All-solid-state battery

Abstract

To provide an all-solid battery capable of improving initial charge / discharge efficiency and cycle characteristics.SOLUTION: An all-solid battery includes a positive electrode layer including a phosphate-based solid electrolyte layer having a NASICON-type structure, a Co-containing phosphate-based positive electrode active material, and a Co-containing phosphate-based solid electrolyte, and a negative electrode layer including a negative electrode active material and a solid electrolyte that does not contain Co.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] In recent years, lithium-ion secondary batteries (Li-ion) batteries have been widely used as power sources for portable electronic devices, wearable devices, and IoT devices due to their high energy density. These Li-ion secondary batteries use flammable organic solvents as electrolytes to transport ions. Batteries using such flammable electrolytes pose significant risks, including electrolyte leakage, smoke generation, and fire. To address these risks and ensure inherent safety, development is underway to replace flammable organic electrolytes with flame-resistant solid electrolytes and to develop all-solid-state batteries with solid-state components. In particular, all-solid-state batteries using oxide-based solid electrolytes, which are highly stable in air, require high-temperature co-firing of various components, including the solid electrolyte, to reduce the grain boundary resistance between solid electrolyte particles.

[0003] For example, as a means for suppressing element diffusion during co-firing, a method has been disclosed in which the same transition metal element as that contained in the active material is added to the solid electrolyte in advance (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-11864 Summary of the Invention [Problem to be solved by the invention]

[0005] This method can suppress elemental diffusion of transition metal elements contained in the electrode active material and improve the active material survival rate during co-firing, which is effective in improving battery capacity, but does not mention the initial charge / discharge efficiency or cycle characteristics.

[0006] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide an all-solid-state battery that can improve the initial charge-discharge efficiency and cycle characteristics. [Means for solving the problem]

[0007] The all-solid-state battery according to the present invention is characterized by comprising: a phosphate-based solid electrolyte layer having a NASICON-type structure; a positive electrode layer containing a Co-containing phosphate-based positive electrode active material and a Co-containing phosphate-based solid electrolyte; and a negative electrode layer containing a negative electrode active material and a Co-free solid electrolyte.

[0008] The all-solid-state battery may operate at an operating voltage of 2.5 V or greater.

[0009] In the all-solid-state battery, the positive electrode active material has a voltage of 4.5 V vs. Li / Li + The negative electrode active material operates at an average operating potential of 2.0 V vs. Li / Li or more. + It may operate at an average operating potential of:

[0010] In the all-solid-state battery, the Co-containing phosphate-based solid electrolyte contained in the positive electrode layer may contain glass ceramics obtained by crystallizing a Co-containing solid electrolyte glass.

[0011] In the Co-containing phosphate-based solid electrolyte contained in the positive electrode layer of the all-solid-state battery, the molar ratio of Co / P may be 16.8 mol % or less.

[0012] In the positive electrode layer and the negative electrode layer of the all-solid-state battery, the solid electrolyte may have an average particle size of 0.1 μm or more and 10 μm or less.

[0013] In the positive electrode layer and the negative electrode layer of the all-solid-state battery, the volume ratio of the solid electrolyte may be 20 to 75 vol. %. [Effects of the Invention]

[0014] According to the present invention, it is possible to provide an all-solid-state battery that can improve the initial charge-discharge efficiency and cycle characteristics. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is a schematic cross-sectional view showing the basic structure of an all-solid-state battery. [Figure 2] FIG. 1 is a schematic cross-sectional view of an all-solid-state battery according to an embodiment. [Figure 3] FIG. 1 is a schematic cross-sectional view of another all-solid-state battery. [Figure 4] FIG. 1 is a diagram illustrating a flow of a method for manufacturing an all-solid-state battery. [Figure 5] 1(a) and 1(b) are diagrams illustrating the lamination process. [Figure 6] FIG. 10 is a diagram showing charge / discharge curves in Example 4. [Figure 7] FIG. 10 is a diagram showing charge / discharge curves of Comparative Example 1. [Figure 8] FIG. 1 is a graph showing cycle characteristics for Examples 1 to 7 and Comparative Examples 1 and 2. DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, embodiments will be described with reference to the drawings.

