Lithium ion conductive material

Abstract

Provided is a lithium ion conductive material capable of forming a solid electrolyte having high lithium ion conductivity at a sintering temperature of 800 DEG C or less. According to the present invention, by providing, in mol% on the basis of oxides, 36.6%-37.3% of a P2O5 component, 43.0%-48.1% of a TiO2 component, 0.6%-3.2% of an Al2O3 component, and 13.9%-17.5% of a Li2O component, the mol% of the Al2O3 component is reduced by 0.3-3.0 mol% compared to the mol% of the Al2O3 component calculated on the basis of the component formula Li1 + xAlxTi2-xP3O12 (x = 0.05-0.4) derived from the components of Ti and Li, and the mol% of the P2O5 component is reduced by 0.3-3.0 mol% compared to the mol% of the Al2O3 component calculated on the basis of the component formula Li1 + xAlxTi2-xP3O12 (x = 0.05-0.4) derived from the components of Ti and Li. According to the present invention, the mol% of the P2O5 component is reduced by 0.2-2.0 mol% compared with the mol% of the P2O5 component calculated based on the above-mentioned component formula, and the lithium ion conduction material comprises the crystalline phase of the NASICON structure of the rhombohedral crystal system or the crystalline phase of Li < 1 + x > Al < x > Ti < 2-x > P3O12 (x > = 0), such that the above-mentioned technical problem can be solved by using the lithium ion conduction material of the crystalline phase of the NASICON structure of the rhombohedral crystal system.

Description

Technical Field

[0001] The present invention relates to a lithium ion conductive material. Background Art

[0002] Lithium-ion secondary batteries, which have high energy density and are capable of both charge and discharge, are widely used for applications such as power sources for electric vehicles and portable terminals.

[0003] Most lithium-ion secondary batteries currently on the market use a liquid electrolyte (electrolyte) to achieve high energy density. Typically, the electrolyte is a solution containing a lithium salt dissolved in an aprotic organic solvent such as a carbonate or cyclic ester.

[0004] However, lithium-ion secondary batteries using liquid electrolytes (electrolyte) are subject to the risk of electrolyte leakage. In addition, organic solvents and the like commonly used in electrolytes are volatile and flammable substances, posing a potential safety hazard.

[0005] Therefore, as the electrolyte of lithium-ion secondary batteries, it is proposed to use solid electrolytes instead of liquid electrolytes (electrolytes) such as organic solvents. In addition, all-solid-state secondary batteries are being developed in which solid electrolytes are used as electrolytes and other components such as electrode layers are also composed of solids.

[0006] Furthermore, typical properties required of a solid electrolyte for an all-solid-state secondary battery include lithium ion conductivity and sintering properties.

[0007] Furthermore, as a solid electrolyte for all-solid secondary batteries, for example, a solid electrolyte with Li added as shown in Non-Patent Document 1 has been studied. 1+x Al x Ti 2-x P3O 12 and LiTi2P3O as shown in Non-Patent Documents 2 and 3. 12 Ceramic electrolyte of components, etc.

[0008] Prior art literature

[0009] Non-patent literature

[0010] Non-patent document 1: Journal of Solid State Chemistry 265(2018)381-386

[0011] Non-patent document 2: Journal of Materials Science 33 (1998) 1549-1553

[0012] Non-patent document 3: Solid State Ionics 47 (1991) 257-264 Summary of the Invention

[0013] Technical problem to be solved by the invention

[0014] It has been reported that the glass ceramic electrolyte shown in Non-Patent Document 1 has a lithium ion conductivity of 1×10 -3 S / cm. However, the sintering temperature during the synthesis is very high, at 1000°C or above. In addition, when sintering is performed after synthesis, a sintering temperature of 900°C or above is also required. In this case, the grain boundary resistance of the solid electrolyte (the resistance of ion conduction generated at the contact interface between particles) becomes higher, so the lithium ion conductivity at 25°C is reduced to 1×10 - 4 In addition, when the battery is integrally formed with the electrode layer, decomposition of the electrode active material (positive electrode active material or negative electrode active material) and reduction in discharge capacity (battery capacity) due to high-temperature sintering are also problematic.

[0015] On the other hand, the ceramic electrolytes shown in Non-Patent Documents 2 and 3 have low intragranular resistance (resistance of ion conduction generated within the particles) but high grain boundary resistance, making it difficult to obtain high lithium ion conductivity. Therefore, a method has been implemented to reduce grain boundary resistance and improve lithium ion conductivity by mixing lithium salts such as Li3PO4 and Li3BO3 and Li3BO3 glass and sintering them. However, the sintering temperature is relatively high at 900°C, and the lithium ion conductivity of the obtained solid electrolyte at 25°C is 1.5 to 3×10 -4 S / cm or so.

[0016] Therefore, an object of the present invention is to provide a lithium ion conductive material capable of forming a solid electrolyte having high lithium ion conductivity by sintering at a temperature of 800° C. or lower.

[0017] Solutions to technical problems

[0018] In order to solve the above technical problems, the present inventors conducted intensive research and found a lithium ion conductive material, which contains, in terms of mol% based on oxides, 36.6% to 37.3% of P2O5, 43.0% to 48.1% of TiO2, 0.6% to 3.2% of Al2O3 and 13.9% to 17.5% of Li2O, and the mol% of the Al2O3 component is the same as the Li2O3 component derived from the Ti and Li components. 1+x Al x Ti 2-x P3O 12The mol% of the Al2O3 component calculated based on the composition formula (x = 0.05 to 0.4) is reduced by 0.3 mol% to 3.0 mol%; the mol% of the P2O5 component is reduced by 0.3 mol% to 3.0 mol% based on the Li 1+x Al x Ti 2-x P3O 12 Compared with the mol% of P2O5 calculated by the composition formula (x = 0.05 to 0.4), the mol% is reduced by 0.2 mol% to 2.0 mol%, and the crystal phase of the NASICON structure of the rhombohedral crystal system or Li 1+x Al x Ti 2-x P3O 12 The crystal phase (x≥0) can form a solid electrolyte (oxide-based solid electrolyte) having high lithium ion conductivity by mixing and sintering the lithium ion conductive material with a lithium-containing lithium ion conductive glass material at 800° C. or lower.

[0019] In addition, a lithium ion conductive material was discovered, which contains, in terms of mol% based on oxides, 34.0% to 36.5% of P2O5, 42.0% to 46.5% of TiO2, 0.6% to 3.1% of Al2O3, 15.0% to 17.6% of Li2O, and 0.5% to 5.0% of SiO2, and the mol% of the Al2O3 component is the same as the Li2O3 component derived from the compositions of Ti, Li, and Si. 1+x+y Al x Ti 2-x Si y P 3-y O 12 (x = 0.05 ~ 0.4, y = 0.05 ~ 0.2) the Al2O3 component mol% calculated by the composition formula, reduced by 0.3mol% ~ 3.0mol%; the P2O5 component mol%, compared with the Li based on the composition of Ti, Li and Si derived 1+x+y Al x Ti 2-x Si y P 3-y O 12 Compared with the mol% of P2O5 calculated by the composition formula (x=0.05~0.4, y=0.05~0.2), the mol% of P2O5 is reduced by 0.2mol%~2.0mol%, and the crystal phase of the NASICON structure of the rhombohedral crystal system, Li 1+x Al x Ti 2-x P3O 12 (x≥0) crystalline phase, or Li1+x+ y Al x Ti 2-x Si y P 3-y O 12 The crystalline phase (x≥0, y≥0) can be formed by mixing and sintering the lithium ion conductive material with a lithium ion conductive glass material containing lithium at a temperature below 800°C to form a solid electrolyte (oxide-based solid electrolyte) with high lithium ion conductivity, thereby completing the present invention.

[0020] That is, the present invention is as follows (1) to (5).

[0021] (1) A lithium ion conductive material comprising, in mol% based on oxides, 36.6% to 37.3% of a P2O5 component, 43.0% to 48.1% of a TiO2 component, 0.6% to 3.2% of an Al2O3 component, and 13.9% to 17.5% of a Li2O component, wherein the mol% of the Al2O3 component is the same as the Li2O3 component derived from the Ti and Li compositions. 1+ x Al x Ti 2-x P3O 12 The mol% of the Al2O3 component calculated based on the composition formula (x = 0.05 to 0.4) is reduced by 0.3 mol% to 3.0 mol%; the mol% of the P2O5 component is reduced by 0.3 mol% to 3.0 mol% based on the Li 1+x Al x Ti 2-x P3O 12 Compared with the mol% of P2O5 calculated by the composition formula (x = 0.05 to 0.4), the mol% is reduced by 0.2 mol% to 2.0 mol%, and the crystal phase of the NASICON structure of the rhombohedral crystal system or Li 1+x Al x Ti 2-x P3O 12 (x≥0) crystalline phase.

