JPS59112577A - Electrode characteristic evaluation method of electrode material for zinc-bromine battery - Google Patents

Abstract

PURPOSE:To make an almost mean potential value possible to be known in a short period of time as well as to improve the efficiency of electrode material evaluation, by substituting the specific resistance value and ten-point mean roughness value of a discharge mean potential value unknown plastic electrode for a relational expression of the discharge mean potential of various electrodes, the specific resistance value and the ten-point mean roughess value. CONSTITUTION:In regard to various plastic electrodes, those of discharge potential V, specific resistance p and ten-point mean roughness Rz are measured, and when a new factor expressed in that as A=RzX10<-4>/p is brought in from the given data and thereby a relationship to the discharge mean potential V is found, the connection between V and ln1/A shows a linear relationship. Hereupon, in regard to a new plastic electrode whose electrode potential remains unmeasured, the specific resistance value and ten-point mean roughness value only are measured, and the measured specific resistance value and the ten-point mean roughness value are led into this linear expression whereby an almost mean potential value is secured in this manner.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for evaluating electrode properties of electrode materials for zinc-bromine batteries.

To examine the electrode characteristics of a battery, there are two methods: 1) Assemble battery constituent materials such as electrodes into a cell, actually charge or discharge the battery, measure the voltage efficiency and Coulomb efficiency, and check the quality of each efficiency. As for the electrochemical reactivity of the electrode, there are methods such as examining the polarization voltage based on various methods, and (2) measuring the electrical conductivity and resistivity for electrically specifying the electrode.

The same is true for zinc-bromine secondary batteries, and the current situation is that the above six methods are used depending on the quality of the electrode material and the dispute, and are being considered from various angles.3 Especially for bromine electrodes,
Strongly corrosive bromine is generated during charging, and through charging and discharging, a direct reaction with bromine takes place at the interface between the U electrode and the liquid, causing damage to the material and surface morphology of the electrode body. It has a great influence on the characteristics of the bromine electrode. Therefore, when evaluating the 4', lr properties as a bromine electrode, first consider the acid resistance to Br2 in the power solution, and then use this evaluation. 4. For materials that are satisfactory, the electrochemical reactivity with living substances is evaluated.For materials that meet the specified requirements in the evaluation, the lifespan as a battery is evaluated. It is necessary to set up several stages of consideration, sift through various materials, and select the most suitable electrode currently available.

From this point of view, the inventors of the present application have established a certain degree of evaluation and selection methods for bromine-resistant materials, have established numerous test items such as bromine diffusion tests, bromine immersion tests, and tensile tests, and have conducted various tests. We are currently considering the 4A fee. As for the lifespan of the battery, we plan to solve many problems in the future and continue to study it through cycle tests, constant power and constant current charging/discharging tests, etc. on the other hand.

Regarding the evaluation of electrochemical reactivity with active materials, it was possible to find out the fact that there is a correlation between various measurement data from the experimental results conducted in 1. Can the method also be applied to batteries? j) was recognized. Therefore, the above matters will be explained in this specification.

First, we will explain the electrochemical evaluation method that can be applied to batteries, then we will discuss the factors used to evaluate electrode performance, namely the specific resistance and ten-point average roughness value, and compare them with the electrochemical evaluation method mentioned above. The correlation with the data obtained from the conventional method will be explained, and finally the invention of the electrode jT value method will be described.

First, the electrochemical evaluation method is a direct polarization measurement method shown in the measurement principle diagram in FIG.

