Synthesis and electrochemical properties of molybdenum doped cathode materials prepared by ultrasonic spray pyrolysis

Abstract

Layered lithium metal oxides, LiMO2 (M = Co, Ni, Mn) and LiMn2O4 have been expanded in the last a few years in the application of rechargeable batteries as cathode materials for lithium secondary batteries. LiCoO2 has been commercialized but has still some limits due to its high cost, low capacity, and environmental problems [1-3]. Recently, T. Ohzuku reported a new concept of one-to-one solid solution with atomic scale of LiNiO2 and LiMnO2, i.e., Li[Ni1/2Mn1/2]O2 [4]. The Li[Ni1/2Mn1/2]O2 delivered a reversible capacity of 150 mAh g-1 in the voltage range of 2.5 to 4.3 V. Yoon et al. reported that Ni2+ and Mn4+ coexist in the layered Li[Ni1/2Mn1/2]O2 structure and Ni2+ ion is oxidized to Ni4+, while Mn4+ ions remain mostly unchanged as Li is de-intercalated from the material [5]. In this study, We have attempted to synthesize molybdenum doping on Li[Ni0.5Mn0.5]O2 using MoO3 precursor.

Experimental Mo doped LiNi(0.5+x)Mn(0.5-2x)MoxO2 (x in 0-0.05) powders were prepared by ultrasonic spray pyrolysis. Ni, Mn nitrate and molybdenum trioxide were used as starting materials for the synthesis of Ni(0.5+x)Mn(0.5-2x)MoxOy powder. The dissolved solution was added into a continuously agitated aqueous citric acid solution. The starting solution was atomized using an ultrasonic nebulizer with a resonant frequency of 1.7 MHz. The aerosol stream was introduced into the vertical quartz reactor heated at 500 oC. The as-prepared powder was thoroughly mixed with LiOH·H2O. After the mixture was softly ground, these were post-heated again at 900 oC in a box furnace.

Results and discussion Figure 1 shows XRD spectra for Li[Ni(0.5+x)Mn(0.5-2x)Mox]O2 (x = 0-0.05) powders. All samples can be indexed based on a hexagonal α-NaFeO2 structure with a space group of R_3m. The XRD pattern of the molybdenum doping Li[Ni(0.5+x)Mn(0.5-2x)Mox]O2 material shows a single phase of layered structure. This may be ascribed that this material derived from precursor has an atomic scale and homogeneously mixed to each other during calcinations process.