JP2021174730A - Aqueous electrolyte solution, aluminum battery, and method for manufacturing aqueous electrolyte solution - Google Patents

Abstract

To provide: an aqueous electrolyte solution which can suppress the overvoltage of an aluminum-containing negative electrode; an aluminum battery having the same; and a method for manufacturing such an aqueous electrolyte solution.SOLUTION: An aqueous electrolyte solution is to be used for an aluminum battery having an aluminum-containing negative electrode. The aqueous electrolyte solution comprises a first compound represented by the following formula (1), and a second compound represented by the following formula (2): Al[(CnF(2n+1)SO2)2 N]3 (1); and H(CnF(2n+1)SO2)2 N (2). In the formulas (1) and (2), n independently represents an integer of 0 up to 4.SELECTED DRAWING: Figure 1

Description

The present disclosure relates to an aqueous electrolyte, an aluminum battery, and a method for producing the aqueous electrolyte.

Conventionally, an aluminum battery using aluminum as a negative electrode material has been proposed because of its large volume specific capacity and low cost.

As an electrolytic solution for this type of aluminum battery, many have been proposed using a non-aqueous electrolytic solution or a room temperature molten salt. Patent Document 1 describes at least one compound selected from the group consisting of aluminum bispentafluoroethanesulfonimide, aluminumbistrifluoromethanesulfonimide, aluminumbisheptafluoropropanesulfonimide and aluminumbisnonafluorobutanesulfonimide. It has been proposed to use an electrolytic solution composed of a room temperature molten salt containing an amide (see JP-A-2017-168234).

On the other hand, the aqueous electrolyte of the aluminum cell, Patent Document 2, a sulfate ion (SO 4 ^_2-) and nitrate ion (NO 3 ^_-) at least one ion and halogen ion selected from the group consisting of electrolytic It has been proposed to use a liquid (see JP-A-2001-319662).

JP-A-2017-168234 Japanese Unexamined Patent Publication No. 2001-319662

The present inventors have studied an aluminum battery to which an aqueous electrolyte is applied because it can be manufactured at low cost without requiring a special manufacturing environment and is excellent in safety. In the aqueous electrolyte solution as shown in Patent Document 2, the degree of dissociation of the electrolyte salt is low, the ionic conductivity is not sufficient, and the overvoltage of the negative electrode containing aluminum may be large. Therefore, the present inventors presume that the aluminum salt having an imide anion is excellent in dissociation with water, select an aluminum salt having an imide anion as the electrolyte salt, prepare an aqueous electrolytic solution, and contain aluminum. The electrochemical behavior of the negative electrode was investigated. As a result, we recognized the problem that the overvoltage of the negative electrode containing aluminum is large.

In view of the above circumstances, an object of the present invention is to provide an aqueous electrolytic solution capable of suppressing an overvoltage of a negative electrode containing aluminum, an aluminum battery provided with the aqueous electrolytic solution, and a method for producing the aqueous electrolytic solution.

The aqueous electrolyte according to one aspect of the present invention is an aqueous electrolyte used in an aluminum battery including a negative electrode containing aluminum, and is a first compound represented by the following formula (1) and the following formula (2). Contains a second compound represented by.
_{Al [(C n F (2n} + 1) SO 2) 2 N] 3 ··· (1)
H (C _n F _{(2n + 1)} SO ₂ ) ₂ N ... (2)
In the above equations (1) and (2), n is an integer of 0 or more and 4 or less independently.

The aluminum battery according to another aspect of the present invention includes a negative electrode containing aluminum and the aqueous electrolyte solution.

The method for producing an aqueous electrolyte according to another aspect of the present invention is a method for producing an aqueous electrolyte used in an aluminum battery including a negative electrode containing aluminum, which is represented by an aqueous solvent and the following formula (1). The first compound to be prepared is mixed with the second compound represented by the following formula (2).
_{Al [(C n F (2n} + 1) SO 2) 2 N] 3 ··· (1)
H (C _n F _{(2n + 1)} SO ₂ ) ₂ N ... (2)
In the above equations (1) and (2), n is an integer of 0 or more and 4 or less independently.

