X-ray photoelectron spectroscopy and electrochemical behaviour of 4 V cathode, Li(Ni1/2Mn1/2)O2 |
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Authors: | K.M. Shaju |
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Affiliation: | Department of Physics, National University of Singapore, Singapore 119260, Singapore |
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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(Ni2+1/2Mn1/24+)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. |
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Keywords: | Li(Ni1/2Mn1/2)O2 Li-ion batteries Layered structure Cathode material X-ray photoelectron spectroscopy |
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