Sodium ion secondary battery component and sodium ion secondary battery

Abstract

The present invention provides: a member for sodium ion secondary batteries, said member being not susceptible to deterioration of the cycle characteristics due to charge and discharge; and a sodium ion secondary battery.　A member 8 for sodium ion secondary batteries, said member 8 being provided with: a solid electrolyte layer 2 having sodium ion conductivity; a sodium metal layer 6 that is composed of sodium metal, while being arranged on one main surface 2b of the solid electrolyte layer 2; and a metal layer 5 that is arranged between the solid electrolyte layer 2 and the sodium metal layer 6, while being composed of a metal that is different from sodium metal.

Description

[Technical Field]

[0001] The present invention relates to a sodium ion secondary battery member and a sodium ion secondary battery. [Background technology]

[0002] Lithium-ion secondary batteries have established themselves as high-capacity, lightweight power sources essential for mobile devices, electric vehicles, and the like. However, current lithium-ion secondary batteries mainly use flammable organic electrolyte solutions as electrolytes, raising concerns about the risk of fire and other problems. To solve this problem, development is underway on lithium-ion secondary batteries that use solid electrolytes instead of organic electrolyte solutions (see, for example, Patent Document 1). Furthermore, due to concerns about issues with lithium, such as the global rise in the price of raw materials, research has been conducted in recent years on sodium-ion secondary batteries as an alternative (see, for example, Patent Document 2). Patent Document 2 describes an embodiment in which a metallic sodium layer is used as the negative electrode layer. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 5-205741 [Patent Document 2] Japanese Patent Application Laid-Open No. 2010-15782 Summary of the Invention [Problem to be solved by the invention]

[0004] Incidentally, secondary batteries used as power sources for electric vehicles and the like are required to have a high energy density in order to extend the cruising distance of the vehicle. In this regard, sodium ion secondary batteries using metallic sodium in the negative electrode as in Patent Document 2 tend to have a higher operating voltage and, as a result, a higher energy density than batteries using other metals in the negative electrode. However, when metallic sodium is used in the negative electrode, there is a problem in that the cycle characteristics due to charge and discharge tend to deteriorate. This tendency is particularly noticeable when β″-alumina is used as the solid electrolyte.

[0005] An object of the present invention is to provide a sodium ion secondary battery member and a sodium ion secondary battery that are excellent in charge / discharge cycle characteristics. [Means for solving the problem]

[0006] The sodium ion secondary battery member according to the present invention is characterized by comprising: a solid electrolyte layer having sodium ion conductivity; a metallic sodium layer disposed on one main surface of the solid electrolyte layer and made of metallic sodium; and a metal layer provided between the solid electrolyte layer and the metallic sodium layer and made of a metal different from the metallic sodium.

[0007] In the present invention, the metal layer is preferably a vapor-deposited film or a sputtered film.

[0008] In the present invention, the metal layer preferably contains at least one metal selected from the group consisting of Sn, Ti, Bi, Au, Al, Cu, Sb, and Pb.

[0009] In the present invention, it is preferable that at least a part of the metal contained in the metal layer is a metal capable of absorbing and releasing sodium ions.

[0010] In the present invention, it is preferable that at least a part of the metal contained in the metal layer is alloyed with the metallic sodium contained in the metallic sodium layer at the interface between the metallic sodium layer and the metal layer.

[0011] A sodium ion secondary battery according to the present invention is characterized by including the above-mentioned sodium ion secondary battery member.

[0012] In the present invention, it is preferable that the solid electrolyte layer has a first main surface and a second main surface facing each other, and includes a positive electrode layer provided on the first main surface of the solid electrolyte layer and an negative electrode layer provided on the second main surface of the solid electrolyte layer, and the negative electrode layer includes the metallic sodium layer and the metal layer. [Effects of the Invention]

