Solid electrolyte materials and all-solid-state batteries

Abstract

To provide a solid electrolyte material capable of forming a solid electrolyte layer with high ionic conductivity.SOLUTION: A solid electrolyte material includes solid electrolyte particles 31 having a NASICON structure and having two or more crystal phases selected from the group consisting of rhombohedral, triclinic, and monoclinic, and crystalline phosphate compound particles 32 having at least one element selected from the group consisting of Zr, Ti, Ge, Al, Hf, Ca, Ba, Sr, Sc, Y, and In and having a crystal structure different from that of the solid electrolyte particles 31, and the existence ratio of the crystalline phosphate compound particles 32 is 10% by volume or more and 60% by volume or less.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a solid electrolyte material and an all-solid-state battery. [Background technology]

[0002] In recent years, electronics technology has made remarkable advances, leading to efforts to make portable electronic devices smaller, lighter, thinner, and more multifunctional. Accordingly, there is a strong demand for smaller, lighter, thinner, and more reliable batteries, which serve as the power source for these electronic devices. Currently, research is being conducted on all-solid-state batteries, which replace the liquid electrolyte of commonly used lithium-ion secondary batteries with a solid electrolyte, with the aim of improving safety.

[0003] Patent Document 1 describes a solid electrolyte obtained by adding 40% by weight or less of an electrolyte with a high glass component consisting of a conductor of the same type of ion to a ceramic electrolyte with high conductivity as the main component and sintering the resulting electrolyte. Table 1 of Patent Document 1 shows that the conductivity at 300°C of a pellet in which 20% by weight of LiAlSiO4 as a powder with a high glass component (mixed component) is added to the main component Li2Zr(PO4)2 is 3.1 x 10 -4 It is stated that the viscosity is S / cm.

[0004] Patent Document 2 describes the general formula Li 1+4x Zr 2-x A highly safe all-solid-state battery has been proposed in which the solid electrolyte layer, which is primarily composed of a solid electrolyte material expressed as (PO4)3 (where 0.1≦x≦0.4), the positive electrode layer, and the negative electrode layer are all made of oxides. In Non-Patent Documents 1 and 2, some elements of LiZr2(PO4)3 are mixed with other elements. A solid electrolyte substituted with Cr is disclosed. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 6-80462 [Patent Document 2] Japanese Patent Application Laid-Open No. 2016-51539 [Non-patent literature]

[0006] [Non-Patent Document 1] Hui Xiea et al., “Li1.2Zr1.9Ca0.1(PO4)3,a room-temperature Li-ion solid electrolyte”, Journal of Power Sources196(2011)7760-7762 [Non-patent document 2] Henghui Xu et al., “Y-Doped NASICON-type LiZr2(PO4)3 Solid Electrolytes for Lithium-Metal Batteries”, Chemistray of Materials29(2017)7206-7212 Summary of the Invention [Problem to be solved by the invention]

[0007] However, all-solid-state batteries having a solid electrolyte layer using conventional solid electrolyte materials have a problem in that their discharge capacity at high rates at room temperature (e.g., 25°C) is insufficient. For this reason, there is a demand for all-solid-state batteries such as all-solid-state lithium-ion secondary batteries to have an even greater discharge capacity at high rates at room temperature.

[0008] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a solid electrolyte material that can be suitably used as a material for a solid electrolyte layer of an all-solid-state battery, and an all-solid-state battery that includes a solid electrolyte layer containing the solid electrolyte material and has a large discharge capacity at a high rate at room temperature. [Means for solving the problem]

[0009] In order to solve the above problems, the present inventors have conducted extensive research, focusing on the solid electrolyte material used in forming the solid electrolyte layer. As a result, the present inventors discovered that a solid electrolyte material containing solid electrolyte particles having a NASICON structure and two or more crystal phases selected from the group consisting of rhombohedral, triclinic, and monoclinic crystals, and crystalline phosphate compound particles containing a specific element and having a different crystal structure from the solid electrolyte particles, and containing the crystalline phosphate compound particles in a specific abundance ratio, led to the present invention. That is, the present invention relates to the following inventions.

[0010] [1] Solid electrolyte particles having a NASICON structure and having two or more crystal phases selected from the group consisting of rhombohedral, triclinic, and monoclinic crystals; and crystalline phosphate compound particles containing at least one element selected from the group consisting of Zr, Ti, Ge, Al, Hf, Ca, Ba, Sr, Sc, Y, and In, and having a crystal structure different from that of the solid electrolyte particles, A solid electrolyte material characterized in that the crystalline phosphate compound particles are present in an amount of 10% by volume or more and 60% by volume or less.

[0011] [2] The solid electrolyte material according to [1], wherein the crystalline phosphate compound particles have an average particle size D of 0.01 μm to 10 μm. [3] A laminate in which a positive electrode layer and a negative electrode layer are stacked with a solid electrolyte layer interposed therebetween, An all-solid-state battery, wherein the solid electrolyte layer contains the solid electrolyte material according to [1] or [2]. [4] The all-solid-state battery according to [3], wherein the laminate is a sintered body. [Effects of the Invention]

[0012] The solid electrolyte material of the present invention comprises solid electrolyte particles having a NASICON structure and two or more crystal phases selected from the group consisting of rhombohedral, triclinic, and monoclinic, and crystalline phosphate compound particles containing at least one element selected from the group consisting of Zr, Ti, Ge, Al, Hf, Ca, Ba, Sr, Sc, Y, and In and having a different crystal structure from the solid electrolyte particles, wherein the content of the crystalline phosphate compound particles is 10% by volume or more and 60% by volume or less. Therefore, the solid electrolyte material of the present invention can form a solid electrolyte layer with high ionic conductivity at room temperature. The all-solid-state battery of the present invention has a solid electrolyte layer containing the solid electrolyte material of the present invention, and therefore has a large discharge capacity at a high rate at room temperature. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a cross-sectional view showing the all-solid-state battery of this embodiment. [Figure 2] FIG. 2 is a schematic cross-sectional view showing an enlarged portion of the solid electrolyte layer 3 of the all-solid-state battery 10 shown in FIG. [Figure 3] FIG. 3 is a cross-sectional view illustrating an example of a solid electrolyte layer of a conventional all-solid-state battery. [Figure 4] FIG. 4 is a chart showing the results of X-ray diffraction measurement of the solid electrolyte material of Example 1-1 (A), the simulation results of X-ray diffraction measurement of ZrP2O7 (B), the simulation results of X-ray diffraction measurement of rhombohedral crystals of LiZr2(PO4)3 (C), the simulation results of X-ray diffraction measurement of triclinic crystals of LiZr2(PO4)3 (D), and the simulation results of X-ray diffraction measurement of monoclinic crystals of LiZr2(PO4)3 (E). DETAILED DESCRIPTION OF THE INVENTION

[0014] In order to solve the above problems and increase the discharge capacity of an all-solid-state battery at a high rate at room temperature, the present inventors have focused on the solid electrolyte layer contained in the all-solid-state battery and conducted extensive research as described below. That is, in order to manufacture an all-solid-state battery with a large discharge capacity at high rates at room temperature, it is preferable to increase the ionic conductivity of the solid electrolyte layer at room temperature. However, the relationship between the ionic conductivity σ of the solid electrolyte material and the temperature T is based on the Arrhenius equation (σ = A exp (-Ea / RT), A: frequency factor, R: gas constant, Ea: activation energy. Therefore, even if a solid electrolyte material has high ionic conductivity at high temperatures, it cannot achieve sufficient ionic conductivity at room temperature (e.g., 25°C).

[0015] Furthermore, it was found that even if a solid electrolyte layer is formed using a solid electrolyte material with high ionic conductivity, the discharge capacity of an all-solid-state battery having this layer at high rates at room temperature cannot be sufficiently increased. The present inventors have conducted extensive research into the reason for this, and as a result, have concluded that this is because the ionic conductivity at the grain boundaries between particles made of the solid electrolyte material contained in the solid electrolyte layer is lower than that within the particles. Therefore, the inventors of the present invention have conducted extensive research into the idea that a solid electrolyte material containing particles made of a conventionally used solid electrolyte material and particles made of a material having a higher resistance than that of the conventionally used solid electrolyte material can be used to form a high ion-conductive layer between adjacent particles of different types, thereby increasing the ionic conductivity of the solid electrolyte layer.

