Engineering the NASICON Electrolyte/Na Anode Interface by Tuning the Phase of Electrolyte for Solid-State Sodium Battery

The commercialization of all-solid-state sodium batteries is currently mainly inhibited by the poor interface between the solid-state electrolyte and electrode. Herein, the interface between NASICON electrolyte and Na anode is engineered by tuning the phase of NASICON with the composition of Na 3.36 Zr 1.64 Sc 0.36 Si 2 PO 12 (NZSSP), which was prepared by the solid-state reactive sintering method. The phase is adjusted by varying the sintering temperature (900–1150 °C) and investigated by X-ray diffraction Rietveld refinement. The sintered NZSSP samples are dominated by the rhombohedral NASICON phase, and its content increases with the sintering temperature, 97% for the 1150 °C-sintered sample, whereas the Na 3 Zr 2 Si 2 PO 12 (NZSP) sample is dominated by the monoclinic NASICON. The scanning electron microscopy and X-ray photoelectron spectroscopy results reveal that the surface microstructure and composition are similar. However, the interfacial impedance ( R inter ) between solid electrolyte and Na anode and the critical current density (CCD) are quite different; R inter decreases and CCD increases with the sintering temperature. The 1150 °C-sintered NZSSP has significantly lower R inter (4.7 vs 316.4 Ω cm 2 ) and higher CCD (0.85 vs 0.1 mA cm –2 ) compared with NZSP at 30 °C. The full battery Na/NZSSP/Na 3 V 2 (PO 4 ) 3 can be stably cycled at 1C for 350 cycles. The contact angle measurement and adsorption energy calculation show that the adhering property of NASICON with Na plays a dominating role. The rhombohedral NASICON exhibits much greater adsorption energy to Na and lower contact angle, which is beneficial for the interfacial property and thus the Na plating/stripping processes. This work demonstrates that engineering the phase of the NASICON electrolyte is an effective strategy to optimize the interfacial property between NASICON and the Na anode.