Fluoride shuttle secondary battery and method of using fluoride shuttle secondary battery

Abstract

This fluoride shuttle secondary battery (1) is provided with a positive electrode (2), a negative electrode (4), and an electrolyte layer (3) provided between the positive electrode (2) and the negative electrode (4), and satisfies at least one of the following (A1) and (B1). (A1) The negative electrode (4) contains a first negative electrode active material and a second negative electrode active material having a composition different from that of the first negative electrode active material, the first negative electrode active material being a first metal fluoride containing a metal (M1) having a melting point of 0-250 DEG C (inclusive). (B1) The positive electrode (2) contains a first positive electrode active material and a second positive electrode active material having a different composition from the first positive electrode active material, the first positive electrode active material is a metal M2, and a metal fluoride represented by M2Fx has a melting point of 0 DEG C or more and 250 DEG C or less (where x represents the valence of M2).

Description

Technical Field

[0001] The present disclosure relates to fluoride shuttling secondary batteries and methods of using fluoride shuttling secondary batteries. Background Art

[0002] As a secondary battery with high energy density, lithium ion secondary batteries are widely used. In addition, lithium ion all-solid batteries using non-flammable inorganic solid electrolytes have been proposed. Such lithium ion all-solid batteries have high safety. Therefore, lithium ion all-solid batteries are widely studied and developed.

[0003] As one of the above-mentioned batteries using solid electrolytes, fluoride ion (F - ) Fluoride shuttle secondary battery with moving fluoride. Fluoride shuttle secondary battery has a high theoretical energy density. As negative electrode materials, examples of using AlF3 or LaF3 are reported. Patent document 1 discloses a fluoride shuttle secondary battery using aluminum fluoride as a negative electrode material. Patent document 2 discloses a fluoride shuttle secondary battery whose negative electrode contains a fluoride containing La.

[0004] Prior Art Literature

[0005] Patent Document 1: International Publication No. 2019 / 187943

[0006] Patent Document 2: Japanese Patent Application Publication No. 2017-84506 Summary of the invention

[0007] Problems to be solved by the invention

[0008] The present disclosure provides a fluoride shuttle secondary battery with improved discharge capacity.

[0009] Means for solving problems

[0010] The fluoride shuttle secondary battery disclosed in the present invention comprises a positive electrode, a negative electrode, and an electrolyte layer disposed between the positive electrode and the negative electrode.

[0011] The fluoride shuttle secondary battery satisfies at least one selected from the following (A1) and (B1):

[0012] (A1) The negative electrode includes a first negative electrode active material and a second negative electrode active material having a composition different from that of the first negative electrode active material, wherein the first negative electrode active material is a first metal fluoride containing a metal M1 having a melting point of 0° C. to 250° C.

[0013] (B1) The positive electrode comprises a first positive electrode active material and a second positive electrode active material having a composition different from that of the first positive electrode active material, wherein the first positive electrode active material is a metal M2, and the composition of M2Fx The metal fluoride represented by has a melting point of 0° C. or higher and 250° C. or lower, wherein x represents the valence of M2.

[0014] Effects of the Invention

[0015] The present disclosure provides a fluoride shuttle secondary battery with improved discharge capacity. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 : is a cross-sectional view schematically showing a fluoride shuttle secondary battery according to an embodiment of the present disclosure.

[0017] Figure 2 It is a cross-sectional view schematically showing a modification of the fluoride shuttle secondary battery according to the embodiment of the present disclosure.

[0018] Figure 3 This is a graph showing the results of a charge and discharge test at 140° C. on the evaluation cell of Example 1. FIG.

[0019] Figure 4A This is a cross-sectional SEM image of the evaluation cell of Example 1 before charge and discharge.

[0020] Figure 4B It is obtained from the measurement results of SEM-EDX Figure 4A The image shown is a mapping image of the distribution of Na.

[0021] Figure 5A This is a cross-sectional SEM image of the evaluation cell of Example 1 after charge and discharge.

[0022] Figure 5B It is obtained from the measurement results of SEM-EDX Figure 5A The image shown is a mapping image of the distribution of Na.

[0023] Figure 6 This is a graph showing the results of a charge and discharge test at 140° C. on the evaluation cell of Comparative Example 1.

[0024] Figure 7 This is a graph showing the results of a charge and discharge test at 140° C. on the evaluation cell of Comparative Example 2.

[0025] Figure 8 This is a graph showing the charge and discharge results of the second cycle of the charge and discharge test at 140° C. for the evaluation cells of Example 1, Comparative Example 1, and Comparative Example 2.

[0026] Fig. 9 This is a graph showing the results of a charge and discharge test of the evaluation cell of Example 1 at 90°C.

[0027] Fig.10 This is a graph showing the results of a charge and discharge test at 90° C. of the evaluation cell of Example 1 after two cycles of operation at 140° C. were performed.

[0028] Fig.11 This is a graph showing the results of a charge and discharge test at 140° C. on the evaluation cell of Example 2.

[0029] Fig.12 This is a graph showing the results of a charge and discharge test at 140° C. on the evaluation cell of Example 3.

[0030] Fig.13 This is a graph showing the results of a charge and discharge test at 140° C. on the evaluation cell of Comparative Example 3.

[0031] Fig.14 This is a graph showing the results of a charge and discharge test at 140° C. on the evaluation cell of Example 4.

[0032] Fig.15 This is a graph showing the results of a charge and discharge test at 140° C. on the evaluation cell of Comparative Example 4. DETAILED DESCRIPTION

[0033] <Embodiments of the present disclosure>

[0034] Hereinafter, a fluoride shuttle secondary battery according to an embodiment of the present disclosure will be described in detail with reference to the accompanying drawings.

[0035] (Implementation Method 1)

[0036] The fluoride shuttle secondary battery is a battery that generates electromotive force by allowing fluoride ions to shuttle in an electrolyte, and undergoing defluorination and fluorination reactions at the positive and negative electrodes, respectively.

[0037] The fluoride shuttle secondary battery according to an embodiment of the present disclosure includes a positive electrode, a negative electrode, and an electrolyte layer provided between the positive electrode and the negative electrode, and satisfies at least one selected from the following (A1) and (B1).

[0038] (A1) The negative electrode includes a first negative electrode active material and a second negative electrode active material having a composition different from that of the first negative electrode active material. The first negative electrode active material is a first metal fluoride containing a metal M1. The metal M1 has a melting point of 0° C. to 250° C.

[0039] (B1) The positive electrode comprises a first positive electrode active material and a second positive electrode active material having a composition different from that of the first positive electrode active material, wherein the first positive electrode active material is a metal M2, and the composition of M2F xThe metal fluoride represented by has a melting point of 0° C. or higher and 250° C. or lower, wherein x represents the valence of M2.

[0040] In the fluoride shuttle secondary battery of the embodiment of the present disclosure, when the above (A1) is satisfied, the negative electrode includes a first negative electrode active material and a second negative electrode active material having a different composition from the first negative electrode active material. The first negative electrode active material is a first metal fluoride containing a metal M1 having a melting point of 0°C or more and 250°C or less. Therefore, in the fluoride shuttle secondary battery of the embodiment of the present disclosure, by charging, the first metal fluoride is defluorinated in the charging reaction of the negative electrode active material to generate metal M1, and the generated metal M1 can be melted. For example, when the battery is operated in an environment above the melting point of the metal M1, the metal M1 generated by the first metal fluoride by charging melts. According to the above configuration, the molten metal M1 diffuses around the negative electrode active material, and good material movement between the negative electrode active materials can be achieved. In addition, in the case where the negative electrode includes a negative electrode active material layer containing a negative electrode active material and a solid electrolyte, good material movement between the negative electrode active material and the solid electrolyte can also be achieved. Therefore, the fluoride shuttle secondary battery of the embodiment of the present disclosure can achieve an improved discharge capacity. The fluoride shuttle secondary battery of the embodiment of the present disclosure can achieve an improved discharge capacity compared to a battery using only the second negative electrode active material as the negative electrode active material, and can also improve the utilization rate of the negative electrode active material and the cycle characteristics of the battery.

