High-Performance Lithium-Ion Hybrid Supercapacitors Based on Lithium Salt/Imidazolium Ionic Liquid Electrolytes and Ni-Doped LiMn2O4 Cathode Materials

In this work, we evaluate the effect of Ni-doping LiMn(2)O(4 )spinels, LiNixMn2-xO4 (0.01 <= x <= 0.10) on the performance of lithium-ion hybrid supercapacitors (Li-HSCs) based on a mixture of 1 M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and a 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMITF-SI) ionic liquid (IL) as the electrolyte and mesoporous carbon as the anode. Although the positive contribution of metal doping of lithium-ion insertion materials in the electrochemical properties is known for Li-ion batteries, this effect is little studied in battery/supercapacitor hybrid full cells based on these compounds, especially with the use of electrolytes based on ionic liquids at room temperature. This issue is addressed in the present work- Among all studied devices, the Li-HSC based on LiNi0.01Mn O-1.99(4) was able to deliver the highest energy density values, in the range of 21.7-40.9 W h kg(-1). Also, the devices based on low nickel-content spinels (x <= 0.03) showed high performance with excellent cycling stability, being able to retain around 79-85% of its initial energy density after 1500 cycles of charge/discharge at 400 mA g(-1).