JP2734057B2 - Battery manufacturing method - Google Patents

Description

The present invention relates to a gas diffusion electrode using oxygen as an active material, an electrolytic solution such as an alkaline aqueous solution, a metal such as zinc, magnesium, and aluminum, or an alcohol, hydrazine,
The present invention relates to a method for producing a battery including a negative electrode active material such as hydrogen.

2. Description of the Related Art Examples of a battery including a gas diffusion electrode and using oxygen as an active material include an air battery and a fuel cell. In particular, in a battery using an alkaline aqueous solution or a neutral aqueous solution as an electrolyte, a gas diffusion electrode (oxygen electrode) according to the vapor pressure inside the battery.
Flow of steam from and out, changes in the concentration of electrolyte in the battery,
A volume change occurred, which affected battery characteristics. The situation will be described with reference to FIG. 2 taking a button-type zinc-air battery as an example. In the figure, 1 is an oxygen electrode (air electrode), and 2 is a porous membrane supporting an oxygen electrode made of polytetrafluoroethylene (PTFE) which has gas diffusibility but blocks liquid. Reference numeral 3 denotes a hole for taking in air from outside, 4 denotes a porous body for supporting an oxygen electrode and diffusing air, 5 and 6 denote separators, and 7 denotes a negative electrode composed of a mixture of an aqueous solution of potassium hydroxide and zinc aluminide. . Generally, an alkaline electrolyte uses an aqueous solution of potassium hydroxide at a concentration of 30 to 35%. For this reason, when the relative humidity is higher than 47 to 59%, external moisture is taken in, the concentration of the electrolytic solution is reduced and the volume is expanded, so that the discharge performance is reduced and the electrolyte is leaked. On the other hand, when the relative humidity is lower than the above range, the electrolytic solution evaporates, resulting in an increase in internal resistance and a decrease in discharge performance. Therefore, there is a problem in the characteristics after long-term storage because they are remarkably affected by the environmental atmosphere, and air cells and fuel cells are designed only for a specific field, and there is a major problem in achieving versatility. Was. In the figure, 8 is a negative electrode container, 9 is an insulating gasket, and 10 is a positive electrode container.

Various measures have conventionally been studied to improve these problems. For example, a substance that reacts with the electrolyte is inserted into a portion around the air hole to prevent leakage of the electrolyte to the outside of the battery. Alternatively, a nonwoven fabric or the like made of paper or a polymer material and an electrolyte absorbing material are provided to prevent leakage of the electrolyte to the outside of the battery. Further, there have been proposals to prevent water vapor or carbon dioxide gas from entering the inside of the battery, even if the supply of oxygen is restricted by making the air holes extremely small. And discharge performance, especially in long-term discharge. The main causes of these are electrolyte dilution and volume expansion due to the penetration of water vapor in the battery,
This is due to the inhibition of the discharge reaction based on the generation of carbonate due to the intrusion of carbon dioxide gas and the obstruction of the air flow path.When the outside air is low in humidity, the evaporation of water in the electrolyte causes the performance to deteriorate. Had become. In recent years, in order to eliminate this cause, a method of controlling the permeation of water vapor or carbon dioxide gas and selectively supplying air to the oxygen electrode through a membrane that preferentially transmits oxygen, for example, a polysiloxane-based nonporous A method using a uniform thin film or a film obtained by integrating a thin film of a metal oxide or an organic compound containing a metal atom with an appropriate porous film has been proposed.

Problems to be Solved by the Invention However, to date, satisfactory discharge performance has been obtained due to insufficient selective oxygen gas permeability and insufficient permeation inhibition of water vapor and carbon dioxide gas. However, it had a technical problem that it could not withstand long-term use and storage, so it had not been put to practical use.

Therefore, the present invention selectively and sufficiently satisfies the oxygen gas in the atmosphere in order to improve the storability of the battery and the performance in long-term use and to obtain a satisfactory discharge performance under discharge conditions from low load to high load. It is an object of the present invention to provide an effective means for taking in the battery at a high speed and preventing the invasion of atmospheric water vapor and carbon dioxide gas into the battery for a long time.

Means for Solving the Problems The present invention is a gas diffusion electrode using oxygen as an active material, and a battery provided with a battery container having an air intake hole communicating with the outside air, the air intake side of the gas diffusion electrode and the inner surface of the battery container. In the meantime, a composite film in which a silica film is formed on a porous substrate by immersing the porous substrate in a treatment liquid obtained by adding boric acid to a saturated aqueous solution of hydrosilicofluoric acid is interposed.

The silica film is a nonporous homogeneous thin film. In order to have a selective permeability for oxygen and to obtain a sufficient oxygen permeation rate and an ability to prevent permeation of water vapor and carbon dioxide, a thickness of usually 3.0 μm or less is suitable. The porous substrate supporting this thin film is easily permeated by gas, and the surface thereof is preferably a microporous film having smoothness and pore diameter suitable for supporting the above thin film uniformly in a non-porous state, The average pore size of the microporous membrane surface is 1.5μ
m or less.

