Nanosized Chevrel phases for dendrite-free zinc–ion based energy storage: unraveling the phase transformations†

The nanoscale form of the Chevrel phase, Mo₆S₈, is demonstrated to be a highly efficient zinc-free anode in aqueous zinc ion hybrid supercapacitors (ZIHSCs). The unique morphological characteristics of the material when its dimensions approach the nanoscale result in fast zinc intercalation kinetics that surpass the ion transport rate reported for some of the most promising materials, such as TiS₂ and TiSe₂. In situ Raman spectroscopy, post-mortem X-ray diffraction, Hard X-ray photoelectron spectroscopy, and density functional theory (DFT) calculations were combined to understand the overall mechanism of the zinc ion (de)intercalation process. The previously unknown formation of the sulfur-deficient Zn_2.9Mo₁₅S₁₉ (Zn_1.6Mo₆S_7.6) phase is identified, leading to a re-evaluation of the mechanism of the (de)intercalation process. A full cell comprised of an activated carbon (YEC-8A) positive electrode delivers a cell capacity of 38 mA h g⁻¹ and an energy density of 43.8 W h kg⁻¹ at a specific current density of 0.2 A g⁻¹. The excellent cycling stability of the device is demonstrated for up to 8000 cycles at 3 A g⁻¹ with a coulombic efficiency close to 100%. Post-mortem microscopic studies reveal the absence of dendrite formation at the nanosized Mo₆S₈ anode, in stark contrast to the state-of-the-art zinc electrode.