WO2013179807A1 - Metal-air secondary battery - Google Patents

Abstract

In order to decrease charging overvoltage, this metal-air secondary battery is provided with a negative electrode member which occludes and releases metal ions, a positive electrode member which ionizes oxygen, and a separator impregnated with an electrolyte and arranged between the negative electrode member and the positive electrode member, and is characterized by the positive electrode member having 2nm or smaller pores, and by the ratio (B/A) of the product volume B, calculated from the discharge capacity of the secondary battery, and the volume A of said pores being 0.1 or less.

Description

Metal air secondary battery

The present invention relates to a chargeable and dischargeable metal air secondary battery.

In recent years, in the automobile industry, hybrid electric vehicles (HEVs) using an electrically driven motor in combination with an engine instead of a conventional automobile using an engine driven by fuel such as gasoline, and an electric vehicle driven only by a motor Development of (EV) is in progress. The performance of these motor vehicles (hereinafter simply referred to as electric vehicles) depends largely on the characteristics of the storage battery, which is a source of electrical energy. Therefore, development of a storage battery having excellent characteristics is in progress.

Lithium ion secondary batteries are characterized by their light weight and high output compared to other conventional secondary batteries, and are widely used in storage batteries mounted in various other devices including electric vehicles. It is done. At present, the weight energy density of the lithium ion secondary battery actually obtained is about 100 Wh / kg, and the theoretical upper limit thereof is considered to be about 400 Wh / kg. However, for the full-scale spread of electric vehicles, a storage battery with a further large capacity is required, and it is also said that a weight energy density of at least about 500 Wh / kg is required. Therefore, there is a demand for development of an innovative battery that can be expected to have a greater weight energy density than a lithium ion secondary battery.

One of the factors limiting the weight energy density of the lithium ion secondary battery is that a lithium-containing transition metal oxide represented by lithium cobaltate is used as a positive electrode material. That is, since the transition metal element which is the constituent element is a heavy metal, when it is incorporated into a storage battery as a positive electrode material, the weight increases and as a result, the weight energy density decreases. Therefore, in order to avoid such limitations, metal-air batteries that use oxygen in the air as the positive electrode material and metal in the negative electrode material have recently attracted attention. When power storage is performed using a metal-air battery as a storage battery, the weight can be reduced as compared with a conventional lithium ion battery, and therefore, cost reduction can be expected.

Conventionally, metal-air batteries using zinc have been put to practical use and used as a power source for hearing aids and the like. However, the metal-air battery so far has remained in practical use as a primary battery, and has not been put into practical use as a chargeable / dischargeable secondary battery.

A major reason for preventing the conventional metal-air battery from becoming a secondary battery is that the charge / discharge energy efficiency is low, and this is mainly because the charge voltage is high. In relation to this, Patent Document 1 discloses the following technology.

Patent Document 1 discloses a configuration using a composite oxide having an alkali metal or an alkaline earth metal, a transition metal, and oxygen in a lithium-air battery as a catalyst.

Moreover, although it is not limited for metal air secondary batteries, the following technique is disclosed by patent document 2 regarding a carbon material.

JP, 2009-252638, A JP 2006-335596 A

In the battery disclosed in Patent Document 1, the charge voltage is as high as about 4.3 V, and the charge / discharge energy efficiency is therefore low.

Moreover, the carbon material disclosed in Patent Document 2 does not mention the charging voltage.

In view of the above, it is an object of the present invention to provide a metal-air secondary battery with reduced charge overpotential.

A metal-air secondary battery according to the present invention comprises a negative electrode member for absorbing and releasing metal ions, a positive electrode member for ionizing oxygen, and a separator impregnated with an electrolyte disposed between the negative electrode member and the positive electrode member. And in the metal-air secondary battery, the positive electrode member has pores of 2 nm or less, and a volume A of the pores and a product volume B calculated from the discharge capacity of the secondary battery. It is characterized in that the ratio (B / A) is 0.1 or less.

According to the present invention, it is possible to achieve a reduction in charge over voltage in a metal-air secondary battery.

It is a schematic diagram which shows the cross section of the metal air secondary battery by one Embodiment of this invention. It is a schematic diagram which shows the structure of the positive electrode member of the metal air secondary battery by one Embodiment of this invention.

A metal-air secondary battery according to an embodiment of the present invention will be described below using the drawings and tables. FIG. 1 is a schematic view showing a cross section of a metal air secondary battery according to an embodiment of the present invention. This metal air secondary battery is a lithium air secondary battery having a battery cell of a joint structure using metal lithium (Li) for the negative electrode.

