Interface Modification Of Lithium Anode And Optimization Of Electrochemical Performance

Nowadays,with the popularization of new energy technology in more and more fields;Lithium-ion batteries with graphite carbon materials as the negative electrode can no longer meet people’s demands for high energy density energy storage batteries.As the metal element with the lowest potential of the standard electrode（-3.04 V）,lithium has a very high theoretical specific capacity(3860 m Ah g^-1)and active electrochemical properties,which has prompted researchers to return their vision to the metal lithium anode.However,due to its chemical activity,lithium metal is prone to irreversible side reactions with electrolytes,thereby consuming a large amount of lithium metal and producing"dead lithium",resulting in a significant reduction in the coulombic efficiency and cycle life of the battery.In addition,the unstable and uneven solid electrolyte interface（SEI）layer can also lead to uneven lithium ion deposition,which seriously affects the cycle stability of the battery.These problems have seriously affected the commercial application of lithium anodes.Therefore,protecting the lithium anode and improving its cycle stability is the key to improving the battery life of lithium metal.In this paper,the uncontrollable growth of lithium dendrites and the cyclic stability of lithium anode are improved by constructing an organic-inorganic composite protective layer and an alloy protective layer on the surface of lithium metal.It includes the following three parts:Undecythioundecanoic acid was coated on the surface of lithium metal to react with lithium metal to form an organic-inorganic composite protective layer.Combined with XPS,SEM and electrochemical tests,it was found that the components such as Li₂S and lithium 11-mercaptoalkanate produced by the reaction could improve the lithium ion transport efficiency and achieve the effect of uniform lithium ion deposition,thereby significantly improving the cycle life of the battery,and the symmetrical battery was extended from 550 h to 2400 h in the ordinary system.The capacity retention rate of lithium iron phosphate batteries has also increased to 93%compared with 78%of ordinary systems.AlCl₃ solution is coated on the surface of lithium metal,and a uniform and dense alloy protective layer is formed in situ during the cycling process,and the lithiophilia of Li-Al alloy is used to further guide the uniform deposition of lithium ions and improve the stability of lithium anode during the cycling process.SEM shows that the protective layer can effectively reduce the production of"dead lithium"and the growth of lithium dendrites.The cycle life of symmetrical batteries at a current density of 0.1 m A cm^-2 is extended by more than 1200 h compared with ordinary systems.The Coulombic efficiency of Li/Cu cells（98%）also proves that the protective layer can effectively reduce the loss of lithium during cycling.Superhydrophobic SiO₂ was doped into PDMS and polymerized into an organic-inorganic composite protective film on the surface of lithium metal.The contact angle proves that the protective layer has the characteristics of hydrophobic（108°）electrophilic electrolyte（30°）,so that the lithium metal with the protective layer is stable for more than 40 minutes in the external environment with a humidity of 60%.Increased the cycle life of symmetrical cells containing 10,000 ppm water in the electrolyte from 50 h to more than 1,000 h.The electrochemical results and SEM plots also show that the protective layer can effectively reduce the lithium-ion transport barrier and inhibit the side reactions between lithium metal interfaces.After assembling the full battery with Li Fe PO₄,the capacity retention rate was above 90%after 200cycles at 1.0 C magnification.Compared with the bare lithium anode,it shows better rate performance and cycle stability.