JPS63205067A - Zinc/iodine secondary battery - Google Patents

Abstract

PURPOSE:To make long-term use possible by using a nitrocellulose porous film as a separator. CONSTITUTION:A nitrocellulose porous film is used as a separator. In order to prevent internal short circuit caused by zinc crystals, the maximum pore size of the nitrocellulose porous film is preferable to be limited to 5.0mum or below, further effective to be limited to 1.0mum or below, and furthermore optimum to be limited to 0.5mum or below. A maximum pore size of 5.0mum or below does not means that pores exceeding 5.0mum are excluded and means that the number of pores having a maximum pore size of 5.0mum or below is 80% or more, preferably 90% or more. By using this separator, no dendritic or mossy zinc crystals are produced and long-term use is made possible.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a zinc/iodine secondary battery, and more particularly to a zinc/iodine secondary battery that can prevent zinc dendrites from occurring on the negative electrode during charging. .

[Prior Art] In recent years, various new batteries have been developed that have excellent features such as small size, light weight, and high capacity.For example, sodium/sulfur secondary batteries and zinc/halogen secondary batteries are known. However, since sodium and halogen are highly reactive, they are difficult to handle (for example, the reaction cannot be controlled), and may cause problems if they leak outside.

The present inventor focused on iodine, which has relatively low reactivity among halogens, and attempted to develop a zinc/iodine secondary battery.

As a result, by using iodine, a complex adduct of iodine and a polymer forming the complex adduct, and a composition in which a carbon material is dispersed therein, as a positive electrode active material,
It was found that it has the potential to be effectively used as a secondary battery.

However, zinc/iodine secondary batteries have an affordable electromotive force of 1.35V, allowing for high output and high capacity, and are highly reliable, but on the other hand, zinc tends to precipitate in the form of dendrites or moss during charging. There's a problem.

It has been found that this precipitate has poor adhesion to the substrate, increases the size of the space, and causes short circuits between the positive and negative electrodes, which impedes the practical application of secondary batteries using zinc as the negative electrode.

Regarding the prevention of zinc dendrites, various effective measures have been proposed for alkaline batteries, but there are few studies on secondary batteries that use acidic electrolytes like this battery, and it is unclear whether effective measures have been found yet. Not yet.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a zinc/iodine secondary battery that overcomes the above-mentioned difficulties and can be used for a long period of time.

[Means for Solving the Problems] As a result of intensive studies to achieve the above object, the present inventors have developed a negative electrode containing zinc as an active material, iodine and a polymer capable of forming a complex adduct with iodine. A zinc/iodine secondary battery having a separator between the positive electrode and a positive electrode comprising a complex adduct of the complex adduct with the active material and a composition in which a carbon material is dispersed therein, characterized in that a porous membrane made of nitrocellulose is used as the separator. We have found that two goals can be achieved with a zinc/iodine secondary battery.

In other words, it is presumed that the deterioration of battery life due to dendrite-like or moss-like precipitation is essentially caused by an internal short circuit between the negative electrode and the positive electrode. In order to create a battery that can withstand the use of batteries, we thought that the above-mentioned difficulties could be solved by a method of physically inhibiting the growth of crystals due to dendrite-like or moss-like precipitation without increasing the internal resistance of the battery.

As a result of various studies regarding separators, it was found that the use of a certain type of separator is effective in improving the process.

Generally, battery separators are made of vinyl chloride, polyethylene, polypropylene, nylon, rubber, phenolic resin, and polyvinyl alcohol.

Cellulose etc. are used. However, which separator is actually used depends on the battery system to which it is applied.

The present invention is a study on separators used in zinc/iodine secondary batteries. To explain in detail, the separator of the present invention is expected to not only prevent contact between the positive and negative electrodes, but also to prevent the growth of zinc crystals in the form of dendrites or moss with mechanical strength. be.

For this reason, the porosity of the separator becomes an important matter. In other words, tentrite-like or moss-like zinc crystals grow as very fine crystals from the negative electrode toward the positive electrode. Therefore, in addition to mechanical strength, it is necessary to prevent zinc crystals from passing through the pores of the separator.

As a result of intensive studies from this point of view, it was found that porous nQ made of nitrocellulose is preferable as the separator for the battery of the present invention. Furthermore, in order to prevent internal short circuits due to zinc crystals, the maximum pore diameter of the nitrocellulose membrane is preferably 5.0 g, m or less, more preferably 1.0 μm or less, and more preferably 0.5 μm or less. I found the following to be optimal.

In the present invention, the maximum pore diameter of 5.0 #L or less does not completely exclude pores larger than 5.0 JLm, but it is more than 80% of the total number of pores, preferably 9
This means that it is sufficient that a% or more is 5.0 Roux or less.

