Molten Salt‐Assisted Synthesis of Single‐Crystalline Nonstoichiometric Li_1+xNi_1–xO₂ with Improved Structural Stability

Abstract Cobalt‐free LiNiO₂ is an attractive cathode material with high energy density and low cost but suffers from severe structural degradation and poor performance. Here, a molten salt‐assisted synthesis combined with a Li‐refeeding strategy is proposed to obtain nonstoichiometric Li_1+xNi_1‐xO₂ with submicron particle size and superior rate performance. The slightly Li‐rich and single‐crystalline characters inhibit Li⁺/Ni²⁺ anti‐site defects and mitigates the undesirable phase evolution. Remarkably, single‐crystalline Li_1.045Ni_0.955O₂ exhibits a high specific capacity (218.7 mAh g⁻¹ at 0.1 C), considerable rate capability (187.0 mAh g⁻¹ at 5 C), and an initial Coulombic efficiency (89.62% at 0.1 C) in the 1.27 Ah pouch full cell employing the graphite anode, significantly outperforming near stoichiometric LiNiO₂. Furthermore, the particulate morphology of Li_1.045Ni_0.955O₂ remains intact at charge voltages up to 4.8 V, whereas near stoichiometric LiNiO₂ features intragranular cracks and irreversible lattice distortion. This study underscores the value of molten salt‐assisted synthesis and Li‐refeeding modification to upgrade Ni‐based layered oxide cathode materials for advanced Li‐ion batteries.