All-solid battery

Abstract

To provide an all-solid battery that can achieve excellent cycle characteristics.SOLUTION: An all-solid battery includes a positive electrode layer including a positive electrode active material that is a phosphate containing Co, and in which a portion of the Co sites is substituted with at least one of Mg, Zn, and Ni, a negative electrode layer including 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 an all-solid-state battery. [Background technology]

[0002] In recent years, secondary batteries have been used in various fields. Secondary batteries using electrolytes have problems such as electrolyte leakage. Therefore, development of all-solid-state batteries that have a solid electrolyte and other components that are also solid is underway. For example, LiCoPO 4 An integrally sintered all-solid-state battery using this positive electrode active material has been disclosed (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2023-41135 A [Non-patent literature]

[0004] [Non-Patent Document 1] “Mixed LiCo0.6M0.4PO4 (M = Mn, Fe, Ni) phosphates: cycling mechanism and thermal stability”, Physical Chemistry Chemical Physics, 2009, 11, 3271-3277 [Non-Patent Document 2] “Identifying the Structure of the Intermediate, Li2 / 3CoPO4, Formed during Electrochemical Cycling of LiCoPO4”, CHEMISTRY OF MATERIALS, 2014, 26, 6193-6205 Summary of the Invention [Problem to be solved by the invention]

[0005] All-solid-state batteries are required to have excellent cycle characteristics. However, in all-solid-state batteries, the charge-discharge cycle may deteriorate.

[0006] The present invention has been made in view of the above problems, and an object thereof is to provide an all-solid-state battery capable of realizing excellent cycle characteristics.

Means for Solving the Problems

[0007] The all-solid-state battery according to the present invention includes a positive electrode layer containing a phosphate containing Co and having a part of Co sites substituted with at least one of Mg, Zn, and Ni as a 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.

[0008] In the all-solid-state battery, the positive electrode active material is represented by the general formula LiCo 1-x M x PO 4 where 0 < x ≦ 0.5, M is at least one of Mg, Zn, or Ni, and may have an olivine-type structure.

[0009] In the positive electrode layer of the all-solid-state battery, the average particle size of the positive electrode active material may be 0.05 μm or more and 5.00 μm or less.

[0010] 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.

[0011] In the all-solid-state battery, the positive electrode layer may contain a phosphate-based solid electrolyte having a NASICON-type structure.

[0012] In the positive electrode layer of the all-solid-state battery, the average particle size of the phosphate-based solid electrolyte may be 0.1 μm or more and 10.0 μm or less.

[0013] 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.

[0014] In the all-solid-state battery, the positive electrode layer may have a thickness of 1 μm or more and 100 μm or less. Effect of the Invention

[0015] 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]

[0016] [Figure 1] FIG. 1 is a schematic cross-sectional view showing a basic structure of an all-solid-state battery. [Diagram 2] FIG. 2 is a schematic cross-sectional view showing details of a positive electrode layer and a negative electrode layer. [Diagram 3] FIG. 1 is a schematic cross-sectional view of a stacked-type all-solid-state battery. [Figure 4] FIG. 2 is a schematic cross-sectional view of another stacked type all-solid-state battery. [Diagram 5] FIG. 1 is a diagram illustrating a flow of a method for producing an all-solid-state battery. [Figure 6] 1(a) and (b) are diagrams illustrating the lamination process. [Figure 7] FIG. 1 is a diagram showing measurement results of cycle characteristics. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] Hereinafter, an embodiment will be described with reference to the drawings.

[0018] (Embodiment) Fig. 1 is a schematic cross-sectional view showing a 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.

[0019] 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 the present 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.

[0020] FIG. 2 is a diagram illustrating the details of the cross section 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 assistant, 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 assistant, 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 ion conductivity. By providing the first internal electrode 10 and the second internal electrode 20 with a conductive assistant, the first internal electrode 10 and the second internal electrode 20 are provided with electrical conductivity.

[0021] 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 for example, a composite lithium phosphate with Ti (for example, LiTi 2 (PO 4 ) 3 ) and the like. Alternatively, Ti can be partially or completely replaced with tetravalent transition metals such as Ge, Sn, Hf, Zr, etc. Also, in order to increase the Li content, it may be partially replaced with trivalent transition metals such as Al, Ga, In, Y, La, etc. More specifically, for example, Li 1+x Al x Ge 2-x (PO 4 ) 3 Or, Li 1+x Al x Zr 2-x (PO 4 ) 3 , Li 1+x Al x Ti 2-x (PO 4 ) 3 For example, Li-Al-Co-Ge-PO 4 The material may be a Co-based material, but it does not have to contain Co.

