFE having a core-shell structure include polytetrafluoroethylene containing a core of high molecular weight polytetrafluoroethylene and a shell of lower molecular weight polytetrafluoroethylene or modified polytetrafluoroethylene in the particles. Examples of such modified polytetrafluoroethylene include the polytetrafluoroethylene described in Japanese Patent Publication No. 2005-527652.

[0043] PTFE in powder form that satisfies the parameters described above can be obtained by conventional manufacturing methods. For example, it can be manufactured by following the manufacturing methods described in International Publication No. 2015-080291 and International Publication No. 2012-086710, etc.

[0044] In the present disclosure, in the mixture for a secondary battery, the lower limit of the content of the binder is preferably 0.2% by mass or more, more preferably 0.3% by mass or more, and still more preferably more than 0.5% by mass. The upper limit of the content of the binder in the mixture for a secondary battery is preferably 10% by mass or less, more preferably 6.0% by mass or less, still more preferably 4% by mass or less, even more preferably 1.7% by mass, and most preferably 1.0% by mass. If the binder is within the above range, it is possible to form a self-supporting sheet with excellent handling properties while suppressing an increase in electrode resistance.

[0045] The solid electrolyte used in the mixture for a secondary battery of the present disclosure is an oxide-based solid electrolyte.

[0046] The above oxide-based solid electrolyte preferably contains oxygen atoms (O), has ionic conductivity of a metal belonging to Group 1 or Group 2 of the periodic table, and has electronic insulation. The oxide-based solid electrolyte has an ionic conductivity of preferably 1×10 -6 S / cm or more, more preferably 5×10 -6 S / cm or more, and particularly preferably 1×10 -5 S / cm or more.

[0047] Specific compound examples include, for example, Li xa La ya TiO3 [xa satisfies 0.3 ≤ xa ≤ 0.7, and ya satisfies 0.3 ≤ ya ≤ 0.7.](LLT); Li xb La yb Zr zb M bb mb O nb (M bb is one or more elements selected from Al, Mg, Ca, Sr, V, Nb, Ta, Ti, Ge, In, and Sn. xb satisfies 5 ≤ xb ≤ 10, yb satisfies 1 ≤ yb ≤ 4, zb satisfies 1 ≤ zb ≤ 4, mb satisfies 0 ≤ mb ≤ 2, and nb satisfies 5 ≤ nb ≤ 20.); Li xc B yc M cc zcO nc (M cc is one or more elements selected from C, S, Al, Si, Ga, Ge, In, and Sn. xc satisfies 0 ≦ xc ≦ 5, yc satisfies 0 ≦ yc ≦ 1, zc satisfies 0 ≦ zc ≦ 1, and nc satisfies 0 ≦ nc ≦ 6.); Li xd (Al, Ga) yd (Ti, Ge) zd Si ad P md O nd (xd satisfies 1 ≦ xd ≦ 3, yd satisfies 0 ≦ yd ≦ 1, zd satisfies 0 ≦ zd ≦ 2, ad satisfies 0 ≦ ad ≦ 1, md satisfies 1 ≦ md ≦ 7, and nd satisfies 3 ≦ nd ≦ 13.); Li (3-2xe) M ee xe D ee O(xe represents a number from 0 or more to 0.1 or less, and M ee represents a divalent metal atom. D ee represents a halogen atom or a combination of two or more halogen atoms.); Li xf Si yf O zf (xf satisfies 1 ≦ xf ≦ 5, yf satisfies 0 < yf ≦ 3, and zf satisfies 1 ≦ zf ≦ 1.): Li xg S yg O zg (xg satisfies 1 ≦ xg ≦ 3, yg satisfies 0 < yg ≦ 2, and zg satisfies 1 ≦ zg ≦ 10.); Li3BO3; Li3BO3 - Li2SO4, Li2O - B2O3 - P2O5, Li2O - SiO2, Li6BaLa2Ta2O 12 、Li3PO (4-3 / 2w) N w (w is w < 1), Li having a LISICON (Lithium super ionic conductor) type crystal structure 3.5 Zn 0.25 GeO4; La having a perovskite type crystal structure 0.55 Li 0.35 TiO3; LiTi2P3O having a NASICON (Natrium super ionic conductor) type crystal structure 12 、Li 1+xh+yh (Al, Ga) xh(Ti,Ge) 2-xh Si yh P 3-yh O 12 (xh satisfies 0 ≤ xh ≤ 1, and yh satisfies 0 ≤ yh ≤ 1.); For example, Li 1.3 Al 0.3 Ti 1.7 Examples include (PO4)3. Li7La3Zr2O has a garnet-type crystal structure. 12 Examples include (LLZ). Furthermore, ceramic materials in which elements have been substituted in LLZ are also known. For example, it is preferable to use materials that contain at least one element selected from the group consisting of Mg, Al, Si, Ca (calcium), Ti, V (vanadium), Ga (gallium), Sr, Y (yttrium), Nb (niobium), Sn (tin), Sb (antimony), Ba (barium), Hf (hafnium), Ta (tantalum), W (tungsten), Bi (bismuth), and lanthanide elements. As a specific example, for example, Li 6.25 La3Zr2Al 0.25 O 12、 Li 6.24 La3Zr2Al 0.24 O 11.98 Li 6.2 Al 0.2 La3Zr 1.8 Ta 0.2 O 12 These are some examples. Furthermore, phosphorus compounds containing Li, P, and O are also desirable. For example, lithium phosphate (Li3PO4); LiPON and LiPOD, which are obtained by substituting some of the oxygen in lithium phosphate with nitrogen. 1 (D 1 Preferably, it is one or more elements selected from Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zr, Nb, Mo, Ru, Ag, Ta, W, Pt, and Au. Furthermore, LiA 1 ON(A 1 This is one or more elements selected from Si, B, Ge, Al, C, and Ga, etc. Other elements such as ) can also be preferably used. Specific examples include Li2O-Al2O3-SiO2-P2O5-TiO2-GeO2 and Li2O-Al2O3-SiO2-P2O5-TiO2.

[0048] The above oxide-based inorganic solid electrolyte preferably contains at least one element selected from the group consisting of Mg, Al, Si, Ca, Ti, Ga, Sr, Nb, Sn, Ba, and W. Oxide-based inorganic solid electrolytes containing these elements are particularly preferred in terms of good Li ion conductivity.

[0049] In particular, the oxide-based solid electrolyte used in this disclosure is preferably a solid electrolyte containing four or more elements in addition to oxygen atoms. The "four or more elements" mentioned above exclude carbon atoms and hydrogen atoms. It is preferable that at least one of the four or more elements is selected from the group consisting of Mg, Al, Si, Ca, Ti, Ga, Sr, Nb, Sn, Ba, and W. The fact that it is a solid electrolyte that satisfies the composition requirement of containing four or more elements in addition to oxygen atoms is advantageous because it can stably provide high ionic conductivity.

[0050] The above oxide-based solid electrolyte is preferably lithium-containing. A lithium-containing oxide-based solid electrolyte is used in solid-state batteries that use lithium ions as carriers and is particularly preferred in that it is an electrochemical device with high energy density.

[0051] The above oxide-based solid electrolyte is preferably an oxide having a crystalline structure. Oxides having a crystalline structure are particularly preferred in terms of good Li ion conductivity. As for oxides having a crystalline structure, there are perovskite-type (La 0.51 Li 0.34 TiO 2.94 etc.), NASICON type (Li 1.3 Al 0.3 Ti 1.7 (PO4)3, etc.), garnet type (Li7La3Zr2O 12(LLZ), Li 6.25 La3Zr2Al 0.25 O 12 Li 6.24 La3Zr2Al 0.24 O 11.98 Li 6.2 Al 0.2 La3Zr 1.8 Ta 0.2 O 12 Examples include the following. Among them, the NASICON type is preferred.