[0017] (Embodiment) Fig. 1 is a schematic cross-sectional view showing the basic structure of an all-solid-state battery 100. 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.

[0018] 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 layer, and the second internal electrode 20 is used as a negative electrode layer.

[0019] 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 having a NASICON structure has high conductivity and is stable in the air. The phosphate-based solid electrolyte is, for example, a phosphate containing lithium. The phosphate is not particularly limited, but examples include composite lithium phosphate salts with Ti (e.g., LiTi2(PO4)3). Alternatively, Ti can be partially or completely substituted with a tetravalent transition metal such as Ge, Sn, Hf, or Zr. Furthermore, to increase the Li content, it may be partially substituted with a trivalent transition metal such as Al, Ga, In, Y, or La. More specifically, for example, Li 1+x Al x Ge 2-x (PO4)3 and Li 1+x Al x Zr 2-x (PO4)3, Li 1+x Al x Ti 2-x (PO4)3, etc. For example, in this embodiment, a Li-Al-Ge-PO4-based material to which Co has been added in advance may be used as the phosphate-based solid electrolyte, similar to the Co-containing phosphate-based solid electrolyte contained in the first internal electrode 10, which is the positive electrode. The phosphate-based solid electrolyte does not need to contain Co.

[0020] When the phosphate-based solid electrolyte contains Co, the solid electrolyte layer 30 is preferably designed so that the Co concentration is higher on the positive electrode side than on the negative electrode side, and preferably the Co concentration is low on the negative electrode side or no Co is contained near the negative electrode. In this case, the effect of improving oxidation resistance near the positive electrode and achieving reduction resistance near the negative electrode can be achieved.

[0021] The first internal electrode 10 used as the positive electrode layer contains a Co-containing phosphate-based positive electrode active material. + It is preferable to use a Co-containing phosphate-based positive electrode active material that operates at the above average potential as the positive electrode active material of the first internal electrode 10. For example, the positive electrode active material may be LiCoPO4, Li2CoP2O7, or Li6Co5(P2O7)4.

[0022] The second internal electrode 20 used as the negative electrode layer contains a negative electrode active material. For example, 2V vs. Li / Li + It is preferable to use a negative electrode active material that operates at the following average potential as the negative electrode active material of the second internal electrode 20. For example, TiO2, Nb2O5, Ti-Nb-O based compounds, etc. Such a negative electrode active material is suitable for use at an average potential of 4.5V 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 to 2.5 V or higher.

[0023] In the production of the first internal electrode 10 and the second internal electrode 20, in addition to these electrode active materials, a solid electrolyte having ion conductivity, a conductive material (conductive additive), etc. are added. For these components, an internal electrode paste can be obtained by uniformly dispersing a binder and a plasticizer in water or an organic solvent. A carbon material or the like may be included as the conductive additive. A metal may be included as the conductive additive. Examples of the metal for the conductive additive include Pd, Ni, Cu, Fe, and alloys containing these.

[0024] Unlike conventional lithium ion secondary batteries that use an electrolytic solution, it is possible to use electrolytes suitable for the positive electrode and the negative electrode in the all-solid-state battery 100. Therefore, in this embodiment, materials with different compositions are used as the solid electrolyte contained in the first internal electrode 10 and the solid electrolyte contained in the second internal electrode 20.

[0025] In this embodiment, a Co-containing phosphate-based solid electrolyte is used as the solid electrolyte contained in the first internal electrode 10. By introducing an appropriate amount of Co into the phosphate-based solid electrolyte, it is possible to improve the oxidation resistance of the positive electrode side. As the Co-containing phosphate-based solid electrolyte, it is preferable to use a Co-added Li-Al-Ge-PO4-based material or the like. Alternatively, it is preferable to use glass ceramics obtained by crystallizing Co-containing solid electrolyte glass as the Co-containing phosphate-based solid electrolyte.

