Solid electrolyte material having lithium ion conductivity

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

Lithium-ion conductive solid electrolyte material

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

[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 a lithium oxide material with high lithium ion conductivity, LiTa ２ P.O. ８ Attempts have been made to improve the characteristics by element substitution based on the basic composition (Patent Documents 1 to 3 and Non-Patent Document 1). ２ P.O. ８ It has been reported that element substitution improves the bulk lithium ion conductivity, and the total lithium ion conductivity measured by electrochemical measurements is up to 10 －３ However, it was revealed that the LiTa ２ P.O. ８ However, sintering at 1000°C or higher is required 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, LiTa was synthesized by mechanochemical reaction using a grinding process. ２ P.O. ８ It has been reported that amorphous powders of LiTa and its element substitution products are synthesized and then fired to produce crystalline solid electrolytes (Patent Document 4). However, this solid electrolyte needs to be fired at high temperatures to crystallize. ２ P.O. ８There is a need for a highly deformable amorphous solid electrolyte material with a chemical composition similar to that of the above, as well as a solid electrolyte with high lithium ion conductivity that can be obtained by sintering this amorphous solid electrolyte material at a low temperature.

[0005] JP 2020-194773 A JP 2021-38100 A JP 2021-38099 A International Publication No. 2021 / 251407

[0006] R. Kim et al. , Chem. Mater. , Vol. 33, 6909 (2021)

[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 sintering the amorphous solid electrolyte material at a low temperature.

[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 P.O. ８ (1.6≦y<2) and is in an amorphous state.

[0010] The chemical formula of the present application is Li １＋ｘ Ta ２－ｘ Hf ｘ P.O. ８ The method for producing a sintered solid electrolyte compact represented by the chemical formula Li １＋ｘ Ta ２－ｘ Hf ｘP.O. ８ The method includes a molding step of molding the amorphous powder to obtain a molded body, and a sintering step of firing the molded body at a temperature of 350°C to 650°C to obtain a sintered body in an amorphous state. ２ P.O. ８ Oxide, chemical formula LiTa ｙ M ２－ｙ P.O. ８ The method for producing a sintered solid electrolyte compact having an oxide represented by the formula (where 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 the 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 a sintered amorphous compact.

[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.

[0012] A conceptual diagram of an all-solid-state lithium secondary battery, which is an example of an electrochemical device of the present invention. ２ P.O. ８ Powder X-ray diffraction pattern of the sintered compact of amorphous LiTa obtained in Example 2. ２ P.O. ８ Graph showing the results of measuring the AC impedance of the sintered compact of amorphous Li obtained in Example 3. １．１ Ta １．９ Hf ０．１ P.O. ８ The sintered compact of Example 4, the amorphous Li １．２ Ta １．８ Hf ０．２ P.O. ８ The sintered compact of Example 5, the amorphous Li １．４ Ta １．６ Hf ０．４ P.O. ８ and the crystalline Li obtained in Comparative Example 1. １．４ Ta １．６ Hf ０．４ P.O. ８ The powder X-ray diffraction patterns of the sintered compacts of the amorphous LiNb obtained in Example 6 are shown. ２ P.O.８ and the amorphous Li obtained in Example 7. ２ Nb ２ P ２ O １１ Powder X-ray diffraction patterns of the sintered compacts of the amorphous LiTa obtained in Example 8. １．８ Bi ０．２ P.O. ８ Powder X-ray diffraction pattern of the sintered compact of amorphous LiHf obtained in Example 9. ２ P.O. ７ Powder X-ray diffraction pattern of the sintered compact of Comparative Example 2. ２ P.O. ８ Powder X-ray diffraction pattern of the sintered compact of amorphous LiTa obtained in Example 10. １．８ Sb ０．２ P.O. ８ 10 shows a powder X-ray diffraction pattern of the sintered compact of Example 1. 11 shows a powder X-ray diffraction pattern of the sintered compact of amorphous Li—Ta—P—O obtained in Example 11, and a powder X-ray diffraction pattern of the sintered compact of amorphous Li—Nb—P—O obtained in Example 12. 12 shows a powder X-ray diffraction pattern of the amorphous composite positive electrode compact obtained in Example 13.

