Solid electrolyte sheets and all-solid-state batteries

Abstract

The present invention provides an all-solid-state battery with excellent productivity and a solid electrolyte sheet that constitutes the all-solid-state battery. [Solution] The solid electrolyte sheet of the present invention is for forming a laminate comprising a positive electrode, a negative electrode, and a solid electrolyte sheet interposed between the positive electrode and the negative electrode, and comprises a porous substrate and a solid electrolyte, wherein the solid electrolyte is held in the voids of the porous substrate, and both sides of the porous substrate are covered with the solid electrolyte, and the porous substrate is positioned biased toward the side that is intended to face the positive electrode in the thickness direction of the solid electrolyte sheet, has a thickness of 50 μm or less, and the thickness of the porous substrate is 3 to 45 μm. The all-solid-state battery of the present invention has a laminate comprising a positive electrode, a negative electrode, and a solid electrolyte sheet interposed between the positive electrode and the negative electrode, wherein the solid electrolyte sheet is the solid electrolyte sheet of the present invention, and the porous substrate is positioned biased toward the positive electrode side in the thickness direction of the solid electrolyte sheet.

Description

Technical Field

[0001] The present invention relates to an all-solid-state battery having excellent productivity and a solid electrolyte sheet constituting the all-solid-state battery.

Background Art

[0002] In recent years, with the development of portable electronic devices such as mobile phones and notebook personal computers, and the commercialization of electric vehicles, there has been a growing need for batteries that are small, lightweight, and have high capacity and high energy density.

[0003] Currently, in lithium batteries, particularly lithium-ion batteries, which can meet this requirement, an organic electrolyte solution containing an organic solvent and a lithium salt is used as a non-aqueous electrolyte.

[0004] With the further development of applicable devices for lithium-ion batteries, there is a demand for further extending the lifespan, increasing the capacity, and enhancing the energy density of lithium-ion batteries. At the same time, high reliability of lithium-ion batteries with extended lifespan, increased capacity, and enhanced energy density is also highly required.

[0005] However, since the organic electrolyte solution used in lithium-ion batteries contains an organic solvent, which is a flammable substance, there is a possibility that the organic electrolyte solution may generate abnormal heat when an abnormal situation such as a short circuit occurs in the battery. In addition, with the recent trend of increasing the energy density of lithium-ion batteries and the amount of organic solvent in the organic electrolyte solution, higher reliability of lithium-ion batteries is required.

[0006] Under the above circumstances, all-solid-state lithium batteries (all-solid-state batteries) that do not use organic solvents have attracted attention. An all-solid-state battery uses a molded body of a solid electrolyte that does not use an organic solvent instead of a conventional organic solvent-based electrolyte, and has no risk of abnormal heat generation of the solid electrolyte and has high safety.

[0007] Furthermore, solid-state batteries are expected to contribute to the development of society while simultaneously providing peace of mind and safety, as they possess not only high safety but also high reliability, high environmental resistance, and a long lifespan, making them maintenance-free batteries. By providing solid-state batteries to society, it is possible to contribute to achieving three of the 17 Sustainable Development Goals (SDGs) established by the United Nations: Goal 3 (Ensure healthy lives and promote well-being for all at all ages), Goal 7 (Ensure access to affordable, reliable, sustainable, and modern energy for all), Goal 11 (Make cities and human settlements inclusive, safe, resilient and sustainable), and Goal 12 (Ensure sustainable consumption and production patterns).

[0008] Furthermore, various studies have been conducted on all-solid-state batteries. For example, Patent Documents 1 to 4 propose a solid electrolyte sheet that combines lithium-ion conductivity and strength by filling the voids of a porous substrate such as a nonwoven fabric with a solid electrolyte, and then constructing an all-solid-state secondary battery using this solid electrolyte sheet.

[0009] Of these, Patent Document 4 shows that by making the thickness of the porous substrate 70% or more of the total thickness of the solid electrolyte sheet, the mechanical strength of the solid electrolyte sheet can be improved, and even when the solid electrolyte sheet is made to a large area, damage to the solid electrolyte and detachment of the solid electrolyte from the porous substrate can be prevented. [Prior art documents] [Patent Documents]

[0010] [Patent Document 1] Japanese Patent Publication No. 2015-153460 [Patent Document 2] Japanese Patent Publication No. 2016-139482 [Patent Document 3] International Publication No. 2019 / 208347 [Patent Document 4] International Publication No. 2020 / 054081 [Overview of the Initiative] [Problems that the invention aims to solve]

[0011] While the technology described in Patent Document 4 makes it possible to provide all-solid-state batteries with excellent discharge characteristics, our investigations have revealed that when a large number of batteries are manufactured, some may have inferior charging characteristics. Therefore, even the technology described in Patent Document 4 still has room for improvement in this respect.

[0012] The present invention has been made in view of the above circumstances, and its object is to provide an all-solid-state battery with excellent productivity and a solid electrolyte sheet constituting the all-solid-state battery. [Means for solving the problem]

[0013] The present invention relates to a solid electrolyte sheet for forming a laminate comprising a positive electrode, a negative electrode, and a solid electrolyte sheet interposed between the positive electrode and the negative electrode, and comprises a porous substrate and a solid electrolyte, wherein the solid electrolyte is held within the voids of the porous substrate, and both sides of the porous substrate are covered with the solid electrolyte, and the porous substrate is positioned biased toward the side that is intended to face the positive electrode in the thickness direction of the solid electrolyte sheet, has a thickness of 50 μm or less, and the thickness of the porous substrate is 3 to 45 μm. Furthermore, the all-solid-state battery of the present invention has a laminate comprising a positive electrode, a negative electrode, and a solid electrolyte sheet interposed between the positive electrode and the negative electrode, wherein the solid electrolyte sheet is the solid electrolyte sheet of the present invention, and the solid electrolyte sheet is characterized in that the porous substrate is positioned biased toward the positive electrode side in the thickness direction of the solid electrolyte sheet. [Effects of the Invention]

[0014] According to the present invention, it is possible to provide an all-solid-state battery with excellent productivity and a solid electrolyte sheet constituting the all-solid-state battery. [Brief explanation of the drawing]

[0015] [Figure 1] This is a schematic partial cross-sectional view showing an example of a laminate having a positive electrode, a negative electrode, and a solid electrolyte sheet according to the all-solid-state battery of the present invention. [Figure 2] This is a partially enlarged view of Figure 1. [Figure 3] This is a schematic plan view illustrating an example of the all-solid-state battery of the present invention. [Figure 4] This is a cross-sectional view taken along line II in Figure 3. [Modes for carrying out the invention]

[0016] In a solid electrolyte sheet, which holds a solid electrolyte in the voids of a porous substrate, if the porous substrate is exposed on its surface, the porous substrate can obstruct ion movement at the interface between the positive and negative electrodes and the solid electrolyte sheet, making the charge-discharge reaction of the positive and negative electrodes prone to becoming non-uniform. For this reason, it is desirable to construct the solid electrolyte sheet so that the constituent materials of the porous substrate are not exposed on the surface of the solid electrolyte sheet, and both sides of the porous substrate are covered with a certain thickness or more of solid electrolyte.

[0017] The porous substrate of the solid electrolyte sheet has a greater impact on ion movement at the negative electrode than at the positive electrode, making it more susceptible to problems such as metal deposition during charging, which could lead to battery charging abnormalities.

[0018] For these reasons, in a solid electrolyte sheet containing a porous substrate, it is desirable that, in addition to the solid electrolyte being held within the voids of the porous substrate, both sides of the porous substrate are covered with the solid electrolyte.

[0019] On the other hand, in order to reduce the internal resistance of an all-solid-state battery, it is desirable to reduce the thickness of the solid electrolyte sheet. However, when attempting to make a solid electrolyte sheet, in which both sides of a porous substrate are covered with solid electrolyte, thinner, it becomes difficult to position the porous substrate at the center in the thickness direction of the solid electrolyte sheet. This makes it easier to form a solid electrolyte sheet in which the porous substrate is biased to one side in the thickness direction. As a result, a difference in the thickness of the solid electrolyte covering the porous substrate occurs on both sides of the porous substrate.

[0020] Furthermore, depending on the manufacturing method, attempting to reduce the thickness of the solid electrolyte sheet may make it impossible to achieve a uniform thickness throughout the sheet, resulting in unevenness in the thickness of the solid electrolyte covering the surface of the porous substrate.

[0021] As a result, on the side where the porous substrate has shifted (the side where the porous substrate is closer to the surface), areas are formed where the constituent materials of the porous substrate are located near the surface of the solid electrolyte sheet.

[0022] Furthermore, it was found that in an all-solid-state battery constructed by arranging the solid electrolyte sheet so that the side of the porous substrate that has shifted faces the negative electrode, the aforementioned charging abnormality problem is likely to occur, and when a large number of batteries are produced, the number of such batteries will increase, which may reduce the productivity of the batteries.

[0023] Therefore, in the all-solid-state battery of the present invention, a solid electrolyte sheet is provided which includes a porous substrate and a solid electrolyte, wherein the solid electrolyte is held in the voids of the porous substrate and both sides of the porous substrate are covered with the solid electrolyte. When the porous substrate is positioned biased to one side, the side on which the porous substrate is biased is positioned towards the positive electrode side (i.e., in the present invention, the case in which the porous substrate is positioned such that the center of the solid electrolyte sheet in the thickness direction coincides with the center of the porous substrate is not included). This makes it possible to suppress the occurrence of the charging abnormalities described above, thereby reducing the number of all-solid-state batteries that cause problems when a large number of batteries are produced, and thus increasing productivity.

