Evaluation of lithium-ion capacitors assembled with pre-lithiated graphite anode and activated carbon cathode

Lithium ion capacitors (LICs) were assembled using pre-lithiated graphite anode and activated carbon (AC) cathode. The cells were tested for their rate capability at 1 C and 10C for 100 and 600 cycles, respectively at two different cut-off voltages. The cell delivered a discharge energy density of 55 Wh kg(-1) (active materials basis) over the potential range of 3.1-4.1 V and 100Wh kg(-1) in the extended cut-off potential of 2.0-4.1 V. The maximum energy density obtained with LIC is about 8 times higher than the energy density obtainable with conventional EDLCs that operates in a voltage window of 0.0-2.5 V. The capacity fade of LIC with cycling is directly correlated with the reduced utilisation of the positive AC material during the charge storage process, which in turn, is caused by the instability of the pre-lithiated graphite negative electrode. The instability of the pre-lithiated graphite electrode resulted in the self-discharge of pre-doped Li, which is believed to be the result of a poorly formed solid electrolyte interface (SEI) on graphite surface. Li pre-doping methodology is shown to play a crucial role and contributes to the stability of the negative electrode and consequently the cell cycling stability. Crown Copyright (C) 2012 Published by Elsevier Ltd. All rights reserved.