JP2853262B2 - Bromine complexing agent for metal-bromine batteries - Google Patents

Description

The present invention relates to a bromine complexing agent for a metal-bromine battery, and more particularly to a bromine complexing agent for a metal-bromine battery having high electric energy efficiency.

B. Summary of the Invention The present invention relates to a bromine complexing agent for a metal-bromine battery, wherein the molar ratio of the halogenated N-methyl N-ethylmorpholinium salt to the halogenated N-methyl N-ethylpyrrolidinium salt is 0.25. : 0.75 to 0.0: 1.0, thereby improving the electric energy efficiency of the metal-bromine battery.

C. Prior Art In recent years, the development of battery power storage systems has been promoted, and as part of this, zinc-bromine batteries have been developed.

This battery is a compact liquid circulation type laminated battery in which an aqueous solution of zinc bromide is used as an electrolyte and a carbon plastic sheet is used as a bipolar electrode plate. When charging, use the negative electrode
Zn ²⁺ + 2e ^- → zinc on the negative electrode plate by the reaction of Zn (1) is deposited, a positive electrode ^{2Br - + Q + · Br -} → Q + · Br 3 - + 2e - If bromine is generated by the reaction of (2) Simultaneously, bromine complex (Q ⁺ B
r ^-) combine with bromine complex compound (Q ⁺ · Br ₃ ^-) to generate.
The bromine complex compound is an oily substance and separates from the electrolyte and precipitates at the bottom of the positive electrode tank.

On the other hand, at the time of discharging, zinc is oxidized by the reverse reaction of the above (1) at the negative electrode to become zinc ions and dissolved in the electrolytic solution, and at the positive electrode, the bromine complex compound is converted into a bromine ion and a bromine complex by the reverse reaction of the above (2). Separation into compounds.

In this way, a bromine-zinc battery can emit high electrical energy through the binding and dissociation of bromine by the bromine complexing agent on each electrode.

Accordingly, the bromine complexing agent forms a bromine complex compound during charging and plays a role in dissociating bromine during discharging, which has a significant effect on the energy efficiency of the bromine-zinc battery.

Therefore, the present inventors have proposed that N-methyl N
-Ethyl morpholinium bromide (hereinafter referred to as MEMB) and N-methyl N-ethylpyrrolidinium bromide (hereinafter referred to as MEPB) in an amount of 1 mol / with respect to an aqueous zinc bromide solution of 3 mol / or less, and further containing chlorine. By adding 1 mol / of a degree improver, the ability to form a bromine complex compound is strengthened, thereby preventing self-discharge due to the diffusion of bromine and reducing the electric resistance of the electrolytic solution.
We succeeded in improving the energy efficiency of zinc batteries.

D. Problems to be Solved by the Invention However, the present inventors used MMB and MEPB as a bromine complexing agent at a concentration of 1 mol /, but later studies showed that even higher molar ratios between MMB and MEPB were used. It has been found that energy efficiency can be obtained.

Therefore, the present invention was devised to solve this problem, and the molar ratio of MEMB to MEPB was 0.25: 0.75 as a bromine complexing agent.
An object of the present invention is to provide a bromine complexing agent for a metal-bromine battery in which the energy efficiency is further enhanced by setting the ratio to 0.0: 1.0.

E. Means and Actions for Solving the Problems The present inventors have found that a metal-bromine battery has a metal complex by adding a bromine complexing agent in a molar ratio of MEMB and MEPB of 0.25: 0.75 to 0.0: 1.0. -Successfully improved the energy efficiency of the bromine battery, and completed the bromine complexing agent for the metal-bromine battery according to the present invention.

That is, the bromine complexing agent of the metal-bromine battery according to the present invention is:
The solution is to set the molar ratio between the halogenated N-methyl N-ethylmorpholinium salt and the halogenated N-methyl N-ethylpyrrolidinium salt to be 0.25: 0.75 to 0.0: 1.0.

 Hereinafter, the present invention will be described in more detail.

First, the bromine complexing agent which is the most characteristic in the electrolytic solution of the metal-bromine battery according to the present invention will be described.

