JPH04137361A - Sealed type nickel-hydrogen storage battery - Google Patents

Abstract

PURPOSE:To increase the oxidation-resistant property of a negative electrode and to improve the stabity of the cell internal pressure and the cycle life by mixing a metallic condition of nickel layer and cobalt layer, and an oxide layer of at least one component of the alloy components to the surface of the alloy powder of a hydrogen storage alloy negative electrode. CONSTITUTION:To the surface of a hydrogen storage alloy, not the alloy condition of nickel and cobalt, but a metallic condition of nickel layer and cobalt layer, and an oxide layer of La, Ce, Co, Mn, or the like which is at least one component of the alloy components are mixed, and a hydrogen storage alloy negative electrode including these powders and a binder, and a nickel oxide positive electrode are contacted closely through a separator to form an electrode body, which is housed in a battery container, and an electrolyte is poured and sealed. As a result, at the oxidation-resistant property in the electrolyte, and in an overcharged condition, the resistance to oxidation to the oxygen gas generated from the positive electrode is increased, and the service life of the battery is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a sealed nickel-hydrogen storage battery using a hydrogen storage alloy that electrochemically absorbs and releases hydrogen reversibly in an electrolytic solution as a negative electrode material. Hydrogen storage alloys, which are active materials that can store and release large amounts of hydrogen, are attracting attention as electrode materials with high energy density, and are being used in sealed nickel-metal hydride storage batteries that aim to increase capacity. Applications are being planned. However, hydrogen storage alloys are easily oxidized in alkaline electrolytes, and the oxidation is accelerated by oxygen gas generated from the positive electrode during overcharging, resulting in the formation of hydroxides on the surface.

This reduces the charging efficiency of the hydrogen storage electrode, which is the negative electrode, and generates a large amount of hydrogen gas in the sealed battery, increasing the internal pressure of the battery, causing leakage and increasing internal resistance of the battery, which shortens the charge/discharge cycle life. It has the disadvantage of being short.

In order to prevent oxidation of the hydrogen storage alloy and extend its life as described above, a hydrogen storage alloy is made of a powder, a catalyst, and a binder that has an oxide film of the alloy component formed in advance on at least a portion of the surface of the hydrogen storage alloy. A nickel-hydrogen storage battery using a hydrogen-absorbing alloy negative electrode has been proposed (Japanese Patent Application Laid-Open No. 1986-2
91862). However, the effect was not sufficient.

Problems to be Solved by the Invention The present invention aims to solve the above problems. That is, the purpose is to improve the stability of battery internal pressure and the cycle life of the battery by increasing the oxidation resistance of the hydrogen storage alloy negative electrode.

Furthermore, the purpose is to suppress the increase in electrical resistance caused by the formation of an oxide film on the alloy surface, thereby making it unnecessary to add a gas dissipation catalyst.

Means for Solving the Problems In order to solve this problem, the present invention provides a surface of a hydrogen storage alloy with a nickel layer and a cobalt layer in a metallic state, and at least one of the alloy components, e.g., instead of nickel or cobalt in an alloy state. L.A.

An electrode body in which a hydrogen storage alloy negative electrode containing a mixture of C6, Go, and Mn oxide layers and containing this powder and a binder and a nickel oxide positive electrode is closely attached via a separator is housed in a battery container. A battery is created by injecting an electrolyte and sealing it.

In addition, the hydrogen-absorbing alloy powder used in the present invention, which has a surface mixed with a metallic nickel layer, a cobalt layer, and an oxide layer of at least one of the alloy components, is prepared by a method or machine in which the powder is pulverized and then immersed in an alkali, washed with water, and dried. It can be adjusted by wet grinding, followed by washing and drying.

Function: According to such a sealed nickel-metal hydride storage battery, the surface of the alloy powder of the hydrogen-absorbing alloy negative electrode contains a metallic nickel layer, a cobalt layer, and an oxide layer of at least one of the alloy components. The oxidation resistance in an alkaline electrolyte and the oxidation resistance against oxygen gas generated from the positive electrode during overcharging are improved, making it possible to improve battery life.

In addition, the formation of such a surface layer shows the effectiveness of the catalyst in accelerating the absorption rate of hydrogen gas, and the electrical resistance of the surface is also lower than that when only an oxide layer is formed. Since the amount of gas generated during charging is suppressed without adding anything, the internal pressure of the battery increases only slightly due to repeated charging and discharging cycles, making it possible to improve the battery life.

