WO2020070932A1 - Lithium-ion secondary battery and method for manufacturing lithium-ion secondary battery - Google Patents

Abstract

A lithium-ion secondary battery (1) consists of layers in the following order: a substrate (10) that serves as a positive electrode current collector layer; an underlayer (20); a positive electrode layer (30) containing a positive electrode active material; a solid electrolyte layer (40) containing an inorganic solid electrolyte; a retaining layer 50 composed of a noble metal or the like; a diffusion prevention layer (60) composed of an amorphous alloy; and a negative electrode current collector layer (70) composed of a noble metal. A surface (10a) of the substrate (10) for laminating the underlayer (20) through to the negative electrode current collector layer (70) has a maximum-minimum height difference, which is the height difference between the maximum height and the minimum height obtained by measuring unevenness in a range of 20 μm × 20 μm by Atomic Force Microscope (AFM), that is established at 78 nm or less. Thus, in a thin-film laminated lithium-ion secondary battery equipped with an inorganic solid electrolyte, a reduction in the capacity retention rate is suppressed.

Description

Lithium ion secondary battery, method of manufacturing lithium ion secondary battery

The present invention relates to a lithium ion secondary battery and a method for manufacturing a lithium ion secondary battery.

携 帯 With the spread of portable electronic devices such as mobile phones and notebook computers, there is a strong demand for the development of small and lightweight secondary batteries with high energy density. As a secondary battery satisfying such requirements, a lithium ion secondary battery is known. A lithium ion secondary battery has a positive electrode including a positive electrode active material, a negative electrode including a negative electrode active material, and an electrolyte having lithium ion conductivity and disposed between the positive electrode and the negative electrode.

In a conventional lithium ion secondary battery, an organic electrolyte or the like has been used as an electrolyte. On the other hand, an all-solid-state and thin-film laminated lithium-ion secondary battery in which a solid electrolyte made of an inorganic material (inorganic solid electrolyte) is used as an electrolyte and the negative electrode, the solid electrolyte, and the positive electrode are all formed of thin films has been proposed. (See Patent Document 1).
Patent Document 1 discloses that a positive electrode current collector layer, a positive electrode active material layer, a solid electrolyte layer, a negative electrode active material layer, and a negative electrode current collector are provided on a substrate made of glass, semiconductor silicon, ceramic, stainless steel, resin, or the like. It is described that a lithium ion secondary battery is formed by stacking layers.

JP 2008-226728 A

In general, the capacity of a lithium ion secondary battery gradually decreases with time after charging, even if the battery is not used. Here, the ratio of the capacity of the lithium ion secondary battery at the time when a predetermined period has elapsed to the initial capacity after the completion of charging, expressed as a percentage, is referred to as a capacity retention rate.
In the case of a thin-film laminated lithium ion secondary battery containing an inorganic solid electrolyte, the capacity retention ratio is likely to decrease, and after charging, even if not particularly used, the lithium ion secondary battery will not function as a power source The time until was sometimes shorter.
An object of the present invention is to suppress a decrease in capacity retention in a thin-film laminated lithium ion secondary battery including an inorganic solid electrolyte.

The lithium ion secondary battery of the present invention comprises: a substrate having a front surface and a back surface; a first polar layer provided on the front surface side of the substrate, for absorbing and releasing lithium ions at a first polarity; A solid electrolyte layer containing an inorganic solid electrolyte having a property, and a second polar layer that occludes and releases lithium ions at a second polarity opposite to the first polarity, wherein Is characterized in that a maximum / minimum height difference which is a height difference between a maximum height and a minimum height obtained by measuring unevenness in a range of 20 μm × 20 μm with an AFM (Atomic Force Microscope) is 78 nm or less. .
In such a lithium ion secondary battery, the substrate may be made of SUS316L, and the solid electrolyte layer may contain LiPON in which a part of oxygen in Li ₃ PO ₄ is replaced with nitrogen. .
Further, the substrate is made of a metal material whose surface is subjected to Ni-P plating, and the solid electrolyte layer contains LiPON in which part of oxygen in Li ₃ PO ₄ is replaced by nitrogen. be able to.
In addition, the first polarity is positive, the second polarity is negative, and the solid electrolyte layer is provided to face the first polar layer, and includes Li ₃ PO ₄ and includes LiNiO ₂ . And a second solid electrolyte layer including LiPON in which a part of oxygen in Li ₃ PO ₄ is replaced by nitrogen and provided in opposition to the second polar layer. can do.
The first polar layer may include LiNiO ₂ and Li ₃ PO ₄ .
In addition, the semiconductor device may further include a base layer provided between the surface of the substrate and the first polar layer, the base layer including LiNiO ₂ and not including Li ₃ PO ₄ .
Further, a metal layer provided opposite to the solid electrolyte layer and made of a platinum group element (Ru, Rh, Pd, Os, Ir, Pt), gold (Au), aluminum (Al), or an alloy thereof is used. Furthermore, the second polar layer may include lithium alloyed with a metal constituting the metal layer.
In addition, the semiconductor device may further include an amorphous layer which is provided to face the metal layer and has an amorphous structure and is made of a metal or an alloy.
The maximum and minimum height difference of the surface of the substrate may be 2.7 nm or less.
The arithmetic mean roughness Ra of the surface of the substrate may be 1.1 nm or less.
From another viewpoint, the method for manufacturing a lithium ion secondary battery of the present invention has a maximum height and a minimum height obtained by measuring unevenness in a range of 20 μm × 20 μm with an AFM (Atomic Force Microscope). A substrate preparation step of preparing a substrate provided with a surface having a maximum / minimum height difference of 78 nm or less, and occluding and releasing lithium ions at a first polarity on the surface side of the substrate. A first polar layer forming step of forming a first polar layer, and a solid electrolyte layer forming a solid electrolyte layer containing an inorganic solid electrolyte having lithium ion conductivity on the first polar layer side provided on the substrate Forming step.
In such a method for manufacturing a lithium ion secondary battery, the substrate preparing step may include preparing the substrate made of SUS316L.
Further, in the substrate preparing step, the substrate made of a metal material plated with Ni-P may be prepared.
In addition, the first polarity is positive, and a platinum group element (Ru, Rh, Pd, Os, Ir, Pt), gold (Au), or aluminum (Al) is formed on the solid electrolyte layer provided on the substrate. Or a metal layer forming step of forming a metal layer made of an alloy thereof, and a step of forming a metal layer comprising the substrate, the first polar layer, the solid electrolyte layer, and the metal layer from the first polar layer. A charging step of performing charging by moving lithium ions to the metal layer via the solid electrolyte layer; and, for the charged laminate, the first polar layer from the metal layer via the solid electrolyte layer. A discharge step of performing discharge by moving lithium ions to the substrate.
In addition, between the metal layer forming step and the charging step, the metal layer may further include an amorphous layer forming step of forming an amorphous layer made of a metal or an alloy having an amorphous structure. May be included.
Further, the first polarity is positive, and in the first polar layer forming step, a composite cathode including LiNiO ₂ and Li ₃ PO ₄ is formed, and in the solid electrolyte layer forming step, Li ₃ PO ₄ is formed. After forming the first solid electrolyte layer containing no LiNiO ₂ , a second solid electrolyte layer containing LiPON in which part of oxygen in Li ₃ PO ₄ is replaced by nitrogen can be formed.
The method may further include, between the substrate preparing step and the first polar layer forming step, an underlayer forming step of forming an underlayer containing LiNiO ₂ and not Li ₃ PO ₄ on the surface of the substrate. Can be characterized.
Further, in the substrate preparing step, the substrate having the maximum and minimum height difference of the surface set to 2.7 nm or less may be prepared.
Further, in the substrate preparing step, the substrate may be prepared such that an arithmetic average roughness Ra of the surface is set to 1.1 nm or less.

