LiNi0.5Mn1.5O4 (LNMO) nanostructures (microspheres composed of nanoparticles) are prepared from urchin-like γ-MnO2 by calcinating under 800°C, the product shows Fd3m-based phase involving minor rock salt phase and Mn3+ ions confirmed by its Raman spectra, X-ray diffraction pattern and electrochemical activities. Furthermore, HRTEM images and EDS line-scanning spectroscopy patterns focusing on a single nanoparticle provide direct observation of intergrowth of two phases that minor P4332 phase is found on the edge of Fd3m body coupled with the varying Mn/Ni ratio. In comparison, the other sample is obtained by adding an annealing treatment at 700°C after calcinating at 800°C, which preserves the nanostructured architecture of C800 and displays all the structural characteristics of pure P4332 phase. As cathode materials for lithium-ion batteries, merely calcined sample receives discharge capacities of 91 mAh•g−1 even at 50C, and 100.5 mAh•g−1 after 300 cycles at 5C, which shows better combination of rate and cycling performances than its counterpart with pure P4332 phase.