The impact of DC bias current on the modeling of lithium iron phosphate and lead-acid batteries observed using electrochemical impedance spectroscopy

Abstract

This paper deploys electrochemical impedance spectroscopy (EIS) to investigate the impact of temperature and dc bias current on battery impedance characteristics. Measured test results are used to demonstrate that, under conditions where the nonlinear Butler-Volmer equation is necessary to model the electrode charge transfer characteristics, the semicircular trajectory that typically appears in the EIS results shrinks in diameter as the battery's dc bias current increases. For a lithium-based battery, the nonlinearity introduced by the Butler-Volmer relationship is more pronounced at low temperature, while lead-acid batteries typically exhibit this nonlinearity even at room temperature. The impact of dc bias current on the battery model and EIS characteristics are thoroughly investigated using a combination of experimental tests combined with theoretical justification based on the Arrhenius equation. The value of using this observed relationship to improve the accuracy of battery models and condition monitors (e.g., state-of charge, etc.) is discussed in the paper.Index Terms -Electrochemical impedance spectroscopy (EIS), electric vehicle (EV), lithium iron phosphate battery, lead-acid battery, State-of-Charge (SOC), State-of-Function (SOF), Arrhenius equation, Butler-Volmer equation

Operando Thermo‐Electrochemical Diagnostics with Au, TiO2, and LiFePO4 as Reference Electrodes in Li‐Ion Pouch Cells

“…This contraction of the semi-circle at high temperatures implies that the impedance and ohmic resistance, charge transfer resistance decrease. [27][28][29] One of the reasons for impedance drops at a high temperature can be a decrease in internal resistances, also resulting in a decrease in voltage drop under load. Furthermore, a decrease in charge transfer resistance with a rise in temperature suggests that the Li-ion insertion/deinsertion process at the electrodes becomes easier.…”

“…Furthermore, a decrease in charge transfer resistance with a rise in temperature suggests that the Li-ion insertion/deinsertion process at the electrodes becomes easier. [27,28] In addition, the first semicircle grows while the second diminishes, which suggests that the SEIrelated effects are the main cause of the decrease in impedance at high temperatures. [27,28] The reduction of the second semicircle may be associated with the depletion of Li-ion from the cathode.…”

“…[27,28] In addition, the first semicircle grows while the second diminishes, which suggests that the SEIrelated effects are the main cause of the decrease in impedance at high temperatures. [27,28] The reduction of the second semicircle may be associated with the depletion of Li-ion from the cathode. [28] The presence of all three reference electrodes is shown to have a negligible impact on the EIS response of the cells, with the possible exception of LFP, suggesting instability at elevated temperatures in line with the differential capacity (Figure 5) analysis.…”

“…[27,28] The reduction of the second semicircle may be associated with the depletion of Li-ion from the cathode. [28] The presence of all three reference electrodes is shown to have a negligible impact on the EIS response of the cells, with the possible exception of LFP, suggesting instability at elevated temperatures in line with the differential capacity (Figure 5) analysis.…”

Novel estimation solution on lithium‐ion battery state of charge with current‐free detection algorithm

“…The battery port voltage and current can be easily measured but cannot be used to predict the SOC directly and precisely. Consequently, three kinds of algorithms for SOC estimation are widely implemented in consideration of application environment, desired accuracy, and design budget [9, 10]. A simple feasible method to predict the SOC is to calculate the integrating currents with an ampere‐hour counting.…”