Towards Rechargeable Aluminum Metal Batteries for Low-Temperature Space & Electromobility Applications

Abstract

Rechargeable aluminum metal batteries are promising next-generation electrochemical energy storage devices due to the high energy density, inherent safety, low cost, earth abundance, and recyclability of aluminum. Aluminum batteries using graphite cathodes and chloroaluminate-containing electrolytes have recently been the focus of intense research in the energy storage and electroplating community, particularly due to their fast-charging capabilities. Engineered graphite cathodes have been shown to exhibit supercapacitor-like rate performance since chloroaluminate anions intercalate into graphite with significant pseudocapacitive characteristics1,2. Batteries with high considerable pseudocapacitive charge storage3 are especially attractive for energy storage systems that need to function at low temperatures and ideally exhibit high specific power. For example, robotic spacecraft that embark on planetary science missions often have typical mission temperature targets of -40 to -60 °C. However, state-of-the-art lithium-ion batteries with predominant faradaic diffusion-limited charge storage suffer from lithium plating, dendritic growth, and severe capacity loss at low temperatures. 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 for low-temperature space missions and electromobility.Herein we present, for the first time, results towards rechargeable aluminum-graphite batteries designed specifically for low-temperature applications that demonstrate high capacity retention and favorable electrochemical kinetics at temperatures down to -40 °C. We first disentangle quantitatively the faradaic diffusion-limited, pseudocapacitive, and capacitive contributions to the overall charge storage for different graphite materials. Moreover, we shed light on the relationships between graphite structure, ion mass transport, and the overall rates of electrochemical aluminum deposition/dissolution and chloroaluminate anion intercalation. We then develop ionic liquid electrolytes with mixed anion-cation compositions to impart disorder and disrupt crystallization at low temperatures. The resulting aluminum-graphite 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 aluminum-graphite batteries for low-temperature space and electromobility applications.