Investigation And Protection Of The Lithium Metal Anode In Lithium Metal Battery

The metal lithium anode is the ultimate ideal negative electrode for high energy density batteries,for its most negative electrode potential(-3.045V vs.standard hydrogen electrode)and the lightest mole mass and density in the metal(6.9 g/mol,0.534 g/cm3).In the background of large developments of the lithium-sulfur,lithium-air and solid-state battery,the lithium metal anode re-pull into the scientist and entrepreneur’s vision.Metal lithium has a high reactivity,uneven deposition and infinite volume expansion,which is the three mountains faced in commercial application.Scientists have proposed many methods for the modification of metallic lithium anode.In the nonaqueous battery system,there are eight aspects can be considered which contain the composited Li-C electrode,coated lithium electrode,the development of new solvent-lithium salt system,exploring additives,coated separator,electrode structure designation,alloy electrode and charging-discharging mode.For the above problems of lithium metal anode,we carried out the following three studies:1)We designed a flattened lithium electrode embedded in a stainless steel sample holder and investigated how the plating/stripping order impact on the surface.In the process of lithium firstly stripping and then plating,moss and dendritic lithium mainly appeared in the hole.Some of them did not disappear when the cell was discharged in the second cycle,indicating the formation of dead lithium" on the lithium metal anode.In the process of lithium deposition on the flat metal lithium surface,after the first charge,the granular lithium is found on the surface,after the first discharge,a considerable quantity of the granular lithium still existed on the surface,and there are some holes appeared on the lithium surface.We believe that the presence of dendritic,granular,moss-like lithium and pore structure is related to the uneven SEI formation on the surface of the lithium electrode and its composition.Therefore,the coverage degree and uniformity of the SEI on the surface of the lithium electrode are an important factor affecting the deposition and delamination of the metal and the cycling performance of the lithium metal.2)We used the SPM equipment platform to develop the force curve and PF-TUNA method to study the metal lithium surface SEI evaluation and struc-ture.The distribution of Young’s modulus on the surface of lithium thin films were characterized by force curve method.The structure and distribution of the Young’s modulus of SEI on the surface of the lithium film after the immersion in the electrolyte were studied.It was found that the surface of the metal lithi-um formed a multi-layer SEI protective layer after immersion.And the high Young’s modulus and the low Young’s modulus layer are alternately distributed.By PF-TUNA method,the size and micro-distribution of the surface current of the metal lithium anode were analyzed for the first time.And the changes of the morphology and current distribution of lithium under different charge and dis-charge state were studied.From a micro perspective,we proposed a mechanism of lithium ion deposition/dissolution on the lithium surface.That is,When the lithium ion is enriched on the surface of the lithium metal,both the deposition and dissociation of lithium are beneficial to the surface morphology of the lithi-um metal and the growth of the SEI.Therefore,in order to achieve the state of high lithium ion concentration on the surface of the metal anode,one of the strategy is low current charging and high current discharging.Which provides a theoretical basis for better design of lithium batteries.3)We have proposed several methods for coating the lithium buffer layer on the surface of metallic lithium from the point of view with the metal lithium treatment of different phase precursors.Modified lithium with an atmospheric treatment method,Li2S-P2-S5 additive protected lithium metal anode,LiPON coated metal lithium and Cu3N coated metal lithium.By further optimizing the process,we obtain a better protected lithium anode and a better result in lithium symmetrical batteries,lithium copper batteries,lithium-sulfur battery system.Based on the above efforts,we have clarified the effect of lithium deposition-stripping sequence on the lithium metal electrode,the structure and distribution of the SEI on the lithium surface and its evolution during the electrochemical process,and then we have modified the lithium metal anode by some means,which get a certain good results.All of these works provide a basis for the research of solid-state lithium metal batteries.