According to the present invention, it is possible to suppress a reduction in the capacity retention ratio in a thin-film laminated lithium ion secondary battery including an inorganic solid electrolyte.

FIG. 2 is a diagram illustrating a cross-sectional configuration of a lithium ion secondary battery according to an embodiment. (A), (b) is a figure which shows the cross-sectional structural example of the board | substrate which comprises the lithium ion secondary battery of embodiment. 4 is a flowchart for explaining a method of manufacturing a lithium ion secondary battery according to an embodiment. (A)-(c) is a figure for demonstrating the procedure of making a holding | maintenance layer porous. (A), (b) is a cross-sectional STEM photograph of the lithium ion secondary battery of the comparative example before the first charge and discharge and after seven charge and discharge. (A), (b) is an enlarged cross-sectional STEM photograph before and after the first charge and discharge of the lithium ion secondary battery of the comparative example seven times.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. Note that the size, thickness, and the like of each part in the drawings referred to in the following description may be different from actual dimensions.

[Configuration of lithium ion secondary battery]
FIG. 1 is a diagram showing a cross-sectional configuration of a lithium ion secondary battery 1 of the present embodiment. As described later, the lithium ion secondary battery 1 of the present embodiment has a structure in which a plurality of layers are stacked. After forming a basic structure by a so-called film forming process, the first charge / discharge operation is performed. Completes the structure.

The lithium ion secondary battery 1 shown in FIG. 1 includes a substrate 10, an underlayer 20 laminated on the substrate 10, a positive electrode layer 30 laminated on the underlayer 20, and a solid layer laminated on the positive electrode layer 30. And an electrolyte layer 40. Here, the solid electrolyte layer 40 covers the peripheral edges of both the base layer 20 and the positive electrode layer 30 and the ends thereof are directly laminated on the substrate 10, so that the solid electrolyte layer 40 covers the base layer 20 and the positive electrode layer 30 together with the substrate 10. I have. Further, this lithium ion secondary battery 1 has a holding layer 50 stacked on the solid electrolyte layer 40, a diffusion prevention layer 60 stacked on the holding layer 50, and a negative electrode collection layer stacked on the diffusion prevention layer 60. And an electric conductor layer 70.

(substrate)
The substrate 10 serves as a base on which the base layer 20 to the negative electrode current collector layer 70 are stacked by a film forming process. The substrate 10 has a front surface 10a and a back surface 10b, and the base layer 20 to the negative electrode current collector layer 70 are stacked on the front surface 10a. The details of the substrate 10 will be described later.

(Underlayer)
The underlayer 20 is a solid thin film, which enhances the adhesion between the substrate 10 and the positive electrode layer 30, as well as a material (particularly a metal material) forming the substrate 10 and a Li ₃ PO ₄ (phosphorus) forming the positive electrode layer 30. (A lithium oxide: described later in detail) is a barrier for suppressing direct contact.
As the base layer 20, which has electron conductivity, Li ₃ PO ₄ and Li ⁺ unlikely to occur corrosion by (Li-ion) or PO ₄ ^3- (phosphate ions) constituting, formed of a metal or metal compound such as Can be used.

Here, in the present embodiment, the underlayer 20 is made of LiNiO ₂ (nickel phosphate). LiNiO ₂ is sometimes used as a positive electrode material of the lithium ion secondary battery 1.

The thickness of the underlayer 20 can be, for example, not less than 5 nm and not more than 50 μm. If the thickness of the underlayer 20 is less than 5 nm, the function as a barrier is reduced, which is not practical. On the other hand, if the thickness of the underlayer 20 exceeds 50 μm, the internal resistance of the battery increases, which is disadvantageous for high-speed charging and discharging.

As a method for manufacturing the underlayer 20, any known film forming method such as various PVD (physical vapor deposition) and various CVD (chemical vapor deposition) may be used, but from the viewpoint of production efficiency, a sputtering method or a vacuum method is used. It is desirable to use an evaporation method.

(Positive electrode layer)
The positive electrode layer 30 as an example of the first polar layer is a solid thin film and contains a positive electrode active material that releases lithium ions during charging and absorbs lithium ions during discharging. Here, the positive electrode active material constituting the positive electrode layer 30 is, for example, a kind selected from manganese (Mn), cobalt (Co), nickel (Ni), iron (Fe), molybdenum (Mo), and vanadium (V). Materials composed of various materials such as oxides, sulfides, and phosphorus oxides containing the above metals can be used. Further, the positive electrode layer 30 may be a composite positive electrode further containing a solid electrolyte. In this embodiment, the positive polarity corresponds to the first polarity.

Here, in the present embodiment, the positive electrode layer 30 is formed of a mixed positive electrode including a positive electrode active material and a solid electrolyte made of an inorganic material (inorganic solid electrolyte). More specifically, the positive electrode layer 30 of the present embodiment has a solid electrolyte region mainly containing an inorganic solid electrolyte and a positive electrode region mainly containing a positive electrode active material. Then, in the positive electrode layer 30, the inorganic solid electrolyte forming the solid electrolyte region and the positive electrode active material forming the positive electrode region are mixed while maintaining each. As a result, in the positive electrode layer 30, one is a matrix (base material) and the other is a filler (particles). Here, in the positive electrode layer 30, it is desirable that the solid electrolyte region be a matrix and the positive electrode region be a filler.

In the present embodiment, the same LiNiO ₂ as the underlayer 20 is used as the positive electrode active material forming the positive electrode layer 30. Li ₃ PO ₄ (lithium phosphate) is used as the inorganic solid electrolyte constituting the positive electrode layer 30. Here, the ratio between the positive electrode active material and the inorganic solid electrolyte in the positive electrode layer 30 may be appropriately selected. However, from the viewpoint of securing both capacity and conductivity, the molar ratio of the positive electrode active material to the inorganic solid electrolyte is from 9: 1 (90%: 10%) to 3: 2 (60%: 40%).

(4) The thickness of the positive electrode layer 30 can be, for example, not less than 10 nm and not more than 40 μm. When the thickness of the positive electrode layer 30 is less than 10 nm, the capacity of the obtained lithium ion secondary battery 1 becomes too small, which is not practical. On the other hand, if the thickness of the positive electrode layer 30 exceeds 40 μm, it takes too much time to form the layer, and the productivity is reduced. However, when the battery capacity required for the lithium ion secondary battery 1 is large, the thickness of the positive electrode layer 30 may be more than 40 μm.

Further, as a method for forming the positive electrode layer 30, a known film forming method such as various PVD or various CVD may be used, but it is preferable to use a sputtering method from the viewpoint of production efficiency.

(Solid electrolyte layer)
The solid electrolyte layer 40 is a solid thin film made of an inorganic material, and includes an inorganic solid electrolyte capable of moving lithium ions by an externally applied electric field.
Then, the solid electrolyte layer 40 of the present embodiment is stacked on the first solid electrolyte layer 41 and the first solid electrolyte layer 41 stacked on the positive electrode layer 30, and is an object to be stacked on the holding layer 50. A second solid electrolyte layer.

[First solid electrolyte layer]
The first solid electrolyte layer 41 of the present embodiment is made of the same Li ₃ PO ₄ as the inorganic solid electrolyte in the positive electrode layer 30.

厚 The thickness of the first solid electrolyte layer 41 can be, for example, not less than 5 nm and not more than 50 nm. When the thickness of the first solid electrolyte layer 41 is less than 5 nm, current leakage between the positive electrode layer 30 and the holding layer 50 easily occurs in the obtained lithium ion secondary battery 1. On the other hand, if the thickness of the first solid electrolyte layer 41 exceeds 50 nm, the internal resistance of the battery increases, which is disadvantageous for high-speed charging and discharging.

