Constructing Bidirectional Fluorine‐Rich Electrode/Electrolyte Interphase Via Solvent Redistribution toward Long‐Term Sodium Battery

The high concentration electrolytes with specific solvation structure could passivate the electrodes to prolong battery cycle life but at the expense of increased cost, which limits the wide application in commercialization. The regular concentration (1 m) electrolytes with suitable properties (viscosity, ionic conductivity, etc.) are cost‐guaranteed, but undesired reactions would always occur and lead to battery degradation during long cycles. To promote the long‐term cycle stability in a cost‐effective way, this work constructs bidirectional fluorine‐rich electrode/electrolyte interphase (EEI) by redistribution of solvents and electrochemical induction. The fluorinated effect with reasonable zoning planning restricts morphological disintegration, meanwhile, forms spatial confinement on cathode. In particular, the obtained cathode electrolyte interphase (CEI) gets the ample ability of Na⁺ transport, which benefits from the fluorinated organics arranged in the epitaxy and the hemi‐carbonate content acting on the thickness. Thus, the electrochemical long cycling performance of F‐NVPOF||F‐CC full cells is significantly enhanced (the decay rate at 1 C per cycle is as low as 0.01%). Such a fluorine‐rich EEI engineering is expected to take transitional layers against the degradation of cells and make ultra‐long cycle batteries possible.