JP3095236B2 - 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.

(Prior Art) A typical alkaline storage battery uses nickel as a positive electrode and cadmium or hydrogen as a negative electrode. Conventionally, a 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) Generally, a paste-type nickel positive electrode is filled with a paste inside a three-dimensional porous substrate serving as a core, and after regulating the paste overflowing from the three-dimensional porous substrate by a slit or the like, drying and drying. 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, at this time, the surface of the nickel positive electrode 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 that occur when the nickel positive electrode is wound, and the battery is removed. 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 it is an object of the present invention to provide a paste-type nickel positive electrode having excellent electrode characteristics without releasing the core of the nickel electrode when the electrode is wound. Is what you do.

[Constitution of the Invention] (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 layer mainly composed of nickel hydroxide on the surface of
Polytetrafluoroethylene is added to the active material paste filled in the substrate and the active material layer formed on the surface of the positive electrode, and is formed to a thickness of 10 to 100 μm. The amount of polytetrafluoroethylene added is 1.0 to 5 with respect to the nickel hydroxide of the active material layer.
The present invention relates to a paste-type nickel positive electrode characterized in that the amount of polytetrafluoroethylene added to the active material layer is more than that of the active material paste.

The reason why the thickness of the active material layer is set to 10 μm to 100 μm is that if the thickness is less than 10 μm, the release of the core is insufficient, and if it exceeds 100 μm, the electrode performance may be adversely affected.

The amount of polytetrafluoroethylene (hereinafter, referred to as PTFE) added to the active material layer is desirably 1.0 to 5% by weight based on nickel hydroxide of the active material layer. If it is less than the above range, no improvement in electrode characteristics will be observed, and if it is more than the above range, the amount of active material will be reduced, affecting the electrode capacity. The method of adding PTFE includes a method of adding the active material layer to the active material paste before applying it to the electrode surface, and a method of adding the paste by spraying or impregnating the surface applied to the electrode surface.

The amount of PTFE in the active material paste filled in the substrate is desirably 3% by weight or less. The porous substrate having a three-dimensional structure includes a nickel fiber sintered body, a nickel felt porous body, and a sponge-like nickel porous body. And the like.

(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.

However, when the active material layer is provided on the substrate surface as described above, there is a problem that the electrode characteristics are deteriorated and the active material is dropped off during a long cycle. This can be improved by adding PTFE to the active material paste and the active material layer. In other words, the PTFE added to the active material paste and the active material layer becomes fibrous and increases the binding between the active materials or between the active material and the core, and further increases the flexibility and electrode strength of the electrode. In this manner, the active material can be prevented from falling off from the electrode when the electrode is wound, and the electrode winding property and the electrode performance can be improved.

Also, due to the fiberization of PTFE on the electrode surface, the contact resistance on the electrode surface decreases, the winding property between the electrode and the separator increases,
As a result, it is possible to prevent winding of the electrode when winding.

However, excessive addition of PTFE causes a decrease in the discharge performance of the electrode. Therefore, the amount of PTFE inside the electrode is reduced, and the amount of PTFE is increased only in the active material layer on the surface.

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

First, nickel hydroxide 90% by weight and nickel powder 10
% Of carboxymethylcellulose and 0.5% by weight of PTFE with respect to nickel hydroxide, and then 45% by weight of pure water was added to the mixed powder, and kneaded to prepare a paste. This paste was filled into a sintered fiber substrate.

Subsequently, a paste to be applied to the electrode surface was prepared. This paste is made in the same way as the paste above, except that
The amount of PTFE is 3.0% by weight. This paste was applied to both sides of the substrate at a time of 20 μm (when the electrodes were completed).

The electrode thus obtained was dried, rolled by a roller press, and adjusted to a thickness of 0.6 mm to produce a paste-type nickel positive electrode such that the capacity per unit volume of the electrode was 650 mAH / cc. A cadmium electrode obtained by a usual method is wound around this paste-type nickel positive electrode through a separator, and an appropriate amount of an electrolytic solution is added thereto.
AH nickel cadmium battery was fabricated.

The fabricated battery was evaluated for the amount of active material dropped off and battery characteristics.

The evaluation of the amount of active material falling off was performed by winding the pasted nickel positive electrode alone on a 4 mm diameter shaft, then rewinding, and further winding three times, and the active material fell off the electrode at that time. This was done by weighing.

The electrode characteristics were evaluated by repeating a cycle of charging at 150% at 0.2 CA and discharging to 1.0 V at 0.2 CA ten times, then discharging at each rate from 1 CA to 5 CA, and applying 1.0 V
The utilization rate for the theoretical capacity was determined from the capacity at the time.

Next, an electrode was prepared in the same manner as in the above example except that the amount of PTFE added to the active material layer on the substrate surface was set to 0, 1, 5, 7, and 10% by weight, and similar tests and evaluations were performed. .

Also, for comparison, in the same manner as in the above example,
The amount of PTFE added was the same for both the paste inside the substrate and the paste on the surface, 0.5% by weight (Comparative Example 1) and
The same tests and evaluations as described above were conducted for the case where the content was 3.0% by weight (Comparative Example 2).

 The results of the above test are shown in FIGS.

FIG. 1 is a diagram showing the relationship between the amount of PTFE added to the active material layer and the amount of the active material dropped off, and FIG. 2 is a diagram showing the relationship between the amount of PTFE added to the active material layer and the rate characteristics.

As shown in FIG. 1, it can be seen that the amount of the electrode active material dropped off is remarkably reduced by the addition of PTFE in the active material layer. FIG. 2 shows that the amount of PTFE added to the active material layer was 7% by weight, 10% by weight.
It can be seen that in the case of weight%, the discharge characteristics of the battery decrease, and when a large amount of PTFE is contained in the substrate as in Comparative Example 2, the discharge characteristics decrease.

From the above results, by adding a larger amount of PTFE to the active material layer on the substrate surface than in the substrate, it is possible to obtain a battery with less falling of the active material and excellent electrode performance.

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 no separation of the substrate when wound with the negative electrode, prevents falling off of the active material layer during winding and poor winding, In addition, there is an effect that the electrode performance is excellent.

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between the amount of PTFE added to the active material layer and the amount of the active material dropped off, and FIG. 2 is a diagram showing the relationship between the amount of PTFE added to the active material layer and the rate characteristics.

──────────────────────────────────────────────────続 き Continuation of front page (72) Inventor Hirohito Teraoka 3-4-10 Minamishinagawa, Shinagawa-ku, Tokyo Inside Toshiba Battery Co., Ltd. (56) References JP-A-61-143941 (JP, A) 52-20235 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01M 4/24-4/32 H01M 4/62

Claims (1)

(57) [Claims] 1. A paste-type nickel positive electrode in which an active material paste containing nickel hydroxide as a main component is filled in a three-dimensional net-like porous substrate, and an active material containing nickel hydroxide as a main component is formed on the surface of the positive electrode. When the material layer is not in the substrate
Polytetrafluoroethylene is added to the active material paste filled in the substrate and the active material layer formed on the surface of the positive electrode, and is formed to a thickness of 10 to 100 μm. The amount of polytetrafluoroethylene added is 1.0 to 5 with respect to the nickel hydroxide of the active material layer.
A paste-type nickel positive electrode, wherein the amount of polytetrafluoroethylene added to the active material layer is greater than that of the active material paste by weight.