JPH024104B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing an electrode for a lead-acid battery, and aims to improve the life of the electrode.

The life of a lead-acid battery is often related to the bonding strength of the active material itself for both the positive and negative electrodes. In particular, in the case of positive electrodes, active material particles become finer due to repeated charging and discharging, weakening of interparticle bonds, softening and falling off, and short-circuiting at various parts due to floating debris. This is often due to bonding strength. In the negative electrode, in addition to deterioration due to shrinkage of the active material, there is also a phenomenon in which the bonding force weakens and the electrode plate becomes soft, especially in areas where pressure is not easily applied to the electrode plate.

To deal with this weakening of active materials, binders are generally used, and methods such as impregnating the electrode with dispersion of polyethylene or polytetrafluoroethylene are applied, but these resins Fine particles are deposited between the active material particles to generate bonding force, but in order to maintain sufficient strength, it is necessary to increase the amount of resin. The increase in resistance is significant. Furthermore, even if active materials and active material materials are kneaded to increase binding strength, fibers and network formation occur inside, which is effective for bonding between large secondary particles, but fine particles of active materials cannot be protected. Furthermore, even if the network is formed, it may be cut during the kneading process, making it difficult to control the conditions.
In other words, the protection of the active material of lead-acid battery electrodes essentially works by protecting the active material particles, which are becoming finer, while forming a porous protective structure, which ultimately Ideally, a bonding force between secondary particles should also be generated, and new materials and manufacturing methods that are compatible with this have been desired.

From this point of view, the present inventors have found that by bringing an aqueous emulsion of polymerizable silicone into contact with an active material in a wet state and adding a drying process to this, an extremely ideal protective structure for the active material can be obtained. I found it. In other words, in the process of water escaping from an aqueous emulsion of polymerizable silicone that has been brought into contact with an active material in a wet state, highly porous silicone rubber-like polymer aggregates adhere to the active material and precipitate, and these aggregates form a bond with each other. It not only binds together and covers the fine particles of the active material, but also grows astride secondary particles and even groups of secondary particles, as if they were contained in large and small porous capsules. For this reason, even if the contained active material is miniaturized, it will not be released from the capsules, and moreover, the capsules will bond with each other to maintain a stable bond between the particles over a long period of time. Furthermore, this polymer is highly elastic and can absorb the strain caused by the expansion and contraction of the active material, thereby preventing the entire electrode from breaking due to stress.

Silicone is generally known as a water repellent, and is mainly used for waterproofing textiles and equipment by dissolving silicone oil in petroleum-based solvents. This impedes the diffusion of the electrolyte into the battery and deteriorates the discharge characteristics. Furthermore, it is not easy to remove the remaining solvent, and treatment at high temperatures causes deterioration of the active material. On the other hand, water-based emulsions not only do not contain the above-mentioned undesirable components, but also the resulting silicone polymer aggregates are porous and have low water repellency, so the extent to which they inhibit the electrolyte from diffusing into the electrodes is small. few.

Normally, silicone is separated into a master emulsion and a catalyst, and they are mixed at the stage of application, but in the case of the present invention, lead, lead oxides, and sulfates in the active material are separated from the neutral region to the alkaline region. It is thought that lead ions, which are minutely dissolved due to their solubility, act as a curing catalyst, so it is not necessarily necessary to add a catalyst. However, in order for the protective layer itself to have elasticity, it is necessary to use a catalyst such as KOH, cesium hydroxide, (CH ₃ ) ₃ SiOK, etc. in the same way as when producing silicone rubber.
It is necessary to bring it into contact with the active material to increase the degree of polymerization and collect rubberization. However, in order to uniformly proceed with rubberization, conditions of approximately 150 to 200°C are required, which do not necessarily match the conditions for processing the active material.
Moreover, if a strong oxidizing agent is added during vulcanization, by-products such as CO ₂ will react with the active material and change the properties of the active material, so care must be taken. Furthermore, although it is not impossible to uniformly produce long-chain polymers, in reality, the manufacturing conditions may not necessarily match the conditions for handling the active material.

