Electrochemical performance of lithium ion capacitors using aqueous electrolyte at high temperature

Aqueous lithium ion capacitors (LICs) with LiFePO4 positive electrodes and activated carbon (AC) negative electrodes were developed and their electrochemical performances were investigated by cyclic voltammetry, galvanostatic charge/discharge, and ac impedance spectroscopy at various temperatures. It is found that the stable voltage window for the aqueous LICs is 0-1.7 V and the optimized mass ratio between the positive electrode and negative electrode is 1:1. The rate capability of the LIC is much higher than that of the LiFePO4 electrodes. The Ohmic resistance and electrochemical impedance of the LiFePO4 and AC electrodes decrease with increasing the temperature, leading to high rate capability of the LIC. The performance of the LIC is deteriorated when it is cycled at 70 degrees C which is caused by the reduction of Fe2+ in LiFePO4. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4798432]