Battery

Abstract

Provided is a battery having a large energy density and excellent output characteristics. A battery according to the present invention relates to goals 12, 3, 7, and 11 of the SDGs.　A battery according to the present invention is characterized by comprising a plurality of unit electrode bodies each having: a positive electrode that has a molded body of a positive-electrode mixture containing a positive electrode active material; a negative electrode having a negative electrode active material layer containing a negative electrode active material; and a separator or a solid electrolyte layer interposed between the positive electrode and the negative electrode. The battery is also characterized in that: the plurality of unit electrode bodies are laminated; the adjacent unit electrode bodies are connected in series; when the electrode area of each of the unit electrode bodies is denoted as S (cm2) and the thickness of each of the unit electrode bodies is denoted as L (cm), L / S≤0.5 and 0.02≤L≤0.20 are satisfied; the molded body of the positive electrode mixture and the negative electrode active material layer each have a porosity of 10% or less; and when the solid electrolyte layer is provided, the porosity of the solid electrolyte layer is 10% or less.

Description

Technical Field

[0001] The present invention relates to a battery having a large energy density and excellent output characteristics.

Background Art

[0002] Currently, various primary batteries and secondary batteries are used for power supply applications of various devices. By providing various batteries to society, among the 17 goals of the Sustainable Development Goals (SDGs) established by the United Nations, Goal 12 (Ensuring sustainable production and consumption patterns), Goal 3 (Ensuring healthy lives and promoting well-being for all people of all ages), Goal 7 (Ensuring access for all people to affordable, reliable and sustainable modern energy), and Goal 11 (Achieving inclusive, safe, resilient and sustainable cities and human settlements) can be contributed to.

[0003] As such primary batteries and secondary batteries, those using a wound electrode body in which a positive electrode and a negative electrode are stacked via a separator and wound in a spiral shape, and those using a laminated electrode body in which a positive electrode and a negative electrode are stacked via a solid electrolyte layer or a separator are known.

[0004] Also, by using a plurality of the above-mentioned laminated electrode bodies stacked, increasing the capacity (increasing the energy density) of the battery has also been carried out. For example, in Patent Document 1, in a laminated battery having a laminate in which a plurality of power generation elements (laminated electrode bodies) each including a positive electrode current collector layer, a positive electrode active material layer, an electrolyte layer, a negative electrode active material layer, and a negative electrode current collector layer are laminated, the ratio h / S of the length h (cm) from one end surface to the other end surface in the lamination direction of the laminate to the electrode area S (cm 2 ) in a cross section orthogonal to the lamination direction of the laminate is made larger than 1, and a laminated battery has been proposed.

[0005] Patent Document 1 states that if the electrode area S is reduced to suppress current unevenness during battery operation, sufficient energy cannot be secured. Therefore, it is possible to increase energy by creating a stacked battery in which multiple power generation elements are stacked such that the ratio h / S of the length h (i.e., the height of the stack) to the electrode area S is greater than 1. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2019-212590 (Claims, paragraph

[0046] , etc.) [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] Incidentally, in the case of batteries, it is often required that they have excellent output characteristics (load characteristics) so that sufficient capacity can be secured even when discharging at large current values. However, with the conventional technology described above, it is not easy to increase the energy density (capacity under light load) of the battery while also improving the output characteristics.

[0008] This invention has been made in view of the above circumstances, and its purpose is to provide a battery with high energy density and excellent output characteristics. [Means for solving the problem]

[0009] The battery of the present invention has a plurality of unit electrode bodies, each having a positive electrode with a molded positive electrode mixture containing a positive electrode active material, a negative electrode with a negative electrode active material layer containing a negative electrode active material, and a solid electrolyte layer or separator interposed between the positive electrode and the negative electrode, wherein the plurality of unit electrode bodies are stacked, adjacent unit electrode bodies are connected in series, and the electrode area of ​​the unit electrode bodies is S(cm²). 2The invention is characterized in that, when the thickness of the unit electrode body is L (cm), L / S ≤ 0.5 and 0.02 ≤ L ≤ 0.20, the molded body of the positive electrode mixture and the negative electrode active material layer both have a porosity of 10% or less, and if the solid electrolyte layer is present, the porosity of the solid electrolyte layer is 10% or less. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide a battery with high energy density and excellent output characteristics. [Brief explanation of the drawing]

[0011] [Figure 1] This is a schematic cross-sectional view showing an example of the battery of the present invention. [Figure 2] This is an explanatory diagram of the measurement area for the porosity of the molded body of the positive electrode mixture. [Figure 3] This is a histogram of the grayscale distribution in scanning electron microscope images to explain binarization. [Modes for carrying out the invention]

[0012] To improve the output characteristics of a battery, it is desirable to increase the surface area between the positive and negative electrodes, for example.

[0013] However, each individual electrode has a solid electrolyte layer or separator between the positive and negative electrodes. Since these do not contribute to the battery's capacity, increasing the number of individual electrodes in the battery to improve output characteristics increases the volume occupied by the separator and solid electrolyte layer within the battery, making it difficult to increase the battery's energy density (capacity).

[0014] The inventors have conducted extensive research and found that in each individual electrode body of a battery, the thickness L (cm) is within a certain range, and the electrode area S (cm) is within a certain range. 2We discovered that when the ratio L / S of the material to the thickness L is below a specific value, and the porosity of the active material-containing portion of the positive electrode and negative electrode, as well as the porosity of the solid electrolyte layer (if a solid electrolyte layer is present), is below a specific value, it is possible to increase the energy density of the battery while improving its output characteristics, thus completing the present invention.

[0015] The battery of the present invention has a plurality of unit electrode bodies, each having a positive electrode with a molded positive electrode mixture containing a positive electrode active material, a negative electrode with a negative electrode active material layer containing a negative electrode active material, and a solid electrolyte layer or separator interposed between the positive electrode and the negative electrode, wherein the plurality of unit electrode bodies are stacked, adjacent unit electrode bodies are connected in series, and the electrode area of ​​the unit electrode bodies is S(cm²). 2 ), where L (cm) is the thickness of the unit electrode body, L / S ≤ 0.5 and 0.02 ≤ L ≤ 0.20, and both the molded body of the positive electrode mixture and the negative electrode active material layer have a porosity of 10% or less, and if the solid electrolyte layer is present, the porosity of the solid electrolyte layer is 10% or less.

