Suppressed Polysulfide Crossover in Li–S Batteries through a High-Flux Graphene Oxide Membrane Supported on a Sulfur Cathode

Utilization
of permselective membranes holds tremendous promise
for retention of the electrode-active material in electrochemical
devices that suffer from electrode instability issues. In a rechargeable
Li–S batterya strong contender to outperform the Li-ion
technologymigration of lithium polysulfides from the sulfur
cathode has been linked to rapid capacity fading and lower Coulombic
efficiency. However, the current approaches for configuring Li–S
cells with permselective membranes suffer from large ohmic polarization,
resulting in low capacity and poor rate capability. To overcome these
issues, we report the facile fabrication of a high-flux graphene oxide
membrane directly onto the sulfur cathode by shear alignment of discotic
nematic liquid crystals of graphene oxide (GO). In conjunction with
a carbon-coated separator, the highly ordered structure of the thin
(∼0.75 μm) membrane and its inherent surface charge retain
a majority of the polysulfides, enabling the cells to deliver very
high initial discharge capacities of 1063 and 1182 mAh gelectrode–1 for electrodes with 70 and 80% sulfur content, respectively, at
the practical 0.5 C rate. The very high sulfur utilization and impressive
capacity retentions of the high sulfur content electrodes result in
some of the highest performance metrics in the literature of Li–S
(e.g., electrode capacity of 835 mAh gelectrode–1 after 100 cycles at 0.5 C with a sulfur content of 80%). We show
that the structural order of the shear-aligned GO membrane is key
in maintaining good kinetics of the charge transfer processes in Li–S
batteries.