Improving the Structure Stability of LiNi0.8Co0.1Mn0.1O2 by Surface Perovskite-like La2Ni0.5Li0.5O4 Self-Assembling and Subsurface La3+ Doping.

The commercialization of high-capacity Ni-rich cathode LiNi0.8Co0.1Mn0.1O2 is still hindered by some defects, such as moderate rate property and inferior high-voltage cycling stability. The main reason is that the structural transformation starts at the surface from layered to spinel and then to the rock salt phase, which will be aggravated under a higher voltage and gradually spread to the bulk region during cycling. Here, we fabricate the LiNi0.8Co0.1Mn0.1O2 surface with the perovskite-like La2Ni0.5Li0.5O4, which possesses good thermostability and Li+-ion diffusion kinetics, to strengthen its surface and subsurface lattice stability. First-principles theory has confirmed the well compatibility of La2Ni0.5Li0.5O4 with LiNi0.8Co0.1Mn0.1O2, thus affording unimpeded channels for fast Li+-ion transport in the same dimensions through these two crystal lattices. On the other hand, during the high-temperature synthesis process, La3+ ions are also doped into the subsurface lattice of LiNi0.8Co0.1Mn0.1O2. After La modification with the two above-mentioned effects, the structure stability of LiNi0.8Co0.1Mn0.1O2 at high operating voltages and after long cycles has been significantly enhanced. Specifically, at 2.75-4.5 V, the first discharge capacity at 0.2C of the La-modified sample is 229.3 mAh g-1 and the 200th capacity retention ratio at 1C has been improved from 63.7 to 90.1%.