[0013] (Solid electrolyte sintered compact) The solid electrolyte sintered compact of 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 a partially crystallized peak 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 P.O. ８ (0≦x≦0.4 (the same applies below)), an oxide represented by the chemical formula LiTa ｙ M ２－ｙ P.O. ８ (M is Bi or Sb, 1.6≦y<2 (the same applies hereinafter)), and oxides composed of Li, Hf or Nb, P, and O.

[0014] Chemical formula Li １＋ｘ Ta ２－ｘ Hfｘ P.O. ８ As the oxide represented by the formula, LiTa ２ P.O. ８ , Li １．１ Ta １．９ Hf ０．１ P.O. ８ , Li １．２ Ta １．８ Hf ０．２ P.O. ８ , and Li １．４ Ta １．６ Hf ０．４ P.O. ８ Chemical formula: LiTa ｙ M ２－ｙ P.O. ８ As the oxide represented by the formula, LiTa １．８ Bi ０．２ P.O. ８ and LiTa １．８ Sb ０．２ P.O. ８ Examples of oxides composed of Li, Hf or Nb, P, and O include LiHf ２ P.O. ７ and LiNb ２ P.O. ８ Examples include:

[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 for producing a sintered solid electrolyte compact) The method for producing a sintered solid electrolyte compact according to the first embodiment of the present application is a method for producing a sintered solid electrolyte compact using a compound having the chemical formula Li １＋ｘ Ta ２－ｘ Hf ｘ P.O. ８ The method for producing a sintered solid electrolyte compact in an amorphous state includes a molding step and a sintering step. In the molding step, which is a broad concept including molding, the oxide represented by the chemical formula Li １＋ｘ Ta ２－ｘ Hf ｘ P.O.８ The powder in an amorphous state is molded to obtain a molded body.

[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] Examples of coating techniques include screen printing, electrophoresis (EPD), doctor blade, spray coating, inkjet, and spin coating, while examples of film formation techniques include vapor deposition, 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 a solid electrolyte as it is in a powder compacted state at room temperature, 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 sintering, which involve molding while heating. Furthermore, a sintered solid electrolyte compact can be obtained by firing the powder compact of the solid electrolyte material obtained at room temperature at a predetermined temperature in an electric furnace or the like. As long as the temperature range allows the sintered solid electrolyte compact produced from the solid electrolyte material to maintain an amorphous state, processes for producing ceramic sintered compacts, 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 formation of the solid electrolyte sintered compact. As long as the oxidation reaction has progressed sufficiently in the powder state, there are no particular restrictions on the firing atmosphere; firing is typically performed in an argon gas atmosphere, a nitrogen gas atmosphere, an oxygen gas atmosphere, or an 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. The crucible material used during firing is not particularly limited as long as it is stable at high temperatures of 350°C or higher. 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 ２ P.O. ８ This is a method for producing a solid electrolyte sintered compact having an oxide and being in an amorphous state. Note that in the method for producing a solid electrolyte sintered compact of the second embodiment, overlapping descriptions with the method for producing a solid electrolyte sintered compact of the first embodiment will be omitted as appropriate. In the production methods of the third and fourth embodiments, overlapping descriptions with the method for producing a solid electrolyte sintered compact of the first embodiment will also be omitted as appropriate.

[0023] The method for manufacturing a solid electrolyte sintered compact according to the second embodiment includes a molding step and a sintering step. ２ P.O. ８ The powder is molded to obtain a green body. In the sintering step, the green body is fired at 350°C or higher and 650°C or lower to obtain a sintered green body in an amorphous state. This sintered green body 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 to use a sintered solid electrolyte compact having a chemical formula of LiTa ｙ M ２－ｙ P.O. ８The method for producing a sintered solid electrolyte compact in an amorphous state includes a molding step and a sintering step. In the molding step, a sintered solid electrolyte compact having an oxide represented by the chemical formula LiTa ｙ M ２－ｙ P.O. ８ The amorphous oxide powder represented by the formula (I) is molded to obtain a molded body. The sintering step is the same as in the second embodiment. The sintered molded body obtained in the sintering step has lithium ion conductivity and can be used as a solid electrolyte.

