Lithium-ion conductive solid electrolyte material

Abstract

Provided is an amorphous solid electrolyte sintered body having a high lithium ion conductivity and obtained by firing a highly deformable amorphous solid electrolyte material at a low temperature.　The solid electrolyte sintered body has an oxide containing: Li; at least one among Ta, Hf, Bi, Sb, and Nb; and P, and is in an amorphous state. The oxide may be represented by the chemical formula Li1+xTa2-xHfxPO8 (0≤x≤0.4). The oxide may be LiTa2PO8. The oxide may be represented by the chemical formula LiTayM2-yPO8 (M is Bi or Sb, 1.6≤y<2). The oxide may be composed of Li, Hf or Nb, P, and O.

Description

[Technical Field]

[0001] The present application relates to an amorphous solid electrolyte material having high lithium ion conductivity and a sintered compact of the solid electrolyte. [Background technology]

[0002] Lithium-ion secondary batteries are widely used as power sources for small electronic devices such as smartphones and laptop computers. In recent years, their use as power sources for large-scale applications such as hybrid and electric vehicles, as well as stationary storage batteries, is expected to expand. Furthermore, from the perspectives of safety and high energy density, research and development is underway on all-solid-state lithium-ion secondary batteries, lithium-air batteries, and all-solid-state lithium-sulfur batteries, which do not use flammable electrolytes. The solid electrolytes used in these electrochemical devices are required to have high lithium-ion conductivity.

[0003] In order to obtain lithium oxide materials with high lithium ion conductivity, attempts have been made to improve the properties by element substitution with LiTa2PO8 as the basic composition (Patent Documents 1 to 3 and Non-Patent Document 1). It has been reported that element substitution of LiTa2PO8 improves the bulk lithium ion conductivity, and the total lithium ion conductivity measured by electrochemical measurement has been shown to be up to 10 -3 However, LiTa2PO8 needs to be sintered at 1000°C or higher to exhibit lithium ion conductivity, and when molded at room temperature or low temperature, the grain boundary resistance is high, making it difficult to obtain high lithium ion conductivity.

[0004] Recently, it has been reported that amorphous powders of LiTa2PO8 and its elemental substitution products are synthesized through a mechanochemical reaction using a milling process, and then sintered to produce a crystalline solid electrolyte (Patent Document 4). However, this solid electrolyte must be sintered at high temperatures to crystallize. There is a need for a highly deformable amorphous solid electrolyte material with a chemical composition similar to LiTa2PO8, as well as a solid electrolyte with high lithium ion conductivity that can be obtained by sintering this amorphous solid electrolyte material at low temperatures. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2020-194773 [Patent Document 2] Patent Publication No. 2021-38100 [Patent Document 3] Patent Publication No. 2021-38099 [Patent Document 4] International Publication No. 2021 / 251407 [Non-patent literature]

[0006] [Non-Patent Document 1] R.Kim et al., Chem.Mater., Vol.33, 6909(2021) Summary of the Invention [Problem to be solved by the invention]

[0007] The present application has been made in view of the above circumstances, and an object of the present application is to provide an amorphous solid electrolyte material having high deformability and an amorphous solid electrolyte sintered compact having high lithium ion conductivity, which is obtained by firing the amorphous solid electrolyte material at a low temperature. [Means for solving the problem]

[0008] The present inventors have discovered that an amorphous sintered compact obtained by molding an amorphous lithium ion conductive oxide containing lithium, a specified metal element, and phosphoric acid and firing this molded body at a low temperature at which crystallization does not occur exhibits high lithium ion conductivity, thereby completing the present invention.

[0009] The solid electrolyte sintered compact of the present application has an oxide containing Li, one or more of Ta, Hf, Bi, Sb, and Nb, and P, and is in an amorphous state. The electrochemical device of the present application has the solid electrolyte sintered compact of the present application and a pair of electrodes sandwiching the solid electrolyte sintered compact. The solid electrolyte material of one embodiment of the present application has an oxide containing Li, one or more of Hf and Nb, and P, and is in an amorphous state. The solid electrolyte material of another embodiment of the present application has a chemical formula LiTa y Sb 2-y It is represented by PO8 (1.6≦y<2) and is in an amorphous state.

[0010] The chemical formula of the present invention is Li 1+x Ta 2-x Hf x The manufacturing method of the solid electrolyte sintered compact represented by PO8 (0≦x≦0.4) is 1+x Ta 2-x Hf x The process involves a molding step of molding amorphous powder to obtain a green body, and a sintering step of firing the green body at a temperature of 350°C to 650°C to obtain a sintered green body in an amorphous state. y M 2-y A method for producing a solid electrolyte sintered compact having an oxide represented by PO8 (M is Bi or Sb, 1.6≦y<2) or an oxide composed of Li, Hf or Nb, P, and O includes a molding step of molding an amorphous oxide to obtain a compact, and a sintering step of firing the compact at 350°C or higher and 650°C or lower to obtain an amorphous sintered compact. [Effects of the Invention]

