Solid electrolyte layer, all-solid-state secondary battery, and method for manufacturing the same

Abstract

A solid electrolyte layer according to the present invention comprises a solid electrolyte and a compound represented by compositional formula MxZr2(PO4)y, where M is at least one selected from the group consisting of Na, K, Mg, Ca, Sr, Ba, Cu, Zn, and Ni, x satisfies 0＜x≤2.5, and y satisfies 2.7≤y≤3.5.

Description

Technical Field

[0001] The present invention relates to a solid electrolyte layer, an all-solid-state secondary battery, and methods for manufacturing them. This application claims priority based on Japanese Patent Application No. 2019-167196 filed in Japan on September 13, 2019, the content of which is incorporated herein by reference.

Background Art

[0002] In recent years, batteries have been used in various applications. Batteries are used, for example, in mobile batteries and the like, and there is a demand for miniaturization, weight reduction, and improvement in reliability. Batteries using an electrolytic solution have problems such as liquid leakage and depletion of the liquid. Therefore, attention has been focused on all-solid-state secondary batteries using a solid electrolyte.

[0003] On the other hand, all-solid-state secondary batteries have a problem in that their output is smaller compared to batteries using an electrolytic solution. Therefore, it is required to increase the ionic conductivity of the solid electrolyte constituting the all-solid-state secondary battery.

[0004] For example, Patent Document 1 describes an all-solid-state secondary battery using oxide-based Li 1.3 Al 0.3 Ti 1.7 (PO 4 ) 3 as a solid electrolyte. Further, Patent Document 2 describes an all-solid-state secondary battery using LiZr 2 (PO 4 ) 3 containing Zr, which is excellent in reduction resistance, as a solid electrolyte. Furthermore, Patent Document 3 describes an all-solid-state secondary battery using Li 1.55 Al 0.2 Zr 1.7 Y0.1Si 0.25 P 2.75 O 12 which is excellent in reduction resistance and has a rhombohedral crystal structure, as a solid electrolyte.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0006] Various solid electrolytes are used in all-solid-state secondary batteries. However, further improvement in ionic conductivity is required, and a solid electrolyte layer with better ionic conductivity is desired.

[0007] The present invention has been made in view of the above circumstances, and an object thereof is to provide a solid electrolyte layer and an all-solid-state secondary battery capable of improving ionic conductivity. Another object is to provide a method for manufacturing a solid electrolyte layer with excellent ionic conductivity and a method for manufacturing an all-solid-state secondary battery.

Means for Solving the Problems

[0008] The inventors have found that when a predetermined compound is added to a solid electrolyte layer containing a solid electrolyte, the ionic conductivity is improved. That is, in order to solve the above problems, the following means are provided.

[0009] (1) The solid electrolyte layer according to the first aspect includes a solid electrolyte and a compound represented by the composition formula M x Zr 2 (PO 4 ) y In the composition formula, M is at least one selected from the group consisting of Na, K, Mg, Ca, Sr, Ba, Cu, Zn, and Ni, x satisfies 0 < x ≦ 2.5, and y satisfies 2.7 ≦ y ≦ 3.5.

[0010] (2) In the solid electrolyte layer according to the above aspect, the abundance ratio of the compound may be 0.1% by volume or more and less than 100% by volume.

[0011] (3) In the solid electrolyte layer according to the above aspect, the average particle diameter of the compound may be 0.01 μm or more and 5 μm or less.

[0012] (4) In the solid electrolyte layer according to the above aspect, the proportion of the part having a rhombohedral crystal structure constituting the solid electrolyte may be 50% by volume or more.

[0013] (5) In the solid electrolyte layer according to the above aspect, the solid electrolyte and the compound may include the same crystal structure.

[0014] (6) In the solid electrolyte layer according to the above aspect, the crystal structure of the compound may include rhombohedrons.

[0015] (7) In the solid electrolyte layer according to the above aspect, in the powder X-ray diffraction pattern obtained by performing X-ray diffraction measurement using CuKα rays, the peak intensity P1 of the peak observed in the range of 19° ≤ 2θ ≤ 22° and the peak intensity P2 of the peak observed in the range of 23° ≤ 2θ ≤ 26° may satisfy the relationship of 0.5 ≤ P2 / P1 ≤ 3.0.

[0016] (8) The all-solid-state secondary battery according to the second aspect includes the solid electrolyte layer according to the above aspect, and a first electrode and a second electrode sandwiching the solid electrolyte layer.

[0017] (9) The method for manufacturing a solid electrolyte layer according to the third aspect includes a step of mixing a solid electrolyte and a compound represented by the composition formula M x Zr 2 (PO 4 ) y and a step of sintering the mixed mixture in a temperature range of 500°C or more and 1000°C or less. In the composition formula, M is at least one selected from the group consisting of Na, K, Mg, Ca, Sr, Ba, Cu, Zn, and Ni, x satisfies 0 < x ≤ 2.5, and y satisfies 2.7 ≤ y ≤ 3.5.

[0018] (10) The manufacturing method of the all-solid-state secondary battery according to the fourth aspect is a manufacturing method of an all-solid-state battery including a solid electrolyte layer manufactured by the manufacturing method of the solid electrolyte layer according to the above aspect, the method comprising: forming a first electrode at a position facing one surface of the solid electrolyte layer; and forming a second electrode at a position facing the other surface of the solid electrolyte layer.

