Graphene Oxide over-Layer on Liquid Metal Coated Cu Current Collector for Improved Cycle Performance of Lithium Metal Anode

Abstract

Lithium metal is a promising anode material for Li-ion batteries because of its high specific capacity and negative electrochemical potential. However, there are two major challenges that need to be overcome before it can be used in practical applications: (1) Formation of dendrites that can cause short circuit of the cell leading to safety issues and (2) decomposition of electrolyte when contacting the reactive lithium metal that shortens the cycle lifetime. Keys to realize the lithium metal anode for practical application is to enable uniform deposition of lithium metal preventing dendrites and develop stable solid electrolyte interface (SEI) layer between lithium metal and the electrolyte.In this work, we propose a liquid metal (LM) coated on a copper current collector with graphene oxide (GO) overlayer to grow a stable SEI to uniformly deposit Li and protect it from direct contact with the electrolyte by SEI grown on GO. First, preconditioning was performed to develop SEI on the top layer of the anode. Ga-Sn-In alloy, which is in a liquid state at room temperature, inproves wetting of lithium promoting the uniform deposition and prevents the nucleation of the dendrites. Due to the high wettability of the LM against lithium and the SEI layer, the lithium deposition takes place between the LM and the to SEI layer preventing direct contact of lithium with the electrolyte and undesired chemical reactions.The effect of GO/LM coating was verified using a Li-Li symmetric cell. The result showed significant reduction in the reaction overpotentials on compared with LM coated and bare Cu current collectors. The low and symmetric reaction potentials were observed even after increasing the current density and areal capacity to 4.0 mA/cm2 and 8.0 mAh/cm2, respectively. Scanning electron microscopy (SEM) analysis of GO/LM coating before and after the conditioning and Li pre-deposition revealed even after the large amount of Li plating (> 6 mAh/cm2) the surface remains flat without any dendrites. This indicates a stable artificial SEI layer was formed and Li was deposited between the LM and the SEI layer. A full-cell test using LiNi1/3Co1/3Mn1/3O2 cathode with GO/LM anode showed much improvement in the cycle lifetime compared with the simple LM-coated and bare Cu. Figure caption : SEM images of SEI development and lithium plating on GO/LM coated Cu current collector. Figure 1