Composite cathode material having a metal-supported carbon catalyst and a transition metal-containing alkali metal oxide

Abstract

The objective is to provide a battery with excellent charge and discharge capacity. [Solution] A composite cathode material comprising an alkali metal oxide and a metal-supported carbon catalyst, wherein the alkali metal oxide contains a transition metal.

Description

[Technical Field]

[0001] The present invention relates to a composite cathode material having a metal-supported carbon catalyst and a transition metal-containing alkali metal oxide. [Background technology]

[0002] Lithium-ion rechargeable batteries are widely used as power sources for electronic devices such as smartphones and mobile PCs, as well as for power tools and electric vehicles where high output and large capacity are required. Furthermore, there is a growing demand for the development of new batteries with even greater charge and discharge capacities.

[0003] Lithium-air batteries have been attracting attention as batteries with a larger theoretical capacity than lithium-ion batteries. However, because lithium-air batteries use porous air electrodes, the Li2O2 and Li2O generated during discharge clog the pores of the air electrodes, hindering the supply of oxygen and its release to the outside environment.

[0004] In contrast to lithium-air batteries, a battery has been proposed that does not suffer from the problem of obstruction of air (oxygen) supply and has a significantly larger theoretical capacity than lithium-ion batteries.

[0005] Patent Document 1 proposes a battery that uses a specific alkali metal compound as the positive electrode active material and utilizes a redox reaction in which the alkali metal of the positive electrode changes between A2O and A2O2 (where A is an alkali metal atom) during charging and discharging.

[0006] However, the above reaction is difficult to carry out with alkali metal oxide A2O alone, which is an insulator. Patent document 2 proposes a non-precious metal / carbon composite catalyst as a catalyst to promote the redox reaction. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Patent No. 6230149 [Patent Document 2] China patent CN112186175A [Overview of the project] [Problems that the invention aims to solve]

[0008] In recent years, there has been a demand for further improvements in the charge and discharge capacity of the above-mentioned batteries.

[0009] Given the above background, the present invention aims to provide a battery with excellent charge and discharge capacity. [Means for solving the problem]

[0010] The inventors, through extensive research on the above-mentioned batteries, focused on the fact that by incorporating a transition metal into the alkali metal oxide, charging and discharging become possible through the oxidation-reduction of LCO and oxide ions. They then discovered that a cathode material, a composite of a transition metal-containing alkali metal oxide and a metal-supported carbon catalyst, exhibits stable charging and discharging through the oxidation-reduction of Co ions in LCO or oxide ions, thus completing the present invention.

[0011] A composite cathode material according to one aspect of the present invention is a composite cathode material comprising an alkali metal oxide and a metal-supported carbon catalyst, wherein the alkali metal oxide contains a transition metal.

[0012] In one aspect of the present invention, it is preferable that the content of the transition metal in the alkali metal oxide is 3% by weight or more and 15% by weight or less.

[0013] In one aspect of the present invention, it is preferable that the transition metal in the alkali metal oxide is one or more selected from the group consisting of Co, Fe, and Cu.

[0014] In one aspect of the present invention, it is preferable that the transition metal in the alkali metal oxide is in a solid solution with respect to the alkali metal oxide.

[0015] In one aspect of the present invention, the content of the metal-supported carbon catalyst in the composite positive electrode material is preferably 15% by weight or more and 45% by weight or less.

[0016] In one aspect of the present invention, the metal-supported carbon catalyst preferably comprises a carbon support and a catalytic metal supported on the carbon support.

[0017] In one aspect of the present invention, the content of the catalytic metal in the metal-supported carbon catalyst is preferably 3% by weight or more and 15% by weight or less.

[0018] In one aspect of the present invention, the carbon support is preferably one or more selected from the group consisting of carbon black, carbon nanofibers, activated carbon, and graphite.

[0019] In one aspect of the present invention, the catalytic metal is a transition metal, and is preferably one or more selected from the group consisting of Ni, Co, Mn, Fe, and Ti.

[0020] In one aspect of the present invention, the alkali metal oxide preferably contains Li2O2 and / or Li2O.

[0021] In one aspect of the present invention, a charging curve preferably has flat portions with a small voltage change relative to a change in charging capacity in a region of 2.0 V to 2.5 V and a region of 3.0 V to 3.2 V.