[0013] According to the present invention, it is possible to provide a sodium ion secondary battery member and a sodium ion secondary battery that are excellent in charge / discharge cycle characteristics. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a schematic cross-sectional view showing a sodium ion secondary battery according to one embodiment of the present invention. [Figure 2] FIG. 2 is a graph showing the relationship between the number of cycles and the average discharge voltage of the test batteries prepared in the examples and comparative examples. [Figure 3] FIG. 3 is a graph showing the relationship between the number of cycles and the discharge capacity retention rate for the test batteries prepared in the examples and comparative examples. [Figure 4] FIG. 4 is a graph showing charge-discharge curves of the test battery prepared in Example 1 at the 1st cycle and the 50th cycle. [Figure 5] FIG. 5 is a graph showing charge-discharge curves of the test battery prepared in Example 2 at the 1st and 50th cycles. [Figure 6]FIG. 6 shows charge-discharge curves for the test battery prepared in Example 3 at the 1st and 50th cycles. [Figure 7] FIG. 7 is a graph showing charge-discharge curves for the test battery prepared in Comparative Example 1 at the 1st and 50th cycles. [Figure 8] FIG. 8 is a schematic cross-sectional view showing a sodium ion secondary battery of a comparative example. DETAILED DESCRIPTION OF THE INVENTION

[0015] Preferred embodiments will be described below. However, the following embodiments are merely examples, and the present invention is not limited to the following embodiments. In addition, in the drawings, components having substantially the same functions may be referred to by the same reference numerals.

[0016] FIG. 1 is a schematic cross-sectional view showing a sodium ion secondary battery (all-solid-state sodium ion secondary battery) according to one embodiment of the present invention. As shown in FIG. 1, the sodium ion secondary battery 1 includes a solid electrolyte layer 2 having sodium ion conductivity. The solid electrolyte layer 2 has a first main surface 2a and a second main surface 2b that face each other. A positive electrode layer 3 is provided on the first main surface 2a of the solid electrolyte layer 2. An anode layer 4 is provided on the second main surface 2b of the solid electrolyte layer 2. The anode layer 4 includes a metal layer 5 and a metallic sodium layer 6. The metallic sodium layer 6 is provided on the metal layer 5. That is, the metal layer 5 is provided between the solid electrolyte layer 2 and the metallic sodium layer 6. The metallic sodium layer 6 is made of metallic sodium. The metal layer 5 is made of a metal different from metallic sodium. A sodium ion secondary battery member 8 is configured by a laminate of the solid electrolyte layer 2 and the anode layer 4 (i.e., a laminate of the solid electrolyte layer 2, the metal layer 5, and the metallic sodium layer 6).

[0017] In the sodium ion secondary battery 1 of this embodiment, the metal layer 5 is provided between the solid electrolyte layer 2 and the metallic sodium layer 6. This can improve the charge / discharge cycle characteristics of the sodium ion secondary battery 1. This can be explained as follows with reference to a comparative example shown in FIG.

[0018] Conventionally, as shown in FIG. 8, a sodium ion secondary battery 101 in which a metallic sodium layer serving as an anode layer 104 is provided directly on the second main surface 102b of a solid electrolyte layer 102 has a problem in that the cycle characteristics due to charge and discharge are easily deteriorated.

[0019] After extensive investigation into the cause, the inventors have found that poor wettability of metallic sodium to the solid electrolyte layer 102 results in poor adhesion between the anode layer 104 and the solid electrolyte layer 102, which causes variations in the in-plane resistance at the interface 107 between the anode layer 104 and the solid electrolyte layer 102 due to repeated charge and discharge, resulting in a problem of deterioration in cycle characteristics. The reasons for the variations in the in-plane resistance at the interface 107 between the anode layer 104 and the solid electrolyte layer 102 are thought to be as follows.

[0020] When a sodium-ion secondary battery 101 as shown in FIG. 8 is charged and discharged, discharge occurs repeatedly, in which sodium ions contained in the anode layer 104 migrate toward the cathode layer 103, and conversely, sodium ions migrate from the cathode layer 103 toward the anode layer 104. However, because metallic sodium contained in the anode layer 104 has poor wettability with the solid electrolyte layer 102, there are portions at the interface 107 where contact between the solid electrolyte layer 102 and the anode layer 104 is insufficient. In the portions where contact between the solid electrolyte layer 102 and the anode layer 104 is insufficient, sodium ions from the cathode layer 103 are unable to migrate to the anode layer 104 and remain on the second main surface 102b of the solid electrolyte layer 102, where they are thought to precipitate as needle-like crystals such as sodium dendrites. These needle-like crystals such as sodium dendrites are thought to be high-resistance regions at the interface 107 between the anode layer 104 and the solid electrolyte layer 102, causing variations in the in-plane resistance of the interface 107. As described above, in the sodium ion secondary battery 101 of the comparative example, repeated charging and discharging causes variations in the in-plane resistance at the interface 107 between the negative electrode layer 104 and the solid electrolyte layer 102, which is thought to result in deterioration of the cycle characteristics.

