Positive electrode active material and all-solid-state battery

Abstract

To provide a positive electrode active material and an all-solid-state battery capable of achieving excellent cycle characteristics.SOLUTION: The positive electrode active material is a positive electrode active material of an alkali metal-based phosphate containing Co, and is a positive electrode active material in which Si forms a solid solution. The all-solid-state battery includes a positive electrode layer containing the positive electrode active material, a negative electrode layer containing a negative electrode active material, and a solid electrolyte layer sandwiched between the positive electrode layer and the negative electrode layer.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a positive electrode active material and an all-solid-state battery. [Background technology]

[0002] In recent years, secondary batteries have been used in a variety of fields. Secondary batteries that use an electrolyte solution have problems such as electrolyte leakage. Therefore, development of all-solid-state batteries that include a solid electrolyte and have other solid components is underway. For example, an integrated sintered all-solid-state battery that uses LiCoPO4 as a positive electrode active material has been disclosed (see, for example, Patent Documents 1 to 3). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2023-41135 [Patent Document 2] Japanese Patent Application Laid-Open No. 2023-33799 [Patent Document 3] Special Publication No. 2008-506243 Summary of the Invention [Problem to be solved by the invention]

[0004] All-solid-state batteries are required to have excellent cycle characteristics, but they may suffer from degradation during charge-discharge cycles.

[0005] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a positive electrode active material and an all-solid-state battery that can achieve excellent cycle characteristics. [Means for solving the problem]

[0006] The positive electrode active material according to the present invention is a positive electrode active material of an alkali metal phosphate containing Co, in which Si forms a solid solution.

[0007] In the above positive electrode active material, a part of the phosphate may be substituted by Si at the P site.

[0008] In the above positive electrode active material, a part of the phosphate may be substituted by at least one element of Mg, Fe, Mn, Zn, and Ni at the Co site.

[0009] In the above positive electrode active material, the phosphate has the general formula M 1-y Co 1-x+y M´ x P 1-y Si y O4 (0 ≦ x ≦ 1, 0 < y < 1), where M is an alkali metal and M´ may be at least one element of Mg, Fe, Mn, Zn, and Ni.

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

[0011] The M of the above positive electrode active material 1-y Co 1-x+y M´ x P 1-y Si y In O4, 0 < y ≦ 0.1 may be satisfied.

[0012] The M of the above positive electrode active material 1-y Co 1-x+y M´ x P 1-y Si y In O4, 0.01 ≦ y ≦ 0.05 may be satisfied.

[0013] In the above positive electrode active material, the phosphate may have an olivine-type structure.

[0014] Another positive electrode active material according to the present invention is a positive electrode active material of an alkali metal-based phosphate containing Co, and when analyzed by XRD, has the general formula M 1-y Co 1-x+y M´ xA peak of a substance represented by PO4 (0 ≦ x ≦ 1, 0 < y < 1) appears, M is an alkali metal, and M' is at least one element selected from Mg, Fe, Mn, Zn, and Ni.

[0015] The all-solid-state battery according to the present invention includes a positive electrode layer containing the positive electrode active material described in any of the above, a negative electrode layer containing a negative electrode active material, and a solid electrolyte layer sandwiched between the positive electrode layer and the negative electrode layer.

[0016] In the positive electrode layer of the all-solid-state battery, the average particle diameter of the positive electrode active material may be 0.05 μm or more and 5.00 μm or less.

[0017] In the cross-section of the positive electrode layer of the all-solid-state battery, the area occupancy ratio occupied by the positive electrode active material may be 40% or more and 75% or less.

[0018] The all-solid-state battery may include, in the positive electrode layer, a phosphate-based solid electrolyte having a NASICON-type structure.

[0019] In the positive electrode layer of the all-solid-state battery, the average particle diameter of the phosphate-based solid electrolyte may be 0.1 μm or more and 10.0 μm or less.

[0020] In the positive electrode layer of the all-solid-state battery, the area occupancy ratio of the phosphate-based solid electrolyte may be 20% or more and 75% or less.

[0021] In the all-solid-state battery, the thickness of the positive electrode layer may be 1 μm or more and 100 μm or less.

Advantages of the Invention

[0022] According to the present invention, it is possible to provide an all-solid-state battery that can achieve excellent cycle characteristics.

Brief Description of the Drawings

[0023] [Figure 1] It is a schematic cross-sectional view showing the basic structure of an all-solid-state battery. [Figure 2] FIG. 2 is a schematic cross-sectional view showing details of a positive electrode layer and a negative electrode layer. [Figure 3] FIG. 1 is a schematic cross-sectional view of a stacked-type all-solid-state battery. [Figure 4] FIG. 1 is a schematic cross-sectional view of another stacked-type all-solid-state battery. [Figure 5] FIG. 1 is a diagram illustrating a flow of a method for manufacturing an all-solid-state battery. [Figure 6] 1(a) and 1(b) are diagrams illustrating the lamination process. [Figure 7] FIG. 10 is a diagram showing measurement results of cycle characteristics. DETAILED DESCRIPTION OF THE INVENTION

[0024] Hereinafter, embodiments will be described with reference to the drawings.

