Simple Way of Making Free-Standing Battery Electrodes and their Use in Enabling Half-Cell Impedance Measurements via μ-Reference Electrode

Free-standing electrodes can be useful for a plethora of diagnostic measurements, as they allow transmissive measurements, stacking of electrodes, and/or measurements where the current collector would be disturbing the signal. Another advantage displayed in this publication is their use in Li-ion battery half-cells to decrease and stabilize the impedance of the counter electrode that is usually made of metallic lithium, allowing to conduct electrochemical impedance spectroscopy of a battery-type working electrode via μ-reference electrode which would otherwise show artefacts over a wide range of frequencies. Using measurements on an equivalent circuit mimicking a Li-ion battery half-cell with a μ-reference electrode we show how such artefacts arise from the large resistance in the μ-reference electrode and the imbalance in working and counter electrode resistance. We also show how the use of a free-standing graphite electrode attached to the Li-metal counter electrode (Li/FSG) reduces the counter electrode resistance and allows an artefact-free impedance measurement of the working electrode via a μ-reference electrode. Finally, we show the stability of the Li/FSG electrode and compare it to a Li-metal electrode.