[0024] Figure 1 shows a schematic partial cross-sectional view of an example of a laminate having a positive electrode, a negative electrode, and a solid electrolyte sheet according to the all-solid-state battery of the present invention. Figure 1 shows the region of the laminate 100 that includes the solid electrolyte sheet 30 and the positive electrode 10 and negative electrode 20 arranged above and below it (that is, Figure 1 is a drawing showing a part of the cross-section of the laminate 100 in which the positive electrode 10, the solid electrolyte sheet 30, and the negative electrode 20 are laminated, in a direction parallel to the lamination direction). Note that in Figure 1, the diagonal lines indicating that it is a cross-section of the porous substrate 31 are omitted in order to facilitate the explanation of the arrangement of each component.

[0025] The solid electrolyte sheet 30 comprises a porous substrate 31 and solid electrolytes 32a and 32b covering both sides thereof. The solid electrolyte is also held within the voids of the porous substrate 31.

[0026] And, the dotted line in the figure is at the central part in the thickness direction of the porous substrate 31, and the dashed-dotted line is at the central part in the thickness direction of the solid electrolyte sheet 30, and the two do not overlap. Thus, in the porous substrate 31, the central part in the thickness direction is not overlapped with the central part in the thickness direction of the solid electrolyte sheet 30 and is positioned biased toward the positive electrode 10 side. That is, in the solid electrolyte sheet 30, the thickness of the solid electrolyte 32a covering one side of the porous substrate 31 and the thickness of the solid electrolyte 32b covering the other side are different. And the solid electrolyte sheet 30 is arranged so that the thinner solid electrolyte 32a side faces the positive electrode 10.

[0027] The all-solid-state battery of the present invention includes a primary battery and a secondary battery.

[0028] <Solid electrolyte sheet> The solid electrolyte sheet includes a porous substrate and a solid electrolyte, the solid electrolyte is held in the voids of the porous substrate, and both sides of the porous substrate are covered with the solid electrolyte.

[0029] The solid electrolyte of the solid electrolyte sheet is not particularly limited as long as it has lithium ion conductivity, and for example, sulfide-based solid electrolytes, hydride-based solid electrolytes, halide-based solid electrolytes, oxide-based solid electrolytes, etc. can be used.

[0030] Examples of the sulfide-based solid electrolyte include particles such as Li2S-P2S5, Li2S-SiS2, Li2S-P2S5-GeS2, Li2S-B2S3-based glass, etc. In addition, in recent years, thio-LISICON type ones [Li 10 GeP2S 12 、Li 9.54 Si 1.74 P 1.44 S 11.7 Cl 0.3 etc., Li 12-12a-b+c+6d-e M 1 3+a-b-c-d M 2 b M 3 c M 4 d M 512-e X e (However, M 1 is Si, Ge or Sn, M 2 is P or V, M 3 is Al, Ga, Y or Sb, M 4 is Zn, Ca, or Ba, M 5 is either S or S and O, X is F, Cl, Br or I, 0 ≦ a < 3, 0 ≦ b + c + d ≦ 3, 0 ≦ e ≦ 3), or an argyrodite-type one [such as Li6PS5Cl, Li 7-f+g PS 6-x Cl x+y (However, 0.05 ≦ f ≦ 0.9, -3.0f + 1.8 ≦ g ≦ -3.0f + 5.7), those represented by Li 7-h PS 6-h Cl i Br j (However, h = i + j, 0 < h ≦ 1.8, 0.1 ≦ i / j ≦ 10.0), etc.] can also be used.

[0031] Examples of the hydride-based solid electrolyte include LiBH4, a solid solution of LiBH4 and the following alkali metal compound (for example, those with a molar ratio of LiBH4 to the alkali metal compound of 1:1 to 20:1). Examples of the alkali metal compound in the solid solution include at least one selected from the group consisting of lithium halides (such as LiI, LiBr, LiF, LiCl), rubidium halides (such as RbI, RbBr, RbF, RbCl), cesium halides (such as CsI, CsBr, CsF, CsCl), lithium amide, rubidium amide, and cesium amide.

[0032] Examples of the halide-based solid electrolyte include monoclinic LiAlCl4, defective spinel-type or layered LiInBr4, monoclinic Li 6-3m Y m X6 (where 0 < m < 2 and X = Cl or Br), etc., and in addition, for example, known ones described in International Publication No. 2020 / 070958 and International Publication No. 2020 / 070955 can also be used.

[0033] Examples of oxide-based solid electrolytes include the garnet-type Li7La3Zr2O 12 , NASICON type Li 1+O Al 1+O Ti 2-O (PO4)3, Li 1+p Al 1+p Ge 2-p (PO4)3, perovskite-type Li 3q La 2 / 3-q Examples include TiO3.

[0034] The solid electrolyte may be one of the examples described above, or two or more may be used in combination. Among these solid electrolytes, sulfide-based solid electrolytes are preferred due to their high lithium ion conductivity, sulfide-based solid electrolytes containing Li and P are more preferred, and argyrodite-type sulfide-based solid electrolytes, which have high lithium ion conductivity and high chemical stability, are even more preferred.

[0035] The solid electrolyte is preferably in the form of particles, and in terms of size, from the viewpoint of further improving the packing ability into the voids of the porous substrate and ensuring good lithium ion conductivity, the average particle diameter is preferably 5 μm or less, and more preferably 2 μm or less. However, if the size of the solid electrolyte particles is too small, there is a risk that handling will be reduced. Also, as will be described later, it is preferable to bind the solid electrolyte particles using a binder in order to keep them well in the voids of the porous substrate or to adhere well to the surface of the porous substrate, but in that case, a larger amount of binder may be required, which may increase the resistance. Therefore, the average particle diameter of the solid electrolyte particles is preferably 0.3 μm or more, and more preferably 0.5 μm or more.

[0036] In this specification, the average particle diameter of solid electrolyte particles and other particles (positive electrode active material, negative electrode active material, etc.) is the 50% diameter value in the volume-based integrated fraction when determining the integrated volume from the smallest particles using a particle size distribution analyzer (such as the Microtrac particle size distribution analyzer "HRA9320" manufactured by Nikkiso Co., Ltd.). 50 ) means.

[0037] The porous substrate of the solid electrolyte sheet is composed of fibrous material, and examples include woven fabrics, nonwoven fabrics, and meshes, with nonwoven fabrics being preferred among these.

[0038] The fiber diameter of the fibrous material constituting the porous substrate is preferably 5 μm or less, and more preferably 0.5 μm or more.

[0039] The material of the fibrous material is not particularly limited as long as it does not react with lithium metal and has insulating properties. For example, polyolefins such as polypropylene and polyethylene; polystyrene; aramid; polyamide-imide; polyimide; nylon; polyesters such as polyethylene terephthalate (PET); polyarylate; cellulose and cellulose-modified resins can be used. Inorganic materials such as glass, alumina, silica, and zirconia may also be used. Polyarylate is a preferred material. The fibrous material can be composed of one or more of the materials exemplified above. Furthermore, the porous substrate may be composed only of fibrous materials of the same material, or it may be composed of a combination of two or more fibrous materials of different materials.

[0040] The basis weight of the porous substrate is 10 g / m², which is sufficient to hold a adequate amount of solid electrolyte to ensure good lithium ion conductivity. 2 Preferably, it is 8 g / m 2 It is more preferable that the following conditions are met, and from the viewpoint of ensuring sufficient strength, 3g / m 2 Preferably, it is 4 g / m 2 It is more preferable that the above conditions are met.

[0041] In solid electrolyte sheets, it is preferable to use a binder to bind the solid electrolyte in order to improve the shape retention of the solid electrolyte sheet by ensuring that the solid electrolyte is well held within the voids of the porous substrate and by improving the adhesion between the solid electrolyte covering the surface of the porous substrate and the porous substrate.

[0042] The binder for the solid electrolyte sheet is preferably one that does not react with the solid electrolyte, and at least one resin selected from the group consisting of butyl rubber, chloropyrene rubber, acrylic resin, and fluororesin is preferably used.

[0043] In a solid electrolyte sheet, the porous substrate is positioned biased towards one surface side in the thickness direction of the solid electrolyte, and the thickness of the solid electrolyte covering the surface of the porous substrate differs between one side and the other. The solid electrolyte sheet is then arranged so that the side with the thinner thickness of the solid electrolyte covering the surface of the porous substrate becomes the positive electrode side.

[0044] In a solid electrolyte sheet, the thickness of the solid electrolyte covering the surface of the porous substrate is preferably such that the distance (A) in the thickness direction of the laminate between the surface of the porous substrate and the positive electrode active material contained in the positive electrode is 1 μm or more, more preferably 3 μm or more. When the solid electrolyte covering the surface of the porous substrate on the side arranged on the positive electrode side has a thickness such that the distance (A) is the aforementioned value, the movement of lithium ions between the positive electrode and the solid electrolyte sheet during charging and discharging of the all-solid-state battery becomes smoother, thus improving the effect of suppressing the occurrence of charging abnormalities, for example.

