Multi-functions of amino thiophenol additives for shielding lithium metal anode in advanced Li-S battery

Abstract

Lithium-sulfur (Li-S) batteries have been considered as a promising candidate for the next generation of battery systems due to their high specific capacity and energy density. However, some barriers impede the application of Li-S batteries, such as the “shuttle effects” of lithium polysulfides (LPS), the poor electrical conductivity of sulfur, and lithium dendrite formation on lithium metal electrodes. Herein, we investigated a series of amino thiophenol as electrolyte additives: 2-amino thiophenol (2-ATP), 3-amino thiophenol (3-ATP), and 4-amino thiophenol (4-ATP); as well as p-phenylenediamine (PPD). These additives react with Li to form a stable and uniform solid electrolyte interphase (SEI) to protect the Li anode and minimize the interaction of Li with soluble LPS. Initial specific capacity at 0.1C and reversible specific capacity after 100 cycles are 1420 and 1043 mAh/g, 1429 and 982 mAh/g, 1148 and 871 mAh/g, 1317 and 791 mAh/g for 4-ATP, 3-ATP, 2-ATP, and PPD, respectively. Long-term cycling testing of Li-S cells was conducted at 0.2C and the cell with 4-ATP additives deliver an initial specific capacity of 1159 mAh/g and capacity retention of 77% after 300 cycles. The morphology and composition of the after-cycled SEI layers were examined by SEM and XPS. The findings suggest amino thiophenols (ATPs) form stable and smooth closed-packed SEI layers, that ameliorate lithium dendrite problems and LPS reactions with Li metal. 4-ATP is found to exhibit the best electrochemical performance followed by 3-ATP, 2-ATP, and PPD, which are in good agreement with the surface morphology. In addition, the amine group can assist the reaction between the thiol group and S8 on the cathode and modify the redox pathway of polysulfide.