Properties of Nickel-Iron Batteries with High-Performance Iron Electrodes

Abstract

Rechargeable nickel-iron batteries were widely used in the first half of the twentieth century and in some of the earliest electric vehicles developed by Thomas Alva Edison. These nickel-iron batteries were known for their reliability and cycle life. However, these batteries have since been replaced in mobile applications because of their low specific energy, poor charging efficiency, and relatively poor discharge rate capabilities [1, 2]. Lithium-ion batteries and nickel metal hydride batteries are the most commonly-used batteries for mobile applications, because of their high specific energy values of 150-200 Wh/kg and 60-100 Wh/kg, respectively. Commercial nickel-iron batteries, however, only have a specific energy of 22-25 Wh/kg [3]. These commercial nickel-iron batteries use heavy electrode constructions with 40-year old pocket plate electrode technology. Further, the iron electrodes in these batteries use excessive mass of iron materials to address the issue of low charging efficiency. There is considerable scope for lightening the electrode construction in nickel-iron batteries especially with the recent improvements in charging efficiency and discharge rate capability made by us with the iron electrodes [4-6]. The long cycle life, low cost, abundant availability of raw materials, relative safety and environmentally friendliness of nickel-iron batteries are compelling features that are critical for a wide range of applications spanning from stationary to mobile energy storage. In our in-house developed sintered iron electrode, we have demonstrated close to 3000 cycles of charge and discharge cycling at C rate, with a charging efficiency of 97%. These batteries can also sustain discharge rates as high as 3C [Figure 1]. To design a high performance nickel-iron battery, we first use a simple model that can predict the specific energy of the battery based on the properties of the electrodes as well as other cell components. Using this model we can identify the specific improvements in specific charge capacity of the electrodes, mass of electrode current collectors, amount of electrolyte and mass of other cell hardware that are necessary to realize a nickel-iron battery with a specific energy as high as 100Wh/kg. We demonstrate the applicability of these calculations to the performance of the cells cycling in our laboratory. 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.