Designing Solvated Double‐Layer Polymer Electrolytes with Molecular Interactions Mediated Stable Interfaces for Sodium Ion Batteries

Abstract Unstable cathode‐electrolyte and/or anode‐electrolyte interface in polymer‐based sodium‐ion batteries (SIBs) will deteriorate their cycle performance. Herein, a unique solvated double‐layer quasi‐solid polymer electrolyte (SDL‐QSPE) with high Na + ion conductivity is designed to simultaneously improve stability on both cathode and anode sides. Different functional fillers are solvated with plasticizers to improve Na + conductivity and thermal stability. The SDL‐QSPE is laminated by cathode‐ and anode‐facing polymer electrolyte to meet the independent interfacial requirements of the two electrodes. The interfacial evolution is elucidated by theoretical calculations and 3D X‐ray microtomography analysis. The Na 0.67 Mn 2/3 Ni 1/3 O 2 |SDL‐QSPE|Na batteries exhibit 80.4 mAh g −1 after 400 cycles at 1 C with the Coulombic efficiency close to 100 %, which significantly outperforms those batteries using the monolayer‐structured QSPE.