JP7782843B2 - Solid electrode layer and method for manufacturing the same - Google Patents

Description

The present invention relates to a solid electrode layer and a method for manufacturing the same.

Lithium secondary batteries, boasting high energy density, are currently widely used as power sources for small portable devices, electric vehicles, and other devices. Furthermore, recently, there has been demand for secondary batteries that can be surface-mounted to substrates using a reflow process, targeting IoT applications such as backup power sources for real-time clocks and wireless communication modules. For such applications, ensuring high heat resistance and safety of secondary batteries is important. Among lithium-ion secondary batteries, all-solid-state lithium-ion secondary batteries using an oxide solid electrolyte do not use flammable organic electrolytes like conventional lithium-ion secondary batteries. Therefore, they are ideal as secondary batteries for substrate mounting, which require high reliability and heat resistance, and are extremely heat-resistant and safe energy storage devices. Furthermore, the oxide solid electrolyte used in these all-solid-state lithium-ion secondary batteries is chemically stable in air, making them highly durable among all-solid-state lithium-ion secondary batteries.

To manufacture an all-solid-state lithium-ion secondary battery, at least the positive electrode layer, solid electrolyte layer, and negative electrode layer are typically joined by sintering. However, when an oxide solid electrolyte is used, a side reaction occurs between the positive electrode active material and the electrolyte during sintering, resulting in the production of impurities that inhibit the battery reaction.

Patent Document 1 describes the use of a Nasicon-type phosphate compound as the solid electrolyte material and a spinel-type oxide containing at least one of Ni and Mn as the positive electrode active material to suppress this side reaction. Patent Document 1 states that this combination prevents the generation of impurities during sintering. However, in reality, when a Nasicon-type phosphate compound is used as the solid electrolyte material, the firing temperature described in Patent Document 1 is insufficient to achieve sintering that bonds the solid electrolyte material and the positive electrode active material. Therefore, the generation of impurities cannot be suppressed during manufacturing at a sintering temperature that achieves bonding, resulting in a deterioration in battery performance.

Furthermore, Patent Document 1 describes the use of a Nasicon-type phosphate compound as the solid electrolyte material and a specific oxide (Nb ₂ O ₅ , WO ₃ , MoO ₃ , Ta ₂ O ₅ , etc.) as the positive electrode active material in order to suppress this side reaction. However, when the oxide described therein is used, the energy density of the all-solid-state lithium ion secondary battery is not sufficient, and since it is not used in current all-solid-state lithium ion secondary batteries, it lacks versatility.

From the above, in order to achieve high-performance battery characteristics, it is necessary not only to suppress the generation of impurities during sintering with the solid electrolyte layer, but also to ensure that the solid electrolyte material and positive electrode active material are dispersed evenly and homogeneously in the positive electrode layer, targeting layered rock salt oxides, which are positive electrode active materials that can be expected to achieve the high performance used in current all-solid-state lithium-ion secondary batteries. However, it cannot be said that this is achieved in Patent Document 1.

On the other hand, Non-Patent Document 1 _{describes that} when a layered rock salt type oxide cathode active material and _{a Li2.2C0.8B0.2O3} solid electrolyte are used, the generation of impurities in the cathode layer is suppressed and the all-solid-state lithium ion secondary battery operates normally. Also, Non-Patent Document ₂ describes that when a layered rock salt type oxide cathode active material and _{a Li3.5Ge0.5V0.5O4} solid electrolyte are mixed by hand, the generation of impurities in the cathode layer is suppressed and the all _- solid-state lithium ion secondary battery operates normally.

International Publication No. 2012/043566

Solid State Ionics, 288, 248-252 (2016). ACS Appl. Energy Mater., 4, 30-34 (2021).

However, in neither of the methods described in Non-Patent Documents 1 and 2 is the solid electrolyte material and the positive electrode active material dispersed evenly and homogeneously in the positive electrode layer, and there is room for improvement in terms of capacity, cycle characteristics, and rate characteristics.

From the above perspective, the objective is to provide a solid electrode layer in which the solid electrolyte material and the positive electrode active material are evenly and homogeneously dispersed within the positive electrode layer, targeting layered rock salt oxides, which are positive electrode active materials that not only suppress the generation of impurities during sintering with the solid electrolyte layer but are also expected to achieve the high performance used in current all-solid-state lithium-ion secondary batteries.

The present inventors have conducted extensive research to achieve the above-mentioned object. As a result, they have found that in a solid electrode layer containing a lysicone-type oxide and a layered rock-salt-type oxide, by reducing the content of materials other than the lysicone-type oxide and the layered rock-salt-type oxide calculated from an X-ray diffraction pattern and by reducing the average diameter and the standard deviation of the average diameter of the diagram obtained by performing Voronoi tessellation on the layered rock-salt-type oxide, the solid electrolyte material and the positive electrode active material can be dispersed evenly and homogeneously in the positive electrode layer, thereby solving the above-mentioned problem. The present invention was completed as a result of further research based on this finding. That is, the present invention includes the following features.
Item 1. A solid electrode layer containing a lysicone-type oxide and a layered rock salt-type oxide,
the content of impurities calculated from an X-ray diffraction pattern of the solid electrode layer is 1.0 mol% or less, with the total amount of the solid electrode layer being 100 mol%,
The average diameter of a figure obtained by performing Voronoi division on the layered rock salt type oxide is 0.50 to 2.00 μm, and
A solid electrode layer in which the standard deviation of the average diameter of a figure obtained by performing Voronoi tessellation on the layered rock salt type oxide is 1.00 μm or less.
Item 2. The lysicone-type oxide is represented by the general formula (1):
Li _x1 M ¹ O _y1 (1)
[In the formula, x1 represents 3.0<x1<4.0, y1 represents 3.8<y1<4.2, and ^M1 represents at least one element selected from the group consisting of Ge, Si, V, Ti, P, and S.]
Item 2. The solid electrode layer according to item 1, wherein the oxide is an oxide represented by the formula:
Item 3. The solid electrode layer according to Item 2, wherein M ¹ contains Ge and/or Si and at least one element selected from the group consisting of V, Ti, P, and S.
Item _{4. The} solid _{electrode layer} according to any _{one of Items 1} to _{3 ,} wherein _{the lithizone - type} oxide is _{Li3.5Ge0.5V0.5O4} , _{Li3.7Ge0.7V0.3O4 , Li3.3Ge0.3V0.7O4 , Li3.75Ge0.75P0.25O4 , Li3.5Ge0.75S0.25O4 ,} or _{Li3.5Si0.25Ti0.25V0.5O4 .}
Item 5. The solid electrode layer according to any one of Items 1 to 4, wherein the lithiated oxide is Li _3.5 Ge _0.5 V _0.5 O ₄ .
Item 6. The layered rock salt type oxide is represented by general formula (2):
^LiM2Oy2 ( ₂ )
[In the formula, y2 represents 1.5<y2<2.5, and ^M2 represents at least one element selected from the group consisting of Co, Mn, Ni, Al, and Li.]
Item 6. The solid electrode layer according to any one of items 1 to 5, wherein the oxide is represented by the formula:
Item 7. The solid electrode layer according to any one of Items 1 to ₆ , wherein _the layered rock salt oxide is _{LiCoO 2} , LiNi _1/3 Mn _1/3 Co _1/3 O ₂ , LiNi _0.5 Mn _0.5 O ₂ , LiNi _0.8 Mn _0.1 Co _0.1 O ₂ , LiNi _0.80 Co 0.15 Al 0.05 _{O 2} , or Li 1.20 Ni _0.16 Mn _0.55 Co _0.09 O 2 .
Item 8. The solid electrode layer according to any one of Items 1 to 7, wherein the layered rock salt oxide is LiCoO ₂ .
Item 9. The solid electrode layer according to any one of Items 1 to 8, which is a solid electrode layer for an all-solid-state lithium ion secondary battery.
Item 10. The solid electrode layer according to any one of Items 1 to 9, which is a solid positive electrode layer.
Item 11. An all-solid-state lithium ion secondary battery comprising the solid electrode layer according to any one of Items 1 to 10.
Item 12. A method for producing a solid electrode layer according to any one of Items 1 to 10, comprising:
A manufacturing method comprising: (1) a step of subjecting a lithiated oxide and a layered rock salt type oxide to a low-crystallization treatment; and (2) a step of heat-treating the low-crystallization product obtained in the step (1) at 600 to 1000°C to obtain a solidified molded body.
Item 13. The manufacturing method according to Item 12, wherein the low crystallization treatment is a mechanical milling treatment and/or a melt quenching treatment.
Item 14. A precursor for a solid electrode layer containing a lysicone-type oxide and a layered rock salt-type oxide,
the content of impurities calculated from an X-ray diffraction pattern of the precursor is 1 mol % or less, with the total amount of the solid electrode layer being 100 mol %,
A solid electrode layer precursor, which has only a peak of a rock salt-type oxide belonging to the space group Fm-3m and a halo peak at 2θ = 5 to 8° in an X-ray diffraction pattern in the range of 2θ = 4 to 26° using synchrotron X-rays with a wavelength of 0.05 nm, but does not have a peak having a maximum value at 2θ = 6 to 7° which is characteristic of a layered rock salt-type oxide.