[0021] In contrast, in the sodium ion secondary battery 1 of this embodiment, the metal layer 5 is provided between the solid electrolyte layer 2 and the metallic sodium layer 6, thereby improving the adhesion between the anode layer 4 and the solid electrolyte layer 2. This makes it possible to make the in-plane resistance uniform at the interface 7 between the anode layer 4 and the solid electrolyte layer 2, making it difficult for bias to occur in the distribution of electrons. Therefore, even when charge and discharge are repeated, sodium ions tend to move uniformly at the interface 7, and as a result, deterioration of the cycle characteristics can be suppressed.

[0022] Each layer constituting the sodium ion secondary battery 1 will be described in detail below.

[0023] (solid electrolyte layer) The solid electrolyte layer 2 is composed of a solid electrolyte having sodium ion conductivity. The solid electrolyte layer 2 can be produced by mixing raw material powders, molding the mixed raw material powders, and then firing the molded product. For example, the solid electrolyte layer 2 can be produced by forming a green sheet from a slurry of the raw material powders, and then firing the green sheet. Alternatively, the solid electrolyte layer 2 may be produced by a sol-gel method.

[0024] Examples of solid electrolyte powders include beta-alumina and NASICON crystals, which have excellent sodium ion conductivity. Among these, beta-alumina is preferred as the solid electrolyte powder. In this case, deterioration of cycle characteristics can be more effectively suppressed.

[0025] Beta alumina exists in two crystal forms: β-alumina (theoretical composition: Na2O·11Al2O3) and β"-alumina (theoretical composition: Na2O·5.3Al2O3). β"-alumina is a metastable substance, so it is usually used with Li2O or MgO added as a stabilizer. β"-alumina has a higher sodium ion conductivity than β-alumina, so it is preferable to use β"-alumina alone or a mixture of β"-alumina and β-alumina. Li2O-stabilized β"-alumina (Na 1.7 Li 0.3 Al 10.7 O 17 ) or MgO-stabilized β”-alumina ((Al 10.32 Mg 0.68 O 16 )(Na 1.68 It is more preferable to use O).

[0026] NASICON crystals include Na3Zr2Si2PO 12 , Na 3.2 Zr 1.3 Si 2.2 P 0.7 O 10.5 , Na3Zr 1.6 Ti 0.4 SiPO 12 , Na3Hf2Si2PO 12 , Na 3.4 Zr0.9 Hf 1.4 Al 0.6 Si 1.2 P 1.8 O 12 , Na3Zr 1.7 Nb 0.24 SiPO 12 , Na 3.6 Ti 0.2 Y 0.7 Si 2.8 O9, Na3Zr 1.88 Y 0.12 SiPO 12 , Na 3.12 Zr 1.88 Y 0.12 SiPO 12 , Na 3.6 Zr 0.13 Yb 1.67 Si 0.11 P 2.9 O 12 etc., especially Na 3.12 Zr 1.88 Y 0.12 SiPO 12 is preferred because it has excellent sodium ion conductivity.

[0027] The thickness of the solid electrolyte layer 2 is preferably in the range of 5 μm to 1500 μm, and more preferably in the range of 20 μm to 200 μm. If the thickness of the solid electrolyte layer 2 is too thin, the mechanical strength decreases and the layer becomes more susceptible to breakage, which makes an internal short circuit more likely to occur. If the thickness of the solid electrolyte layer 2 is too thick, the sodium ion conduction distance during charge and discharge increases, which increases the internal resistance and makes it more likely that the discharge capacity and operating voltage will decrease. In addition, the energy density per unit volume of the sodium ion secondary battery 1 may also decrease.

[0028] (positive electrode layer) The positive electrode layer 3 is not particularly limited as long as it contains a positive electrode active material capable of absorbing and releasing sodium ions and functions as a positive electrode layer.