[0025] A manufacturing method for a solid electrolyte sintered compact according to a fourth embodiment of the present application is a method for manufacturing a solid electrolyte sintered compact that has an oxide composed of Li, Hf or Nb, P, and O and is in an amorphous state. The manufacturing method for a solid electrolyte sintered compact according to the fourth embodiment includes a molding step and a sintering step. In the molding step, powder of an oxide composed of Li, Hf or Nb, P, and O and in an amorphous state is molded to obtain a molded body. In the sintering step, the molded 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, for example, in the form of a powder or small lumps. The solid electrolyte material of the present application is molded and sintered at a low temperature at which crystallization does not occur, to obtain a sintered solid electrolyte compact according to an embodiment of the present application. 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. The oxide containing Li, one or more of Hf and Nb, and P includes LiHf ２ P.O. ７ , LiNb ２ P.O. ８ , Li ２ Nb ２ P ２ O １１ , and the chemical formula Li １＋ｚ Ta ２－ｚ Hf ｚ P.O. ８ (0<z≦0.4 (the same applies hereinafter)).

[0027] Chemical formula Li１＋ｚ Ta ２－ｚ Hf ｚ P.O. ８ As the oxide represented by the formula, Li １．１ Ta １．９ Hf ０．１ P.O. ８ , Li １．２ Ta １．８ Hf ０．２ P.O. ８ , and Li １．４ Ta １．６ Hf ０．４ P.O. ８ The solid electrolyte material of the second embodiment of the present application has the chemical formula LiTa ｙ Sb ２－ｙ P.O. ８ (1.6≦y<2 (the same applies below)) Chemical formula: LiTa ｙ Sb ２－ｙ P.O. ８ As the oxide represented by the formula, LiTa １．８ Sb ０．２ P.O. ８ Examples include:

[0028] (Method for manufacturing a 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 solvent 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 volatilizes, 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] And NH derived from various salts ４ By-products such as Cl and carbides 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 results in the desired 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, and 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, and firing is usually carried out in an oxidizing gas atmosphere such as oxygen or air. The firing time can be set depending on the firing temperature, etc., as long as residual substances such as nitrogen, chlorine, and carbon derived from various salts can be volatilized. There are no particular restrictions on the cooling method after firing, and typically natural cooling (cooling in the furnace) or slow cooling is sufficient. After firing and cooling, the solid electrolyte material can be pulverized as necessary and re-fired at a different firing temperature. The degree of pulverization can be adjusted depending on 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] (Cathode Component) The solid electrolyte material of the present application can be used as a component of a cathode to ensure lithium ion conductivity in the electrode. That is, a molded product obtained by mixing or combining the solid electrolyte material of the present application with a cathode active material is the cathode component. As the cathode active material, a material generally used as a cathode material for lithium ion batteries can be used. For example, LiCoO ２ , LiNiO ２ , Li(Ni,Mn,Co)O ２ , Li(Ni,Co,Al)O ２ , Li ２ MnO ３ -Li(Ni,Mn,Co)O ２ , Li(Ni,Mn) ２ O ４ , Li(Co,Mn) ２ O ４ , Li(Mn,Al) ２ O ４ , LiFePO ４ , LiMnPO ４ , LiCoPO ４ , and LiNiPO ４ Examples of the positive electrode active material include oxides of the above, sulfur, and lithium sulfide.

[0035] In addition, a material that undergoes a reversible lithium intercalation / deintercalation reaction at a high voltage of 2 V or more can be used as the positive electrode active material. Furthermore, to improve the bonding between the positive electrode and the solid electrolyte material and to enhance lithium ion conductivity, the positive electrode member may contain a polymer, oxide, sulfide, hydride, halide, or the like. Furthermore, to improve electronic conductivity in the positive electrode, the positive electrode member 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 in an amorphous state, 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, as 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. Figure 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.

[0038] Example 1: Amorphous LiTa ２ P.O. ８ Preparation of sintered compact of 1.4328 g of TaCl in 50 mL of absolute ethanol in a dry environment. ５ (Rare Metallic, 99.9% (same below)) was dissolved and TaCl ５ A solution was obtained. 0.2301 g of NH ４ H ２ P.O. ４ (Wako Pure Chemical Industries, special grade reagent (hereinafter the same)) was dissolved in NH ４ H ２ P.O.４ An aqueous solution was obtained. 0.0840 g of LiOH·H was added to 100 mL of ion-exchanged water. ２ TaCl 2 was dissolved in the LiOH solution (manufactured by Kojundo Chemical Laboratory, 99% up (hereinafter the same)) to obtain an aqueous LiOH solution. ５ Solution and this NH ４ H ２ P.O. ４ The aqueous solutions were added successively and mixed at 80°C.