One of the ways to solve these difficulties is to
It has been found that it is appropriate to use a one-component room-temperature vulcanizable silicone rubber emulsion as the aqueous silicone emulsion in the case of a main electrode for a lead-acid battery. In other words, this silicone rubber emulsion is produced by polymerizing silicone polymers produced from dimethylpolysiloxane, methylhydrodiene polysiloxane, or their derivatives to various polymerization degrees such as 10 ³ to 10 ⁶ under conditions suitable for rubberization. It is stabilized and emulsionized as an intermediate product, containing almost pure silicone, and forms an extremely elastic silicone aggregate in the process of water evaporation. Moreover, it has the property of forming a porous layer on the surface of the active material during the process of contacting and drying the active material, and the bonding strength between the silicone rubbers produced is strong. Unlike a master emulsion, in which a new crosslinking reaction is bonded by a condensation reaction using a catalyst, silicone, which has already been polymerized to the rubber region, forms a strong bond in the process of water escaping from the emulsion state. It is thought that this occurs, but the mechanism is not yet clear.

In any case, as mentioned above, in the case of a one-component silicone rubber emulsion that is vulcanizable at room temperature, there is no need to apply the rubberization conditions to the conditions for handling the active material, and there is no need to apply the rubberization conditions to the conditions for handling the active material. It is possible to apply a process of contacting with an active material and drying it under conditions under which electrodes for lead-acid batteries can be handled normally, without considering by-products.

The properties of the silicone rubber polymer produced on the surface of the active material during the water dissipation process from the once vulcanized state depend on the liquid properties in the wet material during the water dissipation process. However, the same elastic bodies are not necessarily produced. For example, when dried from acidic sulfuric acid, the bonding strength is somewhat weak, but it shows some swelling, and the porous silicone rubber present in the electrode has little tendency to increase electrolyte resistance. It also has strong elasticity and bonding strength in the neutral to alkaline range,
Furthermore, when made into a strong alkali with caustic potash, the binding strength is strong and it also exhibits some swelling properties. Utilizing the above properties, conditions can be selected depending on whether the lifespan is emphasized or the rapid discharge performance is emphasized. In terms of strength, lifespan, elasticity, etc., it is appropriate for the liquid in the wet material to have a pH of 7 or higher. Note that the degree of alkalinity increases as the water evaporates, so it is not necessary to increase the concentration to an extremely high level. Also, in the process of water dissipation,
The presence of alkali metals such as Li, Na, and K is beneficial, even at levels of several tens of ppm based on the weight of silicone rubber. This is probably due to some kind of catalytic effect when the fine particles of silicone rubber bond with each other during the process of water dissipation.

Furthermore, once dried, the polymer aggregates produced from this silicone rubber emulsion do not dissolve in water again, and when they are brought into contact with the emulsion again and dried, they maintain a strong bond with the resulting polymer. A new polymer population is generated.

Because of the above basic properties, the state of the active material starts from lead or a lead compound or a mixture thereof, and is a product of reaction with water or sulfuric acid added as necessary. Even if the aqueous silicone emulsion comes into contact with the active material compounds of PbO ₂ and Pb after undergoing chemical charging, a polymer group is formed that adheres to the particles in each compound state as it dries. be done.
In addition, since the particles coated at any stage ultimately contribute to the electromotive reaction, all compounds from the starting material to the state where the final electromotive reaction occurs are collectively referred to as the active material herein.

Now, in the present invention, the compound of the active material may be in any state as described above, but the porous structure of the finally formed electrode differs at the stage of applying the present invention, which may affect the battery characteristics. This will give it some characteristics.

Most typically, the active material is loaded into a support;
This is a method in which a dried electrode (including the basic unit of the electrode) is impregnated with an aqueous silicone emulsion and then dried. In this case, there are paste-type electrodes in which a paste-like mixture is applied to a grid such as a grid and then dried, a clay-type electrode in which a porous tube is filled with lead powder (lead or lead oxide), and a porous tube, etc. It can be used in a wide range of applications regardless of the type of electrode, such as a modified clad type in which the electrode is filled with a paste or slurry mixture. The essential advantage is that we can freely select the formulation necessary for electrode reaction, complete the active material porous body, and then form a protective structure of silicone rubber that improves its lifespan. Therefore, the properties of the active material itself can be selected and the lifespan can be improved without essentially changing them. Of course, even if the present invention is applied in an unformed state, chemical charging is possible, so it may be brought into contact with an aqueous silicone emulsion either before or after chemical formation.

Note that silicone aqueous emulsions have good penetrating properties into porous bodies, so even if the present invention is applied to electrodes that already use emulsions or dispersions of other resins, it will not work with emulsions or dispersions of other resins. Even when used together, a sufficient protective structure can be formed to the inside.

