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In the OPINCHARGE Scientific Publications series, we highlight research that advances our understanding of battery behaviour, performance and safety. This publication explores an important diagnostic tool for lithium-ion batteries — reference electrodes, which allow researchers to look beyond the overall battery voltage and investigate what is happening at individual electrodes.
The review “Progress and perspectives on reference electrodes for Li-ion batteries” was authored by Álvaro Doñoro, Olatz Leonet, Ana Fernández-Barquín, Amaia Narbarte-Álvarez, Aroa R. Mainar, Elixabete Ayerbe, Dennis Kopljar, Hans-Jürgen Grande, Idoia Urdampilleta and J. Alberto Blázquez from CIDETEC, the University of the Basque Country (UPV/EHU) and the German Aerospace Center (DLR).
Read the publication: https://zenodo.org/records/20307031
A conventional lithium-ion battery measurement tells us the voltage difference between the positive and negative electrodes. However, it does not directly reveal how each electrode is behaving individually.
Reference electrodes (REs) provide an additional, stable electrochemical reference point. This makes it possible to independently monitor changes in the potential of the anode and cathode during charging and discharging and gain deeper insight into the reactions that determine battery performance.
This information is particularly valuable for detecting degradation mechanisms and determining how close a battery is operating to its electrochemical limits.
One particularly important application is lithium plating.
During fast charging or at low temperatures, the potential of a graphite anode can fall below the level at which lithium can safely intercalate into the material. Instead, metallic lithium may begin to deposit on its surface.
This can reduce battery capacity and increase internal resistance. Under more extreme conditions, lithium dendrites can also grow through the separator, creating a serious safety risk.
By monitoring the anode potential directly, reference electrodes can help researchers identify when lithium plating begins and develop faster charging strategies that remain within safe operating limits.
Designing a reliable reference electrode is not straightforward.
The review examines several possible materials. Lithium metal remains the conventional choice in laboratory experiments, but reactions with the electrolyte can cause its reference potential to change over time. Lithium alloys such as Li-Sn, Li-Al and Li-Bi can offer improved stability, while intercalation materials including LiFePO₄ (LFP) and Li₄Ti₅O₁₂ (LTO) provide well-defined and relatively stable electrochemical potentials.
However, material selection is only part of the challenge. The geometry, position and activation of the reference electrode can all influence measurement accuracy.
An ideal reference electrode should measure what is happening inside the battery without changing the processes it is trying to observe.
If it is too large or incorrectly positioned, it can interfere with lithium-ion transport, change current distribution or increase internal resistance. These effects may then appear in the measurements as apparent battery degradation even when they are actually caused by the reference electrode itself.
Researchers are therefore exploring thin wires, perforated structures and mesh-based designs that minimise disruption while still providing reliable electrochemical measurements.
Reference electrodes could ultimately become more than research tools.
Combined with physics-based battery models and advanced Battery Management Systems (BMS), electrode-level measurements could help distinguish degradation processes at the anode and cathode, improve state estimation and dynamically optimise battery operation.
This could be particularly valuable for fast charging: instead of relying only on conservative predefined limits, future systems could use information about the actual internal electrochemical state of the battery to determine how aggressively it can be charged.
Reference electrodes offer a powerful way to understand what happens inside lithium-ion batteries, but important challenges remain. Long-term stability, potential drift, measurement artefacts and practical integration into commercial cells still need to be addressed.
The review highlights the need to combine materials science, electrochemical engineering and advanced modelling to transform reference electrodes from laboratory probes into reliable sensing components.
By providing a clearer picture of individual electrode behaviour, these technologies could contribute to more precise battery management, safer fast charging and longer battery lifetimes — supporting the development of smarter next-generation lithium-ion batteries.