[0025] (Embodiment) Fig. 1 is a schematic cross-sectional view showing the basic structure of an all-solid-state battery 100 according to an embodiment. As illustrated in Fig. 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 and a second internal electrode 20. The first internal electrode 10 is formed on a first main surface of the solid electrolyte layer 30. The second internal electrode 20 is formed on a second main surface of the solid electrolyte layer 30. The first internal electrode 10, the second internal electrode 20, and the solid electrolyte layer 30 have a structure in which powder materials are sintered.

[0026] 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 a positive electrode, and the other is used as a negative electrode. In this embodiment, as an example, the first internal electrode 10 is used as a positive electrode, and the second internal electrode 20 is used as a negative electrode.

[0027] FIG. 2 is a diagram illustrating detailed cross sections of the first internal electrode 10 and the second internal electrode 20. As illustrated in FIG. 2, the first internal electrode 10 has a structure in which particles of a positive electrode active material 11, particles of a solid electrolyte 12, etc. are dispersed and sintered. The first internal electrode 10 may include a conductive additive, etc., in addition to the positive electrode active material 11 and the solid electrolyte 12. The second internal electrode 20 has a structure in which particles of a negative electrode active material 21, particles of a solid electrolyte 22, etc. are dispersed and sintered. The second internal electrode 20 may include a conductive additive, etc., in addition to the negative electrode active material 21 and the solid electrolyte 22. The first internal electrode 10 includes the positive electrode active material 11 and the second internal electrode 20 includes the negative electrode active material 21, so that the all-solid-state battery 100 can be used as a secondary battery. The first internal electrode 10 includes the solid electrolyte 12 and the second internal electrode 20 includes the solid electrolyte 22, so that the first internal electrode 10 and the second internal electrode 20 have ionic conductivity. By providing the first internal electrode 10 and the second internal electrode 20 with a conductive additive, the first internal electrode 10 and the second internal electrode 20 are provided with electrical conductivity.

[0028] The solid electrolyte layer 30 is mainly composed of a solid electrolyte having ion 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. The phosphate-based solid electrolyte is, for example, a phosphate containing lithium. The phosphate is not particularly limited, but examples thereof include a composite lithium phosphate 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, in order 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-xFor example, a Li-Al-Co-Ge-PO4-based material to which Co has been added in advance may be used, similar to the Co-containing phosphate-based solid electrolyte contained in the first internal electrode 10 used as the positive electrode, but it may not contain Co.

[0029] Solid electrolytes are flame-retardant or non-flammable, and are inherently safer than flammable organic electrolytes. Oxide-based solid electrolytes, which exhibit high ionic conductivity through sintering, have the advantage of having a wider potential window than electrolytes or other solid electrolytes, and being relatively stable in the atmosphere. Phosphate-based solid electrolytes with a NASICON structure, in particular, are oxide-based solid electrolytes with a wide potential window on the high-potential side and high stability in the atmosphere.

[0030] The thickness of the solid electrolyte layer 30 is, for example, 0.5 μm or more and 30 μm or less, 1 μm or more and 20 μm or less, or 2 μm or more and 10 μm or less.

[0031] Here, the positive electrode active material of the first internal electrode 10 will be considered. The positive electrode active material is preferably a material that is unlikely to undergo a chemical reaction with the solid electrolyte even during high-temperature sintering. Therefore, it is conceivable to use an alkali metal phosphate containing Co as the positive electrode active material. For example, LiCoPO4, NaCoPO4, etc. are conceivable to use as the positive electrode active material. However, since alkali metal phosphates containing Co undergo large volume changes during charge and discharge, there is a risk that excellent cycle characteristics may not be obtained. Therefore, the all-solid-state battery 100 according to this embodiment has a configuration that can achieve excellent cycle characteristics. Details will be explained below.

[0032] The inventors of the present invention studied a configuration in which the volume change during charge and discharge can be suppressed and the deterioration of cycle characteristics can be suppressed in an alkali metal-based phosphate containing Co. As a result of intensive research by the inventors, in a phosphate-based positive electrode active material containing a transition metal element, by substituting a part of P (phosphorus) with another element and solid-dissolving it, the crystal structure change during charge and discharge can be suppressed, and it has been found that the cycle deterioration of all-solid-state batteries is suppressed. For example, as the positive electrode active material 11, an alkali metal-based phosphate containing Co and having a part of the P site substituted with Si (silicon) is used, and it has been found that the crystal structure change during charge and discharge is smaller than when Si is not solid-dissolved, and excellent cycle characteristics are realized.

[0033] Therefore, as the positive electrode active material 11, an alkali metal-based phosphate positive electrode active material containing Co and having Si solid-dissolved therein is used. Thereby, excellent cycle characteristics can be realized.

