Correlation between Internal Structure and Electrochemical Impedance Spectroscopy of Multiphase Slurry Systems

Abstract

Slurry for lithium-ion batteries is prepared from an active material, a carbon conductive additive, and a polymeric binder in a solvent, and its morphological change is evaluated over time using electrochemical impedance spectroscopy. A schematic model of the internal structure and dispersion states of the slurry components during 7 days of storage is proposed on the basis of the electrochemical impedance spectroscopy (EIS) measurement. The EIS results reveal that the conductive path constructed by the network structure of the slurry components breaks over time, which can be worsened by mechanical agitation. In order to confirm the morphological change, the slurry is freeze-dried and then prepared to fixate the locations of the slurry components. The existence of a network structure (or flocculation) is verified by morphological observations. In addition, the dispersity index and Micro-CT are introduced as new methods representing the dispersion state of the slurry components.

Microfluidic Electrochemical Impedance Spectroscopy of Carbon Composite Nanofluids

“…A complex nonlinear least-squares (CNLS) method was used for the equivalent circuit design, relevant data processing, and impedance estimation 37 . The data fitting with the equivalent circuit was carried out in a frequency range of 1~100 kHz.…”

Evaluation of the Electrochemical Characterizations of Lithium-Ion Battery (LIB) Slurry with 10-Parameter Electrical Equivalent Circuit (EEC)

“…10a, the electrochemical characteristics of PVDF-NMP solution can be expressed as ohmic resistance R so [ ] and capacitance C SO [F] on account of the charged ions in PVDF-NMP solvent. 8 Meanwhile, a resistor R CT [ ] is also taken into consideration because PVDF polymer chain has the electronically insulating property, which can be dissolved into the NMP solvent as loops and tails. 11 In this regard, the charge transfer resistance of PVDF-NMP solution is represented by R CT [ ].…”

“…11 shows a conventional 8-parameter EEC constructed by Bai. S J et al 8 according to the internal structure of LIB slurry. In this 8-parameter EEC, R CT is charge transfer resistance; CPE E and CPE B denote Warburg impedance and capacitance of binder, respectively; C DL represents electrical double layer capacitance; R SO is the resistance of solvent and R A&C is the conductive additives and active materials.…”

“…e(x k , f) = e (x k , f) + je (x k , f) [ 8 ] where, n denotes the number of EIS measurement points, f ∈ R n represents the applied frequency vector, e (x k , f) ∈ R n and e (x k , f) ∈ R n denote the real and imaginary part of the error vector e(x k , f). e (x k , f) and e (x k , f) are expressed by…”

“…7 The measurements are run over a wide range of frequencies, which allows frequency dependent responses to be properly characterized. In this regard, Bai S J et al 8 analyzed the electrochemical characterizations of LIB slurry by fitting EIS Nyquist and Bode plots with an 8-parameter electrical equivalent circuit (EEC) which was constructed according to the internal structure of LIB slurry. They concluded that the resistances of LiCoO 2 particles, Carbon Black (CB) conductive additives and PVDF binders are increased with time elapse.…”