Positive electrode active material and fluoride ion secondary battery

Abstract

The problem to be solved by the present invention is to provide a positive electrode active material for a fluoride ion secondary battery, the positive electrode active material containing Cu particles and Cu2O particles.

Description

Technical Field

[0001] The present invention relates to a positive electrode active material for a fluoride ion secondary battery and a fluoride ion secondary battery. Background Art

[0002] In recent years, in order to ensure that many people have access to affordable, reliable, sustainable and advanced energy, research and development of secondary batteries that contribute to improving energy efficiency have been underway.

[0003] Patent Document 1 describes a fluoride ion battery having at least a positive electrode active material layer and a solid electrolyte layer. 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.

[0004] [Prior Art Documents]

[0005] (Patent Document)

[0006] Patent Document 1: Japanese Patent Application Laid-Open No. 2018-73753 Summary of the Invention

[0007] [Problems to be Solved by the Invention]

[0008] However, in the fluoride ion battery described in Patent Document 1, when the volume changes due to the expansion and contraction of the positive electrode active material layer during charge and discharge, the volume change is difficult to be absorbed, and as a result, the capacity retention rate decreases. Therefore, it is desired to balance the initial discharge capacity and the capacity retention rate of the fluoride ion secondary battery.

[0009] An object of the present invention is to provide a positive electrode active material that can balance the initial discharge capacity and the capacity retention rate of a fluoride ion secondary battery.

[0010] [Technical Means for Solving the Problems]

[0011] (1) A positive electrode active material for a fluoride ion secondary battery, the positive electrode active material containing Cu particles and Cu2O particles.

[0012] (2) The positive electrode active material according to (1), wherein the mass ratio of the Cu particles to the Cu2O particles is 30 / 70 or more and 70 / 30 or less.

[0013] (3) The positive electrode active material according to (1) or (2), wherein the Cu particles and the Cu2O particles are nanoparticles.

[0014] (4) A fluoride ion secondary battery, which includes a positive electrode mixture layer containing the positive electrode active material according to any one of (1) to (3).

[0015] (Effects of the Invention)

[0016] According to the present invention, a positive electrode active material can be provided that can balance the initial discharge capacity and the capacity retention rate of a fluoride ion secondary battery. Detailed Embodiments

[0017] Hereinafter, embodiments of the present invention will be described.

[0018] [Positive Electrode Active Material]

[0019] The positive electrode active material of the present embodiment is used in a fluoride ion secondary battery and contains Cu particles and Cu2O particles. Therefore, the initial discharge capacity and the capacity retention rate of the fluoride ion secondary battery are balanced. It is presumed that this is because a complex of Cu particles and Cu2O particles is formed during the manufacture of the powder composition for the positive electrode mixture layer described later and / or during the charge and discharge of the fluoride ion secondary battery.

[0020] The mass ratio of Cu particles to Cu2O particles in the positive electrode active material of the present 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 Cu2O particles in the positive electrode active material of the present embodiment is 30 / 70 or more, the initial discharge capacity of the fluoride ion secondary battery increases, and when it is 70 / 30 or less, the capacity retention rate of the fluoride ion secondary battery increases.

[0021] The Cu particles and Cu2O particles are preferably nanoparticles. Thereby, the initial discharge capacity and the capacity retention rate of the fluoride ion secondary battery increase. The particle size of the Cu particles and Cu2O particles is not particularly limited, for example, it is 10 nm or more and 100 nm or less.

[0022] [Fluoride Ion Secondary Battery]

[0023] The fluoride ion secondary battery of the present embodiment includes a positive electrode mixture layer containing the positive electrode active material of the present embodiment. The fluoride ion secondary battery of the present 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)

[0025] The positive electrode mixture layer contains the positive electrode active material of the present embodiment, but may also contain a solid electrolyte, a conductive aid, etc. as needed. In addition, the positive electrode active material of the present embodiment may also contain a positive electrode active material other than Cu particles and Cu2O particles.

[0026] As the positive electrode active material other than Cu particles and Cu2O particles, there is no particular limitation, and for example, Bi particles can be cited.

[0027] As the positive electrode active material other than Cu particles, Cu2O particles and Bi particles, for example, particles of a compound represented by the general formula

[0028] K x Bi 1-x F 3-2x

[0029] (wherein x is 0.02 or more and 0.12 or less).

[0030] can be cited.

[0031] The positive electrode active material other than Cu particles and Cu2O particles is preferably nanoparticles. The particle size of the positive electrode active material other than Cu particles and Cu2O particles is, for example, 10 nm or more and 100 nm or less.

[0032] As the solid electrolyte, as long as it has fluoride ion conductivity and does not de-fluorinate during the discharge of the fluoride ion secondary battery, there is no particular limitation, and for example, metal fluoride particles can be cited. As the metal fluoride particles, for example, Ce 0.92 Sr 0.08 F 2.92 particles can be cited.

[0033] The solid electrolyte is preferably nanoparticles. The particle size of the solid electrolyte is, for example, 10 nm or more and 100 nm or less.

[0034] As the conductive aid, as long as it has electron conductivity, there is no particular limitation, and for example, acetylene black can be cited.

