Unveiling Competitive Coordination in Aqueous Lithium-Ion Electrolytes through Solvent Descriptor Engineering

The narrow electrochemical window and unstable hydrogen evolution reactions (HER) of aqueous electrolytes hinder the potential application of high-voltage lithium-ion batteries. These problems are actually related to the solvation structure of the electrolyte, which is determined by the competition among anions, water molecules, and cosolvent coordinated with Li⁺. Herein, this work proposes a direct solvent descriptor for conveniently designing electrolytes, which facilitates a pronounced level of Li+-TFSI− and Li+-DMAC coordination within the solvation sheath through synergistic effect of the dielectric constant and dipole moment. This strategy significantly reduces the involvement of water in the primary solvation shell and generates stable interfacial chemistry. Such an electrolyte regulated by competitive coordination leads to wide electrochemical stability window of 4.55 V and suppressed HER, thus realizing a 2.5 V LiMn2O4-Li4Ti5O12 full battery with the high discharge capacity of 138.4 mAh g⁻¹ and average Coulombic efficiency of 99% over 1000 cycles at 3 C rate. The proposed strategy of solvation structure modification by regulating cation competitive coordination offers a promising approach for achieving stable aqueous batteries with high energy density.