[0011] According to the present invention, a sintered solid electrolyte compact having lithium ion conductivity can be obtained by molding a highly deformable amorphous solid electrolyte material and firing it at a low temperature at which crystallization does not occur. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a conceptual diagram of an all-solid-state lithium secondary battery, which is an example of an electrochemical device according to the present invention. [Figure 2] 1 is a powder X-ray diffraction pattern of a sintered compact of amorphous LiTa2PO8 obtained in Example 1. [Figure 3] 1 is a graph showing the results of measuring the AC impedance of the sintered compact of amorphous LiTa2PO8 obtained in Example 2. [Figure 4] Powder X-ray diffraction patterns of the sintered compact of amorphous LiTaHfPO obtained in Example 3, the sintered compact of amorphous LiTaHfPO obtained in Example 4, the sintered compact of amorphous LiTaHfPO obtained in Example 5, and the sintered compact of crystalline LiTaHfPO obtained in Comparative Example 1. [Figure 5] 1 shows powder X-ray diffraction patterns of a sintered compact of amorphous LiNb2PO8 obtained in Example 6 and a sintered compact of amorphous Li2Nb2P2O11 obtained in Example 7. [Figure 6] 1 is a powder X-ray diffraction pattern of a sintered compact of amorphous LiTa1.8Bi0.2PO8 obtained in Example 8. [Figure 7] 10 is a powder X-ray diffraction pattern of a sintered compact of amorphous LiHf2PO7 obtained in Example 9. [Figure 8] Comparative Example 2: Powder X-ray diffraction pattern of a sintered compact of crystalline LiTa2PO8 obtained. [Figure 9] 10 is a powder X-ray diffraction pattern of a sintered compact of amorphous LiTa1.8Sb0.2PO8 obtained in Example 10. [Figure 10] 1 shows powder X-ray diffraction patterns of a sintered compact of amorphous Li—Ta—PO obtained in Example 11 and a sintered compact of amorphous Li—Nb—PO obtained in Example 12. [Figure 11] 10 is a powder X-ray diffraction pattern of the amorphous composite positive electrode molded body obtained in Example 13. DETAILED DESCRIPTION OF THE INVENTION

[0013] (Solid electrolyte sintered body) The solid electrolyte sintered compact according to the embodiment of the present application has an oxide containing Li, one or more of Ta, Hf, Bi, Sb, and Nb, and P, and is in an amorphous state. The amorphous state refers to a state in which the powder X-ray diffraction pattern of the substance shows a halo pattern. Note that when the diffraction intensity of the peaks of partial crystallization is lower than the maximum diffraction intensity of the halo pattern, the substance as a whole can be said to be in an amorphous state. The oxide has the chemical formula Li 1+x Ta 2-x Hf x Oxide represented by PO8 (0≦x≦0.4 (same below)), chemical formula LiTa y M 2-y Examples include oxides represented by PO8 (M is Bi or Sb, 1.6≦y<2 (the same applies below)), and oxides composed of Li, Hf or Nb, P, and O.

[0014] Chemical formula Li 1+x Ta 2-x Hf x Oxides expressed as PO8 include LiTa2PO8, Li 1.1 Ta 1.9 Hf 0.1 PO8, Li 1.2 Ta 1.8 Hf 0.2 PO8, and Li 1.4 Ta 1.6 Hf 0.4 PO8, etc. Chemical formula: LiTa y M 2-y The oxides represented by PO8 include LiTa 1.8 Bi 0.2 PO8 and LiTa 1.8 Sb 0.2PO8, etc. Examples of oxides composed of Li, Hf or Nb, P, and O include LiHf2PO7 and LiNb2PO8, etc.

[0015] The solid electrolyte sintered compact of this embodiment can be obtained, for example, by molding powder of an amorphous solid electrolyte material having the same or similar composition as the solid electrolyte sintered compact and firing the molded body at a low temperature at which crystallization does not occur. Therefore, solid electrolytes and electrochemical devices can be produced at low temperatures using the powder of the solid electrolyte material as a raw material.

[0016] (Method of manufacturing a sintered solid electrolyte compact) The method for producing a sintered solid electrolyte compact according to the first embodiment of the present invention is a method for producing a sintered solid electrolyte compact according to the chemical formula Li 1+x Ta 2-x Hf x The method for producing a sintered solid electrolyte compact in an amorphous state includes an oxide represented by the chemical formula LiPO8. The method for producing a sintered solid electrolyte compact in the first embodiment includes a molding step and a sintering step. In the molding step, which is a broad concept including molding, a sintered solid electrolyte compact in an amorphous state is produced. 1+x Ta 2-x Hf x The powder, which is represented by PO8 and is in an amorphous state, is molded to obtain a compact.

[0017] It is preferable to uniformly pulverize the powder before the molding step. For example, the powder can be pulverized wet or dry using a pulverizer such as a mixer, a ball mill, or a planetary ball mill. In the molding step, for example, the powder may be placed in a molding die and pressed while being heated as necessary. There are no particular limitations on the molding form; the powder may be molded into a plate shape by hydrostatic pressure, or may be pressure molded by a method such as uniaxial pressure, or may be molded into a film shape using a coating technique or a film-forming technique.

[0018] Coating techniques include screen printing, electrophoresis (EPD), doctor blade, spray coating, inkjet, and spin coating, while film formation techniques include evaporation, sputtering, chemical vapor deposition (CVD), electrochemical vapor deposition, ion beam deposition, laser ablation, atmospheric pressure plasma film formation, and low-pressure plasma film formation.

[0019] Although the solid electrolyte can be used as is in its room-temperature pressed state, it is preferable to prepare a sintered solid electrolyte compact from the powder of the solid electrolyte material using techniques such as hot pressing, hot isostatic pressing, and electric current sintering, which involve molding while heating. Alternatively, a sintered solid electrolyte compact can be obtained by firing the powder of the solid electrolyte material obtained at room temperature in an electric furnace or similar at a predetermined temperature. As long as the temperature range allows the sintered solid electrolyte compact prepared from the solid electrolyte material to maintain its amorphous state, processes for producing sintered ceramics, such as electric furnace firing, hot press heating, HIP, and SPS, can be used.

[0020] A solid electrolyte sintered compact may be produced from powder of one type of solid electrolyte material, or from powder of two or more types of solid electrolyte materials. Furthermore, a solid electrolyte sintered compact may be produced by mixing powder of a solid electrolyte material with another electrolyte material. Powder of one type of solid electrolyte material can be used as a solid electrolyte as it is, as long as it is a room-temperature compact, sintered body, or coated product.

[0021] In the sintering process, the compact is fired at 350°C to 650°C to obtain an amorphous sintered compact. This sintered compact has lithium ion conductivity and can be used as a solid electrolyte. The firing temperature can generally be set appropriately depending on the powder composition of the solid electrolyte material within a temperature range in which the amorphous state can be maintained even after the solid electrolyte sintered compact is formed. As long as the oxidation reaction has progressed sufficiently in the powder state, there are no particular restrictions on the firing atmosphere; firing is usually performed in an argon gas atmosphere, nitrogen gas atmosphere, oxygen gas atmosphere, or air atmosphere. The firing time can be set depending on the firing temperature, etc. There are also no particular restrictions on the cooling method after firing; typically, natural cooling (cooling in a furnace) or slow cooling is sufficient. There are no particular restrictions on the crucible material used during firing, as long as it is stable at high temperatures above 350°C. Alumina, zirconia, platinum, gold, and stainless steel crucibles or containers can be used.

