The low temperature performance of Li-ion batteries

A symmetric cell was adopted to analyze low temperature performance of Li-ion battery. Results showed that impedances of both Li-ion and symmetric cells are mainly composed of bulk resistance (Rb), surface layer resistance (Rsl) and charge-transfer resistance (Rct). Among these three components, the Rct is most significantly increased and becomes predominant as the temperature falls to below −10 °C. Therefore, we may ascribe the poor low temperature performance of Li-ion battery to the substantially high Rct of the graphite and cathode. Comparing impedance spectra of the symmetric cells, we found that at −30 °C the delithiated graphite and lithiated cathode, both of which correspond to a discharged state in a Li-ion battery, have a much higher Rct than when charged. This means that the Li-ion battery in the discharged state suffers a higher polarization. This result explains the phenomenon that at low temperatures, charging of a discharged Li-ion battery is more difficult than discharging of a charged battery.