In the metal air secondary battery shown in FIG. 1, the positive electrode member 1 and the negative electrode member 3 are disposed with the separator 2 impregnated with the electrolytic solution interposed therebetween, and these constitute one battery cell. An O-ring 4 is disposed around the negative electrode member 3. The battery cell is fixed in a state of being held between the pressure plate 5 and the current collector 6 by the clamping force that the pressure plate 5 receives from the clamping spring 7. An oxygen gas acting as a positive electrode active material is enclosed between the current collector 6 and the oxygen filling valve 8.

The negative electrode member 3 occludes and releases metal ions with the electrolytic solution impregnated in the separator 2. In the present embodiment, disc-shaped metallic lithium having a diameter of 8 mm and a thickness of 1 mm was used as the negative electrode member 3. The electrode area of the negative electrode member 3 can be defined as the area of metal lithium in a portion in contact with the separator 2 and is about 0.5 cm ² . Further, for the separator 2, disk-shaped polyethylene having a diameter of 13 mm larger than that of the negative electrode member 3 was used.

The positive electrode member 1 ionizes oxygen which is a positive electrode active material.

In the metal-air secondary battery of FIG. 1, a discharge reaction represented by the following formulas (1) to (3) is performed at the time of discharge.

(Negative ^{electrode) 2Li → 2Li + + 2e -} --- (1)
(Positive ^{_{side) O 2 + 2Li + + 2e}} - → Li 2 O 2 --- (2)
(All reactions) 2Li + O ₂ → Li ₂ O ₂ --- (3)

On the other hand, at the time of charging, charge reactions represented by the following formulas (4) to (6) are performed.

(Negative ^{electrode) 2Li ← 2Li + + 2e -} --- (4)
(Positive ^{_{side) O 2 + 2Li + + 2e}} - ← Li 2 O 2 --- (5)
(All reactions) 2Li + O ₂ ← Li ₂ O ₂ --- (6)

FIG. 2 is a schematic view showing the configuration of the positive electrode member 1. As shown in FIG. 2, the positive electrode member 1 is configured by mixing a catalyst 1b, a binder 1c and a support 1d and applying the mixture to a substrate 1a. In the present embodiment, the catalyst 1 b, the binder 1 c, and the carrier 1 d are mixed in a weight ratio of 5: 4: 1, respectively, and the mixture is applied to the substrate 1 a to form the positive electrode member 1.

The base material 1a is a conductive substance mainly constituting the positive electrode member 1, and for example, carbon, metal or the like is used. As the substrate 1a, a substrate having a large specific surface area (for example, 100 m ² / g or more) and high electric conductivity is preferable. For example, activated carbon or a metal porous body can be used as the substrate 1a.

The catalyst 1 b is a powdery substance having a function of assisting the reaction of the formula (2) or the reaction of the formula (5) on the positive electrode side to thereby improve the discharge voltage and reduce the charge voltage.

The support 1d has a function of supporting the catalyst 1b on the base 1a, and the binder 1c has a function of binding the base 1a, the catalyst 1b and the support 1d to each other. The details of the substances used as the catalyst 1b, the binder 1c, and the carrier 1d will be described in the respective examples described later.

The size of the positive electrode member 1 is preferably smaller than that of the separator 2 described above and larger than that of the negative electrode member 3. That is, these sizes can be set so that the separator 2 is the largest and becomes smaller in the order of the positive electrode member 1 and the negative electrode member 3.

The separator 2 is impregnated with an electrolytic solution using LiPF ₆ as an electrolyte. As this electrolyte, one in which 1 mol of LiPF ₆ was dissolved in propylene carbonate which is a non-aqueous solvent was used. After several drops of an electrolytic solution are dropped on the surface of the positive electrode member 1 and the surface of the negative electrode member 3 respectively, the separator 2 is sandwiched between the positive electrode member 1 and the negative electrode member 3 with these surfaces inside. The separator 2 was impregnated with

The current collector 6 is a stainless steel mesh having a thickness of 1 mm. In addition, when the base material 1a is made into a metal porous body in the positive electrode member 1 as mentioned above, it is also possible to use this as the current collector 6.

The pressure plate 5 is made of stainless steel, and urges the negative electrode member 3 and the O-ring 4 in the direction of the separator 2 in accordance with the tightening force received from the tightening spring 7. Thus, the negative electrode member 3, the separator 2 and the positive electrode member 1 are in close contact with each other.

