Electrochemical Noise Measurements in Primary Lithium Batteries
Authors: Uzundal Can Berk , Karaoglu Gozde , Ulgut Burak 
Published: February 2020

Electrochemical noise measurements are well known within the corrosion community where information regarding local corrosion events can be extracted from an equilibrium measurement[1]. Extension of these measurements to the batteries can be a valuable non-invasive tool to diagnose the state of the batteries. Although easily measured in the corrosion systems where the amplitudes of the measured noise are in the order of mV’s, in the Li-Ion systems due to the high surface area materials used, noise levels are lower than μV’s. Moreover, this microvolt resolution is required on top of the already high cell voltage (a DC offset) of the Li-Ion batteries which constitutes an instrumentation challenge. To achieve the high resolutions required, the DC offset is removed by subtracting the static part of the voltage signal by the instruments. Measuring the voltage noise of a supercapacitor charged at different voltages revealed that the measured noise content heavily depends on the voltage of the supercapacitor, suggesting that indeed the offset reduction introduces artifacts to the measured voltage[2].
This increasing instrumental noise content at higher voltages prompted us to come up with a new offset reduction scheme. As shown in the Figure-c, by attaching two batteries in an anti-serial connection, it is possible to get rid of the DC offset without introducing artifacts. Moreover, we have designed a switch that can alternate between anti-serial and parallel connections to quickly equilibrate as shown in Figure-a. Using this approach, we measured the otherwise elusive equilibrium voltage noise of primary batteries after suffering a short circuit and monitored their noise levels throughout their recovery process[2]. Primary batteries are of particular interest for a non-invasive measurement such as electrochemical noise since the conventional methods deplete the cell during measurement. For instance, EIS is traditionally thought as a non-invasive measurement, however for primary cells where only the discharge reaction is defined, the measurement needs to be done under a negative DC offset to ensure linearity thus throughout the experiment the cell discharges. Measurement of electrochemical noise, on the other hand, by being a fully equilibrium measurement solves this issue and enables truly non-invasive diagnosis if measured properly.
In this meeting, we will demonstrate noise measurements for primary batteries of various chemistries, as an extension of our published work[2] on primary Lithium batteries of Li/MnO2 chemistry, we will show measurements in even smaller coin cells of the same chemistry, as well as measurements in Zn-Air batteries. We will also show results from our spectroscopic studies to identify the processes that result in the measured noise events such that noise measurements can be used as a complete tool to determine the state of the battery as is the case for the corrosion systems.

References

[1] R.A. Cottis, Interpretation of Electrochemical Noise Data, Corrosion. 57 (2001) 265–285.
[2] C.B. Uzundal, B. Ulgut, A Method for Voltage Noise Measurement and Its Application to Primary Batteries, J. Electrochem. Soc. 165 (2018) A2557–A2562. doi:10.1149/2.0681811jes.

Figure 1