Anode composite material for fluoride ion battery and fluoride ion battery

Abstract

To provide an anode composite material for a fluoride ion battery of which the capacity maintenance rate is improved, and a fluoride ion battery containing such an anode composite material.SOLUTION: An anode composite material for a fluoride ion battery contains a metal element of tin and a fluoride containing lanthanoid elements in a state of discharge. The anode composite material for the fluoride ion battery contains a mixture of the metal element of tin and a metal element of the lanthanoid element and / or an alloy of tin and the lanthanoid element in a state of charge. In the anode composite material, at least one element in lanthanoid elements is cerium and a ratio of mol numbers of tin with respect to mol numbers of lanthanoid elements is 1.0 or more. A fluoride ion battery 1 comprises an anode active material layer 20, and the anode active material layer contains the anode composite material.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a negative electrode composite material for a fluoride ion battery and a fluoride ion battery.

Background Art

[0002] As a high-voltage and high-energy density battery, for example, a lithium-ion battery is known. A lithium-ion battery is a cation-based battery that uses lithium ions as carriers. On the other hand, as an anion-based battery, a fluoride ion battery that uses fluoride ions as carriers is known.

[0003] As a solid electrolyte of a fluoride ion battery, a technique using a fluoride containing a lanthanoid element is known.

[0004] For example, Patent Document 1 discloses a fluoride ion battery in which a solid electrolyte layer contains a solid electrolyte material such as La 1-x Ba x F 3-x (0≦x≦2), and Ce 1-x Ba x F 3-x (0≦x≦2), etc., and a metal simple substance of Pb, Sn, In, Bi, or Sb.

[0005] Patent Document 2 discloses a solid electrolyte used in a fluoride ion battery, which has a composition of Ce 1-x-y La x Sr y F 3-y (0<x, 0<y, 0<x + y<1) and has a crystal phase of a tysonite-type structure.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

[0007] In the fluoride ion batteries of Patent Documents 1 and 2, the solid electrolyte forms a negative electrode active material layer in a self-forming manner. That is, during the charge / discharge reactions of the battery, part or all of the material that functions as the solid electrolyte also functions as the negative electrode active material. In fluoride ion batteries with such a charge / discharge reaction mechanism, there is room for improvement in the capacity retention rate.

[0008] An object of the present disclosure is to provide a negative electrode composite material for a fluoride ion battery having an improved capacity retention rate, and a fluoride ion battery containing such a negative electrode composite material. [Means for solving the problem]

[0009] The present inventors have found that the above problems can be solved by the following means. <Aspect 1> In a discharged state, the battery contains tin metal and a fluoride containing a lanthanide element, At least one of the lanthanide elements is cerium, and the ratio of the number of moles of tin to the number of moles of the lanthanoid element is 1.0 or more; Anode composite material for fluoride-ion batteries. <Aspect 2> 2. The negative electrode composite material of embodiment 1, wherein in the fluoride, the ratio of the number of moles of cerium to the total number of moles of elements other than fluorine is 0.5 or greater. <Aspect 3> The negative electrode composite material according to aspect 1 or 2, wherein the fluoride is a compound represented by the following formula (1): Ce 1-x Ba x F 3-x … (1) (In the formula (1), x is 0.02 or more and 0.3 or less.) <Aspect 4> In a charged state, the battery contains a mixture of elemental tin metal and elemental lanthanoid metal, and / or an alloy of tin and a lanthanoid element, At least one of the lanthanide elements is cerium, and the ratio of the number of moles of tin to the number of moles of the lanthanoid element is 1.0 or more; Anode composite material for fluoride-ion batteries. <Aspect 5> a negative electrode active material layer; and The negative electrode active material layer contains the negative electrode composite material according to any one of aspects 1 to 4. Fluoride-ion battery. [Effects of the Invention]

