An Experimental Method to Determine the Measurement Error of Reference Electrodes within Lithium‐Ion Batteries

Abstract

Reference electrodes (REs) play a crucial role in the accurate assessment and control of battery potentials, but their confidence is overestimated. Researchers have tracked the source of the error to the RE design that blocks the lithium‐ion path between anode and cathode. These errors or potential deviations are mostly modeled or less‐frequently estimated after observing Li plating post‐mortem. This is the first study to showcase an experimental method that allows a more precise error quantification in‐operando of a RE. The key idea is to relate the error‐affected reference potential to an unaffected quantity, such as the cell dilatation. Although our experimental setups are special, this approach can also be applied to different setups and REs. Using the presented method, we provoked Li plating in NMC811/graphite pouch cells and determined the potential deviation of our perforated RE to be 12 mV under fast charging conditions. In contrast to previous studies, we found the error to be positive, offering a new explanation of the error mechanism of REs.

Lithium Plating at the Cell Edge Induced by Anode Overhang during Cycling in Lithium-Ion Batteries: Part I. Modeling and Mechanism

“…In commercial cells, the separator is constantly optimized to increase the energy density, and the thickness of commercially available separators is already in the range of 9 to 16 μm. 9,45,52 Consequently, the trend to thinner separators enforces the inhomogeneous lithiation.…”

“…Other reasons for inhomogeneous lithium plating are pressure distribution and separator pore blocking. [44][45][46] Furthermore, inhomogeneous current density distribution due to cell design or defects was shown to be a reason for lithium plating in experiments [47][48][49][50][51] and simulations. [52][53][54] Since all cells mentioned above had anode overhang areas, these findings contrast the expectation that the anode overhang would reduce the risk of lithium plating, specifically near the negative electrode edges.…”