Enhancing the Cycle Performance of Lithium‐Sulfur Batteries by Coating the Separator with a Cation‐Selective Polymer Layer

Abstract

Lithium‐sulfur batteries are believed to possess the feasibility to power electric vehicles in the future ascribed to the competitive energy density. However, soluble polysulfides continuously shuttle between the sulfur electrode and lithium anode across the separator, which dramatically impairs the battery’s capacity. Herein, the surface of a polypropylene separator (PP film) is successfully modified with a delicately designed cation‐selective polymer layer to suppress the transport of polysulfides. In principle, since bis‐sulfonimide anions groups on the backbone of the polymer are immobilized, only cations can pass through the polymer layer. Furthermore, plenty of ethoxy chains in the polymer can facilitate lithium‐ion mobility. Consequently, in addition to obstructing the movement of negatively charged polysulfides by the electrostatic repulsive force of fixed anions, the coated multi‐functional layer on the PP film also guarantees the smooth conduction of lithium ions. The investigations demonstrate that the battery with the pristine PP film only delivers 228.5 mAh g‐1 after 300 cycles at 2 C with a high capacity fading rate of 60.9%. By contrast, the polymer‐coated sample can release 409.4 mAh g‐1 under the identical test condition and the capacity fading rate sharply declines to 43.2%, illustrating superior cycle performance.

Advanced Separator Materials for Enhanced Electrochemical Performance of Lithium–Sulfur Batteries: Progress and Prospects

“…(a) Diagrammatic sketch of soluble polysulfides mobility in batteries with pristine and cation–selective polymer–coated PP films. (Reproduced with permission from ref . Copyright 2023, WILEY.)…”

“…As shown in Figure 19(a), Li et al 115 presented the cathode side of the separator using a cation−selective polymer layer called Li−BIPDE. This layer exhibited a lithium ion transfer number of 0.83, indicating its ability to selectively allow the transmission of lithium ions.…”