Lithium-rich layered nickel–manganese oxides as high-performance cathode materials: the effects of composition and PEG on performance

Lithium-rich layered nickel–manganese oxide (LRL-NMO) as a cathode material for rechargeable lithium-ion batteries was successfully prepared using an oxalic acid co-precipitation method, with polyethylene glycol (PEG1000) as an additive. The effects of the Ni/Mn ratio and of PEG on the phase purity, morphology, and electrochemical performance of LRL-NMO were investigated with X-ray diffraction, scanning electron microscope, electrochemical impedance spectroscopy, and charge/discharge testing. Li[Li 0.167 Ni 0.25 Mn 0.580 ]O 2 delivered the best electrochemical performance among the various Li[Li 1/3−2 x /3 Ni x Mn 2/3− x /3 ]O 2 (0 < x < 0.5) materials. Furthermore, the sample to which an appropriate amount of PEG had been added showed much smaller and more uniform particle size, higher discharge capacity and energy density, better cycling stability, and lower resistance. The material prepared by adding 9 wt% PEG exhibited high discharge capacity and stability; after 100 cycles at 2 C, it still delivered a discharge capacity of 125.6 mAh g −1 , which was 50 % higher than that of a sample prepared without PEG.