[0016] Figure 1 shows a schematic cross-sectional view of an example of the battery of the present invention. The battery 1 shown in Figure 1 has two unit electrode bodies (laminated electrode bodies) 2, 2 sealed inside an outer casing formed by an outer casing 3, a sealing casing 4, and an annular gasket 5 interposed between them. When using a unit electrode body 2 with a separator 23 interposed between the positive electrode 21 and the negative electrode 22, a non-aqueous electrolyte (not shown) is also contained inside the outer casing.

[0017] The sealing can 4 is fitted into the opening of the outer can 3 via a gasket 5. The open end of the outer can 3 is tightened inward, causing the gasket 5 to come into contact with the sealing can 4, thereby sealing the opening of the outer can 3 and creating a sealed structure inside the battery.

[0018] Each individual unit electrode 2 is constructed by stacking a positive electrode 21 and a negative electrode 22 via a solid electrolyte layer or separator 23. A current collector 6 is interposed between the positive electrode 21 of the upper unit electrode 2 and the negative electrode 22 of the lower unit electrode 2, thus connecting the two unit electrode 2s in series. In the battery 1 shown in Figure 2, the sealing can 4 also serves as the negative electrode terminal by making direct contact with the negative electrode 22 of the upper unit electrode 2 on its inner surface, and the outer casing 3 also serves as the positive electrode terminal by making direct contact with the positive electrode 21 of the lower unit electrode 2 on its inner surface. Depending on the application of the battery, the outer casing can also serve as the negative electrode terminal and the sealing can also serve as the positive electrode terminal.

[0019] As shown in Figure 1, a unit electrode in a battery has a positive electrode, a negative electrode, and a solid electrolyte layer or separator interposed between them, and these are stacked to form the battery. In a battery, there is a stack made up of multiple unit electrode bodies, and in this stack, adjacent unit electrode bodies are connected in series.

[0020] Furthermore, for each individual electrode body, the thickness L (cm) and electrode area S (cm) are as follows: 2 The ratio L / S with respect to the battery is preferably 0.5 or less, more preferably 0.4 or less, and even more preferably 0.3 or less, from the viewpoint of improving the output characteristics of the battery. However, if the L / S in the unit electrode body is too small, it may become difficult to manufacture the unit electrode body, for example, so it is preferable that the L / S be 0.001 or more.

[0021] Furthermore, the thickness L of each individual electrode is preferably 0.02 cm or more, and more preferably 0.05 cm or more, from the viewpoint of increasing the energy density of the battery. However, if the thickness L of the individual electrode is too large, there is a risk that the effect of improving the output characteristics of the battery will be reduced. Therefore, from the viewpoint of further improving the output characteristics of the battery, the thickness L of each individual electrode is preferably 0.20 cm or less, and more preferably 0.16 cm or less.

[0022] The electrode area S of each individual electrode body should be set within the range where L / S and L satisfy the aforementioned values. However, a larger S in the unit electrode body results in better output characteristics, so it is preferable that S be 0.01 or higher, more preferably 0.125 or higher, and even more preferably 0.25 or higher. Furthermore, if S in the unit electrode body is too large, it may become difficult to manufacture a homogeneous unit electrode body, for example, so it is preferable that S be 20 or less, more preferably 10 or less, and even more preferably 5 or less.

[0023] In this specification, the electrode area S of a unit electrode means the area of ​​the portion where the positive electrode, negative electrode, and solid electrolyte layer or separator all overlap when viewed from the stacking direction of the unit electrode. If the battery has multiple unit electrode bodies, it means the average value of the electrode areas of each unit electrode body. In this specification, the thickness L of a unit electrode means the total thickness of the positive electrode, negative electrode, and solid electrolyte layer or separator when viewed from a direction perpendicular to the stacking direction of the unit electrode bodies. If the battery has multiple unit electrode bodies, it means the thickness of the battery divided by the number of unit electrode bodies.

[0024] The present invention includes primary batteries and secondary batteries, and also includes batteries having a solid electrolyte layer interposed between a positive electrode and a negative electrode (all-solid-state batteries), and batteries having a separator interposed between a positive electrode and a negative electrode and a non-aqueous electrolyte containing a solvent (non-aqueous electrolyte solution or gel-like electrolyte) (non-aqueous electrolyte batteries other than all-solid-state batteries).

[0025] (positive electrode) The positive electrode of a battery has a molded body of a positive electrode mixture containing a positive electrode active material. Examples include a structure consisting only of a molded body of a positive electrode mixture, or a structure in which a layer made of a molded body of a positive electrode mixture (positive electrode mixture layer) is formed on a current collector.

[0026] When the battery is a primary battery, the same cathode active materials as those used in conventionally known non-aqueous electrolyte primary batteries can be used. Specifically, for example, manganese dioxide, lithium-containing manganese oxides [e.g., LiMn3O6, and composite oxides having the same crystal structure as manganese dioxide (such as β-type, γ-type, or a structure in which β-type and γ-type are mixed), and the content of Li is 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 lithium-containing composite oxides such as O4 (4 / 3 ≦ a < 7 / 3); vanadium oxides; niobium oxides; titanium oxides; sulfides such as iron disulfide; graphite fluoride; silver sulfides such as Ag2S; nickel oxides such as NiO2: and the like.

[0027] When the battery is a secondary battery, the same cathode active materials as those used in conventionally known non-aqueous electrolyte secondary batteries, that is, active materials capable of occluding and releasing Li (lithium) ions can be used. Specifically, Li 1-x M r Mn 2-r spinel-type lithium manganese composite oxides represented by 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), Li r Mn (1-s-t) Ni s M t O (2-u) F v layered compounds represented by (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), Li 1-x Co 1-r M rLithium cobalt composite oxide represented as 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, and 0≦x≦1, 0≦r≦0.5), Li 1-x Ni 1-r M r Lithium nickel composite oxide represented by 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, and 0 ≤ x ≤ 1, 0 ≤ r ≤ 0.5), Li 1+s-x M 1-r N r PO4F s (wherein 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, and 0≦x≦1, 0≦r≦0.5, 0≦s≦1) Li is an olivine-type composite oxide. 2-x M 1-r N r Examples 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.

[0028] In the case of an all-solid-state 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 output characteristics of the battery.

[0029] In this specification, the average particle diameter of various particles (such as positive electrode active material and solid electrolyte) 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.

[0030] In the case of an all-solid-state secondary 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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] From the viewpoint of increasing the energy density of the battery, the content of the positive electrode active material in the positive electrode mixture is preferably 60 to 85% by mass.