[0026] On the other hand, a solid electrolyte containing no Co is used as the solid electrolyte contained in the second internal electrode 20. This can improve the reduction resistance on the negative electrode side. When the main component solid electrolyte of the solid electrolyte layer 30 does not contain Co, this main component solid electrolyte may be used as the solid electrolyte contained in the second internal electrode 20. Here, "containing no Co" can be defined as 1 / 100 or less of the Co content of the first internal electrode 10, or below the detection limit in SEM-EDS.

[0027] As described above, by using a Co-containing phosphate-based solid electrolyte as the solid electrolyte contained in the first internal electrode 10 and a Co-free solid electrolyte as the solid electrolyte contained in the second internal electrode 20, it is possible to improve the oxidation resistance of the positive electrode side and the reduction resistance of the negative electrode side. This makes it possible to improve the initial charge / discharge efficiency and cycle characteristics. Note that, when the operating voltage of the all-solid-state battery 100 is high, oxidation resistance of the positive electrode side and reduction resistance of the negative electrode side are particularly required, and this effect becomes more pronounced when the operating voltage of the all-solid-state battery 100 is high (for example, when the operating voltage is 2.5 V or higher).

[0028] If the amount of Co in the Co-containing phosphate solid electrolyte contained in the first internal electrode 10 is too large, a Co-containing compound with low electronic conductivity is generated during co-firing, which may result in an increase in internal resistance (ESR). Therefore, it is preferable to set an upper limit on the amount of Co in the Co-containing phosphate solid electrolyte contained in the first internal electrode 10. For example, in the Co-containing phosphate solid electrolyte contained in the first internal electrode 10, the molar ratio of Co / P is preferably 16.8 mol% or less, more preferably 13.5 mol% or less, and even more preferably 10.2 mol% or less.

[0029] On the other hand, if the amount of Co in the Co-containing phosphate solid electrolyte contained in the first internal electrode 10 is too small, oxidation resistance may become insufficient. Therefore, it is preferable to set a lower limit for the amount of Co in the Co-containing phosphate solid electrolyte contained in the first internal electrode 10. For example, in the Co-containing phosphate solid electrolyte contained in the first internal electrode 10, the molar ratio of Co / P is preferably 1.7 mol% or more, more preferably 3.3 mol% or more, and even more preferably 6.7 mol% or more.

[0030] If the average particle size of the solid electrolyte in the first internal electrode 10 and the second internal electrode 20 is too large, high temperatures may be required for sintering and densification. Therefore, it is preferable to set an upper limit to the average particle size of the solid electrolyte in the first internal electrode 10 and the second internal electrode 20. On the other hand, if the average particle size of the solid electrolyte in the first internal electrode 10 and the second internal electrode 20 is too small, the dispersion state of the electrode paste becomes unstable, making it difficult to obtain a dense coating film, and there is a risk that the reactivity during heat treatment of the all-solid-state battery 100 will increase, making interdiffusion reactions more likely to occur. Therefore, it is preferable to set a lower limit to the average particle size of the solid electrolyte in the first internal electrode 10 and the second internal electrode 20. For example, the average particle size of the solid electrolyte in the first internal electrode 10 and the second internal electrode 20 is preferably 0.1 μm or more and 10 μm or less, more preferably 0.5 μm or more and 7 μm or less, and even more preferably 1 μm or more and 5 μm or less.

[0031] Furthermore, if the volume ratio of the solid electrolyte in each of the first internal electrode 10 and the second internal electrode 20 is too high, the amount of electrode active material filled cannot be increased, and the capacity may decrease. Therefore, it is preferable to set an upper limit to the volume ratio of the solid electrolyte in each of the first internal electrode 10 and the second internal electrode 20. On the other hand, if the volume ratio of the solid electrolyte in each of the first internal electrode 10 and the second internal electrode 20 is too low, the ion conduction path may not be secured, and the internal resistance may increase. Therefore, it is preferable to set a lower limit to the volume ratio of the solid electrolyte in each of the first internal electrode 10 and the second internal electrode 20. For example, the volume ratio of the solid electrolyte in each of the first internal electrode 10 and the second internal electrode 20 is preferably about 20 to 75 vol.%, more preferably 25 to 70 vol.%, and even more preferably 30 to 65 vol.%.

