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Solid-State Li-S Electrochemical Reactions in Nanoscale Confinement

  • Author(s): Fu, Chengyin
  • Advisor(s): Guo, Juchen
  • et al.
Abstract

Rechargeable lithium–sulfur (Li–S) batteries continue to be one of the most promising technologies for electrochemical energy storage due to its high theoretical capacity. However, its applications have been hindered by the rapid capacity fading due to the formation of soluble polysulfide intermediates. Despite numerous efforts to address this issue, combatting sulfur loss remains one of the greatest challenges. In order to dramatically improve the performance of these Li–S systems, we require a detailed understanding of the interactions between lithium and sulfur in these complex, heterogeneous electrochemical environments.

The overall goal of this research is to reveal the mechanism of the electrochemical reaction between Li and sub-nano confined sulfur, which exhibits abnormal electrochemical behavior and exceptional cycle stability, and develop novel types of cathode materials in lithium-sulfur batteries by bond lithium polysulfides with host materials to prevent the dissolution using chemical approaches. To investigate the mechanisms of electrochemical reactions between Li and sulfur in nano- and sub-nano- confinements, sulfur is physically infused into the conductive porous carbon matrices, including amorphous microporous carbon and single-walled carbon nanotubes with different pore sizes. We propose that Li ions can only enter the sub-nano pores through desolvation, therefore, the Li-S electrochemical reaction in the sub-nano pores is in solid state. The reactions are also investigated in varies ether- and carbonate-based electrolytes to prove our hypothesis. To investigate the lithiation-delithiation of the covalently bonded sulfur in organosulfur compound, the vulcanized polyisoprene (SPIP) nanowires are synthesized. Electrochemical analysis demonstrates that the sulfur chains in SPIP have distinct electrochemical signatures from those that are characteristic of bulk elemental sulfur. The cyclic voltammetry and galvanostatic cycling data show a distinct multistep charge transfer process and solid-state lithium−sulfur reaction behavior, and it is clear that this new material provides a promising basis for the development of cathodes for rechargeable batteries.

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