[0036] 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 does not need to be included. When a conductive additive is included in the positive electrode mixture, its content is preferably 1.0 part by mass or more, preferably 7.0 parts by mass or less, and more preferably 6.5 parts by mass or less, based on the content of 100 parts by mass of the positive electrode active material.

[0037] Furthermore, a binder can be included in the positive electrode mixture. Specific examples include fluororesins such as polyvinylidene fluoride (PVDF). However, if good moldability can be ensured in forming a molded body of the positive electrode mixture without using a binder, for example, when a sulfide-based solid electrolyte is included in the positive electrode mixture (details will be discussed later), then the positive electrode mixture does not need to contain a binder.

[0038] 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, in the positive electrode mixture, if moldability can be obtained without a binder because it contains a sulfide-based solid electrolyte, its content is preferably 0.5% by mass or less, more preferably 0.3% by mass or less, and even more preferably 0% by mass (i.e., no binder is included).

[0039] If the battery is an all-solid-state battery (all-solid-state primary battery, all-solid-state secondary battery), the positive electrode mixture must contain a solid electrolyte.

[0040] The solid electrolyte to be included in the positive electrode mixture 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.

[0041] Examples of sulfide-based solid electrolytes include particles such as Li2S-P2S5, Li2S-SiS2, Li2S-P2S5-GeS2, and Li2S-B2S3 glass, as well as thio-LISICON type electrolytes, which have recently attracted attention for their high Li ion conductivity. 10 GeP2S 12 Li 9.54 Si 1.74 P 1.44 S 11.7 Cl 0.3 such as, 12-12a-b+c+6d-e M 1 3+a-b-c-d M 2 b M 3 c M 4 d M 5 12-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 X is either S or S and O, and X is F, Cl, Br, or I, with 0 ≤ a < 3, 0 ≤ b + c + d ≤ 3, 0 ≤ e ≤ 3. Those with an argyrodite crystal structure can also be used.

[0042] Examples of the hydride-based solid electrolyte include, for example, LiBH4, a solid solution of LiBH4 and the following alkali metal compound (for example, those having a molar ratio of LiBH4 to the alkali metal compound of 1:1 to 20:1), and the like. 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.

[0043] Examples of the halide-based solid electrolyte include, for example, monoclinic LiAlCl4, defective spinel-type or layered LiInBr4, monoclinic Li 6-3m Y m X6 (where 0 < m < 2 and X = Cl or Br), and the like. In addition, for example, known ones described in International Publication No. 2020 / 070958 and International Publication No. 2020 / 070955 can also be used.

[0044] Examples of the oxide-based solid electrolyte include, for example, 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 TiO3, and the like.

[0045] Among these solid electrolytes, sulfide-based solid electrolytes are preferred because of their high lithium ion conductivity. Sulfide-based solid electrolytes containing Li and P are more preferred. Sulfide-based solid electrolytes having an argyrodite-type crystal structure are even more preferred because they have higher lithium ion conductivity and higher chemical stability.

[0046] As sulfide-based solid electrolytes having an argyrodite-type crystal structure, those represented by the following general composition formula (1) or (2), such as Li6PS5Cl, are particularly preferred.

[0047] Li 7-x+y PS 6-x Cl x+y (1)

[0048] In the general composition formula (1) above, 0.05 ≤ y ≤ 0.9 and -3.0x + 1.8 ≤ y ≤ -3.0x + 5.7.

[0049] Li 7-a PS 6-a Cl b Br c (2)

[0050] In the above general composition formula (2), a = b + c, 0 <a≦1.8、0.1≦b / c≦10.0である。

[0051] The average particle size of the solid electrolyte is preferably 0.1 μm or larger, and more preferably 0.2 μm or larger, from the viewpoint of reducing grain boundary resistance. On the other hand, from the viewpoint of forming a sufficient contact interface between the active material and the solid electrolyte, it is preferably 10 μm or smaller, and more preferably 5 μm or smaller.

[0052] From the viewpoint of further enhancing ionic conductivity within the positive electrode and improving the output characteristics of the battery, the solid electrolyte content in the positive electrode mixture is preferably 10 parts by mass or more, and more preferably 15 parts by mass or more, when the positive electrode active material content is 100 parts by mass. However, if the amount of solid electrolyte in the positive electrode mixture is too high, the amount of other components will decrease, and the effects of those components may be reduced. Therefore, the solid electrolyte content in the positive electrode mixture is preferably 65 parts by mass or less, and more preferably 60 parts by mass or less, when the positive electrode active material content is 100 parts by mass.

[0053] 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.

[0054] A molded positive electrode mixture can be formed, for example, by compressing a positive electrode mixture prepared by mixing a positive electrode active material with conductive additives, binders, solid electrolytes, etc., as needed, using pressure molding or similar methods.

[0055] In the case of a positive electrode having a current collector, it can be manufactured by bonding a molded positive electrode mixture formed by the method described above to the current collector by pressing or other means.

[0056] Alternatively, a positive electrode mixture may be prepared by mixing the positive electrode mixture with a solvent, and this mixture may be applied to a substrate such as a current collector or a solid electrolyte layer facing the positive electrode. After drying, a press treatment may be performed to form a molded body of the positive electrode mixture.

[0057] The solvent for the positive electrode mixture-containing composition can be an organic solvent such as water or N-methyl-2-pyrrolidone (NMP). When the positive electrode mixture-containing composition also contains a solid electrolyte, it is preferable to select a solvent that does not easily degrade the solid electrolyte. In particular, since sulfide-based and hydride-based solid electrolytes undergo chemical reactions with even trace amounts of water, it is preferable to use a non-polar aprotic solvent, such as hydrocarbon solvents like hexane, heptane, octane, nonane, decane, decalin, toluene, and xylene. It is even more preferable to use an ultra-dehydrated solvent with a water content of 0.001% by mass (10 ppm) or less. Furthermore, fluorine-based solvents such as "Bartrell®" from Mitsui DuPont Fluorochemicals, "Zeolora®" from Nippon Zeon Corporation, and "Novec®" from Sumitomo 3M, as well as non-aqueous organic solvents such as dichloromethane and diethyl ether, can also be used.

[0058] Furthermore, from the viewpoint of improving the output characteristics of the battery, the porosity of the molded positive electrode mixture is preferably 10% or less, and more preferably 6% or less. The lower limit of the porosity of the molded positive electrode mixture is, for example, 1%.

[0059] The porosity of the molded body of the positive electrode mixture can be calculated by observing the cross-section of the molded body with a scanning electron microscope (SEM), binarizing the image using image processing, and determining the proportion of the void portion.