[0022] The method for producing a solid electrolyte sintered compact according to the second embodiment of the present invention is a method for producing a solid electrolyte sintered compact that contains LiTaPO oxide and is in an amorphous state. Regarding the method for producing a solid electrolyte sintered compact according to the second embodiment, overlapping descriptions with those of the method for producing a solid electrolyte sintered compact according to the first embodiment will be omitted as appropriate. Regarding the production methods according to the third and fourth embodiments, overlapping descriptions with those of the method for producing a solid electrolyte sintered compact according to the first embodiment will also be omitted as appropriate.

[0023] The method for manufacturing a sintered solid electrolyte compact according to the second embodiment includes a molding step and a sintering step. In the molding step, amorphous LiTaPO powder is molded to obtain a compact. In the sintering step, the compact is fired at 350°C to 650°C to obtain an amorphous sintered compact. This sintered compact has lithium ion conductivity and can be used as a solid electrolyte.

[0024] The method for producing a sintered solid electrolyte compact according to the third embodiment of the present invention is a method for producing a sintered solid electrolyte compact according to the chemical formula LiTa y M 2-yA method for manufacturing a solid electrolyte sintered compact having an oxide represented by PO8 and being in an amorphous state. The method for manufacturing the solid electrolyte sintered compact of the third embodiment includes a forming step and a sintering step. In the forming step, a powder of an oxide represented by the chemical formula LiTa y M 2-y PO8 and being in an amorphous state is formed into a formed body. The sintering step is the same as that of the second embodiment. The sintered compact obtained in the sintering step has lithium ion conductivity and can be used as a solid electrolyte.

[0025] The method for manufacturing the solid electrolyte sintered compact of the fourth embodiment of the present application is a method for manufacturing a solid electrolyte sintered compact having an oxide composed of Li, Hf or Nb, P, and O and being in an amorphous state. The method for manufacturing the solid electrolyte sintered compact of the fourth embodiment includes a forming step and a sintering step. In the forming step, a powder of an oxide composed of Li, Hf or Nb, P, and O and being in an amorphous state is formed into a formed body. In the sintering step, the formed body is fired at 350 °C or higher and 650 °C or lower to obtain a sintered compact in an amorphous state. This sintered compact has lithium ion conductivity and can be used as a solid electrolyte.

[0026] (Solid electrolyte material) The solid electrolyte material of the present application is in an amorphous state and is, for example, a powder or a small lump. If the solid electrolyte material of the present application is formed and fired at a low temperature at which crystallization does not occur, the solid electrolyte sintered compact of the embodiment of the present application can be obtained. The solid electrolyte material of the first embodiment of the present application has an oxide containing Li, one or more of Hf and Nb, and P. Examples of the oxide containing Li, one or more of Hf and Nb, and P include LiHf2PO7, LiNb2PO8, Li2Nb2P2O 11 , and oxides represented by the chemical formula Li 1+z Ta 2-z Hf z PO8 (0 < z ≦ 0.4 (the same applies hereinafter)).

[0027] The chemical formula Li 1+z Ta 2-z Hf zThe oxide represented by PO8 is Li 1.1 Ta 1.9 Hf 0.1 PO8, Li 1.2 Ta 1.8 Hf 0.2 PO8, and Li 1.4 Ta 1.6 Hf 0.4 PO8, etc. The solid electrolyte material of the second embodiment of the present application is a material having the chemical formula LiTa y Sb 2-y It is expressed as PO8 (1.6≦y<2 (same below)). Chemical formula: LiTa y Sb 2-y The oxides represented by PO8 include LiTa 1.8 Sb 0.2 Examples include PO8.

[0028] (Method of manufacturing solid electrolyte material) First, various salts serving as raw materials for the solid electrolyte material are dissolved in solvents to obtain respective solutions. Examples of the various salts include oxides, carbonates, hydroxides, nitrates, ammonium salts, hydrogen ammonium salts, chlorides, and oxychlorides. Examples of the solvents include alcoholic solvents such as methanol, ethanol, hexanol, and propanol, organic solvents such as aromatics and ethers, and water.

[0029] For example, tantalum chloride, bismuth chloride, and hafnium chloride are dissolved in ethanol. Water-soluble salts are dissolved in ion-exchanged water, and salts that are soluble only in non-aqueous solvents are dissolved in organic solvents. The temperature at which various salts are dissolved in the solvent may be any temperature above room temperature and below the boiling point of the solvent. Various salts may be dissolved in the solvent by standing, or by stirring using a stirrer or agitator.

[0030] Next, the solutions are mixed uniformly to obtain a mixed solution. The mixed solution is then heated to a temperature at which the solvent evaporates, resulting in drying and a precipitate. The heating temperature is preferably 50°C or higher and lower than the boiling point of the solvent, more preferably 80°C or higher and lower than the boiling point of the solvent. There are no particular limitations on the heating method, and heating may be performed using a hot plate, an electrically heated muffle furnace, a mantle heater, or the like.

[0031] Then, by-products such as NH4Cl and carbides derived from various salts are removed from the precipitate. Methods for removing by-products include washing with a solution in which only the by-products dissolve, but a simple method of calcining the precipitate is preferred. This is because calcining the precipitate at a predetermined temperature yields the target amorphous solid electrolyte material. The calcination method is not particularly limited, and calcination may be performed using an electrically heated muffle furnace or mantle heater. To obtain an amorphous solid electrolyte material, the calcination temperature is preferably 350°C or higher and 650°C or lower, more preferably 350°C or higher and 600°C or lower, more preferably 350°C or higher and 550°C or lower, and even more preferably 350°C or higher and 500°C or lower.

