Spheroidization: The Impact of Precursor Morphology on Solid‐State Lithiation Process for High‐Quality Ultrahigh‐Nickel Oxide Cathodes

Layered oxides with ultrahigh nickel content are considered promising high energy cathode materials. However, their cycle stability is constrained by a series of heterogeneous structural transformations during the complex solid-state lithiation process. By in-depth investigation into the solid-state lithiation process of LiNi_0.92Co_0.04Mn_0.04O₂, it is found that the protruded parts on the surface of precursor particles tend to be surrounded by locally excessive LiOH, which promotes the formation of a rigid and dense R 3 - m ${{\rm { R}}\mathrel{\mathop{{\rm { 3}}}\limits^{{\rm -}}}{\rm { m}}}$ shell during the early stage of lithiation process. The shell will hinder the diffusion of lithium and topotactic lithiation within the particles, culminating in spatially heterogeneous intermediates that can impair the electrochemical properties of the cathode material. The spheroidization of the precursor can enhance uniformity in structural evolution during solid-phase lithiation. Ultrahigh nickel cathodes derived from spherical precursors demonstrate high initial discharge specific capacity (234.2 mAh g^-1, in the range of 2.7-4.3 V) and capacity retention (89.3 % after 200 cycles), significantly superior to the non-spherical samples. This study not only sheds light on the intricate relationship between precursor shape and structural transformation but also introduces a novel strategy for enhancing cathode performance through precursor spheroidization.