In addition, at the stage of preparing a paste containing lead powder, water, and sulfuric acid as main components, an aqueous emulsion of polymerizable silicone is brought into contact with the active material and kneaded, and this is filled into a support and dried. This can bring about new structural changes. In other words, not only is extremely porous filling possible, but
A strong reinforcing effect occurs during final drying. The result is an electrode that is porous and has excellent rapid discharge characteristics, yet has excellent longevity characteristics.

If this is further kneaded with an aqueous emulsion of polymerizable silicone at a stage before sulfuric acid is added,
Not only is a more porous filling possible, but the overall strength of the electrode is also increased.

Furthermore, when kneading the active material, water-absorbing compounds such as polyethylene oxide, acrylic acid polymer, and water-absorbing materials made by combining acrylic acid with acrylonitrile fibers may be added to the kneaded material to increase the number of volumes in a relatively neutral region. By adding a material capable of absorbing 10 times more water, the porous filling properties and electrode strength of the above-mentioned kneaded product can be efficiently improved.

The reason why a matrix suitable for porous filling as described above is created during kneading and the strength is also improved has not yet been fully elucidated, but it is thought to be approximately as follows.

That is, even though the active material particles are in a wet state during kneading, the active material particles to which the polymerizable silicone emulsion is attached are exposed to the outside air, and the silicone polymer is locally precipitated due to some water dissipation. This can be seen from the fact that the more vigorously the mixture is stirred to incorporate air into the mixture, the more porous it tends to become. Once formed, this rubber-like polymer of silicone does not dissolve in water again, but adsorbs the silicone in the emulsion again, repeating precipitation including the previous precipitate, and locally depositing it into the active material in the kneaded mixture. The silicone continues to grow while remaining in close contact. In this way,
The apparent active material particles are made porous to form a highly porous filling matrix.

When an aqueous silicone emulsion is mixed into the mixture composition and sulfuric acid is added to it, the reaction between water and sulfuric acid from lead powder produces lead sulfate,
Monobasic salts, tribasic salts, tetrabasic salts, or crystal water compounds thereof are formed. In the process of these formations, the active material compound changes due to local water dissipation reactions due to reaction heat, frictional heat, etc., and as a result, silicone rubber polymers infiltrate into the crystals. It is thought that aggregates are formed and the porosity increases further. It is believed that the water-absorbing material serves to trap water that should be liberated from within the active material particles offshore of the active material particles. As a result of the above, the active material particles have an apparent high porosity, and their filling also facilitates filling with high porosity.

The strength of the electrode is not yet complete at this stage. In the final drying stage, water dissipates in the mixture, so that the silicone is heated to porously encapsulate one or more particle groups of active material particles, and furthermore, to encapsulate multiple particle groups. A molecular assembly is formed. In other words, bonds between particles are formed at this time, not during kneading. This means that the bonds formed during kneading will not be broken again during kneading, so the reinforcement of the electrode will not be weakened by kneading. in any case. At this time, silicone is accumulated and bonded during drying while also bonding with silicone polymer aggregates locally formed during kneading, so changes in the active material compound, especially
If silicone is infiltrated into the particles during the growth process, the electrodes will be reinforced more strongly by interaction with new silicone aggregates that form during drying. This effect is achieved by the silicone that is bonded through cross-linking or condensation reaction, and is achieved by sufficiently progressing the rubberization process. When a room temperature vulcanizable silicone rubber emulsion is used, there is a remarkable difference in both the reinforcing effect and the porosity forming effect, and it is extremely efficient and reliable.

The present invention will be explained below using examples.

First, to clarify the effect on the positive electrode,
Paste density as a relatively short electrode in terms of lifetime
An example in which the present invention was applied to an unformed board obtained by applying and drying a low density paste of 3.4 g/cc on a grid is shown.

For the aqueous silicone emulsion, a one-component room-temperature vulcanizable silicone rubber emulsion (silicone molecular weight 10 ⁴ - 10 ⁶ , solid content 45% by weight) is used as a stock solution, which is optionally diluted and the pH is adjusted. , the untreated board was immersed in it, and then pulled out and dried. The drying temperature was set at 100°C ± 10°C, but it is possible to dry at 200°C or lower as long as it does not affect the active material. A nominal 50Ah battery was constructed by combining the four positive electrodes obtained above with a negative electrode obtained by a conventional method, and the lifespan was investigated by repeated charging and discharging, and the influence of the voltage drop during sudden discharge on the diffusion of the liquid was investigated. I also looked into the degree.

To describe the conditions in more detail, in order to see the effect of the presence of alkali metals, A is a case in which the stock solution is diluted 50 times, and Na ₂ SO ₄ is added to it at 10 ppm each.
Those with 100 ppm added were designated as B ₁ and B ₂ .

