All-solid-state battery

Abstract

Provided is an all-solid-state battery capable of achieving excellent cycle characteristics. The all-solid-state battery includes: a positive electrode layer including a positive electrode active material, the positive electrode active material being a phosphate containing Co, a part of the Co site being substituted by at least one of Mg, Zn, and Ni; 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.

Description

Technical Field

[0001] The present invention relates to an all-solid-state battery. Background Art

[0002] In recent years, secondary batteries have been used in various fields. Secondary batteries using electrolytes have problems such as leakage of the electrolyte. Therefore, all-solid batteries with solid electrolytes and other components also made of solids have been developed. For example, the application of LiCoPO 4 An integrally sintered all-solid-state battery having a positive electrode active material (for example, refer to Patent Document 1).

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Publication No. 2023-41135

[0006] Non-patent literature

[0007] Non-patent document 1: “Mixed LiCo 0.6 M 0.4 PO 4 (M=Mn, Fe, Ni)phosphates: cyclingmechanism and thermal stability", Physical Chemistry Chemical Physics, 2009, 11, 3271-3277

[0008] Non-patent document 2: “Identifying the Structure of the Intermediate, Li 2 / 3 CoPO 4 ,Formed during Electrochemical Cycling of LiCoPO 4 ”,CHEMISTRY OF MATERIALS,2014,26,6193-6205 Summary of the invention

[0009] Technical problem to be solved by the invention

[0010] All-solid batteries are required to have excellent cycle characteristics, but all-solid batteries may suffer from poor charge and discharge cycles.

[0011] The present invention has been made in view of the above-mentioned technical problems, and an object of the present invention is to provide an all-solid-state battery capable of achieving excellent cycle characteristics.

[0012] Technical solution for solving technical problems

[0013] The all-solid-state battery of the present invention includes: a positive electrode layer containing a positive electrode active material, the positive electrode active material being a phosphate containing Co, and a part of the Co sites being replaced by at least one of Mg, Zn, and Ni; 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.

[0014] In the above 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, and the above M is at least one of Mg, Zn, or Ni, having an olivine structure.

[0015] In the positive electrode layer of the above all-solid-state battery, the average particle size of the positive electrode active material can be 0.05 μm or more and 5.00 μm or less.

[0016] In the cross-section of the positive electrode layer of the above all-solid-state battery, the area occupancy ratio of the positive electrode active material can be 40% or more and 75% or less.

[0017] In the above all-solid-state battery, the positive electrode layer may include a phosphate-based solid electrolyte having a NASICON structure.

[0018] In the positive electrode layer of the above all-solid-state battery, the average particle size of the phosphate-based solid electrolyte can be 0.1 μm or more and 10.0 μm or less.

[0019] In the positive electrode layer of the above all-solid-state battery, the area occupancy ratio of the phosphate-based solid electrolyte can be 20% or more and 75% or less.

[0020] In the above all-solid-state battery, the thickness of the positive electrode layer can be 1 μm or more and 100 μm or less.

[0021] Advantages of the invention

[0022] According to the present invention, an all-solid-state battery capable of achieving excellent cycle characteristics can be provided. Description of the drawings

[0023] Figure 1 is a schematic cross-sectional view showing the basic structure of an all-solid-state battery.

[0024] Figure 2 is a schematic cross-sectional view showing the details of the positive electrode layer and the negative electrode layer.

[0025] Figure 3 is a schematic cross-sectional view of a stacked all-solid-state battery.

[0026] Figure 4 It is a schematic cross-sectional view of another stacked-type all-solid-state battery.

[0027] Figure 5 This is a diagram illustrating the flow of a method for manufacturing an all-solid-state battery.

[0028] Figure 6 (a) and (b) are diagrams illustrating the lamination process.

[0029] Figure 7 It is a graph showing the measurement results of the cycle characteristics.

