JP3145392B2 - Paste nickel positive electrode - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial application field) The present invention relates to a paste-type nickel positive electrode used for an alkaline storage battery, and more specifically, does not cause short-circuiting of the electrode when the electrode group is wound. And a paste-type nickel positive electrode as described above.

(Prior Art) A typical alkaline storage battery uses nickel as a positive electrode and cadmium or hydrogen as a negative electrode. Conventionally, the nickel positive electrode of such an alkaline storage battery is obtained by impregnating a substrate obtained by molding and sintering carbonyl nickel with an aqueous solution of a nickel salt, and then converting the nickel salt to nickel hydroxide in an aqueous alkaline solution. Manufactured, so-called sintered nickel positive electrodes were common.

However, in recent years, as various electric products have become more portable, this sintered nickel electrode has a limit in increasing the capacity, and the manufacturing process of this nickel electrode is extremely complicated, such as impregnation of active material and conversion process. It is a problem that it is not economical, and as an alternative to the sintered nickel positive electrode, for example, a porous substrate having a three-dimensional structure such as a nickel fiber nonwoven fabric is directly filled with a paste mainly composed of nickel hydroxide. The so-called paste-type nickel positive electrode obtained has been proposed and partially commercialized.

(Problems to be Solved by the Invention) In general, a paste-type nickel positive electrode is prepared by filling a paste into a three-dimensional porous substrate serving as a core, controlling a paste overflowing from the three-dimensional porous substrate by a slit or the like, drying the paste, and then drying the paste. It is manufactured by rolling. The positive electrode thus obtained is wound around a negative electrode via a separator to form an electrode group.

However, the surface of the nickel positive electrode at this time is in a state where the core is exposed, and if this is wound as it is with the counter electrode, the core is released from the electrode due to cracks generated when the nickel positive electrode is wound, and the battery There is a problem that an internal short circuit is likely to occur.

The present invention has been made in view of the above problems, and provides a paste-type nickel positive electrode in which a core of a nickel electrode is not released when an electrode is wound, and therefore, a short circuit of an electrode group does not occur. The purpose is to do so.

[Means for Solving the Problems] The present invention relates to a paste-type nickel positive electrode obtained by filling a three-dimensional net-like porous substrate with an active material paste containing nickel hydroxide as a main component. An active material paste having a thickness of 10 to 100 μm formed by further applying and rolling an active material paste containing nickel hydroxide as a main component and a binder is formed on the surface of the substrate in a state where no substrate is present. And a paste-type nickel positive electrode.

Note that the thickness of the active material layer was set to the above range because 10 μm
If it is less, the release of the core is insufficient, and 100
If the thickness exceeds μm, the electrode performance may be adversely affected.

The active material layer contains nickel hydroxide as a main component, and may be the same as the active material paste filled in the core, but it is not necessary to be the same.

Examples of the porous substrate having a three-dimensional structure include a nickel fiber sintered body, a nickel felt porous body, and a sponge-like nickel porous body.

(Function) The present invention relates to a conventional paste-type nickel positive electrode in which a core composed of a porous substrate is filled with a paste mainly composed of nickel hydroxide, and an active material layer mainly composed of nickel hydroxide on the surface thereof. Is formed in a state where the substrate is not present, so that the core is not exposed when the electrode is wound, and the phenomenon that the core is released by cracking of the electrode does not occur. Therefore, electrode short circuit can be prevented.

(Example) An example of the present invention will be described.

First, 0.3% by weight of carboxymethylcellulose (based on nickel hydroxide) was added to a mixed powder composed of 85% by weight of nickel hydroxide, 10% by weight of cobalt oxide powder and 5% by weight of nickel powder. The mixture was added and kneaded (with respect to nickel hydroxide) to prepare a paste.

After filling this paste into the sintered fiber substrate, the paste was further applied to both surfaces thereof. The amount of coating depends on the thickness of the paste layer on this surface when the electrode is completed.
The amount is such that it becomes 50 μm at a time. Next, it was dried and rolled by a roller press to prepare a paste-type nickel positive electrode such that the capacity per unit volume of the electrode was 650 mAH / cc in a state where the thickness was adjusted to 0.6 mm.

A cadmium electrode obtained by a usual method was wound around this paste-type nickel positive electrode through a separator, and a nickel cadmium battery having a theoretical capacity of about 600 mAH was produced together with an appropriate amount of electrolyte.

For comparison, in the same manner, in the method for producing a nickel positive electrode having no active material layer on the surface of the nickel positive electrode, that is, in the above-described method for producing a nickel positive electrode, the paste was not applied to the surface after filling the paste into the sintered fiber substrate. A nickel positive electrode was manufactured, and thereafter, a battery was manufactured in the same manner.

Further, in the above embodiment, the thickness of the active material layers on both surfaces of the nickel
Electrodes having a thickness of 20, 100, and 200 μm were produced, and a battery was produced in the same manner.

An insulation test and evaluation of battery characteristics were performed for each of the above batteries.

To evaluate the battery characteristics, charge the battery at 150% with 0.2CA,
After repeating a cycle of discharging to 1.0 V at 0.2 CA ten times, the battery is charged to 150% at 0.2 CA, discharged to 1.0 V at each rate, and the utilization rate for the theoretical capacity is obtained from the capacity at that time. The results evaluated by this method are shown in the figure.

 The results of the insulation test are shown in the following table.

As is clear from the above table, it was found that the provision of the active material layer on the surface of the nickel positive electrode significantly reduced the short circuit of the electrode.

Further, as shown in the figure, it was found that when the thickness of the active material layer on the surface of the nickel positive electrode exceeded 100 μm, the rate characteristics of the electrode were adversely affected.

In the above embodiment, a sintered fiber substrate was used as the three-dimensional net-like porous substrate, but a felt-like nickel porous body,
The same effect was obtained by using a sponge-like nickel porous body.

[Effects of the Invention] As described above, the paste-type nickel positive electrode of the present invention has a structure in which the active material layer without the substrate is formed on the surface, and thus, the conventional paste-type nickel positive electrode is wound around the negative electrode via the separator. The occurrence of a short circuit in the battery due to such separation of the substrate can be prevented.

[Brief description of the drawings]

The figure shows the relationship between the rate characteristics of the battery and the thickness of the active material layer on the surface of the nickel positive electrode. A: Electrode surface thickness 0 μm B: Electrode surface thickness 10 μm C: Electrode surface thickness 20 μm D: Electrode surface thickness 50 μm E: Electrode surface thickness 100 μm F: Electrode surface thickness 200 μm

──────────────────────────────────────────────────続 き Continuation of front page (72) Inventor Hirohito Teraoka 3-4-10 Minamishinagawa, Shinagawa-ku, Tokyo Inside Toshiba Battery Corporation (56) References JP-A-61-143941 (JP, A) (58) ) Surveyed field (Int.Cl. ⁷ , DB name) H01M 4/32

Claims (1)

(57) [Claims] 1. A paste-type nickel positive electrode comprising a three-dimensional net-like porous substrate filled with an active material paste containing nickel hydroxide as a main component, and a binder containing nickel hydroxide as a main component on the surface of the positive electrode. A paste-type nickel positive electrode, wherein an active material paste having a thickness of 10 to 100 μm obtained by further applying and rolling an active material paste to which an agent is added is formed without a substrate.