[0060] The porosity of the molded body of the positive electrode mixture is measured as follows: The molded body of the positive electrode mixture is cut along the longest line and parallel to the thickness direction when viewed from the thickness direction. An SEM image of the central part of the cut surface is then obtained.

[0061] Figure 2 is a diagram illustrating the area for measuring the porosity of the molded body of the positive electrode mixture. In the example shown in Figure 2, a cross-section is shown when the positive electrode (molded body of the positive electrode mixture) 21 related to the unit electrode body is cut. The molded body of the positive electrode mixture 21 is viewed from the thickness direction (z direction in Figure 2) and cut in the thickness direction along the line in the width direction (x direction) of the longest width. In the example in Figure 2, the shape of the molded body of the positive electrode mixture 21 viewed from the thickness direction (top view shape) is circular. In this case, the molded body of the positive electrode mixture 21 is cut in the thickness direction along the line passing through the center of the circle. If the top view shape is elliptical, it is cut along the major axis of the ellipse. If the top view shape is rectangular, it is cut along the center line between the two long sides. In the example shown in Figure 2, the area enclosed by the dotted line is the central part.

[0062] The central region is a rectangular area of ​​the molded body of the positive electrode mixture that includes the center of its cross-section [the center in the thickness direction (h / 2 point) and the center in the width direction (w / 2 point)], with a length of 25 μm in the width direction and 19 μm in the thickness direction.

[0063] The SEM image of this rectangular region is binarized using image analysis software (such as ImageJ), with bright contrast (high brightness) representing material and dark contrast (low brightness) representing voids. The porosity is then calculated by determining the area ratio of the void portion.

[0064] The equipment and conditions used are, for example, a scanning electron microscope: Hitachi S4800, detector: backscattered electron-weighted mode, acceleration voltage: 2kV, magnification: 5,000x, acquisition resolution: 2,560 x 1,920, minimum dot length: 9.9nm (equivalent circle diameter: 11.2nm), minimum dot area: 98nm 2 , analysis area: 4.81×10 8 nm 2 It can be done this way.

[0065] The obtained SEM images are converted to grayscale using Photoshop®. A Gaussian filter (0.5 pixels) is used to reduce noise. Next, the histogram of the SEM images is quantified using ImageJ. Figure 3 shows an example of an SEM image histogram. In the histogram, the luminance at the maximum frequency, a, is used as the central value. On the higher luminance side than the central value, the minimum luminance value b at a frequency where the value is 3% or less of the maximum frequency is read. Furthermore, on the lower luminance side than the central value, the luminance d (=ac) at which the value is smaller than the central value by the difference between b and a, c (=ba), is found, and this luminance d is used as the threshold.

[0066] Furthermore, using the image analysis software "Eizo-kun," the SEM image is binarized using the previously determined threshold d to separate it into low-luminance and high-luminance regions. The ratio of the area of ​​the low-luminance region in the SEM image is calculated as the porosity. In this case, the area is 900 nm. 2 (0.09 × 10 -2 μm 2 Low-luminance areas below the threshold (which are smaller than the threshold) are considered noise components and are therefore excluded when determining the void ratio.

[0067] The porosity of the negative electrode active material layer and the solid electrolyte layer, as described later, can also be determined using the same method and conditions as the porosity of the molded positive electrode mixture described above. The porosity of the molded positive electrode mixture, the porosity of the negative electrode active material layer, and the porosity of the solid electrolyte layer described in the following examples are values ​​obtained using the method and conditions described herein.

[0068] From the viewpoint of increasing the density of the positive electrode mixture and reducing the porosity as described above, and further reducing the internal resistance of the positive electrode, it is more preferable that the positive electrode mixture be molded by compressing it using methods such as pressure molding.

[0069] The thickness of the molded positive electrode mixture is usually 50 μm or more, but from the viewpoint of increasing the energy density of the battery, it is preferable to have a thickness of 200 μm or more. Furthermore, the thickness of the molded positive electrode mixture is usually 1200 μm or less, but from the viewpoint of further improving the output characteristics of the battery, it is preferable to have a thickness of 800 μm or less.

[0070] In the case of a positive electrode manufactured by forming a positive electrode mixture layer on a current collector using a positive electrode mixture-containing composition that contains a solvent, the thickness of the positive electrode mixture layer is preferably 50 to 800 μm, and more preferably 500 μm or less from the viewpoint of further improving the output characteristics of the battery.

[0071] (Negative electrode) The negative electrode of a battery has a negative electrode active material layer containing a negative electrode active material, and includes, for example, a molded body of a negative electrode mixture containing a negative electrode active material; a sheet of metal that functions as a negative electrode active material, such as a lithium sheet or a sheet of lithium alloy; and so on. In a negative electrode having a molded body of a negative electrode mixture, the molded body of the negative electrode mixture corresponds to the negative electrode active material layer, and in a sheet of metal that functions as a negative electrode active material, the sheet of metal corresponds to the negative electrode active material layer.

[0072] In the negative electrode active material layer of the negative electrode, from the viewpoint of improving the output characteristics of the battery, its porosity is preferably 10% or less, and more preferably 6% or less. Furthermore, the lower limit of the porosity of the negative electrode active material layer is, for example, 1%, but if the negative electrode active material layer is a metal sheet, its porosity can be set to 0%.

[0073] In the case where the negative electrode is a molded body of a negative electrode mixture containing a negative electrode active material, examples include a molded body (such as a pellet) formed by molding the negative electrode mixture, or a structure in which a layer (negative electrode mixture layer) made of molded bodies of the negative electrode mixture is formed on a current collector.

[0074] 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.

[0075] From the viewpoint of increasing the energy density of the battery, the content of the negative electrode active material in the negative electrode mixture is preferably 40 to 80% by mass.

[0076] The negative electrode mixture may contain a conductive additive. Specific examples include the same conductive additives mentioned earlier as those that can be included in the positive electrode mixture. The content of the conductive additive in the negative electrode mixture is preferably 10 to 30 parts by mass, based on a negative electrode active material content of 100 parts by mass.

[0077] 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.

[0078] 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, in the negative electrode mixture, if moldability can be obtained without a binder because it contains a sulfide-based solid electrolyte, its content is preferably 0.5% by mass or less, more preferably 0.3% by mass or less, and even more preferably 0% by mass (i.e., no binder is included).

