Towards Rechargeable Aluminum-Ionic Liquid Batteries for Low-Temperature Space Applications

Abstract

Batteries operating reliably at low temperatures are required to power robotic spacecraft, particularly those that embark on planetary science missions1. For example, Mars surface missions have typical temperature targets of -40 to -60 °C, while surface mission concepts to the outer planets or Ocean Worlds, such as Europa, have targets down to -180 °C. At low temperatures, state-of-the-art lithium-ion batteries suffer from lithium plating and dendritic growth on the graphite anodes, severe capacity loss associated with sluggish ion diffusion in crystalline transition metal cathodes, and kinetic limitations2. While organic electrolyte mixtures have been developed that enable moderate low-temperature performance, new battery concepts, including those using ionic liquid electrolytes, are needed to enable new paradigms in low or ultra-low temperature space missions. Recently, rechargeable aluminum batteries have been developed that use chloroaluminate-containing ionic liquid electrolytes, which may be suitable alternatives to lithium-based batteries when used under extreme temperatures. Aluminum metal is also distinguished by its high energy density, safety, low cost, and sustainability, which are also key properties for space applications.Herein we present, for the first time, results towards rechargeable Al-batteries designed specifically for low-temperature space missions that demonstrate high capacity retention, long-term cyclability, and favorable electrochemical kinetics at low temperatures down to -40 °C. We focus on the development of ionic liquid electrolytes with mixed anion-cation compositions to impart disorder and disrupt crystallization, while pairing them with functionalized graphite and conducting polymer cathodes.3 , 4 The resulting aluminum batteries were characterized by variable-temperature and rate cyclic voltammetry (CV), galvanostatic cycling, electrochemical impedance spectroscopy (EIS), and solid-state nuclear magnetic resonance (NMR) spectroscopy to understand their reaction mechanisms and factors limiting their rate performance. The ionic liquid electrolyte mixtures were also characterized by a combination of differential scanning calorimetry (DSC) and electrochemical methods to understand their freezing points and electrochemical stability. The results provide fundamental insights into the design of positive electrode materials and ionic liquid electrolyte mixtures in novel batteries for low-temperature space applications.References Bugga, R. V.; Brandon, E. J., Energy Storage for the Next Generation of Robotic Space Exploration. Electrochemical Society Interface 2020, 29 (1), 59-63.Jones, J.-P.; Smart, M. C.; Krause, F. C.; Bugga, R. V., The Effect of Electrolyte Additives upon Lithium Plating during Low Temperature Charging of Graphite-LiNiCoAlO2 Lithium-Ion Three Electrode Cells. Journal of The Electrochemical Society 2020, 167 (2), 020536.Schoetz, T.; Kurniawan, M.; Stich, M.; Peipmann, R.; Efimov, I.; Ispas, A.; Bund, A.; Ponce de Leon, C.; Ueda, M., Understanding the charge storage mechanism of conductive polymers as hybrid battery-capacitor materials in ionic liquids by in situ atomic force microscopy and electrochemical quartz crystal microbalance studies. Journal of Materials Chemistry A 2018, 6 (36), 17787-17799.Xu, J. H.; Turney, D. E.; Jadhav, A. L.; Messinger, R. J., Effects of Graphite Structure and Ion Transport on the Electrochemical Properties of Rechargeable Aluminum–Graphite Batteries. ACS Applied Energy Materials 2019, 2 (11), 7799-7810.