X-ray photoelectron spectroscopy and electrochemical behaviour of 4 V cathode, Li(Ni1/2Mn1/2)O2

Abstract

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(Ni1/2 2+Mn1/2 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. © 2003 Elsevier Science Ltd. All rights reserved.