[0030] Description of Reference Numerals

[0031] 10First internal electrode

[0032] 11Positive electrode active material

[0033] 12 Solid Electrolyte

[0034] 13. First current collector layer

[0035] 20 Second internal electrode

[0036] 21 Negative electrode active material

[0037] 22 Solid Electrolyte

[0038] 23 Second current collector layer

[0039] 30 Solid electrolyte layer

[0040] 40a First external electrode

[0041] 40b Second external electrode

[0042] 50 Overlay

[0043] 51 Solid Electrolyte Green Sheet

[0044] 52 Internal electrode paste

[0045] 53 Reverse pattern

[0046] 54 Cover Sheet

[0047] 55 External electrode paste

[0048] 60 layers

[0049] 100, 100a all-solid-state battery. DETAILED DESCRIPTION

[0050] Hereinafter, embodiments will be described with reference to the drawings.

[0051] (Implementation Method)

[0052] Figure 1 Schematic cross-sectional view showing the basic structure of the all-solid-state battery 100 according to the embodiment. Figure 1 As shown in the example, the all-solid 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 a powder material is sintered.

[0053] When the all-solid 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.

[0054] Figure 2 1 is a diagram illustrating details of a cross section of the first internal electrode 10 and the second internal electrode 20. Figure 2 As shown in the example, 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 and the like 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 and the like 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 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 ion conductivity is obtained in the first internal electrode 10 and the second internal electrode 20. The first internal electrode 10 and the second internal electrode 20 include a conductive additive, so that conductivity is obtained in the first internal electrode 10 and the second internal electrode 20.

[0055] 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 (sodium ion superconductor) structure. The phosphate-based solid electrolyte is, for example, a lithium-containing phosphate. The phosphate is not particularly limited, and examples thereof include a composite lithium phosphate salt (e.g., LiTi) with Ti. 2 (PO 4 ) 3) etc. Alternatively, part or all of Ti may be replaced by a tetravalent transition metal such as Ge, Sn, Hf, Zr, etc. In addition, in order to increase the Li content, part of the Ti may be replaced by a trivalent transition metal such as Al, Ga, In, Y, La, etc. More specifically, for example, Li 1+x Al x Ge 2-x (PO 4 ) 3 , Li 1+x Al x Zr 2-x (PO 4 ) 3 , Li 1+x Al x Ti 2-x (PO 4 ) 3 For example, it may be Li—Al—Co—Ge—PO4 to which Co is preliminarily added, similar to the Co-containing phosphate-based solid electrolyte contained in the first internal electrode 10 used as the positive electrode. 4 Such materials may not contain Co.

[0056] 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 ion conductivity by sintering have advantages over electrolytes and other solid electrolytes, such as a wide potential window and relatively stable in the atmosphere. In particular, phosphate-based solid electrolytes with a NASICON-type structure are oxide-based solid electrolytes with a wide potential window on the high potential side and high atmospheric stability.

[0057] The thickness of solid electrolyte layer 30 is, for example, 0.5 μm to 30 μm, 1 μm to 20 μm, or 2 μm to 10 μm.

[0058] Here, the positive electrode active material of the first internal electrode 10 is studied. The positive electrode active material is preferably a material that is not easy to react chemically with the solid electrolyte even during sintering at high temperature. Therefore, it is considered to use a Co-containing phosphate positive electrode active material. For example, it is considered to use LiCoPO 4 As positive electrode active material. However, LiCoPO 4 Since the volume change during charge and discharge is large, there is a possibility that excellent cycle characteristics cannot be obtained. Therefore, the all-solid-state battery 100 of this embodiment has a structure that can achieve high cycle characteristics. The details are described below.

