Positive electrode and solid battery

Abstract

Provided is a positive electrode for use in a solid battery having further excellent performance. This positive electrode comprises a positive electrode current collector and a positive electrode active material layer provided on the positive electrode current collector. The positive electrode active material layer has: a first positive electrode active material region that is provided on the positive electrode current collector, and that includes a plurality of first positive electrode active material particles to which a solid electrolyte has adhered; and a second positive electrode active material region that is provided on a side opposite to the positive electrode current collector as seen from the first positive electrode active material region, and that includes a plurality of second positive electrode active material particles to which the solid electrolyte has adhered. The volume ratio between the plurality of first positive electrode active material particles and the solid electrolyte in the first positive electrode active material region is within a range of 6:4 to 8:2. The median size of the plurality of second positive electrode active material particles is larger than the median size of the plurality of first positive electrode active material particles.

Description

cathodes and solid-state batteries

[0001] The present technology relates to a positive electrode having a solid electrolyte and a solid-state battery including the positive electrode.

[0002] Due to the widespread use of various electronic devices such as mobile phones, secondary batteries have been developed as small, lightweight power sources that can provide high energy density. These secondary batteries include a positive electrode, a negative electrode, and an electrolyte housed inside an exterior member.

[0003] In recent years, solid-state batteries, which are secondary batteries equipped with solid electrolytes instead of liquid or gel electrolytes containing organic solvents or the like, have been developed (see, for example, Patent Documents 1 and 2).

[0004] JP 2017-157529 A JP 2014-238925 A

[0005] As described in the above-mentioned prior art documents, various studies have been conducted to improve the performance of solid-state batteries, but there is still room for improvement in the performance of solid-state batteries.

[0006] The present technology has been made in view of such problems, and its purpose is to provide a solid-state battery having superior performance and a positive electrode to be used therein.

[0007] A positive electrode according to one embodiment of the present disclosure includes a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector. The positive electrode active material layer includes a first positive electrode active material region disposed on the positive electrode current collector and including a plurality of first positive electrode active material particles having a solid electrolyte (SE) attached thereto, and a second positive electrode active material region disposed on the opposite side of the positive electrode current collector from the first positive electrode active material region and including a plurality of second positive electrode active material particles having a solid electrolyte attached thereto. The volume ratio of the first positive electrode active material particles to the solid electrolyte in the first positive electrode active material region is in the range of 6:4 to 8:2. The median diameter of the second positive electrode active material particles is larger than the median diameter of the first positive electrode active material particles.

[0008] In a solid-state battery using a positive electrode according to an embodiment of the present disclosure, the volume ratio of the first positive electrode active material particles to the solid electrolyte in the first positive electrode active material region, which is relatively closer to the positive electrode current collector than the second positive electrode active material region, is in the range of 6:4 to 8:2. Furthermore, the median diameter of the first positive electrode active material particles is smaller than the median diameter of the second positive electrode active material particles. This results in a greater amount of solid electrolyte surrounding the first positive electrode active material particles. This allows for the formation of good ion conduction paths, resulting in improved rate characteristics without sacrificing energy density and other superior performance.

[0009] Note that the effects of the present disclosure are not necessarily limited to the effects described here, but may be any of a series of effects related to the present disclosure described below.

[0010] Fig. 1 is a schematic cross-sectional view showing an example of a configuration of a solid-state battery according to an embodiment of the present disclosure. Fig. 2 is a schematic cross-sectional view showing an example of a configuration of a positive electrode applied to the solid-state battery shown in Fig. 1.

[0011] An embodiment of the present disclosure will be described in detail below with reference to the drawings. The description will be given in the following order: 0. Overview of the Present Technology 1. One Embodiment 1.1 Configuration of a Solid-State Battery 1.2 Manufacturing Method of a Solid-State Battery 1.3 Actions and Effects of a Solid-State Battery 2. Examples The "solid-state battery" of the present disclosure refers to a battery whose components are solid. For example, the "solid-state battery" of the present disclosure is a stacked solid-state battery formed by stacking multiple layers. The multiple layers are made of, for example, a sintered body. The "solid-state battery" of the present disclosure includes not only secondary batteries that can be repeatedly charged and discharged, but also primary batteries that can only be discharged.

[0012] [0. Outline of the Present Disclosure] First, an outline of the present disclosure will be described. Various studies have been conducted to date on improving the performance of solid-state batteries. Because solid-state batteries include a solid electrolyte, they generally have superior high-temperature resistance and higher safety compared to batteries that use a liquid electrolyte.

[0013] The aforementioned Patent Document 1 proposes a cathode active material layer in which a first active material layer and a second active material layer having different porosities are stacked in this order from the current collector side. Specifically, the porosity of the first active material layer is set to 0% or more but less than 10%, and the porosity of the second active material layer is set to 10% or more but less than 60%, aiming to facilitate impregnation of the cathode active material layer with a solid electrolyte precursor solution during manufacturing. However, in an electrode having such a cathode active material layer, the porosity of the second active material layer is set to 10% or more but less than 60%, which reduces the energy density and raises concerns about a decrease in battery capacity. Furthermore, because the average particle size of the particulate cathode active material constituting the first active material layer is set to 100 nm or more but less than 5 μm, when a coating of an ion-conductive material is formed on the surface of the particulate cathode active material, the volume occupancy of the cathode active material is relatively reduced, which may result in a decrease in battery capacity.

