  The process of anion intercalation in graphite and its reversibility plays a
crucial role in the next generation energy-storage devices. Herein the reaction
mechanism of the aluminum graphite dual ion cell by operando X-ray scattering
from small angles to wide angles is investigated. The staging behavior of the
graphite intercalation compound (GIC) formation, its phase transitions, and its
reversible process are observed for the first time by directly measuring the
repeated intercalation distance, along with the microporosity of the cathode
graphite. The investigation demonstrates complete reversibility of the
electrochemical intercalation process, alongside nano- and micro-structural
reorganization of natural graphite induced by intercalation. This work
represents a new insight into thermodynamic aspects taking place during
intermediate phase transitions in the GIC formation.