[0052] The volume-average particle size of oxide-based solid electrolytes is not particularly limited, but is preferably 0.01 μm or larger, and more preferably 0.03 μm or larger. The upper limit is preferably 100 μm or less, and more preferably 50 μm or less. The average particle size of oxide-based solid electrolyte particles is measured using the following procedure: A 1% by mass dispersion of oxide-based solid electrolyte particles is prepared in a 20 ml sample bottle using water (or heptane if the substance is unstable in water). The diluted dispersion sample is irradiated with 1 kHz ultrasound for 10 minutes and used immediately afterward. Using this dispersion sample, data is acquired 50 times using a laser diffraction / scattering particle size distribution analyzer LA-920 (HORIBA) at a temperature of 25°C using a quartz cell to obtain the volume-average particle size. For other detailed conditions, refer to JIS Z8828:2013 "Particle Size Analysis - Dynamic Light Scattering Method" as needed. Five samples are prepared for each level, and their average value is adopted.

[0053] When considering the reduction of interfacial resistance and the maintenance of the reduced interfacial resistance when used in a solid-state secondary battery, the content of oxide-based solid electrolyte in the solid component of the composite material for secondary batteries is preferably 5% by mass or more, more preferably 9% by mass or more, and particularly preferably 12% by mass or more, in the electrodes, based on 100% by mass of the solid component. As an upper limit, from the viewpoint of battery capacity, it is preferably 60% by mass or less, more preferably 50% by mass or less, and particularly preferably 40% by mass or less. Furthermore, the solid electrolyte layer placed between the positive and negative electrodes is preferably 50% by mass or more, more preferably 60% by mass or more, and particularly preferably 70% by mass or more. As an upper limit, from a similar viewpoint, it is preferably 99.9% by mass or less, more preferably 99.8% by mass or less, and particularly preferably 99.7% by mass or less. The above oxide-based solid electrolytes may be used individually or in combination of two or more types. In this specification, solid content (solid components) refers to components that do not volatilize or evaporate when dried at 170°C under a nitrogen atmosphere for 6 hours.

[0054] The secondary battery mixture of this disclosure is particularly suitable for lithium-ion solid-state secondary batteries. The secondary battery mixture disclosed herein is typically used in sheet form when used in solid secondary batteries.

[0055] The composite sheet for secondary batteries disclosed herein can be used as a positive electrode sheet or a negative electrode sheet. Furthermore, it can also be used as a sheet for a solid electrolyte layer. Of these, the sheet used for electrodes further contains active material particles. The active material particles can be positive electrode active material and negative electrode active material. The composite sheet for secondary batteries of this disclosure can be more preferably used as a positive electrode sheet using positive electrode active material. Furthermore, when used as an electrode sheet, it may contain a conductive additive as needed.

[0056] The following describes electrode active materials, conductive additives, etc.

[0057] (electrode active material) When the composite sheet for secondary batteries of this disclosure is used as a positive electrode sheet, a positive electrode active material is incorporated into the composite sheet for secondary batteries. The positive electrode active material can be any positive electrode active material known as a positive electrode active material for solid-state batteries. In particular, it is preferable to use a positive electrode active material that can intercept and release lithium ions.

[0058] The above positive electrode active material is not particularly limited as long as it can electrochemically occlude and release alkali metal ions. For example, a substance containing an alkali metal and at least one transition metal is preferable. Specific examples include alkali metal-containing transition metal composite oxides, alkali metal-containing transition metal phosphate compounds, conductive polymers, and the like. Among them, as the positive electrode active material, an alkali metal-containing transition metal composite oxide that produces a particularly high voltage is preferable. Examples of the above alkali metal ions include lithium ions, sodium ions, potassium ions, and the like. In a preferred embodiment, the alkali metal ion can be a lithium ion. That is, in this embodiment, the alkali metal ion secondary battery is a lithium ion secondary battery.

[0059] Examples of the above alkali metal-containing transition metal composite oxide include, for example, Formula: M a Mn 2-b M 1 b O4 (In the formula, M is at least one metal selected from the group consisting of Li, Na, and K; 0.9 ≦ a; 0 ≦ b ≦ 1.5; M 1 is at least one metal selected from the group consisting of Fe, Co, Ni, Cu, Zn, Al, Sn, Cr, V, Ti, Mg, Ca, Sr, B, Ga, In, Si, and Ge) an alkali metal-manganese spinel composite oxide represented by, Formula: MNi 1-c M 2 cO2 (In the formula, M is at least one metal selected from the group consisting of Li, Na, and K; 0 ≦ c ≦ 0.5; M 2 is at least one metal selected from the group consisting of Fe, Co, Mn, Cu, Zn, Al, Sn, Cr, V, Ti, Mg, Ca, Sr, B, Ga, In, Si, and Ge) an alkali metal-nickel composite oxide represented by, or, Formula: MCo 1-d M 3 d O2 (wherein M is at least one metal selected from the group consisting of Li, Na, and K; 0 ≤ d ≤ 0.5; M 3 (This refers to at least one metal selected from the group consisting of Fe, Ni, Mn, Cu, Zn, Al, Sn, Cr, V, Ti, Mg, Ca, Sr, B, Ga, In, Si, and Ge.) Examples include alkali metal-cobalt composite oxides represented by . In the above, M is preferably one metal selected from the group consisting of Li, Na, and K, more preferably Li or Na, and even more preferably Li.

[0060] In particular, MCoO2, MMnO2, MNiO2, MMn2O4, and MNi are used because they offer high energy density and can provide high-output secondary batteries. 0.8 Co 0.15 Al 0.05 O2, or MNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 is preferred, and it is preferable that the compound is represented by the following general formula (3). MNi h Co i Mn j M 5 k O2(3) (In the formula, M is at least one metal selected from the group consisting of Li, Na, and K, M 5 (where represents at least one element selected from the group consisting of Fe, Cu, Zn, Al, Sn, Cr, V, Ti, Mg, Ca, Sr, B, Ga, In, Si, and Ge, and (h+i+j+k)=1.0, 0≦h≦1.0, 0≦i≦1.0, 0≦j≦1.5, and 0≦k≦0.2.)

[0061] Examples of the alkali metal-containing transition metal phosphate compounds mentioned above include the following formula (4): M e M 4 f (PO4) g (4) (In the formula, M is at least one metal selected from the group consisting of Li, Na, and K, M 4Herein, M represents at least one selected from the group consisting of V, Ti, Cr, Mn, Fe, Co, Ni, and Cu, and is a compound represented by (0.5 ≤ e ≤ 3, 1 ≤ f ≤ 2, 1 ≤ g ≤ 3). In the above, M is preferably one metal selected from the group consisting of Li, Na, and K, more preferably Li or Na, and even more preferably Li.

[0062] Preferred transition metals for lithium-containing transition metal phosphate compounds include V, Ti, Cr, Mn, Fe, Co, Ni, Cu, etc. Specific examples include iron phosphates such as LiFePO4, Li3Fe2(PO4)3, and LiFeP2O7, cobalt phosphates such as LiCoPO4, and those in which some of the transition metal atoms that make up the main component of these lithium transition metal phosphate compounds are substituted with other elements such as Al, Ti, V, Cr, Mn, Fe, Co, Li, Ni, Cu, Zn, Mg, Ga, Zr, Nb, and Si. The lithium-containing transition metal phosphate compound described above is preferably one having an olivine-type structure.

