All-solid-state batteries

Abstract

According to the present invention, an all-solid-state battery comprises a solid electrolyte layer that includes a first solid electrolyte, a positive electrode layer that is provided on a first principal surface of the solid electrolyte layer and includes a positive electrode active material and a second solid electrolyte, and a negative electrode layer that is provided on a second principal surface of the solid electrolyte layer and includes a negative electrode active material and a third solid electrolyte. At at least one of the positive electrode layer and the negative electrode layer, the average particle diameter of the second solid electrolyte or the third solid electrolyte is no more than 2.5 μm, and the ratio of the average particle diameter of the positive electrode active material to the average particle diameter of the second solid electrolyte or the ratio of the average particle diameter of the negative electrode active material to the average particle diameter of the third solid electrolyte is 0.4–10.　

Description

[Technical Field]

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

[0002] Currently, lithium-ion secondary batteries are used in a variety of fields, including consumer electronics, industrial machinery, and automobiles. However, existing lithium-ion secondary batteries contain an electrolyte, which poses risks such as electrolyte leakage, smoke emission, and fire. Therefore, there is a strong focus on developing all-solid-state lithium-ion secondary batteries that employ an oxide-based solid electrolyte that is stable in the atmosphere (see, for example, Patent Document 1). [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2018-73554 [Patent Document 2] Japanese Patent Publication No. 2021-108258 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] To impart the desired properties to oxide-based solid electrolytes, a sintering process involving heat treatment is necessary.

[0005] To achieve good capacity characteristics, it is desirable to pack the electrode active material and solid electrolyte within the electrode layer as densely as possible so that they have many contact points with each other, and then to more effectively form these contact points through a sintering process. However, improving mutual dispersibility and packing is difficult. For example, in the multi-layered all-solid-state battery manufactured by the manufacturing flow described in Patent Document 2, it is difficult to efficiently improve mutual dispersibility and packing during the production of the electrode composite material.

[0006] This invention has been made in view of the above problems, and aims to provide an all-solid-state battery that can realize a high-density electrode layer. [Means for solving the problem]

[0007] The all-solid-state battery according to the present invention comprises a solid electrolyte layer containing a first solid electrolyte, a positive electrode layer provided on a first main surface of the solid electrolyte layer and containing a positive electrode active material and a second solid electrolyte, and a negative electrode layer provided on a second main surface of the solid electrolyte layer and containing a negative electrode active material and a third solid electrolyte, wherein in at least one of the electrode layers, the average particle size of the second solid electrolyte or the third solid electrolyte is 2.5 μm or less, and the ratio of the average particle size of the positive electrode active material to the average particle size of the second solid electrolyte or the ratio of the average particle size of the negative electrode active material to the average particle size of the third solid electrolyte is 0.4 or more and 10 or less.

[0008] In the above-mentioned all-solid-state battery, the area occupancy rate of the second solid electrolyte or the third solid electrolyte in a cross-section viewed from a direction perpendicular to the direction in which the positive electrode layer and the negative electrode layer face each other may be 25% or more and 75% or less.

[0009] The average particle size of the second solid electrolyte or the third solid electrolyte of the all-solid-state battery described above may be 0.05 μm or larger.

[0010] In the above-mentioned all-solid-state battery, the porosity of at least one of the electrode layers may be 10% or less.

[0011] The second or third solid electrolyte of the all-solid-state battery described above may be a phosphate-based solid electrolyte.

[0012] The second or third solid electrolyte of the all-solid-state battery described above may have a NASICON-type crystal structure.

[0013] In the all-solid-state battery described above, the positive electrode active material may contain Co and P.

[0014] In the all-solid-state battery described above, the second solid electrolyte or the third solid electrolyte may contain Co.

[0015] In the all-solid-state battery described above, the positive electrode active material may contain at least one of LiCoPO4, LiCo2P3O , , Li2CoP2O7, and Li6Co5(P2O7)4.

Advantages of the Invention

[0020] Solid electrolyte layer 30 is mainly composed of a solid electrolyte (first solid electrolyte) having ion conductivity. The solid electrolyte of 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 the property of being stable in the atmosphere. The phosphate-based solid electrolyte is, for example, a phosphate containing lithium. The phosphate is not particularly limited, and examples thereof include lithium composite phosphate salts with Ti (for example, LiTi2(PO4)3). Alternatively, Ti can be partially or entirely replaced with a tetravalent transition metal such as Ge, Sn, Hf, Zr, etc. Also, in order to increase the Li content, it may be partially replaced with a trivalent transition metal such as Al, Ga, In, Y, La, etc. 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-xExamples include (PO4)3. For example, a Li-Al-Ge-PO4 system material is preferred in which the same transition metal as the transition metal contained in the olivine-type crystal structure phosphate contained in the positive electrode layer 10 and the negative electrode layer 20 is pre-added. For example, if the positive electrode layer 10 and the negative electrode layer 20 contain a phosphate containing Co and Li, it is preferable that the solid electrolyte layer 30 contains a Li-Al-Ge-PO4 system material with Co pre-added. In this case, the effect of suppressing the elution of the transition metal contained in the electrode active material into the electrolyte can be obtained. If the positive electrode layer 10 and the negative electrode layer 20 contain a phosphate containing a transition element other than Co and Li, it is preferable that the solid electrolyte layer 30 contains a Li-Al-Ge-PO4 system material with the transition metal pre-added.

