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 a sulfide-based electrolyte and exhibits favorable properties, a secondary battery binder sheet containing the secondary battery binder, and a solid-state secondary battery using the secondary battery binder sheet. Specifically provided is a secondary battery binder containing a sulfide-based solid electrolyte and a binding agent, said secondary battery binder being characterized in that the binding agent is a fibrillary resin. The binding agent 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 solid-state secondary battery sheet 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 and then fibrillated to form binders.

[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 the production of a solid electrolyte layer, a positive electrode, or a negative electrode using an inorganic sulfide having a specific composition in which a crystalline phase and a glass phase coexist as a binder.

[0006] Patent Document 3 discloses a solid electrolyte-containing sheet having a solid electrolyte-containing layer with a thickness of t μm, comprising fibers having an average diameter d of 0.1 to 2 μm and an average length L of 0.2 to 50 mm prepared by electrospinning, microfluidizing, or wet spinning, and containing the fibers and an inorganic solid electrolyte, wherein L and t satisfy the relationship 100 × t ≤ L ≤ 2500 × t.

[0007] Patent Document 4 discloses a method for producing a film by mixing sulfur-based solid ion conductor inorganic particles with a tetrafluoroethylene (TFE) polymer to form a paste, and then calendering or extruding it. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Special Publication No. 2017-517862 [Patent Document 2] International Publication No. 2018-096957 [Patent Document 3] International Publication No. 2019-208347 [Patent Document 4] International Publication No. 2021-043493 [Overview of the project] [Problems that the invention aims to solve]

[0009] This disclosure aims to provide a secondary battery mixture containing a sulfide-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 secondary battery mixture containing a sulfide-based solid electrolyte that is highly productive and can be handled without using a support when forming a secondary battery mixture sheet, and a secondary battery mixture sheet containing the mixture. [Means for solving the problem]

[0010] This disclosure relates to a secondary battery mixture containing a sulfide-based solid electrolyte and a binder, The binder is a fibrillary resin, and this is a composite material for secondary batteries.

[0011] The fibrillated resin described above preferably has a fibrous structure with a median fibril diameter of 100 nm or less. It is preferable that the fibrillary resin is a polytetrafluoroethylene resin.

[0012] The average particle size of the above sulfide-based solid electrolyte is preferably 0.1 μm or more and 20 μm or less. The above sulfide-based solid electrolyte is preferably represented by the following formula (A). aLi2S-bX 1 S2-cLiX 2 -(1-abc)P2S5(A) (However, 0.6≦a≦0.86, 0≦b≦0.333, 0≦c≦0.3, 0.05≦b+c≦0.4, X 1 is Ge, Sn, Ti or Si, X 2 (where b or c is not 0)

[0013] The above-mentioned secondary battery mixture is preferably for lithium-ion solid secondary batteries. The above-mentioned secondary battery mixture is a secondary battery mixture obtained using a raw material composition containing a sulfide-based solid electrolyte and a binder, It is preferable that the binder in the above raw material composition is a powdered fibrillary resin. The above raw material composition preferably contains substantially no liquid medium. The above-mentioned powdered fibrillary resin preferably has a moisture content of 500 ppm or less.

[0014] Preferably, the powdered fibrillary resin is a powdered polytetrafluoroethylene resin. The above-mentioned powdered polytetrafluoroethylene resin preferably has a standard specific gravity of 2.12 to 2.20. The above-mentioned powdered polytetrafluoroethylene resin preferably contains 50% by mass or more of polytetrafluoroethylene resin with a secondary particle size of 450 μm or more. This disclosure also includes a secondary battery mixture sheet containing the above-mentioned secondary battery mixture.

[0015] This disclosure relates to a step (1) of applying shear force while mixing a raw material composition containing a sulfide-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 above-mentioned composite sheet for secondary batteries. [Effects of the Invention]

[0016] In this disclosure, by not using a solvent when forming a composite sheet for secondary batteries containing a sulfide-based solid electrolyte, and by using a powdery binder with low moisture content, it is possible to manufacture batteries with less degradation of the sulfide-based solid electrolyte. Furthermore, this disclosure provides a secondary battery mixture containing a sulfide-based electrolyte that is highly productive and can be handled without using a support when forming a secondary battery mixture sheet, and a secondary battery mixture sheet containing the mixture. [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 sulfide-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 solid secondary battery mixture was generally prepared by coating and drying a slurry containing the same.

