Cathode Kinetics Evaluation in Lean-Electrolyte Lithium-Sulfur Batteries

Lithium-sulfur (Li-S)batteries afford great promiseon achieving practical high energy density beyond lithium-ion batteries.Lean-electrolyte conditions constitute the prerequisite for achievinghigh-energy-density Li-S batteries but inevitably deterioratesbattery performances, especially the sulfur cathode kinetics. Herein,the polarizations of the sulfur cathode are systematically decoupledto identify the key kinetic limiting factor in lean-electrolyte Li-Sbatteries. Concretely, an electrochemical impedance spectroscopy combinedgalvanostatic intermittent titration technique method is developedto decouple the cathodic polarizations into activation, concentration,and ohmic parts. Therein, activation polarization during lithium sulfidenucleation emerges as the dominant polarization as the electrolyte-to-sulfurratio (E/S ratio) decreases, and the sluggish interfacial charge transferkinetics is identified as the main reason for degraded cell performancesunder lean-electrolyte conditions. Accordingly, a lithium bis(fluorosulfonyl)imideelectrolyte is proposed to decrease activation polarization, and Li-Sbatteries adopting this electrolyte provide a discharge capacity of985 mAh g(-1) under a low E/S ratio of 4 & mu;Lmg(-1) at 0.2 C. This work identifies the key kineticlimiting factor of lean-electrolyte Li-S batteries and providesguidance on designing rational promotion strategies to achieve advancedLi-S batteries.