JPH0417274A - Electrolyte of metal-bromine battery - Google Patents

Abstract

PURPOSE:To heighten electric energy efficiency of a metal-bromine battery by adding a conductivity improving agent containing chlorine ion and a bromine complexing agent of N-methyl-N-ethylmorpholinium halide salt and N-methyl-N- ethylpyrrolidinium halide salt in a specified mole ratio to an electrolyte. CONSTITUTION:An aqueous zinc bromide solution in 3 mol/l concentration, a conductivity improving agent having chlorine ion, and a bromine complexing agent of N-methyl-N-ethylmorpholinium halide salt and N-methyl-N- ethylpyrrolidinium in mole ratio within (0.25 : 0.75) to (0.0 : l.0) are contained in an electrolyte. As a result, ability to form a bromine complex compound is heightened and free bromine ion in the electrolyte is decreased. Consequently, self-discharge due to the existance of free bromine ion is decreased and Coulomb efficiency of a zinc-bromine battery and voltage efficiency and energy efficiency are improved.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to an electrolyte for metal-bromine batteries, and more particularly to an electrolyte for metal-bromine batteries with high electrical energy efficiency.

B1 Summary of the Invention The present invention provides a conductivity modifier having chlorine ions and a halogenated N-methyl N-
The molar ratio of ethylmorpholinium salt to halogenated N-methyl N-ethylpyrrolinonium salt is 0.25:0.
By adding a bromine complexing agent of 75-00.1.0, the electrician's energy efficiency in metal-bromine batteries is increased.

C0 Conventional Technology In recent years, the development of battery power storage systems has been promoted.
Zinc-bromine batteries have been developed as part of this cycle.

This battery is a compact liquid circulation type stacked battery that uses a bromine zinc aqueous solution as the electrolyte and carbon plastic sheets as bipolar electrode plates. Z at the negative electrode during charging
Due to the reaction of n''+2e--Zn (1), zinc is precipitated on the negative electrode plate, and 2Br-+Q''・Br--''Q''・
Bromine is generated by the reaction of Br3-+2e-(2) and simultaneously combines with the bromine complex (Q".Br-) to produce a bromine complex (Q"Br*-). This bromine complex compound is separated from the electrolyte as an oily substance and precipitates at the bottom of the positive electrode tank.

On the other hand, during discharging, zinc is oxidized at the negative electrode through the reverse reaction of (1) above, becoming zinc ions and dissolved in the electrolyte, and at the positive electrode, the reverse reaction of (2) above converts bromine complex compounds into bromine ions and bromine complexes. Separate into chemical substances.

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

Therefore, the bromine complexing agent plays the role of forming a bromine complex compound during charging and dissociating bromine during discharging, and has a significant influence on the energy efficiency of the bromine-zinc secondary battery.

Therefore, the present inventors used N-methyl N- as a bromine complexing agent.
Ethylmorpholinium bromide (hereinafter referred to as MEMB) and N-methyl N-ethylpyrrolinium bromide (hereinafter referred to as MEPB) to a zinc bromide aqueous solution of 3 mo12/I or less. By using /& and further adding 1 mo&/a of a conductivity modifier having chlorine, the ability to form a bromine complex compound is strengthened, thereby preventing self-discharge due to bromine diffusion and reducing the electrical resistance of the electrolytic solution. Overall, we succeeded in increasing the energy efficiency of the bromine-zinc secondary battery.

D8 Problems to be Solved by the Invention However, the present inventors used MEMB as a bromine complexing agent.
and MEPB were used at a concentration of Imoff/ff, but subsequent research revealed that even higher energy efficiency could be obtained depending on the molar ratio of MEMB and MEPB.

Therefore, the present invention was devised to solve this problem, and the molar ratio of MEMB and MEPB as a bromine complexing agent is set to 0.
25:0.75-0. The purpose of the present invention is to provide an electrolytic solution for a metal-bromine battery that further improves energy efficiency by increasing the energy efficiency to 21.0.

81 Means and Effects for Solving the Problems The present inventors added a bromine complexing agent to the electrolyte solution of a metal-bromine battery at a molar ratio of M, EMB to 4EPB of 0.25:0.75 to 0.75. 0:
We succeeded in further increasing the energy efficiency of the metal-bromine battery by adding 1.0% of the electrolyte, and completed the electrolyte solution for the metal-bromine battery according to the present invention.

That is, the electrolyte solution of the metal-bromine battery according to the present invention is 3 mo
f! /& The following zinc bromide aqueous solution, conductivity modifier having chlorine ions, and molar ratio of halogenated N-methyl N-ethylmorpholinium salt to halogenated N-methyl N-ethylpyrrolidinium salt is 0 .25: 0.75-0.
The solution is to include a bromine complexing agent with a ratio of 0:1.0.

The present invention will be explained in more detail below.

First, as the electrolyte for the metal-bromine battery according to the present invention, 3
Use a zinc bromide aqueous solution of mo(/Q or less).