[0016] As a result, they discovered that a solid electrolyte layer with high ionic conductivity can be formed by using a solid electrolyte material containing, in a specific ratio, solid electrolyte particles with a NASICON structure and two or more crystal phases selected from the group consisting of rhombohedral, triclinic, and monoclinic, and crystalline phosphate compound particles that contain specific elements and have a different crystal structure from the solid electrolyte particles. Furthermore, the present inventors have confirmed that by forming a solid electrolyte layer of an all-solid-state battery using this solid electrolyte material, an all-solid-state battery having a large discharge capacity at a high rate at room temperature can be obtained, and have conceived the present invention.

[0017] The solid electrolyte material and all-solid-state battery of this embodiment will be described in detail below with reference to the drawings as appropriate. The drawings used in the following description may show characteristic portions enlarged for the sake of clarity of the features of the present invention. Therefore, the dimensional ratios of each component may differ from the actual ones. The materials, dimensions, etc. exemplified in the following description are merely examples, and the present invention is not limited thereto. Appropriate modifications can be made within the scope of the present invention.

[0018] [All-solid battery] 1 is a cross-sectional schematic diagram showing an all-solid-state battery 10 of this embodiment. The all-solid-state battery 10 has a laminate 4, a first external terminal 5, and a second external terminal 6. The first external terminal 5 and the second external terminal 6 are formed of a conductive material. The first external terminal 5 and the second external terminal 6 are in contact with opposing surfaces of the laminate 4, respectively. The first external terminal 5 and the second external terminal 6 extend in a direction intersecting (orthogonal to) the laminate surface of the laminate 4.

[0019] The laminate 4 is formed by laminating a positive electrode layer 1 and a negative electrode layer 2 with a solid electrolyte layer 3 interposed therebetween. The laminate 4 is, for example, a sintered body obtained by sintering. The number of positive electrode layers 1 and negative electrode layers 2 included in the laminate 4 may be one each, or may be two or more. The solid electrolyte layer 3 is located between the positive electrode layer 1 and the negative electrode layer 2, between the positive electrode layer 1 and the second external terminal 6, and between the negative electrode layer 2 and the first external terminal 5. 1, one end of the positive electrode layer 1 is connected to a first external terminal 5. One end of the negative electrode layer 2 is connected to a second external terminal 6.

[0020] The all-solid-state battery 10 is charged or discharged by the exchange of ions between the positive electrode layer 1 and the negative electrode layer 2 via the solid electrolyte layer 3. In this embodiment, as shown in FIG. 1 , a laminated type all-solid-state battery 10 will be described as an example, but a wound type all-solid-state battery may also be used. The all-solid-state battery 10 of this embodiment is used in, for example, laminated batteries, prismatic batteries, cylindrical batteries, coin batteries, button batteries, etc. The all-solid-state battery 10 may also be an injection type battery in which the solid electrolyte layer 3 is dissolved or dispersed in a solvent.

[0021] "Solid electrolyte layer" The solid electrolyte layer 3 can move ions by an externally applied electric field. The solid electrolyte layer 3, for example, conducts lithium ions and inhibits the movement of electrons. Fig. 2 is an enlarged schematic cross-sectional view showing a portion of the solid electrolyte layer 3 of the all-solid-state battery 10 shown in Fig. 1. The solid electrolyte layer 3 contains the solid electrolyte material of this embodiment, which contains solid electrolyte particles 31 and crystalline phosphate compound particles 32.

[0022] 2, reference numeral 33 denotes grain boundaries between solid electrolyte particles 31 and crystalline phosphate compound particles 32, between adjacent solid electrolyte particles 31, and between adjacent crystalline phosphate compound particles 32. Among the grain boundaries 33, high ion-conductive layers 33a are formed at the grain boundaries 33 between the solid electrolyte particles 31 and the crystalline phosphate compound particles 32. The high ion-conductive layers 33a have higher ionic conductivity than the grain boundaries 33 between adjacent solid electrolyte particles 31 and between adjacent crystalline phosphate compound particles 32.

[0023] (solid electrolyte material) The solid electrolyte material of this embodiment used to form the solid electrolyte layer 3 includes solid electrolyte particles 31 and crystalline phosphate compound particles 32. The solid electrolyte material may contain impurity phases such as metal oxides as long as the effects of the present invention are not impaired. The solid electrolyte material preferably consists solely of solid electrolyte particles 31 and crystalline phosphate compound particles 32. The solid electrolyte material may contain only one type of solid electrolyte particles 31 or two or more types. The solid electrolyte material may also contain only one type of crystalline phosphate compound particles 32 or two or more types. The type and number of solid electrolyte particles 31 and crystalline phosphate compound particles 32 contained in the solid electrolyte material can be appropriately determined depending on the application of the all-solid-state battery 10, etc. The solid electrolyte particles 31 and crystalline phosphate compound particles 32 can each be produced using a known method such as a solid-state reaction method.

[0024] (Solid electrolyte particles) The solid electrolyte particles 31 have a NASICON structure and two or more crystalline phases selected from the group consisting of rhombohedral, triclinic, and monoclinic. The ionic conductivities of the rhombohedral, triclinic, and monoclinic crystal phases are different. The ionic conductivities are highest in the rhombohedral, triclinic, and monoclinic crystal phases, respectively. The solid electrolyte layer 3 containing the solid electrolyte material contains grain boundaries where the solid electrolyte particles 31 contact each other and grain boundaries where the crystalline phosphate compound particles 32 contact each other. Because it is difficult to uniformly mix the solid electrolyte particles 31 and the crystalline phosphate compound particles 32, the solid electrolyte layer 3 tends to have a non-uniform distribution of the solid electrolyte particles 31 and the crystalline phosphate compound particles 32. Non-uniform distribution of the solid electrolyte particles 31 and the crystalline phosphate compound particles 32 results in the formation of many grain boundaries where the solid electrolyte particles 31 contact each other and where the crystalline phosphate compound particles 32 contact each other. In this embodiment, since the solid electrolyte particles 31 have two crystalline phases, an ion-conducting layer having a relatively high ionic conductivity is formed at the grain boundary where the solid electrolyte particles 31 contact each other due to the difference in ionic conductivity, i.e., resistance, between the two crystalline phases. As a result, the solid electrolyte material of this embodiment has high ionic conductivity.

[0025] In contrast, for example, when the solid electrolyte particles 31 have only one crystalline phase, an ion-conducting layer with high ionic conductivity is not formed at the grain boundary where the solid electrolyte particles 31 contact each other. Therefore, a solid electrolyte material including solid electrolyte particles having only one crystalline phase has lower ionic conductivity than the solid electrolyte material of this embodiment.

[0026] The crystalline phase of solid electrolyte particle 31 may be two or more selected from the group consisting of rhombohedral, triclinic, and monoclinic, and preferably includes rhombohedral and / or triclinic. Specifically, the crystalline phase of solid electrolyte particle 31 may be a combination of rhombohedral and triclinic, a combination of rhombohedral and monoclinic, a combination of triclinic and monoclinic, or a combination of rhombohedral, triclinic, and monoclinic, and the combination of rhombohedral and triclinic, which has high ionic conductivity, is preferred.

[0027] The proportion of the two or more crystalline phases in the solid electrolyte particles 31 is not particularly limited, but in order to obtain a solid electrolyte material with high ionic conductivity, it is preferable that the solid electrolyte particles 31 contain 50% or more of rhombohedral crystals, which have the highest ionic conductivity among rhombohedral, triclinic, and monoclinic crystals, and more preferably 60% or more of rhombohedral crystals. The proportion of rhombohedral crystals in the solid electrolyte particles 31 is preferably 80% or less, and more preferably 70% or less, because the inclusion of two or more crystalline phases facilitates the formation of an ion-conducting layer with high ionic conductivity at the grain boundaries where the solid electrolyte particles 31 contact each other.

[0028] Solid electrolyte particles 31 having two or more crystal phases can be produced, for example, by the following method. That is, solid electrolyte particles having only rhombohedral crystals, solid electrolyte particles having only triclinic crystals, and solid electrolyte particles having only monoclinic crystals are produced by known production methods, respectively, and then mixed to obtain a desired mixture ratio. Solid electrolyte particles having only rhombohedral crystals can be produced, for example, by a wet method. Solid electrolyte particles having only triclinic crystals can be produced, for example, by a flux method. Solid electrolyte particles having only monoclinic crystals can be produced, for example, by a solid-phase reaction method. The production method for solid electrolyte particles having each crystal phase can be appropriately determined depending on the composition of the solid electrolyte particles.

[0029] The solid electrolyte particles 31 are made of, for example, a compound represented by the following formula (1). Li a A2(PO4)3···(1) (In formula (1), A is at least one element selected from the group consisting of Zr, Ti, Ge, Al, Hf, Ca, Ba, Sr, Sc, Y, and In, and a satisfies 0.9≦a≦1.4.)