The present invention not only suppresses the generation of impurities during sintering with the solid electrolyte layer, but also provides a solid electrode layer in which the solid electrolyte material and the positive electrode active material are evenly and homogeneously dispersed within the positive electrode layer, targeting layered rock salt oxides, which are positive electrode active materials that are expected to achieve the high performance of those used in current all-solid-state lithium-ion secondary batteries.

1 is a powder X-ray diffraction pattern of the low crystallinity product obtained in Reference Example 1. 1 shows powder X-ray diffraction patterns of the positive electrode powders obtained in Example 1 and Comparative Examples 1 and 2, and the low-crystallization product obtained in Reference Example 1. This figure shows experimental and calculated values obtained by Rietveld analysis of the X-ray diffraction pattern of the solid positive electrode layer obtained in Example 1. The inset shows an enlarged view of the range of 2θ = 30 to 40°. The fitting difference between the measured values and the calculated pattern is shown below the X-ray diffraction pattern, and the calculated position of each crystalline phase is also shown below that. These are experimental and calculated values obtained by Rietveld analysis of the X-ray diffraction pattern of the solid positive electrode layer obtained in Comparative Example 2. The inset shows an enlarged view of the range of 2θ = 30 to 40°. The fitting difference between the measured values and the calculated pattern is shown below the X-ray diffraction pattern, and the calculated position of each crystalline phase is also shown below that. 1 is a cross-sectional scanning electron microscope image of the solid positive electrode layer obtained in Example 1. 1 is a cross-sectional scanning electron microscope image of the solid positive electrode layer obtained in Comparative Example 2. FIG. 2 is a diagram showing a cross-sectional scanning electron microscope image of the solid positive electrode layer obtained in Example 1, which has been subjected to image binarization processing. FIG. 10 is a diagram showing a cross-sectional scanning electron microscope image of the solid positive electrode layer obtained in Comparative Example 2, which has been subjected to image binarization processing. FIG. 2 is a diagram showing Voronoi division after binarization of a cross-sectional scanning electron microscope image of the solid positive electrode layer obtained in Example 1. FIG. 10 is a diagram showing Voronoi division after binarization of a cross-sectional scanning electron microscope image of a solid positive electrode layer obtained in Comparative Example 2. 1 is a graph showing the average diameter and standard deviation of the average diameter of Voronoi tessellation patterns for the solid positive electrode layer obtained in Example 1. 10 is a graph showing the average diameter and standard deviation of the average diameter of the Voronoi tessellation diagram for the solid positive electrode layer obtained in Comparative Example 2. FIG. 1 is a diagram showing a layer structure of an all-solid-state lithium secondary battery constructed in Test Example 3. 1 shows charge/discharge curves of the all-solid-state lithium secondary battery of Example 1. 1 shows charge/discharge curves of the all-solid-state lithium secondary battery of Comparative Example 1. 1 shows charge/discharge curves of the all-solid-state lithium secondary battery of Comparative Example 2.

In this specification, the term "containing" encompasses the concepts of "comprise," "consist essentially of," and "consist only of."

In addition, in this specification, when a numerical range is expressed as "A to B," it means "greater than or equal to A and less than or equal to B."

Furthermore, in this specification, Voronoi tessellation refers to a division in which the boundaries of the two closest particles in a binarized image are connected at equal distances, and the average diameter of the figures obtained by performing Voronoi tessellation refers to the diameter of a circle with the area of each figure.

1. Solid Electrode Layer The solid electrode layer of the present invention is a solid electrode layer containing a lithiated oxide and a layered rock salt oxide,
the content of impurities calculated from an X-ray diffraction pattern of the solid electrode layer is 1 mol % or less, with the total amount of the solid electrode layer being 100 mol %,
The average diameter of a figure obtained by performing Voronoi division on the layered rock salt type oxide is 0.5 to 2.0 μm, and
The standard deviation of the average diameter of the figure obtained by subjecting the layered rock salt type oxide to Voronoi division is 1.0 μm or less.

(1-1) Lisicon-type oxide The lisicon-type oxide contained in the solid electrode layer of the present invention means an oxide having a crystal structure similar to γ-Li ₃ PO ₄ (space group: Pnma) or Li ₄ SiO ₄ (space group: P2 ₁ /m), and can be used as a solid electrolyte material because it contains many lithium ions in the structure and has wide lithium ion conduction paths. In other words, the silicon-type oxide can have a γ-Li ₃ PO ₄ type crystal structure or a Li ₄ SiO ₄ type crystal structure. Such lisicon-type oxides are not particularly limited, but examples include:
General formula (1):
Li _x1 M ¹ O _y1 (1)
[In the formula, x1 represents 3.0<x1<4.0, y1 represents 3.8<y1<4.2, and ^M1 represents at least one element selected from the group consisting of Ge, Si, V, Ti, P, and S.]
The oxide represented by the formula: is preferred.

In general formula (1), ^M1 represents at least one selected from the group consisting of Ge, Si, V, Ti, P, and S. Among these, from the viewpoints of suppressing the generation of impurities during sintering with the solid electrolyte layer, uniformly and homogeneously dispersing the solid electrolyte material and the positive electrode active material in the positive electrode layer, and the like, it is preferable that the positive electrode layer contains Ge and/or Si and at least one selected from the group consisting of V, Ti, P, and S, more preferably Ge and at least one selected from the group consisting of V, Ti, P, and S, and even more preferably Ge and V.

In general formula (1), x1 is in the range of 3.0 < x1 < 4.0. From the viewpoints of suppressing the generation of impurities during sintering with the solid electrolyte layer and achieving uniform and homogeneous dispersion of the solid electrolyte material and positive electrode active material in the positive electrode layer, 3.2 < x1 < 3.8 is preferred, and 3.3 < x1 < 3.7 is more preferred.