[0022] (2) A lithium ion conductive material comprising, in mol% based on oxides, 34.0% to 36.5% of a P2O5 component, 42.0% to 46.5% of a TiO2 component, 0.6% to 3.1% of an Al2O3 component, 15.0% to 17.6% of a Li2O component, and 0.5% to 5.0% of a SiO2 component, wherein the mol% of the Al2O3 component is the same as the Li2O3 component derived from the compositions of Ti, Li, and Si. 1+x+y Al x Ti2-x Si y P 3-y O 12 (x = 0.05 ~ 0.4, y = 0.05 ~ 0.2) the Al2O3 component mol% calculated by the composition formula, reduced by 0.3mol% ~ 3.0mol%; the P2O5 component mol%, compared with the Li based on the composition of Ti, Li and Si derived 1+x+y Al x Ti 2-x Si y P 3-y O 12 Compared with the mol% of P2O5 calculated by the composition formula (x=0.05~0.4, y=0.05~0.2), the mol% of P2O5 is reduced by 0.2mol%~2.0mol%, and the crystal phase of the NASICON structure of the rhombohedral crystal system, Li 1+x Al x Ti 2-x P3O 12 (x≥0) crystalline phase, or Li 1+x+y Al x Ti 2-x Si y P 3- y O 12 (x≥0, y≥0) crystalline phase.

[0023] (3) The lithium ion conductive material according to (1) or (2), wherein the lithium ion conductive material is lithium ion conductive glass ceramic.

[0024] (4) A solid electrolyte material obtained by mixing the lithium ion conductive material according to any one of (1) to (3) with a lithium ion conductive glass material containing lithium.

[0025] (5) An all-solid secondary battery formed using a material containing the solid electrolyte material described in (4).

[0026] Effects of the Invention

[0027] According to the present invention, a lithium ion conductive material can be provided, which can form a solid electrolyte having high lithium ion conductivity by mixing and sintering the lithium ion conductive material with a lithium-containing lithium ion conductive glass material at 800° C. or lower. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a synthesis flow chart of the lithium ion conductive glass ceramics of Examples 1 to 4 and Comparative Examples 1 to 3 (Step 1), and the solid electrolytes of Examples 1 to 4 and Comparative Examples 1 to 3 (Step 2).

[0029] Figure 2 This is a graph showing the relationship between the sintering temperature (heat treatment temperature) and the lithium ion conductivity (conductivity) of the solid electrolytes (sintered particles) of Comparative Examples 1, 2, and Example 4 obtained in Step 2.

[0030] Figure 3 This is a graph showing the relationship between the sintering temperature (heat treatment temperature) and the density of the solid electrolytes (sintered particles) of Comparative Examples 1, 2, and Example 4 obtained in Step 2.

[0031] Figure 4 This is a secondary electron image of the fracture surface of the solid electrolyte (sintered particles) of Example 4 obtained in step 2 (photograph used as an accompanying drawing).

[0032] Figure 5 This is a reflected electron image of the fracture surface of the solid electrolyte (sintered particles) of Example 4 obtained in step 2 (photograph used as an accompanying drawing).

[0033] Figure 6 It is a synthesis flow chart of the lithium ion conductive glass ceramics of Examples 5 to 6 and Comparative Example 4 (Step 1-2), and the solid electrolytes of Examples 5 to 6 and Comparative Example 4 (Step 2-2).

[0034] Figure 7 This is a graph showing the relationship between sintering temperature (heat treatment temperature) and lithium ion conductivity (conductivity) for the solid electrolyte (sintered particles) of Example 5 obtained by step 2-2, and the solid electrolytes (sintered particles) of Comparative Example 1 and Example 4 obtained by step 2.

[0035] Figure 8 This is a graph showing the relationship between sintering temperature (heat treatment temperature) and density for the solid electrolyte (sintered particles) of Example 5 obtained in Step 2-2, and the solid electrolytes (sintered particles) of Comparative Example 1 and Example 4 obtained in Step 2.

[0036] Figure 9 This is a secondary electron image of the fracture surface of the solid electrolyte (sintered particles) of Example 5 obtained by step 2-2 (photograph used as an accompanying drawing). DETAILED DESCRIPTION

[0037] The present invention will be described.

[0038] A first embodiment of the present invention is a lithium ion conductive material comprising, in terms of mol% based on oxides, 36.6% to 37.3% of a P2O5 component, 43.0% to 48.1% of a TiO2 component, 0.6% to 3.2% of an Al2O3 component, and 13.9% to 17.5% of a Li2O component, wherein the mol% of the Al2O3 component is the same as the Li2O3 component derived from the Ti and Li compositions. 1+x Al x Ti 2-x P3O 12 The mol% of the Al2O3 component calculated based on the composition formula (x = 0.05 to 0.4) is reduced by 0.3 mol% to 3.0 mol%; the mol% of the P2O5 component is reduced by 0.3 mol% to 3.0 mol% based on the Li 1+ x Al x Ti 2-x P3O 12 Compared with the mol% of P2O5 calculated by the composition formula (x = 0.05 to 0.4), the mol% is reduced by 0.2 mol% to 2.0 mol%, and the crystal phase of the NASICON structure of the rhombohedral crystal system or Li 1+x AlxTi 2-x P3O 12 (x≥0) crystalline phase.

[0039] In addition, a second embodiment of the present invention is a lithium ion conductive material, wherein the material contains, in terms of mol% based on oxides, 34.0% to 36.5% of a P2O5 component, 42.0% to 46.5% of a TiO2 component, 0.6% to 3.1% of an Al2O3 component, 15.0% to 17.6% of a Li2O component, and 0.5% to 5.0% of a SiO2 component, wherein the mol% of the Al2O3 component is the same as the Li2O3 component derived from the compositions of Ti, Li, and Si. 1+x+y Al x Ti 2-x Si y P 3-y O 12 (x = 0.05 ~ 0.4, y = 0.05 ~ 0.2) the Al2O3 component mol% calculated by the composition formula, reduced by 0.3mol% ~ 3.0mol%; the P2O5 component mol%, compared with the Li based on the composition of Ti, Li and Si derived 1+x+y Al x Ti 2-x Si y P 3-y O 12Compared with the mol% of P2O5 calculated by the composition formula (x=0.05~0.4, y=0.05~0.2), the mol% of P2O5 is reduced by 0.2mol%~2.0mol%, and the crystal phase of the NASICON structure of the rhombohedral crystal system, Li 1+x Al x Ti 2-x P3O 12 (x≥0) crystalline phase, or Li 1+x+y Al x Ti 2-x Si y P 3-y O 12 (x≥0, y≥0) crystalline phase.

[0040] Hereinafter, they are sometimes referred to as "lithium ion conductive materials of the present invention."

[0041] It should be noted that the content of each component contained in the lithium ion conductive material of the present invention, for both the first and second embodiments, is expressed in mol% based on the oxide, unless otherwise specified. Here, the content expressed as "mol% based on the oxide" refers to the content of each component contained in the lithium ion conductive material of the present invention, assuming that all oxides, complex salts, metal fluorides, etc. used as raw materials for the lithium ion conductive material of the present invention decompose and form oxides upon melting, with the total molar number of the resulting oxides being taken as 100 mol%. Similarly, the mol% of the Al2O3 component and the PO5 component calculated based on a predetermined compositional formula refers to the content of each component calculated assuming that all components of the predetermined compositional formula decompose and form oxides upon melting, with the total molar number of the resulting oxides being taken as 100 mol%.

[0042] [First embodiment]

[0043] First, the components and crystal phases constituting the first embodiment of the lithium ion conductive material of the present invention will be described.

[0044] <Ingredients>

[0045] Each component constituting the first embodiment of the lithium ion conductive material of the present invention will be described in detail.

[0046] The P2O5 component forms a crystal phase of a NASICON type structure of a rhombohedral system or a Li 1+x Al x Ti 2-x P3O 12The P2O5 content is an essential component required for the formation of a crystalline phase (x ≥ 0). Therefore, the lower limit of the P2O5 content is 36.6%, preferably 36.8%, and more preferably 37.0%. On the other hand, to suppress the formation of other crystalline phases and to minimize the reduction in lithium ion conductivity of the solid electrolyte obtained by low-temperature co-sintering with a lithium-containing lithium-ion conductive glass material, the upper limit of the P2O5 content is 37.3%, preferably 37.2%.

