A comparative analysis of the properties of LiNi0.5Mn0.5O2 and Li1+x Ni0.5Mn0.5O2 (0.2 ≤ x ≤ 0.7) powders, obtained by the freeze drying method, was performed. Lattice parameters of Li1+x Ni0.5Mn0.5O2 decreased considerably with growing amounts of Li until x = 0.3; at x > 0.5 trace amounts of Li2MnO3 are observed by X-ray diffraction (XRD) patterns. X-ray photoelectron spectroscopy (XPS) analysis displayed an increase of Ni3+/Ni2+ ratio at 0.3 < x < 0.5, while Mn 2p spectra were almost identical in all samples. Rechargeable capacity values (V = 2.5–4.6V) increased systematically with x reaching its maximum (185–190mAhg−1) at x = 0.5. Samples with superstoichiometric lithium content also demonstrated good C rate characteristics.