The atomized steel powders with sulfur additives were used as a raw material. The diameter of the powders was on the order of several ten micrometers and the nominal content of sulfur additives was 0.33wt%. For comparison, the powders without sulfur additives (the content of sulfur < 0.015wt%) were also prepared. The powders were placed in the concavity of a stainless plate. The size of the plate was 100 ´ 100 ´ 3 mm3, while the volume of the concavity was 90 ´ 80 ´ 2 mm3. The nominal density of the porous region was 3 gcm-3. As a result, the weight of the active material was estimated to be about 42 g. Then, they were sintered at 1120 °C for 20 min. A solution of 8M KOH was used as an electrolyte. For evaluation of the electrodes without sulfur additives, 0.05% K2S was added to the electrolyte solution. The performance of the electrodes was evaluated by three electrodes cell. The iron-electrode was set as the working electrode and platinum ribbon acts as a counter electrode. Mercury oxide electrode serves as the reference electrode. Commercially available Ni positive electrodes were also used for evaluation. The charge current was 1 A (5 h), while the discharge current was 1 A with a cut-off voltage of 0.8 V.
Figure 1 shows the charge–discharge curves of the sintered porous iron electrodes (a) with and (b) without sulfur additives. It is notable that the iron electrode with sulfur additives exhibits the discharge capacity of over 4000 mAh, which was higher than that for the electrode without sulfur additives. These results implied that the addition of sulfur to the electrode materials, rather than in the electrolytes, was more effective to extract the high potential of iron as negative electrodes. The sulfur-containing atomized steel powders were useful for a high performance iron-based negative electrode.
1) R. D. McKerracher, et al. ChemPlusChem, 80, 323 (2015),
2) A. K. Manohar, et al., J. Electrochem. Soc. 159, A1209 (2012).
3) A. K. Manohar, et al., J. Electrochem. Soc. 160, A2078 (2013).
4) A. K. Manohar, et al., J. Electrochem. Soc. 162, A1864 (2015).
5) C. Yang, et al., J. Electrochem. Soc.164, A418 (2017).
6) E. Shangguan, et al., J. Power Sources. 291, 29 (2015).
7) H. A. Figueredo-Rodriguez, et al., J. Electrochem. Soc. 164, A1148 (2017).
8) A. Ito, et al., J. Power Source, 196, 8154 (2011).
9) Y. Maeda, et al., 25th Annual Meeting of MRS-Japan, Abstracts B1-P10-018 (2015).
10) K. Hayashi, et al., ECS Transactions, 75(18), 111 (2017).