(Invited) in-Situ Impedance of Lithium-Ion Rechargeable Batteries during Charge and Discharge

Abstract

An electrochemical impedance spectroscopy (EIS) is useful method to investigate inner structure and conditions of lithium-ion rechargeable batteries (LIRB) because EIS is nondestructive method to discriminate time constants related to electrolyte/electrode interfaces and protective film formed on negative electrode. The almost impedance measurements of LIRB are generally carried out at an equilibrium-state. The authors would like to emphasize that the galvanostatic control should be employed to measure impedance spectra of LIRB because the information of batteries during operation is more important than that at the equilibrium-state. For example, high power batteries require low charge transfer resistance during the high rate discharge. Stoynov et al. [1] measured impedance spectra of lead acid battery during charge and discharge at galvanostatic polarization. Itagaki et al. [2-4] determined time-dependent impedance spectra of LIRB’s during charge-discharge sequence.Figure 1 shows charge curve of a LIRB and 3D impedance spectra measured during the charge simultaneously. Three impedance spectra were determined by arranging a reference electrode in a laboratory cell of LIRB. The axes of 3D impedance are real and imaginary parts of impedance and time. For example, charge transfer resistance related to the diameter of capacitive loop of (c) positive electrode in high frequency range decreased with increasing the state of charge. In this presentation, the authors show the experimental results of 3D impedance spectra of LIRB, and discuss the intercalation/deintercalation mechanisms of lithium-ion at negative and positive electrodes.