[0045] Furthermore, of the solid electrolyte covering the surface of the porous substrate in the solid electrolyte sheet, the thickness of the side facing the negative electrode is preferably such that the distance (B) in the thickness direction of the laminate between the surface of the porous substrate and the negative electrode active material contained in the negative electrode is 3 μm or more, more preferably 4 μm or more. When the solid electrolyte covering the surface of the porous substrate on the side arranged on the negative electrode side has a thickness such that the distance (B) is the aforementioned value, the effect of suppressing metal deposition during charging and preventing the occurrence of battery charging abnormalities is further improved.

[0046] Furthermore, since the thickness of the solid electrolyte sheet is 50 μm or less, as will be described later, the thickness of the solid electrolyte covering the surface of the porous substrate in the solid electrolyte sheet is also limited. Specifically, of the solid electrolyte covering the surface of the porous substrate in the solid electrolyte sheet, the thickness on the side facing the positive electrode is preferably such that the distance (A) is 15 μm or less, and more preferably such that it is 10 μm or less. Also, of the solid electrolyte covering the surface of the porous substrate in the solid electrolyte sheet, the thickness on the side facing the negative electrode is preferably such that the distance (B) is 15 μm or less, and more preferably such that it is 10 μm or less.

[0047] Furthermore, if the thickness of the solid electrolyte covering one side of the porous substrate in the solid electrolyte sheet differs significantly from the thickness of the solid electrolyte covering the other side, the difference between distance (A) and distance (B) will also be large. However, if this difference becomes too large, the solid electrolyte sheet may become prone to curling, which could reduce the handling properties of the solid electrolyte sheet. Therefore, it is preferable that the difference between distance (A) and distance (B) be 10 μm or less.

[0048] The thickness of the solid electrolyte sheet is 50 μm or less, preferably 30 μm or less, and more preferably 25 μm or less. When the solid electrolyte sheet is this thin, the porous substrate is easily manufactured to be biased towards one surface side in the thickness direction of the solid electrolyte sheet. In this case, the thickness of the thinner part of the solid electrolyte covering the surface of the porous substrate can become very small, and if this surface is placed on the negative electrode side to construct the battery, metal deposition is likely to occur during charging. However, with the all-solid-state battery of the present invention, even when the solid electrolyte sheet is as thin as 50 μm or less, these problems during charging can be avoided.

[0049] Furthermore, the thickness of the solid electrolyte sheet is preferably 5 μm or more, and more preferably 10 μm or more, from the viewpoint of ensuring an appropriate positive-negative electrode distance in a battery using the solid electrolyte sheet, thereby suppressing the occurrence of short circuits and increased resistance.

[0050] In a solid electrolyte sheet, the thickness of the porous substrate is preferably 85% or less, and more preferably 80% or less, from the viewpoint of ensuring smooth lithium ion movement on the positive electrode side and smooth lithium ion movement on the negative electrode side, as well as better suppression of metal deposition that causes charging abnormalities, by having the solid electrolyte covering the surface of the porous substrate with the aforementioned thickness.

[0051] Furthermore, while the porous substrate plays a role in enhancing the shape retention of the solid electrolyte sheet, if the proportion of the porous substrate's thickness to the solid electrolyte sheet is too small, the shape retention of the solid electrolyte sheet may decrease. Also, when the proportion of the porous substrate's thickness to the solid electrolyte sheet is sufficiently large, the effect of facilitating lithium ion movement on the positive electrode side, facilitating lithium ion movement on the negative electrode side, and suppressing metal deposition that causes charging abnormalities becomes more pronounced. For these reasons, the thickness of the porous substrate is preferably 30% or more of the thickness of the solid electrolyte sheet, and more preferably 50% or more.

[0052] The specific thickness of the porous substrate is preferably 3 μm or more, more preferably 8 μm or more, preferably 45 μm or less, and more preferably 25 μm or less.

[0053] In a solid electrolyte sheet, if the porous substrate is biased towards one side in the thickness direction of the solid electrolyte sheet (the positive electrode side in an all-solid-state battery), this can be determined by observing five fields of view at 500x magnification using a scanning electron microscope (SEM) on a cross-section cut perpendicular to the electrode surface from a laminate in which the positive electrode, solid electrolyte sheet, and negative electrode are stacked. The field of view is then divided into 20 equal parts along the length of the solid electrolyte sheet, for a total of 20 locations. When counting the distance between the positive electrode active material and the negative electrode active material relative to each porous substrate, it can be determined that the porous substrate is biased towards the side with the higher count. If there are 15 or more locations without substrate among the above 20 locations, an additional field of view is observed. Furthermore, in a solid electrolyte sheet, if the solid electrolyte covers the surface of the porous substrate, this can be confirmed by observing the presence of the solid electrolyte above and below the porous substrate in the aforementioned field of view. If the solid electrolyte is held within the voids of the porous substrate, this can be confirmed by observing the presence of the solid electrolyte inside the porous substrate in the aforementioned field of view.

[0054] Figure 2 shows a partially enlarged view of Figure 1. Figure 2 shows the vicinity of the laminated surface between the positive electrode 10 and the solid electrolyte sheet 30 in the laminate. Note that in Figure 2, the diagonal lines indicating a cross-section have been omitted to avoid making the drawing complicated. The side of the positive electrode 10 that is in contact with the solid electrolyte sheet 30 contains the positive electrode active material 11, etc. (In Figure 2, only the positive electrode active material 11 is shown). In addition, the surface of the solid electrolyte sheet 30 on the positive electrode 10 side is covered with solid electrolyte 32a on the surface of the porous substrate 31 (In Figure 2, the fibrous material constituting the porous substrate 31 is shown), and solid electrolyte is also held in the voids of the porous substrate 31. The distance (A) as referred to herein means the length between the surface of the porous substrate and the positive electrode active material, which can be determined at the point where the distance in the thickness direction of the laminate is shortest in the aforementioned field of view, i.e., the length of (A) shown in Figure 2. Note that in Figure 2, the solid electrolyte is omitted between the two straight lines used to explain the length of distance (A) and in their vicinity in order to facilitate understanding of the distance (A). However, in reality, the solid electrolyte is present in these locations as well.

[0055] Furthermore, the distance (B) as used herein, like distance (A), refers to the length between the surface of the porous substrate and the negative electrode active material, determined at the point in the thickness direction of the laminate where the distance between them is shortest within the field of view.

[0056] Furthermore, the thickness of the solid electrolyte sheet is determined by the average value of the distances between the positive electrode active material and the negative electrode active material measured at five locations along the length of the solid electrolyte sheet within the aforementioned field of view: the left end, the center, the right end, and two locations in between. In addition, the thickness of the porous substrate is determined by the greater of the following two distances within the aforementioned field of view: the distance at the point where the porous substrate is thickest, or the distance between the upper end of the upper substrate and the lower end of the lower substrate at the point where the substrates overlap with the solid electrolyte in the thickness direction.

[0057] From the viewpoint of ensuring good lithium ion conductivity, the proportion of porous substrate in the solid electrolyte sheet (the proportion of actual volume excluding voids) is preferably 30 vol% or less, and more preferably 25 vol% or less. However, if the proportion of porous substrate in the solid electrolyte sheet is too small, the effect of improving the shape retention of the solid electrolyte sheet may be reduced. Therefore, from the viewpoint of further increasing the strength of the solid electrolyte sheet, the proportion of porous substrate in the solid electrolyte sheet is preferably 5 vol% or more, and more preferably 10 vol% or more.

[0058] Furthermore, the binder content in the solid electrolyte sheet is preferably 0.5% by mass or more, and more preferably 1% by mass or more, of the total amount of solid electrolyte and binder, from the viewpoint of further improving the shape retention of the solid electrolyte sheet. Also, from the viewpoint of limiting the amount of binder to some extent and suppressing a decrease in lithium ion conductivity, it is preferably 5% by mass or less, and more preferably 3% by mass or less.

[0059] There are no particular restrictions on the method for manufacturing the solid electrolyte sheet, but it is preferable to manufacture it by a method that includes the steps of dispersing the solid electrolyte and a binder used as needed in a solvent to form a slurry, and then filling the voids of a porous substrate with this slurry in a wet manner while forming a coating film of the slurry on the surface of the porous substrate. This improves the strength of the solid electrolyte sheet and facilitates the manufacture of large-area solid electrolyte sheets.

[0060] Methods for filling the voids of a porous substrate with a slurry containing a solid electrolyte and forming a coating film of the slurry on the surface of the porous substrate include screen printing, doctor blade method, and immersion method.

[0061] The slurry is prepared by adding a solid electrolyte and, if necessary, a binder to a solvent and mixing. It is preferable to select a solvent for the slurry that does not easily degrade the solid electrolyte. In particular, since sulfide-based solid electrolytes and hydride-based solid electrolytes undergo chemical reactions with even trace amounts of water, it is preferable to use a nonpolar aprotic solvent represented by hydrocarbon solvents such as hexane, heptane, octane, nonane, decane, decalin, toluene, and xylene. It is especially preferable to use an ultra-dehydrated solvent with a water content of 0.001% by mass (10 ppm) or less. In addition, fluorine-based solvents such as "Bartrell®" from Mitsui DuPont Fluorochemicals, "Zeolora®" from Nippon Zeon Corporation, and "Novec®" from Sumitomo 3M Corporation, as well as non-aqueous organic solvents such as dichloromethane and diethyl ether, can also be used.

