Electrode active materials and all-solid-state batteries

Abstract

The present invention provides an electrode active material that can achieve high rate-of-use characteristics and high cycle characteristics, and a high volume-specific capacity, as well as an all-solid-state battery using the electrode active material. [Solution] The electrode active material is Al 1-x M x Nb 11―y N y O 29 It is represented by the composition formula, where x is 0

Description

[Technical Field]

[0001] This invention relates to electrode active materials and all-solid-state batteries. [Background technology]

[0002] In recent years, all-solid-state batteries have been utilized as secondary batteries with high energy density. These all-solid-state batteries require smaller size, lighter weight, and higher capacity and energy density; therefore, development of high-capacity and high-output electrode active materials is underway (see, for example, Patent Documents 1-4 and Non-Patent Document 1). [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] International Publication No. 2022 / 080083 [Patent Document 2] Japanese Patent Publication No. 2010-287496 [Patent Document 2] International Publication No. 2022 / 185717 [Patent Document 3] Japanese Patent Publication No. 2024-50182 [Non-patent literature]

[0004] [Non-Patent Document 1] Appl. Mater. Interface. 2019;11(6): 6089-6096. [Overview of the project] [Problems that the invention aims to solve]

[0005] AlNb 11 O 29 While it has a high volumetric specific capacity, it has the drawback of being difficult to obtain high rate and high cycle characteristics.

[0006] The present invention has been made in view of the above problems, and an object thereof is to provide an electrode active material capable of realizing high rate characteristics and high cycle characteristics and achieving a high volume specific capacity, and a all-solid-state battery using the electrode active material.

Means for Solving the Problems

[0007] The electrode active material according to the present invention contains a negative electrode active material represented by the composition formula of Al 1-x M x Nb 11―y N y O 29 , where x satisfies 0 < x < 0.5, y satisfies 0 ≦ y < 5, M is a tetravalent transition metal element, and N is a pentavalent or higher transition metal element.

[0008] In the above electrode active material, x may satisfy 0.05 ≦ x.

[0009] In the above electrode active material, x may satisfy x ≦ 0.2.

[0010] In the above electrode active material, M may be Hf.

[0011] In the above electrode active material, x and y may satisfy x < y.

[0012] In the above electrode active material, y may satisfy y < 5.

[0013] In the above electrode active material, y may satisfy 0.5 ≦ y ≦ 2.5.

[0014] In the above electrode active material, N may be Ta.

[0015] In the above electrode active material, the negative electrode active material may be the main component.

[0016] In the above electrode active material, the negative electrode active material may be a powder material.

[0017] The all-solid-state battery according to the present invention comprises an oxide-based solid electrolyte layer, a first electrode layer provided on a first main surface of the oxide-based solid electrolyte layer and containing a positive electrode active material, and a second electrode layer provided on a second main surface of the oxide-based solid electrolyte layer and containing the electrode active material. [Effects of the Invention]

[0018] According to the present invention, it is possible to provide an electrode active material that can achieve high rate characteristics and high cycle characteristics, and a high volume specific capacity, as well as an all-solid-state battery using the electrode active material. [Brief explanation of the drawing]

[0019] [Figure 1] This is a schematic cross-sectional view showing the basic structure of an all-solid-state battery. [Figure 2] This is a schematic cross-sectional view. [Figure 3] This is a schematic cross-sectional view of an all-solid-state battery according to an embodiment. [Figure 4] This is a schematic cross-sectional view of another all-solid-state battery. [Figure 5] This diagram illustrates a flow chart of the manufacturing process for all-solid-state batteries. [Figure 6] (a) and (b) are diagrams illustrating the lamination process. [Figure 7] This is a schematic cross-sectional view showing the basic structure of a lithium-ion battery. [Modes for carrying out the invention]

[0020] (First Embodiment) The electrode active material according to the first embodiment will be described below with reference to the drawings.

[0021] The electrode active material according to this embodiment contains a negative electrode active material. The negative electrode active material used in a general Li-ion battery is mainly graphite-based. However, since the operating potential of the graphite-based material is close to the deposition potential of Li, there is a risk of internal short circuit due to Li deposition during charge and discharge. Therefore, it is conceivable to use an oxide-based negative electrode active material. The oxide-based negative electrode active material has a higher operating potential compared to the graphite-based negative electrode active material and does not cause lithium deposition, so it is possible to provide a safe battery that does not cause an internal short circuit during charge and discharge. However, a disadvantage of the oxide-based negative electrode active material is its low capacity.

[0022] For example, as the oxide-based negative electrode active material, TiNb2O7, AlNb 11 O 29 and the like can be mentioned. However, TiNb2O7 has problems in cycle characteristics and rate characteristics when applied to all-solid-state batteries. AlNb 11 O 29 achieves a higher volume specific capacity than TiNb2O7, but has problems in cycle characteristics and rate characteristics.

