A Low-Cost Iron-Based Substrate for Alkaline Battery Electrodes

Abstract

The nickel foam current collector adds significantly to the cost of the positive electrode of nickel-based alkaline batteries.1 Iron is roughly 40 times less expensive than nickel; but iron corrodes at the operating potential of the nickel electrode at pH 14 or higher.2 Thus, for an iron substrate to be viable, it should be protected from anodic corrosion in alkali and the surface must be electrically conducting. We found that a 100 nm thick thermal coating of cobalt ferrite protects iron from corrosion. The protected iron substrate was stable for 1000 h even when anodically polarized at 10 mA cm−2 in 30% potassium hydroxide battery electrolyte.3 The electrical conductivity of the coating could be improved by the incorporation of lithium-ions. The enhanced conductivity was attributed to an increase in the population of Co3+ in the spinel lattice as evidenced from XPS and XAS analyses.4 The nickel electrode on such an inexpensive iron-based substrate exhibited a specific capacity of 0.25 Ah g−1 at C/5 discharge rate, comparable to a nickel hydroxide electrode on expensive nickel foam. The electrode also exhibited no noticeable degradation for 150 cycles at C/2 rate. This robust and economical iron substrate thus presents a unique opportunity for reducing the cost of the nickel electrode in aqueous alkaline batteries.