Superhigh Coulombic Efficiency Lithium–Sulfur Batteries Enabled by In Situ Coating Lithium Sulfide with Polymerizable Electrolyte Additive

Abstract The polysulfide shuttling and electrode structure destruction caused by heterogeneous conversion reactions are the fundamental causes of the poor reversibility of high‐energy‐density lithium–sulfur (Li–S) batteries. The most direct manifestation is the unsatisfactory low Coulombic efficiency (CE). Herein the importance of CE in evaluating Li–S batteries is highlighted and a remedy is presented for such low efficiencies by in situ coating lithium sulfide (Li 2 S), as the cathode, with polymerizable electrolyte additives, where trithiocyanuric acid trilithium salt (TTCA‐Li) is employed for a typical demonstration. The involved reaction catalytically decreases the initial overpotential of Li 2 S, and the produced coating confines the shuttling of lithium polysulfides, thus inhibiting the redistribution of sulfur species and active sulfur loss upon cycling. The prototype full cell where the coated Li 2 S cathode couples with the Li anode has an extremely high CE of over 99.5%, while, in a Li‐free cell, the Li 2 S cathode well matches the lithiated silicon anode in a low N/P ratio of 1.2. This approach shows its practicality and generality through a pouch cell demonstration with a practically high Li 2 S loading and the extension to elemental sulfur‐based batteries by injecting the TTCA‐Li additives into cycling cells.