[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 a sulfide-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] Furthermore, in order to commercialize solid-state secondary batteries, studies are being conducted to improve battery performance, such as battery voltage, as well as to develop methods for industrial production of solid-state secondary batteries. To improve handling when examining the performance of secondary battery mixtures and the mixture sheets containing them, and to improve the manufacturing efficiency of solid-state secondary batteries, it is desirable that the secondary battery mixture sheets constituting the solid-state secondary batteries can be handled without the use of a support. In addition, from the standpoint of manufacturability, it is desirable that these secondary battery mixture sheets can withstand winding with large curvatures when wound into a roll. Therefore, improvement in flexibility is also desired. As described above, this disclosure allows for the manufacture of a composite sheet for secondary batteries without the use of a solvent by using a fibrilous resin as a binder, thus enabling the manufacture of a composite sheet for secondary batteries without the use of a support. Furthermore, by using a sulfide-based solid electrolyte, the composite sheet for secondary batteries of this disclosure can be made easy to handle and possess good flexibility and strength.

[0021] The secondary battery mixture described herein is obtained using a raw material composition containing a sulfide-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, rather than a binder-containing dispersion, 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 improving battery performance. Furthermore, it is possible to produce a battery with excellent ion conductivity.

[0022] 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, conventional solvents that can dissolve binder resins are limited to specific solvents such as butyl butyrate. These react with sulfide-based solid electrolytes and degrade the performance of the sulfide-based solid electrolyte, thus causing 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.

[0023] 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.

[0024] The secondary battery mixture described herein contains a sulfide-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 constituent components of the secondary battery mixture together, thereby achieving the objective of this disclosure. 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.

[0025] Furthermore, it is preferable that the binder in the secondary battery mixture has 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.

[0026] 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.

[0027] 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.

[0028] 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, it is preferably 15 nm or more, more preferably 20 nm or more, and particularly preferably 31 nm or more.

[0029] 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 a sulfide-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).

[0030] In this method, for example, in step (1), by setting the mixing conditions of the raw material composition to 3000 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.

[0031] 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.

[0032] In other words, by applying shear force, the binder powder is fibrillated, and this fibrillation then intertwines with powder components such as sulfide-based solid electrolytes, thereby enabling the production of a composite material for secondary batteries. The manufacturing method will be described later.

[0033] 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.

[0034] The powdered fibrillary resin used as a raw material when preparing the secondary battery mixture 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 sulfide-based solid electrolyte. The above moisture content is more preferably 300 ppm or less.

[0035] 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.

[0036] 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.

[0037] 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 a high-strength composite sheet. 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.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] The above-mentioned powdered PTFE is preferably of an average primary particle size of 150 nm or more, in order to obtain a composite 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.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] In the present disclosure, in the binder for the solid 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. It is even more preferable to exceed 0.5% by mass. The upper limit of the content of the binder in the binder for the solid secondary battery is preferably 10% by mass or less, more preferably 7% by mass or less, particularly preferably 6% by mass or less, still more preferably 4% by mass or less, even more preferably 1.7% by mass or less, and most preferably 1.0% by mass or less. 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.

[0046] The solid electrolyte used in the binder for the solid secondary battery of the present disclosure is a sulfide-based solid electrolyte. Using a sulfide-based solid electrolyte has the advantage of flexibility.

[0047] Examples of the sulfide-based solid electrolyte include a lithium ion conductive inorganic solid electrolyte satisfying the composition represented by the following formula (1). Li a1 M b1 P c1 S d1 A e1 (1) In the formula, M represents an element selected from B, Zn, Sn, Si, Cu, Ga, Sb, Al, Ti, and Ge. A represents an element selected from I, Br, Cl, and F. a1 to e1 represent the composition ratios of the respective elements, and a1:b1:c1:d1:e1 satisfies 1 to 12:0 to 5:1:2 to 12:0 to 10. a1 is preferably 1 to 9, more preferably 1.5 to 7.5. b1 is preferably 0 to 3, more preferably 0 to 1. d1 is preferably 2.5 to 10, more preferably 3.0 to 8.5. e1 is preferably 0 to 5, more preferably 0 to 3.

