Negative electrode, solid-state battery, and manufacturing method of producing laminate

Abstract

To provide a negative electrode that is less likely to be affected by precipitation of metallic lithium or the like, such as an internal short circuit, when it is used as a solid battery, and contributes to energy efficiency.SOLUTION: A negative electrode is a negative electrode of a solid-state battery, and includes: a negative electrode mixture layer formed by filling pores of a porous metal body with a negative electrode mixture containing a negative electrode active material; and a gap layer including a part containing a solid electrolyte and a part to which a gap is provided into the pores of the porous metal body on a solid electrolyte layer side in a thickness direction of the porous metal body that is pressurized in the thickness direction. A specific surface area of the metal porous body before the pressurization is not less than 500 m2 / m3 or more and not more than 6000 m2 / m3.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for producing a negative electrode, a solid-state battery, and a laminate. [Background technology]

[0002] In recent years, research and development into secondary batteries that contribute to energy efficiency has been conducted to ensure that more people have access to affordable, reliable, sustainable, and advanced energy. Solid-state batteries have high energy density and are used in a wide range of applications. In particular, lithium-ion secondary batteries are becoming increasingly important as power sources for electric vehicles (EVs), hybrid electric vehicles (HEVs), and other vehicles.

[0003] A known solid-state battery configuration uses a foam metal as the current collector for the negative electrode to increase the packing density of the electrode active material. In this regard, Patent Document 1 discloses a solid-state battery in which a negative electrode composite is filled into the pores of a porous metal current collector to increase the amount of active material per unit area of ​​the electrode. The electrode in Patent Document 1 utilizes the elasticity of the porous metal to accommodate volume changes during charging and discharging. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2022-108360 Summary of the Invention [Problem to be solved by the invention]

[0005] To contribute to further energy efficiency, solid-state batteries are also required to maintain their battery life even after repeated charge and discharge. For example, required characteristics include the prevention of lithium ions, sodium ions, etc., receiving electrons at the negative electrode during repeated charge and discharge of a solid-state battery, resulting in the deposition of metallic lithium, metallic sodium, etc. on the negative electrode. The deposition of metallic lithium, etc. on the negative electrode can increase the resistance of the solid-state battery by making it easier for gaps to form between the layers, which can also lead to internal short circuits in which the positive and negative electrodes come into electrical contact. This deposition of metallic lithium, etc., is particularly likely to occur in high-capacity negative electrodes.

[0006] In light of this background, an object of the present invention is to provide a negative electrode that is less susceptible to the effects of precipitation of metallic lithium and the like, such as internal short circuits, when used in a solid-state battery, thereby contributing to improved energy efficiency. [Means for solving the problem]

[0007] In order to achieve the above object, a negative electrode according to a first aspect of the present invention is a negative electrode for a solid-state battery, comprising: a negative electrode composite layer formed by filling pores of a porous metal body with a negative electrode composite containing a negative electrode active material; and a void layer having a portion containing a solid electrolyte and a portion in which voids are provided in the pores of the porous metal body, on the solid electrolyte layer side in the thickness direction of the porous metal body that has been pressed in the thickness direction, the void layer having a portion containing a solid electrolyte and a portion in which voids are provided in the pores of the porous metal body, and the specific surface area of ​​the porous metal body before the pressing is 500 m 2 / m 3 More than 6000m 2 / m 3 The following is the result.

[0008] According to this configuration, when deposition of metallic lithium or the like occurs on the negative electrode, deposition of metallic lithium or the like tends to occur intensively within the pores of the metallic porous body that were voids in the void layer, thereby suppressing deposition of metallic lithium or the like on the negative electrode interface, etc. Therefore, when used as a solid-state battery, it is possible to make it less likely that the effects of deposition of metallic lithium or the like, such as internal short circuits, will occur.

[0009] A second aspect of the present invention provides the negative electrode according to the first aspect, wherein the density of the solid electrolyte in the gap layer is 1.5 g / cc or more and less than 1.8 g / cc.

[0010] This configuration makes it possible to both suppress the occurrence of cracks during the manufacturing process of the solid-state battery and suppress the decrease in ion conductivity.

[0011] According to a third aspect of the present invention, in the negative electrode according to the first aspect, in the void layer, the ratio of the volume of the voids in the pores to the volume of the pores of the metal porous body is 10% or less.

[0012] According to this configuration, the decrease in density of the negative electrode is suppressed compared to when the ratio of the volume occupied by voids in the pores to the volume inside the pores of the metal porous body is greater than 10%, and therefore the decrease in energy density associated with the provision of a void layer in the negative electrode can be suppressed.

[0013] A fourth aspect of the present invention provides the negative electrode according to the first aspect, wherein the negative electrode active material contains at least a silicon-based material.

[0014] According to this configuration, a negative electrode containing a silicon-based material as the negative electrode active material can be suitably used.

[0015] The invention according to claim 5 of the present invention is the negative electrode according to claim 4, wherein the negative electrode active material in the negative electrode mixture layer has a basis weight of 3 mg / cm 2 is greater than.