For liquid properties, add NaOH to a 50-fold diluted solution.
was added to make the pH 14, and the acidity was adjusted to 2 molar sulfuric acid using _NaOH and H ₂ SO ₄ .
The ones adjusted to PH7 and PH14 are C ₂ , C ₃ , and C 3 , respectively.
C ₄ was adjusted to a 2 molar NaOH alkaline solution and designated as C ₅ . In addition, D refers to a device to which the present invention is not applied.

Regarding the dilution level, adjust the stock solution to PH14,
Those diluted 10, 100, 1000, and 10000 times were designated as E ₁ , E ₂ , E ₃ , E ₄ , and E ₅ , respectively.

The indicator of voltage drop during sudden discharge is -15℃
The voltage at the 30th second when discharging with a current of 300A,
The life span was defined as the number of cycles at which discharging for 2.5 hours became impossible when discharging for 2.5 hours and charging for 3 hours were repeated at a 3-hour rate. The relationship between the sudden discharge voltage and the lifespan at this time is shown in FIG.

As is clear from the figure, D
Compared to the above, all of the batteries in which the present invention was applied to the positive electrode had an improved lifespan. Among these, A and B ₁ ,
The difference in B ₂ indicates that the presence of alkali metals is effective, and in the C series, alkalinity is superior to acidity in terms of life. It can be seen that the voltage is slightly higher on the acidic side, and even on the alkaline side, the voltage increases as the concentration increases. This confirms that it is related to the swelling property mentioned earlier. E
The series shows that appropriate dilution is necessary to achieve both rapid discharge performance and long life, suggesting that selection should be made depending on the application.

Next, an example of a method of adding an aqueous silicone emulsion to the active material mixture will be explained.

The main ingredients are lead powder with an oxidation degree of 50 to 90%, water, and sulfuric acid, and the ratio of water and sulfuric acid is arbitrarily determined, and various pastes with a paste density of 3.0 to 5.0 g/cc are prepared. Aqueous silicone emulsions were added at various stages of the compounding. For the aqueous silicone emulsion, a one-component room temperature vulcanizable silicone rubber emulsion containing silicone rubber with a solid content of 45% by weight was used as a stock solution. For kneading, a sulfuric acid aqueous solution with a specific gravity of 1.35 is added dropwise to a preliminary mix consisting mainly of lead powder and water over 5 to 30 minutes, and then kneaded for another 5 to 30 minutes.
A 15-minute finishing kneading method was used, and the materials were classified as follows depending on the addition of the silicone aqueous emulsion and the kneading conditions.

In other words, F is the case where the emulsion is added at the pre-kneading stage, G is the case where the emulsion is added at the completion of dropping sulfuric acid, and polyethylene oxide (for lead powder) is added together with the emulsion at the pre-kneading stage.
The solid content of silicone in the emulsion was standardized to 0.6% by weight based on the lead powder in order to clarify the effects of each. Illustrated by example. The stock solution was adjusted in advance to pH 14 or higher with NaOH before use.

The kneaded product was filled into a commercially available grid using the same filling device, and the paste electrode was made into a uniform thickness of about 2 mm. Thereafter, it was dried according to the usual method. Thereafter, a battery was constructed with four positive electrodes and five negative electrodes, and a rapid discharge test and a life test were conducted.

The rapid discharge test was performed using a nominally 45Ah battery, and the discharge time to a final voltage of 1V/cell was determined at -15°C with a current of 300A. The life test consisted of repeating discharging at 8A to a final voltage of 1.7V/cell and charging at 8A for 6 hours.
The number of cycles until reaching 60% of the initial capacity was determined.

First, dimethylpolysiloxane was confirmed as a product from the electrode of the present invention. In case I to which the present invention was not applied, the paste adhered to the belt at the bottom of the filling device and did not form the shape of the electrode plate in the region where the paste density was 3.5 g/cc or less. On the other hand, according to the present invention, it was possible to manufacture electrode plates up to a low density region.

Next, the weight of the active material after drying the electrode plate is shown in FIG. 2 as the weight per cell. This result shows that when the present invention is applied to a case filled in the same way, it is likely to become porous and clogged. This suggests that by applying the present invention during kneading, a matrix is formed that is porously filled during kneading.

