JPS6322415B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in an electrode for a lead-acid battery, which is made by filling a porous support for grid or cladding with a paste-like or slurry-like mixture. The purpose is to improve the product life by filling a support with a kneaded product in which aqueous emulsion of spurge and silicone coexist and drying the product.

The manufacturing method of electrodes filled with a kneaded material, as is well known in the case of paste-type electrodes, is still the mainstream method today because high performance can be obtained relatively easily. However, on the one hand, there was a weakness in lifespan, and in particular there was a limit to the ability to achieve both high capacity and long life. One way to solve this problem is to add a dispersion of fluororesin, such as polytetrafluoroethylene or a copolymer of fluoroethylene and fluoropropylene, to the mixture and knead it. The inventors also investigated in detail the specific conditions for bringing out the excellent characteristics of the electrode, clarified it, and reached a stage where it could be put to practical use.

However, the active material mixture containing the fluororesin dispersion has the following properties, and there is room for improvement in the detailed conditions in the actual manufacturing process.

First, the fluororesin turns into fibers during kneading, and these fibers become intertwined with each other to form a network, which plays a reinforcing role. This results in a plastic material that is so strong that it is often difficult to apply it smoothly to the grid.

Secondly, while the above-mentioned network is formed during kneading,
If the network is cut and the bonds with the active material particles are broken even if fibers are present in the kneaded material, the protective role will be reduced.

Thirdly, the mesh of the network is much larger than the particles of the active material, and when the active material becomes finer during charging and discharging, the particles easily fall out through the mesh, and the active material particles themselves It becomes necessary to increase the strength of

The present invention provides an effective method of providing improvements to these problems.

That is, at the stage of preparing a mixture mainly consisting of lead powder, water, and sulfuric acid, a fluororesin dispersion and an aqueous silicone emulsion are mixed together as composition materials, and then the mixture is filled and dried. It is characterized by

In the aqueous silicone emulsion, the master emulsion and the catalyst are generally separated and stored, and the curing reaction is carried out by mixing them at ^the stage ^of use. The conditions for efficiently producing silicone rubber require a high temperature of nearly 200°C, which often does not necessarily match the conditions suitable for mixing active materials for lead-acid batteries. From this point of view, it is appropriate to use an aqueous silicone emulsion in which the rubberization has been advanced to an intermediate stage and the silicone rubberization has been stabilized, that is, a one-component room temperature vulcanizable silicone rubber emulsion. In this case, simply by dissipating the water, a silicone polymer aggregate with strong rubber-like elasticity is immediately generated. Moreover, although this mechanism has not yet been clarified, unlike silicone bonding reactions such as ordinary crosslinking and condensation, the silicone rubber molecules in the emulsion come close to each other during the process of water dissipation, creating some kind of bonding force. In particular, there is no need for a crosslinking catalyst, and there is no generation of CO ₂ due to side reactions or accompanying deterioration of the active material compound. From such nearly pure long-chain silicones, porous precipitates of polysiloxanes such as dimethylpolysiloxane are obtained, and since they are water-based emulsions, they are not suitable for oil-based liquids dispersed in petroleum-based oils. As such, there is no risk of it remaining in the active material and deteriorating its properties.

Generally, when kneading paste etc., a composition mainly composed of lead powder and water is pre-mixed, and this is mixed with a specific gravity of 1.20 to 1.20.
For example, 5 minutes or 1 hour while dropping 1.45 sulfuric acid.
It is common to knead for more than an hour, if necessary, and then perform final kneading after the dropwise addition of sulfuric acid is completed. Here, the point at which the fluororesin dispersion is mixed is arbitrary, although there are characteristics in how the network is formed, and the effect of improving the lifespan is determined by the addition of the aqueous silicone emulsion at the time when the fluororesin is added. The timing is also arbitrary. This is because the precipitation of the polysiloxane resin from the aqueous silicone emulsion is extremely localized during kneading with a large amount of water, and is mostly completed during the drying process after filling. The superior long-life effect of the present invention is related to this property; unlike fluororesins, where the network structure once formed is destroyed during kneading, silicone aqueous emulsions do not. Instead, at the final drying stage, one or more active material particles are coated in a porous state, and they are elastically connected to protect the active material as if it were contained in connected microcapsules. do. Therefore, even if the fluororesin network is coarse, the structure can accommodate the miniaturization of the active material. An even better feature is that polysiloxane-based polymers that grow in close contact with the secondary particles of the active material at various locations in the large network of the fluororesin, regardless of whether or not the network formed by the fluororesin is destroyed. A portion of the network is incorporated into the molecular assembly and fixed, forming a micro and macro structure as a whole.