[0022] Solid electrolytes are flame-retardant or non-flammable, and are inherently safer than flammable organic electrolytes. In particular, oxide-based solid electrolytes that exhibit high ionic conductivity through sintering have the advantage of having a wider potential window than electrolyte-based and other solid electrolyte-based systems, and being relatively stable in the atmosphere. In particular, phosphate-based solid electrolytes with a NASICON structure are oxide-based solid electrolytes that have a wider potential window on the high-potential side and are highly stable in the atmosphere.

[0023] 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.

[0024] 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 sintering at high temperatures. For this reason, it is considered to use a Co-containing phosphate-based positive electrode active material. For example, LiCoPO 4 However, LiCoPO 4 However, since the volume change during charging and discharging is large, there is a risk that excellent cycle characteristics cannot be obtained. Therefore, the all-solid-state battery 100 according to this embodiment has a configuration that can realize high cycle characteristics. Details will be described below.

[0025] The present inventors have investigated a configuration for suppressing volume change during charging and discharging in a Co-containing phosphate-based positive electrode active material and suppressing deterioration of cycle characteristics. Through intensive research by the present inventors, it has been found that by substituting the Co site in a Co-containing phosphate-based positive electrode active material with another element, volume change during charging and discharging is suppressed and deterioration of cycle characteristics of an all-solid-state battery is suppressed. Specifically, by using, as the positive electrode active material 11, a phosphate containing Co in which a part of the Co site is substituted with at least one of Mg, Zn, and Ni, the volume change during charging and discharging is suppressed to LiCoPO 4 It has been found that the maximum capacitance is smaller than that of the conventional method, and excellent cycle characteristics are achieved.

[0026] In addition, the reaction between the solid electrolyte and the element-substituted positive electrode active material during co-sintering improves the oxidation resistance of the solid electrolyte. The improved oxidation resistance of the solid electrolyte further improves cycle characteristics. For example, the oxidation resistance of the solid electrolyte of the solid electrolyte layer 30 improves. In addition, when the first internal electrode 10 contains a solid electrolyte, the oxidation resistance of the solid electrolyte contained in the first internal electrode 10 improves.

[0027] The positive electrode active material 11 is, for example, a material having the general formula LiCo1-x M x PO 4 It is represented by. M is at least one of Mg, Zn, or Ni and has an olivine-type structure. Since the charge-discharge capacity may decrease if the substitution amount at the Co site is large, it is preferably 0 < x ≦ 0.5, more preferably 0 < x ≦ 0.3. When x ≦ 0.3, excellent characteristics in both charge-discharge capacity and cycle characteristics can be obtained. As an example, the positive electrode active material 11 is LiCo 0.9 Ni 0.1 PO 4 、LiCo 0.9 Zn 0.1 PO 4 、LiCo 0.8 Mg 0.2 PO 4 、LiCo 0.7 Ni 0.3 PO 4 、LiCo 0.7 Mg 0.1 Ni 0.1 Zn 0.1 PO 4 and so on.

[0028] 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-sintering 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.

[0029] 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.

[0030] If the content of the positive electrode active material 11 in the first internal electrode 10 is small, the volumetric 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 this embodiment, the area occupancy ratio of the positive electrode active material 11 in the cross section of the first internal electrode 10 is preferably 40% or more, more preferably 45% or more, and even more preferably 50% or more.

[0031] If the content of the positive electrode active material 11 in the first internal electrode 10 is large, the operation rate of the active material during charging and discharging 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 occupancy 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 further preferably 65% ​​or less.

[0032] 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 structure. This is because the phosphate-based solid electrolyte having a NASICON structure has the property of having a wide potential window on the high potential side and high atmospheric stability. Even if a phosphate-based solid electrolyte having a NASICON structure is used as the solid electrolyte 12, since the positive electrode active material 11 uses a phosphate containing Co, the chemical reaction between the positive electrode active material 11 and the solid electrolyte 12 during sintering can be suppressed. The solid electrolyte 12 can be, for example, the same as the main component solid electrolyte of the solid electrolyte layer 30.

