Expanding the Operational Limits of the Single-Point Impedance Diagnostic for Internal Temperature Monitoring of Lithium-ion Batteries

Instantaneous internal temperature monitoring of a commercial 18650 LiCoO2 lithium-ion battery was performed using a single-point EIS measurement. A correlation between the imaginary impedance, -Z(imag), and internal temperature at 300 Hz was developed that was independent of the battery's state of charge. An Arrhenius-type dependence was applied, and the activation energy for SEI ionic conductivity was found to be 0.13 eV. Two separate temperature-time experiments were conducted with different sequences of temperature, and single-point impedance tests at 300 Hz were performed to validate the correlation. Limitations were observed with the upper temperature range (68 degrees C < T< 95 degrees C), and consequently a secondary, empirical fit was applied for this upper range to improve accuracy. Average differences between actual and fit temperatures decreased around 3-7 degrees C for the upper range with the secondary correlation. The impedance response at this frequency corresponded to the anode/SEI layer, and the SEI is reported to be thermally stable up to around 100 degrees C, at which point decomposition may occur leading to battery deactivation and/or total failure. It is therefore of great importance to be able to track internal battery temperatures up to this critical point of 100 degrees C, and this work demonstrates an expansion of the single-point EIS diagnostic to these elevated temperatures. Published by Elsevier Ltd.