New Insight into the Working Mechanism of Lithium-Sulfur Batteries under a Wide Temperature Range

Sweet potato-derived carbon with a unique solid core/porous layer core/shell structure is used as a conductive substrate for gradually immobilizing sulfur to construct a cathode for Li-S batteries. The first discharge specific capacity of the Li-S batteries with the C-10K@2S composite cathode at 0.1C is around 1645 mAh g(-1), which is very close to the theoretical specific capacity of active sulfur. Especially, after 175 cycles at 0.5C, the maintained specific discharge capacities of the C-10K@2S cathode at -20, 0, 25, and 40 degrees C are about 184.9, 687.2, 795.5, and 758.3 mAh g(-1), respectively, and the cathode is superior to most of the classical carbon form matrices. Working mechanisms of the cathodes under different temperatures are confirmed based on X-ray photoelectron spectroscopy (XPS) and in situ Xray diffraction (XRD) characterizations. Distinctively, during the discharge stage, the widely proposed two-step cathodic reactions occur simultaneously rather than sequentially. In addition, the largely accelerated phase conversion efficiency of the cathode at a higher temperature (from room temperature to 40 degrees C) contributes to its enhanced charge/discharge specific capacity, while the byproduct Li2S2O7 or Li3N irreversibly formed during the cycles limits its application performance at 0 degrees C. These conclusions would be very significant and useful for designing cathodes for Li-S batteries with excellent wide working temperature performance.

Automated summary

The research explores the use of sweet potato-derived carbon as a conductive substrate for immobilizing sulfur to construct a cathode for Li-S batteries, demonstrating excellent stability at different temperatures. XPS and XRD characterizations confirm the working mechanisms of the cathode at different temperatures, revealing that phase conversion efficiency is faster at higher temperatures but limited at 0 degrees Celsius.