[0048] In the present disclosure, the sulfide-based solid electrolyte preferably contains lithium. The sulfide-based solid electrolyte containing lithium is used in a solid battery using lithium ions as carriers, and is particularly preferable in terms of an electrochemical device having a high energy density.

[0049] The composition ratio of each element can be controlled by adjusting the amount of raw material compounds used when producing sulfide-based inorganic solid electrolytes, as shown below.

[0050] The sulfide-based inorganic solid electrolyte may be amorphous (glass) or crystalline (glass-ceramic), or partially crystalline. For example, a Li-PS glass containing Li, P, and S, or a Li-PS glass-ceramic containing Li, P, and S can be used. Sulfide-based inorganic solid electrolytes can be produced by the reaction of at least two raw materials from among lithium sulfide (Li2S), phosphorus sulfide (e.g., diphosphorus pentasulfide (P2S5)), elemental phosphorus, elemental sulfur, sodium sulfide, hydrogen sulfide, lithium halides (e.g., LiI, LiBr, LiCl), and sulfides of the element represented by M above (e.g., SiS2, SnS, GeS2).

[0051] As specific examples of sulfide-based inorganic solid electrolytes, the following are examples of raw material combinations: For example, Li2S-P2S5-LiCl, Li2S-P2S5-H2S, Li2S-P2S5-H2S-LiCl, Li2S-LiI-P2S5, Li2S-LiI-Li2O-P2S5, Li2S-LiBr-P2S5, Li2S-Li2O-P2S5, Li2S-Li3PO4-P2S5, Li2S-P2S5-P2O5, Li2S-P2S5-SiS2, Li2S-P2S5-SiS2-LiCl, Li2S-P2S5-SnS, Li2S-P2S5-Al2S3, Li2S -GeS2, Li2S-GeS2-ZnS, Li2S-Ga2S3, Li2S-GeS2-Ga2S3, Li2S-GeS2-P2S5, Li2S-GeS2-Sb2S5, Li2S-GeS2-Al2S3, Li2S-SiS2, Li2S -Al2S3, Li2S-SiS2-Al2S3, Li2S-SiS2-P2S5, Li2S-SiS2-P2S5-LiI, Li2S-SiS2-LiI, Li2S-SiS2-Li4SiO4, Li2S-SiS2-Li3PO4, Li 10 GeP2S 12 These are some examples. However, the mixing ratio of each ingredient is not specified.

[0052] In particular, the sulfide-based solid electrolyte is preferably one that satisfies the composition shown in formula (A) below. aLi2S-bX 1 S2-cLiX 2 -(1-abc)P2S5(A) (However, 0.6≦a≦0.86, 0≦b≦0.333, 0≦c≦0.3, 0.05≦b+c≦0.4, X 1 is Ge, Sn, Ti or Si, X 2 (where b or c is not 0) The sulfide-based solid electrolyte that satisfies the composition shown in formula (A) above is advantageous in that it can stably provide high ionic conductivity.

[0053] As an example of a sulfide-based solid electrolyte represented by the above formula (A), specifically, 0.714Li2S-0.143SnS2-0.143P2S5(Li 10 SnP2S 12 (LSPS)), 0.625Li2S-0.25LiCl-0.125P2S5(Li6PS5Cl(LPSCl)), 0.715Li2S-0.143GeS2-0.142P2S5(Li 10 GeP2S 12 Any of the following can be used, or a mixture of two or more, selected from (LGPS), etc.

[0054] The average particle size of the sulfide-based solid electrolyte is preferably 0.1 μm or more and 20 μm or less. More preferably, the upper limit is 0.2 μm or more, and even more preferably 0.3 μm or more. More preferably, the upper limit is 18 μm or less, and even more preferably 15 μm or less. If the average particle size of sulfide-based solid electrolytes is less than 0.1 μm, handling the powder may become difficult. On the other hand, if the average particle size of sulfide-based solid electrolytes exceeds 20 μm, press moldability may deteriorate.

