Performance of Rechargeable Sintered Iron Electrodes for Large-Scale Energy Storage (2015)

Large scale energy storage systems are needed to buffer the variability and the intermittency of electricity generated from renewable sources such as solar and wind. The main requirements of such energy storage systems are high efficiency, good rate capability, long life and low cost [1, 2]. Iron-based alkaline batteries are promising for large-scale energy storage due to its low cost, abundance of raw materials, long cycle life and environmentally friendliness [1]. However, commercial iron-based alkaline batteries such as nickel-iron batteries suffer from low charging-efficiency and poor discharge-rate-capability [3]. In a recent communication, we have reported a high-performance iron electrode that operates at a high charging efficiency of 95% and capable of sustaining up to 3C rates during discharge [4]. In this presentation, we will discuss the factors that led to the achieving of 3000 cycles of charge and discharge with an in-house prepared sintered iron electrode. This electrode was repeatedly charged and discharged at the one-hour rate between 0% and 100% state-of- charge (Figure 1). The faradaic efficiency during this cycling is as high as 97%. This robustness and high efficiency of sintered iron electrode under high-rate cycling makes iron based alkaline battery very suitable for large scale energy storage. The iron electrode in this study was prepared by sintering of carbonyl iron onto nickel mesh in an inert atmosphere. The iron electrode was then subjected to repeated charge-discharge cycling in 30% w/v KOH electrolyte in a three-electrode configuration with two sintered nickel-oxide counter electrodes and a mercury/mercuric oxide reference electrode. The sintered structure of iron electrode was one major factors that determined its performance. To achieve high specific capacity, a highly-porous iron electrode was designed. The porosity was needed to accommodate the large difference in molar volume between the charged and discharged product. However, maintaining the electrical connectivity between the particles in the sintered structure was also crucial for sustaining the discharge capacity over large number of cycles. Therefore, an optimal combination of porosity, pore size and pore distribution was important to achieve good utilization and cycle life. Passivation is also an important phenomenon that limits the performance of the sintered iron electrode. Passivation prevents the iron electrode from being completely discharged, especially at high discharge rates. Therefore, continuous “de-passivation” of the electrode was essential for rapid formation, good discharge rate capability and maintenance of the discharge rate capability over thousands of cycles. Acknowledgement The research reported here was supported by the U.S. Department of Energy ARPA-E (GRIDS program, DE-AR0000136), the Loker Hydrocarbon Research Institute, and the University of Southern California. References: 1. S. R. Narayanan, G. K. S. Prakash, A. Manohar, B. Yang, S. Malkhandi, A. Kindler, Solid State Ionics, 216, 105 (2012). 2. Z. Yang, J. Zhang, M. C. W. Kintner-Meyer, X. Lu, D. Choi, J. P. Lemmon, Chem. Rev., 111, 3577, (2011). 3. A. K. Manohar, S. Malkhandi, B. Yang, C. Yang, G. K. Surya Prakash, S. R. Narayanan, J. Electrochem. Soc. 159,A1209 (2012). 4. A. K. Manohar, C. Yang, S. Malkhandi, G. K. Surya Prakash, S. R. Narayanan, J. Electrochem. Soc. 160, A2078 (2013). Figure 1