JP2018206469A - All-solid secondary battery and method for producing all-solid secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a new and improved all-solid-state secondary battery and a method for manufacturing an all-solid-state secondary battery capable of making a short circuit less likely to occur when metallic lithium is included in a negative electrode active material layer. In order to solve the above problems, according to one aspect of the present invention, a positive electrode active material layer, a negative electrode active material layer containing metallic lithium, and a positive electrode active material layer and a negative electrode active material layer are provided. Characterized in that the arithmetic mean roughness Ra of the interface between the positive electrode active material layer and the solid electrolyte layer is 1.0 μm or less, and the density ratio of the solid electrolyte layer is 80% or more. An all-solid secondary battery is provided. [Selection diagram] Figure 1

Description

  The present invention relates to an all-solid secondary battery and a method for producing an all-solid secondary battery.

  In recent years, for example, all-solid secondary batteries disclosed in Patent Documents 1 and 2 have attracted attention. The all solid state secondary battery includes a positive electrode active material layer, a negative electrode active material layer, and a solid electrolyte layer disposed between these active material layers. In an all-solid-state secondary battery, a medium that conducts lithium ions is a solid electrolyte.

  In order to increase the energy density of such an all-solid secondary battery, it has been proposed to use lithium metal as a negative electrode active material. This is because the use of metallic lithium as the negative electrode active material can increase the output while reducing the thickness of the all-solid-state secondary battery.

  On the other hand, in the all-solid secondary battery, since the medium that conducts lithium ions is a solid electrolyte, the battery characteristics can be improved by bringing particles constituting the all-solid secondary battery into close contact with each other. Furthermore, from the viewpoint of increasing the energy density of the all-solid secondary battery, it is desired to reduce the thickness of the solid electrolyte layer.

  For this reason, when producing an all-solid-state secondary battery, an electrode laminate that is a laminate of a positive electrode active material layer, a solid electrolyte layer, and a negative electrode active material layer is often pressed. Thereby, particles can be brought into close contact within each layer and between layers. Furthermore, the solid electrolyte layer can be thinned.

Japanese Patent Laying-Open No. 2015-125872 International Publication No. 2014/010042

  By the way, metallic lithium is very soft. For this reason, when metallic lithium is used as the negative electrode active material, the following problems may occur. That is, when a gap such as a crack is formed on the surface of the solid electrolyte layer, metallic lithium enters the gap when the electrode laminate is pressed. When this gap communicates with the front and back surfaces of the solid electrolyte layer, the metal lithium sometimes reaches the positive electrode active material layer. Therefore, the all solid state secondary battery may be short-circuited. Even when the gap does not communicate with the front and back surfaces, the distance between the metal lithium that has entered the gap and the positive electrode active material layer is shorter than the distance between the metal lithium at the other location and the positive electrode active material layer. Therefore, a short circuit may occur because current concentrates at this point during charging.

  Moreover, when the interface between the positive electrode active material layer and the solid electrolyte layer is rough, the following problem may occur. That is, a protruding portion that protrudes toward the negative electrode active material layer (that is, metallic lithium) is formed on the surface of the positive electrode active material layer. Accordingly, during charging, the distance between the protruding portion and the negative electrode active material layer is shorter than the distance between the other portion of the positive electrode active material layer and the negative electrode active material layer. Therefore, a short circuit may occur because current concentrates at this point during charging.

  Thus, when metal lithium is used as the negative electrode active material of the all-solid secondary battery, a short circuit may occur.

  Therefore, the present invention has been made in view of the above problems, and an object of the present invention is a novel, which can make it difficult for a short circuit to occur when a negative electrode active material layer contains metallic lithium. And it is providing the manufacturing method of the all-solid-state secondary battery improved and the all-solid-state secondary battery.

  In order to solve the above problems, according to an aspect of the present invention, a positive electrode active material layer, a negative electrode active material layer containing metallic lithium, and a solid electrolyte disposed between the positive electrode active material layer and the negative electrode active material layer An arithmetic average roughness Ra of the interface between the positive electrode active material layer and the solid electrolyte layer is 1.0 μm or less, and a density ratio of the solid electrolyte layer is 80% or more, A solid secondary battery is provided.

  According to this aspect, since the arithmetic average roughness Ra of the interface between the positive electrode active material layer and the solid electrolyte layer is 1.0 μm or less, the current becomes more uniform in the solid electrolyte layer when the all-solid secondary battery is charged. It begins to flow. As a result, metallic lithium is deposited more uniformly on the negative electrode active material layer, so that a short circuit is less likely to occur. Furthermore, since the density ratio of the solid electrolyte layer is 80% or more, the gap in the solid electrolyte layer is reduced and reduced. Therefore, a short circuit hardly occurs.

  Here, the density ratio of the positive electrode active material layer may be 60% or more.

  According to this viewpoint, the battery characteristics of the all-solid secondary battery are further improved.

  Further, the maximum height roughness Rz of the interface between the positive electrode active material layer and the solid electrolyte layer may be 4.5 μm or less.

  According to this aspect, the current flows more uniformly in the solid electrolyte layer when the all-solid secondary battery is charged. As a result, metallic lithium is deposited more uniformly on the negative electrode active material layer, so that a short circuit is less likely to occur.

  Further, the thickness of the solid electrolyte layer may be 100 μm or less.

  According to this viewpoint, the energy density of the all solid state secondary battery is improved.

  According to another aspect of the present invention, there is provided a method for producing an all-solid secondary battery for producing the above all-solid secondary battery, comprising a positive electrode active material producing step for producing a positive electrode active material layer, and metallic lithium Press in negative electrode active material layer preparation process for preparing negative electrode active material layer, solid electrolyte layer preparation process for preparing solid electrolyte layer, pre-press process for pre-pressing positive electrode active material layer and solid electrolyte layer, and pre-press process A positive pressing active material layer and a solid electrolyte layer, and a main pressing step for pressing an electrode laminate, which is a laminate of the negative electrode active material layer, and the preliminary pressing step includes converting the positive electrode active material layer into a solid electrolyte layer. A positive electrode active material layer pressing step for pressing the positive electrode active material layer before lamination, and a solid electrolyte layer pressing step for pressing the solid electrolyte layer before laminating the solid electrolyte layer on the negative electrode active material layer. Characterized by the Method for manufacturing a solid-state secondary battery is provided.

  According to this aspect, an all-solid secondary battery having the above characteristics can be manufactured.

  Here, in the positive electrode active material layer pressing step, the positive electrode active material layer may be pressed together with the positive electrode current collector.

  According to this aspect, an all-solid secondary battery having the above characteristics can be manufactured.

  The solid electrolyte layer pressing step may include a solid electrolyte layer single pressing step of pressing the solid electrolyte layer before laminating the solid electrolyte layer on the positive electrode active material layer pressed in the positive electrode active material layer pressing step. Good.

  According to this aspect, an all-solid secondary battery having the above characteristics can be manufactured.

  The solid electrolyte layer pressing step is a laminate of a solid electrolyte layer single pressing step, a solid electrolyte layer pressed in the solid electrolyte layer single pressing step, and a positive electrode active material layer pressed in the positive electrode active material layer pressing step. And a first intermediate laminate pressing step for pressing the first intermediate laminate.

  According to this aspect, an all-solid secondary battery having the above characteristics can be manufactured.

  The solid electrolyte layer pressing step includes a second intermediate laminate press that presses a second intermediate laminate that is a laminate of the solid electrolyte layer and the positive electrode active material layer pressed in the positive electrode active material layer press step. A process may be included.

  According to this aspect, an all-solid secondary battery having the above characteristics can be manufactured.

  As described above, according to the present invention, when metallic lithium is included in the negative electrode active material layer, it is possible to make it difficult for a short circuit to occur.