[0062] As described above, after filling the voids in the porous substrate with slurry and forming a slurry coating on the surface of the porous substrate, the solvent of the slurry is removed by drying, and if necessary, pressure molding is performed to obtain a solid electrolyte sheet.

[0063] As stated above, the method for manufacturing the solid electrolyte sheet is not limited to the wet method described above. For example, when filling the voids of a porous substrate with a solid electrolyte (and a binder used as needed), the solid electrolyte or a mixture of the solid electrolyte and binder may be filled dry, and then pressure molding may be performed. Also, when covering the surface of a porous substrate with a solid electrolyte, a sheet obtained by molding a mixture of the solid electrolyte and binder may be attached to the surface of a sheet in which the voids of the porous substrate have been filled with the solid electrolyte.

[0064] <Positive electrode> The positive electrode of an all-solid-state battery contains a positive electrode mixture containing a positive electrode active material and a solid electrolyte. Examples include a structure in which a layer made of molded positive electrode mixture (positive electrode mixture layer) is formed on a current collector, a structure consisting only of molded positive electrode mixture (pellets, etc.), and a structure in which a positive electrode mixture containing a positive electrode active material and a solid electrolyte is filled into the pores of a conductive porous substrate.

[0065] When an all-solid-state battery is a primary battery, the same positive electrode active material used in conventionally known non-aqueous electrolyte primary batteries can be used. Specifically, for example, manganese dioxide, lithium-containing manganese oxide [for example, LiMn3O6, or composite oxides having the same crystal structure as manganese dioxide (β-type, γ-type, or a structure in which β-type and γ-type are mixed, etc.) and having a Li content of 3.5% by mass or less, preferably 2% by mass or less, more preferably 1.5% by mass or less, particularly preferably 1% by mass or less], Li a Ti 5 / 3 Examples include lithium-containing composite oxides such as O4 (4 / 3 ≤ a < 7 / 3); vanadium oxide; niobium oxide; titanium oxide; sulfides such as iron disulfide; graphite fluoride; silver sulfides such as Ag2S; and nickel oxides such as NiO2.

[0066] Furthermore, if the all-solid-state battery is a rechargeable battery, the same positive electrode active material used in conventionally known non-aqueous electrolyte rechargeable batteries, that is, the same active material capable of intercepting and releasing Li (lithium) ions, can be used. Specifically, Li 1-x M r Mn2-r O4 (where M is at least one element selected from the group consisting of Li, Na, K, B, Mg, Ca, Sr, Ba, Ti, V, Cr, Zr, Fe, Co, Ni, Cu, Zn, Al, Sn, Sb, In, Nb, Ta, Mo, W, Y, Ru and Rh, 0 ≦ x ≦ 1, 0 ≦ r ≦ 1), spinel-type lithium manganese composite oxide, Li r Mn (1-s-t) Ni s M t O (2-u) F v (where M is at least one element selected from the group consisting of Co, Mg, Al, B, Ti, V, Cr, Fe, Cu, Zn, Zr, Mo, Sn, Ca, Sr and W, 0 ≦ r ≦ 1.2, 0 < s < 0.5, 0 ≦ t ≦ 0.5, u + v < 1, -0.1 ≦ u ≦ 0.2, 0 ≦ v ≦ 0.1), layered compound, Li 1-x Co 1-r M r O2 (where M is at least one element selected from the group consisting of Al, Mg, Ti, V, Cr, Zr, Fe, Ni, Cu, Zn, Ga, Ge, Nb, Mo, Sn, Sb and Ba, 0 ≦ x ≦ 1, 0 ≦ r ≦ 0.5), lithium cobalt composite oxide, Li 1-x Ni 1-r M r O2 (where M is at least one element selected from the group consisting of Al, Mg, Ti, Zr, Fe, Co, Cu, Zn, Ga, Ge, Nb, Mo, Sn, Sb and Ba, 0 ≦ x ≦ 1, 0 ≦ r ≦ 0.5), lithium nickel composite oxide, Li 1+s-x M 1-r N r PO4F s (where M is at least one element selected from the group consisting of Fe, Mn and Co, and N is at least one element selected from the group consisting of Al, Mg, Ti, Zr, Ni, Cu, Zn, Ga, Ge, Nb, Mo, Sn, Sb, V and Ba, 0 ≦ x ≦ 1, 0 ≦ r ≦ 0.5, 0 ≦ s ≦ 1), olivine-type composite oxide, Li 2-x M 1-r N rExamples include pyrophosphate compounds represented by P2O7 (where M is at least one element selected from the group consisting of Fe, Mn, and Co, and N is at least one element selected from the group consisting of Al, Mg, Ti, Zr, Ni, Cu, Zn, Ga, Ge, Nb, Mo, Sn, Sb, V, and Ba, with 0≦x≦2 and 0≦r≦0.5). Only one of these may be used, or two or more may be used in combination.

[0067] When an all-solid-state battery is a secondary battery, the average particle size of the positive electrode active material is preferably 1 μm or more, more preferably 2 μm or more, more preferably 10 μm or less, and more preferably 8 μm or less. The positive electrode active material may be primary particles or secondary particles formed by aggregation of primary particles. Using a positive electrode active material with an average particle size within the above range allows for a larger interface with the solid electrolyte contained in the positive electrode, thereby improving the battery's load characteristics.

[0068] In the case of a rechargeable battery, it is preferable that the positive electrode active material has a reaction-inhibiting layer on its surface to suppress the reaction with the solid electrolyte contained in the positive electrode.

[0069] In a molded positive electrode mixture, direct contact between the positive electrode active material and the solid electrolyte can cause the solid electrolyte to oxidize, forming a resistance layer and potentially reducing the ionic conductivity within the molded body. By providing a reaction-inhibiting layer on the surface of the positive electrode active material to suppress its reaction with the solid electrolyte, direct contact between the positive electrode active material and the solid electrolyte can be prevented, thereby suppressing the reduction in ionic conductivity within the molded body due to oxidation of the solid electrolyte.

[0070] The reaction suppression layer should be composed of a material that has ionic conductivity and can suppress the reaction between the positive electrode active material and the solid electrolyte. Examples of materials that can constitute the reaction suppression layer include oxides containing Li and at least one element selected from the group consisting of Nb, P, B, Si, Ge, Ti, and Zr, more specifically, Nb-containing oxides such as LiNbO3, Li3PO4, Li3BO3, Li4SiO4, Li4GeO4, LiTiO3, LiZrO3, and Li2WO4. The reaction suppression layer may contain only one of these oxides, or two or more, and furthermore, multiple of these oxides may form a composite compound. Among these oxides, it is preferable to use an Nb-containing oxide, and more preferable to use LiNbO3.

[0071] The reaction-inhibiting layer is preferably present on the surface in an amount of 0.1 to 1.0 part by mass per 100 parts by mass of positive electrode active material. Within this range, the reaction between the positive electrode active material and the solid electrolyte can be effectively suppressed.

[0072] Methods for forming a reaction-inhibiting layer on the surface of the positive electrode active material include the sol-gel method, mechanofusion method, CVD method, PVD method, and ALD method.

[0073] The content of the positive electrode active material in the positive electrode mixture is preferably 60 to 98% by mass.

[0074] The positive electrode mixture may contain a conductive additive. Specific examples include carbon materials such as graphite (natural graphite, artificial graphite), graphene, carbon black, carbon nanofibers, and carbon nanotubes. However, if Ag2S is used as the active material, conductive Ag is generated during the discharge reaction, so a conductive additive may not be necessary. When a conductive additive is included in the positive electrode mixture, its content is preferably 1 to 10% by mass.

[0075] Furthermore, a binder can be included in the positive electrode mixture. Specific examples include fluororesins such as PVDF and acrylic resins. However, if good moldability can be ensured in forming the molded body of the positive electrode mixture without using a binder, such as when a sulfide-based solid electrolyte is included in the positive electrode mixture (details will be described later), then the positive electrode mixture does not need to contain a binder.

[0076] In the positive electrode mixture, if a binder is required, its content is preferably 15% by mass or less, and more preferably 0.5% by mass or more. On the other hand, if the positive electrode mixture contains a sulfide-based solid electrolyte, the preferred binder content is 0.1% by mass or more and 15% by mass or less, and a more preferred content is 0.5% by mass or more and 5% by mass or less.

[0077] Examples of solid electrolytes to be included in the positive electrode mixture include those exemplified above as solid electrolytes that can be used in solid electrolyte sheets. Among the solid electrolytes exemplified above, sulfide-based solid electrolytes are more preferable because they have high lithium ion conductivity and also have the function of improving the moldability of the positive electrode mixture.

[0078] The solid electrolyte content in the positive electrode mixture is preferably 4 to 40% by mass.

[0079] When a current collector is used for the positive electrode, the current collector can be made of metal foil such as aluminum or stainless steel, perforated metal, mesh, expanded metal, foamed metal, carbon sheet, etc.

[0080] The positive electrode can be manufactured by applying a positive electrode mixture-containing composition (paste, slurry, etc.), which is obtained by dispersing a positive electrode active material and a solid electrolyte with conductive additives, binders, etc. as needed in a solvent, to a current collector, drying it, and then, if necessary, applying pressure molding such as calendering to form a molded positive electrode mixture (positive electrode mixture layer) on the surface of the current collector.

[0081] While water and organic solvents such as N-methyl-2-pyrrolidone (NMP) can be used as solvents for the positive electrode mixture-containing composition, when using a solid electrolyte that is highly reactive with water, it is desirable to select a solvent that does not easily degrade the solid electrolyte, and it is preferable to use the same solvents as those previously exemplified for the slurry used to form the solid electrolyte sheet.

