Electrochemical Properties of Nb-Substituted Zr-Ti-Ni Hydrogen Storage Alloy Negative Electrodes for Nickel-Metal Hydride Batteries

Abstract

Crystal structure, pressure-composition isotherms and electrochemical properties of the Zr0.6−xTi0.4NbxNi (x = 0.01, 0.02, and 0.05) alloys were investigated. Their X-ray diffraction profiles demonstrated that all the Zr0.6−xTi0.4NbxNi alloys consisted of the primary phase with the B33-type orthorhombic structure and the secondary phase with the B2-type Ti0.6Zr0.4Ni cubic structure. Rietveld refinement demonstrated that the atomic fraction of the secondary phase increased with the Nb content. The Zr0.6−xTi0.4NbxNi alloys were lower in hydrogen storage capacity than the Nb-free Zr0.6Ti0.4Ni alloy due to an increase in the abundance of the secondary phase. In the charge-discharge tests with the Zr0.6−xTi0.4NbxNi alloy negative electrodes, all the initial discharge curves had two potential plateaus due to the electrochemical hydrogen desorption of trihydride to monohydride and monohydride to alloy of the primary phase. The total discharge capacities at 333 and 303 K for the Zr0.58Ti0.4Nb0.02Ni alloy negative electrode were 384 and 335 mAh g−1, respectively, which were higher than those of the other Zr0.6−xTi0.4NbxNi and Zr0.6Ti0.4Ni alloy negative electrodes.

Keywords

• hydrogen storage alloy
• Zr-Ti-Nb-Ni system
• rietveld analysis
• negative electrode
• discharge capacity
• nickel-metal hydride battery