[0034] Furthermore, in an alkali metal-based phosphate containing Co, it has been found that by substituting the Co site with another element, the volume change during charge and discharge can be suppressed, and the cycle characteristic deterioration of all-solid-state batteries is suppressed. Therefore, as the positive electrode active material 11, it is preferable to use an alkali metal-based phosphate containing Co, having Si solid-dissolved therein, and having a part of the Co site substituted with at least one of Mg, Fe, Mn, Zn, and Ni.

[0035] The positive electrode active material 11 is, for example, the general formula M 1-y Co 1-x+y M´ x P 1-y Si y O4 (0 ≤ x ≤ 1, 0 < y < 1), M is at least one element of alkali metal elements such as Li (lithium), Na (sodium), etc., M´ is at least one element of Mg (magnesium), Fe (iron), Mn (manganese), Zn (zinc), and Ni (nickel), and has an olivine-type structure. As an example, the positive electrode active material 11 is Li 0.97 Co 1.03 P0.97 Si 0.03 O4, Li 0.98 Co 1.02 P 0.98 Si 0.02 O4, Li 0.98 Co 0.82 Ni 0.2 P 0.98 Si 0.02 O4, Li 0.97 Co 0.88 Ni 0.15 P 0.97 Si 0.03 Such as O4. When multiple types of elements are used as the above M, M 1-y The composition ratio "1 - y" means the composition ratio of the total amount of the multiple types of elements. When multiple types of elements are used as the above M', M' x The composition ratio "x" means the composition ratio of the total amount of the multiple types of elements.

[0036] For example, when the positive electrode active material 11 is analyzed by XRD (X-ray diffraction), the peak of the substance represented by the above general formula M 1-y Co 1-x+y M' x PO4 (0 ≤ x ≤ 1, 0 < y < 1) appears. Also, by performing Rietveld analysis, it is possible to infer that part of the P site is substituted by Si.

[0037] From the perspective of sufficiently improving the recycling characteristics, it is preferable to set a lower limit for the solid solution amount of Si. In this embodiment, in M 1-y Co 1-x+y M' x P 1-y Si y In O4, it is preferable that 0.01 ≤ y, more preferably 0.015 ≤ y, and even more preferably 0.02 ≤ y.

[0038] If the solid solution amount of Si is large, the battery capacity may decrease. Therefore, it is preferable to set an upper limit for the solid solution amount of Si. In this embodiment, in M 1-y Co<​​​​​y In O4, it is preferable that 0 < y ≦ 0.1, more preferably 0 < y ≦ 0.05, and even more preferably 0 < y ≦ 0.04.

[0039] M 1-y Co 1-x+y M´ x P 1-y Si y In O4, if the substitution amount of Co sites is large, the charge-discharge capacity may decrease. Therefore, it is preferable that 0 < x ≦ 0.5, and more preferably 0 < x ≦ 0.3. When x ≦ 0.3, excellent characteristics in both charge-discharge capacity and cycle characteristics can be obtained.

[0040] In the first internal electrode 10, if the average particle size of the positive electrode active material 11 is small, side reactions may proceed during co-firing with the solid electrolyte. Therefore, it is preferable to set a lower limit for the average particle size of the positive electrode active material 11. In the present embodiment, the average particle size of the positive electrode active material 11 is preferably 0.05 μm or more, more preferably 0.08 μm or more, and even more preferably 0.10 μm or more.

[0041] On the other hand, in the first internal electrode 10, if the average particle size of the positive electrode active material 11 is large, the overvoltage during discharge may increase. Therefore, it is preferable to set an upper limit for the average particle size of the positive electrode active material 11. In the present embodiment, the average particle size of the positive electrode active material 11 is preferably 5.00 μm or less, more preferably 1.00 μm or less, and even more preferably 0.50 μm or less.

[0042] In the first internal electrode 10, if the content of the positive electrode active material 11 is low, the volume capacity density of the positive electrode may decrease. Therefore, it is preferable to set a lower limit for the content of the positive electrode active material 11. In the present embodiment, in the cross-section of the first internal electrode 10, the area occupancy ratio occupied by the positive electrode active material 11 is preferably 40% or more, more preferably 45% or more, and even more preferably 50% or more.

[0043] If the content of the positive electrode active material 11 in the first internal electrode 10 is high, the availability of the active material during charge and discharge may decrease. Therefore, it is preferable to set an upper limit on the content of the positive electrode active material 11. In this embodiment, the area occupation ratio of the positive electrode active material 11 in the cross section of the first internal electrode 10 is preferably 75% or less, more preferably 70% or less, and even more preferably 65% ​​or less.

[0044] The solid electrolyte 12 provided in the first internal electrode 10 is not particularly limited, but is preferably a phosphate-based solid electrolyte having a NASICON-type structure. This is because phosphate-based solid electrolytes having a NASICON-type structure have the properties of a wide potential window at high potentials and high atmospheric stability. Even if a phosphate-based solid electrolyte having a NASICON-type structure is used as the solid electrolyte 12, the use of a phosphate containing Co in the positive electrode active material 11 can suppress a chemical reaction between the positive electrode active material 11 and the solid electrolyte 12 during sintering. The solid electrolyte 12 can be, for example, the same as the main solid electrolyte of the solid electrolyte layer 30.

