Thermodynamically Self‐Limiting Presodiation Inducing Homogeneous Inorganic–Organic Polymer‐Skeleton Interphases for Durable Sodium‐Ion Batteries

Abstract Cathode‐side chemical presodiation is a promising route to compensate for initial sodium loss in sodium‐ion batteries (SIBs). However, conventional presodiated cathodes are prone to oversodiation, structural degradation, and consequent cycling instability under excessive thermodynamic impetus, necessitating stringent control over presodiation duration and thereby limiting their universality and practicality. Here, a universal and thermodynamically self‐limiting chemical presodiation is proposed by synergistically integrating sodium diphenyl ketone (Na‐DK) with fluoroethylene carbonate (FEC). Specifically, Na‐DK enables controllable and self‐limiting sodium insertion beyond the stability potential threshold of presodiated cathodes due to diminishing thermodynamic driving force, effectively preventing oversodiation while eliminating the requirement for strict presodiation time control. Simultaneously, Na‐DK initiates a radical‐mediated decomposition of FEC to form homogeneous inorganic–organic polymer‐skeleton cathode‐electrolyte interphases (CEIs) with enhanced mechanical robustness, surpassing conventional PVDF‐derived heterogeneous inorganic‐rich CEIs. Proof‐of‐concept experiments confirm that when applied to the widely used Na 3 V 2 (PO 4 ) 3 cathode, this strategy delivers exceptional cycling stability, retaining 93.5% capacity after 2000 cycles (4000 h) at 1 C and 92.3% after 5000 cycles at 10 C, among the best performances. Full cells exhibit over twofold capacity enhancement and markedly extended cycle life compared to commercial counterparts. More importantly, this strategy is successfully extended to other cathode chemistries (e.g., Na 4 Fe 3 (PO 4 ) 2 P 2 O 7 ), demonstrating its broad applicability.