[0014] In addition, in the above-mentioned Patent Document 2, for example, as shown in Figure 1, the volume ratio of the positive electrode active material to the solid electrolyte material in the second positive electrode active material layer 12b on the solid electrolyte layer 40 side is set to be smaller than the volume ratio of the positive electrode active material to the solid electrolyte material in the first positive electrode active material layer 12a on the positive electrode current collector 11 side. This is intended to improve rate characteristics by increasing the amount of solid electrolyte material on the solid electrolyte layer side to form thicker Li ion conduction paths. However, in the invention of Patent Document 2, since the amount of positive electrode active material in the second positive electrode active material layer 12b is reduced, it seems that a decrease in battery capacity is unavoidable.

[0015] In view of the above circumstances, the present applicant proposes a positive electrode that can achieve higher ion conductivity while suppressing a decrease in battery capacity, and a solid-state battery using the same.

[0016] 1. One Embodiment 1.1 Configuration of Solid-State Battery A configuration of a solid-state battery 100 according to one embodiment of the present disclosure will be described with reference to FIGS. 1 and 2 . FIG. 1 is a schematic cross-sectional view illustrating the configuration of the solid-state battery 100. The solid-state battery 100 has a laminated structure in which a positive electrode 10, a solid electrolyte layer 20, and a negative electrode 30 are laminated in this order. The negative electrode 30 has a negative electrode current collector 31 and a negative electrode active material layer 32. The solid-state battery 100 may have a structure in which a plurality of units are repeatedly laminated, each unit being formed by laminating the positive electrode 10, the solid electrolyte layer 20, the negative electrode 30, and the solid electrolyte layer 20 in this order.

[0017] 2 is a schematic cross-sectional view showing an enlarged view of a portion of the positive electrode 10 and the solid electrolyte layer 20 of the solid battery 100. The positive electrode 10 is an electrode layer containing at least a positive electrode active material. The positive electrode 10 has a positive electrode current collector 11 and a positive electrode active material layer 12.

[0018] The positive electrode current collector 11 is, for example, a metal foil. Examples of materials for the positive electrode current collector 11 include a metal (single metal) selected from the group consisting of Al (aluminum), Cu (copper), Mg (magnesium), Ti (titanium), Fe (iron), Co (cobalt), Ni (nickel), Zn (zinc), Ge (germanium), In (indium), Au (gold), Pt (platinum), Ag (silver), and Pd (palladium), or an alloy containing two or more metal elements selected from the above group. The positive electrode current collector 11 may also be a sintered body. This is to enable the solid-state battery 100 to be formed by co-firing or to reduce the internal resistance of the positive electrode current collector 11. When the positive electrode current collector 11 is a sintered body, the positive electrode current collector 11 may contain a conductive additive and a sintering additive. The conductive additive contained in the positive electrode current collector 11 may be the same type as the conductive additive contained in the positive electrode active material layer 12, for example. The sintering aid contained in the positive electrode current collector 11 may be the same type as the sintering aid contained in the positive electrode active material layer 12, for example.

[0019] The positive electrode current collector 11 may have, for example, a plate, foil, or mesh shape. The surface of the positive electrode current collector 11 may be smooth or may have an irregular surface.

[0020] (Positive Electrode Active Material Layer 12) The positive electrode active material layer 12 contains a positive electrode active material as a main component. The positive electrode active material contained in the positive electrode active material layer 12 is a material that participates in the occlusion and release of ions in the solid-state battery 100 and in the transfer of electrons to and from an external circuit. Ions move between the positive electrode 10 and the negative electrode 30 via the solid electrolyte (i.e., ion conduction). The occlusion and release of ions into the positive electrode active material is accompanied by the oxidation or reduction of the positive electrode active material. Electrons or holes for such an oxidation-reduction reaction are transferred to the positive electrode 10 or the negative electrode 30, thereby allowing charge and discharge to proceed. The positive electrode active material layer 12 contains, for example, lithium ions, sodium ions, protons (H ＋ ), potassium ions (K ＋ ), magnesium ions (Mg ２＋ ), aluminum ions (Al ３＋ ), silver ions (Ag ＋ ), fluoride ion (F － ) or chloride ions (Cl － In other words, the solid-state battery 100 is an all-solid-state secondary battery in which charging and discharging are performed by the ions moving between the positive electrode 10 and the negative electrode 30 via the solid electrolyte.

[0021] (Positive electrode active material) The positive electrode active material contained in the positive electrode 10 may be, for example, at least one selected from the group consisting of a lithium-containing phosphate compound having a Nasicon structure, a lithium-containing phosphate compound having an olivine structure, a lithium-containing layered oxide, and a lithium-containing oxide having a spinel structure. An example of a lithium-containing phosphate compound having a Nasicon structure is Li ３ V ２ (P.O. ４ ) ３ Examples of lithium-containing phosphate compounds having an olivine structure include Li ３ Fe ２ (P.O. ４ ) ３ , LiFePO ４ , LiMnPO ４ , LiFe ０．６ Mn ０．４ P.O. ４An example of a lithium-containing layered oxide is LiCoO ２ , LiCo １／３ Ni １／３ Mn １／３ O ２ , LiCo ０．８ Ni ０．１５ Al ０．０５ O ２ An example of a lithium-containing oxide having a spinel structure is LiMn ２ O ４ , LiNi ０．５ Mn １．５ O ４ etc.

[0022] In addition, the positive electrode active material capable of absorbing and releasing sodium ions may be at least one selected from the group consisting of sodium-containing phosphate compounds having a Nasicon structure, sodium-containing phosphate compounds having an olivine structure, sodium-containing layered oxides, and sodium-containing oxides having a spinel structure.