[0021] As illustrated in Figure 2, the positive electrode layer 10 has a structure in which particles of positive electrode active material 11, solid electrolyte 12 (second solid electrolyte), etc. are dispersed. In addition to the positive electrode active material 11 and solid electrolyte 12, the positive electrode layer 10 may also contain conductive additives, etc. The negative electrode layer 20 has a structure in which particles of negative electrode active material 21, solid electrolyte 22 (third solid electrolyte), etc. are dispersed. In addition to the negative electrode active material 21 and solid electrolyte 22, the negative electrode layer 20 may also contain conductive additives, etc. By having the positive electrode layer 10 comprise the positive electrode active material 11 and the negative electrode layer 20 comprise the negative electrode active material 21, the all-solid-state battery 100 can be used as a secondary battery. By having the positive electrode layer 10 comprise the solid electrolyte 12 and the negative electrode layer 20 comprise the solid electrolyte 22, ionic conductivity is obtained in the positive electrode layer 10 and the negative electrode layer 20. By providing a conductive additive to the positive electrode layer 10 and the negative electrode layer 20, conductivity is obtained in the positive electrode layer 10 and the negative electrode layer 20.

[0022] The positive electrode active material 11 is, for example, an electrode active material having an olivine-type crystal structure. An electrode active material having an olivine-type crystal structure may also be contained in the negative electrode layer 20. Examples of such electrode active materials include phosphates containing a transition metal and lithium. The olivine-type crystal structure is the crystal structure found in natural olivine and can be identified by X-ray diffraction.

[0023] Typical examples of electrode active materials with an olivine-type crystal structure include LiCoPO4 containing Co and P. Phosphates in which the transition metal Co is replaced in this chemical formula can also be used. Here, the ratio of Li and PO4 may vary depending on the valency. It is preferable to use Co, Mn, Fe, Ni, etc., as the transition metal. As a positive electrode active material containing Co and P, LiCo2P3O 10 Li2CoP2O7, Li6Co5(P2O7)4, etc., can also be used.

[0024] For example, if the electrode active material having an olivine-type crystal structure is contained only in the positive electrode layer 10, then this electrode active material acts as the positive electrode active material. If the electrode active material having an olivine-type crystal structure is also contained in the negative electrode layer 20, although the mechanism of action is not fully understood, it is presumed that this is based on the formation of a partial solid solution state with the negative electrode active material, resulting in an increase in discharge capacity and an increase in the operating potential associated with discharge.

[0025] When both the positive electrode layer 10 and the negative electrode layer 20 contain electrode active materials having an olivine-type crystal structure, each electrode active material preferably contains transition metals that may be the same or different from each other. "May be the same or different from each other" means that the electrode active materials contained in the positive electrode layer 10 and the negative electrode layer 20 may contain the same type of transition metal, or they may contain different types of transition metals. The positive electrode layer 10 and the negative electrode layer 20 may contain only one type of transition metal, or they may contain two or more types of transition metals. Preferably, the positive electrode layer 10 and the negative electrode layer 20 contain the same type of transition metal. More preferably, the electrode active materials contained in both electrodes have the same chemical composition. The similarity of the compositions of both internal electrode layers is increased by the inclusion of the same type of transition metal or the same composition of electrode active materials in the positive electrode layer 10 and the negative electrode layer 20. This has the effect of allowing the all-solid-state battery 100 to withstand actual use without malfunction, depending on the application, even if the terminals are connected in reverse (positive and negative).

[0026] The negative electrode layer 20 functions as a negative electrode layer by containing the negative electrode active material 21. By containing the negative electrode active material in only one electrode, it becomes clear that the electrode in question acts as a negative electrode and the other electrode acts as a positive electrode. However, both electrodes may contain a known substance as the negative electrode active material. Regarding the negative electrode active material of the electrodes, prior art in secondary batteries can be appropriately referenced, and examples include compounds such as titanium oxide, lithium titanium composite oxide, lithium titanium composite phosphate, carbon, and lithium vanadium phosphate.

[0027] Solid electrolytes 12 and 22 are not particularly limited as long as they are oxide-based solid electrolytes having ionic conductivity. Solid electrolytes 12 and 22 are, for example, oxide-based solid electrolytes 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 lithium-containing phosphate. The phosphate is not particularly limited, but examples include a lithium phosphate composite salt with Ti (e.g., LiTi2(PO4)3). Alternatively, Ti can be partially or completely substituted with a tetravalent transition metal such as Ge, Sn, Hf, or Zr. Furthermore, 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 Examples include (PO4)3. Solid electrolytes 12 and 22 can be, for example, the same as the main component solid electrolyte of the solid electrolyte layer 30. Alternatively, if the electrode active material contains Co and P, it is preferable that solid electrolytes 12 and 22 contain Co. Although the detailed mechanism is unknown, it is because including Co during co-calcination tends to improve the oxidation resistance stability of the solid electrolyte, thereby making it easier to ensure cycle stability.

[0028] The conductive additives contained in the positive electrode layer 10 and the negative electrode layer 20 may include carbon materials or the like. The conductive additives may also include metals. Examples of metals used as conductive additives include Pd, Ni, Cu, Fe, and alloys containing these.

[0029] The solid electrolyte layer 30 is obtained by firing a solid electrolyte green sheet, which is obtained by coating it with a slurry containing solid electrolyte powder. During the firing process, the solid electrolyte powder is sintered, and the desired properties are obtained.

[0030] The positive electrode layer 10 and the negative electrode layer 20 are obtained by printing a paste containing electrode active material, solid electrolyte, and conductive additive, and then firing it simultaneously with a solid electrolyte green sheet.