[0022] In one aspect of the present invention, when used in the positive electrode of a 2032-type coin battery, the discharge capacity is preferably 240 mAh / g or more. Advantageous Effects of the Invention

[0023] According to the present invention, a battery excellent in charge / discharge capacity can be provided. Brief Description of the Drawings

[0024] [Figure 1] Figure 1 is a schematic cross-sectional view of a coin-type battery used for battery evaluation of an embodiment of the composite cathode material according to one embodiment of the present invention. [Figure 2] Figure 2 is a graph showing the charge-discharge curve obtained from the evaluation of a secondary battery according to one embodiment of the present invention. [Modes for carrying out the invention]

[0025] The composite cathode material of this embodiment will be described below. However, unless otherwise specified, the present invention is not limited to the following detailed description.

[0026] 1.Battery The composite cathode material of this embodiment can achieve a theoretical capacity greater than that of lithium-ion secondary batteries through the use of specific alkali metal compounds. Furthermore, it enables charging and discharging without the need for oxygen molecules, allowing the battery cells to be sealed. This eliminates the problem of air (oxygen) supply obstruction mentioned above in lithium-air batteries.

[0027] When lithium is used as the alkali metal, for example, the reaction equation for the battery is expressed as follows: Reaction at the negative electrode: Li⇔Li + +e - Reaction at the positive electrode: Li2O2 + 2Li + +2e - ⇔2Li2O Overall reaction: Li + 1 / 2Li2O2 ⇔ Li2O

[0028] At the positive electrode, a peroxide formation reaction occurs, specifically the reaction from Li2O to Li2O2 (a reaction from right to left). A side reaction during this process is the evolution of oxygen (2Li2O → O2 + 4Li). + +4e - If this occurs, the generated oxygen can usually be easily reduced to Li2O or Li2O2 inside the sealed battery during discharge. However, since the oxygen generation reaction proceeds during overcharging, it is preferable to charge and discharge with an amount of electricity that does not cause oxygen generation.

[0029] 2. Composite positive electrode material The composite positive electrode material of the present embodiment contains a mixture of Li₂O₂, which is a positive electrode active material, and a metal-supported carbon catalyst. Although redox reaction is difficult with only Li₂O₂ and Li₂O, the above redox reaction can be promoted by incorporating a transition metal into the alkali metal oxide or forming the composite positive electrode material with the metal-supported carbon catalyst. Further, the content of the metal-supported carbon catalyst in the composite positive electrode material is preferably 15% by mass or more and 45% by mass or less.

[0030] 3. Alkali metal oxide The alkali metal oxide of the present embodiment contains a transition metal. Thereby, the charge-discharge reaction can proceed smoothly, and a battery excellent in charge-discharge capacity can be obtained.

[0031] As the alkali metal, one or more selected from the group consisting of Li, Na and K can be used from the viewpoint of theoretical capacity. Further, it is preferable to use Li or Na, and more preferable to use Li.

[0032] Further, it is preferable to use Co, Fe, or Cu as the transition metal element, and it is more preferable to use Co from the viewpoint of cycle characteristics. The content of the transition metal element in the alkali metal oxide is preferably 3% by mass or more and 15% by mass or less. Further, the transition metal element is preferably solid-dissolved in the alkali metal oxide.

[0033] For example, since the alkali metal oxide Li₂O is an insulator, the progress of the above battery reaction may become difficult. When Co is used as the transition metal contained in the alkali metal oxide, it is considered that the above-mentioned battery exhibits stable charge and discharge due to the redox reaction of Co ions in LiCoO₂ (LCO) represented by the following reaction formula. LiCo 3+ O₂⇔Li 1-x Co 4+ O₂+xLi + +xe -

[0034] 4. Metal-supported carbon catalysts The metal-supported carbon catalyst of this embodiment contains a carbon support and a catalyst metal supported on the carbon support.

[0035] The carbon support is a carbon material mainly composed of carbon. The carbon support is not particularly limited, and for example, carbon black such as furnace black, acetylene black, and Ketjen black, activated carbon, graphite, etc., can be used. Alternatively, carbonized organic materials such as phenolic resins and polyimide resins may be used. Furthermore, it is preferable that the carbon support contains nitrogen atoms in its carbon structure.