It is explanatory drawing which shows schematic structure of the all-solid-state secondary battery which concerns on embodiment of this invention. It is explanatory drawing which shows a solid electrolyte layer and its peripheral structure. It is a cross-sectional SEM (scanning electron microscope) photograph which shows the interface of a solid electrolyte layer and a positive electrode active material layer, and its periphery structure. It is explanatory drawing for demonstrating the problem of the conventional all-solid-state secondary battery. It is explanatory drawing for demonstrating the problem of the conventional all-solid-state secondary battery. It is explanatory drawing for demonstrating the problem of the conventional all-solid-state secondary battery. It is a cross-sectional SEM photograph for demonstrating the problem of the conventional all-solid-state secondary battery. It is a cross-sectional SEM photograph for demonstrating the method to measure arithmetic mean roughness Ra of the interface of a solid electrolyte layer and a positive electrode active material layer.

  Exemplary embodiments of the present invention will be described below in detail with reference to the accompanying drawings. In addition, in this specification and drawing, about the component which has the substantially same function structure, duplication description is abbreviate | omitted by attaching | subjecting the same code | symbol.

<1. Study by the Inventor>
As a result of intensive studies on the problems of the all-solid-state secondary battery using metallic lithium as the negative electrode active material, the present inventor has arrived at the all-solid-state secondary battery according to this embodiment. Therefore, first, the study conducted by the present inventor will be described.

  As shown in FIGS. 4 to 7, a conventional all solid state secondary battery 100 using metallic lithium as a negative electrode active material includes a positive electrode active material layer 112, a negative electrode active material layer 122, and a solid electrolyte layer 130. Here, FIGS. 4 to 6 are explanatory views showing the configuration of the conventional all-solid-state secondary battery 100, and FIG. 7 shows cross-sectional SEM photographs corresponding to FIGS. The positive electrode active material layer 112 includes a positive electrode active material 112a, a solid electrolyte 112b, and the like. The solid electrolyte layer 130 includes a solid electrolyte 130a. The negative electrode active material layer 122 is composed of metallic lithium.

  When gaps such as cracks are formed on the surface of the solid electrolyte layer 130, a short circuit may occur. A situation where a short circuit occurs will be described with reference to FIG. As shown in FIG. 4, the solid electrolyte layer 130 has a gap communicating with the front and back surfaces thereof. When an electrode laminate that is a laminate of the positive electrode active material layer 112, the negative electrode active material layer 122, and the solid electrolyte layer 130 is pressed, metallic lithium enters the gaps in the solid electrolyte layer 130. Since the gap between the solid electrolyte layers 130 communicates with the front and back surfaces of the solid electrolyte layer 130, the metal lithium sometimes reaches the positive electrode active material layer 112. Therefore, the all solid state secondary battery may be short-circuited. Further, even when the gap between the solid electrolyte layers 130 does not communicate with the front and back surfaces, the distance between the metal lithium that has entered the gap and the positive electrode active material layer 112 is the distance between the metal lithium and the positive electrode active material layer 112 at other locations. It becomes shorter than the distance. Therefore, a short circuit may occur because current concentrates at this point during charging.

  A short circuit may occur when the interface between the positive electrode active material layer 112 and the solid electrolyte layer 130 is rough. The situation where a short circuit occurs will be described with reference to FIGS. The interface B between the positive electrode active material layer 112 and the solid electrolyte layer 130 is rough, and a protruding portion 112 c is formed on the surface of the positive electrode active material layer 112. Accordingly, during charging, the distance between the protruding portion 112c and the negative electrode active material layer 122 is shorter than the distance between the other portion of the positive electrode active material layer and the negative electrode active material layer 122. Therefore, current is concentrated at this location (location surrounded by the frame A) during charging. That is, a large current flows through the portion surrounded by the frame A. As a result, a lot of metallic lithium is locally deposited at the location, which may cause a short circuit.

  Thus, when metal lithium is used as the negative electrode active material of the all-solid secondary battery, a short circuit may occur. Therefore, the present inventor studied to increase the density of the solid electrolyte layer 130 and to flatten the interface between the positive electrode active material layer 112 and the solid electrolyte layer 130 in order to suppress a short circuit. As the density of the solid electrolyte layer 130 increases, the gap in the solid electrolyte layer 130 decreases and decreases. Furthermore, if the interface between the positive electrode active material layer 112 and the solid electrolyte layer 130 becomes flat, a phenomenon in which a large current flows locally is less likely to occur. As a result, the present inventor has arrived at the all solid state secondary battery according to the present embodiment. Hereinafter, this embodiment will be described in detail.

<2. Configuration of all-solid secondary battery>
Next, based on FIGS. 1-3, the structure of the all-solid-state secondary battery 1 which concerns on this embodiment is demonstrated. As shown in FIG. 1, the all-solid-state secondary battery 1 includes a positive electrode layer 10, a negative electrode layer 20, and a solid electrolyte layer 30.

(2-1. Positive electrode layer)
The positive electrode layer 10 includes a positive electrode current collector 11 and a positive electrode active material layer 12. Examples of the positive electrode current collector 11 include indium (In), copper (Cu), magnesium (Mg), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), and zinc ( Examples thereof include a plate-like body or a foil-like body made of Zn), aluminum (Al), germanium (Ge), lithium (Li) or an alloy thereof. The positive electrode current collector 11 may be omitted.

  The positive electrode active material layer 12 includes a positive electrode active material 12a and a solid electrolyte 12b. The solid electrolyte 12b included in the positive electrode layer 10 may or may not be the same type as the solid electrolyte 12b included in the solid electrolyte layer 30. Details of the solid electrolyte 12 b will be described in detail in the section of the solid electrolyte layer 30.

  The positive electrode active material may be any positive electrode active material capable of reversibly occluding and releasing lithium ions.

  For example, the positive electrode active material includes lithium cobalt oxide (hereinafter referred to as LCO), lithium nickel oxide (lithium nickel oxide), nickel nickel cobalt oxide, and nickel cobalt lithium aluminum oxide (hereinafter referred to as NCA). Lithium salt of nickel cobalt lithium manganate (hereinafter referred to as NCM), lithium manganate, lithium iron phosphate, nickel sulfide, copper sulfide, sulfur, iron oxide, or vanadium oxide (Vanadium oxide) or the like can be used. These positive electrode active materials may be used alone or in combination of two or more.

  Moreover, it is preferable that a positive electrode active material is formed including the lithium salt of the transition metal oxide which has a layered rock salt type structure among the lithium salts mentioned above. Here, “layered” represents a thin sheet-like shape. The “rock salt structure” refers to a sodium chloride structure, which is a kind of crystal structure. Specifically, the face-centered cubic lattice formed by each cation and anion is a unit lattice. It represents a structure that is displaced by a half of the edge.

The lithium salt of a transition metal oxide having such a layered rock-salt structure, for _{example, LiNi x Co y Al z O} 2 (NCA), or _{LiNi x Co y Mn z O 2} (NCM) ( where 0 < and lithium salts of ternary transition metal oxides such as x <1, 0 <y <1, 0 <z <1, and x + y + z = 1).

  When the positive electrode active material includes a lithium salt of a ternary transition metal oxide having the above layered rock salt structure, the energy density and thermal stability of the all-solid secondary battery 1 can be improved.

The positive electrode active material may be covered with a coating layer. Here, the coating layer of this embodiment may be any material as long as it is a known coating layer for the positive electrode active material of the all-solid-state secondary battery. Examples of the coating layer, for _example, Li ₂ O-ZrO 2 or the like.

