Expanded interlayer spacing and additionally exposed edges induced by defects of MoS2 enable facile K-intercalation, rapid K-transport and promoted K-adsorption.

Free-standing electrodes have attracted wide attention for advanced supercapacitors. Herein, direct deposition of CuMnO 2 and CuMnO 2-reduced graphene oxide (rGO) nanocomposite on nickel foam (NF) substrates was performed through a simple hydrothermal process. The simultaneous deposition makes full use of the synergistic effect formed by the large pseudocapacitance of CuMnO 2 and excellent electrical conductivity of rGO, which results a greater performance improvement of the nanocomposite comparing with that of bare CuMnO 2. Remarkably, the CuMnO 2-rGO/NF electrode displays a large specific capacitance of 1727 F g-1 at 3 A g-1 and manifests exceptional cycling stability with a retention ratio of 125% of the initial capacitance over consecutive 5000 cycles. Furthermore, a rGO/NF//CuMnO 2-rGO/NF asymmetric supercapacitor exhibits great electrochemical performance by delivering high energy density (37.5 Wh kg-1) and high power density (4250 W kg-1) as well as excellent cycling stability (3.3% decay after 4000 cycles). The presented results suggest that CuMnO 2-rGO nanocomposite can be considered as a potential candidate for highly stable and high-rate supercapacitors.

Potassium-ion batteries are an emerging energy storage technology that could be a promising alternative to lithium-ion batteries due to the abundance and low cost of potassium. Research on potassium-ion batteries has received considerable attention in recent years. With the progress that has been made, it is important yet challenging to discover electrode materials for potassium-ion batteries. Here, we report pyrrhotite Fe1−xS microcubes as a new anode material for this exciting energy storage technology. The anode delivers a reversible capacity of 418 mAh g−1 with an initial coulombic efficiency of ~70% at 50 mA g−1 and a great rate capability of 123 mAh g−1 at 6 A g−1 as well as good cyclability. Our analysis shows the structural stability of the anode after cycling and reveals surface-dominated K storage at high rates. These merits contribute to the obtained electrochemical performance. Our work may lead to a new class of anode materials based on sulfide chemistry for potassium storage and shed light on the development of new electrochemically active materials for ion storage in a wider range of energy applications.