According to the aqueous electrolytic solution according to one aspect of the present invention, the overvoltage of the negative electrode containing aluminum can be suppressed.

According to the aluminum battery according to another aspect of the present invention, it is possible to provide an aluminum battery in which the overvoltage of the negative electrode containing aluminum is suppressed.

According to the method for producing an aqueous electrolyte according to another aspect of the present invention, it is possible to produce an aqueous electrolyte in which the overvoltage of the aluminum battery can be suppressed.

FIG. 1 is a graph showing an example of an overvoltage measurement result in the aluminum battery of Example 1. FIG. 2 is a graph showing an example of an overvoltage measurement result in the aluminum battery of Comparative Example 1. FIG. 3 is an external perspective view showing an embodiment of an aluminum battery. FIG. 4 is a schematic view showing a power storage device configured by assembling a plurality of batteries according to an embodiment of the present invention.

First, an outline of a method for producing an aqueous electrolyte, an aluminum battery, and an aqueous electrolyte disclosed by the present specification will be described.

The aqueous electrolyte according to one aspect of the present invention is an aqueous electrolyte used in an aluminum battery including a negative electrode containing aluminum (Al), and is a first compound represented by the following formula (1) and the following formula. It contains the second compound represented by (2).
_{Al [(C n F (2n} + 1) SO 2) 2 N] 3 ··· (1)
H (C _n F _{(2n + 1)} SO ₂ ) ₂ N ... (2)
In the above equations (1) and (2), n is an integer of 0 or more and 4 or less independently.

The reason why the overvoltage of the negative electrode containing aluminum becomes large when the aqueous electrolytic solution is applied to the aluminum battery is that an aluminum oxide film is formed on the surface of the negative electrode, and the overvoltage becomes large due to the formation of this oxide film. It is inferred that.

The present inventors have found that when the second compound is added to the aqueous electrolytic solution, the overvoltage of the negative electrode containing aluminum is suppressed. The reason why the overvoltage can be suppressed in this way is not clear, but for example, when the aqueous electrolyte contains the first compound and the second compound, the oxide film on the surface of the negative electrode is removed, and as a result, the above It is presumed that the overvoltage is suppressed both during the dissolution reaction and the precipitation reaction of aluminum at the negative electrode.

As described above, according to the water-based electrolyte, the overvoltage of the negative electrode containing aluminum is suppressed by the water-based electrolyte containing the second compound in addition to the first compound, and thus the water-based electrolysis. The discharge performance of the aluminum battery provided with the liquid can be improved.

Here, the content of the second compound is preferably more than 1 mol / kg.

As described above, when the content of the second compound is more than 1 mol / kg, the overvoltage of the negative electrode containing aluminum can be suppressed more reliably.

The aluminum battery according to another aspect of the present invention includes a negative electrode containing aluminum and the aqueous electrolyte solution.

According to the aluminum battery, since the aluminum battery is provided with the aqueous electrolytic solution, the overvoltage of the negative electrode containing aluminum is suppressed, so that the discharge performance of the aluminum battery provided with the negative electrode containing aluminum is improved. Can be done.

The method for producing an aqueous electrolytic solution according to another aspect of the present invention is a method for producing the aqueous electrolytic solution, which comprises mixing an aqueous solvent, the first compound, and the second compound.

According to the method for producing the aqueous electrolytic solution, as described above, the aqueous electrolytic solution capable of suppressing the overvoltage of the negative electrode containing aluminum and improving the discharge performance of the aluminum battery provided with the negative electrode containing aluminum is produced. Can be done.

The configuration of the aqueous electrolyte solution, the method for producing the aqueous electrolyte solution, the configuration of the aluminum battery, the method for producing the aluminum battery, and other embodiments according to the embodiment of the present invention will be described in detail. The name of each component (each component) used in each embodiment may be different from the name of each component (each component) used in the background technology.

[Aqueous electrolyte]
The aqueous electrolytic solution contains a first compound represented by the following formula (1) and a second compound represented by the following formula (2).
_{Al [(C n F (2n} + 1) SO 2) 2 N] 3 ··· (1)
H (C _n F _{(2n + 1)} SO ₂ ) ₂ N ... (2)
In the above equations (1) and (2), n is an integer of 0 or more and 4 or less independently.
The aqueous electrolyte further contains water.

