Current Status, Problems and Challenges in Lithium-sulfur Batteries

Abstract

Lithium-sulfur battery, fabricated with metal lithium as anode and sulfur as cathode, has received more attention as the most promising high energy power sources due to its high theoretical energy density (2600 Wh/kg). However, there are some serious and unavoidable problems for lithium-sulfur battery based on the dissolution-deposition processes in organic electrolyte, including serious structure change of metallic lithium anode, the lower utilization and poor cycle performance of active materials, which become a big barrier for the research and development of lithium-sulfur battery. The current status, problems and challenges of lithium-sulfur battery are summarized, including the sulfur-based cathode composites, electrolyte and lithium anode

Microporous Carbon Polyhedrons Encapsulated Polyacrylonitrile Nanofibers as Sulfur Immobilizer for Lithium–Sulfur Battery

“…While, the high distribution of sulfur as amorphous state inside micropores of MCPs or heterocyclic rings of dehydrogenated PAN nanofibers is responsible for the high utilization and reversible capacity of sulfur active material. Actually, it is regrettable that the sulfur content in the S/C composites is hard to increase after taking the sulfur utilization into consideration, which is a common feature in the carbonate-based electrolyte as reported previously. ,,,,, …”

“…Therefore, the SEI layer is formed with carbonate solvents on the surface of nanofibers in the initial discharged state, leading to the irreversible capacity and potential polarization. It should be noted here that the good cycle stability of the S/C composites in carbonate-based electrolyte is mainly attributed to the formation of the SEI layer on account of the limited solubility of polysulfides in carbonate-based electrolyte, different from the high solubility of polysulfides in ether-based electrolyte. In the meantime, the content and existing form of sulfur in the S/C composites is very sensitive to the utilization and reversible capacity of sulfur active material in the carbonate-based electrolyte.…”

“…Actually, it is regrettable that the sulfur content in the S/C composites is hard to increase after taking the sulfur utilization into consideration, which is a common feature in the carbonatebased electrolyte as reported previously. 9,10,29,30,41,52 It is demonstrated from above electrochemical performance and SEM observation that the poor utilization of sulfur and fast capacity fade of the S/MCPs-PAN-65 composite is originated from the formation of the thick and dense SEI layer on the surface on nanofibers. To identify the SEI layer, FTIR spectra are collected from the S/MCPs-PAN-65 cathode at the high potential plateau region (at 1.8 V) during the initial discharge process, as shown in Figure 8.…”

“…In particular, the amorphous sulfur in microporous carbon or PAN is indispensable and compatible in the carbonate-based electrolyte. 52 When amorphous sulfur with the low content is distributed uniformly inside MCPs-PAN nanofibers, the SEI layer formed in the discharged state can be turned back almost in the charged state. Here, the thin SEI layer as a protective layer on the surface is important and helpful to ensure the utilization of sulfur active material and good cycle stability of the composite based on the solid−solid reaction mechanism.…”

“…In the meantime, the content and existing form of sulfur in the S/C composites is very sensitive to the utilization and reversible capacity of sulfur active material in the carbonate-based electrolyte. In particular, the amorphous sulfur in microporous carbon or PAN is indispensable and compatible in the carbonate-based electrolyte . When amorphous sulfur with the low content is distributed uniformly inside MCPs-PAN nanofibers, the SEI layer formed in the discharged state can be turned back almost in the charged state.…”