[0082] Furthermore, in addition to the method described above, the molded positive electrode mixture may also be formed by compressing a positive electrode mixture, which is prepared by mixing a positive electrode active material and a solid electrolyte with conductive additives, binders, etc., as needed, using pressure molding or the like. As described above, the molded positive electrode mixture obtained by this method can be used as a positive electrode as is, or it can be used as a positive electrode after being bonded with a current collector by pressing or other means.

[0083] The thickness of the molded positive electrode mixture (positive electrode mixture layer) formed using a positive electrode mixture-containing composition containing a solvent (or, if present, the thickness per side of the current collector) is preferably 10 to 1000 μm. Furthermore, the thickness of the molded positive electrode mixture obtained by pressure molding is preferably 0.15 to 4 mm.

[0084] The thickness of the positive electrode current collector is preferably 0.01 to 0.1 mm.

[0085] Furthermore, when a conductive porous substrate such as perforated metal is used as the positive electrode current collector, the positive electrode can be manufactured, for example, by filling the pores of the conductive porous substrate with the positive electrode mixture, drying it, and then, if necessary, performing pressure molding such as calendering. A positive electrode manufactured by this method can ensure high strength, making it possible to hold a larger area solid electrolyte sheet.

[0086] Furthermore, instead of the aforementioned positive electrode mixture-containing composition, a positive electrode mixture containing a positive electrode active material, a solid electrolyte, a conductive additive, and a binder, but without a solvent, may be dry-filled into the pores of a conductive porous substrate, and then pressure-molded, such as by calendering, as necessary, in order to produce the positive electrode.

[0087] In the case of a positive electrode obtained by filling the pores of a conductive porous substrate with a positive electrode mixture-containing composition or a positive electrode mixture, its thickness is preferably 30 to 4000 μm.

[0088] <Negative electrode> The negative electrode of an all-solid-state battery may consist of, for example, a molded body of a negative electrode mixture containing a negative electrode active material, a lithium sheet, or a lithium alloy sheet. Alternatively, a negative electrode mixture containing a negative electrode active material can be filled into the pores of a conductive porous substrate.

[0089] When the negative electrode is a molded body of a negative electrode mixture containing a negative electrode active material, examples include structures in which a layer made of molded bodies of the negative electrode mixture (negative electrode mixture layer) is formed on the current collector, or structures consisting only of molded bodies made of molded negative electrode mixture (such as pellets).

[0090] When the negative electrode has a molded body of a negative electrode mixture, the negative electrode active material can be, for example, carbon materials such as graphite, or elements such as Si and Sn, as well as elements, compounds (oxides, etc.), and alloys thereof. Lithium metal and lithium alloys (lithium-aluminum alloy, lithium-indium alloy, etc.) can also be used as negative electrode active materials.

[0091] The content of the negative electrode active material in the negative electrode mixture is preferably 10 to 99% by mass.

[0092] The negative electrode mixture may contain a conductive additive. Specific examples include the same conductive additives exemplified earlier that can be included in the positive electrode mixture. The content of the conductive additive in the negative electrode mixture is preferably 1 to 10% by mass.

[0093] Furthermore, a binder can be included in the negative electrode mixture. Specific examples include the same binders mentioned earlier as those that can be included in the positive electrode mixture. However, if good moldability can be ensured in forming the molded body of the negative electrode mixture without using a binder, such as when a sulfide-based solid electrolyte is included in the negative electrode mixture (details will be discussed later), then the negative electrode mixture does not need to contain a binder.

[0094] In the negative electrode mixture, if a binder is required, its content is preferably 15% by mass or less, and more preferably 0.5% by mass or more. On the other hand, if the negative electrode mixture contains a sulfide-based solid electrolyte, the preferred binder content is 0.3% by mass or more and 15% by mass or less, and a more preferred content is 0.7% by mass or more and 7% by mass or less.

[0095] In a negative electrode having a molded negative electrode mixture, a solid electrolyte is included in the negative electrode mixture. Specific examples include the same solid electrolytes exemplified earlier that can be used in solid electrolyte sheets. Among the exemplified solid electrolytes, sulfide-based solid electrolytes are more preferable because they have high lithium ion conductivity and also enhance the moldability of the negative electrode mixture.

[0096] The solid electrolyte content in the negative electrode mixture is preferably 4 to 49% by mass.

[0097] When a current collector is used in a negative electrode having a molded negative electrode mixture, the current collector can be made of copper or nickel foil, perforated metal, mesh, expanded metal, foamed metal, carbon sheet, etc.

[0098] The negative electrode can be manufactured by applying a negative electrode mixture-containing composition (paste, slurry, etc.), which is obtained by dispersing a negative electrode active material, as well as conductive additives, solid electrolytes, and binders as needed, in a solvent, to a current collector, drying it, and then, if necessary, applying pressure molding such as calendering to form a molded negative electrode mixture (negative electrode mixture layer) on the surface of the current collector.

[0099] While organic solvents such as water and NMP can be used as the solvent for the negative electrode mixture-containing composition, when the negative electrode mixture-containing composition also contains a solid electrolyte, it is desirable to select a solvent that does not easily degrade the solid electrolyte, and it is preferable to use the same solvents as those previously exemplified for the slurry used to form the solid electrolyte sheet.

[0100] Furthermore, in addition to the method described above, the molded negative electrode mixture may also be formed by compressing a negative electrode mixture, which is prepared by mixing a negative electrode active material, and optionally added conductive additives, a solid electrolyte, and a binder, using methods such as pressure molding. As described above, the molded negative electrode mixture obtained by such methods can be used as a negative electrode as is, or it can be used as a negative electrode after being bonded with a current collector by pressing or other means.

[0101] The thickness of the molded negative electrode mixture (negative electrode mixture layer) formed using a negative electrode mixture-containing composition containing a solvent (or the thickness per side of the current collector if a current collector is present) is preferably 10 to 1000 μm. Furthermore, the thickness of the molded negative electrode mixture obtained by pressure molding is preferably 0.15 to 4 mm.

[0102] Furthermore, the thickness of the negative electrode current collector is preferably 0.01 to 0.1 mm.

[0103] In the case of a negative electrode having a lithium sheet or a lithium alloy sheet, either these sheets alone or these sheets bonded to a current collector are used.

[0104] Examples of alloying elements for lithium alloys include aluminum, lead, bismuth, indium, and gallium, but aluminum and indium are preferred. The proportion of alloying elements in a lithium alloy (the total proportion if multiple alloying elements are included) is preferably 50 atomic percent or less (in this case, the remainder is lithium and unavoidable impurities).

[0105] Furthermore, in the case of a negative electrode having a lithium alloy sheet, a laminate can be used in which a layer containing alloying elements for forming a lithium alloy is laminated by pressing a layer containing alloying elements for forming a lithium alloy onto the surface of a lithium layer (a layer containing lithium) made of metallic lithium foil or the like, and this laminate is brought into contact with a solid electrolyte in the battery to form a lithium alloy on the surface of the lithium layer and thus serve as the negative electrode. In the case of such a negative electrode, a laminate having a layer containing alloying elements on only one side of the lithium layer may be used, or a laminate having layers containing alloying elements on both sides of the lithium layer may be used. The laminate can be formed, for example, by pressing a metallic lithium foil and a foil made of alloying elements together.

[0106] Furthermore, a current collector can also be used when a lithium alloy is formed within the battery to serve as the negative electrode. For example, a laminate may be used in which a lithium layer is present on one side of the negative electrode current collector, and a layer containing an alloying element is present on the side of the lithium layer opposite the negative electrode current collector. Alternatively, a laminate may be used in which lithium layers are present on both sides of the negative electrode current collector, and a layer containing an alloying element is present on the side of each lithium layer opposite the negative electrode current collector. The negative electrode current collector and the lithium layer (metallic lithium foil) can be laminated by means of compression or other methods.

[0107] For the layer containing the alloying elements in the laminate used as the negative electrode, for example, foil composed of these alloying elements can be used. The thickness of the layer containing the alloying elements is preferably 1 μm or more, more preferably 3 μm or more, preferably 20 μm or less, and more preferably 12 μm or less.

[0108] For the lithium layer in the laminate used as the negative electrode, for example, metallic lithium foil can be used. The thickness of the lithium layer is preferably 0.1 to 1.5 mm. Furthermore, the thickness of the sheet in the negative electrode, which has a sheet of lithium or lithium alloy, is also preferably 0.1 to 1.5 mm.

[0109] If the negative electrode having a lithium sheet or a lithium alloy sheet has a current collector, the current collector can be the same as the current collector previously exemplified as usable for a negative electrode having a molded negative electrode mixture.

[0110] Furthermore, when a conductive porous substrate such as perforated metal is used as the negative electrode current collector, the negative electrode can be manufactured, for example, by filling the pores of the conductive porous substrate with the aforementioned negative electrode mixture composition, drying it, and then, if necessary, performing pressure molding such as calendering. A negative electrode manufactured in this way can be made to have greater strength, making it possible to hold a larger area solid electrolyte sheet.

[0111] Furthermore, instead of the aforementioned negative electrode mixture-containing composition, a negative electrode mixture containing a negative electrode active material, as well as a solid electrolyte, a binder, a conductive additive, etc., but without a solvent, may be dry-filled into the pores of a conductive porous substrate, and pressure-molded, such as by calendering, as necessary, in order to produce the negative electrode.