[0029] Examples of active material crystals that function as positive electrode active materials include sodium transition metal phosphate crystals containing Na, M (M is at least one transition metal element selected from Cr, Fe, Mn, Co, V, and Ni), P, and O. Specific examples include Na2FeP2O7, NaFePO4, Na3V2(PO4)3, Na2NiP2O7, Na 3.64 Ni 2.18 (P2O7)2, Na4Ni3(PO4)2(P2O7), Na2CoP2O7, Na 3.64 Co 2.18 (P2O7)2, etc. The sodium transition metal phosphate crystal is preferred because it has a high capacity and excellent chemical stability. Among them, triclinic crystals belonging to the space group P1 or P-1, especially those of the general formula Na x M y P2O z A crystal represented by the formula (1.2≦x≦2.8, 0.95≦y≦1.6, 6.5≦z≦8) is preferred because it has excellent cycle characteristics. Other active material crystals that act as positive electrode active materials include NaCrO2, Na 0.7 MnO2, NaFe 0.2 Mn 0.4 Ni 0.4 Examples of such crystals include layered sodium transition metal oxide crystals such as O. The positive electrode active material crystals contained in the positive electrode layer 3 may be a single phase in which only one type of crystal is precipitated, or a mixed phase in which multiple types of crystals are precipitated.

[0030] The positive electrode layer 3 can be obtained by applying a slurry containing a positive electrode active material precursor powder to the first main surface 2a of the solid electrolyte layer 2, followed by drying and firing. By firing the positive electrode active material precursor powder, active material crystals are precipitated, and these active material crystals act as the positive electrode active material. The slurry may contain a solid electrolyte powder and a conductive additive. Furthermore, the slurry may contain a binder, a plasticizer, a solvent, or the like, as necessary.

[0031] As the solid electrolyte powder, the same powder as that constituting the solid electrolyte layer 2 described above can be used.

[0032] The conductive additive may be, for example, conductive carbon, such as acetylene black or carbon black.

[0033] (negative electrode layer) The negative electrode layer 4 includes a metal layer 5 and a metallic sodium layer 6 .

[0034] By providing the metal layer 5 between the solid electrolyte layer 2 and the metallic sodium layer 6, it is possible to increase the adhesion between the anode layer 4 and the solid electrolyte layer 2, and to suppress deterioration of the cycle characteristics of the sodium ion secondary battery 1. It is also possible to increase the number of sodium ion conduction paths, and to improve the rate characteristics.

[0035] The metal constituting the metal layer 5 is not particularly limited, but examples thereof include Sn, Ti, Bi, Au, Al, Cu, Sb, and Pb. These metals constituting the metal layer 5 may be used alone or in combination. Furthermore, the metal layer 5 may be composed of a compound of these metals.

[0036] At least a portion of the metal constituting the metal layer 5 may be selected from the above metals capable of absorbing and releasing sodium ions. Examples of such metals include Sn, Bi, and Au. It is particularly preferable to use Au, which has a low absorption and release potential. The use of such a metal is preferable because it alloys with metallic sodium during charge and discharge, thereby further improving the adhesion between the metal layer 5 and the metallic sodium layer 6 and achieving more uniform sodium ion conduction in the anode layer 4. When Au is used for the metal layer 5, the following reaction occurs during charge and discharge, promoting alloying with metallic sodium: First charge reaction: Au + Na → Na2Au First discharge reaction: Na2Au → NaAu2 Second cycle and beyond: NaAu⇔Na2Au

[0037] The metal layer 5 is formed on the second main surface 2b of the solid electrolyte layer 2. Examples of methods for forming the metal layer 5 include physical vapor deposition methods such as vapor deposition or sputtering, and chemical vapor deposition methods such as thermal CVD, MOCVD, and plasma CVD. Other methods for forming the metal layer 5 include plating, the sol-gel method, and liquid phase film formation methods such as spin coating. Of these, the metal layer 5 is preferably a vapor deposition film or a sputtering film. In this case, the adhesion of the anode layer 4 (metal layer 5) to the solid electrolyte layer 2 can be further improved, and deterioration of cycle characteristics can be further suppressed.

[0038] The thickness of the metal layer 5 is preferably 5 nm or more, more preferably 10 nm or more, and preferably 800 nm or less, more preferably 500 nm or less. When the thickness of the metal layer 5 is equal to or greater than the above-mentioned lower limit, adhesion to the solid electrolyte layer 2 can be further improved, and deterioration of cycle characteristics can be further suppressed. Furthermore, when the thickness of the metal layer 5 is equal to or less than the above-mentioned upper limit, volume expansion during charge and discharge can be further suppressed.