Further, as a method for manufacturing the first solid electrolyte layer 41, a known film forming method such as various PVD or various CVD may be used, but from the viewpoint of production efficiency, it is preferable to use a sputtering method.

[Second solid electrolyte layer]
The second solid electrolyte layer 42 of the present embodiment is composed of LiPON (Li ₃ PO _4-x N _x (0 <x) in which a part of oxygen in Li ₃ PO ₄ constituting the first solid electrolyte layer 41 is replaced with nitrogen. <1)).

厚 The thickness of the second solid electrolyte layer 42 can be, for example, 10 nm or more and 10 μm or less. When the thickness of the second solid electrolyte layer 42 is less than 10 nm, current leakage between the positive electrode layer 30 and the holding layer 50 easily occurs in the obtained lithium ion secondary battery 1. On the other hand, when the thickness of the second solid electrolyte layer 42 exceeds 10 μm, the internal resistance of the battery increases, which is disadvantageous for high-speed charging and discharging.

Further, as a method for manufacturing the second solid electrolyte layer 42, a known film forming method such as various PVD or various CVD may be used, but from the viewpoint of production efficiency, it is preferable to use a sputtering method.

[Relationship between first solid electrolyte layer and second solid electrolyte layer]
Thus, in the present embodiment, the first solid electrolyte layer 41 is made of Li ₃ PO ₄ and the second solid electrolyte layer 42 is made of LiPON. That is, both the first solid electrolyte layer 41 and the second solid electrolyte layer 42 contain lithium, phosphorus, and oxygen, respectively.
Here, Li ₃ PO ₄ constituting the first solid electrolyte layer 41 has a higher volume resistivity than LiPON constituting the second solid electrolyte layer 42. For this reason, in the solid electrolyte layer 40 of the present embodiment, the side provided with the first solid electrolyte layer 41 in contact with the positive electrode layer 30 is closer to the side provided with the second solid electrolyte layer 42 in contact with the holding layer 50. Also, the resistance value per unit thickness is high.

Regarding the relationship between the thickness of the first solid electrolyte layer 41 and the thickness of the second solid electrolyte layer 42, whichever may be thicker or the same. However, from the viewpoint of suppressing an increase in the internal resistance of the battery, it is preferable that the thickness of the first solid electrolyte layer 41 is smaller than the thickness of the second solid electrolyte layer 42, and is in the order of two digits or more. More preferably, it is reduced.

(Holding layer)
The holding layer 50 as an example of a metal layer is a solid thin film and has a function of holding lithium ions during charging and releasing lithium ions during discharging. Here, the point that the holding layer 50 of the present embodiment does not itself include a negative electrode active material and is configured to hold lithium functioning as a negative electrode active material therein is different from a general negative electrode layer. Is different. Here, the holding layer 50 of the present embodiment also functions as an example of the second polar layer when lithium is held inside. In this embodiment, the second polarity corresponds to the negative polarity.

The holding layer 50 of the present embodiment has a porous structure, and is constituted by a porous portion (not shown) in which a large number of holes are formed. The porousization of the holding layer 50, that is, the formation of the porous portion, is performed in the first charge / discharge operation after the film formation, and the details will be described later.

材料 As a material for forming the holding layer 50, a platinum group element (Ru, Rh, Pd, Os, Ir, Pt), gold (Au), aluminum (Al), or an alloy thereof can be used. Among these, it is desirable that the holding layer 50 be made of platinum or gold, which is less likely to be oxidized. Further, the holding layer 50 of the present embodiment can be made of the above-mentioned noble metal and metal or a polycrystal of an alloy thereof.

Here, in the present embodiment, the holding layer 50 is made of platinum.

The thickness of the holding layer 50 can be, for example, not less than 10 nm and not more than 40 μm. When the thickness of the holding layer 50 is less than 10 nm, the ability to hold lithium becomes insufficient. On the other hand, if the thickness of the holding layer 50 exceeds 40 μm, the internal resistance of the battery increases, which is disadvantageous for high-speed charging and discharging. However, when the battery capacity required for the lithium ion secondary battery 1 is large, the thickness of the holding layer 50 may be more than 40 μm.

Further, as a method for manufacturing the holding layer 50, a known film forming method such as various PVD or various CVD may be used, but from the viewpoint of production efficiency, it is preferable to use a sputtering method. As a method for manufacturing the porous holding layer 50, it is desirable to employ a method of performing charging and discharging, as described later.

(Diffusion prevention layer)
The diffusion prevention layer 60 as an example of the amorphous layer is a solid thin film, and is for suppressing diffusion of lithium ions held in the holding layer 50 to the outside of the lithium ion secondary battery 1. .
As the diffusion prevention layer 60, a material having an amorphous structure and made of a metal or an alloy can be used. The diffusion prevention layer 60 is preferably made of a metal or an alloy that does not form an intermetallic compound with lithium. Among these, from the viewpoint of corrosion resistance, chromium (Cr) alone or an alloy containing chromium is preferred. Is preferred. The diffusion prevention layer 60 may be formed by laminating a plurality of amorphous layers having different constituent materials (for example, a laminated structure of an amorphous chromium layer and an amorphous chromium titanium alloy layer). Further, the “amorphous structure” in the present embodiment includes not only a structure having an amorphous structure as a whole but also a structure in which microcrystals are precipitated in the amorphous structure. .

Here, in the present embodiment, the diffusion preventing layer 60 is made of an alloy of chromium and titanium (CrTi). Examples of the metal (alloy) that can be used for the diffusion prevention layer 60 include, in addition to CrTi, ZrCuAlNiPdP, CuZr, FeZr, TiZr, CoZrNb, NiNb, NiTiNb, NiP, CuP, NiPCu, NiTi, CrTi, AlTi, FeSiB. , AuSi and the like.

The thickness of the diffusion preventing layer 60 can be, for example, not less than 10 nm and not more than 40 μm. When the thickness of the diffusion preventing layer 60 is less than 10 nm, it is difficult for the lithium that has passed through the holding layer 50 from the solid electrolyte layer 40 side to be blocked by the diffusion preventing layer 60. On the other hand, if the thickness of the diffusion prevention layer 60 exceeds 40 μm, the internal resistance of the battery increases, which is disadvantageous for high-speed charging and discharging.

Further, as a method for manufacturing the diffusion preventing layer 60, a known film forming method such as various PVD or various CVD may be used, but from the viewpoint of production efficiency, it is preferable to use a sputtering method. In particular, when the diffusion prevention layer 60 is made of the above-described chromium-titanium alloy, the chromium-titanium alloy tends to be amorphous when the sputtering method is adopted.

(Negative electrode current collector layer)
The negative electrode current collector layer 70 is a solid thin film having electron conductivity, and has a function of collecting current to the holding layer 50. Here, the material constituting the negative electrode current collector layer 70 is not particularly limited as long as it has electron conductivity, and various metals and conductive materials including alloys of various metals may be used. it can. However, from the viewpoint of suppressing corrosion of the diffusion prevention layer 60, it is preferable to use a chemically stable material, for example, a platinum group element (Ru, Rh, Pd, Os, Ir, Pt) or gold ( Au) or an alloy thereof is preferable.

Here, in the present embodiment, the negative electrode current collector layer 70 is made of the same platinum as the holding layer 50. However, unlike the holding layer 50, the negative electrode current collector layer 70 does not have a porous structure.

厚 The thickness of the negative electrode current collector layer 70 can be, for example, not less than 5 nm and not more than 50 μm. If the thickness of the negative electrode current collector layer 70 is less than 5 nm, the corrosion resistance and the current collecting function will be reduced, and it will not be practical. On the other hand, if the thickness of the negative electrode current collector layer 70 exceeds 50 μm, the internal resistance of the battery increases, which is disadvantageous for high-speed charging and discharging.