[0016] According to this configuration, the weight of the negative electrode active material in the negative electrode mixture layer is 3 mg / cm 2 Compared to the following cases, it is possible to improve the capacity of the solid-state battery while suppressing the decrease in capacity of the solid-state battery due to charging and discharging.

[0017] The invention according to claim 6 of the present invention is the negative electrode according to claim 4, wherein the ratio of the discharge capacity of lithium that can enter the voids in the void layer during charging and discharging to the discharge capacity of the negative electrode active material is 5% or more and 8% or less.

[0018] This configuration makes it possible to secure voids for accommodating metallic lithium and the like that precipitate during charge and discharge, while also suppressing a decrease in energy density.

[0019] A solid state battery according to a seventh aspect of the present invention includes the negative electrode according to any one of the first to sixth aspects, a positive electrode containing lithium, and a solid electrolyte layer.

[0020] In this solid-state battery, when metallic lithium or the like precipitates on the negative electrode, the precipitation of metallic lithium or the like tends to occur intensively in the pores of the porous metal body that were voids in the void layer, thereby suppressing the precipitation of metallic lithium or the like on the negative electrode interface, etc. Therefore, it is possible to make it difficult for the effects of the precipitation of metallic lithium or the like, such as internal short circuits, to occur.

[0021] A method for manufacturing a laminate according to claim 8 of the present invention is a method for manufacturing a laminate including a solid electrolyte layer and a negative electrode, and includes the steps of: applying a negative electrode composite containing a negative electrode active material to a metal porous body, and forming a negative electrode composite layer in which the pores of the metal porous body are filled with the negative electrode composite; pressing a concave-convex portion of a pressurizing device against the surface of the metal porous body on which the negative electrode composite layer has been formed, to form a concave-convex portion on the surface; and applying a solid electrolyte to the surface of the metal porous body on which the concave-convex portion has been formed, to form a void layer having a portion containing the solid electrolyte and a portion where voids are provided in the pores of the metal porous body, and a solid electrolyte layer.

[0022] In a solid-state battery including a laminate manufactured by this manufacturing method, when deposition of metallic lithium or the like occurs on the negative electrode, deposition of metallic lithium or the like tends to occur intensively in the pores of the metallic porous body that were voids in the void layer, thereby suppressing deposition of metallic lithium or the like on the negative electrode interface, etc. Therefore, when used as a solid-state battery, it is possible to make it less likely that effects of deposition of metallic lithium or the like, such as internal short circuits, will occur. [Brief explanation of the drawings]

[0023] [Figure 1] FIG. 2 is a cross-sectional view schematically showing a laminate in a secondary battery. [Figure 2] FIG. 10 is a diagram showing a Cole-Cole plot created from measurement values. [Figure 3] FIG. 10 is a diagram showing the relationship between the porosity of the void layer and the energy density. [Figure 4] FIG. 1A is a diagram illustrating the filling step, and FIG. 1B is a diagram schematically illustrating the metal porous body that has been filled with the negative electrode composite and then dried. [Figure 5] 10 is a diagram for explaining the unevenness forming step. FIG. [Figure 6] FIG. 1 is a diagram showing the capacity of coin-type cells for each cycle in Example 1, Comparative Example 1, and Comparative Example 2. [Figure 7] FIG. 10 is a diagram showing the capacity of coin-type cells for each cycle in Example 2, Comparative Example 3, and Comparative Example 4. DETAILED DESCRIPTION OF THE INVENTION

[0024] Preferred embodiments of the present invention will now be described in detail.

[0025] [Solid battery] The solid-state battery of this embodiment is composed of a plurality of stacked cells, each of which is a unit cell formed by stacking a positive electrode, a solid electrolyte layer, and a negative electrode. However, the number of cells constituting the solid-state battery may be one. Solid-state batteries are known to have advantages such as a low risk of fire, rapid charging, resistance to deterioration, and a long life. On the other hand, solid-state batteries are more susceptible to short-circuiting when metallic lithium or the like precipitates on the negative electrode than secondary batteries with liquid electrolytes.

[0026] In solid-state batteries, the occurrence of a short circuit when metallic lithium or the like is deposited at the negative electrode interface or the like is thought to be caused by the following reasons. In solid-state batteries, the negative electrode and the solid electrolyte layer form a solid-state interface. When metallic lithium is deposited, lithium ions become less conductive at the interface between the negative electrode and the solid electrolyte at the deposition site, and resistance is likely to increase. This makes it more likely that cracks will occur in the electrode or solid electrolyte layer, making it difficult for the cell to function, and the deposited metallic lithium will easily penetrate into the gaps in the solid electrolyte layer, causing a short circuit. In contrast, the negative electrode of this embodiment can easily suppress the deposition of metallic lithium and the like on the negative electrode interface, and therefore, even in the case of a solid-state battery, the battery life is less likely to decrease.

[0027] The solid-state battery of this embodiment may be any of coin, button, cylindrical, rectangular, and laminate types, and is applicable to a wide range of uses, including mobile devices such as mobile phones and laptops, and in-vehicle use.

