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

Abstract 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||Na 3 V 2 (PO 4 ) 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.