Nanocubes of Mo₆S₈ Chevrel phase as active electrode material for aqueous lithium-ion batteries

The development of intrinsically safe and environmentally sustainable energy storage devices is a significant challenge. Recent advances in aqueous rechargeable lithium-ion batteries (ARLIBs) have made considerable steps in this direction. In parallel to the ongoing progress in the design of aqueous electrolytes that expand the electrochemically stable potential window, the design of negative electrode materials exhibiting large capacity and low intercalation potential attracts great research interest. Herein, we report the synthesis of high purity nanoscale Chevrel Phase (CP) Mo₆S₈via a simple, efficient and controllable molecular precursor approach with significantly decreased energy consumption compared to the conventional approaches. Physical characterization of the obtained product confirms the successful formation of CP-Mo₆S₈ and reveals that it is crystalline nanostructured in nature. Due to their unique structural characteristics, the Mo₆S₈ nanocubes exhibit fast kinetics in a 21 m lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) electrolyte as a result of the shorter Li⁺ ion diffusion distance. Full battery cells comprised of Mo₆S₈ and LiMn₂O₄ as negative and positive electrode materials, respectively, operate at 2.23 V delivering a high energy density of 85 W h kg^-1 (calculated on the total mass of active materials) under 0.2 C-rate. At 4 C, the coulombic efficiency (CE) is determined to be 99% increasing to near 100% at certain cycles. Post-mortem physical characterization demonstrates that the Mo₆S₈ anode maintained its crystallinity, thereby exhibiting outstanding cycling stability. The cell outperforms the commonly used vanadium-based (VO₂ (B), V₂O₅) or (NASICON)-type LiTi₂(PO₄)₃ anodes, highlighting the promising character of the nanoscale CP-Mo₆S₈ as a highly efficient anode material. In summary, the proposed synthetic strategy is expected to stimulate novel research towards the widespread application of CP-based materials in various aqueous and non-aqueous energy storage systems.