As a method of manufacturing the negative electrode current collector layer 70, a known film forming method such as various PVD or various CVD may be used, but from the viewpoint of production efficiency, it is preferable to use a sputtering method.

[Structure of substrate]
Next, the substrate 10 used in the present embodiment will be described.
The material forming the substrate 10 is not particularly limited, and various materials such as metal, glass, ceramics, and resin can be adopted.

Here, in the present embodiment, the substrate 10 is made of a metal plate having electron conductivity. Thereby, the substrate 10 is caused to function as a positive electrode current collector layer that collects electric current to the positive electrode layer 30 via the base layer 20.

The thickness of the substrate 10 can be, for example, not less than 20 μm and not more than 2000 μm. If the thickness of the substrate 10 is less than 20 μm, the strength of the lithium ion secondary battery 1 may be insufficient. On the other hand, if the thickness of the substrate 10 exceeds 2000 μm, the volume energy density and the weight energy density decrease due to the increase in the thickness and weight of the battery.

FIG. 2 is a diagram showing a cross-sectional configuration example of a substrate 10 constituting the lithium ion secondary battery 1 of the embodiment. Hereinafter, the substrate 10 shown in FIG. 2A will be referred to as a first configuration example, and the substrate 10 shown in FIG. 2B will be referred to as a second configuration example.

(First configuration example)
In the first configuration example shown in FIG. 2A, the substrate 10 includes a base material 11 made of a single-layer metal plate.
In the first configuration example, various metals and alloys thereof can be used as the metal material forming the base material 11. Here, in the first configuration example, it is desirable to use stainless steel as the substrate 11 from the viewpoint of suppressing corrosion caused by phosphoric acid, and particularly from the viewpoint of suppressing intergranular corrosion, It is desirable to use SUS316, more preferably SUS316L. When LiNiO ₂ is used as the base layer 20 laminated on the base material 11 as in the present embodiment, stainless steel having a coefficient of thermal expansion close to that of LiNiO ₂ is used as the metal material forming the base material 11. Is preferred. Further, when the base material 11 is also used as a positive electrode current collector layer as in the present embodiment, the metal material constituting the base material 11 is hardly corroded even in a high voltage environment and resistant to overdischarge. It is preferable to use stainless steel.
In the first configuration example, the base material 11 forming the substrate 10 is not limited to a single-layer metal plate, and may be formed of a laminate of a plurality of metal plates.

(Second configuration example)
In the second configuration example shown in FIG. 2B, the substrate 10 includes a base material 11 made of a single-layer metal plate, and a coating layer 12 that covers the entire surface of the base material 11.
In the second configuration example, as the metal material forming the base material 11, various metals, their alloys, metal compounds, and the like can be used. Here, in the second configuration example, it is desirable to use aluminum as the base material 11 from the viewpoint of suppressing corrosion caused by lithium.
Note that, in the second configuration example, the base material 11 is not limited to a single-layer metal plate, and may be formed of a laminate of a plurality of metal plates.

Further, in the second configuration example, as a material forming the coating layer 12, various metals, their alloys, metal compounds, or the like can be used. Here, when the substrate 10 formed by forming the coating layer 12 on the base material 11 is adopted, from the viewpoint of suppressing corrosion caused by lithium, CrTi, ZrCuAlNiPdP, CuZr, FeZr, TiZr, CoZrNb, NiNb, It is preferable to use NiTiNb, NiP, CuP, NiPCu, NiTi, AlTi, FeSiB, AuSi, or the like. Among these, from the viewpoint of providing a hard outer peripheral surface capable of mechanical polishing, for example, NiP (nickel-phosphorous, hereinafter referred to as “Ni-P”) formed by an electroless nickel plating method. May be used).
However, the method for forming the coating layer 12 is not limited to the plating method, and various film forming methods may be employed.

In the example shown in FIG. 2B, the substrate 10 is formed by covering the entire surface of the base material 11 with the coating layer 12, but the present invention is not limited to this. For example, as shown in FIG. 1, when the battery structure is formed only on the surface 10 a of the substrate 10, the coating layer 12 may be provided on at least the side of the substrate 10 that becomes the surface 10 a on the substrate 10.

(Maximum height difference)
Next, the maximum and minimum height difference Rmm of the substrate 10 of the present embodiment will be described.
The maximum / minimum height difference Rmm is a measure for defining the smoothness of the laminated surface of the battery structure on the substrate 10 (the surface 10a of the substrate 10 in the present embodiment). The maximum-to-minimum height difference Rmm in the present embodiment is the height between the maximum height and the minimum height obtained by measuring irregularities in a range of 20 μm × 20 μm (square region) with an AFM (Atomic Force Microscope). Defined by the difference. Therefore, the definition of the maximum and minimum height difference Rmm is different from the maximum height Rz defined in, for example, JIS B0601.

Now, the definition of the maximum and minimum height difference Rmm will be described in more detail.
The maximum / minimum height difference Rmm in the present embodiment is obtained, for example, by using a D3100 manufactured by Bruker, which is an AFM apparatus (atomic force microscope system), and acquiring data in an area of 20 μm × 20 μm. Is prepared by using a cubic expression as an approximate polynomial, preparing an image (which has been subjected to “smoothing” processing) converted to a displacement from the reference plane (a positive displacement and a negative displacement may exist), and It can be obtained from the “maximum value−minimum value” of the direction (z displacement).

In the present embodiment, the maximum and minimum height difference Rmm of the surface 10a of the substrate 10 is set to 78 nm or less. Here, in the substrate 10 of the first configuration example shown in FIG. 2A, the maximum and minimum height difference Rmm of the base material 11 located on the front surface 10a side is set to 78 nm or less. In the substrate 10 of the second configuration example shown in FIG. 2B, the maximum and minimum height difference Rmm of the coating layer 12 located on the surface 10a side is set to 78 nm or less.

(Arithmetic mean roughness)
Next, the arithmetic average roughness Ra of the substrate 10 according to the present embodiment will be described.
The arithmetic average roughness Ra is specified, for example, in JIS B0601.
In the present embodiment, the arithmetic mean roughness Ra of the surface 10a of the substrate 10 is preferably 1.1 nm or less.

[Method of manufacturing lithium ion secondary battery]
Now, a method for manufacturing the above-described lithium ion secondary battery 1 will be described.
FIG. 3 is a flowchart for explaining the method for manufacturing the lithium ion secondary battery of the present embodiment.

(Substrate preparation process)
First, a substrate preparation step of preparing a substrate 10 which has been subjected to a surface treatment so that the maximum / minimum height difference Rmm of the surface 10a is 78 (nm) or less is executed (step 10).

Here, the substrate 10 according to the first configuration example shown in FIG. 2A is manufactured by, for example, the following procedure. First, a metal plate is manufactured by a rolling method or the like, and the surface 10a side of the base material 11 obtained by cutting the metal plate is subjected to a general mechanical polishing treatment, and then further subjected to CMP (Chemical Mechanical Polishing). By performing a precision polishing process using a mechanical polishing method or the like, the substrate 10 in which the maximum and minimum height difference Rmm of the surface 10a is set to 78 nm or less is obtained.

{Circle around (2)} The substrate 10 according to the second configuration example shown in FIG. 2B is manufactured by, for example, the following procedure. First, a metal plate is manufactured by a rolling method or the like, and a coating layer 12 made of Ni—P is formed on the entire surface of a base material 11 obtained by cutting the metal plate by an electroless nickel plating method or the like. A laminate of the material 11 and the coating layer 12 is obtained. Then, after performing a general mechanical polishing process on the coating layer 12 positioned on the surface 10a side of the thus obtained laminated body, a polishing process using a CMP method or the like is performed, so that the surface 10a The substrate 10 having the maximum and minimum height difference Rmm set to 78 nm or less is obtained.