The present invention has focused on the characteristics of a silica film formed by immersing a porous substrate in a treatment solution obtained by adding boric acid to a saturated aqueous solution of hydrofluorofluoric acid as a film having excellent oxygen selective permeability. In particular, it is desirable to immerse the porous substrate in a solution obtained by adding 1.0 × 10 ^{-2 to} 4.0 mol / boric acid to a silica-saturated hydrofluoric acid aqueous solution having a concentration of 0.5 to 3.0 mol /, more preferably, 1.0 to 10 mol. 1.5 × 10 ^{-2 to} 5.0 × 10 ^-2 mol / in a silica-saturated hydrofluoric acid aqueous solution having a concentration of
It is desirable to immerse the porous substrate in a solution containing boric acid. The thin film obtained by this method is a dense silica film without pinholes.

Further, the porous substrate supporting the silica film was selected from polyolefins such as polypropylene and polyethylene having excellent alkali resistance, fluororesins, polysulfone, and the like. The microporous membrane may be a single layer, but may have a configuration of two or more layers further integrated with an alkali-resistant nonwoven fabric, if necessary, in order to ensure strength during handling, production or use. .

Conventionally, CVD method, dipping method, sputtering method, etc. have been tried as a method for forming a silica film, but there are many problems such as uniformity and denseness of the silica film, contamination of impurities, generation of defects, etc. . In the present invention, a dense silica film can be obtained only by immersing the porous substrate in a solution near room temperature. In order to apply this composite membrane for batteries that can obtain satisfactory discharge performance even under high load discharge conditions,
It is an important requirement that the oxygen permeation rate be sufficiently high and the ability to block water vapor and carbon dioxide gas permeation is important, but there are many unknowns about these characteristics, and there has been no example of application to batteries. .

The present invention forms a silica film on the surface of a porous substrate by immersing the porous substrate in a treatment solution obtained by adding boric acid to a saturated aqueous solution of hydrofluoric acid in silica, and earnestly uses the obtained composite film for batteries. As a result of the study, the above-mentioned various characteristics were comprehensively satisfied, and it was found that the performance of a battery to which the characteristics were applied was extremely excellent, and the product was completed.

Operation With this configuration, the above-mentioned composite membrane satisfies not only the oxygen permeation rate for batteries but also the effect of shutting off water vapor and carbon dioxide from the atmosphere, as is clear from the results of battery tests in the examples described later. By being in the proper state, both the high load discharge performance required for a practical battery and the performance when discharged for a long time in an atmosphere of high humidity or low humidity are satisfied.

Example A polytetrafluoroethylene porous film having a thickness of 200 μm was used as a porous substrate, and the porous substrate was immersed in a 0.5% hydrogen fluoride solution for 10 minutes to remove dirt on the surface, and washed with water. When immersed in a 1.5 mol / l aqueous solution of silica-saturated hydrofluoric acid containing 2.5 × 10 ^-2 mol of boric acid added to the treatment liquid 1 at 35 ° C. for 24 hours, a 1600 angstrom thick silica film was formed on the surface A composite film formed by deposition and a porous substrate and a silica film was obtained.

The gas permeability of this composite membrane was measured using a differential pressure gas permeability measuring device (GTR-10XD, manufactured by Yanagimoto Seisakusho Co., Ltd.). The water vapor transmission rate of the composite membrane is 8 × 10 ^-4 ml (stp) /
cm is ² · sec · cmHg, conventional much water vapor is not-tight than the existing polymer film, it was found to be a film for yet oxygen transmission of the amount required to discharge characteristics of the battery.

A battery using the composite membrane produced in order to confirm the effect of the present invention, and a battery not using the composite membrane as a comparative example were evaluated by trial production and examined. First, in the case of the comparative example in which no composite membrane was used, the configuration was exactly the same as that in FIG. The battery using the composite membrane is almost the same as that shown in FIG. 2, and as shown in FIG. 1, the composite membrane 11 is interposed between the porous PTFE membrane 2 and the porous body 4 for diffusing oxygen. This is the only difference from FIG.

The shape of the prototype battery is 11.6 mm in diameter and 5.4 mm in total height.
Evaluate the sufficiency of oxygen uptake rate in the battery by continuous discharge at 20 ° C and normal humidity (60% RH) at relatively high load (75Ω). Long-term continuous discharge at ℃, high humidity (90% RH) and low humidity (20% RH), during the long-term discharge, take in water vapor in the atmosphere, evaporate water in the battery, and remove carbon dioxide. The degree of influence on battery performance, such as loading, was evaluated.

 Table 1 shows the performance test results of the prototype battery.

