A FTIR and Raman study of spontaneous reactions occurring at the LiNiyCo(l-y)O2 electrode/non-aqueous electrolyte interface

Spontaneous reactions occurring at the surface of LiNiyCo(1-y) O-2-based el ectrodes during contact with non-aqueous organic electrolytes have been inv estigated by FTIR and Raman spectroscopy. It is found that several types of compounds and/or functional groups are formed on the electrode surface and that these compounds appear to be dependent on the type of electrolyte use d. Thus, for a LiClO4-propylene carbonate (PC) electrolyte, the main reacti on is formation of Li-carbonate, whereas in the case of LiPF6-ethylene carb onate/dimethyl carbonate (EC/DMC) electrolyte formation of P-, O- and F-con taining compounds dominate. Spectroscopic data also show a variation of the LiNi(1-y)CoyO2 crystalline structure during storage in an electrolyte whic h probably is due to a spontaneous deintercalation of the Li ions. An analy sis of the newly formed species is presented and possible reaction mechanis ms are discussed. (C) 2001 Elsevier Science B.V. All rights reserved.