[0041] In the present disclosure, utilization rate refers to the ratio of the actual specific capacity of the active material to the theoretical specific capacity of the active material. In the present disclosure, when it is only recorded as "negative electrode active material", the negative electrode active material includes both the first negative electrode active material and the second negative electrode active material. In the present disclosure, when it is only recorded as "positive electrode active material", the positive electrode active material includes both the first positive electrode active material and the second positive electrode active material.

[0042] In the fluoride shuttle secondary battery of the embodiment of the present disclosure, when the above (B1) is satisfied, the positive electrode comprises a first positive electrode active material and a second positive electrode active material having a composition different from that of the first positive electrode active material, the first positive electrode active material is a metal M2, and the composition of M2F x The metal fluoride represented by has a melting point of 0° C. to 250° C. Therefore, in the fluoride shuttle secondary battery of the embodiment of the present disclosure, the M2F x The metal fluoride indicated can be melted. For example, when the battery is in M2F x When working in an environment above the melting point, M2F generated by metal M2 is charged x Melting. According to the above composition, the melted M2F xDiffusion around the positive electrode active material can achieve good material movement between the positive electrode active materials. In addition, in the case where the positive electrode includes a positive electrode active material layer containing a positive electrode active material and a solid electrolyte, good material movement between the positive electrode active material and the solid electrolyte can also be achieved. Therefore, the fluoride shuttle secondary battery of the embodiment of the present disclosure can achieve an improved discharge capacity. The fluoride shuttle secondary battery of the embodiment of the present disclosure, for example, can achieve an improved discharge capacity compared to a battery using only the second positive electrode active material as the positive electrode active material. In addition, the utilization rate of the positive electrode active material and the cycle characteristics of the battery can be improved.

[0043] In the fluoride shuttle secondary battery of the embodiment of the present disclosure, when the above (A1) is satisfied, the metal M1 can be melted by charging, and when the above (B1) is satisfied, M2F x In the fluoride shuttle secondary battery of the embodiment of the present disclosure, when the above (A1) is satisfied, the metal M1 can be melted during charging, and when the above (B1) is satisfied, the metal M2F x It can melt during charging. When the metal M1 generated by the first metal fluoride in the negative electrode melts during charging, the molten metal M1 diffuses around the negative electrode active material, and good material movement between the negative electrode active materials can be achieved. In addition, in the case where the negative electrode includes a negative electrode active material layer containing a negative electrode active material and a solid electrolyte, good material movement between the negative electrode active material and the solid electrolyte can also be achieved. As a result, the first negative electrode active material and the second negative electrode active material can achieve an increased specific capacity. By charging, the M2F generated by the metal M2 in the positive electrode x When melting, the molten M2F x Diffusion around the positive electrode active material can achieve good material movement between the positive electrode active materials. In addition, in the case where the positive electrode includes a positive electrode active material layer containing a positive electrode active material and a solid electrolyte, good material movement between the positive electrode active material and the solid electrolyte can also be achieved. Thus, the first positive electrode active material and the second positive electrode active material can achieve an increased specific capacity. Therefore, the fluoride shuttle secondary battery of the embodiment of the present disclosure can achieve an increased discharge capacity. In addition, the utilization rate of the negative electrode active material or the positive electrode active material and the cycle characteristics of the battery can be improved.

[0044] The fluoride shuttle secondary battery according to the embodiment of the present disclosure may satisfy both (A1) and (B1) above, or may satisfy either one of them. The fluoride shuttle secondary battery according to the embodiment of the present disclosure may satisfy (A1) above.

[0045] Figure 1 : is a cross-sectional view schematically showing a fluoride shuttle secondary battery according to an embodiment of the present disclosure. Figure 1 The fluoride shuttle secondary battery 1 shown includes a positive electrode 2 , an electrolyte layer 3 , and a negative electrode 4 .

[0046] The electrolyte layer 3 is provided between the positive electrode 2 and the negative electrode 4. The positive electrode 2 includes, for example, a positive electrode current collector 5 and a positive electrode active material layer 6. The negative electrode 4 includes, for example, a negative electrode current collector 7 and a negative electrode active material layer 8.

[0047] The negative electrode active material layer 8 contains a negative electrode active material. The negative electrode active material is a material that can absorb and release fluoride ions as the battery is charged and discharged. Absorption and release include both forms accompanied by chemical reactions with fluoride ions and forms not accompanied by chemical reactions such as intercalation. Chemical reactions include reactions that form compounds and reactions that form non-compound composites such as alloys and solid solutions.

[0048] The negative electrode active material may be a material that exhibits a lower potential, expressed as a standard electrode potential, than the positive electrode active material combined in the fluoride shuttle secondary battery 1 .

[0049] The negative electrode active material layer 8 may include a negative electrode active material and a solid electrolyte. The negative electrode active material may include a first negative electrode active material and a second negative electrode active material having a composition different from that of the first negative electrode active material. In the case where the fluoride shuttle secondary battery of the embodiment of the present disclosure satisfies the above (A1), the negative electrode active material layer 8 includes a first negative electrode active material and a second negative electrode active material having a composition different from that of the first negative electrode active material, and the first negative electrode active material is a first metal fluoride containing a metal M1, and the metal M1 has a melting point of 0°C or more and 250°C or less.

[0050] The metal M1 may include at least one selected from Na, K, Rb, In, Ga, Sn, Cs, Se, and Li. Therefore, the first negative electrode active material may be a first metal fluoride containing at least one selected from Na, K, Rb, In, Ga, Sn, Cs, Se, and Li.

[0051] According to the above structure, when the battery is operated in an environment above the melting point of the metal M1, the first metal fluoride is defluorinated in the charging reaction of the negative electrode active material by charging to generate the metal M1. Then, the generated metal M1 melts and diffuses in the negative electrode active material layer 8. Thus, in the negative electrode active material layer 8, good material movement between the negative electrode active materials or between the negative electrode active materials and the solid electrolyte can be achieved, and the discharge capacity of the fluoride shuttle secondary battery can be improved.

[0052] The metal M1 may have a melting point of 25°C or higher, or 50°C or higher. The metal M1 may have a melting point of 180°C or lower, or 150°C or lower. The metal M1 may have a melting point of 25°C or higher and 180°C or lower. The metal M1 may have a melting point of 50°C or higher and 150°C or lower.

[0053] The metal M1 may contain Na. The metal M1 may be Na. That is, the first metal fluoride may be NaF. According to the above configuration, when the battery operates in an environment above the melting point of Na, Na is melted by charging. As a result, the molten Na diffuses in the negative electrode active material layer 8, and in the negative electrode active material layer 8, good material movement between the negative electrode active materials or between the negative electrode active materials and the solid electrolyte can be achieved, which can improve the discharge capacity of the fluoride shuttle secondary battery.

[0054] The metal M1 may contain Na and at least one selected from K, Rb and Li. The metal M1 may contain Na and K. The metal M1 may be an alloy of Na and other metals. In the case where the metal M1 is an alloy of Na and other elements, the metal M1 is melted by charging at a low temperature, thereby realizing a fluoride shuttle secondary battery with improved discharge capacity when used at a low temperature. The metal M1 may be an alloy of Na and K. In the case where the metal M1 is an alloy of Na and K, the metal M1 is melted by charging at a lower temperature than in the case of a single substance of Na, thereby realizing a fluoride shuttle secondary battery with improved discharge capacity when used at a low temperature.