[0031] Figure 3(a) shows the relationship between porosity in a fired single sheet (electrode layer) and its overall conductivity, obtained by varying the mixing ratio of electrode active material and solid electrolyte. For each mixing ratio, the same composition and average particle size of electrode active material and solid electrolyte were used. Overall conductivity was evaluated by forming an electrode layer by sputtering Au onto both sides of the sample, measuring it at 25°C under conditions of a voltage amplitude of 30mV and a frequency of 0.1Hz to 500kHz, and reading the bulk resistance and grain boundary resistance from the resulting Nyquist plot.

[0032] As illustrated in Figure 3(a), increasing the amount of solid electrolyte tends to decrease the porosity. This is thought to be because a higher amount of solid electrolyte improves sinterability. Along with the decrease in porosity, the overall conductivity increases. Therefore, from the viewpoint of improving sinterability and increasing overall conductivity, a higher ratio of solid electrolyte in the electrode layer is preferable.

[0033] Figure 3(b) is a plot of the relationship between the porosity of the electrode layer and the capacity retention rate after 100 cycles, in relation to the area occupancy rate of the solid electrolyte in the electrode layer, as observed from a cross-section in the stacking thickness direction, for a stacked all-solid-state battery chip using the fired single sheet fabricated in Figure 3(a) as the electrode layer.

[0034] As illustrated in Figure 3(b), the porosity tends to decrease as the area occupancy rate of the solid electrolyte increases. This is thought to be because the sinterability improves as the amount of solid electrolyte increases. Along with the decrease in porosity, the capacity retention rate also decreases. Therefore, from the viewpoint of improving sinterability and increasing the capacity retention rate, it is preferable to have a higher area ratio of solid electrolyte in the electrode layer.

[0035] However, increasing the proportion of solid electrolyte in the electrode layer may reduce the proportion of electrode active material, potentially leading to a decrease in capacity. Therefore, it is desirable to improve sinterability without increasing the proportion of solid electrolyte, and to pack the electrode active material and solid electrolyte in the electrode layer as densely as possible so that they have as many contact points with each other as possible.

[0036] Therefore, at least one of the positive electrode layer 10 and the negative electrode layer 20 according to this embodiment has a configuration that enables high-density packing. As an example, the positive electrode layer 10 will be described in detail.

[0037] First, if the average particle size of the solid electrolyte 12 in the positive electrode layer 10 is too large, the packing efficiency will decrease, which may lead to a decrease in sinterability. Therefore, in this embodiment, an upper limit is set on the average particle size of the solid electrolyte 12 in the positive electrode layer 10. Specifically, the average particle size of the solid electrolyte 12 in the positive electrode layer 10 is set to 2.5 μm or less, preferably 1.5 μm or less, and more preferably 1.0 μm or less.

[0038] On the other hand, if the average particle size of the solid electrolyte 12 in the positive electrode layer 10 is too small, a decrease in packing performance due to aggregation may occur. Therefore, in this embodiment, it is preferable to set a lower limit on the average particle size of the solid electrolyte 12 in the positive electrode layer 10. Specifically, it is preferable that the average particle size of the solid electrolyte 12 in the positive electrode layer 10 be 0.05 μm or more, more preferably 0.1 μm or more, and even more preferably 0.3 μm or more.

[0039] Next, in the positive electrode layer 10, if the ratio of the average particle size of the positive electrode active material 11 to the average particle size of the solid electrolyte 12 (average particle size ratio) is small, aggregation of the active materials may occur, potentially leading to a decrease in packing performance and, consequently, a decrease in sinterability. Therefore, a lower limit is set for the average particle size ratio in the positive electrode layer 10. Specifically, the average particle size ratio in the positive electrode layer 10 should be 0.4 or higher, preferably 0.7 or higher, and more preferably 1.0 or higher. The average particle size ratio in the positive electrode layer 10 is calculated as (average particle size of the positive electrode active material) / (average particle size of the solid electrolyte 12).

[0040] On the other hand, if the ratio of the average particle size of the positive electrode active material 11 to the average particle size of the solid electrolyte 12 (average particle size ratio) in the positive electrode layer 10 is large, the packing performance may decrease, which may lead to a decrease in sinterability. Therefore, an upper limit is set on the average particle size ratio in the positive electrode layer 10. Specifically, the average particle size ratio in the positive electrode layer 10 should be 10 or less, preferably 5.0 or less, and more preferably 3.0 or less.

[0041] As described above, the positive electrode layer 10 can be densely packed if the average particle size of the solid electrolyte 12 is 2.5 μm or less, and the average particle size ratio is 0.4 or more and 10 or less. For example, the porosity of the positive electrode layer 10 is preferably 10% or less, more preferably 7% or less, and even more preferably 5% or less.

[0042] The porosity in the electrode layer can be calculated, for example, by performing cross-sectional processing using a cross-section polisher (CP), acquiring 10 secondary electron images at an acceleration voltage of 5kV and the same magnification using a scanning electron microscope (Hitachi High-Tech Corporation, model: S-4800), and measuring the average occupancy rate of the pore area through image analysis.

[0043] Next, from the viewpoint of obtaining even better sinterability, it is preferable to set a lower limit on the area occupancy rate of the solid electrolyte 12 in the cross-section in the thickness direction of the positive electrode layer 10. For example, in the cross-section in the thickness direction of the positive electrode layer 10, the area occupancy rate of the solid electrolyte 12 is preferably 25% or more, more preferably 30% or more, and even more preferably 40% or more.

