JPH03171564A - Sealed nickel-cadmium battery - Google Patents

Abstract

PURPOSE:To be able to adopt a nickel hydroxide positive plate to which graphite or carbon is added as a conductive material in a sealed battery by limiting the amount of cadmium hydroxide in a negative active material to less than the capacity of a positive active material which is in the discharged state. CONSTITUTION:The content of cadmium hydroxide in a negative active material is limited to 0.95 or less in the weight ratio based on the weight of nickel hydroxide in a positive active material. Polarization at which hydrogen evolution occurs of a negative plate in charging takes place at the same time as or before the completion of charging of a positive plate. The amount of cadmium hydroxide is limited to 0.95 or less in such a way that a battery is assembled when the negative plate is in the charged state, or cadmium hydroxide does not exist in the negative plate, then the positive plate is also made in the charged state. By detecting potential change in the negative plate in the final stage of charging, charging is finished. Oxygen gas evolution in the final stage of charging from the positive plate is thereby practically avoided.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a sealed nickel-cadmium battery, and relates to an oddly closed nickel-cadmium battery having a nickel hydroxide positive electrode plate containing graphite or carbon as a conductive agent. One item.

2. Description of the Related Art Conventionally, a sintered positive electrode plate has been used as the positive electrode plate of a sealed nickel-cadmium battery. Sintered positive electrode plates are manufactured by sintering nickel powder to create a porous body with a pore diameter of approximately 10 μm, and chemically filling the active material into this porous body. Since filling is done by a chemical method, the process is complicated and manufacturing costs are high.

Therefore, in recent years, new nickel hydroxide positive electrode plates have been developed by directly filling active material powder into substrates such as foamed metal nickel or nickel felt, or by applying active material to nickel-plated perforated steel plates or nickel mesh. A so-called paste-type positive electrode plate has been developed, and some of it has been put into practical use. This electrode plate is manufactured by directly filling or coating the active material on the substrate, so the manufacturing cost is lower than that of the sintered Shooke plate.

However, it is known that this paste-type positive electrode plate requires the addition of a conductive agent in order to obtain performance equivalent to that of a sintered-type electrode plate. Metal nickel powder is generally substituted as the conductive agent, but since metal nickel powder has a high specific gravity, it increases the weight of the electrode plate, which is not preferable. Therefore, it has been traditionally used as a conductive agent for boget type positive electrode plates.
Graphite and carbon, which have a smaller specific gravity than metal nickel, are being considered as conductive agents for paste-type positive electrode plates (Japanese Patent Laid-Open No. 143569/1983).

Pocket positive electrode plates are made by wrapping active silica powder, whose main component is nickel hydroxide, in a nickel mesh, etc., and are used as positive electrode plates in open-type nickel-cadmium batteries. It is something.

Problems to be Solved by the Invention Graphite and carbon are considered to be effective conductive agents, but they have the following problems when used in sealed battery systems. Conventional sealed nickel-cadmium batteries are sealed using a method called the Neumann method. This sealed system is designed so that the positive plate becomes fully charged before the negative plate at the end of battery charging, and the negative plate absorbs oxygen gas generated from the positive plate at the end of charging to maintain a sealed system. It is. In this method, FA scum is always generated on the positive electrode plate, and the battery temperature rises due to the scum absorption reaction. Therefore, if graphite or carbon is added to the positive electrode plate, it is easily oxidized and forms carbon roots in the electrolyte. This caused negative effects such as a drop in capacity and a drop in voltage.

For this reason, nickel hydroxide positive electrode plates to which graphite or carbon is added as conductive agents are difficult to apply to sealed batteries, and have been mainly used in open batteries.