[0079] When the battery is an all-solid-state battery, the negative electrode having a molded negative electrode mixture contains a solid electrolyte. Specific examples include the same solid electrolytes exemplified earlier that can be included in the positive electrode mixture. Among the exemplified solid electrolytes, sulfide-based solid electrolytes are preferred because they have high lithium-ion conductivity and enhance the moldability of the negative electrode mixture. More preferably, sulfide-based solid electrolytes having an argyrodite crystal structure are used, and even more preferably, those represented by the general composition formula (1) or (2) are used.

[0080] For the same reasons as in the case of the positive electrode mixture, the average particle size of the solid electrolyte is preferably 0.1 μm or larger, more preferably 0.2 μm or larger, and more preferably 10 μm or smaller, and more preferably 5 μm or smaller.

[0081] From the viewpoint of further enhancing ionic conductivity within the negative electrode and improving the output characteristics of the battery, the solid electrolyte content in the negative electrode mixture is preferably 30 parts by mass or more, and more preferably 35 parts by mass or more, when the negative electrode active material content is 100 parts by mass. However, if the amount of solid electrolyte in the negative electrode mixture is too high, the amount of other components will decrease, and the effects of those components may be reduced. Therefore, the solid electrolyte content in the negative electrode mixture is preferably 130 parts by mass or less, and more preferably 110 parts by mass or less, when the negative electrode active material content is 100 parts by mass.

[0082] 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.

[0083] A molded negative electrode mixture can be formed, for example, by compressing a negative electrode mixture prepared by mixing a negative electrode active material, and optionally added conductive additives, a solid electrolyte, and a binder, using pressure molding or similar methods. In the case of a negative electrode consisting only of a molded negative electrode mixture, it can be manufactured by the method described above.

[0084] In the case of a negative electrode having a current collector, it can be manufactured by bonding a molded negative electrode mixture formed by the method described above to the current collector by pressing or other means.

[0085] Alternatively, a negative electrode mixture may be prepared by mixing the negative electrode mixture with a solvent, and this mixture may be applied to a substrate such as a current collector or a solid electrolyte layer facing the negative electrode. After drying, a press treatment may be performed to form a molded body of the negative electrode mixture.

[0086] While organic solvents such as water and NMP can be used as solvents for negative electrode mixture-containing compositions, when a solid electrolyte is also included in the negative electrode mixture-containing composition, it is desirable to select a solvent that does not easily degrade the solid electrolyte. Therefore, it is preferable to use the same solvents as those previously exemplified for positive electrode mixture-containing compositions containing a solid electrolyte.

[0087] From the viewpoint of increasing the density of the negative electrode mixture and reducing the porosity as described above, and further reducing the internal resistance of the negative electrode, it is more preferable that the negative electrode mixture be molded by compressing it by pressure molding or the like.

[0088] The thickness of the molded negative electrode mixture is usually 50 μm or more, but from the viewpoint of increasing the energy density of the battery, it is preferable to have a thickness of 200 μm or more. Furthermore, the thickness of the molded negative electrode mixture is usually 1200 μm or less, but from the viewpoint of further improving the output characteristics of the battery, it is preferable to have a thickness of 800 μm or less.

[0089] In the case of a negative electrode manufactured by forming a negative electrode mixture layer on a current collector using a negative electrode mixture-containing composition containing a solvent, the thickness of the negative electrode mixture layer is preferably 50 to 800 μm, and more preferably 500 μm or less from the viewpoint of further improving the output characteristics of the battery.

[0090] 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.

[0091] 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).

[0092] 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.

[0093] 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.

[0094] 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.

[0095] 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 1.0 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 1.0 mm.

[0096] Furthermore, 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.

[0097] (solid electrolyte layer) In the case of an all-solid-state battery, the solid electrolyte constituting the solid electrolyte layer interposed between the positive and negative electrodes can be specifically the same as the solid electrolyte previously exemplified as one that can be included in the positive electrode mixture. Among the solid electrolytes exemplified above, those with high lithium-ion conductivity, and GrowthBecause it has the function of improving shapeability, it is preferable to use a sulfide-based solid electrolyte, more preferable to use a sulfide-based solid electrolyte having an argyrodite-type crystal structure, and even more preferable to use one represented by the general composition formula (1) or the general composition formula (2).

[0098] The solid electrolyte layer may have a porous material, such as a resin nonwoven fabric, as a support.

[0099] Furthermore, from the viewpoint of improving the output characteristics of the battery, the porosity of the solid electrolyte layer is preferably 10% or less, and more preferably 6% or less. The lower limit of the porosity of the solid electrolyte layer is, for example, 1%.

[0100] The solid electrolyte layer can be formed by methods such as compressing the solid electrolyte by pressure molding; or by coating a solid electrolyte layer-forming composition, prepared by dispersing the solid electrolyte in a solvent, onto a substrate, positive electrode, or negative electrode, drying it, and then performing pressure molding such as a press treatment as needed. However, it is more preferable to employ the method of compressing the solid electrolyte, as this makes it possible to reduce the porosity of the solid electrolyte layer as described above.

[0101] When selecting a solvent for a composition that forms a solid electrolyte layer, it is desirable to choose one that does not easily degrade the solid electrolyte, and it is preferable to use the same solvents as those previously exemplified for a positive electrode mixture composition containing a solid electrolyte.

[0102] The thickness of the solid electrolyte layer is preferably 10 to 200 μm.

[0103] (Separator) When the battery is not an all-solid-state battery, the separator interposed between the positive and negative electrodes should be one that has sufficient strength and can hold a large amount of non-aqueous electrolyte. From this viewpoint, a microporous film or nonwoven fabric containing polyethylene, polypropylene, or ethylene-propylene copolymer with a thickness of 10 to 50 μm and an aperture ratio of 30 to 70% is preferred.

[0104] (Non-aqueous electrolytes) When the battery is not an all-solid-state battery, a non-aqueous liquid electrolyte (non-aqueous electrolyte solution) is usually used as the non-aqueous electrolyte. This non-aqueous electrolyte solution is prepared by dissolving an electrolyte salt, such as a lithium salt, in an organic solvent. The organic solvent is not particularly limited, but examples include linear esters such as dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, and methyl propyl carbonate; cyclic esters with high dielectric constants such as ethylene carbonate, propylene carbonate, butylene carbonate, and vinylene carbonate; and mixed solvents of linear and cyclic esters. Mixed solvents with linear esters as the main solvent and cyclic esters are particularly suitable.