The reason why the concentration of zinc bromide is set at 73moρ/a or less is that if the concentration of zinc bromide exceeds 3mo(1/(l), the internal resistance of the electrolytic solution increases, resulting in a decrease in energy efficiency.

Further, the conductivity improving agent having chlorine ions according to the present invention includes, for example, potassium chloride (hereinafter referred to as KCg), ammonium chloride (hereinafter referred to as NH2O), and the concentration of chlorine ions is 0.5tnoQ/( ! ~ 4 m
off/(l range, preferably 1mo(1!/C).

The reason why rO,5mo(1/(1 or more)) is set here is that when the chlorine ion is less than 0,5moQ/(!), the liquid resistance of the electrolytic solution becomes high and the energy efficiency decreases.

On the other hand, the reason for setting r 4 moI2/(l or less) is that if chlorine ions exceed 4 mo(1/(l), hydrogen will be generated on the negative electrode side during so-called floating charging, and the energy utilization rate will drop to 50%. Therefore, it can be said that in the electrolyte solution of the metal bromine battery according to the present invention, it is preferable to use a conductivity modifier having a chlorine ion at a concentration of Imo12/12 as a point of balance.

Although not particularly required in the electrolyte solution of the metal-bromine battery according to the present invention, a zinc compound such as ZnC(!2.ZnF2) may be added as a hydrogen generation inhibitor on the negative electrode side. As a result, generation of hydrogen on the negative electrode side during floating charging can be suitably prevented, and the energy utilization rate can be further increased.

Next, the bromine complexing agent that is most characteristic in the electrolyte solution of the metal-bromine battery according to the present invention will be explained.

This bromine complexing agent plays an important role in binding with bromine ions on the positive electrode side during charging, forming a bromine complex, and retaining electrical energy.

In the present invention, the bromine complexing agent is a halogenated N-methyl N-ethylmorpholinium salt, preferably MEMB and a halogenated N-methyl N-ethylpyrrolinonium salt,
Preferably MEPB is 0.25:0.75-0, respectively.
．． Used as a range of 0.1.0. In addition, the sum of the molar concentrations of both is 075 to I moQ/Q, preferably 1
moc/12.

The reason why r 0 is set to 75 moQ/Q or more is because if it is less than this, the ability to form a bromine complex compound decreases, and self-discharge due to free bromine ions occurs. On the other hand, the reason why it is set as "r1moρ/a or less" is because if it exceeds this, the internal resistance of the electrolytic solution increases and the energy efficiency decreases.

Note that the internal resistance of the electrolytic solution can be reduced by adding a conductivity modifier as described above. Considering these things comprehensively, the concentration of the bromine complexing agent is set to r1moρz'l, which is the maximum that allows the internal resistance of the electrolyte, and the presence of free bromine ions is reduced as much as possible, so that the overall It can be said that energy efficiency can be improved. This is the central problem that the present invention aims to achieve, and this problem is achieved by adjusting the molar ratio of the bromine complexing agent MEMB and MEPB to 0.25.0.75 to 0.01.
This can be achieved by setting the range to 0.

Next, MEMB, which is a bromine complexing agent used in the present invention,
The structural formula of MEPB and the reaction formula between this bromine complexing agent and bromine are shown.

MEPB MEMB (N-Methyl
N-methyl N-ethylmorpholinium aphyto) M,
W 194.19 M, W, 210.19 QBr+nBr2: Q (Bra) nBr (Q: bromine complexing agent) (however, n = 1 to 4) Note that metals for which the electrolytic solution according to the present invention can be suitably used - Zinc for bromine batteries
In addition to bromine batteries, examples include cadmium-bromine batteries and nickel-bromine batteries.

F. Examples Hereinafter, a detailed explanation of the electrolyte solution of the metal-bromine battery according to the present invention will be explained based on Reference Examples and Examples.

Reference Example 1 Bromine concentration in supernatant liquid of zinc bromide 3moC/12 aqueous solution (1) Zinc bromide 3mof2/ρ containing bromine addition amount 31
MEMB and MEPB were added as bromine complexing agents in the aqueous solution at 1.0:00 0.75:0.25 0.5 and 0.0, respectively.
5,0.25: 0.75,0.0: 1.0
The bromine concentration (mol2/σ) of the supernatant liquid was measured at liquid temperatures of 22°C, 340°C, and 50°C.

(2) The results are shown in Table 1. As shown in Table 1, MEMB and MEPB were used as bromine complexing agents in the range of 0.250.75 to 0.025.
It can be seen that by adding at a molar ratio of 0:1.0, the bromine concentration in the supernatant liquid of the zinc bromide aqueous solution can be further reduced. This indicates that the higher the molar fraction of MEPB as a bromine complexing agent, the higher the ability to form a bromine complex compound.

Table 1: Supernatant solution of zinc bromide amo&/Q aqueous solution Bromine concentration: 075 to 0.0: It can be seen that the bromine concentration can be reduced by adding at a molar ratio of 0.0:1.0. Note that this is similar to the result shown in Reference Example 1.