[0032] There are no particular restrictions on the container used for firing; glass beakers, non-alumina ceramic containers, gold containers, platinum containers, and alumina containers can be used. There are no particular restrictions on the firing atmosphere; firing is usually carried out in an oxidizing gas atmosphere such as oxygen or air. The firing time can be set according to the firing temperature, etc., as long as residual substances such as nitrogen, chlorine, and carbon derived from various salts can be volatilized. There are also no particular restrictions on the cooling method after firing; however, natural cooling (cooling in the furnace) or slow cooling is usually sufficient. After firing and cooling, the solid electrolyte material can be crushed as needed, and re-fired at a different firing temperature. The degree of crushing can be adjusted according to the firing temperature, etc.

[0033] Other methods are also acceptable as long as the metal components of the solid electrolyte material can be mixed uniformly at the atomic level and the solid electrolyte material can be produced at low temperatures. For example, solid electrolyte materials can be produced by solution processes such as coprecipitation, sol-gel, complex polymerization, and hydrothermal synthesis, as well as gas-phase reaction synthesis processes such as vacuum deposition, sputtering, pulsed laser deposition, and chemical vapor reaction. Solid electrolyte materials can also be produced by mechanochemical reactions such as ball milling.

[0034] (Positive electrode material) The solid electrolyte material of the present application can be used as a constituent of a positive electrode to ensure lithium ion conductivity in the electrode. In other words, a molded product obtained by mixing or combining the solid electrolyte material of the present application with a positive electrode active material constitutes the positive electrode member. Materials commonly used as positive electrode materials for lithium ion batteries can be used as the positive electrode active material. Examples of the positive electrode active material include oxides such as LiCoO2, LiNiO2, Li(Ni,Mn,Co)O2, Li(Ni,Co,Al)O2, Li2MnO3-Li(Ni,Mn,Co)O2, Li(Ni,Mn)2O4, Li(Co,Mn)2O4, Li(Mn,Al)2O4, LiFePO4, LiMnPO4, LiCoPO4, and LiNiPO4, as well as sulfur and lithium sulfide.

[0035] Additionally, materials that undergo reversible lithium intercalation and deintercalation reactions at a high voltage of 2 V or higher can be used as the positive electrode active material. Furthermore, to improve the bond between the positive electrode and the solid electrolyte material and to enhance lithium ion conductivity, the positive electrode material may contain a polymer, oxide, sulfide, hydride, or halide. Furthermore, to improve electronic conductivity in the positive electrode, the positive electrode material may contain a conductive additive such as carbon black, carbon nanotubes, graphite, or titanium oxide.

[0036] (Electrochemical Devices) The solid electrolyte sintered compact of the present application has excellent lithium ion conductivity despite being amorphous, and therefore can be used as a solid electrolyte in electrochemical devices such as all-solid-state lithium secondary batteries, lithium-air batteries, and lithium-sulfur batteries. An all-solid-state lithium secondary battery, which is an example of an electrochemical device, includes the solid electrolyte sintered compact of the present application and a pair of electrodes sandwiching the solid electrolyte sintered compact. Note that the pair of electrodes does not necessarily have to directly sandwich the solid electrolyte sintered compact.

[0037] The solid electrolyte sintered compact of the present application can also be used as a positive electrode member or a negative electrode member. FIG. 1 conceptually shows an all-solid-state lithium secondary battery, which is an example of an electrochemical device according to an embodiment of the present application. The all-solid-state lithium secondary battery includes a housing 1, a positive electrode tab 2, a positive electrode current collector 3, a positive electrode 4, a separator 5, a negative electrode 6, a negative electrode current collector 7, and a negative electrode tab 8. The solid electrolyte sintered compact of the present application can be used as part of the positive electrode 4 or the negative electrode 6, or as the separator 5. [Example]

[0038] Example 1: Preparation of sintered compact of amorphous LiTa2PO8 In a dry environment, 1.4328 g of TaCl5 (Rare Metallic, 99.9% (hereinafter the same)) was dissolved in 50 mL of absolute ethanol to obtain a TaCl5 solution. 0.2301 g of NH4H2PO4 (Wako Pure Chemical Industries, special grade (hereinafter the same)) was dissolved in 50 mL of ion-exchanged water to obtain an NH4H2PO4 aqueous solution. 0.0840 g of LiOH·H2O (Kojundo Chemical Laboratory, 99% up (hereinafter the same)) was dissolved in 100 mL of ion-exchanged water to obtain a LiOH aqueous solution. While stirring the LiOH aqueous solution with a stirrer, the TaCl5 solution and the NH4H2PO4 aqueous solution were added sequentially and mixed at 80°C.

[0039] This mixed solution was dried at 120°C for 15 hours, and the solidified powder was collected and lightly crushed in an agate mortar. The crushed powder was then fired in an oxygen atmosphere at 600°C for 12 hours in a vacuum gas-exchange electric furnace (Denken Hydental, KDF-75plus; hereafter the same) to obtain a white powder of the amorphous compound LiTa2PO8. The chemical composition of this white powder was determined by ICP-OES analysis (Agilent, Agilent 5800) and found to be nearly stoichiometric LiTa2PO8. Furthermore, SEM-EDS analysis (JEOL, JCM-6000; hereafter the same) of this white powder detected Ta and P, but no other metal elements.

[0040] This white powder was wet ball milled using a planetary ball mill (Fritsch, P-7 (hereinafter the same)) and then uniaxially pressed using a tablet press (Nihon Bunko, (hereinafter the same)) to obtain a compact. This compact was placed on an SSA-S alumina plate and sintered in an oxygen atmosphere at 600 °C for 12 hours using a vacuum gas replacement electric furnace to obtain a sintered compact of amorphous LiTa2PO8. When the crystal structure of this sintered compact was examined using a powder X-ray diffractometer (Rigaku, trade name SmartLab (hereinafter the same)), no clear peaks were observed, but a halo characteristic of amorphous solids was observed. The powder X-ray diffraction pattern is shown in Figure 2.