[0045] If the average particle size of the solid electrolyte 12 in the first internal electrode 10 is small, the dispersion state of the electrode paste before firing becomes unstable, making it difficult to obtain a dense coating film, and the reactivity during heat treatment of the all-solid-state battery 100 increases, making interdiffusion reactions more likely to occur, which is undesirable. Therefore, it is preferable to set a lower limit for the average particle size of the solid electrolyte 12 in the first internal electrode 10. In this embodiment, the average particle size of the solid electrolyte 12 in the first internal electrode 10 is preferably 0.1 μm or more, more preferably 0.2 μm or more, and even more preferably 0.3 μm or more.

[0046] On the other hand, if the average particle size of the solid electrolyte 12 in the first internal electrode 10 is large, high temperatures are required for sintering and densification, which is not preferable. Therefore, it is preferable to set an upper limit to the average particle size of the solid electrolyte 12 in the first internal electrode 10. In this embodiment, the average particle size of the solid electrolyte 12 in the first internal electrode 10 is preferably 10.0 μm or less, more preferably 7.0 μm or less, and even more preferably 5.0 μm or less.

[0047] In the first internal electrode 10, if the content of the solid electrolyte 12 is small, ion conduction paths cannot be ensured and the internal resistance increases, which is undesirable. Therefore, it is preferable to set a lower limit for the content of the solid electrolyte 12. In this embodiment, the area occupation ratio of the solid electrolyte 12 in the cross section of the first internal electrode 10 is preferably 15% or more, more preferably 20% or more, and even more preferably 25% or more.

[0048] In the first internal electrode 10, if the content of the solid electrolyte 12 is high, the active material filling amount cannot be increased, resulting in a decrease in capacity, which is undesirable. Therefore, it is preferable to set an upper limit on the content of the solid electrolyte 12. In this embodiment, the area occupation ratio of the solid electrolyte 12 in the cross section of the first internal electrode 10 is preferably 75% or less, more preferably 70% or less, and even more preferably 65% ​​or less.

[0049] The thickness of each first internal electrode 10 is, for example, 1 μm or more and 100 μm or less, 5 μm or more and 50 μm or less, or 10 μm or more and 30 μm or less.

[0050] The negative electrode active material 21 provided in the second internal electrode 20 is not particularly limited as long as it functions as a negative electrode active material. For example, +It is preferable that the negative electrode active material operates at an average potential of 4.7 V vs. Li / Li. Examples include TiO2, Ti-Nb-Ta-O compounds, Al-Nb-Ta-O compounds, and Al-Nb-Hf-Ta-O compounds. Such negative electrode active materials are suitable for use at an average potential of 4.7 V vs. Li / Li. + When combined with a positive electrode active material having the above operating potential, the operating voltage of the all-solid-state battery 100 can be increased.

[0051] The solid electrolyte 22 provided in the second internal electrode 20 is not particularly limited, but is preferably a phosphate-based solid electrolyte having a NASICON-type structure. This is because phosphate-based solid electrolytes having a NASICON-type structure have the properties of a wide potential window on the high-potential side and high atmospheric stability. The solid electrolyte 22 can be, for example, the same as the main solid electrolyte of the solid electrolyte layer 30.

[0052] If the average particle size of the solid electrolyte 22 in the second internal electrode 20 is small, the dispersion state of the electrode paste before firing becomes unstable, making it difficult to obtain a dense coating film, and the reactivity during heat treatment of the all-solid-state battery 100 increases, making interdiffusion reactions more likely to occur, which is undesirable. Therefore, it is preferable to set a lower limit for the average particle size of the solid electrolyte 22 in the second internal electrode 20. In this embodiment, the average particle size of the solid electrolyte 22 in the second internal electrode 20 is preferably 0.1 μm or more, more preferably 0.2 μm or more, and even more preferably 0.5 μm or more.

[0053] On the other hand, if the average particle size of the solid electrolyte 22 in the second internal electrode 20 is large, high temperatures are required for sintering and densification, which is not preferable. Therefore, it is preferable to set an upper limit to the average particle size of the solid electrolyte 22 in the second internal electrode 20. In this embodiment, the average particle size of the solid electrolyte 22 in the second internal electrode 20 is preferably 10.0 μm or less, more preferably 7.0 μm or less, and even more preferably 5.0 μm or less.

[0054] In the second internal electrode 20, if the content of the solid electrolyte 22 is small, ion conduction paths cannot be ensured and the internal resistance increases, which is undesirable. Therefore, it is preferable to set a lower limit for the content of the solid electrolyte 22. In this embodiment, the area occupation ratio of the solid electrolyte 22 in the cross section of the second internal electrode 20 is preferably 15% or more, more preferably 20% or more, and even more preferably 25% or more.

