Applications of AC Impedance Spectroscopy as Characterization and Diagnostic Tool in Li-Metal Battery Cells

Electrochemical Impedance spectroscopy (EIS) is exceptionally powerful and rapidly evolving technique for investigating electrical properties of materials and electrochemical interfacial kinetic processes in wide variety of practical systems and applications. The method offers the most powerful on-line and off-line analysis of the status of investigated media, electrodes, and probes in many different complex time- and space-resolved processes that occur in electrochemical laboratory experiments or over a lifetime of monitored samples, devices, or materials. EIS is useful as an empirical quality control procedure that can also be employed to interpret fundamental electrochemical processes [1, 2]. At NASA Glenn Research Center the EIS technique is being widely and effectively employed in characterization and performance monitoring of rechargeable energy storage devices, such as states of electrodes during charging / discharging cycles in secondary batteries and fuel cells. The technical objective for batteries is to improve the performance of rechargeable cells to meet the energy storage requirements of human missions. The approach is to develop advanced battery components to safely provide substantially higher specific energy for relatively few charge/discharge cycles. In the presented work, impedance spectroscopy and other electrochemical and surface science techniques have been widely applied to monitoring developed lithium-metal battery (LMB) cells, including investigation of the impact of novel ionic liquid electrolytes on cycle life and dendrite growth/suppression on Li anodes. Applications of EIS method allowed for efficient in situ performance monitoring of various types of electrodes and electrolytes used in experimental battery cells. The studies were focused initially on evaluating performance of separate battery components in symmetric lithium coin cells, with a purpose of future complete impedance analysis of full cells with Li anode and dedicated cathode.