Poly(N-methylpyrrole) barrier coating and SiO2 fillers based gel electrolyte for safe and reversible Li–S batteries

Abstract

Lithium-sulfur (Li–S) battery with a modified cathode, and a gel polymeric electrolyte is implemented. A poly(N-methylpyrrole) (PNMPy) coating is applied over a S@reduced graphene oxide (S@RGO) composite and a gel polymeric electrolyte composed of lithium imide, poly(methyl methacrylate), and fumed silica nanoparticles (Li+/PMMA/SiO2) substitutes the conventional liquid electrolyte in a Li–S@RGO-PNMPy cell. The PNMPy overlayer at the S@RGO composite, allows the unobstructed passage of Li-ions between the cathode and the electrolyte during charge-discharge by the virtue of a high Li-ion diffusion coefficient of ∼10−6 cm2 s−1, while it simultaneously functions as a physical barrier and efficiently restricts the polysulfide dissolution and shuttle, thus increasing the capacity retention from 13 to 40%, after 500 cycles. The Li+/PMMA/SiO2 gel is characterized by a liquid-like ionic conductivity that varies from 2.6 to 86 mS cm−1, over a temperature window of 5–75 °C and a wide electrochemical voltage stability window of ∼1–3 V versus Li/Li+, thereby enabling its use in all Li-chalcogenide batteries. Notwithstanding the higher magnitude of stable capacity at the end of 500 charge-discharge cycles of 476 mAh gSulfur−1 for the liquid electrolyte based Li–S@RGO-PNMPy cell, the analogous Li+/PMMA/SiO2 gel based cell demonstrates a superior capacity retention, a better reversibility or Coulombic efficiency response over the cycle life and is safer than its’ liquid counterpart. The simplicity of the two novel approaches relying on the abilities of the PNMPy overlayer and the Li+/PMMA/SiO2 gel in bringing about improvements in the performance of the Li–S cell with technological ramifications is a pivotal step towards developing commercial Li–S batteries.