[0105] Examples of electrolyte salts to be dissolved in organic solvents when preparing non-aqueous electrolytes include LiPF6, LiBF4, LiAsF6, LiSbF6, LiCF3SO3, LiC4F9SO3, LiCF3CO2, Li2C2F4(SO3)2, and LiC n F 2n+1 SO3 (n≧2), LiN(RfSO2)(Rf'SO2), LiC(RfSO2)3, LiN(RfOSO2)2 (where Rf and Rf' are fluoroalkyl groups), etc., can be used individually or in combination of two or more. The concentration of the electrolyte salt in the electrolyte solution is not particularly limited, but it is preferably 0.3 mol / l or higher, more preferably 0.4 mol / l or higher, preferably 1.7 mol / l or lower, and more preferably 1.5 mol / l or lower.

[0106] In addition to the aforementioned non-aqueous electrolyte, a gel-like electrolyte can also be used as the non-aqueous electrolyte for the battery, which is obtained by gelling the aforementioned non-aqueous electrolyte with a gelling agent such as a polymer.

[0107] (electrode body) The positive and negative electrodes are unit electrode bodies stacked via a solid electrolyte layer or separator, and multiple unit electrode bodies are stacked to form a laminate for use in batteries.

[0108] Furthermore, when forming a unit electrode body having a solid electrolyte layer, it is preferable to pressure-molde the positive electrode, negative electrode, and solid electrolyte layer in a stacked state, from the viewpoint of increasing the mechanical strength of the unit electrode body and reducing its internal resistance.

[0109] In a laminate formed by stacking multiple unit electrodes, adjacent unit electrodes are connected in series. There are no particular restrictions on the method of connecting the unit electrodes, but as shown in Figure 1, it is preferable to connect them by interposing a current collector between the positive electrode of one unit electrode and the negative electrode of an adjacent unit electrode.

[0110] The current collector interposed between the unit electrodes can be made of metals that do not react with Li, such as copper, nickel, and iron, or alloys containing these metals (including stainless steel), and can be in the form of foil, perforated metal, mesh, expanded metal, foamed metal, or carbon sheet. The thickness of the current collector interposed between the unit electrodes is preferably 10 to 200 μm.

[0111] The current collector and the unit electrode adjacent to it may simply be stacked on top of each other, or the current collector and the positive or negative electrode adjacent to it may be integrated by bonding or other means.

[0112] Furthermore, in a laminate formed by stacking multiple unit electrodes, the balance between the battery's energy density and output characteristics is better. Therefore, when the number of stacked unit electrodes is x, the thickness L (cm) and electrode area S (cm) of the unit electrodes are considered. 2 The relationship x × L / S is preferably 1 or less, and more preferably 0.9 or less. The lower limit of x × L / S is usually 0.002.

[0113] (Exterior) The battery's casing can be, for example, a battery container having an outer casing and a sealed casing. In other words, a battery with such a battery container as its casing is a flat-type battery.

[0114] In the battery industry, flat-shaped batteries, where the diameter is greater than the height, are called coin-type batteries or button-type batteries. However, there is no clear distinction between coin-type batteries and button-type batteries, and the battery of the present invention, when it is a flat-shaped battery, includes both coin-type and button-type batteries.

[0115] In the case of a battery container whose casing consists of an outer can and a sealing can, as shown in Figure 1, examples include a case where the outer can and the sealing can are crimped together via a gasket, as well as a case where the outer can and the sealing can are bonded together with resin.

[0116] Stainless steel can be used for the outer casing and sealing can. Polypropylene and nylon can be used as gasket materials, and if heat resistance is required due to the battery's application, fluororesins such as tetrafluoroethylene-perfluoroalkoxyethylene copolymer (PFA) and polyphenylene ether (P) can be used. P E) Heat-resistant resins with melting points exceeding 240°C, such as polysulfone (PSF), polyarylate (PAR), polyethersulfone (PES), polyphenylene sulfide (PPS), and polyetheretherketone (PEEK), can also be used. Furthermore, if the battery is used in an application requiring heat resistance, a glass hermetic seal can be used for its sealing.

[0117] The shape of the battery container, which consists of an outer casing and a sealing casing, in plan view may be circular or polygonal, such as a square or rectangle. In the case of a polygon, its corners may be curved.

[0118] Furthermore, the battery casing can also be made of a laminate film, such as an aluminum laminate film, which is a metal laminate film. [Examples]

[0119] The present invention will be described in detail below based on examples. However, the following examples are not intended to limit the present invention.

[0120] Example 1 <Formation of the solid electrolyte layer> A sulfide-based solid electrolyte (Li6PS5Cl) having an argyrodite-type crystal structure with an average particle size of 4 μm was placed into a powder molding die, and pressure molding was performed using a press machine to form a solid electrolyte layer with a thickness of 0.02 mm.

[0121] <Fabrication of the positive electrode> A positive electrode mixture was prepared by mixing a positive electrode active material: LiCoO2 powder consisting of primary particles with an average particle diameter of 5 μm, the same sulfide-based solid electrolyte used in the solid electrolyte layer, and a conductive additive, carbon nanotubes [Showa Denko Corporation's "VGCF" (product name)], in a mass ratio of 62:34:4 and kneading thoroughly. Next, 10 mg of the positive electrode mixture was placed on top of the solid electrolyte layer in the powder molding die, and pressure molding was performed using a press machine to form a positive electrode on the solid electrolyte layer, consisting of a positive electrode mixture molded body with a thickness of 0.076 mm.

[0122] <Fabrication of the negative electrode> Li4Ti5O with an average particle size of 5 μm 12 Next, the same sulfide solid electrolyte used in the solid electrolyte layer and the same carbon nanotubes used in the positive electrode mixture were mixed in a mass ratio of 50:41:9 and thoroughly kneaded to prepare the negative electrode mixture. Then, 13 mg of the negative electrode mixture was placed on the opposite side of the solid electrolyte layer from the positive electrode in the powder molding die, and pressure molding was performed using a press machine to form a negative electrode consisting of a negative electrode mixture molded body with a thickness of 0.127 mm on the solid electrolyte layer. In this way, two unit electrode bodies with a diameter of 7.45 mm and a thickness L of 0.022 cm were produced, in which the positive electrode, solid electrolyte layer, and negative electrode were laminated. The L / S ratio of the obtained unit electrode bodies was 0.051.