[0035] (Positive electrode current collector foil)

[0036] As the positive electrode current collector foil, as long as it has electron conductivity, there is no particular limitation, and for example, metal foils such as gold foil and platinum foil can be cited.

[0037] (Solid electrolyte layer)

[0038] As the solid electrolyte constituting the solid electrolyte layer, as long as it has fluoride ion conductivity and does not de-fluorinate during the discharge of the fluoride ion secondary battery, there is no particular limitation, and for example, metal fluoride can be cited. As the metal fluoride, for example, Ce 0.95Sr 0.05 F 2.85 。

[0039] (Negative electrode mixture layer)

[0040] The negative electrode mixture layer contains a negative electrode active material and may also contain a conductive additive as needed. As the negative electrode active material, there is no particular limitation, and for example, PbSnF4 particles can be cited. As the conductive additive, as long as it has electron conductivity, there is no particular limitation, and for example, acetylene black can be cited.

[0041] (Negative electrode current collector foil)

[0042] As the negative electrode current collector foil, as long as it has electron conductivity, there is no particular limitation, and for example, metal foils such as aluminum foil can be cited.

[0043] The fluoride ion secondary battery of the present embodiment is obtained, for example, by sequentially laminating 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 and then performing press molding. Here, the powder composition for the positive electrode mixture layer contains, for example, the positive electrode active material, the solid electrolyte, and the conductive additive of the present embodiment. In addition, the powder composition for the negative electrode mixture layer contains, for example, the negative electrode active material and the conductive additive.

[0044] The embodiments of the present invention have been described above, but the present invention is not limited to the above embodiments, and the above embodiments can be appropriately changed within the scope of the gist of the present invention.

[0045] [Examples]

[0046] Hereinafter, examples of the present invention will be described, but the present invention is not limited to the examples.

[0047] (K 0.06 Bi 0.94 F 2.88 powder)

[0048] After weighing potassium fluoride (manufactured by High Purity Chemical Research Institute) and bismuth fluoride (manufactured by High Purity Chemical Research Institute), premixing was performed for about 1 hour using an agate mortar and pestle to obtain a raw material mixed powder.

[0049] For the obtained raw material mixed powder, classification treatment was performed using a stainless steel sieve with a mesh size of 500 μm. Then, the raw material mixed powder that did not pass through the sieve was mixed using an agate mortar and pestle and then classification treatment was performed, and the above operations were repeated until all the raw material mixed powder passed through the sieve.

[0050] In addition, in order to prevent the fluoride from absorbing moisture, the weighing, premixing, and classification treatment of the raw materials were performed inside a purge type (DBO type) glove box (manufactured by Miwa Seisakusho).

[0051] Take out the sealed powder hopper containing the classified raw material mixed powder from the glove box and connect it to the high-frequency induction thermal plasma nanoparticle synthesis device TP-40020NPS (manufactured by JEOL Ltd.). Then, supply argon to the plasma torch, melt the raw material mixed powder using thermal plasma to form a raw material melt, and spray the raw material melt into the chamber under reduced pressure. The raw material melt sprayed into the chamber undergoes a cooling process and is nanoparticleized to become K 0.06 Bi 0.94 F 2.88 powder. Then, collect the K 0.06 Bi 0.94 F 2.88 powder with an exhaust filter. After that, block the upstream and downstream of the exhaust filter with a valve, transfer it into the glove box, and recover the K 0.06 Bi 0.94 F 2.88 powder with a particle size of 10 nm or more and 100 nm or less. Here, the composition of the K 0.06 Bi 0.94 F 2.88 powder is analyzed by ICP emission spectrometry.

[0052] (Cu powder)

[0053] Except for using copper (manufactured by High Purity Chemical Research Institute) instead of the raw material mixed powder, the same procedure as for the K 0.06 Bi 0.94 F 2.88 powder is used to obtain Cu powder with a particle size of 10 nm or more and 100 nm or less.

[0054] (Cu2O powder)

[0055] Except for using copper oxide (manufactured by High Purity Chemical Research Institute) instead of the raw material mixed powder, the same procedure as for the K 0.06 Bi 0.94 F 2.88 powder is used to obtain Cu2O powder with a particle size of 10 nm or more and 100 nm or less.

[0056] (Powder composition for negative electrode binder layer)

[0057] Using a 45 mL pot mill made of silicon nitride and 10 balls made of silicon nitride with a diameter of 10 mm, 6 g of lead fluoride (manufactured by the High Purity Chemical Research Institute) and 2.8 g of stannous fluoride (manufactured by the High Purity Chemical Research Institute) were ball-milled and mixed. At this time, after ball-milling and mixing at 600 rpm for 3 hours, it was stopped for 5 minutes, and this cycle was carried out 8 times. Then, 0.619 g of acetylene black was added to 8.669 g of the mixture, and after ball-milling and mixing in the same manner as above, heat treatment was carried out at 400 °C for 1 hour in an argon atmosphere to obtain a powder composition for the negative electrode mixture layer.