[0036] The catalyst metal is preferably a transition metal. It is also preferably one or more selected from the group consisting of Ni, Co, Mn, Fe, and Ti. It is more preferably one or more selected from the group consisting of Ni, Co, and Fe, and from the viewpoint of stabilizing Li2O2, it is preferable to have Ni. Furthermore, the content of the catalyst metal in the metal-supported carbon catalyst is preferably 3% by weight or more and 15% by weight or less.

[0037] 5.Characteristics When the composite cathode material of this embodiment is used, for example, as the positive electrode of a 2032 type coin cell, a high discharge capacity of 240 mAh / g or more can be obtained, demonstrating excellent properties as a composite cathode material. In particular, a discharge capacity of 270 mAh / g or more is preferred. [Examples]

[0038] The present invention will be described in detail below using examples and other references. In the following examples and other references, unless otherwise specified, reagents manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., and preparations made from these reagents, were used. Furthermore, the present invention is not limited in any way by the following examples and other references.

[0039] (Example 1) (1) Production of alkali metal oxides containing transition metals Co3O4 and Li2O powders were weighed so that the molar ratio was Co / Li = 0.1 (corresponding to a transition metal element content of 3.2% by weight in alkali metal oxides). The Co3O4 and Li2O powders were ground and mixed in a ball mill in a glove box under an argon (Ar) atmosphere to obtain a transition metal-containing alkali metal oxide. The ball milling and mixing were carried out using a planetary ball mill at a rotation speed of 600 rpm for 50 hours. Zirconia balls with a ball diameter of 5 mm were used as the grinding media.

[0040] (2) Production of metal-supported carbon catalysts 3 g of phenolic resin (Reditop PSK-2320, manufactured by Gun-ei Chemical Industry Co., Ltd.) was dissolved in 50 mL of acetone. 3 g of nickel phthalocyanine (manufactured by Sigma-Aldrich, Inc.) (corresponding to 3.75% by weight of catalyst metal in the metal-supported carbon catalyst) was added to the resulting solution, and ultrasonic dispersion was performed for 1 hour. The resulting solution was evaporated to dryness in a rotary evaporator at 25°C under vacuum to obtain 6 g of carbon support impregnated with catalyst metal precursor. The obtained carbon support was calcined at 900°C for 5 hours under a flow of Ar gas (oxygen concentration 0.01 vol%) to obtain 4 g of metal-supported carbon catalyst.

[0041] (3) Manufacturing of composite cathode materials Lithium peroxide was weighed so that the weight ratio of the transition metal-containing alkali metal oxide to the obtained metal-supported carbon catalyst was 7:3. The lithium peroxide and metal-supported carbon catalyst were pulverized and mixed in a glove box under an argon (Ar) atmosphere using a ball mill to obtain a composite cathode material. The ball milling and mixing were carried out using a planetary ball mill apparatus at a rotation speed of 400 rpm for 200 hours. Zirconia balls were used as the grinding media.

[0042] (4) Manufacturing of secondary batteries First, the obtained composite cathode material, acetylene black as a conductive agent, and polyvinylidene fluoride (NMP) as a binder were mixed in a weight ratio of 50:33:16 (35% by weight of transition metal-containing alkali metal oxide and 15% by weight of metal-supported carbon catalyst) to form a slurry. This slurry was then spread 1 cm on an Al foil. 2After coating the aluminum foil with 5.0 mg of positive electrode active material per sheet, it was dried in air at 120°C for 30 minutes to remove NMP. The Al foil coated with the composite positive electrode material was cut into strips 66 mm wide and roll-pressed with a load of 1.2 t to produce positive electrode 1. Positive electrode 1 was punched out into a circle with a diameter of 13 mm and dried in a vacuum dryer at 120°C for 12 hours. Using this positive electrode 1, a coin-type battery 10 was fabricated in a glove box with an Ar atmosphere where the dew point was controlled to -80°C.

[0043] For the negative electrode 2, a metallic lithium electrode with a diameter of 17 mm and a thickness of 1 mm was used, and the electrolyte was a 3:7 mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) (manufactured by Toyama Pharmaceutical Co., Ltd.) with 1 M LiBF4 as the supporting electrolyte. For the separator 3, a polyethylene porous membrane with a thickness of 25 μm was used. The coin-type battery 10 was assembled by placing a gasket 4 and a wave washer 5, and then assembling the coin-type battery 10 with a positive electrode can 6 and a negative electrode can 7.