[0023] As shown in FIG. 2, the positive electrode active material layer 12 has a laminated structure in which a first positive electrode active material region L1 and a second positive electrode active material region L2 are laminated in this order on the positive electrode current collector 11.

[0024] The first positive electrode active material region L1 is provided on the positive electrode current collector 11 and is a porous molded body including a plurality of first positive electrode active material particles 1 to which a solid electrolyte SE is attached. The first positive electrode active material particles 1 are particles including the above-described positive electrode active material. The solid electrolyte SE is present around the plurality of first positive electrode active material particles 1. The solid electrolyte SE is also present in the gaps between the plurality of first positive electrode active material particles 1. However, the solid electrolyte SE in the first positive electrode active material region L1 has a plurality of voids. The solid electrolyte SE will be described in detail later. In addition, it is preferable that the volume ratio of the plurality of first positive electrode active material particles 1 to the solid electrolyte SE in the first positive electrode active material region L1 be within a range of 6:4 or more and 8:2 or less.

[0025] The second positive electrode active material region L2 is provided on the opposite side of the positive electrode current collector 11 from the first positive electrode active material region L1. The second positive electrode active material region L2 is a porous molded body including a plurality of second positive electrode active material particles 2 to which a solid electrolyte SE is attached. The second positive electrode active material particles 2 are particles including the above-mentioned positive electrode active material. The positive electrode active material constituting the second positive electrode active material particles 2 may be the same as or different from the positive electrode active material constituting the first positive electrode active material particles 1. The solid electrolyte SE is present around the plurality of second positive electrode active material particles 2. The solid electrolyte SE is also present in the gaps between the plurality of second positive electrode active material particles 2. However, a plurality of voids also exist in the solid electrolyte SE in the second positive electrode active material region L2. Furthermore, the volume ratio of the plurality of second positive electrode active material particles 2 to the solid electrolyte SE in the second positive electrode active material region L2 may be within a range of 6:4 to 8:2.

[0026] The cathode active material layer 12 of the present embodiment is not limited to an embodiment in which the boundary between the first cathode active material region L1 and the second cathode active material region L2 is clear in the cross section of the stack, and may have an embodiment in which the boundary between the first cathode active material region L1 and the second cathode active material region L2 is unclear in the cross section of the stack. Furthermore, the thickness of the first cathode active material region L1 and the thickness of the second cathode active material region L2 may be substantially the same as or different from each other.

[0027] The volume ratio of the plurality of first positive electrode active material particles 1 to the solid electrolyte SE in the first positive electrode active material region L1 can be calculated, for example, from an image of an arbitrary cross section of the first positive electrode active material region L1 along the stacking direction, by calculating the sum of the cross-sectional areas of the plurality of first positive electrode active material particles 1 present in a unit region (for example, region R1 surrounded by a dashed line in Figure 2) and the sum of the cross-sectional area of ​​the solid electrolyte SE present in the unit region (region R1).

[0028] The volume ratio of the plurality of second positive electrode active material particles 2 to the solid electrolyte SE in the second positive electrode active material region L2 can be calculated, for example, from an image of an arbitrary cross section of the second positive electrode active material region L2 along the stacking direction, by calculating the sum of the cross-sectional areas of the plurality of second positive electrode active material particles 2 present in a unit region (for example, region R2 surrounded by a dashed line in Figure 2) and the sum of the cross-sectional area of ​​the solid electrolyte SE present in the unit region (region R2).

[0029] The filling rate F of the positive electrode active material layer 12 can be, for example, 85% or more. The filling rate F here refers to the volume occupancy of the first positive electrode active material particles 1, the second positive electrode active material particles 2, and the solid electrolyte SE present in the positive electrode active material layer 12, and is the volume ratio of the portion other than the voids in the positive electrode active material layer 12. The filling rate F can be calculated, for example, by acquiring an image of an arbitrary cross section of the positive electrode active material layer 12 using a scanning electron microscope (SEM) and using image processing software. Specifically, for example, public domain image processing software, ImageJ, is used to calculate the total area of ​​an arbitrary cross section image (SEM image) of the positive electrode active material layer 12 using "Set Measurement." Next, the contrast portion corresponding to the voids is determined using "Threshold." The "area of ​​the contrast portion corresponding to the voids" is calculated using "Limit to Threshold" in "Set Measurement." The filling rate F is calculated as {(total area of ​​SEM image) - (area of ​​contrast portion corresponding to void)} / (total area of ​​SEM image) x 100 (%).

[0030] In the positive electrode active material layer 12 of the present embodiment, the median diameter of the plurality of second positive electrode active material particles 2 is larger than the median diameter of the plurality of first positive electrode active material particles 1. The median diameter of the plurality of first positive electrode active material particles 1 is, for example, greater than 1 μm and less than 20 μm. The median diameter of the plurality of second positive electrode active material particles is, for example, greater than 1 μm and less than 20 μm.