[0055] If the content of the solid electrolyte 22 in the second internal electrode 20 is high, it is not preferable because the active material filling amount cannot be increased and the capacity decreases. Therefore, it is preferable to set an upper limit on the content of the solid electrolyte 22. In this embodiment, the area occupation ratio of the solid electrolyte 22 in the cross section of the second internal electrode 20 is preferably 75% or less, more preferably 70% or less, and even more preferably 65% ​​or less.

[0056] The thickness of each second internal electrode 20 is, for example, 1 μm or more and 100 μm or less, 5 μm or more and 50 μm or less, or 10 μm or more and 30 μm or less.

[0057] The first internal electrode 10 and the second internal electrode 20 may include a conductive material (conductive additive). A carbon material or the like may be used as the conductive additive. A metal may be used as the conductive additive. Examples of the metal for the conductive additive include Pd, Ni, Cu, Fe, and alloys containing these.

[0058] The average particle diameters of the electrode active material and solid electrolyte in the first internal electrode 10 and the second internal electrode 20 can be measured by the following method. First, a cross-section polisher (CP) or the like is used to expose a cross section of the internal electrode from a direction approximately perpendicular to the lamination thickness direction of the all-solid-state battery. Next, observation is performed using, for example, a scanning electron microscope (manufactured by Hitachi High-Tech Corporation, model: SU-7000) at an acceleration voltage of 5 kV, and the regions of electrode active material particles and solid electrolyte particles in the internal electrode are identified using SEM images at a magnification of 10,000 times and elemental analysis by SEM-EDS. Ten or more locations are observed, and at least ten particle diameters are obtained by selecting particles that exist isolated from other particles from the identified electrode active material particles and solid electrolyte particles. Next, using image analysis software, the particle area of ​​each selected particle is measured, and the circle equivalent diameter (Heywood diameter) is measured from the particle area. The median diameter (D50 value) of each particle is calculated from the particle size distribution obtained by plotting the particle size on the x-axis and the frequency on the y-axis, and this can be defined as the average particle size of each particle.

[0059] The area occupancy rates of the electrode active material and solid electrolyte in the first internal electrode 10 and the second internal electrode 20 can be measured by the following method. First, a cross-section polisher (CP) or the like is used to expose a cross section of the internal electrode from a direction approximately perpendicular to the lamination thickness direction of the all-solid-state battery. Next, observation is performed using, for example, a scanning electron microscope (manufactured by Hitachi High-Tech Corporation, model: SU-7000) at an accelerating voltage of 5 kV, and backscattered electron images of the internal electrode at the same magnification and elemental analysis by SEM-EDS are obtained at 10 locations. Image analysis software is used to identify the areas occupied by the electrode active material and solid electrolyte in the obtained image, and the arithmetic average of each occupancy rate can be calculated.

[0060] The thickness of each layer can be calculated by using a cross-section polisher (CP) or the like to cut a cross section from a direction approximately perpendicular to the stacking thickness direction of the all-solid-state battery, observing the cross section using, for example, a scanning electron microscope (manufactured by Hitachi High-Tech Corporation, model: SU-7000) at an accelerating voltage of 5 kV, measuring backscattered electron images and elemental analysis by SEM-EDS at 10 points to identify the interface of each layer, and calculating the arithmetic average value of the 10 points on each layer.

[0061] (Stacked all-solid-state battery) 3 is a schematic cross-sectional view of a stacked-type all-solid-state battery 100a in which a plurality of battery units are stacked. The all-solid-state battery 100a includes 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 contact two side surfaces, which are two of the four surfaces other than the top and bottom surfaces at the ends in the stacking direction. The two side surfaces may be two adjacent side surfaces or two side surfaces facing each other. In this embodiment, the first external electrode 40a and the second external electrode 40b are provided so as to contact two side surfaces facing each other (hereinafter referred to as two end surfaces).

[0062] In the following description, components having the same composition range, thickness range, and particle size distribution range as those of the all-solid-state battery 100 are denoted by the same reference numerals, and detailed description thereof will be omitted.

[0063] In the all-solid-state battery 100a, a plurality of first internal electrodes 10 and a plurality of second internal electrodes 20 are alternately stacked with solid electrolyte layers 30 interposed therebetween. The edges of the plurality of first internal electrodes 10 are exposed at the first end face of the laminated chip 60 but are not exposed at the second end face. The edges of the plurality of second internal electrodes 20 are exposed at the second end face of the laminated chip 60 but are not exposed at the first end face. As a result, the first internal electrodes 10 and the second internal electrodes 20 are alternately electrically connected 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. In this way, the all-solid-state battery 100a has a structure in which a plurality of battery units are stacked.

[0064] A cover layer 50 is laminated 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, on the upper surface of the first internal electrode 10, which is the uppermost layer). In addition, a cover layer 50 is laminated on the lower surface of the laminated structure (in the example of FIG. 3, on the lower surface of the first internal electrode 10, which is the lowermost layer). The cover layer 50 is mainly composed of an inorganic material containing, for example, Al, Zr, Ti, etc. (for example, Al2O3, ZrO2, TiO2, etc.). The cover layer 50 may contain the main component of the solid electrolyte layer 30 as a main component.

