Solid Electrolyte Interphase Stabilized Pomegranate SnP ₂ O ₇ @PC Anodes Realized Through Kirkendall Effect of MOF for Durable Potassium/Sodium‐Ion Batteries

ABSTRACT Potassium‐ion batteries (PIBs) and sodium‐ion batteries (SIBs) are promising next‐generation energy storage technologies because of their abundant and low‐cost raw materials. However, anodes for PIBs/SIBs often exhibit poor cycling stability, mainly due to particle fragmentation, loss of electrical connectivity, and continuous electrolyte decomposition from repetitive solid electrolyte interphase (SEI) formation. To address these challenges, a biomimetic pomegranate‐like core‐shell SnP 2 O 7 @PC anode (CSP‐SnP 2 O 7 @PC) is synthesised through pyrolysis‐driven Kirkendall effect of tin‐based phosphonate metal‐organic framework (MOF). This multi‐scale design integrates several key features. At the molecular scale, the in situ formation of Sn‐P‐O bonds reduces K + diffusion barriers. The nanoscale dispersion of SnP 2 O 7 within conductive carbon matrix promotes efficient electron and ion transport. Furthermore, microscale structural engineering creates pre‐reserved voids to accommodate volume expansion, suppress SEI overgrowth, and prevent cracking. The optimised anode demonstrates exceptional cycling stability, exhibiting ultralow capacity decay rate of 0.0015% per cycle over 16 000 cycles at 5 A g −1 , and also delivers excellent performance in SIBs. Density functional theory and finite element simulations further reveal beneficial electronic structures and stress distribution, providing fundamental insights for designing durable electrodes through crystal and electronic optimisation. Overall, this study presents an innovative strategy for mitigating volume expansion in high‐capacity battery materials.