A reference electrode or 3rd electrode is added to a battery cell so that the anode and cathode potentials can be referenced against a known point. This is important as when we measure the cell voltage between the anode and cathode it is the difference between them that we are seeing. If we monitor the anode and cathode independently it is possible to establish parameters such as the maximum charge rate.
Three-Electrode All-Solid-State Battery Cycling
EIS spectra (WE vs RE) of the NMC cathode (red), the graphite anode (blue), the full cell (amber), and the sum of the individual electrode spectra (green) (20 °C, 0% SOC, 2 MHz – 100 mHz, NEISYS).
References
- J. Costard, M. Ender, M. Weiss and E. Ivers-Tiffée, Three-Electrode Setups for Lithium-Ion Batteries, Journal of The Electrochemical Society, Volume 164, Number 2, 2017
See also: Electrochemical Impedance Spectroscopy