Abstract:

Lithium-ion capacitor (LIC) using commercial activated carbon as the cathode and graphite as the anode was assembled. The graphite anode was pre-lithiated by a fast, efficient internal short approach, which involved placing graphite in direct contact with lithium foil with electrolyte additive. The effect of pre-lithiation on the electrochemical performance of the LIC was investigated using a conventional Cu current collector (CCC) and pre-punched Cu current collector (PCC). The LICs containing a CCC and PCC were named CLIC and PLIC, respectively. Although the CCC had slightly higher pre-lithiation level and higher energy density in the CLIC, it suffered from a considerable decrease in performance at higher charge-discharge rates. Meanwhile, 90.0% of the initial capacity was maintained in the PLIC, whereas that of the CLIC was only 73.2% after 1000 cycles in the voltage range from 2.0 to 3.8 V. The CCC led to solid electrolyte interphase (SEI) film expansion and Li metal plating with direct contact between graphite and lithium metal. The deposited thick SEI layer could weaken the adhesion of active materials and the current collector. Moreover, the expansion of the SEI layer itself produced electrical resistance and electrical contact loss between the active materials and current collector. In contrast, a thin, stable SEI layer formed on the surface of graphite after pre-lithiated using the PCC. Therefore, the PLIC showed better rate and cycle performance with the smaller self-discharge, voltage drop, and resistance than those of the CLIC.

Key words: Lithium-ion capacitor, Pre-punched Cu foil, Prelithiation, SEI film, Current collector