In general formula (1), y1 is in the range of 3.8<y1<4.2. From the viewpoints of suppressing the generation of impurities during sintering with the solid electrolyte layer and achieving uniform and homogeneous dispersion of the solid electrolyte material and positive electrode active material in the positive electrode layer, 3.9<y1<4.1 is preferred.

_{Examples of lithizone - type oxides that satisfy these conditions include Li3.5Ge0.5V0.5O4 , Li3.7Ge0.7V0.3O4 , Li3.3Ge0.3V0.7O4 , Li3.75Ge0.75P0.25O4 , Li3.5Ge0.75S0.25O4 , and Li3.5Si0.25Ti0.25V0.5O4 . ​ Among} these, from the viewpoints of suppressing the generation of impurities during sintering with the solid electrolyte layer and uniformly and homogeneously dispersing the solid _{electrolyte material and the positive electrode} active material in the positive _electrode layer _{, Li3.5Ge0.5V0.5O4 , Li3.7Ge0.7V0.3O4 , Li3.3Ge0.3V0.7O4 , Li3.75Ge0.75P0.25O4 , Li3.5Ge0.75S0.25O4 , and the like are preferred , and Li3.5Ge0.5V0.5O4 , Li3.7Ge0.7V0.3O4 , Li3.3Ge0.3V0.7O 4} and the like are more preferred, and Li _3.5 Ge _0.5 V _0.5 O ₄ and the like are even more preferred.

These lithizone-type oxides can be used alone or in combination of two or more. Furthermore, these lithizone-type oxides can be publicly known or commercially available products.

(1-2) Layered Rock Salt Oxide Layered rock salt oxides can be used as electrode active materials (particularly positive electrode active materials). There are no particular limitations on such layered rock salt oxides, and examples thereof include oxides represented by the general formula (2):
^LiM2Oy2 ( ₂ )
[In the formula, y2 represents 1.5<y2<2.5, and ^M2 represents at least one element selected from the group consisting of Co, Mn, Ni, Al, and Li.]
The oxide represented by the formula: is preferred.

In general formula (2), ^M2 represents at least one selected from the group consisting of Co, Mn, Ni, Al, and Li. Among these, from the viewpoints of suppressing the generation of impurities during sintering with the solid electrolyte layer, uniformly and homogeneously dispersing the solid electrolyte material and the positive electrode active material in the positive electrode layer, etc., it is preferable that M2 contains at least one selected from the group consisting of Co, Mn, Ni, and Li, more preferably at least one selected from the group consisting of Co, Mn, and Ni, and even more preferably Co.

In general formula (2), y2 represents 1.5<x1<2.5. From the viewpoints of suppressing the generation of impurities during sintering with the solid electrolyte layer and achieving uniform and homogeneous dispersion of the solid electrolyte material and positive electrode active material in the positive electrode layer, 1.7<y2<2.3 is preferred, 1.8<y2<2.2 is more preferred, and 1.9<y2<2.1 is even more preferred.

Examples of layered rock salt oxides that satisfy these conditions include LiCoO ₂ , LiNi _1/3 Mn _1/3 Co _1/3 O ₂ , LiNi _0.5 Mn _0.5 O ₂ , LiNi _0.8 Mn _0.1 Co _0.1 O ₂ , LiNi _0.80 Co _0.15 Al _0.05 O ₂ , and Li _1.20 Ni _0.16 Mn _0.55 Co _0.09 O ₂ . Among these, from the viewpoints of suppressing the generation of impurities during sintering with the solid electrolyte layer and uniformly and homogeneously dispersing the solid electrolyte material and the positive electrode active material in the positive electrode layer, LiCoO ₂ , LiNi _1/3 Mn _1/3 Co _1/3 O ₂ , LiNi _0.5 Mn _0.5 O ₂ , LiNi _0.8 Mn _0.1 Co _0.1 O ₂ , Li _1.20 Ni _0.16 Mn _0.55 Co _0.09 O ₂ and the like are preferred, and LiCoO ₂ , LiNi _1/3 Mn _1/3 Co _1/3 O ₂ , LiNi _0.5 Mn _0.5 O ₂ , LiNi _0.8 Mn _0.1 Co _0.1 O are particularly preferred. ₂ and the like is more preferred, and LiCoO ₂ and the like is even more preferred.

These layered rock salt type oxides can be used alone or in combination of two or more. Furthermore, these layered rock salt type oxides can be publicly known or commercially available products.

(1-3) Solid Electrode Layer In the solid electrode layer of the present invention, the content of the above-mentioned lithizone-type oxide is preferably 10.0 mol% or more, based on the total amount of the solid electrode layer being 100% by mass, from the viewpoints of suppressing the generation of impurities during sintering with the solid electrolyte layer, uniform and homogeneous dispersion of the solid electrolyte material and the positive electrode active material in the positive electrode layer, etc., and more preferably 20.0 mol% or more from the viewpoint of ensuring ion conduction paths in the solid electrolyte. The upper limit of the content of the above-mentioned lithizone-type oxide is not particularly limited, and can usually be 66.7 mol% or less.

In the solid electrode layer of the present invention, the content of the layered rock salt-type oxide described above is preferably 33.3 mol% or more, based on the total amount of the solid electrode layer being 100% by mass, from the viewpoints of suppressing the generation of impurities during sintering with the solid electrolyte layer and uniformly and homogeneously dispersing the solid electrolyte material and the positive electrode active material in the positive electrode layer, and is more preferably 40.0 mol% or more from the viewpoint of the energy density of the battery. There is no particular upper limit to the content of the layered rock salt-type oxide described above, and it can typically be set to 90.0 mol% or less.

In the solid electrode layer of the present invention, the impurity content calculated from the X-ray diffraction pattern of the solid electrode layer is 1.0 mol% or less, preferably 0.1 mol% or less, based on 100 mol% of the total amount of the solid electrode layer. If the impurity content exceeds 1.0 mol%, impurity generation during sintering with the solid electrolyte layer cannot be suppressed, resulting in poor battery performance. There is no particular lower limit for the impurity content, and 0 mol% is most preferable from the standpoint of battery performance. Furthermore, if the solid electrode layer of the present invention does not intentionally contain any electrode constituent materials other than the above-described lithizone-type oxide and layered rock salt-type oxide, the term "impurities" refers to all materials other than the above-described lithizone-type oxide and layered rock salt-type oxide. Furthermore, if the solid electrode layer of the present invention intentionally contains electrode constituent materials such as conductive additives and binders in addition to the above-described lithizone-type oxide and layered rock salt-type oxide, the term "impurities" refers to all materials other than the above-described electrode constituent materials (in other words, the lithizone-type oxide, layered rock salt-type oxide, conductive additives, and binders).

In addition to the lithizone-type oxide and layered rock salt-type oxide, the solid electrode layer of the present invention may also intentionally contain electrode constituent materials that have traditionally been included in all-solid-state lithium-ion secondary batteries, such as conductive additives, binders, plasticizers, etc. Furthermore, in the solid negative electrode layer, the above-mentioned negative electrode active material may be covered with a conductive additive.

