JP3374994B2 - Paste type nickel electrode - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nickel electrode used as a positive electrode of an alkaline secondary battery, and more particularly to a nickel electrode having excellent cycle characteristics. 2. Description of the Related Art In recent years, nickel electrodes used as positive electrodes of alkaline secondary batteries such as nickel-hydrogen storage alloy batteries and nickel-cadmium batteries have increased capacity.
In order to reduce the cost, a metal foam or fibrous metal porous body having a porosity of 95% or more, a pore diameter or a fiber gap of about several μm to 100 μm is used as a substrate having a conductive action, A so-called paste-type nickel electrode that directly holds an active material paste containing nickel as a main component has been used (Japanese Patent Application Laid-Open No. 1-22736).
No. 3). When the above-described metal foam or fibrous metal porous body is used as a substrate, the average diameter of pores or fiber gaps in the substrate is large, so that the active material can be easily filled, and the amount of the active material can be easily filled. Can also be many. However, when the amount of the active material is increased, when a battery is assembled using the nickel electrode,
The swelling due to the generation of γ-NiOOH due to charge and discharge also increases, and as a result, the electrolyte present in the separator is absorbed by the nickel electrode, the electrolyte in the separator decreases, and the internal resistance of the battery increases. Cycle characteristics deteriorate. Therefore, nickel hydroxide [Ni (O
H ₂ )], a method of adding cadmium oxide (CdO) or a zinc compound to suppress the production of γ-NiOOH, to suppress the swelling of the nickel electrode, and to prevent the deterioration of the cycle characteristics of the battery (Japanese Patent Laid-Open No. No. 112574), iron (F
e), calcium (Ca), zinc (Zn), magnesium (Mg), cobalt (Co), etc.
A method has been proposed in which the generation of OOH is suppressed and the swelling of the nickel electrode is suppressed to prevent a decrease in the cycle characteristics of the battery (JP-A-5-41212). [0006] However, even with the above method, swelling of the nickel electrode due to the formation of γ-NiOOH cannot be sufficiently suppressed, and thus the deterioration of the cycle characteristics of the battery can be sufficiently reduced. Could not be suppressed. Accordingly, the present invention solves the problem that the conventional nickel electrode has poor cycle characteristics, suppresses the swelling of the nickel electrode due to the generation of γ-NiOOH due to charge and discharge, and improves the cycle characteristics. An object is to provide an excellent nickel electrode. SUMMARY OF THE INVENTION The present invention relates to a method of forming a swelling of a nickel electrode by forming γ-NiOOH upon charging and discharging by forming a part of a contact point of a lattice of a metal foam of a substrate into a web shape. And a nickel electrode having excellent cycle characteristics is provided. [0009] That is, since a part of the contacts of the grid of the metal foam of the base is web-like, the mechanical strength of the base is improved, whereby the swelling of the nickel electrode due to charging and discharging is suppressed. Thus, the cycle characteristics of the nickel electrode are improved. The active material paste to be filled in the substrate made of the specific metal foam is not particularly limited.
For example, various pastes such as the same active material paste as those conventionally used can be used. The paste-type nickel electrode of the present invention is, for example, a nickel-hydrogen storage alloy battery,
It can be used as a positive electrode of various alkaline secondary batteries such as a cadmium battery and a nickel-zinc battery. Next, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to only these examples. Example 1 A substrate having a thickness of 0.14 mm was manufactured by Nippon Heavy Chemical Industry Co., Ltd.
A nickel foam having a unit weight of 600 kg / cm ² and a porosity of 95% was used. FIG. 1 shows an electron micrograph of the nickel foam at a magnification of 50 times. FIG. 2 is a schematic diagram schematically showing an electron micrograph of the substrate made of the nickel foam shown in FIG. As shown in FIG. 2, in the base made of the nickel foam, a part of the contacts of the grid 1 made of nickel has a web-like shape 2. An active material paste for producing a nickel electrode is:
With respect to 100 parts by weight of nickel hydroxide (containing 2% of zinc and 0.7% of cobalt), 11.6 parts by weight of nickel powder, 2.2 parts by weight of cobalt powder, and cobalt oxide (Co
O) 28 parts by weight, 5.8 parts by weight of carboxymethylcellulose, 5.8 parts by weight of polytetrafluoroethylene dispersion (solid concentration: 60%), 1.8 parts by weight of potassium hydroxide and 49.5 parts by weight of water are added. And kneaded at room temperature for 72 hours. The active material paste for producing a nickel electrode is filled in a substrate made of the above-mentioned specific nickel foam,
After drying at 0 ° C for 1 hour, 2 ton / cm
Pressure was applied under a load of ^{2 to} a thickness of 0.66 mm, which was cut into a length × width of 82 mm × 39 mm, and a current collecting tab was attached to produce a nickel electrode. Comparative Example 1 As a substrate, a nickel foam having a thickness of 0.14 mm, a unit weight of 600 g / cm ² and a porosity of 95%, which was conventionally used by Sumitomo Electric Industries, Ltd., was used. FIG. 3 shows an electron micrograph of the nickel foam body at a magnification of 50 times.
Shown in As shown in FIG. 3, the web-like portions shown in FIG. 2 are not seen at the contacts of the grid of the substrate made of the nickel foam. The substrate made of the nickel foam was filled with the same active material paste as in Example 1 in the same manner as in Example 1.
