ABSTRACT Anion‐intercalation in graphite cathodes enables high‐power, high‐voltage, and low‐cost dual‐ion batteries (DIBs). However, irreversible graphite exfoliation during cycling progressively degrades electrical contacts, a phenomenon that prevailing failure models attribute to substantial volume variations during anion (de)intercalation. Here, we reveal that the irreversible decomposition of co‐intercalated solvents constitutes the critical, yet overlooked driver of exfoliation and the subsequent loss of electrical connectivity. Potential‐dependent operando tracking unveils that co‐intercalated solvents such as ethyl methyl carbonate (EMC) decompose above 4.9 V vs. Li/Li + in the confined gallery space. This process generates gaseous products that induce localized stress heterogeneity, directly triggering exfoliation. In light of this revised mechanism, we revisit the role of fluoroethylene carbonate (FEC) in improving graphite cathode reversibility, and demonstrate that it functions by inhibiting solvent co‐intercalation, contrary to the previously held belief of protective interphase formation. Thus, by clarifying the failure pathway, our work identifies solvent exclusion as a key design principle for high‐voltage graphite cathodes in DIBs.
Zhang et al. (Thu,) studied this question.