Novel Method for Monitoring the Electrochemical Capacitance by In Situ Impedance Spectroscopy as Indicator for Particle Cracking of Nickel-Rich NCMs: Part III. Development of a Simplified Measurement Setup

Abstract

As the optimization of the electrochemical performance of lithium-ion batteries by the adjustment of the composition of the cathode active materials (CAMs) has come to a limit, the focus has shifted to the modification of the morphological aspects. However, new methodologies for the quantification of characteristics such as particle size, particle cracking, and surface area change are needed. A previously reported impedance-based method allows for monitoring the capacitance of CAMs in the positive electrodes as indicator for their surface area but relies on a sophisticated cell setup. In this study, we deduce a stepwise simplification of the capacitance measurements from the setup using a gold-wire reference electrode to a conventional coin half-cell setup, which is commonly used in industry as testing platform for the initial benchmarking of newly developed CAMs. Additionally, it is shown that the CAM capacitance does not have to be extracted from a full impedance spectrum that requires an impedance analyzer, but that it can be obtained solely from a low-frequency single-point impedance measurement, which can be performed with a simple battery cycler. The working principle of this approach is validated using four different cell and electrochemical test hardware configurations (potentiostat, battery cycler) over several charge/discharge cycles.