Ion‐Dipole Interaction Induced Rigid‐Flexible Coupling SEI for Ultrastable Sodium Storage of Microsized Sn Anode

Tin (Sn) anode has been considered as a promising candidate for sodium-ion batteries due to its high theoretical capacity and suitable operating potential. However, they suffer from substantial volume variation during charge/discharge processes, which leads to fast capacity degradation. Herein, we propose a strategy combining solvents with different solvation abilities to regulate ion-dipole interactions, establishing an anion and solvent co-dominated solvation chemistry. This unique solvation chemistry triggers the cooperative decomposition of anions and solvents, generating a mechanically robust yet chemically stable organic-inorganic hybrid solid-electrolyte interphase (SEI) with balanced rigidity and flexibility. The stable SEI effectively mitigates volume variation during charge/discharge processes and suppresses successive electrolyte decomposition. Therefore, the microsized Sn anode exhibits superior cycling stability (high capacity retention of 83.31% after 1000 cycles) and rate performance (270.4 mAh g^-1 at 4.0 A g^-1). More importantly, the Sn||Na₃V₂(PO₄)₃ full cell achieves a remarkable energy density of 235.3 Wh kg^-1. This study demonstrates the feasibility of rigid-flexible coupling SEI, providing a pathway to boost the sodium storage performance of anode materials with huge volume change.