[0023] As a result of the intensive research by the present inventor, it has been found that an oxide in which a part of Al in AlNb 11 O 29 is substituted with a tetravalent transition metal element (hereinafter referred to as transition metal element M) realizes a high volume specific capacity and also realizes high rate characteristics and high cycle characteristics. This is because substituting a tetravalent transition metal element M for the trivalent Al site introduces defects into the crystal lattice, improving conductivity and structural stability.

[0024] However, if the composition ratio of Al decreases, there is a risk that sufficient volume specific capacity cannot be obtained. Therefore, in this embodiment, an upper limit is set for the content of the transition metal element M. Specifically, in this embodiment, Al 1-x M x Nb 11 O 29An oxide represented by the following compositional formula, where 0 < x < 0.5, is used as the negative electrode active material. This enables the realization of a high volume specific capacity, and high rate characteristics and high cycle characteristics can be obtained.

[0025] For example, for powders of Al 1-x M x Nb 11 O 29 containing different amounts of transition metal element M, XRD measurement (X-ray diffraction measurement) is performed, Rietveld analysis is carried out to calculate the lattice constant, and when the obtained lattice constant and volume are plotted, it is confirmed that Al can be substituted by transition metal element M because they lie on a straight line (Vegard's law). Also, Al 1-x M x Nb 11 O 29 belongs to the space group C2 / m.

[0026] From the perspective of sufficiently improving the volume specific capacity, rate characteristics, and cycle characteristics, in the compositional formula of Al 1-x M x Nb 11 O 29 x is preferably 0.05 or more, more preferably 0.07 or more, and even more preferably 0.10 or more.

[0027] On the other hand, if the substitution amount by the transition metal element M is too large, the rate characteristics and cycle characteristics may deteriorate. Therefore, in the compositional formula of Al 1-x M x Nb 11 O 29 it is preferable to set an upper limit for x. In this embodiment, x is preferably 0.2 or less, and more preferably 0.15 or less.

[0028] As the transition metal element M, Hf (hafnium), Sn (tin), Ti (titanium), Zr (zirconium), V (vanadium), Ce (cerium), Mo (molybdenum), W (tungsten), Pr (praseodymium), Ru (ruthenium), etc. can be used.

[0029] The electrode active material may contain an electrode active material other than the negative electrode active material represented by the composition formula Al 1-x M x Nb 11 O 29 However, in the electrode active material, it is preferable that the negative electrode active material represented by the composition formula Al 1-x M x Nb 11 O 29 is the main component. For example, in the electrode active material, it is preferable that the negative electrode active material represented by the composition formula Al 1-x M x Nb 11 O 29 is 80% by volume or more, and preferably 90% by volume or more.

[0030] In addition, by substituting a part of Nb with a transition metal element having a valence of 5 or more (hereinafter referred to as transition metal element N), a high volume specific capacity can be realized, and high rate characteristics and high cycle characteristics can also be realized, and it becomes difficult to react with the solid electrolyte during firing. Therefore, it is preferable to use a negative electrode active material in which a part of Nb in the composition formula Al 1-x M x Nb 11 O 29 is substituted with a transition metal element N. Specifically, it is preferable to use a negative electrode active material represented by the composition formula of Al 1-x M x Nb 11-y N y O 29 (0 ≦ y < 5).

[0031] From the viewpoint of the single-phase ratio, in the composition formula Al 1-x M x Nb 11-y N y O 29 it is preferable that x < y.

[0032] [[ID=6-4]] From the viewpoint of sufficiently improving the rate characteristics and cycle characteristics, in the composition formula Al 1-x M x Nb 11-y N y O 29In this case, y is preferably 0.5 or greater, and more preferably 1.0 or greater.

[0033] On the other hand, the composition formula Al 1-x M x Nb 11-y N y O 29 In this case, if y is too large, the volumetric specific capacity may decrease. Therefore, it is preferable to set an upper limit on y. In this embodiment, it is more preferable that y be 3.0 or less, and even more preferable that y be 2.5 or less.

[0034] Transition metal elements such as Ta (tantalum), Mo (pentavalent molybdenum), and W (pentavalent tungsten) can be used as the N element.

[0035] (Second Embodiment) Figure 1 is a schematic cross-sectional view showing the basic structure of an all-solid-state battery 100 according to the second embodiment. As illustrated in Figure 1, the all-solid-state battery 100 has a structure in which a solid electrolyte layer 30 is sandwiched between a first internal electrode 10 (first electrode layer) and a second internal electrode 20 (second electrode layer). The first internal electrode 10 is formed on the first main surface of the solid electrolyte layer 30. The second internal electrode 20 is formed on the second main surface of the solid electrolyte layer 30. The first internal electrode 10, the solid electrolyte layer 30, and the second internal electrode 20 are sintered bodies of powder material.