[0039] For example, a metal sodium foil can be used as the metal sodium layer 6. The metal sodium foil can be obtained by rolling metal sodium. The metal sodium layer 6 can also be formed by pressing the metal sodium foil onto the metal layer 5 using a press or the like. In this case, the pressing temperature can be, for example, 80°C or higher and 100°C or lower. The pressing pressure can be, for example, 5 MPa or higher and 100 MPa or lower.

[0040] The metallic sodium layer 6 may be formed by charging. Specifically, the metallic sodium layer 6 may be formed by forming only the metal layer 5 on the surface of the solid electrolyte layer 2, and then uniformly precipitating metallic sodium on the surface of the metal layer 5 during charging.

[0041] The thickness of the metallic sodium layer 6 is preferably 1 μm or more, more preferably 5 μm or more, even more preferably 10 μm or more, and preferably 1000 μm or less, more preferably 800 μm or less. When the thickness of the metallic sodium layer 6 is equal to or greater than the above-mentioned lower limit, the handleability can be further improved. When the thickness of the metallic sodium layer 6 is equal to or less than the above-mentioned upper limit, the problem of the end of the metallic sodium layer 6 protruding outside the laminate and wrapping around to the positive electrode layer 3 when the metallic sodium layer 6 is pressure-bonded onto the metal layer 5 can be more reliably prevented.

[0042] In the present invention, at least a part of the metal contained in metal layer 5 may be alloyed with the metallic sodium contained in metallic sodium layer 6. Furthermore, a diffusion layer may be provided at the interface between metal layer 5 and metallic sodium layer 6. The diffusion layer may be an alloy layer of the metal contained in metal layer 5 and the metallic sodium contained in metallic sodium layer 6. When a diffusion layer containing such an alloy is formed, the battery characteristics such as the rate characteristics of the sodium ion secondary battery 1 can be further improved.

[0043] The negative electrode layer 4 may contain a solid electrolyte powder, a conductive additive, and the like, as long as the effects of the present invention are not impaired. The solid electrolyte powder and the conductive additive may be the same as those contained in the positive electrode layer 3 described above.

[0044] (current collector layer) A current collector layer may be provided on each of the positive electrode layer 3 and the negative electrode layer 4. More specifically, a current collector layer may be provided on each of the outer main surfaces of the positive electrode layer 3 and the negative electrode layer 4 opposite to the solid electrolyte layer 2.

[0045] The material of the current collector layer is not particularly limited, but metal materials such as aluminum, titanium, silver, copper, stainless steel, and alloys thereof can be used. The above metal materials can be used alone or in combination. These alloys are alloys containing at least one of the above metals.

[0046] The method for forming the current collector layer is not particularly limited, and examples thereof include physical vapor deposition methods such as vapor deposition or sputtering, and chemical vapor deposition methods such as thermal CVD, MOCVD, and plasma CVD. Other methods for forming the current collector layer include plating, a sol-gel method, and a liquid phase film formation method using spin coating. However, it is preferable to form the current collector layer on the positive electrode layer 3 or the negative electrode layer 4 by a sputtering method, as this provides excellent adhesion.

[0047] The present invention will be described in more detail below with reference to specific examples. The present invention is not limited to the following examples, and can be practiced with appropriate modifications within the scope of the present invention.

[0048] (Examples 1 to 4 and Comparative Example 1) (a) Preparation of cathode layer-solid electrolyte layer component The 2Na2O-Fe2O3-2P2O5 glass, which serves as the precursor of the positive electrode active material in the positive electrode layer, was prepared by the melting method. The resulting 2Na2O-Fe2O3-2P2O5 glass was coarsely pulverized in a ball mill and then wet-pulverized in a planetary ball mill to produce glass powder.

[0049] In addition, β″-alumina (manufactured by Ionotec) was coarsely pulverized in a ball mill and then air-classified to produce a solid electrolyte powder.

[0050] Acetylene black ("SuperC65" manufactured by Timcal) was used as the conductive additive in the positive electrode layer. A glass powder, a solid electrolyte powder, and the conductive additive, which serve as the positive electrode active material precursor, were mixed in a weight ratio of 72:25:3 to obtain a mixture. Next, 10 parts by weight of polypropylene carbonate was added as a binder to the obtained mixture, relative to 100 parts by weight of the mixture. Furthermore, N-methyl-2-pyrrolidone was added as a solvent to form a paste.

[0051] On the other hand, a β″-alumina plate (manufactured by Ionotec) was used as it was for the solid electrolyte layer.

