Positive electrode active material, method for producing positive electrode active material, and fluoride ion secondary battery

Abstract

To provide a positive electrode active material capable of improving the initial discharge capacity of a fluoride ion secondary battery.SOLUTION: The positive electrode active material is used for a fluoride ion secondary battery and includes Cu particles and Bi particles. The positive electrode active material has a first peak existing in a range where a diffraction angle 2θ is 26.2±0.15° in an XRD spectrum measured using Cu-Kα rays, a second peak existing in a range where the diffraction angle 2θ is 30.4±0.25°, and a third peak existing in a range where the diffraction angle 2θ is 27.0±0.25°.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a positive electrode active material used in a fluoride ion secondary battery, a method for producing the positive electrode active material, and a fluoride ion secondary battery. [Background technology]

[0002] In recent years, research and development into secondary batteries that contribute to energy efficiency has been conducted to ensure that many people have access to affordable, reliable, sustainable and advanced energy.

[0003] Patent Document 1 describes a fluoride ion battery having at least a positive electrode active material layer and a solid electrolyte layer, in which the positive electrode active material layer contains positive electrode active material particles mainly composed of Cu and Sn, and the solid electrolyte layer contains a solid electrolyte containing Pb, Sn, and F. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2018-73753 Summary of the Invention [Problem to be solved by the invention]

[0005] However, it is desirable to improve the first discharge capacity of fluoride ion batteries.

[0006] An object of the present invention is to provide a positive electrode active material that can improve the initial discharge capacity of a fluoride ion secondary battery. [Means for solving the problem]

[0007] (1) A positive electrode active material for use in a fluoride ion secondary battery, the positive electrode active material comprising Cu particles and Bi particles, wherein, in an XRD spectrum measured using Cu-Kα radiation, a first peak is present in a range where the diffraction angle 2θ is 26.2±0.15°, a second peak is present in a range where the diffraction angle 2θ is 30.4±0.25°, and a third peak is present in a range where the diffraction angle 2θ is 27.0±0.25°.

[0008] (2) The positive electrode active material according to (1), wherein the intensity ratio of the first peak to the third peak is 0.4 or more.

[0009] (3) The positive electrode active material according to (1) or (2), wherein the Cu particles are nanoparticles.

[0010] (4) A method for producing the positive electrode active material according to any one of (1) to (3), comprising: a mixture of Cu particles, Bi particles, and a compound represented by the general formula K x Bi 1-x F 3-2x (wherein x is 0.02 or more and 0.12 or less). and particles of a compound represented by the formula (I) above, wherein the raw material composition is mixed in a ball mill at a rotation speed of 300 rpm or more and 400 rpm or less for 10 minutes or more and 20 minutes or less, followed by a rest period of 5 minutes or more and 20 minutes or less, and the cycle is repeated 40 times or more and 120 times or less.

[0011] (5) A fluoride ion secondary battery comprising a positive electrode mixture layer containing the positive electrode active material according to any one of (1) to (3). [Effects of the Invention]

[0012] According to the present invention, it is possible to provide a positive electrode active material that can improve the initial discharge capacity of a fluoride ion secondary battery. [Brief explanation of the drawings]

[0013] [Figure 1] 1 shows XRD spectra of powder compositions for a positive electrode mixture layer of Examples 1 to 3 and Comparative Examples 1 to 3. DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, an embodiment of the present invention will be described.

[0015] [Cathode active material] The positive electrode active material of this embodiment is used in a fluoride ion secondary battery and contains Cu particles and Bi particles. Furthermore, in the XRD spectrum of the positive electrode active material of this embodiment measured using Cu-Kα radiation, a first peak is present in the range of a diffraction angle 2θ of 26.2±0.15°, a second peak is present in the range of a diffraction angle 2θ of 30.4±0.25°, and a third peak is present in the range of a diffraction angle 2θ of 27.0±0.25°. This improves the initial discharge capacity of the fluoride ion secondary battery. This is because, as will be described later, when the positive electrode active material is manufactured, the KBiO 2.35 This is presumably due to the formation of fluoride ion-conducting compounds such as F9.

