Modification And Electrochemical Performance Of Three-dimensional Scaffold Based Glass Fiber For Lithium Metal Anode

Lithium metal anodes are regarded as the most promising anode in the new generation of high specific energy batteries owing to superior characteristic of high theoretical specific capacity(3860 m Ah g-1),low reduction potential(-3.04 V versus standard hydrogen electrode)and low mass density(0.53 g cm-3).However,the practical applications of lithium metal batteries are severely hindered by the inherent problems of serious dendrite growth,unlimited volume change and continuous side reactions,which cause the poor cyclability,and even result in internal short-circuit and safety accident.Based on the solution strategy of lowering nucleation barrier,expediting ion transport and regulating lithium ion distribution,functional three-dimensional scaffolds with glass fiber membranes were prepared to realize the uniform lithium metal deposition.In order to solve the electronic conductivity problem of glass fiber scaffold and reduce the lithium metal nucleation overpotential on the scaffold,Au nanoparticles were modified on the surface of glass fiber scaffold by low-temperature vacuum sputtering.The glass fiber scaffolds modified by Au nanoparticles achieve zero nucleation overpotential at the initial stage of lithium deposition through the alloying reaction of the lithium metal and Au.Besides,the glass fiber scaffolds can not only maintain chemical stability during lithium deposition/dissolution process,but also effectively inhibit the volume change due to its high elastic modulus and widely existing pores.Based on the guiding nucleation effect of Au nanoparticles and the excellent stability of glass fiber scaffolds,the modified scaffolds realize the uniform lithium metal deposition without dendrites and the improved cycle life in symmetric batteries.When the charging/discharging current density is 1 m A cm-2,the symmetric batteries can achieve stable cycle over 475 h with a low hysteresis voltage of 21.3 m V.Although the Au nanoparticles decorated on glass fiber scaffold can guide the lithium metal nucleation,during the progress of lithium deposition,the slow lithium ion transport leads to huge concentration polarization,which leads to the uneven lithium metal deposition.In order to solve the problem of slow lithium ion transport during cycling,the mixed electron-ion conductor network was designed based on glass fiber scaffolds.Porous Cu O-C composite layer was modified on the surface of glass fiber films by hightemperature carbonization of Metal-Organic Frameworks HKUST-1,and Cu O was transformed into Cu particles and Li2 O by lithium ion insertion reaction.The Cu and amorphous carbon formed by the reaction constitute the conductive network.At the same time,a widely distributed ion transport network was formed by Li2 O inside the modified layer.Based on the mixed ion-electron conductor network,the symmetric batteries can stably cycle more than 1100 h at the current density of 1 m A cm-2.The cycling lives decrease rapidly at high polarization current density(> 5 m A cm-2)although the mixed ion-electron conductor network can accelerate the lithium ion transport.In order to simultaneously solve the uneven nucleation of lithium on the scaffold and the slow transport of lithium ion,Sn Se-C composite layer was modified on the glass fiber scaffold.The Sn Se-C composite was in-situ converted to Sn and Li2 Se at the first discharge stage,and the Sn metal and lithium further reacted to form Li-Sn alloy.Due to the low nucleation barrier of lithium deposition on Li-Sn alloy,the lithiophilic alloy layer exhibits fast electron transfer kinetics behavior.Meanwhile,the reversible alloying process ensures the continuous low nucleation overpotential during cycling.The Li2 Se generated by the conversion reaction has high lithium ion conductivity,which helps to improve lithium ion transport rate,reduce the concentration polarization and realize the uniform distribution of lithium ion.Due to the synergistic effect of Li-Sn alloy and Li2 Se,the three-dimensional glass fiber scaffold modified by Sn Se-C composite layer realizes the dendrite-free lithium deposition and significantly improves the coulombic efficiency and cycle life.When the current density is 1 m A cm-2,the Li/Sn Se-C anode can stably cycle more than 1100 h with low deposition overpotential of 18 m V.Even if the current density increases to 5 m A cm-2,the Li/Sn Se-C anode can still achieve stable cycle over 250 cycles.In addition to the dendrite growth problem,continuous side reactions seriously affect the coulombic efficiency and cycling stability of lithium metal anodes.Therefore,in order to achieve uniform deposition of lithium metal on the anode surface and avoid decompositions of electrolyte,uniform Sn-MOF layer was modified on the surface of polyaniline/glass fiber scaffold by cation exchange reaction.The Sn-MOF layer contains plenty of porous channels and anion [Sn2(bdc)3]2-framework sites,which promotes the combination of lithium ion with anion framework sites and effective transport in the pore channels.The Sn-MOF layer with fast lithium ion transport,can effectively reduce the concentration gradient on the electrode surface and realize the uniform distribution of lithium ions.More importantly,the Sn-MOFs layer avoids the direct contact between lithium metal and electrolyte,and reduces side reactions in cycle.Based on the Sn-MOF layer modified polyaniline/glass fiber three-dimensional scaffolds,the lithium metal anode successfully avoids the growth of lithium dendrites,and achieves improved the coulombic efficiency and cycle life.When the current density is 1 m A cm-2,the symmetric batteries show the best long cycle performance and can stably cycle more than 1500 h.