Correlation between Battery Performance and Lithium Ion Diffusion in Glyme–Lithium Bis(trifluoromethanesulfonyl)amide Equimolar Complexes

Abstract

Li+ cation diffusion processes during electrochemical reactions in molten glyme–Li[TFSA] (TFSA: bis(trifluoromethanesulfonyl) amide) equimolar complexes were explored in detail. The correlation between the Li+ limiting current density under one-dimensional finite-diffusion conditions and rate capability of [Li metal foil | electrolyte | porous LiCoO2 cathode sheet] electrochemical cells was explored. The diffusion processes in the vicinity of LiCoO2 single particles were also studied using a microelectrode technique. Electrochemical properties of the particles in the electrolytes were characterized by using micrometer-sized particles in contact with a metal microfilament encapsulated in a glass capillary, under conditions where the Li+ cations around the particles could have spherical diffusion profiles. A comparison of the electrochemical behaviors of the LiCoO2 sheet and the single-particle electrode in a typical organic electrolyte (LiClO4 dissolved in propylene carbonate), in a binary ionic liquid (Li[TFSA] dissolved in N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium bis(trifluoromethanesulfonyl)amide), and in the molten complex ([Li(glyme)1][TFSA]) clearly revealed that the Li+ cation flux in the electrolytes dominates the rate capability of the cells using the porous LiCoO2 cathode sheet.