That is, the sample electrode (1) to be measured and the counter electrode (2) constitute a half cell (3), and this half cell (4) is inserted into it.Then, the sample electrode ( 1) and the counter electrode (2) are respectively connected to the power source (5), and between the sample 1.', the i-pole (1) and the pair (bow 2), there is a −γ); “, τ+i1′,
4.II'1. U6! The ``IlL position k 1ll11 of the sample electrode (1) at the density is determined. Note that (6
) is the recorder, (7) is the reference (((i(5, pole, (81(d)
: Gear pillar. Q as an application to TI,
Mainly each 8.0. Potential at Br2 concentration in C (charged) state (L-measured at several points7, constant from those data'1:
All you have to do is draw the Ho-111, front-place pattern at the ε-style Daiho Hohoichi. An example is shown in Fig. 2, 5(・4). That is,
First of all, 3NI・+7'-/IZnBrz + B
r7 solution (temperature -25℃) as electrolytic rlt'i-1
By changing the concentration at 3℃7, some points of S, O
, Adjusting the electrolyte solution for the C-shaped spider 1, then part 1. each'
111, i': Measurement II in FIG. 1 in Y solution;! ,
According to the theory, I1f1' [11, M evening.

Measuring the discharge level of the sample electrode at different densities 4. This operation was performed for all the electrolytes prepared in advance, and the results were graphed as shown in Figure 2. Using this Fig. 2, the degree of electrolytic rf Br2 is set to 4+4i, the potential is set to vertical Q'+l+, and the result is rewritten as the 4th position of discharge at various current densities, as shown in Fig. 6. Figure 6 of Jin shows the discharge successive turns of one cycle of the sample electrode as a bromine electrode for a zinc-bromine battery.
The concentration is 5u/ near the initial stage of discharge, Brze degree Q M/
This means that the near distance corresponds to the final stage of discharge. Therefore, x!
Comparative studies can be made by measuring the +r electrode materials as described above and drawing a discharge level pattern diagram. Fourth
The figure shows a current density of 20 mA/c for three types of electrode materials.
This is a comparison of the 4th discharge of rl. From FIG. 4, it can be seen that the metal electrode PT exhibits a good potential and has excellent characteristics.

In this way (H!i), we measure and compare the discharge level of plastic electrodes, but we also consider other factors at the same time to evaluate electrode performance. Measurement of specific resistance is a way to measure the conductivity of the electrode itself.This is based on the four-point probe method, and the specific resistance ρ (Ω・Crn) of the electrode can be obtained.
One is to look at the shape of the electrode surface, which is the ten-point average roughness R9.
(μ). From this measurement, a relative comparison of electrode area is possible.

Then, for each plastic electrode, the discharge level, specific resistance, and ten-point average roughness were measured using the method of
As a result of examining the obtained data, the following correlation was observed. Figure 5 shows current density of 20 mA/ca K # for electrodes with almost the same surface condition.
- shows an example of the relationship between the average potential V2° and the specific resistance ρ at a Br2 concentration of 3 to 1 M/l. 31' Hitoshi: A:
7: V2OE, 1 From the discharge level curve as shown in Figure 6! In other words, Fig. 5 shows that when the surface condition of the plastic electrode is the same, the smaller the specific resistance, the higher the resistance. The it /F-line drawn in is determined by the least squares method based on the plotted points. Next,
Figure 6 shows the average 1(
This is a plot of the 10-point average roughness Rz and the roughness Rz.
From the figure, it can be seen that if the conductivity of the electrode is the same, the potential will differ depending on the surface condition, and in general, the larger the value of Table 4M, the higher the potential. Therefore, the fifth
From the figure and Fig. 6, there is a correlation between the 4th place of discharge and the specific resistance and roughness of the plastic electrode.If the specific resistance is small and the 10-point average roughness is 752, it is inferred that the 4th place of discharge is high.
1ll will be done. Therefore, the specific resistance value ρ(Ω・C
rn) and the ten-point average roughness RZ(μ) are combined into 4, and A=RzX 10-'/ρ
A new factor [■] was found and the relationship between this value and the discharge average potential VX was studied. FIG. 7 shows an example. ■2o and in (1/A) have a linear relationship (v20= (-0,0385)tn(1/A)
+1.065 correlation coefficient r−-0,96), upper M
My 1ft measurement has come to be expressed as a fact. A in this figure 7 is RZ X 10-4/ρ, tn
The dimensions of ('/A) are [Ω], V,, 0ba2
Br2 concentration at 4th position of discharge at 0 mA/ad: 3.0 to 1.
This is the average value at 0 M/z.

