Rare earth metal-nickel and its manufacturing method, a hydrogen storage alloy, a nickel-hydrogen

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A rare earth metal/nickel-base hydrogen absorbing alloy having a composition represented by formula (1) : (R1-x Lx )(Ni1-y My )z , (wherein R represents La, Ce, Pr, or Nd; L represents Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Y, Sc, Mg, or Ca; and M represents Co, Al, Mn, Fe, Cu, Zr, Ti, Mo, Si, V, Cr, Nb, Hf, Ta, W, B, or C; 0, 01 ≤ x ≤ 0.1; 0 ≤ y ≤ 0.5; and 4.5 ≤ z ≤ 5.0), wherein the content of crystals with the number of reversed-phase boundaries present perpendicularly to the C axis of crystal grains in the alloy being 2 to less than 20 per 20 nm in the direction of the C axis is 10 to less than 95 vol.% and the amount of L in the formula (I) present in the reversed-phase region is 60 to less than 95 % of the amount of L added. The negative electrode for the nickel-hydrogen secondary battery can simultnaneously improve all of the initial activity, battery capacity, and battery life.