[0016] The intensity ratio of the first peak to the third peak is preferably 0.4 or more, and more preferably 0.6 or more. When the intensity ratio of the first peak to the third peak is 0.4 or more, the initial discharge capacity of the fluoride ion secondary battery is improved.

[0017] The Cu particles are preferably nanoparticles, which improves the initial discharge capacity of the fluoride ion secondary battery. The particle size of the Cu particles is not particularly limited, but is, for example, 10 nm to 100 nm.

[0018] The mass ratio of Cu particles to Bi particles in the positive electrode active material of this embodiment is not particularly limited, but is, for example, 1 / 2 to 3. The particle size of the Bi particles is not particularly limited, but is, for example, 20 nm to 1 μm.

[0019] [Method of manufacturing positive electrode active material] The method for producing a positive electrode active material of this embodiment includes: mixing Cu particles, Bi particles, and a compound represented by the general formula K x Bi 1-x F 3-2x (wherein x is 0.02 or more and 0.12 or less). and a raw material composition containing particles of a compound represented by the formula (I) are ball milled at a rotation speed of 200 rpm to 400 rpm for 10 to 20 minutes, followed by a rest period of 5 to 20 minutes, and this cycle is repeated 40 to 120 times. As a result, the initial discharge capacity of the fluoride ion secondary battery is improved. This is because the compound represented by the formula (I) is KBiO. 2.35 This is presumably due to the formation of fluoride ion-conducting compounds such as F9.

[0020] The rotation speed when mixing the raw material composition with a ball mill is 200 rpm or more and 400 rpm or less, but preferably 300 rpm or more and 350 rpm or less. The time for mixing the raw material composition with a ball mill is 10 minutes or more and 20 minutes or less, but preferably 15 minutes or more and 20 minutes or less. The time for resting after mixing the raw material composition with a ball mill is 5 minutes or more and 20 minutes or less, but preferably 5 minutes or more and 10 minutes or less. The number of cycles for mixing the raw material composition with a ball mill and then resting is 40 times or more and 120 times or less, but preferably 80 times or more and 100 times or less.

[0021] The particles of the compound represented by the general formula above are preferably nanoparticles. The particle size of the particles of the compound represented by the general formula above is not particularly limited, but is, for example, 10 nm to 100 nm.

[0022] The raw material composition may further contain, in addition to the positive electrode active material, a solid electrolyte, a conductive additive, etc. In this case, a powder composition for a positive electrode mixture layer containing the positive electrode active material of this embodiment is produced.

[0023] [Fluoride-ion secondary battery] The fluoride ion secondary battery of this embodiment includes a positive electrode mixture layer containing the positive electrode active material of this embodiment. The fluoride ion secondary battery of this embodiment further includes, for example, a positive electrode current collector foil, a solid electrolyte layer, a negative electrode mixture layer, and a negative electrode current collector foil.

[0024] (Positive electrode mixture layer) The positive electrode mixture layer contains the positive electrode active material of this embodiment, and may further contain, as necessary, a solid electrolyte, a conductive additive, etc. The positive electrode active material of this embodiment may further contain a positive electrode active material other than Cu particles and Bi particles.

[0025] The positive electrode active material other than Cu particles and Bi particles is not particularly limited, but may be, for example, a material represented by the general formula K x Bi 1-x F 3-2x (wherein x is 0.02 or more and 0.12 or less). Examples of the compound include particles of the compound represented by the formula:

[0026] The positive electrode active material other than the Cu particles and the Bi particles is preferably in the form of nanoparticles, and the particle size of the positive electrode active material other than the Cu particles and the Bi particles is, for example, 10 nm or more and 100 nm or less.

[0027] The solid electrolyte is not particularly limited as long as it has fluoride ion conductivity and is not defluorinated during discharge of the fluoride ion secondary battery. For example, metal fluoride particles can be used. Examples of the metal fluoride particles include Ce. 0.92 Sr 0.08 F 2.92 Particles can be mentioned.

