In this work, we report an effortless route to synthesize the single-crystalline LiNi0.5Mn0.5O2 nanosheets (NS-LiNi0.5Mn0.5O2) via an in situ conversion of flower-like MnO2 nanosheets. The complete conversion of the MnO2 precursor to layered alpha-NaFeO2-type NS-LiNi0.5Mn0.5O2 has been confirmed by X-ray diffraction, field-emission scanning electron microscopy, transmission electron microscope, and high resolution transmission electron microscope techniques. This two-dimensional (2D) NS-LiNi0.5Mn0.5O2 cathode exhibits a superior cycle performance. An initial discharge capacity of 162 mAh g(-1) could be delivered at 0.6 C rate, and 100% of its initial capacity can be sustained after 100 cycles. The durable cycle performance was ascribed to the intrinsic two-dimensional (2D) nanostructure and high crystallinity that led to fast Li-intercalation kinetics and excellent structural stability. Crown Copyright (C) 2013 Published by Elsevier B.V. All rights reserved.