[0055] The first negative electrode active material or metal M1 can be uniformly mixed with other materials in the negative electrode active material layer 8. The first negative electrode active material or metal M1 can be uniformly distributed in the negative electrode active material layer 8. Thus, good material movement between negative electrode active materials or between negative electrode active materials and solid electrolytes can be achieved, and the discharge capacity of the fluoride shuttle secondary battery can be improved.

[0056] The distribution of the first negative electrode active material or the metal M1 can be confirmed by, for example, SEM-EDX, which is a combination of a scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDX).

[0057] The second negative electrode active material may be a second metal fluoride. The fluorination potential and defluorination potential of the second metal fluoride may be greater than -3.0 V (vs. Pb / PbF2) and less than -1.0 V (vs. Pb / PbF2). By containing such a second negative electrode active material, the fluoride shuttle secondary battery 1 can improve the energy density.

[0058] The second metal fluoride may be at least one selected from LaF3, AlF3, MgF2, CeF3, GdF3, YF3, EuF3, SmF3, NdF3 and TiF3. That is, the second negative electrode active material may be at least one selected from LaF3, AlF3, MgF2, CeF3, GdF3, YF3, EuF3, SmF3, NdF3 and TiF3. By containing such a second negative electrode active material, the fluoride shuttle secondary battery 1 can increase the discharge capacity. It can be set that the first metal fluoride is NaF, and the second metal fluoride is at least one selected from LaF3, AlF3, MgF2, CeF3, GdF3, YF3, EuF3, SmF3, NdF3 and TiF3.

[0059] The second metal fluoride may be at least one selected from LaF3, AlF3, and GdF3. The second metal fluoride may be LaF3. The first metal fluoride may be NaF, and the second metal fluoride may be at least one selected from LaF3, AlF3, and GdF3.

[0060] The difference between the fluorination potential and the defluorination potential of the first metal fluoride and the second metal fluoride may be 0 V or more and 1.0 V or less.

[0061] The mass ratio of the second negative electrode active material in the negative electrode may be greater than the mass ratio of the first negative electrode active material in the negative electrode.

[0062] The negative electrode 4 may further include a third negative electrode active material having a composition different from that of the first negative electrode active material and the second negative electrode active material. The third negative electrode active material may be a third metal fluoride. The third metal fluoride may be, for example, a metal fluoride containing at least one of the metals M1 exemplified, or may be a metal fluoride exemplified as the second metal fluoride. The third metal fluoride may contain a metal that can form an alloy or a solid solution with the metal M1 contained in the first metal fluoride. The third metal fluoride may be KF.

[0063] As the solid electrolyte contained in the negative electrode active material layer 8, a material known as a solid electrolyte material having fluoride ion conductivity can be used. For example, Ce 1-x Sr x F 3-x (0≤x≤1), La 1-x Ca x F 3-x (0≤x≤1), La 1-x Ba x F 3-x (0≤x≤1), La 1-x Sr x F 3-x (0≤x≤1), Ca2-x Ba x F4(0≤x≤2) and Ce 1-x Ba x F 3-x (0≤x≤1) etc.

[0064] The thickness of the negative electrode active material layer 8 is, for example, 1 μm or more and 500 μm or less. The thickness of the negative electrode active material layer 8 may be 1 μm or more and 400 μm or less, and further 30 μm or more and 200 μm or less. When the thickness of the negative electrode active material layer 8 is within these ranges, the energy density of the fluoride shuttle secondary battery 1 can be further improved, and more stable operation can be performed at high output.

[0065] The positive electrode active material layer 6 contains a positive electrode active material. The positive electrode active material is a material that can absorb and release fluoride ions as the fluoride shuttles the charge and discharge of the secondary battery 1. Absorption and release include both forms accompanied by chemical reactions with fluoride ions and forms not accompanied by chemical reactions such as intercalation. Chemical reactions include reactions that form compounds and reactions that form non-compound composites such as alloys and solid solutions.

[0066] The positive electrode active material may be a material that exhibits a higher potential than the negative electrode active material combined in the fluoride shuttle secondary battery 1 in terms of standard electrode potential.

[0067] The positive electrode active material layer 6 in the positive electrode 2 may contain, for example, a positive electrode active material and a solid electrolyte. The positive electrode active material may contain metal Me.

[0068] The metal Me may include, for example, at least one selected from Cu, Bi, Pb, Sb, Fe, Zn, Ni, Mn, Sn, Ag, Cr, In, Ti, and Co. In the positive electrode 2, the metal Me may be a complex such as a single substance, an alloy, and a solid solution. By having a positive electrode 2 containing such a metal Me, the fluoride shuttle secondary battery 1 can increase the charge and discharge capacity.

[0069] The metal Me may be at least one selected from the group consisting of Pb, Cu, Bi, Sn, and Ag. Thus, the energy density of the fluoride shuttle secondary battery 1 can be further improved.

[0070] The positive electrode active material layer 6 may contain two or more positive electrode active materials having compositions different from each other.

[0071] In the case where the fluoride shuttle secondary battery of the embodiment of the present disclosure satisfies the above (B1), the positive electrode active material layer 6 includes a first positive electrode active material and a second positive electrode active material having a composition different from that of the first positive electrode active material, the first positive electrode active material is a metal M2, and the metal M2 is in a state of M2Fx The melting point of the metal fluoride in the state of the metal fluoride represented by is 0° C. or higher and 250° C. or lower. Here, x represents the valence of M2.

[0072] According to the above structure, when the battery is in M2F x When working in an environment above the melting point, the M2F x It melts and diffuses in the positive electrode active material layer 6. This enables good material transfer between the positive electrode active materials or between the positive electrode active materials and the solid electrolyte in the positive electrode active material layer 6, and can improve the discharge capacity of the fluoride shuttle secondary battery.

[0073] M2F x It may have a melting point of 25°C or more and 250°C or less. x The melting point may be 50°C or higher and 250°C or lower.

[0074] The metal M2 as the first positive electrode active material is, for example, at least one selected from Sn, Nb, and Ta.

[0075] The second positive electrode active material may contain at least one metal as the metal Me. The second positive electrode active material may contain at least one metal as the metal Me.

[0076] The mass ratio of the second positive electrode active material in the positive electrode may be greater than the mass ratio of the first positive electrode active material in the positive electrode.

[0077] As the solid electrolyte contained in the positive electrode active material layer 6, a material known as a solid electrolyte material having fluorine ion conductivity can be used. The solid electrolyte contained in the positive electrode active material layer 6 can be the above-mentioned material as the solid electrolyte contained in the negative electrode active material layer 8. The solid electrolyte contained in the positive electrode active material layer 6 can be a material having the same composition as the solid electrolyte contained in the negative electrode active material layer 8.

[0078] The thickness of the positive electrode active material layer 6 is, for example, 1 μm or more and 500 μm or less. The thickness of the positive electrode active material layer 6 may be 1 μm or more and 400 μm or less, and further 50 μm or more and 200 μm or less. When the thickness of the positive electrode active material layer 6 is within these ranges, the energy density of the fluoride shuttle secondary battery 1 can be further improved, and more stable operation can be performed at high output.

[0079] The fluoride shuttle secondary battery according to the embodiment of the present disclosure may include a positive electrode buffer layer between the positive electrode and the electrolyte layer. Figure 2 2 is a cross-sectional view schematically showing a modified example of a fluoride shuttle secondary battery according to an embodiment of the present disclosure. Figure 2As shown, the fluoride shuttle secondary battery 11 includes, for example, a positive electrode buffer layer 9 between the positive electrode active material layer 6 and the electrolyte layer 3 .

[0080] The positive electrode buffer layer 9 is, for example, a layer containing a positive electrode buffer material, which is a compound containing the same metal element as the metal Me contained in the positive electrode active material. According to the above structure, the degradation of the capacity can be suppressed and the cycle characteristics of the fluoride shuttle secondary battery can be improved. For example, in the case where the positive electrode active material is lead, the positive electrode buffer material can be Pb 1-a Sn a F2. Here, a may satisfy, for example, 0≤a≤1, or 0<a<1.

