Nanocoating of Ce-tannic acid metal-organic coordination complex: surface modification of layered Li1.2Mn0.6Ni0.2O2 by CeO2 coating for lithium-ion batteries

Abstract

As a low-cost and environmentally friendly polyphenol, tannic acid (TA) is also a versatile coating molecule as it can strongly bind to substrates with different shapes (such as film and particle). We prepared metal-organic coordination of TA and Ce ions onto the surface of Li1.2Mn0.6Ni0.2O2 (LMNO) and then calcined to synthesize CeO2-coated LMNO. Various physicochemical characterizations were performed to reveal the phase structure and morphology of the pristine, metal-organic coordination complex (MOC), and CeO2-coated LMNO cathodes. It is found that the CeO2-coating layer with a thin thickness of ~ 10 nm is successfully built on the surface of LMNO, which provide a fast pathway for lithium-ion diffusion. The electrochemical performance measurements were used to identify the correlation between CeO2 modification and structural changes. In comparison with the pristine LMNO, the CeO2-modified sample exhibits superior electrochemical properties in terms of specific capacity, rate capability, and cycling performances. Specifically, the LMNO coated with 1 wt% CeO2 via MOC delivers discharge capacities of 270, 152, and 132 mAh g−1 at the current rates of 0.1, 5, and 8 C, respectively, much higher than the pristine LMNO (235, 97, and 86 mAh g−1, respectively) and the sample by blending method (263, 121, and 90 mAh g−1, respectively). The cyclic performance shows that 78.5% of the initial discharge capacity can be retained after 200 cycles at 1 C. Such enhanced electrochemical performance of the surface-modified LMNO can be attributed to the higher Li+ diffusion rate and the lower electrochemical polarization endowed by the uniform and conductive CeO2-coating layer.