Solid electrolyte layer and all-solid-state battery

Abstract

To provide a solid electrolyte layer and an all-solid battery, which are superior in cycle characteristic under a high-temperature high-humidity environment.SOLUTION: A solid electrolyte layer according to an embodiment hereof comprises a first compound represented by LiaM2(PO4)3 (1), and a second compound represented by M'P2O7 (2). In the solid electrolyte layer, the abundance of the second compound is 0.5 vol.% or more and less than 10 vol.%.SELECTED DRAWING: Figure 2

Description

Technical Field

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

Background Art

[0002] In recent years, the development of electronics technology has been remarkable, and the miniaturization, light weight, and thinness, as well as multifunctionalization, of portable electronic devices have been achieved. Along with this, for the battery that serves as the power source of the electronic device, miniaturization, light weight, and improvement in reliability are strongly desired, and all-solid-state batteries using a solid electrolyte as the electrolyte have attracted attention.

[0003] For example, Patent Document 1 describes an all-solid-state battery using Li 1.3 Al 0.3 Ti 1.7 (PO 4 ) 3 as the solid electrolyte. Further, Patent Document 2 describes LiZr containing Zr, which is more excellent in reduction resistance than the solid electrolyte disclosed in Patent Document 1. 2 (PO 4 ) 3 In addition, Patent Document 3 describes an all-solid-state battery using a solid electrolyte in which a part of Zr in LiZr 2 (PO 4 ) 3 is replaced with another element. When a part of Zr in LiZr 2 (PO 4 ) 3 is replaced with another element, the crystal phase is stabilized and the discharge capacity increases.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

[0005] However, for example, LiZr as described in Patent Document 2 2 (PO 4 ) 3 has poor sinterability when sintered, and it is difficult to fabricate a solid electrolyte layer with high density. As a result, moisture or the like may penetrate into the gaps between the solid electrolytes, and the cycle characteristics in a high-temperature and high-humidity environment may not be sufficient in some cases.

[0006] The present invention has been made in view of the above problems, and an object thereof is to provide a solid electrolyte layer and an all-solid-state battery having excellent cycle characteristics in a high-temperature and high-humidity environment. [Means for Solving the Problems]

[0007] To solve the above problems, the following means are provided.

[0008] (1) The solid electrolyte layer according to the first aspect includes a first compound represented by Li a M 2 (PO 4 ) 3 …(1) and a second compound represented by M’P 2 O 7 …(2). In the first compound, a satisfies 0.9 ≦ a ≦ 1.4, M is one or more elements selected from Zr, Ti, Ge, Al, Hf, Ca, Ba, Sr, Sc, Y, and In, in the second compound, M’ is one or more elements selected from Zr, Ti, Ge, Al, Hf, Ca, Ba, Sr, Sc, Y, and In, and the content ratio of the second compound is 0.5% by volume or more and less than 10% by volume.

[0009] (2) In the solid electrolyte layer according to the above aspect, the average particle diameter Da of the first compound and the average particle diameter Db of the second compound may satisfy 0.1 ≦ Da / Db ≦ 20.0.

[0010] (3) In the solid electrolyte layer according to the above aspect, the average particle diameter Db of the second compound may satisfy 0.01 μm ≤ Db ≤ 10 μm.

[0011] (4) The all-solid-state battery according to the second aspect includes the solid electrolyte layer according to the above aspect, a positive electrode, and a negative electrode that sandwich the solid electrolyte layer.

Advantages of the Invention

[0012] The all-solid-state battery using the solid electrolyte layer according to the above aspect is excellent in cycle characteristics under a high-temperature and high-humidity environment.

Brief Description of the Drawings

[0013]

Figure 1

Figure 2

Modes for Carrying Out the Invention

[0014] Hereinafter, the present embodiment 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.

[0015] [All-Solid-State Battery] FIG. 1 is a schematic cross-sectional view of an all-solid-state battery 10 according to the present embodiment. The all-solid-state battery 10 has a laminate 4 and terminal electrodes 5 and 6. The terminal electrodes 5 and 6 are respectively in contact with opposite surfaces of the laminate 4. The terminal electrodes 5 and 6 extend in a direction intersecting (orthogonal) to the lamination surface of the laminate 4.

