Al-doped ZnO-Coated LiNi1/3Mn1/3Co1/3O2 Powder Electrodes: The Effect of a Coating Layer on The Structural and Chemical Stability of The Electrode / Electrolyte Interface

Makvandi A.; Wolff M.; Lobe S.; Heidrich B.; Peterlechner M.; Gammer C.; Uhlenbruck S.; Winter M.; Wilde G.

Abstract

LiNi1/3Mn1/3Co1/3O2 (NMC-111) is one of the most popular cathode materials in Li-ion batteries. However, chemical and structural instabilities of the cathode/electrolyte interface at high charge cut-off voltages cause capacity fading. Surface modifications using metal oxides are promising candidates to suppress capacity fading. Here a systematic study on the degradation mechanism of an uncoated NMC-111 powder electrode is presented. Moreover, the effect of an Al-doped ZnO (Al:ZnO) coating layer on the structural and chemical stabilities of NMC-111 electrode cycled at high charge cut-off voltages is analyzed using X-ray photoelectron spectroscopy, scanning electron microscopy and analytical transmission electron microscopy as well as electrochemical testing. The coating is applied to commercial NMC-111 powder using a microwave-assisted sol-gel synthesis method. In the case of uncoated NMC-111 electrodes, pitting corrosion due to hydrofluoric acid attacking the electrode surface, cation mixing, and an irreversible phase transformation from a trigonal layered to a rock-salt phase occurs, causing capacity fading. While, in the case of Al:ZnO – coated NMC-111 electrodes, pitting corrosion, cation mixing, and the irreversible phase transformation are mitigated. Therefore, the capacity retention and rate capability are improved as the coating layer protects the electrode surface from the direct electrolyte exposure.