[0010] According to the present disclosure, it is possible to provide a negative electrode composite material for a fluoride ion battery having an improved capacity retention rate, and a fluoride ion battery containing such a negative electrode composite material. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a schematic cross-sectional view showing an example of a fluoride ion battery according to the present disclosure. [Figure 2] FIG. 2 shows charge and discharge curves of the fluoride ion battery according to Example 1. [Figure 3] FIG. 3 shows charge / discharge curves of the fluoride ion battery according to Comparative Example 1. [Figure 4] FIG. 4 is a graph showing the change in discharge capacity of the fluoride ion batteries according to Examples 1 to 4. [Figure 5] FIG. 5 is a graph showing the change in discharge capacity of the fluoride ion batteries according to Comparative Examples 1 and 2. In FIG. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, embodiments of the present disclosure will be described in detail. Note that the present disclosure is not limited to the following embodiments, and various modifications can be made within the scope of the present disclosure.

[0013] <<Anode composite material for fluoride-ion batteries>> The negative electrode composite material for a fluoride ion battery according to the present disclosure contains, in a discharged state, tin as a metal and a fluoride containing a lanthanoid element, at least one of which is cerium, and the ratio of the number of moles of tin to the number of moles of the lanthanoid element is 1.0 or greater.

[0014] The present inventors unexpectedly discovered that a negative electrode composite material containing a fluoride containing tin (Sn) and a lanthanoid element (Ln) including at least cerium (Ce), with an Sn / Ln (molar ratio) of 1.0 or greater, can improve the capacity retention of a fluoride-ion battery in a discharged state. Without intending to be bound by any theory, the reason for this is presumed to be as follows. Specifically, the composition ratio and type of reaction product of the defluorination reaction during charging differ depending on the metal / fluoride (molar ratio) and metal species, and therefore the ease with which the refluorination reaction proceeds during discharge is thought to differ. This is thought to result in differences in the reversibility of the battery reaction during constant current operation. Factors that affect the ease with which the discharge reaction proceeds include the interfacial reaction rate and the diffusion rate of fluoride ions. The negative electrode composite material of the present disclosure is thought to be able to improve the capacity retention of a battery because the metal / fluoride (molar ratio) and metal species are appropriately designed.

[0015] <Elemental tin metal> The negative electrode composite material for a fluoride ion battery according to the present disclosure contains, in a discharged state, elemental tin metal, which can form an alloy with elemental lanthanide metal produced by a defluorination reaction during charging.

[0016] <Fluorides containing lanthanide elements> The negative electrode composite material for a fluoride ion battery according to the present disclosure contains a fluoride containing a lanthanoid element in a discharged state. At least one of the lanthanoid elements contained in the fluoride is cerium. The lanthanoid element may include lanthanum in addition to cerium. The fluoride generates the elemental metal of the lanthanoid element through a defluorination reaction during charging. The elemental metal of the lanthanoid element can form an alloy with elemental metal tin.

[0017] In the negative electrode composite material for a fluoride ion battery of the present disclosure, the ratio of the number of moles of tin to the number of moles of lanthanoid element, Sn / Ln (mol) is 1.0 or more. Sn / Ln (mol) may be 1.5 or more, 2.0 or more, 2.5 or more, or 3.0 or more, and may be 5.0 or less, 4.0 or less, 3.5 or less, or 3.0 or less. When Sn / Ln (mol) is within the above range, the capacity retention rate of the battery can be effectively improved. In particular, when Sn / Ln (mol) is close to 3.0, for example, the discharge capacity from the second cycle onward can be made higher than the initial discharge capacity in a cycle test. This is thought to be because an Sn-Ln alloy with a Sn:Ln = 3:1 (mol) ratio is easily formed from elemental tin (Sn) and elemental metal of the lanthanoid element (Ln) generated by a defluorination reaction during charging, and this Sn-Ln alloy effectively functions as an anode active material during discharge.

[0018] <Alkaline earth metals> The fluoride may contain, in addition to a lanthanide element, an alkaline earth metal, for example. The alkaline earth metal is not particularly limited, but may be, for example, calcium, strontium, or barium, particularly barium. The alkaline earth metal can improve the fluoride ion conductivity of the battery.

