JPH0234433B2 - - Google Patents

Description

[Detailed description of the invention]

(a) Field of industrial application The present invention relates to a sealed alkaline storage battery equipped with a paste-type cadmium cathode plate, and in particular to a cathode plate that has improved oxygen gas absorption capacity and reduced hydrogen gas generation from the cathode. Regarding. (b) Prior art Paste-type cadmium cathode plates have superior advantages such as a simpler manufacturing process, lower manufacturing costs, and higher energy density than sintered cadmium cathode plates. Due to poor electron conductivity, the ability to absorb oxygen gas generated from the anode plate due to overcharging is poor, and when used in a sealed battery, the internal gas pressure tends to increase. The oxygen gas absorption reaction by this cadmium cathode plate is expressed by the following equation. Cd+1/2O ₂ +H ₂ O→Cd(OH) ₂ ...(1) In other words, it is a reaction at the gas, liquid, and solid three-phase interface, and the more metal cadmium and oxygen gas come into contact, the more active the reaction is. Since a sintered electrode plate has a conductive matrix of nickel sintered body serving as a base, the charging reaction proceeds uniformly over the entire electrode plate through this conductive matrix, and metal cadmium is likely to be generated near the surface of the electrode plate. However, in paste-type electrode plates, the active material layer has low conductivity, and the charging reaction progresses gradually from near the core to the plate surface, so metallic cadmium is generated near the plate surface, away from the conductive core. It's getting difficult. Therefore, oxygen gas is absorbed only after passing through the electrode plate surface layer, which has poor air permeability, resulting in a low oxygen gas absorption capacity. Further, when the cathode plate is overcharged after being fully charged, it reaches a hydrogen generation potential and begins to generate hydrogen. That is, this is an electrolytic reaction of water, and the following reaction occurs. 2H ₂ O＋2e ^- →20H ^- +H ₂ ↑ ...(2) Unlike oxygen, the hydrogen generated in this way cannot be consumed within the battery, and in order to suppress the generation of hydrogen, the capacity of the cathode plate is generally reduced. It is set to be larger than the capacity of the anode plate and is incorporated into the battery. However, as mentioned above, the paste-type cadmium cathode plate has low conductivity, so the fully charged region within the plate is unevenly distributed near the core.
When rapid charging is performed, the unevenly distributed fully charged regions reach the hydrogen generation potential and local hydrogen generation begins before the entire cathode plate becomes fully charged. It is known that the low oxygen absorption capacity and hydrogen generation can be considerably alleviated by chemical formation after the electrode plate is made, but this effect also disappears with repeated charging and discharging, so it is not sufficient. I can't say that. Therefore, in order to reduce costs, not only paste-type electrodes that do not undergo chemical conversion, but also paste-type electrodes that undergo chemical conversion, it is necessary to charge quickly for 5 hours or 1 hour. Application was difficult. (c) Purpose of the Invention In view of the above, the present invention provides a sealed structure that greatly improves rapid charging performance by improving the oxygen gas absorption capacity of the cathode plate and suppressing the generation of hydrogen gas from the cathode plate during rapid charging. The purpose is to provide a type alkaline storage battery. (d) Structure of the Invention The cathode plate used in the sealed alkaline storage battery of the present invention has a conductive layer made of carbon powder disposed on the surface of a pasty cadmium active material layer having a conductive matrix made of carbon fibers. (E) Example An example of the present invention will be shown and explained below along with a comparative example. Example 1.5 parts by weight of polyethylene fibers and carbon fibers (diameter 7 to 8 microns, long Add 1.0 parts by weight of graphite carbon fiber (1.5 mm in diameter and fired at 2000℃), methylcellulose and water and knead to form a paste.
Apply this paste to both sides of the electrode plate core, and after drying,
It is immersed in a suspension consisting of 100 parts by weight of water, 5 parts by weight of acetylene black and 7 parts by weight of polyvinyl alcohol, and then dried to obtain a cadmium electrode plate. This cadmium electrode plate was combined in an unformed state with a well-known sintered nickel electrode plate and a nylon nonwoven separator, and a caustic potassium electrolyte with a specific gravity of 1.26 was added to produce a sealed nickel-cadmium battery with a nominal capacity of 1200 mAH. This battery is called A. Comparative Example 1 A mixture of 90 parts by weight of cadmium oxide powder and 10 parts by weight of metal cadmium powder was mixed with 3 parts by weight of polyethylene fibers, methylcellulose, and water to form a paste, and this paste was applied to both sides of the electrode plate core. It is then dried to form a cadmium electrode plate. Using this cadmium electrode plate, a sealed nickel-cadmium battery was produced which was otherwise the same as in the example. This battery is called B. Comparative Example 2 In Comparative Example 1, adding polyethylene fiber
The amount was changed to 1.5 parts by weight, and 1.0 parts by weight of the same carbon fiber as in Example was added, and the other conditions were the same as in Comparative Example 1 to prepare a sealed nickel-cadmium battery.
This battery is called C. Comparative Example 3 In Comparative Example 1, the paste was applied to both sides of the electrode plate core, dried, and then immersed in a suspension consisting of 100 parts by weight of water, 5 parts by weight of acetylene black, and 7 parts by weight of polyvinyl alcohol. It is dried to form a cadmium electrode plate. A sealed alkaline storage battery was fabricated using this cadmium electrode plate and otherwise the same as in the example. This battery is designated as D. Batteries A, B, C, and D created as described above were overcharged at 0°C for 18 hours at a 3-hour rate current (400mA), and the internal gas pressure at the end of charging was measured, and then at 1.0C. The internal gas pressure was measured after discharging at a corresponding resistance. Table 1 shows the results. All data are measured on five batteries and expressed as the average value. In addition, the internal gas pressure at the end of overcharging is due to oxygen gas and hydrogen gas generated within the battery, and the residual internal gas pressure is due only to hydrogen gas because oxygen gas is consumed within the battery during discharge. be.