[0016] The laminate 4 has a positive electrode 1, a negative electrode 2, and a solid electrolyte layer 3. The number of layers of the positive electrode 1 and the negative electrode 2 is not limited. The solid electrolyte layer 3 is located between the positive electrode 1 and the negative electrode 2, between the positive electrode 1 and the terminal electrode 6, and between the negative electrode 2 and the terminal electrode 5. One end of the positive electrode 1 is connected to the terminal electrode 5. One end of the negative electrode 2 is connected to the terminal electrode 6.

[0017] The all-solid-state battery 10 is charged or discharged by the transfer of ions through the solid electrolyte layer 3 between the positive electrode 1 and the negative electrode 2. In FIG. 1, a laminated battery is shown, but a wound battery may also be used. The all-solid-state battery 10 is used, for example, in a laminate battery, a prismatic battery, a cylindrical battery, a coin-type battery, a button-type battery, etc. The all-solid-state battery 10 may also be a liquid-injection type in which the solid electrolyte layer 3 is dissolved or dispersed in a solvent.

[0018] "Solid electrolyte layer" The solid electrolyte layer 3 is a substance that can move ions by an externally applied electric field. For example, the solid electrolyte layer 3 conducts lithium ions and inhibits the movement of electrons. The solid electrolyte layer 3 is, for example, a sintered body obtained by sintering.

[0019] FIG. 2 is a schematic cross-sectional view of the solid electrolyte layer 3 according to the present embodiment. The solid electrolyte layer 3 has a first compound 31 and a second compound 32. There are voids 33 between the first compound 31 and the second compound 32, between the first compounds 31, and between the second compounds 32. The solid electrolyte layer 3 may contain substances other than the first compound 31 and the second compound 32. For example, the solid electrolyte layer 3 may have a binder.

[0020] The first compound 31 is Li a M 2 (PO 4 ) 3…(1) is a solid electrolyte represented by the formula. In the composition formula, a satisfies 0.9 ≦ a ≦ 1.4. Although a is basically 1.0, a certain degree of variation is tolerated. In the composition formula, M is one or more elements selected from Zr, Ti, Ge, Al, Hf, Ca, Ba, Sr, Sc, Y, and In. M is an element that has been confirmed to be mutually substitutable. Even when the element is changed, it has been confirmed that the sinterability of the solid electrolyte layer 3 is the same by selecting the optimal firing temperature, selecting an appropriate sintering aid, and adjusting its amount, etc. The first compound 31 is, for example, Li a Zr 2 (PO 4 ) 3 , Li a Ti 2 (PO 4 ) 3 , Li a Zr 1.5 Ti 0.5 (PO 4 ) 3 .

[0021] The second compound 32 is a compound represented by M’P 2 O 7 …(2). In the composition formula, M’ is one or more elements selected from Zr, Ti, Ge, Al, Hf, Ca, Ba, Sr, Sc, Y, and In. M’ is an element that has been confirmed to be mutually substitutable. Even when the element is changed, it has been confirmed that there is no significant difference in the physical properties (crystallinity, size, etc.) of the second compound 32 by adjusting the synthesis conditions (raw material particle size, synthesis temperature, etc.) of the second compound 32. M’ may be the same as M in the composition formula (1). The second compound 32 is, for example, ZrP 2 O 7 , TiP 2 O 7 .

[0022] The volume ratio of the second compound 32 contained in the solid electrolyte layer 3 is 0.5% by volume or more and less than 10.0% by volume. The volume ratio of the second compound 32 contained in the solid electrolyte layer 3 is preferably 2.0% by volume or more and 8.0% by volume or less, more preferably 2.0% by volume or more and 5.0% by volume or less, and still more preferably 3.0% by volume or more and 4.0% by volume or less.

[0023] If the volume ratio of the second compound 32 contained in the solid electrolyte layer 3 is small, sufficient sinterability during sintering cannot be obtained, and the number of voids 33 increases. Moisture and the like easily penetrate into the voids 33, which causes deterioration of the solid electrolyte layer 3. As a result, the cycle characteristics of the all-solid-state battery 10 at high temperature and high humidity deteriorate. On the other hand, the second compound 32 has relatively lower ionic conductivity than the first compound 31. Therefore, if the volume ratio of the second compound 32 contained in the solid electrolyte layer 3 is large, the cycle characteristics at high temperature and high humidity deteriorate.