[0063] Other cathode active materials include MFePO4 and MNi 0.8 Co 0.2 O2, M 1.2 Fe 0.4 Mn 0.4 O2, MNi 0.5 Mn 1.5 Examples include O2, MV3O6, M2MnO3 (wherein M is at least one metal selected from the group consisting of Li, Na, and K). In particular, M2MnO3, MNi 0.5 Mn 1.5 Positive electrode active materials such as O2 are preferable because their crystal structure does not collapse when the secondary battery is operated at a voltage exceeding 4.4V or a voltage of 4.6V or higher. Therefore, electrochemical devices such as secondary batteries using positive electrode materials containing the positive electrode active materials exemplified above are preferable because, even when stored at high temperatures, the remaining capacity does not decrease easily, the rate of resistance increase does not change easily, and the battery performance does not deteriorate even when operated at high voltages.

[0064] Other positive electrode active materials include M2MnO3 and MM6 O₂ (where M is at least one metal selected from the group consisting of Li, Na, and K, and M 6 is also a solid solution material with transition metals such as Co, Ni, Mn, Fe, etc.).

[0065] Examples of the solid solution material include, for example, the general formula Mx[Mn (1-y) M 7 y O z is an alkali metal manganese oxide represented by. Here, M in the formula is at least one metal selected from the group consisting of Li, Na, and K, and M 7 consists of at least one metal element other than M and Mn, and for example, contains one or more elements selected from the group consisting of Co, Ni, Fe, Ti, Mo, W, Cr, Zr, and Sn. Also, the values of x, y, and z in the formula are in the range of 1 < x < 2, 0 ≤ y < 1, and 1.5 < z < 3. Among them, Li 1.2 Mn 0.5 Co 0.14 Ni 0.14 A manganese-containing solid solution material in which LiNiO₂ or LiCoO₂ is solid-dissolved based on Li₂MnO₃ such as O₂ is preferable because it can provide an alkali metal ion secondary battery having a high energy density.

[0066] Also, it is preferable to include lithium phosphate in the positive electrode active material because the continuous charging characteristics are improved. There is no limitation on the use of lithium phosphate, but it is preferably used by mixing with the above positive electrode active material. The amount of lithium phosphate used is preferably at least 0.1% by mass, more preferably at least 0.3% by mass, still more preferably at least 0.5% by mass, and preferably at most 10% by mass, more preferably at most 8% by mass, still more preferably at most 5% by mass, based on the total of the above positive electrode active material and lithium phosphate.

[0067] Examples of the conductive polymers mentioned above include p-doped and n-doped conductive polymers. Examples of conductive polymers include polyacetylene-based polymers, polyphenylene-based polymers, heterocyclic polymers, ionic polymers, ladder and network polymers, etc.

[0068] Among the above-mentioned positive electrode active materials, nickel-containing positive electrode active materials are preferred. By including nickel, the capacity of the active material can be increased, thereby improving battery performance. Furthermore, it is possible to reduce the amount of cobalt, a rare metal, which is advantageous in terms of cost. In particular, it is preferable that the material contains a lithium-nickel composite oxide.

[0069] Lithium-nickel composite oxides include those with the general formula (1): Li y Ni 1-x M x O2 A lithium-nickel composite oxide represented by the formula (wherein x is 0.01 ≤ x ≤ 0.5, y is 0.9 ≤ y ≤ 1.2, and M represents a metal atom (excluding Ni)) is preferred. A positive electrode active material containing a large amount of Ni in this way is beneficial for increasing the capacity of secondary batteries.

[0070] In general formula (1), x is a coefficient that satisfies 0.01 ≤ x ≤ 0.5, and more preferably 0.05 ≤ x ≤ 0.4, and even more preferably 0.10 ≤ x ≤ 0.3, in order to obtain a secondary battery with higher capacity.

[0071] In general formula (1), examples of metal atoms M include V, Ti, Cr, Mn, Fe, Co, Cu, Al, Zn, Mg, Ga, Zr, Si, etc. Preferably, the metal atoms M are transition metals such as V, Ti, Cr, Mn, Fe, Co, Cu, or combinations of the above transition metals with other metals such as Al, Ti, V, Cr, Mn, Fe, Co, Cu, Zn, Mg, Ga, Zr, Si, etc.

[0072] LiNi 0.82 Co 0.15Al 0.03 O2, LiLiLi 0.6 Mn 0.2 Co 0.2 O2 and LiNi 0.8 Mn 0.1 Co 0.1 Preferably, at least one selected from the group consisting of O2, and LiNi 0.82 Co 0.15 Al 0.03 O2 and LiNi 0.8 Mn 0.1 Co 0.1 At least one selected from the group consisting of O2 is more preferable.

[0073] Lithium-nickel composite oxides represented by general formula (1) may be used in combination with other positive electrode active materials. Specific examples of other positive electrode active materials include LiCoO2, LiMnO2, LiMn2O4, Li2MnO3, and LiMn 1.8 Al 0.2 O4, Li4Ti5O 12 , LiFePO4, Li3Fe2(PO4)3, LiFeP2O7, LiCoPO4, Li 1.2 Fe 0.4 Mn 0.4 O2, LiNiO2, LiLi 0.5 Mn 0.3 Co 0.2 Examples include O2.

[0074] Furthermore, a positive electrode active material may be used in which a substance of a different composition is attached to its surface. Examples of surface-attached substances include oxides such as aluminum oxide, silicon oxide, titanium oxide, zirconium oxide, magnesium oxide, calcium oxide, boron oxide, antimony oxide, and bismuth oxide; sulfates such as lithium sulfate, sodium sulfate, potassium sulfate, magnesium sulfate, calcium sulfate, and aluminum sulfate; carbonates such as lithium carbonate, calcium carbonate, and magnesium carbonate; and carbon.

[0075] These surface-adhering substances can be attached to the surface of the positive electrode active material by, for example, dissolving or suspending them in a solvent and impregnating or adding them to the positive electrode active material, followed by drying; dissolving or suspending a surface-adhering substance precursor in a solvent and impregnating and adding it to the positive electrode active material, then reacting it by heating or the like; or adding it to the positive electrode active material precursor and simultaneously firing it. When attaching carbon, a method of mechanically attaching carbonaceous material afterwards, such as activated carbon, can also be used.

[0076] The amount of surface-adhered material is preferably 0.1 ppm or more, more preferably 1 ppm or more, and even more preferably 10 ppm or more, relative to the positive electrode active material by mass, with a lower limit of preferably 20% or less, more preferably 10% or less, and even more preferably 5% or less. The surface-adhered material can suppress the oxidation reaction of the solid electrolyte on the surface of the positive electrode active material, thereby improving battery life. If the amount of adhesion is too small, the effect will not be fully realized, and if it is too large, it may inhibit the movement of lithium ions, which may increase resistance.

[0077] The particle shapes of the positive electrode active material can include conventionally used shapes such as lumpy, polyhedral, spherical, ellipsoidal, plate-like, needle-like, and columnar. Furthermore, primary particles may aggregate to form secondary particles.