[0052] The paste was applied onto the solid electrolyte layer and dried. The amount of the positive electrode active material supported was 4.5 mg / cm. 2 The paste was then applied so that the resulting mixture was baked at 500°C for 30 minutes in a mixed gas of N2 / H2 = 96 / 4 v / v%, thereby producing a positive electrode layer-solid electrolyte layer member.

[0053] Next, a current collector layer made of Al was formed on the surface of the positive electrode layer of the positive electrode layer-solid electrolyte layer member using a sputtering device. The current collector layer had a thickness of 500 nm.

[0054] (b) Preparation of the negative electrode layer In Examples 1 to 4, a metal layer was formed on the main surface of the solid electrolyte layer opposite the positive electrode layer in the positive electrode layer-solid electrolyte layer member using a sputtering device (manufactured by Sanyu Electronics Co., Ltd., product number "SC-701AT"). In Examples 1 and 4, a 77 nm thick Au film was formed as the metal layer. In Example 2, a 48 nm thick Sn film was formed as the metal layer. In Example 3, a 54 nm thick Bi film was formed as the metal layer. In Comparative Example 1, no metal layer was formed.

[0055] Further, metallic sodium foil was obtained by rolling metallic sodium. Next, in Examples 1 to 3, metallic sodium foil was attached to the surface of the above-mentioned metal layer, and in Comparative Example 1, metallic sodium foil was attached to the surface of the above-mentioned solid electrolyte layer, and they were pressed together by a press at 90°C (press pressure: 20 MPa). In this way, a metallic sodium layer with a thickness of 296 μm was formed on the metal layer, and an anode layer was produced. In Example 4, metallic sodium foil was not attached to the surface of the metal layer, and only one charging cycle was performed in the charge-discharge test described below, to uniformly precipitate metallic sodium on the surface of the metal layer. In this way, a metallic sodium layer with a thickness of 3 μm was formed on the surface of the metal layer, and an anode layer was produced. In this way, an all-solid-state sodium ion secondary battery was produced.

[0056] (c) Preparation of test battery The all-solid-state sodium-ion secondary battery obtained by the above steps was placed on the bottom lid of a coin cell, and then the top lid was placed on top to prepare a CR2032 test battery. The formation of the metallic sodium layer in step (b) and step (c) were carried out in an argon atmosphere with a dew point of -70°C or lower.

[0057] (d) Charge / discharge test The prepared CR2032 test battery was subjected to CC (constant current) charging at 30°C from the open circuit voltage to 4.5 V. Next, CC discharging was performed from 4.5 V to 2 V, and the average discharge voltage and discharge capacity were determined. The C rate was evaluated at 0.2 C.

[0058] Figure 2 shows the relationship between the number of cycles and the average discharge voltage for the test batteries prepared in the Examples and Comparative Examples. Figure 3 shows the relationship between the number of cycles and the discharge capacity retention rate for the test batteries prepared in the Examples and Comparative Examples. Figures 4 to 7 show the charge-discharge curves for the first and 50th cycles for the test batteries prepared in Examples 1, 2, 3, and Comparative Example 1, respectively. Table 1 also shows the change in average discharge voltage ((50th cycle / 1st cycle) x 100(%)) and the discharge capacity retention rate ((50th cycle / 1st cycle) x 100(%)) for the test batteries prepared in the Examples and Comparative Examples.

[0059] [Table 1]

[0060] 2 to 7 and Table 1, it is clear that Examples 1 to 4, in which a metal layer was provided between the solid electrolyte layer and the metallic sodium layer, all exhibited excellent charge-discharge cycle characteristics. In addition, it is clear that Comparative Example 1, in which a metal layer was not provided between the solid electrolyte layer and the metallic sodium layer, exhibited deteriorated charge-discharge cycle characteristics.

