Production and electrochemical characterization of Mg[sbnd]Ni alloys by molten salt electrolysis for Ni–MH batteries

Abstract

MgNi alloys are produced by molten salt electrolysis and diffusion method on a nickel plate in KClNaCl based melts. Structure, alloy composition and electrochemical properties of these alloys are evaluated. Electrolyte composition and applied current density parameters are studied for the characterization of the alloys. It is found that MgNi alloys with 45 wt% to 49 wt% Ni content which can be defined as MgNi–type alloys, have both higher discharge capacity and good retaining rate (72%). These alloys are mainly composed of Mg2Ni phases and displayed a maximum discharge capacity of 384 mAhg−1. Increased Ni content is advantageous for the enhancement of the cycle life. At the same time, the discharge capacity of MgNi alloy electrode is found to be decreasing. The highest capacity retaining (85%) rate is observed in the highest Ni content alloys (72 wt% Ni).Electrochemical impedance spectroscopy and potentiodynamic polarization measurements show that the controlling–step of the discharge process changed from a mixed rate–determining process at lower depth of discharge to a mass transfer controlled process at higher depth of discharge. The charge transfer resistance increases from 0.5 Ω to 23 Ω with increasing depth of discharge.