[0081] In the positive electrode 2, for example, the positive electrode active material layer 6 may contain a conductive additive. In addition, in the negative electrode 4, for example, the negative electrode active material layer 8 may contain a conductive additive. When the conductive additive is contained, the resistance of the positive electrode 2 and the negative electrode 4 can be reduced.

[0082] There is no limitation on the conductive aid as long as it has electronic conductivity. Examples of conductive aids include graphites such as natural graphite and artificial graphite; carbon blacks such as acetylene black and Ketjen black; conductive fibers such as carbon fibers and metal fibers; conductive powders such as carbon fluoride and aluminum; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive polymer compounds such as polyaniline, polypyrrole, and polythiophene. For example, by using carbon-based conductive aids such as graphites and carbon blacks, the cost of the fluoride shuttle secondary battery 1 can be reduced.

[0083] The positive electrode current collector 5 and the negative electrode current collector 7 have electron conductivity. The positive electrode current collector 5 and the negative electrode current collector 7 may be made of a material that has electron conductivity and is difficult to corrode in the charge and discharge environment of the fluoride shuttle secondary battery 1 .

[0084] The positive electrode collector 5 is composed of metal materials such as aluminum, gold, platinum, and alloys thereof. There is no limitation on the shape of the positive electrode collector 5, such as a sheet or a film. Sheets and films include foils. Aluminum and its alloys are cheap and easy to make into thin films. The positive electrode collector 5 can be composed of aluminum coated with carbon. The thickness of the positive electrode collector 5 is, for example, greater than 1 μm and less than 30 μm. When the thickness of the positive electrode collector 5 is within this range, the strength of the collector can be more reliably ensured, for example, cracking and breakage of the collector can be suppressed, and the energy density of the fluoride shuttle secondary battery 1 can be more reliably ensured.

[0085] The positive electrode current collector 5 may have a positive electrode terminal.

[0086] The negative electrode current collector 7 is composed of a metal material such as platinum, aluminum, and alloys thereof. There is no limitation on the shape of the negative electrode current collector 7, and it may be a sheet or a film, for example. Sheets and films include foils. Aluminum and its alloys are cheap and easy to make into thin films. The negative electrode current collector 7 may be composed of aluminum coated with carbon. The thickness of the negative electrode current collector 7 is, for example, greater than 1 μm and less than 30 μm. When the thickness of the negative electrode current collector 7 is within this range, the strength of the collector can be more reliably ensured, for example, cracking and breakage of the collector can be suppressed, and the energy density of the fluoride shuttle secondary battery 1 can be more reliably ensured.

[0087] The electrolyte layer 3 is a layer having fluoride ion conductivity in the thickness direction, that is, in the stacking direction of the positive electrode 2 and the negative electrode 4. The electrolyte layer 3 typically does not have electronic conductivity in the thickness direction. The thickness of the electrolyte layer 3 is, for example, greater than 1 μm and less than 1000 μm. The thickness of the electrolyte layer 3 can be greater than 10 μm and less than 800 μm, and further greater than 20 μm and less than 700 μm. When the thickness of the electrolyte layer 3 is within these ranges, the electrical short circuit of the positive electrode 2 and the negative electrode 4 can be suppressed, and the conductivity of the fluoride ions can be more reliably ensured. By being able to more reliably ensure the conductivity of the fluoride ions, a fluoride shuttle secondary battery 1 with higher output characteristics can be constructed.

[0088] The electrolyte layer 3 may include a solid electrolyte. As the solid electrolyte contained in the electrolyte layer 3, a material known as a solid electrolyte material having fluorine ion conductivity can be used. The solid electrolyte contained in the electrolyte layer 3 may be the above-mentioned material as the solid electrolyte contained in the negative electrode active material layer 8. The solid electrolyte contained in the electrolyte layer 3 may be a material having the same composition as the solid electrolyte contained in the negative electrode active material layer 8, or may be a material having the same composition as the solid electrolyte contained in the positive electrode active material layer 6. The electrolyte layer 3 may be a solid electrolyte layer.

[0089] Since the electrolyte layer 3 has the above-mentioned structure, the fluoride shuttle secondary battery 1 can improve the charge and discharge capacity.

[0090] The layer containing the particulate material may also contain a binder for bonding the particles to each other. The binder can improve the bonding between the particles in the layer. In addition, the binder can improve the bonding (adhesion strength) with the adjacent layer. For example, in the case where the positive electrode active material layer 6 or the negative electrode active material layer 8 contains a particulate material, the bonding between the active material layer and the positive electrode collector 5 or the negative electrode collector 7 adjacent to the active material layer can be improved by further containing a binder in these active material layers. The improvement of these bonding properties contributes to the thin filmization of each layer. For example, this is because in the positive electrode active material layer 6 and the negative electrode active material layer 8, the electrode active materials can be brought into more effective contact with each other. In the electrolyte layer 3, the electrolytes can be brought into more effective contact with each other. By thinning each layer, the energy density of the fluoride shuttle secondary battery 1 can be further improved.

[0091] There is no limitation on the binder. The binder can be, for example, a binder, a polymer compound or a rubber polymer composed of a fluorine resin. The fluorine resin constituting the binder includes, for example, polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-hexafluoroethylene copolymer, poly (vinylidene fluoride), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-chlorotrifluoroethylene copolymer, ethylene-tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, vinylidene fluoride-perfluoromethyl vinyl ether-tetrafluoroethylene copolymer, ethylene-chlorotrifluoroethylene copolymer (ECTFE) etc. Examples of polymer compounds include carboxymethyl cellulose, polyacrylonitrile, polyethylene oxide, polypropylene oxide, polyvinyl chloride, polymethyl methacrylate, polymethyl acrylate, polymethacrylic acid, polyacrylic acid, polyvinyl alcohol, polyvinylidene chloride, polyethylene imine, polymethacrylonitrile, polyvinyl acetate, polyimide, polyamic acid, polyamide-imide, polyethylene, polypropylene, ethylene-propylene-diene terpolymer, polyvinyl acetate, nitrocellulose, ethylene-acrylic acid copolymer, ethylene-methacrylic acid copolymer, ethylene-methyl acrylate copolymer, ethylene-methyl methacrylate copolymer, polyester resin, monoalkyltrialkoxysilane polymer, polymer obtained by copolymerizing a monoalkyltrialkoxysilane polymer with a tetraalkoxysilane monomer, and the like. Rubber polymers include, for example, styrene-butadiene rubber (SBR), butadiene rubber (BR), styrene-isoprene copolymer, isobutylene-isoprene copolymer (butyl rubber), acrylonitrile-butadiene rubber, ethylene-propylene-diene copolymer, acrylonitrile-butadiene copolymer (NBR), hydrogenated SBR, hydrogenated NBR, ethylene-propylene-diene rubber (EPDM), sulfonated EPDM, etc.

[0092] In the case where the binder is an insulating material that does not conduct fluorine ions, an insulating material that does not conduct electrons, or an insulating material that does not conduct fluorine ions and electrons, if the content of the binder in each layer is too large, the charge and discharge characteristics of the battery may be reduced, or the energy density may be reduced. From this viewpoint, the content of the binder in the layer containing the binder as any of the above insulating materials is, for example, 20% by mass or less, and may be 5% by mass or less.

[0093] The binder may have fluorine ion conductivity. As a binder having fluorine ion conductivity, for example, an ion conductive polymer to which a metal fluoride is added can be cited. When the binder has fluorine ion conductivity, the fluorine ion conductivity is improved compared to an insulating binder, and it can be expected that the charge-discharge characteristics and energy density will be improved.