[0055] The average particle size of sulfide-based solid electrolyte particles is measured using the following procedure. A 1% by mass dispersion of sulfide-based solid electrolyte particles is prepared by diluting it with water (or heptane if the substance is unstable in water) in a 20 ml sample bottle. The diluted dispersion sample is irradiated with 1 kHz ultrasound for 10 minutes and used for testing immediately thereafter. 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 with 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.

[0056] The method for adjusting the average particle size of the sulfide solid electrolyte is not particularly limited, but for example, it can be done as follows: Known grinders or classifiers are used. For example, mortars, sand mills, ball mills, jet mills, or sieves are suitably used. Depending on the properties of the solid electrolyte, water or a solvent such as ethanol may be added during grinding. Classification is preferable to obtain the desired particle size. Classification is not particularly limited and can be performed using sieves, wind classifiers, etc.

[0057] The content of sulfide-based solid electrolyte in the solid component of a secondary battery mixture 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, considering the reduction of interfacial resistance and the maintenance of the reduced interfacial resistance when used in a solid secondary battery. 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-mentioned sulfide-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.

[0058] 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.

[0059] 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.

[0060] The following describes electrode active materials, conductive additives, etc.

[0061] (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.

[0062] The positive electrode active material is not particularly limited as long as it is capable of electrochemically intercepting and releasing alkali metal ions, but for example, a material containing an alkali metal and at least one transition metal is preferred. Specific examples include alkali metal-containing transition metal composite oxides, alkali metal-containing transition metal phosphate compounds, and conductive polymers. In particular, as the positive electrode active material, alkali metal-containing transition metal composite oxides that produce high voltage are preferred. Examples of the alkali metal ions include lithium ions, sodium ions, potassium ions, etc. In a preferred embodiment, the alkali metal ion may be a lithium ion. That is, in this embodiment, the alkali metal ion secondary battery is a lithium ion secondary battery.

[0063] Examples of the alkali metal-containing transition metal composite oxides mentioned above include: Formula:M a Mn 2-b M 1 b O4 (wherein 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 This refers to alkali metal-manganese spinel composite oxides, which are represented by 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. Formula:MNi 1-c M 2 cO2 (wherein M is at least one metal selected from the group consisting of Li, Na, and K; 0 ≤ c ≤ 0.5; M 2 (This refers to an alkali metal-nickel composite oxide represented by 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), 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.

[0064] 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.)

[0065] 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.

[0066] 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.

[0067] 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.

[0068] 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 a transition metal such as Co, Ni, Mn, Fe, etc.) and solid solution materials thereof can also be mentioned.

[0069] 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 Li2MnO3 is preferable because it can provide an alkali metal ion secondary battery having a high energy density.

[0070] In addition, 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 preferable to mix and use the above-mentioned positive electrode active material and lithium phosphate. The amount of lithium phosphate used is preferably at least 0.1% by mass, more preferably at least 0.3% by mass, and still more preferably at least 0.5% by mass, and the upper limit is preferably at most 10% by mass, more preferably at most 8% by mass, and still more preferably at most 5% by mass, based on the total of the above-mentioned positive electrode active material and lithium phosphate.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] 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 an upper 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 will inhibit the movement of lithium ions, increasing resistance. There are cases where this is the case.

[0075] 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.

[0076] 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 3 The 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.

[0077] 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.

[0078] 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.

[0079] 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.

[0080] 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.

[0081] 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.

[0082] 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.

[0083] 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.

[0084] 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.

[0085] 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 0.33 Examples 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.

[0086] 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 94.8% by mass or less, more preferably 90.5% by mass or less, and particularly preferably 87.5% 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 and strength of the positive electrode may be insufficient.

[0087] 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 12Examples 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.

[0088] The content of the above-mentioned 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 94.8% by mass or less, more preferably 90.5% by mass or less, and particularly preferably 87.5% by mass or less. If the content of the negative electrode active material in the negative electrode mixture is too low, the electrical capacity may be insufficient. Conversely, if the content is too high, the electron / ion conductivity and strength of the negative electrode may be insufficient.

[0089] (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.

