Sulfur-Carbon Electrode with PEO-LiFSI-PVDF Composite Coating for High-Rate and Long-Life Lithium-Sulfur Batteries

Abstract

To address the problem of the serious capacity fading in lithium-sulfur batteries, a multi-functional PEO(polyethylene oxide)/LiFSI (lithium bis(fluorosulfonyl)imide)/PVDF (polyvinylidene fluoride) (PLP) gel polymer electrolyte is exploited by coating PLP on a carbon nanotubes (CNTs) based sulfur cathode (PLP-S/CNTs) with a controlled thermal annealing process. The annealing process leads to the conformal infusion of PLP through the matrix of S/CNTs with retaining the amorphous phase of the PLP, which enhance the rate performance compared to the bare S/CNTs. The PLP coating drives the transformation of more elemental sulfur to Li2S2/Li2S without forming intermediary product by restraining soluble-polysulfides formation. Furthermore, the PLP coating successfully inhibits the dissolution of Li2Sx (x > 4) in PEO and prevents the loss of active material in the cathode, which is confirmed by density functional theory calculations. Comprehensively, the PLP coating applied to the surface of the S/CNTs cathode exhibit significantly suppressed shuttle effect and greatly improve long-term cycle stability of the lithium-sulfur battery. The synthesized PLP-coated S/CNTs composite cathode demonstrates a high specific capacity of 573.6 mAh g(-1) at a current density of 0.5 C after 1 000 cycles, even achieving 318.1 mAh g(-1) at an extremely high C-rate (6 C). which is unprecedented performance among the reported studies on coating technology.