Tailoring Alumina Based Interphases on Lithium Ion Cathodes

In this work, artificial aluminum-bearing interphases are formed on LiNi0.5Mn0.3Co0.2O2 (NMC532) cathodes via wet-chemical surface treatments with different solvents, aluminum precursors, loading levels, and annealing conditions. The effects of different surface-treatment conditions on interphase chemistries, morphologies, and local atomic environments are studied with the combination of surface-sensitive electron microscopy and local-probe solid state nuclear magnetic resonance techniques. A variation of Al2O3 , LiAlO2, and other lithium-bearing species with different phases and morphologies are formed as an interphase on top of NMC532, controlled by the polarity of solvent systems, the corrosivity of aluminum salts, the initial alumina loading, and the annealing temperature. The nature of these initial surface interphases shows great influence on electrode impedance, initial capacities, and capacity retention rates in electrochemical tests. Post-electrochemistry characterizations on cycled cathodes show that surface LiAlO2 phases are relatively stable against the potential HF etching, whereas Al2O3 is reacted and consumed. Both half-cell and full-cell testing results of cathodes treated by optimized protocols demonstrate remarkable improvements in the capacity retention compared with the baseline. These fundamental understandings on interphase chemistries provide deep insights to the control of cathode surfaces and map-out important guidelines for the design of scalable cathode coatings. (C) The Author(s) 2018. Published by ECS.