Interphase stabilization via carbon hybridization control unlocks stable potassium-ion batteries

Potassium-ion batteries (PIBs) employing hard carbon (HC) anodes are often hampered by low initial Coulombic efficiency (ICE), primarily resulting from irreversible electrolyte degradation and unstable solid electrolyte interphase (SEI) formation. Conventional strategies have largely focused on tuning surface properties, while the key role of carbon hybridization in interfacial electrochemistry remains underexplored. In this work, we demonstrate that precise control over carbon hybridization via regulated pyrolysis can significantly mitigate side reactions. By creating a tunable structural gradient, we achieve an optimized HC material with a high ICE of 90.6% and a reversible capacity of 284.7 mAh g⁻¹. Multidisciplinary analyses decipher the underlying mechanism for the enhanced ICE and charge storage chemistry. The practical applicability of this material is confirmed in full-cell configurations, delivering 296.2 Wh kg⁻¹ specific energy and sustaining 75.3% capacity retention over 2,000 cycles. This study offers new directions for rational design of HC-based anodes in PIBs.