[0123] <Battery assembly> Flexible graphite sheet "PERMA-FOIL" (product name) manufactured by Toyo Tanso Co., Ltd. (thickness: 0.1 mm, apparent density: 1.1 g / cm³)3 Three pieces were prepared, each punched out to the same size as the unit electrode, and one of them was placed on the inner bottom surface of a stainless steel sealed can fitted with a polypropylene annular gasket. Next, one of the unit electrodes was placed on top of the graphite sheet with the negative electrode facing the graphite sheet, and a second graphite sheet was placed on top of that as a current collector. Furthermore, another unit electrode was placed on top with the negative electrode facing the graphite sheet, and finally A solid-state secondary battery with the structure shown in Figure 1, having two unit electrodes connected in series via a graphite sheet (current collector), was fabricated by placing the remaining graphite sheet on the positive electrode of the unit electrode body, covering it with a stainless steel outer casing, and then crimping the open end of the outer casing inward to seal it. Note that Figure 1 does not show the sealing casing or the graphite sheet placed between the outer casing and the laminated electrode body.

[0124] Example 2 Except for changing the amounts used to 25 mg of positive electrode compound and 33 mg of negative electrode compound, two unit electrode bodies with L = 0.053 cm and L / S = 0.121 were prepared in the same manner as in Example 1, and an all-solid-state secondary battery was prepared in the same manner as in Example 1, except that these unit electrode bodies were used.

[0125] Example 3 Except for changing the amounts used to 35 mg of positive electrode compound and 46 mg of negative electrode compound, two unit electrode bodies with L = 0.073 cm and L / S = 0.167 were prepared in the same manner as in Example 1, and an all-solid-state secondary battery was prepared in the same manner as in Example 1, except that these unit electrode bodies were used.

[0126] Example 4 Except for changing the amounts used to 52 mg of positive electrode compound and 69 mg of negative electrode compound, two unit electrode bodies with L = 0.107 cm and L / S = 0.246 were prepared in the same manner as in Example 1, and an all-solid-state secondary battery was prepared in the same manner as in Example 1, except that these unit electrode bodies were used.

[0127] Example 5 Except for changing the amounts used to 76 mg of positive electrode compound and 100 mg of negative electrode compound, two unit electrode bodies with L = 0.156 cm and L / S = 0.358 were prepared in the same manner as in Example 1, and an all-solid-state secondary battery was prepared in the same manner as in Example 1, except that these unit electrode bodies were used.

[0128] Example 6 Except for changing the amounts used to 300 mg of positive electrode compound and 396 mg of negative electrode compound, two unit electrode bodies with a diameter of 16 mm, a length of 0.134 cm, and an L / S ratio of 0.067 were prepared in the same manner as in Example 1, and an all-solid-state secondary battery was prepared in the same manner as in Example 1, except that these unit electrode bodies were used.

[0129] Example 7 Except for changing the amounts used to 41 mg of positive electrode compound and 54 mg of negative electrode compound, three unit electrode bodies with a diameter of 6.7 mm, a length of 0.105 cm, and an L / S ratio of 0.297 were prepared in the same manner as in Example 1.

[0130] Four graphite sheets, the same as those used in Example 1, were punched out to the same size as the unit electrodes. One of these sheets was placed on the inner bottom surface of a stainless steel sealed can fitted with a polypropylene annular gasket. Next, one of the unit electrodes was placed on top of the graphite sheet with the negative electrode facing the graphite sheet, and a second graphite sheet was placed on top of that as a current collector. Furthermore, the second unit electrode was placed on top with the negative electrode facing the second graphite sheet, and a third graphite sheet was placed on top of that as a current collector. Subsequently, the third unit electrode was placed on top with the negative electrode facing the third graphite sheet, and then a fourth graphite sheet was placed on the positive electrode of the third unit electrode. After covering it with a stainless steel outer can, the open end of the outer can was crimped inward to seal it, thereby creating an all-solid-state secondary battery with a laminate having three unit electrodes connected in series via graphite sheets (current collectors).

[0131] Example 8 Positive electrode active material consisting of primary particles with an average particle size of 5 μm: LiCoO2 powder, and Example 1 The same sulfide-based solid electrolyte used in the solid electrolyte layer, carbon nanotubes (Showa Denko Corporation's "VGCF" product name) as a conductive additive, and PVDF as a binder were mixed in a mass ratio of 61.5:34:4:0.5 and thoroughly kneaded to prepare the positive electrode mixture.

[0132] Li4Ti5O with an average particle size of 5 μm 12 The same sulfide solid electrolyte used in the positive electrode mixture, the same carbon nanotubes used in the positive electrode mixture, and the binder PVdF were mixed in a mass ratio of 49.5:41:9:0.5 and thoroughly kneaded to prepare the negative electrode mixture.

[0133] Then, using these positive electrode and negative electrode mixtures, two unit electrode bodies with L = 0.156 cm and L / S = 0.358 were prepared in the same manner as in Example 1, except that the amounts used were changed to 76 mg for the positive electrode mixture and 100 mg for the negative electrode mixture. An all-solid-state secondary battery was then prepared in the same manner as in Example 1, except that these unit electrode bodies were used.

[0134] Comparative Example 1 Except for changing the amounts used to 1 mg of positive electrode compound and 1.3 mg of negative electrode compound, two unit electrode bodies with L = 0.004 cm and L / S = 0.009 were prepared in the same manner as in Example 1, and an all-solid-state secondary battery was prepared in the same manner as in Example 1, except that these unit electrode bodies were used.

[0135] Comparative Example 2 Except for changing the amounts used to 50 mg of positive electrode compound and 66 mg of negative electrode compound, two unit electrode bodies with a diameter of 5.7 mm, a length of 0.175 cm, and an L / S ratio of 0.686 were prepared in the same manner as in Example 1, and an all-solid-state secondary battery was prepared in the same manner as in Example 1, except that these unit electrode bodies were used.

[0136] Comparative Example 3 Except for changing the amounts used to 109 mg of positive electrode compound and 144 mg of negative electrode compound, two unit electrode bodies with L = 0.223 cm and L / S = 0.511 were prepared in the same manner as in Example 1, and an all-solid-state secondary battery was prepared in the same manner as in Example 1, except that these unit electrode bodies were used.

[0137] Comparative Example 4 Except for changing the amounts used to 76 mg of positive electrode compound and 100 mg of negative electrode compound, and adjusting the pressure to adjust the thickness of the positive electrode compound molded body and the negative electrode compound molded body, two unit electrode bodies with L = 0.169 cm and L / S = 0.387 were prepared in the same manner as in Example 1, and an all-solid-state secondary battery was prepared in the same manner as in Example 1, except that these unit electrode bodies were used.

[0138] The following evaluations were performed on the all-solid-state secondary batteries in the examples and comparative examples.

