JPH1064505A - Zinc-bromine battery separator - Google Patents

Abstract

(57) [Summary] [PROBLEMS] By regulating the film thickness and the distance between posts in a post-mounted separator used in a zinc-bromine battery,
It is an object of the present invention to improve battery performance by preventing a decrease in battery efficiency due to the deflection of a separator. SOLUTION: Based on a mechanical model relating to “bending” of a separator having a large number of projecting posts protruding on both front and back surfaces, a design value of a bending amount between posts due to a differential pressure and a design value of a distance between posts are determined for each film thickness. Provided is a zinc-bromine battery separator which determines the optimum separator film thickness and post distance in order to maintain the battery efficiency to the maximum from the relationship between the inter-post distance and the shielding efficiency of the electrolyte. . When the film thickness of the separator is 0.4 mm to 1.0 mm, the distance between the posts is 5 mm to 10 mm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a separator which is a constituent member of an electrolyte circulation type laminated secondary battery, particularly a zinc-bromine battery.

[0002]

2. Description of the Related Art A zinc-bromine battery is a secondary battery in which bromine is used as a positive electrode active material and zinc is used as a negative electrode active material.
It is used for storing electric power at night when power demand is small and releasing it during the day.

[0003] The bromine generated on the positive electrode side during charging reacts with the bromine complexing agent added to the electrolytic solution, returns to the storage tank as an oily precipitate, and is discharged into the unit cell by a pump during discharging. It is sent and reduced. The component of the electrolyte is ZnBr ₂
An aqueous solution, a salt such as NH ₄ Cl for lowering resistance, Pb, Sn, quaternary ammonium salts for preventing dendrite on the negative electrode zinc side and promoting uniform electrodeposition, and a bromine complexing agent is there. A separator is interposed between the positive electrode and the negative electrode to prevent self-discharge caused by bromine generated at the positive electrode diffusing into the negative electrode and reacting with zinc.

The chemical reaction of this zinc-bromine battery is as follows:

[0005]

[Chemical Formula 1] During charging: positive electrode: 2Br ⁻ → Br ₂ + 2e ⁻ , negative electrode: Zn ⁺⁺ + 2e ⁻ → Zn Discharging: positive electrode: 2Br ⁻ ← Br ₂ + 2e ⁻ , negative electrode: Zn ⁺⁺ + 2e ⁻ ← Zn It is represented by

This zinc-bromine battery mainly has a bipolar type electrode, a battery body in which a plurality of unit cells (single cells) are electrically stacked in series, an electrolytic solution storage tank, and an electrolytic solution between them. It is composed of a pump and a piping system for circulating the liquid.

FIG. 5 is an exploded perspective view showing an example of a battery main body constituting the zinc-bromine battery. An insulating frame 1b is provided on the outer periphery of an electrode portion 1a of a flat bipolar intermediate electrode 1.
The frame 2 a is formed on the outer periphery of the separator 3 in the same manner. The separator plate 2 and, if necessary, the packing 4 and the spacer mesh 5 are stacked on the intermediate electrode 1 to form a single cell, and a plurality of the single cells are laminated to form a battery body.

[0008] At both ends of the stacked battery main body, a collecting electrode 7 having a collecting mesh 6, a pair of tightening end plates 8,
A holding laminated end plate 9 located on the inside thereof is arranged. Then, a bolt (not shown) is passed between the two tightening end plates 8 and 8, and the bolts are tightened to form a battery body integrally laminated and fixed.

The fastening end plate 8 is made of glass fiber epoxy, and the collecting electrode 7 is formed by disposing a plastic electrode 7a at the center and covering the outside with an insulating frame. The separator 3 is made of a microporous film made of polyethylene, and the frame 2a is made of an insulator.

In each unit cell of the battery body configured as described above, each intermediate electrode 1 and the frame 2a of the separator plate 2 are provided.
Positive electrode manifold 10 formed at the upper and lower two corners of
Then, the electrolyte flows in and out of the negative electrode manifold 11 through the channel 12 and the micro channel 13 provided in the frame 2a of the separator plate 2, respectively.

The basic part of the zinc-bromine battery is constituted by a structure in which a framed separator 3 and a large number of framed intermediate electrodes 1 are stacked. Then, ZnBr ₂ as an electrolytic solution is circulated through gaps between these stacked bodies by driving a pump (not shown) to perform charging / discharging as a function of the battery based on the chemical reaction.