[0036] When the all-solid-state battery 100 is used as a secondary battery, one of the first internal electrode 10 and the second internal electrode 20 is used as the positive electrode and the other as the negative electrode. In this embodiment, as an example, the first internal electrode 10 is used as the positive electrode and the second internal electrode 20 is used as the negative electrode.

[0037] The solid electrolyte layer 30 mainly consists of a solid electrolyte having ionic conductivity. The solid electrolyte of the solid electrolyte layer 30 is, for example, an oxide-based solid electrolyte having lithium ion conductivity. The solid electrolyte is, for example, a phosphate-based solid electrolyte having a NASICON structure. A phosphate-based solid electrolyte having a NASICON structure has the properties of high conductivity and stability in the atmosphere. The phosphate-based solid electrolyte is, for example, a lithium-containing phosphate. The phosphate is not particularly limited, but examples include a lithium phosphate composite salt with Ti (e.g., LiTi2(PO4)3). Alternatively, Ti can be partially or completely substituted with a tetravalent transition metal such as Ge, Sn, Hf, or Zr. Furthermore, to increase the Li content, it may be partially substituted with a trivalent transition metal such as Al, Ga, In, Y, or La. More specifically, for example, Li 1+x Al x Ge 2-x (PO4)3 and Li 1+x Al x Zr 2-x (PO4)3, Li 1+x Al x Ti 2-x Examples include (PO4)3.

[0038] As illustrated in Figure 2, the first internal electrode 10 has a structure in which an electrode active material 11, a solid electrolyte 12, a conductive additive 13, etc., are dispersed. The second internal electrode 20 has a structure in which an electrode active material 21, a solid electrolyte 22, a conductive additive 23, etc., are dispersed. By providing the electrode active material 11 in the first internal electrode 10 and the electrode active material 21 in the second internal electrode 20, the all-solid-state battery 100 can be used as a secondary battery. By providing the solid electrolyte 12 in the first internal electrode 10 and the solid electrolyte 22 in the second internal electrode 20, ionic conductivity is obtained in the first internal electrode 10 and the second internal electrode 20. By providing the conductive additive 13 in the first internal electrode 10 and the conductive additive 23 in the second internal electrode 20, conductivity is obtained in the first internal electrode 10 and the second internal electrode 20. The solid electrolytes 12 and 22 may be, for example, the same solid electrolyte as the solid electrolyte layer 30, or they may be different solid electrolytes.

[0039] The electrode active material 11 is, for example, an electrode active material having an olivine-type crystal structure. Examples of such an electrode active material include phosphates containing a transition metal and lithium. The olivine-type crystal structure is the crystal of natural olivine and can be identified by X-ray diffraction.

[0040] As a typical example of the electrode active material having an olivine-type crystal structure, LiCoPO4 containing Co or the like can be used. It is also possible to use phosphates in which Co, a transition metal, is replaced in this chemical formula. Here, the ratios of Li and PO4 can vary depending on the valence. Preferably, Co, Mn, Fe, Ni, etc. are used as the transition metal.

[0041] As the conductive aids 13 and 23, carbon materials or the like are used. Metals may be used as the conductive aids 13 and 23. Examples of the metal of the conductive aid include Pd, Ni, Cu, Fe, and alloys containing these.

[0042] In the present embodiment, the electrode active material described in the first embodiment is used for the electrode active material 21. Specifically, a negative electrode active material represented by the composition formula of Al 1-x M x Nb 11-y N y O 29 (0 < x < 0.5, 0 < y < 5) is used. Thereby, a high volume specific capacity is realized, high rate characteristics and high cycle characteristics are also realized, and an effect that it becomes difficult to react with the solid electrolyte during firing is obtained.

[0043] In the second internal electrode 20, if the average particle size of the electrode active material 21 is too large, the internal resistance of the electrode may increase, making high-speed charging and discharging difficult. If the average particle size is too small, the reactivity during heat treatment may increase, and it may also inhibit the sintering and densification of the solid electrolyte. Therefore, the average particle size of the electrode active material 21 in the second internal electrode 20 is preferably 0.5 μm or more and 10 μm or less, more preferably 0.7 μm or more and 6.0 μm or less, and even more preferably 1.0 μm or more and 4.0 μm or less.

[0044] Figure 3 is a schematic cross-sectional view of a stacked all-solid-state battery 100a, in which multiple battery units are stacked. The all-solid-state battery 100a comprises a stacked chip 60 having a substantially rectangular parallelepiped shape. In the stacked chip 60, a first external electrode 40a and a second external electrode 40b are provided so as to be in contact with two side surfaces, which are two of the four surfaces other than the top and bottom surfaces at the stacking direction ends. These two side surfaces may be adjacent to each other or may be two opposing sides. In this embodiment, the first external electrode 40a and the second external electrode 40b are provided so as to be in contact with two opposing side surfaces (hereinafter referred to as two end surfaces).

