JP3011454B2 - Hydrogen storage alloy for secondary batteries - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to a hydrogen storage alloy for a secondary battery used as a negative electrode material for an alkaline secondary battery.

(Prior Art) It is known that an alkaline secondary battery using a LaNi ₅ hydrogen storage alloy as a negative electrode has a higher capacity and a higher energy density than a nickel-cadmium secondary battery having the same volume. Such an alkaline secondary battery is characterized in that corrosion due to the reaction of the hydrogen storage alloy with the electrolytic solution and pulverization due to repetition of hydrogen storage and release during charge / discharge lowers the charge / discharge cycle life. Determine the final battery characteristics.

For this reason, many reports have been made to improve the characteristics by diversifying the hydrogen storage alloy. As a typical example, the Ni portion of the LaNi ₅ hydrogen storage alloy is represented by Co, Al, M
It is known that substitution with n, Fe, Cr, or the like reduces the hydrogen equilibrium pressure at the time of absorbing and releasing hydrogen, and improves the corrosion resistance of the alloy. In addition, L of the LaNi _5- based hydrogen storage alloy
It is also known that substituting part a with another rare earth element can improve the cycle life of the secondary battery.

By the way, when producing a negative electrode from a hydrogen storage alloy, by using an alloy powder activated by hydrogenation in advance, or by using a mechanically pulverized alloy and charging it after battery production and before shipping. An electrochemically hydrogen activated alloy powder is used. Since hydrogen activation (hydrogen storage) is performed in any of the alloy powders, the hydrogen storage alloy undergoes volume expansion. However, the order LaNi ₅ type hydrogen absorbing alloy and the hydrogen storage alloy of Ni and La and other elements substitutions have high homogeneity in high purity, it said volume is no portion where the strain is concentrated upon inflation, a rather slight in manufacturing Cracks are caused due to uneven concentration of alloy components caused by the difference in conditions, and a large difference occurs in the manner of the cracks. as a result,
The particle size distribution of the hydrogen-absorbing alloy particles cracked by the hydrogenation may be remarkably widened, or the average particle size may significantly change depending on the production lot. Therefore, the alkaline secondary battery incorporating the negative electrode produced from the hydrogen-activated hydrogen storage alloy has a problem that the characteristics such as the life are varied.

(Problems to be Solved by the Invention) The present invention has been made in order to solve the above-mentioned conventional problems, and the signal of cracks due to volume expansion at the time of hydrogen absorption is almost constant, and the particle size distribution is narrow and average. An object of the present invention is to provide a hydrogen storage alloy for a secondary battery capable of achieving a uniform particle size.

[Constitution of the Invention] (Means for Solving the Problems) The hydrogen storage alloy for a secondary battery according to the present invention has a general formula LnNi _{x Ay} , where Ln is at least one rare earth element containing Y, A is at least one of Co, Al, Fe, Si, Cr, Cu, Mn, x,
y represents x> 3.5, y <2.0, 4.5 <x + y <5.5, respectively, and has a precipitate phase in which oxygen and a rare earth element are combined in a stage before pulverization, and includes this precipitate phase The alloy has an oxygen content of 10 to 80 ppm released when heated at 1450 ° C. or more in an inert gas atmosphere.

The composition of Ln in the general formula representing the hydrogen storage alloy is La
40-50% by weight, Ce 0-10% by weight, Pr 5-15% by weight, Nd30-
45% by weight, other rare earth elements and impurities 0-5% by weight
It is desirable that A in the general formula is Co, M
More preferably, it is composed of three elements of n and Al.

The reason why x and y in the general formula representing the hydrogen storage alloy are limited is that if they deviate from the above range, it becomes impossible to reduce the hydrogen equilibrium pressure during hydrogen storage / release and to improve corrosion resistance. is there.

In the precipitation phase of the alloy, in an inert gas atmosphere, 14
The reason for limiting the amount of oxygen released when heated at 50 ° C. or more is as follows. If the amount of oxygen in the precipitated phase is less than 10 ppm, it is not only difficult to sufficiently induce cracks due to volume expansion during hydrogen storage, but also the number of cracks may be reduced. On the other hand, when the oxygen content of the precipitated phase exceeds 80 ppm, cracks due to volume expansion during hydrogen storage become remarkable, and when a negative electrode produced from the hydrogen storage alloy is incorporated in a secondary battery, the contact area with the electrolytic solution is increased. May increase more than necessary and accelerate the progress of corrosion of the hydrogen storage alloy.

As the oxygen source in the alloy, for example, SiO ₂ mixed in the alloy composition before melting can be mentioned.

