Enhancing Cycle Stability in LiNiO₂ with Phase transition suppression via Crystalline Disordered Surface Layer

Ni-rich layered oxides are promising cathode materials for lithium-ion batteries but require improved stability to meet performance demands. To address this, doping and surface modification are commonly employed stabilization strategies, each offering distinct benefits. Doping primarily suppresses phase transitions, thereby reducing volume changes, while surface coatings protect the material by minimizing continuous reactions with electrolytes during cycling. Consequently, these approaches are often used in combination to enhance material stability. This study demonstrates that a crystalline disordered surface layer can effectively suppress structural changes without doping. Notably, the thickness of the disordered surface layer is successfully controlled during synthesis for the first time. The results reveal that the formation rate of the layered structure plays a critical role in controlling the rock-salt disordered surface layer. Although a thicker crystalline disordered surface layer in single-crystal LiNiO₂ resulted in a slight capacity reduction, it exhibits significantly improved capacity retention, maintaining up to 84% of its capacity after 500 cycles in a full-cell test, while also substantially reducing voltage decay. This study provides insights, demonstrating that well-controlled surface modification can simultaneously protect the surface and mitigate structural changes, paving the way for the development of stable cathode materials.