Abstract:

The discharge behavior and uniformity of lithium-ion batteries were experimentally investigated at
low temperatures. The discharge test and electrochemical impedance spectroscopy (EIS) test were conducted
for several commercial 18650 type cells. The cell average capacity decreases by 58.4% with the capacity
standard deviation increasing by 6.6 times when the temperature decreases from 25 ℃ to -20 ℃ . The charge
transfer resistance (Rct) dramatically increases, dominating other types of resistance. The cell impedance
variations, mainly in the Rct, increase significantly at lower temperatures. A linear correlation between
the capacity and the over-potential resistance is established by statistics from 15 cells. Therefore, at low
temperatures, the cell-to-cell capacity variation increase is attributed to the cell over-potential resistance (mainly
the Rct) variation increase.