Errors in the reference electrode measurements in real lithium-ion batteries

Abstract

Reference electrodes (REs) implanted in lithium-ion batteries are essential indicators in the fields of health monitoring and safety management. The non-destructive charging profiles, for example, are usually determined by electrode potential measurements performed with the RE. However, errors in RE potential measurements, resulting in seriously flawed conclusions, are seldom discussed in real lithium-ion batteries. This study investigates the reliability of anode potentials measured with a Li/Cu RE implanted in commercial cells. Artefacts are advanced in RE measurements based on the inconsistency of measured anode potentials and lithium plating behaviors, and further validated by the excess anode overpotential while charging to high state of charge at high rates. Furthermore, artefact phenomenon is reflected in the electrochemical model highlighting the RE blocking of the Li-ion flow. Inhomogeneous lithium intercalation currents at the anode-separator interface are revealed to bring out the excess anode overpotential in RE measurements. Finally, the impact of critical parameters on potential artefacts is examined, and proper RE sizes and battery operating conditions are proposed to ensure the reliability of potential measurements. This work emphasizes the existence of artefacts in RE potential measurements, and provides a useful guide on eliminating errors and improving accuracy of RE in real lithium-ion batteries.