In addition, in the present invention, the appropriate thickness of the oxide mixed layer formed on the surface is in the range of 200 to 2000, and the amount of non-alloyed metal nickel and metal cobalt mixed in this oxide mixed layer is 0 as the saturation magnetization amount
．． The range of 0.05 to 12 emu/g is appropriate, and the BET specific surface area of the hydrogen storage alloy powder having these surface properties is optimally in the range of 0.1 to 1 tsvf/g.

Example Embodiments of the present invention will be described below with reference to the drawings.

As the composition of the hydrogen storage alloy, 'm'ix, s sMn
o, 4AlO, 3co0.75 (Ml is Mitshu Metal) was selected and ground by a mechanical method such as a jet mill or a ball mill to prepare an alloy powder having a predetermined average particle size.

Next, this powder is mixed with KO, which is an alkaline solution and has a specific gravity of 1.35.
After being immersed in an H aqueous solution at 80'C for 30 minutes, it was washed with water and dried.

The surface properties of this powder were determined by the thickness of the oxide layer and oxygen analysis using Ohne electron spectroscopy and combustion-infrared spectroscopy. Regarding nickel and cobalt in the metallic state, this alloy is weakly magnetic, and when nickel or cobalt becomes a single metallic state, it changes to a ferromagnetic material, so it is possible to quantify it by measuring the saturation magnetic susceptibility. be.

Furthermore, since these elements have a slower dissolution rate in a KOH aqueous solution than other elements in the alloy, it is easily presumed that they are present in the surface layer. The specific surface area was measured by the BIT method using nitrogen gas.

In the same manner, an alloy powder with a predetermined particle size was prepared, and then K
Powder samples with different surface properties were prepared by changing the OH concentration, treatment temperature, treatment time, and drying temperature in stages. These powder samples were made into a beinet shape with a 5 wt % aqueous solution of polyvinyl alcohol, filled into a porous nickel foam material serving as an electrode base, dried, and pressurized to obtain a hydrogen storage electrode. Next, a foamed nickel positive electrode obtained by a known method (theoretical charging charge of 1050 to 1100 mmh) was used as a nickel oxide positive electrode, a polyamide nonwoven fabric was used as the separator, and 40 g/min of lithium hydroxide was used as the electrolyte. Each dissolved KOH aqueous solution with a specific gravity of 1300 was used and combined with the negative electrode to form a sealed nickel-metal hydride storage battery of AA size (mu λ size) with a nominal capacity of 1000 mAh.

These batteries were charged at a constant temperature of 20°C for 15 hours with a 4 cm charger for the first cycle, and at V3 from the second cycle onwards.
It was conducted for 4.5 hours at Cmm. Also, the discharge is Q,,2C! up to the second cycle. It is constant, 0.50 mm is constant after the third cycle, and the final voltage is 1. I went as an ov.

FIG. 1 shows the relationship between the cycle life and the battery internal pressure after 10 cycles and the thickness of the oxide layer on the alloy surface.

FIG. 2 shows the amount of nickel and cobalt in the non-alloyed metal state mixed in the oxide mixed layer on the alloy surface in terms of the saturation magnetization amount, and shows the relationship between the saturation magnetization amount and the cycle life. FIG. 3 shows the relationship between BIT specific surface area and cycle life. The cycle life in the figure is expressed by the number of cycles at which the discharge capacity becomes a bar at the nominal capacity.

As is clear from FIGS. 1, 2, and 3, the thickness of the mixed oxide layer ranges from about 200 to 2000.
It can be seen that the magnetization amount is in the range of about 0.05 to 12 evau/g, and the BEET specific surface area is in the range of about 0.1 to 10 rrf/g, and the cycle life is longer in each case. Furthermore, as is clear from FIG. 1, by forming such surface properties, the internal pressure of the battery can be maintained at a low level. The above has described an example using an alkali immersion treatment, but there is also a method in which the alloy is pulverized by wet pulverization, and a method in which an oxide layer of a predetermined thickness is formed on the alloy surface by air oxidation, and then nickel or cobalt is vapor-deposited. A similar effect can also be obtained by

Effects of the Invention As detailed above, according to the present invention, it is possible to provide a sealed nickel-metal hydride storage battery that has a long battery life and can suppress the increase in internal pressure of the battery due to oxygen and hydrogen generated within the battery. .