(Underlayer forming step)
Then, the substrate 10 is mounted on a sputtering device (not shown), and a base layer forming step of forming the base layer 20 on the surface 10a of the substrate 10 is performed (Step 20).

(Positive electrode layer forming step)
Next, a positive electrode layer forming step of forming the positive electrode layer 30 on the underlayer 20 (an example of a first polar layer forming step) is performed by the sputtering apparatus (step 30).

In the case of using a mixed material positive electrode as the positive electrode layer 30, sputtering using a sputtering target containing a positive electrode active material and an inorganic solid electrolyte may be performed, or a sputtering target containing a positive electrode active material and an inorganic solid electrolyte may be used. Co-sputtering using the above sputtering target.

(Solid electrolyte layer forming step)
Subsequently, a solid electrolyte layer forming step of forming the solid electrolyte layer 40 on the positive electrode layer 30 is performed by the sputtering device (step 40). Here, in the solid electrolyte layer forming step of Step 40, a first solid electrolyte layer forming step of forming the first solid electrolyte layer 41 on the positive electrode layer 30 is performed (Step 41), and the first solid electrolyte layer 41 is formed on the first solid electrolyte layer 41. A second solid electrolyte layer forming step of forming the second solid electrolyte layer 42 is performed (Step 42).

When Li ₃ PO ₄ is used for the first solid electrolyte layer 41 and LiPON is used for the second solid electrolyte layer 42, a sputtering target containing lithium, phosphorus and oxygen is used, and the first solid electrolyte layer is formed under an atmosphere containing no nitrogen. It is preferable that the first solid electrolyte layer 41 is formed, and then the second solid electrolyte layer 42 is formed in an atmosphere containing nitrogen.

(Retaining layer forming step)
Next, a holding layer forming step (an example of a metal layer forming step) for forming the holding layer 50 on the second solid electrolyte layer 42 of the solid electrolyte layer 40 is performed by the sputtering apparatus (step 50).

(Diffusion prevention layer forming step)
Then, a diffusion preventing layer forming step (an example of an amorphous layer forming step) for forming the diffusion preventing layer 60 on the holding layer 50 is performed by the sputtering apparatus (step 60).

(Negative electrode current collector layer forming step)
Then, a negative electrode current collector layer forming step of forming the negative electrode current collector layer 70 on the diffusion prevention layer 60 is performed by the sputtering device (step 70).
By performing these steps 10 to 70, the basic structure of the lithium ion secondary battery 1 is obtained. Then, the basic structure of the lithium ion secondary battery 1 is removed from the sputtering device.

(First charging process)
Subsequently, an initial charging step (an example of a charging step) for performing a first charging is performed on the basic structure of the lithium ion secondary battery 1 removed from the sputtering apparatus (step 80).

(First discharge process)
Then, an initial discharge step (an example of a discharge step) for performing a first discharge is performed on the charged basic structure of the lithium ion secondary battery 1 (step 90). By these initial charging and initial discharging, the holding layer 50 is made porous, that is, a porous portion and a large number of pores are formed, and the lithium ion secondary battery 1 shown in FIG. 1 is obtained.

[Porosification of holding layer]
Now, the above-described porous formation of the holding layer 50 will be described in more detail.
FIG. 4 is a diagram for explaining a procedure for making the holding layer 50 porous, and is an enlarged view of the holding layer 50 and the periphery thereof. Here, FIG. 4A shows the state after the film formation and before the first charge (between Step 70 and Step 80), and FIG. 4B shows the state after the first charge and before the first discharge (Step 80 and Step 90). 4C), and FIG. 4C shows a state after the first discharge (after step 90).

(After film formation and before initial charge)
First, in the state “after film formation and before initial charging” shown in FIG. 4A, the holding layer 50 is dense. The thickness of the holding layer 50 is the thickness of the holding layer t50, the thickness of the diffusion prevention layer 60 is the thickness of the diffusion prevention layer t60, and the thickness of the negative electrode current collector layer 70 is the thickness of the negative electrode current collector layer. It is t70.

(After initial charging and before initial discharging)
When charging (initial charging) the lithium ion secondary battery 1 shown in FIG. 4A, the positive electrode of the DC power supply is provided on the substrate 10 (see FIG. 1), and the DC power supply is provided on the negative electrode current collector layer 70. Negative electrodes are respectively connected. Then, as shown in FIG. 4B, lithium ions (Li ⁺ ) constituting the positive electrode active material in the positive electrode layer 30 move to the holding layer 50 via the solid electrolyte layer 40. That is, in the charging operation, the lithium ions move in the thickness direction of the lithium ion secondary battery 1 (upward in FIG. 4B).

At this time, the lithium ions that have moved from the positive electrode layer 30 side to the holding layer 50 side are alloyed with the metal constituting the holding layer 50. For example, when the holding layer 50 is made of platinum (Pt), in the holding layer 50, lithium and platinum are alloyed (solid solution, formation of an intermetallic compound, or eutectic).

(4) Part of the lithium ions that have entered the holding layer 50 passes through the holding layer 50 and reaches the boundary with the diffusion preventing layer 60. Here, the diffusion prevention layer 60 of the present embodiment is made of a metal or an alloy having an amorphous structure, and the number of grain boundaries is significantly smaller than that of the holding layer 50 having a polycrystalline structure. ing. For this reason, the lithium ions that have reached the boundary between the holding layer 50 and the diffusion prevention layer 60 are less likely to enter the diffusion prevention layer 60, and thus maintain the state held in the holding layer 50.

(4) In the state where the initial charging operation has been completed, the lithium ions that have moved from the positive electrode layer 30 to the holding layer 50 are held by the holding layer 50. At this time, it is considered that the lithium ions that have moved to the holding layer 50 are held by the holding layer 50 by alloying with platinum or by precipitating metallic lithium in the platinum.

Here, as shown in FIG. 4B, in the lithium ion secondary battery 1 after the first charge and before the first discharge, the holding layer thickness t50 is changed from the film formation shown in FIG. More than the state. That is, the volume of the holding layer 50 increases by the first charging. This is considered to be due to the fact that lithium and platinum are alloyed in the holding layer 50. On the other hand, the thickness t60 of the diffusion prevention layer does not substantially change before and after the first charge. That is, the volume of the diffusion prevention layer 60 is not substantially changed by the first charge. This is considered to be due to the fact that lithium hardly enters the diffusion preventing layer 60. This means that the thickness t70 of the negative electrode current collector layer does not substantially change before and after the first charge, that is, the volume of the negative electrode current collector layer 70 does not substantially change before and after the first charge (negative electrode current collector). It is considered that the platinum constituting the electric conductor layer 70 is not made porous and remains dense like the platinum constituting the holding layer 50).

(After the first discharge)
When discharging (initial discharge) the lithium ion secondary battery 1 shown in FIG. 4B, a positive electrode of a load is provided on the substrate 10 (see FIG. 1), and a negative electrode of the load is provided on the negative electrode current collector layer 70. The electrodes are respectively connected. Then, as shown in FIG. 4C, the lithium ions (Li ⁺ ) held in the holding layer 50 move to the positive electrode layer 30 via the solid electrolyte layer 40. That is, in the discharging operation, the lithium ions move in the thickness direction of the lithium ion secondary battery 1 (downward in FIG. 4C) and are held by the positive electrode layer 30. Accordingly, a DC current is supplied to the load.

At this time, in the holding layer 50, the alloy of lithium and platinum is dealloyed (dissolution of the metallic lithium when metallic lithium is precipitated) with the release of lithium. Then, as a result of dealloying in the holding layer 50, the holding layer 50 is made porous, and becomes a porous portion 51 in which a large number of holes 52 are formed. The porous portion 51 obtained in this way is substantially made of metal (for example, platinum). However, in the state where the first discharge is completed, lithium does not completely disappear inside the holding layer 50, and some lithium which does not move by the discharge operation remains.

