Protective spinel coating for Li1.17 Ni0.17 Mn0.50 Co0.17 O2 cathode for Li-ion batteries through single-source precursor approach

Abstract

The Li1.17 Ni0.17 Mn0.50 Co0.17 O2 Li-rich NMC positive electrode (cathode) for lithium-ion batteries has been coated with nanocrystals of the LiMn1.5 Co0.5 O4 high-voltage spinel cathode material. The coating was applied through a single-source precursor approach by a deposition of the molecular precursor LiMn1.5 Co0.5 (thd)5 (thd = 2,2,6,6-tetramethyl-3,5-heptanedionate) dissolved in diethyl ether, followed by thermal decomposition at 400◦ C inair resulting in a chemically homogeneous cubic spinel. The structure and chemical composition of the coatings, deposited on the model SiO2 spheres and Li-rich NMC crystallites, were analyzed using powder X-ray diffraction, electron diffraction, high angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), and energy-dispersive X-ray (EDX) mapping. The coated material containing 12 wt.% of spinel demonstrates a significantly improved first cycle Coulombic efficiency of 92% with a high first cycle discharge capacity of 290 mAhg−1. The coating also improves the capacity and voltage retention monitored over 25 galvanostatic charge–discharge cycles, although a complete suppression of the capacity and voltage fade is not achieved.