[0024] Also, the average particle size Da of the first compound 31 and the average particle size Db of the second compound 32 preferably satisfy 0.1 ≦ Da / Db ≦ 20.0, more preferably satisfy 0.1 ≦ Da / Db ≦ 10.0, still more preferably satisfy 0.5 ≦ Da / Db ≦ 5.0, and particularly preferably satisfy 1.0 ≦ Da / Db ≦ 3.0. When the average particle sizes Da and Db satisfy the above relationship, the sinterability of the solid electrolyte layer 3 is improved and the number of voids 33 decreases. As a result, the cycle characteristics of the all-solid-state battery 10 at high temperature and high humidity are improved. Here, the average particle sizes Da and Db are obtained as follows.

[0025] First, a cross-section of the solid electrolyte layer 3 is cut out, and the smooth cross-section produced by processing with a cross-section polisher (CP) is observed with a scanning electron microscope (SEM) for a backscattered electron composite image. In the observation image obtained at this time, the first compound 31 and the second compound 32 are discriminated based on the difference in contrast. It is also possible to confirm the compositions of the first compound 31 and the second compound 32 using energy dispersive X-ray analysis (EDS) and perform discrimination. When no clear difference in contrast is observed, the first compound 31 and the second compound 32 can be discriminated by obtaining an X-ray mapping image by EDS.

[0026] Thereafter, the average particle diameter Da of the first compound 31 and the average particle diameter Db of the second compound 32 are measured. Specifically, after measuring the longest diameters of all the first compounds 31 and the second compounds 32 as much as possible in the observation field of view, the average values are obtained, and thus the average particle diameters Da and Db are obtained.

[0027] The average particle diameter Da of the first compound 31 is preferably, for example, 0.5 μm or more and 10 μm or less. The average particle diameter Db of the second compound 32 is preferably, for example, 0.01 μm or more and 10 μm or less, more preferably 0.1 μm or more and 2.0 μm or less, and still more preferably 0.3 μm or more and 1.0 μm or less.

[0028] "Positive electrode" As shown in FIG. 1, the positive electrode 1 has, for example, a positive electrode current collector 1A and a positive electrode active material layer 1B containing a positive electrode active material.

[0029] (Positive electrode current collector) The positive electrode current collector 1A has high conductivity. The positive electrode current collector 1A is, for example, a metal such as silver, palladium, gold, platinum, aluminum, copper, nickel, stainless steel, iron, and their alloys, a conductive resin, etc. The positive electrode current collector 1A may be in each form of powder, foil, punching, and expansion.

[0030] (Positive electrode active material layer) The positive electrode active material layer 1B is formed on one side or both sides of the positive electrode current collector 1A. The positive electrode active material layer 1B contains a positive electrode active material. The positive electrode active material layer 1B may contain a conductive auxiliary agent, a binder, and the above-mentioned solid electrolyte.

[0031] (Positive electrode active material) The positive electrode active material is not particularly limited as long as it can reversibly proceed with the release and occlusion of lithium ions, and the desorption and insertion of lithium ions. For example, the positive electrode active materials used in known lithium-ion secondary batteries can be used.

[0032] The positive electrode active material is, for example, a composite transition metal oxide, a transition metal fluoride, a polyanion, a transition metal sulfide, a transition metal oxyfluoride, a transition metal oxysulfide, or a transition metal oxynitride.

