Electrochemical analysis on the role of disulfide bonds in polysulfide-co-polyoxide as cathode active binder for enhanced storage capacity of lithium-metal batteries

The present article is aimed at elucidation on the role of disulfide bonds in enhancement of energy storage capacity of lithium metal battery using polysulfide-co-polyoxide as cathode active binder in lithium metal batteries. Upon photocuring via ‘thiol-ene’ reaction, the resulting thioplast-co-trimethylolpropane ethoxylate triacrylate (TMPETA) co-network is flexible containing disulfide and ether oxygen moieties. Ionic conductivity of the polymer electrolyte membrane containing Thioplast-co-TMPETA network/plasticizer/lithium salt reaches the superionic conductor level of 10−3 S cm−1 at room temperature. To further improve the electrochemical performance, Thioplast-co-TMPETA co-networks were used as a binder, in lieu of polyvinylidene fluoride (PVDF), for lithium iron phosphate (LFP) cathode. Of particular interest is the achievement of a high overall specific capacity of ∼265 mAh g−1 initially which stabilizes at ∼185 mAh g−1 after 35 cycles. These values certainly exceeded the theoretical value of 170 mAh g−1 for neat LFP cathode. This capacity enhancement may be attributed to the disulfide bonds of polysulfide constituent undergoing SS bond scission followed by electron acceptor-donor interactions between sulfide radicals and Li cations. Moreover, the polysulfide-co-polyoxide binder also works as a cathode active material with a specific capacity of 122–103 mAh g−1 in the potential range of 1.0–3.0 V showing reasonable capacity retention of ∼85% and Coulombic efficiency of ∼97%.