Smaller Sulfur Molecules Promise Better Lithium–Sulfur Batteries

Abstract

The lithium-sulfur battery holds a high theoretical energy density, 4-5 times that of today's lithium-ion batteries, yet its applications have been hindered by poor electronic conductivity of the sulfur cathode and, most importantly, the rapid fading of its capacity due to the formation of soluble polysulfide intermediates (Li(2)S(n), n = 4-8). Despite numerous efforts concerning this issue, combatting sulfur loss remains one of the greatest challenges. Here we show that this problem can be effectively diminished by controlling the sulfur as smaller allotropes. Metastable small sulfur molecules of S(2-4) were synthesized in the confined space of a conductive microporous carbon matrix. The confined S(2-4) as a new cathode material can totally avoid the unfavorable transition between the commonly used large S(8) and S(4)(2-). Li-S batteries based on this concept exhibit unprecedented electrochemical behavior with high specific capacity, good cycling stability, and superior rate capability, which promise a practicable battery with high energy density for applications in portable electronics, electric vehicles, and large-scale energy storage systems.

Advanced High Energy Density Secondary Batteries with Multi‐Electron Reaction Materials

“…The sulfur cathode suffers from low electrochemical utilization and poor cycle life owing to the insulating nature of S and the Li 2 S discharge product, and the shuttling of lithium polysulfide species 2, 244. Enormous progress has been achieved in terms of capacity and static life during the past few years to overcome these issues, by employing sulfur‐carbon or sulfur‐conductive polymer nano‐composites or carbon‐coated separators 2, 245. These strategies not only restrain the “shuttle effect”, but also improve the electrical conductivity of the cathode.…”

Leaf‐Like Graphene‐Oxide‐Wrapped Sulfur for High‐Performance Lithium–Sulfur Battery

“…However, the insulating nature of sulfur (S) and its reaction products (i.e., Li 2 S), the large volume expansion from S to Li 2 S, along with the dissolution of lithium polysulfide intermediates (i.e., Li 2 S x , 4 ≤ x ≤ 8) into liquid electrolyte and the consequent shuttling effect between the anode and cathode, makes it generally display poor rate ability, limited cycle life and severe self‐discharge 1, 2, 3, 4, 5, 6, 7. Therefore, a variety of strategies have been pursued to circumvent the sulfur cathode problems, including optimization of organic electrolytes8, 9 and fabrication of sulfur‐conductive polymer composites10, 11 and sulfur–carbon‐based composites 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45. Among these approaches, porous‐carbon/sulfur composites12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23 are more attractive because porous carbon can i...…”

“…Therefore, a variety of strategies have been pursued to circumvent the sulfur cathode problems, including optimization of organic electrolytes8, 9 and fabrication of sulfur‐conductive polymer composites10, 11 and sulfur–carbon‐based composites 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45. Among these approaches, porous‐carbon/sulfur composites12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23 are more attractive because porous carbon can improve the electronic conductivity, accommodate the volume change, and suppress the dissolution of polysulfides. As a result, significant improvements in the utilization of sulfur and cyclability have been achieved by smartly designing porous‐carbon/sulfur composites 12, 13, 14, 15, 16, 17, 18, 19, 20, …”

“…Among these approaches, porous‐carbon/sulfur composites12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23 are more attractive because porous carbon can improve the electronic conductivity, accommodate the volume change, and suppress the dissolution of polysulfides. As a result, significant improvements in the utilization of sulfur and cyclability have been achieved by smartly designing porous‐carbon/sulfur composites 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23. However, limited sulfur content (usually below 70%)12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23 in the carbon/sulfur (C/S) composites still limits the practical application of Li–S battery.…”

“…As a result, significant improvements in the utilization of sulfur and cyclability have been achieved by smartly designing porous‐carbon/sulfur composites 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23. However, limited sulfur content (usually below 70%)12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23 in the carbon/sulfur (C/S) composites still limits the practical application of Li–S battery. Especially, a lot of promising performances were achieved by low mass loading of sulfur on the electrode 13, 16, 20, 21, 23.…”