[0059] The inventors of the present invention have studied the structure that can suppress the volume change during charge and discharge and the degradation of cycle characteristics in Co-containing phosphate positive electrode active materials. Through in-depth research by the inventors of the present invention, it was found that in Co-containing phosphate positive electrode active materials, by replacing the Co site with other elements, the volume change during charge and discharge can be suppressed, and the degradation of the cycle characteristics of the all-solid-state battery can be suppressed. Specifically, it was found that as the positive electrode active material 11, by using a phosphate containing Co and an active material in which a part of the Co site is replaced by at least one of Mg, Zn and Ni, the volume change during charge and discharge is greater than that of LiCoPO 4 Small, excellent cycle characteristics can be achieved.

[0060] In addition, the oxidation resistance of the solid electrolyte is improved by the reaction between the positive electrode active material and the solid electrolyte after element substitution during co-sintering. The oxidation resistance of the solid electrolyte is improved, and the cycle characteristics are further improved. For example, the oxidation resistance of the solid electrolyte of the solid electrolyte layer 30 is improved. In addition, when the first internal electrode 10 includes a solid electrolyte, the oxidation resistance of the solid electrolyte included in the first internal electrode 10 is improved.

[0061] The positive electrode active material 11 is, for example, LiCo 1-x M x PO 4 M is at least one of Mg, Zn or Ni and has an olivine structure. If the amount of substitution at the Co site is large, the charge and discharge capacity may decrease, so it is preferably 0<x≤0.5, and more preferably 0<x≤0.3. When x≤0.3, both the charge and discharge capacity and the cycle characteristics can be excellent. 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 wait.

[0062] In the first internal electrode 10, if the average particle size of the positive electrode active material 11 is small, a side reaction may occur during the integral 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 further preferably 0.10 μm or more.

[0063] 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 on 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 further preferably 0.50 μm or less.

[0064] In the first internal electrode 10, if the content of the positive electrode active material 11 is small, the volume capacity density of the positive electrode may be reduced. 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 of the positive electrode active material 11 is preferably 40% or more, more preferably 45% or more, and further preferably 50% or more.

[0065] In the first internal electrode 10, if the content of the positive electrode active material 11 is high, the utilization rate of the active material during charge and discharge may be reduced. Therefore, it is preferable to set an upper limit on 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 75% or less, more preferably 70% or less, and further preferably 65% ​​or less.

[0066] The solid electrolyte 12 of the first internal electrode 10 is not particularly limited, and is preferably a phosphate solid electrolyte having a NASICON structure. This is because the phosphate solid electrolyte having a NASICON structure has the properties of a wide potential window on the high potential side and high atmospheric stability. In addition, even if a phosphate 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 can be suppressed during sintering. The solid electrolyte 12 can be the same as the main component solid electrolyte of the solid electrolyte layer 30, for example.

[0067] 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, it is difficult to obtain a dense coating film, and the reactivity during the heat treatment of the all-solid battery 100 increases, and mutual diffusion reactions are likely to occur, so it is not preferred. Therefore, it is preferred to set a lower limit for the average particle size of the solid electrolyte 12 in the first internal electrode 10. In the present 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 further preferably 0.3 μm or more.

[0068] On the other hand, in the first internal electrode 10, if the average particle size of the solid electrolyte 12 is large, high temperature is required for sintering densification, which is not preferred. Therefore, it is preferred to set an upper limit on the average particle size of the solid electrolyte 12 in the first internal electrode 10. In the present 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 further preferably 5.0 μm or less.

[0069] In the first internal electrode 10, if the content of the solid electrolyte 12 is small, the ion conduction path cannot be ensured, and the internal resistance becomes high, which is not preferred. Therefore, it is preferred to set a lower limit for the content of the solid electrolyte 12. In the present embodiment, in the cross section of the first internal electrode 10, the area occupancy ratio occupied by the solid electrolyte 12 is preferably 15% or more, more preferably 20% or more, and further preferably 25% or more.