[0028] [Laminate] 1 is a cross-sectional view schematically showing a laminate 1 of a solid-state battery. The laminate 1 includes a solid electrolyte layer 10 and an anode 20. The solid electrolyte layer 10 is laminated on the anode 20. Although not shown, in the solid-state battery, a cathode (not shown) is laminated on the solid electrolyte layer 10.

[0029] (solid electrolyte layer) The solid electrolyte layer 10 includes a solid electrolyte 11. The solid electrolyte 11 of this embodiment is not only provided in the solid electrolyte layer 10, but also in the pores of the porous metal body 21 of the negative electrode 20, which will be described later. Examples of the solid electrolyte 11 include sulfide-based solid electrolyte materials, oxide-based solid electrolyte materials, nitride-based solid electrolyte materials, and halide-based solid electrolyte materials. Examples of the sulfide-based solid electrolyte materials include LPS-based halogens (Cl, Br, I), Li2S-P2S5, and Li2S-P2S5-LiI. The term "Li2S-P2S5" above refers to a sulfide-based solid electrolyte material obtained using a raw material composition containing Li2S and P2S5, and the same applies to other terms. Examples of the oxide-based solid electrolyte materials include NASICON-type oxides, garnet-type oxides, and perovskite-type oxides. Examples of the NASICON-type oxides include oxides containing Li, Al, Ti, P, and O (e.g., Li 1.5 A l0.5 Ti 1.5 (PO4)3). Examples of garnet-type oxides include oxides containing Li, La, Zr, and O (e.g., Li7La3Zr2O 12 Examples of perovskite oxides include oxides containing Li, La, Ti, and O (for example, LiLaTiO3).

[0030] The particle size of the solid electrolyte 11 is preferably greater than 0.5 μm and less than 5 μm. If the particle size of the solid electrolyte 11 is 0.5 μm or less, the solid electrolyte 11 is likely to be insufficiently dispersed when preparing a slurry of the solid electrolyte 11, and it becomes difficult to adjust the viscosity of the slurry, making it difficult to apply the slurry. If the particle size of the solid electrolyte 11 is 5 μm or more, the solid electrolyte 11 is likely to be uniformly disposed within the pores of the porous metal body 21, making it more likely that the solid electrolyte 11 will be applied unevenly to the porous metal body 21. Furthermore, if the solid electrolyte 11 is applied unevenly to the porous metal body 21, the electrical resistance is likely to increase.

[0031] The solid electrolyte layer 10 preferably comprises 90 parts by mass or more and 97 parts by mass or less of the solid electrolyte 11 and 3 parts by mass or more and 10 parts by mass or less of the binder. The thickness of the solid electrolyte layer 10 is not particularly limited because various embodiments are used depending on the specifications of the cell, but is preferably, for example, 10 μm or more and 50 μm or less. The electrical resistance of the solid electrolyte layer 10 is determined by impedance measurement. The electronic conductivity of the solid electrolyte layer 10 is determined by measuring the electrical resistivity of the solid electrolyte layer 10 or by using a scanning probe microscope. The thickness and density of the solid electrolyte layer 10 are determined by using a scanning electron microscope (SEM) after CP processing.

[0032] (Negative electrode) The negative electrode 20 includes a porous metal body 21 as a current collector and a negative electrode composite material 22 . The metal porous body 21 has pores that are continuous with one another. In this embodiment, the pores of the metal porous body 21 are filled with a negative electrode composite 22. Examples of the metal porous body include mesh, woven fabric, nonwoven fabric, embossed body, punched body, expanded body, and foamed body. Examples of metals used for the metal porous body include nickel, aluminum, stainless steel, titanium, copper, and silver. The current collector made of a porous metal has a large surface area. Therefore, by filling this current collector with a negative electrode mixture containing a negative electrode active material, the amount of active material per unit area of ​​the electrode can be increased. Therefore, the negative electrode of this embodiment has a high energy density when used in a solid-state battery.

[0033] The negative electrode composite 22 includes a negative electrode active material. The negative electrode active material is not particularly limited as long as it can absorb and release lithium ions, and examples thereof include silicon-based materials, carbon-based materials, and metal-based materials. The negative electrode 20 of this embodiment is suitably used when the negative electrode active material included in the negative electrode composite 22 is a silicon-based material. When the negative electrode active material is a silicon-based material, the silicon tends to expand and contract during repeated charge and discharge in a solid-state battery. This tends to cause the negative electrode active material to slide off the current collector, destabilizing the interface and accelerating the deposition of metallic lithium. On the other hand, in the negative electrode 20 of this embodiment, the current collector is a porous metal body 21, so the negative electrode active material is less likely to slide off.

[0034] Examples of the negative electrode active material include silicon-based materials such as Si, SiO, and SiO2, carbon-based materials such as artificial graphite, natural graphite, hard carbon, and soft carbon, and metal-based materials such as metallic lithium, lithium alloys, metal oxides, metal sulfides, and metal nitrides. Furthermore, negative electrode mixture 22 may contain solid electrolyte 11, a binder, and a conductive additive.

[0035] The negative electrode composite 22 preferably comprises 65 parts by mass or more and 75 parts by mass or less of a negative electrode active material, 23 parts by mass or more and 33 parts by mass or less of a solid electrolyte 11, 1 part by mass of a binder, and 1 part by mass of a conductive additive. The electrical resistance, electronic conductivity, thickness, and density of negative electrode composite material 22 are measured by the same methods as those for solid electrolyte layer 10.

