An in-situ generated Bi-based sodiophilic substrate with high structural stability for high-performance sodium metal batteries

Sodium(Na)metal anode exhibits a potential candidate in next-generation rechargeable batteries owing to its advantages of high earth abundance and low cost.Unfortunately,the practical development of sodium metal batteries is inherently plagued by challenges such as the side reactions and the growth of Na dendrites.Herein we report a highly stable Bi-based“sodiophilic”substrate to stabilize Na anode,which is created by in-situ electrochemical reactions of 3D hierarchical porous Bi_(2)MoO_(6)(BMO)microspheres.BMO is initially transformed into the Bi“nanoseeds”embedded in the Na-Mo-O matrix.Subsequently,the Bi nanoseeds working as preferential nucleation sites through the formation of BiNa alloy enable the non-dendritic Na deposition.The asymmetric cells based on such BMO-based substrate can deliver a long-term cycling for 600 cycles at a large capacity of 4 m Ah cm^(-2) and for 800 cycles at a high current density of 10 m A cm^(-2).Even at a high depth of discharge(66.67%),the Na-predeposited BMO(Na@BMO)electrodes can cycle for more than 1600 h.The limited Na@BMO anodes coupled with the Na_(3)V_(2)(PO_(4))_(3) cathodes(N/P ratio of 3)in full cells also show excellent electrochemical performance with a capacity retention of about 97.4%after 1100 cycles at 2 C.

Facile Fabrication of Ag Nanocrystals Encapsulated in Nitrogen-doped Fibrous Carbon as an Efficient Catalyst for Lithium Oxygen Batteries

A facile synthesis of Ag nanocrystals encapsulated in nitrogen-doped carbon fiber(NCF)is proposed,based on the simultaneous reaction between pyrrole and Ag^(+)ions in an aqueous solvent followed by a heat treatment.The as-prepared Ag/NCF demonstrated superior catalytic behavior toward ORR and OER.Besides improved cycling stability,a much lower discharge/charge gap of 0.89 V(vs Li/Li^(+))compared with 1.38 V for NCF cathode with a fixed capacity of 500 m Ah g^(-1)was obtained in lithium oxygen batteries.The introduction of Ag crystals into NCF facilitates the oxygen reduction reaction/oxygen evolution reaction kinetics.X-ray diffraction analysis coupled with Raman spectroscopy confirmed that Ag/NCF cathode could reversibly catalyze Li_(2)O_(2)formation and decomposition.The NCF matrix offers a conductive network to realize rapid mass transfer and the encapsulated Ag nanocrystals supplied effective catalytic active sites.The combined action between both contributes to the superior electrocatalytic performance.

Hybrid working mechanism enables highly reversible Zn electrodes

Zn dendrite growth and water-related side reactions have been criticized to hinder actual applications of aqueous Zn-ion batteries.To address these issues,a series of Zn interfacial modifications of building solid/electrolyte interphase(SEI)and nucleation layers have been widely proposed,however,their effectiveness remains debatable.Here,we report a boron nitride(BN)/Nafion layer on the Zn surface to efficiently solve Zn problems through combining the hybrid working mechanisms of SEI and nucleation layers.In our protective layer,Nafion exhibits the SEI mechanism by blocking water from the Zn surface and providing abundant channels for rapid Zn^(2+)þtransmission,whilst BN nanosheets induce Zn deposition underneath with a preferred(002)orientation.Accordingly,dendrite-free and side-reaction-free Zn electrode with(002)deposition under the protective layer is realized for the first time,as reflected by its high reversibility with average Coulombic efficiency of 99.2%for>3000 h.The protected Zn electrode also shows excellent performance in full cells when coupling with polyaniline cathode under the strict condition of lean electrolyte addition.This work highlights insights for designing highly reversible metal electrodes towards practical applications.

Effects of carbon on electrochemical performance of red phosphorus(P) and carbon composite as anode for sodium ion batteries

Red phosphorus/graphite(P/G) and red phosphorus/carbon nanotube(P/CNT) composites were prepared by ball milling red phosphorus with CNTs and graphite, respectively. The electrochemical results show superior electrochemical performances of the P/G and P/CNT composites compared with that of the reference sample milled with Super-P carbon. After 70 cycles, the P/G and P/CNT composites remained771.6 and 431.7 mA h g^(-1), with 68 % and 50 % capacity retention, respectively. With increasing the milling time(20 h), CNTs were cut into short pieces and then broken into carbon rings and sheets which were well mixed with red phosphorus. The morphology of the P/CNT composite can buffer the large volume changes from alloying and de-alloying during cycling, resulting in the enhanced cycling stability.

Double interface regulation: Toward highly stable lithium metal anode with high utilization

The undesirable Li dendrite growth and other knock-on issues have signifi-cantly plagued the application of Li metal anodes(LMAs).Herein,we report that the synergistic regulation of double interfaces adjacent to the metallic Li anode can effectively prevent the dendritic Li growth,significantly improving the cycling performance of LMAs under harsh conditions including high cur-rent density and high depth of discharge.Thorough comparison of electrolytes demonstrated that 1 M lithium bis(fluorosulfonyl)imide(LiFSI)in 1,2-dimethoxyethane(DME)can yield a robust and lithiophobic LiF-rich upper interface(solid electrolyte interphase).Besides,the Sb-based buffer layer forms a lithiophilic lower interface on current collector.The synergy of the upper and lower interfacial engineering plays an important role for outstanding cyclability of LMAs.Consequently,the plating/stripping of Li can be stably repeated for 835 and 329 cycles with an average Coulombic efficiency(CE)above 99%at 1 and 3 mA h cm?2,respectively.Surprisingly,the Li||Li symmetric cell can even withstand the baptism of current density up to 20 mA cm?2.The excellent performance validates that the facile synergistic regulating of interfaces adjacent to the metallic Li anode provides an effective pathway to stabilize LMAs.

Comparison of Few-layer Graphene Prepared from Natural Graphite through Fast Synthesis Approach

We report the synthesis of high quality few-layer graphene on a large scale using high purity natural graphite from Sri Lanka. A novel thermal method was adapted to prepare graphene from intermediate graphite oxide, which was obtained by heating the intermediate at low temperature （above 150 ℃） in air for 5 min and subsequent heating at 500℃ in Argon for 15 min. The samples were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, Raman spec- troscopy etc. The properties and the performance of graphene were observed to depend on the graphite source. The reduced graphite oxide from Kahatagaha graphite source exhibits higher Brunauer-Emmett- Teller specific surface area -500 m^2 g^-1 and stable specific capacity as an anode in Li-ion batteries, whereas Bogala graphite showed higher initial irreversibility and higher capacity as anode, exceeding the theo- retical specific capacity of graphite. Both graphenes showed high electrical conductivity. The graphene, which exists in stacks of only a few layers, supposed to be 2-6 layers, would be promising for a vast variety of applications.