The conductive additive may be one or more of the following: graphite; carbon black (acetylene black, ketjen black, etc.); amorphous carbon materials such as carbon materials with amorphous carbon formed on the surface; fibrous carbon (vapor-grown carbon fiber, carbon fiber obtained by spinning pitch and then carbonizing it, etc.); carbon nanotubes (various multi-layer or single-layer carbon nanotubes); conductive metal particles (palladium, etc.); conductive oxide particles (ruthenium oxide, etc.).

When a conductive additive is intentionally included in the solid electrode layer of the present invention, the content of the conductive additive is preferably 0.01 to 20.0 mass%, and more preferably 0.1 to 5.0 mass%, based on 100 mass% of the total amount of the solid electrode layer of the present invention, from the viewpoint of battery performance, etc.

For example, acrylic resin can be used as the binder, and for example, phthalate ester can be used as the plasticizer.

When a binder is intentionally contained in the solid electrode layer of the present invention, the content of the binder is preferably 0.01 to 10.0 mass%, and more preferably 0.1 to 5.0 mass%, based on 100 mass% of the total amount of the solid electrode layer of the present invention, from the viewpoint of battery performance, etc.

In the solid electrode layer of the present invention, the average diameter of the figures obtained by performing Voronoi tessellation on the layered rock salt oxide is 0.50 to 2.00 μm, preferably 0.55 to 1.50 μm. It is difficult to manufacture a solid electrode layer in which the average diameter of the figures obtained by performing Voronoi tessellation is 0.50 μm or less. On the other hand, if the average diameter of the figures obtained by performing Voronoi tessellation exceeds 2.00 μm, the solid electrode layer will be destroyed due to the expansion and contraction of the positive electrode active material during battery operation, resulting in poor capacity, cycle characteristics, and rate characteristics, especially cycle characteristics.

In the solid electrode layer of the present invention, the standard deviation of the average diameter of the figures obtained by performing Voronoi tessellation on the layered rock salt oxide is 1.00 μm or less, preferably 0.01 to 0.80 μm. By setting the standard deviation of the average diameter of the figures obtained by performing Voronoi tessellation to 1.00 μm or less, it is possible to evenly and homogeneously disperse the solid electrolyte material and the positive electrode active material in the positive electrode layer. Furthermore, if the standard deviation of the average diameter of the figures obtained by performing Voronoi tessellation exceeds 1.00 μm, it is not possible to evenly and homogeneously disperse the solid electrolyte material and the positive electrode active material in the positive electrode layer, resulting in poor capacity, cycle characteristics, and rate characteristics.

The thickness of the solid electrode layer of the present invention is not particularly limited, but is preferably 5 μm or more from the viewpoint of ease of molding into an all-solid-state lithium-ion secondary battery, and is preferably 5 to 200 μm from the viewpoint of ensuring energy density by making it more compact, and is even more preferably 5 to 50 μm from the viewpoint of easily demonstrating battery performance, particularly appropriate rate characteristics.

The solid electrode layer of the present invention, which satisfies the above conditions, not only suppresses the generation of impurities during sintering with the solid electrolyte layer, but also targets layered rock salt oxides, which are cathode active materials that are expected to achieve the high performance used in current all-solid-state lithium-ion secondary batteries, and is a solid electrode layer (particularly a solid cathode layer) in which the solid electrolyte material and cathode active material are evenly and homogeneously dispersed within the cathode layer. Therefore, when an all-solid-state lithium-ion secondary battery is formed using this solid electrode layer, it exhibits excellent battery properties such as capacity, cycle characteristics, and rate characteristics, and is useful as a solid electrode layer (particularly a solid cathode layer for an all-solid-state lithium-ion secondary battery).

2. All-Solid-State Lithium-Ion Secondary Battery The all-solid-state lithium-ion secondary battery of the present invention is not particularly limited as long as it includes the above-described solid electrode layer of the present invention, and other configurations can be the same as those of a conventional all-solid-state lithium-ion secondary battery.

Such an all-solid-state lithium-ion secondary battery of the present invention can typically be an all-solid-state lithium secondary battery comprising (laminated) a positive electrode current collector foil, a solid positive electrode layer, a solid electrolyte layer, a solid negative electrode layer, and a negative electrode current collector foil in this order.

Furthermore, as described above, the all-solid-state lithium-ion secondary battery of the present invention not only suppresses the generation of impurities during sintering with the solid electrolyte layer, but also targets layered rock salt oxides, which are cathode active materials that are expected to achieve the high performance used in current all-solid-state lithium-ion secondary batteries, and has a solid electrode layer in which the solid electrolyte material and cathode active material are evenly and homogeneously dispersed within the cathode layer, thereby suppressing the generation of impurities even when the layers are sintered. For this reason, it is preferable that the layers of the all-solid-state lithium-ion secondary battery of the present invention be joined together.

In the present invention, the term "all-solid-state lithium-ion secondary battery" is a concept that also encompasses all-solid-state lithium secondary batteries that use lithium metal as the negative electrode layer.

The solid electrode layer of the present invention may also be used as a solid negative electrode layer, but is preferably used as a solid positive electrode layer, since the solid electrolyte material and positive electrode active material are evenly and homogeneously dispersed in the positive electrode layer, and the layered rock salt oxide is a positive electrode active material that is expected to achieve high performance similar to that used in current all-solid-state lithium-ion secondary batteries.

There are no particular restrictions on the material of the positive electrode current collector foil, and various metals, alloys, carbon materials, etc. can be used. Examples include gold, aluminum, copper, stainless steel, nickel, titanium, or alloys of these, and carbon materials.

There are no particular restrictions on the thickness of the positive electrode current collector foil, but from the perspective of ensuring energy density by making it more compact within the range that can be molded into an all-solid-state battery, a thickness of 5 to 50 μm is preferred.

Examples of the solid electrolyte constituting the solid electrolyte layer include, in addition to the above-mentioned lithiated oxides, oxides having a perovskite structure containing lithium (such as (Li, La) TiO ₃ ), Nasicon-type oxides (Li _1+n+m M _n E _2-n Si _m P _3-m O ₁₂ ; 0≦n≦0.4, 0<m≦0.6, M represents Al and/or Ga. E represents at least one selected from the group consisting of Ti, Ge and Zr), garnet-type oxides (such as Li ₇ La ₃ Zr ₂ O ₁₂ ), etc., and the like. From the viewpoints of suppressing the generation of impurities during sintering with the solid electrolyte layer, uniform and homogeneous dispersion of the solid electrolyte material and the positive electrode active material in the positive electrode layer, etc., the above-mentioned lithiated oxides are preferred. In particular, it is preferable to use the same material as the solid electrolyte contained in the solid positive electrode layer from the viewpoints of ease of bonding between the solid electrolyte layer and the solid positive electrode layer, ionic conductivity, etc.

Examples of the negative electrode active material constituting the solid negative electrode layer include lithium metal, lithium-storing carbonaceous material, lithium alloys (Li—Al alloys, Li—In alloys, Li—Sn alloys, etc.), lithium titanium oxides or lithium-storing titanium oxides (Li ₄ Ti ₅ O ₁₂ , anatase TiO ₂ , etc.), silicon, silicon-containing compounds (SiO 2 , SiC, etc.), Nasicon-type oxides (Li _1+n+m M _n E _2-n Si _m P _3-m O ₁₂ ; 0≦n≦0.4, 0<m≦0.6, M represents Al and/or Ga, and E represents at least one selected from the group consisting of Ti, Ge, and Zr). From the viewpoint of the energy density of the entire all-solid-state lithium-ion secondary battery, etc., lithium metal and lithium-storing carbonaceous material are preferred, and from the viewpoint of the safety of the entire all-solid-state lithium-ion secondary battery, lithium titanium oxide or lithium-storing titanium oxide is preferred.