[0036] Furthermore, the particle size of the negative electrode active material is preferably greater than 0.1 μm and less than 10 μm. If the particle size of the negative electrode active material is 0.1 μm or less, the negative electrode active material is likely to be insufficiently dispersed when preparing a slurry of the negative electrode composite 22 containing the negative electrode active material, and it becomes difficult to adjust the viscosity of the slurry, making it difficult to apply the slurry. If the particle size of the negative electrode active material is 1 μm or more, the negative electrode active material is likely to be difficult to uniformly fill the pores of the porous metal body 21, making it more likely that the negative electrode composite 22 will be unevenly applied to the porous metal body 21. If the negative electrode composite 22 is unevenly applied to the porous metal body 21, the electrical resistance is likely to increase.

[0037] The layers constituting negative electrode 20 are made up of negative electrode composite layer 201 and void layer 202. Negative electrode mixture layer 201 is a layer formed by filling pores of porous metal body 21 with negative electrode mixture 22. The weight of the negative electrode active material in negative electrode mixture layer 201 is 3 mg / cm. 2 The weight of the negative electrode active material in negative electrode composite layer 201 is preferably greater than 3 mg / cm 2 When the thickness is larger than 10 μm, the capacity of the solid-state battery can be improved. The thickness of negative electrode mixture layer 201 is not particularly limited because various embodiments are used depending on the specifications of the cell, but it is preferably, for example, 10 μm or more and 200 μm or less.

[0038] Void layer 202 is located on negative electrode composite layer 201 and is made of porous metal body 21 and solid electrolyte 11. More specifically, void layer 202 is made up of a portion where solid electrolyte 11 is provided and void portion 23, where at least a portion of the inside of the pores of porous metal body 21 is void and does not contain either solid electrolyte 11 or negative electrode composite 22. Therefore, void layer 202 can also be regarded as a low-density layer in which the density of solid electrolyte 11 is lower than that of solid electrolyte layer 10. In FIG. 1, the metal porous body 21 is shown only in the void portion 23 of the void layer 202, but the metal porous body 21 is also provided in the portion of the void layer 201 where the anode composite 22 is filled and in the portion of the void layer 202 where the solid electrolyte 11 is filled.

[0039] The negative electrode 20 of this embodiment has a negative electrode composite layer 201 and a void layer 202, thereby achieving a high energy density as a solid-state battery. Specifically, during repeated charge and discharge as a solid-state battery, lithium ions and electrons present near the negative electrode 20 are easily transported to the voids 23 along the metal skeleton of the porous metal body 21 and the solid electrolyte 11 in the void layer 202, and the lithium ions are easily stably precipitated as metallic lithium in the voids 23. This solid-state battery allows for more control over the location of lithium precipitation than conventional solid-state batteries in which metallic lithium precipitates at random locations on the negative electrode. This suppresses internal short circuits and other problems caused by the precipitation of metallic lithium in conventional solid-state batteries, resulting in a solid-state battery with excellent cycle characteristics. That is, in this embodiment, the void layer 202 having the voids 23 is provided in the negative electrode 20 to accommodate metallic lithium precipitated during charge and discharge.

[0040] 1, the upper portion of the void layer 202 is filled with the solid electrolyte 11 without providing the void portion 23, but this is not limiting. The void portion 23 may be provided in the void layer 202 at any position in the vertical direction.

[0041] (positive electrode) The positive electrode has a positive electrode mixture containing a positive electrode active material. The positive electrode active material is not particularly limited as long as it can absorb and release lithium ions. Examples of the positive electrode active material include LiCoO2, Li(Ni 5 / 10 Co 2 / 10 Mn 3 / 10 )O2, Li(Ni 6 / 10 Co 2 / 10 Mn 2 / 10 )O2, Li(Ni 8 / 10 Co 1 / 10 Mn 1 / 10 )O2, Li(Ni 0.8 Co 0.15 A l0.05 )O2, Li(Ni 1 / 6 Co 4 / 6 Mn 1 / 6 )O2, Li(Ni 1 / 3 Co 1 / 3 Mn 1 / 3)O2, LiCoO4, LiMn2O4, LiNiO2, LiFePO4, lithium sulfide, etc.

[0042] (Other ingredients) The solid-state battery may contain other components in addition to the materials described above. The other components are not particularly limited, and may be any components that can be used when fabricating a solid-state battery. Examples of the other components include a conductive additive and a binder. Examples of the conductive additive include acetylene black. Examples of the binder for the positive electrode include polyvinylidene fluoride. Examples of the binder for the negative electrode include sodium carboxymethyl cellulose, styrene butadiene rubber, and sodium polyacrylate.

[0043] [Characteristics of laminates] Next, the characteristic configuration of the laminate 1 of this embodiment will be described.