[0065] The first internal electrode 10 and the second internal electrode 20 may each include a current collector layer. For example, as illustrated in FIG. 4, a first current collector layer 13 may be provided within the first internal electrode 10. Furthermore, a second current collector layer 23 may be provided within the second internal electrode 20. The first current collector layer 13 and the second current collector layer 23 are mainly composed of a conductive material. For example, metal, carbon, or the like can be used as the conductive material for the first current collector layer 13 and the second current collector layer 23. Connecting the first current collector layer 13 to the first external electrode 40a and connecting the second current collector layer 23 to the second external electrode 40b improves current collection efficiency.

[0066] Next, a description will be given of a method for manufacturing the all-solid-state battery 100a illustrated in Fig. 5. Fig. 5 is a diagram illustrating a flow of the method for manufacturing the all-solid-state battery 100a.

[0067] (Process for producing raw material powder for solid electrolyte layer) First, raw material powder for the solid electrolyte layer that constitutes the above-described solid electrolyte layer 30 is prepared. For example, raw materials, additives, etc. are mixed and the raw material powder for the solid electrolyte layer can be prepared using a solid-phase synthesis method or the like. The obtained raw material powder can be adjusted to a desired average particle size by dry-milling. For example, the desired average particle size is adjusted using a planetary ball mill with 5 mm diameter ZrO2 balls.

[0068] (Cover layer raw material powder production process) Next, a ceramic raw material powder for the cover layer 50 is prepared. For example, raw materials, additives, etc. are mixed and the raw material powder for the cover layer can be prepared using a solid-phase synthesis method or the like. The obtained raw material powder can be adjusted to a desired average particle size by dry milling. For example, the desired average particle size is adjusted using a planetary ball mill with 5 mm diameter ZrO2 balls. If the solid electrolyte layer 30 and the cover layer 50 have the same composition, the raw material powder for the solid electrolyte layer can be used instead.

[0069] (Internal electrode paste manufacturing process) Next, internal electrode pastes for producing the first internal electrode 10 and the second internal electrode 20 are separately prepared. For example, the internal electrode pastes can be obtained by uniformly dispersing a conductive additive, an electrode active material, a solid electrolyte material, a sintering additive, a binder, a plasticizer, etc. in water or an organic solvent. The solid electrolyte paste described above may be used as the solid electrolyte material. A carbon material or the like may be used as the conductive additive. A metal may also be used as the conductive additive. Examples of metals for the conductive additive include Pd, Ni, Cu, Fe, and alloys containing these. Pd, Ni, Cu, Fe, alloys containing these, and various carbon materials may also be used.

[0070] As the electrode active material contained in the second internal electrode 20, the powder material of the positive electrode active material 11 described above is used.

[0071] The sintering aid of the internal electrode paste contains one or more glass components such as Li-BO based compounds, Li-Si-O based compounds, Li-CO based compounds, Li-SO based compounds, and Li-PO based compounds.

[0072] (External electrode paste manufacturing process) Next, an external electrode paste for producing the first external electrode 40a and the second external electrode 40b is prepared. For example, the external electrode paste can be obtained by uniformly dispersing a conductive material, glass frit, a binder, a plasticizer, etc. in water or an organic solvent.

[0073] (Solid electrolyte green sheet manufacturing process) The raw material powder for the solid electrolyte layer is uniformly dispersed in an aqueous or organic solvent along with a binder, dispersant, plasticizer, etc., and then wet-pulverized to obtain a solid electrolyte slurry with a desired average particle size. This process can be performed using a bead mill, wet jet mill, various kneaders, high-pressure homogenizers, etc., with the bead mill being preferred because it allows for simultaneous adjustment of particle size distribution and dispersion. A binder is added to the resulting solid electrolyte slurry to obtain a solid electrolyte paste. The resulting solid electrolyte paste can be coated to produce a solid electrolyte green sheet 51. The coating method is not particularly limited, and can include slot die coating, reverse coating, gravure coating, bar coating, doctor blade coating, etc. The particle size distribution after wet-pulverization can be measured, for example, using a laser diffraction measurement device using laser diffraction scattering.

[0074] (Lamination process) As shown in FIG. 6( a), an internal electrode paste 52 is printed on one side of a solid electrolyte green sheet 51. A reverse pattern 53 is printed on the area of ​​the solid electrolyte green sheet 51 where the internal electrode paste 52 is not printed. The reverse pattern 53 may be the same as the solid electrolyte green sheet 51. After printing, multiple solid electrolyte green sheets 51 are stacked with alternating offsets. As shown in FIG. 6( b), a laminate is obtained by pressing cover sheets 54 from above and below in the stacking direction. In this case, a laminate having a substantially rectangular parallelepiped shape is obtained, with the internal electrode paste 52 for the first internal electrode 10 exposed on one end surface and the internal electrode paste 52 for the second internal electrode 20 exposed on the other end surface. The cover sheet 54 can be formed by applying raw material powder for the cover layer using a method similar to that used in the solid electrolyte green sheet preparation process. The cover sheet 54 is formed thicker than the solid electrolyte green sheet 51. The thickness may be increased during coating, or by stacking multiple coated sheets.