  Further, when the positive electrode active material is formed of a lithium salt of a ternary transition metal oxide such as NCA or NCM and contains nickel (Ni) as the positive electrode active material, the capacity density of the all-solid-state secondary battery 1 The metal elution from the positive electrode active material in the charged state can be reduced. Thereby, the all-solid-state secondary battery 1 which concerns on this embodiment can improve the long-term reliability in a charge condition, and a cycle (cycle) characteristic.

  Here, examples of the shape of the positive electrode active material include particle shapes such as a true sphere and an oval sphere. Further, the particle size of the positive electrode active material is not particularly limited, and may be in a range applicable to the positive electrode active material of a conventional all-solid secondary battery. The content of the positive electrode active material in the positive electrode layer 10 is not particularly limited as long as it is applicable to the positive electrode layer of the conventional all-solid secondary battery.

  In addition to the positive electrode active material and the solid electrolyte 12b described above, the positive electrode layer 10 is appropriately mixed with additives such as, for example, a conductive additive, a binder, a filler, a dispersant, and an ionic conductive auxiliary. May be.

  Examples of the conductive additive that can be blended in the positive electrode layer 10 include graphite, carbon black, acetylene black, ketjen black, carbon fiber, and metal powder. Examples of the binder that can be blended in the positive electrode layer 10 include styrene butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, and polyethylene. . Furthermore, as a filler, a dispersing agent, an ionic conduction aid, and the like that can be blended in the positive electrode layer 10, known materials that are generally used for electrodes of lithium ion secondary batteries can be used.

  When the positive electrode active material layer 12 includes a positive electrode active material, a solid electrolyte 12b, and a binder, the cell capacity (capacity per unit cell) of the all-solid secondary battery 1 can be increased.

  The density ratio of the positive electrode active material layer 12 is preferably 60% or more. In this case, the battery characteristics of the all solid state secondary battery 1 are further improved. Here, the density ratio of the positive electrode active material layer 12 is the ratio of the bulk density to the true density of the positive electrode active material layer 12. The true density of the positive electrode active material layer 12 is calculated based on the nominal density of each material constituting the positive electrode active material layer and the mass ratio of these materials. Note that the filling rate of the positive electrode active material layer 12 may be measured by observing a cross section of the positive electrode active material layer 12 with an SEM, and the filling rate may be used as the density ratio.

  Here, as a method of setting the density ratio of the positive electrode active material layer 12 to a value within the above range, a method of pressing the positive electrode active material layer 12 in the manufacturing process of the all-solid-state secondary battery 1 may be mentioned. In the present embodiment, the positive electrode active material layer 12 is pressed before the positive electrode active material layer 12 is laminated on the solid electrolyte layer 30. Thereby, the density ratio of the positive electrode active material layer 12 can be set to a value within the above range. Moreover, although mentioned later for details, the interface B (refer FIG.2 and FIG.3) of the positive electrode active material layer 12 and the solid electrolyte layer 30 can be made flat. The upper limit of the density ratio is not particularly limited, but it is preferably 95% or less when the positive electrode active material is crystalline such as a lithium salt of a transition metal oxide. If the density ratio is higher than 95%, the positive electrode active material layer 12 may break. And when a crack generate | occur | produces in the positive electrode active material layer 12, a battery characteristic may fall. In the case where the positive electrode active material is amorphous such as sulfur, the density ratio may be less than 100% or 99.5% or less due to restrictions on the performance of the manufacturing apparatus.

(2-2. Negative electrode layer)
The negative electrode layer 20 includes a negative electrode current collector 21 and a negative electrode active material layer 22. Examples of the negative electrode current collector 21 include indium (In), copper (Cu), magnesium (Mg), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), and zinc ( Examples thereof include a plate-like body or a foil-like body made of Zn), aluminum (Al), germanium (Ge), lithium (Li) or an alloy thereof. The negative electrode current collector 21 may be omitted.

  The negative electrode active material layer 22 contains metallic lithium. The negative electrode active material layer 22 may be composed only of metallic lithium, or metallic lithium and other metallic active materials (indium (In), aluminum (Al), tin (Sn), silicon (Si), etc.) An alloy of Preferably, the negative electrode active material layer 22 is composed only of metallic lithium. Thereby, the energy density of the all-solid-state secondary battery 1 can be improved.

(2-3. Solid electrolyte layer)
The solid electrolyte layer 30 is formed between the positive electrode layer 10 and the negative electrode layer 20, and includes a solid electrolyte 30a.

The solid electrolyte 30a is made of, for example, a sulfide-based solid electrolyte material. Examples of the sulfide-based solid electrolyte material include Li ₂ S—P ₂ S ₅ , Li ₂ S—P ₂ S ₅ —LiX (X is a halogen element, such as I or Cl), Li ₂ S—P ₂ S _{5, for example. -Li 2 O, Li 2 S-} P 2 S 5 -Li 2 O-LiI, Li 2 S-SiS 2, Li2 S -SiS 2 -LiI, Li 2 S-SiS 2 -LiBr, Li 2 S-SiS 2 _{-LiCl, Li 2 S-SiS 2} -B 2 S 3 -LiI, Li 2 S-SiS 2 -P 2 S 5 -LiI, Li 2 S-B 2 S 3, Li 2 S-P 2 S 5 -Z _m S _{n (m, n} is any positive number, Z is Ge, and Zn, or _{Ga), Li 2 S-GeS} 2, Li 2 S-SiS 2 -Li 3 PO 4, Li 2 S-SiS 2 - Li _p MO _{q (p, q} is a positive number, M is P, Si, Ge B, Al, either Ga or In), and the like. Here, the sulfide-based solid electrolyte material is produced by processing a starting material (for example, Li ₂ S, P ₂ S _5, etc.) by a melt quenching method, a mechanical milling method, or the like. Further, heat treatment may be further performed after these treatments. The solid electrolyte may be amorphous, crystalline, or a mixture of both.

Further, as the solid electrolyte 30a, it is preferable to use a material containing at least sulfur (S), phosphorus (P) and lithium (Li) as constituent elements among the above-mentioned sulfide solid electrolyte materials, and particularly Li ₂ SP. it is more preferable to use those containing ₂ S _5.

Here, the case of using those containing _Li 2 _S-P 2 _{S 5} as a sulfide-based solid electrolyte material to form a solid electrolyte 30a, the mixing molar ratio of Li ₂ S and _P 2 _{S 5,} for example, Li ₂ S: P ₂ S ₅ = 50: 50 to 90:10 may be selected. The solid electrolyte layer 30 may further contain a binder. Examples of the binder contained in the solid electrolyte layer 30 include styrene butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, and polyethylene. The binder in the solid electrolyte layer 30 may be the same as or different from the binder in the positive electrode active material layer 12.

  The density ratio of the solid electrolyte layer 30 is 80% or more. In this case, the gap in the solid electrolyte layer 30 is reduced and reduced. Therefore, it is difficult for a short circuit to occur. Here, the density ratio of the solid electrolyte layer 30 is a ratio of the bulk density to the true density of the solid electrolyte layer 30. The true density of the solid electrolyte layer 30 can be calculated based on the nominal density of each material constituting the solid electrolyte layer 30 and the mass ratio of each material. Note that the filling rate of the solid electrolyte layer 30 may be measured by observing a cross section of the solid electrolyte layer 30 with an SEM, and the filling rate may be used as the density ratio.

  Here, as a method of setting the density ratio of the solid electrolyte layer 30 to a value within the above range, a method of pressing the solid electrolyte layer 30 in the manufacturing process of the all-solid secondary battery 1 may be mentioned. In the present embodiment, the solid electrolyte layer 30 is pressed before the solid electrolyte layer 30 is laminated on the negative electrode active material layer 22. Thereby, the density ratio of the solid electrolyte layer 30 can be set to a value within the above range. The upper limit value of the density ratio is not particularly limited, but the density ratio may be less than 100% or 99.5% or less due to constraints such as the performance of the manufacturing apparatus.

