| Lithium metal as the lightest metal(0.534 g cm-3),which has a highest theoretical specific capacity(3860 m Ah g-1)and lowest reduction potential（-3.04 V,vs.SHE）,is the next generation of high capacity secondary battery anode material,named"holy grail".However,the inhomogeneous deposition/stripping processes of the lithium metal will form dendrites,leading to low coulombic efficiency（CE）,fast capacity fade,large consumption of electrolyte and unsafety.These issues in lithium metal anode could be solved by tailoring anode structures and modified Solid electrolyte interphase（SEI）.In this thesis,a new strategy of in situ generation of stable SEI on porous structures in lithium metal was proposed based on the fluorocarbon doped nanotubes（CNTs）and the stabilization of the anode,which is a new approach for the preparation of practical lithium metal anode.The electrochemical performances of lithium metal batteries（LMBs）and the deposition/stripping mechanism of LMBs were studied.The main research and conclusions are as follows:（1）In this study,fluorine was doped on the surface of CNTs by a simple method.By infrared spectroscopy,X-ray photoelectron spectroscopy,Raman spectroscopy and transmission electron microscopy,it was found that theπ-πbond on the surface of CNTs was broken during the treatment process to form CxF bond,and oxygen-containing functional groups such as carboxyl groups,carbonyl groups and hydroxyl groups were also added,which make lithiophilic for CNTs.Moreover,the affinity between CNTs and electrolyte was studied,and it was found that the fluorination process greatly improved the affinity between them,and improved the efficiency ofthe redox reaction on the negative electrode.In addition,the DFT was used to calculate the binding energy between the groups of fluorinated CNTs and lithium ions.The results are consistent with the experimental results.The EDS results show that the reaction of fluorine groups with lithium ions leads to the formation of in situ enriched Li F in SEI.The in situ Li F strategy can effectively reduce the grain size of inorganic components in SEI,and improve the ionic conductivity of SEI,thereby provide more Li-ion transport channels.（2）Electrochemical tests show that the modified lithium anode with higher cyclic stability.The SEM results show that SEI has obvious inhibition on the growth of the dendrites.The average CE of lithium metal in semi-symmetric battery cycle is increased obviously（99.58%）.Li-FCMF|LFP battery has more stable cycle performance,which remains in 135 m Ah g-1（0.5 C）after about 500 cycles,the corresponding capacity remain at a rate of 95.1%.The deposition/stripping cyclic performance of the Li-FCMF composite symmetric batteries was also tested under the current density of 0.5 m A cm-2 and the condition of 0.25 m Ah cm-2.It runs over1600 h（800 cycles）,and its polarization voltage is only 20.5 m V at cycles.In this work,a novel dendrite inhibition strategy is proposed,which can effectively affect the composition and structure of SEI on the surface of lithium metal anode,thereby improving the Li+transport and deposition behaviors on the surface of anode.（3）The three-dimensional porous structure of the FCMF provides the initial lithium metal accommodation space for the deposition of Lithium metal.At the same time,on the surface of CNTs,CxF bonds contact with lithium atoms to generate Li F through redox reaction.When the three-dimensional porous framework was filled,the high conductivity of CNTs improved the efficiency of the reaction between lithium metal and CxF,resulting in the enrichment of Li F in the surface SEI.The modified SEI has high ionic conductivity and guides the homogeneous deposition of lithium metal,and withoutlithium dendrites occured.It maybe due to the rich Li F in SEI that solve the deficiency of tariling lithium metal can only accommodate a certain amount of lithium metal,and rich in Li F SEI film can also inhibit the occurrence of side reactions,so as to improve the cycling performance of lithium metal anode. |
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