Characterization of lithium electrode in lithium imides/ethylene carbonate, and cyclic ether electrolytes - I. Surface morphology and lithium cycling efficiency

The surface and cross-sectional morphologies of deposited lithium on a nickel substrate in LiN(SO2C2F5)(2) (LiBETI) electrolytes with ethylene carbonate (EC) + tetrahydropyran (THP), dimethoxyethane, dimethylcarbonate (DMC), propylenecarbonate (PC), gamma-butyrolactone (GBL) (1: 1) binary solvents were investigated by scanning electron microscopy observation. Dendritic morphology of deposited lithium was observed in DMC-, PC-, and GBL-containing solvents. However, deposited lithium in a EC + THP electrolyte exhibited a fine particle-like morphology and had a thinner surface film. The EC + THP electrolyte provided excellent performance based on the results of cycling characteristics using a Li/LiCoO2 cell and Li/Ni cell. The morphology of deposited lithium in an EC + tetrahydrofuran electrolyte was strongly influenced by the kind of solutes. In LiBETI electrolyte, freshly deposited lithium exhibited uniform and fine particle-like morphology. In contrast, dendritic morphology was observed in LiN(SO2C2F5)(2) (LiTFSI) electrolyte, resulting in a subsequent decrease in the lithium cycling efficiency. Electrolyte temperature was also an important factor influencing the lithium surface and efficiency. The use of LiTFSI electrolyte at elevated temperatures could suppress dendritic formation, resulting in excellent efficiency and cycling characteristics. We confirmed that the lithium surface morphology correlated well with the lithium cycling efficiency and the efficiency was strongly influenced by combinations of solvents and solutes. (C) 2004 The Electrochemical Society.