If the solid negative electrode layer has low electronic conductivity, the solid positive electrode layer and the solid negative electrode layer may contain a conductive additive. Furthermore, in the solid negative electrode layer, the negative electrode active material may be covered with a conductive additive.

Conductive additives that can be used include, for example, one or more of graphite; carbon black (acetylene black, ketjen black, etc.); amorphous carbon materials such as carbon materials with amorphous carbon formed on the surface; fibrous carbon (vapor-grown carbon fiber, carbon fiber obtained by spinning pitch and then carbonizing it, etc.); carbon nanotubes (various multi- or single-walled carbon nanotubes); conductive metal particles (palladium, etc.); and conductive oxide particles (ruthenium oxide, etc.). When a conductive additive is contained in the negative electrode layer, the content of the conductive additive is preferably 0.01 to 20.0 parts by mass, and more preferably 0.1 to 5.0 parts by mass, per 100 parts by mass of the total weight of the negative electrode active material and solid electrolyte, from the perspective of the overall energy density of the all-solid-state lithium-ion secondary battery, etc.

In addition to the above components, the solid negative electrode layer can also contain various additives such as binders (e.g., acrylic resins) and plasticizers (e.g., phthalate esters). In this case, the content of the additives is preferably within a range that does not impair the effects of the present invention. Specifically, the content is preferably 0.01 to 10.0 parts by mass, and more preferably 0.1 to 5.0 parts by mass, per 100 parts by mass of the total weight of the negative electrode active material and solid electrolyte.

There are no particular restrictions on the thickness of the solid negative electrode layer, but from the perspective of ensuring energy density by making it more compact within the range that can be molded into an all-solid-state lithium-ion secondary battery, a thickness of 10 to 1000 μm is preferred, and 10 to 50 μm is more preferred.

There are no particular restrictions on the material of the negative electrode current collector foil, and various metals, alloys, carbon materials, etc. can be used. For such negative electrode current collector foil, materials with a melting point of 660 to 1727°C, particularly 660 to 1445°C, are preferred, as they can be sufficiently bonded to the negative electrode layer under low temperature and high pressure conditions. Examples of materials with such melting points include gold, aluminum, copper, stainless steel, nickel, titanium, or alloys of these, and carbon materials.

As described above, it is preferable that the layers of the all-solid-state lithium-ion secondary battery of the present invention be bonded together. In particular, the solid electrode layer of the present invention can suppress the generation of impurities when bonding the solid electrode layer and the solid electrolyte layer, so it is preferable that at least the solid electrode layer (particularly the solid cathode layer) and the solid electrolyte layer are bonded together.

The all-solid-state lithium-ion secondary battery of the present invention preferably comprises (is stacked with) a positive electrode current collector foil, a solid positive electrode layer, a solid electrolyte layer, a solid negative electrode layer, and a negative electrode current collector foil in this order; however, a separate laminate consisting of a solid positive electrode layer, a solid electrolyte layer, and a negative solid electrode layer may be connected in series or parallel between the positive electrode current collector foil and the solid positive electrode layer, or between the solid negative electrode layer and the negative electrode current collector foil. In this case, an insulating layer, a solid electrolyte layer, etc. may be disposed between each laminate (between the solid positive electrode layer and the solid negative electrode layer) as needed. In this case, too, it is preferable that all components are bonded together.

3. Method for Producing the Solid Electrode Layer The method for producing the solid electrode layer of the present invention is not particularly limited. For example,
The present invention can be obtained by a manufacturing method including: (1) a step of subjecting a lithiated oxide and a layered rock salt type oxide to a low crystallization treatment; and (2) a step of heat-treating the low crystallization product obtained in the step (1) at 600 to 1000°C to obtain a solidified molded body.

(3-1) Process (1)
The lithizone-type oxide and layered rock salt-type oxide can be those described above. By using the lithizone-type oxide and layered rock salt-type oxide described above, the proportion of impurities in the resulting solid electrode layer can be reduced.

There are no particular restrictions on the low-crystallization treatment, as long as it can reduce the crystallinity when mixing the lithizone-type oxide and layered rock salt-type oxide. For example, mechanical milling and/or melt-quenching can be used.

Mechanical milling, also known as mechanochemical processing, is a method of grinding and mixing raw materials while applying mechanical energy. With this method, the raw materials are subjected to mechanical impact and friction, which causes the lithiated oxide and layered rock salt oxide to come into vigorous contact with each other, resulting in micronization and a reaction of the raw materials. In other words, mixing, grinding, and reaction occur simultaneously. This makes it possible to more reliably react the raw materials and reduce their crystallinity without heating them to high temperatures. Mechanical milling can sometimes produce metastable crystal structures that cannot be achieved by conventional heat treatment.

Specific examples of mechanical milling include mixing and grinding using mechanical grinding devices such as ball mills, bead mills, rod mills, vibration mills, disc mills, hammer mills, and jet mills.

The mixing ratio of these raw materials can be adjusted to be similar to the content in the desired solid electrode layer.

For example, assuming the total amount of raw materials is 100% by mass, 10.0 to 66.7 mol%, preferably 20.0 to 66.7 mol%, of the lithiated oxide can be used, and 33.3 to 90.0 mol%, preferably 40.0 to 90.0 mol%, of the layered rock salt-type oxide can be used.

There are no particular limitations on the duration of the mechanical milling process, and the mechanical milling process can be carried out for any length of time until the desired low-crystallization material is precipitated.

For example, mechanical milling can be carried out with an energy consumption of approximately 0.1 to 100 kWh per 1 kg of raw material for a processing time of approximately 0.1 to 200 hours. This mechanical milling can also be carried out in multiple steps, with breaks in between as needed.

In addition, in step (1), a low-crystallization product can also be obtained by heating and melting the lithiated oxide and layered rock salt oxide, followed by rapid cooling.

There are no particular restrictions on the heating temperature during the melt-quenching process, but given the melting points of the lithiated oxide and layered rock salt oxide, a temperature of 1000°C or higher is preferred, with 1000 to 1200°C being more preferred.

The heating time in the melt-quenching process is not particularly limited, but from the viewpoint of easily obtaining a low-crystallization product in step (1), 0 to 48 hours is preferable, and 0 to 12 hours is more preferable. It is also possible to set the heating time to 0 hours, i.e., to immediately cool the material once the maximum temperature is reached.

The heating atmosphere in the melt-quenching process is not particularly limited, but it is preferable to perform the process in an inert gas atmosphere such as nitrogen gas or argon gas, or in a vacuum, as this makes it easier to prevent side reactions.

The molten raw material can then be rapidly cooled.

Quenching methods typically involve contacting a refrigerant with molten raw materials. "Contact" includes cases where the refrigerant directly contacts the molten raw materials, as well as cases where the refrigerant indirectly contacts the molten raw materials via a reaction vessel or the like. The temperature of the refrigerant is not particularly limited, but is, for example, -200 to 30°C, or alternatively, -10 to 30°C, or -10 to 20°C. The refrigerant may be liquid, solid, or gas. Specific examples of refrigerants include water, ice, metal, air, and liquid nitrogen. Quenching methods include, for example, water cooling, air cooling, and single-roll cooling.

