Accelerating the sulfur redox kinetics in weakly-solvating lithium‒sulfur batteries under lean-electrolyte conditions

Lithium–sulfur (Li–S) batteries are promising in realizing high energy density but hindered by limited cycling lifespan due to the corrosion of lithium metal anode by soluble lithium polysulfides. Employing weakly-solvating electrolyte effectively prolongs the cycling lifespan via suppressing the anode corrosion but inevitably results in severe cathode capacity degradation under lean-electrolyte conditions. Herein, the lean-electrolyte sulfur redox kinetics is systematically evaluated in weakly-solvating Li‒S batteries to guide target kinetic promotion strategy design. High activation polarization caused by sluggish interfacial charge transfer kinetics is identified as the key limiting factor by polarization decoupling. Smaller Li₂S nuclei and thinner Li₂S deposition are formed to render reduced deposition capacity. To overcome the above challenge, a bis(fluorosulfonyl)imide lithium electrolyte is designed to realize a discharge capacity of 984 mAh g ⁻¹ at 0.2 C under a lean electrolyte volume of 5 μL mg⁻¹ in weakly-solvating Li–S batteries. This work affords rational guidance for accelerating the sulfur redox kinetics toward lean-electrolyte and weakly-solvating Li‒S batteries.