This study aims to increase the knowledge on the interactions that occur at the electrode/electrolyte interface in carbon-based electric double layer capacitors (EDLC) when solventfree ionic liquids are used as electrolytes. Many previous studies found in the literature are conducted using theoretical approaches and they are unable to model all the variables and the complexity of an actual device with a complex carbon surface and an ionic liquid (IL). Here, the compatibility between imidazolium ionic liquids and different carbon materialsan activated carbon (AC), a mesoporous carbon (MES), multi-walled carbon nanotubes (MWCNT), and reduced graphene oxide (RGO) -is empirically investigated applying synchronous chronopotentiometric tests to various symmetrical EDLCs. The study of the simultaneous evolution of the cell and electrode potentials of the various carbon/ILs cells, monitoring the evolution of specific capacitances and electrical resistances for each independent electrode, allows inferring about the ion-electrode compatibility, the limiting factors for charge accumulation and its impacts on the performance of the global cell. The results indicate that the sp 2 structures of MWCNT and RGO favor interactions with the EMI + cation on the negative electrode.In the positive electrodes, MES and AC favor interactions with the BF4and TFSIanions, respectively, yielding a higher specific capacitance and lower resistance.
A hybrid SC prepared with mesoporous carbon as the negative electrode, LiFePO 4 as the positive electrode and a LiTFSI/imidazolium ionic liquid solution as electrolyte is presented. The cell was conceived on the basis that it offers all the safety features of ionic liquids (IL) and LiFePO 4 , in addition to the advantages of a high energy density device.Most of the high performance hybrids so far reported in the literature employ aqueous or organic electrolytes, whereas studies of hybrid cells based on IL still rare. Here, a fundamental study was conducted to understand how the different interfaces and mechanisms operate in a hybrid system based on IL electrolyte, and how this affects cell performance. This device was mainly characterized using cyclic chronopotentiometry that allows cell voltage and electrode potentials to be simultaneously recorded. By means of this technique, it was possible to evaluate the overall behavior of the hybrid cell and the faradaic and capacitive electrodes simultaneously, and to compare it with the performance of selected standard cells. The results show that the cell is able to attain an energy density of 43.3 W h kg -1 at 0.010 A g -1 (C/5 in relation to LiFePO 4 ), while maintaining a good cycling performance.
In
this work, we evaluate the effect of Ni-doping LiMn2O4 spinels, LiNi
x
Mn2–x
O4 (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
(EMITFSI) 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 LiNi0.01Mn1.99O4 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.
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