[0044] (Specific surface area of ​​porous metal body) The specific surface area of ​​the porous metal body 21 is controlled in accordance with the pressure applied when the negative electrode 20 is formed or when the cell is formed. Before being pressurized, the specific surface area of ​​the porous metal body 21 is 500 m 2 / m 3 More than 6000m 2 / m 3 It is preferable that the specific surface area of ​​the porous metal body 21 is measured by a mercury porosimeter. The specific surface area of ​​the porous metal body 21 before pressure application is 6000 m 2 / m 3 If it is larger than 1000 kJ / cm 2 , the strength of the porous metal body 21 will be reduced, and cracks may occur in the porous metal body 21 as the solid-state battery is charged and discharged, making it difficult to ensure the function of the solid-state battery. In addition, the specific surface area of ​​the porous metal body 21 before pressurization is 500 m 2 / m 3If the contact area is less than 1 / 2 mm, the contact area between the porous metal body 21 and the solid electrolyte 11 and the contact area between the metal skeletons of the porous metal body 21 are small, making it difficult to form an electron transfer path (electron path), which increases the electrical resistance and makes it difficult for metallic lithium to precipitate during charging and discharging. Also, the solid electrolyte 11 provided in the pores of the porous metal body 21 tends to be unevenly distributed, which increases the diffusion resistance.

[0045] Table 1 shows the relationship between the specific surface area and electrical resistivity of the porous metal body 21 before pressure is applied.

[0046] [Table 1]

[0047] Table 1 shows the electrical resistivity of three porous metal bodies 21 each having a different specific surface area before pressure is applied. As shown in Table 1, when the specific surface area before pressure is applied is 100 m 2 / m 3 The porous metal body 21 has a specific surface area of ​​500 m before being pressurized. 2 / m 3 Porous metal 21 and 6000m 2 / m 3 The metal porous body 21 has a higher electrical resistivity than the metal porous body 21.

[0048] 2 is a diagram showing a Cole-Cole plot created from measurement values ​​obtained by measuring the impedance of a solid-state battery while changing the frequency of an AC voltage applied to the negative electrode 20. The solid-state battery used for the measurement had a specific surface area of ​​200 m2 of porous metal body 21 before pressure application. 2 / m 3 and a porous metal body having a specific surface area of ​​5800 m before being pressurized. 2 / m 3 2, the horizontal axis represents the real component of the impedance, and the vertical axis represents the imaginary component of the impedance.

[0049] In the Cole-Cole plot shown in Fig. 2, the intercept of the first Y-axis is taken as an estimated value of electronic resistance, and the intercept of the right semicircle Y-axis is taken as an estimated value of diffusion resistance. As shown in Fig. 2, when the specific surface area of ​​the porous metal body 21 before pressurization is 5800 m 2 / m 3 The specific surface area of ​​the porous metal body 21 before pressure is 200 m 2 / m 3 It was confirmed that the solid-state battery including the negative electrode 20 having the above structure had higher electrical resistance and diffusion resistance.

[0050] (Density of solid electrolyte in the gap layer) In the gap layer 202, the density of the solid electrolyte 11 is preferably 1.5 g / cc or more and less than 1.8 g / cc. If the density of the solid electrolyte 11 in the void layer 202 is 1.8 g / cc or more, cracks may occur in the void layer 202 when the negative electrode 20 is pressurized in the cell formation process. If the density of the solid electrolyte 11 in the void layer 202 is less than 1.5 g / cc, the energy density decreases and the contact area between particles of the solid electrolyte 11 in the void layer 202 decreases, which tends to reduce ion conductivity. In this case, the ion diffusion resistance of the cell increases, which may lead to deterioration of rate characteristics, such as difficulty in rapid charging of the solid battery.

[0051] The density of the solid electrolyte 11 in the gap layer 202 is controlled by the pressure that is applied when the negative electrode 20 and the solid electrolyte layer 10 are pressed by a roll press to form the laminate 1 . Furthermore, a vertical cross section of the void layer 202 is prepared by irradiating the laminate 1 with an argon beam, and the prepared cross section of the void layer 202 is observed with an electron microscope to measure the thickness of the void layer 202. Then, the density of the solid electrolyte 11 in the void layer 202 is calculated from the measured thickness of the void layer 202 and the weight per unit area of ​​the solid electrolyte 11 in the void layer 202.

[0052] (porosity of void layer) In the void layer 202, the ratio of the volume occupied by the voids of the void portion 23 to the volume inside the pores of the porous metal body 21 is preferably 10% or less. Hereinafter, the ratio of the volume occupied by the voids of the void portion 23 to the volume inside the pores of the porous metal body 21 in the void layer 202 may be referred to as the porosity of the void layer 202. If the porosity of the void layer 202 is greater than 10%, the density of the negative electrode 20 decreases, and therefore the thickness of the negative electrode 20 required to ensure the capacity of the solid-state battery increases. Also, if the thickness of the negative electrode 20 increases, the number of cells constituting a solid-state battery of a predetermined thickness decreases, which may result in a decrease in the energy density of the solid-state battery. Furthermore, the initial capacity ratio (N / P ratio) of the positive electrode to the negative electrode 20 in the solid-state battery is likely to deviate from the target value, which may lead to the progression of degradation accompanied by a decrease in the capacity of the solid-state battery.

