Non-Foam-Type Nickel Electrodes Using Various Binders for Ni-MH Batteries

Abstract

New paste-type positive electrodes for nickel/metal-hydride (Ni/MH) batteries were prepared using low-cost punched metal substrate and binders with high adhesive strength. Their charge-discharge properties were evaluated using cylindrical sealed batteries. Electrochemical stability of the binders was investigated by means of cyclic voltammetry. For sealed batteries using epoxy resin, styrene butadiene rubber, and poly(vinyl acetate) as positive electrode binders, cell voltage continued to increase at the end stage of charging, and leakage was observed after charging test at 1 C rate. In cyclic voltammetry of these binders in alkaline solution, the anodic peak current was much larger than the cathodic peak current, suggesting their electrochemical oxidation. As a mechanism of leakage, consumption of oxygen by oxidation of binder and consequent formation of hydrogen at the negative electrode was proposed. The battery using polystyrene acrylic acid ester (PSA) as a binder showed no leakage during charging and the highest charge efficiency of more than 80% at 1 C rate. The cycle life of this battery was longer than 350 cycles. It was demonstrated that PSA is a suitable binder for electrodes with two-dimensional substrate. © 2004 The Electrochemical Society. All rights reserved.