A mechanistic perspective of anion intercalation in graphite cathodes for dual-ion batteries

Graphite cathodes enable high-voltage dual-ion batteries (DIBs) through reversible anion intercalation. However, the molecular identity and dynamic evolution of intercalated anionic species, which critically govern the thermodynamic stability and electrochemical reversibility of this process, remain insufficiently understood. This Perspective synthesizes emerging evidence challenging the prevalent but oversimplified “naked anion” intercalation model, emphasizing how solvent co-intercalation potentially influences thermodynamic equilibria, interlayer anion transport kinetics, and charge storage mechanisms. The structural evolution of graphite during anion intercalation is also critically analyzed, with a focus on how interlayer spacing adjustments evolve during electrochemical cycling under solvent co-intercalation conditions. Furthermore, we present a systematic analysis of anion packing configurations within solvent-containing interlayers and their intrinsic link to theoretical capacity limits, offering new insights for optimizing intercalation efficiency. To advance the field, targeted research directions encompassing operando characterization of speciation dynamics, multiscale modeling of solvent co-intercalation pathways and mechanistic investigation into the origins of voltage hysteresis, are proposed to inform the rational design of next-generation high-performance DIB systems.