Vanadium carbide MXenes for electrochemical energy storage: Synthesis, composite design, performance limits, and sustainability considerations

Vanadium carbide MXenes (VM) are promising electrode materials for electrochemical energy storage because of their metallic conductivity, multivalent vanadium redox chemistry, tunable surface terminations, and ion-accessible layered structures. However, their practical use is limited by synthetic difficulties, oxidation instability, nanosheet restacking, uncontrolled surface chemistry, and performance degradation during long-term cycling. This review critically examines the synthesis, structural features, environmental implications, composite design strategies, and electrochemical performance of VM-based electrodes for supercapacitors and metal-ion batteries. Special attention is given to HF-based and HF-free synthesis routes, including molten-salt, electrochemical, gas-phase, and bio-assisted methods. A screening-level cradle-to-gate assessment is discussed to identify major environmental hotspots in VM production, particularly prolonged heating, drying, water consumption, fluoride-containing waste, and MAX-phase synthesis. The review further analyzes how interface engineering, intercalation, pillaring, surface functionalization, and hybrid 0D/1D/2D architectures address the intrinsic limitations of VM by improving ion transport, electronic coupling, structural stability, and electrochemical accessibility. The analysis also highlights that many high-performing VM composites derive substantial capacity from secondary active phases, requiring careful deconvolution of the true role of VM. Finally, future directions are proposed for safer synthesis, controlled surface chemistry, realistic electrochemical evaluation, and sustainability-guided scale-up of VM-based energy-storage electrodes.