[0047] The TiO2 component also forms a crystal phase of a NASICON structure of a rhombohedral system or a Li 1+x Al x Ti 2-x P3O 12 The TiO2 content is an essential component required for the formation of a crystalline phase (x ≥ 0). Therefore, the lower limit of the TiO2 content is 43.0%, preferably 43.2%, and more preferably 43.5%. On the other hand, from the perspective of minimizing the reduction in lithium ion conductivity of the solid electrolyte obtained by low-temperature mixing and sintering with a lithium-containing lithium-ion conductive glass material, the upper limit of the TiO2 content is 48.1%, preferably 47.0%, more preferably 46.0%, and even more preferably 45.0%.

[0048] The Al2O3 component also forms a crystal phase of a NASICON structure of a rhombohedral system or a Li 1+x Al x Ti 2-x P3O 12 (x ≥ 0) is an essential component required for the crystalline phase. Therefore, the lower limit of the Al2O3 content is 0.6%, preferably 0.8%, more preferably 1.0%, even more preferably 1.2%, further preferably 1.5%, and even more preferably 2.0%. On the other hand, from the perspective of suppressing the formation of other crystalline phases and preventing a decrease in the lithium ion conductivity of the solid electrolyte obtained by low-temperature co-sintering with a lithium-containing lithium-ion conductive glass material, the upper limit of the Al2O3 content is 3.2%, preferably 3.0%, more preferably 2.8%, and even more preferably 2.6%.

[0049] The Li2O component, in the first embodiment of the lithium ion conductive material of the present invention, imparts lithium ion conductivity and forms a crystal phase of a rhombohedral NASICON structure or a Li 1+x Al x Ti 2-x P3O 12(x ≥ 0) is an essential component required for the crystalline phase. Therefore, the lower limit of the content of the Li2O component is 13.9%, preferably 15.0%, and more preferably 16.0%. On the other hand, from the perspective of improving the chemical durability of the first embodiment of the lithium ion conductive material of the present invention and improving morphological stability, the upper limit of the content of the Li2O component is 17.5%, preferably 17.2%, more preferably 17.0%, and even more preferably 16.7%.

[0050] Furthermore, in the first embodiment of the lithium ion conductive material of the present invention, as an optional component, one or more components selected from the group consisting of a ZrO 2 component, a Y 2 O 3 component, a Sc 2 O 3 component, a CaO component, a MgO component, and a SnO 2 component may be contained.

[0051] The ZrO2 component is an optional component that stabilizes the crystal structure of the crystalline phase in the first embodiment of the lithium ion conductive material of the present invention and improves recyclability. Therefore, the lower limit of the ZrO2 content is preferably 0.5%, more preferably 1.0%, and even more preferably 2.0%. On the other hand, from the perspective of easily forming a rhombohedral NASICON-type crystal phase, the upper limit of the ZrO2 content is preferably 5.0%, more preferably 4.0%, and even more preferably 3.0%.

[0052] Both the Y2O3 component and the Sc2O3 component are optional components that can adjust the lithium ion conductivity of the first embodiment of the lithium ion conductive material of the present invention and can also adjust the mechanical strength and size of the crystalline phase. Therefore, the lower limit of either the Y2O3 content or the Sc2O3 content is preferably 0.1%, more preferably 0.5%, and even more preferably 1.0%. On the other hand, from the perspective of suppressing the formation of other crystalline phases and ensuring that the lithium ion conductivity of the solid electrolyte obtained by low-temperature co-sintering with a lithium-containing lithium ion conductive glass material is not reduced, the upper limit of either the Y2O3 content or the Sc2O3 content is preferably 2.0%, and more preferably 1.5%.

[0053] CaO and MgO are optional components that, through valence balance, can increase the content of Li in the crystal phase, thereby improving lithium ion conductivity. Therefore, the lower limit of either the CaO content or the MgO content is preferably 0.5%, more preferably 1.0%, and even more preferably 2.0%. On the other hand, to avoid a decrease in the lithium ion conductivity of the solid electrolyte obtained by low-temperature mixing and sintering with a lithium-containing lithium-ion conductive glass material, the upper limit of either the CaO content or the MgO content is preferably 5.0%, more preferably 4.0%, and even more preferably 3.0%.

[0054] The SnO2 component is an optional component that promotes the crystallization of the crystalline phase in the first embodiment of the lithium-ion conductive material of the present invention. Therefore, the lower limit of the SnO2 content is preferably 0.1%, more preferably 0.5%, and even more preferably 1.0%. On the other hand, from the perspective of minimizing the reduction in lithium ion conductivity of the solid electrolyte obtained by low-temperature co-sintering with a lithium-containing lithium-ion conductive glass material, the upper limit of the SnO2 content is preferably 2.0%, and more preferably 1.5%.

[0055] In addition, in the first embodiment of the lithium ion conductive material of the present invention, an inorganic component containing boron (B) or fluorine (F) may be contained. However, in the first embodiment of the lithium ion conductive material of the present invention, it is preferred to reduce the content of sulfur (S) as much as possible (for example, less than 1%, further less than 0.1%, etc.), and more preferably not contain it. This is because by reducing the S component, the possibility of generating harmful gases such as hydrogen sulfide can be reduced in all-solid-state secondary batteries using a solid electrolyte obtained by low-temperature mixing and sintering with a lithium-containing lithium ion conductive glass material. In addition, in order to avoid a decrease in lithium ion conductivity, it is also preferred to reduce the content of alkaline metal components (such as Na and K) other than Li as much as possible, and more preferably not contain it.

[0056] Furthermore, in the first embodiment of the lithium ion conductive material of the present invention, the mol% of the Al2O3 component described above is the same as the Li2O3 component derived from the composition of Ti and Li. 1+x Al x Ti 2-x P3O 12 Compared to the mol% of the Al2O3 component calculated using the composition formula (x = 0.05 to 0.4, preferably x = 0.1 to 0.3), the mol% of the Al2O3 component is reduced by 0.3 to 3.0 mol%. It should be noted that the lower limit of this range is preferably 0.4 mol%, more preferably 0.5 mol%, and even more preferably 1.0 mol%. The upper limit of this range is preferably 2.8 mol%, more preferably 2.5 mol%.

[0057] Here, Li 1+x Al x Ti 2-x P3O 12 (x = 0.05 to 0.4) is a basic component of LATP, which is a solid electrolyte material having a structure of Li, Al, Ti, and PO4. It can be derived from the composition of Al or from the compositions of Ti and Li. However, in the first embodiment of the lithium ion conductive material of the present invention, Li derived from the compositions of Ti and Li is used. 1+x Al x Ti 2- x P3O 12 The calculation was performed based on the composition formula (x = 0.05 to 0.4).

[0058] Specifically, for example, when the composition of Ti is 1.7 and the composition of Li is 1.3, the composition of Al is 0.3, and the Li 1.3 Al 0.3 Ti 1.7 P3O 12 . And, it is sufficient that the actual mol% of the Al2O3 component is reduced by 0.3mol% to 3.0mol% compared to the mol% of the Al2O3 component calculated based on the derived composition formula. It should be noted that in the first embodiment of the lithium ion conductive material of the present invention, the above-mentioned Li derived from the composition of Ti and Li 1+x Al x Ti 2-x P3O 12 (x = 0.05 to 0.4), more preferably Li 1.3 Al 0.3 Ti 1.7 P3O 12 .

[0059] Furthermore, in the first embodiment of the lithium ion conductive material of the present invention, the mol% of the P2O5 component described above is the same as the Li ion conductive material derived from the above-mentioned Ti and Li compositions. 1+x Al x Ti 2-x P3O 12 Compared to the mol% of the P2O5 component calculated using the composition formula (x = 0.05 to 0.4), the mol% decrease is 0.2 to 2.0 mol%. It should be noted that the lower limit of this range is preferably 0.3 mol%. Furthermore, the upper limit of this range is preferably 1.5 mol%, more preferably 1.2 mol%, even more preferably 1.0 mol%, and further preferably 0.8 mol%. The derived composition formula is the same as above.

[0060] By having the Al2O3 component and the P2O5 component in the above-mentioned contents, in the first embodiment of the lithium ion conductive material of the present invention, when mixed with a lithium-containing lithium ion conductive glass material (particularly a Li2O-P2O5-Al2O3 glass material) and sintered at a low temperature, the lithium ion conductive glass material reacts with the material of the first embodiment at the particle interface of the material of the first embodiment, and the reaction product exists at the particle interface, thereby obtaining a solid electrolyte with high lithium ion conductivity.

[0061] <Crystalline phase>

[0062] The crystal phase included in the first embodiment of the lithium ion conductive material of the present invention will be described in detail.