[0090] When a conductive additive is used, it is typically contained in the electrode active material layer 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.

[0091] (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.

[0092] 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 mixture decreases, which may lead to problems such as a decrease in battery capacity or an increase in resistance between active materials.

[0093] In the composite sheet for secondary batteries of this disclosure, the binder content is typically 0.2% by mass or more, preferably 0.3% by mass or more, more preferably 0.5% by mass or more, and also typically 10% by mass or less, preferably 6.0% by mass or less, more preferably 4% by mass or less, even more preferably 1.7% by mass or less, and most preferably 1.0% by mass or less. If the binder content 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 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.

[0094] (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.

[0095] 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 a composite sheet for secondary batteries having [the specified characteristic].

[0096] 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.

[0097] 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 may proceed excessively, which may result in a composite sheet with inferior strength.

[0098] 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 step (1) above, in which the raw material composition is mixed to disperse the binder. In step (A) above, it is preferable to mix with the smallest possible shear force.

[0099] 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 500 rpm or less. Preferably it is 20 rpm or more, more preferably 30 rpm or more, even more preferably 40 rpm or more, and also preferably 400 rpm or less, more preferably 300 rpm or less, and even more preferably in the range of 200 rpm. 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, it is possible to process the material into the desired sheet shape in a shorter amount of time.

[0100] 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.

[0101] 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.

[0102] 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).

[0103] In step (2) above, forming into a bulk form 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.

[0104] Specific rolling methods in step (3) above include methods using a roll press, a flat plate press, a calender roll machine, etc.

[0105] 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.

[0106] 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.

[0107] 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.

[0108] 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), or (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.

[0109] 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.

[0110] 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 PTFE during mixing and rolling to promote fibrillation, and then rolling the mixture into a sheet, within the above-mentioned range, a fibrous structure with a median fibril diameter of 100 nm or less can be obtained.

[0111] 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.

[0112] 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.

[0113] As the shape of the current collector, in the case of a metal material, examples include metal foil, metal cylinder, metal coil, metal plate, expanded metal, punched metal, foamed metal, etc.; in the case of a carbon material, examples include carbon plate, carbon thin film, carbon cylinder, etc. Among these, metal foil is preferred. Note that the metal foil may be formed in a mesh shape as appropriate. The thickness of the metal foil is arbitrary, but it 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, the strength required as a current collector may be insufficient. Conversely, if the metal foil is thicker than this range, the handleability may be impaired.

[0114] Also, it is preferable that a conductive auxiliary agent is applied to the surface of the current collector from the viewpoint of reducing the electrical contact resistance between the current collector and the positive electrode mixture sheet. Examples of the conductive auxiliary agent include carbon and noble metals such as gold, platinum, and silver.

[0115] The positive electrode can be manufactured by a conventional method. For example, a method of laminating the above-mentioned positive electrode sheet and the current collector via an adhesive and drying can be mentioned.

[0116] The density of the positive electrode sheet is preferably 2.0 g / cm 3 or more, more preferably 2.1 g / cm 3 or more, still more preferably 2.3 g / cm 3 or more, and preferably 4.0 g / cm 3 or less, more preferably 3.9 g / cm 3 or less, still more preferably 3.8 g / cm 3 or less within the following range. If it exceeds this range, the conductivity between the active materials may decrease, the battery resistance may increase, and high output may not be obtained. If it is below this range, the content of the active material that is hard and prone to cracking is low, and the battery may have a low capacity.

[0117] 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.

[0118] 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.

[0119] (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.

[0120] 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.

[0121] The manufacturing of the negative electrode may be carried out according to a conventional method. For example, a method of laminating the sheet for negative electrode and the current collector via an adhesive and then drying is available.

[0122] The density of the sheet for negative electrode is preferably 1.3 g / cm 3 or more, more preferably 1.4 g / cm 3 or more, still more preferably 1.5 g / cm 3 or more, and preferably 2.0 g / cm 3 or less, more preferably 1.9 g / cm 3 or less, still more preferably 1.8 g / cm 3 within the following range. If it exceeds this range, the permeability of the solid electrolyte near the interface between the current collector and the active material decreases, and particularly the charge-discharge characteristics at a high current density deteriorate, and high output may not be obtained. If it is less than this range, the conductivity between the active materials decreases, the battery resistance increases, and high output may not be obtained.

