Highly Stable Lithium Metal Anode:Structure Design And Electrochemical Performance Research

Lithium(Li)metal,as an anode material for batteries,possesses ten times higher theoretical specific capacity(3860 mA h g-1)than that of graphite electrode(372 mA h g-1),so it has a broad prospect for application.However,there are a series of problems hindering its development in practical application,including the following three aspects:(1)The morphology of Li metal tends to be porous and dendritic during the cycling process,which further aggravates the side reaction with the electrolyte and eventually leads to serious powderization of the electrode.(2)Li metal has a high activity and the lowest redox potential(-3.04 V vs SHE).As a result,violent side reactions would occur in the cycle process,which would cause continuous consumption of active substances and electrolyte,and serious passivation of electrode.(3)Due to the intrinsic configuration of batteries,the deposition of Li metal would cause extremely unbalanced internal stress,so there is a tendency to grow dendrites in the area with lower stress,which further aggravates the side reaction.Finally,the performance and span life of Li metal batteries are reduced.In view of the above problem,we effectively reduced the uneven deposition of Li metal and interface reaction through designing current collectors and building stable surface layers,so as to realize stable performance and long span life in Li metal batteries.The specific research contents are as follows:1.Dendrite-free Li metal deposition was realized by silver(Ag)nanoparticles,which could induce uniform spherical deposition of Li metal.In this work,the uniform spherical deposition of Li metal on the surface was controlled by a copper(Cu)collector with uniform distribution of Ag nanoparticles,and the dendrite growth caused by uneven deposition was prevented.In addition,due to the presence of Ag metal on the electrode surface,the deposition overpotential of Li metal can be obviously reduced,which makes Li metal deposition proceed in the mixed control region of diffusion and kinetic.In the meanwhile,a larger deposition current was obtained.The half-battery can achieve coulombic efficiency of 99%;The symmetrical battery can cycle stably for 800 h and maintain a low overpotential of 24 mV.The Li‖LiFePO4 battery still has a capacity of 140 mA h g-1 after 150 cycles.2.Elastic three-dimensional lipophilic material realizes uniform stress distribution and alleviated dendrite growth in Li metal battery.In our study,we found that stress is another important factor to induce dendrite growth.The deposition and stripping of Li metal in Cu foil and rigid 3D collector induce uneven stress distribution,which promotes the growth of Li metal to a stress-free direction and forms dendrite.This work uses 3D graphene with elastic property as the current collector to relieve the uneven stress distribution in the battery to solve the problem of dendrite growth.Firstly,by controlling the reduction methods of graphene oxide(GO),the GO with the maximum stress and strain capacity was served as the current collector.Secondly,Ag particles were introduced as nucleation sites to induce uniform deposition of Li metal inside.Finally,the dynamically uniform distribution of stress inside the battery is realized,and no dendrite growth occurs in Li metal anode.The symmetrical battery can achieve stable cycle performance of more than 1900 h.The Li‖LiNi0.8Co0.1Mn0.1O2 battery can still maintain a capacity of 95 mA h cm-2 at 10 C.3.The lithium chloride(LiCl)and polysilane composite surface protective layer was constructed by in-situ protective reaction of Li metal and chlorosilane,which can work in lithium oxygen(Li-O2)battery.The side reaction of Li metal anode is another factor causing the attenuation of battery performance.Therefore,we used the wurtz reaction between Li metal and dichlorodimethylsilane,generating LiCl and silane compound protective layer in Li metal surface,to prevent the corrosion of electrolyte and oxygen to Li metal.In addition,the protective layer can not only realize uniform lithium deposition,but also eliminate the primary Li dendrite and obtain dendrite-free of Li metal.The symmetric battery can cycle stably for 2800 h at 1 mA cm-2 and the overpotential maintains at 21 mV.The performance of Li-O2 battery has been significantly improved with stable cycle of more than 200 cycles;The Li‖LiNi0.8Co0.1Mn0.1O2 battery has a stable cycle of 300 cycles and still maintains a capacity of 100 mA h g-1.4.The surface protective layer of lithium amalgam was constructed by in-situ reaction of Li metal and liquid mercury,which can be used in Li-O2 battery.As a common way to alleviate metal corrosion,alloy can also be used in Li metal anode protection and improve the stability of Li metal.Mercury is the only liquid metal at room temperature,and can form alloys with most metals.Therefore,we use the rapid alloy reaction between Li metal and mercury to form Li3Hg phase on the surface of Li metal.This surface protection layer remains stable and smooth in the oxygen-rich environment.The alloy layer can achieve uniform deposition of Li metal,inhibit the dendrite growth and prevent the corrosion of Li metal by electrolyte and oxygen.The symmetrical battery can cycle stably for more than 6000 h and the overpotential maintains at～20 mV.The corresponding Li-O2 battery can cycle more than 100 times.