[0032] 2 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).

[0033] 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.

[0034] 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.

[0035] 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. 2, 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. 2, 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, Si, Zr, Ti, etc. (for example, Al2O3, SiO2, ZrO2, TiO2, etc.). The cover layer 50 may contain the main component of the solid electrolyte layer 30 as a main component.

[0036] The first internal electrode 10 and the second internal electrode 20 may each include a current collector layer. For example, as illustrated in FIG. 3, a first current collector layer 11 may be provided within the first internal electrode 10. Furthermore, a second current collector layer 21 may be provided within the second internal electrode 20. The first current collector layer 11 and the second current collector layer 21 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 11 and the second current collector layer 21. Connecting the first current collector layer 11 to the first external electrode 40a and connecting the second current collector layer 21 to the second external electrode 40b improves current collection efficiency.

[0037] Next, a description will be given of a method for manufacturing the all-solid-state battery 100a illustrated in Fig. 2. Fig. 4 is a diagram illustrating the flow of the method for manufacturing the all-solid-state battery 100a.

[0038] (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, a melt quenching method, or the like. The obtained raw material powder can be dry-pulverized to adjust it to a desired average particle size. For example, the desired average particle size is adjusted using a planetary ball mill with 5 mm diameter ZrO2 balls.

[0039] (Cover layer raw material powder production process) First, a ceramic raw material powder for the cover layer 50 is prepared. For example, raw materials, additives, etc. are mixed and solid-phase synthesis is used to prepare the raw material powder for the cover layer. The obtained raw material powder can be dry-milled to adjust the average particle size to the desired size. For example, the desired average particle size is adjusted using a planetary ball mill with 5 mm diameter ZrO2 balls.

[0040] (Internal electrode paste manufacturing process) Next, an internal electrode paste for producing the first internal electrode 10 and the second internal electrode 20 is prepared. For example, the internal electrode paste 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 material may be the above-mentioned solid electrolyte paste. 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 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. If the first internal electrode 10 and the second internal electrode 20 have different compositions, a paste for each internal electrode may be prepared separately.

[0041] 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.

[0042] (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.

[0043] (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.

[0044] (Lamination process) As illustrated in FIG. 5( 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 illustrated in FIG. 5( 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.

[0045] 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.

[0046] (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.

[0047] 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. [Example]

[0048] Hereinafter, all-solid-state batteries were fabricated according to the embodiments, and their characteristics were investigated.

[0049] Example 1 For the positive electrode, 4.5V vs. Li / Li + LiCoPO4 was used as the positive electrode active material with the above average operating potential, LAGP glass was used as the solid electrolyte, and Co3O4 was used as the Co source to be added to the solid electrolyte. The positive electrode active material, conductive additive, solid electrolyte, and Co3O4 were weighed out in a mass ratio of 35:10:54.5:0.5 and mixed in a mortar with the addition of an appropriate amount of binder to produce positive electrode granulated powder.

[0050] For the negative electrode, 2V vs. Li / Li + TiO2 was used as the negative electrode active material with the following average operating potential, and LAGP glass was used as the solid electrolyte. The negative electrode active material, conductive additive, and solid electrolyte were weighed out in a mass ratio of 35:10:55, and mixed in a mortar with the addition of an appropriate amount of binder to produce negative electrode granulated powder.

[0051] A predetermined amount of LAGP glass was molded in a mold to produce a solid electrolyte layer 300 μm thick. Then, predetermined amounts of positive electrode granulated powder and negative electrode granulated powder were placed on both sides of the solid electrolyte layer, and the resulting compact was press-molded to produce a molded body. The molded body was fired at a predetermined temperature to produce an all-solid-state battery. During the firing process, a Co-containing phosphate-based solid electrolyte was obtained in the positive electrode. The Co / P molar ratio in this Co-containing phosphate-based solid electrolyte was 1.7 mol%.

