Phase Transition Mediated Solvation Structure Regulation in Quasi‐Solid‐State Composite Electrolyte for High‐Voltage Sodium Batteries

Quasi‐solid‐state composite electrolytes (QSSEs) represent a promising approach to fabricating high‐energy rechargeable batteries, but their practical implementation is hindered by structural instability and interfacial incompatibility. In this study, a QSSE was prepared with the aid of a molecular reinforcer, thioctic acid, which induces a polymer conformational change to a high‐dielectric phase for improved ion transport and strengthens the structural durability, even with rich porosity, due to the strong and dynamic complexing bonds. As a result, the ionic conductivity and electrochemical stability of the QSSE are significantly enhanced to 5.0 × 10 − 4 S cm −1 and 5.1 V. Moreover, the greatly reduced activation energy (0.11 eV) and the electrolyte‐derived inorganic‐rich interphases facilitate ion migration across the electrolyte‐electrode interfaces and enable simultaneous stabilization of both cathode and anode with thin and stable protection layers. Accordingly, Na|Na 3 V 2 (PO 4 ) 3 F 3 cells assembled with the designed QSSE exhibit excellent rate capability and cycling stability at a high cut‐off voltage of 4.4 V (vs. Na + /Na), delivering a capacity of 94.1 mA h g − 1 with 93.4% retention after 600 cycles at 1 C. This work offers a viable strategy for developing high‐energy‐density batteries.