A 2.6 m Aqueous Electrolyte for High-Energy-Density Lithium-Ion Pouch Cells Using NbO ₂ Anode

Niobium-based oxides are promising high-energy-density anodes (>300 mAh g–1 at 1.0–2.0 V vs Li+/Li) but face challenges with conventional aqueous electrolytes. Herein, we develop a cost-effective, dilute aqueous electrolyte modulated by methylurea (MU), a nonflammable, low-toxicity cosolvent. Leveraging its donor–acceptor amphiphilicity and structural asymmetry, MU enhances miscibility with salt and water, enabling a 2.6 m solution with a distinctive solvation structure: an inner sheath dominated by MU and anions, and an outer layer where water is anchored by MU. This configuration reduces water activity and promotes a robust organic–inorganic interphase, effectively suppressing hydrogen evolution and extending the cathodic stability limit to 1.2 V vs Li+/Li. Pouch cells of NbO2|LiCoO2 and NbO2|LiMn2O4 show 96% capacity retention after 24 h at 100% state of charge, along with stable cycling over 150 cycles at 0.25 C. This strategy enhances aqueous battery performance while maintaining safety and cost-efficiency, advancing practical implementation.