  Nonaqueous aluminum-ion batteries are an interesting emerging energy storage
technology, offering a plethora of advantages over existing grid energy storage
solutions. Carbonaceous and graphitic materials are an appealing cathode
material in this system, thanks to their low cost and excellent rate
capabilities. The phenomenon of poor Coulombic efficiency in the first cycle,
however, is a known issue among some types of carbons, the reasons for which
are yet to be fully understood. In this work, we propose that such processes
are caused by the formation of a solid-electrolyte interphase, in a similar
fashion to graphite anodes in lithium-ion batteries. Using electrospun carbon
nanofibers as a model material with tunable crystallinity, the cause of such
phenomena was found to be linked to the presence of surface defects in the
cathode material, and was further amplified by high surface area. The simple
use of a binder polymer, however, helps mitigating the issue by shielding
surface defects from direct contact with the electrolyte.
