Surface enrichment and diffusion enabling gradient-doping and coating of Ni-rich cathode toward Li-ion batteries.

Critical barriers to layered Ni-rich cathode commercialisation include their rapid capacity fading and thermal runaway from crystal disintegration and their interfacial instability. Structure combines surface modification is the ultimate choice to overcome these. Here, a synchronous gradient Al-doped and LiAlO2-coated LiNi0.9Co0.1O2 cathode is designed and prepared by using an oxalate-assisted deposition and subsequent thermally driven diffusion method. Theoretical calculations, in situ X-ray diffraction results and finite-element simulation verify that Al3+ moves to the tetrahedral interstices prior to Ni2+ that eliminates the Li/Ni disorder and internal structure stress. The Li+-conductive LiAlO2 skin prevents electrolyte penetration of the boundaries and reduces side reactions. These help the Ni-rich cathode maintain a 97.4% cycle performance after 100 cycles, and a rapid charging ability of 127.7 mAh g−1 at 20 C. A 3.5-Ah pouch cell with the cathode and graphite anode showed more than a 500-long cycle life with only a 5.6% capacity loss. The commercialisation of promising Ni-rich cathodes is limited by capacity fading and thermal runaway. Here, the authors design a gradient Al-doped and LiAlO2-coated LiNi0.9Co0.1O2 cathode, which addresses the crystal degradation and interfacial instability and thus improves the cycle and thermal stabilities.