Novel Methodology of General Scaling-Approach Normalization of Impedance Parameters of Insertion Battery Electrodes – Case Study on Ni-Rich NMC Cathode: Part I. Experimental and Preliminary Analysis

In PART-1 of this paper, we present a generally applicable experimental methodology and a preliminary analysis strategy that can help researchers in the field of batteries to perform relevant measurements and a simple initial check of the self-consistency of the obtained impedance data of lithium-ion insertion electrodes. Using a model system based on a Ni-rich NMC active material, we demonstrate the necessary experimental steps to perform reliable and accurate impedance measurements of active electrodes (cells) and the characterization techniques required for a meaningful analysis of the obtained impedance data. We demonstrate the practical application of a simple preliminary analysis in which mass normalization of impedance spectra together with the assumption of ideal capacitive behavior allows access to the total (chemical) insertion capacitance, <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>C</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="italic">total</mml:mi> </mml:mrow> </mml:msub> </mml:math> , of the studied active material in an electrode. Furthermore, we show for the first time that there is an exact quantitative relationship (equality) between <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>C</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="italic">total</mml:mi> </mml:mrow> </mml:msub> </mml:math> , and the differential capacitance, <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>C</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>d</mml:mi> </mml:mrow> </mml:msub> </mml:math> , of porous insertion electrodes. A series of impedance data obtained by systematically varying the NMC cathode mass (thickness) is further analyzed step by step in PART-2. Therein, we explain in detail the approach of analyzing impedance spectra using an advanced physics-based Transmission Line Model (TLM) and demonstrate the practical applicability of the scaling methodology. The main objective of PART-1 is to provide experimenters with directly applicable tools and skills to develop a basic intuition for exploring and explaining the key phenomena observed in the impedance responses of porous Li-ion insertion cathodes. PART-2 will highlight the major advantages of analyzing impedance data using physics-based models. Any model that is based on elements with physical meaning and is correct should pass the “consistency test” included in the scaling relations.