(Function) The hydrogen storage alloy according to the present invention is represented by LnNi _x A _y ,
In the stage before pulverization, has a precipitated phase in which oxygen and a rare earth element are combined, and the alloy containing this precipitated phase is released in an inert gas atmosphere at a temperature of 1450 ° C. or more when heated at 1450 ° C. or more.
with ppm. When hydrogen is stored in such a hydrogen storage alloy in a hydrogen activation step or the like, for example, the hydrogen storage capacity of the precipitated phase in which the predetermined amount of oxygen and the rare earth element are located at the grain boundary portion is increased by the hydrogen storage capacity of the matrix portion. Is significantly different from the above, so that the strain accompanying the volume expansion at the time of occlusion of hydrogen concentrates on the above-mentioned precipitated phase and causes cracks. As a result, the progress of cracks due to volume expansion during hydrogen storage can be substantially constant, and a narrow particle size distribution and a uniform average particle size can be achieved. Therefore, by using the negative electrode made from such a hydrogen storage alloy, the surface area of the negative electrode, that is, the rate of increase of the contact area with the alkaline electrolyte can be kept constant, and the corrosion deterioration rate of the hydrogen storage alloy due to the reaction with the electrolyte can be reduced. Since it can be kept constant, an alkaline secondary battery having a long cycle life and stable characteristics can be obtained.

(Example) Hereinafter, an example of the present invention will be described in detail.

Example First, commercially available lanthanum-enriched misch metal Mm (approximate abundance ratio of main constituent elements; La 45% by weight, Ce 5% by weight, Pr 10% by weight, Nd 40% by weight), Ni, Co, Mn, Al and a small amount of SiO ₂ Mm _1.0 Ni _4.2 Co _0.2 Mn _0.3
Twenty alloy samples having a composition of Al _0.3 were prepared and annealed at 1000 ° C. for 10 hours in an inert atmosphere. Each of these 20 samples was mechanically pulverized into particles having a particle size of 90% by weight or more and 75 μm or less. Subsequently, 96% by weight of 25 to 75 μm alloy particles obtained by sieving the alloy particle diameter and 4 parts by weight of polytetrafluoroethylene are mixed, and kneaded and pressed on a nickel net to produce a hydrogen storage alloy negative electrode. did. Subsequently, these hydrogen storage alloy negative electrodes were wound together with a nickel electrode for a nickel-cadmium battery via a separator to form an electrode group. A KOH electrolyte was injected, and a secondary battery having a positive electrode capacity of 1000 mAh and a negative electrode capacity of 1500 mAh was assembled.

On the other hand, about 20 samples of the alloy 20 in the raw material stage after the above-mentioned annealing were used.
Weigh 3 g, heat these alloys under an inert gas atmosphere,
The total amount of oxygen released above 1450 ° C. was measured. The results are shown in Table 1 below.

About the obtained secondary battery, charging; 1000 mA, 90 minutes,
Discharge; charge and discharge were repeated under the conditions of 1000 mA and a cutoff voltage of 1 V, and the number of cycles required for the battery internal pressure to exceed 15 kg / cm ² at the end of charging was measured. The results are shown in Table 1 below together with the total amount of oxygen released from the alloy particles.

As is clear from the above Table 1, a hydrogen storage alloy negative electrode produced using an alloy having a total oxygen amount of 10 to 80 ppm released at 1450 ° C. or higher when heated in an inert gas atmosphere at the raw material stage was incorporated. Rechargeable batteries (No. 4 to 15 in Table 1)
It can be seen that the cycle life is superior to that of the secondary batteries (Nos. 1 to 3 and Nos. 16 to 20 in Table 1) using alloys whose total oxygen amount is out of the above range.

[Effects of the Invention] As described in detail above, according to the hydrogen storage alloy according to the present invention, the progress of cracks due to volume expansion during hydrogen storage is almost constant, and a narrow particle size distribution and a uniform average particle size can be achieved. Further, by using the negative electrode made of such a hydrogen storage alloy, a remarkable effect such as a secondary battery having an excellent cycle life can be obtained.

Continuing on the front page (72) Inventor Hiroshi Endo 1 Toshiba Research Consulting Co., Ltd., Komukai Toshiba-cho, Kawasaki-shi, Kanagawa Prefecture (72) Inventor Kazuta Takeno 3-4-1-10 Minamishinagawa, Shinagawa-ku, Tokyo Inside Toshiba Battery Co., Ltd. (72) Inventor Momoko Takemura 1, Komukai Toshiba-cho, Saiwai-ku, Kawasaki-shi, Kanagawa Prefecture Toshiba Research Institute, Inc. (56) References JP-A-2-277737 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) C22C 19/00 H01M 4/24 H01M 4/38

Claims (1)

(57) [Claims] 1. The general formula LnNi _{x Ay} , wherein Ln is at least one of rare earth elements including Y.
A is at least one of Co, Al, Fe, Si, Cr, Cu, Mn, x, y
Represents an x> 3.5, y <2.0, 4.5 <x + y <5.5, respectively, and has a precipitate phase in which oxygen and a rare earth element are combined in a stage before pulverization, and an alloy containing this precipitate phase Is a hydrogen storage alloy for secondary batteries, characterized by having an oxygen content of 10 to 80 ppm released when heated at 1450 ° C. or more in an inert gas atmosphere.