[0070] In the first internal electrode 10, if the content of the solid electrolyte 12 is too high, the active material filling amount cannot be increased, and the capacity is reduced, which is not preferred. Therefore, it is preferred to set an upper limit on the content of the solid electrolyte 12. In the present embodiment, in the cross section of the first internal electrode 10, the area occupancy ratio occupied by the solid electrolyte 12 is preferably 75% or less, more preferably 70% or less, and further preferably 65% ​​or less.

[0071] 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.

[0072] The negative electrode active material 21 included 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 to have a negative electrode active material at 2V vs. Li / Li + The negative electrode active material that works at the following average potential. For example, TiO 2 , Ti-Nb-Ta-O, Al-Nb-Ta-O compounds, etc. Such negative electrode active materials are 4.7V vs.Li / Li +When the positive electrode active materials having the above operating potentials are combined, the operating voltage of the all-solid-state battery 100 can be increased.

[0073] The solid electrolyte 22 of the second internal electrode 20 is not particularly limited, but is preferably a phosphate solid electrolyte having a NASICON structure. This is because a phosphate solid electrolyte having a NASICON structure has a wide potential window on the high potential side and high atmospheric stability. The solid electrolyte 22 may be the same as the main component solid electrolyte of the solid electrolyte layer 30, for example.

[0074] 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, it is difficult to obtain a dense coating film, and the reactivity during the heat treatment of the all-solid battery 100 increases, and mutual diffusion reactions are likely to occur, so it is not preferred. Therefore, it is preferred to set a lower limit for the average particle size of the solid electrolyte 22 in the second internal electrode 20. In the present 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 further preferably 0.5 μm or more.

[0075] On the other hand, in the second internal electrode 20, if the average particle size of the solid electrolyte 22 is large, high temperature is required for sintering densification, which is not preferred. Therefore, it is preferred to set an upper limit on the average particle size of the solid electrolyte 22 in the second internal electrode 20. In the present 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 further preferably 5.0 μm or less.

[0076] In the second internal electrode 20, if the content of the solid electrolyte 22 is small, the ion conduction path cannot be ensured, and the internal resistance becomes high, which is not preferred. Therefore, it is preferred to set a lower limit for the content of the solid electrolyte 22. In the present embodiment, in the cross section of the second internal electrode 20, the area occupancy ratio occupied by the solid electrolyte 22 is preferably 15% or more, more preferably 20% or more, and further preferably 25% or more.

[0077] In the second internal electrode 20, if the content of the solid electrolyte 22 is too much, the active material filling amount cannot be increased, and the capacity is reduced, which is not preferred. Therefore, it is preferred to set an upper limit on the content of the solid electrolyte 22. In the present embodiment, in the cross section of the second internal electrode 20, the area occupancy ratio occupied by the solid electrolyte 22 is preferably 75% or less, more preferably 70% or less, and further preferably 65% ​​or less.

[0078] The thickness of each second inner 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.

[0079] In addition, the first internal electrode 10 and the second internal electrode 20 may also include a conductive material (conductive aid). As the conductive aid, a carbon material or the like may be used. As the conductive aid, a metal may be used. Examples of the metal of the conductive aid include Pd, Ni, Cu, Fe, and alloys thereof.

[0080] 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 polisher (CP) or the like is used to expose the cross section of the internal electrode in a direction approximately perpendicular to the stacking thickness direction of the all-solid-state battery. Next, for example, a scanning electron microscope (manufactured by Hitachi High-Tech Co., Ltd., model: SU-7000) is used for observation at an accelerating voltage of 5 kV, and the area of ​​the electrode active material particles and the solid electrolyte particles in the internal electrode is determined by SEM images at a magnification of 10,000 times and elemental analysis based on SEM-EDS. Observe more than 10 places, and for the electrode active material particles and solid electrolyte particles determined, select the particles that exist in isolation from other particles, and obtain at least 10 or more particle sizes. Next, use image analysis software to measure the particle area of ​​each selected particle, measure the equivalent circle diameter (Heywood diameter) based on the particle area, and calculate the median particle size (D50 value) of each particle based on the particle size distribution obtained by plotting the particle size on the x-axis and the frequency on the y-axis, which can be defined as the average particle size of each particle.