[0033] The positive electrode active material is, for example, lithium cobaltate (LiCoO 2 ), lithium nickelate (LiNiO 2 ), lithium manganese spinel (LiMn 2 O 4 ), and a composite metal oxide represented by the general formula: LiNi x Co y Mn z M a O 2 (where x + y + z + a = 1, 0 ≤ x ≤ 1, 0 ≤ y ≤ 1, 0 ≤ z ≤ 1, 0 ≤ a ≤ 1, and M is one or more elements selected from Al, Mg, Nb, Ti, Cu, Zn, and Cr), a lithium vanadium compound (LiV 2 O 5 , Li 3 V 2 (PO 4 ) 3 , LiVOPO 4 ), an olivine-type LiMPO 4 (where M represents one or more elements selected from Co, Ni, Mn, Fe, Mg, V, Nb, Ti, Al, and Zr), lithium titanate (Li 4 Ti 5 O 12 ), LiNi x Co y Al z O 2 (0.9 < x + y + z < 1.1), etc.

[0034] Also, as the positive electrode active material, a positive electrode active material that does not contain lithium can also be used. These positive electrode active materials can be used by arranging a negative electrode active material previously doped with metallic lithium or lithium ions in the negative electrode and starting the battery from discharge. For example, lithium-free metal oxides (MnO 2 , V 2 O 5 , etc.), lithium-free metal sulfides (MoS 2etc.), lithium-free fluorides (FeF 3 , VF 3 etc.) are examples of these cathode active materials.

[0035] (Conductive aid) The conductive aid is not particularly limited as long as it can improve the electron conductivity in the cathode active material layer 1B, and known conductive aids can be used. Examples of the conductive aid 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, or mixtures thereof. The conductive aid may be in the form of powder or fiber.

[0036] (Binder) The binder joins the cathode current collector 1A and the cathode active material layer 1B, the cathode active material layer 1B and the solid electrolyte layer 3, and various materials constituting the cathode active material layer 1B.

[0037] The binder can be used within a range that does not impair the function of the cathode active material layer 1B. If not necessary, the binder may not be contained. The content of the binder in the cathode active material layer 1B is, for example, 0.5 to 30% by volume of the cathode active material layer. When the content of the binder is sufficiently small, the resistance of the cathode active material layer 1B becomes sufficiently low.

[0038] The binder may be any material capable of the above-described bonding. For example, fluororesins such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE) can be mentioned. Further, in addition to the above, as the binder, for example, cellulose, styrene-butadiene rubber, ethylene-propylene rubber, polyimide resin, polyamideimide resin, etc. may be used. Also, a conductive polymer having electronic conductivity or an ion-conductive polymer having ion conductivity may be used as the binder. Examples of the conductive polymer having electronic conductivity include polyacetylene. In this case, since the binder also exhibits the function of the conductive auxiliary particles, it is not necessary to add a conductive auxiliary. As the ion-conductive polymer having ion conductivity, for example, those that conduct lithium ions can be used, and monomers of polymer compounds (polyether-based polymer compounds such as polyethylene oxide and polypropylene oxide, polyphosphazene, etc.) and 4 LiBF 4 LiPF 6 etc., lithium salts or alkali metal salts mainly composed of lithium, etc. can be mentioned. Examples of the polymerization initiator used for the complexation include, for example, a photopolymerization initiator or a thermal polymerization initiator compatible with the above monomers. The properties required for the binder include oxidation-reduction resistance and good adhesiveness.

[0039] (Solid electrolyte) The solid electrolyte contained in the positive electrode active material layer 1B improves the ion conduction in the positive electrode active material layer 1B. The solid electrolyte is the same as that contained in the above solid electrolyte layer 3.

[0040] "Negative electrode" As shown in FIG. 1, the negative electrode 2 has, for example, a negative electrode current collector 2A and a negative electrode active material layer 2B containing a negative electrode active material.

[0041] (Negative electrode current collector) The negative electrode current collector 2A is the same as the positive electrode current collector 1A.

[0042] (Negative electrode active material layer) The negative electrode active material layer 2B is formed on one or both sides of the negative electrode current collector 2A. The negative electrode active material layer 2B contains a negative electrode active material. The negative electrode active material layer 2B may contain a conductive assistant, a binder, and the above-mentioned solid electrolyte.

[0043] (Negative electrode active material) The negative electrode active material is a compound capable of occluding and releasing ions. The negative electrode active material is a compound showing a lower potential than the positive electrode active material. As the negative electrode active material, the same material as the positive electrode active material can be used. Considering the potential of the negative electrode active material and the potential of the positive electrode active material, the negative electrode active material and the positive electrode active material used in the all-solid-state battery 10 are determined.

