Development of Electrically Conductive ZrO2-CaO-Fe2O3-V2O5 Glass and Glass-Ceramics as a New Cathode Active Material for Na-ion Batteries with High Performance

Glass-ceramics xZrO2•10Fe2O3•(90-x)V2O5 with ‘x’ between 0 and 30 mol% and yZrO2･(20-y)CaO･10Fe2O3･70 V2O5 glass with ‘y’ between 0 and 20 mol%, respectively abbreviated as xZFV and yZCFV, before and after heat treatment at 500 °C for 100 min, were evaluated as potential cathode-active materials for sodium-ion batteries (SIBs). Relationships between physical properties and local structure of xZFV and yZCFV glass-ceramics were investigated by 57Fe-Mössbauer spectroscopy, V K-edge X-ray absorption near edge structure (XANES), X-ray diffractometry (XRD), DC four-probe method and differential thermal analysis (DTA). SIBs containing heat-treated xZFV glass-ceramics showed the highest discharge capacity of 153 mA h g−1 under a current density of 50 mA•g−1, which exhibited a high electrical conductivity of 1.8 × 10−2 Scm−1. Precipitation of V0.05Zr0.95O2 and Fe2V4O13 nanoparticles were confirmed from the XRD pattern of the heat-treated 20ZFV glass, consistent with the lower energy of the pre-edge peak at 5467 eV in the V K-edge XANES spectrum. This result is associated with the reduction of vanadium ions from VV to VIV. It is concluded that the precipitation of stable vanadium bronze phases with high electrical conductivity and structural stability effectively enable the high SIB capacity of these materials.