Effects of Mn and Al doping on the structure and electrochemical performance of cobalt-free ultra-high-nickel cathodes

As demand for high-energy-density batteries grows, cobalt-free ultra-high‑nickel cathodes like LiNiO₂ are poised to revolutionize next-generation energy storage solutions. However, their practical use is hindered by structural degradation caused by phase transitions, oxygen loss, and detrimental interfacial reactions triggered by the strong oxidizing nature of Ni 4+ formed under high voltage, which together lead to rapid capacity degradation and poor cycling stability. To overcome these challenges, effective doping strategies are crucial. This study systematically examines the potential of Mn and Al doping to enhance the stability of LiNiO₂ using in situ XRD, TEM, XPS, and electrochemical testing. The results show that, while both Mn and Al doping enhance structural stability and cycling performance, they operate through different mechanisms. In particular, 4 mol% Al doping remarkably suppresses c-axis expansion, enhances phase transition reversibility, and achieves capacity retention of 84.8 % after 100 cycles at 1C. In contrast, LiNiO₂ exhibits good tolerance toward Mn doping up to 10 mol%, which helps mitigate structural degradation; however, the capacity retention remains moderate at 80.3 %. While Al doping primarily enhances electrochemical performance, Mn doping contributes to preserving the structural integrity of the cathode at higher concentrations. Our study reveals their complementary roles, providing a strategy to address structural challenges and advance sustainable cobalt-free energy storage solutions.