Novel Core−Shell-Structured Li[(Ni0.8Co0.2)0.8(Ni0.5Mn0.5)0.2]O2 via Coprecipitation as Positive Electrode Material for Lithium Secondary Batteries

Abstract

We have successfully synthesized a spherical core−shell structure based on Li[(Ni_0.8Co_0.2)_0.8(Ni_0.5Mn_0.5)_0.2]O₂ via a coprecipitation route. According to the careful examination by scanning electron microscopy (SEM), transmission electron microscopy energy-dispersive spectroscopy (TEM-EDS), and X-ray diffraction (XRD), it was found that the core−shell particle consisted of Li[Ni_0.8Co_0.2]O₂ as the core and Li[Ni_0.5Mn_0.5]O₂ as the shell, of which the thickness was estimated to be 1 to ∼1.5 μm. Both the core and shell were dense as confirmed by SEM. Though the core−shell-structured Li[(Ni_0.8Co_0.2)_0.8(Ni_0.5Mn_0.5)_0.2]O₂ delivered a slightly reduced initial discharge capacity, the capacity retention and thermal stability were significantly improved relative to those of the Li[Ni_0.8Co_0.2]O₂ electrode without the Li[Ni_0.5Mn_0.5]O₂ shell. The carbon/Li[Ni_0.8Co_0.2]O₂ pouch cell underwent an explosive ignition during the nail penetration test, whereas the carbon/Li[(Ni_0.8Co_0.2)_0.8(Ni_0.5Mn_0.5)_0.2]O₂ cell remained stable, demonstrating the superior thermal stability of the core−shell electrode. As a new positive electrode material, the core−shell-structured Li[(Ni_0.8Co_0.2)_0.8(Ni_0.5Mn_0.5)_0.2]O₂ is a significant breakthrough in the development of high-capacity lithium secondary batteries.