JPH0799693B2 - Paste type nickel positive electrode - Google Patents

Description

TECHNICAL FIELD The present invention relates to an improvement in a pasted nickel positive electrode.

[Prior Art and Problems] A typical alkaline secondary battery uses nickel as a positive electrode and uses cadmium, zinc, or hydrogen as a negative electrode. As a nickel positive electrode of such an alkaline secondary battery, conventionally, for example, a substrate obtained by molding and sintering carbonyl nickel is impregnated with an aqueous solution of a nickel salt, and then the nickel salt is converted into nickel hydroxide in an alkaline aqueous solution. There is known a so-called sintered nickel electrode manufactured by sintering. However, since the nickel positive electrode requires extremely complicated operations such as a manufacturing process of a sintered substrate, an impregnation of an active material, and a conversion process, there is a problem that mass productivity is poor.

Therefore, as an alternative to the sintered nickel positive electrode, nickel hydroxide is made into a paste with water together with appropriate additives, conductive materials, and binders, and the paste-like active material is formed into a foam metal or a sintered fiber. A so-called paste-type nickel positive electrode has been proposed in which a conductive positive electrode having a three-dimensional structure is coated and filled to form a nickel positive electrode. However, in such a paste type nickel positive electrode, it is difficult to reduce the cost because it is necessary to use a very expensive foam metal or sintered fiber.

Therefore, in order to reduce the cost of the paste-type nickel positive electrode, it is desired to use a conductive core having a two-dimensional structure such as punched metal or wire mesh instead of expensive foam metal or sintered fiber. . However, when the above-mentioned paste-like active material is coated and filled on the conductive core having a two-dimensional structure, the active material is not sufficiently retained, and a good conductive matrix is formed in the active material. However, it has been difficult to obtain a satisfactory paste-type nickel positive electrode.

The present invention has been made to solve the above-mentioned conventional problems, and improves the packing density of the active material with respect to the conductive core having a two-dimensional structure and the utilization rate of the active material during discharge, Prevents the active material from falling off the conductive core due to repetition
It is intended to provide a paste-type nickel positive electrode that achieves further cost reduction.

[Means for Solving Problems] The present invention provides a nickel positive electrode obtained by filling a conductive core having a two-dimensional structure with a paste active material containing nickel hydroxide as a main component. The paste type nickel positive electrode is characterized in that a short fiber made of nickel, nickel alloy or stainless steel having a length of 2 to 20 mm is mixed in the substance in an amount of 0.2 to 5.0% by weight based on the weight of the dry active material.

Examples of the conductive core having a two-dimensional structure include wire mesh, punched metal, expanded metal and the like.

Among the short fibers to be mixed in the paste-like active material, examples of the nickel alloy include Inconel and the like. The reason for limiting the length and blending amount of such short fibers to the above range is as follows. That is,
If the length of the short fibers is less than 2 mm, a conductive matrix that functions well as a holder for the active material cannot be formed, and the packing density of the active material in the conductive core and the utilization rate of the active material during discharge are improved. In addition, it is not possible to sufficiently prevent the active material from falling off the conductive core, but if the length exceeds 20 mm, the fibers will be entangled during kneading and the dispersion of the fiber distribution and the kneading workability will be significantly impaired. is there. On the other hand,
When it is less than 0.2% by weight, it is not possible to form a conductive matrix that functions well as a support and a conductor for the active material, the packing density of the active material in the conductive core, and improvement of the utilization rate of the active material during discharge, Further, it is not possible to sufficiently prevent the active material from falling off from the conductive core, and if the content of the active material exceeds 5.0% by weight, the fibers are entangled with each other during kneading, and the fiber distribution is not uniform. That is, the compounding amount (absolute capacity) of nickel hydroxide is decreased, and the cost is increased. The diameter of the short fibers is preferably in the range of 5 to 15 μm.

[Operation] According to the present invention, by coating and filling a conductive core having a two-dimensional structure with a paste-like active material in which a predetermined amount of a short fiber made of nickel, a nickel alloy or stainless steel is mixed. Since the short fibers form a matrix in the active material and act as a holder for the active material and a conductor, the packing density of the active material in the conductive core and the utilization rate of the active material during discharging can be improved. . In addition, since the short fibers act as a support for the active material, it is possible to prevent the active material from falling out of the core when charging and discharging are repeated, so that the performance of the paste type nickel positive electrode is greatly improved. Can be obtained. At the same time, since a conductive core having a two-dimensional structure such as punched metal or wire mesh can be used, a conventional sintering method or a conductive core having a three-dimensional structure such as foam metal or sintered fiber can be used. The cost can be remarkably reduced as compared with the paste type nickel positive electrode used.