Advantages of the Invention

[0019] According to the solid electrolyte layer and the all-solid-state secondary battery according to the above aspect, the ionic conductivity can be enhanced. Further, according to the manufacturing method of the solid electrolyte layer and the manufacturing method of the all-solid-state secondary battery according to the above aspect, a solid electrolyte layer and an all-solid-state secondary battery excellent in ionic conductivity can be obtained.

Brief Description of the Drawings

[0020]

Figure 1

Modes for Carrying Out the Invention

[0021] Hereinafter, the present invention will be described in detail with appropriate reference to the drawings. The drawings used in the following description may show, for the sake of clarity, the characteristic parts enlarged for the sake of convenience, and the dimensional ratios of the respective components may be different from the actual ones. The materials, dimensions, etc. exemplified in the following description are merely examples, and the present invention is not limited thereto, and can be appropriately modified and implemented without changing the gist thereof.

[0022] [All-Solid-State Secondary Battery] FIG. 1 is an enlarged cross-sectional schematic view of a main part of an all-solid-state secondary battery according to the first embodiment. As shown in FIG. 1, the all-solid-state secondary battery 10 includes a laminate 4 having a positive electrode layer 1, a negative electrode layer 2, and a solid electrolyte layer 3. The positive electrode layer 1 is an example of a first electrode layer (first electrode), and the negative electrode layer 2 is an example of a second electrode layer (second electrode). Either the first electrode layer or the second electrode layer functions as a positive electrode, and the other functions as a negative electrode. The positive and negative of the electrode layer change depending on which polarity is connected to the external terminal.

[0023] The positive electrode layers 1 are each connected to a first external terminal 5, and the negative electrode layers 2 are each connected to a second external terminal 6. The first external terminal 5 and the second external terminal 6 are electrical contacts with the outside.

[0024] (Laminate) The laminate 4 has a positive electrode layer 1, a negative electrode layer 2, and a solid electrolyte layer 3. In the laminate 4, they are alternately laminated via the solid electrolyte layer 3. That is, the positive electrode layer 1 is formed at a position facing one surface (main surface) of the solid electrolyte layer 3, and the negative electrode layer 2 is formed at a position facing the other surface (main surface) opposite to the one surface. Charging and discharging of the all-solid-state secondary battery 10 are performed by the transfer of lithium ions between the positive electrode layer 1 and the negative electrode layer 2 via the solid electrolyte layer 3.

[0025] "Solid electrolyte layer" The solid electrolyte layer 3 contains a solid electrolyte and a predetermined compound (hereinafter referred to as MZP). The solid electrolyte and MZP are, for example, mixed in the solid electrolyte layer 3.

[0026] The solid electrolyte is a substance (e.g., particles) that can move ions by an externally applied electric field. For example, lithium ions move within the solid electrolyte by an externally applied electric field.

[0027] The solid electrolyte contains, for example, lithium. The solid electrolyte may be, for example, any of an oxide-based material and a sulfide-based material. The solid electrolyte may be, for example, any of a perovskite-type compound, a silicon-type compound, a garnet-type compound, a NASICON-type compound, a thiolsilicon-type compound, a glass compound, and a phosphate compound. La 0.5 Li 0.5 TiO 3 is an example of a perovskite-type compound. Li 14 Zn(GeO 4 ) 4 is an example of a silicon-type compound. Li 7 La 3 Zr 2 O 12 is an example of a garnet-type compound. LiZr 2 (PO 4 ) 3 , Li 1.3 Al 0.3 Ti 1.7 (PO 4 ) 3 , Li 1.5 Al 0.5 Ge 1.5 (PO 4 ) 3 , Li 1.55 Al 0.2 Zr 1.7 Si 0.25 P 9.75 O 12 , Li 1.4 Na 0.1 Zr 1.5 Al 0.5 (PO 4 ) 3 , Li 1.4 Ca 0.25 Er 0.3 Zr 1.7 (PO 4 ) 3.2 , Li 1.4 Ca 0.25 Yb 0.3 Zr 1.7 (PO 4 ) 3.2 is an example of a NASICON-type compound. Li 3.25 Ge 0.25 P 0.75 S 4 , Li 3 PS4 is an example of a thiorichon-type compound. Li 2 S-P 2 S 5 、Li 2 O-V 2 O 5 -SiO 2 is an example of a glass compound. Li 3 PO 4 、Li 3.5 Si 0.5 P 0.5 O 4 、Li 2.9 PO 3.3 N 0.46 is an example of a phosphate compound. The solid electrolyte may contain one or more of these compounds.

[0028] The solid electrolyte is, for example, a NASICON-type compound and has, for example, a rhombohedral crystal structure. In the solid electrolyte, the proportion of the portion having a rhombohedral crystal structure is preferably 50% by volume or more and 98% by volume or less, and more preferably 50% by volume or more and 95% by volume or less.

[0029] The shape of the solid electrolyte is not particularly limited. The shape of the solid electrolyte is, for example, spherical, ellipsoidal, needle-like, plate-like, flaky, tubular, wire-like, rod-like, or amorphous. The particle size of the solid electrolyte is, for example, 0.1 μm or more and 10 μm or less, and may also be 0.3 μm or more and 9 μm or less. The particle size of the particles is determined from the measured value (D50) obtained by measuring the particle size distribution. D50 is the diameter of the particles at which the integrated value in the distribution curve obtained by measuring the particle size distribution is 50%. The particle size distribution of the particles is measured, for example, by a particle size distribution measuring device using the laser diffraction / scattering method (Microtrac method).

[0030] MZP is a compound represented by the composition formula MxZr 2 (PO) 4 . M is at least one selected from the group consisting of Na, K, Mg, Ca, Sr, Ba, Cu, Zn, and Ni, x satisfies 0 < x ≦ 2.5, and y satisfies 2.7 ≦ y ≦ 3.5.

