Solvation structure regulation for an ether/ether biphasic electrolyte to balance cathodic and anodic reactions in metal-based batteries

Abstract

Soluble redox mediators (RMs) can promote the performance of metal rechargeable batteries, such as lithium redox flow batteries (LRFBs), lithium sulfur and lithium oxygen (Li–O₂) batteries. Unfortunately, RMs in the electrolyte can easily corrode the metal anode and its surface solid-state electrolyte interphase, eventually leading to lower energy efficiency and poor cycling performance. In this work, by regulating the electrolyte solvation structure via the difference in the solvation ability of solvents ethylene glycol dibutyl ether (EGDE) and tetraglyme (G4) for Li salts, an ether/ether biphasic liquid electrolyte (BLE) is constructed. Furthermore, based on the principle of “like dissolves like,” the RMs are confined to the catholyte region, thereby suppressing the shuttle effect and enhancing the cyclic stability of the Li anode. The BLE is highly compatible with cathodic and anodic reactions, thereby improving the cycling performance of lithium redox flow batteries (LRFBs) and Li–O₂ batteries. Remarkably, the capacity retention of the LRFBs is boosted to 80.8% after 1300 h of cycling with a stable coulombic efficiency (CE) of approximately 100% in cells with BLE compared with those with a single-phase liquid electrolyte (SLE) (capacity retention: 11.3%; CE: 65.9%). The lifespan of RM-mediated Li–O₂ cells in the BLE is more than nine times longer than those in the SLE. The present study provides new insight into balancing the stability of the anodic and cathodic reactions by regulating the solvation structure of the two electrolyte solvents.