Trapping of Polysulfides with Sulfur‐Rich Poly Ionic Liquid Cathode Materials for Ultralong‐Life Lithium–Sulfur Batteries

Abstract

Sulfur‐rich polymers synthesized by inverse vulcanization are promising cathodes for Li–S batteries and can suppress the shuttle effect to improve the cycling properties of Li–S batteries. However, developing a sulfur‐rich copolymer with new chemical functionality to enhance performance of Li–S batteries remains a huge challenge. In this report, a sulfur‐rich polymer cathode containing ionic liquid segments named poly(sulfur‐co‐1‐vinyl‐3‐allylimidazolium bromide) [poly(S‐co‐DVIMBr)] was obtained by the inverse vulcanization of S8 with DVIMBr and used as cathode for the first time. This sulfur‐rich poly ionic liquid cathode showed effective suppression of the shuttle effect through joint effects of the stable chemical bonding of C−S and strong cation absorption for lithium polysulfides, which was confirmed by DFT calculations. In particular, the Li–S cell with poly(S‐co‐DVIMBr) cathode delivered high capacity retention of 90.22 % even over 900 cycles. Developing sulfur‐rich poly ionic liquids may provide a new strategy of introducing the functional groups with cations into the cathode materials for suppressing the shuttle effect and improving the performance of Li–S batteries.

Combined first-principles statistical mechanics approach to sulfur structure in organic cathode hosts for polymer based lithium–sulfur (Li–S) batteries

“…17 Numerous studies have been conducted on the usage of different organosulfur compounds as cathode materials. [18][19][20] Here, conjugated polymers emerged as promising candidates due to their good conductivity, 21,22 ability to suppress the shuttle effect by confining the sulfur content, [23][24][25][26] and tolerance to large volume expansion during lithiation. [27][28][29] Among them, thiol-containing polymers are one example where the -SH groups can be crosslinked with sulfur via covalent bonds.…”

Polymer Electrode Materials for Lithium‐Ion Batteries

“…Profiting from the chemical confinement of strong C–S bonds and the electrostatic absorption between cations and polysulfides, an unexceptionable capacity retention rate of 90.2% at 2 C after 900 cycles was presented (Figure 19e). [ 194 ]…”

“…d) Molecular structure and e) long cycle performance of poly(S-co-DVIMBr). Adapted with permission [194]. Copyright 2020, WILEY-VCH.…”

Functional polymers for lithium metal batteries

“…Such polymer exhibited an initial specific discharge capacity of 1100 mAh/g and a long-term cycling performance of 823 mAh/g at 100 cycles at a rate of C/10, which is superior to pure S 8 and represented the highest value for polymer-based sulfur cathodes reported to date. A similar approach was used to copolymerize S 8 with an ionic liquid based crosslinker,1-vinyl-3-al-lylimidazolium bromide (DVIMBr), to form poly(S-co -DVIMBr) [391] . The introduction of imidazolium-based ion pairs served to further anchor intermediate polysulfide while improving the ionic conductivity within the electrode.…”