[0019] In particular, the fluoride may be a compound represented by the following formula (1): Ce 1-x Ba x F 3-x … (1) (In formula (1), x is 0.02 or more and 0.3 or less.)

[0020] x may be 0.05 or more, 0.08 or more, or 0.1 or more, and may be 0.25 or less, 0.2 or less, 0.15 or less, or 0.1 or less. In particular, x may be 0.1. That is, the fluoride is Ce 0.9 Ba 0.1 F 2.9 When x is within the above range, the effect of the alkaline earth metal such as barium in improving the fluoride ion conductivity of the battery is further enhanced.

[0021] In the fluoride, the ratio of the number of moles of cerium to the total number of moles of elements other than fluorine may be 0.5 or more. That is, for example, when the fluoride is composed of cerium, barium, and fluorine, the number of moles of cerium / (number of moles of cerium + number of moles of barium) may be 0.5 or more. This ratio may be 0.6 or more, 0.7 or more, 0.8 or more, or 0.9 or more, and may be less than 1.0 or 0.9 or less. This ratio may also be 1.0. That is, all elements other than fluorine in the fluoride may be cerium, in which case the fluoride may be cerium fluoride represented by CeF3.

[0022] The fluoride may be prepared by applying mechanical shock to a raw material compound containing the element that constitutes the fluoride to cause a reaction, or may be a commercially available product. For example, the fluoride may be Ce 1-x Ba x F 3-x In the case of a compound represented by the formula (I), it can be prepared by mixing and reacting cerium fluoride (CeF3) and barium fluoride (BaF2). An example of a mixing method is mixing by mechanical milling. Specifically, a method of mixing using a ball mill can be mentioned. For example, when the fluoride is CeF3, a commercially available product can be used.

[0023] The method for preparing the negative electrode composite material for a fluoride ion battery in a discharged state according to the present disclosure is not particularly limited, and an example thereof is a method in which a mechanical impact is applied to raw material compounds. An example of a method for applying a mechanical impact is mixing by mechanical milling. Specifically, a method in which mixing is performed using a ball mill is exemplified.

[0024] The negative electrode composite material for a fluoride ion battery according to the present disclosure contains, in a charged state, a mixture of elemental metal tin and elemental metal lanthanoids, and / or an alloy of tin and lanthanoids, wherein at least one of the lanthanoids is cerium, and the ratio of the number of moles of tin to the number of moles of the lanthanoids is 1.0 or greater.

[0025] As described above, in the negative electrode composite material for a fluoride ion battery of the present disclosure, a defluorination reaction occurs upon charging. This generates a product defluorinated from the lanthanoid element (Ln) metal element and / or Sn-Ln alloy, and fluoride. Specifically, for example, the negative electrode composite material for a fluoride ion battery of the present disclosure in a discharged state contains only the metal element Sn and Ce. 0.9 Ba 0.1 F 2.9 In this case, the defluorination reaction that accompanies charging produces elemental Ce and / or an Sn—Ce alloy, and BaF 2 .

[0026] 《Negative electrode mixture》 The negative electrode composite material of the present disclosure may form a negative electrode mixture. In the present disclosure, the term "negative electrode mixture" refers to a composition that can form a negative electrode active material layer, either as is or by further containing other components. The negative electrode mixture may optionally contain a conductive additive and a binder.

[0027] <Anode composite material> For the negative electrode composite material of the present disclosure, reference can be made to the above description regarding the negative electrode composite material of the present disclosure.

[0028] <Conductive additive> Examples of the conductive additive include carbon materials, such as carbon blacks such as acetylene black, ketjen black, furnace black, and thermal black, graphene, fullerene, and carbon nanotubes.

[0029] <binder> Examples of the binder include fluorine-based binders such as polyvinylidene fluoride (PVdF) and polytetrafluoroethylene (PTFE).