Means for Solving the Problems In a sealed nickel cadmium battery equipped with a nickel hydroxide positive electrode plate containing graphite or carbon as a conductive agent, the present invention provides at least a negative electrode active material to prevent oxidation of graphite or carbon in the positive electrode plate. The amount of cadmium hydroxide contained in the cadmium hydroxide is made to be less than the capacity of the positive electrode active material in the discharged state, that is, the polarization leading to hydrogen generation in the negative electrode plate during charging occurs at the same time as or before the completion of charging of the positive electrode plate. It is characterized by:

A battery having such a function can be defined by the ratio of the positive electrode active material to the negative electrode active material. This point will be explained in more detail below.

The valence of the active material of the positive electrode in the discharged state and the charged state may vary depending on its composition and charge/discharge conditions, or it may be considered that the valence is at least 2.0 in the discharged state and about 3.2 in the charged state. On the other hand, the active material of the negative electrode can be considered to have a valence of 2.0 in a discharged state and a valence of 0.0 in a charged state. Therefore, the active material of the positive electrode is charged by a 1- and 2-electron reaction, and the active material of the negative electrode is charged by a 2-electron reaction. The active material of the positive electrode is 1
．． If it is charged by a two-electron reaction, the amount of electricity required to charge the divalent active material (nickel hydroxide) Ig is 0.
It is 3417^11. Since the negative electrode active material is charged by a two-electron reaction, the amount of electricity required to charge the divalent active material (cadmium hydroxide) Ig is 0. 3662
6 Therefore, if the content of cadmium hydroxide in the negative electrode active material is 0.95 times or less by weight relative to the nickel hydroxide in the positive electrode active material, hydrogen buildup will occur in the negative electrode plate during charging. Polarization will occur at the same time or before the positive plate is fully charged.

As described above, in the present invention, the amount of cadmium hydroxide in the negative electrode plate needs to be 0.95 times or less the amount of the positive electrode active material.

As a specific method, the amount of cadmium hydroxide is Og,
That is, a method may be adopted in which the negative electrode plate is assembled into the battery in a charged state. In this case, the positive electrode plate also needs to be brought into a charged state.

Alternatively, a positive electrode plate and a negative electrode plate in a discharged state may be assembled into a battery, and the battery may be sealed after overcharging.

The ratio of the amounts of active materials in the positive electrode plate and the negative electrode plate used in these methods may be any value, but in the state after sealing, the above-mentioned relationship is satisfied, that is, the content of cadmium hydroxide in the negative electrode plate is The weight ratio is less than 0.95 times the amount of nickel hydroxide in the positive electrode active material. Here, the value of 0.95 times is based on the amount of nickel hydroxide and cadmium hydroxide involved in charging the positive electrode active material and the negative electrode active material, and the value of 0.95 times is based on the amount of nickel hydroxide and cadmium hydroxide that are involved in charging the positive electrode active material and the negative electrode active material. It goes without saying that this value will naturally differ if nickel hydroxide or domium hydroxide with a large amount of hydroxide is present.

Function The battery of the present invention has an electrode configuration in which polarization that leads to hydrogen generation occurs on the negative electrode plate before the completion of charging of the positive electrode plate during charging, and by detecting the potential change of the negative electrode plate at the end of charging and terminating charging, the positive electrode plate This virtually eliminates the generation of oxygen scum that accompanies the final stages of charging. Graphite and carbon added to the positive electrode plate are stable because they do not easily generate oxygen scum, and nickel hydroxide positive electrode plates made with these conductive agents can be used even in sealed batteries. Further, regarding the shape of graphite or carbon to be added, a short fiber shape can provide a larger discharge capacity with the same weight addition than the conventional scale shape.

Example The present invention will be explained below using preferred embodiments.

[Example 1] 95 parts by weight of nickel hydroxide powder (manufactured by Tanaka Chemical Research Institute),
4 parts by weight of metallic cobalt (manufactured by MHO) and 1 part by weight of artificial graphite (manufactured by LONZA, LN600) were mixed, and a paste containing CMC was added to form a paste.