[0078] The tap density of the positive electrode active material is preferably 0.5 g / cm³. 3 More preferably 0.8 g / cm³ 3 More preferably 1.0 g / cm³ 3The above is the case. If the tap density of the positive electrode active material falls below the above lower limit, the amount of dispersion medium required during the formation of the positive electrode active material layer increases, as does the amount of conductive material and binder required, which may restrict the filling rate of the positive electrode active material into the positive electrode active material layer and thus limit the battery capacity. By using a composite oxide powder with a high tap density, a high-density positive electrode active material layer can be formed. Generally, a higher tap density is preferable, and there is no particular upper limit, but if it is too high, the diffusion of lithium ions using the solid electrolyte as a medium within the positive electrode active material layer becomes the rate-limiting step, which may lead to a decrease in load characteristics. Therefore, the upper limit is preferably 4.0 g / cm³. 3 More preferably, 3.7 g / cm³ 3 More preferably, 3.5 g / cm³ 3 The following applies: In this disclosure, the tap density is defined as the powder packing density (tap density) g / cm³ obtained when 5-10 g of positive electrode active material powder is placed in a 10 ml glass graduated cylinder and tapped 200 times with a stroke of approximately 20 mm. 3 We will seek it as follows.

[0079] The median diameter d50 of the positive electrode active material particles (or secondary particle diameter if primary particles aggregate to form secondary particles) is preferably 0.3 μm or more, more preferably 0.5 μm or more, even more preferably 0.8 μm or more, and most preferably 1.0 μm or more. It is also preferably 30 μm or less, more preferably 27 μm or less, even more preferably 25 μm or less, and most preferably 22 μm or less. If it falls below the lower limit, it may not be possible to obtain a high tap density product, and if it exceeds the upper limit, the diffusion of lithium within the particles will take longer, which may lead to a decrease in battery performance or problems such as streaking when creating the positive electrode of the battery, i.e., when slurrying the active material with conductive material and binder etc. in a solvent and coating it into a thin film. Here, by mixing two or more of the above positive electrode active materials having different median diameters d50, the packing performance during positive electrode creation can be further improved.

[0080] In this disclosure, the median diameter d50 is measured using a known laser diffraction / scattering particle size distribution analyzer. When using the HORIBA LA-920 as the particle size distribution analyzer, a 0.1% by mass aqueous solution of sodium hexametaphosphate is used as the dispersion medium during measurement, and the measurement is performed after ultrasonic dispersion for 5 minutes with the measurement refractive index set to 1.24.

[0081] When primary particles aggregate to form secondary particles, the average primary particle diameter of the positive electrode active material is preferably 0.05 μm or more, more preferably 0.1 μm or more, and even more preferably 0.2 μm or more. The upper limit is preferably 5 μm or less, more preferably 4 μm or less, even more preferably 3 μm or less, and most preferably 2 μm or less. Exceeding the upper limit makes it difficult to form spherical secondary particles, which can adversely affect powder packing properties and significantly reduce the specific surface area, potentially leading to a decrease in battery performance such as output characteristics. Conversely, below the lower limit usually results in problems such as poor reversibility of charge and discharge due to underdeveloped crystals.

[0082] In this disclosure, the average primary particle diameter of the positive electrode active material is measured by observation using a scanning electron microscope (SEM). Specifically, it is determined by taking a photograph at 10,000x magnification, finding the longest value of the intercept between the left and right boundaries of the primary particles relative to a horizontal line for any 50 primary particles, and taking the average value.

[0083] The BET specific surface area of ​​the positive electrode active material is preferably 0.1 m². 2 / g or more, more preferably 0.2m 2 / g or more, more preferably 0.3m 2 The value is 1 / g or more, and the upper limit is preferably 50m 2 / g or less, more preferably 40m 2 / g or less, more preferably 30m 2 It is less than / g. If the BET specific surface area is smaller than this range, battery performance tends to decrease, and if it is larger, it becomes difficult to increase the tap density, which can cause problems with coating when forming the positive electrode active material layer.

[0084] In this disclosure, the BET specific surface area is defined as the value measured by a nitrogen adsorption BET single-point method using a gas flow method, after pre-drying the sample at 150°C for 30 minutes under nitrogen flow using a surface area meter (for example, a fully automatic surface area measuring device manufactured by Okura Riken Co., Ltd.), and then using a nitrogen-helium mixed gas that has been precisely adjusted so that the relative pressure of nitrogen to atmospheric pressure is 0.3.

[0085] When the secondary battery of this disclosure is used as a large lithium-ion secondary battery for hybrid vehicles or distributed power sources, high output is required, so it is preferable that the particles of the positive electrode active material consist mainly of secondary particles. The positive electrode active material particles preferably contain 0.5 to 7.0 volume percent of fine particles with an average secondary particle diameter of 40 μm or less and an average primary particle diameter of 1 μm or less. By including fine particles with an average primary particle diameter of 1 μm or less, the contact area with the solid electrolyte is increased, which allows for faster diffusion of lithium ions between the all-solid-state secondary battery sheet and the solid electrolyte, and as a result, the output performance of the battery can be improved.

[0086] For the production of positive electrode active materials, general methods for producing inorganic compounds are used. In particular, various methods can be considered for producing spherical or ellipsoidal active materials. For example, a method can be used in which transition metal raw materials are dissolved or pulverized and dispersed in a solvent such as water, the pH is adjusted while stirring to create and recover spherical precursors, these are dried as needed, and then a Li source such as LiOH, Li2CO3, or LiNO3 is added and calcined at a high temperature to obtain the active material.

[0087] For the manufacture of the positive electrode, the positive electrode active material may be used alone, or two or more materials with different compositions may be used in any combination or ratio. In this case, a preferred combination is LiCoO2 and LiNi 0.33 Co 0.33 Mn 0.33Examples include combinations with ternary systems such as O2, combinations of LiCoO2 and LiMn2O4 or a combination in which part of the Mn is substituted with other transition metals, or combinations of LiFePO4 and LiCoO2 or a combination in which part of the Co is substituted with other transition metals.

[0088] The content of the above-mentioned positive electrode active material is preferably 40 to 95% by mass, and more preferably 50 to 91% by mass, in the positive electrode mixture, in terms of high battery capacity. Furthermore, the content of the positive electrode active material is preferably 40% by mass or more, more preferably 50% by mass or more, and particularly preferably 60% by mass or more. The upper limit is preferably 95% by mass or less, more preferably 91% by mass or less, and particularly preferably 88% by mass or less. If the content of the positive electrode active material in the positive electrode mixture is too low, the electrical capacity may be insufficient. Conversely, if the content is too high, the electron / ion conductivity of the positive electrode and the electrode strength may be insufficient.

[0089] The above-mentioned negative electrode active material is not particularly limited and includes, for example, lithium metal, artificial graphite, graphite carbon fiber, resin-fired carbon, pyrolysis vapor-grown carbon, coke, mesocarbon microbeads (MCMB), furfuryl alcohol resin-fired carbon, polyacene, pitch-based carbon fiber, vapor-grown carbon fiber, natural graphite, and carbonaceous materials such as non-graphitizable carbon, silicon and silicon-containing compounds such as silicon alloys, Li4Ti5O 12 Examples include any one of the following, or a mixture of two or more. Among these, materials containing at least a portion of carbonaceous material, or silicon-containing compounds, can be used particularly suitably.

[0090] The content of the above-mentioned negative electrode active material is preferably 40 to 95% by mass, and more preferably 50 to 91% by mass, in order to increase the volume of the resulting secondary battery composite sheet. Furthermore, the content of the negative electrode active material is preferably 40% by mass or more, more preferably 50% by mass or more, and particularly preferably 60% by mass or more. The upper limit is preferably 95% by mass or less, more preferably 91% by mass or less, and particularly preferably 88% by mass or less.

