(25d) Invited: Charge Storage Mechanisms and Ion Transport in Aluminum-Graphite Batteries

Rechargeable aluminum-graphite batteries are an emerging energy storage technology with great promise: they exhibit high rate performance, cyclability, and discharge voltage (ca. 2V), while both electrodes are globally abundant, low cost, non-toxic, and non-flammable. Such batteries use chloroaluminate-containing electrolytes, where chloroaluminate anions reversibly intercalate within the graphitic layers. However, the relationship between the graphitic cathode structure, particularly at a local level, and its bulk electrochemical properties are not well understood. Here, charge storage mechanisms and ion transport in graphitic cathodes are investigated and analyzed with respect to electrochemical performance. Three types of graphites (pyrolytic, natural and synthetic) were studied, as well as the effects of exfoliation. Solid-state magic-angle-spinning NMR measurements on intercalated graphitic cathodes reveal chloroaluminate anions in different local environments and with different mobilities that evolve as a function of state-of-charge. X-ray diffraction, electron microscopy, nitrogen adsorption, and Raman spectroscopy reveal additional insights into the graphitic structures and intercalation mechanism. Rate-dependent cyclic voltammetry and galvanostatic cyling measurements were conducted and analyzed to better understand how ion transport affects rate performance. Faradaic and capacitive contributions to charge storage will also be discussed. The results reveal insights into charge storage and ion transport within graphitic structures in chloroaluminate-containing electrolytes, which can be used to design and optimize improved graphitic cathodes for rechargeable aluminum batteries.