MXene (2D titanium carbide) as the electrode material for supercapacitors has been studied extensively and deeply in recent years. In order to enhance the electrochemical performance of MXene, CoS2 nanoparticles grown on MXene surface are constructed by a simple one‐step solvent thermal method. CoS2 nanoparticles play a crucial part in increasing the active sites of metal ions on the surface of MXene. In three‐electrode system, the obtained MXene/CoS2 composite delivers high performance. Its specific capacitance can be up to 1320 F g−1 at a current density of 1 A g−1 and it shows remarkable cycle performance with 78.4% after 3000 cycles at 10 A g−1. Moreover, the asymmetric supercapacitors (ASCs) with reduced graphene oxide as the negative electrode and MXene/CoS2 composite as the positive electrode exhibit a wide potential window of 1.6 V and high energy density (28.8 Wh kg−1) at a power density of 800 W kg−1. After 5000 cycles, the ASCs maintain 98% of initial specific capacitance at 5 A g−1. These results can effectively promote the application in the supercapacitor materials.

The volume of the metallic lithium anode in allsolid-state Li metal batteries increases significantly due to the lithium dendrite formation during the battery cycling, and the rough surface of lithium metal also reduces Li-ion transport in Li/electrolyte interface. In this work, we developed a solid polymer composite by adding the lowcost Si 3 N 4 particles to protect the lithium anode in allsolid-state batteries. The Fourier transform infrared spectroscopy (FTIR) data show that the surface of 10 wt % Si 3 N 4 particles interacts with the polyethylene oxide (PEO) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt; the interaction restricts the anion mobility and improves the ionic conductivity (1 9 10 -4 SÁcm -1 ) and lithium-ion transference number (0.28) of the composite electrolyte. The lithium metal anode is well protected by the composite electrolyte in all-solid-state cells, including symmetric and Li/LiFePO 4 cells. The lithium dendrite growth suppression by this composite electrolyte indicates the possible application of these low-cost composite electrolytes for lithium metal protection.

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