Here, as shown in FIG. 4C, in the lithium ion secondary battery 1 after the first discharge, the holding layer thickness t50 is larger than the state after the first charge and before the first discharge shown in FIG. 4B. Decrease. This is considered to be due to the fact that the alloy of lithium and platinum is dealloyed in the holding layer 50. This is supported by the fact that the shape of the holes 52 formed in the holding layer 50 by the first discharge is flattened so that the thickness direction is smaller than the plane direction. Further, as shown in FIG. 4C, in the lithium ion secondary battery 1 after the initial discharge, the holding layer thickness t50 is larger than the state after the film formation and before the first charge shown in FIG. I do. This is considered to be due to the fact that the holding layer 50 is made porous by the first charging and the first discharging, that is, a large number of holes 52 are formed in the holding layer 50. On the other hand, the thickness t60 of the diffusion prevention layer and the thickness t70 of the negative electrode current collector layer are not substantially changed before and after the first discharge.

[Others]
In this embodiment, the base layer 20, the positive electrode layer 30, the solid electrolyte layer 40, the holding layer 50, the diffusion preventing layer 60, and the negative electrode current collector layer 70 are sequentially stacked on the surface 10a of the substrate 10. Thus, the basic structure of the lithium ion secondary battery 1 was formed. That is, a configuration is adopted in which the positive electrode layer 30 is arranged on the side closer to the substrate 10 and the holding layer 50 is arranged on the side farther from the substrate 10. However, the configuration is not limited to this, and a configuration in which the holding layer 50 is arranged on the side closer to the substrate 10 and the positive electrode layer 30 is arranged on the side farther from the substrate 10 may be adopted. However, in this case, the order of lamination of each layer on the substrate 10 is opposite to that described above.

In the present embodiment, the basic structure of the lithium ion secondary battery 1 is formed on one surface of the substrate 10, that is, on the surface 10a. However, the present invention is not limited to this. In addition to forming the basic structure of the lithium ion secondary battery 1 on the front surface 10a of the substrate 10, another lithium The basic structure of the ion secondary battery 1 may be formed. In this case, it is necessary to set the maximum / minimum height difference Rmm on the back surface 10b of the substrate 10 to 78 nm or less, similarly to the front surface 10a.

Hereinafter, the present invention will be described in more detail based on examples. However, the present invention is not limited to the following examples unless it exceeds the gist.
The inventor manufactured three types of lithium ion secondary batteries 1 (Examples 1 and 2 and Comparative Example), and evaluated the respective structures and various electrical characteristics.

[Example 1]
First, in Example 1, among the lithium ion secondary batteries 1 described in the above embodiment, those using the substrate 10 of the first configuration example shown in FIG. 2A were used. That is, in Example 1, the lithium ion secondary battery 1 including the substrate 10 formed of the base material 11 and having its surface 10a polished to the maximum and minimum height difference Rmm ≦ 78 nm was used.

[Example 2]
Further, in Example 2, among the lithium ion secondary batteries 1 described in the above embodiment, those using the substrate 10 of the second configuration example shown in FIG. 2B were used. In No. 2, a lithium ion secondary battery 1 including a substrate 10 composed of a base material 11 and a coating layer 12 and having its surface 10a polished to a maximum and minimum height difference Rmm ≦ 78 nm was used.

[Comparative Example]
On the other hand, in the comparative example, although the basic configuration itself is the same as that of the first embodiment, a lithium ion secondary battery 1 having a substrate 10 whose surface 10a is polished to a maximum / minimum height difference Rmm> 400 nm is used. Was.

[Specific Configurations of Examples and Comparative Examples]
Next, a specific configuration of the lithium ion secondary battery 1 according to the example and the comparative example will be described.

(Structure of substrate)
Table 1 shows the configuration of the substrate 10 in the lithium ion secondary batteries 1 according to Examples 1 and 2 and Comparative Example. Here, Table 1 shows the constituent materials of the base material 11 constituting the substrate 10, the presence or absence of the coating layer 12 on the substrate 10 (if any), the presence or absence of the CMP process on the substrate 10, The relationship between the thickness, the maximum and minimum height difference Rmm of the surface 10a of the substrate 10, and the arithmetic average roughness Ra is shown.

Now, each substrate 10 will be described.
[Example 1]
In Example 1, the substrate 10 had a single-layer structure of the base material 11. That is, the configuration was such that the substrate 10 did not include the coating layer 12. In Example 1, SUS316L was used as the base material 11 and the thickness thereof was 0.1 (mm). Furthermore, in Example 1, after performing a general mechanical polishing process on the surface 10a of the substrate 10, a CMP process was further performed. As a result, the maximum and minimum height difference Rmm of the surface 10a of the substrate 10 was 78 (nm), and the arithmetic average roughness Ra was 1.19 (nm).

[Example 2]
In Example 2, the substrate 10 had a laminated structure of the base material 11 and the coating layer 12. In Example 2, Al (aluminum) was used as the base material 11 and the thickness was set to 0.1 (mm), which is the same as that in Example 1. In Example 2, Ni—P was used as the coating layer 12. The coating layer 12 was attached to the substrate 11 by using an electroless nickel plating method. Further, in the second embodiment, as in the first embodiment, the surface 10a of the substrate 10 is subjected to a general mechanical polishing process, and further subjected to a CMP process. As a result, the maximum and minimum height difference Rmm of the surface 10a of the substrate 10 is 2.7 (nm) smaller than that of the first embodiment, and the arithmetic average roughness Ra is 0.499 (nm) smaller than that of the first embodiment. It became.

(Comparative example)
In the comparative example, the substrate 10 had the same single-layer structure of the base material 11 as in Example 1. That is, the configuration was such that the substrate 10 did not include the coating layer 12. In the comparative example, SUS316L was used as the base material 11 and the thickness was set to 0.1 (mm), as in Example 1. However, in the comparative example, unlike the first embodiment, only the general mechanical polishing process is performed on the surface 10a of the substrate 10, and the CMP process is not performed. As a result, the maximum and minimum height difference Rmm of the surface 10a of the substrate 10 is 438 (nm), which is larger than that of the first and second embodiments, and the arithmetic average roughness Ra is 61.2 (greater than that of the first and second embodiments). nm).

(Structure of each layer except substrate)
Table 2 shows a configuration other than the substrate 10 in the lithium ion secondary batteries 1 according to Examples 1 and 2 and Comparative Example. Here, Table 2 shows the relationship between the name of each layer excluding the substrate 10 and the material constituting each layer and its thickness.

[Example 1]
First, a first embodiment will be described.
For the underlayer 20, LiNiO ₂ formed by a sputtering method was used. The thickness of the underlayer 20 was 200 nm.
For the positive electrode layer 30, LiNiO ₂ and Li ₃ PO ₄ formed by a sputtering method were used. The thickness of the positive electrode layer 30 was 1000 nm. The ratio (molar ratio) between LiNiO ₂ and Li ₃ PO ₄ in the positive electrode layer 30 was 73:27.
For the first solid electrolyte layer 41 constituting the solid electrolyte layer 40, Li ₃ PO ₄ formed by a sputtering method was used. The thickness of the first solid electrolyte layer 41 was 20 nm.
For the second solid electrolyte layer 42 constituting the solid electrolyte layer 40, LiPON formed by a sputtering method was used. The thickness of the second solid electrolyte layer 42 was 980 nm. Therefore, the entire thickness of the solid electrolyte layer 40 is set to 1000 nm.
For the holding layer 50, Pt formed by a sputtering method was used. The thickness of the holding layer 50 was 410 nm.
For the diffusion prevention layer 60, CrTi formed by a sputtering method was used. The thickness of the diffusion prevention layer 60 was 50 nm.
For the negative electrode current collector layer 70, Pt formed by a sputtering method was used. The thickness of the negative electrode current collector layer 70 was 100 nm.