[0033] In the first internal electrode 10, if the average particle size of the solid electrolyte 12 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 it easier for interdiffusion reactions to occur, which is not preferable. 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.

[0034] On the other hand, in the first internal electrode 10, if the average particle size of the solid electrolyte 12 is large, a high temperature is required for sintering and densification, which is not preferable. Therefore, it is preferable to set an upper limit on 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.

[0035] In the first internal electrode 10, if the content of the solid electrolyte 12 is small, the ion conduction path cannot be secured and the internal resistance becomes high, which is not preferable. Therefore, it is preferable to set a lower limit for the content of the solid electrolyte 12. In this embodiment, the area occupancy 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.

[0036] In the first internal electrode 10, if the content of the solid electrolyte 12 is large, the active material filling amount cannot be increased and the capacity decreases, 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 occupancy 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.

[0037] The thickness of each first internal electrode 10 is, for example, not less than 1 μm and not more than 100 μm, not less than 5 μm and not more than 50 μm, or not less than 10 μm and not more than 30 μm.

[0038] 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, + The negative electrode active material is preferably one that operates at the following average potential: For example, TiO 2 Such negative electrode active materials include Ti-Nb-Ta-O and Al-Nb-Ta-O compounds. + 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.

[0039] The solid electrolyte 22 in the second internal electrode 20 is not particularly limited, but is preferably a phosphate-based solid electrolyte having a NASICON structure. This is because the phosphate-based solid electrolyte having a NASICON structure has 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.

[0040] In the second internal electrode 20, if the average particle size of the solid electrolyte 22 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 it easier for interdiffusion reactions to occur, which is not preferable. 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.

[0041] On the other hand, in the second internal electrode 20, if the average particle size of the solid electrolyte 22 is large, a high temperature is required for sintering and densification, which is not preferable. Therefore, it is preferable to set an upper limit on 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.

[0042] In the second internal electrode 20, if the content of the solid electrolyte 22 is small, the ion conduction path cannot be secured and the internal resistance increases, which is not preferable. Therefore, it is preferable to set a lower limit for the content of the solid electrolyte 22. In this embodiment, the area occupancy 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.

[0043] In the second internal electrode 20, if the content of the solid electrolyte 22 is large, the active material filling amount cannot be increased and the capacity decreases, which is not preferable. Therefore, it is preferable to set an upper limit on the content of the solid electrolyte 22. In this embodiment, the area occupancy 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.

[0044] The thickness of each second internal electrode 20 is, for example, not less than 1 μm and not more than 100 μm, not less than 5 μm and not more than 50 μm, or not less than 10 μm and not more than 30 μm.

[0045] The first internal electrode 10 and the second internal electrode 20 may include a conductive material (conductive assistant). A carbon material or the like may be used as the conductive assistant. A metal may be used as the conductive assistant. Examples of the metal of the conductive assistant include Pd, Ni, Cu, Fe, and alloys containing these metals.

[0046] The average particle size of the electrode active material and the 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 of the internal electrode is processed from a direction substantially perpendicular to the lamination thickness direction of the all-solid-state battery using a cross-section polisher (CP) or the like. Next, for example, a scanning electron microscope (manufactured by Hitachi High-Tech Corporation, model: SU-7000) is used for observation at an acceleration voltage of 5 kV, and the electrode active material particles and the solid electrolyte particle regions in the internal electrode are identified by 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 or more particle sizes 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.

[0047] The area occupancy rates of the electrode active material and the 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 of the internal electrode is processed from a direction substantially perpendicular to the lamination thickness direction of the all-solid-state battery using a cross-section polisher (CP) or the like. Next, for example, a scanning electron microscope (manufactured by Hitachi High-Tech Corporation, model: SU-7000) is used for observation at an acceleration voltage of 5 kV, and 10 points are obtained by the same magnification of the backscattered electron image of the internal electrode and elemental analysis by SEM-EDS. Using image analysis software, the areas of the electrode active material and the solid electrolyte occupying the acquired image can be identified, and the arithmetic average value of each occupancy rate can be calculated.