[0028] The solid electrolyte is preferably in the form of nanoparticles, and the particle size of the solid electrolyte is, for example, 10 nm or more and 100 nm or less.

[0029] The conductive additive is not particularly limited as long as it has electronic conductivity, and examples thereof include acetylene black.

[0030] (Positive current collector foil) The positive electrode current collector foil is not particularly limited as long as it has electronic conductivity, and examples thereof include metal foils such as gold foil and platinum foil.

[0031] (solid electrolyte layer) The solid electrolyte constituting the solid electrolyte layer is not particularly limited as long as it has fluoride ion conductivity and is not defluorinated during discharge of the fluoride ion secondary battery. For example, metal fluorides can be used. Examples of metal fluorides include Ce. 0.95 Sr 0.05 F 2.85 Examples include:

[0032] (Negative electrode mixture layer) The negative electrode mixture layer contains a negative electrode active material and may further contain a conductive additive, etc., as necessary. The negative electrode active material is not particularly limited, but examples thereof include PbSnF4 particles. The conductive additive is not particularly limited as long as it has electronic conductivity, but examples thereof include acetylene black.

[0033] (negative electrode current collecting foil) The negative electrode current collector foil is not particularly limited as long as it has electronic conductivity, and examples thereof include metal foils such as aluminum foil.

[0034] The fluoride ion secondary battery of this embodiment can be obtained, for example, by sequentially stacking a positive electrode current collector foil, a powder composition for a positive electrode mixture layer, a solid electrolyte layer, a powder composition for a negative electrode mixture layer, and a negative electrode current collector foil, followed by press molding. Here, the powder composition for the positive electrode mixture layer contains, for example, the positive electrode active material of this embodiment, a solid electrolyte, and a conductive additive. Also, the powder composition for the negative electrode mixture layer contains, for example, a negative electrode active material and a conductive additive.

[0035] Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and the above-described embodiments may be modified as appropriate within the scope of the spirit of the present invention. [Example]

[0036] Examples of the present invention will be described below, but the present invention is not limited to these examples.

[0037] (K 0.06 Bi 0.94 F 2.88powder) Potassium fluoride (manufactured by Kojundo Chemical Laboratory) and bismuth fluoride (manufactured by Kojundo Chemical Laboratory) were weighed and then premixed for about 1 hour using an agate mortar and pestle to obtain a raw material mixed powder.

[0038] The resulting raw material mixed powder was classified using a stainless steel mesh with 500 μm openings. Next, the raw material mixed powder that did not pass through the mesh was mixed using an agate mortar and pestle, and then classified, until all the raw material mixed powder passed through the mesh.

[0039] The weighing, pre-mixing and classification of the raw materials were carried out in a purged (DBO type) glove box (manufactured by Miwa Seisakusho) to prevent moisture absorption by the fluoride.

[0040] The sealed powder hopper containing the classified raw material mixed powder was removed from the glove box and connected to a high-frequency induction thermal plasma nanoparticle synthesis device TP-40020NPS (manufactured by JEOL Ltd.). Next, argon gas was supplied to the plasma torch, and the raw material mixed powder was melted by thermal plasma to form a raw material melt, which was then sprayed into a chamber in a reduced pressure environment. The raw material melt sprayed into the chamber was cooled and turned into nanoparticles, and then K 0.06 Bi 0.94 F 2.88 It became powder. Then, K was filtered through the exhaust filter. 0.06 Bi 0.94 F 2.88 After collecting the powder, valves are used to block the upstream and downstream of the exhaust filter, and the powder is transported into a glove box. 0.06 Bi 0.94 F 2.88 The powder was collected. 0.06 Bi 0.94 F 2.88 The composition of the powder was analyzed by ICP atomic emission spectroscopy.

[0041] (Cu powder) Instead of the raw material powder mixture, copper (manufactured by Kojundo Chemical Laboratory) was used. 0.06 Bi 0.94 F 2.88 In the same manner as in the powder, Cu powder having a particle size of 10 nm or more and 100 nm or less was obtained.

