Layered Li(Ni1/2Mn1/2)O2 was prepared by the solution and mixed hydroxide methods, characterised by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) and studied by cyclic voltammetry (CV) and charge discharge cycling in CC and CCCV modes at room temperature (r.t.) and at 50°C. The XPS studies show about 8% of Ni3+ and Mn3+ ions are present in Li(Ni2+ 1/2Mn1/2 4+)O2 due to valency-degeneracy. The compound prepared at 950°C, 12 h, solution method gives a second cycle discharge capacity of 150 mA h g−1 (2.5–4.4 V) at a specific current of 30 mA g−1 and retains 137 mA h g−1 at the end of 40 cycles. CV shows that the redox process at 3.7–4.0 V corresponds to Ni2+↔Ni4+ and clear indication of Mn3+/4+ couple was noted at 4.2–4.5 V. The observed capacity–fading (2.5–4.4 V) is shown to be contributed by the polarisation at the end of charging. The cathodic capacity is stable up to 40 cycles in the voltage window, 2.5–4.2 V both at room temperature and 50°C.