[0112] In the case of a negative electrode obtained by filling the pores of a conductive porous substrate with a negative electrode mixture-containing composition or a negative electrode mixture, its thickness is preferably 30 to 4000 μm.

[0113] <Laminate (electrode body)> The positive and negative electrodes can be used in all-solid-state batteries in the form of a laminated electrode body, which is formed by stacking solid electrolyte sheets, or a wound electrode body, which is formed by winding this laminated electrode body.

[0114] Furthermore, when forming the laminate, it is preferable to pressure-molde the positive electrode, negative electrode, and solid electrolyte sheet in a laminated state, from the viewpoint of increasing the mechanical strength of the laminate (in this case, the thickness of the solid electrolyte sheet after pressure molding will satisfy the aforementioned value).

[0115] <Format of all-solid-state batteries> Figures 3 and 4 show schematic diagrams illustrating an example of an all-solid-state battery. Figure 3 is a plan view of the all-solid-state battery, and Figure 4 is a cross-sectional view taken along line II of Figure 3.

[0116] The all-solid-state battery 1 shown in Figures 3 and 4 houses a laminated body 100 within a laminated film casing 400 made of two metal laminated films. The laminated film casing 400 is sealed by heat-sealing the upper and lower metal laminated films at its outer periphery. The laminated body 100 is composed of a positive electrode, a negative electrode, and the solid electrolyte sheet interposed between them, all laminated together.

[0117] Note that in Figure 4, in order to avoid making the drawing complicated, the individual layers constituting the laminate film outer casing 400 and the individual components (positive electrode, negative electrode, solid electrolyte sheet) forming the laminate 100 are not shown separately.

[0118] The positive electrode of the laminate 100 is connected to the positive electrode external terminal 200 within the all-solid-state battery 1, and although not shown in the figure, the negative electrode of the laminate 100 is also connected to the negative electrode external terminal 300 within the all-solid-state battery 1. The positive electrode external terminal 200 and the negative electrode external terminal 300 have one end extended to the outside of the laminate film casing 400 so that they can be connected to external devices.

[0119] There are no particular restrictions on the form of all-solid-state batteries. In addition to the sheet-like (laminated) form shown in Figure 3, various other forms are possible, such as flat (including coin-shaped and button-shaped) and cylindrical (cylindrical and rectangular (rectangular)) shapes. Furthermore, as the outer casing (battery case) that houses the laminate containing the negative electrode, positive electrode, and solid electrolyte sheet, a metal laminate film can be used, or a combination of a metal can with an opening (outer can) and a lid (sealed can) can be used.

[0120] Specifically, a sheet-shaped (laminated) battery can be manufactured by layering two metal laminate films or by folding a single metal laminate film and sealing the edges. Flat-shaped (coin-shaped, button-shaped, etc.) or cylindrical batteries can be manufactured by crimping the outer casing and sealing casing together with a gasket, or by welding the outer casing and sealing casing together.

[0121] Furthermore, when using an outer casing with a crimped seal, the gasket material interposed between the outer casing and the sealed casing can be made of polypropylene (PP), nylon, etc. In addition, if particularly high heat resistance is required due to the battery's application, heat-resistant resins with a melting point or thermal decomposition temperature of 200°C or higher can be used, such as fluororesins such as tetrafluoroethylene-perfluoroalkoxyethylene copolymer (PFA), polyphenylene ether (PPE), polysulfone (PSF), polyarylate (PAR), polyethersulfone (PES), polyphenylene sulfide (PPS), and polyetheretherketone (PEEK). Also, when the battery is applied to an application requiring heat resistance, a glass hermetic seal can be used for the seal.

[0122] The shape of the exterior body in plan view may be circular, or it may be a polygon such as a square or rectangle. In the case of a polygon, its corners may be curved. [Examples]

[0123] The present invention will be described in detail below based on examples. However, the following examples are not intended to limit the present invention.

[0124] Example 1 <Preparation of solid electrolyte sheets> Using xylene ("super dehydrated" grade) as the solvent, a mixture of sulfide-based solid electrolyte (Li6PS5Cl) particles with an average particle size of 1 μm, an acrylic resin binder, and a dispersant was prepared in a mass ratio of 100:3:1 and with a solid content of 40%. The mixture was stirred in a sinker mixer for 10 minutes to prepare a homogeneous slurry. In this slurry, a material with a thickness of 15 μm and a basis weight of 8 g / m² was added. 2 The slurry was applied to a PET nonwoven fabric (Hirose Paper Co., Ltd.'s "05TH-8") by passing it through a 40 μm gap and then pulling it up at a 45-degree angle to the bottom surface using an applicator. After applying the slurry to the PET nonwoven fabric, a solid electrolyte sheet was obtained by vacuum drying at 120°C for 1 hour. In the solid electrolyte sheet, the proportion of binder in the total amount of solid electrolyte particles and binder was 2.9% by mass.

[0125] <Fabrication of the positive electrode> Using xylene ("super dehydrated" grade) as the solvent, LiNi particles with an average particle size of 3 μm were formed, with an amorphous composite oxide of Li and Nb on the surface. 0.6 Co 0.2 Mn 0.2 O2, a sulfide solid electrolyte (Li6PS5Cl), a conductive additive carbon nanotube (Showa Denko Corporation's "VGCF" (product name)), and an acrylic resin binder were mixed in a mass ratio of 70:24:3:3, with a solid content ratio of 60%, and stirred in a sinker mixer for 10 minutes to prepare a homogeneous slurry. This slurry was applied to a 20 μm thick aluminum foil using an applicator with a gap of 200 μm, and vacuum dried at 120°C to obtain a cathode.

[0126] <Fabrication of the negative electrode> Using xylene ("super dehydrated" grade) as the solvent, graphite with an average particle size of 20 μm, a sulfide solid electrolyte (Li6PS5Cl), a conductive additive carbon nanotube [Showa Denko Corporation's "VGCF" (product name)], and an acrylic resin binder were mixed in a mass ratio of 50:44:3:3, so that the solid content ratio was 50%, and the mixture was stirred in a sinker mixer for 10 minutes to prepare a uniform slurry. This slurry was applied to a 20 μm thick SUS foil using an applicator with a gap of 160 μm, and the negative electrode was obtained by vacuum drying at 120°C.

[0127] <Battery assembly> The positive electrode, negative electrode, and solid electrolyte sheet are all punched out to a size of 10 mm in diameter, stacked in the order of positive electrode - solid electrolyte sheet - negative electrode between upper and lower SUS pins, and placed in a PET tube at a load capacity of 10 tons / cm². 2 The cell (all-solid-state secondary battery) was pressurized and sealed to prevent contact with the atmosphere, allowing for charging and discharging. In the laminate, which is constructed by stacking the positive electrode, solid electrolyte sheet, and negative electrode in that order, the side of the solid electrolyte sheet that was the bottom surface when the slurry was applied using the applicator was positioned to face the negative electrode.

[0128] For a portion of the multiple cells produced, a laminate consisting of a positive electrode, a solid electrolyte sheet, and a negative electrode was removed. Using the method described above, it was confirmed that the solid electrolyte covered both sides of the porous substrate in the solid electrolyte sheet, that the porous substrate was positioned biased toward the positive electrode side, and that solid electrolyte particles were held within the voids of the porous substrate. Furthermore, for this laminate, the distance on the positive electrode side (A), the distance on the negative electrode side (B), the thickness of the porous substrate (PET nonwoven fabric), and the thickness of the solid electrolyte sheet, measured using the method described above, were 1 μm, 5 μm, 15 μm, and 21 μm, respectively, and the thickness of the porous substrate was 71% of the thickness of the solid electrolyte sheet.

[0129] Example 2 A solid electrolyte sheet was prepared in the same manner as in Example 1, except that when applying the slurry to the PET nonwoven fabric, the applicator was modified to lift it through a 50 μm gap at a 45-degree angle to the bottom surface. A cell (all-solid-state secondary battery) was then prepared in the same manner as in Example 1, except that this solid electrolyte sheet was used.

[0130] For a portion of the multiple cells fabricated, a laminate consisting of a positive electrode, a solid electrolyte sheet, and a negative electrode was removed. Using the method described above, it was confirmed that the solid electrolyte covered both sides of the porous substrate in the solid electrolyte sheet, that the porous substrate in the solid electrolyte sheet was positioned biased toward the positive electrode side, and that solid electrolyte particles were held within the voids of the porous substrate. Furthermore, for this laminate, the distance on the positive electrode side (A), the distance on the negative electrode side (B), the thickness of the porous substrate, and the thickness of the solid electrolyte sheet, measured using the method described above, were 5 μm, 10 μm, 15 μm, and 30 μm, respectively, and the thickness of the porous substrate was 50% of the thickness of the solid electrolyte sheet.

[0131] Example 3 A solid electrolyte sheet was prepared in the same manner as in Example 1, except that when applying the slurry to the PET nonwoven fabric, the applicator was modified to lift it through a 30 μm gap at a 45-degree angle to the bottom surface. A cell (all-solid-state secondary battery) was then prepared in the same manner as in Example 1, except that this solid electrolyte sheet was used.