[0042] (Ce 0.92 Sr 0.08 F 2.92 powder) Cerium fluoride (manufactured by Kojundo Chemical Laboratory) and strontium fluoride (manufactured by Kojundo Chemical Laboratory) were weighed and then premixed for about 1 hour using an agate mortar and pestle to obtain a raw material mixed powder.

[0043] The raw material powder mixture obtained was used. 0.06 Bi 0.94 F 2.88 Ce with a particle size of 10 nm to 100 nm is prepared in the same manner as the powder. 0.92 Sr 0.08 F 2.92 The powder was obtained. 0.92 Sr 0.08 F 2.92 The composition of the powder was analyzed by ICP atomic emission spectroscopy.

[0044] (Powder composition for negative electrode mixture layer) Using a 45 mL silicon nitride pot mill and ten 10 mm diameter silicon nitride balls, 6 g of lead fluoride (manufactured by Kojundo Chemical Laboratory Co., Ltd.) and 2.8 g of stannous fluoride (manufactured by Kojundo Chemical Laboratory Co., Ltd.) were mixed in a ball mill. This was done by mixing the ball mill at 600 rpm for 3 hours followed by a 5-minute break, 8 times. Next, 0.619 g of acetylene black was added to 8.669 g of the mixture, and the mixture was mixed in a ball mill in the same manner as above. Then, the mixture was heat-treated at 400 ° C for 1 hour under an argon atmosphere to obtain a powder composition for a negative electrode mixture layer.

[0045] (Ce 0.95 Sr 0.05 F 2.85 powder) 19.3510 g of cerium fluoride (manufactured by Kojundo Chemical Laboratory) and 0.6490 g of strontium fluoride (manufactured by Kojundo Chemical Laboratory) were mixed in a ball mill and then fired at 1100°C for 6 hours in an argon atmosphere to obtain Ce. 0.95 Sr 0.05 F 2.85 The powder was obtained by ball mill mixing at 600 rpm for 1 hour followed by a 5-minute break, which was repeated 40 times.

[0046] [Example 1] (Powder composition for positive electrode mixture layer) A powder composition for a positive electrode mixture layer was prepared in a purged (DBO type) glove box (manufactured by Miwa Seisakusho) filled with Ar gas. Specifically, 0.524 g of Cu powder, 0.175 g of Bi powder (manufactured by Kojundo Chemical Laboratory Co., Ltd.), and K 0.06 Bi 0.94 F 2.88 0.267 g of powder and 0.023 g of acetylene black (manufactured by Denki Kagaku Kogyo Co., Ltd.) as a conductive additive were weighed. Next, using a 45 mL silicon nitride pot mill and 40 g of silicon nitride balls with a diameter of 2 mm, the weighed material was ball milled in 8 g of cyclohexane, and then dried on a hot plate at 65 ° C. to obtain a powder composition for a positive electrode mixture layer. When mixing the weighed material in the ball mill, a cycle of mixing at 300 rpm for 15 minutes followed by a 5-minute break was performed 40 times.

[0047] (cell) A cell was fabricated using an alumina tube with an inner diameter of 10 mm in a purged glove box (DBO type) (Miwa Manufacturing Co., Ltd.) filled with Ar gas. 0.95 Sr 0.05 F 2.85150 mg of the powder was uniaxially pressed at a surface pressure of 740 MPa to obtain a solid electrolyte layer. Next, Pt foil as a positive electrode current collector foil, 10 mg of a powder composition for a positive electrode mixture layer, 30 mg of a powder composition for a solid electrolyte layer and a negative electrode mixture layer, and Al foil as a negative electrode current collector foil were sequentially stacked, and then uniaxially pressed at 700 MPa to obtain a cell. Next, the cell was sealed in a glass container with a confining pressure of approximately 340 MPa applied.

[0048] [Example 2] A cell was obtained in the same manner as in Example 1, except that when mixing the weighed materials in the ball mill, a cycle of mixing in the ball mill at 400 rpm for 15 minutes followed by a 5-minute break was repeated 40 times.

