Properties of Thin Lithium Metal Electrode in Carbonate Electrolytes

Abstract

The utilization of Li anode in Li-ion batteries is still illusive to date: In addition to the significant safety hazard, Li anode suffers from inferior cycle stability. Furthermore, the majority of the lab-scale investigations uses thick Li foils as the study subject, which can behave extremely differently from the practical Li anode. To provide a realistic baseline to evaluate the electrochemical performance of Li anode in liquid electrolytes, the electrochemical and micromorphological properties of thin Li film (50 µm) are investigated in this study. The deposition-stripping coulombic efficiency (CE) of the thin lithium electrode and the cycle life of the symmetric cell under various conditions are measured combined with microscopic and spectroscopic characterizations. The failure mechanism of the symmetric cells is also investigated. Our results indicates the average CE is strongly related to the cycling parameters including area capacity (depth of Li utilization), C rate and cycle number; and indicating loose relationship with the type of Li salts and concentration due to beneficial surface compounds. Meanwhile, CE has no correlation to the cycle lives of the symmetric cells, which is clearly dictated by the areal capacity and C rate. Our results also suggest that the failing of symmetric cells is due to “soft shorting” (direct contact of SEI covered Li) due to the separator breach induced by the drastic volume change of Li electrode during deposition.