Inspired by the Cu-driven conversion reaction: how anionic properties dictate the electrochemical performance of vanadium sulfide

Abstract

The so-called “activation process” of the VS₂/SNC anode in sodium-ion batteries actually results from the Cu current collector-involved electrochemical reactions. Metallic Cu with a strong sulfiphilic property endows the VS₂/SNC anode with a high reversible capacity of 586.9 mA h g⁻¹ even after 500 cycles, but only when using the electrolyte of 1.0 M NaPF₆ diglyme can such a favorable cycle stability be presented. Once the electrolyte of 1.0 M NaCF₃SO₃ diglyme is adopted, the device exhibits large overpotentials and its capacity decays dramatically. Examining the solvation structures and electrode/electrolyte interface properties, it is confirmed that the anionic property of the electrolyte plays a significant role in determining the electrochemical performance of metal sulfides. Triflate anions with a strong donicity not only aggravate the shuttle effect but also hinder the Na⁺ transport at the electrode/electrolyte interface, resulting in poor reversibility and sluggish kinetics of the anode, and such an interaction is intensified in Cu₂S due to the soft acceptor characteristics of Cu (I).