Developing High-Purity Sodium Oxychloride Solid-State Electrolyte for Sodium-Ion Batteries — 14p — Karen Ly, Kamden Bryant, Alevtina Smirnova

Sodium-ion batteries have attracted significant attention as an alternative energy source to lithium-ion batteries. Solid-state sodium oxyhalides (Na₃OX, X = Cl, Br, I) have the advantages of easy synthesis from cheap raw materials. In this study, sodium oxychloride (Na₃OCl) antiperovskite was synthesized using a microwave furnace, the first instance in currently available literature. Using the microwave furnace also significantly decreased the reaction time when compared to other published procedures. The ionic conductivity of Na₃OCl pellets was determined using electrochemical impedance spectroscopy (EIS). Na₃OCl was hot pressed between sodiated hard carbon in a PEEK lined split cell with stainless steel current collectors. The symmetric cell was tested at room temperature with varying external pressures (1 MPa to 12 MPa). Symmetric cells were also tested at constant external pressure (6 MPa) from room temperature to 80˚C.

Arrhenius plots demonstrated linear behavior in the whole temperature range with a calculated activation energy of 0.98 eV. The melting and crystallization temperatures were determined using differential scanning calorimetry (DSC). The purity of as-synthesized Na₃OCl was evaluated using x-ray diffraction (XRD). The results on chemical composition and crystal-to-glass phase transformations were produced from in-situ X-ray diffraction (XRD) spectroscopy in the temperature range from 25˚C up to the melting point of Na₃OCl. Cross-sectional SEM images of the Na₃OCl pellets showed regions that were dense, but also regions with many pores (≤ 5 μm). SEM also showed microcracks that ranged from 1-5 μm. Future work will investigate methods of minimizing pores and microcracks during the cell manufacturing process as these surface features can impede efficient ionic movement.

South Dakota School of Mines & Technology
Alevtina Smirnova