[Table] As is clear from Table 1, the battery A of the present invention has higher internal gas pressure after overcharging and higher internal gas pressure after discharging than battery B using a conventional paste-type cadmium cathode plate. It can be seen that the results have been greatly improved, and even better results have been obtained compared to comparative batteries C and D. This is because the cathode plate of the present invention has a carbon fiber matrix formed inside the active material layer, so the conductivity within the electrode plate is increased, and the hydrogen generation potential is partially reached within the electrode plate at an early stage. In addition, since the active material layer has a conductive layer made of carbon powder on the surface of the active material layer, conduction occurs through the carbon fibers inside the active material layer or the metal cadmium that is a charging product. Even when the core body and the conductive layer made of carbon powder are partially electrically connected, metal cadmium is generated on the surface of the active material layer through the conductive layer, so the oxygen gas absorption capacity is high. This is due to the fact that it has been greatly improved. Table 2 shows the internal gas pressures for batteries A and D after overcharging for 5 hours at 0°C at a 3 hour rate current and after resistive discharge.

[Table] Both batteries A and D have an internal gas pressure of 0 after discharge.
Kg/cm ² , no hydrogen gas is generated, and the internal gas pressure increases only slightly due to oxygen gas. Regarding hydrogen gas generation, considering the results in Table 1,
It can be seen that this is caused by extreme overcharging. The drawing also shows the relationship between overcharging time and internal gas pressure for batteries A, B, C, and D during 3-hour rate charging at 0°C. It is clear that it is excellent. In the present invention, carbon is used for the matrix inside the active material layer and the conductive layer on the surface of the active material layer, but when metal is used as a conductive material instead of carbon, the following problems arise. When using metal fibers as a matrix inside the active material layer, it is difficult to uniformly disperse the metal fibers during paste kneading. When metal cadmium is used, the effect cannot be sustained because the metal cadmium directly participates in charge/discharge reactions and becomes cadmium hydroxide with low conductivity. When aluminum, zinc, tin, lead, copper, etc. are used, the effect is lost because they dissolve into the alkaline electrolyte. In addition, zinc forms needle-shaped crystals on the cathode surface through charge-discharge reactions, causing internal short circuits and shortening battery life, while lead accelerates deterioration of electrode plate capacity, and copper causes Cu ²⁺ ←→
The reaction of Cu ³⁺ promotes battery self-discharge. When iron, nickel, cobalt, platinum, etc. are used, the hydrogen overvoltage is small, which causes significant hydrogen gas to be generated from the cathode during overcharging, leading to destruction of the sealed battery internal system. Gold, silver, and other metals that are produced in small amounts are much more expensive than carbon powder, making it difficult to put them into practical use. Other metals that are close to non-metallic elements and substances called conductive metal oxides are also not effective because they have low conductivity, are less effective, or are expensive. On the other hand, carbon is (1) stable in alkaline electrolyte, (2) does not participate in charge/discharge reactions and has no effect on battery characteristics, and (3) does not cause significant hydrogen gas generation due to reduction in hydrogen overvoltage. (4) It has the characteristics of being inexpensive, and can be said to be a superior and more effective material compared to metals. When the carbon added inside the active material layer is in the form of fibers, the conductivity within the electrode plate is better than when it is in the form of powder, and in addition to acting as a conductive material, carbon fibers also have some Since it also has a reinforcing effect, it is possible to reduce the amount of reinforcing resin fibers added, suppress a decrease in the amount of active material filled, and improve the electrical conductivity of the entire electrode plate. (F) Effects of the Invention The cathode plate used in the sealed alkaline storage battery of the present invention has a conductive layer of carbon powder provided on the surface of a pasty cadmium active material layer having a conductive matrix made of carbon fibers. It is possible to easily and inexpensively improve the oxygen gas absorption capacity without chemical formation, suppress hydrogen gas generation, and provide a sealed alkaline storage battery with greatly improved rapid charging performance. Then,
Its industrial utility value is great.

[Brief explanation of drawings]

The drawing shows the relationship between overcharging time and internal gas pressure for the battery A of the present invention and comparative batteries B to D.

Claims (1)

[Claims] 1. A sealed alkaline storage battery comprising a cathode plate formed by providing a conductive layer of carbon powder on the surface of a paste-like cadmium active material layer having a conductive matrix made of carbon fibers.