[Example 2]
Next, a second embodiment will be described.
For the underlayer 20, LiNiO ₂ formed by a sputtering method was used. The thickness of the underlayer 20 was 200 nm.
For the positive electrode layer 30, LiNiO ₂ and Li ₃ PO ₄ formed by a sputtering method were used. The thickness of the positive electrode layer 30 was 800 nm. The ratio (molar ratio) between LiNiO ₂ and Li ₃ PO ₄ in the positive electrode layer 30 was 73:27.
For the first solid electrolyte layer 41 constituting the solid electrolyte layer 40, Li ₃ PO ₄ formed by a sputtering method was used. The thickness of the first solid electrolyte layer 41 was 20 nm.
For the second solid electrolyte layer 42 constituting the solid electrolyte layer 40, LiPON formed by a sputtering method was used. The thickness of the second solid electrolyte layer 42 was 980 nm. Therefore, the entire thickness of the solid electrolyte layer 40 is set to 1000 nm.
For the holding layer 50, Pt formed by a sputtering method was used. The thickness of the holding layer 50 was 60 nm.
For the diffusion prevention layer 60, CrTi formed by a sputtering method was used. The thickness of the diffusion prevention layer 60 was 200 nm.
For the negative electrode current collector layer 70, Pt formed by a sputtering method was used. The thickness of the negative electrode current collector layer 70 was 60 nm.

(Comparative example)
Further, a comparative example will be described.
In the comparative example, the constituent materials and thicknesses of the respective layers from the base layer 20 to the negative electrode current collector layer 70 were the same as those in Example 1. Therefore, Example 1 and Comparative Example differ only in the flatness of the surface 10a of the substrate 10 (base material 11).

(4) The basic structure of each lithium ion secondary battery 1 thus obtained was initially charged and discharged, whereby a lithium ion secondary battery 1 was obtained. In addition, the thickness of the holding layer 50 was increased from the respective initial values by performing the initial charge / discharge.

[Evaluation of lithium ion secondary battery]
Here, as a scale for evaluating each of the lithium ion secondary batteries 1 of Examples 1 and 2 and the comparative example, the structure (crystal structure and cross-sectional structure) of the lithium ion secondary battery 1 and the electrical characteristics (capacity maintenance) Rate).

(Crystal structure)
First, the crystal structure will be described. The inventor measured the electron diffraction pattern of each of the lithium ion secondary batteries 1 of Examples 1 and 2 and the comparative example, and thereby determined the crystal structure (crystallization) of each layer constituting the lithium ion secondary battery 1. , Amorphization).

In the lithium ion secondary batteries 1 of Examples 1 and 2, the substrate 10, the holding layer 50, and the negative electrode current collector layer 70 were each crystallized. On the other hand, the underlayer 20, the first solid electrolyte layer 41, the second solid electrolyte layer 42, and the diffusion prevention layer 60 were amorphous. In the positive electrode layer 30, a crystallized region and an amorphous region were mixed, and a crystallized region was scattered with respect to the amorphous region.
On the other hand, the lithium ion secondary battery 1 of the comparative example also exhibited the same crystal structure as the layers constituting the lithium ion secondary batteries 1 of Examples 1 and 2.

(Cross section structure)
Next, a cross-sectional structure will be described.
(Comparative example)
FIG. 5A is a cross-sectional STEM photograph of the lithium ion secondary battery 1 of the comparative example before the first charge / discharge. FIG. 5B is a cross-sectional STEM photograph of the lithium ion secondary battery 1 of the comparative example after seven times of charge and discharge. Further, FIG. 6A is an enlarged cross-sectional STEM photograph of the lithium ion secondary battery 1 of the comparative example before the first charge / discharge. FIG. 6B is an enlarged cross-sectional STEM photograph of the lithium ion secondary battery 1 of the comparative example after seven times of charge and discharge. These STEM photographs were taken using an HD-2300 ultra-thin film evaluation device manufactured by Hitachi High-Technologies Corporation (the same applies hereinafter). Here, FIG. 5 (a) corresponds to FIG. 6 (a), and FIG. 5 (b) corresponds to FIG. 6 (b). However, since the photographing positions are different between the STEM photograph shown in FIG. 5A and FIG. 6A and the STEM photograph shown in FIG. 5B and FIG. Not.
In the following description, the state before the first charge and discharge may be simply referred to as “before charge and discharge”, and the state after seven times charge and discharge may be simply referred to as “after charge and discharge”.

Now, the cross-sectional structure of the lithium-ion secondary battery 1 of the comparative example will be described with reference to FIGS.
First, focusing on the holding layer 50, it can be seen that the thickness after charging / discharging is larger than that before charging / discharging. Further, focusing on the diffusion prevention layer 60 and the negative electrode current collector layer 70, it can be seen that the respective thicknesses hardly change before and after charging and discharging.

Before the charge and discharge, the base layer 20 to the negative electrode current collector layer 70 have irregularities (undulations) due to the flatness of the surface 10a of the substrate 10 to be laminated. You can see that. On the other hand, after the charge and discharge, in addition to the above-described flatness of the surface 10a of the substrate 10, the base layer 20 to the negative electrode current collector layer 70 have the positive electrode layer 30 to the holding layer 50 due to the movement of lithium ions. It can be seen that the unevenness caused by the influence of the expansion and contraction in the thickness direction is further increased.

In particular, as shown in FIG. 5B and FIG. 6B, after charging / discharging, the portion of the interface between the holding layer 50 and the diffusion preventing layer 60 having a V-shaped cross section is held. It can be seen that huge voids (white areas in FIG. 5B and dark areas in FIG. 6B) are generated on the layer 50 side. Such voids are much larger than the holes 52 (see FIG. 4C) formed in the holding layer 50 due to charge and discharge, and in a region having a V-shaped cross section, the negative electrode current collector This may be a factor that causes leakage of lithium to the layer 70 side. In addition, such voids may be a factor that causes the retention layer 50 and the diffusion prevention layer 60 to peel off.

(Capacity maintenance rate)
For each of the lithium ion secondary batteries 1 of Examples 1 and 2 and Comparative Example, the charge / discharge characteristics were measured, and the capacity retention was evaluated using the measurement results of the charge / discharge characteristics. As a device for measuring charge / discharge characteristics, a charge / discharge device HJ1020mSD8 manufactured by Hokuto Denko KK was used.

容量 Here, the capacity retention ratio is a percentage of the capacity of the lithium ion secondary battery 1 at the time when a predetermined period has elapsed with respect to the initial capacity after the completion of charging. In this case, the higher the value of the capacity retention ratio, the better, and the maximum is 100%. Here, the capacity retention rate after full charge and after 3 hours was evaluated.

Table 3 shows the capacity retention of the lithium ion secondary batteries 1 according to Examples 1 and 2 and Comparative Example. Here, Table 3 is expressed as a ratio of the configuration of the substrate 10, the maximum and minimum height difference Rmm and the arithmetic average roughness Ra on each surface 10a, and the discharge capacity immediately after full charge and after 3 hours after full charge. It shows the relationship with the capacity retention rate. Here, in Example 1 and Comparative Example, the current value during charging was 20 mA, and in Example 2, the current value during charging was 2.7 mA. This is because the area (footprint) of the lithium ion secondary battery 1 was the same in Example 1 and the comparative example, whereas the area of the lithium ion secondary battery 1 was This is due to the fact that it was smaller than the comparative example.

