Nickel-metal hydride secondary cell and negative electrode therefor

摘要

A nickel-metal hydride secondary cell holds therein an electrode group and an alkaline electrolyte solution containing NaOH as a main constituent of its solute. The electrode group has positive and negative electrodes lapped one over the other with a separator therebetween. The negative electrode contains a hydrogen absorbing alloy having a composition represented by the general formula: (RE1-xTx)1-yMgyNiz-aAla (where RE is at least one element selected from among Y, Sc and rare-earth elements, T is at least one element selected from among Zr, V and Ca, and subscripts x, y, z and a are values respectively satisfying 0≦x, 0.05≦y≦0.35, 2.8≦z≦3.9, and 0.10≦a≦0.25), the hydrogen absorbing alloy has a crystal structure in which an AB2 subunit and an AB5 subunit are superimposed one upon the other, and Cr is substituted for part of the Ni.

主权项

1. A nickel-metal hydride secondary cell comprising a container, and an electrode group hermetically contained in the container together with an alkaline electrolyte solution, the electrode group including a separator, a negative electrode and a positive electrode,
wherein the negative electrode contains a hydrogen absorbing alloy having a composition represented by a general formula: (RE1-xTx)1-yMgyNiz-aAla (where RE is at least one element selected from among Y, Sc and rare-earth elements, T is at least one element selected from among Zr, V and Ca, and subscripts x, y, z and a are values respectively satisfying 0≦x, 0.05≦y≦0.35, 2.8≦z≦3.9, and 0.10≦a≦0.25), the hydrogen absorbing alloy has a crystal structure in which an AB2 subunit and an AB5 subunit are superimposed one upon the other, Cr is substituted for part of the Ni, a sum of the elements represented by RE and T and the Mg is 1 mole, and a content of the Cr is 0.01 moles or more and 0.02 moles or less.