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In Situ DRIFTS Analysis of Solid‐Electrolyte Interphase Formation on Li‐Rich Li 1.2 Ni 0.2 Mn 0.6 O 2 and LiCoO 2 Cathodes during Oxidative Electrolyte Decomposition
Author(s) -
Teshager Minbale Admas,
Lin Shawn D.,
Hwang BingJoe,
Wang FuMing,
Hy Sunny,
Haregewoin Atetegeb Meaza
Publication year - 2016
Publication title -
chemelectrochem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.182
H-Index - 59
ISSN - 2196-0216
DOI - 10.1002/celc.201500290
Subject(s) - electrolyte , chemistry , cathode , lithium (medication) , interphase , decomposition , transition metal , adsorption , analytical chemistry (journal) , inorganic chemistry , electrode , catalysis , medicine , organic chemistry , biology , genetics , endocrinology , biochemistry , chromatography
In situ diffuse reflectance infrared Fourier‐transformed spectroscopy (DRIFTS) investigations have been made to examine solid‐electrolyte interphase (SEI) formation on lithium‐rich Li 1.2 Ni 0.2 Mn 0.6 O 2 (LLNMO) and LiCoO 2 cathodes during first‐ and second‐cycle charging and discharging. This DRIFTS technique allows us to clarify SEI formation with different charging voltages. Both cathodes revealed the formation of the same surface species during first‐cycle charging, initially including ethylene carbonate (EC) adsorption, and SEI species, for example, ROCOF, RCOOR, Li 2 CO 3 , ROCO 2 Li, and PF x , are formed above the onset potential, namely 4.0 and 4.5 V for LiCoO 2 and LLNMO, respectively. The onset potentials correspond to the upper limit of the reversible redox potential range for transition‐metal couples (e.g. Co 3+ /Co 4+ in LiCoO 2 and Ni 2+ /Ni 4+ in LLNMO), which account for the intrinsic instability of these cathode materials. Such results suggest the participation of intermediate reactive oxygen species in SEI formation. SEI species continue to form during the discharge process when the potential is scanned cathodically below 3.6 and 4.0 V for LiCoO 2 and LLNMO, respectively. Similar SEI species are also observed during the second cycle charge–discharge over LLNMO, where additional oxidized species such as carboxylate (−COO−) and CO 2 are also found during charging. With the exception of PF x , all of the observed SEI species can be attributed to the oxidative decomposition of the organic solvent, EC. Finally, possible reaction mechanisms related to the oxidative decomposition of EC are discussed.