The aqueous electrolytic solution contains an aqueous solvent such as water and the first compound and the second compound mixed in the aqueous solvent. The aqueous solvent means water or a mixed solvent containing water as a main component. Examples of the solvent other than water constituting the mixed solvent include organic solvents (lower alcohols, lower ketones, etc.) that can be uniformly mixed with water. The upper limit of the content of water in the aqueous solvent is 100% by mass. The lower limit of the water content is preferably 80% by mass or more, more preferably 90% by mass or more, further preferably 95% by mass or more, and particularly preferably 99% by mass or more.

<First compound>
The first compound is represented by the above formula (1). Specifically, the first compound is
1-1 compound (n = 0, aluminum bis (fluorosulfone) imide) represented by the following formula (1-1),
The first and second compounds represented by the following formula (1-2) (n = 1, aluminum bis (trifluoromethanesulfon) imide; hereinafter also referred to as _{"Al (TFSI) 3"),}
The 1-3 compound (n = 2, aluminum bis (pentafluoroethane sulfone) imide) represented by the following formula (1-3),
The 1-4 compound (n = 3, aluminum bis (heptafluoropropanesulfone) imide) represented by the following formula (1-4),
The 1st-5th compound represented by the following formula (1-5) (n = 4, aluminum bis (nonafluorobutane sulfone) imide)
Can be mentioned.
Al [(FSO ₂ ) ₂ N] ₃ ... (1-1)
Al [(CF ₃ SO ₂ ) ₂ N] ₃ ... (1-2)
Al [(CF ₃ CF ₂ SO ₂ ) ₂ N] ₃ ... (1-3)
Al [(CF ₃ CF ₂ CF ₂ SO ₂ ) ₂ N] ₃ ... (1-4)
Al [(CF ₃ CF ₂ CF ₂ CF ₂ SO ₂ ) ₂ N] ₃ ... (1-5)

Of these, as the first compound, the above-mentioned 1-2 compound (Al (TFSI) ₃ ) is preferable.

The content of the first compound in the aqueous electrolytic solution is not particularly limited and may be appropriately set. For example, as the lower limit of the content of the first compound in 1 kg of the aqueous electrolytic solution, 1 mol / kg is preferable, and 2 mol / kg is more preferable. When the content is at least the above lower limit, an aluminum battery using the aqueous electrolyte can exhibit sufficient battery performance. On the other hand, the upper limit is not particularly limited, but is preferably 5 mol / kg, and more preferably 4 mol / kg. When the content is not more than the above upper limit, there is an advantage that the viscosity of the electrolytic solution can be lowered and the electrolytic solution having a small solution resistance can be obtained.

<Second compound>
The second compound is represented by the above formula (2). Specifically, the second compound is
2-1 compound (n = 0, bis (fluorosulfone) imide) represented by the following formula (2-1),
2-2 compound represented by the following formula (2-2) (n = 1, bis (trifluoromethanesulfon) imide; hereinafter also referred to as "HTFSI"),
No. 2-3 compound (n = 2, bis (pentafluoroethane sulfone) imide) represented by the following formula (2-3),
The 2nd-4th compound (n = 3, bis (heptafluoropropanesulfone) imide) represented by the following formula (2-4),
The 2-5th compound represented by the following formula (2-5) (n = 4, bis (nonafluorobutane sulfone) imide)
Can be mentioned.
H (FSO ₂ ) ₂ N ... (2-1)
H (CF ₃ SO ₂ ) ₂ N ... (2-2)
H (CF ₃ CF ₂ SO ₂ ) ₂ N ... (2-3)
H (CF ₃ CF ₂ CF ₂ SO ₂ ) ₂ N ... (2-4)
H (CF ₃ CF ₂ CF ₂ CF ₂ SO ₂ ) ₂ N ... (2-5)

Of these, as the second compound, the above-mentioned 2-2 compound (HTFSI) is preferable.