[0123] The thickness of the negative electrode is not particularly limited, but from the viewpoints of high capacity and high output, the thickness of the mixture sheet obtained by subtracting the thickness of the metal foil of the current collector is preferably 10 μm or more, more preferably 20 μm or more as the lower limit with respect to one side of the current collector, and preferably 500 μm or less, more preferably 450 μm or less.

[0124] (Solid secondary battery) The present disclosure is also a solid secondary battery using the above mixture sheet for secondary battery. As the solid secondary battery, an all-solid secondary battery or a solid secondary battery with a hybrid structure combining a gel-like polymer electrolyte and a solid electrolyte may be used. Also, the solid secondary battery is preferably a lithium-ion battery.

[0125] 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.

[0126] The laminated structure of the solid secondary battery in this disclosure 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 a sulfide-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.

[0127] (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.

[0128] (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 sulfide-based solid batteries, etc., as described above, but specific examples include cylindrical, prismatic, coin-type, laminated type, etc.

[0129] 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]

[0130] 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.

[0131] [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.

[0132] [Example 2] Powdered PTFE-2 was prepared using example 3 from International Publication No. 2015-080291 as a reference.

[0133] [Example 3] Powdered PTFE-3 was prepared based on example 1 of international publication No. 2012 / 086710.

[0134] [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.

[0135] [Table 1]

[0136] (Example 1) Sulfide solid electrolyte Li 10 SnP2S 12 (LSPS, 0.714Li2S-0.143SnS2-0.143P2S5) (average particle size: 7 μm) and powdered PTFE-1 were weighed and mixed with a high-speed mixer (500 rpm, 1 minute). The stirring was performed after cooling the container 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 warming the container to 60°C. The solid content was adjusted so that the mass ratio of solid electrolyte to binder was 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 rolled sheet obtained earlier was roughly crushed by folding it in half, then reshaped into a bulk form. This process of promoting fibrillation was repeated four times by rolling it into a sheet on a flat plate using metal rolls. 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 fed into a press machine 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 120μm. Note that the above work was performed inside an Ar glow box (dew point approximately -80°C).

[0137] (Example 2) Sulfide solid electrolyte Li 10 SnP2S 12 (LSPS) and powdered PTFE-2 were weighed, and sheet molding was performed using the same procedure as in Example 1. The composition ratio was adjusted to the mass ratio shown in Table 2.

[0138] (Example 3) Sulfide solid electrolyte Li 10 SnP2S 12(LSPS) and powdered PTFE-3 were weighed, and sheet molding was performed using the same procedure as in Example 1. The composition ratio was adjusted to the mass ratio shown in Table 2.

[0139] (Example 4) Sulfide solid electrolyte Li 10 SnP2S 12 (LSPS) and powdered PTFE-4 were weighed, and sheet molding was performed using the same procedure as in Example 1. The composition ratio was adjusted to the mass ratio shown in Table 2.

[0140] (Example 5) Sulfide solid electrolyte Li6PS5Cl (LPSCl, 0.625Li2S-0.25LiCl-0.125P2S 5 (Average particle size: 8 μm) and powdered PTFE-1 were weighed, and sheet molding was performed using the same procedure as in Example 1. The composition ratio was adjusted to the mass ratio shown in Table 2.

[0141] (Example 6) Cathode active material LiNi 0.8 Mn 0.1 Co 0.1 O2, sulfide-based solid electrolyte LPSCl (average particle size: 8 μm), and powdered PTFE-1 were weighed, and sheet molding was performed using the same procedure as in Example 1. The composition ratio was adjusted to the mass ratio shown in Table 3.

[0142] (Example 7) Cathode active material LiNi 0.8 Co 0.15 Al 0.05 O2, sulfide-based solid electrolyte LPSCl (average particle size: 8 μm), and powdered PTFE-1 were weighed, and sheet molding was performed using the same procedure as in Example 1. The composition ratio was adjusted to the mass ratio shown in Table 3.