In addition, the pore diameter refers to the diameter when the pore is circular, and when the pore is not circular, the diameter of the circle when converted to a circle with the same area.

Furthermore, when the pore diameters are different between the front and back surfaces of the nitrocellulose membrane, the pore diameter refers to the smaller diameter.

It is preferable that the pores are dispersed in large numbers on the membrane surface, but for example, per unit surface m (rTI') of the membrane,
It is preferable that the pores have a size of 0.3 to 0.9 m'.

Furthermore, the separator of the present invention also includes a case where a nitrocellulose membrane is used in combination with another separator (for example, a nitrocellulose membrane, an ion exchange membrane, etc.).

In the present invention, examples of the polymer capable of forming a complex adduct with iodine include polyacrylonitrile, polyvinyl alcohol, polyvinyl acetate, nylon-6, polyurethane, polytetramethylene ether, poly-2-vinylpyridine, etc. However, it is of course not limited to these.

As the liquid electrolyte, an aqueous zinc iodide solution or a solution to which ammonium chloride, potassium chloride, sodium chloride, potassium bromide, ammonium iodide, potassium iodide, etc. are added as an auxiliary electrolyte is used as in the conventional case.

Further, in the present invention, since an aqueous solution is used as the electrolyte, it is more preferable that the separator has wood-philic properties so as not to increase the internal resistance of the battery.

[Example] Hereinafter, preferred embodiments of the present invention will be described in more detail with reference to Examples. In this example, "parts" means "parts by weight" unless otherwise specified.

Example 1 10 parts of micronized nylon-6 (manufactured by Toshi Co., Ltd.) was mixed with 25 parts of formic acid.
15 parts of Ketjenblack KB-ECJ (trademark of AKZO Co., Ltd.) of about 30 to 200 mesh was dispersed therein with thorough mixing.

The pulverized resin carbon composite containing the solvent obtained in this way was directly processed using a powder molding press manufactured by Riken Seiki Co., Ltd.
A positive electrode was obtained by pressing into a disk shape at a pressure of 600 kg/crn'.

The obtained positive electrode was dried to have a diameter of 2h+m and a thickness of 2.6-
-, a disc-shaped positive electrode weighing 770B was obtained.

The structure of the battery assembled according to this example is shown in FIG.

The previously prepared disk-shaped positive electrode was used as the positive electrode 10, and the negative electrode 20 was a zinc plate (20 mm in diameter and 0.3 mm thick) (
(manufactured by Mitsui Kinzoku Mining Co., Ltd.) was used. The electrolytic solution was composed of 2.5 mol/alternate zinc iodide and 6 mol/alternate ammonium chloride and was used by impregnating glass fibrosis paper 30 with 2.2 g on the positive electrode side and 2 g on the negative electrode side. The separator 40 was a nitrocellulose membrane with a maximum pore diameter of 0.2 JLII and a thickness of 1:15 p (Toyo Kagaku Co., Ltd.). (manufactured by Sangyo Co., Ltd.) was sandwiched between glass mms paper 30 containing electrolyte as shown in Figure 1,
The battery was configured.

In FIG. 1, 60 and 60' are a support, 70 is a packing, 80 is a lead wire, and 90 is a platinum current collector.

The experiment was conducted at 25° C. under a nitrogen stream and started with charging under the condition of a constant current of 10 μ^. Charging was performed to a final voltage of 1.5V, and discharging was performed to a final voltage of 0.9V. The initial short circuit current (Isc) during the first discharge was 148 A/am'. Also, the open circuit voltage (Voc) at this time is 1. :lSV.

After that, charge to the final voltage of 1.5V, and the final voltage is 0.9V.
I recreated the charge/discharge test that discharges the battery up to the maximum.

As a result, the energy efficiency and current efficiency remained almost unchanged even after 100 cycles.

Example 2 Micronized polymethylene glycol ether (manufactured by DuPont, trade name "Teratane", average molecular weight 1z9oo) 6
Dissolve 5 parts in benzene and add about 30 mesh to 2
00 mesh carbon m fiber powder rCF-0 manufactured by Gunei Chemical Industry Co., Ltd.
35 parts of 8BT J was dispersed with thorough mixing.

The pulverized resin carbon composite containing the solvent obtained in this way was directly processed using a powder molding press manufactured by Riken Seiki Co., Ltd.
A positive electrode was obtained by pressing into a disk shape at a pressure of 600 kg/crt+'. The obtained positive electrode was dried to a diameter of 20 mm.
(2) A disk-shaped positive electrode with a thickness of 2.5 mm and a weight of 780 mg was obtained.

The structure of the battery assembled according to this example is the same as that shown in FIG. 1 above.