The bromine complexing agent combines with bromine ions on the positive electrode side during charging to form a bromine complex compound, and plays an important role of retaining electric energy.

In the present invention, as a bromine complexing agent, a halogenated N-methyl N-ethylmorpholinium salt, preferably MEMB and a halogenated N-methyl N-ethylpyrrolidinium salt, preferably MEPB are each 0.25: 0.75 to 0.0: Use as a range of 1.0. The sum of the molar concentrations of both is 0.75 to 1 mol /
, Preferably 1 mol /. Here, the reason why the content is set to “0.75 mol / or more” is that if the content is less than 0.75 mol / min, the ability to form a bromine complex compound decreases, and self-discharge occurs due to free bromine ions. On the other hand, the reason why it is set to “1 mol / or less” is that if it exceeds this, the internal resistance of the electrolytic solution increases and the energy efficiency decreases.

It should be noted that the internal resistance of the electrolytic solution can be reduced by adding a conductivity improver as described above. Considering these factors comprehensively, the concentration of the bromine complexing agent is set to 1 mol /, which is the maximum acceptable internal resistance of the electrolyte, and the total amount of bromine ions is reduced as much as possible. It can be said that energy efficiency can be improved. This is the central problem to be achieved by the present invention, and this problem can be achieved by setting the molar ratio of the bromine complexing agent, MEMB and MEPB, to the range of 0.25: 0.75 to 0.0: 1.0. .

Next, the structural formulas of the bromine complexing agents MEMB and MEPB used in the present invention and the reaction formulas of the bromine complexing agent and bromine are shown.

In addition, as a metal-bromine battery in which the bromine complexing agent according to the present invention can be preferably used, a cadmium-bromine battery, a nickel-bromine battery and the like can be mentioned in addition to a zinc-bromine battery.

F. Examples Hereinafter, a detailed description of the bromine complexing agent of the metal-bromine battery according to the present invention will be described based on examples.

Example 1 Bromine concentration of supernatant of 3 mol of zinc bromide / aqueous solution (1) MEMB and MEPB were used as bromine complexing agents in a 3 mol / aqueous solution of zinc bromide containing 3 ml of bromine at 1.0: 00 and 0.75: 0, respectively.
25,0.5: 0.5,0.25: 0.75,0.0: 1.0
The bromine concentration (mol /) of the supernatant at 22 ° C, 40 ° C and 50 ° C was measured.

(2) The results are shown in Table 1. As shown in Table 1, it can be seen that the bromine concentration in the supernatant of the aqueous zinc bromide solution can be further reduced by adding MEMB and MEPB as the bromine complexing agent in a molar ratio of 0.25: 0.75 to 0.0: 1.0. This indicates that the higher the mole fraction of MEPB as the bromine complexing agent, the higher the ability to form a bromine complex compound.

Example 2 Zinc bromide 1 mol / aqueous solution supernatant bromine concentration (1) Zinc bromide 1 mol / water instead of zinc bromide 3 mol / water solution
Supernatant bromine concentration (mol /) was measured in the same manner as in Example 1 except that an aqueous solution was used.

(2) The results are shown in Table 2. As shown in Table 2, it can be seen that the bromine concentration can be reduced by adding MEMB and MEPB as the bromine complexing agent in a molar ratio of 0.25: 0.75 to 0.1: 1.0. This is the same as the result shown in the first embodiment.

Example 3 Supernatant bromine concentration of 1 mol of zinc bromide / aqueous solution (1) Supernatant bromine concentration (mol /) was measured in the same manner as in Example 2 except that bromine addition amount of 20 ml was used instead of bromine addition amount of 3 ml. did.

(2) The results are shown in Table 3. As shown in Table 3, it is found that the bromine concentration can be reduced by adding MEMB and MEPB as the bromine complexing agent in a molar ratio of 0.25: 0.75 to 0.0: 1.0. This is the same as the results shown in Examples 1 and 2.