This paste was filled into nickel felt (manufactured by Sorapec) with a basis weight of 600 g/I2, and dried to a thickness of 0. 8I
Pressed to n. Then, after chemical charging and discharging, it was cut, and the theoretical capacity was 300 I^h, and the dimensions were 54 ll x 14 x.
O. A paste-type positive electrode plate of 81111 was manufactured. next,
Dimensions: 55mnx 15lIx 0.7n+m, 200lA of cadmium hydroxide, 100lA of metal cadmium
A cadmium negative electrode plate with a theoretical capacity of 300 nAh containing 300 nAh was fabricated. This one positive electrode plate, two negative electrode plates and a thickness of 0.2111
A separator made of polypropylene non-woven fabric (FT310 manufactured by Nippon Vilene Co., Ltd.) was combined to form an electrode plate group, placed in a rectangular metal container, and electrolyte solution (5.8M K
OH aqueous solution) was injected. This battery was charged with a current of 30m8 for 16 hours and then sealed to produce a sealed nickel-cadmium battery A according to the present invention. In this state, there is almost no cadmium hydroxide in the negative electrode plate, and the content of cadmium hydroxide in the negative electrode plate in the discharge state is approximately 095 times the content of nickel hydroxide in the positive electrode plate.

[Example 2] 95 parts by weight of Nigel hydroxide powder, 4 parts by weight of metallic cobalt, and 1 part by weight of graphite fibers (SG-241 manufactured by Dainippon Ink) having a fiber diameter of about 10 μm and a fiber length of about 100 μm were mixed to form a mixture containing mainly CMC. A paste was added to the paste. Using this paste, the same method as in Example 1 was used to obtain a theoretical capacity of 300 nAh and dimensions of 54 ln x 14 nm x 0.8.
A +nn paste type positive electrode plate was manufactured. This single positive electrode plate was combined with the same negative electrode plate 2 and separator as in Example 1, charged in the same manner as in Example 1, and then sealed to produce a sealed nickel-cadmium battery B according to the present invention.

In this state, there is almost no cadmium hydroxide in the negative electrode plate, and the content of cadmium hydroxide in the negative electrode plate in the discharge state is about 0.95 times the content of nickel hydroxide in the positive electrode plate.

[Example 3] 89 parts by weight of nickel hydroxide powder, 8 parts by weight of metallic cobalt, and 3 parts by weight of graphite fibers (SG241 manufactured by Dainippon Ink) having a fiber diameter of about 13 μm and a fiber length of about 130 μm were mixed, and a mixture containing mainly CMC was mixed. Add a paste to make a paste. Apply this paste to a thickness of 0. 0811In perforated steel plate, and after drying, the thickness is Q. I pressed it to 8+111. Then, after charging and discharging, it is disconnected and the theoretical capacity is 26
01'lAh, dimensions 54v++x 14nlx 0.8
An n+n paste type positive electrode plate was manufactured. One positive electrode plate, the same two negative electrode plates as in Example 1, and a separator were combined with silk, charged in the same manner as in Example 1, and then sealed to produce a sealed nickel-cadmium battery C according to the present invention. In this state, there is almost no cadmium hydroxide in the negative electrode plate, and the content of cadmium hydroxide in the negative electrode plate in the discharge state is about 0.95 times the content of nickel hydroxide in the positive electrode plate.

[Comparative Example 1] One positive electrode plate shown in Example 1, two cadmium negative electrode plates shown in Example 1, and a separator were combined and sealed immediately after injection of electrolyte to create a sealed type for comparison. Niggel~Cadmium battery D was manufactured.

[Comparative Example 2] One positive electrode plate shown in Example 2, two cadmium negative electrode plates shown in Example 1, and a separator were strung together, gfI was closed immediately after injection of electrolyte, and comparison σ A sealed nickel-cadmium battery E was manufactured for this purpose.

[Comparative Example 3] One positive electrode plate shown in Example 3, two cadmium negative electrode plates shown in Example 1, and a separator were combined and sealed immediately after injection of electrolyte to create a sealed type for comparison. Bamboo was made of Niggeroo cadmium battery F.

