Robust Solid-State Na-CO₂ Battery with Na_2.7Zr₂Si₂PO_11.7F_0.3-PVDF-HFP Composite Solid Electrolyte and Na₁₅Sn₄/Na...

Solid-state Na-CO₂ batteries are a kind of energy storage devices that can immobilize and convert CO₂. They have the advantages of both solid-state batteries and metal-air batteries. High-performance solid electrolyte and electrode materials are important for improving the performance of solid-state Na-CO₂ batteries. In this work, we investigate the influence of fluorine doping on the structure and ionic conductivity of Na₃Zr₂Si₂PO₁₂ (NZSP). An ionic conductive solid electrolyte membrane was prepared by compositing the inorganic solid electrolyte Na_2.7Zr₂Si₂PO_11.7F_0.3 (NZSPF3) with poly(vinylidene fluoride)-co-hexafluoropropylene (PVDF-HFP). It shows an ionic conductivity of up to 2.17 × 10^-4 S cm^-1 at room temperature, a high sodium ionic transfer number of ∼0.70, a broad electrochemical window of ∼5.18 V, and better mechanical strength. Furthermore, we studied the Na₁₅Sn₄/Na composite foil with the ability to inhibit dendrite as the anode for solid-state Na-CO₂ batteries. Through density functional theory (DFT) calculations, the Na₁₅Sn₄ particle has been verified with a strong sodiophilic property, which reduces the nucleation barrier during the deposition process, leading to a lower overpotential. The symmetric cell assembled with the composite solid-state electrolyte NZSPF3-PVDF-HFP and Na₁₅Sn₄/Na composite anode can inhibit the growth of Na dendrites effectively and maintain the stability of the whole cell structure. Solid-state Na-CO₂ batteries assembled with Ru-carbon nanotube (Ru-CNTs) as cathode catalysts exhibit a high discharge capacity of 6371.8 mAh g^-1 at 200 mA g^-1, excellent cycling stability for 1100 h, and good rate performance. This work provides a promising strategy for designing high-performance solid-state Na-CO₂ batteries.