Mechanistic implications of Li–S cell function through modification of organo-sulfur cathode architectures

Abstract

Copolymeric organo-sulfur based electrodes provide a unique framework to explore and subsequently improve lithium-sulfur (Li-S) cells. There is a general difference in the way copolymers trap lithium during cell function...

Investigation of low molecular weight sulfur–limonene polysulfide electrodes in Li–S cells

“…The reaction mixture was then cooled to 135 C (i.e., lower temperature but still at a molten state) and subjected to 7 mbar of pressure for 5 h, followed by an additional 2 h maintained at 75 C (i.e., solid phase) to distill p-cymene and other volatile byproducts before cooling to room temperature to yield the copolymeric product. Electrochemical performance of Li-S cells (with similar electrode/electrolyte compositions and cycling conditions) using inverse-vulcanized copolymer electrodes prepared using inverse vulcanized copolymers (i) poly(S-r-DIB), (ii) poly(S-r-squalene), and (iii) poly(S-r-limonene) with 10 wt% crosslinking monomer and 90 wt% elemental sulfur from literature 14,17,20,21,33 and from this work. Note, corresponding mechanistic studies on poly(S-r-DIB) 21 and poly(S-r-squalene) 20 were performed under the same conditions and coin cell fabrication regime Monomer (10 wt%) ) salts in a 1 : 1 v/v mixture of 1,3-dioxolane and 1,2-dimethoxyethane following compositions used in previous work related to poly(S-r-DIB).…”

“…27 In 1,5-diene squalene, the large number of fragment permutations resulted in high molecular weight copolymers with low chain mobility as suggested by limited solubility in non-polar aprotic solvents 31 and supported by the solid-state NMR studies of the copolymer. 20 This low chain mobility in poly(S-r-squalene) proved to be less effective in improving Li-S cell capacity retention (Table 1, $67% initial capacity at 20th discharge, cycled at C/10 or 167.5 mA g À1 ) 20 compared to poly(Sr-DIB) (Table 1, $74% initial capacity at 20th discharge, cycled at C/10 or 167.5 mA g À1 ). 14,21 Despite this result for poly(S-rsqualene), the polymer from 1,5-diene limonene, poly(S-rlimonene), initially developed by Crockett et al, 15,32 exhibits high capacity retention values (Table 1, 97% of initial capacity at 300th discharge, cycled at 0.5C, 1C undened) 33 surpassing that of poly(S-r-DIB).…”

“…Previous reports have shown inuence of the copolymers beyond these parameters, such as improvements on homogeneity in distribution of the sulfur active material 18,19 as well as on adsorbed electrolytic lithium salts and SEI formation. 20,21 Furthermore, the choice of crosslinker has also been demonstrated to impact other properties of the copolymer e.g., dominant crystalline sulfur phase, [21][22][23] exibility, durability, and susceptibility to bond scission upon heating or in solvents such as NMP during cathode preparation. 24,25 Considering the impact of crosslinkers on the copolymeric architecture Regioselectivity is generally considered unpredictable in freeradical polymerization reactions (thus forming otherwise unexpected or thermodynamically less favorable byproducts).…”

“…Whilst both sides can be totally consumed upon inverse vulcanization, preferential reactivity to the less sterically hindered exocyclic alkene may inuence the morphology of the copolymeric network. Moreover, like squalene, 20 limonene is a 1,5-diene with a greater susceptibility to dehydrogenation reactions compared to conjugated dienes with aromatic functionalities such as 1,3diisopropenylbenzene (DIB), and therefore a larger number of copolymer fragment permutations would be intuitively expected. 27 In 1,5-diene squalene, the large number of fragment permutations resulted in high molecular weight copolymers with low chain mobility as suggested by limited solubility in non-polar aprotic solvents 31 and supported by the solid-state NMR studies of the copolymer.…”

Recent Breakthroughs in the Bottleneck of Cathode Materials for Li–S Batteries

“…As the host sulfur cathode materials, MOFs expose the active sites to chemically adsorb LiPSs, and the porous MOF provides channels for the transfer of Li + , the encapsulation and volume expansion of sulfur, and the conduction of electrons . In addition, MOF-derived metal compounds also inherit the carbon skeleton structures of MOFs, increase sulfur contents, and promote reaction kinetics. , The S–N bonds and C–S bonds cyclized by conductive polymer and S at high temperature can anchor LiPSs to prevent diffusion and catalyze the conversion to Li 2 S to further alleviate the shuttle effect. − More importantly, the synergistic effect of double or multiple doping between the above sulfur cathode host materials can greatly optimize the electrochemical performance of Li–S batteries . The sulfur cathode host materials doped with O, N, and S heteroatoms can greatly enhance the conversion performance and chemical absorption of LiPSs due to the polarity of the C–O/C–N/C–S bonds.…”