[0039] 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 (KDF-75plus manufactured by Denken Hi-Dental (hereinafter the same)) to obtain the amorphous compound LiTa. ２ P.O. ８ The chemical composition of this white powder was examined by ICP-OES analysis (Agilent, Agilent 5800), and it was found to be a nearly stoichiometric LiTa powder. ２ P.O. ８ Furthermore, as a result of SEM-EDS analysis (JCM-6000, manufactured by JEOL Ltd. (hereinafter the same)) of this white powder, Ta and P were detected, but no metal elements other than Ta were detected.

[0040] This white powder was wet ball milled using a planetary ball mill (P-7, manufactured by Fritsch (hereinafter the same)), and then uniaxially pressed using a tablet press (manufactured by JASCO (hereinafter the same)) to obtain a compact. This compact was placed on an SSA-S alumina plate and fired in a vacuum gas replacement type electric furnace at 600°C for 12 hours in an oxygen atmosphere to obtain amorphous LiTa. ２ P.O. ８ The crystal structure of this sintered compact was examined using a powder X-ray diffractometer (manufactured by Rigaku Corporation, trade name SmartLab (hereinafter the same)). 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 2.

[0041] Example 2: Amorphous LiTa ２ P.O. ８Preparation of sintered compact (Li excess) LiOH.H ２ The amorphous compound LiTa was prepared in the same manner as in Example 1, except that the amount of O used was 1.1 times that of Example 1, i.e., 0.0923 g, which is 10 mol % in excess. ２ P.O. ８ White powder and amorphous LiTa ２ P.O. ８ A sintered compact 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. Furthermore, for this sintered compact, the resistance value was determined from the arc of the Nyquist plot using a frequency response analyzer (FRA) (manufactured by Solartron, Model 1260 (hereinafter the same)), and the conductivity was calculated from this resistance value.

[0042] The impedance was measured under 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 (the same applies 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 0.5 S / cm. It was revealed that the sintered compact of this example had high lithium ion conductivity despite being in an amorphous state. ２ P.O. ８ This is thought to be because the white powder of (I) has high moldability, and the particle interfaces of the powder were bonded together despite 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 P.O. ８ Preparation of powder and sintered compacts: In a dry environment, 1.3612 g of TaCl was dissolved in 50 mL of absolute ethanol. ５ and 0.0641 g of HfCl ４ (Fujifilm Wako Pure Chemical Industries, 99.9% (same below)) was dissolved and TaCl ５ HfCl ４ A solution was obtained. 0.2301 g of NH ４ H ２ P.O. ４ Dissolve NH４ H ２ P.O. ４ An aqueous solution was obtained. 0.1016 g of LiOH·H was added to 100 mL of ion-exchanged water. ２ The TaCl was dissolved in the LiOH solution to obtain an aqueous solution. ５ HfCl ４ Solution and this NH ４ H ２ P.O. ４ The aqueous solutions were added sequentially and mixed at 80° C. The mixed solution contained the following components: １．１ Ta １．９ Hf ０．１ P.O. ８ The amount of LiOH contained is 1.1 times by mole, i.e., 10 mol % in excess of that of the above.

[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 the amorphous compound Li １．１ Ta １．９ Hf ０．１ P.O. ８ A white powder of Ta was obtained. As a result of SEM-EDS analysis of this white powder, Ta, Hf, and P were detected, 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 an oxygen atmosphere at 600°C for 12 hours using a vacuum gas replacement type electric furnace to obtain amorphous Li. １．１ Ta １．９ Hf ０．１ P.O. ８ A sintered compact of 1000 kJ / cm2 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 in the same manner as in Example 1. The total lithium ion conductivity of this sintered compact was 9.34 x 10 －８It was revealed 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 P.O. ８ Preparation of powder and sintered compact of TaCl ５ , HfCl ４ , and LiOH·H ２ The amorphous compound Li was prepared in the same manner as in Example 3, except that the amounts of O used were changed to 1.2896 g, 0.1281 g, and 0.1108 g, respectively. １．２ Ta １．８ Hf ０．２ P.O. ８ White powder and amorphous Li １．２ Ta １．８ Hf ０．２ P.O. ８ The mixed solution of raw materials contained Li １．２ Ta １．８ Hf ０．２ P.O. ８ The amount of LiOH contained was 1.1 times by mole, i.e., 10 mol % excess, compared to the amount of LiOH contained in the solution.