[0044] On the other hand, if the area occupancy rate of the solid electrolyte 12 in the cross-section in the thickness direction of the positive electrode layer 10 is too large, the content ratio of the positive electrode active material 11 may decrease, which may reduce the capacity. Therefore, it is preferable to set an upper limit on the area occupancy rate of the solid electrolyte 12 in the cross-section in the thickness direction of the positive electrode layer 10. In this embodiment, the area occupancy rate of the solid electrolyte 12 in the cross-section in the thickness direction of the positive electrode layer 10 is preferably 75% or less, more preferably 65% ​​or less, and even more preferably 60% or less.

[0045] The average particle size of the electrode active material and solid electrolyte in the electrode layer can be measured by the following method. First, a cross-section of the electrode layer is prepared using a cross-section polisher (CP) or the like, from a direction approximately perpendicular to the stacking thickness direction of the all-solid-state battery. Next, observation is performed using a scanning electron microscope (Hitachi High-Tech Corporation, model: SU-7000) at an acceleration voltage of 5kV, and the regions of active material particles and solid electrolyte particles in the positive or negative electrode within the electrode layer are identified by SEM images at a magnification of 10,000x and elemental analysis by SEM-EDS. After observing 10 or more locations, at least 10 particle sizes are obtained by selecting particles that exist in isolation from other particles in the identified positive or negative electrode active material particles and solid electrolyte particles. Next, using image analysis software, the particle area of ​​each selected particle is measured, the equivalent diameter (Heywood diameter) is measured from the particle area, and 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.

[0046] Furthermore, the area occupancy rates of the electrode active material and solid electrolyte in the electrode layer can be measured by the following method. First, the electrode layer is prepared by cutting a cross section using a cross-section polisher (CP) or the like, from a direction approximately perpendicular to the stacking thickness direction of the all-solid-state battery. Next, for example, a scanning electron microscope (Hitachi High-Tech Corporation, model: SU-7000) is used to observe the layer at an acceleration voltage of 5kV, and backscattered electron images and elemental analysis by SEM-EDS are obtained at 10 locations in the positive or negative electrode layer at the same magnification. Using image analysis software, the regions of the active material and solid electrolyte occupying the acquired images can be identified, and the respective area occupancy rates can be calculated by the arithmetic mean of each.

[0047] Although the above explanation focuses on the positive electrode layer 10 as an example, the negative electrode layer 20 may have the same numerical ranges as the positive electrode layer 10 in terms of the area occupancy rate of the solid electrolyte, the average particle size of the solid electrolyte, and the average particle size ratio.

[0048] The thickness of the solid electrolyte layer 30 is, for example, 0.5 μm to 100 μm, 1 μm to 50 μm, or 2 μm to 20 μm. The thickness of the positive electrode layer 10 is, for example, 1 μm to 500 μm, 2 μm to 400 μm, or 5 μm to 300 μm. The thickness of the negative electrode layer 20 is, for example, 1 μm to 500 μm, 2 μm to 400 μm, or 5 μm to 300 μm.

[0049] The thickness of each layer can be determined by performing a cross-sectional machining process using a cross-section polisher (CP) or the like, from a direction approximately perpendicular to the stacking thickness direction of the all-solid-state battery. For example, the thickness can be observed using a scanning electron microscope (Hitachi High-Tech Corporation, model: SU-7000) at an acceleration voltage of 5kV, and elemental analysis by backscattered electron images and SEM-EDS is performed at 10 locations to identify the interface of each layer. The thickness can then be calculated using the arithmetic mean of the 10 points for each layer.

[0050] (Stacked solid-state battery) Figure 4 is a schematic cross-sectional view of a stacked all-solid-state battery 100a, in which multiple battery units are stacked. The all-solid-state battery 100a comprises 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 be in contact with two side surfaces, which are two of the four surfaces other than the top and bottom surfaces at the stacking direction ends. These two side surfaces may be adjacent to each other or may be two opposing sides. In this embodiment, the first external electrode 40a and the second external electrode 40b are provided so as to be in contact with two opposing side surfaces (hereinafter referred to as two end surfaces).

[0051] In the following description, components having the same composition range, thickness range, and particle size distribution range as the all-solid-state battery 100 will be given the same reference numerals, and detailed explanations will be omitted.

[0052] In the all-solid-state battery 100a, multiple positive electrode layers 10 and multiple negative electrode layers 20 are alternately stacked via a solid electrolyte layer 30. The edges of the multiple positive electrode layers 10 are exposed on the first end face of the stacked chip 60, but not on the second end face. The edges of the multiple negative electrode layers 20 are exposed on the second end face of the stacked chip 60, but not on the first end face. As a result, the positive electrode layers 10 and negative electrode layers 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. Thus, the all-solid-state battery 100a has a structure in which multiple battery units are stacked.

[0053] A cover layer 50 is laminated on the upper surface of the laminated structure of the positive electrode layer 10, the solid electrolyte layer 30, and the negative electrode layer 20 (in the example of Figure 4, the upper surface of the topmost positive electrode layer 10). A cover layer 50 is also laminated on the lower surface of the laminated structure (in the example of Figure 4, the lower surface of the bottommost positive electrode layer 10). The cover layer 50 is mainly composed of inorganic materials containing, for example, Al, Zr, and Ti (e.g., Al2O3, ZrO2, TiO2, etc.). The cover layer 50 may also mainly contain the main components of the solid electrolyte layer 30.

