Quantitative Analysis of Cation Selectivity of the Electrodes in Multi-ion Electrolytes Based on 2H-Phase MoS2

Multi-ion batteries and supercapacitors are promising as energy storage devices. However, the intercalation/deintercation of various cations on the electrodes in the hybrid electrolytes is not clearly understood. Herein, the selectivity of different cations (viz., K+, Na+, Li+) in hybrid aqueous electrolytes based on hierarchical 2H-phase MoS2 is investigated by combining experimental and theoretical methods. A quantitative method based on first-principles calculations is proposed to enumerate the cation selectivity in hybrid aqueous electrolytes. It indicates that the eventual intercalation of various cations in the MoS2 interlayer space is mainly reliant on the competition reactions of the various cations in the hybrid electrolytes into the electrode. The chemical potentials related to the molar ratio and the binding energy of different cations into the electrode play a pivotal role in such selectivity of the cations. This mechanism is tested using the MoS2@ACC (flower-like MoS2 grown on the active carbon cloth substrate) electrode, which is fabricated in one-step using the simple hydrothermal technique. The theoretical cation selectivity is also reinforced by the experimental results based on the 2H-MoS2@ACC electrodes. Overall, this study provides a fundamental understanding of the electrochemical storage behavior between electrolytes and electrodes for multi-ion capacitors.