Entropy‐Driven Polymer Electrolyte with Liquid Single‐Atoms for Fast‐Charging Solid‐State Sodium Batteries

The rate of interfacial transport and bulk transport of Na⁺ are determining steps that restrict fast-charging in solid polymer electrolytes (SPEs). Owing to the high interfacial compatibility, SPEs can reduce the interfacial impedance associated with ionic conduction. Despite the ability of high interfacial compatibility in the SPEs to promote the interfacial ion transfer, there remains no known material capable of concurrently boosting bulk-phase ionic conductivity and mechanical strength. Specifically, the study reports an entropy-driven strategy based on dynamic liquid single atoms that rapidly rearranges polymer chains into entropy-increased regions, accelerating polymer complexation and dissociation to facilitate ion transport for fast-charging. Meanwhile, dynamic stress regulation by liquid atoms enhances the mechanical strength of the electrolyte. An independently designed stress-monitoring electrolytic cell is employed to perform in situ monitoring of the stress-voltage relationship. The novel SPE exhibits the capacity of 85.6 mAh g^-1 at 10 C, and the capacity retention of 91.76% after 1000 cycles at 10 C. Cell has the capability of 5-minute fast-charging with 19.8 µm thickness for the full-capacity at 10 C. Ah-level engineering application cells have the retention of 93.69% after 600 cycles at 1 C. Electrolytes incorporating liquid single-atoms offer new strategies for fast charging.