LiNi0.5Mn1.5O4 nanorods wrapped with graphene nanosheets have been prepared and investigated as high energy and high power cathode material for lithium-ion batteries. The structural characterization by X-ray diffraction, Raman spectroscopy, and Fourier transform infrared spectroscopy indicates the LiNi0.5Mn1.5O4 nanorods prepared from β-MnO2 nanowires have ordered spinel structure with P4332 space group. The morphological characterization by scanning electron microscopy and transmission electron microscopy reveals that the LiNi0.5Mn1.5O4 nanorods of 100–200 nm in diameter are well dispersed and wrapped in the graphene nanosheets for the composite. Benefiting from the highly conductive matrix provided by graphene nanosheets and one-dimensional nanostructure of the ordered spinel, the composite electrode exhibits superior rate capability and cycling stability. As a result, the LiNi0.5Mn1.5O4-graphene composite electrode delivers reversible capacities of 127.6 and 80.8 mAh g−1 at 0.1 and 10 C, respectively, and shows 94% capacity retention after 200 cycles at 1 C, greatly outperforming the bare LiNi0.5Mn1.5O4 nanorod cathode. The outstanding performance of the LiNi0.5Mn1.5O4-graphene composite makes it promising as cathode material for developing high energy and high power lithium-ion batteries.
High tap density LiNi0.5Mn1.5O4 nanorod clusters composed of well-crystallined LiNi0.5Mn1.5O4 nanorods with diameter of about 150 nm and length of about 1 μm were synthesized by a template method. β-MnO2 nanorods synthesized by a hydrothermal method were used as the template. LiNi0.5.Mn1.5O4 nanorod clusters were then synthesized by solid-state reaction of a mixture containing β-MnO2 nanorods, nickel acetate, and lithium hydroxide. It is found that a preheat treatment and grinding of the precursor for the solid state reaction is critical to form pure phase ordered LiNi0.5Mn1.5O4 and the nanorod cluster structure. LiNi0.5Mn1.5O4 nanorod clusters can deliver charge and discharge capacities as high as 140.61 mA h g(-1) and 128.42 mA h g(-1), respectively, at a 0.1 C rate between 3.0 and 4.9 V versus Li/Li+. Moreover, the nanorod clusters exhibit high power capability, maintaining capacities of 105.90 and 98.05 mA h g(-1) at 2 C and 5 C rates, respectively.
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