The previously prepared disc-shaped positive electrode was used as the positive electrode 10, and as the negative electrode 20, a zinc plate (
(manufactured by Mitsui Kinzoku Acupuncture Co., Ltd.) was used. Electrolyte is 2.5 mol/i
of zinc iodide and 6 mol/m of ammonium chloride were placed on glass fiber i1ti1M paper 30 on the positive electrode side.
g and the negative electrode side were impregnated with 2 g. Separator
40 is “Neosebuta CM-1 membrane” manufactured by Tokuyama Soda Co., Ltd.
As shown in Figure 1, a nitrocellulose membrane (manufactured by Toyo Kagaku Sangyo Co., Ltd.) with a maximum pore diameter of 0.2μ and a thickness of 135 mm is used as a separator. It was sandwiched between two pieces of miscellaneous filter paper 30 to form a battery.

The experiment was conducted at 25° C. under a nitrogen stream, and started with charging under the condition of a constant current of 10 μA. Charging is done at a final voltage of 1. The discharge was carried out to SV, and the discharge was carried out to a final voltage of 0.9V. The initial short-circuit current (l5c) at the first discharge was 158/crn'. Also, the open circuit voltage (Voc) at this time is 1.35V
Met. Thereafter, a charge/discharge test was repeated in which the battery was charged to a final voltage of 1.5V and discharged to a final voltage of 0.9V.

As a result, the energy efficiency and current efficiency remained almost unchanged even after 100 cycles.

Example 3 In Example 2, the separator 50 had a pore diameter of 1.
0JLs, batteries were made in the same manner except that a 135 gm thick nitrocellulose membrane (manufactured by Toyo Kagaku Sangyo Co., Ltd.) was used.
I completed it.

The experiment was conducted at 25° C. under a nitrogen stream, and started with charging under constant current conditions of IOmA. Charging was carried out to a final voltage of 1.5V, and discharging was carried out to a final voltage of 0.9V. The initial short circuit current (Isc) during the first discharge was 172 mA/crn'. Further, the open circuit voltage (Voc) at this time was 1.35V. Thereafter, a charge/discharge test was performed in which the battery was charged to a final voltage of 1.5V and discharged to a final voltage of 0.9V.

As a result, the energy efficiency and current efficiency remained almost unchanged even after 100 cycles.

Comparative Example 1 A battery was constructed in the same manner as in Example 1 except that the nitrocellulose porous membrane 50 was not provided.

The experiment was conducted at 25° C. under a nitrogen stream and started with charging under the condition of a constant current of 10 mA. Charging was performed to a final voltage of 1.5v, and discharging was performed to a final voltage of 0.9v. The initial short circuit current (l5c) during the first discharge was 150 mA/crn'. Further, the open circuit voltage (Voc) at this time was 1.34V. Thereafter, a charge/discharge test was repeated in which the battery was charged to the final voltages i and sv and discharged to the final voltage of 0.9v.

As a result, the energy efficiency even after 1(1(l cycles),
Although the current efficiency remained almost unchanged, when a large number of the same batteries were made and a charge/discharge test was performed, troubles caused by dendrites occurred with a failure rate of 20 to 35% in charge/discharge tests up to 50 cycles. Further, in charge/discharge tests up to 100 cycles, troubles caused by dendrites occurred with a failure rate of 60 to 80%.

However, in Examples 1, 2, and 3, as shown in Table 1, the failure rate due to dendrites was extremely low.

Table 1 Effects of C'A Ming] As described above, according to the present invention, since tentite-like or moss-like zinc crystals are not generated, long-term use is possible, and high reliability and productivity can be achieved. A zinc/iodine secondary battery with high properties can be provided. The secondary battery obtained by the present invention exhibits particularly advantageous effects when used as a button-type secondary battery, a cylindrical secondary battery, and a prismatic secondary battery, and has industrial utility value as a new type of secondary battery. It's expensive.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view showing one example of the configuration of a secondary battery of the present invention. lO: Positive electrode 20: Negative electrode 30: Glass fibrosis paper 40: Separator 50: Separator 60: Support 60': Support 70: Packing 80: Lead wire 90: Platinum current collector

Claims (2)

[Claims] (1) A negative electrode that uses zinc as an active material, a complex adduct of iodine and a polymer capable of forming a complex adduct with iodine, and a positive electrode that uses as an active material a composition in which a carbon material is dispersed. A zinc/iodine secondary battery having a separator therebetween, characterized in that a porous membrane made of nitrocellulose is used as the separator. (2) The maximum pore diameter of the nitrocellulose porous membrane is 5.0μ
2. The zinc/iodine secondary battery according to claim 1, wherein the zinc/iodine secondary battery is less than or equal to m.