[0045] In the following description, components having the same composition range, thickness range, and particle size distribution range as the all-solid-state battery 100 will be given the same reference numerals, and detailed explanations will be omitted.

[0046] In the all-solid-state battery 100a, multiple first internal electrodes 10 and multiple second internal electrodes 20 are alternately stacked via a solid electrolyte layer 30. The edges of the multiple first internal electrodes 10 are exposed on the first end face of the stacked chip 60, but not on the second end face. The edges of the multiple second internal electrodes 20 are exposed on the second end face of the stacked chip 60, but not on the first end face. As a result, the first internal electrodes 10 and the second internal electrodes 20 are alternately conductive to the first external electrode 40a and the second external electrode 40b. The solid electrolyte layer 30 extends from the first external electrode 40a to the second external electrode 40b. Thus, the all-solid-state battery 100a has a structure in which multiple battery units are stacked.

[0047] On the upper surface of the laminated structure of the first internal electrode 10, the solid electrolyte layer 30, and the second internal electrode 20 (in the example of FIG. 3, the upper surface of the uppermost first internal electrode 10), a cover layer 50 is laminated. Also, on the lower surface of the laminated structure (in the example of FIG. 3, the lower surface of the lowermost first internal electrode 10), a cover layer 50 is laminated. The cover layer 50 mainly consists of an inorganic material containing, for example, Al, Zr, Ti, etc. (such as Al2O3, ZrO2, TiO2, etc.). The cover layer 50 may contain the main component of the solid electrolyte layer 30 as the main component.

[0048] The first internal electrode 10 and the second internal electrode 20 may include a current collector layer. For example, as illustrated in FIG. 4, a first current collector layer 15 may be provided within the first internal electrode 10. Also, a second current collector layer 25 may be provided within the second internal electrode 20. The first current collector layer 15 and the second current collector layer 25 mainly consist of a conductive material. For example, metals, carbon, etc. can be used as the conductive material for the first current collector layer 15 and the second current collector layer 25. By connecting the first current collector layer 15 to the first external electrode 40a and connecting the second current collector layer 25 to the second external electrode 40b, the current collection efficiency is improved.

[0049] Subsequently, the manufacturing method of the all-solid-state battery 100a illustrated in FIG. 3 will be described. FIG. 5 is a diagram illustrating the flow of the manufacturing method of the all-solid-state battery 100a.

[0050] (Production process of the negative electrode active material powder) Al 1-x M x Nb 11-y N y O 29 (0 < x < 0.5, 0 < y < 5), raw materials such as AlNb 11 O 29 , oxides of transition metal element M, oxides of transition metal element N, etc., are weighed and mixed. After mixing, it is calcined at 1100 °C in the atmosphere, and the obtained calcined powder is subjected to a crushing process again. Then, by heat-treating at a temperature of 1300 °C or higher in the atmosphere, the target Al 1-x M x Nb 11-y Ny O 29 Obtain a composite powder where (0 < x < 0.5, 0 < y < 5). After re-kneading the composite powder, sieve it through a #150 stainless steel mesh to obtain the negative electrode active material powder.

[0051] (Process for producing raw material powder for solid electrolyte layer) First, produce the raw material powder for the solid electrolyte layer that constitutes the above-mentioned solid electrolyte layer 30. For example, by mixing raw materials, additives, etc. and using a solid-phase synthesis method or the like, the raw material powder for the solid electrolyte layer can be produced. The obtained raw material powder can be adjusted to a desired average particle size by dry grinding. For example, use a planetary ball mill with 5 mmφ ZrO2 balls to adjust to the desired average particle size.

[0052] (Process for producing raw material powder for cover layer) First, produce the raw material powder of the ceramics that constitutes the above-mentioned cover layer 50. For example, by mixing raw materials, additives, etc. and using a solid-phase synthesis method or the like, the raw material powder for the cover layer can be produced. The obtained raw material powder can be adjusted to a desired average particle size by dry grinding. For example, use a planetary ball mill with 5 mmφ ZrO2 balls to adjust to the desired average particle size.