[Examples of the Invention] Examples of the present invention will be described in detail below.

First, 90 parts by weight of nickel hydroxide and 10 parts by weight of nickel powder were kneaded with 0.3 part by weight of carboxymethyl cellulose and 30 parts by weight of water, and then the kneaded product had a wire diameter of 8 μm and a length of 1 m.
2.0 wt% of nickel short fibers of m, 2 mm, 5 mm, 10 mm, 15 mm, 20 mm and 25 mm were mixed with the active material in a dry state and further kneaded to prepare 7 kinds of pastes. Subsequently, these pastes were coated and filled in a punched metal, dried, and then roll pressed to produce a paste-type nickel positive electrode.

Each of the obtained nickel positive electrodes was incorporated into a battery to produce an alkaline secondary battery, and a charge / discharge test was performed on these secondary batteries to examine the capacity per unit volume of the nickel positive electrode. As a result, the characteristic diagram shown in FIG. 1 was obtained. As is clear from FIG. 1, the blending amount of the nickel short fibers is 0.2 to 5.0% by weight.
It can be seen that the capacity per unit volume of the nickel positive electrode can be effectively increased to 300 to 400 mAH / cc by using the short fiber having a length of 2 to 20 mm within the range (2.0% by weight). .

Also, 90 parts by weight of nickel hydroxide and 10 parts by weight of nickel powder were kneaded with 0.3 part by weight of carboxymethyl cellulose and 30 parts by weight of water, and a short nickel fiber having a wire diameter of 8 μm and a length of 10 mm was used as a dry active material. On the other hand, 0% by weight, 0.1% by weight, 0.2% by weight, 1.0% by weight, 2.0% by weight, 3.0% by weight,
A paste type nickel positive electrode was produced in the same manner as the above method except that 9 kinds of pastes prepared by blending 4.0% by weight, 5.0% by weight and 6.0% by weight were used.

Each of the obtained nickel positive electrodes was incorporated into a battery to produce an alkaline secondary battery, and a charge / discharge test was performed on these secondary batteries to examine the capacity per unit volume of the nickel positive electrode. As a result, the characteristic diagram shown in FIG. 2 was obtained. As is clear from FIG. 2, when the length of the nickel short fibers is within the range of 2 to 20 mm (10 mm), the blending amount of the short fibers is set to 0.2 to 5.0% by weight, and It can be seen that the capacity can be effectively increased to 300 to 400 mAH / cc.

Furthermore, the paste type nickel positive electrode produced by using a paste containing 0.2 to 5.0% by weight of nickel short fibers having a length of 2 to 20 mm has a good cycle life without the active material falling off during repeated charge and discharge. It was realized.

Although the short fibers made of nickel are used in the above embodiments, the same effect as in the embodiments can be obtained by using nickel alloy such as Inconel or short fibers of stainless steel.

[Effects of the Invention] As described in detail above, according to the present invention, the packing density of the active material in the conductive core having a two-dimensional structure and the utilization rate of the active material at the time of discharge are improved, and the charge and discharge are repeated. It is possible to provide a long-life, high-performance paste-type nickel positive electrode that prevents the active material from falling off and achieves further cost reduction.

[Brief description of drawings]

FIG. 1 is a characteristic diagram showing the relationship between the length of the short nickel fibers blended in the paste and the capacity per unit volume of the nickel positive electrode, and FIG. 2 is the blending amount of the short nickel fibers in the paste and the unit volume of the nickel positive electrode. It is a characteristic view showing the relationship with the capacity per hit.

Front page continuation (72) Inventor Kunihiko Sasaki 1 Komukai Toshiba-cho, Kouki-ku, Kawasaki-shi, Kanagawa Inside the Toshiba Research Institute Co., Ltd. (56) Reference JP-A-52-74842

Claims (1)

[Claims] 1. A nickel positive electrode comprising a conductive core having a two-dimensional structure and a paste-like active material containing nickel hydroxide as a main component, wherein the paste-like active material has a length of 2 to 20 mm. Short fiber made of nickel, nickel alloy or stainless steel is 0.2 to 5.0 with respect to the weight of the active material in a dry state.
A paste-type nickel positive electrode characterized by being blended in a weight percentage.