High-performance Li-Ion hybrid supercapacitor based on LiMn 2 O 4 in ionic liquid electrolyte

In this paper, we report a high-performance Li-ion hybrid supercapacitor (Li-HEC) based on LiMn 2 O 4 in an imidazolium ionic liquid medium. The investigation of this type of cell is rare in the literature because hybrid devices constructed with ionic liquid (IL) are a challenge due to the coupling of distinct mechanisms (faradaic and electrostatic) of charge accumulation in a medium of high viscosity and low diffusion coefficient. The desire to overcome this challenge is motivated by the safety advantages brought by the usage of ILs as electrolytes, such as their low vapor pressure and non-flammability. Here, a spinel-LiMn 2 O 4, with adequate morphology and tridimensional insertion/de-insertion mechanism, is applied as a faradaic electrode in order to maximize the energy density in a Li-HEC, while maintaining the highest power density of the electric double layer capacitors. Complete cells are optimized with a mesoporous carbon as a capacitive electrode and a 1 M lithium bis(trifluorosulfonyl)imide (LiTFSI)/1-ethyl-3-methylimidazolium bis(trifluoromethane)sulfonamide (EMITFSI) as electrolyte. Finally, we demonstrate that when compared to hybrid cells employing aqueous and organic electrolytes, this Li-HEC can rival their energy and power densities while maintaining excellent cycling stability.