[0044] (Conductive assistant) The conductive assistant improves the electron conductivity of the negative electrode active material layer 2B. As the conductive assistant, the same material as the positive electrode active material layer 1B can be used.

[0045] (Binder) The binder joins 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 various materials constituting the negative electrode active material layer 2B. As the binder, the same material as the positive electrode active material layer 1B can be used. The content ratio of the binder can also be the same as that of the positive electrode active material layer 1B. If the binder is unnecessary, it may not be contained.

[0046] (Solid electrolyte) The solid electrolyte contained in the negative electrode active material layer 2B improves the ion conduction in the negative electrode active material layer 2B. The solid electrolyte is the same as that contained in the above-mentioned solid electrolyte layer 3.

[0047] At least one of the positive electrode active material layer 1B, the negative electrode active material layer 2B, and the solid electrolyte layer 3 may contain a non-aqueous electrolyte, an ionic liquid, or a gel electrolyte. When these substances are contained in any of the above, the rate characteristics, which are one of the battery characteristics, are improved.

[0048] (Manufacturing method of all-solid-state battery) Next, a method for manufacturing the all-solid-state battery 10 will be described. First, the laminate 4 is produced. The laminate 4 is produced, for example, by a co-firing method or a sequential firing method.

[0049] The co-firing method is a method of producing the laminate 4 by co-firing after laminating the materials for forming each layer. The sequential firing method is a method of performing firing every time each layer is formed. The co-firing method can produce the laminate 4 with fewer working steps than the sequential firing method. Also, the laminate 4 produced by the co-firing method becomes denser than the laminate 4 produced using the sequential firing method. Hereinafter, the case of using the co-firing method will be described as an example.

[0050] 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 pastes. The solid electrolyte layer 3 is made into a paste from a material in which the first compound 31 and the second compound 32 are mixed. Each of the first compound 31 and the second compound 32 can be produced by a solid-phase reaction method or the like. The average particle diameters Da and Db can be adjusted by the milling time of each of the first compound 31 and the second compound 32.

[0051] The method for making each material into a paste is not particularly limited. For example, a method of mixing the powder of each material with a vehicle to obtain a paste is used. Here, the vehicle is a general term for the medium in the liquid phase. The vehicle includes a solvent and a binder.

[0052] Next, a green sheet is produced. The green sheet is obtained by applying the paste produced for each material onto a base material such as a PET (polyethylene terephthalate) film, drying it if necessary, and then peeling off the base material. The method for applying the paste is not particularly limited. For example, known methods such as screen printing, coating, transfer, and doctor blade can be used.

[0053] Next, the green sheets prepared for each material are stacked in a desired order and number of layers to produce a stacked sheet. When stacking the green sheets, alignment, cutting, etc. are performed as necessary. For example, when manufacturing a parallel type or series-parallel type battery, alignment is performed so that the end faces of the positive electrode current collector 1A and the negative electrode current collector 2A do not coincide, and the respective green sheets are stacked.

[0054] The stacked sheet may be produced by using a method of manufacturing a positive electrode unit and a negative electrode unit and stacking these units. The positive electrode unit is a stacked sheet in which a solid electrolyte layer 3, a positive electrode active material layer 1B, a positive electrode current collector 1A, and a positive electrode active material layer 1B are stacked in this order. The negative electrode unit is a stacked sheet in which a solid electrolyte layer 3, a negative electrode active material layer 2B, a negative electrode current collector 2A, and a negative electrode active material layer 2B are stacked in this order. Stacking is performed such 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 such that the positive electrode active material layer 1B of the positive electrode unit faces the solid electrolyte layer 3 of the negative electrode unit.

[0055] Next, the produced stacked sheet is pressurized all at once to enhance the adhesion of each layer. The pressurization can be performed, for example, by die pressing, warm water isotropic pressure pressing (WIP), cold water isotropic pressure pressing (CIP), hydrostatic pressure pressing, etc. The pressurization is preferably performed while heating. The heating temperature during pressure bonding is, for example, set to 40 to 95°C. Next, the pressurized laminate is cut using a dicing device to form chips. Then, by performing a debinding treatment and firing on the chips, a laminate 4 made of a sintered body is obtained.

