Investigating Intercalation of Chloroaluminate Anions in Graphene-Based Materials for Rechargeable Aluminum-Ion Batteries

Development of energy storage systems with high energy and power density, high safety, long cycle life, and low cost is crucial for various applications, including portable electronics and grid storage of renewable energies. Among various battery technologies, rechargeable aluminum ion batteries are particularly attractive due to the abundance, low cost, and safety of aluminum. However, unlike lithium ion batteries, many aspects of the fundamental intercalation processes and dynamics in these aluminum-based battery systems remain unresolved. In this study, we investigate the intercalation of chloroaluminate ions in atomically thin carbon cathodes using mesoscopic devices for charge transport and operando optical microscopy. These measurements provide insights into the energetics and dynamics of intercalation processes in atomically thin samples. We compare the atomically thin single crystal measurements to the cycling response of a high-performance rechargeable aluminum ion battery consisting of a few-layer graphene–multiwall carbon nanotube composite cathode. Our findings show that these nano-composites exhibit a high specific capacity and cyclic stability at high current densities, with a ~3-fold improvement in overall ion diffusivity in the aluminum ion battery. However, the battery cells still exhibit chloroaluminate diffusivities less than ~1% of those in mesoscopic single crystals. Our results highlight the distinction between intrinsic and ensemble electrochemical behavior in aluminum-based batteries and demonstrate that engineering ion transport to enhance diffusivity in these devices can lead to significant improvements in battery performance.