[0044] (5) Evaluation of secondary batteries Using the above-mentioned secondary battery, charge and discharge tests were performed at a temperature of 20°C, within a potential range of 3.5V to 1.5V with a lithium reference potential, and with a current density of 22.5mA / g.

[0045] (Comparative Example 1) A secondary battery was manufactured and evaluated under the same conditions as in Example 1, except that a transition metal-containing alkali metal oxide, acetylene black as a conductive agent, and polyvinylidene fluoride (NMP) as a binder were mixed in a weight ratio of 35:48:16 (35% by weight of the transition metal-containing alkali metal oxide).

[0046] (Comparative Example 2) A secondary battery was manufactured and evaluated under the same conditions as in Example 1, except that the mixing of Co3O4 and Li2O powders was performed without using a ball mill.

[0047] Figure 2 shows graphs illustrating the charge and discharge curves for the examples and comparative examples. In Example 1, two flat sections were observed in the 2.0V to 2.5V and 3.0V to 3.2V regions during charging, where the voltage change was small in response to the change in charge capacity. On the other hand, these flat sections were not observed in Comparative Examples 1 and 2. The discharge capacities for Example, Comparative Example 1, and Comparative Example 2 were 240mAh / g, 185mAh / g, and 165mAh / g, respectively. These flat sections in the charge curve in Example 1 are thought to be due to the good contact between the alkali metal oxide and the metal-supported carbon catalyst, which reduced the resistance within the positive electrode active material and lowered the overvoltage. As a result, the discharge capacity is also thought to have increased in the examples.

[0048] Although each embodiment and example of the present invention has been described in detail above, it will be readily apparent to those skilled in the art that many modifications are possible without substantially departing from the novel aspects and effects of the present invention. Therefore, all such modifications are considered to fall within the scope of the present invention.

[0049] For example, any term that appears at least once in the specification or drawings alongside a broader or synonymous term may be replaced with that different term anywhere in the specification or drawings. Furthermore, the configuration and operation of the composite cathode material having a metal-supported carbon catalyst and an alkali metal oxide are not limited to those described in the embodiments and examples of the present invention, and various modifications are possible. [Explanation of symbols]

[0050] 1 Positive electrode (evaluation electrode), 2 Negative electrode, 3 Separator, 4 Gasket, 5 Wave washer, 6 Positive electrode can, 7 Negative electrode can, 10 Coin-type battery (for evaluation)

Claims

1. A composite cathode material comprising an alkali metal oxide and a metal-supported carbon catalyst, wherein the alkali metal oxide contains a transition metal.

2. The composite cathode material according to claim 1, characterized in that the content of the transition metal in the alkali metal oxide is 3% by weight or more and 15% by weight or less.

3. The composite cathode material according to claim 1 or 2, characterized in that the transition metal in the alkali metal oxide is one or more selected from the group consisting of Co, Fe, and Cu.

4. The composite cathode material according to claim 1 or 2, characterized in that the transition metal in the alkali metal oxide is solid-dissolved in the alkali metal oxide.

5. The composite cathode material according to claim 1 or 2, characterized in that the content of the metal-supported carbon catalyst in the composite cathode material is 15% by weight or more and 45% by weight or less.

6. The composite cathode material according to claim 1 or 2, characterized in that the metal-supported carbon catalyst contains a carbon carrier and a catalyst metal supported on the carbon carrier.

7. The composite cathode material according to claim 6, characterized in that the content of the catalyst metal in the metal-supported carbon catalyst is 3% by weight or more and 15% by weight or less.

8. The composite cathode material according to claim 6, characterized in that the carbon support is one or more selected from the group consisting of carbon black, carbon nanofibers, activated carbon, and graphite.

9. The composite cathode material according to claim 6, characterized in that the catalyst metal is a transition metal, and is one or more selected from the group consisting of Ni, Co, Mn, Fe, and Ti.

10. The alkali metal oxide is Li ２ O ２ and / or Li ２ A composite cathode material according to claim 1 or 2, characterized by containing O.

11. The composite cathode material according to claim 1 or 2, characterized in that it has flat portions in the 2.0V to 2.5V region and the 3.0V to 3.2V region of the charging curve in which the change in voltage with respect to the change in charging capacity is small.

12. The composite positive electrode material according to claim 1 or 2, characterized in that when used as the positive electrode of a 2032 type coin cell, it has a discharge capacity of 240 mAh / g or more.

Images