[0058] (Ce 0.95 Sr 0.05 F 2.85 powder)

[0059] After ball-milling and mixing 19.3510 g of cerium fluoride (manufactured by the High Purity Chemical Research Institute) and 0.6490 g of strontium fluoride (manufactured by the High Purity Chemical Research Institute), sintering was carried out at 1100 °C for 6 hours in an argon atmosphere to obtain Ce 0.95 Sr 0.05 F 2.85 powder. When carrying out ball-milling and mixing, after ball-milling and mixing at 600 rpm for 1 hour, it was stopped for 5 minutes, and this cycle was carried out 40 times.

[0060] [Comparative Example 1]

[0061] (Powder composition for the positive electrode mixture layer)

[0062] Inside a purge type (DBO type) glove box (manufactured by Miwa Seisakusho) filled with Ar gas, a powder composition for the positive electrode mixture layer was prepared. Specifically, 0.532 g of Cu powder as the positive electrode active material, 0.178 g of Bi powder (manufactured by the High Purity Chemical Research Institute), and 0.267 g of K 0.06 Bi 0.94 F 2.88 powder, and 0.023 g of acetylene black (manufactured by Denki Kagaku Kogyo) as the conductive assistant were weighed. Then, using a 45 mL pot mill made of silicon nitride and 40 g of balls made of silicon nitride with a diameter of 2 mm, the weighed substances were ball-milled and mixed in 8 g of cyclohexane, and then dried on a hot plate at 65 °C to obtain a powder composition for the positive electrode mixture layer. When ball-milling and mixing the weighed substances, after ball-milling and mixing at 300 rpm for 15 minutes, it was stopped for 5 minutes, and this cycle was carried out 80 times.

[0063] (Single battery)

[0064] Inside a purge type (DBO type) glove box (manufactured by Miwa Seisakusho) filled with Ar gas, a single battery was fabricated using an alumina tube with an inner diameter of 10 mm. Specifically, first, Ce 0.95 Sr0.05 F 2.85 The solid electrolyte layer was obtained by uniaxially pressing 150 mg of powder at a surface pressure of 740 MPa. Subsequently, a Pt foil as a positive current collector foil, 10 mg of a powder composition for a positive electrode mixture layer, the solid electrolyte layer, 30 mg of a powder composition for a negative electrode mixture layer, and an Al foil as a negative current collector foil were sequentially laminated and then uniaxially pressed at 700 MPa to obtain a battery cell. Subsequently, the battery cell was sealed in a closed glass container under a confinement pressure of about 340 MPa.

[0065] [Example 1]

[0066] A battery 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 Cu2O powder were used instead of 0.532 g of Cu powder.

[0067] [Example 2]

[0068] A battery 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 Cu2O powder were used instead of 0.532 g of Cu powder.

[0069] [Example 3]

[0070] A battery 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 Cu2O powder were used instead of 0.532 g of Cu powder.

[0071] [Comparative Example 2]

[0072] A battery cell was obtained in the same manner as in Comparative Example 1, except that Cu2O powder was used instead of Cu powder.

[0073] [Discharge Capacity]

[0074] Using a potentiostat / galvanostat SI1287 / 1255B (manufactured by Solartron), the inside of the glass container was depressurized using a vacuum pump, and the glass container was placed in a thermostat, and the temperature was set to 140 °C to perform a constant current charge-discharge test of the battery cell. Specifically, first, a current of 0.393 mA was passed, and then a current of 0.039 mA was passed to charge to a voltage of 1.5 V (vs. Pb / PbF2). Subsequently, a current of 0.393 mA was passed, and then a current of 0.039 mA was passed to discharge to a voltage of -0.5 V (vs. Pb / PbF2). At this time, the above cycle was performed 10 times to obtain the discharge capacity.

[0075] [Capacity Retention Rate]

[0076] The ratio of the discharge capacity in the 10th cycle to the initial discharge capacity was determined as the capacity retention rate.

[0077] Table 1 shows the evaluation results of the initial discharge capacity and the capacity retention rate of the battery cell. In addition, the initial discharge capacity is the capacity per 1 g of the positive electrode mixture layer.

[0078] [Table 1]

[0079] Mass ratio (Cu / Cu20) Initial discharge capacity [mAh g-1] Capacity retention rate [%] Example 1 70 / 30 409 83 Example 2 50 / 50 384 92 Example 3 30 / 70 370 97 Comparative Example 1 100 / 0 418 59 Comparative Example 2 0 / 100 327 100

[0080] As can be seen from Table 1, the initial discharge capacity and the capacity retention rate of the battery cells of Examples 1 to 3 were well-balanced. In contrast, for the battery cell of Comparative Example 1, since the positive electrode active material did not contain Cu2O particles, the capacity retention rate was low. In addition, for the battery cell of Comparative Example 2, since the positive electrode active material did not contain Cu particles, the initial discharge capacity was low.

Claims

1. A positive electrode active material for a fluoride ion secondary battery, wherein the positive electrode active material contains Cu particles and Cu2O particles.

2. The positive electrode active material according to claim 1, wherein, The mass ratio of the Cu particles to the Cu2O particles is 30 / 70 or more and 70 / 30 or less.

3. The positive electrode active material according to claim 1 or 2, wherein, The Cu particles and the Cu2O 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.