Use of three-terminal impedance spectroscopy to characterize sodium-ion batteries at various stages of cycle life

The use of 3-terminal measurements to separate different impedance components of a prototype sodium-ion battery is outlined. By addition of a sodium metal reference electrode, the two electrode-electrolyte interfaces can be measured separately and changes monitored at various stages of battery cycle life. The impedance of a freshly-constructed cell is dominated by the blocking capacitance of the anode-electrolyte interface and the charge-transfer resistance at the cathode-electrolyte interface. The variation of these components during charge and discharge cycling provide a method to monitor evolution of cell performance.