[0041] Example 2: Preparation of sintered compact of amorphous LiTaPO (Li excess) A white powder of the amorphous compound LiTa2PO8 and a sintered compact of amorphous LiTa2PO8 were obtained in the same manner as in Example 1, except that the amount of LiOH·HO used was 1.1 times that of Example 1, i.e., 0.0923 g, a 10 mol% excess. When the crystal structure of this sintered compact was examined using a powder X-ray diffractometer, no clear peaks were observed, and a halo characteristic of amorphous solids was observed. Furthermore, the resistance of this sintered compact was determined from the arc of the Nyquist plot using a frequency response analyzer (FRA) (Solartron, Model 1260 (hereinafter the same)). The conductivity was calculated from this resistance value.

[0042] The impedance was measured under the conditions of a frequency of 32 MHz to 100 Hz and an amplitude voltage of 100 mV, and an Au electrode was used as the blocking electrode (same below). The results of this impedance measurement are shown in Figure 3. From the measurement results at room temperature, the total conductivity of lithium ions was found to be 2.16 × 10 -7 The calculated conductivity was 1.5 S / cm. It was revealed that the sintered compact of this example had high lithium ion conductivity despite being in an amorphous state. This is thought to be because the white powder of the amorphous compound LiTa2PO8 has high moldability, and the particle interfaces of the powder were bonded together even at the low sintering temperature of 600°C, which would not cause crystallization.

[0043] Example 3: Amorphous Li 1.1 Ta 1.9 Hf 0.1 Preparation of PO8 powder and sintered compacts In a dry environment, 1.3612 g of TaCl5 and 0.0641 g of HfCl4 (Fujifilm Wako Pure Chemical Industries, 99.9% (hereinafter the same)) were dissolved in 50 mL of absolute ethanol to obtain a TaCl5·HfCl4 solution. 0.2301 g of NH4H2PO4 was dissolved in 50 mL of ion-exchanged water to obtain an NH4H2PO4 aqueous solution. 0.1016 g of LiOH·H2O was dissolved in 100 mL of ion-exchanged water to obtain a LiOH aqueous solution. While stirring the LiOH aqueous solution with a stirrer, the TaCl5·HfCl4 solution and the NH4H2PO4 aqueous solution were added in turn and mixed at 80°C. Note that this mixed solution contains a composition of Li 1.1 Ta 1.9 Hf 0.1 It contains 1.1 moles of LiOH, or 10 mol% excess, compared to PO8.

[0044] This mixed solution was dried at 120°C for 15 hours, and the dried and solidified powder was collected and lightly crushed in an agate mortar. The crushed powder was fired in an oxygen atmosphere at 600°C for 12 hours using a vacuum gas replacement type electric furnace to obtain amorphous compound Li. 1.1 Ta 1.9 Hf 0.1A white powder of PO8 was obtained. SEM-EDS analysis of this white powder detected Ta, Hf, and P, but no metal elements other than Ta and Hf were detected. This white powder was wet ball milled using a planetary ball mill, and then uniaxially pressed using a tablet press to obtain a compact.

[0045] This compact was placed on an SSA-S alumina plate and fired in a vacuum gas replacement type electric furnace in an oxygen atmosphere at 600°C for 12 hours to obtain amorphous Li. 1.1 Ta 1.9 Hf 0.1 A sintered compact of PO8 was obtained. When the crystal structure of this sintered compact was examined using a powder X-ray diffractometer, no clear peaks were observed, and a halo characteristic of an amorphous solid was observed. The powder X-ray diffraction pattern is shown in Figure 4. The electrical conductivity of this sintered compact was calculated using the same method as in Example 1. The total lithium ion conductivity of this sintered compact was 9.34 x 10 -8 It was found that the sintered compact of this example had lithium ion conductivity despite being in an amorphous solid state.

[0046] Example 4: Amorphous Li 1.2 Ta 1.8 Hf 0.2 Preparation of PO8 powder and sintered compacts The amorphous compound Li was prepared in the same manner as in Example 3, except that the amounts of TaCl, HfCl, and LiOH·H were changed to 1.2896 g, 0.1281 g, and 0.1108 g, respectively. 1.2 Ta 1.8 Hf 0.2 White powder of PO8 and amorphous Li 1.2 Ta 1.8 Hf 0.2 A sintered compact of PO8 was obtained. The raw material mixture solution contained the composition Li 1.2 Ta 1.8 Hf 0.2 It contained 1.1 moles of LiOH, i.e., 10 mol% excess, compared to PO8.

[0047] SEM-EDS analysis of this white powder detected Ta, Hf, and P, but no metal elements other than Ta and Hf. Furthermore, when the crystal structure of this sintered compact was examined using a powder X-ray diffractometer, no clear peaks were observed, and a halo characteristic of an amorphous solid was observed. The powder X-ray diffraction pattern is shown in Figure 4. Furthermore, the electrical conductivity of this sintered compact was calculated using the same method as in Example 1. The total lithium ion conductivity of this sintered compact was 5.41 x 10 -8 It was found that the sintered compact of this example had lithium ion conductivity despite being in an amorphous solid state.

[0048] Example 5: Amorphous Li 1.4 Ta 1.6 Hf 0.4 Preparation of PO8 powder Amorphous compound Li was prepared in the same manner as in Example 3, except that the amounts of TaCl5, HfCl4, and LiOH·H2O used were changed to 1.1463 g, 0.2562 g, and 0.1292 g, respectively, and the firing temperature was changed to 500 °C. 1.4 Ta 1.6 Hf 0.4 The white powder of PO8 was obtained. 1.4 Ta 1.6 Hf 0.4 It contained 1.1 moles of LiOH, i.e., 10 mol% excess, compared to PO8.

[0049] SEM-EDS analysis of this white powder detected Ta, Hf, and P, but no other metal elements were detected. Furthermore, when the crystal structure of this white powder was examined using a powder X-ray diffractometer, slight peaks suggesting crystallization were present, but a halo characteristic of an amorphous solid was observed as the main phase. This suggests that a composition ratio of Hf to PO8 of 0.4 is the upper limit for forming an amorphous powder. Figure 4 shows the powder X-ray diffraction pattern. By molding this white powder and firing it at 500°C, amorphous Li 1.4 Ta 1.6 Hf 0.4It is believed that a sintered compact of PO8 can be obtained.