[0031] MZP preferably includes, for example, the same crystal structure as that of the solid electrolyte. Further, the crystal structure of MZP preferably includes, for example, rhombohedral crystals. If the crystal structures of MZP and the solid electrolyte are the same, the path through which ions are conducted is less likely to be disrupted, and the ionic conductivity is enhanced. Also, rhombohedral crystals can three-dimensionally secure the path through which ions are conducted.

[0032] MZP exists, for example, in a particulate form within the solid electrolyte layer 3. The shape of MZP is not particularly limited. The shape of MZP is, for example, spherical, ellipsoidal, needle-like, plate-like, scaly, tube-like, wire-like, rod-like, or amorphous. The particle size of MZP is, for example, 0.01 μm or more and 5 μm or less, preferably 0.3 μm or more and 3 μm or less.

[0033] The abundance ratio of MZP with respect to the solid electrolyte is, for example, 0.1% by volume or more and less than 100% by volume, preferably 30% by volume or more and 96% by volume or less, more preferably 40% by volume or more and 70% by volume or less.

[0034] The detection of the abundance ratio of MZP and the solid electrolyte in the solid electrolyte layer 3 is performed, for example, using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). First, elemental mapping of the cross-section obtained by cutting the solid electrolyte layer 3 is performed using LA-ICP. The elemental mapping is performed, for example, for Li, M (where M is at least one selected from the group consisting of Na, K, Mg, Ca, Sr, Ba, Cu, Zn, and Ni), Zr, P, and O, respectively. Then, the composition of each particle confirmed on the cross-section is calculated from the mapping results, and it is determined whether each particle is a solid electrolyte or MZP. Then, the ratio of the area of the solid electrolyte to the area of MZP on the cross-section is obtained. The same operation is performed for 20 images of the cross-sections, and the average value of the ratio of the solid electrolyte to MZP is obtained. This average value is the abundance ratio of MZP and the solid electrolyte.

[0035] Furthermore, considering that the brightness obtained depends on the composition of the particles, for example, by performing image processing on an image obtained using a scanning electron microscope (SEM) or a transmission electron microscope (TEM), the area ratio of the solid electrolyte and MZP can be calculated. From the comparison of the calculated area ratios of the solid electrolyte and MZP, the abundance ratio of MZP and the solid electrolyte can be determined.

[0036] When X-ray diffraction measurement is performed on the solid electrolyte layer 3 using CuKα rays, diffraction peaks are confirmed. In the powder X-ray diffraction pattern obtained by performing X-ray diffraction measurement using CuKα rays, the peak in the range of 19° ≤ 2θ ≤ 22° is referred to as the first peak, the peak in the range of 23° ≤ 2θ ≤ 26° is referred to as the second peak, and the peak in the range of 30° ≤ 2θ ≤ 36° is referred to as the third peak.

[0037] The peak intensity P1 of the first peak and the peak intensity P2 of the second peak satisfy, for example, the relationship of 0.5 ≤ P2 / P1 ≤ 3.0, preferably the relationship of 0.8 ≤ P2 / P1 ≤ 2.0. Also, the peak intensity P1 of the first peak and the peak intensity P3 of the third peak satisfy, for example, the relationship of 0.5 ≤ P3 / P1 ≤ 3.0.

[0038] The solid electrolyte layer 3 may contain substances other than the solid electrolyte and MZP. The solid electrolyte layer 3 may contain, for example, a sintering aid or the like.

[0039] The sintering aid is not particularly limited as long as it can lower the sintering temperature. Although not limited to these examples, for example, lithium compounds such as lithium carbonate, lithium hydroxide, and lithium phosphate, and H 3 BO 3 boron compounds such as these, and compounds composed of lithium and boron are preferably used as the sintering aid.

[0040] "Positive electrode layer and negative electrode layer" The positive electrode layer 1 has a positive electrode current collector layer 1A and a positive electrode active material layer 1B containing a positive electrode active material. The negative electrode layer 2 has a negative electrode current collector layer 2A and a negative electrode active material layer 2B containing a negative electrode active material.

[0041] The positive electrode current collector layer 1A and the negative electrode current collector layer 2A are excellent in conductivity. The positive electrode current collector layer 1A and the negative electrode current collector layer 2A are, for example, silver, palladium, gold, platinum, aluminum, copper, or nickel. Copper hardly reacts with the positive electrode active material, the negative electrode active material, and the solid electrolyte. For example, when copper is used for the positive electrode current collector layer 1A and the negative electrode current collector layer 2A, the internal resistance of the all-solid-state secondary battery 10 can be reduced. The materials constituting the positive electrode current collector layer 1A and the negative electrode current collector layer 2A may be the same or different.

[0042] The positive electrode active material layer 1B is formed on one or both sides of the positive electrode current collector layer 1A. The positive electrode active material layer 1B may not be provided on the surface of the positive electrode current collector layer 1A on the side where the opposing negative electrode layer 2 does not exist. Further, the negative electrode active material layer 2B is formed on one or both sides of the negative electrode current collector layer 2A. The negative electrode active material layer 2B may not be provided on the surface of the negative electrode current collector layer 2A on the side where the opposing positive electrode layer 1 does not exist. For example, the positive electrode layer 1 or the negative electrode layer 2 located in the uppermost layer or the lowermost layer of the laminate 4 may not have the positive electrode active material layer 1B or the negative electrode active material layer 2B on one side.