[0091] (Conductive additive) Any known conductive material can be used as the conductive additive mentioned above. Specific examples include metallic materials such as copper and nickel, graphite such as natural graphite and artificial graphite, carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black, and carbon materials such as needle coke, carbon nanotubes, fullerenes, and amorphous carbon such as VGCF. These may be used individually or in any combination and ratio of two or more materials.

[0092] When a conductive additive is used, it is typically contained in the electrode sheet at a concentration of 0.01% by mass or more, preferably 0.1% by mass or more, more preferably 0.5% by mass or more, and typically 50% by mass or less, preferably 30% by mass or less, and more preferably 15% by mass or less. If the content is lower than this range, the conductivity may be insufficient. Conversely, if the content is higher than this range, the battery capacity may decrease.

[0093] (Other ingredients) The composite sheet for secondary batteries may further contain a thermoplastic resin. Examples of thermoplastic resins include vinylidene fluoride, polypropylene, polyethylene, polystyrene, polyethylene terephthalate, and polyethylene oxide. One type may be used alone, or two or more types may be used in any combination and ratio.

[0094] The ratio of thermoplastic resin to electrode active material is typically 0.01% by mass or more, preferably 0.05% by mass or more, more preferably 0.10% by mass or more, and typically within the range of 3.0% by mass or less, preferably 2.5% by mass or less, and more preferably 2.0% by mass or less. Adding thermoplastic resin can improve the mechanical strength of the electrode. If this range is exceeded, the proportion of active material in the electrode mixture decreases, which may lead to problems such as a decrease in battery capacity or an increase in resistance between active materials.

[0095] In the composite sheet for secondary batteries of this disclosure, the binder content is preferably 0.2% by mass or more, more preferably 0.3% by mass or more, and more preferably more than 0.5% by mass, as the proportion of the binder in the composite sheet for secondary batteries. Furthermore, it is preferably 10% by mass or less, more preferably 8% by mass or less, and most preferably 6% by mass or less. If the proportion of binder is too low, the active material cannot be sufficiently held within the composite sheet for secondary batteries, resulting in insufficient mechanical strength of the composite sheet for secondary batteries and potentially degrading battery performance such as cycle characteristics. On the other hand, if it is too high, it may lead to a decrease in battery capacity and conductivity.

[0096] (Manufacturing method) The method for producing a composite sheet for secondary batteries according to this disclosure preferably involves using a raw material composition obtained by mixing the above-mentioned components and forming it into a sheet. In sheet formation, since a drying step can be omitted, it is preferable to reduce or completely eliminate the use of a liquid medium and apply shear stress to the powdered raw material composition without preparing a slurry. In addition, a small amount of solvent may be added as a lubricant to reduce the load on the equipment. The solvent is preferably an organic solvent, and the amount of solvent contained is preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 3% by mass or less, relative to the raw material composition.

[0097] The manufacturing method of the composite sheet for secondary batteries described herein is not limited, but an example of a specific manufacturing method is shown below. The composite sheet for secondary batteries disclosed herein is (1) A step in which shear force is applied while mixing a raw material composition containing an oxide-based solid electrolyte and a binder. Step (2) involves forming the secondary battery mixture obtained in step (1) into a bulk form, and Step (3) involves rolling the bulk secondary battery mixture obtained in step (2) into a sheet. It can be obtained by a method for manufacturing electrode mixture sheets for secondary batteries having [the specified characteristic].

[0098] In step (1) above, when shear force is applied while mixing the raw material composition, the resulting secondary battery mixture exists in a state without a defined form, with oxide-based solid electrolyte, binder, etc., simply mixed together. Specific mixing methods include using a W-type mixer, V-type mixer, drum-type mixer, ribbon mixer, conical screw-type mixer, single-shaft kneader, twin-shaft kneader, mix muller, agitator mixer, planetary mixer, Henschel mixer, high-speed mixer, etc.

[0099] In step (1) above, the mixing conditions can be appropriately set by adjusting the rotation speed and mixing time. For example, the rotation speed is preferably 15,000 rpm or less. Preferably it is 10 rpm or more, more preferably 1,000 rpm or more, even more preferably 3,000 rpm or more, and also preferably 12,000 rpm or less, more preferably 11,000 rpm or less, and even more preferably 10,000 rpm. If it is below the above range, mixing will take a long time and will affect productivity. If it is above the above range, fibrillation will proceed excessively, which may result in an electrode mixture sheet with inferior strength.

[0100] In step (1) described above, it is preferable to carry out the process at 30°C or higher, and more preferably at 60°C or higher. Furthermore, it is preferable to include a step (A) before the above step (1) in which the raw material composition is mixed to disperse the binder. In the above step (A), it is preferable to suppress fibrillation and mix with the smallest possible shear force.

[0101] In step (A) described above, the mixing conditions can be appropriately set by adjusting the rotation speed and mixing time. For example, the rotation speed is preferably 1000 rpm or less. Preferably it is 10 rpm or more, more preferably 15 rpm or more, even more preferably 20 rpm or more, and also preferably in the range of 500 rpm or less. In step (A) described above, it is preferable to perform the mixing at a temperature of 19°C or lower. By using this temperature range, the dispersibility of the binder can be improved, allowing for processing into a more uniform, desired sheet.

[0102] PTFE has two transition temperatures, at approximately 19°C and 30°C. Below 19°C, PTFE can be easily mixed while maintaining its shape. However, above 19°C, the structure of PTFE particles loosens, making them more sensitive to mechanical shear. Above 30°C, a higher degree of fibrillation occurs.

[0103] Therefore, when using PTFE resin as a fibrillating resin, it is preferable to carry out the above step (A) at a temperature of 19°C or lower, preferably 0°C to 19°C. In other words, in such a process (A), it is preferable to mix and homogenize without causing fibrillation. Then, it is preferable to cause fibrillation in the subsequent processes (1) to (5).

[0104] As described above, the above raw material composition preferably contains substantially no liquid medium and is preferably in powder form. In a powder raw material composition, the liquid medium content is preferably 1% by mass or less.

[0105] In step (2) above, forming into a bulk means forming the composite material for secondary batteries into a single mass. Specific methods for forming materials into bulk include extrusion molding and press molding. Furthermore, "bulk form" does not specify a particular shape, but rather refers to a state in which there is a single mass, and includes forms such as rod-shaped, sheet-shaped, spherical, and cube-shaped. The size of the mass is preferably such that the diameter of its cross-section or the shortest side is 10,000 μm or more. More preferably, it is 20,000 μm or more.

[0106] Specific rolling methods in step (3) above include methods using a roll press, a flat plate press, a calender roll machine, etc.

[0107] Furthermore, it is preferable to have a step (4) after step (3) in which a larger load is applied to the obtained rolled sheet and it is further rolled into a thinner sheet. It is also preferable to repeat step (4). In this way, rather than thinning the rolled sheet all at once, rolling it little by little in stages results in better flexibility. The number of times step (4) is performed is preferably 2 to 10 times, and more preferably 3 to 9 times. Specific rolling methods include, for example, a method in which two or more rolls are rotated and the rolled sheet is passed between them to process it into a thinner sheet.

[0108] Furthermore, from the viewpoint of adjusting the fibril diameter, it is also preferable to have a step (5) after step (3) or step (4) in which the rolled sheet is roughly crushed, then reshaped into a bulk form, and rolled into a sheet form again. It is also preferable to repeat step (5). The number of times step (5) is performed is preferably 1 to 12 times, and more preferably 2 to 11 times.

