Energetics of Na+ Transport through the Electrode/Cathode Interface in Single Solvent Electrolytes

The activation energy of desolvation for Na-ion electrolyte systems were studied using temperature dependent electrochemical impedance spectroscopy (EIS). Propylene carbonate (PC) and tetraglyme were chosen as solvents in single solvent electrolyte solution coupled with NaClO4, NaPF6, NaAsF6, NaBF4, and NaOFt salts. The results demonstrate the insertion and desolvation processes are extremely fast at or above room temperature. The data shows under optimal salt chemistry the desolvation activation energy is less than 21 kJ/mole. This is in contrast to the similar to 50 kJ/mole measured for analogous Li systems. The dominant factor affecting performance was the anion. Indeed, anions with lower donor numbers (PF6-, AsF6-) had more than 30 kJ/mole lower desolvation energies than species like NaBF4 and NaOFt. (C) 2017 The Electrochemical Society. All rights reserved.