[0030] The method for preparing the negative electrode composite is not particularly limited, but an example is a method of mixing each component that can constitute the negative electrode composite. At this time, the components of the negative electrode composite material and other components can be mixed simultaneously. An example of a mixing method is mixing by mechanical milling. Specifically, a method of mixing using a ball mill device can be mentioned.

[0031] Fluoride-ion battery As illustrated in Fig. 1, the fluoride ion battery 1 of the present disclosure has an anode active material layer 20, and the anode active material layer contains the anode composite material of the present disclosure. The anode active material layer may contain an anode mixture including the anode composite material of the present disclosure. The fluoride ion battery 1 of the present disclosure may have, in this order, an anode current collector 10, an anode active material layer 20, an electrolyte layer 30, a cathode current collector 40, and a cathode active material layer 50.

[0032] The fluoride ion battery of the present disclosure may be a liquid-based battery containing an electrolytic solution as an electrolyte layer, or may be a solid-state battery having a solid electrolyte layer as an electrolyte layer. Regarding the present disclosure, a "solid-state battery" refers to a battery that uses at least a solid electrolyte as an electrolyte, and therefore a solid-state battery may use a combination of a solid electrolyte and a liquid electrolyte as an electrolyte. The solid-state battery of the present disclosure may also be an all-solid-state battery, i.e., a battery that uses only a solid electrolyte as an electrolyte.

[0033] <Negative electrode current collector> Examples of materials for the negative electrode current collector include stainless steel (SUS), copper, nickel, iron, titanium, platinum, and carbon. Examples of the shape of the negative electrode current collector include foil, mesh, and porous shapes.

[0034] <Negative electrode active material layer> The negative electrode active material layer contains the negative electrode composite material of the present disclosure. For the negative electrode composite material of the present disclosure, reference can be made to the above description regarding the negative electrode composite material of the present disclosure.

[0035] The thickness of the negative electrode active material layer is not particularly limited and can be adjusted appropriately depending on the configuration of the battery.

[0036] <Electrolyte layer> When the fluoride ion battery of the present disclosure is a liquid battery, the electrolyte layer may be composed of, for example, an electrolyte solution and an optional separator.

[0037] The electrolyte can contain, for example, a fluoride salt and an organic solvent.

[0038] The separator is not particularly limited as long as it has a composition that can withstand the range of use of a fluoride ion battery.

[0039] When the fluoride ion battery of the present disclosure is a solid-state battery, the electrolyte layer may be, for example, a layer including a solid electrolyte, in which case the electrolyte layer may optionally contain a binder.

[0040] The solid electrolyte is not particularly limited as long as it is a material that can be used in a fluoride ion battery. For example, the solid electrolyte may have a fluorination / defluorination potential that is lower than that of the fluoride that contributes to the battery reaction in the negative electrode active material layer.

[0041] For the binder, reference can be made to the above description regarding the negative electrode mixture of the present disclosure.

[0042] <Cathode active material layer> The positive electrode active material layer of the present disclosure is a layer containing at least a positive electrode active material, and may optionally contain a solid electrolyte, a conductive additive, and a binder.

[0043] The positive electrode active material is typically an active material that defluorinates during discharge. Examples of the positive electrode active material include simple metals, alloys, metal oxides, and fluorides thereof. Examples of metal elements contained in the positive electrode active material include Cu, Ag, Ni, Co, Pb, Mn, Au, Pt, Rh, V, Os, Ru, Fe, Cr, Bi, Nb, Sb, Ti, Sn, and Zn.

[0044] For the solid electrolyte, reference can be made to the above description of the electrolyte layer of the present disclosure, and for the conductive additive and binder, reference can be made to the above description of the negative electrode mixture of the present disclosure.

[0045] The thickness of the positive electrode active material layer is not particularly limited and can be adjusted appropriately depending on the configuration of the battery.

