Fabrication and characterization of high energy density lithium-rich nickel manganese cobalt oxide cathode thin films

Journal Article · Wed Jan 01 00:00:00 EST 2014 · Journal of Power Sources

OSTI ID:1133538

Baggetto, Loic ^[1]; Mohanty, Debasish ^[1]; Meisner, Roberta Ann ^[1]; Daniel, Claus ^[1]; Wood, III, David L ^[1]; Dudney, Nancy J ^[1]; Veith, Gabriel M ^[1]

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1. ORNL

This paper reports a method to prepare Li-rich NMC (Li1.2Mn0.55Ni0.15Co0.1O2) thin film cathodes for Li-ion batteries using magnetron sputtering and post-annealing in O2. The use of thin films with no binder and conductive additives enables to study in detail the surface reaction chemistry upon cycling as well as the microstructural changes in the bulk. We show that it is essential to control the deposition pressure to obtain the expected layered(R-3m)-layered(C2/m) structure, thus providing large reversible capacities up to 270 mAh g-1 and voltage profiles close to those expected. This is substantiated by TEM/SAED results showing that the films consist of a layered structure with trigonal symmetry in which Li/TM ordering is achieved. The study of various XPS core levels determines that the surface is comprised of Mn4+, Co3+ and Ni2+ cations inside an O2- framework. The losses mechanisms are studied during long cycling. After 184 cycles, the microstructure does not reveal the presence of Li/TM ordering, which supports that Li2MnO3 conversion is irreversible. In addition, we characterize that the surface chemistry evolves significantly upon cycling. The surface of cycled discharged electrodes is mostly made of inorganic species (LiF, Lix POy Fz , LixPFy), along with small amounts of organic species with C-O and O-C=O groups such as PEO, LiOR and LiCO2R. Moreover, the results support that Ni and Co migrate into the bulk whereas Mn is enriched at the surface. In the case of Mn, the reduction of Mn4+ into Mn3+ is clearly evidenced, as expected from the activation of Li2MnO3 domains.

• Research Organization: Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). High Temperature Materials Lab. (HTML)
• Sponsoring Organization: USDOE Office of Science (SC)
• DOE Contract Number: DE-AC05-00OR22725
• OSTI ID: 1133538
• Journal Information: Journal of Power Sources, Vol. 4
• Country of Publication: United States
• Language: English