Bifunctional hydrogen-bonding cross-linked polymeric binder for high sulfur loading cathodes in lithium/sulfur batteries

Abstract

Construction of high sulfur loading electrode is one of the effective ways to achieve high specific energy density lithium/sulfur batteries. Therefore, the optimization of polymeric binders has been considered as effective strategy to improve the volume changes of sulfur electrodes during charge/discharge processes. In this work, an effective route for the preparation of three dimensional polymeric binder (PAA-PANI) via multiple hydrogen bonds was developed and fabricated through in situ polymerization between polyacrylic acid (PAA) and polyaniline (PANI), which possess bifunctional effects on high sulfur loading cathodes in lithium/sulfur batteries. The carboxyl polar groups of PAA could effectively adsorb polysulfides and the conductive PANI enhance the electronic conductivity of the sulfur electrode. The three dimensional polymeric binder of PAA-PANI has enhanced the active material adhesion, mechanical properties and electronic conductivity, which decreased overpotential polarization, improved the lithium ions diffusion coefficient, and reduced the self-discharge. More importantly, the PAA-PANI functional binder could alleviate the expansion of high sulfur loading electrode. Taking advantages of PAA-PANI binder, the carbon nanotubes modified sulfur electrode (CNTs@S; sulfur content: 84.3 wt%) with PAA-PANI binder exhibits an initial discharge capacity of 906 mAh g–1 at 2.56 mA cm–2 (0.3 C) under a sulfur loading of 5.1 mg cm–2. Even at higher current density of 8.54 mA cm–2 (1 C), the PAA-PANI binder electrode delivers a high capacity of 846 mAh g–1. Moreover, with an extremely high areal sulfur loading of 17 mg cm–2, the cathode shows an areal specific capacity of 16.7 mAh cm–2.