[0132] For a portion of the multiple cells fabricated, a laminate consisting of a positive electrode, a solid electrolyte sheet, and a negative electrode was removed. Using the method described above, it was confirmed that the solid electrolyte covered both sides of the porous substrate in the solid electrolyte sheet, that the porous substrate in the solid electrolyte sheet was positioned biased toward the positive electrode side, and that solid electrolyte particles were held within the voids of the porous substrate. Furthermore, for this laminate, the distance on the positive electrode side (A), the distance on the negative electrode side (B), the thickness of the porous substrate, and the thickness of the solid electrolyte sheet, measured using the method described above, were 1 μm, 3 μm, 15 μm, and 19 μm, respectively, and the thickness of the porous substrate was 79% of the thickness of the solid electrolyte sheet.

[0133] Example 4 A solid electrolyte sheet was prepared in the same manner as in Example 1, except that when applying the slurry to the PET nonwoven fabric, the applicator was modified to lift it through a 20 μm gap at a 45-degree angle to the bottom surface. A cell (all-solid-state secondary battery) was then prepared in the same manner as in Example 1, except that this solid electrolyte sheet was used.

[0134] For a portion of the multiple cells fabricated, a laminate consisting of a positive electrode, a solid electrolyte sheet, and a negative electrode was removed. Using the method described above, it was confirmed that the solid electrolyte covered both sides of the porous substrate in the solid electrolyte sheet, that the porous substrate in the solid electrolyte sheet was positioned biased toward the positive electrode side, and that solid electrolyte particles were held within the voids of the porous substrate. Furthermore, for this laminate, the distance on the positive electrode side (A), the distance on the negative electrode side (B), the thickness of the porous substrate, and the thickness of the solid electrolyte sheet, measured using the method described above, were 1 μm, 3 μm, 6 μm, and 10 μm, respectively, and the thickness of the porous substrate was 60% of the thickness of the solid electrolyte sheet.

[0135] Example 5 A solid electrolyte sheet was prepared in the same manner as in Example 1, except that when applying the slurry to the PET nonwoven fabric, the applicator was modified to lift it through a 60 μm gap at a 45-degree angle to the bottom surface. A cell (all-solid-state secondary battery) was then prepared in the same manner as in Example 1, except that this solid electrolyte sheet was used.

[0136] For a portion of the multiple cells fabricated, a laminate consisting of a positive electrode, a solid electrolyte sheet, and a negative electrode was removed. Using the method described above, it was confirmed that the solid electrolyte covered both sides of the porous substrate in the solid electrolyte sheet, that the porous substrate in the solid electrolyte sheet was positioned biased toward the positive electrode side, and that solid electrolyte particles were held within the voids of the porous substrate. Furthermore, for this laminate, the distance on the positive electrode side (A), the distance on the negative electrode side (B), the thickness of the porous substrate, and the thickness of the solid electrolyte sheet, measured using the method described above, were 1 μm, 3 μm, 46 μm, and 50 μm, respectively, and the thickness of the porous substrate was 92% of the thickness of the solid electrolyte sheet.

[0137] Example 6 A solid electrolyte sheet was prepared in the same manner as in Example 1, except that when applying the slurry to the PET nonwoven fabric, the applicator was modified to lift it through a 60 μm gap at a 50-degree angle to the bottom surface. A cell (all-solid-state secondary battery) was then prepared in the same manner as in Example 1, except that this solid electrolyte sheet was used.

[0138] For a portion of the multiple cells fabricated, a laminate consisting of a positive electrode, a solid electrolyte sheet, and a negative electrode was removed. Using the method described above, it was confirmed that the solid electrolyte covered both sides of the porous substrate in the solid electrolyte sheet, that the porous substrate in the solid electrolyte sheet was positioned biased toward the positive electrode side, and that solid electrolyte particles were held within the voids of the porous substrate. Furthermore, for this laminate, the distance on the positive electrode side (A), the distance on the negative electrode side (B), the thickness of the porous substrate, and the thickness of the solid electrolyte sheet, measured using the method described above, were 5 μm, 20 μm, 15 μm, and 40 μm, respectively, and the thickness of the porous substrate was 38% of the thickness of the solid electrolyte sheet.

[0139] Example 7 A solid electrolyte sheet was prepared in the same manner as in Example 1, except that when applying the slurry to the PET nonwoven fabric, the applicator was modified to lift it through a 15 μm gap at a 45-degree angle to the bottom surface. A cell (all-solid-state secondary battery) was then prepared in the same manner as in Example 1, except that this solid electrolyte sheet was used.

[0140] For a portion of the multiple cells fabricated, a laminate consisting of a positive electrode, a solid electrolyte sheet, and a negative electrode was removed. Using the method described above, it was confirmed that the solid electrolyte covered both sides of the porous substrate in the solid electrolyte sheet, that the porous substrate in the solid electrolyte sheet was positioned biased toward the positive electrode side, and that solid electrolyte particles were held within the voids of the porous substrate. Furthermore, for this laminate, the distance on the positive electrode side (A), the distance on the negative electrode side (B), the thickness of the porous substrate, and the thickness of the solid electrolyte sheet, measured using the method described above, were 1 μm, 3 μm, 5 μm, and 9 μm, respectively, and the thickness of the porous substrate was 56% of the thickness of the solid electrolyte sheet.

[0141] Comparative Example 1 A solid electrolyte sheet was prepared in the same manner as in Example 1, except that when applying the slurry to the PET nonwoven fabric, the applicator was modified to lift it through a 30 μm gap at a 60-degree angle to the bottom surface. A cell (all-solid-state secondary battery) was then prepared in the same manner as in Example 1, except that this solid electrolyte sheet was used.

[0142] For a portion of the cells fabricated, a laminate consisting of a positive electrode, a solid electrolyte sheet, and a negative electrode was removed, and the position of the porous substrate on the solid electrolyte sheet was confirmed using the method described above. It was found to be biased towards the positive electrode side, but the positive electrode side surface of the porous substrate was not covered with solid electrolyte. At this time, it was confirmed that solid electrolyte particles were held within the voids of the porous substrate. Furthermore, for this laminate, the distance on the positive electrode side (A), the distance on the negative electrode side (B), the thickness of the porous substrate, and the thickness of the solid electrolyte sheet, measured using the method described above, were 0 μm, 5 μm, 15 μm, and 20 μm, respectively, and the thickness of the porous substrate was 75% of the thickness of the solid electrolyte sheet.

[0143] Comparative Example 2 A solid electrolyte sheet was prepared in the same manner as in Example 1, except that when applying the slurry to the PET nonwoven fabric, the applicator was modified to lift it through a 40 μm gap at a 10-degree angle to the bottom surface. A cell (all-solid-state secondary battery) was then prepared in the same manner as in Example 1, except that this solid electrolyte sheet was used.

[0144] For a portion of the cells fabricated, a laminate consisting of a positive electrode, a solid electrolyte sheet, and a negative electrode was removed, and the position of the porous substrate in the solid electrolyte sheet was confirmed using the method described above. It was found to be biased towards the negative electrode side. At this time, it was confirmed that solid electrolyte particles were held within the voids of the porous substrate. Furthermore, for this laminate, the distance on the positive electrode side (A), the distance on the negative electrode side (B), the thickness of the porous substrate, and the thickness of the solid electrolyte sheet, measured using the method described above, were 5 μm, 2 μm, 15 μm, and 22 μm, respectively, and the thickness of the porous substrate was 68% of the thickness of the solid electrolyte sheet.

[0145] Comparative Example 3 A solid electrolyte sheet was prepared in the same manner as in Example 1, except that when applying the slurry to the PET nonwoven fabric, the applicator was modified to lift it through a 30 μm gap at a 0-degree angle to the bottom surface. A cell (all-solid-state secondary battery) was then prepared in the same manner as in Example 1, except that this solid electrolyte sheet was used.

[0146] For a portion of the multiple cells fabricated, a laminate consisting of a positive electrode, a solid electrolyte sheet, and a negative electrode was removed, and the position of the porous substrate on the solid electrolyte sheet was confirmed using the method described above. It was found to be biased towards the negative electrode side, and the negative electrode side surface of the porous substrate was not covered with solid electrolyte. Furthermore, it was confirmed that solid electrolyte particles were held within the voids of the porous substrate. In addition, for this laminate, the distance on the positive electrode side (A), the distance on the negative electrode side (B), the thickness of the porous substrate, and the thickness of the solid electrolyte sheet, measured using the method described above, were 5 μm, 0 μm, 15 μm, and 20 μm, respectively, and the thickness of the porous substrate was 75% of the thickness of the solid electrolyte sheet.

[0147] Comparative Example 4 A solid electrolyte sheet was prepared in the same manner as in Example 1, except that when applying the slurry to the PET nonwoven fabric, the applicator was modified to lift it through a 15 μm gap at a 30-degree angle to the bottom surface. A cell (all-solid-state secondary battery) was then prepared in the same manner as in Example 1, except that this solid electrolyte sheet was used.

[0148] For a portion of the cells fabricated, a laminate consisting of a positive electrode, a solid electrolyte sheet, and a negative electrode was removed, and the position of the porous substrate on the solid electrolyte sheet was confirmed using the method described above. It was found that the porous substrate was not biased to either side, and both sides of the porous substrate were not covered with solid electrolyte. Furthermore, it was confirmed that solid electrolyte particles were held within the voids of the porous substrate. In addition, for this laminate, the distance on the positive electrode side (A), the distance on the negative electrode side (B), the thickness of the porous substrate, and the thickness of the solid electrolyte sheet, measured using the method described above, were 0 μm, 0 μm, 15 μm, and 15 μm, respectively, and the thickness of the porous substrate was 100% of the thickness of the solid electrolyte sheet.