  The thickness of the solid electrolyte layer 30 is preferably 100 μm or less. Thereby, the energy density of the all-solid-state secondary battery 1 can be raised. In addition, as a method of setting the thickness of the solid electrolyte layer 30 to a value within the above range, a method of pressing the solid electrolyte layer 30 may be mentioned.

(2-4. Interface state between positive electrode active material layer and solid electrolyte layer)
In the present embodiment, as shown in FIGS. 2 and 3, the interface B between the positive electrode active material layer 12 and the solid electrolyte layer 30 is flat. Specifically, the arithmetic average roughness Ra of the interface B is 1.0 μm or less. The maximum height roughness Rz of the interface B is preferably 4.5 μm or less.

  Here, a method of measuring the arithmetic average roughness Ra and the maximum height roughness Rz of the interface B will be described with reference to FIG. FIG. 8 shows a cross-sectional SEM photograph in the vicinity of the interface B. First, a cross-sectional SEM photograph of the all-solid-state secondary battery 1 is acquired. Then, a portion in the vicinity of the interface B (portion shown in FIG. 8) is cut out from the cross-sectional SEM photograph. Note that this step may be omitted. Next, the positive electrode active material 12a in contact with the solid electrolyte layer 30 is extracted from the cross-sectional SEM photograph. Next, a point P closest to the solid electrolyte layer 30 is extracted from these positive electrode active materials 12a. Next, a roughness curve passing through these points P is measured, and an arithmetic average roughness Ra and a maximum height roughness Rz are measured based on the roughness curve. Specific measurement can be performed, for example, using ImageJ, which is analysis software of the National Institutes of Health (NIH). In Examples described later, the arithmetic average roughness Ra and the maximum height roughness Rz were measured by this method. The roughness curve shows the interface B described above.

  In the present embodiment, since the arithmetic average roughness Ra of the interface B is 1.0 μm or less, the current flows more uniformly in the solid electrolyte layer 30 when the all-solid secondary battery 1 is charged. As a result, metallic lithium is deposited more uniformly on the negative electrode active material layer 22, so that a short circuit is less likely to occur.

  Even when the arithmetic average roughness Ra is 1.0 μm or less, the maximum height roughness Rz may be increased. And there is a possibility that the current concentrates at a location where the maximum height roughness Rz is large. For this reason, it is preferable that the maximum height roughness Rz is 4.5 μm or less. Thereby, the current flows more uniformly in the solid electrolyte layer 30 when the all-solid-state secondary battery 1 is charged. Since the arithmetic average roughness Ra and the maximum height roughness Rz are preferably as small as possible, the lower limit value is not particularly limited. However, the arithmetic average roughness Ra may be 0.2 μm or more, and the maximum height roughness Rz may be 1.5 μm or more due to constraints such as the performance of the manufacturing apparatus.

<3. Manufacturing method of lithium ion secondary battery>
Then, the manufacturing method of the all-solid-state secondary battery 1 which concerns on this embodiment is demonstrated. The all-solid-state secondary battery 1 according to this embodiment can be manufactured by stacking the above layers after manufacturing the positive electrode layer 10, the negative electrode layer 20, and the solid electrolyte layer 30, respectively. The positive electrode layer 10, the negative electrode layer 20, and the solid electrolyte layer 30 can be produced by a known method.

(3-1. Positive electrode layer manufacturing step)
The positive electrode active material can be produced by a known method. Subsequently, the produced positive electrode active material, a solid electrolyte produced by a method described later, and various additives are mixed and added to a nonpolar solvent to form a slurry or paste. Furthermore, the obtained slurry or paste is applied onto the positive electrode current collector 11, dried, and then rolled, whereby the positive electrode layer 10 can be obtained. Instead of using the positive electrode current collector 11, the positive electrode layer 10 may be produced by compacting a mixture of a positive electrode active material and various additives into a pellet shape.

(3-2. Negative electrode layer manufacturing step)
The negative electrode layer 20 is produced by laminating a metal foil (containing metal lithium) that becomes the negative electrode active material layer 22 on the negative electrode current collector 21.

(3-3. Solid electrolyte layer manufacturing process)
The solid electrolyte layer 30 can be made of a solid electrolyte formed of a sulfide-based solid electrolyte material.

  First, the starting material is processed by a melt quenching method or a mechanical milling method.

For example, when the melt quenching method is used, a predetermined amount of starting materials (for example, Li ₂ S, P ₂ S _5, etc.) are mixed, and the pellets are reacted at a predetermined reaction temperature in a vacuum, and then rapidly cooled. By doing so, a sulfide-based solid electrolyte material can be produced. The reaction temperature of the mixture of Li ₂ S and P ₂ S ₅ is preferably 400 ° C. to 1000 ° C., more preferably 800 ° C. to 900 ° C. Moreover, reaction time becomes like this. Preferably it is 0.1 to 12 hours, More preferably, it is 1 to 12 hours. Furthermore, the quenching temperature of the reaction product is usually 10 ° C. or less, preferably 0 ° C. or less, and the quenching rate is usually about 1 ° C./sec to 10000 ° C./sec, preferably 1 ° C./sec to 1000 ° C. It is about ° C / sec.

In addition, when using the mechanical milling method, a sulfide-based solid electrolyte material can be produced by stirring and reacting starting materials (for example, Li ₂ S, P ₂ S _5, etc.) using a ball mill or the like. . In addition, although the stirring speed and stirring time in the mechanical milling method are not particularly limited, the faster the stirring speed, the faster the generation rate of the sulfide-based solid electrolyte material, and the longer the stirring time, the more the sulfide-based solid electrolyte material. The conversion rate of the raw material can be increased.

  Thereafter, the mixed raw material obtained by the melt quenching method or the mechanical milling method is heat-treated at a predetermined temperature and then pulverized to produce a particulate solid electrolyte. When the solid electrolyte has a glass transition point, it may change from amorphous to crystalline by heat treatment.

  Subsequently, the solid electrolyte obtained by the above method is formed by using a known film formation method such as an aerosol deposition method, a cold spray method, or a sputtering method. The solid electrolyte layer 30 can be produced. In addition, the solid electrolyte layer 30 may be produced by pressurizing solid electrolyte particles alone. Moreover, the solid electrolyte layer 30 may produce the solid electrolyte layer 30 by mixing a solid electrolyte, a solvent, and a binder, applying, drying, and pressurizing.

(4. Pressing process)
Next, a pressing process is performed. The press process of this embodiment is divided into a preliminary press process and a main press process.

(4-1. Preliminary pressing process)
In the preliminary pressing step, the positive electrode active material layer and the solid electrolyte layer are preliminary pressed. Specifically, the preliminary pressing step includes a positive electrode active material layer pressing step and a solid electrolyte layer pressing step.

(4-1-1. Positive electrode active material layer pressing step)
In the positive electrode active material layer pressing step, the positive electrode active material layer 12 is pressed before the positive electrode active material layer 12 is laminated on the solid electrolyte layer 30. Here, the positive electrode active material layer 12 is pressed together with the positive electrode current collector 11. Thereby, since the surface of the positive electrode active material layer 12 can be flattened, the arithmetic average roughness Ra and the maximum height roughness Rz of the interface B can be set to values within the above-described ranges. Note that even if the solid electrolyte layer 30 is laminated on the positive electrode active material layer 12 and these laminates are pressed, the arithmetic average roughness Ra and the maximum height roughness Rz of the interface B are values within the above-described ranges. It cannot be.

  The method for pressing the positive electrode active material layer 12 is not particularly limited, and may be a pressing method used for manufacturing a conventional all-solid secondary battery. For example, the positive electrode active material layer 12 may be pressed by a roll press or the like.