[0056] The debinding treatment can be performed as a process separate from the firing process. When the debinding process is performed, the binder component contained in the chip is thermally decomposed before the firing process, and it is possible to suppress the rapid decomposition of the binder component in the firing process. The debinding process is performed, for example, by heating at a temperature of 300 to 800°C for 0.1 to 10 hours in a nitrogen atmosphere. The debinding process may be performed in an argon atmosphere or a nitrogen-hydrogen mixed atmosphere instead of the nitrogen atmosphere if it is a reducing atmosphere.

[0057] The firing process is carried out, for example, by placing the chip on a ceramic table. The firing is carried out, for example, by heating to 600 to 1000 °C in a nitrogen atmosphere. The firing time is, for example, 0.1 to 3 hours. In the case of a sintering process, if it is a reducing atmosphere, instead of a nitrogen atmosphere, it may be carried out, for example, in an argon atmosphere or a nitrogen-hydrogen mixed atmosphere.

[0058] Further, the sintered laminate 4 (sintered body) may be placed in a cylindrical container together with an abrasive such as alumina and barrel-polished. Thereby, chamfering of the corners of the laminate can be achieved. The polishing may be carried out using sandblasting. Sandblasting is preferable because it can remove only specific parts.

[0059] Terminal electrodes 5 and 6 are formed on the opposing side surfaces of the produced laminate 4. The terminal electrodes 5 and 6 can be formed respectively using means such as a sputtering method, a dipping method, a screen printing method, a spray coating method, etc. By going through the above steps, the all-solid-state battery 10 can be produced. When the terminal electrodes 5 and 6 are formed only on predetermined parts, masking is performed with a tape or the like and the above treatment is carried out.

[0060] The solid electrolyte layer 3 according to this embodiment has the first compound 31 and the second compound 32, so that the sinterability is improved and voids 33 are less likely to be formed. The voids 33 are likely to allow moisture and the like to penetrate, which is one of the causes of the deterioration of the solid electrolyte layer 3. The solid electrolyte layer 3 according to this embodiment is less likely to deteriorate even in a high-temperature and high-humidity environment because there are few voids 33. As a result, the all-solid-state battery 10 according to this embodiment has excellent cycle characteristics in high temperature and high humidity.

[0061] 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 changes of the configuration are possible without departing from the spirit of the present invention.

Examples

[0062] "Example 1" As the first compound (solid electrolyte), LiZr 2 (PO 4 ) 3 was prepared, and as the second compound, ZrP 2 O 7 was prepared. Then, each was milled for a predetermined time and sieved to adjust their respective particle sizes. The average particle size Da of the first compound was set to 1 μm, and the average particle size Db of the second compound was set to 0.5 μm. Then, the first compound and the second compound were mixed so that the volume percentage of the second compound was 0.5 volume %.

[0063] Next, 100 parts of ethanol and 200 parts of toluene were added as solvents to 100 parts of the prepared mixed powder, and wet mixing was performed using a ball mill. Then, 16 parts of a polyvinyl butyral-based binder and 4.8 parts of benzyl butyl phthalate were added as plasticizers and mixed to prepare a paste for the solid electrolyte layer. The paste for the solid electrolyte layer was sheet-formed using the doctor blade method with a PET film as the base material to obtain a solid electrolyte layer sheet. The thickness of each solid electrolyte layer sheet was set to 15 μm.

[0064] Next, a paste for the positive electrode active material layer and a paste for the negative electrode active material layer were prepared. These pastes were prepared by adding 15 parts of ethyl cellulose as a binder and 65 parts of dihydroterpineol as a solvent to 100 parts of the powder of Li 3 V 2 (PO 4 ) 3 and mixing and dispersing them.

[0065] Next, a paste for the positive electrode current collector and a paste for the negative electrode current collector were prepared. These pastes were prepared by the following procedure. First, Cu was used as the current collector. Then, for the paste, Cu and Li 3 V 2 (PO 4 ) 3They were mixed so that the volume ratio thereof was 80:20. Then, 10 parts of ethyl cellulose as a binder and 50 parts of dihydroterpineol as a solvent were added to 100 parts of this powder, followed by mixing and dispersion to prepare a paste.