[0049] [Example 3] A cell was obtained in the same manner as in Example 1, except that when mixing the weighed materials in the ball mill, a cycle of mixing in the ball mill at 300 rpm for 15 minutes followed by a 5-minute break was repeated 80 times.

[0050] [Comparative Example 1] A cell was obtained in the same manner as in Example 1, except that when mixing the weighed materials in the ball mill, a cycle of mixing in the ball mill at 100 rpm for 15 minutes followed by a 5-minute break was repeated 40 times.

[0051] Comparative Example 2 A cell was obtained in the same manner as in Example 1, except that when mixing the weighed materials in the ball mill, a cycle of mixing in the ball mill at 200 rpm for 15 minutes followed by a 5-minute break was repeated 40 times.

[0052] Comparative Example 3 A cell was obtained in the same manner as in Example 1, except that when mixing the weighed materials in the ball mill, a cycle of mixing in the ball mill at 200 rpm for 15 minutes followed by a 5-minute break was repeated 80 times.

[0053] [XRD spectrum] The XRD spectrum of the powder composition for the positive electrode mixture layer was measured using a fully automated multipurpose X-ray diffractometer SmartLab (manufactured by Rigaku Corporation) with Cu-Kα radiation (λ=1.5418 Å) as the X-ray.

[0054] FIG. 1 shows the XRD spectra of the powder compositions for the positive electrode mixture layer of Examples 1 to 3 and Comparative Examples 1 to 3.

[0055] [Discharge capacity] A constant current charge-discharge test was performed on the cell using a potentio / galvanostat SI1287 / 1255B (manufactured by Solartron). The pressure inside the glass container was reduced using a vacuum pump, and the glass container was placed in a thermostatic chamber at 140°C. Specifically, a current of 0.120 mA was first applied, followed by a current of 0.040 mA, and the cell was charged until the voltage reached 1.5 V (vs. Pb / PbF2). Next, a current of 0.120 mA was applied, followed by a current of 0.040 mA, and the cell was discharged until the voltage reached -0.5 V (vs. Pb / PbF2), and the discharge capacity was determined.

[0056] The evaluation results of the initial discharge capacity of the cell are shown in Table 1. The initial discharge capacity is the capacity per gram of the positive electrode mixture layer.

[0057] [Table 1]

[0058] It can be seen from Table 1 that the initial discharge capacities are high in the cells of Examples 1 to 3. In contrast, the initial discharge capacities are low in the cells of Comparative Examples 1 to 3 because there is no peak in the range of 30.4±0.25° in the XRD spectrum of the positive electrode active material.

Claims

1. A positive electrode active material used in a fluoride ion secondary battery, containing Cu particles and Bi particles, A positive electrode active material, in which, in an XRD spectrum measured using Cu-Kα radiation, a first peak exists in a range where the diffraction angle 2θ is 26.2±0.15°, a second peak exists in a range where the diffraction angle 2θ is 30.4±0.25°, and a third peak exists in a range where the diffraction angle 2θ is 27.0±0.25°.

2. 2. The positive electrode active material according to claim 1, wherein an intensity ratio of the first peak to the third peak is 0.4 or more.

3. The positive electrode active material according to claim 1 , wherein the Cu particles are nanoparticles.

4. A method for producing the positive electrode active material according to claim 1 or 2, comprising: Cu particles, Bi particles, and a compound represented by the general formula K ｘ Bi １－ｘ F ３－２ｘ (In the formula, x is 0.02 or more and 0.12 or less.) and particles of a compound represented by the formula (I) above, wherein the raw material composition is mixed in a ball mill at a rotation speed of 200 rpm or more and 400 rpm or less for 10 minutes or more and 20 minutes or less, followed by a rest period of 5 minutes or more and 20 minutes or less, and the cycle is repeated 40 times or more and 120 times or less.

5. A fluoride ion secondary battery comprising a positive electrode mixture layer containing the positive electrode active material according to claim 1 or 2.

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