Suppression of lithium dendrite growth by introducing a low reduction potential complex cation in the electrolyte

A low reduction potential complex cation (LRPCC) N-methyl-N-butylpiperidinium was introduced to the LiPF₆/EC/DEC electrolyte to investigate its effect on the interface properties of a lithium anode. The reduction of N-methyl-N-butylpiperidinium LRPCC is analyzed by density functional theory (DFT) calculations using the Gaussian 09 package. Lithium dendrites and fractured metal Li are examined by scanning electron microscopy (SEM) and X-ray diffraction (XRD) respectively. The solid electrolyte interface (SEI) film of the metal Li surface is analyzed by X-ray photoelectron spectroscopy (XPS). It is indicated that the LUMO energy level of the LRPCC is higher than lithium ion's one. It exhibits a better electrostatic shield around the initial protuberances, reducing the growth of the Li dendrites. The shield effect could play a role even at a higher current density and a wider electrostatic repulsion shield owing to the stronger reduction resistance ability and the higher concentration of the LRPCC. It is demonstrated that there is an interaction among Li dendrites, dead Li and the SEI film. It is shown that the electrolyte containing the complex ion can effectively enhance the coulombic efficiency of Li deposition as well.