容量 The capacity retention rate in Example 1 was 98.8%. Further, the capacity retention ratio in Example 2 was 99.9%, which was higher than that in Example 1. On the other hand, the capacity retention ratio in the comparative example was 77.6%, which was lower than that in Examples 1 and 2.

[About the trend of capacity retention rate]
From the above, it can be said that the following tendency is observed in the capacity retention ratio.
First, in the first and second embodiments in which the maximum / minimum height difference Rmm of the substrate 10 is set to 78 (nm) or less, the capacity retention ratio is higher than in the comparative example in which the maximum / minimum height difference Rmm is set to more than 400 (nm). Was high. This is because the flatness of the surface 10a of the substrate 10 is set to be significantly higher than in the past, whereby the flatness of the base layer 20 to the negative electrode current collector layer 70 formed on the substrate 10 is improved, and Accordingly, it is considered that the leakage of lithium due to the V-shaped cross-sectional structure (see FIGS. 5 and 6) as in the comparative example was suppressed. In the case where leakage of lithium occurs, a path for passing lithium is formed in the diffusion prevention layer 60, so that the capacity retention ratio is reduced.

In the second embodiment in which the maximum and minimum height difference Rmm of the substrate 10 is set to 2.7 (nm), the capacity retention ratio is higher than in the first embodiment in which the maximum and minimum height difference Rmm is set to 78 (nm). it was high. This is also considered to be due to the fact that the flatness of the surface 10a of the substrate 10 is higher in the second embodiment than in the first embodiment.

DESCRIPTION OF SYMBOLS 1 ... lithium ion secondary battery, 10 ... board | substrate, 10a ... front surface, 10b ... back surface, 11 ... base material, 12 ... coating layer, 20 ... underlayer, 30 ... positive electrode layer, 40 ... solid electrolyte layer, 41 ... 1st Solid electrolyte layer, 42: second solid electrolyte layer, 50: holding layer, 51: porous portion, 52: void, 60: diffusion preventing layer, 70: negative electrode current collector layer

Claims (19)

1. A substrate having a front surface and a back surface;
   A first polar layer provided on the front surface side of the substrate and occluding and releasing lithium ions at a first polarity;
   A solid electrolyte layer containing an inorganic solid electrolyte having lithium ion conductivity,
   A second polar layer that occludes and releases lithium ions at a second polarity opposite to the first polarity, and
   The surface of the substrate has a maximum minimum height difference of 78 nm or less, which is a height difference between a maximum height and a minimum height obtained by measuring unevenness in a range of 20 μm × 20 μm with an AFM (Atomic Force Microscope). A lithium ion secondary battery characterized by the above-mentioned.
2. The substrate is made of SUS316L;
   The lithium ion secondary battery according to claim 1, characterized in that it comprises a LiPON which the solid electrolyte layer is substituted for part of oxygen in the Li ₃ PO ₄ with nitrogen.
3. The substrate is made of a metal material having Ni-P plating on the surface,
   The lithium ion secondary battery according to claim 1, characterized in that it comprises a LiPON which the solid electrolyte layer is substituted for part of oxygen in the Li ₃ PO ₄ with nitrogen.
4. The first polarity is positive, the second polarity is negative,
   The solid electrolyte layer,
   A first solid electrolyte layer provided opposite to the first polar layer and containing Li ₃ PO ₄ and not containing LiNiO ₂ ;
   4. A second solid electrolyte layer comprising LiPON which is provided to face the second polar layer and includes LiPON in which a part of oxygen in Li ₃ PO ₄ is replaced by nitrogen. Lithium ion secondary battery.
5. The first polarity layer is a lithium ion secondary battery according to claim 4, characterized in that it contains LiNiO ₂ and Li ₃ PO _4.
6. It provided between said surface and said first polarity layer of the substrate, a lithium ion secondary battery according to claim 5, further comprising a base layer containing no Li ₃ PO ₄ include LiNiO _2.
7. A metal layer provided opposite to the solid electrolyte layer and made of a platinum group element (Ru, Rh, Pd, Os, Ir, Pt), gold (Au), aluminum (Al), or an alloy thereof is further provided. And
   The lithium ion secondary battery according to any one of claims 4 to 6, wherein the second polar layer contains lithium alloyed with a metal constituting the metal layer.
8. The lithium ion secondary battery according to claim 7, further comprising an amorphous layer provided opposite to the metal layer and having an amorphous structure and made of a metal or an alloy.
9. The lithium ion secondary battery according to any one of claims 1 to 8, wherein the maximum and minimum height difference of the surface of the substrate is 2.7 nm or less.
10. The lithium ion secondary battery according to any one of claims 1 to 9, wherein the arithmetic mean roughness Ra of the surface of the substrate is 1.1 nm or less.
11. A substrate provided with a surface having a maximum / minimum height difference of 78 nm or less, which is a height difference between a maximum height and a minimum height obtained by measuring unevenness in a range of 20 μm × 20 μm with an AFM (Atomic Force Microscope). A substrate preparation step for preparing,
    A first polar layer forming step of forming a first polar layer for absorbing and releasing lithium ions with a first polarity on the front surface side of the substrate;
    Forming a solid electrolyte layer containing an inorganic solid electrolyte having lithium ion conductivity on the first polar layer side provided on the substrate.
12. The method for manufacturing a lithium ion secondary battery according to claim 11, wherein in the substrate preparing step, the substrate made of SUS316L is prepared.
13. 12. The method of manufacturing a lithium ion secondary battery according to claim 11, wherein in the substrate preparing step, the substrate made of a metal material plated with Ni—P is prepared.
14. The first polarity is positive;
    A metal layer made of a platinum group element (Ru, Rh, Pd, Os, Ir, Pt), gold (Au), aluminum (Al), or an alloy thereof is formed on the solid electrolyte layer provided on the substrate. Forming a metal layer forming step;
    For the laminate including the substrate, the first polar layer, the solid electrolyte layer, and the metal layer, charging is performed by moving lithium ions from the first polar layer to the metal layer via the solid electrolyte layer. A charging process to be performed;
    12. The method according to claim 11, further comprising: discharging the charged layered product by moving lithium ions from the metal layer to the first polar layer via the solid electrolyte layer. 14. The method for producing a lithium ion secondary battery according to any one of claims 13 to 13.
15. Between the metal layer forming step and the charging step, the metal layer further includes an amorphous layer forming step of forming an amorphous layer made of a metal or an alloy having an amorphous structure. The method for producing a lithium ion secondary battery according to claim 14, wherein:
16. The first polarity is positive;
    In the first polar layer forming step, a mixed material positive electrode including LiNiO ₂ and Li ₃ PO ₄ is formed,
    In the solid electrolyte layer forming step, after forming a first solid electrolyte layer containing Li ₃ PO ₄ and not containing LiNiO ₂ , a second solid electrolyte containing LiPON in which part of oxygen in Li ₃ PO ₄ has been replaced with nitrogen The method for manufacturing a lithium ion secondary battery according to any one of claims 11 to 15, wherein a layer is formed.
17. Between the substrate preparing step and the first polar layer forming step, the method further includes an underlayer forming step of forming an underlayer containing LiNiO ₂ and not Li ₃ PO ₄ on the surface of the substrate. The method for manufacturing a lithium ion secondary battery according to any one of claims 11 to 16.
18. The lithium ion secondary battery according to any one of claims 11 to 17, wherein in the substrate preparing step, the substrate having the maximum and minimum height difference of the surface set to 2.7 nm or less is prepared. Manufacturing method.
19. The lithium ion secondary battery according to any one of claims 11 to 18, wherein in the substrate preparing step, the substrate having an arithmetic mean roughness Ra of the surface set to 1.1 nm or less is prepared. Manufacturing method.

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