RU2132101C1 - Water-absorbing alloy for manufacturing electrodes - Google Patents

Abstract

FIELD: production of negative electrodes for alkali storage batteries. SUBSTANCE: composition is defined by following equation

Description

 The present invention relates to hydrogen-absorbing alloys from which a negative electrode for alkaline batteries is made. In particular, a cathode for nickel-metal hydride batteries used in various electronic devices is made from hydrogen-absorbing alloys.

Known hydrogen-absorbing alloy for the manufacture of an electrode of the general formula MmNi _a CO _b Al _c , where 3.0≤a≥4.5; 0.3≤b≥1.3; 0.2≤c≥0.8; 4.0≤a + b + x≥5.5, and Mm is a mixture of rare earth elements [1]. The specific hydrogen capacity of these alloys is not more than 270 mA • h / g.

Closest to the proposed is a hydrogen-absorbing alloy for the manufacture of an electrode of General formula
MmNi _x (Co _a Mn _b Al _c ) _y ,
where 3.0≤x≥4.3; 0.7≤y≥1.7; 4.3≤ (x + y) ≥5.5; 0.2≤a≥1.0; 0.2≤b≥0.8; 0.1≤c≥0.5 [2]. The specific hydrogen capacity of the electrodes made from these alloys does not exceed 270 mA • h / g.

 The problem of the invention is to obtain a hydrogen-absorbing alloy for an electrode with a higher specific hydrogen capacity.

The problem to be solved is achieved by the proposed hydrogen-absorbing alloy for an electrode of the general formula
Mm _(1-x) La _x Ni _a Co _b Mn _c Al _d Mo _y ,
where 0.15≤x≤0.25; 3.75≤a≤3.85; 0.2≤b≤0.3; 0.35≤c≤0.45; 0.35≤d≤0.45; 0.02≤y≤0.1; 4.85≤a + b + c + d≤4.95.

the difference of the proposed hydrogen-absorbing alloy is the additional content of molybdenum in it with the general formula
Mm _(1-x) La _x Ni _a Co _b Mn _c Al _d Mo _y ,
where 0.15≤x≤0.25; 3.75≤a≤3.85; 0.2≤b≤0.3; 0.35≤c ± 0.45; 0.35≤d≤0.45; 0.02≤y≤0.1; 4.85≤a + b + c + d≤4.95.

 The introduction of molybdenum within the specified limits allows to obtain a hydrogen-absorbing alloy with a specific hydrogen capacity of 290-315 mA • h / g. An increase and decrease in the molybdenum content leads to a decrease in the specific hydrogen capacity to ~ 270 mA • h / g.

 Hydrogen-absorbing alloys are prepared by fusion of a mixture containing Mm-26.7 - 27.0; La-6.6 - 6.7; Ni-53.1-53.9; Co-2.8 - 4.3; Mn-5.2 - 6.0; Al-2.3 - 2.5; Mo-0.5 - 2.3 wt.%. Melting is carried out in an induction furnace on a copper water-cooled hearth in an atmosphere of purified argon.

 The obtained alloys are analyzed by the method of constructing P, c-isotherms and the electrochemical method of measuring discharge curves.

Based on the P, c-isotherms, the equilibrium pressure of hydrogen is determined, which for the proposed alloys is 0.3 - 0.8 atm at 25 ^o C.

For the manufacture of electrodes, the obtained hydrogen-absorbing alloys are mechanically crushed to a granule size of ~ 70 μm. The alloy powder is thoroughly mixed with electrolytic copper powder (granule size ~ 50 μm) in a ratio of 1: 4 and pressed under pressure of 2 t / m ² into tablets with a diameter of ~ 0.7 cm.

 The proposed invention is illustrated by the following examples.