[0053] The porosity of the void layer 202 is controlled by the pressure that is applied when the negative electrode 20 and the solid electrolyte layer 10 are pressed by a roll press to form the laminate 1 . The porosity of the porous layer 202 is measured by a gas adsorption method.

[0054] Fig. 3 is a diagram showing the relationship between the porosity of the void layer 202 and the energy density. Fig. 3 shows the energy densities of four solid-state batteries provided with solid electrolytes 11 having different densities in the void layer 202. The energy density of each solid-state battery is shown for each porosity of the void layer 202.

[0055] As shown in FIG. 3, it was confirmed that when the density of the solid electrolyte 11 in the void layer 202 is 1.4 g / cc, the energy density of the solid battery is lower than when the density of the solid electrolyte 11 in the void layer 202 is 1.5 g / cc, 1.6 g / cc, and 1.8 g / cc. Furthermore, it was confirmed that in any of the solid state batteries, when the porosity of the void layer 202 is greater than 10%, the energy density of the solid state battery decreases significantly.

[0056] (Lithium discharge ratio to negative electrode active material) The ratio of the discharge capacity of lithium that can enter the voids in the void portions 23 of the void layer 202 during charge and discharge to the discharge capacity of the negative electrode active material in the negative electrode 20 is preferably 5% or more and 8% or less. Note that the lithium that can enter the voids in the void portions 23 of the void layer 202 during charge and discharge refers to metallic lithium that exists in the void layer 202 when all of the voids previously provided in the void portions 23 are filled with metallic lithium that precipitates during charge and discharge. Furthermore, the ratio of the discharge capacity of lithium that can enter the voids in the void portions 23 of the void layer 202 during charge and discharge to the discharge capacity of the negative electrode active material in the negative electrode 20 may be referred to hereinafter as the discharge ratio of lithium to the negative electrode active material. If the ratio of discharged lithium to the negative electrode active material is less than 5%, the voids 23 may be insufficient to accommodate metallic lithium that precipitates during charging and discharging. Furthermore, if the ratio of discharged lithium to the negative electrode active material is greater than 8%, the thickness of the negative electrode 20 required to ensure the capacity of the solid-state battery increases. Furthermore, if the thickness of the negative electrode 20 increases, the number of cells that constitute a solid-state battery of a predetermined thickness decreases, which may result in a decrease in the energy density of the solid-state battery.

[0057] [Solid-state battery manufacturing method] Next, a method for manufacturing a solid-state battery will be described. The solid state battery of this embodiment is manufactured by an anode manufacturing process of manufacturing the anode 20, a laminate manufacturing process of manufacturing the laminate 1 by laminating the solid electrolyte layer 10 on the anode 20, and a lamination process of laminating the cathode on the laminate 1. The anode manufacturing process also includes a filling process of filling and applying the anode composite 22 into the pores of the metal porous body 21, and an irregularity forming process of forming irregularities on the metal porous body 21 filled with the anode composite 22.

[0058] (filling process) Fig. 4(A) is a diagram for explaining the filling step, and Fig. 4(B) is a diagram schematically showing porous metal body 21 that has been filled and coated with negative electrode composite material 22 and then dried. 4(A), two coaters 30 and two plungers 40 are used to fill and coat the pores of the porous metal body 21 with the negative electrode composite material 22. In this embodiment, the plungers 40 push out the negative electrode composite material 22 that has been filled as a slurry into the coaters 30, thereby discharging the slurry from the coaters 30. The coaters 30 are provided on both outer sides of the porous metal body 21 in the thickness direction, and discharge the slurry onto both sides of the porous metal body 21, thereby filling and coating the pores of the porous metal body 21 with the slurry.

[0059] Furthermore, the coater 30 and plunger 40 are capable of moving in the longitudinal direction of the porous metal body 21 (the vertical direction in the illustrated example). The plunger 40 controls the force with which it pushes the slurry filled in the coater 30 while moving together with the coater 30, thereby controlling whether or not the slurry is discharged from the coater 30. In other words, by controlling the force with which it pushes the slurry filled in the coater 30, the plunger 40 controls whether or not the slurry is filled and applied into the pores of the porous metal body 21, depending on the position of the porous metal body 21 in the longitudinal direction.

[0060] After the pores of the porous metal body 21 are filled with the slurry, the porous metal body 21 is dried with the thickness direction facing up and down. During this drying process, the slurry filled and coated in the pores of the porous metal body 21 is immersed in the lower part due to gravity. Therefore, as shown in FIG. 4(B), in the dried porous metal body 21, a layer in which the pores are not filled with the negative electrode composite material 22 is formed on top of a layer in which the pores are filled with the negative electrode composite material 22.

[0061] (Irregularity forming process) FIG. 5 is a diagram for explaining the unevenness forming step. After the above-mentioned filling step, the porous metal body 21 is pressed by a roll press 50, which is a pressurizing device, as shown in FIG. The roll press 50 includes an uneven roller 51, which is an example of an uneven portion having an uneven surface, and a perfect circular roller 52, which has a perfect circular surface. The uneven roller 51 and the perfect circular roller 52 are provided on different sides of the porous metal body 21 in the thickness direction, and sandwich and press the porous metal body 21. More specifically, the uneven roller 51 presses the layer side of the porous metal body 21 that is not filled with the negative electrode composite material 22, and the perfect circular roller 52 presses the layer side of the porous metal body 21 that is filled with the negative electrode composite material 22. The specific surface area of ​​the porous metal body 21 is controlled according to the pressure applied to the porous metal body 21 by the pressing of the roll press 50.