[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 in the same manner as in Example 1. The total lithium ion conductivity of this sintered compact was 5.41 x 10 －８ It was revealed 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 P.O. ８ Preparation of powder of TaCl ５ , HfCl ４, and LiOH·H ２ The amorphous compound Li was prepared in the same manner as in Example 3, except that the amounts of O 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 P.O. ８ The raw material mixture solution contained a white powder of the composition Li １．４ Ta １．６ Hf ０．４ P.O. ８ The amount of LiOH contained was 1.1 times by mole, i.e., 10 mol % excess, compared to the amount of LiOH contained in the solution.

[0049] As a result of SEM-EDS analysis of this white powder, Ta, Hf, and P were detected, but no metal elements other than Ta and Hf were detected. Furthermore, when the crystal structure of this white powder was examined using a powder X-ray diffractometer, a slight peak suggesting crystallization was present, but a halo characteristic of an amorphous solid was observed as the main phase. From this, it was found that PO ８ It was suggested that a composition ratio of 0.4 of Hf to Li is the upper limit for forming amorphous powder. The powder X-ray diffraction pattern is shown in Figure 4. By molding this white powder and firing it at 500 °C, amorphous Li １．４ Ta １．６ Hf ０．４ P.O. ８ It is believed that a sintered compact having the above properties can be obtained.

[0050] Comparative example 1: Li １．４ Ta １．６ Hf ０．４ P.O. ８ The same procedure as in Example 5 was repeated except that the firing temperature was changed to 700°C. １．４ Ta １．６ Hf ０．４ P.O. ８ When the crystal structure of this white powder was examined using a powder X-ray diffractometer, it was found that Ta ２ O ５Clear peaks corresponding to the above were observed, and it was found that the powder X-ray diffraction pattern was not an amorphous single phase. The powder X-ray diffraction pattern is shown in Figure 4. It is thought that the white powder containing crystalline parts was obtained because the calcination was performed at 700°C, which is higher than that in Example 5.

[0051] Example 6: Amorphous LiNb ２ P.O. ８ Preparation of powder and sintered compacts: In a dry environment, 1.0807 g of NbCl was dissolved in 50 mL of absolute ethanol. ５ (Rare Metallic, 99.9% (same below)) was dissolved in NbCl ５ A solution was obtained. 0.2301 g of NH ４ H ２ P.O. ４ Dissolve NH ４ H ２ P.O. ４ An aqueous solution was obtained. 0.0840 g of LiOH·H was added to 100 mL of ion-exchanged water. ２ The NbCl O was dissolved in the LiOH solution to obtain an aqueous solution. While stirring the LiOH solution with a stirrer, the NbCl O was added to the LiOH solution. ５ Solution and this NH ４ H ２ P.O. ４ The aqueous solutions were added sequentially and mixed at 80° C. The mixed solution contained a composition of LiNb ２ P.O. ８ Li, Nb, and P are contained in the same amount ratio as that of the alloy.

[0052] This mixed solution was dried at 120°C for 15 hours, and the dried and solidified powder was collected. The solidified powder was heated to 350°C and then lightly crushed in an agate mortar. The crushed powder was fired in air at 500°C in a muffle furnace (manufactured by Yamato Scientific, FP101 (hereinafter the same)) for 12 hours to obtain amorphous LiNb. ２ P.O. ８ As a result of SEM-EDS analysis of this white powder, Nb and P were detected, but no metal elements other than Nb were detected.

[0053] In the same manner as in Example 5, amorphous LiNb was obtained from this white powder. ２ P.O. ８A 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 6.32 x 10 －８ It was revealed that the sintered compact of this example had lithium ion conductivity despite being in an amorphous solid state.

[0054] Example 7: Amorphous Li ２ Nb ２ P ２ O １１ Preparation of powder and sintered compacts NH ４ H ２ P.O. ４ and LiOH.H ２ The amorphous compound Li was prepared in the same manner as in Example 6, except that the amounts of O used were changed to 0.4602 g and 0.1680 g, respectively. ２ Nb ２ P ２ O １１ The raw material mixture solution contained a white powder of the composition Li ２ Nb ２ P ２ O １１ The white powder contained Li, Nb, and P in the same amount of substance ratio as in Example 1. As a result of SEM-EDS analysis of this white powder, Nb and P were detected, but no metal elements other than Nb were detected.