[0063] The first embodiment of the lithium ion conductive material of the present invention contains the above-mentioned components in predetermined amounts and contains a crystal phase of a rhombohedral NASICON structure (Li-substituted NASICON structure) or a Li 1+x Al x Ti 2-x P3O 12 (x≥0, preferably 2>x≥0, more preferably 0.6≥x≥0) crystalline phase. That is, it contains at least one of these crystalline phases. It should be noted that, although the crystalline phases included in the first embodiment of the lithium ion conductive material of the present invention are preferably all any one or more of the above-mentioned crystalline phases, they may contain a portion of other lithium ion conductive crystalline phases (for example, LISICON type, perovskite type, garnet type, etc.). Even in this case, among all the crystalline phases included in the first embodiment of the lithium ion conductive material of the present invention, the total amount of the above-mentioned crystalline phases is preferably 80% by mass or more, more preferably 90% by mass or more, and further preferably 95% by mass or more. That is, it is preferred that the above-mentioned crystalline phase is the main crystalline phase.

[0064] [Second embodiment]

[0065] Next, the components and crystal phases constituting the second embodiment of the lithium ion conductive material of the present invention will be described.

[0066] <Ingredients>

[0067] Each component constituting the second embodiment of the lithium ion conductive material of the present invention will be described in detail.

[0068] The P2O5 component forms a crystal phase of a rhombohedral NASICON structure in the second embodiment of the lithium ion conductive material of the present invention, Li1+x Al x Ti 2-x P3O 12 (x≥0) crystalline phase, or Li 1+x+y Al x Ti 2-x Si y P 3-y O 12 The P2O5 content is an essential component required for the formation of a crystalline phase (x ≥ 0, y ≥ 0). Therefore, the lower limit of the P2O5 content is 34.0%, preferably 34.4%, and more preferably 34.8%. On the other hand, to suppress the formation of other crystalline phases and to minimize the reduction in lithium ion conductivity of the solid electrolyte obtained by low-temperature mixing and sintering with a lithium-containing lithium-ion conductive glass material, the upper limit of the P2O5 content is 36.5%, preferably 36.0%, more preferably 35.5%, and even more preferably 35.2%.

[0069] The TiO2 component also forms a crystal phase of a rhombohedral NASICON structure in the second embodiment of the lithium ion conductive material of the present invention, 1+x Al x Ti 2-x P3O 12 (x≥0) crystalline phase, or Li 1+x+y Al x Ti 2-x Si y P 3-y O 12 The TiO2 content is an essential component required for the crystal phase (x≥0, y≥0). Therefore, the lower limit of the TiO2 content is 42.0%, preferably 43.0%, more preferably 44.0%, and even more preferably 44.3%. On the other hand, based on the view that the lithium ion conductivity of the solid electrolyte obtained by low-temperature mixing and sintering with a lithium-containing lithium ion conductive glass material is unlikely to decrease, the upper limit of the TiO2 content is 46.5%, preferably 46.0%, more preferably 45.5%, and even more preferably 45.2%.

[0070] The Al2O3 component also forms a crystal phase of a rhombohedral NASICON structure in the second embodiment of the lithium ion conductive material of the present invention, 1+x Al x Ti 2-x P3O 12 (x≥0) crystalline phase, or Li 1+x+y Al x Ti 2-x Si y P 3-y O12 The Al2O3 content is an essential component required for the formation of a crystalline phase (x ≥ 0, y ≥ 0). Therefore, the lower limit of the Al2O3 content is preferably 0.6%, more preferably 0.8%, even more preferably 1.0%, and even more preferably 1.2%. On the other hand, to suppress the formation of other crystalline phases and to minimize the reduction in lithium ion conductivity of the solid electrolyte obtained by low-temperature co-sintering with a lithium-containing lithium-ion conductive glass material, the upper limit of the Al2O3 content is 3.1%, preferably 2.5%, more preferably 2.2%, and even more preferably 2.0%.

[0071] The Li2O component, in the second embodiment of the lithium ion conductive material of the present invention, imparts lithium ion conductivity and forms a crystal phase of a rhombohedral NASICON structure, Li 1+x Al x Ti 2-x P3O 12 (x≥0) crystalline phase, or Li 1+x+y Al x Ti 2-x Si y P 3-y O 12 Li2O is an essential component required for the crystalline phase (x ≥ 0, y ≥ 0). Therefore, the lower limit of the content of the Li2O component is 15.0%, preferably 15.5%, and more preferably 16.0%. On the other hand, from the perspective of improving the chemical durability of the second embodiment of the lithium ion conductive material of the present invention and enhancing morphological stability, the upper limit of the content of the Li2O component is 17.6%, preferably 17.0%, and more preferably 16.5%.

[0072] In the second embodiment of the lithium ion conductive material of the present invention, the SiO2 component forms a crystal phase of a rhombohedral NASICON structure or a Li 1+x+y Al x Ti 2-x Si y P 3-y O 12 The SiO2 content is an essential component required for the formation of a crystalline phase (x ≥ 0, y ≥ 0). Therefore, the lower limit of the SiO2 content is preferably 0.5%, more preferably 1.0%, and even more preferably 1.5%. On the other hand, from the perspective of facilitating the formation of the desired crystalline phase and preventing crystals from easily adjoining each other and thus reducing lithium ion conductivity, the upper limit of the SiO2 content is 5.0%, more preferably 4.0%, even more preferably 3.0%, and even more preferably 2.6%.

[0073] Furthermore, in the second embodiment of the lithium ion conductive material of the present invention, as in the first embodiment described above, one or more components selected from the group consisting of a ZrO component, a YO component, a ScO component, a CaO component, a MgO component, and a SnO component may be contained as optional components. Furthermore, the contents of these components may be the same as in the first embodiment described above.

[0074] Similarly, the second embodiment of the lithium-ion conductive material of the present invention may contain an inorganic component containing boron (B) or fluorine (F). However, the sulfur (S) content is preferably minimized (e.g., less than 1%, further less than 0.1%), and more preferably, it is not contained. Similarly, the content of alkaline metal components other than Li (such as Na and K) is preferably minimized, and more preferably, it is not contained.

[0075] Furthermore, in the second embodiment of the lithium ion conductive material of the present invention, the mol% of the Al2O3 component described above and the Li 1+x+y Al x Ti 2-x Si y P 3-y O 12 Compared to the mol% of the Al2O3 component calculated using the composition formula (x = 0.05 to 0.4, y = 0.05 to 0.2, preferably x = 0.1 to 0.3, y = 0.05 to 0.15), the mol% of the Al2O3 component is reduced by 0.3 to 3.0 mol%. It should be noted that the lower limit of this range is preferably 0.4 mol%, more preferably 0.5 mol%. The upper limit of this range is preferably 2.8 mol%, more preferably 2.5 mol%, even more preferably 2.0 mol%, and further preferably 1.5 mol%.

[0076] Here, Li 1+x+y Al x Ti 2-x Si y P 3-y O 12 (x = 0.05 to 0.4, y = 0.05 to 0.2), which is also a basic component of LATP as a solid electrolyte material having a Li, Al, Ti, PO4 structure, can be derived from the composition of Al and Si, or from the composition of Ti, Li and Si. However, in the second embodiment of the lithium ion conductive material of the present invention, Li derived from the composition of Ti, Li and Si is used. 1+x+y Al x Ti 2-x Si y P 3-y O12 The calculation was performed based on the composition formula (x=0.05-0.4, y=0.05-0.2).

[0077] Specifically, for example, when the composition of Ti is 1.8, the composition of Si is 0.1, the composition of Li is 1.3, and the composition of Al is 0.2, it can be derived that Li 1.3 Al 0.2 Ti 1.8 Si 0.1 P 2.9 O 12 . And, it is sufficient that the actual mol% of the Al2O3 component is reduced by 0.3mol% to 3.0mol% compared to the mol% of the Al2O3 component calculated based on the derived composition formula. It should be noted that in the second embodiment of the lithium ion conductive material of the present invention, the above-mentioned Li2O3 derived from the composition of Ti, Li and Si is 1+x+y Al x Ti 2-x Si y P 3-y O 12 (x = 0.05 to 0.4, y = 0.05 to 0.2), more preferably Li 1.3 Al 0.2 Ti 1.8 Si 0.1 P 2.9 O 12 .

[0078] Furthermore, in the second embodiment of the lithium ion conductive material of the present invention, the mol% of the P2O5 component described above is the same as the Li ion conductive material derived from the above compositions of Ti, Li, and Si. 1+x+y Al x Ti 2-x Si y P 3-y O 12 Compared to the mol% of the P2O5 component calculated using the composition formula (x = 0.05 to 0.4, y = 0.05 to 0.2), the mol% decrease is 0.2 to 2.0 mol%. It should be noted that the lower limit of this range is preferably 0.3 mol%, more preferably 0.5 mol%, and even more preferably 0.8 mol%. Furthermore, the upper limit of this range is preferably 1.5 mol%, and more preferably 1.2 mol%. The derived composition formula is the same as above.