[0053] (Process for producing paste for internal electrode) Next, an internal electrode paste is prepared for the fabrication of the first internal electrode 10 and the second internal electrode 20 described above. For example, an internal electrode paste can be obtained by uniformly dispersing a conductive additive, electrode active material, solid electrolyte material, sintering aid, binder, plasticizer, etc., in water or an organic solvent. As the solid electrolyte material, the raw material powder for the solid electrolyte layer described above may be used. As a conductive additive, carbon materials may be used. As a conductive additive, metals may also be used. Examples of metals used as conductive additives include Pd, Ni, Cu, Fe, and alloys containing these. Pd, Ni, Cu, Fe, alloys containing these, and various carbon materials may be used further. If the composition of the first internal electrode 10 and the second internal electrode 20 is different, each internal electrode paste may be prepared individually. Also, if the electrode active material 21 of the second internal electrode 20 contains multiple types of negative electrode active materials, these multiple types of negative electrode active materials may be included in the internal electrode paste.

[0054] The paste for internal electrodes contains, for example, one or more glass components such as Li-BO compounds, Li-Si-O compounds, Li-CO compounds, Li-SO compounds, and Li-PO compounds as sintering aids.

[0055] (Process for preparing paste for external electrodes) Next, an external electrode paste is prepared for the fabrication of the first external electrode 40a and the second external electrode 40b described above. For example, an external electrode paste can be obtained by uniformly dispersing a conductive material, glass frit, binder, plasticizer, etc., in water or an organic solvent.

[0056] (Solid electrolyte green sheet manufacturing process) A solid electrolyte slurry having a desired average particle size is obtained by uniformly dispersing raw material powder for the solid electrolyte layer in an aqueous solvent or organic solvent together with a binder, dispersant, plasticizer, etc., and then performing wet grinding. At this time, a bead mill, wet jet mill, various kneaders, high-pressure homogenizer, etc. can be used, and it is preferable to use a bead mill from the viewpoint that particle size distribution adjustment and dispersion can be performed simultaneously. A binder is added to the obtained solid electrolyte slurry to obtain a solid electrolyte paste. A solid electrolyte green sheet 51 can be produced by coating with the obtained solid electrolyte paste. The coating method is not particularly limited, and a slot die method, reverse coating method, gravure coating method, bar coating method, doctor blade method, etc. can be used. The particle size distribution after wet grinding can be measured, for example, using a laser diffraction measuring device using the laser diffraction scattering method.

[0057] (Lamination process) As illustrated in Figure 6(a), an internal electrode paste 52 is printed on one surface of a solid electrolyte green sheet 51. An inverse pattern 53 is printed on the areas of the solid electrolyte green sheet 51 where the internal electrode paste 52 is not printed. The same material as the solid electrolyte green sheet 51 can be used as the inverse pattern 53. Multiple printed solid electrolyte green sheets 51 are stacked alternately with a slight offset. As illustrated in Figure 6(b), a laminate is obtained by pressing a cover sheet 54 onto the top and bottom of the stacking direction. In this case, a laminate with a roughly rectangular parallelepiped shape is obtained such that the internal electrode paste 52 is alternately exposed on two end faces of the laminate. The cover sheet 54 can be formed by coating it with raw material powder for the cover layer using the same method as in the solid electrolyte green sheet manufacturing process. The cover sheet 54 is formed to be thicker than the solid electrolyte green sheet 51. It may be made thicker during coating, or it may be made thicker by stacking multiple coated sheets.

[0058] Next, the external electrode paste 55 is applied to each of the two end faces using a dipping method or the like, and then dried. This yields a molded body for forming the all-solid-state battery 100a.

[0059] (Firing process) Next, the obtained laminate is fired. The firing conditions are in an oxidizing atmosphere or a non-oxidizing atmosphere, and the maximum temperature can be preferably 400°C to 1000°C, more preferably 500°C to 900°C, etc., without particular limitation. A step of holding at a temperature lower than the maximum temperature in an oxidizing atmosphere may be provided to sufficiently remove the binder before reaching the maximum temperature. In order to reduce the process cost, it is desirable to fire at the lowest possible temperature. After firing, a re-oxidation treatment may be performed. Through the above steps, the all-solid-state battery 100a is produced.

[0060] Note that by laminating the internal electrode paste, the current collector paste containing the conductive material, and the internal electrode paste in this order, a current collector layer can be formed in the first internal electrode 10 and the second internal electrode 20.

[0061] According to the manufacturing method according to this embodiment, Al 1-x M x Nb 11-y N y O 29 Since the negative electrode active material having the composition formula of (0 < x < 0.5, 0 < y < 5) is used, the reaction between the negative electrode active material and the solid electrolyte during firing can be suppressed. Thereby, in the all-solid-state battery 100a, a high volume specific capacity is obtained, and high rate characteristics and high cycle characteristics are realized.

