JP3135239B2 - Nickel positive electrode for batteries - Google Patents

Description

The present invention relates to a nickel positive electrode for a battery,
Specifically, the present invention is applied to a non-sintered nickel positive electrode for an alkaline battery.

2. Description of the Related Art A nickel positive electrode for a battery generally has a metal cylindrical, bag-shaped, or lattice-shaped support filled with an active material, or a metal sintered body filled with an active material. The former using a cylindrical, bag-shaped or lattice-shaped support has the advantage that the filling capacity can be increased, but has the disadvantage that the high-rate discharge characteristics are poor. Further, the latter using a metal sintered body support has an advantage that the high rate discharge characteristics are excellent, but has a disadvantage that the filling capacity is small.
In order to improve both disadvantages, a battery electrode using a foamed metal having a continuous three-dimensional network structure having a high porosity as a support has recently been proposed. This method of filling the foamed metal with the active material can be said to be an electrode suitable for high capacity and high rate discharge.

Problems to be Solved by the Invention When a nickel positive electrode is used for a secondary battery such as a nickel cadmium storage battery, the nickel active material expands and contracts during charging and discharging, and the nickel plate is repeatedly charged and discharged. Causes swelling. The expansion of the electrode plate causes compression of the separator provided between the positive electrode and the negative electrode, causing a short circuit between the positive electrode and the negative electrode, or a deterioration in life due to uneven distribution of the electrolyte present in the battery. Such expansion of the nickel positive electrode becomes remarkable particularly in the non-sintered type in which the strength of the active material holding member is weaker than that in the sintered type. In order to solve such a problem, for example, as disclosed in JP-A-59-83347, in order to prevent expansion and contraction of a nickel active material, a mixed use of nickel hydroxide powder and a zinc compound is used. Proposed, but leaves room for further improvement.

The present invention solves such problems, while maintaining the advantage of the high capacity of the non-sintered nickel positive electrode, by improving the charge-discharge cycle life characteristics that are inferior to the sintered nickel positive electrode, It is intended to provide a high capacity, high performance nickel positive electrode.

Means for Solving the Problems The present invention uses, as a nickel hydroxide active material powder used for a non-sintered nickel positive electrode, a powder having a zinc compound powder layer fixed on the surface thereof.

Action The nickel active material undergoes a volume change due to the movement of protons due to charge and discharge or a change in crystal form.

Since the nickel positive electrode is usually initially filled with a nickel hydroxide active material at a high density, the volume change of expansion and contraction due to charging and discharging of the nickel active material causes expansion as an electrode plate. This is probably because the active material powder is miniaturized due to a change in volume at the time of charge and discharge, and the bulk specific gravity of the active material powder is reduced. A particularly remarkable change in volume due to charge and discharge of the active material is the formation of nickel oxyhydroxide (γ type) having a low specific gravity due to overcharging. As a means for suppressing the formation of γ-type nickel oxyhydroxide, addition of a zinc compound has been proposed, and a eutectic powder of nickel hydroxide and zinc hydroxide is used as an active material of a non-sintered nickel positive electrode. If a mixed powder of nickel hydroxide and zinc hydroxide is used, the life characteristics are improved to some extent.

The present inventors have studied in detail the expansion of the electrode plate due to miniaturization at the time of charge and discharge of the active material powder, the finer active material,
In particular, they have been found to be remarkable on the surface of the active material powder.

The suppression of the formation of γ-type nickel oxyhydroxide by the addition of the zinc compound is considered to be due to the suppression of expansion between the nickel layers by the presence of zinc ions between the nickel layers in the nickel hydroxide crystal.

Since the miniaturization of the active material powder due to charge and discharge is particularly remarkable on the surface of the powder, only the zinc compound added for suppressing the zinc compound existing on the surface of the nickel hydroxide powder is effective. In the eutectic active material powder of nickel hydroxide and zinc hydroxide used for the nickel positive electrode, the zinc compound present inside nickel hydroxide does not work effectively, and nickel hydroxide and zinc hydroxide are mixed. In the case where zinc hydroxide is used as it is, only the zinc hydroxide present on the surface of nickel hydroxide contributes to the improvement of the life, and the effect of zinc hydroxide is not efficiently exhibited.

On the other hand, in the present invention, since the nickel hydroxide active material powder having the zinc compound layer fixed on the surface is used as the active material for the non-sintered nickel positive electrode, the effect of the zinc compound is effectively exhibited, The addition of a small amount of a zinc compound significantly improves the charge / discharge life of a non-sintered nickel positive electrode.

Examples Hereinafter, the present invention will be described in detail with reference to examples.

An active material powder in which a layer of zinc hydroxide powder having an average particle size of about 1 μm is immobilized on the surface of nickel hydroxide powder having an average particle size of about 20 μm is prepared. The immobilization of the zinc hydroxide powder layer on the nickel hydroxide surface was performed by a method (hybridization) of immobilizing the child particles (zinc hydroxide) on the surface of the base particles (nickel hydroxide) by mechanical impact. . At this time, the molar ratio of nickel hydroxide to zinc hydroxide in the active material powder was 90:10 to 99: 1.

The active material powder is kneaded with water to form a paste, filled into sponge-like metallic nickel having a porosity of about 95%, and then subjected to pressure processing to form a single positive electrode plate. (A) was obtained. As a comparative example,
A positive electrode obtained by a similar method using an active material containing zinc hydroxide in the form of a eutectic in nickel hydroxide was trial-produced, and this was (b)
And As another comparative example, a positive electrode obtained by filling a mixed paste of nickel hydroxide powder and zinc hydroxide by a normal mixing method was prototyped, and this was designated as (c).

