Positive electrode active material and fluoride ion secondary battery

Abstract

To provide a positive electrode active material capable of improving the initial discharge capacity and the capacity maintenance rate of a fluoride ion secondary battery.SOLUTION: A positive electrode active material is used for a fluoride ion secondary battery and contains Cu particles and Cu2O particles.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a positive electrode active material used in a fluoride ion secondary battery 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, in the fluoride ion battery described in Patent Document 1, when the positive electrode active material layer expands and contracts during charge and discharge, causing a change in volume, the volume change is difficult to absorb, resulting in a low capacity retention rate. Therefore, it is desired to achieve both an initial discharge capacity and a capacity retention rate for fluoride ion secondary batteries.

[0006] An object of the present invention is to provide a positive electrode active material that can achieve both a high initial discharge capacity and a high capacity retention rate for 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 Cu2O particles.

[0008] (2) The positive electrode active material according to (1), wherein a mass ratio of the Cu particles to the Cu2O particles is 30 / 70 or more and 70 / 30 or less.

[0009] (3) The positive electrode active material according to (1) or (2), wherein the Cu particles and the Cu2O particles are nanoparticles.

[0010] (4) 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]

[0011] According to the present invention, it is possible to provide a positive electrode active material that can achieve both a good initial discharge capacity and a good capacity retention rate for a fluoride ion secondary battery. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, an embodiment of the present invention will be described.

[0013] [Cathode active material] The positive electrode active material of this embodiment is used in a fluoride ion secondary battery and contains Cu particles and CuO particles. Therefore, the initial discharge capacity and capacity retention rate of the fluoride ion secondary battery are both satisfactory. This is presumably due to the formation of a complex of Cu particles and CuO particles during the production of a powder composition for a positive electrode mixture layer (described later) and / or during charge and discharge of the fluoride ion secondary battery.

[0014] The mass ratio of Cu particles to CuO particles in the positive electrode active material of this embodiment is preferably 30 / 70 or more and 70 / 30 or less, and more preferably 40 / 60 or more and 60 / 40 or less. When the mass ratio of Cu particles to CuO particles in the positive electrode active material of this embodiment is 30 / 70 or more, the initial discharge capacity of the fluoride ion secondary battery becomes high, and when it is 70 / 30 or less, the capacity retention rate of the fluoride ion secondary battery becomes high.

[0015] The Cu particles and Cu2O particles are preferably nanoparticles, which increases the initial discharge capacity and capacity retention rate of the fluoride ion secondary battery. The particle diameters of the Cu particles and Cu2O particles are not particularly limited, but are, for example, 10 nm to 100 nm.

[0016] [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.

[0017] (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 CuO particles.

[0018] The positive electrode active material other than Cu particles and Cu 2 O particles is not particularly limited, but may be, for example, Bi particles.

[0019] Examples of the positive electrode active material other than Cu particles, CuO particles, and Bi particles include 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). Examples of the compound include particles of the compound represented by the formula:

[0020] The positive electrode active material other than the Cu particles and Cu2O particles is preferably nanoparticles, and the particle size of the positive electrode active material other than the Cu particles and Cu2O particles is, for example, 10 nm or more and 100 nm or less.

[0021] 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.

[0022] 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.

[0023] The conductive additive is not particularly limited as long as it has electronic conductivity, and examples thereof include acetylene black.

[0024] (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.

[0025] (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:

[0026] (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.

[0027] (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.

[0028] 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.

[0029] 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]

[0030] Examples of the present invention will be described below, but the present invention is not limited to these examples.

[0031] (K 0.06 Bi 0.94 F 2.88 powder) 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.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] (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.

[0036] (Cu2O powder) The same procedure was used except that cupric oxide (manufactured by Kojundo Chemical Laboratory) was used instead of the raw material mixed powder. 0.06 Bi 0.94 F 2.88 In the same manner as the powder, Cu2O powder having a particle size of 10 nm or more and 100 nm or less was obtained.

[0037] (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.

[0038] (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.

[0039] [Comparative 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, 0.532 g of Cu powder, 0.178 g of Bi powder (manufactured by Kojundo Chemical Laboratory Co., Ltd.), and K were used as positive electrode active materials. 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 80 times.

[0040] (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 2.85 150 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.

[0041] [Example 1] A cell was obtained in the same manner as in Comparative Example 1, except that 0.372 g of Cu powder and 0.160 g of Cu 2 O powder were used instead of 0.532 g of Cu powder.

[0042] [Example 2] A cell was obtained in the same manner as in Comparative Example 1, except that 0.266 g of Cu powder and 0.266 g of Cu 2 O powder were used instead of 0.532 g of Cu powder.

[0043] [Example 3] A cell was obtained in the same manner as in Comparative Example 1, except that 0.160 g of Cu powder and 0.372 g of Cu 2 O powder were used instead of 0.532 g of Cu powder.

[0044] Comparative Example 2 A cell was obtained in the same manner as in Comparative Example 1, except that Cu2O powder was used instead of Cu powder.

[0045] [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 0.393 mA was applied, followed by a current of 0.039 mA, and the cell was charged until the voltage reached 1.5 V (vs. Pb / PbF2). Next, a current of 0.393 mA was applied, followed by a current of 0.039 mA, and the cell was discharged until the voltage reached -0.5 V (vs. Pb / PbF2). This cycle was repeated 10 times, and the discharge capacity was determined.

[0046] [Capacity maintenance rate] The ratio of the discharge capacity at the 10th cycle to the initial discharge capacity was calculated and used as the capacity retention rate.

[0047] The evaluation results of the initial discharge capacity and capacity retention rate of the cell are shown in Table 1. The initial discharge capacity is the capacity per gram of the positive electrode mixture layer.

[0048] [Table 1]

[0049] Table 1 shows that the cells of Examples 1 to 3 have both high initial discharge capacity and high capacity retention. In contrast, the cell of Comparative Example 1 has a low capacity retention because the positive electrode active material does not contain CuO particles. The cell of Comparative Example 2 has a low initial discharge capacity because the positive electrode active material does not contain Cu particles.

Claims

1. A positive electrode active material used in a fluoride ion secondary battery, Cu particles and Cu ２ A positive electrode active material comprising O particles.

2. The Cu ２ 2. The positive electrode active material according to claim 1, wherein a mass ratio of the Cu particles to the O particles is 30 / 70 or more and 70 / 30 or less.

3. The Cu particles and the Cu ２ The positive electrode active material according to claim 1 or 2, wherein the O particles are nanoparticles.

4. 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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