[0031] A coating containing an ion-conductive material may be present on at least a portion of the interface between the first positive electrode active material particle 1 and the solid electrolyte SE and at least a portion of the interface between the second positive electrode active material particle 2 and the solid electrolyte SE. The thickness of the coating is, for example, 1 nm or more and 100 nm or less. The ion-conductive material here is, for example, a compound represented by LiXY. Here, X is at least one element selected from B (boron), Al (aluminum), Si (silicon), P (phosphorus), Ti (titanium), Ge (germanium), Zr (zirconium), Nb (niobium), In (indium), Sn (tin), Hf (hafnium), Ta (tantalum), and W (tungsten), and Y is at least one element selected from O (oxygen), S (sulfur), F (fluorine), Cl (chlorine), Br (bromine), and I (iodine). The ion-conductive material constituting the coating is, for example, LiNbO ３ is

[0032] (Solid electrolyte layer 20 and solid electrolyte SE) The solid electrolyte layer 20 includes a solid electrolyte SE. The solid electrolyte SE is present not only in the solid electrolyte layer 20 but also in each of the first positive electrode active material region L1 and the second positive electrode active material region L2 in the positive electrode active material layer 12. Furthermore, a portion of the solid electrolyte SE is in contact with the positive electrode current collector 11 near the interface between the first positive electrode active material region L1 and the positive electrode current collector 11.

[0033] The solid electrolyte SE is a material capable of conducting ions such as lithium ions or sodium ions. In particular, the solid electrolyte constituting the battery constituent unit in a solid-state battery constitutes a solid electrolyte layer 20 capable of conducting, for example, lithium ions between the positive electrode 10 and the negative electrode 30. Specific examples of the solid electrolyte include lithium-containing phosphate compounds having a Nasicon structure, oxides having a perovskite structure, and oxides having a garnet or garnet-like structure. Examples of lithium-containing phosphate compounds having a Nasicon structure include LixMy(PO ４ ) ３ (1≦x≦2, 1≦y≦2, M is at least one selected from the group consisting of Ti, Ge, Al, Ga and Zr). An example of a lithium-containing phosphate compound having a Nasicon structure is Li１．２ Al ０．２ Ti １．８ (P.O. ４ ) ３ Examples of oxides having a perovskite structure include La ０．５５ Li ０．３５ TiO ３ Examples of oxides having a garnet-type or garnet-like structure include Li ７ La ３ Zr ２ O １２ Examples of the solid electrolyte capable of conducting sodium ions include sodium-containing phosphate compounds having a Nasicon structure, oxides having a perovskite structure, and oxides having a garnet or garnet-like structure. Examples of the sodium-containing phosphate compounds having a Nasicon structure include NaxMy(PO ４ ) ３ (1≦x≦2, 1≦y≦2, M is at least one selected from the group consisting of Ti, Ge, Al, Ga and Zr).

[0034] The solid electrolyte layer 20 may contain a sintering aid. The sintering aid that can be contained in the solid electrolyte layer 20 may be selected from, for example, the same materials as the sintering aids that can be contained in the positive electrode 10 and the negative electrode 30.

[0035] (Negative electrode 30) The negative electrode 30 is an electrode layer containing at least a negative electrode active material. The negative electrode 30 has a negative electrode current collector 31 and a negative electrode active material layer 32. The negative electrode current collector 31 is, for example, a metal foil such as copper foil. The negative electrode current collector 31 may also be a sintered body. This is to enable the solid state battery 100 to be formed by integral firing or to reduce the internal resistance of the negative electrode current collector. When the negative electrode current collector is a sintered body, the negative electrode current collector may contain a conductive additive and a sintering additive.

[0036] (Negative Electrode Active Material) The negative electrode active material contained in the negative electrode 30, like the positive electrode active material contained in the positive electrode 10, is a material that participates in the occlusion and release of ions in the solid state battery 100 and in the transfer of electrons to and from an external circuit. Ions move between the positive electrode 10 and the negative electrode 30 via the solid electrolyte layer 20 (i.e., ion conduction). The occlusion and release of ions in the negative electrode active material is accompanied by the oxidation or reduction of the negative electrode active material. Electrons or holes for such an oxidation-reduction reaction are transferred to and from the positive electrode 10 or the negative electrode 30, thereby allowing charge and discharge to proceed. The negative electrode active material may be, for example, lithium ions, sodium ions, protons (H ＋ ), potassium ions (K ＋ ), magnesium ions (Mg ２＋ ), aluminum ions (Al ３＋ ), silver ions (Ag ＋ ), fluoride ion (F － ) or chloride ions (Cl － ) can be absorbed and released. Examples of the negative electrode active material contained in the negative electrode 30 include at least one selected from the group consisting of an oxide containing at least one element selected from the group consisting of Ti, Si, Sn, Cr, Fe, Nb, and Mo, a graphite-lithium compound, a lithium alloy, a lithium-containing phosphate compound having a Nasicon structure, a lithium-containing phosphate compound having an olivine structure, and a lithium-containing oxide having a spinel structure. An example of a lithium alloy is Li-Al. An example of a lithium-containing phosphate compound having a Nasicon structure is Li. ３ V ２ (P.O. ４ ) ３ , LiTi ２ (P.O. ４ ) ３ Examples of lithium-containing phosphate compounds having an olivine structure include Li ３ Fe ２ (P.O. ４ ) ３ , LiCuPO ４ Examples of lithium-containing oxides having a spinel structure include Li ４ Ti ５ O１２ etc.

[0037] In addition, examples of negative electrode active materials capable of absorbing and releasing sodium ions include at least one selected from the group consisting of sodium-containing phosphate compounds having a Nasicon structure, sodium-containing phosphate compounds having an olivine structure, and sodium-containing oxides having a spinel structure.

[0038] <1.2 Manufacturing Method of Solid-State Battery 100> An example of a manufacturing method of the solid-state battery 100 will be described. When manufacturing the solid-state battery 100, a printing method such as a screen printing method, a green sheet method using a green sheet, or a combination of these methods can be used. One manufacturing method will be described below as an example, but the present disclosure is not limited to the manufacturing method described below. Furthermore, the chronological matters such as the order of description below are merely for the convenience of explanation, and the present disclosure is not limited to those matters.