Table 2: Amount of bromine added in the supernatant liquid of zinc bromide 1 mo ρ/ρ aqueous solution 3 ts Reference example 2 Bromine concentration in the supernatant liquid of zinc bromide 1 mo Q/Q aqueous solution (1) Odor added in place of zinc bromide 3 mo ρ/ρ aqueous solution Zinc chloride 1
The supernatant bromine concentration (mo(/C)) was measured in the same manner as in Reference Example I except that mo12/(!Aqueous solution was used.

(2) The results are shown in Table 2. As shown in Table 2, MEMB and MEPB were used as bromine complexing agents in an amount of 0.25 bromine added.
3 m (1 Reference Example 3 Bromine concentration in supernatant liquid of zinc bromide 1mof7/ρ aqueous solution (1) Added amount of bromine 20 * (!
The supernatant liquid bromine concentration (mo(10) was measured in the same manner as in Reference Example 2 except that bromine concentration (mo(10) was used.

(2) The results are shown in Table 3. As shown in Table 3, MEMB and MEPB were mixed as bromine complexing agents from 0.25:0.75 to
It can be seen that the bromine concentration can be reduced by adding at a molar ratio of 0.0:1.0. Note that this is similar to the results shown in Reference Examples 1 and 2.

(Left below) Table 3 = Zinc bromide 1 moC/(2 Aqueous solution supernatant bromine concentration Bromine addition amount 20 m (7) (1) Zinc bromide 1 containing bromine concentration 0, 3 moQ/ρ
Bromine complexing agents (MEMB, MEPB) in moρ/Q aqueous solution
mixture) I mo(1/(MEPB in l is 0)
．． It was added at a mole fraction of 25%, 50%, 75%, and IQO%, and the bromine concentration (moσ/a) in the supernatant liquid was measured at liquid temperatures of 22°C, 40°C, and 50°C.

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

(1) The bromine concentration (mo(/(1)) of the supernatant solution was measured in the same manner as in Reference Example 4 except that a 1/Q aqueous solution of zinc bromide was used instead of a 1 mof2/12 aqueous solution of zinc bromide.

(2) The results are shown in Figure 2. As shown in FIG. 2, similar to FIG. 1, 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.

(1) Bromine concentration 2 instead of bromine concentration 0.3moρ/a
, 0 mof! The supernatant bromine concentration (moc/12) was measured in the same manner as in Reference Example 4 except that /Q was used.

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

(1) Zinc bromine 2.25 moQ, /ρ aqueous solution, zinc chloride 0,4 mof2/Q, ammonium chloride 1,0
mof! / Q, and bromine complexing agent 1mof! /12, MEM is used as the bromine complexing agent.
E and MEPB are respectively 0.25:0.75. o, o
: Added at a molar ratio of 1.0, electrode area 830 cm2
An operational test was conducted on a zinc-bromine battery consisting of five stacked cells.

(2) In addition, a zinc-bromine battery was subjected to an operational test in the same manner as in Example 1, except that MEMB and MEPB were added as bromine complexing agents at a molar ratio of 0.5:0.5, respectively. This was used as a comparative example.

(3) The test results of (1) and (2) are shown in Table 4.

As shown in Table 4, as the bromine complexing agent shown in Example 1 (1), MEMB and MEPB were mixed in a ratio of 0.25:0.
MEMB and MEP were added as bromine complexing agents shown in Comparative Example (2) in a molar ratio of 75,0.0 and 1.0.
It can be seen that the coulombic efficiency, voltage efficiency, and energy efficiency are superior to those in which B is added at a molar ratio of 0.5:0.5.

(Margin below) Table 4 Test results when using zinc-bromine battery electrolyte Composition of electrolyte ZnBr.

nCQv NH4Cρ Bromine complexing agent G0 Effect of the invention 2.25 0.45 1.0 1.0 mo(!/ρ mo(1/Q moρ/ρ rnoQ/(1) The present invention is constructed as described above. Therefore, free bromine ions in the electrolyte can be reduced by odor.

Therefore, the electrolyte solution of the zinc-bromine battery according to the present invention can reduce self-discharge due to the presence of free bromine ions, thereby improving the coulombic efficiency, voltage efficiency, and energy efficiency of the zinc-bromine battery.

[Brief explanation of drawings]

Figures 1 to 3 are graphs showing the relationship between the molar fraction of MEPB in the bromine complexing agent and the bromine concentration in the supernatant liquid. The ability to form other complex compounds can be enhanced, and this Figure 1 shows the molar fraction of MEPB in 1mof/1 bromine-strengthening agent.

Claims (1)

[Claims] (1) Zinc bromide aqueous solution of 3 mol/l or less, conductivity improver having chlorine ions, and halogenated N-methyl N-
The molar ratio of ethylmorpholinium salt and halogenated N-methyl N-ethylpyrrolidinium salt is 0.25:0.75
A metal-bromine battery electrolyte comprising a bromine complexing agent of ~0.0:1.0.