  The specific pressing pressure can vary depending on the pressing device, the material of the positive electrode active material layer 12, and the like. However, since the arithmetic average roughness Ra and the maximum height roughness Rz of the interface B tend to be lower as the press pressure is higher, the arithmetic average roughness Ra and the maximum height roughness Rz of the interface B are within the ranges described above. What is necessary is just to adjust a press pressure so that it may become the value of.

(4-1-2. Solid electrolyte layer pressing step)
In the solid electrolyte layer pressing step, the solid electrolyte layer 30 is pressed before the solid electrolyte layer 30 is laminated on the negative electrode active material layer 22. Thereby, the density ratio of the solid electrolyte layer 30 can be set to a value within the above-described range. Even if the solid electrolyte layer 30 is laminated on the negative electrode active material layer 22 and then the laminate is pressed, the density ratio of the solid electrolyte layer 30 cannot be set to a value within the above-described range. The solid electrolyte layer pressing step is classified into the following three types. Any method can obtain the effect of the present embodiment, but the second method is most preferable.

  A specific pressing method for performing the solid electrolyte layer pressing step is not particularly limited, and may be a pressing method used for manufacturing a conventional all-solid secondary battery. For example, the solid electrolyte layer 30 may be pressed by a roll press or the like.

  The specific pressing pressure can vary depending on the pressing device, the material of the solid electrolyte layer 30, and the like. However, since the density ratio of the solid electrolyte layer 30 tends to increase as the press pressure increases, the press pressure may be adjusted so that the density ratio of the solid electrolyte layer 30 is within the above-described range.

(4-1-2-1. First method)
The first method includes a solid electrolyte layer single pressing step. In the solid electrolyte layer single pressing step, the solid electrolyte layer 30 is pressed before the solid electrolyte layer 30 is stacked on the positive electrode active material layer 12 pressed in the positive electrode active material layer pressing step. Therefore, in the first method, the solid electrolyte layer 30 is pressed before the solid electrolyte layer 30 is laminated on the negative electrode active material layer 22. Thereby, the density ratio of the solid electrolyte layer 30 can be set to a value within the above-described range. Further, in the first method, the solid electrolyte layer 30 is pressed alone before the solid electrolyte layer 30 is laminated on the positive electrode active material layer 12. Therefore, the density ratio of the solid electrolyte layer 30 can be increased more reliably. Furthermore, in the press process described later, since the solid electrolyte layer 30 after pressing is laminated on the positive electrode active material layer 12, the arithmetic average roughness Ra and the maximum height roughness Rz of the interface B are more reliably reduced. can do. In addition, since the 1st method does not perform the 1st intermediate | middle laminated body press process mentioned later, there exists a tendency for the density ratio of the solid electrolyte layer 30 to fall a little compared with the 2nd method.

(4-1-2-2. Second method)
The second method includes the solid electrolyte layer single pressing step described above and the first intermediate laminate pressing step. In the solid electrolyte layer single pressing step, the solid electrolyte layer 30 is pressed before the solid electrolyte layer 30 is stacked on the positive electrode active material layer 12 pressed in the positive electrode active material layer pressing step. In the first intermediate laminate pressing step, the first is a laminate of the solid electrolyte layer 30 pressed in the solid electrolyte layer single pressing step and the positive electrode active material layer 12 pressed in the positive electrode active material layer pressing step. The intermediate laminate is pressed.

  In the second method, the solid electrolyte layer 30 is pressed before the solid electrolyte layer 30 is laminated on the negative electrode active material layer 22. Thereby, the density ratio of the solid electrolyte layer 30 can be set to a value within the above-described range. Furthermore, in the second method, the solid electrolyte layer 30 is pressed alone before the solid electrolyte layer 30 is laminated on the positive electrode active material layer 12. Therefore, the density ratio of the solid electrolyte layer 30 can be increased more reliably, and the arithmetic average roughness Ra and the maximum height roughness Rz of the interface B can be more reliably reduced.

(4-1-2-3. Third method)
The third method is to press the second intermediate laminate that is a laminate of the solid electrolyte layer 30 and the positive electrode active material layer 12 pressed in the positive electrode active material layer pressing step. It can be said that the third method is a method in which the solid electrolyte layer single pressing step is excluded from the second method.

  In the third method, the solid electrolyte layer 30 before pressing is laminated on the positive electrode active material layer 12. Therefore, the solid electrolyte layer 30 having a rough surface may be stacked on the positive electrode active material layer 12. However, since the solid electrolyte layer 30 is softer than the positive electrode active material layer 12, the surface shape of the solid electrolyte layer 30 can follow the surface shape of the positive electrode active material layer 12. Therefore, the arithmetic average roughness Ra and the maximum height roughness Rz of the interface B are values within the above-described ranges. However, since the solid electrolyte layer single pressing step is omitted, the arithmetic average roughness Ra and the maximum height roughness Rz of the interface B tend to be slightly higher than those of the first and second methods. However, since the solid electrolyte layer 30 is pressed before the solid electrolyte layer 30 is laminated on the negative electrode active material layer 22, the same effects as those of the first and second methods can be obtained.

  In addition, it is preferable that the density ratio of the positive electrode active material layer 12 and the solid electrolyte layer 30 becomes a value (60% or 80% or more) in the numerical range described above when the preliminary pressing step is completed.

(4-2. This press process)
In this pressing step, the positive electrode active material layer 12 (that is, the positive electrode layer 10) and the solid electrolyte layer 30 pressed in the preliminary pressing step and the negative electrode active material layer 22 (that is, the negative electrode layer 20) are laminated to form an electrode. A laminate is produced. Next, the electrode laminate is pressed. Through the above steps, the all-solid-state secondary battery 1 is manufactured. A specific pressing method for performing this pressing step is not particularly limited, and may be a pressing method used for manufacturing a conventional all-solid secondary battery. For example, the present pressing process may be performed by a roll press or the like.

(1. Example 1)
Next, examples of the present embodiment will be described. In Example 1, an all-solid secondary battery was produced by the following steps.

(1-1. Production of positive electrode layer)
LiNi _0.8 Co _0.15 Al _0.05 O ₂ (NCA) ternary powder as a positive electrode active material and Li ₂ S—P ₂ S ₅ as a sulfide-based solid electrolyte (molar ratio 75:25) The crystalline powder and the vapor-grown carbon fiber powder as a conductive additive were weighed at a mass ratio of 60: 35: 5 and mixed using a rotation and revolution mixer.

  Next, to this mixed powder, a dehydrated xylene solution in which SBR as a binder is dissolved is added so that SBR is 5.0% by mass with respect to the total mass of the mixed powder, and the primary mixed liquid is added. Generated. Furthermore, a secondary mixed solution was generated by adding an appropriate amount of dehydrated xylene for viscosity adjustment to the primary mixed solution. Furthermore, in order to improve the dispersibility of the mixed powder, the zirconia balls having a diameter of 5 mm are arranged so that the space, the mixed powder, and the zirconia balls each occupy 1/3 of the total volume of the kneading container. It poured into the next liquid mixture. The tertiary mixture thus produced was charged into a rotating and revolving mixer (mixer) and stirred at 3000 rpm for 3 minutes to produce a positive electrode layer coating solution.

  Next, an aluminum foil current collector having a thickness of 20 μm was prepared as a positive electrode current collector, and the positive electrode current collector was placed on a desktop screen printing machine, and the thickness was 2.0 cm × 2.0 cm. The positive electrode layer coating solution was applied onto the sheet using a 150 μm metal mask. Thereafter, the sheet coated with the positive electrode layer coating solution was dried on a hot plate at 60 ° C. for 30 minutes, and then vacuum dried at 80 ° C. for 12 hours. Thereby, the positive electrode layer was formed on the positive electrode current collector. The total thickness of the positive electrode current collector and the positive electrode layer after drying was around 165 μm.

