(A) study on high performance lithium ion capacitos with functionalized graphene

Abstract

Lithium ion capacitors (LICs) have recently drawn considerable attention because they utilize the ad-vantages of supercapacitors (high power) and lithium ion batteries (high energy). However, the energy densi-ties of conventional LICs, which consist of a pair of graphite and activated carbon electrodes, are limited by the small capacities of the activated carbon cathodes. To overcome this limitation, we have engaged urea-reduced graphene oxide. The amide functional groups generated during the urea reduction facilitate the enoli-zation processes for reversible Li binding, which improves the specific capacity by 37 % compared to those of conventional systems such as activated carbon and hydrazine-reduced graphene oxide. Utilizing the increased Li binding capability, when evaluated based on the mass of the active materials on both sides, the LICs based on urea-reduced graphene oxide deliver a specific energy density of ~106 $Wh/kg_{total}$ and a specific power den-sity of~4200 $W/kg_{total}$ with perfect capacity retention up to 1000 cylces. These values are far superior to those of previously reported LICs and supercapacitors, which suggests that appropriately treated graphene can be a promising electrode material for LICs