[0109] In step (5), specific methods for roughly crushing the rolled sheet and forming it into a bulk form include folding the rolled sheet, forming it into a rod or thin film sheet, or chipping it. In this disclosure, "rough crushing" means changing the form of the rolled sheet obtained in step (3) or step (4) to another form in order to roll it into a sheet in the next step, and includes cases such as simply folding the rolled sheet.

[0110] Alternatively, step (4) may be performed after step (5), and this process may be repeated. Furthermore, uniaxial stretching or biaxial stretching may be performed in steps (2) or (3), (4), and (5). Furthermore, the fibril diameter (median value) can also be adjusted by the degree of coarse crushing in process (5). Steps (2) to (5) are preferably carried out at 30°C or higher, and more preferably at 60°C or higher.

[0111] In the above steps (3), (4), or (5), the rolling rate is preferably 10% or more, more preferably 20% or more, and also preferably 80% or less, more preferably 65% ​​or less, and even more preferably 50% or less. If it is below the above range, the time required will increase with the number of rolling cycles, affecting productivity. If it is above the above range, fibrillation may proceed excessively, potentially resulting in a composite sheet with inferior strength and flexibility. The rolling ratio, as used here, refers to the percentage reduction in thickness after rolling compared to the thickness of the sample before rolling. The sample before rolling may be in bulk form or in sheet form. The thickness of the sample refers to the thickness in the direction in which the load is applied during rolling.

[0112] As mentioned above, PTFE powder undergoes fibrillation when shear force is applied. However, to obtain a fibrous structure with a median fibril diameter of 100 nm or less, excessive shear stress can accelerate fibrillation too much, impairing flexibility. Conversely, weak shear stress may not provide sufficient strength. Therefore, by applying appropriate shear stress to the PTFE during mixing and rolling to promote fibrillation, and then rolling the mixture into a sheet, within the above-mentioned range, it is possible to obtain a fibrous structure with a median fibril diameter of 100 nm or less.

[0113] As described above, the composite sheet for secondary batteries disclosed herein can be either a positive electrode sheet or a negative electrode sheet. Furthermore, it can also be a sheet for a solid electrolyte layer. When using a composite sheet for the positive electrode or a negative electrode, the positive electrode active material or negative electrode active material should be mixed together with the solid electrolyte and binder during the manufacturing of the composite sheet for secondary batteries.

[0114] The positive and negative electrodes will be explained below. (positive electrode) In this disclosure, the positive electrode is preferably composed of a current collector and the positive electrode sheet described above. Suitable materials for the positive electrode current collector include metals such as aluminum, titanium, tantalum, stainless steel, and nickel, or their alloys; and carbon materials such as carbon cloth and carbon paper. Among these, metal materials, particularly aluminum or its alloys, are preferred.

[0115] Examples of current collector shapes include metal foil, metal cylinders, metal coils, metal plates, expanded metal, punched metal, and foamed metal in the case of metal materials, and carbon plates, carbon thin films, and carbon cylinders in the case of carbon materials. Of these, metal foil is preferred. The metal foil may be formed into a mesh shape as appropriate. The thickness of the metal foil is arbitrary, but is usually 1 μm or more, preferably 3 μm or more, more preferably 5 μm or more, and usually 1 mm or less, preferably 100 μm or less, more preferably 50 μm or less. If the metal foil is thinner than this range, it may lack the strength required for a current collector. Conversely, if the metal foil is thicker than this range, its handling may be impaired.

[0116] Furthermore, it is preferable that a conductive additive is applied to the surface of the current collector, as this reduces the electrical contact resistance between the current collector and the positive electrode compound sheet. Examples of conductive additives include carbon and precious metals such as gold, platinum, and silver.

[0117] The positive electrode can be manufactured by conventional methods. For example, one method involves laminating the positive electrode sheet and the current collector with an adhesive and then drying them.

[0118] The density of the positive electrode sheet is preferably 2.0 g / cm³. 3 More preferably 2.1 g / cm³ 3 More preferably 2.3 g / cm³ 3 The above applies, and preferably 4.0 g / cm³. 3 More preferably, 3.9 g / cm³ 3 More preferably, 3.8 g / cm³ 3The following range applies. Exceeding this range can reduce conductivity between active materials, increase battery resistance, and prevent high output from being achieved. Exceeding this range can result in a low content of hard, brittle active materials, potentially leading to a battery with low capacity.

[0119] The thickness of the positive electrode is not particularly limited, but from the viewpoint of high capacity and high output, the thickness of the composite sheet, after subtracting the thickness of the current collector, is preferably 10 μm or more, more preferably 20 μm or more, and preferably 500 μm or less, and more preferably 450 μm or less, with respect to one side of the current collector.

[0120] Furthermore, a positive electrode with a different composition attached to its surface may also be used. Examples of surface-attached substances include oxides such as aluminum oxide, silicon oxide, titanium oxide, zirconium oxide, magnesium oxide, calcium oxide, boron oxide, antimony oxide, and bismuth oxide; sulfates such as lithium sulfate, sodium sulfate, potassium sulfate, magnesium sulfate, calcium sulfate, and aluminum sulfate; carbonates such as lithium carbonate, calcium carbonate, and magnesium carbonate; and carbon.

[0121] (Negative electrode) In this disclosure, the negative electrode is preferably composed of a current collector and the negative electrode sheet described above. Suitable materials for the negative electrode current collector include metals such as copper, nickel, titanium, tantalum, and stainless steel, or their alloys; and carbon materials such as carbon cloth and carbon paper. Among these, metal materials, particularly copper, nickel, or their alloys, are preferred.

[0122] Examples of current collector shapes include metal foil, metal cylinders, metal coils, metal plates, expanded metal, punched metal, and foamed metal in the case of metal materials, and carbon plates, carbon thin films, and carbon cylinders in the case of carbon materials. Of these, metal foil is preferred. The metal foil may be formed into a mesh shape as appropriate. The thickness of the metal foil is arbitrary, but is usually 1 μm or more, preferably 3 μm or more, more preferably 5 μm or more, and usually 1 mm or less, preferably 100 μm or less, and more preferably 50 μm or less. If the metal foil is thinner than this range, it may lack the necessary strength as a current collector. Conversely, if the metal foil is thicker than this range, its handling may be impaired.

[0123] The negative electrode can be manufactured by conventional methods. For example, one method involves laminating the negative electrode sheet and the current collector with an adhesive and then drying them.

[0124] The density of the negative electrode sheet is preferably 1.3 g / cm³. 3 More preferably 1.4 g / cm³ 3 More preferably 1.5 g / cm³ 3 The above is true, and preferably 2.0 g / cm³. 3 More preferably, 1.9 g / cm³ 3 More preferably, 1.8 g / cm³ 3 The range is as follows. If the range is exceeded, the permeability of the solid electrolyte to the interface between the current collector and the active material decreases, which can lead to a decline in charge-discharge characteristics, especially at high current densities, and may prevent high output from being obtained. Conversely, if the range is below this, the conductivity between the active materials decreases, increasing the battery resistance and potentially preventing high output from being obtained.

[0125] The thickness of the negative electrode is not particularly limited, but from the viewpoint of high capacity and high output, the thickness of the composite sheet, after subtracting the thickness of the metal foil of the current collector, is preferably 10 μm or more, more preferably 20 μm or more, and preferably 500 μm or less, and more preferably 450 μm or less, as a lower limit for one side of the current collector.

