Tuning the Surface Morphology and Pseudocapacitance of MnO₂ by a Facile Green Method Employing Organic Reducing Sugars

In the present work, three different MnO₂ nanostructures, nanoneedles, hollow tubes, and nanorods of MnO₂, have been synthesized by a simple redox reaction between permanganate and organic sugars at room temperature. The MnO₂ 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 MnO₂ material. The nanoneedles and hollow tubes were found to be β-MnO₂, while the nanorods were α-MnO₂. The formation of different MnO₂ 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-MnO₂ nanostructures. Among all three MnO₂ samples, β-MnO₂ composed of nanoneedles delivered a large specific capacitance, <i>C</i>_S (∼365 F g^–1 at 0.5 A g^–1) with improved rate capability (56% retention at 12 A g^–1) and excellent cyclability (82% retention at 2000 cycles). The elegant combination of the high specific surface area (∼146 m² g^–1) and 1D-nanoneedle structure of β-MnO₂, enhances the electrode–electrolyte contact area and hence provides a number of active sites for fast charge–discharge propagations

Stabilizing Li₁₀SnP₂S₁₂/Li Interface via an in Situ Formed Solid Electrolyte Interphase Layer

Despite the extremely high ionic conductivity, the commercialization of Li₁₀GeP₂S₁₂-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 Li₁₀SnP₂S₁₂ (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 bis­(trifluoromethanesulfonyl)­imide (LiTFSI)/<i>N</i>-propyl-<i>N</i>-methyl pyrrolidinium bis­(trifluoromethanesulfonyl)­imide (Pyr₁₃TFSI) 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/Pyr₁₃TFSI 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^–2. Furthermore, the effects of different Li salts on the interfacial modification is also compared and investigated. It is shown that lithium bis­(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