[0054] The positive electrode layer 10 and the negative electrode layer 20 may include a current collector layer. For example, as illustrated in Figure 5, a first current collector layer 13 may be provided within the positive electrode layer 10. Also, a second current collector layer 23 may be provided within the negative electrode layer 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 for the first current collector layer 13 and the second current collector layer 23. By connecting the first current collector layer 13 to the first external electrode 40a and the second current collector layer 23 to the second external electrode 40b, the current collection efficiency is improved.

[0055] Next, we will explain the manufacturing method of the all-solid-state battery 100a exemplified in Figure 4. Figure 6 is a diagram illustrating the flow of the manufacturing method of the all-solid-state battery 100a.

[0056] (Process for preparing raw material powder for the solid electrolyte layer) First, a raw material powder for the solid electrolyte layer that constitutes the solid electrolyte layer 30 described above is prepared. For example, a raw material powder for an oxide-based solid electrolyte 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 the desired average particle size by dry grinding. For example, the desired average particle size can be adjusted using a planetary ball mill with 5 mmφ ZrO2 balls.

[0057] (Process for preparing raw material powder for the cover layer) First, the raw material powder for the ceramics constituting the cover layer 50 is prepared. For example, raw materials and additives can be mixed and a solid-phase synthesis method can be used to produce the raw material powder for the cover layer. The obtained raw material powder can be adjusted to the desired average particle size by dry grinding. For example, the desired average particle size can be adjusted using a planetary ball mill with 5 mmφ ZrO2 balls. If the solid electrolyte layer 30 and the cover layer 50 have the same composition, the raw material powder for the solid electrolyte layer can be used as a substitute.

[0058] (Process for preparing electrode layer paste) Next, internal electrode pastes for fabricating the positive electrode layer 10 and negative electrode layer 20 described above are prepared individually. For example, an internal electrode paste can be obtained by uniformly dispersing a conductive additive, electrode active material, solid electrolyte material, sintering aid, binder, plasticizer, etc., in water or an organic solvent. The solid electrolyte paste described above may be used as the solid electrolyte material. Carbon materials may be used as the conductive additive. Metals may also be used as the conductive additive. Examples of metals used as conductive additives include Pd, Ni, Cu, Fe, and alloys containing these. Pd, Ni, Cu, Fe, alloys containing these, and various carbon materials may be used further.

[0059] The paste for internal electrodes contains, for example, one or more glass components such as Li-BO compounds, Li-Si-O compounds, Li-CO compounds, Li-SO compounds, and Li-PO compounds as sintering aids.

[0060] Furthermore, in the paste for the internal electrodes, it is preferable that the average particle size of the solid electrolyte material be 2.5 μm or less. In addition, it is preferable that the ratio of the average particle size of the electrode active material to the average particle size of the solid electrolyte material be within the range of 0.4 to 10.

[0061] (Process for preparing paste for external electrodes) Next, an external electrode paste is prepared for the fabrication of the first external electrode 40a and the second external electrode 40b described above. For example, an external electrode paste can be obtained by uniformly dispersing a conductive material, glass frit, binder, plasticizer, etc., in water or an organic solvent.

[0062] (Solid electrolyte green sheet manufacturing process) A solid electrolyte slurry having a desired average particle size is obtained by uniformly dispersing raw material powder for the solid electrolyte layer in an aqueous solvent or organic solvent together with a binder, dispersant, plasticizer, etc., and then performing wet grinding. At this time, a bead mill, wet jet mill, various kneaders, high-pressure homogenizer, etc. can be used, and it is preferable to use a bead mill from the viewpoint that particle size distribution adjustment and dispersion can be performed simultaneously. A binder is added to the obtained solid electrolyte slurry to obtain a solid electrolyte paste. A solid electrolyte green sheet 51 can be produced by coating with the obtained solid electrolyte paste. The coating method is not particularly limited, and a slot die method, reverse coating method, gravure coating method, bar coating method, doctor blade method, etc. can be used. The particle size distribution after wet grinding can be measured, for example, using a laser diffraction measuring device using the laser diffraction scattering method.

[0063] (Lamination process) As illustrated in Figure 7(a), an internal electrode paste 52 is printed on one surface of a solid electrolyte green sheet 51. An inverse pattern 53 is printed on the areas of the solid electrolyte green sheet 51 where the internal electrode paste 52 is not printed. The same material as the solid electrolyte green sheet 51 can be used as the inverse pattern 53. Multiple printed solid electrolyte green sheets 51 are stacked alternately with a slight offset. As illustrated in Figure 7(b), a laminate is obtained by pressing a cover sheet 54 onto the top and bottom of the stacking direction. In this case, a laminate with a roughly rectangular parallelepiped shape is obtained such that the internal electrode paste 52 for the positive electrode layer 10 is exposed on one end face and the internal electrode paste 52 for the negative electrode layer 20 is exposed on the other end face. The cover sheet 54 can be formed by coating the raw material powder for the cover layer using the same method as in the solid electrolyte green sheet manufacturing process. The cover sheet 54 is formed to be thicker than the solid electrolyte green sheet 51. It may be made thicker during coating, or it may be made thicker by stacking multiple coated sheets.

[0064] Next, the external electrode paste 55 is applied to each of the two end faces using a dipping method or the like, and then dried. This yields a molded body for forming the all-solid-state battery 100a.

[0065] (Firing process) Next, the resulting laminate is fired. The firing conditions are under an oxidizing or non-oxidizing atmosphere, and the maximum temperature is preferably 400°C to 1000°C, more preferably 500°C to 900°C, but there are no particular limitations. To sufficiently remove the binder before reaching the maximum temperature, a step may be included in which the laminate is held at a temperature lower than the maximum temperature in an oxidizing atmosphere. To reduce process costs, it is desirable to fire at the lowest possible temperature. After firing, a re-oxidation treatment may be performed. Through the above steps, an all-solid-state battery 100a is produced.