[0055] In the same manner as in Example 6, amorphous Li was extracted from this white powder. ２ Nb ２ P ２ O 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 －８It was revealed 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 P.O. ８ Preparation of sintered compact of 1.2896 g of TaCl in 50 mL of absolute ethanol in a dry environment. ５ and 0.1261 g of BiCl ３ (High Purity Chemical Laboratory, 99.99%) was dissolved in TaCl ５ BiCl ３ A solution was obtained. 0.2301 g of NH ４ H ２ P.O. ４ Dissolve NH ４ H ２ P.O. ４ An aqueous solution was obtained. 0.0923 g of LiOH·H was added to 100 mL of ion-exchanged water. ２ The TaCl was dissolved in the LiOH solution to obtain an aqueous solution. ５ BiCl ４ Solution and this NH ４ H ２ P.O. ４ The aqueous solutions were added in order and mixed at 80° C. The mixed solution had the composition LiTa １．８ Bi ０．２ P.O. ８ The amount of LiOH contained is 1.1 times by mole, i.e., 10 mol % in excess of that of the above.

[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 an amorphous compound LiTa. １．８ Bi ０．２ P.O. ８ A white powder of Ta was obtained. As a result of SEM-EDS analysis of this white powder, Ta, Bi, and P were detected, 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 P.O. ８ A sintered compact of 1000 kJ / cm2 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 in the same manner as in Example 1. The total lithium ion conductivity of this sintered compact was 8.28 x 10 －９ It was revealed that the sintered compact of this example had lithium ion conductivity despite being in an amorphous solid state.

[0059] Example 9: Amorphous LiHf ２ P.O. ７ Preparation of powder: In a dry environment, 1.2812 g of HfCl was dissolved in 50 mL of absolute ethanol. ４ Dissolve HfCl ４ A solution was obtained. 0.2301 g of NH ４ H ２ P.O. ４ Dissolve NH ４ H ２ P.O. ４ An aqueous solution was obtained. 0.0923 g of LiOH·H was added to 100 mL of ion-exchanged water. ２ The HfCl was dissolved in the LiOH solution to obtain an aqueous solution. While stirring the LiOH solution with a stirrer, the HfCl ４ Solution and this NH ４ H ２ P.O. ４ The aqueous solutions were added sequentially and mixed at 80° C. The mixed solution was dried at 120° C. for 15 hours, and the dried and solidified powder was collected. The solidified powder was heated to 350° C. and then lightly crushed in an agate mortar.

[0060] The pulverized powder was fired in a muffle furnace at 500°C in air for 12 hours to obtain amorphous LiHf ２ P.O. ７A white powder of the formula (I) was obtained. SEM-EDS analysis of this white powder detected Hf and P, but no metal elements other than Hf 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. The powder X-ray diffraction pattern is shown in Figure 7. This white powder was molded and fired at 500°C to obtain amorphous LiHf ２ P.O. ７ It is believed that a sintered compact having the above properties can be obtained.

[0061] Comparative Example 2: Crystalline LiTa ２ P.O. ８ Preparation of sintered compact of amorphous LiTa in the same manner as in Example 2 ２ P.O. ８ This compact was placed on an SSA-S alumina plate and fired in a vacuum gas replacement type electric furnace at 1000°C for 12 hours in an oxygen atmosphere to obtain a crystalline LiTa. ２ P.O. ８ The sintered compact was obtained. The crystal structure of this sintered compact was examined using a powder X-ray diffractometer, and it was confirmed to be crystalline and to be an almost single phase of the known monoclinic system and space group C2 / c. The powder X-ray diffraction pattern is shown in Figure 8.

[0062] Example 10: Amorphous LiTa １．８ Sb ０．２ P.O. ８ Preparation of powder and sintered compacts: In a dry environment, 1.2896 g of TaCl was dissolved in 50 mL of absolute ethanol. ５ and 0.09125 g of SbCl ３ (Fujifilm Wako Pure Chemical Industries, special grade reagent) was dissolved in TaCl ５ SbCl ３ A solution was obtained. 0.2301 g of NH ４ H ２ P.O. ４ Dissolve NH ４ H ２ P.O. ４ An aqueous solution was obtained. 0.0923 g of LiOH·H was added to 100 mL of ion-exchanged water. ２The TaCl was dissolved in the LiOH solution to obtain an aqueous solution. ５ SbCl ３ Solution and this NH ４ H ２ P.O. ４ The aqueous solutions were added in order and mixed at 80° C. The mixed solution had the composition LiTa １．８ Sb ０．２ P.O. ８ The amount of LiOH contained is 1.1 times by mole, i.e., 10 mol % in excess of that of the above.