[0079] By having the Al2O3 component and the P2O5 component in the above-mentioned contents, in the second embodiment of the lithium ion conductive material of the present invention, when mixed with a lithium-containing lithium ion conductive glass material (particularly a Li2O-P2O5-Al2O3 glass material) and sintered at a low temperature, the lithium ion conductive glass material reacts with the material of the second embodiment at the particle interface of the material of the second embodiment, and the reaction product exists at the particle interface, thereby also obtaining a solid electrolyte with high lithium ion conductivity.

[0080] <Crystalline phase>

[0081] The crystal phase included in the second embodiment of the lithium ion conductive material of the present invention will be described in detail.

[0082] The second embodiment of the lithium ion conductive material of the present invention contains the above-mentioned components in predetermined amounts, and contains a crystal phase of a rhombohedral NASICON structure (Li-substituted NASICON structure) composed of at least a part of the components, Li 1+x Al x Ti 2-x P3O 12 (x≥0, preferably 2>x≥0, more preferably 0.6≥x≥0) crystalline phase, or Li 1+x+y Al x Ti 2-x Si y P 3-y O 12 (x≥0, y≥0, preferably 2>x≥0, 3>y≥0, more preferably 0.6≥x≥0, 1≥y≥0) crystalline phase. That is, it contains at least one of these crystalline phases. It should be noted that the crystalline phases included in the second embodiment of the lithium ion conductive material of the present invention are preferably all any one or more of the above-mentioned crystalline phases, but may contain a portion of other lithium ion conductive crystalline phases (for example, LISICON type, perovskite type, garnet type, etc.). Even in this case, among all the crystalline phases included in the second embodiment of the lithium ion conductive material of the present invention, the total amount of the above-mentioned crystalline phases is preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more. That is, it is preferred that the above-mentioned crystalline phase is the main crystalline phase.

[0083] [Form, characteristics, etc.]

[0084] Next, the form, characteristics, etc. of the lithium ion conductive material (first embodiment and second embodiment) of the present invention will be described in detail.

[0085] The lithium-ion conductive material of the present invention is preferably in the form of a powder, as it is mixed with a lithium-containing lithium-ion conductive glass material and sintered at low temperature to form a solid electrolyte (oxide-based solid electrolyte) (a material for low-temperature sintering). Therefore, from the perspective of ease of handling during low-temperature mixing and sintering, the powder is preferably in the form of a powder. The particles contained in the powder are not particularly limited, as they can be finely pulverized upon use. However, the particle size is preferably approximately 1 / 10 of the diameter of zirconia beads, which are micronized to prevent aggregation, etc., with a maximum particle size of 200 μm or less and an average particle size of 100 μm or less.

[0086] Here, the “maximum particle size” and “average particle size” of particles in the present invention refer to the maximum particle size and the volume-based average particle size measured by a laser diffraction / scattering particle size distribution analyzer.

[0087] The lithium ion conductivity of the lithium ion conductive material of the present invention at 25°C (lithium ion conductivity of the material before low-temperature mixing and sintering) is not limited, but is preferably 1.0×10 -4 S / cm or more, more preferably 2.0×10 - 4 S / cm or more, and more preferably 3.0×10 -4 S / cm or more, more preferably 4.0×10 -4 S / cm or more. And its density is not limited, but it is preferably 2.3g / cm 3 More than 2.5 g / cm 3 More than 2.6 g / cm 3 above.

[0088] Furthermore, the lithium-ion conductive material of the present invention is preferably, though not limited thereto, a lithium-ion conductive glass ceramic containing a glassy phase (amorphous phase). This is because mixing with a lithium-containing lithium-ion conductive glass material and sintering at low temperature can easily form a solid electrolyte with higher lithium-ion conductivity.

[0089] Here, the "glass ceramic" in the present invention includes a crystalline phase and an amorphous phase (non-crystalline phase) formed by heat treatment, wherein the crystalline phase is obtained by heat treating raw glass to precipitate the crystalline phase, or the crystalline phase is synthesized by heat treating raw glass and other materials. In other words, it is a mixture of ceramics and glass.

[0090] The lithium ion conductive material of the present invention having the above structure can be pulverized and mixed with a lithium-containing lithium ion conductive glass material and sintered at 800°C or below (e.g., 600-800°C, or 620-800°C, or 650-780°C) to improve the lithium ion conductivity and obtain a material having high lithium ion conductivity (e.g., lithium ion conductivity of 2.0×10 -4 S / cm or more, or 3.0×10 -4 S / cm or more, or 3.5×10 -4 S / cm or above, or 4.5×10 -4 S / cm or more, or 5.0×10 -4 S / cm or more, or 1.0×10 -3 S / cm or more). In addition, the obtained solid electrolyte has a density above a certain level (e.g. 2.3 g / cm 3 Above, or 2.5g / cm 3 Above, or 2.6g / cm 3 Although conventional lithium ion conductive materials may have a reduced lithium ion conductivity due to such mixed sintering, the lithium ion conductive material of the present invention has the above-mentioned characteristics and can be suitably used as a raw material for manufacturing a low-temperature sintered solid electrolyte (oxide-based solid electrolyte) (a component raw material of a low-temperature sintered solid electrolyte material).

[0091] [Method for producing the lithium ion conductive material of the present invention]

[0092] Next, the method for producing the lithium ion conductive material of the present invention will be described in detail.

[0093] The lithium-ion conductive material of the present invention can be manufactured using conventional methods for manufacturing inorganic materials, such as firing and melting inorganic materials, and mixed sintering. Furthermore, although not limited thereto, when manufacturing lithium-ion conductive glass-ceramics, it is preferably manufactured using a method comprising the following steps: vitrifying a vitrified raw material to obtain raw material glass (lithium-containing lithium-ion conductive glass material); obtaining a mixture with other raw materials; and mixing (e.g., co-pulverizing) and sintering the mixture with the raw material glass and other raw materials to obtain a sintered body of lithium-ion conductive glass-ceramics. Furthermore, it is preferably manufactured using a method comprising the following steps: vitrifying a vitrified raw material to obtain raw material glass (lithium-containing lithium-ion conductive glass material); mixing the raw material glass with other raw materials and pre-firing to obtain a calcined body; and mixing (e.g., co-pulverizing) and sintering the calcined body with the other raw materials to obtain a sintered body of lithium-ion conductive glass-ceramics.

[0094] It should be noted that the sintering temperature in the step of obtaining the above-mentioned sintered body is preferably, although not limited thereto, 1000°C or higher, and more preferably 1000°C or higher and 1200°C or lower.

[0095] Although not limited thereto, the raw material glass described above is preferably a Li₂O—P₂O₅—Al₂O₃ glass (glass whose basic components are Li₂O—P₂O₅—Al₂O₃) or a Li₂O—P₂O₅ glass (glass whose basic components are Li₂O—P₂O₅). In the second embodiment, it is preferably a Li₂O—P₂O₅—SiO₂—Al₂O₃ glass (glass whose basic components are Li₂O—P₂O₅—SiO₂) or a Li₂O—P₂O₅—SiO₂ glass (glass whose basic components are Li₂O—P₂O₅—SiO₂). Note that these raw materials may also contain Y₂O₃ or the like. Furthermore, in either the first or second embodiment, the mixture is preferably a titanium phosphate / titanium oxide (TiP₂Oₐ-TiO₂) mixture obtained by mixing and firing orthophosphoric acid (H₃PO₄) and titanium oxide (TiO₂).

[0096] [Method for producing a solid electrolyte using the lithium ion conductive material of the present invention]

[0097] Next, a method for producing a solid electrolyte using the lithium ion conductive material of the present invention will be described in detail.

[0098] A solid electrolyte using the lithium ion conductive material of the present invention can be manufactured by a method comprising the following steps: a step of mixing the lithium ion conductive material of the present invention obtained by the manufacturing method described above with a lithium-containing lithium ion conductive glass material (glass electrolyte) as a sintering aid to prepare a solid electrolyte material; and a step of sintering the obtained solid electrolyte material at a sintering temperature below 800°C to form a solid electrolyte (oxide-based solid electrolyte).

[0099] It should be noted that in the production of the solid electrolyte material, it is preferred to mix and pulverize the lithium-ion conductive material of the present invention (the first or second embodiment described above) with a lithium-containing lithium-ion conductive glass material as a sintering aid. In other words, it is preferred to pulverize them separately before mixing, or to pulverize them after mixing. Furthermore, pulverization can be performed before or after mixing. Furthermore, the lithium-containing lithium-ion conductive glass material preferably uses a Li₂O-P₂O₅-Al₂O₃-based glass (a glass electrolyte whose basic components are Li₂O-P₂O₅-Al₂O₃).