In this embodiment, the oxygen filling valve 8 is opened, and oxygen gas having a concentration of 99.9% is flowed at a flow rate of 500 ml / min for about 10 to 15 minutes to flow into the battery cell from the outside of the current collector 6. The Thereafter, by closing the oxygen filling valve 8, oxygen gas was filled in the battery cell.

In addition, the assembly of the metal air secondary battery as described above was performed in a glove box.

Next, details of the catalyst 1b, the binder 1c, and the carrier 1d will be described. In this embodiment, manganese dioxide (MnO ₂ ) is used as the catalyst 1b, carbon is used as the carrier 1d, and polyvinylidene fluoride (PVDF) is used as the binder 1c. In addition, carbon was used as the carrier 1d. Specific examples thereof will be described below based on Table 1 as Examples 1 to 7 and Comparative Example 1. Table 1 shows a list of materials used in Examples 1 to 7 of the present invention and Comparative Example 1 and an average charging voltage.

Example 1
In Example 1, as the carrier 1d, one having a total pore volume of 15.8 mL / g (wherein g represents the weight of the carrier, and the same applies hereinafter) and a micropore volume of 2 nm or less of 0.499 mL / g The positive electrode member 1 was configured using.

(Examples 2 to 7)
In Examples 2 to 7, the positive electrode member 1 was similarly configured using the carrier 1d shown in Table 1.

(Comparative example 1)
In Comparative Example 1, the positive electrode member 1 was formed of the same material as the carrier 1 d shown in Example 7.

Next, experimental results of charge / discharge evaluation using the metal-air secondary battery according to the present embodiment will be described. In the present embodiment, using the metal air secondary batteries according to the above-described Examples 1 to 7 and Comparative Example 1, experiments of charge / discharge evaluation as follows were conducted.

Here, as charge and discharge condition, when a 0.5 cm ² of electrode area, as described above, when discharging a constant current discharge of 0.1 mA / cm ^2, during charging of 0.02 mA / cm ² Constant current charging was performed. At this time, the average voltage at the time of charge was measured, and is shown in Table 1 as an average charge voltage.

In the experiment, each metal air secondary battery of each of Examples 1 to 7 and Comparative Example 1 was placed in a terminal-equipped desiccator, and after argon gas was sealed in the inside of the desiccator, charge / discharge evaluation of the outer terminal of the desiccator It attached to the device and measured.

The average charging voltage obtained by this experiment is shown in Table 1. As shown in the table, it was found that the average charge voltage increased to 4 V when the pore volume of 2 nm or less and the product volume occupancy ratio exceeded 10%.

In addition, it was found that the charge voltage is low when the ratio of pore volume / total pore volume at an average charge voltage of 2 nm or less is at least 15% or more.

The result is considered as follows.

As the number of pores having a size of ₂ nm or less increases, the size at which Li ₂ O _2, which is an insulator, is deposited is smaller, so it is considered that decomposition is likely to occur during charging. However, as shown in the examples, according to our study, we have found for the first time that the charge overpotential rises when the ratio of the product volume to the pore volume of 2 nm or less becomes a certain level or more. . Such a finding is considered to be a charge over voltage as a metal-air secondary battery, even in a material whose pores of 2 nm or less are 90% or more of the total pore volume as shown in JP-A-2006-335596. In order to reduce the amount of product, the amount of product, ie, the discharge capacity, must be regulated.

By defining the ratio of the pore volume of the carrier 1d and the product volume defined by the discharge capacity according to the experimental results as described above, it is possible to provide a metal air secondary battery with a low charge overpotential. .

According to the embodiment described above, the metal-air secondary battery is disposed between the negative electrode member 3 for absorbing and releasing lithium ions, the positive electrode member 1 for ionizing oxygen, the negative electrode member 3 and the positive electrode member 1. In the product volume B calculated from the pore volume A of the positive electrode member and the maximum discharge capacity x (Ah) of the metal-air secondary battery, the B / A ratio is provided. Since x is controlled and used so as to be equal to or less than a predetermined value, it is possible to achieve the reduction of the charge over voltage in the metal-air secondary battery.

In particular, as shown in Examples 1 to 7, the pores have pores of 2 nm or less, and charging is performed when the ratio of the product volume calculated from the pore volume to the maximum discharge capacity is 0.1 or less. The voltage can be reduced. Here, the pore of 2 nm or less is defined by the BET method.

Further, as shown in Examples 1 to 7, when the ratio of the pore volume of 2 nm or less to the total pore volume is at least 15% or more, the charge voltage can be reduced.

Furthermore, as shown in Examples 1 to 7, although carbon is used as the carrier 1d, the present invention is not limited to this, and a conductive material such as aluminum, nickel, SUS or the like may be used. These conductive materials may themselves have pores, or may be formed by solidifying powder to form a positive electrode member.

