In Situ Formed Protective Barrier Enabled by Sulfur@Titanium Carbide (MXene) Ink for Achieving High‐Capacity, Long Lifetime Li‐S Batteries

Abstract

Sulfur (S) is an attractive cathode material with advantages including high theoretical capacity and low cost. However, issues such as the lithium polysulfide shuttle effect and its insulating properties greatly limit the future applications of lithium‐sulfur (Li‐S) batteries. Here, a viscous aqueous ink with nanoscale S uniformly decorated on the polar, metallically conductive titanium carbide MXene nanosheets (S@Ti3C2Tx) is reported to address these issues. Importantly, it is observed that the conductive Ti3C2Tx mediator efficiently chemisorbs the soluble polysulfides and converts them into thiosulfate/sulfate. The in situ formed sulfate complex layer acts as a thick protective barrier, which significantly retards the shuttling of polysulfides upon cycling and improves the sulfur utilization. Consequently, the binder‐free, robust, highly electrically conductive composite film exhibits outstanding electrochemical performance, including high capacities (1244–1350 mAh g‐1), excellent rate handling, and impressive cycling stability (0.035–0.048% capacity loss per cycle), surpassing the best MXene‐S batteries known. The fabrication of a pouch cell based on the freestanding S@Ti3C2Tx film is also reported. The prototype device showcases high capacities and excellent mechanical flexibility. Considering the broad family of MXenes and their unique roles in immobilizing the polysulfides, various S@MXene composites can be similarly fabricated with promising Li+ storage capability and long lifetime performance.

Hydrous RuO2‐Decorated MXene Coordinating with Silver Nanowire Inks Enabling Fully Printed Micro‐Supercapacitors with Extraordinary Volumetric Performance

“…Following exfoliation, hydrous RuO 2 nanoparticles were deposited in situ on the Mxene nanosheets by admixing a RuCl 3 solution into a well-dispersed MXene suspension. [29,30] These interactions effectively limit the self-growth and spontaneous agglomeration of RuO 2 ·xH 2 O, [31,32] resulting in monodispersed RuO 2 nanoparticles decorated on the nanosheets. [29] Following deposition of the Ru ions, hydrous RuO 2 nanoparticles were subsequently formed through oxidation of the Ru 3+ .…”

Two‐Dimensional Transition Metal Carbides and Nitrides (MXenes): Synthesis, Properties, and Electrochemical Energy Storage Applications

“…By utilizing the conversion type materials (such as sulfur, S) and fabricating Li‐S batteries, the capacities and energy densities can be much improved. The layered conductive MXenes can be used either as efficient hosts for accommodating a high amount of sulfur, or a protective membrane to suppress the shuttle effect of polysulfides (LiPSs) . Besides, MXene nanosheets also possess a high aspect ratio, rendering a good flexibility which can be used as conductive binder for these battery materials and maintain the mechanical stability of the electrodes.…”

“…However, in that report, a large amount of TiO 2 was found in the X‐ray photoelectron spectroscopy (XPS) of Ti 2 C‐S composites, rendering it is difficult to tell if the suppressed LiPSs shuttle effect is due to the intrinsic surface of MXene or because of the as‐oxidized TiO 2 , since the latter has been shown to be effective in retarding the LiPSs diffusion process . Alternatively, Zhang et al reported a S@Ti 3 C 2 T x composite viscous ink which can be directly casted onto Al foil (and other various substrates) as the cathode. The Ti 3 C 2 T x flakes in the obtained S@Ti 3 C 2 T x films were continuously cross‐linked to each other and efficiently wrapped the S nanoparticles uniformly (Figure b) .…”

“…Alternatively, Zhang et al reported a S@Ti 3 C 2 T x composite viscous ink which can be directly casted onto Al foil (and other various substrates) as the cathode. The Ti 3 C 2 T x flakes in the obtained S@Ti 3 C 2 T x films were continuously cross‐linked to each other and efficiently wrapped the S nanoparticles uniformly (Figure b) . Assisted by DFT calculations and XPS results, they observed the in‐situ formation of a thick sulfate complex from the interactions between the surface‐terminated hydroxyl groups and the long‐chain LIPSs.…”

“…Assisted by DFT calculations and XPS results, they observed the in‐situ formation of a thick sulfate complex from the interactions between the surface‐terminated hydroxyl groups and the long‐chain LIPSs. The sulfate complex layer covered the MXene surface tightly and efficiently blocked the polysulfides migration . Consequently, the S@Ti 3 C 2 T x free‐standing electrodes exhibited high capacities (1350 mAh g −1 in 50% S and 1244 mAh g −1 in 70% S electrodes), as well as ultralow capacity decay rates (<0.04 % per cycle after cycling) .…”