Molecular polysulfide-scavenging sulfurized–triazine polymer enable high energy density Li-S battery under lean electrolyte

Abstract

Lean electrolyte with low electrolyte/sulfur (E/S) ratio is a crucial step for the advancement of high energy density lithium-sulfur (Li-S) batteries. However, the low E/S introduces serious kinetics issues where the cell can only last for a few cycles. Here, aiming to overcome the operational constraints, we rationally design covalently grafted sulfurized–triazine polymeric (STP) cathodes housing > 60% sulfur capable of cycling under lean electrolyte. As-developed STP cathodes at lean E/S: 4, 6, and 8 µL mgs–1 show improved sulfur reactivity and cycle-life, delivering 522, 574, and 601 mAh gs–1 at the 200th cycle. Further, at sulfur loading 5 mg cm–2 with E/S: 6 µL mgs–1, the Li-S cell exhibits 588 mAh gs–1 capacity with 93% Coulombic efficiency. Experimental and modeling tools reveal that the triazine cathode support allows covalent grafting and good wettability beneficial for facile Li ion and sulfur reactivity. As a result, the generated polysulfide is concurrently regulated in a molecularly fashion via bulk-immobilization involving abundant pyridinic–N and pyrrolic–N to confine within the electrode. Extending to construct a practical lean Li-S pouch cell with sulfur, lithium, and electrolyte accounting 53.7% cell's mass delivers an energy density of 371 Wh kg–1 that is par to the predicted values under lean electrolyte. Our study provides an invaluable resource in a potential way and future directions for developing practical high energy Li-S batteries.