[0043] The positive electrode active material layer 1B and the negative electrode active material layer 2B contain a positive electrode active material and a negative electrode active material that exchange electrons. In addition, it may contain a conductive assistant, an ion conductive assistant, a binder, and the like. It is preferable that the positive electrode active material and the negative electrode active material can efficiently insert and desorb lithium ions.

[0044] The positive electrode active material and the negative electrode active material are, for example, transition metal oxides and transition metal composite oxides. Specifically, the positive electrode active material and the negative electrode active material are, for example, lithium manganese composite oxide Li 2 Mn a Ma 1-a O 3 (0.8 ≦ a ≦ 1, Ma = Co, Ni), lithium cobalt oxide (LiCoO 2 ), lithium nickel oxide (LiNiO 2 ), lithium manganese spinel (LiMn 2 O 4 ), general formula: LiNi x Coy Mn z O 2 (x + y + z = 1, 0 ≤ x ≤ 1, 0 ≤ y ≤ 1, 0 ≤ z ≤ 1) represented composite metal oxide, lithium vanadium compound (LiV 2 O 5 ), olivine-type LiMbPO 4 (where Mb is one or more elements selected from Co, Ni, Mn, Fe, Mg, Nb, Ti, Al, Zr), lithium vanadium phosphate (Li 3 V 2 (PO 4 ) 3 or LiVOPO 4 ), Li 2 MnO 3 -LiMcO 2 (Mc = Mn, Co, Ni) represented Li-excess system solid solution cathode, lithium titanate (Li 4 Ti 5 O 12 ), Li s Ni t Co u Al v O 2 (0.9 < s < 1.3, 0.9 < t + u + v < 1.1) represented composite metal oxide, etc.

[0045] Examples of the conductive assistant include carbon materials such as carbon black, acetylene black, ketjen black, carbon nanotubes, graphite, graphene, activated carbon, metal materials such as gold, silver, palladium, platinum, copper, tin, and conductive oxides such as indium tin oxide (ITO), titanium oxide, tin oxide, zinc oxide, tungsten oxide, etc.

[0046] Examples of the ion-conductive assistant include solid electrolytes. Specifically, for example, the same materials as those used for the solid electrolyte layer 3 can be used.

[0047] When using a solid electrolyte as the ion-conductive assistant, it is preferable that the ion-conductive assistant and the solid electrolyte used for the solid electrolyte layer 3 use the same material.

[0048] There is no clear distinction between the active materials that make up the positive electrode active material layer 1B or the negative electrode active material layer 2B. By comparing the potentials of two types of compounds, the compound with a more noble potential can be used as the positive electrode active material, and the compound with a more base potential can be used as the negative electrode active material.

[0049] In addition, the positive electrode current collector layer 1A and the negative electrode current collector layer 2A may each contain a positive electrode active material and a negative electrode active material. The content ratio of the active material contained in each current collector is not particularly limited as long as it functions as a current collector. For example, it is preferable that the positive electrode current collector / positive electrode active material or the negative electrode current collector / negative electrode active material is in the range of 90 / 10 to 70 / 30 by volume ratio.

[0050] When the positive electrode current collector layer 1A and the negative electrode current collector layer 2A each contain a positive electrode active material and a negative electrode active material, the adhesion between the positive electrode current collector layer 1A and the positive electrode active material layer 1B and between the negative electrode current collector layer 2A and the negative electrode active material layer 2B is improved.

[0051] (Terminal) The first external terminal 5 and the second external terminal 6 are made of, for example, a material with excellent conductivity. The first external terminal 5 and the second external terminal 6 are, for example, any one of silver, gold, platinum, aluminum, copper, tin, nickel, chromium, and titanium. The first external terminal 5 and the second external terminal 6 may be a single layer or multiple layers.

[0052] (Protection layer) The all-solid-state secondary battery 10 may have a protection layer on its outer periphery that electrically, physically, and chemically protects the laminate 4 and the terminals. The protection layer is preferably made of a material that is excellent in insulation, durability, and moisture resistance and is environmentally safe. The protection layer is, for example, glass, ceramics, a thermosetting resin, or a photocurable resin. The material of the protection layer may be only one type or a combination of multiple types. The protection layer may be a single layer or multiple layers. The protection layer is preferably an organic-inorganic hybrid obtained by mixing a thermosetting resin and ceramic powder.

[0053] Next, a method for manufacturing an all-solid-state secondary battery according to this embodiment will be described. The all-solid-state secondary battery 10 may be manufactured by a simultaneous firing method or a sequential firing method. The simultaneous firing method is a method in which materials for forming each layer are laminated and then fired all at once. The sequential firing method is a method in which firing is performed each time a layer is laminated. The simultaneous firing method has a simpler working process than the sequential firing method. Also, the laminate 4 manufactured by the simultaneous firing method is denser than the laminate 4 manufactured by the sequential firing method. Hereinafter, the case of using the simultaneous firing method will be described as an example.

[0054] First, pastes for each layer constituting the laminate 4 are prepared. Materials for the positive electrode current collector layer 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 layer 2A are each made into a paste. The method of making into a paste is not particularly limited. For example, a paste can be obtained by mixing powders of each material in a vehicle. A vehicle is a general term for a medium in a liquid phase. A vehicle contains a solvent and a binder.

[0055] For the paste of the solid electrolyte layer 3, a mixture of the solid electrolyte and MZP is added to the vehicle. The solid electrolyte and MZP are mixed without being pulverized respectively.