[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 an amorphous compound LiTa. １．８ Sb ０．２ P.O. ８ 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 P.O. ８ The crystalline 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—P—O compound powder and compact In the same manner as in Example 1, white powders were obtained for amorphous Li—Ta—P—O compounds with a Li:Ta:P=2:2:1 composition, a Li:Ta:P=2:1:1 composition, a Li:Ta:P=8:5:4 composition, a Li:Ta:P=4:3:2 composition, and a Li:Ta:P=10:7:3 composition. When the crystal structure 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 FIG.

[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 powder 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 determined 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 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 was calculated to be 8.96 × 10 S / cm. Because the compacts of this example were in an amorphous state, they had a certain degree of plasticity, and it was confirmed that even the compacts had lithium ion conductivity. 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, 3.35×10 －８ It was found that a higher conductivity could be obtained by sintering at a low temperature of 500°C.

[0068] Example 12: Preparation of amorphous Li—Nb—P—O compound powder and compact

[0046] In the same manner as in Example 6, a white powder was obtained as an amorphous Li—Nb—P—O compound having a Li:Nb:P=2:2:1 composition. When the crystal structure 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 FIG.

[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 determined 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 －９The compacts of this example were confirmed to have a certain degree of plasticity due to their amorphous state, and to have lithium ion conductivity even as compacts. The total conductivity of the 500°C sintered compacts was 3.62 × 10 －８ It was found that a 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 prepared using the white powder with a composition of Li:Ta:P=2:1:1 obtained in Example 11 as the electrolyte of the composite positive electrode. ２ (Cellseed C-5H, manufactured by Nippon Chemical Industry Co., Ltd.) was used to mix the electrolyte powder and LiCoO ２ The powders 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, which was then fired in an argon gas atmosphere at 400°C for 2 hours to produce a composite positive electrode sintered compact.

[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 has a resistance of 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, the halo derived from the amorphous solid electrolyte and the LiCoO ２ Only the diffraction pattern due to the phase was measured, and it was confirmed that there were no reaction products, etc. From the above, it became 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: Preparation of an All-Solid-State Battery. The white powder obtained in Example 1 was filled into a 10 mm diameter hot press mold (manufactured by AS ONE Corporation) and held at 400 °C and 374 MPa for 2 hours using a hot press machine (manufactured by AS ONE Corporation). A disk-shaped amorphous sintered compact approximately 0.3 mm thick was obtained. 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 prepare 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 (manufactured by Hokuto Denko Corporation, HJ1020mSD8). The capacity corresponding to the charge / discharge reaction was observed, confirming the operation of the all-solid-state battery.

[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 having an oxide containing Li, one or more of Ta, Hf, Bi, Sb and Nb, and P, and being in an amorphous state.

2. In claim 1, The oxide has the formula Li １＋ｘ T ２－ｘ Hf ｘ P.O. ８ (0≦x≦0.4).

3. In claim 2, The oxide is LiTa ２ P.O. ８ A solid electrolyte sintered compact.

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

5. In claim 1, The oxide is composed of Li, Hf or Nb, P, and O.

6. A solid electrolyte material that contains Li, at least one of Hf and Nb, and P, and has an oxide that does not contain Ta, and is in an amorphous state.

7. Chemical formula Li １＋ｚ T 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 (y<1.6) (1.6≦y<2) and is an amorphous solid electrolyte material.

9. Chemical formula Li １＋ｘ T ２－ｘ Hf ｘ P.O. ８ (0≦x≦0.4) and forming the amorphous powder to obtain a molded body; a sintering step of sintering the molded body at 350° C. or more and 650° C. or less 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 oxide in an amorphous state to obtain a formed body; a sintering step of sintering the molded body at 350° C. or more and 650° C. or less to obtain a sintered molded body in an amorphous state; The method for producing a sintered solid electrolyte compact according to any one of claims 3 to 5, comprising the steps of:

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