[0094] (Implementation Method 2)

[0095] The method of using the battery in Embodiment 2 is a method of using a fluoride shuttle secondary battery having a positive electrode, a negative electrode, and an electrolyte layer provided between the positive electrode and the negative electrode, and satisfies at least one selected from the following (A2) and (B2).

[0096] (A2) The negative electrode includes a first negative electrode active material and a second negative electrode active material having a composition different from that of the first negative electrode active material, the first negative electrode active material is a first metal fluoride containing a metal M1, and the method of use includes charging at a temperature higher than a temperature at which the metal M1 melts.

[0097] (B2) The positive electrode comprises a first positive electrode active material and a second positive electrode active material having a composition different from that of the first positive electrode active material, wherein the first positive electrode active material is a metal M2, and the method of use comprises: x The charging is performed at a temperature higher than the melting temperature of the fluoride represented by . wherein x represents the valence of M2.

[0098] When the method of use of embodiment 2 satisfies the above (A2), it includes charging at a temperature above the temperature at which the metal M1 is melted. Therefore, by charging, the metal M1 generated by the first metal fluoride in the negative electrode is melted. According to the above structure, the molten metal M1 diffuses around the negative electrode active material, and good material movement between the negative electrode active materials can be achieved. In addition, in the case where the negative electrode includes a negative electrode active material layer containing a negative electrode active material and a solid electrolyte, good material movement between the negative electrode active material and the solid electrolyte can also be achieved. Therefore, the method of use of the embodiment of the present disclosure can increase the discharge capacity of the fluoride shuttle secondary battery. In addition, the method of use of the embodiment of the present disclosure can improve the utilization rate of the negative electrode active material and the cycle characteristics of the battery.

[0099] When the method of use of the second embodiment satisfies the above (B2), including using M2F x Therefore, during charging, M2F generated from metal M2 in the positive electrode x Melting. According to the above composition, the melted M2F x Diffusion around the positive electrode active material can achieve good material movement between the positive electrode active materials. In addition, in the case where the positive electrode includes a positive electrode active material layer containing a positive electrode active material and a solid electrolyte, good material movement between the positive electrode active material and the solid electrolyte can also be achieved. Therefore, the method of use of the embodiment of the present disclosure can improve the discharge capacity of the fluoride shuttle secondary battery. In addition, the method of use of the embodiment of the present disclosure can improve the utilization rate of the positive electrode active material and the cycle characteristics of the battery.

[0100] The method of use of embodiment 2 can satisfy the above (A2).

[0101] The fluoride shuttle secondary battery used in the method of use of the second embodiment may be the fluoride shuttle secondary battery of the first embodiment.

[0102] When the method of use of the second embodiment satisfies the above (A2), it is not stipulated that the battery should be charged and used only under the temperature condition where M1 melts, but all methods of charging and using the battery under the temperature where M1 melts are included. That is, when the method of use of the second embodiment satisfies the above (A2), as long as the highest temperature during charging reaches the temperature at which M1 melts, it also includes methods of using the battery under the environment where the lowest temperature is the temperature at which M1 does not melt. In addition, when the method of use of the second embodiment satisfies the above (B2), it is not stipulated that the battery should be charged and used only under the temperature condition where M2F melts. x The battery is not charged and used under melting temperature conditions, but is included in the M2F x That is, when the method of use of embodiment 2 satisfies the above (B2), as long as the maximum temperature during charging reaches M2F x The melting temperature is also included in the minimum temperature of M2F x This method is used in an environment where the temperature does not melt.

[0103] (Other embodiments)

[0104] (Note)

[0105] The following technical solutions are disclosed through the description of the above embodiments.

[0106] (Technical Solution 1)

[0107] A fluoride shuttle secondary battery comprises a positive electrode, a negative electrode, and an electrolyte layer disposed between the positive electrode and the negative electrode, wherein the fluoride shuttle secondary battery satisfies at least one selected from the following (A1) and (B1).

[0108] (A1) The negative electrode includes a first negative electrode active material and a second negative electrode active material having a composition different from that of the first negative electrode active material, wherein the first negative electrode active material is a first metal fluoride containing a metal M1 having a melting point of 0° C. to 250° C.

[0109] (B1) The positive electrode comprises a first positive electrode active material and a second positive electrode active material having a composition different from that of the first positive electrode active material, wherein the first positive electrode active material is a metal M2, and the composition of M2F x The metal fluoride represented by has a melting point of 0° C. or higher and 250° C. or lower, wherein x represents the valence of M2.

[0110] According to this structure, by charging, the metal M1 in the negative electrode melts, or the metal fluoride M2F in the positive electrode x For example, when the battery is operated in an environment above the melting point of the metal M1, the first metal fluoride is defluorinated during the charging reaction of the negative electrode active material to generate the metal M1, and the generated metal M1 melts. x When working in an environment above the melting point, the metal M2 is fluorinated to generate M2F in the charging reaction of the positive electrode active material. x , the generated M2F x Melting. According to the above constitution, the molten metal M1 or M2F x Diffusion around the negative electrode active material or the positive electrode active material can achieve good material movement between the negative electrode active materials or between the positive electrode active materials. Therefore, the negative electrode active material or the positive electrode active material can achieve an increased specific capacity. Therefore, the fluoride shuttle secondary battery of the embodiment of the present disclosure can achieve an increased discharge capacity. In addition, the utilization rate of the active material and the cycle characteristics of the battery can be improved.

[0111] (Technical Solution 2)

[0112] According to the fluoride shuttle secondary battery described in technical solution 1, when the above (A1) is satisfied, the metal M1 is melted by charging, and when the above (B1) is satisfied, the M2F xMelting by charging. According to this structure, the molten metal M1 diffuses around the negative electrode active material, and good material transfer between the negative electrode active materials can be achieved. In addition, in the case where the negative electrode includes a negative electrode active material layer containing a negative electrode active material and a solid electrolyte, good material transfer between the negative electrode active material and the solid electrolyte can also be achieved. Alternatively, the molten M2F x Diffusion around the positive electrode active material can achieve good material movement between the positive electrode active materials. In addition, in the case where the positive electrode includes a positive electrode active material layer containing a positive electrode active material and a solid electrolyte, good material movement between the positive electrode active material and the solid electrolyte can also be achieved. Therefore, a fluoride shuttle secondary battery with improved discharge capacity can be achieved. In addition, the utilization rate of the active material and the cycle characteristics of the battery can be improved.

[0113] (Technical Solution 3)

[0114] The fluoride shuttle secondary battery according to technical solution 1 or 2 satisfies the above (A1). According to this structure, by charging, the metal M1 generated and melted by the first metal fluoride diffuses around the negative electrode active material, and good material movement between the negative electrode active materials can be achieved. In addition, in the case where the negative electrode includes a negative electrode active material layer containing a negative electrode active material and a solid electrolyte, good material movement between the negative electrode active material and the solid electrolyte can also be achieved. Thus, a fluoride shuttle secondary battery with improved discharge capacity can be realized. In addition, the utilization rate of the negative electrode active material and the cycle characteristics of the battery can be improved.

[0115] (Technical Solution 4)

[0116] According to the fluoride shuttle secondary battery described in any one of technical solutions 1 to 3, the metal M1 has a melting point of more than 25°C and less than 180°C. According to this structure, when working at a temperature higher than the above melting point, the metal M1 melts. As a result, the molten metal M1 generated by the first metal fluoride diffuses around the negative electrode active material, and good material movement between the negative electrode active materials can be achieved. In addition, in the case where the negative electrode includes a negative electrode active material layer containing a negative electrode active material and a solid electrolyte, good material movement between the negative electrode active material and the solid electrolyte can also be achieved. Thus, a fluoride shuttle secondary battery with improved discharge capacity can be realized. In addition, the utilization rate of the negative electrode active material and the cycle characteristics of the battery can be improved.