[0066] Furthermore, by sequentially layering 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 positive electrode layer 10 and the negative electrode layer 20. [Examples]

[0067] A solid-state battery was fabricated according to the following embodiment, and its characteristics were investigated.

[0068] (Examples 1-6 and Comparative Examples 1-3) LiCoPO4 was used as the positive electrode active material, LAGP as the solid electrolyte, and Co3O4 as the Co source added to the solid electrolyte. The positive electrode active material, electron conduction aid, solid electrolyte, and Co3O4 were weighed in a mass ratio of 35:10:54.5:0.5, and a dispersant, plasticizer, organic solvent, and organic binder were added and kneaded to prepare an internal electrode paste for the positive electrode layer.

[0069] TiO2 was used as the negative electrode active material, and LAGP was used as the solid electrolyte. The negative electrode active material, electron conduction aid, and solid electrolyte were weighed in a mass ratio of 35:10:55, and a dispersant, plasticizer, organic solvent, and organic binder were added and kneaded to prepare an internal electrode paste for the negative electrode layer.

[0070] Using LAGP as the solid electrolyte, a solid electrolyte green sheet was prepared using a slurry consisting of an organic binder, a dispersant, a plasticizer, and an organic solvent.

[0071] An internal electrode paste for the positive electrode layer was applied to a first solid electrolyte green sheet by screen printing. An internal electrode paste for the negative electrode layer was applied to a second solid electrolyte green sheet by screen printing. The internal electrode paste for the positive electrode layer and the internal electrode paste for the negative electrode layer were made to have the same thickness. Multiple first solid electrolyte green sheets and multiple second solid electrolyte green sheets were stacked so that the positive electrode layer and the negative electrode layer were alternately pulled out from the left and right to obtain a green chip for a stacked all-solid-state battery. The green chip was sintered by degreasing and firing, and an external electrode paste was applied, formed, and cured to form an external electrode, thereby obtaining a stacked all-solid-state battery.

[0072] For each of Examples 1-6 and Comparative Examples 1-3, the average particle size of the electrode active material in the positive electrode layer (positive electrode active material) and the electrode active material in the negative electrode layer (negative electrode active material) was measured. In addition, the average particle size of the solid electrolyte in the positive electrode layer and the average particle size of the solid electrolyte in the negative electrode layer were measured. For each of the positive and negative electrode layers, the ratio of the average particle size of the electrode active material to the average particle size of the solid electrolyte (average particle size ratio) was measured.

[0073] In Example 1, the average particle size of the positive electrode active material in the positive electrode layer and the average particle size of the negative electrode active material in the negative electrode layer were 0.98 μm. The average particle size of the solid electrolyte in the positive electrode layer and the average particle size of the solid electrolyte in the negative electrode layer were 0.79 μm. The average particle size ratio in the positive electrode layer and the negative electrode layer was 1.24.

[0074] In Example 2, the average particle size of the positive electrode active material in the positive electrode layer and the average particle size of the negative electrode active material in the negative electrode layer was 3.02 μm. The average particle size of the solid electrolyte in the positive electrode layer and the average particle size of the solid electrolyte in the negative electrode layer was 0.79 μm. The average particle size ratio in the positive electrode layer and the negative electrode layer was 3.82.

[0075] In Example 3, the average particle size of the positive electrode active material in the positive electrode layer and the average particle size of the negative electrode active material in the negative electrode layer was 0.98 μm. The average particle size of the solid electrolyte in the positive electrode layer and the average particle size of the solid electrolyte in the negative electrode layer was 1.05 μm. The average particle size ratio in the positive electrode layer and the negative electrode layer was 0.93.

[0076] In Example 4, the average particle size of the positive electrode active material in the positive electrode layer and the average particle size of the negative electrode active material in the negative electrode layer were 0.98 μm. The average particle size of the solid electrolyte in the positive electrode layer and the average particle size of the solid electrolyte in the negative electrode layer were 2.21 μm. The average particle size ratio in the positive electrode layer and the negative electrode layer was 0.44.

[0077] In Example 5, the average particle size of the positive electrode active material in the positive electrode layer and the average particle size of the negative electrode active material in the negative electrode layer was 6.99 μm. The average particle size of the solid electrolyte in the positive electrode layer and the average particle size of the solid electrolyte in the negative electrode layer was 0.79 μm. The average particle size ratio in the positive electrode layer and the negative electrode layer was 8.85.

[0078] In Example 6, the average particle size of the positive electrode active material in the positive electrode layer and the average particle size of the negative electrode active material in the negative electrode layer were 0.49 μm. The average particle size of the solid electrolyte in the positive electrode layer and the average particle size of the solid electrolyte in the negative electrode layer were 0.79 μm. The average particle size ratio in the positive electrode layer and the negative electrode layer was 0.62.

[0079] In Comparative Example 1, the average particle size of the positive electrode active material in the positive electrode layer and the average particle size of the negative electrode active material in the negative electrode layer was 0.98 μm. The average particle size of the solid electrolyte in the positive electrode layer and the average particle size of the solid electrolyte in the negative electrode layer were 2.66 μm. The average particle size ratio in the positive electrode layer and the negative electrode layer was 0.37.

