Improving the Structure Stability of LiNiCoMnO by Surface Perovskite-like LaNiLiO Self-Assembling and Subsurface La Doping.

The commercialization of high-capacity Ni-rich cathode LiNiCoMnO 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 LiNiCoMnO surface with the perovskite-like LaNiLiO, 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 LaNiLiO with LiNiCoMnO, 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, La ions are also doped into the subsurface lattice of LiNiCoMnO. After La modification with the two above-mentioned effects, the structure stability of LiNiCoMnO 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 and the 200th capacity retention ratio at 1C has been improved from 63.7 to 90.1%.