Cathode\nKinetics Evaluation in Lean-Electrolyte Lithium–Sulfur\nBatteries

Abstract

Lithium–sulfur (Li–S)\nbatteries afford great promise\non achieving practical high energy density beyond lithium-ion batteries.\nLean-electrolyte conditions constitute the prerequisite for achieving\nhigh-energy-density Li–S batteries but inevitably deteriorates\nbattery performances, especially the sulfur cathode kinetics. Herein,\nthe polarizations of the sulfur cathode are systematically decoupled\nto identify the key kinetic limiting factor in lean-electrolyte Li–S\nbatteries. Concretely, an electrochemical impedance spectroscopy combined\ngalvanostatic intermittent titration technique method is developed\nto decouple the cathodic polarizations into activation, concentration,\nand ohmic parts. Therein, activation polarization during lithium sulfide\nnucleation emerges as the dominant polarization as the electrolyte-to-sulfur\nratio (E/S ratio) decreases, and the sluggish interfacial charge transfer\nkinetics is identified as the main reason for degraded cell performances\nunder lean-electrolyte conditions. Accordingly, a lithium bis(fluorosulfonyl)imide\nelectrolyte is proposed to decrease activation polarization, and Li–S\nbatteries adopting this electrolyte provide a discharge capacity of\n985 mAh g^–1 under a low E/S ratio of 4 μL\nmg^–1 at 0.2 C. This work identifies the key kinetic\nlimiting factor of lean-electrolyte Li–S batteries and provides\nguidance on designing rational promotion strategies to achieve advanced\nLi–S batteries.