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.

Metal–Organic Frameworks-Derived Porous Yolk–Shell MoP/Cu_(3)P@carbon Microcages as High-Performance Anodes for Sodium-Ion Batteries

Transitional metal phosphides(TMPs)anode materials usually have large volume change and weak diffusion kinetics,leading to poor cycle stability.Combining TMPs with conductive carbon matrix has been widely used to boost sodium storage.However,it still needs to make efforts in the rational and facile design of nano/micro-structural TMPs/carbon hybrid anode material.Herein,a MOFs-derived strategy is developed to synthesize porous yolk–shell Mo P/Cu_(3)P@carbon microcages(Mo P/Cu_(3)P@C)through in situ and confined phosphidation reaction as a high-performance sodium-ion batteries anode.This yolk–shell structure can offer adequate internal space to buffer the large volume expansion,shorten diffusion distance,and create more active sites of Na+.Especially,the Cu nanoparticles generated from Cu_(3)P have remarkable electronic conductivity of 5.73107S m-1(the second most conductive metal)to benefit transporting electrons.And the introduction of Mo(Mo P has high theoretical capacity of 633 mA h g^(-1))can enhance the reversible capacity of the whole anode material.Therefore,these porous yolk–shell Mo P/Cu_(3)P@carbon microcages possess excellent reversible capacity of 307.8 mA h g^(-1)at 1.0 A g^(-1)and extraordinary cycle stability of 132.1 m A h g^(-1)at 5.0 A g^(-1)even after 6000 cycles.

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.

The discovery of interfacial electronic interaction within cobalt boride@MXene for high performance lithium-sulfur batteries

Lithium-sulfur battery is strongly considered as the most promising next-generation energy storage system because of the high theoretical specific capacity.The serious"shuttle effect"and sluggish reaction kinetic limited the commercial application of lithium-sulfur battery.Many hetero structure s were applied to accelerate polysulfides conversion and suppress their migration in lithium-sulfur batteries.Nevertheless,the effect of the interface in heterostructure was not clear.Here,the Co_(2)B@MXene heterostructure is synthesized through chemical reactions at room temperature and employed as the interlayer material for Li-S batteries.The theoretical calculations and experimental results indicate that the interfacial electronic interaction of Co_(2)B@MXene induce the transfer of electrons from Co_(2)B to MXene,enhancing the catalytic ability and favoring fast redox kinetics of the polysulfides,and the theoretical calculations also reveal the underlying mechanisms for the electron transfer is that the two materials have different Fermi energy levels.The cell with Co_(2)B@MXene exhibits a high initial capacity of1577 mAh/g at 0.1 C and an ultralow capacity decay of 0.0088%per cycle over 2000 cycles at 2 C.Even at5.1 mg/cm^(2) of sulfur loading,the cell with Co_(2)B@MXene delivers 5.2 mAh/cm^(2) at 0.2 C.

High lithiophilic nitrogen-doped carbon nanotube arrays prepared by in-situ catalyze for lithium metal anode

Lithium metal has a very outstanding theoretical capacity(3860 mAh/g)and is one of the most superior anode materials for high energy density batteries.However,the uncontrollable dendrite growth and the fo rmation of"dead lithium"are the important hidden dangers of short cycle life and low safety.However,the uncontrollable dendrite growth and the fo rmation of dead lithium leads to short cycle life and hidden dange r,which hinder its practical application.Controlling the nucleation and growth process of lithium is an effective strategy to inhibit lithium dendrite.Herein,a simple in situ self-catalytic method is used to construct nitrogen doped carbon nanotube arrays on stainless steel mesh(N-CNT@SS)as a lithium composite anode.The N-doped CNTs provide a great number of N-functional groups,which enhance the lithiophilic of anode and provide a large number of uniform nucleation sites,hence it has excellent structural stability for cycles.The arrays provide neat lithium-ion transport channels to uniform lithiumion flux and inhibits dendrite generation,revealed by the COMSOL multi-physics concentration field simulation.The N-CNT@SS composite anode sustain stable at 98.9%over 300 cycles at 1 mA/cm2.NCNT@SS as the anode is coupled LiFePO_(4)(LFP)as the cathode construct a full battery,demonstrating excellent cycling stability with a capacity of 152.33 mAh/g and capacity retaining ratio of 95.4%after 100 cycles at 0.5 C.

Fabrication of layered structure VS4 anchor in 3D graphene aerogels as a new cathode material for lithium ion batteries

VS4 has gained more and more attention for its high theoretical capacity (449 mAh/g with 3e^- transfer) in lithium ion batteries (LIBs). Herein, a layered structure VS4 anchored in graphene aerogels is prepared and first reported as cathode material for LIBs. VS4@GAs composite exhibits an exceptional high initial reversible capacity (511 mAh/g), an excellent high-rate capability (191 mAh/g at the 5 C), and an excellent cyclic stability (239 mAh/g after 15 cycles).

Kinetically enhanced electrochemical redox reactions by chemical bridging SnO_(2)and graphene sponges toward high-rate and long-cycle lithium ion battery

Graphene has been widely used to improve the electrochemical performance in rate and cycling stability for SnO_(2).However,the mechanism of the synergistic effect and the interfacial interaction between SnO_(2)and graphene are still not fully understood.Herein,we put forward a novel,cost effective strategy to construct hierarchical SnO_(2)nanoclusters anchored on the graphene sponges for lithium storage by in situ self assembly.The result shows that the synergistic effect and interfacial interaction origin form the existence of strong oxygen bridges between SnO_(2)and graphene via the C-O-Sn linkage.It is demonstrated for the first time that the interfacial interaction by C-O-Sn bonding plays a crucial role in the rate and cycling stability both experimentally and theoretically.Thus,the SnO_(2)@graphene sponges exhibit remarkable rate capability(a reversible capability of 1141,997,912,831,693,536,and 302 mA h g^(-1)at 0.2 C,0.5 C,1 C,2 C,5 C,10 C and 20 C,respectively)and cycling performance(after 625 cycles at 6 A g^(-1)with a capacity retention of 537 m A h g^(-1)).