Structural and electrochemical characteristics of Al2O3-modified LiNi0.5Mn1.5O4 cathode materials for lithium-ion batteries

Abstract

The high-voltage spinel LiNi0.5Mn1.5O4 (LNMO) is a potential cathode material for lithium-ion batteries with outstanding energy density and power density. Here, we document a facile approach to prepare Al2O3-modified LNMO cathode materials. The Al2O3-modified LNMO materials were synthesized via a one-step solid-state reaction and then modified with Al2O3 via a wet chemical technique. The impacts of Al2O3 modification on the structure and electrochemical properties of LNMO materials were examined by X-ray diffraction, Fourier-transform infrared spectroscopy, Raman spectroscopy, scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, charge-discharge tests, cyclic voltammetry measurements, electrochemical impedance spectroscopy, and aging tests. Throughout the modification process, several Al3+ were noted to substitute for Ni2+, resulting in a decrease of Mn4+ to Mn3+; this increased the electronic conductivity and lowered the electrochemical polarization of the LNMO material. An amorphous Al2O3 coating layer developed on the surface of the LNMO particles in the modification, and this could alleviate the strike of HF caused by electrolyte decomposition as well as the development of a solid electrolyte interphase. Thus, the 0.5 wt% Al2O3-modified LNMO material had decreased Rsf and Rct and greater DLi values with a rate capability and cycling stability better than LNMO. The rate capability was 105.6 and 83.3 mAh g–1 at high C rates of 5 C and 7 C, as opposed to 83.3 and 54.9 mAh g–1, respectively; the room temperature (25 °C) capacity retention was 92.6% at 1 C after 200 cycles, as opposed to 87.0%. The high-temperature (55 °C) capacity retention was 90.9% at 1 C rate after 200 cycles as opposed to 86.5%. Thus, this is an easy and feasible method to improve the electrochemical performance of LNMO cathode materials for industrialization.