Batteries A, B, and C are batteries in which terminal voltage C increases at the end of charging due to polarization that leads to hydrogen generation in the cadmium negative electrode plate, and batteries D, E, and F exhibit polarization that leads to hydrogen generation in the negative electrode plate. It is not a conventional type battery.

These batteries were subjected to a charge/discharge cycle test under the following conditions.

[Charging] Batteries A and B were charged at a constant current with a current of 300 +nA until the terminal voltage reached 1.70V, and then charged at a constant voltage of 1.70V for 10 minutes.

Battery C: With a current of 260 nA, the terminal voltage is 1. Constant current charging is performed until the voltage reaches 70V, and then constant voltage charging is performed for 10 minutes at 1.70V.

Batteries D and E are charged at a constant current with a current of 3001118, and charging is terminated when the terminal voltage of the batteries drops by 10 nV from the peak due to the gas absorption reaction.

The battery F is charged at a constant current of 260 n^, and when the terminal voltage of the battery drops by 10 lV from the peak due to the gas absorption reaction, charging is terminated.

[Discharge] Battery A. B. D. E With a current of 300 nA, the terminal voltage is Q. Discharge until it reaches 8V.

Discharge batteries C and F with a current of 260m until the terminal voltage reaches 0.8V.

[Temperature] 20±2°C Batteries A, B, and C were charged by a method suitable for charging the batteries of the present invention, in which the batteries were charged to a constant voltage with a constant current, and then charged with a constant voltage. battery d. Charging of E and F was carried out using a method commonly used as a rapid charging method for sealed batteries, in which charging was performed at a constant current and the charging was terminated by detecting a drop in voltage at the time of full charge.

Figure 1 shows battery A. The results of cycle tests B, D and E are shown. These use nickel felt for the substrate of the positive electrode plate. It can be seen that batteries A and B according to the present invention have a lower discharge capacity at the beginning of the charge/discharge cycle than conventional batteries D and E, but have good capacity retention. In conventional batteries, the carbon in the positive electrode plate was oxidized during charging, increasing the concentration of carbonate radicals in the electrolyte and gradually decreasing the discharge capacity. In addition, battery A in which scale-like graphite was added to the positive electrode plate
It can be seen that batteries B and D to which short fibers were added had a larger discharge capacity and better capacity retention than B and C. The large discharge capacity is thought to be due to the fact that short fibers have better dispersibility in the active material than scales. This is thought to be due to the fact that the surface area of short fibers is smaller than that of short fibers.

Figure 2 shows the cycle test results for batteries C and F9.
It can be seen that the battery of the present invention has good capacity retention even when a perforated steel plate is used as the substrate of the positive electrode plate.

Effects of the Invention As described above, although the nickel-cadmium battery according to the present invention uses graphite or carbon for the positive electrode plate, there is no generation of oxygen gas in the positive electrode plate, so the charging/discharging cycle is difficult. A sealed nickel-cadmium battery with a long life and little loss of capacity even after repeated use is possible. Further, if graphite or carbon is used in the form of short fibers, a battery with higher performance is possible.

[Brief explanation of the drawing]

FIG. 1 and FIG. 2 are diagrams showing the results of a charge/discharge cycle test of a battery according to the present invention and a comparative battery. Noboru 1 Ryo Nabu 7 Le Internai 7 ｝Re Satoshi

Claims (1)

[Claims] 1. In a sealed nickel-cadmium battery equipped with a nickel hydroxide positive electrode plate containing graphite or carbon as a conductive agent, the content of cadmium hydroxide in the negative electrode active material is greater than that of the positive electrode active material in terms of weight ratio. A sealed nickel-cadmium battery, characterized in that it is 0.95 times or less of the nickel hydroxide contained therein. 2. The sealed nickel-cadmium battery according to claim 1, wherein the graphite or carbon has a short fiber shape.