[0046] <Positive electrode current collector> Examples of materials for the positive electrode current collector include lead, stainless steel (SUS), aluminum, nickel, iron, titanium, platinum, and carbon. Examples of the shape of the positive electrode current collector include foil, mesh, and porous shapes. [Example]

[0047] Example 1 <Preparation of negative electrode mixture containing negative electrode composite material> A specified amount of tin (Sn) powder and cerium barium fluoride (Ce) as a fluoride containing a lanthanide element are mixed. 0.9 Ba 0.1 F 2.9A powder of cerium dioxide (Sn) and acetylene black (AB) powder as a conductive additive were mechanically milled and mixed using a ball mill (Fritsch, Planetary Ball Mill Premium Line PL-7) to obtain a powdered negative electrode composite material containing the negative electrode composite material. The Sn / Ce (molar ratio) was set to 1.0. The amount of AB added was 3% by mass of the total negative electrode composite material. The ball mill mixing was carried out in a dry argon atmosphere at a table rotation speed of 200 rpm for 3 hours.

[0048] Fabrication of an all-solid-state fluoride-ion battery as a test half-cell (Formation of negative electrode active material layer) 15 mg of the above powder of the negative electrode mixture was used to form a green compact, thereby obtaining a negative electrode active material layer (working electrode).

[0049] (Electrolyte layer formation) Lanthanum barium fluoride (La 0.9 Ba 0.1 F 2.9 ) 150 mg of the powder was used to form a compact, which provided the electrolyte layer.

[0050] (Formation of positive electrode active material layer) A 50 mg mixture of lead fluoride (PbF2) powder as the positive electrode active material and AB powder as the conductive additive was formed into a powder compact, thereby obtaining a positive electrode active material layer (counter electrode). The AB content of the mixture was 5 mass% of the total mixture. Furthermore, a 220 mg Pb plate was pressed onto one surface of the formed positive electrode active material layer. The use of the Pb plate in a half-cell charge-discharge test is expected to suppress the deterioration of cycle capacity on the counter electrode side. However, the Pb plate is not an essential component of the present disclosure.

[0051] (Battery construction) An all-solid-state fluoride ion battery of Example 1 was fabricated by laminating a platinum foil as a negative electrode current collector, a negative electrode active material layer, an electrolyte layer, a positive electrode active material layer, and an aluminum foil as a positive electrode current collector in this order. The Pb plate was laminated so as to be in contact with the positive electrode current collector. The diameter of the all-solid-state fluoride ion battery was 11.28 mm. This all-solid-state fluoride ion battery was placed in a ceramic cylindrical container with an inner diameter of 11.28 mm, and was fixed by being sandwiched between stainless steel cylinders with a diameter of 11.28 mm from both sides of the negative electrode current collector and the positive electrode current collector.

[0052] Example 2 An all-solid-state fluoride ion battery of Example 2 was produced in the same manner as in Example 1, except that the Sn / Ce (mol) ratio was set to 1.5.

[0053] Example 3 An all-solid-state fluoride ion battery of Example 3 was produced in the same manner as in Example 1, except that Sn / Ce (mol) was set to 3.0.

[0054] Example 4 Ce is used as a fluoride powder, which is the raw material for the negative electrode composite material. 0.9 Ba 0.1 F 2.9 An all-solid-state fluoride ion battery of Example 4 was fabricated in the same manner as in Example 3, except that cerium fluoride (CeF3) was used instead of .

[0055] Comparative Example 1 An all-solid-state fluoride ion battery of Comparative Example 1 was fabricated in the same manner as in Example 1, except that the Sn / Ce (mol) ratio was set to 0.5.

[0056] Comparative Example 2 As the metallic material used as the raw material for the negative electrode composite material, indium (In) was used instead of Sn, and Ce was used as fluoride powder. 0.9 Ba 0.1 F 2.9 Instead of La 0.9 Ba 0.1 F 2.9An all-solid-state fluoride ion battery of Comparative Example 2 was produced in the same manner as in Example 3, except that the above was used.

