Metallic 1T phase MoS₂ nanosheets as supercapacitor electrode materials

Efficient intercalation of ions in layered materials forms the basis of electrochemical energy storage devices such as batteries and capacitors. Recent research has focused on the exfoliation of layered materials and then restacking the two-dimensional exfoliated nanosheets to form electrodes with enhanced electrochemical response. Here, we show that chemically exfoliated nanosheets of MoS₂ containing a high concentration of the metallic 1T phase can electrochemically intercalate ions such as H⁺, Li⁺, Na⁺ and K⁺ with extraordinary efficiency and achieve capacitance values ranging from ∼400 to ∼700 F cm^-3 in a variety of aqueous electrolytes. We also demonstrate that this material is suitable for high-voltage (3.5 V) operation in non-aqueous organic electrolytes, showing prime volumetric energy and power density values, coulombic efficiencies in excess of 95%, and stability over 5,000 cycles. As we show by X-ray diffraction analysis, these favourable electrochemical properties of 1T MoS₂ layers are mainly a result of their hydrophilicity and high electrical conductivity, as well as the ability of the exfoliated layers to dynamically expand and intercalate the various ions.