[0050] Comparative example 1: Li 1.4 Ta 1.6 Hf 0.4 Preparation of PO8 powder Li was prepared in the same manner as in Example 5, except that the firing temperature was changed to 700°C. 1.4 Ta 1.6 Hf 0.4 A white powder of PO8 was obtained. When the crystal structure of this white powder was examined using a powder X-ray diffractometer, clear peaks corresponding to Ta2O5 and other elements were observed, indicating that it was not an amorphous single phase. The powder X-ray diffraction pattern is shown in Figure 4. It is believed that the white powder obtained contained crystalline portions because it was fired at a higher temperature of 700°C than in Example 5.

[0051] Example 6: Preparation of amorphous LiNb2PO8 powder and sintered compact In a dry environment, 1.0807 g of NbCl5 (Rare Metallic, 99.9% (same below)) was dissolved in 50 mL of absolute ethanol to obtain an NbCl5 solution. 0.2301 g of NH4H2PO4 was dissolved in 50 mL of ion-exchanged water to obtain an NH4H2PO4 aqueous solution. 0.0840 g of LiOH·H2O was dissolved in 100 mL of ion-exchanged water to obtain an LiOH aqueous solution. While stirring the LiOH aqueous solution with a stirrer, the NbCl5 solution and the NH4H2PO4 aqueous solution were added sequentially and mixed at 80°C. This mixed solution contains Li, Nb, and P in the same molar ratio as the composition LiNb2PO8.

[0052] This mixed solution was dried at 120°C for 15 hours, and the dried, solidified powder was collected. This solidified powder was heated to 350°C and then lightly crushed in an agate mortar. This crushed powder was fired in air at 500°C for 12 hours in a muffle furnace (Yamato Scientific, FP101 (hereinafter the same)), yielding a white powder of amorphous LiNb2PO8. SEM-EDS analysis of this white powder detected Nb and P, but no metal elements other than Nb.

[0053] A sintered compact of amorphous LiNb2PO8 was produced from this white powder in the same manner as in Example 5. When the crystal structure of this sintered compact was examined using a powder X-ray diffractometer, no clear peaks were observed, and a halo characteristic of amorphous solids was observed. The powder X-ray diffraction pattern is shown in Figure 5. The electrical conductivity of this sintered compact was calculated in the same manner as in Example 1. The total lithium ion conductivity of this sintered compact was 6.32 x 10 -8 It was found that the sintered compact of this example had lithium ion conductivity despite being in an amorphous solid state.

[0054] Example 7: Amorphous LiNbP0 11 Preparation of powder and sintered compacts The amorphous compound Li2Nb2P2O was prepared in the same manner as in Example 6, except that the amounts of NH4H2PO4 and LiOH·H2O used were changed to 0.4602 g and 0.1680 g, respectively. 11 The raw material mixture solution had the composition Li2Nb2P2O 11 It contained Li, Nb, and P in the same substance ratio as in the above. SEM-EDS analysis of this white powder detected Nb and P, but no other metal elements were detected.

[0055] In the same manner as in Example 6, amorphous Li2Nb2P2O was obtained from this white powder. 11 A sintered compact was produced. When the crystal structure of this sintered compact was examined using a powder X-ray diffractometer, no clear peaks were observed, and a halo characteristic of an amorphous solid was observed. The powder X-ray diffraction pattern is shown in Figure 5. The electrical conductivity of this sintered compact was calculated in the same manner as in Example 1. The total lithium ion conductivity of this sintered compact was 2.82 x 10 -8 It was found that the sintered compact of this example had lithium ion conductivity despite being in an amorphous solid state.

[0056] Example 8: Amorphous LiTa 1.8 Bi 0.2 Preparation of sintered compacts of PO8 In a dry environment, 1.2896 g of TaCl5 and 0.1261 g of BiCl3 (Kojundo Chemical Laboratory, 99.99%) were dissolved in 50 mL of absolute ethanol to obtain a TaCl5·BiCl3 solution. 0.2301 g of NH4H2PO4 was dissolved in 50 mL of ion-exchanged water to obtain an NH4H2PO4 aqueous solution. 0.0923 g of LiOH·H2O was dissolved in 100 mL of ion-exchanged water to obtain a LiOH aqueous solution. While stirring the LiOH aqueous solution with a stirrer, the TaCl5·BiCl4 solution and the NH4H2PO4 aqueous solution were added in turn and mixed at 80°C. This mixed solution had the following composition: LiTa 1.8 Bi 0.2 It contains 1.1 moles of LiOH, or 10 mol% excess, compared to PO8.

[0057] This mixed solution was dried at 120°C for 15 hours, and the dried and solidified powder was collected and lightly crushed in an agate mortar. The crushed powder was fired in an oxygen atmosphere at 500°C for 12 hours using a vacuum gas replacement type electric furnace to obtain the amorphous compound LiTa 1.8 Bi 0.2 A white powder of PO8 was obtained. SEM-EDS analysis of this white powder detected Ta, Bi, and P, but no metal elements other than Ta and Bi were detected. This white powder was wet ball milled using a planetary ball mill, and then uniaxially pressed using a tablet press to obtain a compact.

[0058] This compact was placed on an SSA-S alumina plate and fired in an oxygen atmosphere at 500°C for 12 hours using a vacuum gas replacement type electric furnace to obtain amorphous LiTa 1.8 Bi 0.2 A sintered compact of PO8 was obtained. When the crystal structure of this sintered compact was examined using a powder X-ray diffractometer, no clear peaks were observed, and a halo characteristic of an amorphous solid was observed. The powder X-ray diffraction pattern is shown in Figure 6. The electrical conductivity of this sintered compact was calculated using the same method as in Example 1. The total lithium ion conductivity of this sintered compact was 8.28 x 10 -9It was found that the sintered compact of this example had lithium ion conductivity despite being in an amorphous solid state.