This has a deep relationship with discharge characteristics, especially during rapid discharge. − of a battery composed of each of the above electrodes
Figure 3 shows the relationship between discharge capacity per weight of active material and life at 15°C and 300A. As is clear from this figure, the battery to which the present invention is applied has a high overall discharge capacity per weight of active material during rapid discharge, and by enabling porous filling, rapid discharge It can be seen that the utilization rate of the active material increases. In addition to this, although there is still a property like I, in which the more porous the electrode is, the longer the lifespan will be, it can be seen that the decrease in the lifespan is significantly smaller compared to the degree to which the utilization rate is improved. . In other words, this provides one means of achieving both rapid discharge performance and improvement of life span, which have been considered difficult in the past.

Furthermore, regarding the amount of silicone, H
Based on the method of P ₁ to P ₃ , 5, 10, 20, the silicone solid content is 0.01, 0.05, 0.1% by weight based on the lead powder.
The results for extreme regions are shown in FIG. ₃ , with weight percentages _Q1 to Q3. In other words, it is possible to achieve high porosity filling over a wide range of addition amounts, and it is also possible to improve lifespan, indicating that the formulation can be selected depending on whether rapid discharge performance or longevity is important. It also shows that even in densely packed areas with low utilization rates, there is a long-life effect.

Although porous filling is now possible during kneading,
For P ₂ whose lifespan is still insufficient, use the undiluted solution.
P 2 ', which is obtained by diluting 20 times and adding the step of dipping _the electrode plate obtained in P ₂ , is shown in FIG. The results show that there was no significant decrease in rapid discharge performance, and that the lifespan was significantly improved. In other words, if the amount of silicone during kneading is insufficient, the reinforcing structure in the final drying stage will be weak, but it is possible to fully restore the life of the completed electrode by immersing the emulsion in it and drying it. Of course, repeating the soak-drying process helps improve longevity. It is also possible to arbitrarily combine steps A, B, C, E, etc. of dipping and drying.

Regarding the negative electrode, since the active material is ultimately spongy lead and has good conductivity, and the number of negative electrodes is greater than that of the positive electrode, there is no significant difference in rapid discharge performance.
Therefore, we conducted a life test to examine the characteristics in terms of life by combining an existing positive electrode treated with C ₄ conditions and a chemically formed negative electrode treated with P ₂ '. As a result, although the conventional negative electrode still showed sufficient negative electrode capacity after 220 cycles, the planar electrode plate at the end, where group pressure is less likely to be applied,
Weakening of the active material was observed. In contrast, the electrode of the present invention showed almost no damage and was found to have improved strength.

As described above, the present invention enables active material particles to be isolated by applying a step of contacting the active material with an aqueous silicone emulsion in a wet state and a step of removing water in the manufacturing process of the main electrode for lead-acid batteries. Then, a porous silicone rubber film is formed over multiple particles or even multiple particle groups, and these are connected to each other to provide elasticity and elasticity that protects the particles as they become finer and the bonds between the particle groups. This makes it possible to form a strong reinforced structure and extend the lifespan. Furthermore, by bringing the emulsion and the active material into contact during kneading, the present invention not only forms a porous matrix to be filled in the next filling process, but also facilitates improvement in the utilization rate during sudden discharge.
The final drying stage completes a structure that prevents a decrease in service life even in such a porous state.

In addition, since Toray Silicone SE1980 aqueous coating (one-component room temperature vulcanization type silicone rubber emulsion) manufactured by Toray Silicone Co., Ltd. can be applied to the silicone aqueous emulsion as in the examples, emulsifiers contained in commercially available products, Even if surfactants and impurities are present, it is thought that they will not affect battery performance.

Since the present invention produces excellent characteristics through the process described above, the basic process of the present invention and the reinforcement structure can be applied not only to the embodiments but also to paste-type electrodes, clad-type electrodes, and other similar electrodes. As long as the processes involved are similar, the effects of the present invention will be exerted.

As described above, the present invention broadly improves the life span of lead-acid batteries and further enhances their reliability, and its industrial value is extremely large.

[Brief explanation of drawings]

Figure 1 is a diagram showing the relationship between voltage and life during rapid discharge of lead-acid batteries using various electrodes, Figure 2 is a diagram showing the relationship between paste density and filling amount of various electrodes, and Figure 3 is per active material. FIG. 3 is a diagram showing the relationship between sudden discharge capacity and life.

[Claims]

1. A positive electrode grid for a lead-acid battery, characterized by having a coating made of a water-soluble polymer on the surface of the outer frame of the positive electrode grid.

Claims (1)

A method for producing an electrode for a lead-acid battery according to item 3 of the scope of the request.