Preparation And Electrochemical Performance Of Flexible Carbon Nanofiber Membrane Doped With Manganese Compound For Interlayer Of Lithium Metal Battery

With the shortage of fossil fuel and the exacerbation of environmental pollution,it has aroused extensive attention for efficient energy storage technology and rechargeable devices.At present,lithium(Li)metal battery,including lithium-sulfur(Li-S)battery,lithium-oxygen(Li-O2)battery and other high energy Li metal based batteries,is regarded as one of the promising next-generation energy storage systems due to the high theoretical specific capacity,energy density and low cost.Meanwhile,metallic Li is also selected as great anode material because of its high theoretical specific capacity(3860 mAh g-1),ligh-weight(0.53g cm-3)and low redox electrochemical potential(-3.04V compared with the standard hydrogen electrode).Although Li metal based battery possesses potential advantages such as high energy density,excellent cycling stability,outstanding power density and long cycle life,there are still many challenges needing to be overcame for Li metal anode in practical application.The first one is the growth of the Li dendrite during Li stripping/plating process.According to the proposed theoretical mechanisms,the fomation of Li dendrite mainly attributes to hemispherical tips with high electric field attracting more Li ion,leading faster deposition on the surface and finally coming into being dendrites.Once the growth of Li dendrite becomes uncontrollable during deposition process,which would lead to plenty of clusters of "dead Li" and the short circuit of battery,even safety hazard.The second one is the instability of solid electrolyte interphase(SEI)layer.The SEI layer is easily wrecked by the volume change and dendrite growth of Li anode during charge-discharge cycling process,which can cause low Coulombic efficiency,large consumption of electrolyte and short lifetime.Ultimately,these emerged shortcomings impede the commercialization of Li metal battery over the past decades.In this work,a novel flexible Mn-based carbon nanofiber interlayers were rationally designed and prepared by electro-blow spinning and carbonization method.Especially,the representative MnS carbon nanofiber(MnS-CNFs)film and MnF2 porous carbon nanofiber(MnF2-PCNFs)film were respectively applied as interlayer to combine with Li as composite anode to investigate their application performance.After systematic research,the cyclic stability of interlayer modified LCO-Li batteries(MnS-CNFs:initial capacity of 143 mAh g-1 and retention rate of 70%after 100 cycles,MnF2-PCNFS:initial capacity of 137 mAh g-1 and retention rate of 90%after100 cycles)were obviously improved when compared with pristine LCO-Li battery(initial capacity of 133 mAh g-1 and retention rate of 45%after 100 cycles)at the current density of 3 mA cm-2.The modified symmetric Li battery exhibits stable Li deposition-stripping behavior without cell short-circuit during 150 cycles.The higher performance of modified battery compared with pure Li metal battery might be attributed to the introduction of flexible Mn-based carbon nanofiber interlayers.On the one hand,the flexible films with self-support and porous structure could act as transitional layer to accommodate the volume expansion of Li metal and facilitate more Li insert into the interior/surface of carbon nanofibers.On the other hand,the 3D interconnected carbon nanofiber skeletons doped MnS and MnF2 could provide more active sites to guide the Li deposition and stripping more sufficient and homogeneous.