[0117] (Technical Solution 5)

[0118] According to the fluoride shuttle secondary battery described in any one of technical solutions 1 to 4, the metal M1 contains Na. According to this structure, when the battery operates in an environment above the melting point of Na, the Na generated by the first metal fluoride melts by charging. As a result, the molten Na diffuses around the negative electrode active material, and good material movement between the negative electrode active materials can be achieved. In addition, in the case where the negative electrode includes a negative electrode active material layer containing a negative electrode active material and a solid electrolyte, good material movement between the negative electrode active material and the solid electrolyte can also be achieved. As a result, the discharge capacity of the fluoride shuttle secondary battery can be improved.

[0119] (Technical Solution 6)

[0120] According to the fluoride shuttle secondary battery of any one of claims 1 to 5, the metal M1 includes Na and at least one selected from K, Rb and Li. According to this structure, a fluoride shuttle secondary battery having an improved discharge capacity when used at a low temperature can be realized.

[0121] (Technical Solution 7)

[0122] According to the fluoride shuttle secondary battery of any one of technical solutions 1 to 6, the second negative electrode active material is a second metal fluoride, and the fluorination potential and defluorination potential of the second metal fluoride are greater than -3.0V (vs. Pb / PbF2) and less than -1.0V (vs. Pb / PbF2). According to this structure, the energy density of the fluoride shuttle secondary battery can be improved.

[0123] (Technical Solution 8)

[0124] According to any one of technical solutions 1 to 7 of the fluoride shuttle secondary battery, the second negative electrode active material is a second metal fluoride, and the difference between the fluorination potential and the defluorination potential of the first metal fluoride and the second metal fluoride is greater than or equal to 0 V and less than or equal to 1.0 V. According to this structure, the discharge capacity of the fluoride shuttle secondary battery can be increased.

[0125] (Technical Solution 9)

[0126] According to any one of technical solutions 1 to 8 of the fluoride shuttle secondary battery, the second negative electrode active material is at least one selected from LaF3, AlF3, MgF2, CeF3, GdF3, YF3, EuF3, SmF3, NdF3 and TiF3. According to this structure, the discharge capacity of the fluoride shuttle secondary battery can be increased.

[0127] (Technical Solution 10)

[0128] According to the fluoride shuttle secondary battery described in any one of technical solutions 1 to 9, the metal M1 includes Na, and the second negative electrode active material is at least one selected from LaF3, AlF3, MgF2, CeF3, GdF3, YF3, EuF3, SmF3, NdF3 and TiF3. According to this structure, the discharge capacity of the fluoride shuttle secondary battery can be increased.

[0129] (Technical Solution 11)

[0130] A method for using a fluoride shuttle secondary battery, the fluoride shuttle secondary battery comprising a positive electrode, a negative electrode, and an electrolyte layer disposed between the positive electrode and the negative electrode, wherein the method for using satisfies at least one of the following (A2) and (B2):

[0131] (A2) The negative electrode includes a first negative electrode active material and a second negative electrode active material having a composition different from that of the first negative electrode active material, the first negative electrode active material is a first metal fluoride containing a metal M1, and the method of use includes charging at a temperature above a temperature at which the metal M1 is melted.

[0132] (B2) The positive electrode comprises a first positive electrode active material and a second positive electrode active material having a composition different from that of the first positive electrode active material, wherein the first positive electrode active material is a metal M2, and the method of use comprises: x The charging is performed at a temperature higher than the melting temperature of the fluoride represented by . wherein x represents the valence of M2.

[0133] According to this structure, during charging, the first metal fluoride is defluorinated in the charging reaction of the negative electrode to generate metal M1, and the generated metal M1 melts. Alternatively, during charging, the metal M2 is fluorinated in the charging reaction of the positive electrode to generate M2F x , the generated M2F x So, the molten metal M1 or M2F x Diffusion in the negative electrode active material layer or the positive electrode active material layer can achieve good material movement between particles of the active material. Therefore, the method of use recorded in technical solution 11 can improve the discharge capacity of the fluoride shuttle secondary battery. In addition, the method of use recorded in technical solution 11 can improve the utilization rate of the active material and the cycle characteristics of the battery.

[0134] Example

[0135] The present disclosure is described in more detail below using examples. The following examples are merely examples of implementation and are not intended to limit the present disclosure.

[0136] [Example 1]

[0137] (Production of solid electrolyte materials)

[0138] After mixing CaF2 powder (manufactured by Kojun Chemical Research Institute Co., Ltd.) and BaF2 powder (manufactured by Kojun Chemical Research Institute Co., Ltd.) at a molar ratio of CaF2:BaF2=1:1, the mixture was ground for 10 hours using a planetary ball mill. 0.5 Ba 0.5 F2 represents a solid electrolyte material (hereinafter referred to as BCF).

[0139] (Production of positive electrode buffer material)

[0140] PbF2 powder (manufactured by Kojun Chemical Research Institute Co., Ltd.) and SnF2 powder (manufactured by Kojun Chemical Research Institute Co., Ltd.) were mixed at a weight ratio of PbF2:SnF2=15:7, and then ground for 24 hours using a planetary ball mill. 0.58 Sn 0.42 The compound represented by F2 (hereinafter referred to as PSF).

[0141] The PSF prepared as described above and acetylene black (hereinafter referred to as AB) (manufactured by DENKA Corporation) as a conductive aid were mixed at a mass ratio of PSF:AB=14:1, and then milled for 10 hours using a planetary ball mill to obtain a positive electrode buffer material composed of PSF+AB.

[0142] (Preparation of negative electrode mixture)

[0143] The BCF as the solid electrolyte material and the AB as the conductive additive prepared as described above were mixed at a mass ratio of BCF:AB=61:4, and then milled for 10 hours using a planetary ball mill.

[0144] NaF powder (manufactured by Sigma-Aldrich) and LaF3 (manufactured by Sigma-Aldrich) as active materials were added to the above-mentioned BCF+AB mixture. After mixing at a mass ratio of BCF+AB:NaF:LaF3=65:6:29, the mixture was ground for 10 hours using a planetary ball mill. In this way, a negative electrode mixture was obtained.

[0145] (Production of Evaluation Unit)

[0146] 10 mg of the powder of the negative electrode mixture prepared as described above, 100 mg of the powder of BCF as a solid electrolyte material, 30 mg of the powder of PSF+AB as a positive electrode buffer material, a lead foil (manufactured by Nilaco, with a thickness of 200 μm) as a positive electrode active material layer, and an aluminum foil (manufactured by Nilaco, with a thickness of 10 μm) as a positive electrode collector were stacked in this order in a mold with a diameter of 10 mmφ and press-formed. A platinum foil (manufactured by Nilaco, with a thickness of 20 μm) as a negative electrode collector was arranged on the upper part of the layer composed of the negative electrode mixture (i.e., the negative electrode active material layer) in the obtained stack, and the evaluation unit of Example 1 was obtained.

[0147] (Evaluation of fluoride shuttle secondary batteries)

[0148] The charge and discharge evaluation of the fluoride shuttle secondary battery was performed using the evaluation cell of Example 1. The charge and discharge evaluation was performed using a potentiostat (SP300 manufactured by Bio-Logic). The temperature was set to 140°C, and a constant current charge and discharge test was performed with a current of 40 μA for charge and 40 μA for discharge. Figure 3 This is a graph showing the results of the charge and discharge test of the evaluation unit of Example 1 at 140°C. The horizontal axis is the specific capacity, which represents the capacity per unit mass of the negative electrode active material, and represents the amount of charge or discharge. The theoretical specific capacity of the negative electrode used in Example 1 is 450 mAh / g. In Example 1, after the second cycle, the discharge capacity is almost consistent with the theory, and there is no degradation and it is stable.