[0062] (Third Embodiment)<FIG. 7 is a schematic cross-sectional view showing the basic structure of a lithium ion battery according to the second embodiment. As illustrated in FIG. 7, in the lithium ion battery, a separator 3 is disposed on a Li metal 2 that functions as a counter electrode, a positive electrode 1 is disposed on the separator 3, and a current collector member 4 is disposed on the positive electrode 1. The electrolyte is impregnated in the positive electrode 1 and the separator 3. The positive electrode 1 and the Li metal 2 are shielded by the separator 3. The positive electrode 1 includes an electrode active material 1a, a conductive powder 1b, and a binder. The conductive powder 1b is a conductive material such as acetylene black, for example. The current collector member 4 is an aluminum foil or the like. The illustration of the binder is omitted.

[0063] The electrode active material 1a is the electrode active material described in the first embodiment. Specifically, a negative electrode active material represented by the composition formula of Al 1-x M x Nb 11-y N y O 29 (0 < x < 0.5, 0 ≦ y < 5) is used. Thereby, a high volume specific capacity is realized, and high rate characteristics and high cycle characteristics are also realized.

Examples

[0064] (Example 1) Al 0.95 Hf 0.05 Nb 11 O 29 Raw materials were weighed so as to have the composition ratio of, and were kneaded and mixed. After mixing, they were calcined at 1100° C. in the air, the obtained calcined powder was kneaded again, and the target Al 0.95 Hf 0.05 Nb 11 O 29 synthetic powder was obtained by heat treatment at 1300° C. in the air. After the synthetic powder was kneaded again, it was sieved through a #150 stainless mesh to obtain a negative electrode active material powder.

[0065] An electrode slurry was prepared by mixing negative electrode active material powder, PVdF binder, and acetylene black in a weight ratio of 80:10:10 and diluting it with NMP, then forming a coating film on aluminum foil. A negative electrode half-cell was constructed with a separator in between and a metallic lithium foil placed as the counter electrode. This half-cell was sealed in a 2032 coin cell using 1M LiPF6 EC:DEC (1:2 vol%) as the electrolyte. DEC is diethyl carbonate, and EC is ethylene carbonate.

[0066] (Example 2) Al 0.9 Hf 0.1 Nb 11 O 29 The raw materials were weighed and ground and mixed to achieve the specified composition ratio. Other conditions were the same as in Example 1.

[0067] (Example 3) Al 0.85 Hf 0.15 Nb 11 O 29 The raw materials were weighed and ground and mixed to achieve the specified composition ratio. Other conditions were the same as in Example 1.

[0068] (Example 4) Al 0.8 Hf 0.2 Nb 11 O 29 The raw materials were weighed and ground and mixed to achieve the specified composition ratio. Other conditions were the same as in Example 1.

[0069] (Example 5) Al 0.95 Hf 0.05 Nb9Ta2O 29 The raw materials were weighed and ground and mixed to achieve the specified composition ratio. Other conditions were the same as in Example 1.

[0070] (Example 6) Al 0.90 Hf 0.1 Nb9Ta2O 29 The raw materials were weighed and ground and mixed to achieve the specified composition ratio. Other conditions were the same as in Example 1.

[0071] (Example 7) Al 0.85 Hf 0.15 Nb9Ta2O 29 The raw materials were weighed and ground and mixed to achieve the specified composition ratio. Other conditions were the same as in Example 1.

[0072] (Example 8) Al 0.8 Hf 0.2 Nb9Ta2O 29 The raw materials were weighed and ground and mixed to achieve the specified composition ratio. Other conditions were the same as in Example 1.

[0073] (Comparative Example 1) AlNb 11 O 29 The raw materials were weighed and ground and mixed to achieve the specified composition ratio. Other conditions were the same as in Example 1.

[0074] (Comparative Example 2) Al 0.5 Hf 0.5 Nb 11 O 29 The raw materials were weighed and ground and mixed to achieve the specified composition ratio. Other conditions were the same as in Example 1.

[0075] (Comparative Example 3) Al 0.9 Hf 0.1 Nb6Ta5O 29 The raw materials were weighed and ground and mixed to achieve the specified composition ratio. Other conditions were the same as in Example 1.

[0076] (discharge capacity) The discharge capacity was measured for each of Examples 1-8 and Comparative Examples 1-3. The discharge capacity was measured in a constant temperature bath at 25°C with a cutoff potential of 1.0V-3.0V (vs. Li / Li). + The discharge capacity was measured by performing CC charge and discharge at 0.2C. In Example 1, the discharge capacity was 1148 mAh / cm². 3 In Example 2, the capacitance was 1160 mAh / cm². 3 In Example 3, the capacity was 1134 mAh / cm².3 In Example 4, the capacity was 1201 mAh / cm². 3 In Example 5, the capacity was 999 mAh / cm². 3 In Example 6, the capacity was 1032 mAh / cm². 3 In Example 7, the capacity was 1068 mAh / cm². 3 In Example 8, the capacity was 1005 mAh / cm². 3 In Comparative Example 1, the rate was 1122 mAh / cm². 3 In Comparative Example 2, the figure was 1059 mAh / cm². 3 In Comparative Example 3, the rate was 263 mAh / cm². 3 That was the case.

