Hydrogen storage alloy for alkaline storage battery and alkaline storage battery using the same

Example 1

[0093]Cells for evaluation in which hydrogen storage alloys No. 1 to 90 having the element compositions shown in Table 1 below are used as the negative-electrode active material are produced by the procedure to be described below, and experiments for evaluating their characteristics are conducted. Alloys No. 1 to 70 shown in Table 1 are alloy examples that comply with the conditions of the present invention (examples of the invention), and No. 71 to 90 are alloy examples that do not meet the conditions of the present invention (comparative examples). Alloy No. 71 that is a comparative example is used as a reference alloy for evaluating cell characteristics.

[0094](Production of Negative-Electrode Active Material)

[0095]The raw materials (Sm, La, Pr, Nd, Mg, Ti, Zr, Hf, Ni, Co, V, Nb, Ta, Cr, Mo, W, Mn, Fe, Cu, Al, Si, P, and B, each with a purity of 99% or higher) of alloys No. 1 to 90 shown in Table 1 are dissolved using a high-frequency induction heating furnace in an argon at

Example 2

[0121](Production of Negative-Electrode Active Material)

[0122]A hydrogen storage alloy having an element composition of (La0.75Sm0.25)0.70Mg0.30Ni2.90Mn0.10 is dissolved using a high-frequency induction heating furnace in an argon atmosphere (Ar: 90 vol %, 0.15 MPa) and cast to obtain an ingot. Then, this ingot is subjected to heat treatment of holding it in an argon atmosphere (Ar: 100 vol %, 0.5 MPa) at 960° C. (the alloy's melting point Tm minus 50° C.) for ten hours. Thereafter, this ingot is roughly pulverized, and then finely pulverized to the particle sizes shown in Table 2 to obtain samples (negative-electrode active materials) for cell evaluation. Samples No. B1 to B5 shown in Table 2 are obtained by finely pulverizing the ingot using a wet bead mill, and samples No. B6 to B9 are obtained by finely pulverizing the ingot using an ACM pulverizer.

[0123]As an alloy of a comparative example, an alloy of MmNi4.0Co0.4Mn0.3Al0.3 (sample No. BZ) is dissolved, heat-treated, and

Example 3

[0128](Production of Negative-Electrode Active Material)

[0129]A hydrogen storage alloy having an element composition of (La0.75Sm0.25)0.70Mg0.30Ni2.90Al0.05Mn0.05 is dissolved using a high-frequency induction heating furnace in an argon atmosphere (Ar: 100 vol %, 0.1 MPa) and cast to obtain an ingot. Then, this ingot is subjected to heat treatment of holding it in an argon atmosphere (Ar: 90 vol %, 0.1 MPa) at 1000° C. (the alloy's melting point Tm minus 50° C.) for ten hours. Thereafter, this ingot is roughly pulverized, and then finely pulverized to 10.2 μm as a D50 on a basis of mass using a wet bead mill.

[0130]Then, surface treatment by the following two standards is performed on the finely pulverized alloy powder to obtain samples (negative-electrode active materials) for cell evaluation.[0131]Alkali treatment: immersing the alloy in a 60° C. aqueous sodium hydroxide containing 40 mass % of NaOH, under the condition of a solid to liquid ratio of 1:2, for two hours (sample