The center portion of the intermediate electrode 1 and the separator 3 is formed into a predetermined thickness by extrusion, and then cut into a set shape. The intermediate electrode 1 and the separator 3 are arranged at the center of the injection molding machine, and are integrated by injection molding so that the outer insulating frame portion is welded to the central component. Further, the current collecting electrode 7 is manufactured by incorporating a carbon plastic electrode in a sheet-shaped insulating frame material and integrating the same based on heat press means under predetermined temperature and pressure conditions using a mold (not shown). . The carbon plastic electrode is a member formed by mixing polyethylene and carbon graphite, and has corrosion resistance to bromine.

The separator 3 is formed by melting and mixing silica and dioctyl phthalate (hereinafter referred to as DOP) with a high-density polyethylene resin (usually abbreviated as HDPE), and then extracting DOP with a solvent to make the separator 3 porous. A porous membrane is used. The average pore size of this microporous membrane is about 100 °.

In the above zinc-bromine battery, bromine generated on the positive electrode side during charging reacts with a bromine complexing agent (quaternary ammonium salt) contained in the electrolyte to form an oily bromine complex at the bottom of the positive electrode tank. The stored, uncomplexed bromine becomes Br ₃ ^- ions and dissolves in the electrolyte, and zinc deposits on the carbon plastic electrode.

[0015] The zinc-bromine battery thus constructed is
It has been confirmed that the battery efficiency of a 50 kW class battery is about 80%, and the total energy efficiency is about 70%.

[0016]

In order to prevent the contact between the intermediate electrode 1 and the separator 3 and to secure a flow path for the electrolyte, the packing 4 and the spacer mesh 5 are stacked on the separator plate 2 and then the intermediate electrode 1 is removed. A method of laminating the spacer mesh 5 is used.
Are formed by spot welding on both sides of the substrate. However, such means requires extra man-hours and members, and
Although heat welding can be automated, the setting of the spacer mesh 5 cannot be automated, which is disadvantageous in terms of cost. In addition, since the spacer mesh 5 is an insulating material, the internal resistance is increased, and the voltage efficiency is reduced. There is a problem that.

FIGS. 6 and 7 show enlarged examples of the shape of the spacer mesh 5. Reference numeral 15 denotes a warp and 16 denotes a weft. The weft 16 and the warp 15 form a grid-like spacer mesh 5. . This grid shape has a large effect on the shielding rate of the electrolytic solution. The larger the grid spacing, the smaller the shielding rate. However, if the grid spacing is too large, the separator 11 is likely to contact the intermediate electrode. Occurs.

Although the lattice spacing with the shielding ratio reduced to 15% was determined as the optimum value, it is necessary to further reduce the shielding ratio in order to improve the battery efficiency. Therefore, as shown in FIGS. 8 and 9, a post-equipped separator having a large number of projecting posts 3 a protruding from both sides of the separator 3 has been developed. In this example, the projecting post 3
The shapes of the a and 3a and the pitch p between the posts 3a are important, but if the size of the pitch p is inappropriate, as shown in FIG. Therefore, it is important to consider the deflection of the separator 3 together with the shielding ratio, since "bending" may occur with respect to 1 and the battery efficiency may be reduced.

However, no basic data has been obtained on the "deflection" of the separator 3 from the prior art, and there is a problem that unevenness of the flow of the electrolytic solution occurs due to such a deflection amount. When the separator 3 and the intermediate electrode 1 come into contact with each other, zinc dendrite (needle-shaped crystals) is generated, which causes a problem that battery efficiency is reduced.

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and by limiting the film thickness and the distance between posts (post pitch) in the post-attached separator, it is possible to reduce the decrease in battery efficiency due to the deflection of the separator. It is an object of the present invention to provide a separator for a zinc-bromine battery which can prevent such a problem and enhance the performance of the battery.

[0021]

In order to achieve the above object, the present invention forms a unit cell by stacking a post-mounted separator having a large number of projecting posts on the front and back surfaces and an intermediate electrode, and an intermediate electrode. A zinc-bromine battery in which a plurality of single cells are stacked to form a battery main body, and a pair of current collecting electrodes and a tightening end plate are arranged at both ends of the battery main body to be integrally laminated and fixed. Based on the mechanical model relating to the "deflection" of the separator, the design value of the amount of deflection between posts and the distance between posts due to the differential pressure in the separator with posts is determined for each film thickness, the distance between the posts and the shielding factor of the electrolytic solution are determined. Thus, a zinc-bromine battery separator having an optimum separator film thickness and post-post distance determined to maintain the battery efficiency to the maximum is provided.

