Redox process and lithiation mechanism of amorphous vanadium-silicon materials as lithium-ion battery anode

Abstract

V2O5-TeO2 (VT) is a vanadium-based amorphous lithium-ion battery (LIB) anode material that exhibits a high specific energy, but its low-capacity retention rate and low conductivity limit its widespread application. Different amounts of Si were introduced into VT anode materials to increase their initial discharge capacity and conductivity, which regulated the vanadium redox reaction. 67 V2O5-30TeO2-3Si (VTS3) exhibited the highest conductivity and V4+ content (49.8%). When the Si content was increased, the V4+ content decreased, indicating that Si successfully regulated the redox reaction. The results showed that VTS3 had a high initial discharge capacity of 1187.3 mAh g−1, while that of VT was only 906.5 mAh g−1. After 50 charge-discharge cycles, the retention rates of VT and VTS3 were 15.6% and 25.0%, respectively. After cycling, the precipitation of nanocrystals, especially LiV2O5, from the glass matrix improved the capacity retention of VTS3 by enhancing reversible lithium insertion. The synergy of this disordered-ordered transition improved the discharge capacity and reversibility. Density functional theory (DFT) calculations showed that due to the substitution of Si, the gap between Highest Occupied Molecular Orbital (HOMO) and HOMO-1 was shortened, Li-O electron aggregation was enhanced, the structure was improved, and electronic conductivity was enhanced. At the same time, sufficient Si content increased the initial specific capacity but reduced the retention rate, which was because the volume expansion during the charge-discharge cycle reduced the number of active sites. This work offers a new strategy for preparing LIB electrode materials by introducing Si to regulate redox reactions and precipitate nanocrystals.