[0030] In the compound represented by formula (1), A is at least one element selected from the group consisting of Zr, Ti, Ge, Al, Hf, Ca, Ba, Sr, Sc, Y, and In. In the compound represented by formula (1), A is an element that has been confirmed to be mutually substitutable. In the compound represented by formula (1), A is preferably at least one element selected from the group consisting of Zr, Al, Ba, Ca, Sr, and Y. This is because an all-solid-state battery 10 including a solid electrolyte layer 3 containing solid electrolyte particles 31 represented by formula (1) has a larger discharge capacity at a high rate at room temperature.

[0031] In the compound represented by formula (1), a satisfies 0.9≦a≦1.4. a is preferably close to 1, and more preferably 1. This is because the solid electrolyte layer 3 containing the compound represented by formula (1) has higher ionic conductivity. Examples of the compound represented by formula (1) include LiZr2(PO4)3, Li 1.3 Al 0.3 Ti 1.7 (PO4)3, etc.

[0032] The solid electrolyte particles 31 preferably have an average particle diameter of 0.01 μm to 20 μm. When the average particle diameter of the solid electrolyte particles 31 is 0.01 μm or more, the amount of high-ion-conductive layers 33a formed between the solid electrolyte particles 31 and the crystalline phosphate compound particles 32 increases in the solid electrolyte layer 3 formed using the solid electrolyte material. As a result, the ionic conductivity of the solid electrolyte layer 3 is further increased, and the all-solid-state battery 10 including the solid electrolyte layer 3 has a larger high-rate discharge capacity at room temperature. When the average particle diameter of the solid electrolyte particles 31 is 20 μm or less, the high-ion-conductive layers 33a formed between the solid electrolyte particles 31 and the crystalline phosphate compound particles 32 are less likely to be disrupted by the presence of the solid electrolyte particles 31, and the high-ion-conductive layers 33a are less likely to become discontinuous. As a result, the ionic conductivity of the solid electrolyte layer 3 is further increased, and the all-solid-state battery 10 including the solid electrolyte layer 3 has a larger high-rate discharge capacity at room temperature. The average particle size of the solid electrolyte particles 31 can be adjusted by, for example, the time for milling the solid electrolyte particles 31 .

[0033] (Crystalline phosphate compound particles) The crystalline phosphate compound particles 32 have a higher resistance than the solid electrolyte particles 31. Therefore, a high ion-conductive layer 33a is formed at the grain boundary 33 between the solid electrolyte particles 31 and the crystalline phosphate compound particles 32. Because the crystalline phosphate compound particles 32 are crystalline particles with a different crystal structure from that of the solid electrolyte particles 31, they are less likely to react with the solid electrolyte particles 31 than amorphous particles, and are less likely to cause decomposition of the crystal structure of the solid electrolyte particles 31. This allows the solid electrolyte particles 31 to maintain a crystalline phase with high ion conductivity, increasing the ion conductivity of the solid electrolyte material.

[0034] The crystalline phosphate compound particles 32 are made of a crystalline phosphate compound containing at least one element selected from the group consisting of Zr, Ti, Ge, Al, Hf, Ca, Ba, Sr, Sc, Y, and In. The crystalline phosphate compound particles 32 preferably do not contain an element that acts as an ion conductor through the solid electrolyte particles 31. This is because the crystalline phosphate compound particles 32 containing an element that acts as an ion conductor themselves become ion conductors, which can prevent a decrease in the ionic conductivity of the high ion-conducting layer 33a formed at the grain boundary 33 between the solid electrolyte particles 31 and the crystalline phosphate compound particles 32. The crystalline phosphate compound particles 32 in the solid electrolyte material of this embodiment preferably do not contain Li, an element that acts as an ion conductor through the solid electrolyte particles 31.

[0035] Examples of the crystalline phosphate compound particles 32 include ZrP2O7, TiP2O7, GeP2O7, AlPO4, HfP2O7, CaP2O7, Ba3(PO4)2, Sr3(PO4)2, ScPO4, YPO4, InPO4, and LiAlP2O7. These crystalline phosphate compound particles 32 do not have a NASICON structure and therefore have a different crystal structure from that of the solid electrolyte particles 31.

[0036] Among these, the crystalline phosphate compound particles 32 are preferably made of an inorganic condensed phosphate compound, and more preferably made of an inorganic condensed phosphate compound represented by the following formula (2). Although the mechanism is not clear, this is because the crystalline phosphate compound particles 32 made of an inorganic condensed phosphate compound are unlikely to react with the solid electrolyte particles 31 to form a high-resistance reaction layer between the solid electrolyte particles 31 and the crystalline phosphate compound particles 32. MP2O7···(2) (In formula (2), M is at least one element selected from the group consisting of Zr, Ti, Ge, Hf, and Ca.)

[0037] In the compound represented by formula (2), M is at least one element selected from the group consisting of Zr, Ti, Ge, Hf, and Ca. In the compound represented by formula (2), M is an element confirmed to be mutually substitutable. In the compound represented by formula (2), M is more preferably at least one element selected from the group consisting of Zr and Ca. This is because an all-solid-state battery 10 including a solid electrolyte layer 3 containing the compound represented by formula (2) will have a larger discharge capacity at a high rate at room temperature.

[0038] M in the compound represented by formula (2) may be the same as or different from A in the compound represented by formula (1), and is preferably the same. When M in the compound represented by formula (2) and A in the compound represented by formula (1) are the same, the solid electrolyte particles 31 and the crystalline phosphate compound particles 32 are less likely to react with each other, and a high-resistance reaction layer is less likely to be formed between the solid electrolyte particles 31 and the crystalline phosphate compound particles 32. Therefore, an all-solid-state battery 10 including a solid electrolyte layer 3 formed using a solid electrolyte material has a larger discharge capacity at high rates at room temperature.

[0039] The average particle diameter D of the crystalline phosphate compound particles 32 is preferably 0.01 μm to 10 μm, more preferably 0.01 μm to 3 μm, and even more preferably 0.05 μm to 1.5 μm. When the average particle diameter D is 0.01 μm or more, the crystalline phosphate compound particles 32 are less likely to aggregate with each other, and therefore, aggregates of the crystalline phosphate compound particles 32 are less likely to form. This prevents the high ion conductive layer 33a formed at the grain boundary 33 between the solid electrolyte particles 31 and the crystalline phosphate compound particles 32 from becoming discontinuous due to aggregates of the crystalline phosphate compound particles 32 present in the solid electrolyte layer 3 formed using a solid electrolyte material. As a result, the ionic conductivity of the solid electrolyte layer 3 is increased, and the all-solid-state battery 10 including the solid electrolyte layer 3 has a larger discharge capacity at high rate at room temperature.

[0040] Furthermore, when the average particle diameter D is 10 μm or less, a sufficient number of contact points between the solid electrolyte particles 31 and the crystalline phosphate compound particles 32 can be ensured in the solid electrolyte layer 3 formed using the solid electrolyte material. As a result, the high ion conductive layer 33a formed at the grain boundaries 33 between the solid electrolyte particles 31 and the crystalline phosphate compound particles 32 is sufficiently increased in the solid electrolyte layer 3. Therefore, when the average particle diameter D is 10 μm or less, the high ion conductive layer 33a is less likely to be discontinuous due to the presence of the solid electrolyte particles 31, the ionic conductivity of the solid electrolyte layer 3 is further increased, and the all-solid-state battery 10 including the solid electrolyte layer 3 has a larger discharge capacity at high rate at room temperature. The average particle size D of the crystalline phosphate compound particles 32 can be adjusted, for example, by the time for which the crystalline phosphate compound particles 32 are milled.

[0041] The proportion of the crystalline phosphate compound particles 32 contained in the solid electrolyte material of this embodiment is 10% by volume to 60% by volume, preferably 15% by volume to 50% by volume, and more preferably 25% by volume to 45% by volume. Because the proportion of the crystalline phosphate compound particles 32 is 10% by volume to 60% by volume, the solid electrolyte layer 3 formed using the solid electrolyte material has a sufficiently large amount of high ion-conductive layers 33a formed at the grain boundaries 33 between the solid electrolyte particles 31 and the crystalline phosphate compound particles 32. Furthermore, because the proportion of the crystalline phosphate compound particles 32 is 60% by volume or less, the formation of excessively large grain boundaries 33 between the crystalline phosphate compound particles 32 with low ionic conductivity can be prevented. As a result, the ionic conductivity of the solid electrolyte layer 3 is increased, and the all-solid-state battery 10 including the solid electrolyte layer 3 has a larger discharge capacity at high rates at room temperature.