[0077] Discharge capacity is 990mAh / cm² 3 If the discharge capacity is as above, it will be judged as passing ("○"), and the discharge capacity is 990mAh / cm². 3 If the discharge capacity was less than the specified value, it was judged as a failure ("×"). The discharge capacities of Examples 1-8 and Comparative Examples 1 and 2 were judged as passing ("○"). The discharge capacity of Comparative Example 3 was judged as failing ("×"). This is thought to be because a large portion of the Nb was replaced by Ta, resulting in y≧5, a rapid increase in the proportion of the secondary phase, and a decrease in the proportion of the active material.

[0078] (Cycle characteristics) The cycle characteristics were measured for each of Examples 1-8 and Comparative Examples 1-3. The cycle characteristics were measured in a constant temperature bath at 25°C with a cutoff potential of 1.0V-3.0V (vs. Li / Li). + The capacity retention rate was evaluated by performing 100 cycles of CC charge-discharge at 0.2C and then calculating the capacity retention rate from the initial discharge capacity. The capacity retention rates after 100 cycles were 82.2% for Example 1, 83.8% for Example 2, 84.1% for Example 3, 82.5% for Example 4, 91.2% for Example 5, 92.9% for Example 6, 92.6% for Example 7, 91.7% for Example 8, 80.5% for Comparative Example 1, 81.6% for Comparative Example 2, and 89.5% for Comparative Example 3.

[0079] If the capacity retention rate after 100 cycles was 81% or higher, the cycle characteristics were judged as passing ("○"), and if the capacity retention rate after 100 cycles was less than 81%, the cycle characteristics were judged as failing ("×"). The cycle characteristics of Examples 1 to 8 and Comparative Examples 2 and 3 were judged as passing ("○"). On the other hand, the cycle characteristics of Comparative Example 1 were judged as failing ("×"). This is thought to be because a large portion of the Al was replaced with Hf, resulting in x ≥ 0.5, and thus significant cycle degradation of the electrode.

[0080] (Rate characteristics) The rate characteristics were investigated for each of Examples 1-8 and Comparative Examples 1-3. Specifically, the capacity ratio to 0.5C discharge at a discharge rate of 5C was measured. The rate characteristics were 81.5% for Example 1, 82.2% for Example 2, 81.9% for Example 3, 81.8% for Example 4, 82.4% for Example 5, 84.4% for Example 6, 83.7% for Example 7, 82.9% for Example 8, 81.0% for Comparative Example 1, 72.2% for Comparative Example 2, and 68.2% for Comparative Example 3.

[0081] If the rate characteristic exceeded 81%, it was judged as passing ("○"), and if the rate characteristic was 81% or less, it was judged as failing ("×"). The rate characteristics of Examples 1 to 8 were judged as passing ("○"). On the other hand, the rate characteristic of Comparative Example 1 was judged as failing ("×"). This is thought to be because some of the Al was not substituted, and therefore the rate characteristic was not improved. The rate characteristic of Comparative Example 2 was also judged as failing ("×"). This is thought to be because much of the Al was substituted with Hf, resulting in x≧0.5, and the deterioration of the electrode's rate characteristic became significant. The rate characteristic of Comparative Example 3 was also judged as failing ("×"). This is thought to be because much of the Nb was substituted with Ta, resulting in y≧5, and the secondary phase caused the rate characteristic to deteriorate.

[0082] (Overall assessment) When all of the discharge capacity, cycle characteristics, and rate characteristics passed, the comprehensive judgment was considered a pass "〇", and if any one of them failed, the comprehensive judgment was considered a fail "×". All of Examples 1 to 8 were judged to pass the comprehensive judgment "〇". This is considered to be because the negative electrode active material having the composition formula of Al 1-x M x Nb 11―y N y O 29 (0 < x < 0.5, 0 ≦ y < 11) was used. On the other hand, Comparative Example 1 was judged to fail the comprehensive judgment "×". This is considered to be because Al was not substituted. Also, Comparative Example 1 was judged to fail the comprehensive judgment "×". This is considered to be because x ≧ 0.5. Also, Comparative Example 3 was judged to fail the comprehensive judgment "×". This is considered to be because y ≧ 5. The results are shown in Table 1.

Table 1

[0083] (Example 9) Al 0.9 Hf 0.1 Nb9Ta2O 29 The raw materials were weighed so as to have the composition ratio, and were kneaded and mixed. After mixing, they were calcined at 1100 °C in the air, the obtained calcined powder was kneaded again, and further heat-treated at 1300 °C in the air to obtain the target Al 0.9 Hf 0.1 Nb9Ta2O 29 synthetic powder. After kneading the synthetic powder again, it was sieved through a #150 stainless steel mesh to obtain the negative electrode active material powder.