In the embodiment described above, although the examples using MnO ₂ as the catalyst 1b in the examples 1 to 7 and the comparative example 1 are shown, since the main point of the present invention relates to the carrier 1d, May be a commonly used noble metal catalyst such as Pt or an oxide.

In the embodiment described above, an example was described in which the separator 2 was impregnated with an electrolytic solution using LiPF ₆ as the electrolyte and propylene carbonate as the solvent, but it is used in general lithium ion batteries and the like. Other non-aqueous electrolytes may be used. That is, as solvents other than propylene carbonate, for example, ethylene carbonate, butylene carbonate, vinylene carbonate, γ-butyrolactone, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, 1,2-dimethoxyethane, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, methyl propionate, ethyl propionate, phosphoric acid triester, trimethoxymethane, dioxolane, diethyl ether, sulfolane, 3-methyl-2-oxazolidinone, tetrahydrofuran, 1,2-dioxane Ethoxyethane, chloroethylene carbonate, chloropropylene carbonate and the like can be used. Desirably, among these, it is preferable to use a high boiling cyclic compound as a solvent.

Furthermore, a solid electrolyte supported by a polymer such as ethylene oxide, acrylonitrile, vinylidene fluoride, methyl methacrylate, hexafluoropropylene or the like, an ionic liquid or the like may be used instead of the non-aqueous electrolytic solution.

Further, as an electrolyte other than LiPF _6, it may be used other electrolytes utilized in ordinary lithium ion secondary battery or the like. For example, can be used as _{LiBF 4, LiClO 4, LiCF 3} SO 3, LiCF 3 CO 2, LiAsF 6, LiSbF 6, LiTFSI such an electrolyte. Alternatively, a lithium salt such as an imide salt of lithium represented by lithium trifluoromethanesulfonimide can also be used as the electrolyte.

Alternatively, a polymer of ethylene oxide, acrylonitrile, vinylidene fluoride, methyl methacrylate, or hexafluoropropylene may be used as a gel electrolyte impregnated with a non-aqueous electrolyte.

In the above embodiment, an example is described in which the negative electrode member 3 occludes and releases lithium ions by using metal lithium as the negative electrode member 3, but the negative electrode member 3 occludes and releases ions of other metals May be For example, by using a metal such as Na, Ca, Mg, Zn, Al, or Fe as the negative electrode member 3, the negative electrode member 3 can occlude and release these ions.

Although the example which used PVDF as the binder 1c was demonstrated in the said embodiment, you may use the other binder (binder) used by a general lithium ion secondary battery etc. For example, a fluorine-based resin such as polytetrafluoroethylene (PTFE), styrene butadiene rubber (SBR) or the like can be used as the binder 1c.

Although the example which used polyethylene for the separator 2 was demonstrated in the said embodiment, you may use the other material utilized with a general lithium ion secondary battery etc. For example, the separator 2 can be configured using a porous separator such as polypropylene or a glass ceramic having metal ion conductivity.

Although the said embodiment demonstrated the example which used the battery cell of coupling structure, the form of a battery cell is not limited to this. For example, battery cells such as laminate type and cylindrical type can also be used. That is, as long as the reaction of the metal-air secondary battery can be confirmed, the present invention does not depend on the form of the battery cell.

REFERENCE SIGNS LIST 1 positive electrode member 1 a base 1 b catalyst 1 c binder 1 d carrier 2 separator 2 negative electrode member 4 O ring 5 pressing plate 6 current collector 7 tightening spring 8 oxygen filled valve

Claims (5)

A metal air secondary battery having a negative electrode member for absorbing and releasing metal ions, a positive electrode member for ionizing oxygen, and a separator impregnated with an electrolyte disposed between the negative electrode member and the positive electrode member ,
The positive electrode member has pores of 2 nm or less,
The metal air secondary battery, wherein the ratio (B / A) of the pore volume A to the product volume B calculated from the discharge capacity of the secondary battery is 0.1 or less. The metal air secondary battery according to claim 1, wherein the positive electrode member is a conductive material. The metal air secondary battery according to claim 1, wherein the pores of the positive electrode member have pores of 2 nm or less measured by a BET method. The metal air secondary battery according to claim 1, wherein a ratio of a pore volume of 2 nm or less to a total pore volume in the pores of the positive electrode member is 15% or more. The metal-air secondary battery according to claim 1, wherein the negative electrode member occludes and releases ions of any one of Li, Na, Ca, Mg, Zn, Al and Fe.

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