PNNL

Abstract

The separator is an important component in rechargeable lithium (Li) metal batteries, however, less attention has been focused on it. In this work, several representative separators, such as polyethylene, polypropylene, and such polyolefin separators with coatings of ceramic and polymeric materials, were selected to assemble into Li||Cu and Li||Li coin cells to test the Coulombic efficiency values of Li metal and the cycling stability in a low voltage environment less than 1 V. Moreover, two representative electrolytes of LiPF6 and LiTFSI-LiBOB in carbonate solvent mixture were also employed to systematically study their interactions with the separators in Li metal cells. It was found that the separators could largely affect the Coulombic efficiency values and cycling stability of Li metal cells, especially when using the LiPF6 electrolyte, which is probably due to the effect of the trace amount of HF in the LiPF6 electrolyte. Among these separators, polyethylene separator is the most stable one with Li metal. This work gave some reasonable explanations for the above phenomena, which could provide references for Li metal battery studies when employing Li||Cu and Li||Li cells conducted in the low voltage environment.