After all, it can be said that the electrical conductivity of the effective reaction part of the plastic electrode, which reacts with the active material of the plastic electrode, is higher, the potential is higher. From the experimental data, the estimated value is 60 mA/cm2.
In the fourth discharge position up to, the above correlation was high, and the linear equation was recognized to be appropriate.

Therefore, from the above facts, plastic'lit on the contrary.

The potential characteristics of the pole can be inferred from its specific resistance value and ten-point average roughness. In other words, how much discharge will occur with the new plastic electrode whose electric potential has not yet been measured?
ll'3', ? in Figure 7, without actually measuring the potential. Inserting the specific resistance value and the ten-point average roughness value into the formula for N (thus, the approximate average potential value can be calculated). This speeds up the evaluation of the electrode material 181. , ``jeru'', which takes effect by 4s+1 when a large number of L, JR, and Gokushu charges are separated in a short period of time.

As mentioned above, the main part of electrode characteristic evaluation (X1) is potential measurement and data analysis;
'This allows relative comparison of electrodes. Next, we calculated the discharge average potential, specific resistance, and ten points E17- from the experimental data.
A correlation with phrase roughness was obtained, and from the linear equation, 11J
- Emission to a plastic electric current of unknown position value (tff
fl 6111 is now possible, and the speedup of electrode evaluation is now =r.

To evaluate the material of the bromine electrode of a zinc-bromine battery, the electrode potential is measured based on the measurement principle diagram shown in Figure 1, and a discharge particle surface diagram for one cycle at a constant current density is created. This method is easier than the method of actually assembling various electrode materials into a cell, performing charging and discharging, and evaluating the efficiency at that time, and has the advantage of being able to compare a large number of materials in a short time.

The above method is more effective for comparing the battery's discharge characteristics than the conventional electrode evaluation method using polarization measurement, which measures and compares polarization with electrolytes in specific S, O, and C states. It can be said that this is an accurate evaluation method.

Specific resistance I16ρ [
Ω・m] and the ten-point average roughness RZ (μ) value, it was found that Br21~3M/l for the plastic electrode.
A linear correlation is recognized between the average potential ■ and ρ, and between V and Rz, and furthermore, A = R, where ρ and Rz, which are independent factors, are expressed as one factor.
A correlation was also observed between Z X 10-4/ρ and V. Especially the average type at a current density of 60 mAltrl 1,
A linear correlation was observed for the position Vx.

From this, it was found that for plastic electrodes, those with a small specific resistance value and a large surface roughness generally have a high resistance value.

From the above experimental results, for many plastic electrode materials whose discharge levels are unknown, the average 'ilL level V and 7n(1
From the linear equation of /A), the approximate average '1 (L position) can now be easily determined in a short period of time, improving the efficiency of electrode material evaluation.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the principle of electrode potential measurement, Fig. 2 is a diagram showing the discharge 4th position surface line at each]1r2 concentration, and Fig. 6 is a diagram showing the discharge 4th position curve of the electrode. Figure 5 is a diagram showing the fourth-position discharge curve of the polar charge, and Figure 5 is a diagram showing the relationship between the specific resistance value and average potential of electrode materials with almost the same surface condition.
Figure 6 is a diagram showing the relationship between the surface roughness and average potential of electrodes with almost the same specific resistance, and the 7th μm is the 4th level of average discharge V.
FIG. 2 is a diagram showing the relationship between RzXlo-4/ρ[v] and RzXlo-4/ρ[v].

Claims (1)

[Claims] The discharge average potential, specific resistance value, and 10-point average roughness value of various electrodes are determined, and a correlation equation is obtained between them. 1. A method for evaluating electrode characteristics of an electrode material for a zinc-bromine battery, which comprises estimating a discharge average potential of the plastic electrode by substituting an average roughness value.