Bypassing the rocksalt intermediate: A low-temperature route to high-performance LiNiO₂ cathodes with suppressed phase transformation

Layered lithium nickel oxide (LiNiO₂) is a promising cathode for high-energy lithium batteries, yet its conventional high-temperature solid-state (HS) synthesis inevitably involves an “ordered layered → disordered rocksalt → ordered layered” phase transformation, leading to structural defects and limited electrochemical performance. Here, we report a low-temperature reaction−high-temperature crystallization (LR-HC) strategy that decouples lithiation from crystallization, enabling topotactic conversion of Ni(OH)₂ into highly ordered LiNiO₂ while bypassing the detrimental rocksalt intermediate. The LR-HC product crystallized at 700°C for only 1 h exhibits an exceptionally low rocksalt phase content on the surface and delivers an initial discharge capacity exceeding 220 mAh g⁻¹ with an initial Coulombic efficiency above 90%. Remarkably, it retains 72.48% of its capacity after 200 cycles at 0.5C, far outperforming the HS counterpart (53.10%). Operando XRD during cycling further demonstrates that the enhanced stability originates from a reduced c-axis contraction (4.19% vs. 6.43%) and a more reversible H2-H3 phase transition. The LR-HC strategy also proves versatile for synthesizing other high-nickel layered oxides (e.g., Ni₉₅Co₅, Ni₉₅Mn₅), offering mechanistic insights into defect suppression and structural ordering for advanced cathode materials.