[0042] The content of the crystalline phosphate compound particles 32 contained in the solid electrolyte material forming the solid electrolyte layer 3 can be determined, for example, by the method described below. The all-solid-state battery 10 is cut parallel to the stacking direction of the laminate 4 using a cross-section polisher (CP) to expose a cross section of the solid electrolyte layer 3. The exposed cross section is then observed at 10,000x magnification using a scanning electron microscope (SEM) to obtain backscattered electron composition images of 10 fields of view.

[0043] The bright and dark contrast particles in the resulting backscattered electron composition images of the 10 fields of view are each subjected to composition analysis using energy dispersive X-ray analysis (EDS) to distinguish between solid electrolyte particles 31 and crystalline phosphate compound particles 32. Each backscattered electron composition image is then converted into a monochrome image and binarized, and the number of pixels in the area corresponding to crystalline phosphate compound particles 32 in each field of view is measured and added together. The volume (%) of the crystalline phosphate compound particles 32 is then calculated for each field of view using the formula below, and the average value for the 10 fields of view is taken as the volume of the crystalline phosphate compound particles 32. Volume (%) of crystalline phosphate compound particles 32 = Number of pixels of crystalline phosphate compound particles 32 in the field of view ÷ Total number of pixels in the field of view × 100%

[0044] The average particle diameter D of the crystalline phosphate compound particles 32 is determined by measuring the longest diameter of 100 observable crystalline phosphate compound particles 32 identified by the above method within the field of view of the backscattered electron composition image obtained by the above method, and calculating the average value. The average particle size of the solid electrolyte particles 31 can be determined from the backscattered electron composition image obtained by the above method, similarly to the average particle size D of the crystalline phosphate compound particles 32.

[0045] (other substances) The solid electrolyte layer 3 may contain not only the solid electrolyte material of this embodiment but also other substances different from the solid electrolyte material. Examples of other substances include sintering aids. If unnecessary, the other substances may not be contained. When the laminate 4 is a sintered body, if other substances are used as materials for the solid electrolyte layer 3 together with the solid electrolyte material for manufacturing reasons such as improving productivity and yield when forming the solid electrolyte layer 3, the other substances in the solid electrolyte layer 3 may remain without being removed during the sintering process or the like for manufacturing the laminate 4.

[0046] Any sintering aid may be used as long as it has the effect of improving sinterability. Specific examples of the sintering aid include compounds containing lithium (Li), boron (B), zinc (Zn), bismuth (Bi), and the like, and active materials for forming the positive electrode layer 1 and / or the negative electrode layer 2.

[0047] "Positive electrode layer" 1, the positive electrode layer 1 includes, for example, a positive electrode current collector 1A and a positive electrode active material layer 1B. As shown in FIG. 1, the positive electrode active material layer 1B may be formed on both sides of the positive electrode current collector 1A, or may be formed on only one side.

[0048] (Positive electrode current collector) The positive electrode current collector 1A has high electrical conductivity. The positive electrode current collector 1A contains a conductive material such as a metal, such as silver, palladium, gold, platinum, aluminum, copper, nickel, stainless steel, or iron, or an alloy thereof, or a conductive resin. The positive electrode current collector 1A may contain a positive electrode active material such as a lithium vanadium compound (LiV2O5, Li3V2(PO4)3, or LiVOPO4). The positive electrode current collector 1A may be in the form of a powder, foil, punched, or expanded.

[0049] (Cathode active material layer) The positive electrode active material layer 1B contains a positive electrode active material and may also contain a conductive additive, a binder, and a solid electrolyte.

[0050] (Cathode active material) The positive electrode active material is not particularly limited as long as it can reversibly release and store lithium ions and desorb and insert lithium ions. For example, a positive electrode active material used in a known lithium ion secondary battery can be used.

[0051] The positive electrode active material is preferably one or more selected from the group consisting of composite transition metal oxides, transition metal fluorides, polyanions, transition metal sulfides, transition metal oxyfluorides, transition metal oxysulfides, and transition metal oxynitrides, and preferably contains a PO group-containing polyanion for the reasons described below. The PO4 group-containing polyanion contains PO4 tetrahedra in its structure. The solid electrolyte particles 31 having a NASICON structure in the solid electrolyte layer 3 also contain PO4 tetrahedra in their crystal structure. This results in a low-resistance interface between the positive electrode active material layer 1B of the positive electrode layer 1 and the solid electrolyte layer 3. As a result, Li ions move more smoothly in the all-solid-state battery 10, resulting in higher output.

[0052] Examples of the PO4-based polyanion include lithium vanadium compounds (Li3V2(PO4)3, LiVOPO4), olivine-type LiMPO4 (where M represents one or more elements selected from Co, Ni, Mn, Fe, Mg, V, Nb, Ti, Al, Zr), and the like.

[0053] Examples of the positive electrode active material include lithium cobaltate (LiCoO2), lithium nickelate (LiNiO2), lithium manganese spinel (LiMn2O4), and a composite metal oxide represented by the general formula: LiNi x Co y Mn z M a O2 (x + y + z + a = 1, 0 ≤ x ≤ 1, 0 ≤ y ≤ 1, 0 ≤ z ≤ 1, 0 ≤ a ≤ 1, M represents one or more elements selected from Al, Mg, Nb, Ti, Cu, Zn, Cr), lithium titanate (Li4Ti5O 12 ), LiNi<> x Co y Al z O2 (0.9 < x + y + z < 1.1), etc. may be used.

[0054] As the positive electrode active material, a positive electrode active material not containing lithium may be used. The positive electrode active material not containing lithium can be used by previously disposing a negative electrode active material doped with metallic lithium and / or lithium ions in the negative electrode layer 2 and starting the all-solid-state battery 10 from discharge. Examples of the positive electrode active material not containing lithium include metal oxides (MnO2, V2O5, etc.), metal sulfides (MoS2, etc.), fluorides (FeF3, VF3, etc.), and the like.

[0055] (Conductive aid) The conductive additive is not particularly limited as long as it improves the electronic conductivity in the positive electrode active material layer 1B, and known conductive additives can be used. Examples of the conductive additive include carbon-based materials such as graphite, carbon black, graphene, and carbon nanotubes; metals such as gold, platinum, silver, palladium, aluminum, copper, nickel, stainless steel, and iron; conductive oxides such as ITO; and mixtures thereof. The conductive additive may be in the form of powder or fiber.

[0056] (binding material) The binder bonds the positive electrode current collector 1A and the positive electrode active material layer 1B, the positive electrode active material layer 1B and the solid electrolyte layer 3, and the various materials constituting the positive electrode active material layer 1B. The binder can be used within a range that does not impair the function of the positive electrode active material layer 1B. If the binder is unnecessary, it does not have to be contained. The content of the binder in the positive electrode active material layer 1B is, for example, 0.5 to 30% by volume of the positive electrode active material layer. If the content of the binder is sufficiently low, the resistance of the positive electrode active material layer 1B becomes sufficiently low.

[0057] The binder may be any material capable of forming the above-described bond, such as fluororesins such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE). In addition to the above, binders may also be used, such as cellulose, styrene-butadiene rubber, ethylene-propylene rubber, polyimide resin, and polyamide-imide resin. Furthermore, conductive polymers with electronic conductivity or ionic conductive polymers with ionic conductivity may also be used as binders. Examples of conductive polymers with electronic conductivity include polyacetylene. In this case, the binder also functions as conductive additive particles, so no conductive additive is required. Examples of ionic conductive polymers with ionic conductivity include those that conduct lithium ions. Specifically, examples include composites of monomers of polymer compounds (polyether-based polymer compounds such as polyethylene oxide and polypropylene oxide, polyphosphazene, etc.) with lithium salts or lithium-based alkali metal salts such as LiClO4, LiBF4, and LiPF6. Examples of polymerization initiators used for compounding include photopolymerization initiators or thermal polymerization initiators that are compatible with the above-mentioned monomers. Required properties of the binder include oxidation / reduction resistance and good adhesiveness.

[0058] (solid electrolyte) The solid electrolyte contained in the positive electrode active material layer 1B improves the ionic conductivity in the positive electrode active material layer 1B. A known solid electrolyte can be used. The solid electrolyte may be the same as the solid electrolyte material used in the solid electrolyte layer 3 described above.

[0059] "Negative electrode layer" 1, the negative electrode layer 2 includes, for example, a negative electrode current collector 2A and a negative electrode active material layer 2B. As shown in FIG. 1, the negative electrode active material layer 2B may be formed on both sides of the negative electrode current collector 2A, or may be formed on only one side.

