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.
The chromatic transition from blue
to red in polydiacetylene (PDA)
membranes can be used for optical sensing in various applications
ranging from use as chemosensors to the quality control of foods and
medicines. The preparation of PDAs embedded in poly(vinyl alcohol)
(PVA) can be considered one of the simplest and most viable methodologies
for obtaining membranes with colorimetric responses. However, it is
still a scientific challenge to understand how the polymeric matrix
affects the chromatic transition of PDAs and how to control it. In
this work, PDA/PVA hydrogels were prepared to study its thermochromism.
The colorimetric responses of these hydrogels were compared with that
of PDA vesicle suspensions in order to show how the matrix of PVA
affects the color transition. Theoretical calculations have been carried
out to provide atomistic insights into the involved mechanism, showing
how the noncovalent interactions with the PVA matrix decrease the
rotational energy barrier of the PDA. Finally, in an attempt to modulate
the thermochromism of the hydrogels, membranes were obtained by gelling
PDA/L64 blends in the PVA matrix, using different concentrations of
the L64 copolymer. The results showed that the chromatic transition
of the PDA/L64/PVA membranes is more sensitive at lower temperatures
with increasing L64 concentration.
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