[0066] Next, the positive electrode unit and the negative electrode unit were produced by the following procedure. First, on the above solid electrolyte layer sheet, a paste for positive electrode active material was printed with a thickness of 5 μm using screen printing. Next, the printed paste for positive electrode active material was dried at 80°C for 5 minutes. Then, on the dried paste for positive electrode active material, a paste for current collector was printed with a thickness of 5 μm using screen printing. Next, the printed paste for positive electrode current collector was dried at 80°C for 5 minutes. Then, on the dried paste for positive electrode current collector, a paste for positive electrode active material was printed again with a thickness of 5 μm using screen printing and dried. Thereafter, the PET film was peeled off. In this way, a positive electrode unit in which a positive electrode active material layer / a positive electrode current collector layer / a positive electrode active material layer were laminated in this order on the main surface of the solid electrolyte layer was obtained.

[0067] Also, by the same procedure, a negative electrode unit in which a negative electrode active material layer / a negative electrode current collector layer / a negative electrode active material layer were laminated in this order on the main surface of the solid electrolyte layer was obtained.

[0068] The laminate was produced by stacking 5 solid electrolyte layer sheets, and alternately stacking 50 electrode units (25 positive electrode units and 25 negative electrode units) thereon through the solid electrolyte. At this time, the units were stacked with a shift so that the current collector layer of the odd-numbered electrode units extended only to one end face, and the current collector layer of the even-numbered electrode units extended only to the opposite end face. 6 solid electrolyte layer sheets were stacked on the stacked units. Thereafter, this was molded by thermocompression bonding and then cut to produce a laminated chip. Thereafter, the laminated chip was co-fired to obtain a laminate. The co-firing was performed by heating at a rate of 200°C / hour in a nitrogen atmosphere up to a firing temperature of 800°C, holding at that temperature for 2 hours, and then naturally cooling after firing.

[0069] Then, the sintered laminate was cut in the lamination direction parallel to the cross-section polisher (CP), and the cross-section thus obtained was analyzed by SEM and EDS to determine the average particle sizes of the first compound and the second compound. The average particle size Da of the first compound and the average particle size Db of the second compound did not change significantly from the time of paste preparation. The average particle size Da of the first compound was 1 μm, and the average particle size Db of the second compound was 0.5 μm. Therefore, the ratio of the average particle size Da of the first compound to the average particle size Db of the second compound was Da / Db = 2.0.

[0070] Then, a first external terminal and a second external terminal were attached to the sintered laminate (sintered body) by a known method to fabricate an all-solid-state battery.

[0071] Then, the cycle characteristics of the fabricated all-solid-state battery were measured. The cycle characteristics were measured by sandwiching the first external terminal and the second external terminal with spring probes so that they faced each other and repeating charge-discharge tests under the conditions of a temperature of 40°C and a humidity of 93%. The measurement conditions were that the current during both charging and discharging was 20 μA, and the cut-off voltages during charging and discharging were 1.6 V and 0 V, respectively. The cycle characteristics of Example 1 were 60%. The capacity during the first discharge was defined as the initial discharge capacity. The cycle characteristics were obtained by dividing the discharge capacity at the 100th cycle by the initial discharge capacity.

[0072] "Examples 2 to 10, Comparative Example 1, Comparative Example 2" Examples 2 to 10, Comparative Example 1, and Comparative Example 2 differ from Example 1 in that the mixing ratio of the first compound and the second compound is different. As a result, Examples 2 to 10, Comparative Example 1, and Comparative Example 2 have a different proportion of the second compound present in the solid electrolyte layer from Example 1. With other conditions being the same as in Example 1, the cycle characteristics in a high-temperature and high-humidity environment were determined. The results are summarized in Table 1 below.

[0073]

Table 1

[0074] Examples 1 to 10, in which the proportion of the second compound was 0.5% by volume or more and less than 10% by volume, had better cycle characteristics than Comparative Examples 1 and 2 outside this range.