From the viewpoint of low crystallization efficiency, the cooling rate during quenching is preferably, for example, 1 K/sec or more, more preferably 100 K/sec or more, and even more preferably 1000 K/sec or more. Furthermore, the quenching in the present invention is preferably a process of cooling the raw material until its temperature drops to 20°C or less, and more preferably to 0°C or less.

The low-crystallization material obtained in step (1) is a solid electrode layer precursor containing lithiated oxide and rock-salt oxide, and in an X-ray diffraction pattern using synchrotron X-rays with a wavelength of 0.5 Å in the range of 2θ = 4 to 26°, it has only peaks of rock-salt oxides belonging to the space group Fm-3m and a halo peak near 2θ = 5 to 8°, but does not have a peak with a maximum value at 2θ = 6 to 7°, which is characteristic of layered rock-salt oxides (such as space groups R-3m).

By undergoing low-crystallization treatment, the layered rock-salt oxide becomes a rock-salt oxide. Here, rock-salt oxide refers to an oxide with a rock-salt structure that does not have a layered structure.

(3-2) Process (2)
In step (2), the low-crystallization product that has been once low-crystallized in step (1) can be re-crystallized by heat-treating it to obtain a solidified molded body, thereby obtaining the solid electrode layer of the present invention.

The heating temperature during the heat treatment is not particularly limited, but from the viewpoint of facilitating the production of the solid electrode layer of the present invention, a temperature of 600 to 1000°C is preferred, and 700 to 980°C is more preferred. The time for which the temperature is maintained within the above heating temperature range is preferably 1 to 12 hours, from the viewpoints of facilitating the suppression of defects due to volatilization of the low-crystallization material that was once low-crystallized in step (1), facilitating sufficient crystallization, and facilitating the production of the solid electrode layer of the present invention.

As a method for such heat treatment, for example, electric furnace sintering can be used. However, in the case of direct current sintering (SPS), the heating temperature and heating time tend to be insufficient, resulting in insufficient crystallization and making it impossible to obtain the solid electrode layer of the present invention.

Electric furnace sintering can be performed by placing the low-crystallization material that has been first low-crystallized in step (1) into an electric furnace and then heating it.

The above-mentioned step (2) can be carried out immediately after step (1), or, if necessary, step (2) can be carried out after a powder compaction treatment.

4. Method for Producing All-Solid-State Lithium Ion Secondary Battery The method for producing the all-solid-state lithium secondary battery of the present invention is not particularly limited. For example,
(3) By using a method including a method of heating a sample including the positive electrode current collecting foil, the solid positive electrode layer (the solid electrode layer of the present invention), the solid electrolyte layer, the solid negative electrode layer, and the negative electrode current collecting foil in this order, by using electric furnace sintering, current sintering, or the like, the members to be joined can be firmly joined together, and the all-solid-state lithium ion secondary battery of the present invention can be produced.

Examples of the positive electrode current collector foil, solid positive electrode layer (solid electrode layer of the present invention), solid electrolyte layer, solid negative electrode layer, and negative electrode current collector foil include those described above. With regard to the solid positive electrode layer (solid electrode layer of the present invention), the solidified molded body obtained in step (2) above can be used as is as the solid positive electrode layer (solid electrode layer of the present invention). Alternatively, the solidified molded body obtained in step (2) above can be crushed into powder and then shaped into the shape of the solid positive electrode layer (solid electrode layer of the present invention) by a heating step such as electric furnace sintering or electric current sintering, thereby producing an all-solid-state lithium secondary battery of the present invention. The positive electrode current collector foil, solid positive electrode layer (solid electrode layer of the present invention), solid electrolyte layer, solid negative electrode layer, and negative electrode current collector foil before the heating step can also be prepared by a green sheet production method in which slurries prepared using a solvent, binder, etc. are coated and dried, thereby producing an all-solid-state lithium-ion secondary battery of the present invention.

Specifically, electric current sintering involves filling each layer into a conductive mold (conductive container) and passing a current, preferably a direct current pulse, through the conductive mold (conductive container) (a method known as spark plasma sintering, pulsed electric current sintering, plasma activated sintering, etc.). This heats the conductive mold (conductive container) due to Joule heat, heating and bonding each layer inside the conductive mold (conductive container). The atmosphere during this electric current sintering process is preferably a non-oxidizing atmosphere. Furthermore, electric current sintering can be performed under normal pressure, but it is preferable to perform electric current sintering under pressure.

Specific methods include filling each layer into a conductive mold (conductive container), and then applying a pulsed (ON-OFF switching) direct current while applying pressure, preferably in a non-oxidizing atmosphere.

The material of the conductive mold (conductive container) is not particularly limited as long as it is conductive. For example, materials made from carbon, iron, iron oxide, aluminum, tungsten carbide, etc., as well as materials made from a mixture of carbon and/or iron oxide with silicon nitride, etc., can also be suitably used.

To further suppress side reactions, the electric sintering process is preferably carried out in a non-oxidizing atmosphere, such as an inert gas atmosphere of argon or nitrogen, or a reducing atmosphere such as hydrogen. Alternatively, the process may be carried out under reduced pressure with a sufficiently low oxygen concentration, for example, a reduced oxygen partial pressure of 20 Pa or less (particularly 1 to 20 Pa).

Specific processing involves using a container that can ensure a sufficiently sealed state as the conductive mold (conductive container), and creating a non-oxidizing atmosphere inside the container. Furthermore, the conductive mold (conductive container) does not need to be completely sealed; when using an incompletely sealed container, the container can be placed inside a reaction chamber, and a non-oxidizing atmosphere can be created inside the reaction chamber. This allows each layer to be sintered in a non-oxidizing atmosphere. In this case, it is preferable to create an inert gas atmosphere or reducing gas atmosphere of 0.01 MPa or higher (particularly 0.05 to 0.2 MPa) inside the reaction chamber, for example.

By applying a DC pulse current to a conductive mold (conductive container) filled with each layer, the conductive container is heated by Joule heat, and the layers are heated and bonded together to form an all-solid-state lithium-ion secondary battery. This method allows the desired all-solid-state lithium-ion secondary battery of the present invention to be produced in a short time of 30 minutes or less.

The pressure applied to each layer is preferably 5 to 60 MPa, more preferably 10 to 50 MPa, from the viewpoint of ensuring sufficient bonding.

The device used for electric current sintering is not particularly limited, as long as it is capable of heating, cooling, pressurizing, etc. each layer and can apply the current necessary for discharge. For example, a commercially available electric current sintering device (spark plasma sintering device) can be used. Such electric current sintering devices and their principles are disclosed, for example, in Japanese Patent Application Laid-Open No. 10-251070.

The present invention will be described in detail below based on examples. However, the following examples do not limit the present invention.

In the following examples and comparative examples, operations were carried out in a glove box under an argon atmosphere unless otherwise specified.

Reference example 1
As a solid electrolyte material, a lithiated oxide (Li _3.5 Ge _0.5 V _0.5 O ₄ ) powder prepared by the synthesis method of Non-Patent Document 2 and as a positive electrode active material, a commercially available layered rock salt oxide (LiCoO ₂ ) were mixed in a molar ratio of 1:2.

The resulting mixture was subjected to a low-crystallization treatment by mechanical milling at room temperature for 45 hours using a Fritsch Pulverisette 7 planetary ball mill, with 90 g of 4 mm zirconia balls enclosed in a 45 ml zirconia container at 350 rpm.

