Synthesis of Exfoliated Graphite Cathodes with Improved Ionic Conductivity and High-Rate Capacity for Aluminum-Graphite Batteries

A wide range of industries including electric vehicles and grid-scale energy storage are looking to researchers to discover low-cost next generation batteries that can perform efficiently over many cycles. Aluminum-graphite batteries have emerged as a leading option in this regard due to the extremely low cost of the electrode’s raw materials and for Al’s high theoretical volumetric charge storage capacity, which surpasses conventional anode metals like lithium, zinc, and magnesium. However, Al-graphite batteries have historically been unable to perform well at high rates of charge and discharge. Here, I show that ultrasonic exfoliation of the graphite – a technique used to turn many-layered graphite into few-layered graphene-like particles – can be employed to make cathodes that show improved performance at high rates compared to unexfoliated graphite cathodes. Using galvanostatic cycling, variable-rate cycling, and galvanostatic intermittent titration technique we investigate possible differences in the electrochemistry of the pristine and exfoliated graphite samples, particularly with respect to the capacity retention at high rates and the diffusivity of the anionic species, AlCl₄^-, during charging/discharging. We also employ a range of materials characterization methods including transmission electron microscopy, atomic force microscopy, and dynamic light scattering in order to better understand how the microscopic structural changes to the graphite caused by the ultrasonic exfoliation could explain the improved performance of the exfoliated graphite cathodes. Our findings demonstrate that ultrasonicated graphite cathodes deliver better capacity retention at high rates, a result that can be attributed in part to notable changes in particle size, especially the thickness, and faster ionic diffusion in the exfoliated graphite compared to the pristine graphite. The results establish that exfoliation of graphite is an easy and economical method to improve the performance of Al-graphite batteries, helping move this emerging battery chemistry one step further toward commercial viability.