[0149] The following evaluations were performed on the cells of the examples and comparative examples, as well as the solid electrolyte sheets used in these cells.

[0150] <Charging characteristics evaluation> For the cells in the examples and comparative examples, constant current charging was performed at a current of 0.05C until the voltage reached 4.2V, followed by constant voltage charging at 4.2V until the current value reached 0.01C, and then constant current discharge was performed at a current value of 0.05C until the voltage reached 2.0V. The capacity during constant current charging-constant voltage charging (charging capacity) and the capacity during constant voltage discharge (discharge capacity) were measured. For each cell, the charge-discharge efficiency was determined by expressing the ratio of discharge capacity to charge capacity as a percentage. For each example and comparative example, the charge-discharge efficiency was determined for 100 cells, and cells with a charge-discharge efficiency of 50% or less were judged to have a charging abnormality, and the defect rate (%), which is the percentage of cells with a charging abnormality, was calculated.

[0151] <Evaluation of the presence or absence of short circuits before charging> For each cell in the examples and comparative examples, the battery voltage was measured before charging after assembly. Cells with a voltage of 0.2V or higher were marked "○", those with a voltage of 0.1V or higher were marked "△", and those with a voltage below 0.1V were marked "×". Batteries with a ○ or △ rating can be said to have suppressed short circuits before charging.

[0152] <Discharge Load Characteristics Evaluation> For each cell in the example, constant current charging and constant voltage charging were performed under the same conditions as during the charging characteristics evaluation, and constant current discharge was performed under the same conditions as during the charging characteristics evaluation, except that the current value was changed to 5C, to determine the discharge capacity (5C discharge capacity). Then, for each battery, the capacity retention rate was calculated by dividing the 5C discharge capacity by the discharge capacity (0.05C discharge capacity) obtained during the charging characteristics evaluation and expressing the result as a percentage, and the discharge load characteristics of each battery were evaluated. In the above evaluation, a capacity retention rate of 35% or more was marked "○", 20% or more was marked "△", and less than 20% was marked "×". Batteries with a ○ or △ rating can be said to have good discharge load characteristics.

[0153] <Evaluation of handling properties of solid electrolyte sheets> For each cell in the examples and comparative examples, the laminate consisting of a positive electrode, a solid electrolyte sheet, and a negative electrode was placed in a PET tube and pressurized, and the delamination state between the solid electrolyte sheet and the electrodes (positive and / or negative electrode) was checked. In the above evaluation, "○" indicated no delamination, "△" indicated that the area of ​​the delaminated portion was less than 1 / 3, and "×" indicated that delamination occurred over an area of ​​1 / 3 or more. Solid electrolyte sheets that received evaluations of ○ and △ can be said to have good handling properties.

[0154] Table 1 shows the composition of the solid electrolyte sheets used in the cells of the examples and comparative examples, and Table 2 shows the evaluation results. In Table 1, the "Thickness Ratio" in the column for porous substrate refers to the ratio of the thickness of the porous substrate to the thickness of the solid electrolyte sheet. Also, in Table 2, "-" in the "Discharge Load Characteristics" column means that it was not evaluated.

[0155] [Table 1]

[0156] [Table 2]

[0157] As shown in Tables 1 and 2, the cells of Examples 1 to 7, which use a solid electrolyte sheet comprising a porous substrate and a solid electrolyte, wherein the solid electrolyte is held within the voids of the porous substrate and both sides of the porous substrate are covered with the solid electrolyte, and which have an electrode body arranged so that the porous substrate is biased toward the positive electrode side, showed a low defect rate and a suppression of the number of cells exhibiting charging abnormalities when multiple units were produced, demonstrating excellent productivity.

[0158] In contrast, the cells of Comparative Example 1, which have a solid electrolyte sheet in which the porous substrate is positioned biased toward the positive electrode side but the positive electrode side of the porous substrate is not covered with the solid electrolyte; the cells of Comparative Example 2, which have a solid electrolyte sheet in which the porous substrate is positioned biased toward the negative electrode side; the cells of Comparative Example 3, which have a solid electrolyte sheet in which the porous substrate is positioned biased toward the negative electrode side and the negative electrode side of the porous substrate is not covered with the solid electrolyte; and the cells of Comparative Example 4, which have a solid electrolyte sheet in which both sides of the porous substrate are not covered with the solid electrolyte, all had a high defect rate and poor productivity.

[0159] Furthermore, the cells in Examples 1-3 and 6, in which the overall thickness of the solid electrolyte sheet and the thickness of the porous substrate were more suitable, showed very good suppression of short circuits before charging, and also exhibited good discharge load characteristics. Compared to the solid electrolyte sheets used in these cells, the cell in Example 4, in which the solid electrolyte sheet and porous substrate were slightly thinner, showed a slightly inferior effect in suppressing short circuits before charging, and the cell in Example 7, in which these were even thinner, showed an even worse effect in suppressing short circuits before charging. In addition, the cell in Example 5, which used a solid electrolyte sheet with a thicker porous substrate compared to the solid electrolyte sheets used in Examples 1-3 and 6, exhibited inferior discharge load characteristics.

[0160] Furthermore, in the cell of Example 6, the thickness of the solid electrolyte covering one side of the solid electrolyte sheet used was greater than the thickness of the solid electrolyte covering the other side. As a result, the difference between distance (A) and distance (B) was relatively large. However, these solid electrolyte sheets were prone to curling, which made them more susceptible to delamination from the electrodes in the laminate, resulting in poorer handling compared to the solid electrolyte sheets used in other examples.

[0161] The present invention can also be implemented in forms other than those described herein, without departing from its spirit. The embodiments disclosed herein are examples, and the present invention is not limited to these embodiments. The scope of the present invention shall be interpreted in accordance with the claims attached, which take precedence over the description herein, and all modifications within the scope equivalent to the claims are included in the claims. [Industrial applicability]

[0162] The all-solid-state battery of the present invention can be applied to the same uses as conventional primary and secondary batteries, but because it has a solid electrolyte instead of an organic electrolyte, it has excellent heat resistance and can be preferably used in applications that are exposed to high temperatures. [Explanation of Symbols]

[0163] 1 All-solid-state battery 10 positive electrode 11 Cathode active material 20 negative electrode 30 Solid Electrolyte Sheets 31 Porous substrate 32a, 32b solid electrolyte 100 Laminate having positive electrode, negative electrode and solid electrolyte sheet 200 Positive external terminal 300 Negative external terminal 400 Laminate film outer casing

Claims

1. A solid electrolyte sheet for forming a laminate comprising a positive electrode, a negative electrode, and a solid electrolyte sheet interposed between the positive electrode and the negative electrode, The material comprises a porous substrate and a solid electrolyte, wherein the solid electrolyte is held within the voids of the porous substrate, and both sides of the porous substrate are covered with the solid electrolyte. The porous substrate is positioned in the thickness direction of the solid electrolyte sheet, biased toward the side that is intended to face the positive electrode. A solid electrolyte sheet characterized by having a thickness of 50 μm or less, and the thickness of the porous substrate being 3 to 45 μm.

2. The solid electrolyte sheet according to claim 1, wherein the two solid electrolyte layers covering both sides of the porous substrate have different thicknesses.

3. The solid electrolyte sheet according to claim 1, wherein the thickness of the porous substrate is 30 to 85% of the thickness of the solid electrolyte sheet.

4. The solid electrolyte sheet according to claim 1, wherein the thickness is 5 to 50 μm.

5. The solid electrolyte sheet according to claim 1, wherein the porous substrate is composed of a fibrous material.

6. The solid electrolyte sheet according to claim 5, wherein the fibrous material is composed of cellulose, cellulose modified, polyolefin, polyester, polyarylate, aramid, polyamide-imide, polyimide, glass, alumina, or silica.

7. The solid electrolyte sheet according to claim 1, wherein the porous substrate is a nonwoven fabric.

8. The solid electrolyte sheet according to claim 1, comprising solid electrolyte particles as the solid electrolyte.

9. The solid electrolyte sheet according to claim 8, wherein the particles of the solid electrolyte have an average particle diameter of 0.3 to 5 μm.

10. The solid electrolyte sheet according to claim 8, wherein the solid electrolyte particles include particles of a sulfide-based solid electrolyte.

11. An all-solid-state battery having a laminate comprising a positive electrode, a negative electrode, and a solid electrolyte sheet interposed between the positive electrode and the negative electrode, The solid electrolyte sheet is the solid electrolyte sheet according to any one of claims 1 to 10. The all-solid-state battery is characterized in that the solid electrolyte sheet is arranged such that the porous substrate is biased toward the positive electrode side in the thickness direction of the solid electrolyte sheet.

12. The all-solid-state battery according to claim 11, wherein, on the negative electrode side of the solid electrolyte sheet, the distance between the surface of the porous substrate and the negative electrode active material contained in the negative electrode in the thickness direction of the laminate is 3 to 15 μm.

13. The all-solid-state battery according to claim 11, wherein, on the positive electrode side of the solid electrolyte sheet, the distance between the surface of the porous substrate and the positive electrode active material contained in the positive electrode in the thickness direction of the laminate is 1 to 15 μm.

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