[0100] The sintering temperature in the step of forming the solid electrolyte is not limited as long as it is 800° C. or lower, but is more preferably 780° C. or lower, even more preferably 760° C. or lower, and further preferably 740° C. or lower.

[0101] Furthermore, during the sintering, a layer (such as a sheet-like positive electrode layer and a negative electrode layer, etc.) that becomes an electrode layer of an all-solid secondary battery can be formed integrally. A known layer can be used as the electrode layer. For example, an electrode layer for an all-solid secondary battery can be obtained by mixing an electrode active material (positive electrode active material or negative electrode active material) with a conductive additive, an inorganic binder, etc. as needed and then sintering the mixed electrode active material (positive electrode active material or negative electrode active material) can be used. Moreover, an all-solid secondary battery can be formed by integrally forming the material containing the above-mentioned solid electrolyte material at low temperature. It should be noted that as positive electrode active materials, there can be exemplified: NASICON-type LiV2(PO4)3, olivine-type Li x J y MtPO4 (wherein J is at least one selected from Al, Mg, and W, Mt is at least one selected from Ni, Co, Fe, and Mn, and x satisfies 0.9≤x≤1.5 and y satisfies 0≤y≤0.2), layered oxides, spinel-type oxides, and the like. In addition, examples of negative electrode active materials include: crystalline oxides including NASICON, olivine, and spinel types, rutile oxides, anatase oxides, amorphous metal oxides, and metal alloys. Furthermore, examples of conductive additives include: carbon compounds such as graphite, activated carbon, and carbon nanotubes; at least one metal selected from Ni, Fe, Mn, Co, Mo, Cr, Ag, and Cu; and alloys thereof; metals such as titanium, stainless steel, and aluminum; and precious metals such as platinum, gold, ruthenium, and rhodium.

[0102] The embodiment described above is only an example for easy understanding of the present invention and does not limit the present invention. That is, the composition, crystal phase, etc. described above can certainly be changed or improved without departing from the purpose of the present invention, and their equivalents are also included in the present invention.

[0103] Hereinafter, embodiments of the present invention will be described. However, the present invention is not limited to the following embodiments, and various modifications are possible within the technical concept of the present invention.

[0104] [Example]

[0105] according to Figure 1According to the synthesis flow chart (an example of a method for producing lithium-ion conductive glass ceramics) shown in FIG, after vitrification of the vitrified raw material to produce raw glass, the raw material is mixed with other raw materials, pulverized, dried, and sintered, or formed and then sintered, thereby producing the lithium-ion conductive glass ceramics of Comparative Examples 1 to 3 and Examples 1 to 4 (Step 1). Furthermore, to compare their performance, these lithium-ion conductive glass ceramics are mixed with a lithium-ion conductive glass material (sintering aid) and pulverized, followed by low-temperature sintering, simulating the interface formation during sintering of an all-solid-state secondary battery. The solid electrolytes of Comparative Examples 1 to 3 and Examples 1 to 4 are also produced (Step 2). Specifically, the production is carried out according to the following procedure.

[0106] First, the following supplementary explanation is given of Step 1. In Step 1, lithium metaphosphate, aluminum phosphate, and silicon dioxide (if included in the components) are melted and vitrified, and then titanium oxide and orthophosphoric acid are mixed and fired to obtain a mixture (fired body), which is then pulverized and sintered to produce lithium ion conductive glass ceramics.

[0107] <Production of Raw Glass>

[0108] Lithium metaphosphate (LiPO3) and aluminum phosphate (Al(PO3)3), or lithium metaphosphate (LiPO3) and aluminum phosphate (Al(PO3)3) with silicon dioxide (SiO2), are blended to achieve the stoichiometric ratios shown in Table 1 below, calculated as mol% based on the oxides. These are placed in a platinum pot, melted and vitrified at temperatures above 1100°C while being thoroughly stirred, and then cast onto a metal casting plate to produce various raw glass materials as amorphous materials. The yield of recovered raw glass, including the raw glass adhering to the platinum pot, is consistently over 99% by weight.

[0109] <Preparation of Titanium Phosphate and Titanium Oxide Mixture>

[0110] Titanium oxide (TiO2) and orthophosphoric acid (H3PO4, 89 wt%) were blended to achieve the stoichiometric ratios shown in Table 1 below, calculated as mol% based on the oxides. These were mixed using a rotary / revolutionary mixer (manufactured by Thinky, produced by Rentaro Awatori), placed in a beaker manufactured by Pyrex (registered trademark), and calcined at 550°C for 5 hours to produce various titanium phosphate / titanium oxide (TiP2O7-TiO2) mixtures.

[0111]

Table 1

[0112]

[0113] Synthesis of Lithium-Ion Conductive Glass-Ceramics

[0114] The various raw glass materials and the various titanium phosphate / titanium oxide mixtures described above were each ground to a size of 106 μm or less and then blended to achieve the stoichiometric ratios shown in Table 1 above, expressed as mol% based on the oxides. 1-Propanol was then added and the mixture was ground and mixed using a planetary ball mill at 250 rpm for 2 hours (5 minutes of grinding followed by a 1-minute pause) using 2 mm φ zirconium oxide beads (YTZ beads, manufactured by Nikkato Co., Ltd.) and a 500 cc zirconium oxide pot. The resulting powder paste was separated from the zirconium oxide beads using a sieve and then dried using a rack-type solvent recovery dryer (manufactured by Soso Chemical Industry Co., Ltd.).

[0115] The dried mixed powder was pulverized using an alumina mortar and pestle until it could pass through a 500 μm mesh. 1.5 g of the powder was then taken and molded using a 20 mm diameter mold under a pressure of 20 kN to obtain pellets for lithium ion conductivity measurement.

[0116] Then, the dried mixed powder without crushing was placed in a platinum pot. Separately, the particles for measuring lithium ion conductivity were placed on a platinum plate and sintered at 1100°C for 1 hour in the atmosphere to obtain sintered bodies and sintered body particles of Comparative Examples 1 to 3 and Examples 1 to 4, which are lithium ion conductive glass ceramics. The steps so far are referred to as Step 1 ( Figure 1 ). It should be noted that, Figure 1 An example is shown in which silicon dioxide is not used.

[0117] The compositions of P2O5 and Al2O3 expressed in mol% on an oxide basis of each sintered body and sintered body particle obtained in step 1 are compared with the Li 1+x Al x Ti 2-x P3O 12 (x=0.05~0.4) 1.3 Al 0.3 Ti 1.7 P3O 12 (same composition as Comparative Example 1), or the difference between the Li 1+x+y Al x Ti 2-x Si y P 3-y O 12 (x = 0.05 ~ 0.4, y = 0.05 ~ 0.2) 1.3 Al 0.2 Ti 1.8 Si 0.1 P2.9 O 12 The differences in the calculated compositions (mol%) of the P2O5 and Al2O3 components (the same as those of Comparative Example 3) are shown in Table 1 above. That is, Comparative Example 2, Example 1, and Example 2 show the differences in composition from Comparative Example 1, and Examples 3 and Example 4 show the differences in composition from Comparative Example 3. As can be seen from Table 1 above, the lithium ion conductive glass ceramics of Comparative Example 2 obtained in Step 1 contain more P2O5 and Al2O3 (in other words, AlPO4) than the above-derived composition formula. On the other hand, the lithium ion conductive glass ceramics of Examples 1 to 4 obtained in Step 1 contain less P2O5 and Al2O3 (in other words, AlPO4) than the above-derived composition formula. Figure 1 ).

[0118] Next, gold electrodes were formed on both surfaces of the resulting sintered particles using a magnetron sputtering apparatus (SC-701HMC, manufactured by Sanyu Electronics Co., Ltd.) as barrier electrodes. Impedance measurements were performed using an electrochemical evaluation apparatus (SP300, manufactured by Bio-Logic Co., Ltd.) at 25°C under the conditions of a frequency of 0.1 Hz to 7 MHz, an amplitude voltage of 10 mV, and an open-circuit voltage to calculate the lithium ion conductivity. Furthermore, the surface of each sintered particle was polished using #800 and #2000 water-resistant abrasive paper and 1-propanol. After drying, the diameter, thickness, and weight were measured using a caliper, a micrometer, and an electronic balance to calculate the density. The lithium ion conductivity and density of each sintered particle obtained in step 1 are shown in Table 2 below.