(1-2. Production of solid electrolyte layer)
Li ₂ S—P ₂ S ₅ (molar ratio 75:25) as a sulfide-based solid electrolyte In a dehydrated xylene solution in which SBR is dissolved in crystalline powder, SBR is 2.0 mass% with respect to the total mass of the mixed powder. Was added to form a primary mixed solution. Furthermore, a secondary mixed solution was generated by adding an appropriate amount of dehydrated xylene for viscosity adjustment to the primary mixed solution. Furthermore, in order to improve the dispersibility of the mixed powder, a zirconia ball having a diameter of 5 mm is changed into a tertiary mixed liquid so that the space, the mixed powder, and the zirconia ball each occupy 1/3 of the total volume of the kneading container. I put it in. The tertiary mixture produced in this way was put into a rotation and revolution mixer and stirred at 3000 rpm for 3 minutes to produce an electrolyte layer coating solution.

  A base material made of polyethylene terephthalate (PET) (PET base material) is placed on a desktop screen printing machine, and an electrolyte layer coating solution is applied using a metal mask having a pore size of 2.5 cm × 2.5 cm and a thickness of 300 μm. Coating was performed on a PET substrate. Then, after drying on a 40 degreeC hotplate for 10 minutes, it was vacuum-dried at 40 degreeC for 12 hours. Thereby, a solid electrolyte layer was formed. The total thickness of the solid electrolyte layer after drying was around 180 μm.

(1-3. Production of negative electrode layer)
A nickel foil current collector having a thickness of 20 μm is prepared as a negative electrode current collector, and a negative electrode layer is formed by bonding a metal lithium foil having a width of 2.2 cm × 2.2 cm and a thickness of 30 μm to the negative electrode current collector. Produced.

(1-4. Production of all-solid secondary battery)
In Example 1, the preliminary press process was performed by the following processes. That is, the positive electrode layer was pressed with a pressure of 10 tons by a uniaxial press. Thereby, the positive electrode active material layer pressing step was performed. The bulk density of the positive electrode active material layer after pressing was 2.23 g / cc. The pressed positive electrode active material layer was punched with a Thomson blade having a diameter of 10 mm, and the height and mass were measured. The bulk density of the positive electrode active material layer was estimated by dividing the mass of the punched electrode layer by the volume.

  Next, a solid electrolyte layer pressing step was performed. In Example 1, the 2nd method was employ | adopted as a solid electrolyte layer preparation process. Specifically, the solid electrolyte layer was pressed with a pressure of 10 tons with a uniaxial press (solid electrolyte layer single press step). The solid electrolyte layer was pressed with a PET substrate. The bulk density of the solid electrolyte layer after pressing was 1.53 g / cc. The bulk density of the solid electrolyte layer was estimated using a method similar to the method of estimating the bulk density of the positive electrode active material.

  Subsequently, the positive electrode layer was punched with a Thomson blade having a diameter of 11 mm, and the solid electrolyte layer and the positive electrode layer on the PET substrate were laminated so that the solid electrolyte layer and the positive electrode active material layer faced each other. Next, the solid electrolyte layer and the positive electrode layer were bonded together by a dry lamination method using a roll press machine having a roll gap of 150 μm. This produced the 1st intermediate | middle laminated body. Subsequently, the 1st intermediate laminated body was pressed by the pressure of 10 tons with the uniaxial press (1st intermediate laminated body press process). The bulk density of the positive electrode active material layer after pressing was 2.27 g / cc, and the bulk density of the solid electrolyte layer was 1.56 g / cc. The thickness of the solid electrolyte layer was about 90 μm. The preliminary press process was performed by the above process.

Next, the density ratio of the positive electrode active material layer and the solid electrolyte layer was calculated based on the bulk density after the preliminary pressing step. Specifically, the nominal densities of NCA, Li ₂ S—P ₂ S ₅ (molar ratio 75:25) crystalline powder, and conductive aid are 4.6 g / cc, 1.8 g / cc and 2. 1 g / cc. Therefore, the true density of the positive electrode active material layer is 3.50 g / cc (= 4.6 × 0.6 + 1.8 × 0.35 + 2.1 × 0.05), and the true density of the solid electrolyte layer is 1.8 g. / Cc. Therefore, the density ratio of the positive electrode active material layer is 64.9% (= 2.27 / 3.50), and the density ratio of the solid electrolyte layer is 86.7% (= 1.56 / 1.8). In this example, in order to simplify the calculation, the binder is not taken into consideration in the calculation of the true density. Since the binder is used in a smaller amount than other components, the result is hardly affected even if the binder is not taken into consideration. In addition, if the density ratio at this time is a value in the above-described numerical range, the density ratio after the pressing step is necessarily in the above-described numerical range.

  Further, the arithmetic average roughness Ra and the maximum height roughness Rz of the interface B were measured in the following steps. That is, the cross section of the first intermediate laminate was cut out using ion milling (manufactured by Hitachi High-Technologies: E-3500). Subsequently, the cross-sectional part was observed with FE-SEM (JEOL Ltd .: JSM-7800F), and a cross-sectional SEM image was obtained. FIG. 3 is a cross-sectional SEM image of Example 1. Subsequently, the arithmetic average roughness Ra and the maximum height roughness Rz of the interface B were measured by the method described above.

  Subsequently, the negative electrode layer was punched with a Thomson blade having a diameter of 13 mm, and the first intermediate laminate and the negative electrode layer were laminated so that the solid electrolyte layer and the negative electrode active material layer faced each other, thereby preparing an electrode laminate. Subsequently, the electrode laminated body was pressed with a pressure of 3 tons by a uniaxial press. That is, this press process was performed. The thickness of the solid electrolyte layer after this pressing step was 85 μm.

  Next, the electrode laminate after this pressing step was placed in an aluminum laminate film having terminals attached thereto, and evacuated to 100 Pa with a vacuum machine. Subsequently, heat seal was performed, and the electrode laminate was sealed in a laminate film. This produced the all-solid-state secondary battery (test cell).

(1-5. Presence of short circuit)
The presence or absence of a short circuit in the test cell was determined by the open circuit voltage of the test cell. Specifically, the closed circuit voltage of the test cell was measured, and it was determined that a short circuit occurred when the voltage was 2.4 V or less. The following cycle life test was not performed on the short circuit.

(1-6. Cycle life test)
The obtained test cell was charged at 45 ° C. with a constant current of 0.13 mA to an upper limit voltage of 4.0 V, and a charge / discharge cycle of discharging 0.13 mA to a discharge end voltage of 2.5 V was repeated 50 cycles. The ratio of the discharge capacity at the 50th cycle to the discharge capacity at the first cycle (initial capacity) was defined as the discharge capacity maintenance rate. The discharge capacity was measured by a charge / discharge evaluation apparatus TOSCAT-3100 manufactured by Toyo System. The discharge capacity retention ratio is a parameter indicating cycle characteristics, and the larger the value, the better the cycle characteristics. Table 1 summarizes the characteristics and evaluation results of each example and comparative example.

(2. Example 2)
The same test as in Example 1 was performed except that the third method was performed as the solid electrolyte layer pressing step. Specifically, in Example 2, the following preliminary pressing process was performed.

  The positive electrode layer 10 was pressed at a pressure of 10 tons with a uniaxial press (positive electrode active material layer pressing step). The bulk density of the positive electrode active material layer after pressing was 2.26 g / cc.