[0052] The fabricated all-solid-state battery was subjected to AC resistance measurement at 1 kHz in an 80°C thermostatic chamber, which was found to be 345 Ω. Subsequently, a constant-current charge-discharge test was conducted for 100 cycles at a current of 0.2 C in the range of 1.5 V to 3.5 V. The initial charge-discharge efficiency was calculated from the initial charge and discharge current capacities and found to be 58%. Furthermore, the capacity retention after 100 cycles was calculated from the discharge and discharge current capacities at the 100th cycle and found to be 60%.

[0053] Example 2 An all-solid-state battery was fabricated in the same manner as in Example 1, except that the mass ratio of the positive electrode active material, conductive additive, solid electrolyte, and Co3O4 in the positive electrode granulated powder was 35:10:54:1. In the Co-containing phosphate-based solid electrolyte of the positive electrode, the molar ratio of Co / P was 3.3 mol%.

[0054] The fabricated all-solid-state battery was subjected to AC resistance measurement at 1 kHz in an 80°C constant temperature bath, which was found to be 340 Ω. A 100-cycle constant current charge-discharge test was then conducted at a current of 0.2 C. The initial charge-discharge efficiency was calculated from the initial charge and discharge current capacities and found to be 62%. Furthermore, the capacity retention rate after 100 cycles was calculated from the discharge and discharge current capacities at the 100th cycle and found to be 75%.

[0055] Example 3 An all-solid-state battery was fabricated in the same manner as in Example 1, except that the mass ratio of the positive electrode active material, conductive additive, solid electrolyte, and Co3O4 in the positive electrode granulated powder was 35:10:53:2. In the Co-containing phosphate-based solid electrolyte of the positive electrode, the molar ratio of Co / P was 6.7 mol%.

[0056] The fabricated all-solid-state battery was measured for AC resistance at 1 kHz in an 80°C thermostatic chamber, and found to have a resistance of 321 Ω. It was then subjected to a 100-cycle constant-current charge-discharge test at a current of 0.2 C. The initial charge-discharge efficiency was calculated from the initial charge and discharge current capacities and found to be 65%. Furthermore, the capacity retention rate after 100 cycles was calculated from the discharge current capacity at the 100th cycle and the initial discharge current capacity and found to be 83%.

[0057] Example 4 An all-solid-state battery was fabricated in the same manner as in Example 1, except that the mass ratio of the positive electrode active material, conductive additive, solid electrolyte, and Co3O4 in the positive electrode granulated powder was 35:10:52:3. In the Co-containing phosphate-based solid electrolyte of the positive electrode, the molar ratio of Co / P was 10.2 mol%.

[0058] The fabricated all-solid-state battery was measured for AC resistance at 1 kHz in an 80°C thermostatic chamber, and found to have a resistance of 310 Ω. It was then subjected to a 100-cycle constant-current charge-discharge test at a current of 0.2 C. The initial charge-discharge efficiency was calculated from the initial charge and discharge current capacities and found to be 67%. Furthermore, the capacity retention rate after 100 cycles was calculated from the discharge and discharge current capacities at the 100th cycle and found to be 81%.

[0059] Example 5 An all-solid-state battery was fabricated in the same manner as in Example 1, except that the mass ratio of the positive electrode active material, conductive additive, solid electrolyte, and Co3O4 in the positive electrode granulated powder was 35:10:51:4. In the Co-containing phosphate-based solid electrolyte of the positive electrode, the molar ratio of Co / P was 13.5 mol%.

[0060] The fabricated all-solid-state battery was measured for AC resistance at 1 kHz in an 80°C thermostatic chamber, and found to have a resistance of 332 Ω. It was then subjected to a 100-cycle constant-current charge-discharge test at a current of 0.2 C. The initial charge-discharge efficiency was calculated from the initial charge and discharge current capacities and found to be 69%. Furthermore, the capacity retention rate after 100 cycles was calculated from the discharge current capacity at the 100th cycle and the initial discharge current capacity and found to be 80%.