[0119] <Mixing of lithium-ion conductive glass ceramic and lithium-ion conductive glass material and low-temperature sintering: Step 2>

[0120] Next, step 2 is described in the following order. First, each sintered body (not the pellets obtained in step 1) and a 56 mol% Li₂O-38 mol% P₂O5-6 mol% Al₂O₃ glass (lithium-ion conductive glass material (glass electrolyte)) serving as a sintering aid were ground to a size of 106 μm or less. The mixture was then mixed to a ratio of 88% by weight of the sintered body to 12% by weight of the lithium-ion conductive glass material. 1-Propanol was then added to the mixture. The mixture was ground and mixed using a planetary ball mill with 2 mm diameter zirconia beads (YTZ beads, manufactured by Nikkato Co., Ltd.) and a 500 cc zirconia jar at 250 rpm for 2 hours (5 minutes of grinding followed by a 1-minute pause). The ground paste was separated from the zirconia beads using a sieve and then dried using a rack-type solvent recovery dryer (manufactured by Soso Chemical Industry Co., Ltd.).

[0121] The dried mixed powder was pulverized using an alumina mortar and pestle until it passed through a 500 μm mesh. 1.5 g of the powder was then molded using a 20 mm diameter mold under a pressure of 20 kN to obtain various pellets for measuring lithium ion conductivity.

[0122] After the particles for measuring lithium ion conductivity were heat-treated at 580°C, 620°C, 660°C, 700°C, 740°C or 780°C for 1 hour in the atmosphere to obtain sintered particles as a solid electrolyte, the lithium ion conductivity and density of these particles were calculated in the same manner as the calculation of the sintered particles in step 1 described above. It should be noted that the lithium ion conductivity and density of each sintered particle obtained by sintering at 780°C in step 2 are shown in Table 2 below. In addition, for Comparative Example 1, Comparative Example 2 and Example 4, the lithium ion conductivity (conductivity) and density of the sintered particles obtained at each sintering temperature were calculated in Table 2. Figure 2 as well as Figure 3 Shown in.

[0123]

Table 2

[0124]

[0125] <Evaluation Results>

[0126] From this result, it can be confirmed that the sintered particles of Comparative Examples 1 to 3 obtained in step 1 all have 5×10 - 4 S / cm or higher. In particular, the sintered particles of Comparative Example 2, although requiring a high sintering temperature of 1100°C, achieved a similar lithium ion conductivity to that of 1.2×10 -3 S / cm, there is no difference in the lithium ion conductivity between the literature values. However, the lithium ion conductivity of the sintered particles of Comparative Examples 1 to 3 obtained in step 2 is reduced to 1 / 2 to 1 / 3 of the lithium ion conductivity of the sintered particles obtained in step 1. On the other hand, in Examples 1 to 4, it is shown that the sintered particles obtained in step 2 all have higher lithium ion conductivity than the sintered particles obtained in step 1. Furthermore, even when compared with the sintered particles of Comparative Examples 1 to 3 obtained in step 2, they have higher lithium ion conductivity than them. In particular, it can be confirmed that the sintered particles of Example 3 obtained in step 2, which simulates the interface formation during the sintering of an all-solid-state secondary battery, have a lithium ion conductivity of 1.5×10 -3 S / cm, which is a very high lithium ion conductivity for LATP-based oxide solid electrolytes.

[0127] As shown in Table 1 above, any one of the components of the sintered particles (lithium ion conductive glass ceramics) of Examples 1 to 4 obtained in Step 1, the Al2O3 component and the P2O5 component (actually the AlPO4 component), and the Li as the basic component of LATP derived from the Ti and Li components 1.3 Al 0.3 Ti 1.7 P3O 12 (the composition of Comparative Example 1), or compared with Li as the basic component of LATP derived from the compositions of Ti, Li, and Si. 1.3 Al 0.2 Ti 1.8 Si 0.1 P 2.9 O 12 Compared with the components of Comparative Example 3, the amount of each is reduced to a certain extent. This is considered to be because when the lithium ion conductive glass material (glass electrolyte) of the Li2O-P2O5-Al2O3 system is mixed and sintered at a low temperature in step 2, the glass electrolyte reacts with the lithium ion conductive glass ceramic at the particle interface, and the reaction product exists at the particle interface, thereby avoiding the excessive amount of glass electrolyte (about 1×10 -7 S / cm) exists at the particle interfaces. Furthermore, in Comparative Examples 1 to 3, the sintered particles (lithium-ion conductive glass ceramics) obtained in Step 1 were the most suitable. Therefore, it is believed that the sintered particles (solid electrolyte) obtained in Step 2 have lower lithium-ion conductivity the more glass electrolyte is present at the particle interfaces. Furthermore, it is believed that if too little glass electrolyte is mixed in Step 2, the glass electrolyte cannot fully function, resulting in a decrease in the density and lithium-ion conductivity of the resulting sintered particles (solid electrolyte).

[0128] It should be noted that the secondary electron image of the fracture surface of the sintered particles obtained by sintering at 780°C in step 2 of Example 4 is Figure 4 As shown in Figure 5 As shown in . This observation and detection were performed using an electron microscope JSM-700HR manufactured by JEOL Ltd. Usually, when observing at a low acceleration voltage of about 5 kV, the secondary electron image can observe the information on the surface of the particles, and the reflected electron image can observe the information on the inside of the particles. The positions that cannot be seen in the reflected electron image can be seen in the secondary electron image, which shows that there are attachments on the surface of the particles of the sintered body particles. This image is an image of a broken surface, so it can be inferred that there are attachments (reaction products of the glass electrolyte and the lithium ion conductive glass ceramic) on the particle interface, and it can be inferred that the glass electrolyte is conducive to the interface formation of the particles.

[0129] Further, according to Figure 6 According to the synthesis flow chart (variation of the method for producing lithium-ion conductive glass-ceramics) shown in the figure, after vitrifying the vitrified raw material to produce the raw glass, the other raw materials are kneaded and pre-fired, and then mixed with other raw materials and pulverized before sintering, or formed and then sintered, thereby producing the lithium-ion conductive glass-ceramics of Comparative Example 4 and Examples 5-6 (Step 1-2). In addition, to compare their performance, these lithium-ion conductive glass-ceramics were mixed and pulverized with a lithium-ion conductive glass material (sintering aid) and low-temperature sintered to produce the solid electrolytes of Comparative Example 4 and Examples 5-6 (Step 2-2), simulating the interface formation during sintering of an all-solid-state secondary battery. Specifically, the production was carried out according to the following procedure.

[0130] First, the following supplementary explanation is provided for Step 1-2. In Step 1-2, lithium metaphosphate and silicon dioxide (if included in the composition) are melted and vitrified. Titanium oxide, orthophosphoric acid, and aluminum phosphate are then kneaded and pre-fired to produce a calcined body. The calcined body is then mixed with lithium metaphosphate, pulverized, and sintered to produce a lithium-ion conductive glass-ceramic.

[0131] <Production of Raw Glass>

[0132] Lithium metaphosphate (LiPO3) or lithium metaphosphate (LiPO3) and silicon dioxide (SiO2) are blended to achieve the stoichiometric ratios shown in Table 3 below, calculated as mol% based on oxides. Since lithium metaphosphate is also mixed after pre-firing, a quantity half the stoichiometric ratio is used here. This is placed in a platinum pot, melted and vitrified at a temperature above 1100°C while being thoroughly stirred, and then cast onto a metal casting plate to obtain various raw glass materials as amorphous materials. The raw glass recovered, including any adhering to the platinum pot, has a weight ratio of at least 99%.

[0133] <Making of raw materials: glass, titanium oxide, orthophosphoric acid, and aluminum phosphate calcined body>

[0134] Titanium oxide (TiO2), orthophosphoric acid (H3PO4, 89 wt%), aluminum phosphate (Al(PO3)3), and the above-mentioned raw glass were mixed to achieve the stoichiometric ratios shown in Table 3 below, based on mol% of the oxides. After kneading using a rotary / revolutionary mixer (manufactured by Thinky, produced by Rentaro Awatori), the mixture was placed in a beaker manufactured by Pyrex (registered trademark) and fired at 550°C for 5 hours to obtain a calcined mixture of the various raw glass materials, titanium oxide, orthophosphoric acid, and aluminum phosphate.

[0135]

Table 3

[0136]

[0137] Synthesis of Lithium-Ion Conductive Glass-Ceramics

[0138] The calcined body and lithium metaphosphate were each ground to a size of 106 μm or less and then mixed to achieve the stoichiometric ratios shown in Table 3, calculated as mol% based on oxides. 1-Propanol was then added and the mixture was ground and mixed using a planetary ball mill at 250 rpm for 2 hours (5 minutes of grinding followed by a 1-minute pause) using 2 mm φ zirconium oxide beads (YTZ beads, manufactured by Nikkato) and a 500 cc zirconium oxide jar. The resulting powder paste was separated from the zirconium oxide beads using a sieve and then dried using a rack-type solvent recovery dryer (manufactured by Soso Chemical Industry Co., Ltd.).