The content of the second compound in the aqueous electrolytic solution is not particularly limited and can be appropriately set. For example, the lower limit of the content of the second compound in 1 kg of the aqueous electrolytic solution is preferably more than 1 mol / kg, more preferably 2 mol / kg. When the content is at least the above lower limit, the overvoltage of the negative electrode containing aluminum can be further suppressed. On the other hand, the upper limit is not particularly limited, but is preferably 5 mol / kg, and more preferably 4 mol / kg. When the content is not more than the above upper limit, there is an advantage that an excessive decrease in pH of the aqueous electrolytic solution is suppressed, and thus excessive corrosion of aluminum is suppressed.

(Measurement of HTFSI concentration)
^{The 1} H-NMR method is used for measuring the HTFSI concentration in the aqueous electrolyte solution of the present embodiment. Evaporated water of the aqueous electrolyte solution to be measured is dissolved in a heavy solvent, and a reference substance having a specific concentration is added ^{to perform 1} H-NMR measurement. The HTFSI proton signal is detected at the singlet. Therefore, the concentration of HTFSI is quantified by the area ratio of the signal of HTFSI and the signal of the reference substance. The deuterated solvent is deuterated dimethyl sulfoxide. The reference substance is 1,1,2,2-tetrachlorethylene.

When measuring the aluminum concentration and TFSI concentration by ICP in addition to the measurement of HTFSI concentration by ^{the above 1} H-NMR method for each aqueous electrolytic solution, the above ICP is obtained from the above HTFSI concentration measured by the ^{above 1 H-NMR method.} The value obtained by subtracting the TFSI concentration measured by is consistent with the aluminum concentration measured by the ICP.

The lower limit of the pH of the aqueous electrolytic solution is preferably 1. On the other hand, as the upper limit of the pH of the aqueous electrolytic solution, 5 is preferable, and 4 is more preferable. When the upper limit of the pH is in the above range, the overvoltage of the negative electrode containing aluminum is appropriately suppressed.

The aqueous electrolytic solution may contain components other than the aqueous solvent, the first compound and the second compound as long as the effects of the present invention are not impaired. Examples of the other components include various additives contained in an aqueous electrolyte solution of a general aluminum battery. However, the content of these other components may be preferably 5% by mass or less, and more preferably 1% by mass or less.

[Manufacturing method of aqueous electrolyte]
The method for producing the aqueous electrolytic solution is not particularly limited, and known methods can be combined. For example, the method for producing the aqueous electrolyte solution comprises mixing the aqueous solvent, the first compound, and the second compound. Specifically, for example, the aqueous electrolytic solution can be obtained by adding the first compound, the second compound and the like to the aqueous solvent and mixing them.

[Aluminum battery configuration]
The aluminum battery according to the embodiment of the present invention includes a negative electrode containing aluminum and the above-mentioned aqueous electrolyte solution. The aluminum battery further includes a positive electrode. The positive electrode and the negative electrode usually form an electrode body laminated or wound via a separator. The electrode body is housed in a container, and the aqueous electrolytic solution is filled in the container. The aqueous electrolyte is interposed between the positive electrode and the negative electrode. Examples of the aluminum battery include a primary battery and a secondary battery.

<Negative electrode>
The negative electrode contains alnium. The negative electrode contains a negative electrode active material capable of releasing metal ions, and this negative electrode active material contains aluminum. The negative electrode active material may contain an aluminum atom. That is, the negative electrode active material contains aluminum (elemental substance) or an aluminum alloy as a metal, or an aluminum compound as a metal compound.

Examples of the metal element forming an alloy with the aluminum include Zn, In, Bi, Sn, Si, Ga and the like, and the metal element may be one or more.

For example, an Al—Sn alloy having a Sn content of 0.5% by mass or more and 5.0% by mass or less, an Al—In alloy having an In content of 0.5% by mass or more and 5.0% by mass or less, and the like can be mentioned. Can be done.

<Aqueous electrolyte>
As the aqueous electrolyte, the above-mentioned aqueous electrolyte is used.