[0126] (Solid secondary battery) This disclosure also relates to a solid-state secondary battery using the above-mentioned composite sheet for secondary batteries. The solid-state rechargeable battery may be an all-solid-state rechargeable battery, or a hybrid solid-state rechargeable battery that combines a gel-like polymer electrolyte with a solid electrolyte. Furthermore, the solid-state rechargeable battery is preferably a lithium-ion solid-state rechargeable battery.

[0127] The solid-state secondary battery of this disclosure is a solid-state secondary battery comprising a positive electrode, a negative electrode, and a solid electrolyte layer interposed between the positive electrode and the negative electrode, wherein the positive electrode, negative electrode, and solid electrolyte layer contain the composite sheet for secondary batteries of this disclosure described above, which is a positive electrode sheet, a negative electrode sheet, or a solid electrolyte layer sheet. However, the solid-state secondary battery of this disclosure may also use a composite sheet for secondary batteries other than the composite sheet for secondary batteries of this disclosure in part of the positive electrode, negative electrode, and solid electrolyte layer.

[0128] The laminated structure of the solid secondary battery described herein comprises a positive electrode comprising a positive electrode sheet and a positive electrode current collector, a negative electrode comprising a negative electrode sheet and a negative electrode current collector, and an oxide-based solid electrolyte layer sandwiched between the positive electrode and the negative electrode. The separator and battery case used in the solid-state secondary battery related to this disclosure will be described in detail below.

[0129] (Separator) The solid-state secondary battery of this disclosure may include a separator between the positive electrode and the negative electrode. Examples of the separator include porous membranes such as polyethylene and polypropylene; and nonwoven fabrics such as resin nonwoven fabrics such as polypropylene and glass fiber nonwoven fabrics.

[0130] (Battery design) The solid-state secondary battery of this disclosure may further include a battery case. The shape of the battery case used in this disclosure is not particularly limited as long as it can accommodate the positive electrode, negative electrode, electrolyte layer for oxide-based solid batteries, etc. as described above, but specific examples include cylindrical, prismatic, coin-type, laminated type, etc.

[0131] The method for manufacturing a solid-state secondary battery according to this disclosure may, for example, involve first stacking the positive electrode, solid electrolyte layer sheet, and negative electrode in order and then pressing them to form a solid-state secondary battery. By using the composite sheet for secondary batteries of this disclosure, it is possible to manufacture solid secondary batteries with low moisture content in the system, resulting in solid secondary batteries with good performance, which is preferable. [Examples]

[0132] The present disclosure will be described in detail below based on examples. In the following examples, unless otherwise specified, "parts" and "%" represent "parts by mass" and "% by mass," respectively.

[0133] [Example 1] When 367 g of TFE (35.6% by mass of the total polymerized TFE of 1032 g) had been consumed since the start of polymerization, an aqueous solution of 12.0 mg of hydroquinone dissolved in 20 ml of water was injected into the TFE as a radical scavenger (concentration of 4.0 ppm relative to the aqueous medium). Polymerization continued thereafter, and when the amount of TFE polymerized reached 1000 g from the start of polymerization, the supply of TFE was stopped, the gas in the system was immediately released to restore atmospheric pressure, and the polymerization reaction was terminated to obtain an aqueous polytetrafluoroethylene dispersion (solid content 31.2% by mass). The obtained aqueous polytetrafluoroethylene dispersion was diluted to a solid content concentration of 15%, and gently stirred in a container with a stirrer in the presence of nitric acid to solidify the polytetrafluoroethylene. The solidified polytetrafluoroethylene was separated and dried at 160°C for 18 hours to obtain powdered PTFE-1.

[0134] [Example 2] Powdered PTFE-2 was prepared using example 3 from International Publication No. 2015-080291 as a reference.

[0135] [Example 3] Powdered PTFE-3 was prepared based on example 1 of international publication no. 2012 / 086710.

[0136] [Example 4] Powdered PTFE-4 was prepared based on Preparation Example 1 of International Patent No. 2012-063622. Table 1 shows the physical properties of the fabricated PTFE.

[0137] [Table 1]

[0138] (Example 1) Oxide solid electrolyte Li 6.25 La3Zr2Al 0.25 O 12 The powdered PTFE-1 was weighed and mixed with a high-speed mixer (500 rpm, 1 minute). The stirring was performed after the container was cooled to 10°C. Then, the mixture was stirred with a high-speed mixer (10000 rpm, 3 minutes) to obtain the mixture. The stirring was performed after the container was heated to 60°C. The composition ratio was set to a mass ratio of solid electrolyte:binding agent = 98.5:1.5. The powdered PTFE-1 was dried in a vacuum dryer at 50°C for 1 hour before use. The powdered PTFE was previously sieved using a stainless steel sieve with a mesh size of 500 μm, and the material remaining on the sieve was used. The resulting mixture was formed into a bulk material and then rolled into a sheet. The rolling was carried out at a temperature of 80°C. Subsequently, the obtained rolled sheet was roughly crushed by folding it in half, then reshaped into a bulk form, and the fibrillation process was repeated four times by rolling it into a sheet using metal rolls on a flat plate. After that, further rolling was performed to obtain a sheet-like solid electrolyte layer with a thickness of 500 μm. Furthermore, the sheet-like solid electrolyte layer was cut out and placed in a roll press machine heated to 80°C for rolling. Furthermore, the thickness was adjusted by repeatedly applying a load of 5kN. The gap was adjusted so that the final thickness of the solid electrolyte layer was 150μm. The above work was carried out in an environment with a dew point of approximately -60°C.

[0139] (Example 2) Oxide solid electrolyte Li 6.25 La3Zr2Al 0.25 O12 The powdered PTFE-2 was weighed, and sheet molding was performed using the same procedure as in Example 1. The composition ratio was set to solid electrolyte:binder = 99.2:0.8 by mass.

[0140] (Example 3) Oxide solid electrolyte Li 6.25 La3Zr2Al 0.25 O 12 The powdered PTFE-3 was weighed, and sheet molding was performed using the same procedure as in Example 1. The composition ratio was set to solid electrolyte:binder = 98.5:1.5 by mass.

[0141] (Example 4) Oxide solid electrolyte Li 6.25 La3Zr2Al 0.25 O 12 The powdered PTFE-4 was weighed, and sheet molding was performed using the same procedure as in Example 1. The composition ratio was set to a mass ratio of solid electrolyte:binding agent = 98.5:1.5.

[0142] (Example 5) Oxide solid electrolyte Li 1.3 A l0.3 Ti 1.7 P3O 12 Powdered PTFE-1 was weighed, and sheet molding was performed using the same procedure as in Example 1. The composition ratio was set to solid electrolyte:binder = 98.5:1.5 by mass.

[0143] (Example 6) Oxide solid electrolyte Li 6.2 Al 0.2 La3Zr 1.8 Ta 0.2 O 12 (NANOMYTE® SOX-30) and powdered PTFE-1 were weighed, and sheet molding was performed using the same procedure as in Example 1. The composition ratio was set to solid electrolyte:binder = 98.5:1.5 by mass.

[0144] (Example 7) Oxide solid electrolyte Li 6.24 La3Zr2Al0.24 O 11.98 (NANOMYTE® SOX-25) and powdered PTFE-1 were weighed, and sheet molding was performed using the same procedure as in Example 1. The composition ratio was set to solid electrolyte:binding agent = 98.5:1.5 by mass.

[0145] (Example 8) Active material LiNi 0.8 Mn 0.1 Co 0.1 O2, oxide solid electrolyte Li 1.3 Al 0.3 Ti 1.7 P3O 12 The powdered PTFE-1 was weighed, and sheet molding was performed using the same procedure as in Example 1. The composition ratio was set to be active material:solid electrolyte:binding agent = 80.2:19:0.8 by mass.

