Effect of Mg2+/F? co-doping on electrochemical performance of LiNi0.5Mn1.5O4 for 5 V lithium-ion batteries

By Wei, Aijia; Li, Wen; Chang, Qian; Bai, Xue; He, Rui; Zhang, Lihui; Liu, Zhenfa; Wang, Yanji
Published in Electrochimica Acta 2019

Abstract

Mg2+/F? co-doped LiNi0.5Mn1.5O4 cathode material was synthesized by a facile one-step solid-state process. The effect of Mg2+/F? co-doping on grain morphology, phase structure, and electrochemical properties was studied by a series of characterizations. Scanning-electron-microscopy images show that Mg2+/F? co-doped LiNi0.5Mn1.5O4 (denoted LNMO-MF) particles grow larger than pure LiNi0.5Mn1.5O4 particles. X-ray diffraction, Raman spectra, Fourier transformation infrared spectroscopy, X-ray photoelectron spectroscopy, and cyclic-voltammetry tests indicate that all samples mainly display a Fd-3m space group and more Mn3+ ions in the LNMO-MF sample after Mg2+/F? co-doping, which is conducive to increasing the cationic disorder degree and enhancing the electronic conductivity of electrode material. Results show that the LNMO-MF cathode material delivers an excellent rate performance with discharge capacities of 142, 144, 140 136, 132, 124, 115, and 100 mAh g?1 at 0.2, 0.5, 1, 2, 3, 5, 7, and 10C (1C = 140 mAh g?1), respectively. Remarkably, LNMO-MF also shows cycling stability with a capacity retention of 86.2% at 5C after 400 cycles, which is much higher than that of pure LiNi0.5Mn1.5O4 (67.7%). The improvement of LNMO-MF's electrochemical properties could be ascribed to the Mg2+/F? co-doping, delivering a more stable structure, better crystallinity, the highest Li+ diffusion coefficient, and the lowest charge-transfer resistance.

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