In Table 1, the discharge end voltage is 0.9V,
The change in weight indicates an increase or decrease before and after the discharge test, and is a numerical value mainly indicating uptake of moisture during discharge or some degree of evaporation.

First, in a high load test at 20 ° C and normal humidity, the discharge period is short,
Since the influence of moisture uptake and evaporation and the influence of carbon dioxide gas are small, it is not necessary to consider the performance of the battery as long as the supply rate of oxygen is sufficient to prevent the permeation of moisture and carbon dioxide gas. Therefore, under such conditions, excellent characteristics can be obtained even in the comparative example. On the other hand, in the above-mentioned prototype, the discharge characteristics equivalent to those of the comparative example were obtained, and this result indicates that the rate at which oxygen permeated the composite membrane sufficiently followed the rate of oxygen consumed in the discharge reaction. Is shown.

On the other hand, in the case of low-load discharge, since the discharge period is long, in the case where the outside air is at high humidity or low humidity, moisture and carbon dioxide gas, especially at the time of high humidity or low humidity, are required to obtain excellent battery characteristics in preventing permeation of moisture. It becomes important. The battery of the comparative example having no moisture or carbon dioxide gas permeation prevention mechanism has a voltage drop during discharge due to depletion of moisture or congestion of air holes due to leakage due to excessive intake of moisture, Only a capacity corresponding to a part of the discharge capacity obtained in the high load test is obtained. Needless to say, leakage during discharge is a serious problem in practical use. In contrast,
The examples show extremely excellent performance, and these have capacities almost equal to the discharge capacity of the high load test. These tendencies are the same whether the test atmosphere is high humidity or low humidity. This indicates that, in the case of the example, the effect of preventing moisture permeation of the composite membrane is sufficiently exhibited.

To summarize the above, a prototype battery using a composite membrane in which a silica film is formed on a porous substrate by immersing the porous substrate in a treatment solution obtained by adding boric acid to a saturated aqueous solution of hydrosilicofluoric acid. It can be concluded that the battery has excellent high-load characteristics and low-load characteristics, has a good change in the external atmosphere, and can provide an excellent battery particularly when an alkali-resistant porous film is used for the support. Furthermore, the same effect can be obtained by using the porous substrate shown in the examples with other porous substrates having alkalinity (for example, a nylon microporous film).

In addition, the composite membrane of the present invention was installed via a porous body for air diffusion between the battery container and the battery container in the above embodiment, but the composite membrane of the present invention was a microporous membrane, and in some cases, further integrated with a nonwoven fabric. It is composed of a support, and there is no difference in battery characteristics even when the porous body for air diffusion is removed. However, if the strength of the composite membrane is not sufficient and the composite membrane is deformed toward the air intake hole, the porous membrane is provided to keep the composite membrane in a stable shape. Furthermore, in the above embodiment, the composite membrane of the present invention was installed via a porous membrane supporting the oxygen electrode between the oxygen membrane and the oxygen electrode. However, if the strength of the oxygen electrode is sufficient, the porous membrane is unnecessary and is excluded. However, the battery characteristics do not change. Also, it was confirmed that an air battery using an aqueous solution of a neutral salt such as ammonium chloride or zinc chloride as an electrolytic solution had the same effect as the battery using an alkaline electrolytic solution shown in Examples. Thus, the operation of the present invention can be explained for the same reason as in the embodiment.

Effects of the Invention As is apparent from the above description, according to the oxygen gas diffusion electrode of the present invention, excellent practical performance from high load to low load of a battery using a neutral or alkaline aqueous solution as an electrolyte, and excellent The effect of being able to provide liquid leakage resistance and long-term storage properties is obtained.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a button-type zinc-air battery used for studying the examples and comparative examples of the present invention, and FIG. 2 is a cross-sectional view of a conventional button-type zinc-air battery not using a composite membrane. 1 ... oxygen electrode (air electrode) 2 ... water repellent membrane 3 ... air intake hole 4 ... porous membrane 5, 6 ... separator 7
Negative electrode zinc, 8 negative electrode container, 9 insulating gasket, 10
...... Positive electrode container, 11 ... Composite membrane.

Claims (2)

(57) [Claims] A gas diffusion electrode using oxygen as an active material; and a battery container having an air intake hole communicating with the outside air. A silicon fluoride is provided between an air intake side of the gas diffusion electrode and an inner surface of the battery container. A method for producing a battery, characterized in that a composite film having a silica film formed on a porous substrate is interposed by immersing the porous substrate in a treatment solution obtained by adding boric acid to a saturated aqueous solution of hydrofluoric acid in silica. . 2. The method according to claim 1, wherein the porous substrate forming the composite film is an alkali-resistant microporous film containing any one of polyolefin, fluororesin and polysulfone as a main component. The method for producing the battery according to the above.