Charge Transfer Kinetics of the Sodium|Na3.4Zr2Si2.4P0.6O12 Interface

The sodium super ionic conductor (NaSICON) is a promising solid electrolyte for sodium-ion batteries due to its high ionic conductivity and chemical stability against sodium metal. However, charge-transfer kinetics at the sodium|NaSICON interface near sodium’s melting point are not well quantified, limiting predictive modeling. Temperature-dependent impedance spectroscopy on sodium|Na3.4Zr2Si2.4P0.6O12 cells (70–135 °C) showed an interfacial activation energy of 0.788 ± 0.014 eV, with no discontinuity at sodium’s melting point. Butler–Volmer analysis at 135 °C gave an exchange current density of 7.42 ± 0.94 mA cm–2, trending exponentially with temperature. A 150 nm Sn coating reduced activation energy to 0.738 ± 0.006 eV and improved exchange current density to 12.9 ± 0.03 mA cm–2 at 135 °C. Three-electrode measurements revealed asymmetric behavior, with plating showing a nucleation overpotential spike and stripping a gradual overpotential rise. These findings provide kinetic benchmarks for near-molten sodium|NaSICON interfaces.