Evolution of electrochemical redox activity and capacity in vanadium-enriched solid-solution MXene-derived oxides for Li-ion batteries

Abstract

Solid-solution MXenes emerged as promising precursors for the synthesis of bilayered vanadium oxides (BVOs), offering the ability to introduce multiple transition metals and tune electrochemical properties. However, limited understanding of transition metal site incorporation in the resulting oxides has hindered reliable design. Here, we report the transformation of vanadium-enriched (NbyV2-y)CTx (y = 0.00, 0.25, 0.50) MXenes into MXene-derived BVOs via a two-step dissolution–recrystallization process. Increasing Nb content in the precursor leads to more polycrystalline oxides, reflecting cation size mismatch and its effect on long-range particle growth. Electrochemical testing of (NbyV2-y)CTx-derived oxides in non-aqueous Li-ion cells reveals new redox features at lower potentials and higher charge storage capacities, reaching up to 495 mAh g⁻¹ at 20 mA g⁻¹ (1.0–4.0 V) for the Nb0.50V1.50CTx-derived oxide, along with enhanced rate capability. Atomic-level characterization confirms uniform Nb distribution, indicating that Nb forms substitutional defects within the bilayers which, for the first time, leads to intralayer Nb-doped BVO with superior electrochemical activity relative to the parent phase. These findings demonstrate that solid-solution MXenes enable heterogeneous atom doping directly within the layered framework, offering a powerful route to novel doped oxides with enhanced functional properties beyond those achievable by conventional methods.