The thickness of the separator is from 0.4 mm to 1.0.
mm, the distance between the posts is 5 mm to 10 mm.

In the battery using such a separator, contact with the intermediate electrode due to the occurrence of the deflection of the separator is prevented, and no dendrite is generated due to electrodeposition in the film. Also, a zinc-bromine battery having good shielding efficiency of the post-type separator and good voltage efficiency, current efficiency, and battery efficiency of the zinc-bromine battery constituted by using the present separator can be obtained.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawings, a specific embodiment of a zinc-bromine battery separator according to the present invention will be described in detail by attaching the same reference numerals to the same components as those described above. . In the present embodiment, in order to increase the voltage efficiency of the zinc-bromine battery, the separator thickness and the distance between the posts in a post-mounted separator in which a number of projecting posts are protruded on both the front and back surfaces of the separator are regulated. It is a feature.

FIGS. 1 (A) and 1 (B) show a mechanical model in which four equally distributed loads are fixed on the deflection of the separator 3, and the deflection W of the separator 3 when a pressure P is applied.
(Mm) can be expressed by the following equation (1). still,
This model is fixed at both ends. W = α {(P · a ⁴ ) / (E · h ³ )} (1) α: Shape factor P: Pressure (kg / Mm ² ) a: Length of side (mm) E: Modulus of elasticity (kg / mm ² ) h: Thickness (mm) This mechanical model is a basic expression of deflection and bending stress.
There are a fixed-end type and a supported-end type, but these have different stress coefficients.

FIG. 2 is a graph showing the relationship between the deflection (mm) between the posts due to the differential pressure and the distance (pitch) between the posts in the separator with posts for each film thickness. The elastic modulus of the separator 3 is 40 (kgf / mm ² ), which is measured in a state of being wet with water. The differential pressure is 0.1 on the left axis
(Kg / cm ² ) and 0.5 (kg / cm ² ) on the right axis. 0.5 (kg / cm ² ) on the right axis corresponds to the pump pressure.

In FIG. 2, the value obtained by the finite element analysis of 0.6 mm is shown by a solid line. Although this finite element analysis is closer to the actual model, it takes a considerable amount of time to make various changes. It is considered that the slight deviation is due to the inclusion of elements supported at both ends with the post as a fulcrum. In addition, according to the three-dimensional analysis using the finite element, it has been found that the fixed-both-end model can obtain a better result than the model of the both-end supporting type.

Since the electrolyte flows on both sides of the membrane constituting the separator 3, the pressure difference between the two electrodes is applied to the membrane, and the pump pressure is not applied directly to the membrane. The differential pressure is about 0.1
(Kg / cm ² ), the safety factor was set to 5 times, and the design reference pressure was 0.5 (kg / cm ² ). Since the distance between the poles is 0.8 to 1.0 (mm), the safety factor is 20.
And the design standard deflection amount was 0.05 (mm).

Although it is difficult to determine the basis of the safety factor with respect to the amount of deflection of the separator membrane, it is desirable to take 10 to 100 times as a normal safety factor. In this example, the safety factor was set to 5 times the pressure, 20 times the deflection amount, and 100 times the safety factor.

Based on the above, the design value of the distance between posts (pitch) was determined for each film thickness. Table 1 shows the results.

[0031]

[Table 1]

According to Table 1, the pitch (mm) increases as the film thickness increases. FIG. 3 is a graph showing the relationship between the distance between posts and the shielding rate (%) of the electrolytic solution. According to FIG. 3, the shielding ratio tends to increase sharply when the distance between the posts is 5 mm or less, and this increase in the shielding ratio leads to a decrease in the area of the electrode and the membrane, which causes a reduction in the battery efficiency. Therefore, even if the film thickness is 0.4 mm or less, the distance between the posts needs to be 5 mm or more.

In order to verify the above conclusion, separator films having various post-to-post distances were prepared by press molding to obtain sample films, and the sample films were assembled in a battery and subjected to a charge / discharge test. The distance between posts is 4mm, 8mm, and 10mm.
And the film thickness was unified to 0.8 mm.

As a separator material, dioctyl phthalate (hereinafter abbreviated as DOP) is added to high-density polyethylene resin.
% And about 20% by weight of silica particles. Instead of the high-density polyethylene resin, polyvinylidene fluoride can be used. A microporous membrane is obtained by extracting the DOP with a solvent, and the microporous membrane is set in a mold to form the posts 3a, 3a.

