Electrochemical Performance of Sintered Porous Negative Electrodes Fabricated with Atomized Powders for Iron-Based Alkaline Rechargeable Batteries

Abstract

The electrochemical performance of porously sintered iron-based negative electrodes was examined to assess their suitability for application to high performance alkaline rechargeable batteries. Atomized iron-based powders with and without sulfur were used as raw materials of the electrodes. In order to clarify the discharge-charge mechanism, effects of additives such as K2S, Bi2S3 and LiOH on the electrochemical reaction were also discussed based on the results of cyclic voltammetry in conjunction with changes in the chemical bonds along with the depth from the electrode surface. It was found that the electrochemical performance of the iron electrodes (atomized iron-based powders without sulfur) was improved when K2S was added to the electrolyte of 8 M KOH. The discharge capacity was two times larger than those having the LiOH or Bi2S3 additive in the electrolytes. Furthermore, the discharge curves showed three distinct potential plateaus at about −1.0, −0.9 and −0.7 V vs. Hg/HgO, indicating that oxidation reaction was induced by sulfur additive in the electrolyte. It was revealed by X-ray photoelectron spectroscopy (XPS) analysis that the surface of the iron was uniformly covered with FeS of about 200 nm in thickness in the vicinity of the electrode surface. It is obvious from the XPS spectra that formation of FeS was the primary reaction on the electrode surfaces. Owing to the above-mentioned reaction, the discharge capacity for the negative electrodes fabricated with the sulfur-containing iron-based atomized powders increased with the number of cycles and reached 200 mAhg−1(Fe) at the 15th cycle, and maintained the behavior up to 25 cycles with a Coulombic efficiency of around 100%.