Testing Lithium-Ion Battery with the Internal Reference Electrode: An Insight into the Blocking Effect

Abstract

Long-term stability of reference electrode is a major issue in lithium-ion batteries. A composite Ni-Li reference electrode (RE) with a longer lifetime than traditional Cu-wire Li reference electrodes is proposed in this study. However, the larger size of the Ni-Li RE creates a blocking effect when positioned internally in the battery. The blocking effect manifests as an abnormal feature in the measured electrode potential. A two-dimensional (2D) finite element model of the cell with an internal RE is constructed to investigate the mechanism of the blocking effect. The internal RE blocks the path of local current flow in the electrolyte, and decreases the electrochemical reaction rate of particles in the anode and cathode, leading to measurement errors. Characteristic lengths of RE and applied currents were examined as parameters in the finite element model to determine their effect on the magnitude of error. A useful guide is provided for proper selection of size of RE and applied current in dynamic tests of lithium-ion batteries.

A Toolbox of Reference Electrodes for Lithium Batteries

“…[74] The underlying issue here is defined as the "blocking effect" of the RE in resistive organic electrolytes, as gradients in electrolyte concentration are produced near the RE during the dynamic cycling of the cell (Figure 10c). [75] This phenomenon introduces artifacts in the establishment of a stable RE potential, and thus affects the accurate detection of WE potential. [73a] Copyright 2016, The Authors, published by ECS.…”

“…c) The electrolyte concentration evolution in the vicinity of RE at a discharge rate of 0.5 C. Reproduced under terms of the CC BY license. [ 75 ] Copyright 2018, The Authors, published by ECS. d) Fast‐charging protocol with additional anode‐potentiostatic procedure without lithium plating.…”

“…Copyright 2020, Elsevier. c) The electrolyte concentration evolution in the vicinity of RE at a discharge rate of 0.5 C. Reproduced under terms of the CC BY license [75]. Copyright 2018, The Authors, published by ECS.…”

Critical Review of the Use of Reference Electrodes in Li-Ion Batteries: A Diagnostic Perspective

“…Significant efforts have also been made to implement cylindrical [24,35,38,43,72,154] and pouch [31,36,63,64,70,71,75,94,98,[155][156][157] cells with an RE (Figure 18a,b). Besides the practical difficulties associated with positioning the RE, particularly in cylindrical cells where significant modification of the cell is required, neither the location nor the geometry of the RE is optimal to obtain artefact-free EIS measurements [36,72].…”

Electrochemical impedance spectroscopy

“…176 Although artifacts such as current leaking and short circuit have been associated with placing the lithium metal reference electrode between the two electrodes. 177 For durable use of reference electrodes in lithium-ion batteries, in-situ electrochemical alloying a thin insulated gold wire with lithium 178 and plating Li in nickel mesh 179 are a couple of potential routes. Such reference electrodes can last reliably for months, which is extremely valuable for diagnosing cells under cycling.…”