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Despite the extremely high ionic conductivity, the commercialization of LiGePS-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 LiSnPS (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)/ N-propyl- N-methyl pyrrolidinium bis(trifluoromethanesulfonyl)imide (PyrTFSI) 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/PyrTFSI 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. 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.

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Spinel NiCo 2 O 4 material has received considerable attention as an excellent supercapacitor material. In this study, we report facile and cost-effective solvothermal method for the synthesis of mesoporous NiCo 2 O 4 anchored on reduced graphene oxide (rGO). The electrochemical activity of the NiCo 2 O 4 -rGO and pristine NiCo 2 O 4 materials were evaluated by cyclic voltammetry (CV), chronopotentiometry (CP) and electrochemical impedance spectroscopy (EIS). The NiCo 2 O 4 -rGO composite electrode shows high specific capacitance value of 870 F g -1 at current density of 2 A g -1 and it retains 600 F g -1 capacitance even at high current density of 20 A g -1 . Pristine NiCo 2 O 4 shows poor capacitance value of 315 F g -1 at 2 A g -1 and it retains only 191 F g -1 at 10 A g -1 . Further, NiCo 2 O 4 -rGO nanocomposite shows excellent cyclic performance with 90% capacitance retention even after 5000 charge-discharge cycles at high current density of 4 A g -1 , whereas pristine NiCo 2 O 4 electrode shows only 45% capacitance retention. The high specific capacitance, remarkable rate capability and excellent cycling performance offered by NiCo 2 O 4 -rGO composite is attributed to the high surface area and high conductivity. In addition, rGO Recently, different NiCo 2 O 4 -graphene hybrid nanocomposites have been designed by different approaches and their performance tested for supercapacitors. 26, 34-39 For example, Wang et al. synthesised NiCo 2 O 4 -rGO composite using self-assembly method by exfoliatingNi-Co hydroxides and assembling with GO followed by heat treatment. These self-assembled 2D nanosheets of NiCo 2 O 4 -rGO composite exhibits higher specific capacitance of 835 F g -1