Interfacial Processes of Lithium Ion Batteries by FTIR Spectroscopy

Lithium-ion batteries (LIBs) are one of the important electrochemical power sources for low- or zero-emission hybrid electrical and electrical vehicles, energy-efficient cargo ships and locomotives, and aerospace in the modern society. The difficulties in mastering the electrode/electrolyte interface have slowed down the progress of LIBs. Interfacial processes of lithium ion batteries include mainly insertion/extraction of lithium ion, solvation/desolvation of lithium with solvents, formation and variation of solid electrolyte interphase (SEI) layer, and decomposition of electrolyte. Interfacial processes directly affect the efficiency of electrochemical energy conversion and storage, such as the cycling ability, the lifetime and the reversible capacity, as well as the safety issue of lithium ion batteries. The characterization of the interface processes at a molecular level by FTIR spectroscopy is one of the key subjects, as it is helpful for the improvement the performance of lithium ion batteries and development of non-aqueous theory. Recent progresses about the application of FTIR spectroscopy in lithium ion batteries are reviewed. This review put emphasis on; (a) the characterization of chemical composition and variation of SEI layer on cycled or aged electrode materials by ex situ FTIR spectroscopy, and (b) the investigation of decomposition of electrolyte, formation of SEI layer and the insertion/extraction of lithium ion by both in-situ FTIR reflection spectroscopy and in situ FTIR transmission spectroscopy.