We report the facile preparation of spinel type LiNi_0.5Mn_1.5O₄ with hierarchical micro–nano structures (LNMO-HMs) and their application as cathode materials for rechargeable lithium-ion batteries. The LNMO-HMs, which were synthesized through a poly(ethylene glycol) (PEG)-assisted co-precipitation route, have a particle size of 5–10 μm, which are composed of nano-particles with a size of about 200 nm. The effect of PEG on the phase purity and morphology of the LNMO products was studied. It was found that as the molecular weight of PEG increased, the lithium nickel oxide impurity decreased at first and then increased slightly. The average size of the nano-particles also showed a similar trend of first a decrease and then an increase, while the secondary micro-particles were enlarged with longer PEG chains. Raman mapping technology proved that the P4₃32 phase and the Fd3m phase LNMO coexist in the as-prepared samples, but the latter is the mainstay. When applied as cathode materials for lithium-ion batteries, PEG4000-assisted LNMO-HMs showed a remarkably high rate capability and cycling stability. The deliverable discharge capacity exceeded 120 mAh g⁻¹ at 40 C current rate and the capacity retention approached 89% after 150 cycles at 5 C current rate, showing the potential in the application of high rate discharge.