[0060] (Negative electrode current collector) The negative electrode current collector 2A is the same as the positive electrode current collector 1A. (Negative electrode active material layer) The negative electrode active material layer 2B contains a negative electrode active material and may contain a conductive additive, a binder, and a solid electrolyte.

[0061] (Negative electrode active material) The negative electrode active material is a compound capable of absorbing and releasing ions. The negative electrode active material is a compound that exhibits a lower potential than the positive electrode active material. The negative electrode active material may be the same material as the positive electrode active material. The negative electrode active material and the positive electrode active material to be used in the all-solid-state battery 10 are determined in consideration of the potential of the negative electrode active material and the potential of the positive electrode active material.

[0062] The negative electrode active material preferably contains a PO4 group-containing polyanion for the following reasons. The PO4 group-containing polyanion contains PO4 tetrahedra in its structure. This improves bonding at the interface between the negative electrode active material layer 2B of the negative electrode layer 2 and the solid electrolyte layer 3, whose crystalline structure contains PO4 tetrahedra, and also forms a low-resistance interface. As a result, Li ions move more smoothly in the all-solid-state battery 10, resulting in higher output.

[0063] (Conductive additive) The conductive additive improves the electronic conductivity of the negative electrode active material layer 2 B. The conductive additive may be the same material as that used for the positive electrode active material layer 1 B. (binding material) The binder bonds the negative electrode current collector 2A and the negative electrode active material layer 2B, the negative electrode active material layer 2B and the solid electrolyte layer 3, and the various materials constituting the negative electrode active material layer 2B. The binder may be the same as that used for the positive electrode active material layer 1B. The binder content may also be the same as that for the positive electrode active material layer 1B. If a binder is not necessary, it need not be contained.

[0064] (solid electrolyte) The solid electrolyte contained in the negative electrode active material layer 2B improves ion conduction within the negative electrode active material layer 2B. A known solid electrolyte can be used as the solid electrolyte. The solid electrolyte may be the same as the solid electrolyte material used in the solid electrolyte layer 3 described above.

[0065] At least one of the positive electrode active material layer 1B, the negative electrode active material layer 2B, and the solid electrolyte layer 3 of the all-solid-state battery 10 may contain a non-aqueous electrolyte solution, an ionic liquid, or a gel electrolyte.

[0066] [Manufacturing method for all-solid-state batteries] Next, a method for manufacturing the all-solid-state battery 10 will be described. First, the laminate 4 is produced. The laminate 4 can be produced using, for example, a co-firing method or a sequential firing method, and is preferably produced using the co-firing method. The co-firing method is a method in which the materials for forming each layer are stacked and then fired all at once to produce the laminate 4. The sequential firing method is a method in which firing is performed after each layer is formed. The co-firing method can produce the laminate 4 with fewer steps than the sequential firing method. Furthermore, the laminate 4 produced by the co-firing method is denser than the laminate 4 produced by the sequential firing method. Below, a method for producing the laminate 4 will be described using an example in which the laminate 4 is produced using the co-firing method.

[0067] First, the materials for the positive electrode current collector 1A, the positive electrode active material layer 1B, the solid electrolyte layer 3, the negative electrode active material layer 2B, and the negative electrode current collector 2A that constitute the laminate 4 are made into a paste to produce a paste corresponding to the material for each layer. The paste of the solid electrolyte layer 3 contains solid electrolyte particles 31 and crystalline phosphate compound particles 32, and is obtained by forming the above-mentioned solid electrolyte material containing the crystalline phosphate compound particles 32 at a predetermined volume ratio into a paste.

[0068] The method for forming each material into a paste is not particularly limited, and for example, a method of mixing powder of each material with a vehicle to obtain a paste can be used. Here, the term "vehicle" is a general term for a medium in a liquid phase. In this embodiment, the vehicle includes a solvent, a binder, and a plasticizer.

[0069] Next, lamination sheets are prepared corresponding to the respective layers constituting the laminate 4. The lamination sheets are obtained, for example, by applying a paste prepared for each material of the respective layers constituting the laminate 4 onto a substrate such as a PET (polyethylene terephthalate) film, drying as necessary, and then peeling off the substrate. The method for applying the paste to the substrate is not particularly limited, and known methods such as screen printing, coating, transfer, and doctor blade methods can be used.

[0070] Next, lamination sheets corresponding to each layer constituting the laminate 4 are stacked in the desired order and in the desired number of layers to produce green sheets that will become the laminate 4. When stacking the lamination sheets, alignment, cutting, etc. are performed as necessary. For example, when producing a parallel or series-parallel battery as the all-solid-state battery 10, alignment is performed so that the end face of the positive electrode current collector 1A and the end face of the negative electrode current collector 2A do not coincide, and the lamination sheets corresponding to each layer are stacked.

[0071] The green sheets that will become the laminate 4 may be produced by a method in which positive electrode units and negative electrode units are produced in advance and then laminated. The positive electrode unit is a sheet obtained by laminating a solid electrolyte layer 3, a positive electrode active material layer 1B, a positive electrode current collector 1A, and a lamination sheet that will become the positive electrode active material layer 1B, in this order. The negative electrode unit is a sheet obtained by laminating a solid electrolyte layer 3, a negative electrode active material layer 2B, a negative electrode current collector 2A, and a lamination sheet that will become the negative electrode active material layer 2B, in this order. The positive electrode unit and the negative electrode unit are alternately laminated so that the solid electrolyte layer 3 of the positive electrode unit faces the negative electrode active material layer 2B of the negative electrode unit, or so that the positive electrode active material layer 1B of the positive electrode unit faces the solid electrolyte layer 3 of the negative electrode unit.

[0072] Next, the produced green sheets are pressed together to increase the adhesion of each layer and form a laminate. Pressing can be performed, for example, by a mold press, hot isostatic pressing (WIP), cold isostatic pressing (CIP), isostatic pressing, etc. Pressing is preferably performed while heating. The heating temperature during pressing can be, for example, 40 to 95°C. Next, the laminate obtained after pressing is cut into chips using a dicing device. The resulting chips are then subjected to binder removal treatment and sintering. This results in a laminate 4 made of a sintered body.

[0073] The firing step can be carried out, for example, by placing the chip on a ceramic stand. The firing step can be, for example, a step of heating to 600 to 1000°C in a nitrogen atmosphere. The firing time can be, for example, 0.1 to 3 hours. The firing step can be carried out in a reducing atmosphere, and instead of a nitrogen atmosphere, it can be carried out in, for example, an argon atmosphere or a nitrogen-hydrogen mixed atmosphere.

[0074] The binder removal process may be carried out before the firing process as a separate process. If the binder removal process is carried out before the firing process, binder components such as solvents, binders, and plasticizers contained in the chips are thermally decomposed before the firing process. Therefore, the binder components can be prevented from suddenly decomposing during the firing process. The binder removal step is carried out, for example, by heating in a nitrogen atmosphere at a temperature of 300 to 800°C for 0.1 to 10 hours. The binder removal step can be carried out in a reducing atmosphere, and may be carried out in an argon atmosphere or a nitrogen / hydrogen mixed atmosphere instead of a nitrogen atmosphere.

[0075] The sintered laminate 4 (sintered body) may be placed in a cylindrical container together with an abrasive such as alumina and polished by barrel polishing. This allows the corners of the laminate 4 to be chamfered. The laminate 4 may also be polished by sandblasting. Sandblasting is preferred because it allows only specific portions of the surface of the laminate 4 to be polished.

[0076] Next, a first external terminal 5 and a second external terminal 6 are formed on the opposing side surfaces of the fabricated laminate 4. The first external terminal 5 and the second external terminal 6 can be formed using methods such as sputtering, dipping, screen printing, and spray coating. When the first external terminal 5 and the second external terminal 6 are formed only on predetermined portions, the side surfaces of the laminate 4 are partially masked with tape or the like before the above process is carried out. Through the above steps, the all-solid-state battery 10 can be manufactured.

[0077] The solid electrolyte material of this embodiment includes solid electrolyte particles 31 having a NASICON structure and crystalline phosphate compound particles 32 containing at least one element selected from the group consisting of Zr, Ti, Ge, Al, Hf, Ca, Ba, Sr, Sc, Y, and In, and the presence ratio of the crystalline phosphate compound particles is 10% by volume or more and 60% by volume or less. Therefore, the solid electrolyte material of this embodiment can form a solid electrolyte layer 3 with high ionic conductivity, as shown below.