 Example 1

A mixture containing Mm-26.96; La-6.71; Ni-53.15; Co-4.27; Mn -5.97; Al-2.48; Mo-0.48 weight. %, melted in an induction furnace on a water-cooled hearth in an argon atmosphere. An alloy is obtained with the formula Mm _0.8 La _0.2 Ni _3.75 Co _0.3 Mn _0.45 Al _0.38 Mo _0.02 .

The obtained alloy ingot is mechanically crushed to a granule size of ~ 70 μm. 0.02 g of alloy powder is thoroughly mixed with 0.08 g of copper powder and pressed under pressure of 2 t / m ² into a tablet. Get an electrode.

 To determine the specific hydrogen intensity of the alloy, the fabricated electrode is strengthened using a Pt current collector in the working part of a 3-electrode electrochemical cell filled with IM KOH solution. The auxiliary electrode is a Pt wire. The reference electrode is a reversible hydrogen electrode in 1 M KOH (OVE).

 The electrode is charged with a current of -4 mA (C / 1.5, where C is the hydrogen capacity in mA • h / g) for 2 hours, and then discharged with a current of 1 mA (C / 6) to a potential of 0.3 V (OVE).

 The specific hydrogen intensity of the alloy is calculated from the discharge curve (Fig. 1).

 The charge-discharge process is repeated many times. The specific hydrogen intensity of the alloy obtained in the first five charge-discharge cycles is shown in Table 1.

 With an increase in the discharge rate of the electrode from C / 6 to C, a decrease in the specific hydrogen intensity by ~ 20% is observed.

 When alternating charge-discharge processes for 10 days, a significant decrease in the discharge capacity of the electrode is not observed.

 Example 2 is carried out analogously to example 1, except for the content of components in the mixture.

A mixture containing Mm-26.78; La-6.66; Ni-53.49; Co-3.53; Mn-5.93; Al-2.46; Mo-1.15 weight. %, melted in an induction furnace on a water-cooled hearth in an argon atmosphere. An alloy is obtained with the formula Mm _0.8 La _0.2 Ni _3.8 Co _0.25 Mn _0.45 Al _0.38 Mo _0.05 .

 The specific hydrogen intensity of the alloy obtained in the first five charge-discharge cycles is shown in Table 1.

 Example 3 is carried out analogously to example 1, except for the content of components in the mixture.

A mixture containing Mm-26.72; La-6.65; Ni-53.80; Co-2.82; Mn-5.26; Al-2.45; Mo-2.30 weight. %, melted in an induction furnace on a water-cooled hearth in an argon atmosphere. An alloy is obtained with the formula Mm _0.8 La _0.2 Ni _3.8 Co _0.2 Mn _0.4 Al _0.38 Mo _0.1 .

 The specific hydrogen intensity of the alloy obtained in the first five charge-discharge cycles is shown in Table 1.

 Thus, the proposed hydrogen-absorbing alloy for the manufacture of the electrode allows to increase the specific hydrogen capacity to 290 - 315 mA • h / g.

 The electrodes of the proposed hydrogen-absorbing alloy are easily activated and can operate for more than 500 cycles. Hydrogen absorption and desorption reactions proceed at them at a fairly high rate.

Literature:
[1] Pat. US 5,242,766, publ. 09/07/1993. Cl. 429-59; H 01 M 4/38
[2] Application 62-20245 [87 20.245] Japan, publ. 01/21/1987. Cl. H 01 M 4/38.

Claims (1)

Hydrogen-absorbing alloy for the manufacture of an electrode containing mischmetal (Mm), nickel, cobalt, manganese and aluminum, characterized in that the alloy composition is additionally introduced molybdenum with the General formula
Mm _(1-x) La _x Ni _a Co _b Mn _c Al _d Mo _y , where 0.15 ≤ x ≤ 0.25;
3.75 ≤ a ≤ 3.85;
0.2 ≤ b ≤ 0.3;
0.35 ≤ c ≤ 0.45;
0.35 ≤ d ≤ 0.45;
0.02 ≤ y ≤ 0.1;
4.85 ≤ a + b + c + d + y ≤ 4.95

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