[0056] Next, a green sheet is prepared. A green sheet is obtained by processing a paste into a sheet shape. For example, a green sheet can be obtained by applying a paste to a base material such as PET (polyethylene terephthalate) in a desired order, drying it if necessary, and then peeling it from the base material. The method of applying the paste is not particularly limited. For example, known methods such as screen printing, coating, transfer, doctor blade, and inkjet can be adopted.

[0057] The prepared green sheets are stacked in a desired order and number of layers. Alignment, cutting, etc. are performed as necessary to produce a laminate. When manufacturing a parallel type or a series-parallel type battery, the positive electrode current collector layer and the negative electrode current collector layer are aligned so that the end faces of the positive electrode current collector layer and the negative electrode current collector layer do not coincide.

[0058] The laminate may be produced after preparing the positive electrode active material layer unit and the negative electrode active material layer unit described below.

[0059] First, a paste for the solid electrolyte layer is formed into a sheet shape on a PET film by the doctor blade method and dried. Next, a paste for the positive electrode active material layer is printed on the green sheet of the solid electrolyte layer by screen printing and dried.

[0060] Next, a paste for the positive electrode current collector layer is printed on the dried paste for the positive electrode active material layer by screen printing and dried. Further, a paste for the positive electrode active material layer is printed again on the dried paste for the positive electrode current collector layer by screen printing and dried. Then, the PET film is peeled off to produce a positive electrode unit. The positive electrode unit has a solid electrolyte layer 3 / a positive electrode active material layer 1B / a positive electrode current collector layer 1A / a positive electrode active material layer 1B laminated in this order.

[0061] The negative electrode unit is also produced in the same procedure. The negative electrode unit has a solid electrolyte layer 3 / a negative electrode active material layer 2B / a negative electrode current collector layer 2A / a negative electrode active material layer 2B laminated in this order.

[0062] Next, the positive electrode unit and the negative electrode unit are laminated. The positive electrode unit and the negative electrode unit are laminated so that the solid electrolyte layers of the respective units do not face each other. The laminated laminate has a positive electrode active material layer 1B / a positive electrode current collector layer 1A / a positive electrode active material layer 1B / a solid electrolyte layer 3 / a negative electrode active material layer 2B / a negative electrode current collector layer 2A / a negative electrode active material layer 2B / a solid electrolyte layer 3 laminated in this order. The positive electrode unit and the negative electrode unit are stacked with a shift so that the positive electrode current collector layer 1A is exposed on the first end face of the laminate and the negative electrode current collector layer 2A is exposed on the second end face opposite to the first end face. On the uppermost layer and the lowermost layer in the lamination direction, for example, sheets for the solid electrolyte layer with a predetermined thickness are further stacked and dried.

[0063] Next, the fabricated laminate is pressure-bonded all at once. The pressure bonding is performed while heating. The heating temperature is, for example, 40 to 95°C. Next, the pressure-bonded laminate is sintered. Sintering means heating in a temperature range of 500°C or higher and 1000°C or lower, for example, in a nitrogen atmosphere. The firing time is, for example, 0.1 to 3 hours. The laminate 4 is obtained by sintering. At this time, the solid electrolyte layer 3 containing the solid electrolyte and MZP is obtained. By the pressure bonding here, a positive electrode (first electrode) is formed at a position facing one surface of the solid electrolyte layer 3, and a negative electrode (second electrode) is formed at a position facing the other surface (the surface opposite to one surface) of the solid electrolyte layer 3.

[0064] The sintered body may be put into a cylindrical container together with an abrasive such as alumina and barrel-polished. The corners of the sintered body are chamfered by polishing. The polishing may be performed by sandblasting or the like.

[0065] Finally, a first external terminal 5 and a second external terminal 6 are attached to the laminate 4. The first external terminal 5 and the second external terminal 6 are each formed so as to be in electrical contact with the positive electrode current collector layer 1A or the negative electrode current collector layer 2A. For example, the first external terminal 5 is connected to the positive electrode current collector layer 1A exposed from the side surface of the laminate 4, and the second external terminal 6 is connected to the negative electrode current collector layer 2A exposed from the side surface of the laminate 4. The first external terminal 5 and the second external terminal 6 can be fabricated by, for example, sputtering, dipping, spray coating, or the like.

[0066] The solid electrolyte layer 3 according to the present embodiment is excellent in ionic conductivity by containing MZP. The reason is not clear, but it is considered that the layers of MZP are expanded by M ions, a path through which lithium ions can easily pass is formed in the solid electrolyte layer 3, and the conductivity of lithium ions in the solid electrolyte layer 3 is improved.

[0067] The solid electrolyte and MZP preferably include the same crystal structure. The case where the crystal structures of the solid electrolyte particles and MZP are the same will be described as an example. Lithium ions move through the gaps between the crystal lattices in the solid electrolyte layer 3. Lithium ions move between sites where lithium ions in the solid electrolyte layer 3 can enter.

[0068] When the entire solid electrolyte layer 3 is made of a solid electrolyte, the path between these sites is formed by lithium ions that maintain the crystal structure. When the entire solid electrolyte layer 3 is made of a solid electrolyte, the width of this path is substantially constant in the solid electrolyte layer 3. On the other hand, when MZP is added to the solid electrolyte layer 3, a part of the path in the solid electrolyte layer 3 expands. The M ion (M is at least one selected from the group consisting of Na, K, Mg, Ca, Sr, Ba, Cu, Zn, and Ni) has a larger ionic radius than the lithium ion and widens the gap between the crystal lattices in the crystal structure. That is, when the solid electrolyte layer 3 contains MZP, from the perspective of lithium ions, a wide path is formed in the solid electrolyte layer 3. As a result, the solid electrolyte layer 3 according to this embodiment is considered to have improved ionic conductivity.