[0078] Although the mechanism by which the solid electrolyte layer 3 with high ionic conductivity is formed is unclear, a charged double layer is typically formed at the interface between the insulator and the ion conductor. In this embodiment, the insulator corresponds to the crystalline phosphate compound particle 32, and the ion conductor corresponds to the solid electrolyte particle 31. The charged double layer increases the lattice defect concentration at the grain boundary between the crystalline phosphate compound particle 32 (insulator) and the solid electrolyte particle 31 (ion conductor). Furthermore, the concentration of intrinsic lattice defects present near the crystal surface of the solid electrolyte particle 31 is higher than that inside the crystal of the solid electrolyte particle 31 in thermal equilibrium. Furthermore, in ionic crystals, the formation energies of cation defects and anion defects are different, so either defect exists in excess. Furthermore, by creating defects with a different charge near the grain boundary of the ionic crystal to cancel the charge of the excess defect, the electrical conductivity near the grain boundary of the ionic crystal increases. This results in the formation of the high ion conductivity layer 33a of this embodiment. As a result, it is presumed that the solid electrolyte layer 3 containing the solid electrolyte material of this embodiment has high ionic conductivity.

[0079] The all-solid-state battery 10 of this embodiment includes a laminate 4 in which a positive electrode layer 1 and a negative electrode layer 2 are stacked with a solid electrolyte layer 3 interposed therebetween, and the solid electrolyte layer 3 includes the solid electrolytic material of this embodiment. Therefore, the all-solid-state battery 10 of this embodiment includes a solid electrolyte layer 3 that contains the above-mentioned solid electrolyte material and has high ionic conductivity, and therefore has a large discharge capacity at a high rate at room temperature.

[0080] In contrast, in an all-solid-state battery having a solid electrolyte layer containing a conventional solid electrolyte material, it has been difficult to increase the ionic conductivity of the solid electrolyte layer, as will be described below. Fig. 3 is a cross-sectional schematic diagram illustrating an example of a solid electrolyte layer of a conventional all-solid-state battery. The solid electrolyte layer shown in Fig. 3 contains a solid electrolyte material including solid electrolyte particles 31 with a NASICON structure. In Fig. 3, reference numeral 33 denotes grain boundaries between the solid electrolyte particles 31.

[0081] Solid electrolyte particles 31 with a NASICON structure have high ionic conductivity within the particles. However, in the solid electrolyte layer shown in Figure 3, the ionic conductivity of the grain boundaries 33 between the solid electrolyte particles 31 is lower than that within the solid electrolyte particles 31, so it was not possible to sufficiently increase the ionic conductivity of the solid electrolyte layer. As a result, all-solid-state batteries equipped with the solid electrolyte layer shown in Figure 3 had high internal resistance and small discharge capacity at high rates at room temperature.

[0082] The above describes the embodiments of the present invention in detail with reference to the drawings. However, each configuration and combination thereof in each embodiment is an example, and additions, omissions, substitutions, and other modifications of the configurations are possible within the scope that does not deviate from the spirit of the present invention. [Example]

[0083] "Example 1-1" (solid electrolyte material) Rhombohedral LiZr2(PO4)3 was prepared by a wet process, triclinic LiZr2(PO4)3 was prepared by a flux process, and monoclinic LiZr2(PO4)3 was prepared by a solid-state reaction method. X-ray diffraction measurements were performed on each of the obtained LiZr2(PO4)3 crystal phases using an X-ray diffractometer (PANlytical X'pert PRO) using CuKα radiation, and it was confirmed that they were the desired crystal phases. Thereafter, rhombohedral LiZr2(PO4)3 and triclinic LiZr2(PO4)3 were weighed and mixed to obtain the crystal phase ratio shown in Table 1, thereby obtaining solid electrolyte particles 31. The obtained solid electrolyte particles 31 were milled for a predetermined time and sieved to obtain an average particle size of 1 μm.

[0084] ZrP2O7 was prepared as the crystalline phosphate compound particles 32. The crystalline phosphate compound particles 32 were milled for a predetermined time and sieved to have an average particle diameter D of 0.1 μm. The average particle diameters of the solid electrolyte particles 31 and the crystalline phosphate compound particles 32 were determined by observing 100 particles using a scanning electron microscope (SEM), measuring their longest diameters, and calculating the average value according to the above-mentioned method.

[0085] Thereafter, the volume ratio of the solid electrolyte particles 31 to the crystalline phosphate compound particles 32 was adjusted, and the solid electrolyte particles 31 and the crystalline phosphate compound particles 32 were mixed to obtain the solid electrolyte material of Example 1-1 in which the presence ratio of the crystalline phosphate compound particles 32 was 30% by volume.

[0086] The solid electrolyte material of Example 1-1 thus obtained was subjected to X-ray diffraction measurement using an X-ray diffractometer (PANlytical X'pert PRO) using CuKα radiation under the conditions of a tube voltage of 45 kV, a tube current of 40 mA, a measurement range of 2θ = 10 to 70°, a sampling width of 0.0167°, and a scanning speed of 0.02° / s. When performing X-ray diffraction measurement of the solid electrolyte material, the background diffraction intensity was measured using only the glass sample holder, and the diffraction intensity of the sample was corrected by subtracting the background diffraction intensity from the diffraction intensity obtained by measuring a sample taken from the solid electrolyte material. The results are shown in Figure 4.

[0087] 4 is a chart showing (A) the results of X-ray diffraction measurement of the solid electrolyte material of Example 1-1, (B) the results of simulation of X-ray diffraction measurement of ZrP2O7, (C) the results of simulation of X-ray diffraction measurement of rhombohedral crystals of LiZr2(PO4)3, (D) the results of simulation of X-ray diffraction measurement of triclinic crystals of LiZr2(PO4)3, and (E) the results of simulation of X-ray diffraction measurement of monoclinic crystals of LiZr2(PO4)3. In FIG. 4, the horizontal axis represents the diffraction angle 2θ (°), and the vertical axis represents the X-ray peak intensity (au).

[0088] The simulation results (B) to (E) shown in FIG. 4 were calculated by performing a simulation using the Rietveld method based on the crystallographic information file of each crystalline phase.

[0089] Using the result (A) of X-ray diffraction measurement of the solid electrolyte material of Example 1-1 shown in FIG. 4, the proportion of the crystalline phase of the solid electrolyte particles 31 (LiZr(PO)) contained in the solid electrolyte material was determined by the method shown below. That is, for the chart shown by (A) in FIG. 4, the crystalline phase of LiZr2(PO4)3 was identified using the peak (near 2θ=31.5°) derived from the (116) plane of the rhombohedral crystal in the chart shown by (C), the peak (near 2θ=28.0°) derived from the (20-2) plane of the triclinic crystal in the chart shown by (D), and the peak (near 2θ=15.7°) derived from the (110) plane of the monoclinic crystal in the chart shown by (E).

[0090] Then, when the peak intensity of the rhombohedral crystal was taken as 100, the peak intensity of the triclinic crystal was corrected to be 100 relative to the peak intensity of the rhombohedral crystal by multiplying the peak intensity of the triclinic crystal by 1.56 to calculate the relative value of the peak intensity of the triclinic crystal to the peak intensity of the rhombohedral crystal. Similarly, when the peak intensity of the rhombohedral crystal was taken as 100, the peak intensity of the monoclinic crystal was corrected to be 100 relative to the peak intensity of the rhombohedral crystal by multiplying the peak intensity of the monoclinic crystal by 2.08 to calculate the relative value of the peak intensity of the monoclinic crystal to the peak intensity of the rhombohedral crystal. Using the results, the proportion of each crystalline phase was calculated using the following formula. The proportion of each crystalline phase was calculated by rounding off the value to one decimal place.

[0091] Rhombohedral ratio (%) = rhombohedral peak intensity / (rhombohedral peak intensity + relative value of triclinic peak intensity + relative value of monoclinic peak intensity) × 100 Triclinic ratio (%) = relative value of triclinic peak intensity / (rhombohedral peak intensity + relative value of triclinic peak intensity + relative value of monoclinic peak intensity) × 100 Monoclinic ratio (%) = relative value of monoclinic peak intensity / (rhombohedral peak intensity + relative value of triclinic peak intensity + relative value of monoclinic peak intensity) × 100

[0092] As a result, the crystalline phase ratios of the solid electrolyte particles 31 (LiZr2(PO4)3) contained in the solid electrolyte material of Example 1-1 were 65% rhombohedral, 35% triclinic, and 0% monoclinic, and it was confirmed that the solid electrolyte particles 31 had two crystalline phases, rhombohedral and triclinic.

[0093] 4, the chart showing the results (A) of X-ray diffraction measurement of the solid electrolyte material of Example 1-1 did not show any broad peaks indicating an amorphous phase. This confirmed that the solid electrolyte material of Example 1-1 was composed only of crystalline compounds, and that the crystalline phosphate compound particles 32 (ZrP2O7) had crystallinity.

