Investigation\nof\nSolid Polymer Electrolytes for NASICON-Type\nSolid-State Symmetric Sodium-Ion Battery

The inevitable shift toward renewable\nenergy and electrification\nnecessitates earth-abundant sodium reserves for next-generation Na-based\nenergy storage technologies. By coupling the benefits of solid electrolytes\nover traditional nonaqueous electrolytes due to their safety hazards,\nsolid-state sodium-ion batteries hold huge prospects in the future.\nThis work presents a comprehensively developed solid-state sodium-ion\nsymmetric full cell operating at room temperature enabled through\na poly(vinylidene fluoride-<i>co</i>-hexafluoropropylene)\n(PVDF-HFP)-based polymer electrolyte and modified NASICON-structured\npositive and negative electrodes. Among the investigated polymer electrolytes,\nPVDF-HFP-NaTFSI was found to outperform other counterparts by achieving\na higher ionic conductivity and delivered an appreciable electrochemical\nstability window. By further delving into the properties of PVDF-HFP-NaTFSI,\nit was found to possess the least crystallinity, minimal porous structure,\nlowest melting point, and fusion enthalpy, indicating better ion transport\nthan other investigated polymer electrolytes. The as-assembled solid-state\nbattery revealed a storage capacity of 74 mAh g<sup>–1</sup> at 0.1 C with a specific energy density of 130 Wh kg<sub>cathode_active_material</sub><sup>–1</sup> and demonstrated an impressive capacity retention\nof 84% of the initial capacity after 200 cycles. The structure and\nmorphology retention of the cycled electrode and electrolyte through\npostmortem analysis bolster the electrochemo-mechanical stability\nof the developed solid cell. The findings reported here on polymer\nelectrolytes persuade expedient solutions for developing ambient temperature\nsolid-state sodium-ion batteries with promising electrochemical performance\nfor commercialization in the near future.