Hybrid aqueous electrolyte design for interfacial stabilization in high-energy-density and long-life LiNi0.8Mn0.1Co0.1O2−Li4Ti5O12 lithium-ion batteries

The development of aqueous electrolytes with high ionic conductivities and wide voltage windows is essential for achieving safe and high-energy-density lithium-ion batteries (LIBs). Tetraethylene glycol (TEG)-based hybrid aqueous electrolytes are potential candidates for suppressing H 2 O decomposition by forming hydrogen bonds with H 2 O. However, the intermolecular hydrogen bonds between TEG molecules, combined with high Li salt concentration (10 m), significantly reduce ionic conductivity of TEG-based aqueous electrolytes. In this study, 2-cyanoethyl ether (CEE) was utilized as a co-solvent to formulate a hybrid aqueous electrolyte, which exhibited an enhanced electrochemical stability window of up to 4.6 V and a high ionic conductivity of 1.36 mS cm −1 at 25 °C. In addition, the CEE facilitated the formation of a uniform and robust interface layer on both the LiNi 0.8 Mn 0.1 Co 0.1 O 2 (NMC811) and Li 4 Ti 5 O 12 (LTO) electrodes, consisting of an inorganic-rich inner layer and an organic-rich outer layer. Consequently, the NMC811||LTO full cells incorporating the CEE-based hybrid aqueous electrolyte achieved a high energy density of 128 Wh kg −1 at 1C. Notably, the fabricated cells retained 72% of their initial capacities even after 300 cycles, with an average coulombic efficiency of 99.6%. This paper presents a practical approach for advancing the fabrication of high-energy-density aqueous LIBs. • A hybrid aqueous electrolyte was prepared using 2-cyanoethyl ether (CEE) and H 2 O. • The hybrid aqueous electrolyte exhibited the enhanced electrochemical properties. • The CEE facilitated the formation of a stable SEI and CEI on both NMC811 and LTO. • The NMC811||LTO battery reached 300 cycles with 72% capacity retention at 1C. • The aqueous batteries exhibited a high energy density of 128 Wh kg −1 at 1C.