[0094] (All-solid-state battery) To 100 parts of the solid electrolyte material of Example 1-1, 100 parts of ethanol and 200 parts of toluene as solvents were added and mixed using a ball mill. Further, 16 parts of a polyvinyl butyral binder as a binding agent and 4.8 parts of benzyl butyl phthalate as a plasticizer were added and mixed to form a paste for the solid electrolyte layer 3. Next, the paste of the solid electrolyte layer 3 was applied onto a PET film substrate by a doctor blade method, dried, and formed into a sheet to obtain a solid electrolyte layer sheet in which the lamination sheet of the solid electrolyte layer 3 was integrated onto the substrate. The thickness of the solid electrolyte layer 3 was 15 μm.

[0095] Next, a paste for a positive electrode active material layer and a paste for a negative electrode active material layer were prepared by adding 15 parts of ethyl cellulose as a binder and 65 parts of dihydroterpineol as a solvent to 100 parts of Li3V2(PO4)3 powder, and mixing and dispersing the mixture.

[0096] Next, pastes for the positive electrode current collector and the negative electrode current collector were prepared by mixing copper powder as a conductive material and Li3V2(PO4)3 as an active material in a volume ratio of 80:20 to 100 parts of the powder, adding 10 parts of ethyl cellulose as a binder and 50 parts of dihydroterpineol as a solvent, and mixing and dispersing the mixture.

[0097] Next, a positive electrode unit and a negative electrode unit were fabricated by the following method. First, a cathode active material paste was printed onto the solid electrolyte layer sheet using screen printing to a thickness of 5 μm. Next, the printed cathode active material paste was dried at 80°C for 5 minutes. Then, a cathode current collector paste was printed onto the dried cathode active material paste using screen printing to a thickness of 5 μm. Next, the printed cathode current collector paste was dried at 80°C for 5 minutes. Then, a cathode active material paste was printed again onto the dried cathode current collector paste using screen printing to a thickness of 5 μm and dried. Thereafter, the substrate made of PET film was peeled off from the solid electrolyte layer sheet.

[0098] In this way, a positive electrode unit was obtained in which the positive electrode active material layer 1B, the positive electrode current collector 1A, and the lamination sheet that would become the positive electrode active material layer 1B were laminated in this order on the main surface of the lamination sheet for the solid electrolyte layer 3. Furthermore, using the same method as for the positive electrode unit, a negative electrode unit was obtained in which a sheet for lamination that would become the negative electrode active material layer 2B, the negative electrode current collector 2A, and a sheet for lamination that would become the negative electrode active material layer 2B were laminated in this order on the main surface of the sheet for lamination of the solid electrolyte layer 3.

[0099] Thereafter, five lamination sheets for the solid electrolyte layer 3, which were obtained by peeling the substrate from the solid electrolyte layer sheets, were stacked, and eight positive electrode units and eight negative electrode units were stacked alternately on top of them with the lamination sheets for the solid electrolyte layer 3 interposed therebetween. At this time, the positive electrode units and negative electrode units were stacked with a shift so that the positive electrode current collector 1A of the positive electrode unit extended only on one end surface, and the negative electrode current collector 2A of the negative electrode unit extended only on the opposite end surface. Thereafter, six more lamination sheets for the solid electrolyte layer 3 were stacked on top of the stack of positive electrode units and negative electrode units.

[0100] The laminated chips were then formed by thermocompression bonding and cut to produce laminated chips. The laminated chips were then co-fired to obtain laminate 4. The co-firing step involved heating the chips in a nitrogen atmosphere at a rate of 200°C / hour up to a firing temperature of 800°C, holding the chips at 800°C for 2 hours, and then allowing the chips to cool naturally.

[0101] Thereafter, the fired laminate 4 was cut parallel to the lamination direction using a cross-section polisher (CP) to expose the cross section of the solid electrolyte layer 3. The exposed cross section was then analyzed using SEM and EDS according to the above-described method to determine the abundance of the crystalline phosphate compound particles 32 contained in the solid electrolyte material forming the solid electrolyte layer 3 and the average particle diameters of the crystalline phosphate compound particles 32 and the solid electrolyte particles 31.

[0102] As a result, the proportion of the crystalline phosphate compound particles 32 contained in the solid electrolyte material forming the solid electrolyte layer 3 was 30% by volume, which was not significantly different from the proportion of the crystalline phosphate compound particles 32 contained in the solid electrolyte material used to manufacture the solid electrolyte layer 3. The average particle size of the solid electrolyte particles 31 was 1 μm, which was not significantly different from the average particle size of the solid electrolyte particles 31 in the solid electrolyte material used to manufacture the solid electrolyte layer 3. Furthermore, the average particle diameter D of the crystalline phosphate compound particles 32 was 0.1 μm, which was not significantly different from the average particle diameter D of the crystalline phosphate compound particles 32 in the solid electrolyte material used to manufacture the solid electrolyte layer 3.

[0103] Furthermore, composition analysis was performed using the above-mentioned SEM and EDS method, and it was confirmed from the ratio of Zr to P that the solid electrolyte particles 31 were LiZr2(PO4)3 and the crystalline phosphate compound particles 32 were ZrP2O7.

[0104] Furthermore, a cross section of the laminate 4 obtained in the same manner as the cross section analyzed using SEM and EDS was subjected to composition analysis of a micro-area using a STEM-EELS method, which combines a scanning transmission electron microscope (STEM) and electron energy loss spectroscopy (EELS), to confirm the compositions of the solid electrolyte particles 31 and the crystalline phosphate compound particles 32. From the results, the composition of the solid electrolyte particles 31 observed in the cross section was calculated, and it was confirmed that the solid electrolyte particles 31 were LiZr2(PO4)3. Furthermore, the composition of the crystalline phosphate compound particles 32 observed in the cross section was calculated, and it was confirmed that the crystalline phosphate compound particles 32 were ZrP2O7 and did not contain Li.

[0105] Furthermore, the sintered laminate 4 was dry-polished in the lamination direction, and the solid electrolyte material forming the solid electrolyte layer 3 was subjected to X-ray diffraction measurement in the same manner as the solid electrolyte material of Example 1-1 used in producing the solid electrolyte layer 3. As a result, similarly to the solid electrolyte material of Example 1-1, the solid electrolyte material forming the solid electrolyte layer 3 did not show any broad peaks indicating an amorphous (non-crystalline) phase, and it was confirmed that it consisted only of crystalline compounds, and that the crystalline phosphate compound particles 32 (ZrP2O7) had crystallinity. Furthermore, there was no significant change in the proportion of the crystalline phase of the solid electrolyte material (LiZr2(PO4)3) forming the solid electrolyte layer 3. As with the solid electrolyte material of Example 1-1, the rhombohedral fraction was 65%, the triclinic fraction was 35%, and the monoclinic fraction was 0%, confirming that the solid electrolyte particles 31 had two crystalline phases, rhombohedral and triclinic.

[0106] Thereafter, a first external terminal 5 and a second external terminal 6 were formed on the side surfaces of the laminate 4 (sintered body) by a known method, the positive electrode layer 1 and the first external terminal 5 were connected, and the negative electrode layer 2 and the second external terminal 6 were connected, thereby producing the all-solid-state battery 10 shown in FIG. 1 .

[0107] (Battery evaluation) The charge / discharge characteristics of the obtained all-solid-state battery 10 were evaluated using the following method. The charge / discharge current was expressed as a C rate. The C rate is expressed as nC (μA) (n is a number) and refers to the current value at which the nominal capacity (μAh) can be charged / discharged at 1 / n (h). For example, 1C is the current value at which the nominal capacity can be charged / discharged in 1 hour. 2C is the current value at which the nominal capacity can be charged / discharged in 0.5 hours. Therefore, for example, in the case of an all-solid-state battery with a nominal capacity of 60 μAh, the current at 0.2C is 12 μA (calculation formula: 60 μAh × 0.2 = 12 μA), the current at 0.5C is 30 μA, and the current at 1C is 60 μA.

[0108] The all-solid-state battery 10 obtained in Example 1-1 was subjected to constant current charging (CC charging) at a constant current of 0.2 C rate in an environment of 25° C. until the battery voltage reached 1.6 V, and then discharged (CC discharging) at a constant current of 0.2 C rate until the battery voltage reached 0 V, and the discharge capacity (μAh) at that time was measured. The results are shown in Table 1.