FIG. 1 shows a schematic configuration of the active material powder of each positive electrode. FIG. 1a shows the active material powder of the positive electrode according to the present invention, in which 1 indicates nickel hydroxide powder, 2 indicates zinc hydroxide powder, and b and c indicate configurations of the active material powder of the comparative example. .

Using these positive electrodes and a conventional paste-type cadmium negative electrode, a sealed nickel cadmium storage battery equivalent to 1.5 Ah was prototyped, and the battery characteristics were evaluated.

The battery was charged at 1 CmA for 1.5 hours at an ambient temperature of 20 ° C to evaluate the charge-discharge cycle life characteristics.
The charge / discharge of discharging for 1.5 hours with a resistance equivalent to A was repeated, and the maintenance ratio of the discharge capacity to the initial discharge capacity and the discharge characteristics were evaluated. The discharge characteristics were evaluated by the ratio of the discharge capacity at 3 CmA to the discharge capacity of 0.2 CmA at 20 ° C.

FIG. 2 shows a battery A using the positive electrode (a) according to the present invention,
In the batteries B and C using the positive electrodes (b) and (c) of the comparative examples, the amount of zinc hydroxide added to the nickel hydroxide active material and the capacity retention ratio become 80% or less of the initial capacity. It is a figure showing the relationship of the number of charge / discharge cycles. In the battery A using the positive electrode of the present invention, good life characteristics can be obtained with a smaller amount of zinc hydroxide than in Comparative Examples B and C. It is considered that the amount of addition should be about 1% or more in terms of molar ratio to nickel hydroxide. This is presumably because zinc hydroxide added to the surface of the nickel hydroxide most effectively acts on the nickel hydroxide powder, as described above and shown in FIG.

FIG. 3 also shows the addition molar ratio of zinc hydroxide and 20 ° C., 3
FIG. 4 is a diagram showing a relationship between discharge capacity ratios in CmA discharge.
In Comparative Examples B and C, the discharge characteristics were not deteriorated even when the ratio of zinc hydroxide added was increased. However, in the case of using the positive electrode according to the present invention, the discharge was increased by adding about 5% or more of zinc hydroxide. The characteristics have deteriorated. This is because, in the present invention, a layer of zinc hydroxide is immobilized on the surface of nickel hydroxide, so that when the amount of addition is large, the movement of the electrolytic solution on the surface of nickel hydroxide is obstructed, and the discharge characteristics Is considered to deteriorate. Therefore, it is considered that the appropriate ratio of nickel hydroxide to zinc hydroxide is about 99: 1 to 95: 5 in molar ratio. The same can be said for the particle sizes of nickel hydroxide and zinc hydroxide. If the particle size of the zinc hydroxide is too small, the layer of the zinc hydroxide on the nickel hydroxide becomes dense and the discharge characteristics deteriorate. On the other hand, if the particle size is too large, the surface of the nickel hydroxide particles cannot be sufficiently covered, so that the effect on the life characteristics cannot be sufficiently obtained.

Table 1 shows that, according to the present invention, 95: 5 molar ratio of zinc hydroxide powder was
2 shows the relationship between the average particle size of zinc hydroxide and the battery characteristics when arranged at a ratio of.

As described above, if the average particle size of zinc hydroxide disposed on the surface of the nickel hydroxide powder is too large, the life characteristics are reduced, so the upper limit of the average particle size is the average particle size of nickel hydroxide. About 1/10, and if the average particle size is too small, the discharge characteristics will deteriorate, the lower limit is
It is considered to be about 1/100 of the average particle size of nickel hydroxide. Therefore, it is considered that the average particle size of zinc hydroxide is appropriately about 1/10 to 1/100 of the average particle size of nickel hydroxide.

In this embodiment, zinc hydroxide is used as the zinc compound. However, similar effects can be obtained with zinc oxide or a mixture thereof.

As described above, according to the present invention, the disadvantages of the conventional non-sintered nickel positive electrode are improved, and a high capacity and high performance nickel positive electrode can be obtained.

[Brief description of the drawings]

1 (a), (b) and (c) are schematic diagrams of an active material powder in a nickel positive electrode, FIG. 2 is a diagram showing the relationship between the molar ratio of zinc hydroxide and the number of charge / discharge cycles, and FIG. FIG. 3 is a view showing a relationship between a molar ratio of zinc hydroxide and a discharge capacity ratio.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Tokuyuki Fujioka 1006 Kazuma Kadoma, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd. (56) References JP-A-63-218154 (JP, A) JP-A-59-112574 (JP, A) JP-A-63-301461 (JP, A) JP-A-59-83347 (JP, A)

Claims (2)

(57) [Claims] 1. A nickel positive electrode in which an active material powder mixture mainly composed of nickel hydroxide powder is filled in a metal substrate or a support, and the surface of said nickel hydroxide powder is made of zinc hydroxide powder or zinc oxide powder. A powder layer of any one of the above, or a mixture thereof, is fixed by hybridization, and the nickel hydroxide powder and the zinc hydroxide powder layer-fixed on the surface of the nickel hydroxide powder; The compounding ratio with zinc oxide powder is
A nickel positive electrode for batteries, wherein the molar ratio is in the range of 99: 1 to 95: 5. 2. The battery according to claim 1, wherein the average particle size of the zinc hydroxide powder and the zinc oxide powder is in the range of 1/10 to 1/100 of the average particle size of the nickel hydroxide powder. For nickel positive electrode.