Dual-Functional V 2 C MXene Assembly in Facilitating the Sulfur Evolution Kinetics and Li-Ion Sieving towards Practical Lithium-Sulfur Batteries.

Lithium-sulfur (Li-S) batteries are considered as one of the most promising candidates to achieve the energy density of 500 Wh kg -1 . However, the challenges of shuttle effect, sluggish sulfur conversion kinetics and lithium dendrite growth severely obstruct the practical implementation. Herein, multi-scale V 2 C MXene (VC) with spherical confinement structure is designed as a high-efficiency bi-functional promotor for the evolution of sulfur and lithium species in Li-S batteries. Combining the synchrotron X-ray three-dimensional nano-computed tomography (X-ray 3D nano-CT), small angle neutron scattering (SANS) techniques and first-principle calculation, we reveal that the activity of VC can be maximized by tuning the scale and the as-attained functions are conducted as follows: (i) The VC acts as the efficient lithium polysulfide (LiPS) scavenger due to the large number of active sites. (ii) The VC exhibits significantly improved electrocatalytic function for the Li 2 S nucleation and decomposition reaction kinetics owing to the scale effect. (iii) The VC can regulate the dynamic behavior of Li + and thus stabilize the lithium plating/stripping effectively on account of the unique ion sieving effect. The synchronous optimization of cathode and anode endows the Li-S batteries with superior rate capability and cycling stability, e.g. the battery with a high sulfur loading of 8.1 mg cm -2 enables a high areal capacity of 8.1 mA h cm -2 at a low E/S ratio of 4 μL mg S -1 . This article is protected by copyright. All rights reserved.