[0057] "evaluation" For each example, the fluoride ion battery was tested in a sealed container under vacuum at a test temperature of 140°C and a current density of 0.05mA / cm. 2 The test half-cells were charged and discharged five times at 1000 kJ / s. However, in Example 4 and Comparative Example 2, they were charged and discharged ten times. This was to evaluate the relationship between capacity degradation and the number of charge / discharge cycles. In the test half-cells fabricated this time, the working electrode (negative electrode) was connected to the positive wiring, and the counter electrode (positive electrode) was connected to the negative wiring, so negative values ​​were displayed as the battery voltage. In this setting, the end-of-charge voltage and the end-of-discharge voltage were −2.4 V and −1.0 V, respectively. An electrochemical measurement system equipped with a frequency response analyzer (VMP-300 High-Performance Electrochemical Measurement System, manufactured by Biologic Inc.) was used for the charge / discharge test. Due to the defluorination reaction accompanying the charging in this test, a mixture of elemental metal Sn and elemental metal Ce, and / or an Sn-Ce alloy, was present in the negative electrode active material layer.

[0058] "result" As a result of the above charge / discharge tests, the charge / discharge curves of Example 1 and Comparative Example 1 are shown in Figures 2 and 3, respectively. Here, the side where the battery voltage value becomes more negative corresponds to charging, and the side where this value approaches 0 corresponds to discharging.

[0059] Furthermore, the results of the charge-discharge tests for each example are shown in Figure 4 (Example) and Figure 5 (Comparative Example). From the results of Example 4 and Comparative Example 2, it was confirmed that the presence or absence of a tendency for capacity degradation can be determined by the increase or decrease in discharge capacity from the second to fifth cycles. Therefore, the ratio of the discharge capacity at the fifth cycle to the discharge capacity at the second cycle was defined as the capacity retention rate, and the presence or absence of a tendency for capacity degradation was determined. The discharge capacities and capacity retention rates at the second and fifth cycles are shown in Table 1. When the capacity retention rate was 100% or more, it was determined that there was no tendency for capacity degradation, and when the capacity retention rate was less than 100%, it was determined that there was a tendency for capacity degradation. The discharge capacity of each test is shown as a specific capacity normalized by the weight of the negative electrode composite.

[0060] [Table 1]

[0061] 2 to 5 and Table 1, capacity degradation was suppressed in the batteries of the examples containing the negative electrode composite material of the present disclosure, which contained simple metal Sn and a fluoride containing the lanthanoid element Ce, and had an Sn / Ce (molar) ratio of 1.0 or more. In particular, Example 3, in which the fluoride, which is the raw material of the negative electrode composite material, contained barium and had an Sn / Ce (molar) ratio of 3.0, had the largest discharge capacity. [Explanation of symbols]

[0062] 1. Fluoride-ion battery 10 Negative electrode current collector 20 Negative electrode active material layer 30 Solid electrolyte layer 40 Cathode active material layer 50 Positive electrode current collector

Claims

1. In a discharged state, the battery contains tin metal and a fluoride containing a lanthanide element, At least one of the lanthanide elements is cerium, and the ratio of the number of moles of tin to the number of moles of the lanthanoid element is 1.0 or more; Anode composite material for fluoride-ion batteries.

2. 2. The negative electrode composite material according to claim 1, wherein in the fluoride, the ratio of the number of moles of the cerium to the total number of moles of elements other than fluorine is 0.5 or more.

3. The negative electrode composite material according to claim 1 or 2, wherein the fluoride is a compound represented by the following formula (1): Yes １－ｘ No ｘ F ３－ｘ … (1) (In the formula (1), x is 0.02 or more and 0.3 or less).

4. In a charged state, the battery contains a mixture of elemental tin metal and elemental lanthanoid metal, and / or an alloy of tin and a lanthanoid element, At least one of the lanthanide elements is cerium, and the ratio of the number of moles of tin to the number of moles of the lanthanoid element is 1.0 or more; Anode composite material for fluoride-ion batteries.

5. a negative electrode active material layer; and The negative electrode active material layer contains the negative electrode composite material according to claim 1 or 4. Fluoride-ion battery.

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