[0149] The cross sections of the evaluation cell of Example 1 before and after charge and discharge were subjected to SEM-EDX. Figure 4A This is a cross-sectional SEM image of the evaluation cell of Example 1 before charge and discharge. Figure 4B It is obtained from the measurement results of SEM-EDX Figure 4A Mapped image of the distribution of Na in the image shown. Figure 5A This is a cross-sectional SEM image of the evaluation cell of Example 1 after charge and discharge. Figure 5B It is obtained from the measurement results of SEM-EDX Figure 5A The distribution of Na in the image is shown in the figure. The white part of each mapping image indicates that the concentration of Na is high. Figure 4B It can be seen that before charging and discharging, Na elements exist scattered in the negative electrode, but due to Figure 5B It can be seen that after charge and discharge, the Na element is uniformly present in the negative electrode.

[0150] [Comparative Example 1]

[0151] (Production of Evaluation Unit)

[0152] An evaluation cell of Comparative Example 1 was prepared in the same manner as in Example 1 except that NaF was not added in the preparation of the negative electrode mixture and BCF+AB and LaF 3 were mixed at a mass ratio of BCF+AB:LaF 3 = 65:35.

[0153] (Evaluation of fluoride shuttle secondary batteries)

[0154] In the same manner as in Example 1, the charge and discharge evaluation of the fluoride shuttle secondary battery was carried out using the evaluation cell of Comparative Example 1. Figure 6 This is a graph showing the results of the charge and discharge test of the evaluation unit of Comparative Example 1 at 140°C. The horizontal axis is the specific capacity, which represents the capacity per unit mass of the negative electrode active material, and represents the amount of charge or discharge. The theoretical specific capacity of the negative electrode used in Comparative Example 1 is 410 mAh / g. In Comparative Example 1, the second cycle shows a discharge capacity that is almost consistent with the theory, but the capacity decreases when the cycle is repeated.

[0155] [Comparative Example 2]

[0156] (Production of Evaluation Unit)

[0157] An evaluation cell of Comparative Example 2 was prepared in the same manner as in Example 1 except that LaF 3 was not added in the preparation of the negative electrode mixture and BCF+AB and NaF were mixed at a mass ratio of BCF+AB:NaF=65:35.

[0158] (Evaluation of fluoride shuttle secondary batteries)

[0159] In the same manner as in Example 1, the charge and discharge evaluation of the fluoride shuttle secondary battery was carried out using the evaluation cell of Comparative Example 2. Figure 7 It is a graph showing the results of the charge and discharge test of the evaluation unit of Comparative Example 2 at 140°C. The horizontal axis is the specific capacity, which represents the capacity per unit mass of the negative electrode active material, and represents the amount of charge or discharge. In Comparative Example 2, the discharge capacity of the first cycle is 200mAh / g, and the discharge capacity after the second cycle is small, which is less than 50mAh / g, and the charge and discharge characteristics are extremely low. In addition, the theoretical specific capacity of the negative electrode used in Comparative Example 2 is 638mAh / g, and the utilization rate is also extremely low.

[0160] Figure 8It is a graph showing the charge and discharge results of the second cycle of the charge and discharge test at 140°C for the evaluation units of Example 1, Comparative Example 1 and Comparative Example 2. The horizontal axis is the specific capacity, which represents the capacity per unit mass of the negative electrode active material, and represents the amount of charge or discharge. The unit of Example 1, in which the negative electrode contains NaF and LaF3 as active materials, exhibits a discharge capacity of about 450mAh / g. The unit of Comparative Example 1, in which the negative electrode contains only LaF3 as an active material, exhibits a discharge capacity of about 400mAh / g. Compared with Comparative Example 1, Example 1 has a larger discharge capacity. The unit of Comparative Example 2, in which the negative electrode contains only NaF as an active material, exhibits almost no charge and discharge capacity.

[0161] Based on these results, the optimization of the characteristics of the battery to which NaF is added is assumed as follows.

[0162] During charging, NaF is defluorinated to generate Na metal. Since the battery operating temperature is 140°C, which is above the melting point of Na metal (98°C), the Na metal melts and becomes liquid. The liquidized Na metal diffuses between the particles of the negative electrode mixture and diffuses on the interface between BCF as a solid electrolyte and LaF3 as an active material. It is believed that due to the diffused Na metal, the material transport at the interface becomes good, leading to the optimization of such battery characteristics.

[0163] In order to verify this assumption, a charge and discharge test was performed in the same manner as in Example 1, with the temperature being set to 90° C., on the same cell as the evaluation cell of Example 1. Fig. 9 This is a graph showing the results of the charge and discharge test of the evaluation unit of Example 1 at 90°C. The horizontal axis is the specific capacity, which represents the capacity per unit mass of the negative electrode active material, and represents the amount of charge or discharge. The charge and discharge characteristics were measured at 90°C, a temperature lower than the melting point of Na metal, and the capacity was very low, less than 100 mAh / g. In addition, the same unit as the evaluation unit of Example 1 was operated for two cycles at 140°C, and then the temperature was set to 90°C to measure the charge and discharge characteristics. Fig.10 This is a graph showing the results of the charge and discharge test at 90°C for the evaluation unit of Example 1 after two cycles at 140°C. The horizontal axis is the specific capacity, which represents the capacity per unit mass of the negative electrode active material, and represents the amount of charge or discharge. Fig.10 It can be seen that the discharge capacity is lower than that at 140°C, and the capacity deteriorates when the cycle is repeated. As a result, good characteristics are not obtained. Therefore, it can be seen that when the operating temperature of the battery is above the melting point of Na metal, the evaluation cell of Example 1 can achieve good charge and discharge characteristics.

[0164] [Example 2]

[0165] (Production of Evaluation Unit)

[0166] In the preparation of the negative electrode mixture, NaF to which 10 mol% KF (manufactured by Sigma-Aldrich) was added was used instead of NaF. That is, BCF+AB, NaF, KF, and LaF3 were mixed at a mass ratio of BCF+AB:NaF:KF:LaF3=65:5.15:0.85:29. Except for this matter, the evaluation cell of Example 2 was prepared in the same manner as Example 1.

[0167] (Evaluation of fluoride shuttle secondary batteries)

[0168] In the same manner as in Example 1, the charge and discharge evaluation of the fluoride shuttle secondary battery was carried out using the evaluation cell of Example 2. Fig.11 This is a graph showing the results of the charge and discharge test at 140°C for the evaluation unit of Example 2. The horizontal axis is the specific capacity, which represents the capacity per unit mass of the negative electrode active material, and represents the amount of charge or discharge. The theoretical specific capacity of the negative electrode used in Example 2 is 447 mAh / g, and in the second cycle, it shows an excellent discharge capacity that is almost consistent with the theory.

[0169] according to Fig.11 The results shown above show that good discharge capacity was also confirmed when KF was further contained as the negative electrode active material.

[0170] [Example 3]

[0171] (Production of Evaluation Unit)

[0172] In the preparation of the negative electrode mixture, GdF3 (manufactured by Sigma-Aldrich Co.) was used instead of LaF3. That is, BCF+AB, NaF and GdF3 were mixed in a mass ratio of BCF+AB:NaF:GdF3=65:6:29. The evaluation cell of Example 3 was prepared in the same manner as Example 1, except that the above-mentioned method was used to prepare the negative electrode mixture.

[0173] (Evaluation of fluoride shuttle secondary batteries)

[0174] In the same manner as in Example 1, the charge and discharge evaluation of the fluoride shuttle secondary battery was carried out using the evaluation cell of Example 3. Fig.12 This is a graph showing the results of the charge and discharge test of the evaluation unit of Example 3 at 140°C. The horizontal axis is the specific capacity, which represents the capacity per unit mass of the negative electrode active material, and represents the amount of charge or discharge. The theoretical specific capacity of the negative electrode used in Example 3 is 418 mAh / g. In Example 3, after the second cycle, the discharge capacity is almost consistent with the theory, and there is no degradation and it is stable.