[0062] Furthermore, with the porous metal body 21 sandwiched and pressed between the uneven roller 51 and the circular roller 52, the uneven roller 51 rotates counterclockwise in the figure and the circular roller 52 rotates clockwise in the figure, thereby moving along the longitudinal direction of the porous metal body 21. As a result, the porous metal body 21 is pressurized along the longitudinal direction, and an uneven portion 210 consisting of recessed recesses 211 and protruding protrusions 212 is formed on the surface of the porous metal body 21 on the side pressed by the uneven roller 51. The uneven portion 210 is formed from the portions of the porous metal body 21 whose pores are not filled with the negative electrode composite material 22, as shown in FIG. 4(B). Therefore, the uneven portion 210 of the porous metal body 21 is the portion where the pores are not filled with the negative electrode composite material 22.

[0063] (Laminate manufacturing process) Next, solid electrolyte 11 is applied to the pressurized porous metal body 21. In this embodiment, solid electrolyte 11 is applied to the surface of the concave-convex portions 210 of the porous metal body 21. At this time, the solid electrolyte 11 fills the concave portions 211 of the porous metal body 21, and the solid electrolyte 11 is piled up on the surface of the convex portions 212. Furthermore, by stacking the solid electrolyte 11 in layers not only on the surface of the concave-convex portions 210 but also on the concave-convex portions 210 and then roll-pressing, the negative electrode 20 composed of the negative electrode composite layer 201 and the void layer 202 shown in FIG. 1 is formed, and the laminate 1 composed of this negative electrode 20 and the solid electrolyte layer 10 is also formed. Here, the void portions 23 of the porous metal body 21 shown in FIG. 1 are the portions inside the pores of the convex portions 212 of the porous metal body 21 shown in FIG. 5. As long as voids are provided in at least some of the pores of the protrusions 212 of the porous metal body 21, the pores of the protrusions 212 may or may not contain solid electrolyte 11.

[0064] (Lamination process) Next, a positive electrode is further laminated on the formed laminate 1, and the laminate is pressed by a uniaxial press to form one unit cell as a solid-state battery. [Example]

[0065] Examples of the present invention will be described below, but the present invention is not limited to the following examples.

[0066] [Example 1] (Fabrication of coin-type cells (solid-state batteries)) A negative electrode composite slurry was prepared using 65 parts by mass of silicon as a negative electrode active material, 33 parts by mass of a solid electrolyte, 1 part by mass of a binder, and 1 part by mass of a conductive additive. Next, the obtained slurry was filled into a current collector having a specific surface area of ​​5800 m by the method shown in FIG. 4(A). 2 / m 3 The porous metal body is then dried, and the porous metal body is then pressed using the method shown in Figure 5 as the roughness forming process, resulting in a weight of 5 mg / cm. 2A negative electrode mixture layer containing the negative electrode active material was formed, and irregularities were formed on the surface of the metal porous body. Next, a solid electrolyte slurry was prepared using 90 parts by mass of the solid electrolyte and 10 parts by mass of the binder, and the obtained slurry was applied to the surface of the metal porous body on which the irregularities were formed. The metal porous body was then dried and pressed using a roll press to produce the laminate shown in FIG. 1. Furthermore, a slurry of a positive electrode composite made of lithium was prepared, and the obtained slurry was applied to the stack. The stack was then dried, and a uniaxial press process was performed to pressurize the stack at a pressure of 3 MPa, thereby producing a coin-shaped cell with a diameter of 10 mm.

[0067] [Example 2] The weight of the negative electrode active material in the negative electrode mixture layer is 10 mg / cm 2 A coin-type cell of Example 2 was produced in the same manner as in Example 1, except that:

[0068] [Comparative Example 1] A negative electrode was fabricated in the same manner as in Example 1, except that copper foil was used as a current collector, and the negative electrode mixture was placed on the copper foil and pressed using a smooth roll press. The negative electrode was fabricated in the same manner as in Example 1, with the negative electrode mixture layer having a basis weight of 5 mg / cm. 2 A coin-shaped cell of Comparative Example 1 having a diameter of 10 mm was produced. In the negative electrode of this coin-shaped cell of Comparative Example 1, a metal porous body was not used, and no void layer as shown in FIG. 1 was formed.

[0069] Comparative Example 2 It is used as a current collector with the negative electrode mixture filled into the pores and has a specific surface area of ​​200m 2 / m 3 The negative electrode was fabricated by the same method as in Example 1, except that a smooth roll press was used to pressurize a porous metal body having a negative electrode active material weight of 5 mg / cm. 2A coin-type cell of Comparative Example 2 having a diameter of 10 mm was fabricated. The negative electrode of the coin-type cell of Comparative Example 2 is the same as that of Examples 1 and 2 in that a porous metal body is used, but differs from that of Examples 1 and 2 in that no void layer as shown in FIG. 1 is formed.