[0069] This principle is a discussion only when the crystal structures of the solid electrolyte and MZP are the same. On the other hand, as can also be confirmed in the examples described later, when the crystal structures of the solid electrolyte and MZP are different, the same effect was confirmed even when the solid electrolyte was amorphous (glass). Although this principle is not clear, it is possible that the presence of portions in the solid electrolyte layer 3 where lithium ions can easily pass due to MZP makes it easier for lithium ions to undergo hopping conduction or the like, thereby improving the ionic conductivity of the solid electrolyte layer 3.

[0070] In addition, the all-solid-state secondary battery fabricated using this solid electrolyte layer has little voltage loss in the solid electrolyte layer, and the active material that contributes to the battery capacity can efficiently use energy. Therefore, the capacity of the all-solid-state secondary battery can be increased.

[0071] As described above, the embodiments of the present invention have been described in detail with reference to the drawings. However, each configuration and their combinations in each embodiment are examples, and additions, omissions, substitutions, and other modifications of the configuration are possible without departing from the spirit of the present invention.

Examples

[0072] (Example 1) LiZr was used as the solid electrolyte 2 (PO 4 ) 3 was prepared by the following procedure. First, LiOH·H 2 O, ZrO(NO 3 ) 2 ·2H 2 O, NH 4 (H 2 PO 4 ) were weighed in a weighing ratio and dissolved in water respectively. The respective solutions were mixed, the pH was adjusted, and then heated to 100 °C and gradually cooled. It was confirmed that the solid electrolyte of Example 1 had a rhombohedral crystal structure.

[0073] In the same procedure, Ca 0.5 Zr 2 (PO 4 ) 3 was prepared by the following procedure. First, Ca(NO 3 ) 2 ·4H 2 O, ZrO(NO 3 ) 2 ·2H 2 O, NH 4 (H 2 PO 4 ) were weighed in a weighing ratio and dissolved in water respectively. The respective solutions were mixed, the pH was adjusted, and then heated to 100 °C and gradually cooled. It was confirmed that the MZP of Example 1 had a rhombohedral crystal structure.

[0074] Then, the particle size distribution of the obtained solid electrolyte was measured. The particle size distribution was measured using a particle size distribution measuring device that uses the laser diffraction / scattering method (Microtrac method).

[0075] Next, the prepared LiZr 2 (PO 4 ) 3 and Ca 0.5 Zr 2 (PO 4 ) 3 were mixed in equal amounts and sintered in a temperature range of 700 °C or higher and 1000 °C or lower.

[0076] Then, X-ray diffraction measurement was performed on the fabricated solid electrolyte layer using CuKα rays. As a result, the ratio P2 / P1 of the peak intensity P1 of the first peak to the peak intensity P2 of the second peak was 0.88. The ionic conductivity of the fabricated solid electrolyte layer was also measured. The ionic conductivity was measured using an impedance analyzer (manufactured by Solartron, model number SI1260) under the conditions of an amplitude of 50 mV and a frequency range of 0.5 Hz to 1 MHz by connecting electrodes to both sides of the disk-shaped solid electrolyte. The ionic conductivity of the solid electrolyte of Example 1 was 8.10×10 -6 S / cm.

[0077] (Comparative Example 1) Comparative Example 1 is different from Example 1 in that MZP was not added to the solid electrolyte layer. Other conditions were the same as those in Example 1. The ionic conductivity of the solid electrolyte of Comparative Example 1 was 1.02×10 -7 S / cm.

[0078] When comparing Example 1 and Comparative Example 1, the ionic conductivity of Example 1 with MZP added is higher than that of Comparative Example 1.

[0079] (Examples 2 to 8) Examples 2 to 8 are different from Example 1 in that the material of the solid electrolyte constituting the solid electrolyte layer was changed. Other conditions were the same as those in Example 1.

[0080] In Example 2, the solid electrolyte was Li 1.3 Al 0.3 Ti 1.7 (PO 4 ) 3 . In Example 3, the solid electrolyte was Li 1.5 Al 0.5 Ge 1.5 (PO 4 ) 3 . In Example 4, the solid electrolyte was Li 1.55 Al 0.2 Zr 1.7 Si 0.25 P 9.75 O 12 . Example 5 used a solid electrolyte of Li 1.4 Na 0.1 Zr 1.5 Al 0.5 (PO 4 ) 3 . Example 6 used a solid electrolyte of Li 1.4 Ca 0.25 Er 0.3 Zr 1.7 (PO 4 ) 3.2 . Example 7 used a solid electrolyte of Li 1.4 Ca 0.25 Yb 0.3 Zr 1.7 (PO 4 ) 3.2 . Example 8 used a solid electrolyte of 70Li 2 S-30P 2 S 5 .

[0081] The crystal structures of Examples 2 to 7 were rhombohedral crystals. In Example 8, the diffraction peaks obtained by X-ray diffraction were broad, indicating a glass structure.

[0082] (Comparative Examples 2 to 8) Comparative Examples 2 to 8 were each different from Examples 2 to 8 in that MZP was not added to the solid electrolyte layer. The ionic conductivity was determined under the same conditions as in Examples 2 to 8.

[0083] Comparing Examples 2 to 8 with Comparative Examples 2 to 8, in each case, the addition of MZP to the solid electrolyte layer improved the ionic conductivity. The results of Examples 1 to 8 and Comparative Examples 1 to 8 are summarized in Table 1.