[0146] (Example 9) Active material LiNi 0.5 Mn 1.5 O4, oxide solid electrolyte Li 1.3 Al 0.3 Ti 1.7 P3O 12 The powdered PTFE-1 was weighed, and sheet molding was performed using the same procedure as in Example 1. The composition ratio was set to be active material:solid electrolyte:binding agent = 80.2:19:0.8 by mass.

[0147] Each test was conducted using the following method. [Measurement of moisture content] The powdered PTFE was dried in a vacuum dryer at 50°C for 1 hour before use. The moisture content of the vacuum-dried PTFE was measured using a Karl Fischer moisture meter (ADP-511 / MKC-510N, manufactured by Kyoto Electronics Manufacturing Co., Ltd.) equipped with a boat-type moisture vaporizer. The moisture was heated to 210°C in the vaporizer and the vaporized moisture was measured. Nitrogen gas was used as the carrier gas at a flow rate of 200 mL / min, and the measurement time was 30 minutes. ChemAqua was used as the Karl Fischer reagent. The sample volume was 1.5 g.

[0148] [Fibril diameter of PTFE (median)] (1) Using a scanning electron microscope (S-4800 model, manufactured by Hitachi, Ltd.), magnified images (7000x) of the sheet-like solid electrolyte layer are taken and images are obtained. (2) Draw two lines horizontally at equal intervals on this image to divide the image into three equal parts. (3) For all PTFE fibers on the straight line above, measure the diameter at three points for each PTFE fiber and take the average value as the diameter of that PTFE fiber. The three measurement points are selected as the intersection of the PTFE fiber and the straight line, and points shifted 0.5 μm above and below the intersection. (Excludes unfiberized PTFE primary particles). (4) Perform the procedure in (3) above for all PTFE fibers that lie in the straight line below. (5) Starting from the first image, move 1 mm to the right of the screen and take another picture, then measure the diameter of the PTFE fibers according to (3) and (4) above. Repeat this process until the number of measured fibers exceeds 80, at which point the process is complete. (6) The median of the diameters of all the PTFE fibers measured above was used as the fibril diameter.

[0149] [Flexibility Assessment] The prepared solid electrolyte sheet was cut into 2cm x 6cm sections to create test specimens. After wrapping them around a 4mm diameter rod, the specimens were visually inspected and evaluated according to the following criteria. A "○" was given if no scratches or cracks were found, and a "×" was given if cracks were found.

[0150] [Intensity Measurement] A digital force gauge (IMADA ZTS-20N) was used to measure the strength of 4mm wide strip-shaped electrode mixture test pieces under a force flow rate of 100mm / min. The chuck distance was 30mm. Displacement was applied until fracture, and the maximum stress measured was defined as the strength of each sample. The test was performed five times, and the average value was used as the evaluation result.

[0151] The test results are shown in Tables 2 and 3.

[0152] [Table 2]

[0153] [Table 3]

[0154] <Ionic conductivity of solid electrolyte mixture sheet> The solid electrolyte mixture sheets from Examples 6 and 7 were cut to an appropriate size, and gold was deposited on both sides. Then, the solid electrolyte mixture sheets were punched out into a Φ10 mm circle and placed in a pressure cell. The cell's screws were tightened to 8 N, and electrodes were attached to the top and bottom of the cell. A schematic cross-sectional view of the pressure cell used is shown in Figure 1. For this sample, an impedance analyzer manufactured by Toyo Technica was used, with a temperature of 50°C, AC amplitude modulation of 10mV, and a frequency of 5 × 10⁻¹⁰. 6 Ionic conductivity was measured under conditions of ~0.1 Hz. Example 6 is 5 × 10 -5 S / cm, Example 7: 3 × 10 -5 The value was S / cm.

[0155] The results in Tables 2 and 3 show that the sheet-like solid electrolyte layer of the example exhibited excellent physical properties. [Industrial applicability]

[0156] The secondary battery mixture and secondary battery mixture sheets containing the same can be used in the manufacture of solid secondary batteries. [Explanation of symbols]

[0157] 1: Screw 2: Nut 3: Insulating sheet 4: Solid electrolyte mixture sheet 5: Gold deposition 6:Top electrode 7: Lower electrode

Claims

1. A composite material for electrodes of a solid-state secondary battery, comprising an oxide-based solid electrolyte and a binder, The aforementioned binder is a fibrillary resin having a fibrous structure with a median fibril diameter of 100 nm or less, and is a composite material for electrodes of a solid-state secondary battery.

2. The electrode mixture for a solid secondary battery according to claim 1, wherein the fibrillary resin is a polytetrafluoroethylene resin.

3. A composite electrode for a solid-state secondary battery according to claim 1, obtained using a raw material composition containing an oxide-based solid electrolyte and a binder, The electrode mixture for a solid-state secondary battery according to claim 1, wherein the binder in the raw material composition is a powdered fibrillary resin.

4. The raw material composition is substantially free of a liquid medium, as described in claim 3, for use as an electrode mixture for a secondary battery.

5. The compound for electrodes of a solid secondary battery according to claim 3 or 4, wherein the powdered fibrillary resin has a moisture content of 500 ppm or less.

6. The electrode mixture for a solid secondary battery according to claim 3 or 4, wherein the powdered fibrillary resin is a powdered polytetrafluoroethylene resin.

7. The compound for electrodes of a solid secondary battery according to claim 6, wherein the powdered polytetrafluoroethylene resin has a standard specific gravity of 2.12 to 2.

20.

8. The powdered polytetrafluoroethylene resin is a composite material for electrodes of a solid secondary battery according to claim 6, comprising 50% by mass or more of polytetrafluoroethylene resin having a secondary particle size of 450 μm or more.

9. The powdered polytetrafluoroethylene resin is a composite material for electrodes of a solid secondary battery according to claim 6, comprising 80% by mass or more of polytetrafluoroethylene resin having a secondary particle size of 450 μm or more.

10. The electrode mixture for a solid secondary battery according to claim 1 or 2, wherein the oxide-based solid electrolyte is a solid electrolyte containing four or more elements (excluding carbon atoms and hydrogen atoms) in addition to oxygen atoms.

11. The electrode mixture for a solid secondary battery according to claim 10, wherein at least one of the four or more elements is selected from the group consisting of Mg, Al, Si, Ca, Ti, Ga, Sr, Nb, Sn, Ba, and W.

12. An electrode mixture for a solid-state secondary battery according to claim 1 or 2, comprising a nickel-containing positive electrode active material.

13. A solid-state secondary battery electrode mixture sheet comprising the solid-state secondary battery electrode mixture according to claim 1 or 2.

14. An electrode comprising an electrode mixture sheet for a solid-state secondary battery according to claim 13.

15. Step (1): Applying shear force while mixing a raw material composition containing an oxide-based solid electrolyte and a binder. Step (2) involves forming the electrode mixture for the solid secondary battery obtained in step (1) into a bulk form, and Step (3) involves rolling the bulk solid-state electrode mixture obtained in step (2) into a sheet. A method for manufacturing an electrode composite sheet for a solid secondary battery having the following: the binder is a powdered fibrillary resin, A method for manufacturing an electrode mixture sheet for a solid-state secondary battery, characterized in that the fibrilous resin of the manufactured electrode mixture sheet for a solid-state secondary battery has a fibrous structure with a median fibril diameter of 100 nm or less.

16. A solid-state secondary battery having the electrode described in claim 14.

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