Correlating Structural Changes with Electrochemical Activity in the Defect Perovskite Type ReO3 | AIChE

Correlating Structural Changes with Electrochemical Activity in the Defect Perovskite Type ReO3

Rhenium Oxide (ReO3) was investigated for use as a novel cathode material for rechargeable battery applications. ReO3 was synthesized by dissolving Re2O7 in methanol in a round bottom flask, followed by heating to 250 °C to form ReO3 nanoparticles. Upon evaporation of methanol, the ReO3 particles were deposited on the bottom of the flask. The particles were characterized using Transmission Electron Microscopy (TEM) and X-Ray Diffraction (XRD) pattern analysis. The material was shown to adopt the defect perovskite structure with a vacant A-site. Guest ion insertion was then studied electrochemically via Cyclic Voltammetry (CV) and Galvanostatic Cycling with Potential Limitation (GCPL). Both lithium and sodium was inserted during electrochemical studies. CV scans were used to study phase changes in the material upon ion insertion and GCPL was used to characterize cell performance in Swagelok and three electrode cells. Thick film ReO3 electrodes were used with Swagelok cells and microelectrodes were used for characterizing redox processes in three electrode cells. Either lithium or sodium hexafluorophosphate was used as the electrolyte, depending on the ion being inserted. The electrolyte solvent was ethylene carbonate (EC) and dimethyl carbonate (DMC). Structural changes during ion insertion were studied using a Swagelok in-situ cell with a beryllium window during XRD. The diffraction patterns show the distortion of the crystal structure as guest ions are introduced. Upon the intercalation of a single lithium ion per unit cell, the crystal distorts and contracts. The Re octahedra were shown to twist inwards upon lithiation by a single Li ion. Upon insertion of a second ion the unit ReO3 cell returns to the original volume. Despite returning to the original cell volume, the structure maintains distortion and octahedral twist. Sodium intercalation was also studied using CV and GCPL to characterize phase changes and cell performance. Sodium insertion during battery cycling was studied using in-situ XRD. Compared to lithium intercalation, far less structural distortion was observed possibly owing to sodium ion size matching the interstitial space of the ReO3 cell.