Hydrogen-storing alloy electrode and secondary cell using the same

1. A hydrogen-storing alloy electrode comprising:

first hydrogen-storing alloy particles having composition expressed by general expression (I):

(La a1 Ce b1 Pr c1 Nd d1 (A1) e1 ) 1−x Mg x (Ni 1−y (T1) y ) z

where A1 represents at least one element selected from a group consisting of Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Ca, Sr, Sc, Y, Ti, Zr and Hf; T1 represents at least one element selected from a group consisting of V, Nb, Ta, Cr, Mo, Mn, Fe, Co, Al, Ga, Zn, Sn, In, Cu, Si, P and B; a1, b1, c1, d1 and e1 are in the range of 0<a1≦0.25, 0≦b1, 0≦c1, 0≦d1 and 0≦e1 and satisfy the relation a1+b1+c1+d1+e1=1; and x, y and z are in the range of 0<x<1, 0≦y≦0.5 and 2.5≦z≦4.5; and

second hydrogen-storing alloy particles having composition expressed by general expression (II):

La a2 Ce b2 Pr c2 Nd d2 (A2) e2 (Ni 1-f (T2) f ) i

where A2 represents at least one element selected from a group consisting of Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Ca, Sr, Sc, Y, Ti, Zr and Hf; T 2 represents at least one element selected from a group consisting of V, Nb, Ta, Cr, Mo, Mn, Fe, Co, Al, Ga, Zn, Sn, In, Cu, Si, P and B; a2, b2, c2, d2 and e2 are in the range of 0≦a2, 0≦b2, 0.01≦c2, 0.01≦d2 and 0≦e2 and satisfy the relation a2+b2+c2+d2+e2=1; and f and i are in the range of 0≦f≦1 and 4.5≦i≦5.5.

2. The electrode according to claim 1 , wherein

the proportion of the mass of the second hydrogen-storing alloy particles relative to the total mass of the first and second hydrogen-storing alloy particles is in the range of 5% to 50%.

3. The electrode according to claim 2 , wherein

b1 in general expression (I) is 0.2 or smaller, and

b2 in general expression (II) is 0.05 or greater.

4. The electrode according to claim 3 , wherein

b2 in general expression (II) is 0.1 or greater.

5. The electrode according to claim 4 , wherein

c1 in general expression (I) is 0.30 or smaller.

6. The electrode according to claim 4 , wherein

d1 in general expression (I) is 0.30 or smaller.

7. The electrode according to claim 2 , wherein

the first hydrogen-storing alloy particles are lower in equilibrium hydrogen pressure than the second hydrogen-storing alloy particles.

8. The electrode according to claim 2 , wherein

the first hydrogen-storing alloy particles are greater in average particle size than the second hydrogen-storing alloy particles.

9. A secondary cell, comprising:

a positive-electrode plate;

a hydrogen-storing alloy electrode as a negative-electrode plate, the electrode including,

first hydrogen-storing alloy particles having composition expressed by general expression (I):

(La a1 Ce b1 Pr c1 Nd d1 (A1) e1 ) 1−x Mg x (Ni 1−y (T1) y ) z

where A1 represents at least one element selected from a group consisting of Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Ca, Sr, Sc, Y, Ti, Zr and Hf; T1 represents at least one element selected from a group consisting of V, Nb, Ta, Cr, Mo, Mn, Fe, Co, Al, Ga, Zn, Sn, In, Cu, Si, P and B; a1, b1, c1, d1 and e1 are in the range of 0<a1≦0.25, 0≦b1, 0≦c1, 0≦d1 and 0≦e1 and satisfy the relation a1+b1+c1+d1+e1=1; and x, y and z are in the range of 0<x<1, 0≦y≦0.5 and 2.5≦z≦4.5, and,

second hydrogen-storing alloy particles having composition expressed by general expression (II):

La a2 Ce b2 Pr c2 Nd d2 (A2) e2 (Ni 1−f (T2) f ) i

where A2 represents at least one element selected from a group consisting of Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Ca, Sr, Sc, Y, Ti, Zr and Hf; T2 represents at least one element selected from a group consisting of V, Nb, Ta, Cr, Mo, Mn, Fe, Co, Al, Ga, Zn, Sn, In, Cu, Si, P and B; a2, b2, c2, d2 and e2 are in the range of 0≦a2, 0≦b2, 0.01≦c2, 0.01≦d2 and 0≦e2 and satisfy the relation a2+b2+c2+d2+e2=1; and f and i are in the range of 0≦f≦1 and 4.5≦i≦5.5; and

a separator inserted between the positive-electrode plate and the negative-electrode plate and holding an alkaline electrolyte.

10. The secondary cell according to claim 9 , wherein

the secondary cell comprises a cylindrical case having an outside diameter in the range of 13.5 mm to 14.5 mm,

an electrode assembly including the positive-electrode plate, the negative-electrode plate and the separator rolled up together is set in the case with the outermost turn of the negative-electrode plate being in contact with the inner circumferential surface of the case,

the secondary cell has a volume energy density in the range of 340 Wh/l to 450 Wh/l, and

the volumetric proportion of the positive-electrode plate is in the range of 48% to 60%.

11. The secondary cell according to claim 10 , wherein

the proportion of the mass of the second hydrogen-storing alloy particles relative to the total mass of the first and second hydrogen-storing alloy particles is in the range of 5% to 50%.

12. The secondary cell according to claim 11 , wherein

b1 in general expression (I) is 0.2 or smaller, and

b2 in general expression (II) is 0.05 or greater.

13. The secondary cell according to claim 12 , wherein

b2 in general expression (II) is 0.1 or greater.

14. The secondary cell according to claim 13 , wherein

c1 in general expression (I) is 0.30 or smaller.

15. The secondary cell according to claim 13 , wherein

d1 in general expression (I) is 0.30 or smaller.

16. The secondary cell according to claim 11 , wherein

the first hydrogen-storing alloy particles are lower in equilibrium hydrogen pressure than the second hydrogen-storing alloy particles.

17. The secondary cell according to claim 11 , wherein

the first hydrogen-storing alloy particles are greater in average particle size than the second hydrogen-storing alloy particles.