[0061] In addition, when the X-ray diffraction patterns of the metal layer before the charge-discharge test, after the first charge, after the first discharge, after the second charge cycle, and after the second discharge cycle in Example 1 were confirmed, it was confirmed that metallic sodium and Au reacted to precipitate Na2Au crystals and NaAu2 crystals. From this, it was confirmed that when Au is used as the metal layer, the above-mentioned reaction occurs with charge and discharge, and alloying with metallic sodium progresses. [Explanation of symbols]

[0062] 1...Sodium ion secondary battery 2...Solid electrolyte layer 2a...first principal surface 2b...Second main surface 3...Positive electrode layer 4...Anode layer 5...Metal layer 6...Metallic sodium layer 7…Interface 8...Sodium ion secondary battery components

Claims

1. a solid electrolyte layer having sodium ion conductivity; a metallic sodium layer disposed on one main surface of the solid electrolyte layer and made of metallic sodium; a metal layer provided between the solid electrolyte layer and the metallic sodium layer and made of a metal different from the metallic sodium; Equipped with The metal layer is made of at least one of Bi and Au (provided that the solid electrolyte layer is made of A ２ S-M ｘ S ｙ (A is selected from Li and Na, M is selected from P, Si, Ge, B, Al, Sn, Sb and Ga, and x and y are numbers that give a stoichiometric ratio depending on the type of M).

2. The sodium ion secondary battery member according to claim 1 , wherein the metal layer is a vapor-deposited film or a sputtered film.

3. 3. The sodium ion secondary battery member according to claim 1, wherein at least a part of the metal contained in the metal layer is a metal capable of absorbing and releasing sodium ions.

4. 4. The sodium ion secondary battery member according to claim 1, wherein at least a part of the metal contained in the metal layer is alloyed with the metallic sodium contained in the metallic sodium layer at an interface between the metallic sodium layer and the metal layer.

5. A component for a sodium ion secondary battery described in any one of claims 1 to 4, wherein the metal layer contains Au.

6. A component for a sodium ion secondary battery described in any one of claims 1 to 5, wherein the metal layer is a sputtering film.

7. A component for a sodium ion secondary battery described in any one of claims 1 to 6, wherein the thickness of the metal layer is 54 nm or more and 500 nm or less.

8. A sodium ion secondary battery comprising the sodium ion secondary battery member according to any one of claims 1 to 7.

9. the solid electrolyte layer has a first main surface and a second main surface that are opposed to each other; a positive electrode layer provided on the first main surface of the solid electrolyte layer; an anode layer provided on the second main surface of the solid electrolyte layer; Equipped with The sodium ion secondary battery according to claim 8 , wherein the negative electrode layer comprises the metallic sodium layer and the metal layer.

10. A solid electrolyte layer having sodium ion conductivity; a metallic sodium layer disposed on one main surface of the solid electrolyte layer and made of metallic sodium; a metal layer provided between the solid electrolyte layer and the metallic sodium layer and made of a metal different from the metallic sodium; Equipped with A sodium ion secondary battery member in which the metal layer is made of at least one metal selected from the group consisting of Sn, Bi, and Au (excluding those in which the solid electrolyte layer contains a solid electrolyte represented by A2S-MxSy (A is selected from Li and Na, M is selected from P, Si, Ge, B, Al, Sn, Sb, and Ga, and x and y are numbers that give a stoichiometric ratio depending on the type of M)), a positive electrode layer disposed on the other main surface of the solid electrolyte layer; Equipped with a sodium ion secondary battery, the positive electrode layer comprising a positive electrode active material made of a sodium transition metal phosphate crystal containing Na, M (M is at least one transition metal element selected from Cr, Fe, Mn, Co, V, and Ni), P, and O.

11. A sodium ion secondary battery as described in claim 10, wherein the metal layer is a vapor deposition film or a sputtering film.

12. A sodium ion secondary battery as described in claim 10 or 11, wherein at least a portion of the metal contained in the metal layer is a metal capable of absorbing and releasing sodium ions.

13. A sodium ion secondary battery described in any one of claims 10 to 12, wherein at the interface between the metallic sodium layer and the metal layer, at least a portion of the metal contained in the metal layer is alloyed with the metallic sodium contained in the metallic sodium layer.

14. The solid electrolyte layer having a first principal surface and a second principal surface facing each other, the positive electrode layer is provided on the first main surface of the solid electrolyte layer, The sodium ion secondary battery according to any one of claims 10 to 13, wherein a negative electrode layer including the metallic sodium layer and the metal layer is provided on the second main surface of the solid electrolyte layer.

15. A sodium ion secondary battery described in any one of claims 10 to 14, wherein the metal layer contains at least one of Bi and Au.

16. A sodium ion secondary battery described in any one of claims 10 to 15, wherein the metal layer is a sputtered film.

17. A sodium ion secondary battery described in any one of claims 10 to 16, wherein the thickness of the metal layer is 48 nm or more and 500 nm or less.

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