[0143] (Example 8) Sulfide solid electrolyte Li 10 GeP2S 12 LGPS (manufactured by Ampcera, average particle size: 18 μm) and powdered PTFE-2 were weighed, and sheet molding was performed using the same procedure as in Example 1. The composition ratio was adjusted to the mass ratio shown in Table 3.

[0144] 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.

[0145] [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.

[0146] [Ionic conductivity measurement] The conductivity was measured using the following method. Gold electrodes were fabricated on the surface of the prepared solid electrolyte sheet by sputtering, and then punched out to a diameter of Φ10 mm. These electrodes were sandwiched between stainless steel current collectors and sealed to form a measurement cell. After leaving this cell in an 80°C constant temperature bath for 12 hours, AC impedance measurements were performed using an impedance analyzer (Solartron 1260 model) in the frequency range of 0.1 Hz to 8 MHz to determine the ionic conductivity.

[0147] [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.

[0148] [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.

[0149] The test results are shown in Tables 2 and 3.

[0150] [Table 2]

[0151] [Table 3]

[0152] The results in Tables 2 and 3 show that the sheet-like solid electrolyte layer of the example exhibited excellent physical properties.

[0153] Next, a gold electrode was fabricated on the surface of the positive electrode mixture sheet prepared in Example 8 by sputtering. Then, the solid electrolyte sheet prepared in Example 2, Li foil, and insulating sheet were layered on top of each other and integrated by uniaxial molding with a load of 60kN for 3 minutes, and a Φ10mm punched half-cell was produced. The fabricated half-cell was placed in a flat cell and left in a 25°C chamber for 12 hours. Charging and discharging were performed at 0.1C (0.05C cutoff). After performing 8 charge-discharge cycles, the capacity retention rate after the 8th cycle was 98.4%, with the 3rd cycle being set to 100%. [Industrial applicability]

[0154] The secondary battery mixture and secondary battery mixture sheets containing the same can be used in the manufacture of solid secondary batteries.

Claims

1. A secondary battery mixture containing a sulfide-based solid electrolyte and a binder, The binder is a fibrillary resin having a fibrous structure with a median fibril diameter of 70 nm or less. The binder content is 0.3% by mass or more and 1.5% by mass or less in the solid secondary battery mixture. A composite material for secondary batteries, characterized in that the average particle size of the sulfide solid electrolyte is 0.1 μm or more and 20 μm or less.

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

3. The secondary battery mixture according to claim 1 or 2, wherein the sulfide solid electrolyte is represented by the following formula (A). aLi ２ S-bX １ S ２ -cLiX ２ -(1-a-b-c)P ２ S ５ (A) (However, 0.6 ≤ a ≤ 0.86, 0 ​​≤ b ≤ 0.333, 0 ≤ c ≤ 0.3, 0.05 ≤ b + c ≤ 0.4, X １ is Ge, Sn, Ti or Si, X ２ (where b or c is not 0)

4. The secondary battery mixture according to claim 1 or 2, which is for lithium-ion solid secondary batteries.

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

6. The raw material composition is substantially free of a liquid medium, as described in claim 5 for the secondary battery mixture.

7. The secondary battery mixture according to claim 5 or 6, wherein the powdered fibrillary resin has a moisture content of 500 ppm or less.

8. The secondary battery mixture according to claim 5 or 6, wherein the powdered fibrillary resin is a powdered polytetrafluoroethylene resin.

9. The compound for secondary batteries according to claim 8, wherein the powdered polytetrafluoroethylene resin has a standard specific gravity of 2.12 to 2.

20.

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

11. A secondary battery mixture sheet comprising the secondary battery mixture according to claim 1 or 2.

12. (1) A step in which shear force is applied while mixing a raw material composition containing a sulfide-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. A method for manufacturing a composite sheet for secondary batteries, wherein the binder is a powdered fibrillary resin, A method for manufacturing a composite sheet for secondary batteries, characterized in that the binder content in the manufactured composite sheet for secondary batteries is 0.3% by mass or more and 1.5% by mass or less, and the fibrillary resin has a fibrous structure with a median fibril diameter of 70 nm or less.

13. A solid secondary battery having a composite sheet for secondary batteries as described in claim 11.

Images