The prepared post-attached sample film was cut into a predetermined size, framed, assembled into an 800 cm ² , 10-cell battery and operated. As operating conditions,
A charge / discharge test was performed at a liquid temperature of 30 ° C., a charge of 15 (mA / cm ² ) for 8 hours, and a discharge of 20 (mA / cm ² ) and a cutoff of 1 (V / cell).

FIG. 4 is a graph showing the charging / discharging characteristics according to the distance between the posts. When the pitch is 4 mm, the charging time is short, and dendrites may be generated. Then, 8 hours after charging, each sample film was disassembled, and the occurrence of bending of the film and dendrite was confirmed.

As a result, the sample film having a post-to-post distance of 10 mm bends, and the intermediate electrode 1 and the separator film are in contact with each other. At this contact portion, electrodeposition into the film proceeds, and dendrite is generated. Turned out to be. On the other hand, the sample films having the distance between the posts of 4 mm and 8 mm have no contact with the intermediate electrode 1 and no dendrite is generated.

Table 2 shows the shielding ratio, voltage efficiency, Coulomb efficiency, and energy efficiency of the post type separator prepared at the above-mentioned inter-post distance (pitch) in comparison with the conventional spacer type.

[0039]

[Table 2]

According to Table 2, when the pitch is 4 mm, the shielding efficiency is increased and the voltage efficiency is low. When the pitch is 10 mm, the dendrite is generated due to the bending, the effective area is reduced, and the voltage efficiency and coulomb are reduced. Both efficiency values were low. On the other hand, when the pitch was 8 mm, the above problem did not occur, and it was confirmed that the voltage efficiency and the energy efficiency increased as compared with the conventional spacer method due to the decrease in the shielding ratio. Was done.

[0041]

As described above in detail, according to the separator of the zinc-bromine battery according to the present invention, the thickness and the distance between the posts in the separator having a large number of projecting posts on both the front and back surfaces are determined. The restriction based on the theoretical analysis of the separator's "bending" prevents the separator from coming into contact with the intermediate electrode due to the bending of the separator, and may cause uneven flow of the electrolyte due to the amount of bending. Eliminates the occurrence of dendrites caused by electrodeposition, and improves the shielding efficiency of the separator and the voltage efficiency, current efficiency, and battery efficiency of the zinc-bromine battery constructed using this separator. Increased zinc-
A bromine battery separator can be provided.

[Brief description of the drawings]

FIG. 1A is a schematic diagram showing a mechanical model in which four sides of an equally distributed load are fixed with respect to the deflection of a separator. FIG.
(B) is a plan view of the separator.

FIG. 2 is a graph showing the relationship between the amount of deflection between posts due to a differential pressure and the distance between posts for each film thickness.

FIG. 3 is a graph showing a relationship between a distance between posts and a shielding rate of an electrolytic solution.

FIG. 4 is a graph showing charge / discharge characteristics according to the distance between posts.

FIG. 5 is an exploded perspective view of a main part showing a battery body of a zinc-bromine battery.

FIG. 6 is an enlarged plan view showing a shape example of a conventional spacer mesh.

FIG. 7 is a side view of FIG. 6;

FIG. 8 is a plan view showing an example of a post-mounted separator provided with protruding posts.

FIG. 9 is a side view of FIG. 8;

FIG. 10 is a side view showing a state where “deflection” occurs in a conventional separator.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Intermediate electrode 3 ... Separator 6 ... Collector mesh 7 ... Collector electrode 8 ... Clamping end plate 9 ... Laminated end plate 10 ... Positive electrode manifold 11 ... Negative electrode manifold 12 ... Channel 13 ... Microchannel 15 ... Grid-like spacer 16, 18 Projection 17 Separator material

Claims (2)

[Claims] 1. A single cell is formed by stacking a post-equipped separator having a large number of projecting posts on the front and back surfaces and an intermediate electrode, and forming a single cell by stacking a plurality of the single cells to form a battery body. In a zinc-bromine battery in which a pair of current collecting electrodes and a fastening end plate are arranged at both ends of the battery body and integrally laminated and fixed, based on a mechanical model related to `` bending '' of the separator, Calculate the design value of the amount of deflection between posts and the distance between posts due to the differential pressure of the post-separated separator for each film thickness. A separator for a zinc-bromine battery, wherein a separator thickness and a distance between posts are determined. 2. The separator has a thickness of 0.4 mm to 1.0 m.
2. The separator for a zinc-bromine battery according to claim 1, wherein the distance between the posts is 5 mm to 10 mm when the distance is m.