Improving the electrochemical performance of single crystal LiNi0.5Mn1.5O4 cathode materials by Y–Ti doping and unannealing process

Abstract

In recent years, due to the rising price of cobalt, people have been increasingly interested in LiNi0.5Mn1.5O4 (LNMO) cathode materials, and many studies researches have been carried out on the preparation and modification of LNMO. However, the codoping of Y and Ti and the choice of annealing and unannealing processes after doping are less explored. In this study, single-crystal LNMO particles and Y, Ti-doped LiNi0.45Mn1.45O4 particles were prepared by a simple sol-gel method under annealing and unannealing processes, respectively. Four samples were analyzed by X-ray powder diffraction, Raman spectra, Fourier transform infrared spectroscopy and electron paramagnetic resonance. By these means, it was found that the samples doped and not annealed had the largest amount of disordered structures and oxygen vacancies (OVs). Scanning electron microscopy showed that the doped and unannealed samples had more exposed (100) crystal planes than the other samples, and after multiple cycles, this sample had the smoothest surface morphology. Electrochemical tests show that the doped and unannealed samples exhibit excellent electrochemical performance, with a Coulombic efficiency of 93.94% in the first cycle, a specific capacity of 126.74 mAh⋅g−1 after 500 cycles at a rate of 1 C, and a specific capacity of 126.74 mAh⋅g−1 at a rate of 5 C. After 500 cycles, the specific capacity is 111.1 mAh⋅g−1.