Simple Strategy for Synthesizing LiNi_0.8Co_0.15Al_0.05O₂ Using CoAl-LDH Nanosheet-Coated Ni(OH)₂ as the Precursor: Dual Effects of the Buffer Layer and Synergistic Diffusion

Ni-rich layered oxide LiNi_0.8Co_0.15Al_0.05O₂ is a promising cathode material for high-power lithium-ion batteries due to its high energy density and low cost. However, obtaining LiNi_0.8Co_0.15Al_0.05O₂ with a large and uniform particle size and without undesired Al-related phases using some conventional synthesis methods is quite difficult. These problems seriously affect the electrochemical performance of LiNi_0.8Co_0.15Al_0.05O₂, thus impeding its wide application. Here, we propose a simple strategy to synthesize LiNi_0.8Co_0.15Al_0.05O₂ using CoAl-layered double hydroxide (CoAl-LDH) nanosheet-coated Ni(OH)₂ as the precursor. Compared with LiNi_0.8Co_0.15Al_0.05O₂ synthesized from nickel-cobalt-aluminum hydroxide and Al(OH)₃-coated nickel-cobalt hydroxide precursors, LiNi_0.8Co_0.15Al_0.05O₂ produced using the proposed approach showed good sphericity, a large and uniform particle size, a pure phase, and excellent electrochemical performance. The superior properties are attributed to the dual effects of the buffer layer and synergistic diffusion. Specifically, the CoAl-LDH coating layer reacts with LiOH during the lithiation-calcination process to form a Li_1-x(Co_0.75Al_0.25)_1+xO₂ mesophase as the buffer layer, which increases the formation temperature of the layered structure and reduces Li⁺/Ni²⁺ cation mixing, making a well-ordered crystal structure. Moreover, spectroscopic analysis results and density functional theory calculations indicated a synergistic diffusion effect between Co and Al, and the presence of Co on the surface promotes the diffusion of Al during the lithiation-calcination process, thus avoiding the formation of undesired Al-related phases and allowing for a uniform element distribution.