High-Performance Lithium–Sulfur\nBatteries via\nMolecular Complexation

Abstract

Beyond lithium-ion technologies, lithium–sulfur\nbatteries\nstand out because of their multielectron redox reactions and high\ntheoretical specific energy (2500 Wh kg^–1). However,\nthe intrinsic irreversible transformation of soluble lithium polysulfides\nto solid short-chain sulfur species (Li₂S₂ and\nLi₂S) and the associated large volume change of electrode\nmaterials significantly impair the long-term stability of the battery.\nHere we present a liquid sulfur electrode consisting of lithium thiophosphate\ncomplexes dissolved in organic solvents that enable the bonding and\nstorage of discharge reaction products without precipitation. Insights\ngarnered from coupled spectroscopic and density functional theory\nstudies guide the complex molecular design, complexation mechanism,\nand associated electrochemical reaction mechanism. With the novel\ncomplexes as cathode materials, high specific capacity (1425 mAh\ng^–1 at 0.2 C) and excellent cycling stability (80%\nretention after 400 cycles at 0.5 C) are achieved at room temperature.\nMoreover, the highly reversible all-liquid electrochemical conversion\nenables excellent low-temperature battery operability (>400 mAh\ng^–1 at −40 °C and >200 mAh g^–1 at −60 °C). This work opens new avenues\nto design and\ntailor the sulfur electrode for enhanced electrochemical performance\nacross a wide operating temperature range.