Simple Strategy for Synthesizing LiNi0.8Co0.15Al0.05O2 Using CoAl-LDH Nanosheet-Coated Ni(OH)2 as the Precursor: Dual Effects of the Buffer Layer and Synergistic Diffusion.

Ni-rich layered oxide LiNi0.8Co0.15Al0.05O2 is a promising cathode material for high-power lithium-ion batteries due to its high energy density and low cost. However, obtaining LiNi0.8Co0.15Al0.05O2 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 LiNi0.8Co0.15Al0.05O2, thus impeding its wide application. Here, we propose a simple strategy to synthesize LiNi0.8Co0.15Al0.05O2 using CoAl-layered double hydroxide (CoAl-LDH) nanosheet-coated Ni(OH)2 as the precursor. Compared with LiNi0.8Co0.15Al0.05O2 synthesized from nickel-cobalt-aluminum hydroxide and Al(OH)3-coated nickel-cobalt hydroxide precursors, LiNi0.8Co0.15Al0.05O2 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 Li1-x(Co0.75Al0.25)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.