[0139] <Output Characteristics Evaluation> The C-rate at 80% capacity was determined using the following method, and the output characteristics of each battery were evaluated accordingly. For each battery, charging was performed using a combination of constant current charging, where the battery voltage was 5.2V (7.8V only in Example 7) at a current of 0.02C, and constant voltage charging, where the current value was reduced to 0.002C at a voltage of 5.2V (7.8V only in Example 7). Subsequently, constant current discharge was performed, where the battery voltage was 2.0V (3.0V only in Example 7) at a current of 0.02C, and the 0.02C discharge capacity of each battery was measured.

[0140] For each battery after measuring its 0.02C discharge capacity, constant current-constant voltage charging was performed under the same conditions as during the 0.02C discharge capacity measurement. A series of operations were then performed, in which a constant current discharge was carried out at an arbitrary current value until the battery voltage reached 2.0V (3.0V only in Example 7), while varying the current value during constant current discharge. The maximum current value that yielded 80% of the 0.02C discharge capacity was determined, and this value was set to 0.02 The C-rate at 80% capacity was calculated by dividing by the C-discharge capacity. A battery with a higher C-rate at 80% capacity is considered to have superior output characteristics.

[0141] <Energy Density> For each battery, assuming an operating voltage of 4.6V (6.9V only for Example 7) when determining the 0.02C discharge capacity in the output characteristic evaluation, the energy density of each battery was determined by dividing the value obtained by multiplying the 0.02C discharge capacity by the operating voltage (Wh) by the battery volume (L).

[0142] The configuration of the unit electrode for each battery in the examples and comparative examples is shown in Tables 1 and 2, and the evaluation results are shown in Table 3.

[0143] [Table 1]

[0144] [Table 2]

[0145] [Table 3]

[0146] As shown in Tables 1 to 3, the all-solid-state secondary batteries of Examples 1 to 8, which have multiple unit electrodes connected in series with adjacent unit electrodes, have suitable L / S and L values, and have suitable porosity of the molded positive electrode mixture, molded negative electrode mixture, and solid electrolyte layer, exhibited a high C rate at 80% capacity, excellent output characteristics, and high energy density.

[0147] In contrast, the battery of Comparative Example 1, which used a unit electrode body that was too thin, had a low energy density. Furthermore, the battery of Comparative Example 2, which used a unit electrode body with an excessively large L / S ratio, the battery of Comparative Example 3, which used a unit electrode body with excessively large L / S and L ratios, and the battery of Comparative Example 4, which used a unit electrode body with excessively large porosity in the molded positive electrode mixture, the molded negative electrode mixture, and the solid electrolyte layer, all had a low C-rate at 80% capacity and poor output characteristics.

[0148] 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]

[0149] The battery of the present invention can be applied to the same uses as conventionally known primary and secondary batteries. [Explanation of Symbols]

[0150] 1 battery 2 Unit electrode body 21 Positive electrode 22 Negative electrode 23. Solid electrolyte layer or separator 3. Outer can 4 Sealed cans 5 Gasket

Claims

1. A battery comprising a plurality of unit electrode bodies, each having a positive electrode having a molded body of a positive electrode mixture containing a positive electrode active material, a negative electrode having a negative electrode active material layer containing a negative electrode active material, and a solid electrolyte layer interposed between the positive electrode and the negative electrode, wherein the plurality of unit electrode bodies are stacked together, The adjacent unit electrode bodies are connected in series, The electrode area of ​​the unit electrode body is S (cm²) ２ ) and when the thickness of the unit electrode body is L (cm), then 0.121 ≤ L / S ≤ 0.5 and 0.02 ≤ L ≤ 0.20, A battery characterized in that the molded body of the positive electrode mixture and the negative electrode active material layer both have a porosity of 10% or less, and the solid electrolyte layer has a porosity of 10% or less.

2. The battery according to claim 1, wherein x × L / S ≤ 1, where x is the total number of unit electrodes.

3. The battery according to claim 1, wherein L / S ≤ 0.

3.

4. The battery according to claim 1, wherein 0.05 ≤ L ≤ 0.

20.

5. The battery according to claim 1, wherein S is 20 or less.

6. The battery according to claim 1, wherein the content of the positive electrode active material in the positive electrode mixture is 60 to 85% by mass.

7. The battery according to claim 6, wherein the positive electrode mixture further comprises a solid electrolyte and a conductive additive, and when the content of the positive electrode active material in the positive electrode mixture is 100 parts by mass, the content of the solid electrolyte is 10 to 65 parts by mass and the content of the conductive additive is 1.0 to 6.5 parts by mass.

8. The positive electrode mixture contains a sulfide-based solid electrolyte as the solid electrolyte, according to claim 7. The battery.

9. The battery according to claim 1, wherein the positive electrode mixture does not contain a binder, or contains a binder, and the binder content is 0.5% by mass or less.

10. The battery according to claim 1, wherein the negative electrode has a molded body of a negative electrode mixture containing a negative electrode active material as the negative electrode active material layer, and the content of the negative electrode active material in the negative electrode mixture is 40 to 80% by mass.

11. The battery according to claim 10, wherein the negative electrode mixture further contains a solid electrolyte, and when the content of the negative electrode active material in the negative electrode mixture is 100 parts by mass, the content of the solid electrolyte is 30 to 130 parts by mass.

12. The battery according to claim 11, wherein the negative electrode mixture contains a sulfide-based solid electrolyte as the solid electrolyte.

13. The battery according to claim 10, wherein the negative electrode mixture does not contain a binder, or contains a binder, and the binder content is 0.5% by mass or less.

14. The battery according to claim 1, wherein the solid electrolyte layer contains a sulfide-based solid electrolyte.

15. The battery according to claim 8, 12, or 14, wherein the sulfide-based solid electrolyte contains a sulfide-based solid electrolyte having an argyrodite-type crystal structure represented by the following general composition formula (1) or (2). Li ７－ｘ＋ｙ PS ６－ｘ Cl ｘ＋ｙ (1) [In the above general compositional formula (1), 0.05 ≤ y ≤ 0.9 and -3.0x + 1.8 ≤ y ≤ -3.0x + 5.7] Li ７－ａ PS ６－ａ Cl ｂ Br ｃ (2) [In the above general compositional formula (2), a = b + c, 0 < a ≤ 1.8, and 0.1 ≤ b / c ≤ 10.0]

16. The battery according to claim 1, wherein the thickness of the solid electrolyte layer is 10 to 200 μm.

17. The battery according to claim 1, wherein a current collector is placed between adjacent unit electrode bodies, and the adjacent unit electrode bodies are connected in series by the current collector.

Images