[0075] Next, external electrode paste 55 is applied to each of the two end faces by dipping or the like and then dried, thereby obtaining a molded body for forming the all-solid-state battery 100a.

[0076] (Firing process) Next, the obtained laminate is fired. The firing conditions are not particularly limited, and may be in an oxidizing atmosphere or a non-oxidizing atmosphere, with the maximum temperature preferably being 400°C to 1000°C, more preferably 500°C to 900°C. A step of maintaining the temperature in an oxidizing atmosphere at a temperature lower than the maximum temperature may be provided in order to thoroughly remove the binder before the maximum temperature is reached. In order to reduce process costs, it is desirable to fire at as low a temperature as possible. After firing, a re-oxidation treatment may be performed. Through the above steps, an all-solid-state battery 100a is produced.

[0077] In addition, by sequentially stacking the internal electrode paste, the current collector paste containing a conductive material, and the internal electrode paste, a current collector layer can be formed within the first internal electrode 10 and the second internal electrode 20.

[0078] According to the manufacturing method of this embodiment, a powder material of the positive electrode active material 11 is used in the internal electrode paste for producing the first internal electrode 10, so that the first internal electrode 10 containing the positive electrode active material 11 can be produced. As a result, an all-solid-state battery with excellent cycle characteristics can be produced. Note that a powder material having the same composition as the positive electrode active material 11 may be used. Alternatively, the positive electrode active material 11 may be synthesized by mixing each material for synthesizing the positive electrode active material 11 (for example, a Co-containing phosphate such as LiCoPO4 or NaCoPO4 with an oxide of Si, Mg, Fe, Mn, Zn, Ni, or the like) and performing a heat treatment. Alternatively, each material for synthesizing the positive electrode active material 11 may be included in the internal electrode paste for producing the first internal electrode 10, and the positive electrode active material 11 may be synthesized during the firing process. [Example]

[0079] Hereinafter, all-solid-state batteries were fabricated according to the embodiments, and their characteristics were investigated.

[0080] Example 1 The positive electrode is made of Li with an average particle size adjusted to 0.20 μm. 0.99 Co 1.01 P 0.99 Si 0.01 The positive electrode active material was O4, and the solid electrolyte was a Li-Al-Co-Ge-PO4 NASICON-type phosphate glass solid electrolyte. A positive electrode paste with a weight ratio of positive electrode active material, carbon conductive additive, and solid electrolyte of 45:10:45 was prepared and printed on a solid electrolyte sheet.

[0081] The negative electrode is made of TiTa with an average particle size adjusted to 1.00 μm. 1.5 Nb 0.5 The negative electrode active material was O7, and the solid electrolyte was Li-Al-Ge-PO4 glass. A negative electrode paste with a weight ratio of negative electrode active material, carbon conductive additive, and solid electrolyte of 35:10:55 was prepared and printed on a solid electrolyte sheet.

[0082] The positive electrode printed sheet piece and the negative electrode printed sheet piece were stacked together with the reference electrode sheet piece and press-molded to produce a molded body. The molded body was then fired multiple times at a specified environment and temperature to produce an all-solid-state battery with a reference electrode.

[0083] Example 2 The positive electrode is made of Li with an average particle size adjusted to 0.2 μm. 0.98 Co 1.02 P 0.98 Si 0.02 An all-solid-state battery was fabricated in the same manner as in Example 1, except that O4 positive electrode active material was used.

[0084] Example 3 The positive electrode is made of Li with an average particle size adjusted to 0.2 μm. 0.95 Co 1.05 P 0.95 Si 0.05 An all-solid-state battery was fabricated in the same manner as in Example 1, except that O4 positive electrode active material was used.

[0085] Example 4 The positive electrode is made of Li with an average particle size adjusted to 0.2 μm.0.98 Co 0.82 Ni 0.2 P 0.98 Si 0.02 An all-solid-state battery was fabricated in the same manner as in Example 1, except that O4 positive electrode active material was used.

[0086] Example 5 The positive electrode is made of Li with an average particle size adjusted to 0.2 μm. 0.97 Co 0.88 Ni 0.15 P 0.97 Si 0.03 An all-solid-state battery was fabricated in the same manner as in Example 1, except that O4 positive electrode active material was used.

[0087] Example 6 The positive electrode is made of Li with an average particle size adjusted to 0.2 μm. 0.975 Co 0.875 Ni 0.1 Zn 0.05 P 0.975 Si 0.025 An all-solid-state battery was fabricated in the same manner as in Example 1, except that O4 positive electrode active material was used.

[0088] (Comparative Example 1) An all-solid-state battery was fabricated and evaluated in the same manner as in Example 1, except that a LiCoPO4 positive electrode active material with an average particle size adjusted to 0.2 μm was used for the positive electrode.