Another effect is that when fluororesin dispersion and silicone aqueous emulsion are kneaded in the coexistence, the elasticity and viscosity of the kneaded plastic material decreases compared to when only fluororesin is added and kneaded. , the workability of coating is improved. This effect can be particularly greatly improved by adding the silicone emulsion immediately after or before the addition of the fluororesin dispersion, ie, while the fluororesin has not yet fully formed into a network. Since a network of fluororesin can also be observed, this phenomenon is not simply due to the suppression of fibrosis of fluororesin, but has something to do with the local precipitation of polysiloxane resin during kneading. I think that the. For such local precipitation of silicone polymers, the coexistence of water-absorbing substances such as polyethylene oxide is effective, and these have a positive effect on life span and enable porous filling.

As described above, the present invention not only improves the workability when kneading a fluororesin dispersion, but also allows the fluororesin network to be destroyed even if it is destroyed during kneading. is held together by aggregates of polysiloxane resin precipitated between secondary particles,
Furthermore, it is clear that the fine particles of each active material are densely protected by an aggregate of porous polysiloxane resin, creating a new structure that combines the protection of the fine particles and the protection between groups of particles.

The ratio of the solid components to the lead powder in the fluoropolymer dispersion is arbitrary, but it depends on the amount of water and sulfuric acid, but if the amount is increased too much, the filling properties and rapid discharge properties will deteriorate. 0.05 to 1% by weight is realistic. In this range, the network of the network tends to be relatively coarse, and in this range, the effect of the present invention, that is, the effect of suppressing the dropping of fine particles when kneading an aqueous silicone emulsion, becomes more pronounced. In addition, the solid content in the silicone aqueous emulsion at that time was 0.05 based on the weight of lead powder.
~5% by weight is suitable. This value was measured under the condition that some water in the kneaded material was released to the outside of the electrode during filling, and the silicone resin component present in the emulsion state was released to the outside of the system, and the difference in paste density before and after filling was measured. 0.05-1 in the range 0.2-1
When the concentration is low and the density difference exceeds 1 when pressed by a dehydrator or a dry cloth, it is better to add 1 to 5% by weight in order to suppress the voltage drop and improve the service life.

Of course, the fluororesin dispersion of the present invention can be infiltrated with silicone emulsion into the paste pole completed by kneading only the fluororesin and dried, so that the fine particles can be protected later. The structure can be repaired by impregnating an electrode that has been kneaded, applied, and dried in the coexistence of an aqueous silicone emulsion with an aqueous silicone emulsion and then dried. However, aggregates of polysiloxane resin that precipitate locally during kneading are formed by being embedded inside the active material as the active material particles grow, so the polysiloxane resin that is repaired later is Combines with polymer aggregates,
A reinforcing structure is assembled from the inside and outside of the active material.

In addition, water-absorbing compounds, long and short fibers,
There is no problem in adding other additives for adjusting the existing paste mixture.

Hereinafter, the effects of the present invention will be illustrated by examples.

Example 1 1 kg of lead powder (oxidation degree 50-90%) according to the usual method
Preliminarily mix 200 c.c. of water, add 100 c.c. of sulfuric acid with a specific gravity of 1.35, and mix over a period of approximately 10 to 30 minutes, and perform final mixing for an additional 5 to 15 minutes. At the stage of preparing the Natsuta paste, an aqueous dispersion of fluororesin was added during preliminary kneading so that the solid content of polytetrafluoroethylene was 0.5% by weight based on the lead powder. Product (A), a one-component room-temperature vulcanizable silicone rubber emulsion as an aqueous silicone emulsion, a silicone solid content of 0.5% by weight based on lead powder, and an aqueous dispersion of polytetrafluoroethylene as a resin content of lead. 0.5% by weight of the powder was added during preliminary kneading (B),
A mixture C was prepared without adding anything.

In the first stage of evaluation, the paste (A) was highly elastic and spongy, making it extremely difficult to fill the paste into the grid. (C) is easy to fill, but
It adhered to the grid bedding and it was difficult to separate the electrode from the bedding. (B) feels a little harder than (C), but it is easy to separate from the sheet, has the same amount of fluororesin as (A), and has elasticity, but has extremely good filling properties and is easy to separate from the cloth. It was hot.

Next, the above paste was applied to an expanded grid having an area of about 148 cm ² , and using the positive electrode plates that had been aged and dried in a conventional manner, a battery was constructed with four positive electrodes and five negative electrodes, and the battery life was examined. In order to further clarify the effects of the present invention, a polyethylene porous material was used as a separator instead of a glass mat used in conventional batteries.

The battery obtained above was repeatedly discharged at a current of 20 A for 1 hour and at a current of 5 A for 5 hours, and discharged to 1.7 V at 20 A every 25 cycles.