[0084] Li 1+x Al x Ge 2-x(PO4)3 powder was uniformly dispersed in an aqueous solvent or organic solvent together with a binder, dispersant, plasticizer, etc., and wet-milled to obtain a solid electrolyte slurry having a desired average particle size. This slurry was then coated to obtain a solid electrolyte green sheet. Subsequently, a paste containing positive electrode active material powder was printed onto the solid electrolyte green sheet. A paste containing negative electrode active material powder was printed onto another solid electrolyte green sheet. Multiple printed solid electrolyte green sheets were stacked alternately with a slight offset and then fired.

[0085] (Reference example 1) In Reference Example 1, Al 0.9 Hf 0.1 Nb 11 O 29 The raw materials were weighed and ground and mixed to achieve the specified composition ratio. Other conditions were the same as in Example 9.

[0086] (Reference example 2) In reference example 2, AlNb9Ta2O 29 The raw materials were weighed and ground and mixed to achieve the specified composition ratio. Other conditions were the same as in Example 9.

[0087] (Reaction temperature with solid electrolytes) For each of Example 9 and Reference Examples 1 and 2, the reaction temperature with the solid electrolyte was measured. Specifically, an experiment was conducted in which the negative electrode active material powder was mixed with the solid electrolyte LAGP in a 50:50 volume ratio and heat-treated in air. The temperature at which the different phases began to form was measured as the reaction temperature with the solid electrolyte. The reaction temperature with the solid electrolyte was 710°C for Example 9, 660°C for Reference Example 1, and 710°C for Reference Example 2. From these results, it can be seen that simultaneous firing with the solid electrolyte is possible by substituting a portion of Nb with Ta.

[0088] Discharge capacity and cycle characteristics were investigated using the same method as in Examples 1-8 and Comparative Examples 1-3. The cycle characteristics were measured over 30 cycles. In Example 9, the discharge capacity was 858 mAh / cm². 3The following discharge capacity was obtained. In Example 9, a capacity retention rate of 91.1% was obtained. On the other hand, in Reference Example 1, battery operation could not be obtained, and the cycle characteristics could not be measured. This was because AlNb failed during the firing process. 11 O 29 This is thought to be because it reacted with the solid electrolyte, generating other compounds. In Reference Example 2, the same cycle characteristics as in Example 9 were not obtained. From this, it can be seen that in Example 9, by substituting some of Al with Hf and some of Nb with Ta, it is possible to operate even in an all-solid-state battery and improve the cycle characteristics. [Table 2]

[0089] Although embodiments of the present invention have been described in detail above, the present invention is not limited to these specific embodiments, and various modifications and changes are possible within the scope of the gist of the present invention as described in the claims. [Explanation of Symbols]

[0090] 10 1st internal electrode 11 Electrode active material 12 Solid electrolyte 13 Conductive additives 15. First current collector layer 20 Second internal electrode 21 Electrode active material 22 Solid electrolyte 23 Conductive additive 25. Second current collector layer 30 Solid electrolyte layer 40a First external electrode 40b 2nd external electrode 50 Cover Layers 51 Solid Electrolyte Green Sheet 52 Paste for internal electrodes 53 Reverse Pattern 54 Cover Sheets 55 Paste for external electrodes 60 stacked chips 100,100a solid state battery

Claims

1. Al １－ｘ M ｘ Nb １１―ｙ N ｙ O ２９ An electrode active material comprising a negative electrode active material represented by the composition formula, wherein x satisfies 0 < x < 0.5, y satisfies 0 ≤ y < 5, M is a tetravalent transition metal element, and N is a pentavalent or higher transition metal element.

2. The electrode active material according to claim 1, wherein x satisfies 0.05 ≤ x.

3. The electrode active material according to claim 1, wherein x satisfies x ≤ 0.

2.

4. The electrode active material according to claim 2 or claim 3, wherein M is Hf.

5. The electrode active material according to claim 1, wherein x and y satisfy x < y.

6. The electrode active material according to claim 1, wherein y satisfies y < 5.

7. The electrode active material according to claim 1, wherein y satisfies 0.5 ≤ y ≤ 2.

5.

8. The electrode active material according to claim 6 or claim 7, wherein N is Ta.

9. The electrode active material according to claim 1, wherein the electrode active material contains 80% or more by volume of the negative electrode active material.

10. The electrode active material according to claim 1, wherein the negative electrode active material is a powder material.

11. Oxide-based solid electrolyte layer, A first electrode layer containing a positive electrode active material is provided on the first main surface of the oxide-based solid electrolyte layer, A solid-state battery comprising: a second electrode layer provided on the second main surface of the oxide-based solid electrolyte layer and containing an electrode active material according to any one of claims 1 to 10.

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