<Positive electrode>
The positive electrode has a positive electrode active material layer containing a positive electrode active material. Further, the positive electrode may have a positive electrode base material.

(Positive electrode active material layer)
Examples of the positive electrode active material contained in the positive electrode active material layer include transition metal oxides and sulfur. Examples of the transition metal oxide include manganese dioxide, lead dioxide, silver oxide, iron oxide, molybdenum oxide and the like.

The positive electrode active material layer contains a conductive auxiliary agent, a binder (binding agent) and the like as arbitrary components.

Examples of the conductive auxiliary agent include natural or artificial graphite, carbon black such as furnace black, acetylene black and ketjen black, activated carbon, metal, metal oxide, conductive ceramics and the like. The content of the conductive agent in the positive electrode active material layer is preferably in the range of 1% by mass or more and 20% by mass or less. By setting the content of the conductive agent in the above range, the electron conductivity in the positive electrode mixture layer can be sufficiently enhanced, and the positive electrode reaction can be made sufficient.

Examples of the binder include fluororesins (polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), etc.), thermoplastic resins such as polyethylene, polypropylene, polyimide, and polyacrylic acid; ethylene-propylene-diene rubber (EPDM), sulfonated. Elastomers such as EPDM and fluororubber; thermoplastic polymers and the like can be mentioned.

(Positive electrode base material)
The positive electrode base material is a base material having conductivity. Examples of the material of the positive electrode base material include metals such as nickel, stainless steel, molybdenum, and titanium, alloys thereof, carbon materials, titanium nitride, and the like.

<Separator>
A separator that prevents the movement of electrons between the positive electrode and the negative electrode can be arranged between the positive electrode and the negative electrode. As the material of the separator, for example, a woven fabric, a non-woven fabric, a porous resin film or the like is used. Among these, a porous resin film is preferable. As the main component of the porous resin film, polyolefins such as polyethylene and polypropylene are preferable from the viewpoint of strength. Further, a porous resin film obtained by combining these resins with a resin such as aramid or polyimide may be used.

<Specific configuration of aluminum battery>
The shape of the aluminum battery of the present embodiment is not particularly limited, and examples thereof include a cylindrical battery, a laminated film type battery, a square type battery, a flat type battery, a coin type battery, and a button type battery.
FIG. 3 shows an aluminum battery 1 as an example of a square battery. The figure is a perspective view of the inside of the case. The electrode body 2 having the positive electrode and the negative electrode wound around the separator is housed in the square case (container) 3. The positive electrode is electrically connected to the positive electrode terminal 4 via the positive electrode lead 41. The negative electrode is electrically connected to the negative electrode terminal 5 via the negative electrode lead 51.

The present invention can also be realized as a power storage device including a plurality of the above batteries. An embodiment of the power storage device is shown in FIG. In FIG. 4, the power storage device 30 includes a plurality of power storage units 20. Each power storage unit 20 includes a plurality of batteries 1.

<Manufacturing method of aluminum battery>
The method for producing the aluminum battery is not particularly limited, and known methods can be combined. For example, producing a negative electrode and a positive electrode, accommodating a pair of these electrodes (negative electrode and positive electrode) in a battery container, injecting an aqueous electrolytic solution into the battery container, sealing the injection port after the injection, etc. Allows you to obtain an aluminum battery. As the negative electrode, for example, a plate-like body made of an aluminum alloy may be produced. Further, the positive electrode may be produced, for example, by laminating a positive electrode active material layer on at least one surface side of the positive electrode base material. The lamination of the active material layer can be performed by a known method.

<Other Embodiments>
The aqueous electrolyte and the aluminum battery of the present invention are not limited to the above embodiments, and various modifications may be made without departing from the gist of the present invention. For example, the configuration of one embodiment can be added to the configuration of another embodiment, and a part of the configuration of one embodiment can be replaced with the configuration of another embodiment or a well-known technique. In addition, some of the configurations of certain embodiments can be deleted. Further, a well-known technique can be added to the configuration of a certain embodiment.

Hereinafter, the present invention will be described in more detail with reference to Examples. The present invention is not limited to the following examples.

