Trace Metal Impurities Induce Differences in Lithium–Sulfur Batteries

Carbon nanotubes (CNTs) with exceptional conductivity have been widely adopted in lithium-sulfur (Li-S) batteries. While trace metal impurities in CNTs have demonstrated electrocatalytic activity in various catalytic processes, their influence on sulfur electrocatalysis in Li-S batteries has been largely overlooked. Herein, we reveal that the trace metal impurities content in CNTs significantly improves the specific capacity and cycling performance of Li-S batteries by analyzing both our own results and previous literature with CNTs as the sulfur hosts. Even under lean electrolyte conditions (E/S ratio of 5 μL mg_s^-1), we demonstrate that a small content of metal impurities in CNTs (∼2 wt %) could account for a 14.3% increase in specific capacity and a 14.1% increase in capacity retention under a high sulfur loading of 3.5 mg cm^-2. The electron transfer from confined metal catalysts within CNTs leads to electron accumulation at the carbon interface, facilitating electron donation to adsorbed sulfur species and lowering the energy barrier for Li₂S formation.