[0084]

Table 1

[0085] (Examples 9 to 20) Examples 9 to 20 are different from Example 1 in that the material of the MZP constituting the solid electrolyte layer is changed. Other conditions were the same as in Example 1. Note that the MZP of Example 15 is CuZr of Example 11 2 (PO 4 ) 3 After synthesis, an oxidation treatment was performed. The oxidation treatment was carried out, for example, by heating under temperature conditions of 300°C or higher and 600°C or lower.

[0086] In Example 9, the MZP was NaZr 2 (PO 4 ) 3 . In Example 10, the MZP was KZr 2 (PO 4 ) 3 . In Example 11, the MZP was CuZr 2 (PO 4 ) 3 . In Example 12, the MZP was Mg 0.5 Zr 2 (PO 4 ) 3 . In Example 13, the MZP was Sr 0.5 Zr 2 (PO 4 ) 3 . In Example 14, the MZP was Ba 0.5 Zr 2 (PO 4 ) 3 . In Example 15, the MZP was Cu 0.5 Zr 2 (PO 4 ) 3 . In Example 16, the MZP was Ni 0.5 Zr 2 (PO 4 ) 3 . In Example 17, the MZP was Zn 0.5 Zr 2 (PO4)3 In Example 18, the MZP was Ca 0.38 Sr 0.12 Zr2 (PO 4 ) 3 was used. Example 19 used MZP as Ca 0.25 Sr 0.25 Zr 2 (PO 4 ) 3 was used. Example 20 used MZP as Ca 0.20 Sr 0.30 Zr 2 (PO 4 ) 3 was used.

[0087] The results of Examples 9 to 20 were summarized in Table 2. For comparison, the results of Example 1 and Comparative Example 1 were shown in Table 2. The ionic conductivities of Examples 9 to 20 were all improved compared with Comparative Example 1.

[0088] [Table 2]

[0089] (Examples 21 to 31, Comparative Example 9) Examples 21 to 31 and Comparative Example 9 were different from Example 1 in that the volume ratio of the solid electrolyte to MZP in the solid electrolyte layer was changed. Other conditions were the same as those in Example 1.

[0090] In Example 21, the abundance ratio of MZP was 1% by volume. In Example 22, the abundance ratio of MZP was 10% by volume. In Example 23, the abundance ratio of MZP was 20% by volume. In Example 24, the abundance ratio of MZP was 25% by volume. In Example 25, the abundance ratio of MZP was 30% by volume. In Example 26, the abundance ratio of MZP was 40% by volume. In Example 27, the abundance ratio of MZP was 70% by volume. In Example 28, the abundance ratio of MZP was 75% by volume. In Example 29, the abundance ratio of MZP was 80% by volume. Example 30 had a molar ratio of MZP of 90% by volume. Example 31 had a molar ratio of MZP of 96% by volume. Comparative Example 9 had a molar ratio of MZP of 100% by volume.

[0091] The results of Examples 21 to 30 and Comparative Example 9 are summarized in Table 3. For comparison, the results of Example 1 and Comparative Example 1 are shown in Table 3. The ionic conductivity varied depending on the abundance ratio of the solid electrolyte and MZP.

[0092]

Table 3

[0093] (Examples 32 to 37) Examples 32 to 37 differed from Example 1 in that the particle size of MZP in the solid electrolyte layer was changed. Other conditions were the same as in Example 1. The particle size of MZP was adjusted by sieving using meshes with different aperture sizes.

[0094] In Example 32, the particle size of MZP was 0.20 μm. In Example 33, the particle size of MZP was 0.34 μm. In Example 34, the particle size of MZP was 0.50 μm. In Example 35, the particle size of MZP was 3.20 μm. In Example 36, the particle size of MZP was 5.00 μm. In Example 37, the particle size of MZP was 6.20 μm.

[0095] The results of Examples 32 to 37 are summarized in Table 4. For comparison, the results of Example 1 are shown in Table 4. The ionic conductivity varied depending on the particle size of MZP.

[0096]

Table 4

[0097] (Examples 38 to 41, Comparative Example 10 and Comparative Example 11) Examples 38 to 41 are different from Example 1 in that the crystal structures of the solid electrolyte and MZP were changed. Other conditions were the same as those in Example 1. Comparative Examples 10 and 11 are different from Comparative Example 1 in that the crystal structure of the solid electrolyte was changed. Other conditions were the same as those in Comparative Example 1.

[0098] Since LiZr2(PO4)3 can select a plurality of crystal structures, the crystal structure was changed by varying the manufacturing conditions. Triclinic LiZr2(PO4)3 was prepared using the flux method, with a melting temperature of 1200 °C and obtained by slow cooling. The monoclinic solid electrolyte was prepared using the flux method, with a melting temperature of 900 °C and obtained by slow cooling. On the other hand, since MZP can in principle select only one crystal structure depending on the composition, the crystal structure was changed by changing the material type.

[0099] In Example 38, the crystal phase of the solid electrolyte was triclinic, and MZP was Ca0.5Zr2(PO4)3 (crystal phase is rhombohedral). In Example 39, the crystal phase of the solid electrolyte was monoclinic, and MZP was Ca0.5Zr2(PO4)3 (crystal phase is rhombohedral). In Example 40, the crystal phase of the solid electrolyte was monoclinic, and MZP was Mg0.5Zr2(PO4)3 (crystal phase is monoclinic). In Example 41, the crystal phase of the solid electrolyte was monoclinic, and MZP was Zn0.5Zr2(PO4)3 (crystal phase is monoclinic). In Comparative Example 10, the crystal phase of the solid electrolyte was monoclinic. In Comparative Example 11, the crystal phase of the solid electrolyte was triclinic.

