High-Index Faceted Nanocrystals as Highly Efficient Bifunctional Electrocatalysts for High-Performance Lithium-Sulfur Batteries

Precisely regulating of the surface structure of crystalline materials to improve their catalytic activity for lithium polysulfides is urgently needed for high-performance lithium-sulfur(Li-S)batteries.Herein,high-index faceted iron oxide(Fe_(2)O_(3))nanocrystals anchored on reduced graphene oxide are developed as highly efficient bifunctional electrocatalysts,effectively improving the electrochemical performance of Li-S batteries.The theoretical and experimental results all indicate that high-index Fe_(2)O_(3)crystal facets with abundant unsaturated coordinated Fe sites not only have strong adsorption capacity to anchor polysulfides but also have high catalytic activity to facilitate the redox transformation of polysulfides and reduce the decomposition energy barrier of Li_(2)S.The Li-S batteries with these bifunctional electrocatalysts exhibit high initial capacity of 1521 mAh g^(-1)at 0.1 C and excellent cycling performance with a low capacity fading of 0.025%per cycle during 1600 cycles at 2 C.Even with a high sulfur loading of 9.41 mg cm^(-2),a remarkable areal capacity of 7.61 mAh cm^(-2)was maintained after 85 cycles.This work provides a new strategy to improve the catalytic activity of nanocrystals through the crystal facet engineering,deepening the comprehending of facet-dependent activity of catalysts in Li-S chemistry,affording a novel perspective for the design of advanced sulfur electrodes.

Heterogeneous Mediator Enabling Three-Dimensional Growth of Lithium Sulfide for High-Performance Lithium-Sulfur Batteries

Two-dimensional(2D)deposition regime of insulating lithium sulfide(Li_(2)S)is a major obstacle to achieve high reversible capacity in the conventional glyme-based lithium-sulfur(Li-S)batteries as it leads to rapid loss of active electrode surface and low sulfur utilization.Achieving three-dimensional(3D)growth of Li_(2)S is therefore considered to be necessary,but the available strategies are mainly based on the electrolyte manipulations,which inevitably lead to added complexity of the electrode-electrolyte compatibility and,in particular,instability of the lithium anode.In this work,we have developed a heterogeneous polysulfide mediator composed of discrete Mo_(5)N_(6) anchored on graphene,which functions on the cathode side,to regulate the deposition mode of Li_(2)S.Mo_(5)N_(6) can efficiently boost the formation of Li_(2)S as demonstrated by a series of experimental and computational results.More importantly,the discrete distribution of Mo_(5)N_(6) nucleants on graphene postpones the merging of adjacent Li_(2)S nuclei to promote their isotropic growth.Thus,3D deposits of Li_(2)S is guided by the heterogeneous mediator.Benefiting from these unique superiorities,Li-S cells with high rate capability of 954 mAh g^(-1) at 2 C and long cycle life exceeding 1000 cycles are realized without advanced lithium anode protection.