[0139] The dried mixed powder was pulverized using an alumina mortar and pestle until it could pass through a 500 μm mesh. 1.5 g of the powder was then taken and molded using a 20 mm diameter mold under a pressure of 20 kN to obtain pellets for lithium ion conductivity measurement.

[0140] Then, the dried mixed powder without crushing was placed in a platinum pot. Separately, the particles for measuring lithium ion conductivity were placed on a platinum plate and sintered at 1000°C for 1 hour in the atmosphere to obtain sintered bodies and sintered body particles of Comparative Example 4 and Examples 5-6 of lithium ion conductive glass ceramics. The steps so far are referred to as Steps 1-2 ( Figure 6 ). It should be noted that, Figure 6 An example is shown in which silicon dioxide is used.

[0141] The compositions of P2O5 and Al2O3 expressed in mol% on an oxide basis of the sintered bodies and sintered body particles of Examples 5 and 6 obtained in Step 1-2 were compared with the Li 1+x Al x Ti 2-x P3O 12 (x=0.05~0.4) 1.3 Al 0.3 Ti 1.7 P3O 12 (the same composition as that of Comparative Example 1 described above), or Li derived from the compositions of Ti, Li, and Si 1+x+y Al x Ti 2-x Si y P 3-y O 12(x = 0.05 ~ 0.4, y = 0.05 ~ 0.2) 1.3 Al 0.2 Ti 1.8 Si 0.1 P 2.9 O 12 The differences in the calculated P2O5 and Al2O3 compositions (the same as those of Comparative Example 4) (mol %) are shown in Table 3. Specifically, Example 5 shows the difference in composition from Comparative Example 4, and Example 6 shows the difference in composition from Comparative Example 1 described above. As can be seen in Table 3, the lithium-ion conductive glass-ceramics of Examples 5 and 6, obtained in Steps 1-2, have a certain reduction in P2O5 and Al2O3 (in other words, AlPO4) compared to the derived composition formulas.

[0142] Next, gold electrodes were formed on both surfaces of the resulting sintered particles using a magnetron sputtering apparatus (SC-701HMC, manufactured by Sanyu Electronics Co., Ltd.) as barrier electrodes. Impedance measurements were performed using an electrochemical evaluation apparatus (SP300, manufactured by Bio-Logic Co., Ltd.) at 25°C under the conditions of a frequency of 0.1 Hz to 7 MHz, an amplitude voltage of 10 mV, and an open-circuit voltage to calculate the lithium ion conductivity. Furthermore, the surface of each sintered particle was polished using #800 and #2000 water-resistant abrasive paper and 1-propanol. After drying, the diameter, thickness, and weight were measured using a caliper, a micrometer, and an electronic balance to calculate the density. The lithium ion conductivity and density of each sintered particle obtained in steps 1-2 are shown in Table 4 below.

[0143] <Mixing of lithium-ion conductive glass ceramic and lithium-ion conductive glass material and low-temperature sintering: Step 2-2>

[0144] Next, step 2-2 is described in the following order. First, each sintered body (not the pellets obtained in step 1-2) and a 56 mol% Li₂O-38 mol% P₂O5-6 mol% Al₂O₃ glass (lithium ion conductive glass material (glass electrolyte)) serving as a sintering aid are ground to a size of 106 μm or less. The mixture is then mixed to a ratio of 88% by weight of the sintered body to 12% by weight of the lithium ion conductive glass material. 1-Propanol is then added to the mixture. The mixture is ground and mixed using a planetary ball mill with 2 mm diameter zirconia beads (YTZ beads, manufactured by Nikkato Co., Ltd.) and a 500 cc zirconia jar at 250 rpm for 2 hours (5 minutes of grinding followed by a 1-minute pause). The ground paste is separated from the zirconia beads using a sieve and then dried using a rack-type solvent recovery dryer (manufactured by Soso Chemical Industry Co., Ltd.).

[0145] The dried mixed powder was crushed using an alumina mortar and pestle until it could pass through a 500 μm mesh. 1.5 g of the powder was then taken and molded using a 20 mm diameter mold under a pressure of 20 kN to obtain various pellets for measuring lithium ion conductivity.

[0146] After the particles for measuring lithium ion conductivity are heat-treated at 650°C, 700°C, 740°C, 760°C, 780°C or 800°C for 1 hour in the atmosphere to obtain sintered particles as a solid electrolyte, the lithium ion conductivity and density of these particles are calculated using the same method as the calculation of the sintered particles in step 1-2 described above. It should be noted that the lithium ion conductivity and density of each sintered particle obtained by sintering at 740°C in step 2-2 are shown in Table 4 below. In addition, for Example 5, the relationship between the lithium ion conductivity (conductivity) and density of the sintered particles obtained according to each sintering temperature is compared with the comparative example 1 and Example 4 described above. Figure 7 as well as Figure 8 Shown in.

[0147]

Table 4

[0148]

[0149] <Evaluation Results>

[0150] From this result, it can be confirmed that the sintered particles of Examples 5 and 6 obtained in Step 1-2 all have 4×10 -4 S / cm or higher. This is consistent with the trend of Examples 1 to 4 described above. On the other hand, it was confirmed that even at a low sintering temperature of 740°C in step 2-2, which simulates the interface formation during sintering of an all-solid-state secondary battery, a lithium ion conductivity of more than 2×10 -4 S / cm, and the density is also greater than 2.6g / cm 3 of solid electrolytes.

[0151] It should be noted that the secondary electron image of the fracture surface of the sintered particles obtained by sintering at 700°C in step 2-2 of Example 5 is Figure 9 The observation and detection were performed using an electron microscope JSM-700HR manufactured by JEOL Ltd. under the same conditions as Figure 4 This result confirms that even when sintering is performed at 700°C, the bonding between the particles is sufficient.

[0152] This application claims priority based on Japanese patent application No. 2021-060218, filed on March 31, 2021, the disclosure of which is incorporated herein in its entirety.

Claims

1. A solid electrolyte, wherein: The solid electrolyte is formed by mixing lithium ion conductive glass ceramics and lithium ion conductive glass material containing lithium and sintering them, and The lithium ion conductive glass ceramics contain, in terms of mol% based on oxides: 36.6% to 37.3% P2O5 composition, 43.0% to 48.1% TiO2 content, 0.6% to 3.2% Al2O3 composition, and 13.9% to 17.5% Li2O composition, and Does not contain B ingredients, The mol% of the Al2O3 component is the same as the Li mol% derived from the Ti and Li components. 1+x Al x Ti 2-x P3O 12 Compared with the mol% of Al2O3 calculated by the composition formula, it is reduced by 0.3mol% to 3.0mol%, where x = 0.05 to 0.

4. The mol% of the P2O5 component is the same as the Li mol% derived from the Ti and Li components. 1+x Al x Ti 2-x P3O 12 Compared with the mol% of P2O5 calculated by the composition formula, it is reduced by 0.2mol% to 2.0mol%, where x = 0.05 to 0.

4. And, including Li 1+x Al x Ti 2-x P3O 12 crystalline phase, where x≥0.

2. A solid electrolyte, wherein: The solid electrolyte is formed by mixing lithium ion conductive glass ceramics and lithium ion conductive glass material containing lithium and sintering them, and The lithium ion conductive glass ceramics contain, in terms of mol% based on oxides: 34.0% to 36.5% P2O5 content, 42.0% to 46.5% TiO2 content, 0.6% to 3.1% Al2O3 composition, 15.0% to 17.6% Li2O content, and 0.5% to 5.0% SiO2 content, and Does not contain B ingredients, The mol% of the Al2O3 component is the same as the Li mol% derived from the Ti, Li and Si components. 1+x+y Al x Ti 2-x Si y P 3-y O 12 Compared with the mol% of Al2O3 calculated by the composition formula, it is reduced by 0.3mol% to 3.0mol%, where x = 0.05 to 0.4, y = 0.05 to 0.2, The mol% of the P2O5 component is the same as the Li mol% derived from the Ti, Li and Si components. 1+x+y Al x Ti 2-x PcqI 3-y O 12 Compared with the mol% of P2O5 calculated by the composition formula, it is reduced by 0.2mol% to 2.0mol%, wherein x = 0.05 to 0.4, y = 0.05 to 0.2, And, including Li 1+x+y Al x Ti 2-x Si y P 3-y O 12 A crystalline phase, wherein x≥0, y≥0.

3. An all-solid secondary battery formed by a material containing the solid electrolyte material according to claim 1 or 2.

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