Rational rock-salt phase engineering of a nickel-rich layered cathode interface for enhanced rate and cycling stability

Ni-rich layered cathodes are promising for achieving high energy density, yet suffer from dramatic rate and capacity decay on cycling, which originates from chemo-mechanical failures with fast growth of an electrical and ionic insulating rock-salt phase on the surface. Apart from general approaches of applying inert coating layers, here we regulate the chemistry and structure of the inevitable rock-salt phase, and construct a robust and coherent interface with high electrical and ionic conductivity. Non-metallic N with Al has been co-doped into the interlayer rock-salt phase and the near-surface layered structure. Using atomic-level imaging, spectroscopic analysis, and density-functional-theory calculations, we reveal that Al-N co-doped in the rock-salt phase not only preserves fast Li-transfer pathways, but also increases electron density at the Fermi energy level, enhancing Li-ion diffusion and electron transfer across the rock-salt phase. More importantly, Al-N co-doping stabilizes lattice oxygen (O2-) and reduces interfacial lattice strain, restricting the accelerated accumulation of the rock-salt phase, thereby inhibiting intergranular cracking along cycles. This delicate interface engineering endows LiNi0.83Co0.12Mn0.05O2 with a superior rate capacity of 172.3 mA h g-1 at 3C and a high capacity retention of 96.5% after 200 cycles at 1C. Our findings demonstrate a general strategy with practical significance for mitigating the degradation of Ni-rich layered cathodes. Engineering the rock-salt phase by Al-N co-doping has been realized for nickel-rich layered cathodes, enhancing Li+ diffusion kinetics, electric conductivity, chemical stability, and mechanical coherence for mitigating chemo-mechanical degradation.