V-substitution function on polyoxometalate catalyst for rapid conversion of polyselenides in Li-Se batteries

The major challenge for selenium cathode is the sluggish reaction kinetics and shutting effect of polyselenides upon repeated cycles, which needs an elaborate design of cathode materials to achieve the excellent cycle performance. In this work, we design a composite with hollow shell structure, which contains V-substituted Keggin H4PW11VO40 (PW11V), CoFe2O4 and C components, as a selenium host matrix to endow the rapid conversion and high efficiency fixation of polyselenides. The appropriate V atom substitution in PW11V ensures the solidity of hollow shell, and PW11V can be used as an electrocatalyst to accelerate reversible transformation of polyselenides. DFT calculations indicate V atom implantation can induce the increase of Li-O bonding strength, and thus expressively enhance the chemical adsorption of polyselenides on PW11V as well as effectively restrain active material loss and polyselenides dissolution. The efficient capture of polyselenides also further improves the catalytic activity of PW11V. Consequently, Li-Se batteries demonstrate superior reversible capacity of 534 mAh g-1 under 0.2C after 300 cycles and low average capacity recession rate of 0.037% during 1000 cycles of charge-discharge even under a higher rate of 1C. This work reveals the availability of V-substituted POM molecular cluster catalysts in Li-Se batteries and provides a promising strategy for the design of advanced catalysts with hollow shell structure in other energy storage fields.