Engineering anion defects of ternary V-S-Se layered cathodes for ultrafast zinc ion storage

In this work, a novel stainless-steel (SS) supported lattice-mismatched V-S-Se layered compound (VSySe2−x-SS) with high selenium (Se) vacancy was synthesized by tailoring the molar ratio of S to Se. The difference between the radii of Se and S results in lattice mismatches for a large number of Se vacancies, and the highest vacancy with the ultrafast zinc (Zn) storage performance are achieved by tuning a molar ratio of sulfur (S) to Se. More interestingly, with the introduction of Se vacancies, additional redox peaks of S appear, and creates more mass-transport channels as well as active sites for Zn2+ toward fast reaction kinetics. Density functional theory (DFT) calculations confirm that the Se defects can also effectively reduce the adsorption energy of Zn2+ ions on VS0.5Se2−x-SS for more reversible adsorption/desorption process of Zn2+ ions. Consequently, the specific capacity of the VS0.5Se2−x-SS electrode is as high as 188.1 mAh g−1 after 70 cycles at 0.6 A g−1, while accomplishing an excellent rate capability and satisfactory cycle stability. In addition, an assembled flexible quasi-solid state VS0.5Se2−x-SS//Zn battery also display good cycle stability, excellent electrochemical performance, and good environmental adaptability under different malignant environments including bending, soaking, hammering, weighing, washing and cutting. This work demonstrates a facile approach for electrode modifications used in Zn2+ ion batteries, holding great promise for practical applications and shedding lights on fundamentals of defects effects on battery performance.