Performance of Sintered Iron Electrodes for Rechargeable Alkaline Batteries for Large Scale Energy Storage

With increased concerns about fossil fuel depletion and carbon dioxide emissions, renewable power generation from solar and wind sources is a promising solution for meeting our increasing need of energy. However, with renewable power there is a principal issue of power availability to match the demands. Therefore, inexpensive, long life and high-rate- capable energy storage systems are needed.

Iron based alkaline batteries are a promising candidate for large scale energy storage due to its low cost and abundance of raw material, long cycle life and high theoretical energy density of iron electrodes. [1] Despite these advantages, historically, iron electrodes have had low charging efficiency due to the hydrogen evolution reaction, and low utilization rate and poor rate capability due to the non-conducting nature of the discharge product. [2] In this study, a sintered iron electrode with high charging efficiency, high utilization rate and long cycle life is presented.

The iron electrode in this study was prepared by loading carbonyl iron on to a degreased nickel mesh and sintering under inert atmosphere. The iron electrode was then tested in a three-electrode configuration with two sintered nickel-oxide counter electrodes and a mercuric oxide reference electrode was used for electrode potential measurements. Sodium sulfide was added into the electrolyte to prevent passivation.

After the initial formation cycles, the utilization rate of the sintered iron electrode stabilized at   0.23 Ah/g. About 80% of this value was realized at C rate (Figure 1).  This type of performance is very promising for large-scale energy storage applications since the high rate capability is necessary for rapid load-leveling. Following initial characterization of capacity, the electrodes were subjected to charge/discharge cycles with C/2 rate over 500 cycles without any significant change in capacity. The average faradaic efficiency during this high rate cycling is above 96% (Figure 2).

The properties of long cycle life and high faradaic efficiency are expected to lower the cost of implementing and operating iron-based energy storage systems. The future work of this study is focused on understanding the role of electrode design parameters (porosity, thickness and pore utilization) and sulfide additives on the performance of the iron electrode.

Acknowledgement

The research reported here was supported by the U.S. Department of Energy ARPA-E (GRIDS program, DEAR0000136), the Loker Hydrocarbon Research Institute, and the University of Southern California.

References

1. S.R. Narayanan, G. K. Surya Prakash, A. Manohar, B. Yang, S. Malkhandi, A. Kindler, Solid State Ionics, 216, 105 (2012).

2. A. K. Manohar, S. Malkhandi, B. Yang, C. Yang, G. K. Surya Prakash, S. R. Narayanan, J. Electrochem. Soc., 159 (8), A1209 (2012).