[0081] In addition, the area occupancy 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, the cross-section exposure processing of the internal electrode is performed from a direction approximately perpendicular to the stacking thickness direction of the all-solid-state battery using a cross-section polisher (CP) or the like. Then, for example, a scanning electron microscope (manufactured by Hitachi High-Tech Co., Ltd., model: SU-7000) is used for observation at an accelerating voltage of 5 kV to obtain reflected electron images of 10 internal electrodes at the same magnification and elemental analysis based on SEM-EDS. Using image analysis software, the areas of the electrode active material and the solid electrolyte occupying the acquired image can be determined, and the arithmetic mean of each area occupancy rate can be used for calculation.

[0082] In addition, the thickness of each layer can be calculated as follows: using a cross-section polisher (CP) or the like, cross-section exposure processing is performed in a direction roughly perpendicular to the stacking thickness direction of the all-solid-state battery. For example, a scanning electron microscope (manufactured by Hitachi High-Tech Co., Ltd., model: SU-7000) can be used for observation at an acceleration voltage of 5 kV, and reflected electron images at 10 locations and elemental analysis based on SEM-EDS are measured to determine the interface of each layer, and the calculation is based on the arithmetic mean of the 10 locations in each layer.

[0083] (Laminar all-solid-state battery)

[0084] Figure 3 It is a schematic cross-sectional view of a stacked all-solid battery 100a in which a plurality of unit batteries are stacked. The all-solid battery 100a includes a stacking sheet 60 having a substantially rectangular shape. In the stacking sheet 60, a first external electrode 40a and a second external electrode 40b are provided in a manner that contacts two of the four surfaces other than the upper surface and the lower surface at the end of the stacking direction, i.e., two side surfaces. The two side surfaces may be two adjacent side surfaces or two side surfaces opposite to each other. In the present embodiment, a first external electrode 40a and a second external electrode 40b are provided in a manner that contacts two side surfaces opposite to each other (hereinafter referred to as two end surfaces).

[0085] In the following description, portions having the same composition range, the same thickness range, and the same particle size distribution range as those of the all-solid-state battery 100 are denoted by the same reference numerals, and detailed description thereof is omitted.

[0086] In the all-solid 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 therebetween. The end edges of the plurality of first internal electrodes 10 are exposed at the first end face of the laminate sheet 60, but not at the second end face. The end edges of the plurality of second internal electrodes 20 are exposed at the second end face of the laminate sheet 60, but not at the first end face. Thus, the first internal electrode 10 and the second internal electrode 20 are alternately conductive with the first external electrode 40a and the second external electrode 40b. In addition, the solid electrolyte layer 30 extends from the first external electrode 40a to the second external electrode 40b. In this way, the all-solid battery 100a has a structure in which a plurality of unit cells are stacked.

[0087] On the upper surface (at the Figure 3 In the example of the upper surface of the first internal electrode 10 of the uppermost layer, a cover layer 50 is stacked. Figure 3The cover layer 50 is also stacked on the lower surface of the first internal electrode 10 (in the example of the lowermost layer). The cover layer 50 is made of an inorganic material (for example, Al2O3) containing Al, Zr, Ti, etc. 2 O 3 、ZrO 2 、TiO 2 The covering layer 50 may contain the main component of the solid electrolyte layer 30 as a main component.

[0088] The first internal electrode 10 and the second internal electrode 20 may include a current collector layer. Figure 4 As shown in the example, the first collector layer 13 may be provided in the first internal electrode 10. In addition, the second collector layer 23 may be provided in the second internal electrode 20. The first collector layer 13 and the second 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 collector layer 13 and the second collector layer 23. By connecting the first collector layer 13 to the first external electrode 40a and connecting the second collector layer 23 to the second external electrode 40b, the current collection efficiency is improved.

