A tailored highly solvating electrolyte toward ultra lean-electrolyte Li–S batteries
Zixiong Shi, Simil Thomas, Zhengnan Tian, Dong Guo, Zhiming Zhao, Yizhou Wang, Shuo Li, Nimer Wehbe, Abdul‐Hamid Emwas, Osman M. Bakr, Omar F. Mohammed, Husam N. Alshareef
Abstract
Low electrolyte usage is a key to attaining high-energy-density lithium–sulfur (Li–S) batteries. However, this is still a tremendous challenge for traditional ether-based electrolytes that follow a dissolution–precipitation mechanism. Highly solvating electrolytes, which can facilitate polysulfide dissolution and alter reaction pathway, are considered a promising strategy. Nonetheless, mechanistic understanding and kinetic evaluation remain insufficient while the principle of Li<sub>2</sub>S nucleation and dissociation has not been elucidated. Herein, we unveil the Li-ion solvation and polysulfide speciation in the solvents with different denticity and donicity. The origin of S<sub>3</sub><sup>•–</sup> radical-directed path and three-dimensional Li<sub>2</sub>S precipitation in high-donicity electrolytes has been uncovered. It is revealed that ammonium ions enable the facile dissolution and dissociation of Li<sub>2</sub>S via Lewis acid-base interaction and H···S<sup>2–</sup> binding. Consequently, Li–S batteries with a low electrolyte and sulfur (<em>E/S</em>) ratio of 5 μL·mg<sub>s</sub><sup>–1</sup> achieve a high capacity of 1092 mAh·g<sup>–1</sup>. Even at a harsh <em>E/S</em> ratio of 3 μL·mg<sub>s</sub><sup>–1</sup> and a high sulfur loading of 4 mg·cm<sup>–2</sup>, they still sustain a stable operation over 30 cycles. Our work sheds light on the underlying reaction mechanism and rationalizes the design of highly solvating electrolytes, which in turn opens a new avenue for achieving pragmatic lean-electrolyte Li–S batteries.