[0100] The results of Examples 38 to 41 are summarized in Table 5. Table 5 shows the results of Example 1, Example 12, Example 17 and Comparative Example 1 for comparison. Rhombohedral crystals are more likely to ensure a three-dimensional path for ion conduction. When the crystal phase of the solid electrolyte or MZP is rhombohedral, the ionic conductivity is higher than when the crystal phase is monoclinic or triclinic. Also, even when the solid electrolyte is monoclinic or triclinic, adding MZP to the solid electrolyte layer improved the ionic conductivity.

[0101]

Table 5

[0102] (Examples 42 to 49) Examples 42 to 49 are different from Example 1 in that the relationship of the peak intensity ratio in the X-ray diffraction of MZP was changed. Other conditions were the same as those in Example 1. The peak intensity ratio in the X-ray diffraction of MZP was adjusted by changing the heating conditions during firing. The heating conditions are specifically, for example, the heating temperature, heating time, temperature rising time, temperature falling time, and the presence or absence of weighting. The heating temperature is the time during which the temperature condition is heated constantly, the heating time is the time of heating at a constant temperature, the temperature rising time is the time from the start of heating to the heating temperature, and the temperature falling time is the cooling time from the heating temperature to room temperature. The higher the heating temperature, the smaller the peak intensity. When the temperature rising time was short, the peak intensity ratio became large. When the temperature falling time was short, the peak intensity ratio became small. When fired with weighting added, the peak intensity ratio became larger than when no weighting was added.

[0103] In Example 42, the peak intensity ratio of the first peak and the second peak was set to 0.43. In Example 43, the peak intensity ratio of the first peak and the second peak was set to 0.46. In Example 44, the peak intensity ratio of the first peak and the second peak was set to 0.53. In Example 45, the peak intensity ratio of the first peak and the second peak was set to 0.64. In Example 46, the peak intensity ratio of the first peak and the second peak was set to 1.20. In Example 47, the peak intensity ratio of the first peak and the second peak was set to 1.40. In Example 48, the peak intensity ratio of the first peak and the second peak was set to 2.10. In Example 49, the peak intensity ratio of the first peak and the second peak was set to 2.40.

[0104]

Table 6

[0105] The results of Examples 42 to 49 were summarized in Table 6. For comparison, the results of Example 1 were shown in Table 6. The ionic conductivity varied by changing the value of P2 / P1.

Explanation of Signs

[0106] 1... positive electrode layer, 1A... positive electrode current collector layer, 1B... positive electrode active material layer, 2... negative electrode layer, 2A... negative electrode current collector layer, 2B... negative electrode active material layer, 3... solid electrolyte layer, 4... laminate, 5... first external terminal, 6... second external terminal

Claims

1. A solid electrolyte and a compound represented by the composition formula M ｘ Zr ２ (PO ４ ) ｙ and, In the above compositional formula, M is at least one selected from the group consisting of Na, K, Mg, Ca, Sr, Ba, Cu, Zn, and Ni, x satisfies 0 < x ≤ 2.5, y satisfies 2.7 ≤ y ≤ 3.5, the average particle size of the above compound is 0.01 μm or more and 5 μm or less, the above solid electrolyte contains lithium, a solid electrolyte layer in which the above solid electrolyte and the above compound contain the same crystal structure.

2. The solid electrolyte layer according to Claim 1, wherein the abundance ratio of the above compound with respect to the above solid electrolyte is 0.1% by volume or more and less than 100% by volume.

3. The solid electrolyte layer according to any one of Claims 1 or 2, wherein the ratio of the portion having a rhombohedral crystal structure in the above solid electrolyte is 50% by volume or more.

4. The solid electrolyte layer according to any one of Claims 1 to 3, wherein the crystal structure of the above compound contains rhombohedra.

5. In the powder X-ray diffraction pattern obtained by performing X-ray diffraction measurement using CuKα rays, the peak intensity P1 of the peak observed in the range of 19° ≤ 2θ ≤ 22° and the peak intensity P2 of the peak observed in the range of 23° ≤ 2θ ≤ 26° satisfy the relationship of 0.5 ≤ P2 / P1 ≤ 3.

0. The solid electrolyte layer according to any one of Claims 1 to 4.

6. An all-solid-state secondary battery comprising the solid electrolyte layer according to any one of Claims 1 to 5, and a first electrode and a second electrode sandwiching the solid electrolyte layer.

7. A solid electrolyte and a compound represented by the composition formula M ｘ Zr ２ (PO ４ ) ｙ and mixing them having a step of sintering the mixed mixture in a temperature range of 500°C or higher and 1000°C or lower, In the above compositional formula, M is at least one selected from the group consisting of Na, K, Mg, Ca, Sr, Ba, Cu, Zn, and Ni, x satisfies 0 < x ≤ 2.5, y satisfies 2.7 ≤ y ≤ 3.5, the average particle size of the above compound is 0.01 μm or more and 5 μm or less, the above solid electrolyte contains lithium, A method for manufacturing a solid electrolyte layer in which the above solid electrolyte and the above compound contain the same crystal structure.

8. A method for manufacturing an all-solid-state battery including a solid electrolyte layer manufactured by the method for manufacturing a solid electrolyte layer according to Claim 7, a step of forming a first electrode at a position facing one surface of the above solid electrolyte layer, a step of forming a second electrode at a position facing the other surface of the above solid electrolyte layer. A method for manufacturing an all-solid-state battery.

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