[0039] First, the positive electrode 10 is fabricated. Specifically, a plurality of first positive electrode active material particles 1 having a predetermined median diameter are prepared, and then LiNbO ３ Next, a plurality of first positive electrode active material particles 1 coated with the ion-conductive material are mixed with a solid electrolyte SE at a predetermined volume ratio (e.g., 6:4) to prepare a first positive electrode active material mixture. Similarly, a plurality of second positive electrode active material particles 2 having a predetermined median diameter are prepared, and then LiNbO is coated on the plurality of second positive electrode active material particles 2 using a tumbling fluidized bed coating device. ３The second cathode active material particles 2 are coated with an ion-conductive material such as ZnO. Then, the second cathode active material particles 2 coated with the ion-conductive material are mixed with a solid electrolyte SE at a predetermined volume ratio (e.g., 6:4) to form a second cathode active material mixture. Next, a cathode current collector 11 is prepared, and the first cathode active material mixture is applied to the surface of the cathode current collector 11 to form a first cathode active material region L1. The second cathode active material mixture is then applied to the first cathode active material region L1 to form a second cathode active material region L2. The first cathode active material region L1 and the second cathode active material region L2 are sequentially stacked on the cathode current collector 11, and the laminate is pressure-molded using a press to form a cathode active material layer 12. The cathode 10 is thus obtained.

[0040] Next, the negative electrode 30 is fabricated. Specifically, a negative electrode active material mixture is fabricated by kneading a plurality of negative electrode active material particles and a solid electrolyte SE at a predetermined volume ratio (for example, 6:4). Next, a negative electrode current collector 31 is prepared, and the above-described negative electrode active material mixture is applied to the surface of the negative electrode current collector 31. Thereafter, the negative electrode active material mixture applied to the negative electrode current collector 31 is pressure-molded using a press, thereby forming a negative electrode active material layer 32 on the negative electrode current collector 31. In this manner, the negative electrode 30 is obtained.

[0041] Finally, the positive electrode 10, the solid electrolyte layer 20, and the negative electrode 30 are stacked in this order to form a laminate, and then the laminate is compressed using a press, thereby producing the solid battery 100.

[0042] <1.3 Functions and Effects of Solid-State Batteries> Important characteristics required for solid-state batteries generally include volumetric energy density, high-rate charge / discharge characteristics, and durability. These characteristics are often rate-determined by the cathode of the solid-state battery. Common strategies for improving volumetric energy density include increasing the geometric packing density by broadening the particle size distribution or using a cathode active material with a bimodal particle size distribution. To improve high-rate charge / discharge characteristics, a commonly known strategy is to increase the reactive surface area by using smaller cathode active material particles. However, simply reducing the particle size of the cathode active material particles reduces the packing density of the cathode active material particles in the cathode active material layer. Furthermore, to suppress the reaction between the cathode active material particles and the solid electrolyte and improve the durability of the cathode active material particles, it is desirable to provide a coating made of an ion-conductive material at the interface between the cathode active material particles and the solid electrolyte. However, since the coating film needs to have a certain thickness, the smaller the particle size of the positive electrode active material particles, the larger the volume of the coating film in the positive electrode active material layer becomes relative to the volume of the positive electrode active material particles. Therefore, reducing the particle size of the positive electrode active material particles also causes a secondary problem of a decrease in the energy density per volume of active material.

[0043] In the solid-state battery 100 of this embodiment, the positive electrode active material layer 12 has a first positive electrode active material region L1 and a second positive electrode active material region L2 stacked in this order from the positive electrode current collector 11 side. Here, the volume ratio of the plurality of first positive electrode active material particles 1 to the solid electrolyte SE in the first positive electrode active material region L1 is within the range of 6:4 to 8:2. Furthermore, the median diameter of the plurality of first positive electrode active material particles 1 is smaller than the median diameter of the plurality of second positive electrode active material particles 2. Therefore, a larger amount of solid electrolyte SE is present around the plurality of first positive electrode active material particles 1. Therefore, a good ion conduction path is formed in the solid-state battery 100 including the positive electrode 10, thereby achieving better performance, such as improved rate characteristics without sacrificing energy density.

[0044] In the solid state battery 100 of this embodiment, at least a part of the interface between the first cathode active material particles 1 and the solid electrolyte SE and at least a part of the interface between the second cathode active material particles 2 and the solid electrolyte SE are covered with LiNbO ３ Since a coating containing an ion-conducting material such as ZnO is present, a better ion-conducting path can be formed, and better performance can be achieved.

[0045] In the solid-state battery 100 of the present embodiment, a portion of the solid electrolyte SE is in contact with the positive electrode current collector 11 near the interface between the first positive electrode active material region L1 and the positive electrode current collector 11. This allows the solid-state battery 100 to form a better ion conduction path, thereby achieving even better performance. [2. Examples] Examples of the present disclosure will be described.

[0046] Example 1 As described below, a solid-state battery (half cell) for evaluation was fabricated including the positive electrode (evaluation electrode) of the present disclosure shown in Figure 1, a reference electrode as its counter electrode, and a solid electrolyte layer provided between the positive electrode and the reference electrode, and the battery characteristics were evaluated. However, an indium-lithium alloy foil was used as the reference electrode.

