Aluminium-sodium targeted co-doping to boost the electrochemical stability of full concentration gradient Ni-rich...

Structural engineering of full concentration gradient (FCG) offers promising prospects for improving the interface and thermal stability of Ni-rich layered cathodes. However, the Ni content in the core of FCG cathode particle is higher than that on the surface, resulting in rapid structural deterioration at the particle core during cycling. To directionally strengthen the structural stability at the cores of FCG cathode particles, this study proposes a dual-cation targeted co-doping strategy that coordinates gradient Al doping with uniform Na doping. Al-Na co-doped FCG Li_1-yNa_yNi_0.80Co_0.05Mn_0.15-xAl_xO₂ (FNCM-A_xN_y) cathodes were successfully prepared through a combined in-situ and wet-chemistry method. As confirmed in experimental and theoretical studies, the particle core is structurally stabilized by the directional distribution of Al and Na within the particles, the formation of strong AlO bonds, and the provision of Na pillar ions in the bulk, which alleviate lattice shrinkage and structural collapse of the particles during the cycling process. Moreover, Al-Na co-doping enhances the diffusion kinetics by widening the ion- diffusion channels and reducing the diffusion barriers. Consequently, the capacity retention of the as-prepared FNCM-A_0.1N₁ cathode (co-doped with 0.1 mol% Al and 1 mol% Na) after 200 cycles at a rate of 1C reached 93 %, considerably outperforming both the pristine cathode (81 %) and the Al-doped cathode (87 %). Our study provides a novel idea to enhance the electrochemical stability by targeting strengthening the structural stability at the particle core of FCG Ni-rich layered cathodes.