Synergistically Accelerating Adsorption-Electrocataysis of Sulfur Species via Interfacial Built-In Electric Field of SnS -MXene Mott-Schottky Heterojunction in Li-S Batteries.

Developing efficient heterojunction electrocatalysts and uncovering their atomic-level interfacial mechanism in promoting sulfur-species adsorption-electrocatalysis are interesting yet challenging in lithium-sulfur batteries (LSBs). Here, multifunctional SnS -MXene Mott-Schottky heterojunctions with interfacial built-in electric field (BIEF) are developed, as a model to decipher their BIEF effect for accelerating synergistic adsorption-electrocatalysis of bidirectional sulfur conversion. Theoretical and experimental analysis confirm that because Ti atoms in MXene easily lost electrons, whereas S atoms in SnS easily gain electrons, and under Mott-Schottky influence, SnS -MXene heterojunction forms the spontaneous BIEF, leading to the electronic flow from MXene to SnS , so SnS surface easily bonds with more lithium polysulfides. Moreover, the hetero-interface quickly propels abundant Li /electron transfer, so greatly lowering Li S nucleation/decomposition barrier, promoting bidirectional sulfur conversion. Therefore, S/SnS -MXene cathode displays a high reversible capacity (1,188.5 mAh g at 0.2 C) and a stable long-life span with 500 cycles (≈82.7% retention at 1.0 C). Importantly, the thick sulfur cathode (sulfur loading: 8.0 mg cm ) presents a large areal capacity of 7.35 mAh cm at lean electrolyte of 5.0 µL mg . This work verifies the substantive mechanism that how BIEF optimizes the catalytic performance of heterojunctions and provides an effective strategy for deigning efficient bidirectional Li-S catalysts in LSBs.