Electrochemical Performance And Mechanism Of Dendrite-free Li-metal Battery Modified By Diamond Like Carbon Separator

Commercial lithium-ion batteries can not meet the demand of high energy density in the existing market currently,so it is imperative to develop the next generation of high specific energy batteries.In the next generation of high specific energy batteries,rechargeable Li-metal batteries(LMBs)as a high energy density battery have become a new research hotspot.However,the practical application of LMBs is hindered by a series of hazards caused by the formation of non-uniform lithium dendrites on the Li-metal anode.The inhibition of lithium dendrites has become a major chalenge for the constructing high-performance LMBs.The basic principles underpinning lithium dendrite growth comprise the transport of cations/anions in electrolyte,electron coupled Li-ion transfer on anode,and chemical/mechanical evolutions of anode-electrolyte interphase.Based on the above principle,how to control the growth of lithium dendrite effectively is the main problem of LMBs.Although great progress has been made,the problem of lithium dendrite is still very prominent,which needs further understanding and research.In this study,a new strategy of diamond-like carbon(DLC)coating deposited on polypropylene(PP)separator by magnetron sputtering technology was proposed.After the PP-DLC separator was assembled into lithium metal battery,it was transformed into high modulus diamond-like carbon(PP-DLC)composite separator with super lithium ion conduction performance by in-situ chemical lithium ion.DLC coating has excelent chemical corrosion resistance,electrical insulation and high Young's modulus(?100 GPa),which can effectively prevent the growth of Li dendrite(the young's modulus of Li dendrite is?6.9 GPa).In addition,the high modulus PP-DLC separator enables the lithium metal anode to achieve unprecedented cycle efficiency and maintain almost complete structure after long cycle.Among them,Li||Li symmetrical cell based on PP-DLC separator shows uniform dendrite-free Li deposition,Li||Cu half cell still has 98.7%Coulombic efficiency after 450 cycles,and Li||NCM/LFP full cels show good long cycle stability even under high cathode active mass loading(?9 mg cm^-2).Using magnetron sputtering technology combined with carbon target to deposit a DLC layer on PP separator,the operation process is simple,and mass production can be realized.In order to clarify the mechanism of the excelent electrochemical reaction of DLC layer for LMBs.In this paper,theoretical calculation and experimental analysis are combined to carry our in-depth research.As a typical amorphous material,DLC is isotropic,so the DLC coating after lithium can be used as the conduction channel of lithium ion,so that lithium ion can be uniformly deposited on the surface of lithium anode after passing through the separator.For this reason,we use the first principles calculation to prove that when the lithium metal contacts the DLC film of electronic insulation,it will be gradually lithiated,which will transform the DLC coating into a fast lithium-ion conductor.The above conclusion was confirmed by XPS and GD-OES analysis of the assembled separator.Subsequently,the finite element method(FEM)was used to simulate the diffusion behavior of Li-ions passing through the PP-DLC separator.The results indicating that the PP-DLC separator can uniformly redistribute Li-ions,which will promote the homogeneous nucleation of Li-ions on the Li-metal anode to inhibit the growth of Li-dendrites.