A Study Of Solid Electrolyte Interphase Of Lithium Metal Anode

Lithium metal is considered to be an ideal anode material for the next generation battery system,artributing to its high specific energy(3860 mAh g-1),low reduction potential(-3.04 V vs standard hydrogen electrode)and low density(0.59 g cm 3).However,due to the growth of Lithium dendrite and low Coulombic efficiency,the practical application of Lithium metal is limited.Solid Electrolyte Interphace(SEI)is a transitional phase with Li+ ion conductivity and electronic insulation,which is produced by side reaction between Lithium and electrolyte.It can physically isolate the contact between Li anode and electrolyte,and passivating the further consumption of electrolyte.The mechanical strength of native SEI is too low to accommodate the huge volume changes before and after the Lithium deposition/striping,resulting in the non-uniform deposition of Lithium metal at the rupture of SEI,which aggravates the growth of the Lithium dendrite.Therefore,if the Li ions conductivity is guaranteed,increasing the mechanical strength of SEI can alleviate even inhibit the growth of Lithium dendrite.Based on the above thought,two methods are adopted to modify the native SEI as below,which alleviates the growth of the Lithium dendrite and improves the Coulombic efficiency and the cycle life of the battery.1.In Situ Formating of a chemically stable and mechanically strong SEI.The side reaction between Organic sulfuric esters and Li anode is prior to solvent and Li salt.Based on this reaction,we added a micro amount of sulfates in the electrolyte to induce the reaction of Lithium metal and sulfate to produce a layer of Li2O/Li2S-rich SEI.The SEI has a higher Young’s modulus and better ion conductivity compared with native SEI,effectively alleviating the growth of Lithium dendrite.The cycle stability of Cu|Li half cell has been improved to 160 cycles with over 97%of Coulombic efficiency.2.Li3N artificial SEI with high mechanical strength and high ion conductivity.A solid electrolyte membrane of Li3N with high mechanical strength can be obtained on the surface of Li anode by passing the N2 flow through the Li foil surface.The artificial SEI instead of the native SEI can inhibit the growth of Lithium dendrite and improve the cycling performance of Li anode.In this work,the reaction conditions were optimized,and the Li3N SEI coated Li anode with thickness of range in 100 nm～10 m was prepared.The Li|Li cell can cycle over 700 h under a current density of 0.5 mA cm-2.The cycle life and efficiency of full cells matched with NCM cathode were improved as well.