  Subsequently, the positive electrode layer was punched with a Thomson blade having a diameter of 11 mm, and the solid electrolyte layer and the positive electrode layer on the PET substrate were laminated so that the solid electrolyte layer and the positive electrode active material layer faced each other. Subsequently, the solid electrolyte layer and the positive electrode layer were bonded together by a dry lamination method using a roll press machine having a roll gap of 150 μm. This produced the 2nd intermediate laminated body. Subsequently, the 2nd intermediate laminated body was pressed by the pressure of 10 tons with the uniaxial press (2nd intermediate laminated body press process). The bulk density of the positive electrode active material layer after pressing was 2.29 g / cc, and the bulk density of the solid electrolyte layer was 1.55 g / cc. The preliminary press process was performed by the above process. Then, the process similar to Example 1 was performed. The arithmetic average roughness Ra and the maximum height roughness Rz of the interface B were measured using the second intermediate laminate after the preliminary pressing. The results are summarized in Table 1.

(3. Example 3)
The same test as in Example 1 was performed except that the first method was performed as the solid electrolyte layer pressing step. Specifically, in Example 3, the following preliminary pressing process was performed.

  That is, the positive electrode layer 10 was pressed at a pressure of 10 tons with a uniaxial press (positive electrode active material layer pressing step). The bulk density of the positive electrode active material layer after pressing was 2.24 g / cc.

  Next, the solid electrolyte layer was pressed with a pressure of 10 tons with a uniaxial press (solid electrolyte layer single press step). The solid electrolyte layer was pressed with a PET substrate. The bulk density of the solid electrolyte layer after pressing was 1.53 g / cc. The preliminary press process was performed by the above process.

  Next, the positive electrode layer and the negative electrode layer were punched with the Thomson blade used in Example 1, and the positive electrode layer, the solid electrolyte layer, and the negative electrode layer were laminated so that the solid electrolyte layer and each active material layer faced each other. A laminate was produced. Subsequently, the electrode laminated body was pressed with a pressure of 3 tons by a uniaxial press. That is, this press process was performed. Thereafter, the same test as in Example 1 was performed. In addition, arithmetic mean roughness Ra and maximum height roughness Rz of the interface B were measured using the electrode laminated body after this press.

(4. Example 4)
The same test as in Example 1 was performed except that the pressing pressure in the first intermediate laminate pressing step was 15 tons.

(5. Example 5)
The same test as in Example 1 was performed except that the pressing pressure in the positive electrode active material layer pressing step and the solid electrolyte layer single pressing step was 7 tons.

(6. Example 6)
The same test as in Example 2 was performed except that the pressing pressure in the positive electrode active material layer pressing step was changed to 7 tons.

(7. Example 7)
In Example 7, a positive electrode active material layer and a solid electrolyte layer were produced by the following steps. That is, an NCA ternary powder, a Li ₂ S—P ₂ S ₅ (molar ratio 75:25) amorphous powder as a sulfide-based solid electrolyte, and a vapor-grown carbon fiber powder as a conductive additive A positive electrode active material layer was produced in the same manner as in Example 4 except that it was used by weighing at a mass ratio of 90: 7: 3. Further, the same process as _{Li 2 S-P 2 S 5} ( molar ratio 75:25) was used amorphous powder Example 4 of the sulfide-based solid electrolyte, to prepare a solid electrolyte layer.

  Moreover, the following processes were performed as a preliminary press process. That is, the positive electrode layer was pressed at a pressure of 15 tons with a uniaxial press while evacuating (positive electrode active material layer pressing step). Next, the solid electrolyte layer was pressed at a pressure of 15 tons with a uniaxial press while evacuating (solid electrolyte layer single pressing step). Then, the process (specifically 1st intermediate | middle laminated body press process) similar to Example 4 was performed. The preliminary press process was performed by the above process. The bulk density of the positive electrode active material layer after the preliminary pressing step was 3.82 g / cc. Further, the bulk density of the solid electrolyte layer after the preliminary pressing was 1.77 g / cc. The true density of the positive electrode active material layer at this time is 4.33 g / cc (= 4.6 × 0.9 + 1.8 × 0.07 + 2.1 × 0.03), and the density ratio is 88.2% ( = 3.82 / 4.33). The true density of the solid electrolyte layer is 98.3% (= 1.77 / 1.8). The other steps were the same as in Example 4.

(8. Comparative Example 1)
The same test as in Example 1 was performed except that the positive electrode active material layer pressing step and the solid electrolyte layer single pressing step were not performed. FIG. 7 shows a cross-sectional SEM photograph used for measurement of arithmetic average roughness Ra and maximum height roughness Rz of Comparative Example 1.

(9. Comparative Example 2)
The same test as in Example 1 was performed except that all the pressing pressures in the preliminary pressing step were changed to 3 tons.

(10. Comparative Example 3)
The same test as in Example 1 was performed except that the positive electrode active material layer pressing step was not performed.

(11. Comparative Example 4)
The same test as in Example 3 was performed except that the positive electrode active material layer pressing step was not performed.

(12. Comparative Example 5)
The same test as in Example 3 was performed except that the solid electrolyte layer single pressing step was not performed.

(13. Comparative Example 6)
The same test as in Comparative Example 1 was performed, except that a metal mask having a thickness of 600 μm was used for the production of the solid electrolyte layer.

(14. Comparative Example 7)
The same test as in Example 3 was performed except that the preliminary pressing step was not performed. That is, in the comparative example 7, only this press process was performed. The bulk density of each layer, the arithmetic average roughness Ra of the interface B, and the maximum height roughness Rz were measured using the electrode laminate after this pressing.

(15. Reference Example 1)
A test similar to that of Comparative Example 1 was performed except that a metal mask having a thickness of 1200 μm was used for the production of the solid electrolyte layer.

(16. Reference example 2)
A test similar to that of Comparative Example 1 was performed, except that the negative electrode layer was produced by the following steps. That is, graphite powder (which was vacuum-dried at 80 ° C. for 24 hours) as a negative electrode active material and polyvinylidene fluoride (PVdF) as a binder were weighed at a mass ratio of 95.0: 5.0. Then, these materials and an appropriate amount of N-methyl-2-pyrrolidone (NMP) are put into a rotation and revolution mixer, stirred at 3000 rpm for 3 minutes, and then subjected to defoaming treatment for 1 minute, whereby a negative electrode layer coating liquid is obtained. Generated.

  Next, a nickel foil current collector having a thickness of 20 μm is prepared as a negative electrode current collector, and the electrolyte layer coating solution is applied onto the nickel current collector using a metal mask having a pore size of 2.2 cm × 2.2 cm and a thickness of 250 μm. Coated. The sheet coated with the negative electrode layer coating solution was housed in a dryer heated to 80 ° C. and dried for 15 minutes. Further, the dried sheet was vacuum dried at 80 ° C. for 24 hours. This produced the negative electrode layer. The thickness of the negative electrode layer was around 140 μm.

(17. Reference example 3)
In Reference Example 3, a nonaqueous electrolyte secondary battery was produced by the following process. Thereafter, a cycle life test was conducted in the same manner as in Example 1.

(17-1. Preparation of positive electrode layer)
NCA ternary powder as a positive electrode active material and acetylene black as a conductive additive were weighed in a 97: 3 mass ratio and mixed. Next, an NMP solution in which PVdF as a binder was dissolved was added to the mixed powder so that the PVdF was 3.0% by mass with respect to the total mass of the mixed powder to produce a primary mixed solution. Furthermore, a secondary mixture was produced by adding an appropriate amount of NMP to the primary mixture for viscosity adjustment. The secondary mixed solution thus produced was put into a rotation and revolution mixer and stirred at 2000 rpm for 3 minutes to produce a positive electrode layer coating solution.

  Next, an aluminum foil current collector having a thickness of 20 μm was prepared as a positive electrode current collector, and the positive electrode current collector was placed on a desktop screen printing machine, and a metal mask having a hole diameter of 2.0 cm × 2.0 cm and a thickness of 150 μm. The positive electrode layer coating solution was applied onto the sheet using Then, after drying the sheet | seat with which the positive electrode layer coating liquid was coated with a 100 degreeC hotplate for 30 minutes, it was vacuum-dried at 180 degreeC for 12 hours. Thereby, the positive electrode active material layer was formed on the positive electrode current collector. The total thickness of the positive electrode current collector and the positive electrode active material layer after drying was around 120 μm.