[0070] Comparative Example 3 The weight of the negative electrode active material in the negative electrode mixture layer is 10 mg / cm 2 A coin-type cell of Comparative Example 3 was produced in the same manner as in Comparative Example 1, except that:

[0071] Comparative Example 4 The weight of the negative electrode active material in the negative electrode mixture layer is 10 mg / cm 2 A coin-type cell of Comparative Example 4 was produced in the same manner as in Comparative Example 2, except that:

[0072] [Coin cell evaluation] Using the obtained coin-type cell, a charge-discharge test was carried out at a temperature of 60°C at a rate of 0.05 C with a cutoff potential of 1.2 V to 0 V. The above operation was carried out at C rates of 1.0 C, 2.0 C, and 3.0 C, and the capacity during charge-discharge was measured for each cycle.

[0073] Fig. 6 is a diagram showing the capacity of the coin cell for each cycle in Example 1, Comparative Example 1, and Comparative Example 2. The capacity shown in Fig. 6 is the ratio of the capacity of the coin cell after charge and discharge to the capacity of the coin cell before charge and discharge. In Example 1, the capacity tends to be less likely to decrease even after repeated cycles compared to Comparative Examples 1 and 2, and it was confirmed that a high capacity is maintained even after repeated cycles. From the above results, it can be seen that a solid-state battery including a negative electrode provided with a void layer having a portion containing a solid electrolyte and a portion containing voids in the pores of a metal porous body suppresses internal short circuits due to the precipitation of metallic lithium, and provides excellent durability (cycle characteristics).

[0074] Fig. 7 is a diagram showing the capacity of the coin cell for each cycle in Example 2, Comparative Example 3, and Comparative Example 4. The capacity shown in Fig. 7 is the ratio of the capacity of the coin cell after charge and discharge to the capacity of the coin cell before charge and discharge. In Example 2, the capacity was less likely to decrease even after repeated cycles compared to Comparative Examples 3 and 4, and it was confirmed that a high capacity was maintained even after repeated cycles. In particular, when the basis weight of the negative electrode active material in the negative electrode mixture layer was 10 mg / cm 2 In this case, the weight of the negative electrode active material in the negative electrode mixture layer is 5 mg / cm 2 It can be seen that the capacity tends to decrease more easily with repeated cycles than when the negative electrode is provided with a void layer as in Example 2, whereas the solid state battery provided with a void layer as in Example 2 exhibits excellent durability (cycle characteristics).

[0075] From the above results, it was found that the present invention can provide a negative electrode that is less susceptible to the effects of precipitation of metallic lithium and the like, such as internal short circuits, when used in a solid-state battery. [Explanation of symbols]

[0076] 1...Laminate 10...Solid electrolyte layer 11...Solid electrolyte 20...Negative electrode 21...Porous metal 22...Negative electrode composite material 23...Void part 201...Negative electrode composite material layer 202...Void layer

Claims

1. A negative electrode of a solid-state battery, a negative electrode composite layer formed by filling pores of a metal porous body with a negative electrode composite containing a negative electrode active material; a void layer having a portion containing a solid electrolyte and a portion in which voids are provided in pores of the metal porous body, on a solid electrolyte layer side in the thickness direction of the metal porous body pressurized in the thickness direction; The specific surface area of ​​the porous metal body before the pressure application is 500 m ２ / m ３ Over 6000m ２ / m ３ Below is the negative electrode.

2. 2. The negative electrode according to claim 1, wherein the density of the solid electrolyte in the void layer is 1.5 g / cc or more and less than 1.8 g / cc.

3. 2 . The negative electrode according to claim 1 , wherein in the void layer, a ratio of a volume occupied by the voids within the pores to a volume within the pores of the metal porous body is 10% or less.

4. The negative electrode according to claim 1 , wherein the negative electrode active material includes at least a silicon-based material.

5. The weight per unit area of ​​the negative electrode active material in the negative electrode mixture layer is 3 mg / cm ２ The negative electrode of claim 4 , wherein

6. 5. The negative electrode according to claim 4, wherein a ratio of a discharge capacity of lithium that can enter the voids of the void layer during charging and discharging to a discharge capacity of the negative electrode active material is 5% or more and 8% or less.

7. A solid-state battery comprising the negative electrode according to claim 1 , a positive electrode containing lithium, and a solid electrolyte layer.

8. A method for manufacturing a laminate including a solid electrolyte layer and a negative electrode, a step of applying a negative electrode composite material containing a negative electrode active material to a porous metal body to form a negative electrode composite layer in which the pores of the porous metal body are filled with the negative electrode composite material; a step of pressing a concave-convex portion of a pressurizing device against a surface of the metal porous body on which the negative electrode composite layer has been formed, to form a concave-convex portion on the surface; a step of applying a solid electrolyte to the surface of the porous metal body on which the concave-convex portion is formed, to form a void layer having a portion containing the solid electrolyte and a portion where voids are provided in the pores of the porous metal body, and a solid electrolyte layer; A method for producing a laminate, comprising:

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