Effect of Zr doping on LiNi0.5Mn1.5O4 with ordered or disordered structures

Zr-doped LiNi0.5Mn1.49Zr0.01O4 and pristine LiNi0.5Mn1.5O4 with ordered and disordered structures were prepared by a low-temperature solution combustion synthesis method. The phase compositions, structural ordering and micro-morphologies of the products were characterized by X-ray diffraction, energy-dispersive spectroscopy, inductive coupled plasma, Fourier transform infrared spectroscopy, scanning electron microscopy, and transmission electron microscopy measurements. The electrochemical performances of the products were investigated by charge/discharge testing, cyclic voltammetry, and electrochemical impedance spectroscopy. The results indicate that the effects of Zr doping on ordered or disordered LiNi0.5Mn1.5O4 are different. Ordered LiNi0.5Mn1.49Zr0.01O4 shows much better cycling stability and rate capability than that of ordered LiNi0.5Mn1.5O4. In contrast, the cycling stability of disordered LiNi0.5Mn1.5O4 changes little, and the rate capability decreases after Zr doping. After 200 cycles at 1 C, the capacity retentions of ordered LiNi0.5Mn1.49Zr0.01O4 and LiNi0.5Mn1.5O4 are 95.0% and 78.0%, respectively, while the capacity retentions of disordered LiNi0.5Mn1.49Zr0.01O4 and LiNi0.5Mn1.5O4 are 98.6% and 95.1%, respectively. In particular, the specific capacity of ordered LiNi0.5Mn1.49Zr0.01O4 is as high as 129.4 mA h/g and retains 94.5% after 100 cycles at 10 C, whereas the specific capacity of ordered LiNi0.5Mn1.5O4 is only 103.0 mA h/g and retains 84.0% at the same conditions. The excellent electrochemical performance of ordered LiNi0.5Mn1.49Zr0.01O4 could be attributed to its better crystallinity, higher lithium diffusion coefficient (DLi), and lower polarization.