[0089] Next, Figure 3 A method for manufacturing the all-solid-state battery 100a exemplified in FIG. 1 is described. Figure 5 It is a diagram illustrating the flow of a method for manufacturing the all-solid-state battery 100 a.

[0090] (Step of preparing raw material powder for solid electrolyte layer)

[0091] First, a raw material powder for a solid electrolyte layer constituting the solid electrolyte layer 30 is prepared. For example, the raw material powder for the solid electrolyte layer can be prepared by mixing raw materials, additives, etc. and using a solid phase synthesis method. The obtained raw material powder can be adjusted to a desired average particle size by dry pulverizing. For example, by using 5 mm φ ZrO 2 The balls of the planetary ball mill are adjusted to the desired average particle size.

[0092] (Process for producing raw material powder for covering layer)

[0093] Next, a raw material powder of the ceramic constituting the above-mentioned covering layer 50 is prepared. For example, the raw material powder for the covering layer can be prepared by mixing raw materials, additives, etc. and using a solid phase synthesis method. The obtained raw material powder can be adjusted to a desired average particle size by dry grinding. For example, by using 5 mmφ ZrO 2 The balls of the planetary ball mill are adjusted to a desired average particle size. 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 interchangeably.

[0094] (Internal electrode paste preparation process)

[0095] Next, internal electrode pastes for making the first internal electrode 10 and the second internal electrode 20 are prepared respectively. For example, the internal electrode paste can be obtained by uniformly dispersing a conductive aid, an electrode active material, a solid electrolyte material, a sintering aid, a binder, a plasticizer, etc. in water or an organic solvent. As a solid electrolyte material, the above-mentioned solid electrolyte paste can be used. As a conductive aid, a carbon material or the like is used. As a conductive aid, a metal can be used. As a metal of a conductive aid, Pd, Ni, Cu, Fe, alloys containing them, etc. can be exemplified. Pd, Ni, Cu, Fe, alloys containing them, various carbon materials, etc. can also be further used.

[0096] The sintering aid of the internal electrode paste may include, for example, a glass component containing any one or more of Li-BO based compounds, Li-Si-O based compounds, Li-CO based compounds, Li-SO based compounds, and Li-PO based compounds.

[0097] (External electrode paste preparation process)

[0098] Next, an external electrode paste for forming 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.

[0099] (Solid Electrolyte Green Sheet Production Process)

[0100] The raw material powder for the solid electrolyte layer is uniformly dispersed in an aqueous solvent or an organic solvent together with a binding material, a dispersant, a plasticizer, etc., and wet-crushed to obtain a solid electrolyte slurry having a desired average particle size. At this time, a bead mill, a wet airflow mill, various kneading machines, a high-pressure homogenizer, etc. can be used. From the viewpoint that the particle size distribution can be adjusted and dispersed at the same time, a bead mill is preferably used. A binder is added to the obtained solid electrolyte slurry to obtain a solid electrolyte paste. By applying the obtained solid electrolyte paste, a solid electrolyte raw sheet 51 can be made. The coating method is not particularly limited, and a slit die method, a reverse coating method, a gravure coating method, a rod coating method, a scraper method, etc. can be used. The particle size distribution after wet crushing can be measured, for example, using a laser diffraction measuring device using a laser diffraction scattering method.