[0048] The thickness of each layer can be measured by using a cross-section polisher (CP) or the like to cut a cross section from a direction approximately perpendicular to the stack thickness direction of the all-solid-state battery, observing the cross section at an accelerating voltage of 5 kV using, for example, a scanning electron microscope (manufactured by Hitachi High-Tech Corporation, model: SU-7000), measuring backscattered electron images and elemental analysis by SEM-EDS at 10 points to distinguish the interface of each layer, and calculating the arithmetic average value of the 10 points on each layer.

[0049] (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 upper and lower surfaces at the ends in the stacking direction. The two side surfaces may be two adjacent side surfaces, or may be 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).

[0050] 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.

[0051] 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 a solid electrolyte layer 30 interposed therebetween. The edges of the plurality of first internal electrodes 10 are exposed to the first end face of the stacked chip 60, but are not exposed to the second end face. The edges of the plurality of second internal electrodes 20 are exposed to the second end face of the stacked chip 60, but are not exposed to the first end face. As a result, the first internal electrodes 10 and the second internal electrodes 20 are alternately conductive to the first external electrode 40a and the second external electrode 40b. The solid electrolyte layer 30 extends from the first external electrode 40a to the second external electrode 40b. In this way, the all-solid-state battery 100a has a structure in which a plurality of battery units are stacked.

[0052] 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, the upper surface of the uppermost first internal electrode 10). In addition, a cover layer 50 is laminated on the lower surface of the laminated structure (in the example of FIG. 3, the lower surface of the lowermost first internal electrode 10). The cover layer 50 is made of an inorganic material containing, for example, Al, Zr, Ti, etc. (for example, Al 2 O 3 , ZrO 2 , TiO 2 The cover layer 50 may contain the main component of the solid electrolyte layer 30 as a main component.

[0053] The first internal electrode 10 and the second internal electrode 20 may include a current collector layer. For example, as illustrated in FIG. 4, a first current collector layer 13 may be provided in the first internal electrode 10. Also, a second current collector layer 23 may be provided in 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, etc. can be used as the conductive material of the first current collector layer 13 and the second current collector layer 23. The current collection efficiency is improved by 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.

[0054] 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.

[0055] (Process for producing raw powder for solid electrolyte layer) First, raw material powder for the solid electrolyte layer constituting the above-mentioned 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 by using a solid-phase synthesis method or the like. The obtained raw material powder can be dry-pulverized to adjust the average particle size to a desired size. For example, ZrO 2 The powder is adjusted to the desired average particle size using a planetary ball mill.

[0056] (Cover layer raw powder preparation process) Next, the raw material powder of the ceramics that constitutes the above-mentioned cover layer 50 is prepared. For example, the raw material powder for the cover layer can be prepared by mixing the raw materials, additives, etc., and using a solid-phase synthesis method or the like. The obtained raw material powder can be dry-pulverized to adjust the average particle size to a desired size. For example, ZrO 2 The powder is adjusted to a desired average particle size using a planetary ball mill. When 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.

[0057] (Internal electrode paste manufacturing process) Next, the internal electrode paste for producing the first internal electrode 10 and the second internal electrode 20 is separately produced. For example, the internal electrode paste can be obtained by uniformly dispersing a conductive assistant, an electrode active material, a solid electrolyte material, a sintering assistant, a binder, a plasticizer, and the like in water or an organic solvent. The above-mentioned solid electrolyte paste may be used as the solid electrolyte material. A carbon material or the like is used as the conductive assistant. A metal may be used as the conductive assistant. Examples of the metal of the conductive assistant include Pd, Ni, Cu, Fe, and alloys containing these. Pd, Ni, Cu, Fe, alloys containing these, and various carbon materials may also be used.

[0058] The sintering aid in 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.

[0059] (External electrode paste manufacturing process) Next, an external electrode paste for producing the above-mentioned first external electrode 40a and second external electrode 40b is prepared. For example, the external electrode paste can be obtained by uniformly dispersing a conductive material, a glass frit, a binder, a plasticizer, etc. in water or an organic solvent.

