Lithium Borate Containing Bifunctional Binder To Address Both Ion Transporting and Polysulfide Trapping for High-Performance Li-S Batteries.

A slightly cross-linked lithium borate containing single ion-conducting polymer (LBSIP) as a bifunctional binder for lithium sulfur batteries is designed and fabricated via a one-step thiol-ene click reaction. The LBSIP binder exhibits a maximum peeling strength of over 600 mN mm-1 between the sulfur cathode and aluminum foil, together showing a high lithium ion diffusion coefficient of 2.1 × 10-12 cm2 s-1. Owing to the unique electron-donating groups, the binder can provide a good ionic conductive network and a dramatically enhanced polysulfide-trapping feature. The strong interaction between electron-donating groups of LBSIP with Li2S6 was confirmed by the 7Li-NMR analysis and density-functional theory calculation. The cathode using the LBSIP binder exhibited a high Coulombic efficiency of ∼100% and an initial specific capacity of 712 mAh g-1 with a capacity fading rate of 0.06% per cycle after 500 cycles at 0.5 C. Even at a high current rate of 2 C, a reversible capacity of over 500 mAh g-1 was still obtained. However, the capacity of the cathode using the PVDF binder decreased to 331 mAh g-1 after 180 cycles at 0.5 C. This work is very attractive for the rational design of functional binders for Li-S batteries with both ion-transporting and polysulfide-trapping features.