Stabilizing the polysulfide shuttle while ensuring high sulfur loading holds the key to realizing high theoretical energy of lithium-sulfur (Li-S) batteries. Herein, we present an electrocatalysis approach to demonstrate preferential adsorption of a soluble polysulfide species, formed during discharge process, toward the catalyst anchored sites of graphene and their efficient transformation to long-chain polysulfides in the subsequent redox process. Uniform dispersion of catalyst nanoparticles on graphene layers has shown a 40% enhancement in the specific capacity over pristine graphene and stability over 100 cycles with a Coulombic efficiency of 99.3% at a current rate of 0.2 C. Interaction between electrocatalyst and polysulfides has been evaluated by conducting X-ray photoelectron spectroscopy and electron microscopy studies at various electrochemical conditions.

No abstract

No abstract

Lithium-sulfur (Li-S) chemistry is projected to be one of the most promising for next-generation battery technology, and controlling the inherent "polysulfide shuttle" process has become a key research topic in the field. Regulating intermediary polysulfide dissolution by understanding the metamorphosis is essential for realizing stable and high-energy-density Li-S batteries. As of yet, a clear consensus on the basic surface/interfacial properties of the sulfur electrode has not been achieved, although the catalytic phenomenon has been shown to result in enhanced cell stability. Herein, we present evidence that the polysulfide shuttle in a Li-S battery can be stabilized by using electrocatalytic transition metal dichalcogenides (TMDs). Physicochemical transformations at the electrode/electrolyte interface of atomically thin monolayer/few-layer TMDs were elucidated using a combination of spectroscopic and microscopic analysis techniques. Preferential adsorption of higher order liquid polysulfides and subsequent conversion to lower order solid species in the form of dendrite-like structures on the edge sites of TMDs have been demonstrated. Further, detailed electrochemical properties such as activation energy, exchange current density, rate capabilities, cycle life, etc. have been investigated by synthesizing catalytically active nanostructured TMDs in bulk quantity using a liquid-based shear-exfoliation method. Unveiling a specific capacity of 590 mAh g at 0.5 C rate and stability over 350 cycles clearly indicates yet another promising application of two-dimensional TMDs.

With the unique-layered structure, MXenes show potential as electrodes in energy-storage devices including lithium-ion (Li ) capacitors and batteries. However, the low Li -storage capacity hinders the application of MXenes in place of commercial carbon materials. Here, the vanadium carbide (V C) MXene with engineered interlayer spacing for desirable storage capacity is demonstrated. The interlayer distance of pristine V C MXene is controllably tuned to 0.735 nm resulting in improved Li-ion capacity of 686.7 mA h g at 0.1 A g , the best MXene-based Li -storage capacity reported so far. Further, cobalt ions are stably intercalated into the interlayer of V C MXene to form a new interlayer-expanded structure via strong V-O-Co bonding. The intercalated V C MXene electrodes not only exhibit superior capacity up to 1117.3 mA h g at 0.1 A g , but also deliver a significantly ultralong cycling stability over 15 000 cycles. These results clearly suggest that MXene materials with an engineered interlayer distance will be a rational route for realizing them as superstable and high-performance Li capacitor electrodes.