[0060] (Solid electrolyte green sheet manufacturing process) The raw material powder for the solid electrolyte layer is uniformly dispersed in an aqueous or organic solvent together with a binder, a dispersant, a plasticizer, etc., and wet-pulverized to obtain a solid electrolyte slurry having a desired average particle size. At this time, a bead mill, a wet jet mill, various kneaders, a high-pressure homogenizer, etc. can be used, and it is preferable to use a bead mill from the viewpoint of simultaneously adjusting the particle size distribution and dispersing. A binder is added to the obtained solid electrolyte slurry to obtain a solid electrolyte paste. The obtained solid electrolyte paste is coated to produce a solid electrolyte green sheet 51. The coating method is not particularly limited, and a slot die method, a reverse coat method, a gravure coat method, a bar coat method, a doctor blade method, etc. can be used. The particle size distribution after wet-pulverization can be measured, for example, using a laser diffraction measurement device using a laser diffraction scattering method.

[0061] (Lamination process) As illustrated in FIG. 6(a), the internal electrode paste 52 is printed on one side of the solid electrolyte green sheet 51. In the area on the solid electrolyte green sheet 51 where the internal electrode paste 52 is not printed, the reverse pattern 53 is printed. The reverse pattern 53 can be the same as the solid electrolyte green sheet 51. The printed solid electrolyte green sheets 51 are alternately shifted and stacked. As illustrated in FIG. 6(b), the cover sheets 54 are pressed from above and below in the stacking direction to obtain a laminate. In this case, a laminate having a substantially rectangular parallelepiped shape is obtained so that the internal electrode paste 52 for the first internal electrode 10 is exposed on one end surface of the laminate and the internal electrode paste 52 for the second internal electrode 20 is exposed on the other end surface of the laminate. The cover sheet 54 can be formed by applying the raw material powder for the cover layer in the same manner as in the solid electrolyte green sheet preparation process. The cover sheet 54 is formed to be thicker than the solid electrolyte green sheet 51. The thickness may be increased during coating, or by stacking a number of coated sheets.

[0062] Next, the external electrode paste 55 is applied to each of the two end faces by a dipping method or the like, and then dried. This provides a molded body for forming the all-solid-state battery 100a.

[0063] (Firing process) Next, the obtained laminate is fired. The firing conditions are not particularly limited, and may be in an oxidizing or non-oxidizing atmosphere, and the maximum temperature is preferably 400°C to 1000°C, more preferably 500°C to 900°C, etc. In order to sufficiently remove the binder before the maximum temperature is reached, a step of maintaining the temperature in an oxidizing atmosphere at a temperature lower than the maximum temperature may be provided. In order to reduce process costs, it is desirable to fire at as low a temperature as possible. After firing, a reoxidation treatment may be performed. Through the above steps, an all-solid-state battery 100a is produced.

[0064] In addition, a collector layer can be formed in the first internal electrode 10 and the second internal electrode 20 by sequentially stacking an internal electrode paste, a collector paste containing a conductive material, and an internal electrode paste. EXAMPLES

[0065] An all-solid-state battery was fabricated according to the embodiment below, and its characteristics were examined.

[0066] Example 1 The positive electrode is made of LiCo with an average particle size of 0.60 μm. 0.9 Ni 0.1 PO 4 The positive electrode active material is Li-Al-Co-Ge-PO 4 A NASICON-type phosphate-based glass solid electrolyte was used. A positive electrode paste with a weight ratio of positive electrode active material, carbon conductive assistant, and solid electrolyte of 45:10:45 was prepared and printed on a solid electrolyte sheet.

[0067] The negative electrode is made of TiTa with an average particle size adjusted to 1.00 μm. 2-x Nb x O 7-δ The negative electrode active material is Li-Al-Ge-PO4 A negative electrode paste with a weight ratio of negative electrode active material, carbon conductive assistant, and solid electrolyte of 35:10:55 was prepared and printed on a solid electrolyte sheet.

[0068] The positive electrode printed sheet piece and the negative electrode printed sheet piece were laminated together with the reference electrode sheet piece and pressed to produce a molded body. The molded body was fired multiple times at a specified environment and temperature to produce an all-solid-state battery with a reference electrode.

[0069] Example 2 The positive electrode is LiCo with an average particle size adjusted to 0.60 μm. 0.9 Zinc 0.1 PO 4 An all-solid-state battery was produced in the same manner as in Example 1, except that a positive electrode active material was used.

[0070] Example 3 The positive electrode is LiCo with an average particle size adjusted to 0.60 μm. 0.8 Mg 0.2 PO 4 An all-solid-state battery was produced in the same manner as in Example 1, except that a positive electrode active material was used.

