Development of diverse aluminium concentration gradient profiles in Ni-rich layered cathodes for enhanced electrochemical and thermal performances

Nickel (Ni)-rich cathodes with elemental concentration gradients within particles have attracted great interest due to their considerably enhanced interfacial stability and electrochemical performance for advanced Li-ion batteries. In this study, we shift our focus from traditional research centered on the optimal chemical compositions in Ni-rich cathode powders with concentration gradients; instead, we decipher the interrelated effects of aluminium (Al) concentration gradient profiles on electrochemical performance and thermal stability. We successfully obtained LiNi_0.95Al_0.05O₂ powders with different Al-gradient profiles by controlling the synthesis parameters, including the co-precipitation schedules of Al/Ni sources and sintering time. Using a combination of focused ion beam (FIB) and energy dispersive spectroscopy (EDS), we analyzed Al dispersion across the particle cross-sections. Remarkably, a greater Al concentration gradient across particles enhanced cathode-electrolyte interphase (CEI) stability during extended cycles, as evidenced by X-ray photoelectron spectroscopy (XPS) and electrochemical impedance spectroscopy (EIS). Consequently, the LiNi_0.95Al_0.05O₂ cathode with greater Al concentration gradients exhibited enhanced capacity retention, C-rate performance, and thermal stability compared to LiNi_0.95Al_0.05O₂ with lower Al gradients or Al-free LiNiO₂ cathodes. This result underscores the crucial role of the elemental gradient profile, highlighting it as an equally important aspect in the optimization of cathode chemical compositions.