2 research outputs found
Tuning the Surface Morphology and Pseudocapacitance of MnO<sub>2</sub> by a Facile Green Method Employing Organic Reducing Sugars
In
the present work, three different MnO<sub>2</sub> nanostructures,
nanoneedles, hollow tubes, and nanorods of MnO<sub>2</sub>, have been
synthesized by a simple redox reaction between permanganate and organic
sugars at room temperature. The MnO<sub>2</sub> samples were characterized
by a variety of analytical techniques. The results illustrate that
the organic reducing sugars of mannose, galactose, and glucose effectively
tune the morphology, crystallinity, and pore structure of the MnO<sub>2</sub> material. The nanoneedles and hollow tubes were found to
be β-MnO<sub>2</sub>, while the nanorods were α-MnO<sub>2</sub>. The formation of different MnO<sub>2</sub> nanostructures
appears to be a kinetically driven process that proceeds in a quite
distinctive way in the presence of different organic reducing sugars.
Cyclic voltammetry (CV), galvanostatic charge/discharge (GCD), and
electrochemical impedance spectroscopy (EIS) tests were conducted
to evaluate the charge storage behavior of the α- and β-MnO<sub>2</sub> nanostructures. Among all three MnO<sub>2</sub> samples,
β-MnO<sub>2</sub> composed of nanoneedles delivered a large
specific capacitance, <i>C</i><sub>S</sub> (∼365
F g<sup>–1</sup> at 0.5 A g<sup>–1</sup>) with improved
rate capability (56% retention at 12 A g<sup>–1</sup>) and
excellent cyclability (82% retention at 2000 cycles). The elegant
combination of the high specific surface area (∼146 m<sup>2</sup> g<sup>–1</sup>) and 1D-nanoneedle structure of β-MnO<sub>2</sub>, enhances the electrode–electrolyte contact area and
hence provides a number of active sites for fast charge–discharge
propagations
Stabilizing Li<sub>10</sub>SnP<sub>2</sub>S<sub>12</sub>/Li Interface via an in Situ Formed Solid Electrolyte Interphase Layer
Despite the extremely
high ionic conductivity, the commercialization
of Li<sub>10</sub>GeP<sub>2</sub>S<sub>12</sub>-type materials is
hindered by the poor stability against Li metal. Herein, to address
that issue, a simple strategy is proposed and demonstrated for the
first time, i.e., in situ modification of the interface between Li
metal and Li<sub>10</sub>SnP<sub>2</sub>S<sub>12</sub> (LSPS) by pretreatment
with specific ionic liquid and salts. X-ray photoelectron spectroscopy
and electrochemical impedance spectroscopy results reveal that a stable
solid electrolyte interphase (SEI) layer instead of a mixed conducting
layer is formed on Li metal by adding 1.5 M lithium bisÂ(trifluoromethanesulfonyl)Âimide
(LiTFSI)/<i>N</i>-propyl-<i>N</i>-methyl pyrrolidinium
bisÂ(trifluoromethanesulfonyl)Âimide (Pyr<sub>13</sub>TFSI) ionic liquid,
where ionic liquid not only acts as a wetting agent but also improves
the stability at the Li/LSPS interface. This stable SEI layer can
prevent LSPS from directly contacting the Li metal and further decomposition,
and the Li/LSPS/Li symmetric cell with 1.5 M LiTFSI/Pyr<sub>13</sub>TFSI attains a stable cycle life of over 1000 h with both the charge
and discharge voltages reaching about 50 mV at 0.038 mA cm<sup>–2</sup>. Furthermore, the effects of different Li salts on the interfacial
modification is also compared and investigated. It is shown that lithium
bisÂ(fluorosulfonyl) imide (LiFSI) salt causes the enrichment of LiF
in the SEI layer and results in a higher resistance of the cell upon
a long cycling life