[0071] Example 4 The positive electrode is LiCo with an average particle size adjusted to 0.60 μm. 0.7 Ni 0.3 PO 4 An all-solid-state battery was produced in the same manner as in Example 1, except that a positive electrode active material was used.

[0072] Example 5 The positive electrode is LiCo with an average particle size adjusted to 0.60 μm. 0.7 Mg 0.1 Ni 0.1 Zinc 0.1 PO 4 An all-solid-state battery was produced in the same manner as in Example 1, except that a positive electrode active material was used.

[0073] Comparative Example 1 The positive electrode is LiCoPO with an average particle size adjusted to 0.60 μm. 4An all-solid-state battery was produced and evaluated in the same manner as in Example 1, except that a positive electrode active material was used.

[0074] (Cycle characteristics) Next, the capacity retention rate after repeated charging and discharging was measured for each of Examples 1 to 5 and Comparative Example 1. The charging and discharging test was performed in a thermostatic chamber at 25° C. with a current of 0.2 C rate and a 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 1. The results are shown in Fig. 7. As shown in Fig. 7, compared with Comparative Example 1, the discharge capacity retention rates of Examples 1 to 5 were maintained high.

[0075] For example, in Example 1, the discharge capacity retention rate after 30 cycles based on the initial discharge capacity was 65.1%. In Example 2, the discharge capacity retention rate after 30 cycles based on the initial discharge capacity was 65.0%. In Example 3, the discharge capacity retention rate after 30 cycles based on the initial discharge capacity was 79.7%. In Example 4, the discharge capacity retention rate after 30 cycles based on the initial discharge capacity was 94.1%. In Example 5, the discharge capacity retention rate after 30 cycles based on the initial discharge capacity was 89.1%. In Comparative Example 1, the discharge capacity retention rate after 30 cycles based on the initial discharge capacity was 60.7%. The results are shown in Table 1. [Table 1]

[0076] As described above, the discharge capacity retention rates of Examples 1 to 5 were higher than that of Comparative Example 1. This is believed to be because the use of a positive electrode active material that is a Co-containing phosphate in which a portion of the Co sites is substituted with at least one of Mg, Zn, and Ni suppresses volumetric changes during charging and discharging.

[0077] (open circuit voltage) Furthermore, for Examples 1 to 5 and Comparative Example, the open circuit potential (V) after the first charge and ΔV (mV) = charge cutoff potential - open circuit potential after the first charge were measured. A small ΔV indicates a small energy loss at the end of charge. Compared to the Comparative Example, ΔV was small in Examples 1 to 5. This is considered to be because the oxidation resistance of the solid electrolyte was improved by the reaction between the solid electrolyte and the positive electrode active material with element substitution during co-sintering. This result leads to an improvement in the cycle characteristics by improving the oxidation resistance of the solid electrolyte.

[0078] 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 described in the claims. [Explanation of symbols]

[0079] 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 collector layer 30 Solid electrolyte layer 40a First external electrode 40b 2nd external electrode 50 Cover Layer 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 layer including a positive electrode active material that is a phosphate containing Co, in which a part of the Co site is substituted with at least one of Mg, Zn, and Ni; a negative electrode layer including a negative electrode active material; a solid electrolyte layer sandwiched between the positive electrode layer and the negative electrode layer.

2. The positive electrode active material has the general formula LiCo １－ｘ M ｘ P.O. ４ 2. The all-solid-state battery according to claim 1, wherein x is represented by the formula: 0<x≦0.5, and M is at least one of Mg, Zn, and Ni, and has an olivine structure.

3. 2. The all-solid-state battery according to claim 1, 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.

4. 2. The all-solid-state battery according to claim 1, wherein an area occupancy ratio of the positive electrode active material in a cross section of the positive electrode layer is 40% or more and 75% or less.

5. The all-solid-state battery according to claim 1 , wherein the positive electrode layer contains a phosphate-based solid electrolyte having a NASICON type structure.

6. 6. The all-solid-state battery according to claim 5, 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.

7. 6. The all-solid-state battery according to claim 5, wherein an area occupancy ratio of the phosphate-based solid electrolyte in the positive electrode layer is 20% or more and 75% or less.

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

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