(Preparation of aqueous electrolyte)
The aqueous electrolytes of Comparative Examples 1 and 2 and Examples 1 and 2 were prepared by mixing _{Al (TFSI) 3} and HTFSI with water at the composition ratios shown in Table 1 below. The pH and HTFSI concentration of each of the obtained aqueous electrolytes were measured by the following measuring methods.

(Measurement of pH)
The pH of each aqueous electrolyte was measured using a compact pH meter (LAQUAtwin, manufactured by HORIBA, Ltd.).

(Measurement of HTFSI concentration)
The concentration of HTFSI was quantified by the ^{above 1 H-NMR method.} It was speculated that this quantification would measure the concentration of undissociated HTFSI.

(Preparation of evaluation cell)
Under the following conditions, a pouch cell for overvoltage evaluation was prepared using each aqueous electrolyte.
-Positive electrode: Al foil (thickness: 20 μm, area: 3 x 4 cm ² )
-Negative electrode: Al foil (thickness: 20 μm, area: 3 x 4 cm ² )
・ Lead of each electrode: Nickel ・ Amount of aqueous electrolyte: 0.5mL
・ Separator: Non-woven fabric ・ Torque when the compression jig is attached: 15cN ・ m

(Measurement of overvoltage)
Each pouch cell was placed in a constant temperature bath at 25 ° C., and the overvoltage was measured. Specifically, a constant current was repeatedly applied to the pouch cell placed in the constant temperature bath for a certain period of time while reversing the direction of current flow under the measurement conditions shown below, and the voltage change at that time was observed. .. Among the observation results, the results of Example 1 and Comparative Example 1 are shown in FIGS. 1 and 2. Then, in the 20th cycle, the average value of the polarization value at the time of oxidation and the polarization value at the time of reduction was defined as an overvoltage (V) with 0V as a reference. The results are shown in Table 1.
-Measurement conditions Current value: 10 μAcm- ² (actual current value: 120 μA)
Current application time: Oxidation: 1 hour, Reduction: 1 hour, Pause: 5 minutes each

As shown in Table 1, it was shown _{that the inclusion of Al (TFSI) 3} and HTFSI in the aqueous electrolyte suppresses the overvoltage of the negative electrode containing aluminum. That is, it was shown that the aqueous electrolytic solution containing the first compound and the second compound can suppress the overvoltage of the negative electrode containing aluminum. Further, as can be seen from FIGS. 1 and 2, by applying the aqueous electrolyte solution according to one aspect of the present invention, both the overvoltage associated with the aluminum dissolution reaction and the overvoltage associated with the aluminum precipitation reaction are suppressed. Rukoto has been shown. Therefore, the present invention can be applied to an aluminum primary battery and an aluminum secondary battery.

1 Aluminum battery 2 Electrode body 3 Case 4 Positive terminal 41 Positive lead 5 Negative terminal 51 Negative lead 20 Power storage unit 30 Power storage device

Claims (4)

An aqueous electrolyte used in an aluminum battery having a negative electrode containing aluminum.
The first compound represented by the following formula (1) and
An aqueous electrolytic solution containing the second compound represented by the following formula (2).
_{Al [(C n F (2n} + 1) SO 2) 2 N] 3 ··· (1)
H (C _n F _{(2n + 1)} SO ₂ ) ₂ N ... (2)
In the above equations (1) and (2), n is an integer of 0 or more and 4 or less independently. The aqueous electrolytic solution according to claim 1, wherein the content of the second compound is more than 1 mol / kg. A negative electrode containing aluminum and
An aluminum battery comprising the aqueous electrolyte according to claim 1 or 2. A method for producing an aqueous electrolyte used in an aluminum battery having a negative electrode containing aluminum.
A method for producing an aqueous electrolytic solution, which comprises mixing an aqueous solvent, a first compound represented by the following formula (1), and a second compound represented by the following formula (2).
_{Al [(C n F (2n} + 1) SO 2) 2 N] 3 ··· (1)
H (C _n F _{(2n + 1)} SO ₂ ) ₂ N ... (2)
In the above equations (1) and (2), n is an integer of 0 or more and 4 or less independently.

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