[0047] (Fabrication of Positive Electrode) First, an aluminum (Al) foil was prepared as a positive electrode current collector. Next, a plurality of first positive electrode active material particles were prepared using Li(Ni) ０．５ Co ０．２ Mn ０．３ ) O ２ The first positive electrode active material particles were coated with LiNbO, an ion conductive material. ３ The resultant was coated with a target thickness of 5 nm using a rolling fluidized coating device (Powrex Corporation, "MP-01"). ３ a plurality of first positive electrode active material particles coated with Li as a solid electrolyte; ６ P.S. ５ The first positive electrode active material mixture was prepared by kneading the Li(Ni) particles with a median diameter D50(2) of 10.0 μm with Cl at a volume ratio of 6:4. ０．５ Co ０．２Mn ０．３ ) O ２ The second positive electrode active material particles were coated with LiNbO3, an ion conductive material, to a target thickness of 5 nm using a rolling fluidized coating device ("MP-01" manufactured by Powrex Corporation). ３ a plurality of second positive electrode active material particles coated with Li as a solid electrolyte; ６ P.S. ５ A second positive electrode active material mixture was prepared by kneading SiO2 and Cl at a volume ratio of 6:4. Next, the first positive electrode active material mixture was applied to the surface of a positive electrode current collector to prepare a first positive electrode active material region, and the second positive electrode active material mixture was applied to the first positive electrode active material region to prepare a second positive electrode active material region. The first positive electrode active material region and the second positive electrode active material region were then stacked in order on the positive electrode current collector, and the stack was press-molded at a pressure of 98 MPa using a press to form a positive electrode active material layer, thereby obtaining a positive electrode. In this example, the thicknesses of the positive electrode active material region and the positive electrode active material region were each 30 μm.

[0048] (Fabrication of Solid-State Battery (Half Cell)) A solid electrolyte layer (also called a separator) made of the solid electrolyte Li6PS5Cl was bonded to the positive electrode obtained as described above, and then pressure molding was performed in a press at 98 MPa and then at 588 MPa to form a laminate of the positive electrode and the solid electrolyte layer. Furthermore, an indium-lithium alloy foil was bonded as a negative electrode to the side opposite the positive electrode from the solid electrolyte layer, thereby obtaining a solid-state battery (half cell).

[0049] (Evaluation of Battery Characteristics) The battery characteristics of the solid battery of Example 1 were evaluated, and the results shown in Table 1 were obtained. Here, the charge capacity [mAh / g] was measured when the solid battery of Example 1 was charged at a 2C rate in a room temperature environment. 1C is the magnitude of the current that fully charges (or discharges) the theoretical capacity of the battery in 1 hour during constant current charging and discharging. Furthermore, the solid battery of Example 1 was cut in the stacking direction to expose a cross section along the stacking direction, and an image of the cross section was obtained using a scanning electron microscope (SEM). The image of the cross section was analyzed to measure the packing ratio of the plurality of first positive electrode active material particles and the plurality of second positive electrode active material particles in the entire positive electrode active material layer.

[0050]

[0051] Example 2 As shown in Table 1, a plurality of first positive electrode active material particles were prepared using Li(Ni) particles having a median diameter D50(1) of 2.0 μm. ０．５ Co ０．２ Mn ０．３ ) O ２ and a plurality of second positive electrode active material particles each having a median diameter D50(2) of 5.0 μm. ０．５ Co ０．２ Mn ０．３ ) O ２ A solid state battery of Example 2 was fabricated in the same manner as in Example 1, except that the solid state battery of Example 2 was fabricated using the same material as in Example 1. Thereafter, the battery characteristics of the solid state battery of Example 2 were evaluated in the same manner as in Example 1. The results are also shown in Table 1.

[0052] Example 3 As shown in Table 1, a plurality of first positive electrode active material particles were prepared using Li(Ni) particles having a median diameter D50(1) of 2.0 μm. ０．５ Co ０．２ Mn ０．３ ) O ２ A solid state battery of Example 3 was fabricated in the same manner as in Example 1, except that the solid state battery of Example 3 was fabricated using the same material as in Example 1. Thereafter, the battery characteristics of the solid state battery of Example 3 were evaluated in the same manner as in Example 1. The results are also shown in Table 1.

[0053] Example 4 As shown in Table 1, a plurality of first positive electrode active material particles and Li as a solid electrolyte were used. ６ P.S.５ a volume ratio of the second positive electrode active material particles to the solid electrolyte and a volume ratio of the second positive electrode active material particles to the solid electrolyte; ６ P.S. ５ A solid state battery of Example 4 was fabricated in the same manner as in Example 1, except that the volume ratio of SiO2 to Cl was set to 7:3 in both cases. Thereafter, the battery characteristics of the solid state battery of Example 4 were evaluated in the same manner as in Example 1. The results are also shown in Table 1.

[0054] Example 5 A plurality of first positive electrode active material particles and a plurality of second positive electrode active material particles each containing LiNbO ３ A solid state battery of Example 5 was fabricated in the same manner as in Example 2, except that no coating was performed. Thereafter, the battery characteristics of the solid state battery of Example 5 were evaluated in the same manner as in Example 1. The results are also shown in Table 1.

[0055] <Comparative Example 1> As shown in Table 1, a plurality of first positive electrode active material particles and a plurality of second positive electrode active material particles were prepared using Li(Ni) particles having median diameters D50(1) and D50(2) of 7.5 μm. ０．５ Co ０．２ Mn ０．３ ) O ２ A solid state battery of Comparative Example 1 was fabricated in the same manner as in Example 1, except that the following were used: 1) The battery characteristics of the solid state battery of Comparative Example 1 were then evaluated in the same manner as in Example 1. The results are also shown in Table 1.