[0059] Example 9: Preparation of amorphous LiHf2PO7 powder In a dry environment, 1.2812 g of HfCl4 was dissolved in 50 mL of absolute ethanol to obtain a HfCl4 solution. 0.2301 g of NH4H2PO4 was dissolved in 50 mL of ion-exchanged water to obtain a NH4H2PO4 aqueous solution. 0.0923 g of LiOH·H2O was dissolved in 100 mL of ion-exchanged water to obtain a LiOH aqueous solution. While stirring the LiOH aqueous solution with a stirrer, the HfCl4 solution and the NH4H2PO4 aqueous solution were added sequentially and mixed at 80 °C. This mixed solution was dried at 120 °C for 15 hours, and the dried, solidified powder was collected. The solidified powder was heated to 350 °C and then lightly crushed in an agate mortar.

[0060] This ground powder was fired in a muffle furnace in air at 500°C for 12 hours to obtain a white powder of amorphous LiHf2PO7. SEM-EDS analysis of this white powder detected Hf and P, but no other metal elements were detected. Furthermore, when the crystal structure of this white powder was examined using a powder X-ray diffractometer, slight peaks suggestive of crystallization were present, but a halo characteristic of an amorphous solid was observed as the main phase. The powder X-ray diffraction pattern is shown in Figure 7. It is believed that sintered compacts of amorphous LiHf2PO7 can be obtained by molding this white powder and firing it at 500°C.

[0061] Comparative Example 2: Preparation of sintered compact of crystalline LiTa2PO8 A white powder compact of amorphous LiTaPO was obtained in the same manner as in Example 2. This compact was placed on an SSA-S alumina plate and sintered in an oxygen atmosphere at 1000°C for 12 hours using a vacuum gas replacement electric furnace to obtain a sintered compact of crystalline LiTaPO. The crystal structure of this sintered compact was examined using a powder X-ray diffractometer, confirming that it was crystalline and consisted of a nearly single phase of the known monoclinic system and space group C / c. The powder X-ray diffraction pattern is shown in Figure 8.

[0062] Example 10: Amorphous LiTa 1.8 Sb 0.2 Preparation of PO8 powder and sintered compacts In a dry environment, 1.2896 g of TaCl5 and 0.09125 g of SbCl3 (Fujifilm Wako Pure Chemical Industries, special grade reagent) were dissolved in 50 mL of absolute ethanol to obtain a TaCl5·SbCl3 solution. 0.2301 g of NH4H2PO4 was dissolved in 50 mL of ion-exchanged water to obtain an NH4H2PO4 aqueous solution. 0.0923 g of LiOH·H2O was dissolved in 100 mL of ion-exchanged water to obtain a LiOH aqueous solution. While stirring the LiOH aqueous solution with a stirrer, the TaCl5·SbCl3 solution and the NH4H2PO4 aqueous solution were added in turn and mixed at 80°C. This mixed solution had the following composition: LiTa 1.8 Sb 0.2 It contains 1.1 moles of LiOH, or 10 mol% excess, compared to PO8.

[0063] This mixed solution was dried at 120°C for 15 hours, and the dried and solidified powder was collected and lightly crushed in an agate mortar. The crushed powder was fired in an oxygen atmosphere at 500°C for 12 hours using a vacuum gas replacement type electric furnace to obtain the amorphous compound LiTa 1.8 Sb 0.2 A white powder of PO8 was obtained. This white powder was pulverized in a wet ball mill and then uniaxially pressed using a tablet press to obtain a compact.

[0064] This compact was placed on an SSA-S alumina plate and fired in an oxygen atmosphere at 500°C for 12 hours using a vacuum gas replacement type electric furnace to obtain amorphous LiTa 1.8 Sb 0.2 A sintered compact of PO8 was obtained. When the crystal structure of this sintered compact was examined using a powder X-ray diffractometer, no clear peaks were observed, and a halo characteristic of an amorphous solid was observed. The powder X-ray diffraction pattern is shown in Figure 9.

[0065] Example 11: Preparation of amorphous Li-Ta-PO compound powder and compact As in Example 1, white powders were obtained for amorphous Li-Ta-PO compounds with Li:Ta:P=2:2:1 composition, Li:Ta:P=2:1:1 composition, Li:Ta:P=8:5:4 composition, Li:Ta:P=4:3:2 composition, and Li:Ta:P=10:7:3 composition. When the crystal structure was examined using a powder X-ray diffractometer, no clear peaks were observed, but a halo characteristic of amorphous solids was observed. The powder X-ray diffraction patterns are shown in Figure 10.

[0066] For the Li:Ta:P = 2:1:1 composition, a uniaxially pressed compact was produced using a tablet press. For the Li:Ta:P = 2:2:1 and 2:1:1 compositions, the compact was fired in an oxygen atmosphere at 500°C for 12 hours to produce a sintered compact.

[0067] For these compacts, the resistance values ​​were obtained from the arcs of the Nyquist plot using a frequency response analyzer, and the electrical conductivity was calculated from these resistance values. From the measurement results at room temperature, the total electrical conductivity of the compact with a Li:Ta:P=2:1:1 composition was 4.35×10 -9 The total electrical conductivity of the compacts of this example, which are amorphous, is somewhat plastic, and it was confirmed that they have lithium ion conductivity even as compacts. In addition, the total electrical conductivity of the compacts sintered at 500°C with Li:Ta:P=2:2:1 and 2:1:1 compositions was 8.96×10 -9 S / cm, 3.35 x 10 -8 It was found that an even higher conductivity could be obtained by sintering at a low temperature of 500°C.

[0068] Example 12: Preparation of amorphous Li-Nb-PO compound powder and compact As in Example 6, a white powder of amorphous Li—Nb—PO compound with a Li:Nb:P=2:2:1 composition was obtained. When the crystal structure was examined using a powder X-ray diffractometer, no clear peaks were observed, but a halo characteristic of amorphous solids was observed. The powder X-ray diffraction pattern is shown in Figure 10.