  A first pressure molding was performed on the positive electrode layer at a pressure of 3 tons using a uniaxial press. The density of the positive electrode layer after pressurization was 2.33 g / cc. The positive electrode layer was beaten with a Thomson blade having a diameter of 11 mm.

(17-2. Production of negative electrode layer)
A copper foil current collector with a thickness of 20 μm was prepared as a negative electrode current collector, and a metal lithium foil with a thickness of 30 μm was bonded to prepare a negative electrode layer. The negative electrode layer was beaten with a Thomson blade having a diameter of 13 mm.

(17-3. Production of non-aqueous electrolyte secondary battery)
As the separator, a porous polyethylene film (φ15.5 mm, thickness 12 μm) was used. An electrode laminate was produced by sandwiching the separator between the positive electrode layer and the negative electrode layer. The electrode laminate was processed into a 2032 coin half cell.

  Next, lithium hexafluorophosphate (LiPF6) is adjusted to a concentration of 1.3 mol / L in a nonaqueous solvent in which ethylene carbonate and dimethyl carbonate are mixed at a volume ratio of 3: 7. To obtain an electrolyte solution. The separator was impregnated with the electrolytic solution by injecting the manufactured electrolytic solution into a 2032 coin half cell. Thereby, a non-aqueous electrolyte secondary battery was produced.

  The nominal densities of NCA and acetylene black are 4.6 g / cc and 2.1 g / cc, respectively. Therefore, the true density of the positive electrode active material layer is 4.53 g / cc (= 4.6 × 0.97 + 2.1 × 0.03), and the density ratio is 51.4% (= 2.33 / 4.53). It becomes.

  According to Table 1, since Examples 1 to 7 satisfy the requirements of the present embodiment, they do not cause a short circuit immediately after fabrication and have a high maintenance rate (in other words, a short circuit is difficult to occur). In Example 7, since an amorphous solid electrolyte was used, the initial capacity was slightly lower than in the other examples. However, the value was not a problem for practical use. In contrast, in Comparative Example 1, since the positive electrode active material layer pressing step and the solid electrolyte layer single pressing step were not performed, the interface B became rough. For this reason, a short circuit occurred early during charging and discharging.

  In Comparative Example 2, since the press pressure was low, the interface B became rough and the density ratio of each layer became small. For this reason, a short circuit occurred immediately after the test cell was produced. In Comparative Examples 3 and 4, since the positive electrode active material layer pressing step was not performed, the interface B became rough. For this reason, a short circuit occurred early during charging and discharging. In Comparative Example 4, since the first intermediate laminate pressing process was not performed, the density ratio of the positive electrode active material layer was also reduced. In Comparative Example 5, since the solid electrolyte layer single pressing step was not performed, the density ratio of the solid electrolyte layer was reduced. For this reason, a short circuit occurred immediately after the test cell was produced. In addition, the thickness of the solid electrolyte layer was increased. In Comparative Example 6, since the solid electrolyte layer was thicker than in Comparative Example 1, the number of cycles until the short circuit increased slightly, but the short circuit could not be avoided. In Comparative Example 7, since the preliminary pressing process was not performed, not only the interface B was formed but also the density ratio of each layer was reduced. For this reason, a short circuit occurred immediately after the test cell was produced.

  In Reference Example 1, the solid electrolyte layer in Comparative Example 1 is very thick. By making the solid electrolyte layer very thick, a short circuit could be suppressed, but the energy density became extremely small. Therefore, it is not practical. In Reference Example 2, the negative electrode active material in Comparative Example 1 is made of graphite. When the negative electrode active material is made of graphite, the problem focused on by the present embodiment does not arise in the first place, but the energy density becomes small. Reference Example 3 is a nonaqueous electrolyte secondary battery. When compared with Examples 1 to 7, it can be seen that Examples 1 to 7 have the same characteristics as Reference Example 3. Therefore, Examples 1-7 can enjoy the merit (for example, higher safety | security etc.) of an all-solid-state secondary battery, implement | achieving the battery characteristic comparable as a nonaqueous electrolyte secondary battery.

  The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the present invention is not limited to such examples. It is obvious that a person having ordinary knowledge in the technical field to which the present invention pertains can come up with various changes or modifications within the scope of the technical idea described in the claims. Of course, it is understood that these also belong to the technical scope of the present invention.

DESCRIPTION OF SYMBOLS 1 All-solid-state secondary battery 10 Positive electrode layer 11 Positive electrode collector 12 Positive electrode active material layer 20 Negative electrode layer 21 Negative electrode collector 22 Negative electrode active material layer 30 Solid electrolyte layer

Claims (9)

A positive electrode active material layer;
A negative electrode active material layer containing metallic lithium;
A solid electrolyte layer disposed between the positive electrode active material layer and the negative electrode active material layer,
The arithmetic average roughness Ra of the interface between the positive electrode active material layer and the solid electrolyte layer is 1.0 μm or less,
An all-solid secondary battery, wherein a density ratio of the solid electrolyte layer is 80% or more.   The all-solid-state secondary battery according to claim 1, wherein a density ratio of the positive electrode active material layer is 60% or more.   3. The all-solid-state secondary battery according to claim 1, wherein a maximum height roughness Rz of an interface between the positive electrode active material layer and the solid electrolyte layer is 4.5 μm or less.   The all-solid-state secondary battery according to claim 1, wherein a thickness of the solid electrolyte layer is 100 μm or less. A method for producing an all-solid-state secondary battery for producing the all-solid-state secondary battery according to claim 1,
A positive electrode active material production step of producing a positive electrode active material layer;
A negative electrode active material layer preparation step of preparing a negative electrode active material layer containing metallic lithium;
A solid electrolyte layer production step for producing a solid electrolyte layer;
A pre-pressing step of pre-pressing the positive electrode active material layer and the solid electrolyte layer;
Pressing the electrode laminate, which is a laminate of the positive electrode active material layer and the solid electrolyte layer pressed in the preliminary press step, and the negative electrode active material layer, and
The preliminary pressing step
A positive electrode active material layer pressing step of pressing the positive electrode active material layer before laminating the positive electrode active material layer on the solid electrolyte layer;
A solid electrolyte layer pressing step of pressing the solid electrolyte layer before laminating the solid electrolyte layer on the negative electrode active material layer.   6. The method for producing an all-solid-state secondary battery according to claim 5, wherein, in the positive electrode active material layer pressing step, the positive electrode active material layer is pressed together with a positive electrode current collector. The solid electrolyte layer pressing step includes:
The solid electrolyte layer single press step of pressing the solid electrolyte layer before laminating the solid electrolyte layer on the positive electrode active material layer pressed in the positive electrode active material layer pressing step. 7. A method for producing an all solid state secondary battery according to 5 or 6. The solid electrolyte layer pressing step includes:
The solid electrolyte layer single pressing step;
A first intermediate laminate is pressed, which is a laminate of the solid electrolyte layer pressed in the solid electrolyte layer single pressing step and the positive electrode active material layer pressed in the positive electrode active material layer pressing step. The method for producing an all-solid-state secondary battery according to claim 7, comprising: an intermediate laminate pressing step. The solid electrolyte layer pressing step includes:
Including a second intermediate laminate pressing step of pressing a second intermediate laminate that is a laminate of the solid electrolyte layer and the positive electrode active material layer pressed in the positive electrode active material layer pressing step. The manufacturing method of the all-solid-state secondary battery of Claim 5 or 6.