Example 4 1 mol / mol of zinc bromide / mol ratio of MEPB in bromine complexing agent (MEMB, MEPB mixture) in aqueous solution (%)
And the supernatant bromine concentration (1) 1 mol / mol of bromine complexing agent (MEMB / MEPB mixture) in 1 mol / mol of zinc bromide containing 0.3 mol / of bromine, and 0,25%, 50%, The bromine concentration of the supernatant liquid at a liquid temperature of 22 ° C, 40 ° C, and 50 ° C was added at a molar fraction of 75% and 100% (mol /).
Was measured.

(2) The results are shown in FIG. As shown in FIG. 1, it can be seen that the bromine concentration in the zinc bromide aqueous solution decreases as the mole fraction of MEPB as the bromine complexing agent increases. This indicates that the higher the mole fraction of MEPB as the bromine complexing agent, the higher the ability to form a bromine complex compound.

Example 5 3 mol of zinc bromide / mol of MEPB in 1 mol / bromine complexing agent (MEMB, MEPB mixture) in aqueous solution (%)
Relationship between the concentration of bromine and the supernatant liquid (1) Zinc bromide 3 mol /
Supernatant bromine concentration (mol /) was measured in the same manner as in Example 4 except that an aqueous solution was used.

(2) The results are shown in FIG. As shown in FIG. 2, almost the same as FIG. 1, the higher the mole fraction of MEPB as the bromine complexing agent, the higher the ability to form a bromine complex compound.

Example 6 1 mol / mol mol of zinc bromide / MEPB in bromine complexing agent (mixture of MEMB and MEPB) (%) in aqueous solution
(1) The bromine concentration (mol /) in the supernatant was measured in the same manner as in Example 4 except that the bromine concentration was 2.0 mol / instead of 0.3 mol /.

(2) The results are shown in FIG. As shown in FIG. 3, almost the same as FIGS. 1 and 2, it can be seen that the higher the molar fraction of MEPB as the bromine complexing agent, the higher the ability to form a bromine complex compound.

Example 7 Test results when the bromine complexing agent according to the present invention was used in a zinc-bromine battery (1) 2.25 mol of zinc bromine / aqueous solution, 0.4 mol of zinc chloride /
, Ammonium chloride 1.0 mol /, and bromine complexing agent 1 mol /
In the electrolytic solution composition, ME was used as the bromine complexing agent.
MB and MEPB were added at a molar ratio of 0.25: 0.75 and 0.0: 1.0, respectively, and an operation test of a zinc-bromine battery in which five cells were stacked with an electrode area of 830 cm ² was performed.

(2) MEMB and MEPB as bromine complexing agents are each 0.5:
A comparative example was obtained by performing an operation test of a zinc-bromine battery in the same manner as in Example 7 except that the addition was performed at a molar ratio of 0.5.

(3) Table 4 shows the test results of (1) and (2). Table 4
As shown in Example 7, as the bromine complexing agent shown in Example 7 (1)
MEMB and MEPB were added at a molar ratio of 0.25: 0.75 and 0.0: 1.0, respectively, to obtain ME as a bromine complexing agent shown in Comparative Example (2).
It can be seen that the coulomb efficiency, voltage efficiency and energy efficiency are superior to those in which MB and MEPB are added in a molar ratio of 0.5: 0.5.

Composition of electrolytic solution ZnBr ₂ 2.25 mol / ZnCl ₂ 0.45 mol / NH ₄ Cl 1.0 mol / bromine complexing agent 1.0 mol / G. Effect of the Invention Since the present invention is constituted as described above, formation of a bromine complex compound Capacity can be increased, thereby reducing free bromine ions in the electrolyte.

Therefore, according to the bromine complexing agent of the zinc-bromine battery according to the present invention, self-discharge due to the presence of free bromine ions can be reduced, and thus the coulomb efficiency, voltage efficiency and energy efficiency of the zinc-bromine battery can be improved. .

[Brief description of the drawings]

1 to 3 are graphs showing the relationship between the mole fraction of MEPB in the bromine complexing agent and the bromine concentration in the supernatant.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H01M 12/08

Claims (1)

(57) [Claims] A metal characterized in that the molar ratio of halogenated N-methyl N-ethylmorpholinium salt to halogenated N-methyl N-ethylpyrrolidinium salt is 0.25: 0.75 to 0.0: 1.0. A bromine complexing agent for bromine batteries.