[0109] "Examples 1-2 to 1-3" The all-solid-state battery 10 obtained in Example 1-1 was subjected to constant current charging (CC charging) at a constant current of 0.2 C rate in an environment of 25°C until the battery voltage reached 1.6 V, as in Example 1-1. Thereafter, the battery was discharged at a constant current of 0.5 C rate or 1 C rate until the battery voltage reached 0 V (CC discharging), and the discharge capacity (μAh) at that time was measured. The results are shown in Table 1.

[0110] "Examples 1-4 to 1-42, Comparative Examples 1-1 to 1-15" A laminate 4 was produced in the same manner as in Example 1-1, except that the crystalline phosphate compound particles 32 had the composition shown in Table 1 or Table 2, and the solid electrolyte particles 31 had the composition shown in Table 1 or Table 2.

[0111] For the laminates 4 of Examples 1-4 to 1-42 and Comparative Examples 1-1 to 1-15, the proportion of crystalline phosphate compound particles 32 contained in the solid electrolyte material forming the solid electrolyte layer 3 was confirmed in the same manner as in Example 1-1. The result was 30% by volume. Furthermore, measurements were performed in the same manner as in Example 1-1, and the average particle diameter D of the solid electrolyte particles 31 was 1 μm, and the average particle diameter D of the crystalline phosphate compound particles 32 was 0.1 μm. Furthermore, the compositions of the solid electrolyte particles 31 and the crystalline phosphate compound particles 32 were measured in the same manner as in Example 1-1, and it was confirmed that they were the compositions shown in Table 1 or Table 2. The proportion of the crystalline phase in the solid electrolyte particles 31 was measured in the same manner as in Example 1-1. The results are shown in Table 1 or Table 2.

[0112] Furthermore, the solid electrolyte materials forming the solid electrolyte layers 3 of the laminates 4 of Examples 1-4 to 1-42 and Comparative Examples 1-1 to 1-12 were subjected to X-ray diffraction measurement in the same manner as in Example 1-1. As a result, it was confirmed that the crystalline phosphate compound particles 32 contained in the solid electrolyte materials were crystalline. For Comparative Examples 1-13 to 1-15, a broad peak indicating an amorphous phase was observed in the chart showing the results of X-ray diffraction measurement of the solid electrolyte material, confirming that the phosphate compound particles were amorphous.

[0113] Thereafter, all-solid-state batteries 10 were fabricated in the same manner as in Example 1-1 using the laminates 4 of Examples 1-4 to 1-42 and Comparative Examples 1-1 to 1-15, respectively. The obtained all-solid-state battery 10 was subjected to constant current charging (CC charging) in the same manner as in Example 1-1, and then discharged (CC discharging) at a constant current at a discharge rate (discharge current) shown in Table 1 or Table 2 until the battery voltage reached 0 V, and the discharge capacity (μAh) at that time was measured. The results are shown in Table 1 or Table 2.

[0114] [Table 1]

[0115] [Table 2]

[0116] As shown in Tables 1 and 2, the all-solid-state batteries of Examples 1-1 to 1-42 had larger discharge capacities when measured under the same conditions (discharge rate and current value) than the all-solid-state batteries of Comparative Examples 1-1 to 1-3 and 1-13 to 1-15. This is presumably because the all-solid-state batteries of Examples 1-1 to 1-42 were provided with a solid electrolyte layer 3 containing crystalline phosphate compound particles 32, and therefore had high ionic conductivity of the solid electrolyte layer 3. Furthermore, the all-solid-state batteries of Examples 1-1 to 1-9 had larger discharge capacities when measured under the same conditions (discharge rate and current value) than the all-solid-state batteries of Comparative Examples 1-4 to 1-12. This is presumably due to the high ionic conductivity of the solid electrolyte layer 3, which includes solid electrolyte particles 31 having a NASICON structure and two or more crystal phases selected from the group consisting of rhombohedral, triclinic, and monoclinic.

[0117] "Examples 2-1 to 2-11, Comparative Examples 2-1 to 2-4" An all-solid-state battery 10 was fabricated in the same manner as in Example 1-1, except that the abundance ratio of the crystalline phosphate compound particles 32 in the solid electrolyte material used to manufacture the solid electrolyte layer 3 was changed to the abundance ratio of the crystalline phosphate compound particles 32 contained in the solid electrolyte layer 3 shown in Table 3. The discharge capacity (μAh) of the obtained all-solid-state battery 10 was measured in the same manner as in Example 1-1. The results are shown in Table 3.

[0118] [Table 3]

[0119] The all-solid-state batteries of Example 1-1 shown in Table 1 and Examples 2-1 to 2-11 shown in Table 3, which have a solid electrolyte layer 3 with a crystalline phosphate compound particle content of 10% by volume or more and 60% by volume or less, had larger discharge capacities than the all-solid-state batteries of Comparative Examples 2-1 to 2-2, which have a solid electrolyte layer 3 with a crystalline phosphate compound particle content of less than 10% by volume, and the all-solid-state batteries of Comparative Examples 2-3 to 2-4, which have a solid electrolyte layer 3 with a crystalline phosphate compound particle content of more than 60% by volume.

[0120] In particular, as shown in Tables 1 and 3, the all-solid-state batteries of Examples 1-1 and 2-2 to 2-9, which had a solid electrolyte layer 3 with a content of crystalline phosphate compound particles of 15% by volume or more and 50% by volume or less, had a large discharge capacity of 50 μAh or more. Furthermore, the all-solid-state batteries of Examples 1-1 and 2-4 to 2-8, which had a solid electrolyte layer 3 with a content of crystalline phosphate compound particles of 25% by volume or more and 45% by volume or less, had a large discharge capacity of 55 μAh or more.

[0121] "Examples 3-1 to 3-11" An all-solid-state battery 10 was fabricated in the same manner as in Example 1-1, except that the average particle diameter D of the crystalline phosphate compound particles 32 in the solid electrolyte material used to produce the solid electrolyte layer 3 was changed to the average particle diameter D of the crystalline phosphate compound particles 32 contained in the solid electrolyte layer 3 shown in Table 4. The discharge capacity (μAh) of the obtained all-solid-state battery 10 was measured in the same manner as in Example 1-1. The results are shown in Table 4.

[0122] [Table 4]

[0123] As shown in Table 4, the all-solid-state batteries of Examples 3-1 to 3-11, which had a solid electrolyte layer 3 in which the average particle diameter D of the crystalline phosphate compound particles 32 was 0.01 μm to 10 μm, had larger discharge capacities than the all-solid-state battery of Comparative Example 1-1, which had a solid electrolyte layer 3 that did not contain the crystalline phosphate compound particles 32. In particular, the all-solid-state batteries of Example 1-1 shown in Table 1 and Examples 3-1 to 3-9 shown in Table 4, which include a solid electrolyte layer 3 in which the average particle diameter D of the crystalline phosphate compound particles 32 is 0.01 μm to 3 μm, had a large discharge capacity of 50 μAh or more. Furthermore, the all-solid-state batteries of Example 1-1 shown in Table 1 and Examples 3-2 to 3-7 shown in Table 4, which include a solid electrolyte layer 3 in which the average particle diameter D of the crystalline phosphate compound particles 32 is 0.05 μm to 1.5 μm, had a large discharge capacity of 55 μAh or more. [Explanation of symbols]

[0124] 1...positive electrode layer, 1A...positive electrode current collector, 1B...positive electrode active material layer, 2...negative electrode layer, 2A...negative electrode current collector, 2B...negative electrode active material layer, 3...solid electrolyte layer, 4...laminated body, 5...first external terminal, 6...second external terminal, 10...all-solid-state battery, 31...solid electrolyte particles, 32...crystalline phosphate compound particles, 33...grain boundary, 33a...high ion conductive layer.

Claims

1. solid electrolyte particles having a NASICON structure and having two or more crystal phases selected from the group consisting of rhombohedral, triclinic, and monoclinic; and crystalline phosphate compound particles containing at least one element selected from the group consisting of Zr, Ti, Ge, Al, Hf, Ca, Ba, Sr, Sc, Y, and In, and having a crystal structure different from that of the solid electrolyte particles, A solid electrolyte material characterized in that the content of the crystalline phosphate compound particles is 10% by volume or more and 60% by volume or less.

2. 2. The solid electrolyte material according to claim 1, wherein the crystalline phosphate compound particles have an average particle diameter D of 0.01 μm to 10 μm.

3. a laminate in which a positive electrode layer and a negative electrode layer are stacked with a solid electrolyte layer interposed therebetween, An all-solid-state battery, wherein the solid electrolyte layer comprises the solid electrolyte material according to claim 1 or 2.

4. The all-solid-state battery according to claim 3 , wherein the laminate is a sintered body.

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