Precursor primary particle structure governs lithiation reconstruction and single-crystal formation of ultrahigh-nickel cathodes

Abstract

Understanding how the primary particle structure governs lithiation reconstruction and single-crystal formation in ultrahigh-nickel cathodes is crucial for simultaneously achieving high energy density and structural durability. However, this intrinsic relationship remains difficult to resolve in conventional micron-sized precursor systems because transport limitations and reaction heterogeneity are often intertwined during thermal reconstruction. Herein, uniform nanosized Ni_0.92Co_0.04Mn_0.04(OH)₂ precursors synthesized by microchannel coprecipitation were employed as a model system to isolate the role of primary particle structural characteristics. Sulfate- and acetate-based coprecipitation systems were employed to fabricate precursors with differentiated primary particle structures in particle size and crystallographic orientation. It is demonstrated that the primary particle structures favorable for single-crystal formation cannot merely accelerate the lithiation process but, more importantly, enable superior synchronization between lithiation kinetics and structural ordering throughout the calcination process. Such structural characteristics promote intergranular fusion and efficient grain-boundary elimination, leading to a highly integrated single-crystal LiNi_0.92Co_0.04Mn_0.04O₂ (NCM92) cathode with low Li/Ni disorder (2.1%), fewer oxygen vacancies, and superior structural integrity. By contrast, precursor structures with smaller particles and less coherent crystallographic organization undergo rapid initial lithiation but tend to produce incomplete crystallographic fusion, resulting in quasi-single-crystal products with residual grain boundaries and higher defect concentrations. Consequently, the optimized cathode exhibits markedly improved electrochemical and thermal stability. This work reveals that the key to robust single-crystal formation lies in effectively coupling lithiation reactivity with crystal ordering and establishes a structure-guided framework for the rational design of durable ultrahigh-nickel cathodes.