Revisiting the Role of Conductivity and Polarity of Host Materials for Long‐Life Lithium–Sulfur Battery

Abstract

Despite their high theoretical energy density and low cost, lithium–sulfur batteries (LSBs) suffer from poor cycle life and low energy efficiency owing to the polysulfides shuttle and the electronic insulating nature of sulfur. Conductivity and polarity are two critical parameters for the search of optimal sulfur host materials. However, their role in immobilizing polysulfides and enhancing redox kinetics for long‐life LSBs are not fully understood. This work has conducted an evaluation on the role of polarity over conductivity by using a polar but nonconductive platelet ordered mesoporous silica (pOMS) and its replica platelet ordered mesoporous carbon (pOMC), which is conductive but nonpolar. It is found that the polar pOMS/S cathode with a sulfur mass fraction of 80 wt% demonstrates outstanding long‐term cycle stability for 2000 cycles even at a high current density of 2C. Furthermore, the pOMS/S cathode with a high sulfur loading of 6.5 mg cm−2 illustrates high areal and volumetric capacities with high capacity retention. Complementary physical and electrochemical probes clearly show that surface polarity and structure are more dominant factors for sulfur utilization efficiency and long‐life, while the conductivity can be compensated by the conductive agent involved as a required electrode material during electrode preparation. The present findings shed new light on the design principles of sulfur hosts towards long‐life and highly efficient LSBs.

Room‐Temperature Sodium–Sulfur Batteries and Beyond: Realizing Practical High Energy Systems through Anode, Cathode, and Electrolyte Engineering

“…Representing a paradigm shift, Amine, Yu, and colleagues demonstrated the importance of surface polarity over conductivity as the dominant factor for an ideal sulfur‐host. [ 220 ] In their latest study, two mesoporous hosts with similar pore structures were contrasted: nonconductive but highly polar mesoporous silica versus highly conductive but nonpolar mesoporous carbon. Despite higher initial capacity (i.e., sulfur utilization) of the carbon host as one would expect from its better conductivity, polar mesoporous silica exhibited better polysulfide confinement with 54% capacity retention after 2000 cycles, compared to only 15% in nonpolar mesoporous carbon, with Coulombic efficiencies of 96% and 83%, respectively.…”

Manipulating metal–sulfur interactions for achieving high‐performance S cathodes for room temperature Li/Na–sulfur batteries

“…The advantages of advanced RT-Li/Na sulfur systems offer the high theoretical energy density of Li/Na metals, their similar chemical properties, the natural abundance of elements, capability for low-temperature operation, and environmental friendliness. [7][8][9][10][11][12][13][14][15][16][17] These advantages of RT-Li/S and RT-Na/S cells make them two of the most promising candidates for energy storage devices in the near future. [18][19][20] Challenges, however, still remained for achieving efficient conversion reactions of sulfur species, which limit the application of RT-Li/Na sulfur batteries with regard to low reversible capacity as well as rapid capacity decay.…”

“…Rechargeable lithium/sodium–sulfur cells, working at room temperature (RT‐Li/S and RT‐Na/S cells), as the most important parts of metal batteries, have been extensively investigated and partially commercialized. The advantages of advanced RT‐Li/Na sulfur systems offer the high theoretical energy density of Li/Na metals, their similar chemical properties, the natural abundance of elements, capability for low‐temperature operation, and environmental friendliness 7–17 . These advantages of RT‐Li/S and RT‐Na/S cells make them two of the most promising candidates for energy storage devices in the near future 18–20 .…”

Recent Advances of Freestanding Cathodes for Li‐S Batteries

“…Particularly, the formed intermediate long‐chain LPSs can easily dissolve into organic electrolytes and diffuse between the cathode and the anode driven by the concentration gradient, which is the commonly called “shuttle effect”, leading to a severe loss of active materials, severe self‐discharge and rapid capacity decay of the battery [9,10] . Besides, due to the insulting nature of elemental sulfur and discharged product Li 2 S, Li−S cells usually have a high internal resistance, resulting in poor rate performance and low utilization of active S material [11] . Furthermore, since the density difference between the sulfur and discharged product Li 2 S, the cathode suffers from a huge volume change (∼80%) during discharge/charge processes, further causing the inferior cycling stability of electrodes [12] …”