Dual‐Functional Additive Reshapes Lifetime Limit of Potassium‐Ion Batteries

Potassium-ion batteries (PIBs) are being considered as the sustainable alternative to lithium-ion systems, yet their specific energy and cycling lifespan is hindered by irreversible potassium loss due to solid electrolyte interphase (SEI) formation and SEI instability-induced ion depletion. Here, by employing an integrated computational-experimental selection framework, we identify a dual-functional additive that contributes to both active potassium compensation and SEI stability. Consequently, the additive-integrated coin-type full-cell with a K₂Mn[Fe(CN)₆] cathode and a graphite anode delivers a specific energy of 334.9 Wh kg^-1 and achieves a cycling lifespan of 1700 cycles at 0.5C with 88.32% capacity retention. Similarly, the effectiveness of the additive is also demonstrated in the pouch-type cell, which maintains 80.64% capacity after 3000 cycles at 0.5C. Mechanistic investigations by multimodal advanced characterizations and theoretical calculations indicate that the decomposition of the additive not only provides additional active potassium-ions to replenish SEI-related losses but also promotes the formation of an inorganic-rich and mechanically robust SEI, both of which contribute to the enhanced specific energy and substantially extended cycling lifespan of PIBs. This work greatly advances the electrochemical performance of PIBs and provides fresh insights for developing multifunctional additives to synergistically realize active ion compensation and controlled interfacial engineering.