[0056] <Comparative Example 2> As shown in Table 1, a plurality of first positive electrode active material particles were prepared using Li(Ni) ０．５ Co ０．２ Mn ０．３ ) O ２ and a plurality of second positive electrode active material particles each having a median diameter D50(2) of 5.0 μm. ０．５ Co ０．２ Mn ０．３ ) O ２ A solid state battery of Comparative Example 2 was fabricated in the same manner as in Example 1, except that the battery was changed to use the same material as in Example 1. Thereafter, the battery characteristics of the solid state battery of Comparative Example 2 were evaluated in the same manner as in Example 1. The results are also shown in Table 1.

[0057] Comparative Example 3 As shown in Table 1, a plurality of first positive electrode active material particles and a plurality of second positive electrode active material particles were prepared using Li(Ni) ０．５ Co ０．２ Mn ０．３ ) O ２ A solid state battery of Comparative Example 3 was fabricated in the same manner as in Example 1, except that the following were used: 1) The battery characteristics of the solid state battery of Comparative Example 3 were then evaluated in the same manner as in Example 1. The results are also shown in Table 1.

[0058] Comparative Example 4 As shown in Table 1, a plurality of second positive electrode active material particles were prepared using Li(Ni) ０．５ Co ０．２ Mn ０．３ ) O ２ A solid state battery of Comparative Example 4 was fabricated in the same manner as in Example 1, except that the battery was changed to use the same material as in Example 1. Thereafter, the battery characteristics of the solid state battery of Comparative Example 4 were evaluated in the same manner as in Example 1. The results are also shown in Table 1.

[0059] Comparative Example 5 As shown in Table 1, a plurality of first positive electrode active material particles and a plurality of second positive electrode active material particles were prepared using Li(Ni) ０．５ Co ０．２ Mn ０．３ ) O ２ A solid state battery of Comparative Example 5 was fabricated in the same manner as in Example 1, except that the following were used: 1) The battery characteristics of the solid state battery of Comparative Example 5 were then evaluated in the same manner as in Example 1. The results are also shown in Table 1.

[0060] Comparative Example 6 As shown in Table 1, a plurality of first positive electrode active material particles and a plurality of second positive electrode active material particles were prepared using Li(Ni) ０．５ Co ０．２ Mn ０．３ ) O ２ A solid state battery of Comparative Example 7 was fabricated in the same manner as in Example 1, except that the following were used: 1) The battery characteristics of the solid state battery of Comparative Example 7 were then evaluated in the same manner as in Example 1. The results are also shown in Table 1.

[0061] Comparative Example 7 A plurality of first positive electrode active material particles and a plurality of second positive electrode active material particles each containing LiNbO ３ A solid state battery of Comparative Example 8 was fabricated in the same manner as in Comparative Example 4, except that no coating was performed. Thereafter, the battery characteristics of the solid state battery of Comparative Example 8 were evaluated in the same manner as in Example 1. The results are also shown in Table 1.

[0062] Comparative Example 8 As shown in Table 1, a plurality of first positive electrode active material particles and Li as a solid electrolyte were used. ６ P.S. ５ a volume ratio of the second positive electrode active material particles to the solid electrolyte and a volume ratio of the second positive electrode active material particles to the solid electrolyte; ６ P.S. ５ A solid state battery of Comparative Example 9 was fabricated in the same manner as in Comparative Example 2, except that the volume ratio of SiO2 to Cl was set to 7:3 in both cases. Thereafter, the battery characteristics of the solid state battery of Comparative Example 9 were evaluated in the same manner as in Example 1. The results are also shown in Table 1.

[0063] Comparative Example 9 As shown in Table 1, a plurality of first positive electrode active material particles and Li as a solid electrolyte were used. ６ P.S. ５ a volume ratio of the second positive electrode active material particles to the solid electrolyte and a volume ratio of the second positive electrode active material particles to the solid electrolyte; ６ P.S. ５ A solid state battery of Comparative Example 10 was fabricated in the same manner as in Example 1, except that the volume ratio of SiO2 to Cl was 5:5 in both cases. Thereafter, the battery characteristics of the solid state battery of Comparative Example 10 were evaluated in the same manner as in Example 1. The results are also shown in Table 1.

[0064] [Discussion] As shown in Table 1, Examples 1 to 4 achieved both a high charge capacity and a high volumetric energy density compared to Comparative Examples 1 to 9. This is thought to be because, in Examples 1 to 4, the volume ratio of the first positive electrode active material particles to the solid electrolyte was 6:4 or 7:3, and the median diameter D50(2) of the plurality of second positive electrode active material particles was larger than the median diameter D50(1) of the plurality of first positive electrode active material particles, thereby forming a good ion conduction path in the positive electrode active material layer and improving the ion conductivity in the positive electrode. Furthermore, Example 5 and Comparative Example 7, unlike Examples 1 to 4, contained LiNbO in each of the first positive electrode active material particles and the second positive electrode active material particles.３ In Example 5 and Comparative Example 7, no coating was formed on the first positive electrode active material particles or the second positive electrode active material particles. However, a comparison of the two shows clear differences in both charge capacity and volumetric energy density. That is, Example 5 exhibits higher values ​​for both charge capacity and volumetric energy density than Comparative Example 7. This is thought to be because, in Example 5, the volume ratio of the first positive electrode active material particles to the solid electrolyte was 6:4 or 7:3, and the median diameter D50(2) of the plurality of second positive electrode active material particles was larger than the median diameter D50(1) of the plurality of first positive electrode active material particles. This resulted in the formation of favorable ion conduction paths in the positive electrode active material layer, improving the ion conductivity of the positive electrode.