[0061] Example 6 An all-solid-state battery was fabricated in the same manner as in Example 1, except that the mass ratio of the positive electrode active material, conductive additive, solid electrolyte, and Co3O4 in the positive electrode granulated powder was 35:10:50:5. In the Co-containing phosphate-based solid electrolyte of the positive electrode, the molar ratio of Co / P was 16.8 mol%.

[0062] The fabricated all-solid-state battery was measured for AC resistance at 1 kHz in an 80°C thermostatic chamber, and found to have a resistance of 380 Ω. It was then subjected to a 100-cycle constant-current charge-discharge test at a current of 0.2 C. The initial charge-discharge efficiency was calculated from the initial charge and discharge current capacities and found to be 69%. Furthermore, the capacity retention rate after 100 cycles was calculated from the discharge current capacity at the 100th cycle and the initial discharge current capacity and found to be 75%.

[0063] Example 7 An all-solid-state battery was fabricated in the same manner as in Example 1, except that the mass ratio of the positive electrode active material, conductive additive, solid electrolyte, and Co3O4 in the positive electrode granulated powder was 35:10:49:6. In the Co-containing phosphate-based solid electrolyte of the positive electrode, the molar ratio of Co / P was 20 mol%.

[0064] The fabricated all-solid-state battery was measured for AC resistance at 1 kHz in an 80°C thermostatic chamber, and the result was 932 Ω. It was then subjected to a 100-cycle constant-current charge-discharge test at a current of 0.2 C. The initial charge-discharge efficiency was calculated from the initial charge and discharge current capacities and found to be 68%. Furthermore, the capacity retention after 100 cycles was calculated from the discharge and discharge current capacities at the 100th cycle and found to be 73%.

[0065] (Comparative Example 1) An all-solid-state battery was fabricated in the same manner as in Example 1, except that the mass ratio of the positive electrode active material, conductive additive, and solid electrolyte in the positive electrode granulated powder was 35:10:55. Therefore, in Comparative Example 1, Co was not added to the phosphate-based solid electrolyte of the positive electrode.

[0066] The fabricated all-solid-state battery was subjected to AC resistance measurement at 1 kHz in an 80°C thermostatic chamber, which was found to be 323 Ω. It was then subjected to a 100-cycle constant-current charge-discharge test at a current of 0.2 C. The initial charge-discharge efficiency was calculated from the initial charge current capacity and discharge current capacity, which was found to be 50%. Furthermore, the capacity retention rate after 100 cycles was calculated from the discharge current capacity at the 100th cycle and the initial discharge current capacity, which was found to be 52%.

[0067] (Comparative Example 2) An all-solid-state battery was fabricated in the same manner as in Example 1, except that the mass ratio of the positive electrode granulated powder containing the positive electrode active material, conductive additive, solid electrolyte, and Co3O4 was 35:10:53:2, and the mass ratio of the negative electrode granulated powder containing the negative electrode active material, conductive additive, solid electrolyte, and Co3O4 was 35:10:54.5:0.5. Therefore, Co was also added to the negative electrode solid electrolyte. In the Co-containing phosphate-based positive electrode solid electrolyte, the molar ratio of Co / P was 6.7 mol%.

[0068] The fabricated all-solid-state battery was measured for AC resistance at 1 kHz in an 80°C thermostatic chamber, and found to have a resistance of 314 Ω. It was then subjected to a 100-cycle constant-current charge-discharge test at a current of 0.2 C. The initial charge-discharge efficiency was calculated from the initial charge and discharge current capacities and found to be 30%. Furthermore, the capacity retention rate after 100 cycles was calculated from the discharge and discharge current capacities at the 100th cycle and found to be 5%.

