Liquid Metal Coating for Improving Li-Anode Cyclability

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) electrolyte consumption and 2) dendrite. Lithium being thermodynamically reactive, it decomposes the electrolyte in contact. The dendrite causes short circuit in the battery creating safety issues, and the detachment of the dendrite from the electrode leads to irreversible capacity loss. The exposure of fresh lithium surface associated with the chipping action leads to the further decomposition of the electrolyte.In this work, we propose a liquid metal (LM) as a semi-solid liquid interface (SSLI) layer to uniformly deposit Li and protect it from direct contact with the electrolyte. Ga-Sn-In alloy, which is in a liquid state at room temperature, was dispersed on a Li metal or directly on a copper current collector as a SSLI layer. Elements in the LM alloy with Li to form a “solid” layer. It is energetically favorable for Li to alloy with these elements than to plate on the film. This high “wettability” of the film against Li promote the uniform deposition and suppresses the nucleation of the dendrites. It will also prevent Li from directly contacting the electrolyte to mitigate undesired chemical reactions.The effect of LM coating was verified using a Li-Li symmetric cell. The cells without LM failed only after few cycles. The huge increase in the voltage corresponds to significant growth of SEI on the lithium electrode. On the other hand, the cell with LM coating was able to cycle for 100 cycles. A full-cell test using LiNi1/3Co1/3Mn1/3O2 cathode with copper current collector without excess Li was also tested. The result showed much improvement in the cycle lifetime with the LM coating. Scanning Electron Microscopy analysis of the coating layer was performed after the battery cycle test to confirm the ability of the LM coating to reduce the formation of dendrite at the surface. Figure caption : SEM micrographs of (A) Cu current collector and (B) the surface after battery cycle test for with and without LM coating. Smooth LM coating was achieved to reduce the surface roughness on the Cu film, and the Li dendrite formation on the surface was reduced by the LM coating. Figure 1