LiFSI to improve lithium deposition in carbonate electrolyte

Abstract

Lithium metal is a promising anode material for the secondary lithium batteries due to its high specific capacity and low redox potential. However, these batteries cannot be commercially applied before severe issues can be well addressed such as the low stripping/plating capacity ratio and uncontrolled growth of dendrites of the lithium metal. Although the lithium can be plated/stripped stably for hundreds of cycles in the half cells, the narrow electrochemical window restricts the application of the ether-based electrolytes in high-voltage lithium batteries. Herein, we evaluate the feasibility of using lithium bis(fluorosulfonyl)imide (LiFSI) as the salt to improve the cycling stability of lithium in a carbonate electrolyte in which a stable solid electrolyte interphase (SEI) film is otherwise not available to protect the metallic lithium. It is found that LiFSI effectively suppresses the generation of “dead” lithium and the side reactions by forming a LiF-rich and compact SEI layer on top of the deposited lithium and therefore stabilizes the lithium plating/stripping cycling in the carbonate electrolyte. As a verification to these properties, the long-term cycling performance of a Li||Li4Ti5O12 cell with limited lithium loading is evaluated in the LiFSI-carbonate electrolyte. Our findings indicate that LiFSI-carbonate electrolyte can be a promising solution to the high-voltage secondary lithium batteries.