[0080] In Comparative Example 2, the average particle size of the positive electrode active material in the positive electrode layer and the average particle size of the negative electrode active material in the negative electrode layer were 8.13 μm. The average particle size of the solid electrolyte in the positive electrode layer and the average particle size of the solid electrolyte in the negative electrode layer were 0.79 μm. The average particle size ratio in the positive electrode layer and the negative electrode layer was 10.29.

[0081] In Comparative Example 3, the average particle size of the positive electrode active material in the positive electrode layer and the average particle size of the negative electrode active material in the negative electrode layer were 0.30 μm. The average particle size of the solid electrolyte in the positive electrode layer and the average particle size of the solid electrolyte in the negative electrode layer were 0.79 μm. The average particle size ratio in the positive electrode layer and the negative electrode layer was 0.38.

[0082] (porosity) Next, the porosity of the positive and negative electrode layers was measured for each of Examples 1-6 and Comparative Examples 1-3. In Example 1, the porosity of the positive and negative electrode layers was 4.9%. In Example 2, the porosity of the positive and negative electrode layers was 5.6%. In Example 3, the porosity of the positive and negative electrode layers was 6.2%. In Example 4, the porosity of the positive and negative electrode layers was 8.0%. In Example 5, the porosity of the positive and negative electrode layers was 8.4%. In Example 6, the porosity of the positive and negative electrode layers was 9.3%. In Comparative Example 1, the porosity of the positive and negative electrode layers was 11.0%. In Comparative Example 2, the porosity of the positive and negative electrode layers was 10.3%. In Comparative Example 3, the porosity of the positive and negative electrode layers was 12.2%.

[0083] Porosity was judged as good ("○") if it was less than 5%, somewhat good ("△") if it was between 5% and less than 10%, and poor ("×") if it was 10% or more. In Comparative Examples 1 to 3, the porosity was judged as poor ("×"). In Comparative Example 1, this is thought to be because the average particle size of the solid electrolyte was large, exceeding 2.5 μm, and the average particle size ratio was small, less than 0.4. In Comparative Example 2, this is thought to be because the average particle size ratio was large, exceeding 10. In Comparative Example 3, this is thought to be because the average particle size ratio was small, less than 0.4.

[0084] (Capacitance characteristics) Next, the capacity retention rate after 100 cycles was measured for each of Examples 1-6 and Comparative Examples 1-3. The charge-discharge test was performed at room temperature at 10 μA / cm². 2 After charging to 3.4V at a given current density, a 10-minute pause was taken, and then the battery was discharged to 0V at the same current density. This process was repeated 100 times for measurement. The capacity retention rate was defined as the discharge capacity after 100 cycles divided by the initial discharge capacity. A capacity retention rate of 80% or more after 100 cycles was judged as excellent ("◎"), 70% or more but less than 80% was judged as good ("〇"), 60% or more but less than 70% was judged as somewhat good ("△"), and less than 60% was judged as poor ("×").

[0085] In Comparative Examples 1-3, the capacity characteristics were judged as poor ("×"). This is thought to be because the porosity exceeded 10%.

[0086] The overall evaluation for Examples 1-6 and Comparative Examples 1-3 is described below. If the capacitance characteristics were good ("〇") or very good ("◎") and the porosity of the electrode layer was good ("〇"), the overall evaluation was very good ("◎"). If at least the capacitance characteristics were good ("〇") or very good ("◎"), the overall evaluation was good ("〇"). If at least the capacitance characteristics were somewhat good ("△"), the overall evaluation was somewhat good ("△"). If at least the capacitance characteristics were poor ("×"), the overall evaluation was poor ("×"). The results are shown in Table 1. [Table 1]

[0087] For each of Examples 1-6 and Comparative Examples 1-3, the area occupancy rate of the solid electrolyte in the positive electrode layer and the area occupancy rate of the solid electrolyte in the negative electrode layer were measured. In Example 1, the area occupancy rate of the solid electrolyte in the positive electrode layer and the area occupancy rate of the solid electrolyte in the negative electrode layer were 45%. In Example 2, the area occupancy rate of the solid electrolyte in the positive electrode layer and the area occupancy rate of the solid electrolyte in the negative electrode layer were 42%. In Example 3, the area occupancy rate of the solid electrolyte in the positive electrode layer and the area occupancy rate of the solid electrolyte in the negative electrode layer were 41%. In Example 4, the area occupancy rate of the solid electrolyte in the positive electrode layer and the area occupancy rate of the solid electrolyte in the negative electrode layer were 39%. In Example 5, the area occupancy rate of the solid electrolyte in the positive electrode layer and the area occupancy rate of the solid electrolyte in the negative electrode layer were 36%. In Example 6, the area occupancy rate of the solid electrolyte in the positive electrode layer and the area occupancy rate of the solid electrolyte in the negative electrode layer were 36%. In Comparative Example 1, the area occupancy rate of the solid electrolyte in the positive electrode layer and the area occupancy rate of the solid electrolyte in the negative electrode layer were 34%. In Comparative Example 2, the area occupancy rate of the solid electrolyte in the positive electrode layer and the area occupancy rate of the solid electrolyte in the negative electrode layer were 34%. In Comparative Example 3, the area occupancy rate of the solid electrolyte in the positive electrode layer and the area occupancy rate of the solid electrolyte in the negative electrode layer were 34%.