Comparative Reference Example 1
As a solid electrolyte material, a lithiated oxide (Li _3.5 Ge _0.5 V _0.5 O ₄ ) powder prepared by the synthesis method of Non-Patent Document 2 and as a positive electrode active material, a commercially available layered rock salt oxide (LiCoO ₂ ) were mixed in a molar ratio of 1:2.

The resulting mixture was mixed by hand in a mortar at room temperature for 15 minutes.

Example 1
The low-crystallization product obtained in Reference Example 1 was subjected to a powder compaction treatment using a uniaxial press at room temperature under a pressure of 400 MPa for 1 minute.

Then, it was fired in an electric furnace at 900°C for 12 hours to obtain the positive electrode layer of Example 1.

Furthermore, after cooling to room temperature, it was pulverized in a mortar to obtain the positive electrode powder of Example 1.

Comparative Example 1
The low-crystallization material obtained in Reference Example 1 was packed into a graphite mold with an inner diameter of 10 mm and placed in an electric sintering machine. The tungsten carbide mold and the current-carrying portion including the electrode portion were placed in a vacuum chamber. The chamber was evacuated to a vacuum (approximately 5 Pa or less) and then filled with high-purity argon gas up to atmospheric pressure. A pulse current of approximately 200 A was then applied to the graphite mold. The vicinity of the tungsten carbide mold was heated at a heating rate of approximately 50°C/min, reaching 400°C 12 minutes after the start of pulse current application. The current application and pressure were then immediately stopped, and the material was allowed to cool naturally, obtaining a positive electrode layer of Comparative Example 1.

Furthermore, after cooling to room temperature, the reaction product was removed from the tungsten carbide mold and pulverized in a mortar to obtain the positive electrode powder of Comparative Example 1.

Comparative Example 2
The low-crystallization product obtained in Comparative Reference Example 1 was subjected to a powder compaction treatment using a uniaxial press at room temperature under a pressure of 400 MPa for 1 minute.

Then, it was fired in an electric furnace at 900°C for 12 hours to obtain the positive electrode layer of Comparative Example 2.

Furthermore, after cooling to room temperature, it was pulverized in a mortar to obtain the positive electrode powder of Comparative Example 2.

Test Example 1: X-ray Diffraction Measurement Powder X-ray diffraction measurement using synchrotron X-rays with a wavelength of 0.05 nm was performed on the low-crystallization product obtained in Reference Example 1. The results are shown in Figures 1 and _2. For reference, Figure ₁ also shows the peaks of the raw materials, i.e., _lithiated oxide ( _{Li3.5Ge0.5V0.5O4} ) and layered rock salt oxide ( _LiCoO2 ).

As a result, in Reference Example 1, the peaks of lithiated oxide (Li _3.5 Ge _0.5 V _0.5 O ₄ ) and layered rock salt oxide (LiCoO ₂ ) disappeared due to the low crystallization treatment, and the peak with a maximum at 2θ = 6 to 7°, which is a peak specific to layered rock salt oxide, was not observed, and only the peak of rock salt oxide belonging to the space group Fm-3m and the halo peak at 2θ = 5 to 8° were observed. From this, it can be understood that in Reference Example 1, low crystallization was achieved and a non-layered rock salt oxide was produced.

Next, powder X-ray diffraction measurements were performed using synchrotron X-rays with a wavelength of 0.05 nm on the pulverized positive electrode powders obtained in Example 1 and Comparative Examples 1 and 2. The results are shown in Figure 2.

As a result, in Comparative Example 1, although sintering was performed by electric current sintering, the temperature was insufficient, and therefore crystallization did not occur. As with Reference Example 1, no peak with a maximum at 2θ = 6 to 7°, which is a peak specific to layered rock salt-type oxides, was observed, and only the peak of non-layered rock salt-type oxides and a halo peak at 2θ = 5 to 8° were observed.

In Comparative Example 2, the mixture had not yet reached low crystallinity at the time of manual mixing as in Comparative Reference Example 1, and peaks of both the lithiated oxide (Li _3.5 Ge _0.5 V _0.5 O ₄ ) and the layered rock salt oxide (LiCoO ₂ ) were observed.

On the other hand, in Example 1, although the crystallinity was reduced by the ball mill treatment, the heat treatment was performed at a sufficient temperature, so that peaks of both the lithiated oxide (Li _3.5 Ge _0.5 V _0.5 O ₄ ) and the layered rock salt oxide (LiCoO ₂ ) were observed.

Next, the impurity phases in the positive electrode layers of the examples and comparative examples were confirmed by X-ray diffraction using synchrotron X-rays with a wavelength of 0.05 nm. Figures 3 and 4 show the experimental and calculated values obtained by Rietveld analysis of the X-ray diffraction patterns for the positive electrode powders obtained in Example 1 and Comparative Example 2. Figures 3 and 4 also show the fitting difference between the measured values and the calculated pattern below the X-ray diffraction patterns, and further below that, the calculated position of each crystalline phase is also shown. As a result, the proportion of impurity phases was 0.0 mol% in both Example 1 and Comparative Example 2.

Test Example 2: Electron Microscope Observation Cross-sectional scanning electron microscope observation was performed on the solid positive electrode layers obtained in Example 1 and Comparative Example 2 to an extent that at least 500 figures obtained by the subsequent Voronoi tessellation could be extracted. The results are shown in Figures 5 and 6 (Figure 5: 5000x magnification, Figure ₆ : _{500x magnification} ). The lithiated oxide ( _{Li3.5Ge0.5V0.5O4} ) used as the solid electrolyte material is shown in dark gray, and the layered rock salt oxide ( _LiCoO2 ) used as the positive electrode active material is shown in light gray.

The cross-sectional scanning electron microscope images obtained (Figs. 5 and 6) were binarized using Otsu's algorithm, which has been previously reported (IEEE Trans. Syst. Man Cybern., 9 (1) 1979, 62-66). The results are shown in Figs. 7 and 8. Here, the lithiated oxide (Li _3.5 Ge _0.5 V _0.5 O ₄ ), which is the solid electrolyte material, is displayed in white, and the layered rock salt oxide (LiCoO ₂ ), which is the positive electrode active material, is displayed in black. By making the contrast between the two clear, the subsequent Voronoi tessellation image processing can be performed appropriately.

Using the images (Figs. 7 and 8) obtained by binarizing the cross-sectional scanning electron microscope images, Voronoi tessellation was performed with the layered rock-salt oxide (LiCoO ₂ ), which is the positive electrode active material, at the center. The results are shown in Figs. 9 and 10. Here, Voronoi tessellation refers to a division that connects the boundaries of the two closest layered rock-salt oxide (LiCoO ₂ ) particles (black) in the binarized image at equal distances.

The average diameter and standard deviation of the average diameter were measured from the figures obtained by Voronoi tessellation (FIGS. 9 and 10). The results are shown in FIGS. 11 and 12. As a result, for the solid positive electrode layer of Example 1, the average diameter of the figure obtained by Voronoi tessellation centered on the layered rock salt oxide (LiCoO ₂ ) was 0.68 μm, and the standard deviation of the average diameter was 0.28 μm. Furthermore, for the solid positive electrode layer of Comparative Example 2, the average diameter of the figure obtained by Voronoi tessellation centered on the layered rock salt oxide (LiCoO ₂ ) was 7.28 μm, and the standard deviation of the average diameter was 3.13.

