Electrochemical impedance study on the low temperature of Li-ion batteries

Cycling performance of Li-ion cells was studied by using electrochemical impedance spectroscopy (EIS). Results showed that total resistance (R-cell) of the Li-ion cells is mainly composed of bulk resistance (R-b), solid-state interface resistance (R-sei) and charge-transfer resistance (R-ct). During cycling, the R-b and R-sei remain unchanged while the R-ct displays two minima in the same voltage regions where the major peaks of differential capacities are present. The R-ct can be linked to kinetics of the cell electrochemical reaction. In response to the temperature change, the R-b and R-sei vary in a very similar manner, while the R-ct shows significant difference. In the fully charged and discharged states as well as at the low temperatures (less than or equal to20degreesC), the R-cell of the Li-ion cells is predominated by the R-ct Using the term of the R-ct we explained two low temperature phenomena of the Li-ion battery: (1) charging of a fully discharged cell is much more difficult than discharging of a fully charged cell, and (2) both the power (operating voltage) and energy (delivered capacity) are substantially reduced. (C) 2003 Elsevier Ltd. All rights reserved.