[0089] (Cycle characteristics) Next, the discharge capacity (mAh / g) after repeated charge and discharge was measured for each of Examples 1 to 6 and Comparative Example 1. The charge and discharge test was carried out in a thermostatic chamber at 25°C with a current of 0.2 C rate and a positive electrode potential of 4.30 V to 5.05 V vs Li / Li + A constant current charge / discharge test was carried out within the range of 1000 mA / s. The results are shown in Figure 7 and Table 1.

[0090] The initial discharge capacity was 97.19 mAh / g in Example 1, 90.68 mAh / g in Example 2, 64.11 mAh / g in Example 3, 97.72 mAh / g in Example 4, 97.17 mAh / g in Example 5, 120.09 mAh / g in Example 6, and 111.7 mAh / g in Comparative Example 1. The discharge capacity retention rate after 100 cycles based on the initial discharge capacity was 67.50% in Example 1, 83.93% in Example 2, 92.61% in Example 3, 91.09% in Example 4, 91.34% in Example 5, 80.84% ​​in Example 6, and 66.84% in Comparative Example 1. Thus, compared to Comparative Example 1, the discharge capacity retention rates of Examples 1 to 6 were maintained at a high level. [Table 1]

[0091] As described above, the discharge capacity retention rates of Examples 1 to 6 were higher than that of Comparative Example 1. This is thought to be because the use of a positive electrode active material that is an alkali metal phosphate containing Co and in which Si is dissolved in a solid solution suppresses volume changes during charge and discharge.

[0092] Although the embodiments of the present invention have been described in detail above, the present invention is not limited to such specific embodiments, and various modifications and variations are possible within the scope of the gist of the present invention as defined in the claims. [Explanation of symbols]

[0093] 10 1st internal electrode 11 Cathode active material 12 Solid electrolyte 13 First current collector layer 20 Second internal electrode 21 Negative electrode active material 22 Solid electrolyte 23 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 Internal electrode paste 53 Reverse pattern 54 Cover Sheet 55 External electrode paste 60 stacked chips 100,100a solid state battery

Claims

1. A positive electrode active material of an alkali metal phosphate containing Co, A positive electrode active material in which Si is dissolved.

2. The positive electrode active material according to claim 1 , wherein the P site of the phosphate is partially substituted with Si.

3. 2. The positive electrode active material according to claim 1, wherein the phosphate has a portion of Co sites substituted with at least one element selected from the group consisting of Mg, Fe, Mn, Zn, and Ni.

4. The phosphate salt has the general formula M １－ｙ Co １－ｘ＋ｙ M' ｘ P １－ｙ Si ｙ O ４ (0≦x≦1, 0<y<1), M is an alkali metal; 2. The positive electrode active material according to claim 1, wherein M' is at least one element selected from the group consisting of Mg, Mn, Fe, Zn, and Ni.

5. The positive electrode active material according to claim 4 , wherein M is Li.

6. Said M １－ｙ Co １－ｘ＋ｙ M' ｘ P １－ｙ Si ｙ O ４ The positive electrode active material according to claim 4 , wherein 0<y≦0.

1.

7. Said M １－ｙ Co １－ｘ＋ｙ M' ｘ P １－ｙ Si ｙ O ４ 5. The positive electrode active material according to claim 4, wherein y satisfies 0.01≦y≦0.

05.

8. The positive electrode active material according to claim 1 , wherein the phosphate has an olivine structure.

9. A positive electrode active material of an alkali metal phosphate containing Co, When analyzed by XRD, the compound has the general formula M １－ｙ Co １－ｘ＋ｙ M' ｘ P.O. ４ A peak of a substance expressed as (0≦x≦1, 0<y<1) appears. M is an alkali metal; M' is at least one element selected from the group consisting of Mg, Fe, Mn, Zn, and Ni.

10. A positive electrode layer containing the positive electrode active material according to any one of claims 1 to 9; a negative electrode layer containing a negative electrode active material; a solid electrolyte layer sandwiched between the positive electrode layer and the negative electrode layer.

11. The all-solid-state battery according to claim 10 , wherein in the positive electrode layer, the positive electrode active material has an average particle size of 0.05 μm or more and 5.00 μm or less.

12. The all-solid-state battery according to claim 10 , wherein an area occupied by the positive electrode active material in a cross section of the positive electrode layer is 40% or more and 75% or less.

13. The all-solid-state battery according to claim 10 , wherein the positive electrode layer contains a phosphate-based solid electrolyte having a NASICON structure.

14. 14. The all-solid-state battery according to claim 13, wherein in the positive electrode layer, the average particle size of the phosphate-based solid electrolyte is 0.1 μm or more and 10.0 μm or less.

15. 14. The all-solid-state battery according to claim 13, wherein the area occupancy ratio of the phosphate-based solid electrolyte in the positive electrode layer is 20% or more and 75% or less.

16. The all-solid-state battery according to claim 10 , wherein the thickness of the positive electrode layer is 1 μm or more and 100 μm or less.

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