[0069] Furthermore, a uniaxially pressed powder compact was produced using a tablet press, and the powder compact was sintered in an oxygen atmosphere at 500°C for 12 hours to obtain a sintered compact.

[0070] For these compacts, the resistance values ​​were obtained from the arcs of the Nyquist plots using a frequency response analyzer, and the electrical conductivity was calculated from the resistance values. From the measurement results at room temperature, the total electrical conductivity of the compacts was 3.02 × 10 -9 The total conductivity of the compacts of this example was calculated to be 3.62 × 10 S / cm. Since the compacts of this example are in an amorphous state, they have a certain degree of plasticity, and it was confirmed that even the compacts have lithium ion conductivity. In addition, the total conductivity of the compacts sintered at 500°C was 3.62 × 10 -8 It was found that an even higher conductivity could be obtained by sintering at a low temperature of 500°C.

[0071] Example 13: Preparation of amorphous composite positive electrode A composite positive electrode was fabricated using the white powder with a Li:Ta:P = 2:1:1 composition obtained in Example 11 as the electrolyte for the composite positive electrode. LiCoO (Cellseed C-5H, manufactured by Nippon Chemical Industry Co., Ltd.) was used as the positive electrode active material. The electrolyte powder and LiCoO powder were mixed in a weight ratio of 1:1 using an agate mortar, and then uniaxially pressed using a tablet press to produce a green compact. The green compact was then fired in an argon gas atmosphere at 400°C for 2 hours to produce a sintered green compact for the composite positive electrode.

[0072] The resistance value of the prepared composite positive electrode compact was determined from the arc of the Nyquist plot using a frequency response analyzer, and the lithium ion conductivity was calculated from this resistance value. From the measurement results at room temperature, the total conductivity of the compact was 10 -9 S / cm order, and the sintered body at 400°C for 2 hours was 10 -8 Although these values ​​are high for ionic resistance, it is clear that a conductive path is established within the composite positive electrode, and that the amorphous body has plasticity, which has prevented an increase in the interfacial resistance with the positive electrode active material.

[0073] The powder X-ray diffraction patterns measured after pulverizing the composite positive electrode are shown in Figure 11. In both the room-temperature compact and the 400°C sintered compact, only the halo derived from the amorphous solid electrolyte and the diffraction pattern derived from the LiCoO2 phase were observed, confirming the absence of reaction products. From the above, it is clear that the amorphous solid electrolyte of the present invention can be used as a composite positive electrode for all-solid-state batteries.

[0074] Example 14: Fabrication of all-solid-state battery The white powder obtained in Example 1 was filled into a 10 mm diameter heat press mold (manufactured by AS ONE Corporation) and held at 400°C and 374 MPa for 2 hours using a heat press machine (manufactured by AS ONE Corporation) to obtain a disk-shaped amorphous sintered compact approximately 0.3 mm thick. This amorphous sintered compact and the mold constituted a composite electrode layer comprising a solid electrolyte layer and one electrode layer. Furthermore, a polymer electrolyte sheet and a metallic lithium sheet, which would form the other electrode layer, were sequentially attached to the exposed surface of the solid electrolyte layer to produce an all-solid-state battery. A constant-current charge-discharge test was performed on this all-solid-state battery at 60°C using a charge-discharge tester (HJ1020mSD8 manufactured by Hokuto Denko Corporation). The capacity corresponding to the charge-discharge reaction was observed, confirming the operation of the all-solid-state battery. [Industrial Applicability]

[0075] The amorphous solid electrolyte material of the present invention has high moldability. When this solid electrolyte material is molded and sintered at low temperature, an amorphous solid electrolyte sintered compact is obtained. This solid electrolyte sintered compact has high lithium ion conductivity. Therefore, by using the amorphous solid electrolyte material of the present invention, electrochemical devices such as solid electrolytes and all-solid-state batteries can be produced at low temperatures.

Claims

1. A sintered compact of a solid electrolyte in an amorphous state, which comprises an oxide containing Li, Ta, one or more of Hf and Sb, and P.

2. In claim 1, The oxide has the chemical formula Li １＋ｘ Ta ２－ｘ Hf ｘ P.O. ８ (0.1≦x≦0.4)

3. A solid electrolyte sintered compact in an amorphous state, which is composed of Li, Ta, P, and O, and has an oxide with a composition ratio Li / Ta of 1 or more and 2 or less.

4. In claim 1, The oxide has the chemical formula LiTa ｙ Sb ２－ｙ P.O. ８ (1.6≦y<2)

5. A solid electrolyte sintered compact having an oxide composed of Li, Nb in an amount equal to or greater than the mole percent of Hf or Li, P, and O, and being in an amorphous state.

6. A solid electrolyte material having an oxide containing Li, at least one of Hf and Nb in an amount of at least mol % of Li, and P, but not containing Ta, and being in an amorphous state.

7. Chemical formula Li １＋ｚ Ta ２－ｚ Hf ｚ P.O. ８ (0<z≦0.4) and is in an amorphous state.

8. Chemical formula LiTa ｙ Sb ２－ｙ P.O. ８ (1.6≦y<2) and is an amorphous solid electrolyte material.

9. Chemical formula Li １＋ｘ Ta ２－ｘ Hf ｘ P.O. ８ a molding step of molding the amorphous powder, wherein x is represented by 0.1≦x≦0.4, to obtain a molded body; a sintering step of firing the molded body at 350°C or higher and 650°C or lower to obtain a sintered molded body in an amorphous state; The method for producing a sintered solid electrolyte compact according to claim 2, comprising the steps of:

10. a forming step of forming the amorphous oxide to obtain a formed body; a sintering step of firing the molded body at 350°C or higher and 650°C or lower to obtain a sintered molded body in an amorphous state; 6. The method for producing a sintered compact of a solid electrolyte according to claim 3, comprising the steps of:

11. A solid electrolyte sintered compact according to any one of claims 1 to 5, a pair of electrodes sandwiching the solid electrolyte sintered compact; An electrochemical device comprising:

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