[0069] The initial charge-discharge efficiency and cycle characteristics were examined for Examples 1 to 7 and Comparative Examples 1 and 2. If the initial charge-discharge efficiency was greater than 50%, the initial charge-discharge efficiency was judged to be acceptable, and if the capacity retention rate was 60% or greater, the cycle characteristics were judged to be acceptable. If both the initial charge-discharge efficiency and the cycle characteristics were acceptable, the battery was judged to be acceptable (good). If either the initial charge-discharge efficiency or the cycle characteristics were unacceptable, the battery was judged to be unacceptable (poor). The results are shown in Table 1. [Table 1]

[0070] Fig. 6 is a diagram showing the charge / discharge curve of Example 4. Fig. 7 is a diagram showing the charge / discharge curve of Comparative Example 1. The initial charge / discharge efficiency can be calculated from the charge / discharge curve. Fig. 8 is a diagram showing the cycle characteristics of Examples 1 to 7 and Comparative Examples 1 and 2. In Fig. 8, the horizontal axis represents the number of cycles, and the vertical axis represents the remaining capacity rate.

[0071] As shown in Table 1, Comparative Example 1 failed to pass both the initial charge-discharge efficiency and the cycle characteristics. This is thought to be because the oxidation resistance of the positive electrode was reduced by not using a Co-containing phosphate-based solid electrolyte for the positive electrode solid electrolyte. Comparative Example 2 also failed to pass both the initial charge-discharge efficiency and the cycle characteristics. This is thought to be because the reduction resistance of the negative electrode was reduced by using a Co-containing solid electrolyte for the negative electrode solid electrolyte.

[0072] In contrast, Examples 1 to 7 passed both the initial charge-discharge efficiency and the cycle characteristics. This is thought to be because the use of a Co-containing phosphate-based solid electrolyte for the positive electrode solid electrolyte improved the oxidation resistance of the positive electrode, and the use of a Co-free solid electrolyte for the negative electrode solid electrolyte improved the reduction resistance of the negative electrode.

[0073] In Example 7, the ESR was larger than in Examples 1 to 6. This is thought to be due to the high Co content in the Co-containing phosphate solid electrolyte contained in the positive electrode. From this result, it can be seen that, from the viewpoint of suppressing ESR, it is preferable to set the Co / P molar ratio in the Co-containing phosphate solid electrolyte contained in the positive electrode to 16.8 mol% or less.

[0074] In any of Examples 1 to 7, the results of Examples 1 to 7 can be obtained even when a phosphate-based solid electrolyte to which Co element has been added in advance is used in the positive electrode granulated powder, instead of using a solid electrolyte and Co3O4. Furthermore, although Examples 1 to 7 were evaluated using opposing batteries, the same effects can be obtained in the stacked battery according to the embodiment.

[0075] 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]

[0076] 10 1st internal electrode 11 First current collector layer 20 Second internal electrode 21 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 phosphate-based solid electrolyte layer having a NASICON structure; a positive electrode layer including a Co-containing phosphate-based positive electrode active material and a Co-containing phosphate-based solid electrolyte; An all-solid-state battery comprising: an anode layer including an anode active material and a Co-free solid electrolyte.

2. 2. The all-solid-state battery according to claim 1, which operates at an operating voltage of 2.5 V or more.

3. The positive electrode active material is 4.5 V vs. Li / Li ＋ Operates at an average operating potential of The negative electrode active material has a voltage of 2.0 V vs. Li / Li ＋ 3. The all-solid-state battery according to claim 2, which operates at an average operating potential of:

4. 4. The all-solid-state battery according to claim 1, wherein the Co-containing phosphate-based solid electrolyte contained in the positive electrode layer includes glass ceramics obtained by crystallizing a Co-containing solid electrolyte glass.

5. 5. The all-solid-state battery according to claim 1, wherein the Co / P molar ratio in the Co-containing phosphate-based solid electrolyte contained in the positive electrode layer is 16.8 mol% or less.

6. 6. The all-solid-state battery according to claim 1, wherein the average particle size of the solid electrolyte in the positive electrode layer and the negative electrode layer is 0.1 μm or more and 10 μm or less.

7. 7. The all-solid-state battery according to claim 1, wherein the volume ratio of the solid electrolyte in the positive electrode layer and the negative electrode layer is 20 to 75 vol. %.

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