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

Highlights: • The ordered and disordered LiNi_0.5Mn_1.5O₄ and LiNi_0.5Mn_1.49Zr_0.01O₄ were prepared. • The effects of Zr doping on ordered and disordered LiNi_0.5Mn_1.5O₄ are different. • The ordered LiNi_0.5Mn_1.49Zr_0.01O₄ exhibits excellent electrochemical performances. Zr-doped LiNi_0.5Mn_1.49Z_r0.01O₄ and pristine LiNi_0.5Mn_1.5O₄ 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 LiNi_0.5Mn_1.5O₄ are different. Ordered LiNi_0.5Mn_1.49Z_r0.01O₄ shows much better cycling stability and rate capability than that of ordered LiNi_0.5Mn_1.5O₄. In contrast, the cycling stability of disordered LiNi_0.5Mn_1.5O₄ changes little, and the rate capability decreases after Zr doping. After 200 cycles at 1 C, the capacity retentions of ordered LiNi_0.5Mn_1.49Zr_0.01O₄ and LiNi_0.5Mn_1.5O₄ are 95.0% and 78.0%, respectively, while the capacity retentions of disordered LiNi_0.5Mn_1.49Zr_0.01O₄ and LiNi_0.5Mn_1.5O₄ are 98.6% and 95.1%, respectively. In particular, the specific capacity of ordered LiNi_0.5Mn_1.49Zr_0.01O₄ 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 LiNi_0.5Mn_1.5O₄ is only 103.0 mA h/g and retains 84.0% at the same conditions. The excellent electrochemical performance of ordered LiNi_0.5Mn_1.49Zr_0.01O₄ could be attributed to its better crystallinity, higher lithium diffusion coefficient (D_Li), and lower polarization.