Jiangong Zhu

Studies on the medium-frequency impedance arc for Lithium-ion batteries considering various alternating current amplitudes

An impedance measurement approach with various current amplitudes is proposed to investigate the impedance behavior of power Lithium-ion battery in the frequency domain. Notably, the impedance arc is divided into amplitude-independent response in the high-frequency range and amplitude-dependent response in medium-frequency range. A shrinking of semi-circle diameter of the impedance arc at medium-frequency part of measured spectrum is distinctly observed with rising current amplitude. Thus, a series of particular experiments are performed to facilitate the interpretation of the phenomenon. The possible influencing factors for the battery, including its state of charge, internal pressure, and temperature rise during the high-rate short-time charge/discharge, are illustrated and excluded for analysis, respectively. Based on the analysis of Butler-Volmer equation and Arrhenius empirical equation, a formula, which contains temperature and current known to influence the charge-transfer resistance, is derived logically. It indicates that the charge-transfer resistance reduces as the current amplitude increases at a fixed temperature, which fundamentally dominates the shrinking of the semi-circle at medium frequencies. Therefore, the medium-frequency impedance arc is able to represent the chemical reaction process, even under large current excitation (within a certain range).

A new electrochemical impedance spectroscopy model of a high-power lithium-ion battery

This paper presents an electrochemical impedance spectroscopy battery model including an electrical double layer capacitance, which can comprehensively depict the internal state of the battery. Based on the porous electrode theory, this model can obtain a complete spectrum of cell impendence. In addition, the EIS data recorded by an appropriate measurement instrument are consistent with the records of theoretical impedance derived from the model in terms of room temperature. To establish the relationship between internal parameters and external spectrum, a virtual simulation experiment is conducted to illustrate the effect of key parameters on EIS. According to the simulation experimental results, the model can be used to identify internal parameters based on the practical external spectrum. In the last part of the paper, a preliminary parameter identification strategy is proposed to study the relationship between battery internal parameters and external conditions.

Preliminary Study on the Influence of Internal Temperature Gradient on EIS Measurement and Characterization for Li-Ion Batteries

Battery characteristics in the conditions with/without internal temperature gradient are believed to be different, which imposes difficulty in characterization and modeling of the performance of battery cells, and relatively few studies have conducted the investigation of the effects of thermal gradients on battery characteristics. This paper makes a preliminary study on the influence of internal temperature gradient on EIS (electrochemical impedance spectroscopy) measurement and characterization. Several experiments are designed and implemented to facilitate the investigation. Experimental results and analysis show that the dependence of cell impedance on temperature can be fitted with the Arrhneius law, and the effect of SOC on the impedance is not as much as that of temperature. Moreover, the presence of the temperature gradients decreases the cell impedance when compared to the conditions without temperature gradients, and the higher the gradient, the smaller the amplitude of the measured impedance. With the equivalent circuit model fitting of the EIS measurements, it is found that the temperature gradient mainly influences Rsei and Rct. Based on analysis, a method to use the identified Rsei and Rct under different temperature gradients to re- construct the possible internal temperature distribution of the battery cell is also proposed.

Lithium-Ion Battery Internal Resistance Model Based on the Porous Electrode Theory

A one-dimensional electrochemical DC pulse simplified model for an 8Ah lithium ion phosphate battery monomer is built with the help of COMSOL software on the base of the porous electrode theory. Based on the experimental data and analysis, the model can be optimized by putting the values of effective conductivity and the concentration of the lithium at different temperature as well as the equilibrium potentials of active materials into the model. This model can reflect the pulse property of the battery very well. Through the DC pulse model, we can analyze how the internal parameters influence the battery internal resistance, which provides a reference for improving the battery design.