Ion intercalation, redox, and interfacial mechanisms of MXene-based negative-electrode systems for rechargeable batteries.

MXenes combine metallic conductivity, redox-active transition-metal layers, and chemically tunable surfaces, making them attractive components of negative-electrode systems for lithium-, sodium-, potassium-, zinc-, and multivalent-ion batteries. However, interpreting MXene-based negative-electrode systems only by reversible capacity obscures the coupled processes that determine their electrochemical behavior. This mini review reframes MXene-based negative-electrode systems around the coupled logic of ion entry, charge compensation, and structural evolution. We discuss how interlayer galleries, surface terminations, confined water or solvent molecules, and metal-center redox cooperate or compete during charge storage. Particular emphasis is placed on the distinction between true intercalation, pseudo-intercalation, surface pseudocapacitance, partner-phase conversion/alloying in MXene-containing hybrid anodes, and electrolyte-regulated desolvation. Recent examples across alkali, aqueous zinc, and multivalent systems show that high-rate performance is obtained when ion access, electron transport, and lattice breathing are balanced rather than maximized independently. We highlight operando and multiscale measurements needed to connect local coordination changes with electrode-level kinetics, and we propose design principles for MXene-based negative-electrode systems that preserve redox accessibility while limiting restacking, oxidation, and parasitic interfacial reactions.