[0175] [Comparative Example 3]

[0176] (Production of Evaluation Unit)

[0177] In the preparation of the negative electrode mixture, GdF3 (manufactured by Sigma-Aldrich Co.) was used instead of LaF3, that is, BCF+AB and GdF3 were mixed in a mass ratio of BCF+AB:GdF3=65:35. The evaluation cell of Comparative Example 3 was prepared in the same manner as Comparative Example 1, except that

[0178] (Evaluation of fluoride shuttle secondary batteries)

[0179] In the same manner as in Example 1, the charge and discharge evaluation of the fluoride shuttle secondary battery was carried out using the evaluation cell of Comparative Example 3. Fig.13 This is a graph showing the results of the charge and discharge test at 140°C for the evaluation unit of Comparative Example 3. The horizontal axis is the specific capacity, which represents the capacity per unit mass of the negative electrode active material, and represents the amount of charge or discharge. The theoretical specific capacity of the negative electrode used in Comparative Example 3 is 375 mAh / g, but the discharge capacity of Comparative Example 3 is lower than the theoretical specific capacity, and the capacity further decreases when the cycle is repeated.

[0180] It can be seen from Example 3 and Comparative Example 3 that, when GdF3 is contained as the negative electrode active material, the discharge capacity of the battery is improved by adding NaF, as in the case of containing LaF3. In addition, improvements in cycle characteristics and utilization rate are also confirmed.

[0181] [Example 4]

[0182] (Production of Evaluation Unit)

[0183] In the preparation of the negative electrode mixture, AlF3 (manufactured by Sigma-Aldrich Co.) was used instead of LaF3, that is, BCF+AB, NaF and AlF3 were mixed in a mass ratio of BCF+AB:NaF:AlF3=65:6:29. The evaluation unit of Example 4 was prepared in the same manner as Example 1, except that

[0184] (Evaluation of fluoride shuttle secondary batteries)

[0185] In the same manner as in Example 1, the charge and discharge evaluation of the fluoride shuttle secondary battery was carried out using the evaluation cell of Example 4. Fig.14 This is a graph showing the results of the charge and discharge test of the evaluation unit of Example 4 at 140°C. The horizontal axis is the specific capacity, which represents the capacity per unit mass of the negative electrode active material, and represents the amount of charge or discharge. In Example 4, after the second cycle, an excellent discharge capacity of about 600 mAh / g was shown, and there was no degradation and it was stable. In addition, the theoretical specific capacity of the negative electrode used in Example 4 is 851 mAh / g.

[0186] [Comparative Example 4]

[0187] (Production of Evaluation Unit)

[0188] In the preparation of the negative electrode mixture, AlF3 (manufactured by Sigma-Aldrich Co.) was used instead of LaF3, that is, BCF+AB and AlF3 were mixed in a mass ratio of BCF+AB:AlF3=65:35. The evaluation cell of Comparative Example 4 was prepared in the same manner as Comparative Example 1, except that

[0189] (Evaluation of fluoride shuttle secondary batteries)

[0190] In the same manner as in Example 1, the charge and discharge evaluation of the fluoride shuttle secondary battery was carried out using the evaluation cell of Comparative Example 4. Fig.15 This is a graph showing the results of charge and discharge tests at 140°C on the evaluation cell of Comparative Example 4. The theoretical specific capacity of the negative electrode used in Comparative Example 4 is 957 mAh / g, but the discharge capacity is only about 400 mAh / g, which is smaller than that of the battery of Example 4.

[0191] It can be seen from Example 4 and Comparative Example 4 that, when AlF3 is contained as the negative electrode active material, the discharge capacity of the battery is improved by adding NaF, similarly to the case of containing LaF3. In addition, an improvement in the utilization rate is also confirmed.

[0192] The fluoride shuttle secondary battery disclosed in the present invention is not limited to the above-mentioned embodiments, and various deformations and changes can be made within the scope of the invention described in the claims. For example, in order to solve part or all of the above-mentioned problems, or to achieve part or all of the above-mentioned effects, the technical features shown in the embodiments described in the scheme for implementing the invention can be appropriately replaced or combined. In addition, if the technical feature is not described as a necessary feature in this specification, it can be appropriately deleted.

[0193] Industrial Availability

[0194] The fluoride shuttle secondary battery disclosed in the present invention is expected to be applied to various applications as a secondary battery with improved discharge capacity.

Claims

1. A fluoride shuttle secondary battery comprising a positive electrode, a negative electrode, and an electrolyte layer disposed between the positive electrode and the negative electrode, The fluoride shuttle secondary battery satisfies at least one selected from the following A1 and B1, A1: The negative electrode comprises a first negative electrode active material and a second negative electrode active material having a composition different from that of the first negative electrode active material, the first negative electrode active material is a first metal fluoride containing a metal M1, and the metal M1 has a melting point of 0° C. or more and 250° C. or less, B1: The positive electrode comprises a first positive electrode active material and a second positive electrode active material having a composition different from that of the first positive electrode active material, wherein the first positive electrode active material is a metal M2, and is composed of M2F x The metal fluoride represented by has a melting point of 0°C or more and 250°C or less, wherein x represents the valence of M2.

2. The fluoride shuttle secondary battery according to claim 1, When A1 is satisfied, the metal M1 is melted by charging. When B1 is satisfied, the M2F x Melted by charging.

3. The fluoride shuttle secondary battery according to claim 1, Satisfies the above A1.

4. The fluoride shuttle secondary battery according to claim 1, The metal M1 has a melting point of 25° C. or more and 180° C. or less.

5. The fluoride shuttle secondary battery according to claim 1, The metal M1 includes Na.

6. The fluoride shuttle secondary battery according to claim 1, The metal M1 includes Na and at least one selected from the group consisting of K, Rb, and Li.

7. The fluoride shuttle secondary battery according to claim 1, The second negative electrode active material is a second metal fluoride, The fluorination potential and defluorination potential of the second metal fluoride are greater than -3.0 V vs. Pb / PbF2 and less than -1.0 V vs. Pb / PbF2.

8. The fluoride shuttle secondary battery according to claim 1, The second negative electrode active material is a second metal fluoride, The difference between the fluorination potential and the defluorination potential of the first metal fluoride and the second metal fluoride is 0 V or more and 1.0 V or less.

9. The fluoride shuttle secondary battery according to claim 1, The second negative electrode active material is at least one selected from LaF3, AlF3, MgF2, CeF3, GdF3, YF3, EuF3, SmF3, NdF3 and TiF3.

10. The fluoride shuttle secondary battery according to claim 1, The metal M1 comprises Na, The second negative electrode active material is at least one selected from LaF3, AlF3, MgF2, CeF3, GdF3, YF3, EuF3, SmF3, NdF3 and TiF3.

11. A method for using a fluoride shuttle secondary battery, the fluoride shuttle secondary battery comprising a positive electrode, a negative electrode, and an electrolyte layer disposed between the positive electrode and the negative electrode, The method of use satisfies at least one selected from the following A2 and B2, A2: The negative electrode comprises a first negative electrode active material and a second negative electrode active material having a composition different from that of the first negative electrode active material, the first negative electrode active material is a first metal fluoride containing a metal M1, and the method of use comprises charging at a temperature above a temperature at which the metal M1 melts, B2: The positive electrode comprises a first positive electrode active material and a second positive electrode active material having a composition different from that of the first positive electrode active material, wherein the first positive electrode active material is a metal M2, and the method of use comprises: x The charging is carried out at a temperature above the melting temperature of the fluoride, wherein x represents the valence of M2.

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