[Brief explanation of the drawing]

Figure 1 shows the relationship between the thickness of the oxide layer on the surface of the negative electrode alloy of a sealed nickel-metal hydride storage battery according to an embodiment of the present invention, the number of charge/discharge cycles until the discharge capacity reaches the nominal capacity, and the battery internal pressure. The characteristic diagram, Figure 2, shows the amount of nickel and cobalt mixed with oxides on the surface of the negative electrode alloy of the sealed nickel-metal hydride storage battery of the embodiment of the present invention, and the number of charge/discharge cycles until the discharge capacity reaches the nominal capacity. Figure 3 shows the relationship between the BET specific surface area of the negative electrode alloy of the sealed nickel-metal hydride storage battery of the embodiment of the present invention and the number of charge/discharge cycles until the discharge capacity reaches the nominal capacity. FIG. Name of agent: Patent attorney Akira Okaji and 2 others #-”?
CS Meki◆@

Claims (1)

[Claims] (1) A positive electrode whose main constituent material is a metal oxide, and a negative electrode whose main constituent material is a hydrogen storage alloy that can electrochemically absorb and release hydrogen, which is an active material. , an alkaline electrolyte, and a separator, and the surface of the hydrogen storage alloy of the negative electrode is not composed of nickel or cobalt in an alloy state, but a nickel layer and a cobalt layer in a metallic state, and an oxide layer of at least one of the alloy components. A sealed nickel-metal hydride storage battery characterized in that (2) the composition of the hydrogen storage alloy of the negative electrode is expressed by the general formula A_1_-
_xB_xC_y (However, A is La alone, a mixture of rare earth elements, or misch metal, B is Ti, Zr, C
one of a, Y, Hf or a mixture thereof, 0≦
x≦0.2, and C is Ni, Co, Mn, Al, Fe
, Cu, Cr, or a mixture thereof, y>3.5 in the case of Ni, y≦1.0 in the case of Co, M
y≦0.6 for n, y≦0.5 for Al, y≦0.3 for Fe, y≦1.0 for Cu, y≦ for Cr.
0.3 and 4.7≦y≦5.3). The sealed nickel-hydrogen storage battery according to claim 1. (3) The composition of the hydrogen storage alloy of the negative electrode is expressed by the general formula A_1_-
＿xB_xC_yD_z (However, A is La alone, a mixture of rare earth elements, or misch metal, B is Ti, Z
r, Ca, Y, Hf, or a mixture thereof, 0≦x≦0.2, and C is Ni, Co, Mn, A
1, Fe, Cu, and Cr, or a mixture thereof; in the case of Ni, y≧3.5; in the case of Co, y≦1.
0, y≦0.6 for Mn, y≦0.5 for Al, F
In the case of e, y≦0.3, in the case of Cu, y≦1.0, and in the case of Cr, y≦0.3, D is one of V, In, Tl, Ga or a mixture thereof, 0.0 for V
2≦Z≦0.3, In case of 0.02≦Z≦0.1, T
0.02≦Z≦0.1 for l, 0.02≦ for Ga
Z≦0.1, and 4.7≦y+z≦5.3)
A sealed nickel-metal hydride storage battery according to claim 1, characterized in that: (4) The amount of nickel and cobalt in the metallic state of the surface layer of the hydrogen storage alloy is 0.05 to 12 emu/g in terms of saturation magnetization.
A sealed nickel-metal hydride storage battery according to claim 1, characterized in that: (6) The thickness of the oxide mixed layer on the surface of the hydrogen storage alloy is 20
The sealed nickel-hydrogen storage battery according to claim 1, characterized in that the thickness is 0 to 2000 Å. (6) The BET specific surface area of the hydrogen storage alloy is 0.1 to 10
Claim 1 characterized in that m^2/g
Sealed nickel-metal hydride storage battery as described in section. (7) The sealed nickel-hydrogen storage battery according to claim 1, wherein the surface of the hydrogen-absorbing alloy powder is subjected to alkali immersion treatment. (8) The sealed nickel-hydrogen storage battery according to claim 1, wherein the surface of the hydrogen-absorbing alloy powder is improved by wet pulverization.