Electrochemical Investigations of Sulfur‐Decorated Organic Materials as Cathodes for Alkali Batteries

Abstract

Alkali metal–sulfur batteries (particularly, lithium/sodium‐ sulfur (Li/Na–S)) have attracted much attention because of their high energy density, the natural abundance of sulfur, and environmental friendliness. However, Li/Na–S batteries still face big challenges, such as limited cycle life, poor conductivity, large volume changes, and the “shuttle effect” caused by the high solubility of Li/Na–polysulfides. Herein, novel organosulfur‐containing materials, i.e., bis(4‐hydroxy‐2,2,6,6‐tetramethylpiperidin‐1‐yl)disulfide (BiTEMPS‐OH) and 2,4‐thiophene/arene copolymer (TAC) are proposed as cathode materials for Li and Na batteries. BiTEMPS‐OH shows an initial discharge/charge capacity of 353/192 mAh g−1 and a capacity of 62 mAh g−1 after 200 cycles at 100 mA g−1 in ether‐based Li‐ion electrolyte. Meanwhile, TAC has an initial discharge/charge capacity of 270/248 mAh g−1 and better cycling performance (106 mAh g−1 after 200 cycles) than BiTEMPS‐OH in the same electrolyte. However, the rate capability of TAC is limited by the slow diffusion of Li‐ions. Both materials show inferior electrochemical performances in Na battery cells compared to the Li analogs. X‐ray powder diffraction reveals that BiTEMPS‐OH loses its crystalline structure permanently upon cycling in Li battery cells. X‐ray photoelectron spectroscopy demonstrates the cleavage and partially reversible formation of S−S bonds in BiTEMPS‐OH and the formation/decomposition of thick solid electrolyte interphase on the electrode surface of TAC.