[0101] (Lamination process)

[0102] like Figure 6As shown in (a), an internal electrode paste 52 is printed on one side of a solid electrolyte green sheet 51. A reverse pattern 53 is printed in an area of ​​the solid electrolyte green sheet 51 where the internal electrode paste 52 is not printed. As the reverse pattern 53, the same pattern as that of the solid electrolyte green sheet 51 can be used. The printed plurality of solid electrolyte green sheets 51 are stacked in an alternating manner. Figure 6 As shown in (b), a laminate is obtained by pressing a cover sheet 54 from the top and bottom of the stacking direction. In this case, in the laminate, a substantially rectangular laminate is obtained in such a manner that the internal electrode paste 52 for the first internal electrode 10 is exposed on one end face and the internal electrode paste 52 for the second internal electrode 20 is exposed on the other end face. The cover sheet 54 can be formed by applying the raw material powder for the cover layer in the same way as the solid electrolyte green sheet production process. The cover sheet 54 is formed to be thicker than the solid electrolyte green sheet 51. It can be thickened during coating or by overlapping a plurality of coated sheets.

[0103] Next, the external electrode paste 55 is applied to both end surfaces by dipping or the like and then dried. In this way, a molded body for forming the all-solid-state battery 100a is obtained.

[0104] (Firing process)

[0105] Next, the obtained stack is fired. The firing conditions are not particularly limited, and examples thereof include an oxidizing atmosphere or a non-oxidizing atmosphere, with the maximum temperature preferably being 400°C to 1000°C, and more preferably 500°C to 900°C. In order to fully remove the binder until the maximum temperature is reached, a process of maintaining the temperature at a temperature lower than the maximum temperature in an oxidizing atmosphere may be provided. In order to reduce process costs, it is preferred to fire at as low a temperature as possible. After firing, reoxidation treatment may be performed. Through the above process, an all-solid-state battery 100a is generated.

[0106] Furthermore, by sequentially laminating the internal electrode paste, the collector paste containing a conductive material, and the internal electrode paste, it is possible to form a collector layer in the first internal electrode 10 and the second internal electrode 20 .

[0107] [Example]

[0108] Hereinafter, all-solid-state batteries were produced according to the embodiment and their characteristics were investigated.

[0109] (Example 1)

[0110] The positive electrode uses LiCo with an average particle size of 0.60 μm. 0.9 Ni 0.1 PO 4The positive electrode active material uses Li-Al-Co-Ge-PO as a solid electrolyte 4 NASICON-type phosphate glass solid electrolyte. Prepare a positive electrode paste with a weight ratio of positive electrode active material, carbon conductive additive and solid electrolyte of 45:10:45, and print it on a solid electrolyte sheet.

[0111] The negative electrode uses TiTa with an average particle size of 1.00 μm. 2-x Nb x O 7-δ The negative electrode active material uses Li-Al-Ge-PO as a solid electrolyte 4 A negative electrode paste having a weight ratio of 35:10:55 of negative electrode active material, carbon conductive additive and solid electrolyte is prepared and printed on a solid electrolyte sheet.

[0112] The positive electrode printed sheet and the negative electrode printed sheet are stacked together with the reference electrode sheet and pressed to produce a molded body. The produced molded body is fired multiple times in a predetermined environment and temperature to produce an all-solid-state battery with a reference electrode.

[0113] (Example 2)

[0114] The positive electrode uses LiCo with an average particle size of 0.60 μm. 0.9 Zn 0.1 PO 4 An all-solid-state battery was produced in the same manner as in Example 1 except for the change in the positive electrode active material.

[0115] (Example 3)

[0116] The positive electrode uses LiCo with an average particle size of 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 for the change in the positive electrode active material.

[0117] (Example 4)

[0118] The positive electrode uses LiCo with an average particle size of 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 for the change in the positive electrode active material.

[0119] (Example 5)

[0120] The positive electrode uses LiCo with an average particle size of 0.60 μm. 0.7 Mg 0.1 Ni 0.1 Zn 0.1PO 4 An all-solid-state battery was produced in the same manner as in Example 1 except for the change in the positive electrode active material.

[0121] (Comparative Example 1)

[0122] The positive electrode uses LiCoPO with an average particle size of 0.60 μm. 4 An all-solid-state battery was produced and evaluated in the same manner as in Example 1 except for the change in the positive electrode active material.