After drying, pressing, cutting, and attaching a tab, a nickel electrode was produced. Next, a battery was assembled using the nickel electrodes of Example 1 and Comparative Example 1 as positive electrodes, and the degree of swelling and cycle characteristics of the nickel electrodes caused by charging and discharging were examined. First, regarding the swelling of the nickel electrode, a model cell shown in FIG. 4 was prepared using a cadmium electrode as a negative electrode, and an electrode swelling measuring apparatus shown in FIG. 5 was assembled using the model cell. In FIG. 4, reference numeral 10 denotes a model cell, 11 denotes a nickel electrode, and the nickel electrode 11 functions as a positive electrode in the model cell 10.
The nickel electrode produced as described above was cut into 1 cm square. Reference numeral 12 denotes a cadmium electrode. The cadmium electrode 12 functions as a negative electrode in the model cell 10. 13 is a separator made of a glass fiber nonwoven fabric, 14 is an electrolyte, and 30
% Potassium hydroxide aqueous solution, 15 is a weight,
The weight of the weight 15 is 2100 kg / cm ² . In FIG. 5, reference numeral 10 denotes a model cell shown in FIG. 4, reference numeral 20 denotes a swelling detector, reference numeral 21 denotes an amplifier for amplifying the detected swelling, and reference numeral 22 denotes a recorder thereof. In the test, the charged capacity of the nickel electrode used as a positive electrode in the model cell was charged at 1 C for 1.5 hours (corresponding to 150%), and charged at 0.9 V at 1 C.
The charge and discharge were repeated until the nickel electrode (positive electrode) after the charge and discharge was measured. FIG. 6 shows the result. In FIG. 6, open circles indicate the swelling rate of the nickel electrode of Example 1 after discharging, and black circles indicate the swelling rate of the nickel electrode of Example 1 after charging. The open triangle indicates the swelling rate of the nickel electrode of Comparative Example 1 after discharging, and the closed triangle indicates the swelling rate of the nickel electrode of Comparative Example 1 after charging. As shown in FIG. 6, the swelling ratio after 11 cycles was 28% in Comparative Example 1 corresponding to the conventional product, whereas it was 20% in Example 1 of the present invention. There were few. Next, the cycle characteristics were determined as follows. AA batteries were prepared using the nickel electrode as a positive electrode, the hydrogen storage alloy electrode as a negative electrode, and a 30% aqueous solution of potassium hydroxide as an electrolyte.
It investigated by repeating charge and discharge of Cx120% charge and 1C, 0.9V termination. FIG. 7 shows the result.
In addition, the hydrogen storage alloy electrode was produced as follows. Commercially available Ti, Zr, V, Ni, Cr (all of which have a purity of 99.9% or more) were converted to Ti ₁₇ Zr ₁₆ V ₂₃ Ni ₃₇ C
It was weighed so as to obtain a composition of r _7, dissolved by heating in a high frequency melting furnace, to obtain a multi-phase alloy. This alloy was evacuated to 10 ^-4 torr in a pressure vessel, purged with argon three times, and kept under a hydrogen pressure of 14 kg / cm ² for 24 hours, followed by evacuation of hydrogen. By heating to 400 ° C. to completely devolatilize hydrogen, a hydrogen storage alloy powder having a particle size of 20 to 100 μm was obtained. This hydrogen storage alloy powder was pressed against a substrate made of expanded metal of nickel using a roll mill, kept at 875 ° C. for 12 hours in an atmosphere of Ar / H ₂ = 99/1, and cooled to 30 ° C. Cut to thickness 0.3
A hydrogen storage alloy electrode having a length of 3 mm and a length × width of 120 mm × 41 mm was produced. Using this hydrogen storage alloy electrode as a negative electrode,
Using the nickel electrode as a positive electrode, the cycle characteristics examined by repeating charging and discharging at 1C × 120% and termination at 1C and 0.9V are as shown in FIG. As shown in FIG. 7, Comparative Example 1 had 700 cycles until the discharge capacity reached 0.5 Ah, whereas Example 1 of the present invention reduced the discharge capacity to 0.5 Ah. There were 950 cycles until the cycle was completed, and the cycle characteristics were significantly improved as compared with Comparative Example 1. As described above, according to the present invention, by using a metal foam in which a part of a grid contact is in a web shape as a base of a nickel electrode, the nickel electrode accompanying charge / discharge is used. Swelling was suppressed, and a nickel electrode having excellent cycle characteristics could be provided.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an electron micrograph (× 50) showing a metal structure of a nickel foam used as a substrate in Example 1 of the present invention. FIG. 2 is a schematic view schematically showing an electron micrograph of the nickel foam shown in FIG. FIG. 3 is an electron micrograph (magnification: 50) showing a metal structure of a nickel foam used as a substrate in Comparative Example 1. FIG. 4 is a schematic diagram of a model cell using a nickel electrode as a positive electrode. FIG. 5 is a schematic diagram showing an electrode swelling measuring device incorporating the model cell shown in FIG. FIG. 6 is a diagram showing a change in the swelling rate of a nickel electrode with an increase in the number of charge / discharge cycles of a model cell manufactured using the nickel electrode of Example 1 and Comparative Example 1 as a positive electrode and a cadmium electrode as a negative electrode. is there. FIG. 7 is a diagram showing a change in discharge capacity with an increase in the number of charge / discharge cycles of a battery manufactured using the nickel electrode of Example 1 and Comparative Example 1 as a positive electrode and a hydrogen storage alloy electrode as a negative electrode. [Explanation of Signs] 1 Grid 2 Webbed

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Claims (1)

(57) [Claims 1] At least a base material made of a metal foam is filled with an active material paste mainly composed of nickel hydroxide.
A paste-type nickel electrode produced by a step of drying and pressurizing, wherein a part of a contact point of a lattice of a metal foam of the base is web-shaped.