FIG. 1 shows the change in capacity maintenance rate with respect to the initial capacity in this case. From this result, both A and B are superior in lifespan to battery C, and B of the present invention is especially better than battery A. This effect is due to the fact that in the present invention, the active material is not only supported by the large network of fluororesin, but also that the polysiloxane resin that porously covers the active material is further locally bonded to the fluororesin network.
This may be due to the formation of micro and macro protective structures. The above-mentioned essential structural differences do not vary depending on the paste formulation, filling means, or amount of resin added, but are commonly obtained. However, depending on the purpose of the battery, voltage drop may or may not be allowed depending on whether characteristics such as high energy density or high output are desired.

Example 2 When pre-mixing 1 kg of lead powder with 200 c.c. of water according to the usual method, the order of addition was as follows: First, silicone was mixed in a one-component solution at room temperature so that the silicone solid content was 0.5% by weight based on the lead powder. A vulcanized silicone emulsion was added and kneaded for about 3 minutes, and then an aqueous polytetrafluoroethylene dispersion was added and kneaded to a solid content of 0.5% by weight based on the lead powder. Compound (P), during preliminary kneading, first add 0.5% by weight of polytetrafluoroethylene aqueous dispersion to the lead powder as a solid content, and then complete the addition kneading of sulfuric acid. After that, an aqueous emulsion of silicone was added as a solid content of 0.5% by weight to the lead powder and kneaded (Q).The amounts of polytetrafluoroethylene and silicone were the same as in (Q), and during preliminary mixing. Kneaded at the same time (R)
adjusted.

Although both pastes had rubber-like elasticity, the properties of the pastes were slightly weaker than that of (A), and the slippage and filling properties of the pastes were much improved compared to (A). Among them, the filling properties of (Q) and (R) were significantly improved compared to (A).

Next, the life characteristics were investigated in the same manner as in Example 1, and the results are shown in FIG. As a result, (P), (R)
(Q) showed almost the same life course, and (Q) was slightly inferior. For these reasons, by adding silicone emulsion before the polytetrafluoroethylene network forms, it is possible to suppress the degree of decrease in fluidity of the mixture due to the polytetrafluoroethylene network. It can be seen that the filling property is improved. Therefore, adding the aqueous silicone emulsion (Q) after the complete network formation improves the plasticity of the mixture only to a small extent.

The reason why (P) and (R) are the same in terms of life is that the precipitation of silicone polymers from the aqueous silicone emulsion occurs only extremely locally during kneading, and the life-improving stage is the final step. This is thought to be due to the similarity in structure between the protective structure of silicone, which covers even the finest particles, and the large network formed by the fluororesin network during the drying stage in which moisture is removed.

Also, the reason that (P) and (R) have slightly better lifespan than (Q) is related to the fact that silicone aqueous emulsion is added before adding sulfuric acid. In parallel with the change of the active material to sulfide and growth, silicone is locally precipitated in the form of being embedded in the active material particles during the growth process, and is connected to the full-scale coating layer completed at the final drying stage. It is thought that this will provide a strong protective structure.

In addition, the properties change slightly depending on the liquid properties in the kneaded product, and if the acidity is strong, the bonding force of the silicone polymer porous body produced is somewhat weak and exhibits swelling properties, which is preferable for high rate discharge properties, but The lifespan will be slightly reduced. On the contrary, from neutrality to alkalinity, it exhibits strong binding properties, so in order to improve lifespan, it is desirable to have a pH of 7 or higher.

As described above, the present invention has the property that the fluororesin forms a network during kneading after addition of sulfuric acid,
The aqueous emulsion of silicone comes into contact with the active material in a wet state during kneading, and the water dissipation process in the subsequent drying process interacts with the formation of a polymer aggregate that covers the active material in a porous state. It forms a strong protective structure for the active material that cannot be obtained by treatment with either fluororesin or silicone aqueous emulsion alone, and is suitable for both positive and negative electrodes, as well as for the electrodes to which it is applied. Regardless of the shape, it is common to improve the life of electrodes that are filled with active materials that are kneaded and adjusted.

Note that the filling amount is not limited to this example, and conditions suitable for the application can be selected from the viewpoints of lifespan, rapid discharge characteristics, and the like.

[Brief explanation of drawings]

FIG. 1 and FIG. 2 are diagrams showing changes in capacity retention rate due to charging and discharging of lead-acid batteries using various positive electrodes.

Claims (1)

[Claims] 1. At the stage of preparing a mixture containing lead powder, water, and sulfuric acid as main components, a dispersion of fluororesin and an aqueous emulsion of one-component room-temperature vulcanizable silicone rubber are allowed to coexist. knead it, fill it into a support,
A method for producing an electrode for a lead-acid battery, the method comprising the step of drying the electrode. 2. The method for producing an electrode for a lead-acid battery according to claim 1, wherein the pH of the kneaded product in the final kneaded state is 7 or more.