[0065] The present disclosure has been described above with reference to several embodiments, modifications, and examples, but the configuration of the present disclosure is not limited to the configuration described above and can be modified in various ways.

[0066] Specifically, for example, in the above-described embodiment, the positive electrode active material layer 12 has a two-layer structure including a first positive electrode active material region L1 and a second positive electrode active material region L2. However, the solid-state battery of the present disclosure is not limited to this structure. The positive electrode active material layer may have a multilayer structure including, for example, three or more layers containing positive electrode active material particles with different median diameters. In this case, it is preferable that the median diameter of the positive electrode active material particles in the positive electrode active material region located closest to the positive electrode current collector is smaller than the median diameter of the positive electrode active material particles in the other positive electrode active material regions.

[0067] Furthermore, the effects described in this specification are merely examples, and the effects of the present disclosure are not limited to the effects described in this specification. Therefore, other effects may be obtained with respect to the present disclosure.

[0068] Furthermore, the present disclosure may take the following forms. <1> A positive electrode comprising: a positive electrode current collector; and a positive electrode active material layer provided on the positive electrode current collector, wherein the positive electrode active material layer has: a first positive electrode active material region provided on the positive electrode current collector and including a plurality of first positive electrode active material particles having a solid electrolyte attached thereto; and a second positive electrode active material region provided on the opposite side of the positive electrode current collector from the first positive electrode active material region and including a plurality of second positive electrode active material particles having the solid electrolyte attached thereto, wherein a volume ratio of the plurality of first positive electrode active material particles to the solid electrolyte in the first positive electrode active material region is in the range of 6:4 to 8:2, and wherein a median diameter of the plurality of second positive electrode active material particles is larger than a median diameter of the plurality of first positive electrode active material particles. <2> A positive electrode according to <1> above, wherein a volume ratio of the plurality of first positive electrode active material particles to the solid electrolyte in the second positive electrode active material region is in the range of 6:4 to 8:2. <3> The positive electrode according to <1> or <2> above, wherein a coating containing an ion-conductive material is present on at least a portion of the interface between the first positive electrode active material particles and the solid electrolyte and at least a portion of the interface between the second positive electrode active material particles and the solid electrolyte. <4> The positive electrode according to <3> above, wherein the coating contains a compound represented by LiXY as the ion-conductive material, where X is at least one element selected from the group consisting of B (boron), Al (aluminum), Si (silicon), P (phosphorus), Ti (titanium), Ge (germanium), Zr (zirconium), Nb (niobium), In (indium), Sn (tin), Hf (hafnium), Ta (tantalum), and W (tungsten), and Y is at least one element selected from the group consisting of O (oxygen), S (sulfur), F (fluorine), Cl (chlorine), Br (bromine), and I (iodine). <5> The positive electrode according to <3> above, wherein the ion-conductive material is LiNbO ３ <6> The positive electrode according to any one of <1> to <5> above, wherein a part of the solid electrolyte is in contact with the positive electrode current collector. <7> A solid-state battery comprising, in order, the positive electrode according to any one of <1> to <6> above, a solid electrolyte layer, and a negative electrode.

Claims

1. A positive electrode current collector, a positive electrode active material layer provided on the positive electrode current collector, and comprising, the positive electrode active material layer, a first positive electrode active material region provided on the positive electrode current collector and containing a plurality of first positive electrode active material particles to which a solid electrolyte is attached, a second positive electrode active material region provided on the side opposite to the positive electrode current collector when viewed from the first positive electrode active material region and containing a plurality of second positive electrode active material particles to which the solid electrolyte is attached, and having, the volume ratio of the plurality of first positive electrode active material particles and the solid electrolyte in the first positive electrode active material region is included in the range of 6:4 or more and 8:2 or less, a positive electrode in which the median diameter of the plurality of second positive electrode active material particles is larger than the median diameter of the plurality of first positive electrode active material particles.

2. The volume ratio of the plurality of second positive electrode active material particles and the solid electrolyte in the second positive electrode active material region is included in the range of 6:4 or more and 8:2 or less. The positive electrode according to claim 1.

3. A film containing an ion conductive material is present on at least a part of the interface between the first positive electrode active material particles and the solid electrolyte and at least a part of the interface between the second positive electrode active material particles and the solid electrolyte. The positive electrode according to claim 1.

4. When at least one element among B (boron), Al (aluminum), Si (silicon), P (phosphorus), Ti (titanium), Ge (germanium), Zr (zirconium), Nb (niobium), In (indium), Sn (tin), Hf (hafnium), Ta (tantalum) and W (tungsten) is defined as X, and at least one element among O (oxygen), S (sulfur), F (fluorine), Cl (chlorine), Br (bromine) and I (iodine) is defined as Y, the film contains a compound represented by LiXY as the ion conductive material. The positive electrode according to claim 3.

5. The ionic conductive material is LiNbO ３ is The positive electrode according to claim 3.

6. A part of the solid electrolyte is in contact with the positive electrode current collector. The positive electrode according to claim 1.

7. A solid battery comprising, in order, the positive electrode according to any one of claims 1 to 6, a solid electrolyte layer, and a negative electrode.