The purpose of this study was to understand the electrochemical behavior of the interface between porous electrodes and electrolytes of lithium-ion batteries. We propose a new analytical approach that is a combination of the transmission line model theory for cylindrical pores and electrochemical impedance spectroscopy using symmetric cells. Mathematical model and experimental impedance behavior results agree with each other. By mathematically fitting the experimental impedance plots, the individual internal resistance components of the actual porous electrode/electrolyte interface could be described as the following four parameters: electric resistance (R e ), electrolyte bulk resistance, (R sol ), ionic resistance in pores (R ion ), and charge-transfer resistance for lithium intercalation (R ct ). In actual electrodes, the R ion obtained in this study is a characteristic parameter of the porous electrode/electrolyte interface that is important to consider for thick electrodes.
To
clarify the role of conducting carbon in porous electrodes for
lithium-ion batteries on internal resistance, the dependence of internal
resistance on the conductive carbon ratio in positive electrodes was
systematically investigated by applying electrochemical impedance
spectroscopy with symmetric cells. Based on an assessment of the loading-weight
dependence of the porous electrode internal resistance at each conductive
carbon ratio, the dependence of ionic resistance in the pores (R
ion), the charge-transfer resistance (R
ct), and the tortuosity factor (τ) was
compared. As the conductive carbon ratio increased, the slope of linearity
through the origin of R
ion with respect
to the loading weight increased due to an increase in the ion transport
path distance as τ increases in the porous electrodes. This
tendency continues until the pores inside the porous electrode are
sufficiently filled with conductive carbon particles. On the other
hand, all R
ct values for the different
conductive carbon ratios followed the same inverse proportionality
because R
ct depends on the reaction area
of the active material and not on the electrode structure, which is
affected by the conductive carbon ratio. This research will contribute
to the porous electrode design with low resistance and high energy
densities for state-of-the-art lithium-ion batteries.
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