High energy density and lofty thermal stability nickel-rich materials for positive electrode of lithium ion batteries

Ni-rich LiNi0.8Mn0.1Co0.1O2 (NCM811) is one of the most promising electrode materials for Lithium-ion batteries (LIBs). However, its instability at potentials higher than 4.3 V hinders its use in LIBs. To overcome this barrier, we have prepared a core–shell material composed of a core of NCM811 (R-3m) and a monoclinic (C2/m) Li2MnO3 shell. The structure is confirmed by XRD, TEM, and XPS. This core–shell is very different from the conventional core–shell materials. In comparison, the conventional core–shell materials are layered R-3m structures which are instable at highly delithiated state (>4.5 V) due to the high repulsion between the two oxygen atoms facing each other across the empty Li site, while our synthesized material can be safely cycled at high upper cut-off potential of 4.7 V with high capacity retention. Compared to previously reported materials, the materials show substantially improved performance in terms of discharge capacity, energy density, and thermal stability. The upper cut-off potential is elevated from 4.3 to 4.7 V. Differential scanning calorimetry (DSC) results show that the exothermic peak of the core–shell structured material appears at 360 °C with a heat evolution of 575.1 J g−1, while that of the pristine material appears at 250 °C with a heat evolution of 239.1 J g−1.