Tuning electrolyte solvation structure with Co-solvent engineering to enable highly reversible and stable Zn-graphite dual-ion batteries

Abstract

Graphite-based dual-ion batteries (GDIBs) have attracted ever-growing attentions due to its non-transition metal configuration and high working potential. However, the safety concerns associated with the use of organic electrolyte make it unpractical for large-scale energy storage system. Moreover, the anodic limit of aqueous electrolytes, even the improved anodic limit derived from highly concentrated aqueous electrolytes, is not sufficient to support high graphite intercalation voltage. Herein, a co-solvent-induced hybrid aqueous/non-aqueous electrolyte has been proposed to break this bottleneck through regulating the solvation structures around anions. A series of hybrid electrolytes are prepared by controlling dimethyl carbonate (DMC) ratio and the relation between the solvation structures and anion intercalation chemistry is explored, indicating that the mutual interaction between solvent molecules and anions determines the anion intercalation behaviour. The optimized DMC-dominated solvation structures with a mass ratio of DMC to water of 1.2:1 significantly expand the anodic limit of electrolyte up to 2.54 V (vs. Zn/Zn2+). The as-designed Zn-Graphite batteries exhibit an excellent cyclic stability and reversibility (99 % capacity retention after 200 cycles at 200 mA g−1, nearly 98 % Coulombic efficiency). This work provides guidance to achieve the balance between security capability and electrochemical performances through controllable solvation structures.