[0088] (Reference examples 1~6) In Reference Examples 1-6, all-solid-state batteries were prepared using the same procedure as in Examples 1-6 and Comparative Examples 1-3. Under the same preparation conditions as Example 1, the mixing ratio of the electrode composite was changed so that only the area occupancy rate of the solid electrolyte within the electrode layer differed. Charge-discharge tests were performed at room temperature at 10 μA / cm². 2 The initial discharge capacity was measured when the battery was charged to 3.4V at a current density, then discharged for 10 minutes, and then discharged again to 0V at the same current density. Subsequently, the capacity per unit cell was calculated, and the initial capacity per unit cell was judged as "◎" if it was 15μAh or more, "〇" if it was 5μAh or more but less than 15μAh, and "△" if it was less than 5μAh. The results are shown in Table 2. Table 2 also includes the measurement results of the porosity of the positive and negative electrode layers. [Table 2]

[0089] Reference Example 1 is an example where the initial discharge capacity per unit cell was 18 μAh when the area occupancy rate of the solid electrolyte was 50%, and it was judged as "◎". Reference Example 2 is an example where the initial discharge capacity per unit cell was 16 μAh when the area occupancy rate of the solid electrolyte was 43%, and it was judged as "〇". Reference Example 3 is an example where the initial discharge capacity per unit cell was 13 μAh when the area occupancy rate of the solid electrolyte was 64%, and it was judged as "〇". Reference Example 4 is an example where the initial discharge capacity per unit cell was 9 μAh when the area occupancy rate of the solid electrolyte was 32%, and it was judged as "〇". Reference Example 5 is an example where the initial discharge capacity per unit cell was 4 μAh when the area occupancy rate of the solid electrolyte was 81%, and it was judged as "△". Reference Example 6 is an example where the initial discharge capacity per unit cell was 3 μAh when the area occupancy rate of the solid electrolyte was 24%, and it was judged as "△".

[0090] Although embodiments of the present invention have been described in detail above, the present invention is not limited to these specific embodiments, and various modifications and changes are possible within the scope of the gist of the present invention as described in the claims. [Explanation of Symbols]

[0091] 10 Positive electrode layer 11 Cathode active material 12 Solid electrolyte 13. First current collector layer 20 Negative electrode layer 21 Negative electrode active material 22 Solid electrolyte 23. Second current collector layer 30 Solid electrolyte layer 40a First external electrode 40b 2nd external electrode 50 Cover Layer 51 Solid Electrolyte Green Sheet 52 Paste for internal electrodes 53 Reverse Pattern 54 Cover Sheets 55 Paste for external electrodes 60 stacked chips 100,100a solid state battery

Claims

1. A solid electrolyte layer containing a first solid electrolyte, A positive electrode layer is provided on the first main surface of the solid electrolyte layer and is a sintered body containing a positive electrode active material and a second solid electrolyte, The negative electrode layer is provided on the second main surface of the solid electrolyte layer and is a sintered body containing a negative electrode active material and a third solid electrolyte, All-solid-state battery, wherein in at least one of the electrode layers, the positive electrode layer and the negative electrode layer, the average particle size of the second solid electrolyte or the third solid electrolyte is 2.5 μm or less, and the ratio of the average particle size of the positive electrode active material to the average particle size of the second solid electrolyte or the ratio of the average particle size of the negative electrode active material to the average particle size of the third solid electrolyte is 0.4 or more and 10 or less.

2. The all-solid-state battery according to claim 1, wherein in at least one of the electrode layers, the area occupancy rate of the second solid electrolyte or the third solid electrolyte in a cross-section viewed from a direction perpendicular to the direction in which the positive electrode layer and the negative electrode layer face each other is 25% or more and 75% or less.

3. The all-solid-state battery according to claim 1 or claim 2, wherein the average particle size of the second solid electrolyte or the third solid electrolyte is 0.05 μm or more.

4. The all-solid-state battery according to claim 1 or claim 2, wherein the porosity in at least one of the electrode layers is 10% or less.

5. The all-solid-state battery according to claim 1 or claim 2, wherein the second solid electrolyte or the third solid electrolyte is a phosphate-based solid electrolyte.

6. The all-solid-state battery according to claim 1 or claim 2, wherein the second solid electrolyte or the third solid electrolyte has a NASICON-type crystal structure.

7. The all-solid-state battery according to claim 1 or claim 2, wherein the positive electrode active material contains Co and P.

8. The all-solid-state battery according to claim 7, wherein the second solid electrolyte or the third solid electrolyte contains Co.

9. The positive electrode active material is LiCoPO ４ , LiCo ２ P ３ O １０ , Li ２ CoP ２ O ７ , Li ６ Co ５ (P ２ O ７ ) ４ The all-solid-state battery according to claim 7, comprising at least one of the above.

10. A solid electrolyte layer comprising a first solid electrolyte, A positive electrode layer is provided on the first main surface of the solid electrolyte layer and includes a positive electrode active material and a second solid electrolyte, The negative electrode layer is provided on the second main surface of the solid electrolyte layer and includes a negative electrode active material and a third solid electrolyte, In at least one of the electrode layers, the positive electrode layer and the negative electrode layer, the average particle size of the second solid electrolyte or the third solid electrolyte is 2.5 μm or less, and the ratio of the average particle size of the positive electrode active material to the average particle size of the second solid electrolyte or the ratio of the average particle size of the negative electrode active material to the average particle size of the third solid electrolyte is 0.4 or more and 10 or less. All-solid-state battery, wherein in at least one of the electrode layers, the area occupancy rate of the second solid electrolyte or the third solid electrolyte in a cross-section viewed from a direction perpendicular to the direction in which the positive electrode layer and the negative electrode layer face each other is 25% or more and 75% or less.

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