Improving the electrochemical performance of Li-rich Li1.2Ni0.2Mn0.6O2 by using Ni-Mn oxide surface modification

The surface lithium residues on Li-rich layered cathode materials xLi2MnO3·(1-x)LiMO2 (M = Mn, Co, Ni, etc.) are harmful to their electrochemical properties. In this work, the surface lithium residues of Li-rich Li1.2Ni0.2Mn0.6O2 (LNMO) are identified as Li2CO3 and LiOH by Fourier transform IR for the first time. To overcome this issue, Ni/Mn acetates are used to react with the surface lithium residues to form a LiNi0.5Mn1.5O4 spinel coating layer on LNMO particles. Compared with the bare LNMO sample, the 1 wt% LiNi0.5Mn1.5O4 coated LNMO shows improved long-term cycling stability and rate capability both at room temperature and 55°C. The coated one delivers an initial discharge capacity of 236 mAh g−1 with 99.6% capacity retention after 100 cycles at 0.5 C, while it is only 230 mAh g−1 with 91% capacity retention for the bare LNMO. After the surface modification, the rate capacity increases from 155 mAh g−1 to 180 mAh g−1 at 5 C at room temperature while the energy efficiency is improved from 78% to 85%.