Si-doped Vanadium Pentoxide/Graphene Xerogel Nanocomposite Cathodes with Excellent Cycle Life for Li-Ion Batteries

Abstract

Vanadium pentoxide (V2O5) is a promising cathode material for lithium-ion batteries due to its high theoretical specific capacity (443 mAh g⁻¹) and specific energy (1218 Wh kg⁻¹ at 2.75 V). However, its large-scale application is limited by its poor electrical conductivity and structural instability, leading to irreversible capacity loss, consequently, short cycle life, and low-rate capability. In this work, we developed a 3D nanostructured xerogel composite by uniformly doping silicon (Si) into the V2O5 framework, which anchors on the surface of graphene sheets via a sol-gel process. The optimized Si-doped V2O5 on graphene (Si-V2O5@G) composite, containing 10 wt.% Si and 2 wt.% graphene, delivers a high specific capacity of 392 mAh g⁻¹ at 0.1 C rate and excellent cycling stability, 589 cycles with 80 % capacity retention at high rate of 1.0 C, and very low capacity fading rate, 0.03% capacity loss per cycle—significantly surpassing the best performance of up to dated V2O5 work (e.g. the best performance, 160 mAh g⁻¹ and 300 cycles at 0.75C rate and 0.13% capacity loss per cycle). Scanning Transmission Electron Microscopy (STEM) reveals uniform Si distribution, which leads to much larger V2O5 nanoribbons over the graphene sheets (observed using TEM). Such nanocomposite structure is capable of tolerating more structural change during (de)lithiation process, resulting in much improved cycle life. Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) further demonstrate the improved conductivity and structural integrity. X-ray photoelectron Spectroscopy (XPS) manifests the interaction of doped Si with the V-O system. The in-operando XANES and EXAFS analyses suggest the increased multi-valence change among V⁵⁺, V⁴⁺, and V³⁺ states in the (de)lithiation process after Si-doping. Additionally, EXAFS analysis indicates that Si doping effectively stabilizes the local V–O coordination environment, facilitating better Li⁺ insertion/extraction reversibility and reducing the degradation of Si-V2O5@G systems. This work demonstrates a cost-effective, non-metal doping strategy for enhancing the electrochemical performance of high-energy-density metal oxide cathodes for next-generation LIBs.