[0123] (Cycle Characteristics)

[0124] Next, the capacity retention rate after repeated charge and discharge was measured for Examples 1 to 5 and Comparative Example 1. The charge and discharge test was conducted in a thermostatic chamber at 25°C at a current rate of 0.2C at a potential of 4.30V to 5.05V vs Li / Li + The constant current charge and discharge test was carried out within the range of Figure 7 .like Figure 7 As shown, compared with Comparative Example 1, the discharge capacity retention rates of Examples 1 to 5 were maintained higher.

[0125] For example, in Example 1, the discharge capacity retention rate after 30 cycles based on the initial discharge capacity is 65.1%. In Example 2, the discharge capacity retention rate after 30 cycles based on the initial discharge capacity is 65.0%. In Example 3, the discharge capacity retention rate after 30 cycles based on the initial discharge capacity is 79.7%. In Example 4, the discharge capacity retention rate after 30 cycles based on the initial discharge capacity is 94.1%. In Example 5, the discharge capacity retention rate after 30 cycles based on the initial discharge capacity is 89.1%. In Comparative Example 1, the discharge capacity retention rate after 30 cycles based on the initial discharge capacity is 60.7%. The results are shown in Table 1.

[0126] Table 1

[0127]

[0128] As described above, the discharge capacity retention rates of Examples 1 to 5 are higher than that of Comparative Example 1. This is considered to be because the volume change during charge and discharge is suppressed by using a positive electrode active material containing Co phosphate and in which a portion of the Co site is substituted with at least one of Mg, Zn and Ni.

[0129] (Open circuit voltage)

[0130] In addition, for Examples 1 to 5 and Comparative Examples, the open circuit potential (V) after the initial charge and ΔV (mV) = charge cutoff potential - open circuit potential after the initial charge were measured. A smaller ΔV indicates a smaller energy loss at the end of the charge. Compared with the Comparative Examples, ΔV is smaller in Examples 1 to 5. It is believed that this is because the oxidation resistance of the solid electrolyte is improved by the reaction between the positive electrode active material and the solid electrolyte after element substitution during co-sintering. From this result, it can be seen that the cycle characteristics are improved by improving the oxidation resistance of the solid electrolyte.

[0131] As mentioned above, although the embodiment of the present invention is described in detail, the present invention is not limited to this specific embodiment, and various modifications and changes can be made within the scope of the gist of the present invention described in the claims.

Claims

1. An all-solid-state battery, characterized in that: include: A positive electrode layer including a positive electrode active material, wherein the positive electrode active material is a phosphate containing Co, and a portion of the Co site is substituted with at least one of Mg, Zn and Ni; a negative electrode layer comprising a negative electrode active material; and A solid electrolyte layer is sandwiched between the positive electrode layer and the negative electrode layer.

2. The all-solid-state battery according to claim 1, characterized in that: The positive electrode active material is represented by the general formula LiCo 1-x M x PO4, where 0 < x ≤ 0.5, and M is at least one of Mg, Zn, or Ni, and has an olivine structure.

3. The all-solid-state battery according to claim 1 or 2, characterized in that: In the positive electrode layer, an average particle size of the positive electrode active material is 0.05 μm or more and 5.00 μm or less.

4. The all-solid-state battery according to any one of claims 1 to 3, characterized in that: In a cross section of the positive electrode layer, an area occupancy ratio of the positive electrode active material is 40% or more and 75% or less.

5. The all-solid-state battery according to any one of claims 1 to 4, characterized in that: The positive electrode layer includes a phosphate-based solid electrolyte having a NASICON structure.

6. The all-solid-state battery according to claim 5, characterized in that: In the positive electrode layer, the phosphate-based solid electrolyte has an average particle size of 0.1 μm or more and 10.0 μm or less.

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

8. The all-solid-state battery according to any one of claims 1 to 7, characterized in that: The thickness of the positive electrode layer is greater than or equal to 1 μm and less than or equal to 100 μm.

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