Test Example 3: All-Solid-State Lithium-Ion Secondary Battery: ₁₀ mg of the positive electrode powder obtained in Example 1 and Comparative Examples 1 and 2 was spread on 50 mg of solid lithicon-type oxide _{( Li3.5Ge0.5V0.5O4} ) _. The resulting solid electrolyte layer was a thin plate with a diameter of approximately 10 mm and a thickness of approximately 250 μm, and the solid positive electrode layer was a thin plate with a diameter of approximately 10 mm and a thickness of approximately 50 μm. A gold plate with a diameter of 10 mm and a thickness of 100 μm was placed on top of the solid electrolyte layer, and the resulting sintered body was subjected to electric sintering at a pressure of 400 MPa, an applied current of approximately 200 A, and a heating temperature of 450°C for 5 minutes to obtain a sintered body. A 12 mm diameter piece of metallic lithium was attached to the solid electrolyte layer side of the resulting sintered body via a polymer electrolyte made of polyethylene oxide (PEO) with a diameter of approximately 15 mm. This produced the all-solid-state lithium secondary batteries of Example 1 and Comparative Examples 1 and 2. The schematic configuration of the all-solid-state lithium secondary battery is shown in FIG.

Using the all-solid-state lithium secondary batteries of Example 1 and Comparative Examples 1 and 2, in a constant temperature bath at 60°C,
(1) Charging at a constant current of 0.51 mA/cm ² (approximately 0.53 C) to an operating voltage of 4.2 V, and then discharging at a constant current of 0.51 mA/cm ² (approximately 0.53 C) to an operating voltage of 2.0 V (Example 1 and Comparative Example 2)
(2) Charge at a constant current of 0.26 mA/cm ² (approximately 0.27 C) to an operating voltage of 4.2 V, then discharge at a constant current of 0.26 mA/cm ² (approximately 0.27 C) to an operating voltage of 2.0 V (Example 1 and Comparative Example 2)
(3) Charging at a constant current of 0.13 mA/cm ² (approximately 0.13 C) to an operating voltage of 4.2 V, and then discharging at a constant current of 0.13 mA/cm ² (approximately 0.13 C) to an operating voltage of 2.0 V (Example 1 and Comparative Example 2)
(4) Charge at a constant current of 64 μA/cm ² (approximately 0.07 C) to an operating voltage of 4.2 V, then discharge at a constant current of 64 μA/cm ² (approximately 0.07 C) to an operating voltage of 2.0 V (Example 1 and Comparative Examples 1 and 2).
Five charge/discharge cycles were carried out under the four conditions.

The charge/discharge curves for the all-solid-state lithium secondary batteries of Example 1 and Comparative Examples 1 and 2 are shown in Figures 14 to 16.

As a result, in Comparative Example 1, as described above, the solid positive electrode layer obtained was not crystallized, and only the peaks of the non-layered rock-salt oxide were observed. Therefore, it did not contain either the highly conductive lithiated oxide or the layered rock-salt oxide with a high theoretical charge capacity. As a result, the charge/discharge capacity was significantly small even under low load conditions, and the cycle characteristics were also insufficient.

Furthermore, although Comparative Example 2 contains both lithicon-type oxide and layered rock-salt-type oxide, the average diameter of the Voronoi tessellation diagram centered on the layered rock-salt-type oxide and the standard deviation of this average diameter are large, and it can be seen that the capacity, cycle characteristics, and rate characteristics are all insufficient.

In contrast, Example 1 contained both lithizone-type oxide and layered rock-salt-type oxide, had few impurity phases, and had a small average diameter of the Voronoi tessellation diagram centered on the layered rock-salt-type oxide and a small standard deviation of that average diameter, resulting in sufficient improvements in capacity, cycle characteristics, and rate characteristics.

Claims (13)

A solid electrode layer containing a lysicone-type oxide and a layered rock salt-type oxide,
the content of impurities calculated from an X-ray diffraction pattern of the solid electrode layer is 1.0 mol% or less, with the total amount of the solid electrode layer being 100 mol%,
The average diameter of a figure obtained by performing Voronoi division on the layered rock salt type oxide is 0.50 to 2.00 μm, and
A solid electrode layer in which the standard deviation of the average diameter of a figure obtained by performing Voronoi tessellation on the layered rock salt type oxide is 1.00 μm or less. (I) The lysicone-type oxide is represented by the general formula (1):
Li _x1 M ¹ O _y1 (1)
[In the formula, x1 represents 3.0<x1<4.0, y1 represents 3.8<y1<4.2, and ^M1 represents at least one element selected from the group consisting of Ge, Si, V, Ti, P, and S.]
and (II) the layered rock salt type oxide is an oxide represented by the general formula (2):
^LiM2Oy2 ( ₂ )
[In the formula, y2 represents 1.5<y2<2.5, and ^M2 represents at least one element selected from the group consisting of Co, Mn, Ni, Al, and Li.]
is an oxide represented by
The solid electrode layer according to claim 1 , wherein at least one of the following is satisfied: The solid electrode layer according to claim 2 , wherein M ¹ comprises Ge and/or Si and at least one element selected from the group consisting of V, Ti, P, and S. _{4. The} solid _electrode layer _{of claim 3 , wherein the} lithicon _{- type oxide is Li3.5Ge0.5V0.5O4 , Li3.7Ge0.7V0.3O4} , _{Li3.3Ge0.3V0.7O4 , Li3.75Ge0.75P0.25O4 , Li3.5Ge0.75S0.25O4 , or Li3.5Si0.25Ti0.25V0.5O4 . 5. The} solid electrode layer of claim ₄ , wherein the lithicon-type oxide is _{Li3.5Ge0.5V0.5O4} . _{3. The} solid electrode _{layer of} claim _{2 ,} wherein _the layered rock salt _oxide is _LiCoO2 , LiNi1 _{/3Mn1 / 3Co1 / 3O2} , _{LiNi0.5Mn0.5O2} , _{LiNi0.8Mn0.1Co0.1O2 , LiNi0.80Co0.15Al0.05O2 ,} or _{Li1.20Ni0.16Mn0.55Co0.09O2 .} 7. The solid electrode layer of claim 6, wherein the layered rock salt oxide is _LiCoO2 . The solid electrode layer according to any one of claims 1 to 7, which is a solid electrode layer for an all-solid-state lithium-ion secondary battery. A solid electrode layer according to any one of claims 1 to 7, which is a solid positive electrode layer. An all-solid-state lithium-ion secondary battery comprising the solid electrode layer according to any one of claims 1 to 7. A method for producing a solid electrode layer according to any one of claims 1 to 7, comprising:
A manufacturing method comprising: (1) a step of subjecting a lithiated oxide and a layered rock salt type oxide to a low-crystallization treatment; and (2) a step of heat-treating the low-crystallization product obtained in the step (1) at 600 to 1000°C to obtain a solidified molded body. The manufacturing method described in claim 11, wherein the low crystallization treatment is a mechanical milling treatment and/or a melt-quenching treatment. A precursor of a solid electrode layer containing a lithiated oxide and a layered rock salt oxide,
the content of impurities calculated from an X-ray diffraction pattern of the precursor is 1 mol % or less, with the total amount of the solid electrode layer being 100 mol %,
A solid electrode layer precursor, which has only a peak of a rock salt-type oxide belonging to the space group Fm-3m and a halo peak at 2θ = 5 to 8° in an X-ray diffraction pattern in the range of 2θ = 4 to 26° using synchrotron X-rays with a wavelength of 0.05 nm, but does not have a peak having a maximum value at 2θ = 6 to 7° which is characteristic of a layered rock salt-type oxide.