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Owing to their low electronegativity, excellent electrical conductivity, high specific capacitance, and rich electrochemical redox sites, various transition metal sulfides have attracted significant attention as promising pseudocapacitive electrode materials for supercapacitors. However, their relatively poor electrical conductivity and large volume changes seriously hinder their commercial applications. Herein, ternary Co0.33Fe0.67S2 nanoparticles are in situ embedded between graphene nanosheets through a facile one-step hydrothermal approach to form a sandwich-like composite. Because of its unique and robust structure, the graphene nanosheet/Co0.33Fe0.67S2 composite (GCFS-0.33) exhibits a high specific capacitance (310.2 C g–1 at 2 mV s–1) and superb rate capability (61.8% at 200 mV s–1) in 3 M KOH aqueous electrolyte. Using transition metal sulfides simultaneously as both positive and negative electrodes, for the first time, an aqueous asymmetric supercapacitor (ASC) was fabricated with the GCFS-0.33 composite as the negative electrode and sulfidized graphene/CoNiAl-layered double hydroxides as the positive electrode with well-separated potential windows. Our fabricated ASC delivered an excellent energy density of 66.8 Wh kg–1 at a power density of 300.5 W kg–1 and still retained 13.1 Wh kg–1 even at a high power density of 29.4 kW kg–1, which is highly comparable with that of previously reported transition-metal-sulfide-based ASC devices. Moreover, the as-fabricated ASC cell displays impressive long-term cycling stability with a capacitance retention of 102.2% relative to the initial capacitance after 10 000 cycles. This versatile synthetic strategy can be readily extended to synthesize other transition-metal-sulfide-based composites with excellent electrochemical performances.

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MXene-derived TiO2/RGO composite was designed and synthesized by the hydrothermal process as a universal anode for Li-ion and K-ion batteries.

Metallic anodes have high theoretical specific capacities and low electrochemical potentials. However, short-circuit problems caused by dendritic deposition and low Coulombic efficiency limit the cyclic life and safety of metallic anode-based batteries. Herein, dendrite-free and flexible three-dimensional (3D) alkali anodes (Li/Na-Ti 3 C 2 T x -rGO) are constructed by infusing molten lithium (Li) or sodium (Na) metal into 3D porous MXene Ti 3 C 2 T xreduced graphene oxide (Ti 3 C 2 T x -rGO) membranes. Firstprinciples calculations indicate that large fractions of functional groups on the Ti 3 C 2 T x surface lead to the good affinity between the Ti 3 C 2 T x -rGO membrane and molten alkali metal (Li/Na), and the formation of Ti-Li/ Na, O-Li/Na, and F-Li/Na mixed covalent/ionic bonds is extremely critical for uniform electrochemical deposition. Furthermore, the porous structure in Li/Na-Ti 3 C 2 T x -rGO composites results in an effective encapsulation, preventing dendritic growth and exhibiting stable stripping/plating behaviors up to 12 mA•cm −2 and a deeper capacity of 10 mA•h• cm −2 . Stable cycling performances over 300 h (750 cycles) at 5.0 mA•cm −2 for Li-Ti 3 C 2 T x -rGO and 500 h (750 cycles) at 3.0 mA•cm −2 for Na-Ti 3 C 2 T x -GO are achieved. In a full cell with LiFePO 4 cathodes, Li-Ti 3 C 2 T x -rGO electrodes show low polarization and retain 96.6% capacity after 1000 cycles. These findings are based on 2D MXene materials, and the resulting 3D host provides a practical approach for achieving stable and safe alkali metal anodes. KEYWORDS: MXene-Ti 3 C 2 T x , 3D porous film, first-principles calculations, metal anodes (Li/Na), thermal infusion, encapsulation effect