From sparingly solvating to weakly solvating: Fine electrolyte regulation for lean-electrolyte Li-SeS2 batteries

The “solid-liquid-solid” reaction mechanisms of lithium-sulfur/selenium (Li-S/Se) batteries in ether-based electrolytes, which rely on the soluble polysulfides (Li2S4–8, LPSs)/polyselenides (Li2Se4–8, LPSes) intermediates, prevent further reduction of the electrolyte dosage and thus offset the advantages of Li-S/Se batteries in energy density. Using sparingly-solvating electrolytes, in which the dissolution of LPSs/LPSes is suppressed, could reduce the electrolyte dosage. Nevertheless, such electrolytes bring sluggish reaction kinetic and poor compatibility with lithium (Li) anodes. Herein, by regulating the electrolyte structure, we found the weakly-solvating electrolytes, which have slightly higher dissolubility of LPSs/LPSes than the sparingly-solvating ones, could facilitate electrochemical reaction and stabilize Li anodes. The newly formulated electrolyte makes high active materials utilization under conditions of high current densities, high areal mass loadings, and low electrolyte-to-active-material (E/A) ratio possible. The cell with a SeS2 cathode realizes a high discharge capacity of 1047 mAh g−1, 93.2% of its theoretical value (1123 mAh g−1), at 0.1 C. Even with a high areal-mass-loading SeS2 cathode (9.5 mg cm−2), the as-designed electrolyte endows the cell with a high reversible capacity of 713 mAh g−1 under a low E/A ratio of 1 μL mg−1. The as-proposed strategy provides an effective electrolyte-regulation solution to practical high-energy Li-S/Se batteries.