Beyond dopant selection: The critical grain size window as a key performance dictator for Co-free, Ni-rich cathode materials

Despite the immense potential of cobalt-free, nickel-rich cathode materials to replace their cobalt-containing counterparts in lithium-ion batteries (LIBs), their widespread adoption remains hindered by performance limitations. While extensive research has explored various doping strategies to address this challenge, the reported benefits vary significantly, suggesting an incomplete understanding of dopant influence and thus hindering the full potential of these additives. Our investigation into the effect of various dopants on Li(Ni0.95Mn0.05)O2 0.95 Mn 0.05 )O 2 performance yielded a surprising discovery: the LIB performance of transition metal-doped Li(Ni0.95Mn0.05)O2 0.95 Mn 0.05 )O 2 becomes remarkably consistent across different dopant types, provided the calcination conditions are optimized. Regardless of dopant type, a critical grain size window is identified as a key factor influencing the performance of the doped Li(Ni0.95Mn0.05)O2. 0.95 Mn 0.05 )O 2 . Calcination within a specific temperature range is paramount to control this previously overlooked performance determinant, which significantly impacts grain growth, primary particle morphology, and lattice structure. This novel insight allows us to demonstrate that cost-effective dopants such as Ti can achieve performance in stabilizing Li(Ni0.95Mn0.05)O2 0.95 Mn 0.05 )O 2 comparable to that of more expensive, higher- valence alternatives (e.g., Nb, Ta, W, and Mo). This discovery paves the way for developing practical material design processes that meet the stringent requirements of the LIB industry.