Development of an in situ Mediator Dosing Concept for Scanning Electrochemical Microscopy in Lithium-Ion Battery Research

In scanning electrochemical microscopy (SECM), the addition of a redox active species plays an essential role. Those deliberately added mediators may alter results in SECM studies. In investigations of lithium-ion battery (LIB) materials, especially of the positive electrode, the oxidation potentials of commonly used mediator substances such as ferrocene are located within the operation potential of the electrode. Thus, they possibly interfere with the regular charge/discharge processes. In situ studies are therefore in need of approaches reducing or eliminating the use of mediators. Within this publication, a novel mediator dosing (MD) concept is introduced. A capillary was closely positioned at the tip of the scanning probe. By gravity flow, stable flow rates of mediator solution of up to 32.4±0.6 μL h⁻¹ were achieved. These low amounts were found to be sufficient to form a ferrocene zone at the probe tip enabling feedback mode SECM measurements with comparable quality to measurements directly in ferrocene solution. Proof of concept experiments were conducted by investigation of a thin-film electrode with a micro-structured surface. Furthermore, the MD concept was applied in imaging experiments of a commercially available LIB graphite electrode.