[0075] "Examples 11 to 20, Comparative Examples 3 and 4" As the first compound (solid electrolyte), LiTi 2 (PO 4 ) 3 was used, and the difference from Example 1 was that TiP 2 O 7 was used as the second compound. The mixing ratio of the first compound and the second compound was changed, and the cycle characteristics in a high-temperature and high-humidity environment were determined. The results are summarized in Table 2 below.

[0076]

Table 2

[0077] Examples 11 to 20, in which Zr was changed to Ti, and Comparative Examples 3 and 4 also showed the same tendency as Examples 1 to 10, Comparative Examples 1 and 2.

[0078] "Examples 21 to 30, Comparative Examples 5 and 6" As the first compound (solid electrolyte), LiZr 1.5 Ti 0.5 (PO 4 ) 3 was used, and the difference from Example 1 was that Zr 0.75 Ti 0.25 P 2 O 7 was used as the second compound. The mixing ratio of the first compound and the second compound was changed, and the cycle characteristics in a high-temperature and high-humidity environment were determined. The results are summarized in Table 3 below.

[0079]

Table 3

[0080] Examples 21 to 30, in which part of Zr was replaced by Ti, and Comparative Examples 5 and 6 also showed the same tendency as Examples 1 to 10, Comparative Examples 1 and 2.

[0081] Examples 31 to 41 Examples 31 to 41 are different from Example 5 in that the average particle size of the second compound is changed. Along with the change in the average particle size of the second compound, the value of Da / Db obtained by dividing the average particle size Da of the first compound by the average particle size Db of the second compound also differs. The cycle characteristics in each of the high-temperature and high-humidity environments of Examples 31 to 41 were determined. The results are summarized in Table 4 below.

[0082] [Table 4]

[0083] Examples 42 to 54 Examples 42 to 54 are different from Example 5 in that Da / Db obtained by dividing the average particle size Da of the first compound by the average particle size Db of the second compound is fixed at 5.0, and the average particle sizes of the first compound and the second compound are changed. The cycle characteristics in each of the high-temperature and high-humidity environments of Examples 42 to 54 were determined. The results are summarized in Table 5 below.

[0084] [Table 5] Explanation of Reference Numerals

[0085] 1... positive electrode, 1A... positive electrode current collector, 1B... positive electrode active material layer, 2... negative electrode, 2A... negative electrode current collector, 2B... negative electrode active material layer, 3... solid electrolyte layer, 4... laminate, 5, 6... terminal electrodes, 10... all-solid-state battery, 31... first compound, 32... second compound, 33... void

Claims

1. Li ａ M ２ (PO ４ ) ３ … a first compound represented by formula (1), and M'P ２ O ７ ... and a second compound represented by (2). In the first compound, a satisfies 0.9 ≦ a ≦ 1.4, and M is one or more elements selected from Zr, Ti, Ge, Al, Hf, Ca, Ba, Sr, Sc, Y, and In. In the second compound, M' is one or more elements selected from Zr, Ti, Ge, Al, Hf, Ca, Ba, Sr, Sc, Y, and In. The proportion of the second compound is 0.5% by volume or more and less than 10% by volume. A solid electrolyte layer in which the average particle size Da of the first compound and the average particle size Db of the second compound satisfy 0.1 ≦ Da / Db ≦ 20.

0.

2. Li ａ M ２ (PO ４ ) ３ … a first compound represented by (1) and, M'P ２ O ７ ... and a second compound represented by (2). In the first compound, a satisfies 0.9 ≦ a ≦ 1.4, and M is one or more elements selected from Zr, Ti, Ge, Al, Hf, Ca, Ba, Sr, Sc, Y, and In. In the second compound, M' is one or more elements selected from Zr, Ti, Ge, Al, Hf, Ca, Ba, Sr, Sc, Y, and In. The proportion of the second compound is 0.5% by volume or more and less than 10% by volume. A solid electrolyte layer in which the average particle size Db of the second compound satisfies 0.01 μm ≦ Db ≦ 10 μm.

3. An all-solid-state battery comprising the solid electrolyte layer according to Claim 1 or 2, a positive electrode, and a negative electrode sandwiching the solid electrolyte layer.

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