ABSTRACT
Li-rich Mn-based oxides (LRMOs) are promising cathode materials for next-generation lithium-ion batteries (LIBs) with high specific energy (≈900 Wh kg-1 ) because of anionic redox contribution. However, LRMOs suffer from issues such as irreversible release of lattice oxygen, transition metal (TM) dissolution, and parasitic cathode-electrolyte reactions. Herein, a facile, scalable route to build homogenous and ultrathin Li2 TiO3 (LTO) coating layer on the primary particles of LRMO through molten salt (LiCl) assisted solid-liquid reaction between TiO2 and Li1.08 Mn0.54 Co0.13 Ni0.13 O2 is reported. The prepared LTO-coated Li1.08 Mn0.54 Co0.13 Ni0.13 O2 (LTO@LRMO) exhibits 99.7% capacity retention and 95.3% voltage retention over 125 cycles at 0.2 C, significantly outperforming uncoated LRMO. Combined characterizations of differential electrochemical mass spectrometry, in situ X-ray diffraction, and ex situ X-ray photoelectron spectroscopy evidence significantly suppressed oxygen release, phase transition, and interfacial reactions. Further analysis of cycled electrodes reveals that the LTO coating layer inhibits TM dissolution and prevents the lithium anode from TM crossover effect. This study expands the primary particle coating strategy to upgrade LRMO cathode materials for advanced LIBs.
ABSTRACT
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.
